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October 4

Seeing bullets (with no tracers) streak through the air using IR goggles

Would bullets (with no tracers) be very visible if you were to observe them using IR goggles? —Preceding unsigned comment added by ScienceApe (talk • contribs) 16:38, 4 October 2008 (UTC)

There are two main types of IR goggles and cameras. There are night vision ones that work user near-IR (nearer to visible light, that is) which work by capturing the reflected IR in the same way that visible light is used. They often come with an IR light that illuminates the area with IR so it can be seen (if you watch night vision video you can often see that there's a light shining on the middle of the image and around the edge is much darker). There is then thermal imaging which uses far-IR and captures IR emitted directly by the objects before of their heat. I believe bullets are fairly warm, so would show up well on thermal imaging, but I see no reason why they would show up any better than anything else under night vision. --Tango (talk) 16:57, 4 October 2008 (UTC)

Yes, very visible. Well, the thermal imaging ones at least, as Tango said.

edit: You may want to consider these things though:

• A bullet is small and fast, so seeing it will be really hard using goggles, a camera will have a better chance.
• As noted in the link, the bullet will cool down in flight.

- Dammit (talk) 22:17, 4 October 2008 (UTC)

The night vision goggle (NVG) type can see emitted IR as well as reflected - but the higher frequencies that NVG's are sensitive to are not normally emitted in much quantity by things that are merely warm. However, a piece of "red hot" steel is obvious even to the naked eye (that's why we call it "red" hot). Hence, something that's just a little cooler than red hot would be highly visible by radiated IR in NVG's. The lower frequency detectors in InfraRed cameras (such as you might find on a combat helicopter, drone or fighter/bomber) are able to see radiated IR across a wider range and are sensitive enough to see things that are just a fraction of a degree above their environment - you can see warm 'tracks' left by a vehicle driving by for example! I've worked a lot with both kinds of sensor - you can't see regular bullets in flight with either of them - there just isn't enough light (IR or otherwise) and it's not there for long enough. Also, the resolution of both NVG's and IR cameras is nowhere near fine enough to pick up something that small at a distance. But tracer is highly visible to both because it produces a lot of visible light (which the NVG can see) and the cloud of combustion products is large enough and hot enough for the IR camera to pick up. The 'rangerats' stuff that User:Dammit provided is deceptive. Firstly they aren't using regular NVG's or military IR - they are using some kind of very fancy IR camera that's specifically designed for measuring temperature rather than for seeing well at night (this is obvious from the 'false color' images on their site - military stuff doesn't use false color - the images are invariably monochromatic, and typically green). Secondly they say that the bullet was only visible fairly briefly just as it left the barrel of the gun - a fraction of a second later, it was too cool to register on their equipment. SteveBaker (talk) 11:56, 6 October 2008 (UTC)

Please read better before of calling something deceptive. The only thing fancy about the camera used is that it is a high speed one, other than that it's not all that different from thermal imaging goggles. Also they don't write that the bullet was only visible briefly, in fact they could have followed it right to the target if the camera could pan fast enough (see the link to the shot apple on the article). They just used a static camera pointed at the muzzle and selected the first image where the bullet came out of the gas cloud (before that bullet it was not visible). - Dammit (talk) 23:40, 8 October 2008 (UTC)

Is this understandable?

Quite confusing IMO.

Our sail car is trapezoidal with two horizontal extensions, one on each side of the car in the back. The extensions are created using four straws. Two are linked together to form what appears to be one long straw in the very back (creating the rear base of the trapezoid as well), so that only very ends of the 'straw' are part of the extension. It holds two wheels on each extension, both (wheels) kept from sliding by two pins placed beside each wheel, the pins being stuck into the straw. The other two straws are on opposite sides of the car and in front of the rear straw. They support the wheels as well (the support pins are stuck through them after being stuck through the rear straw), but they bend towards the front of the car upon clearing the extensions. These straws bend upon reaching the front, creating the smaller (shorter) top (front) base of the trapezoid by connecting at the center of the front base. The front ends of the straws then hold two more wheels near the bent area. Right at the bend of each of the two front straws are two more straws are pinned to each one of the straws just aforementioned. These two straws converge and meet at the midpoint of the rear straw.

Roughly halfway between the extensions and the midpoint of the rear straw are straws extending vertically upwards. These straws are connected to a sail. The sails is bent inwards and is supported by a crossbeam at the top.

Rest assured, for the prototype actually worked.

--hello, i'm a member | talk to me! 22:21, 4 October 2008 (UTC)

Clarification is needed here. Is this native English language or a translation? (For that matter, please provide proper attribution when quoting extensive text on a GFDL site such as Wikipedia - who said that, where?)

And in particular, what does "straw" mean in context? Drinking straw, wheat straw, something else? Once you attribute that quote, we may be able to shed some light. Franamax (talk) 05:11, 5 October 2008 (UTC)

It seems to be some kind of little toy made with drinking straws. To answer the question: yes, this text is confusing. I got lost in the first sentence because I could not visualise the "sides" and the "back" of the trapezoid. A diagram would help. Itsmejudith (talk) 15:44, 5 October 2008 (UTC)

Is there any way I can clarify the passage? 'Front' and 'back' are arbitrary positions (they were defined on a whim...doesn't really matter too much) and yes, those straws are drinking ones. --hello, i'm a member | talk to me! 15:57, 5 October 2008 (UTC)

I second Itsmejudith...a diagram would help immensely. Even a very simple sketch would clarify what is where relative to what else. Alternately, a more technical diagram could have labeled parts replace this entire paragraph! DMacks (talk) 16:09, 5 October 2008 (UTC)

Assuming that I have a diagram, would this passage still be confusing? I know my question isn't all that answerable... --hello, i'm a member | talk to me! 16:28, 5 October 2008 (UTC)

The description is confusing and ungrammatical in places. It sounds like a first draft. In the fourth sentence, it's not clear what the pronoun "It" refers to. Perhaps if the text said "The rear axle," with that axle defined by what straws it was made of, all would be clearer. In the fifth sentence, instead of "in front of the rear straw" it should say "at the front of the trapezoid" to give a point of reference. In the sixth sentence replace "they" with an explicit declaration of what is referred to. In the 7th sentence, it is not clear in what direction the front straws bend: is the outside end of a front straw closer to the rear, or farther from the rear than the center of the front line of the trapezoid? In the 8th sentence, "the bent area" is undefined. The 9th sentence is vague and confusing, and contains an extra "are." If the front 2 wheels are on straws which are bent, then are their axes not parallel to the axes of the rear wheels? It sounds like the front wheels point at an angle, which would make it difficult for the device to move forward without dragging the front wheels, which would want to roll in different directions from the back wheels and each other. Sentence 11 does not specify which straws are "the extensions" it refers to: front, back, or all four? How many straws point upwards in sentence 11, and where are they located in the trapezoid? Sentence 12: Specify the arrangement of the sail. Sentence 13: "Bent inwards" is vague. To move forward in a wind, the sail would need to be parallel to the rear axle to maximize thrust from wind coming from the rear, or at some lesser angle such as 45 degrees to take advantage of side winds and produce forward movement. Sentence 14: It "worked?" Even a crackerbox would move in a strong wind. How fast did it move in what speed of a wind coming from what direction? Edison (talk) 20:44, 5 October 2008 (UTC)

October 5

How to Get Gray Hair

I understand there is a multitude of products in current circulation designed to rid people of gray hair, which is a process that I am not in the market for. I actually want the exact opposite. My hair is a dark brown/black, and I want it to have a nice Andy Warhol/Randy Newman gray tone. What should I look into regarding this? Is it even possible? Thank you folks. Kenjibeast (talk) 02:36, 5 October 2008 (UTC)

Hydrogen peroxide and ammonia will strip the color out of your hair, but it will leave it a whitish blonde, not gray. :( --Russoc4 (talk) 03:11, 5 October 2008 (UTC)

Keep in mind that Warhol wore a wig. Dying your hair to that level of white is possible but it's not easy and it's not very good for the hair. I don't know how you'd get it gray rather than white, though. --98.217.8.46 (talk) 04:01, 5 October 2008 (UTC)

Get a stressful job or go to graduate school in some crazy competitive field like biochem. It's guaranteed to work though it does take some time. Comes with free wrinkles too ;) Sjschen (talk) 04:20, 5 October 2008 (UTC)

Just wait: time has a tendency to take care of such things. ៛ Bielle (talk) 04:31, 5 October 2008 (UTC)

This evidence is anecdotal, but ever notice how all the US presidents look so old after just 4-8 years? Stress does seem to assist with the graying. This does pose the question, does stress induced graying recover with the relief of stress? Sjschen (talk) 04:49, 5 October 2008 (UTC)

That's not just anecdotal, plenty of others have noticed it too. I've read articles on it, but I can't find any now. It looks like ABC had a slideshow on it, but has since taken it offline. Plasticup ^T/C 15:45, 5 October 2008 (UTC)

Playing devil's advocate for a moment, I think it's worth noting that most new Presidents are into what might be charitably described as 'late middle age' by the time that they take office. According to List of United States Presidents by age, the average age of a new President is 55 years. Add four or eight years on to that, and and they're eligible for senior's discounts at a lot of retailers. In other words, they look so old because they've gotten so old. Compare photographs of the average non-President at ages 55 and 63, and you might notice that they've aged, too. TenOfAllTrades(talk) 19:42, 5 October 2008 (UTC)

I considered that, yes. I think it would be interesting to test it. Plasticup ^T/C 19:53, 5 October 2008 (UTC)

Even the young presidents (Clinton, Kennedy) look much older after a few years in office. --Carnildo (talk) 22:24, 5 October 2008 (UTC)

In that case, how does stress induce greying? How does melanine production get turned off in such a manner? Sjschen (talk) 21:04, 5 October 2008 (UTC)

Exactly. ---J.S (T/C/WRE) 01:31, 6 October 2008 (UTC)

This sounds like a problem that actors would be faced with, as they may have to play the same character at different ages. I suggest trying a supplier of theatrical cosmetics. --Anonymous, 04:44 UTC, October 5, 2008.

Having teenage children is a tried and true method for getting gray hair. You also might ask to borrow some teenagers if the time constraints of raising your own are a problem. Edison (talk) 20:22, 5 October 2008 (UTC)

Scientific American took up the question of stress and gray hair. There are some other interesting notes there, too. Keep in mind the hair isn't just one shade of gray -- as the melanocyte cells fail, there's less and less pigment; when there's none, the hair appears white. Also, blondes seem to turn gray later, because the white doesn't stand out as much against the blonde. --- OtherDave (talk) 00:59, 7 October 2008 (UTC)

Alright, apart from getting a wig, looking for theatrical cosmetics, and applications of constant stress, are there any permanent methods to grey my hair out? By permanent I don't mean forever, I just mean it won't wash out, dig? Thanks folks, you've been a great help so far. Kenjibeast (talk) 05:59, 7 October 2008 (UTC)

A suggestion: if getting a new colour is about applying a colour, and greying is a process of colour loss, it's unlikely there's a colour to give you grey on top of your dark hair. But – you could have someone make it blond to white and add a toner (example[1]). There are also British made water colour hair colours that go into a paintbox range that show up best on lightened hair, but can't find them through google. PS what colour was Warhol's original hair? Julia Rossi (talk) 06:57, 11 October 2008 (UTC)

Nomex

How fire/heat resistant is Nomex? I can find all sorts of words like "very" and "extremely", but no hard numbers. --67.185.172.158 (talk) 09:12, 5 October 2008 (UTC)

Nomex is meant to save you from flash injury, it's not really made for running into fires. As such, you won't necessarily find "hard" numbers. Suffice to say, if a pool of flammable liquid ignites 20 feet away, you're better off wearing Nomex. The ejected flammable liquid won't hit your skin and the flames will bounce. If you end up lying in a pool of burning hydrocarbons, you will still have to get up and run. Franamax (talk) 09:39, 5 October 2008 (UTC)

[2] "The rate of material decomposition and charring rate is high only after the temperature greatly exceeds 350°С; however, the material does not melt." Also a bunch of other figures not related to using it for protection (e.g. [The unique combination of electrical and mechanical strength, heat resistance (temperature rating of 220°С]). Perhaps you can find some graphs showing decomposition and stuff, but I don't really see how you can get any 'harder' then that. I presume precisely what it does will depend on the temperature and time period of exposure and whether it's a naked flame. As Franamax says I think the primary point of Nomex is that it stops flames from hitting your skin and it doesn't itself catch fire in most situations you'd expect to encounter. It's not some sort of extrme insulator so you've still going to get burnt if you stay in a fire/hot temperature for too long Nil Einne (talk) 10:24, 5 October 2008 (UTC)

I smell an experiment! Plasticup ^T/C 15:42, 5 October 2008 (UTC)

We'd better hope that the experiment doesn't lead to our smelling a burnt body. --M1ss1ontomars2k4 (talk) 21:17, 5 October 2008 (UTC)

Fire-suite manufactures do internal testing and are loathe to share their results. It's the same in any very specialized industry... the research is just too expensive to share with their competitors. ---J.S (T/C/WRE) 01:35, 6 October 2008 (UTC)

Nomex coveralls are also horribly uncomfortable, since they retain your sweat. I always used Proban^TM, which was treated cotton, and I got away with it 'cause I was the manufacturer's rep and could explain that I threw them away after ten washings. In any of my safety-trainings (one per chemical plant) I was told the rule that no sleeves could be rolled up, and that Nomex was the just-in-case for "uncontrolled ignitions" and that all normal evacuation procedures must be followed. Ironically, the protection of the coveralls would mean that only your hands and face would be hideously burnt, but you'd still be alive. I've since eased out of that field of work... Franamax (talk) 23:01, 6 October 2008 (UTC)

Err...franamax, as a firefighter, allow me to advise you to qualify your first statement. Nomex hoods are standard issue for firefighters in the united states and therefore are literally made for running into fires. Granted, the protection the hood gives is limited and the first area that usually gets burned (the ears) is under the hood's jurisdiction. NFPA standard 1971 probably has something to say about them if you can find a copy. --Shaggorama (talk) 07:27, 7 October 2008 (UTC)

Hyperthyroidism and the risks of general asesthesia/surgery

I was recently scheduled for a hysterectomy and the Surgeon cancelled the surgery because of the TSH result from my pre-op blood test. If the T3 & T4 results are in the reference range is there a risk of going under general anesthesia? If so, are they and what are the statistics? —Preceding unsigned comment added by Istaffordcomcastnet (talk • contribs) 17:04, 5 October 2008 (UTC)

Your surgeon, your consultant and other doctors involved in your treatment know your medical history and your test results and are obviously a much more reliable source of information than random strangers on the internet. So ... wouldn't it be better to put your questions to them ? Gandalf61 (talk) 17:26, 5 October 2008 (UTC)

There does appear to be an interaction between thyroid horormones and some specific anesthetics and/or major surgery. Googling for t3 t4 tsh anesthesia finds some refs. Even though this isn't (to my reading) a request for medical advice, your doctor could at least tell you the specific guidelines he's following. That would be a great starting point to finding out the basis for those guidelines and the risks that specific deviations would entail. DMacks (talk) 17:31, 5 October 2008 (UTC)

Reasons people mumble - hearing loss, etc.

I'm curious as to the physical reasons people mumble. Specifically, I heard someone say recently that some older people start talking lower because of hearing loss. That sounded strange, because I would think, instinctively, one would speak louder with a hearing loss. I supose the issue could be the "internal volume control," so to speak, where the person just *thinks* they're speaking normally because they're used to not hearing much, anyway. It just seems so counter-intuitive.; it seems that once you get that volume down when you're a child, it stays, unless you think you have to speak louder.

Also, considering the person mentioned older people, I wonder if mumbling could be due to a heart problem, with not enough oxygen coming to the person. Although, I always though those weak voices of dying people in movies and TV were just dramatized; sure, my grandparents' voices sounded a little weaker toward the end, but not *that* weak. Thanks.Somebody or his brother (talk) 19:33, 5 October 2008 (UTC)

In my experience, some muttering is passive aggression. Mumble first, then when someone asks for clarification shout "I SAID...." Other mumbling may reflect shyness or a defense mechanism for fear of being attacked for saying something. Also consider that when it seems like other people are mumbling, it might actually reflect a hearing loss on the part of the listener. Edison (talk) 20:51, 5 October 2008 (UTC)

Much of our speech habits is controlled/re-enforced by hearing our own voice or the voice of others. If we lose our hearing we lose that reference and the habits can slip. Ever notice how weird it is to talk with really good sound protection on?

Speculation... If an older person is losing their hearing then it's possible they are told a few times too many that they are talking loud... and then they over-compensate in response. ---J.S (T/C/WRE) 01:29, 6 October 2008 (UTC)

A rather simplistic explanation: Humans are inherently designed to put forth the least amount of energy required to complete a given task. If that task is communicating a message, there is not point in speaking in a loud, clear voice when a soft mumble will likely work just fine. I ride the bus most days. I hear conversations that sound like, "Isa you gur edda sto." "Mudu?" "Yaw." "Aw, shu gedda da mun etta." It may sound like nonsense, but it is the minimum effort required for the two to converse. Sometimes it fails. I was one of my favorite Chinese food restaurants and the lady in front of me ordered "frump fry fie". The guy at the register didn't understand. She asked again for "frump fry fie". He didn't understand. After going back and forth a large number of times, a cop behind me asked her if she wanted "shrimp fried rice." She replied "Fu!" -- kainaw™ 03:34, 6 October 2008 (UTC)

I agree with these answers. In addition, though, think about a feedback loop. Will the person get positively or negatively reinforced when they begin to dabble in mumbling behavior. The answer is positive reinforcement, so they will keep winding down the slippery slope. Plus, you gave stated information that it is about older people. Society has norms for providing people these unfortunate feedbacks. Its just an interesting theory, not quite yet a paradox. It was good though, I liked reading and answering your question. Thanks Sentriclecub (talk) 18:39, 6 October 2008 (UTC)

Loss of hearing acuity would sever the feedback link between spoken volume and perceived volume. Also, the volume of your own speaking is largely transmitted through your own skull, so problems at the eardrum mechanism would cause other people's voices to decrease in perceived volume more than your own. It is only the younger cellphone generation who have decided that the solution to poor audio is to SPEAK LOUDER into their own phone. (Incidentally people, you don't have to face outwards on your balcony to get better reception, although it does let everyone know how cool you are. And ain't it strange how all the phones work so well indoors in wintertime, but in summer you suddenly need to give me all the details of your life?) If you can't accurately assess your own relative vocal loudness, it's hard to say whether your own loudness would increase or decrease.

That said, I am well-known in various workplaces as "talks to himself" - so to some extent, mumbling is also a vocalized internal conversation. Franamax (talk) 22:37, 6 October 2008 (UTC)

I'm the same, Franamax. One of my kids once mentioned in passing how I was talking to myself when I was typing something on my computer. I said I wasn't aware of it, but if it was true, I must have had something on my mind and it would have been a one-off experience. I was humbled when he said "Dad, you do it all the time". Others have since commented on this. Maybe I'm the Glenn Gould of Wikipedia. My experience of increasing deafness is that I'm more and more often asked to speak up. Apparently, to my interlocutors I'm mumbling, but to me I'm speaking at what I think is a normal volume. What people hear in their own heads when they're speaking is not the same as others hear them. I'm reminded of this whenever I'm watching TV and munching on a snack. Whenever I take a bite, I momentarily lose what I'm listening to, and I've learned to do most of my munching during the ad breaks. -- JackofOz (talk) 23:45, 6 October 2008 (UTC)

Well luckily I'm showing no signs whatsoever of aging. There is an increasing trend to smaller font sizes and lower light levels in general, but I'm sure that will change back in time. I too have noticed the new more loudly-crunching snacks that prevent one from hearing the program. This will all doubtless be fixed when the US Democrats come to power. Or was it the Republicans? I'll consider this when I've finished my nap. :) Franamax (talk) 01:09, 7 October 2008 (UTC)

"When in doubt, mumble" -- James H. Boren. I know I do that a lot. — DanielLC 23:50, 6 October 2008 (UTC)

On a related "what you hear in your head and what others hear is not the same" topic... I very much like to sing when I program. In my head, I hear a voice somewhat in tune with what is coming out of my speakers. To everyone else, my voice is monotone, nasal, and very annoying. Hence, I do most of my programming at home, at night, after the family is asleep. -- kainaw™ 01:21, 7 October 2008 (UTC)

You should probably get a small headset-microphone and plug that into your sound-card so you can mix a little of your voice into whatever it is you are singing along to so you can hear yourself as others do. SteveBaker (talk) 11:35, 7 October 2008 (UTC)

Blindness and visual artefacts

Do people who are blind from birth 'see' visual phenomenons, artefacts or hallucinations, perhaps due to the lack of stimulation of the visual cortex? Has anyone got links or refs on that subject. Thank you. 190.244.186.234 (talk) 21:38, 5 October 2008 (UTC)

Ah, I already found this: Charles_Bonnet_syndrome. 190.244.186.234 (talk) 21:43, 5 October 2008 (UTC)

That article doesn't mention persons who are blind from birth. That syndrome seems to afflict persons who lose their sight later in life. Plasticup ^T/C 04:10, 6 October 2008 (UTC)

Almost the exact same question was asked about a month ago and given (in my opinion) thorough treatment. Check out the response here. --Shaggorama (talk) 06:13, 7 October 2008 (UTC)

Hurray! Fanx. OP. 190.220.104.35 (talk) 15:38, 7 October 2008 (UTC)

extrusion of rock

What do the extrusion of rock form? Thanks, from my son - for his Science homework. —Preceding unsigned comment added by 76.69.48.237 (talk) 22:12, 5 October 2008 (UTC)

All kinds of neat stuff. Extrusive article is a good place to start. -- Finlay McWalter | Talk 22:14, 5 October 2008 (UTC)

October 6

Sleep Noises

As people fall asleep I've noticed (through my limited experience) they make some sighs/moans/grunts/little noises. Is there a cause, or reason for this?207.172.71.243 (talk) 00:14, 6 October 2008 (UTC)

According to our articles on sleep stages and myoclonus, these seem to result from normal involuntary muscle movements when entering the "N1" stage of sleep. Claiming my unsigned edit from 22:21 06Oct08. Franamax (talk) 01:49, 8 October 2008 (UTC)

See hypnagogia and hypnic jerk for related subjects, although I don't see anything specifically about making noises. --Anonymous, 22:24 UTC, October 6, 2008.

Volume of human voice

Is an increase in the volume of a human voice, be it shouting, talking louder, or full-on-screaming--mostly created through the larynx, or lungs?

I'm really just wondering about the ability for humans to raise and lower the volume of their voices, how is that controlled?207.172.71.243 (talk) 00:19, 6 October 2008 (UTC)

I do not know for sure, but I think it's controlled by the volume of air permitted to pass over the lungs... much in the same way that a whistle gets louder as you blow harder into it. ---J.S (T/C/WRE) 01:24, 6 October 2008 (UTC)

Today is a bad day for people NOT doing experiments here on the science desk! Put your hand just in front of your mouth...whisper something...did you feel any air flow? Probably not. Now yell as loud as you can...do you feel air flow now? I guess so...hence a greater volume of air is being moved when you shout. Now - how on earth could your larynx cause air to flow? Just feel what happens to your lungs when you shout - it's really obvious. The larynx controls the pitch (frequency) of the sound - not the volume. SteveBaker (talk) 13:26, 6 October 2008 (UTC)

Well, the larynx certainly enters into the picture. When you produce a soft sound at a given frequency, your vocal cords open and close at that frequency. When you shout at the same frequency, your vocal cords open and close at the very same frequency. When a greater volume of air passes, the vocal cords must open more widely, i.e. they vibrate with a greater amplitude. To achieve that requires that the laryngeal muscles be kept tighter. Amplitude corresponds to volume. The increased amplitude of the vocal cords is transmitted to the resonant cavities (chest, sinuses) resulting in the louder sound. By the way, to be precise, it isn't your lungs that cause the increased air flow, it's the diaphragm and chest muscles. --NorwegianBlue ^talk 19:05, 6 October 2008 (UTC)

That's right. Trained singers (and speakers) keep good control of their diaphragm so that they can control the amount of air (well, CO2 to be precise) they expel. That way they can sing a long phrase, in which the volume might vary from soft to loud and back again, without needing to take a breath and in the process interrupt the musical phrasing. If they try to do it by just allowing their lungs to deflate, they'll run out of breath too quickly. Far better to use a taut diaphragm to push the air out in a controlled way. -- JackofOz (talk) 23:33, 6 October 2008 (UTC)

Jack, not to be a stickler or anything, it's actually air (N, O2, CO2, etc) your exhaling... with co2 being only a minority part of it. ---J.S (T/C/WRE) 03:39, 7 October 2008 (UTC)

Thanks, J.S. I'll remember that. Also not to be a stickler, but let me repay the kindness by alerting you that it's "you're exhaling"  :) -- JackofOz (talk) 01:22, 8 October 2008 (UTC)

What Jack is referring to is commonly known as the rule, "Sing/Speak from your stomach, not your chest." Some people naturally use their diaphragm. Others use their chest. The voice produced usually sounds very different. -- kainaw™ 03:45, 7 October 2008 (UTC)

Hypnic jerk

Is there a way to decrease the strength and frequency of hypnic jerks? Plasticup ^T/C 02:22, 6 October 2008 (UTC)

Not medically speaking mind you but it seems to occur more when I'm sleep deprived so in my case I'd say to me-self "get more sleep"  ;) -hydnjo talk 03:09, 6 October 2008 (UTC)

Are they, neurologically speaking, similar to seizures? Have they ever been treated with anti-seizure medications? Plasticup ^T/C 03:37, 6 October 2008 (UTC)

Now that is seeking medical advice and therefor we'all must resist the temptation to further diagnose or offer treatment suggestions for the affliction of which you speak - seriously. -hydnjo talk 03:56, 6 October 2008 (UTC)

Oh darn, because I really was going to walk down to my local pharmacy and buy some anti-seizure meds. I just want to know where the science stands. Humor me, I promise I won't sue. Plasticup ^T/C 04:05, 6 October 2008 (UTC)

If you wanted to know where the science stands, you would search medical journals for "hypnic jerk" and "seizure". Instead, you are asking random strangers who likely have no medical experience of any kind. It shouldn't be too difficult to understand how stupid that appears. A proper question would something like, "Does anyone have any links to medical studies on hypnic jerk?" For, you see, this is a reference desk, not a "does anyone have any medical opinions based on years of watching the Simpsons and Family Guy that I can use to try and diagnose and treat an annoying problem that I think I might have" desk. -- kainaw™ 04:09, 6 October 2008 (UTC)

Don't be facetious. A link to a medical journal is exactly what I am looking for. If you cannot answer without referring to the Simpsons then don't answer. Leave it for someone else. Plasticup ^T/C 04:13, 6 October 2008 (UTC)

C'mon now Plas, no one is being a dick here, we're just trying to comply with the arduously arrived at guidelines with regard to the phrasing of your question. Of course a different phrasing would bring a different response. -hydnjo talk 04:26, 6 October 2008 (UTC)

That is more or less the definition of facetious. Why should the wording matter? If someone is aware of an article in a medical journal on this subject they will share it no matter how I word the question. Besides, where did I ask for advice? I have only asked for information. Plasticup ^T/C 04:39, 6 October 2008 (UTC)

Unfortunately, the result of being stepped upon by the "community" in these matters has left the desks with an uneasy feeling about all things that could be interpreted as "medical advice". I agree with you but past experiences have left us impotent. So, careful wording is more important than you could imagine but please try:

I'm seeking information beyond what is cited in the Hypnic jerk article. Specifically, and in neurological terms is that jerk similar to a seizure and has it ever been treated with anti-seizure medications such as gabapentin or the like? Any links besides those available when I googled "hypnic jerk"would be appreciated. Thank you (wimp-ally ), (say), - hydnjo talk 05:18, 6 October 2008 (UTC)

Yes but it falls into personal experience which I don't want to publish here. If you wish I would be glad to share my experiences via email. (say), - hydnjo talk 05:41, 6 October 2008 (UTC)

I'm glad to see that nobody's succumbed to the temptation of calling you a "hydnjic jerk" just because they disagree with you, Hydnjo.  :) -- JackofOz (talk) 23:23, 6 October 2008 (UTC)

At the risk of stepping into the discussion, here is a reference that appears to be freely available in PubMed. It appears to be a general review about sleep disorders but has a small section on "Sleep Starts (Hypnic Jerks)". There seems to be a dearth of medical research into this subject, but according to this reference there are no known treatments. Perhaps someone interested in the subject could improve the Hypnic jerk article? —Preceding unsigned comment added by Medical geneticist (talk • contribs) 13:59, 6 October 2008 (UTC)

Hypnic jerks are at one end of a spectrum leading up to periodic limb movement disorder (nocturnal myoclonus). Hypnic jerks are usually regarded as a trivial normal phenomenon. If your patient's hypnic jerks are so disruptive that he/she is considering taking medication, it is more likely to represent periodic limb movement disorder. I recommend referral to a sleep specialist (in the UK a subspecialty among pulmonologists) for a sleep study. Treatment options for PLMD are the dopamine agonists ropinirole and pramipexole. Axl ¤ [Talk] 19:23, 6 October 2008 (UTC)

multinucleate cells

What's the difference between a syncytium and a coenocyte? --Anakata (talk) 03:03, 6 October 2008 (UTC)

The articles say a syncytium is "cell-like" (but, presumably, not a cell) with multiple nucleii, while a coenocyte is a "cell" with multiple nucleii. And that's as far as I can go. ៛ Bielle (talk) 04:46, 6 October 2008 (UTC)

Maroon Clowns

Transferred from Miscellaneous desk Gwinva (talk)

Can a Gold-stripe maroon clown fish and a normal Maroon clown mate together?--Pufferfish4 (talk) 20:19, 5 October 2008 (UTC)

I couldn't find anything, but I bet the folks at http://www.fishforums.net/ would be able to help you. Alternatively, you could ask some of the contributors at Wikipedia:WikiProject Fishes. If they don't know the answer offhand I bet they would know where to look. Plasticup ^T/C 03:52, 6 October 2008 (UTC)

Languages in dreams

Has anyone ever researched languages in dreams? I was speaking with a couple of friends (both Greek Cypriots who are fluent in English), both of whom said that they dream both in English and in Greek. Any idea if such is common? I looked at dream, and I couldn't find anything even about speaking in dreams in general, let alone the language in which the speech is conducted. Nyttend (talk) 04:49, 6 October 2008 (UTC)

Well, speaking for myself, I certainly dream both in English and Finnish, absolutely. I think someone brought this up here before, but I can't seem to find that discussion now. -- Captain Disdain (talk) 07:30, 6 October 2008 (UTC)

In contrast, I'm fluent in Hindi, English and Bengali but have never had a dream in any language apart from hindi, which is my native language.Leif edling (talk) 11:37, 6 October 2008 (UTC)

I don't remember my dreams but in waking life I don't think in language much anyway except when thinking about communicating with other people. It's more about connections and movement and probabilities - gut feel but structured if you like. Dmcq (talk) 12:17, 6 October 2008 (UTC)

I used to dream in broken Spanish. It was horribly frustrating, because my limited language skills would impede the progress of my dream. Apparently this book discusses a "pidgin Malayalam used by Todas in trance states", but I couldn't find the passage. Plasticup ^T/C 15:57, 6 October 2008 (UTC)

I've always thought that the assumption that most people experience the world in generally the same way was a particularly limiting facet of contemporary psychology. How most people see the world is often confused with how everyone sees the world. --Shaggorama (talk) 05:58, 7 October 2008 (UTC)

For info, I dreamed in French for about two years and after a gap began to dream in French again until I tracked it down to an early life event. After that English only (so far). Julia Rossi (talk) 07:14, 11 October 2008 (UTC)

marine engineering

ship is using heavy oil during sailing in sea.But in port it is using diesel oil why —Preceding unsigned comment added by Rajulramachandran (talk • contribs) 07:35, 6 October 2008 (UTC)

I presume that the heavy oil is used for running the main engines - but in port they only need smaller diesel generators to produce electricity. But that's just speculation. SteveBaker (talk) 11:33, 6 October 2008 (UTC)

Ships at sea use bunker oil, pretty much the worst and dirtiest petroleum-based product there is. The lower parts of an oil refinery fractionator produce a very low quality type of oil, and in particular, the wash zone just above the inlet feed is used to remove heavy metals from the stream. This is the most worthless of crap in the petroleum (NB asphalt is even worse, but it goes out the bottom and gets put on roads, also vast effort is expended on getting anything good out by means of the vacuum fractionator). All the junk that can still flow gets sold somewhere, and that somewhere is ships at sea, where no-one can hear you scream. No right thinking harbourmaster would allow such junk to be burnt anywhere near people - so ships switch over to half-decent fuel when they come into port. Out on the ocean, they use the really cheap and nasty stuff. Franamax (talk) 22:02, 6 October 2008 (UTC)

SOUND

WILL SOUND PASS THROUG SOLIDS —Preceding unsigned comment added by 59.93.6.27 (talk) 11:49, 6 October 2008 (UTC)

Yes, see the article named sound. It normally goes very well through solids and liquids as well as the air, the only problem it has is going between different mediums - that's why soundproofing is made of mixtures of odd shaped materials and air. Dmcq (talk) 12:22, 6 October 2008 (UTC)

This being the science desk - I recommend an experiment (actually, a "thought experiment" should do here). Sit inside a car on busy road - shut all the doors and windows and turn the engine and radio off. Can you hear the other cars on the road? Yes? Then sound passed through the solid surface of the car. Sound is just a vibration. The air vibrates - your ears pick up that vibration. In the case of our experiment, vibrations in the air outside of the window caused the glass to vibrate. On the inside of the car, the vibration of the glass started the air inside the car vibrating - and that's what you could hear. If you gently touch the glass with your fingertip as a big truck goes by - you can feel the glass vibrating. SteveBaker (talk) 13:19, 6 October 2008 (UTC)

I think that is wrong. it could it ber comming from throught the air conditioning pipe from outside and not throught the solids? —Preceding unsigned comment added by 194.80.240.66 (talk) 14:27, 6 October 2008 (UTC)

Have you ever heard a sound? If so, it's because it went right through your solid eardrum. --Sean 14:41, 6 October 2008 (UTC)

Even those not blessed with the faculty of sound can feel low tones resonating in their chest cavity. Plasticup ^T/C 15:50, 6 October 2008 (UTC)

Sound actually travels *faster* through most (all?) solid objects than air. In steel, sound travels at 5,100 m·s^-1, about 15 times faster than in air. If you yell at your friend underwater, it will get to them about 4 times faster than having a conversation above ground. -- MacAddct1984 ^{(talk • contribs)} 18:57, 6 October 2008 (UTC)

It should be possible to demonstrate this if you have access to a straight metal bar at least 100 feet (30 meters) long and preferably somewhat more (an abandoned railway track would be ideal, but please don't try it on a working railway, where you might get run over by a train!). Perhaps you can find a long, continuous metal railing somewhere in a public park or plaza. Okay, now you need a friend to assist you, or maybe you can trick an enemy into doing it, if you don't have any friends. :-)

Have your assistant bang on the bar every few seconds with something hard like a rock or a small hammer (if the bar has a decorative finish, it would be safer to stand a flat piece of metal on top of it and bang on that, to avoid damage). If you stand far enough away along the bar, you will hear the sound lagging behind the your assistant's motions. 100 feet will give a lag of about 1/10 second; at 200 feet the lag is 1/5 second and will be more obvious. Now put one ear against the bar and you should hear the tapping in that ear ahead of the other ear. That proves that the sound is traveling through the solid bar faster than the air, and therefore that the sound is traveling through the solid. --Anonymous, 22:39 UTC, October 6, 2008.

the question is backwards. the fact is, sound doesn't pass through a solid, the solid carries the sound. if there's nothing to carry the sound, well in space nobody can hear you scream. Gzuckier (talk) 06:13, 11 October 2008 (UTC)

Light from the remote visible in the video image?

when i has my video camera and my tv remote i can sees the light from the remote in the video camera but not irl, so what is the thing thats happerning here? why is this? —Preceding unsigned comment added by 194.80.240.66 (talk) 12:19, 6 October 2008 (UTC)

I moved the question from the Miscellaneous dek, as this is really a Science question. (Also retitled it.)

It's pretty simple: your eyes can only see light within a certain visual spectrum. The infrared light your remote emits is outside that spectrum, and thus it isn't visible to the naked eye. The video camera, however, detects it. (Not all cameras do this; it's a question of filtering the light properly, and cheaper or older models in particular don't necessarily do it very well.) Therefore, when you look at the video image, it looks as if there's a light shining from the remote. (And there is, you just don't normally see it.) -- Captain Disdain (talk) 13:24, 6 October 2008 (UTC)

Ah, thank you. Also i has another question = with thr remote when i use it near an readio on fm or longwave i head a buzzing noise from the radio. but only when the remote was in useing. again, how would light be affecting my radio? —Preceding unsigned comment added by 194.80.240.66 (talk) 14:25, 6 October 2008 (UTC)

While I'm not sure of exactly what frequencies would be responsible, it's worth remembering that light and radio waves are both forms of electromagnetic radiation -- they're just at different frequencies. Infrared and radio are far enough off, though, that I don't think this is necessarily what's responsible. If you use the remote next to the radio, you get interference, right? But I bet if you back 10 feet away and just point the remote at the radio (and then press buttons), nothing happens. That would suggest that it's not the IR light but rather the circuitry internal to the remote that's responsible. Circuits tend to leak EM radiation as well, and remotes aren't likely to be shielded to prevent interference at close range. Electronic circuits are also more likely to operate at frequencies near common radio bands. — Lomn 14:43, 6 October 2008 (UTC)

(ec) That's nothing to do with the IR light - it's because the remote contains a small computer. Computers do their calculations at rates that vary a lot from machine to machine. Your PC probably has a processor that runs between 1GHz and 3GHz - but the small computer inside the remote has to operate for long periods on one tiny battery and it doesn't have much work to do to figure out what IR light pulses to send when you push a particular button - so it's pretty slow...perhaps below 1MHz. At those sorts of frequency, the speed that the computer works at is close to the frequencies that your radio is designed to pick out of the air and amplify. The radio has to be sensitive enough to pick up very faint radio signals from a transmitter 20 miles away - so if the computer circuitry in your remote is leaking even a tiny amount of radio waves and you hold it close enough to the radio - then the radio will pick up the signal and you'll hear it. Back in the early days of home computers, I had a TRS-80 computer - which didn't have a sound chip inside. Some enterprising programmers figured out how to make the computer play music by running certain program sequences that could be picked up by holding a radio close to the computer chip! SteveBaker (talk) 14:46, 6 October 2008 (UTC)

certain brands of cameras can turn into effective IR cameras by removing an internal IR filter, and thus became notorious a few years ago for taking pictures of people through their clothes. still available if you lurk around the unsavory parts of the internet. Gzuckier (talk) 06:16, 11 October 2008 (UTC)

Biology word

I'm having trouble recalling a word that began with the letter "A", having something to do with organs becoming unimportant / unused over time, like the appendix, or tonsils. —Preceding unsigned comment added by 69.16.88.147 (talk) 15:18, 6 October 2008 (UTC)

It doesn't begin with "A", but I have heard the term vestigial structure used to describe those phenomenon. Plasticup ^T/C 15:24, 6 October 2008 (UTC)

(edit conflict) Such organs are called vestigial. The only word beginning with 'A' that I can think of that could be relevant is atrophy, which could be used to describe an organ shrinking down to a small remnant of what it was when it was being used, however I don't think that would be a strictly correct use of the word. --Tango (talk) 15:25, 6 October 2008 (UTC)

Adventitious? "Developing in an unusual place or from an unusual source", though that may be even further afield. -- 128.104.112.147 (talk) 23:03, 6 October 2008 (UTC)

Atrophy? — DanielLC 23:42, 6 October 2008 (UTC)

Atrophy doesn't seem quite right - that suggests a single creature losing an organ during it's lifetime. Here we're presumably talking in an evolutionary sense - like creatures who spend their entire lives in caves gradually evolve into a form that has no eyes (see: troglobite). Adaptation would perhaps be an appropriate term - but it means a lot more than just losing organs. Regressive evolution is another term that you see a lot. SteveBaker (talk) 11:28, 7 October 2008 (UTC)

Atavism? -- Ferkelparade π 15:33, 7 October 2008 (UTC)

Debunking Ghosts

They say that ghosts are not real and that most scientists say they truly don't exist and have proven so. Exactly what scientists are they referring to? I am looking to get specific branches of science that these scientists are from. --Anilmanohar (talk) 15:38, 6 October 2008 (UTC)

See Princeton Engineering Anomalies Research Lab and everyone who criticized their poorly designed experiments. That would be physicists, psychologists, chemists, economists, and statisticians. That lab, by the way, was eventually closed as an embarrassment to the good name of Princeton University. Plasticup ^T/C 15:46, 6 October 2008 (UTC)

It's not really possible to prove something like "ghosts don't exist", and no reputable scientist is likely to claim to have done so. What they can confidently say is more along the lines of "there is no evidence that ghosts exist", and then it's up to you to decide whether you believe in things for which there is no evidence. --Sean 15:58, 6 October 2008 (UTC)

I don't think anyone believes in things for which they think there's no evidence. Some people just think that there is evidence that ghosts exist, in the form of bright spots in photographs or mysteriously moving objects or what have you. So I think the operative question is, who scientifically investigates the evidence proffered by such people? I don't think the answer is CSICOP, in spite of its name. They have on occasion scientifically investigated a claim of the paranormal, but mostly they seem to report the claims and scoff at them without any substantial investigation. -- BenRG (talk) 17:02, 6 October 2008 (UTC)

It's notable that the claims of the existence of a hypothetical or doubtful entity cannot be refuted by experiments. There is only scope for affirming the existence of such entities (eg the case of the mountain gorilla). So long as there is no experiment affirming the existence of such entities (especially something as preposterous as ghosts) I think it would be safe to presume there aren't any. As far as branches of science go, parapsychology is a field of related research.Leif edling (talk) 16:56, 6 October 2008 (UTC)

In such cases where proving a negative is impossible, we have to fall back on a scientific principle called Occam's razor. This isn't a law of science - but it's a good principle to live by. It says that if all else is equal and there are multiple explanations for a phenomenon, you should pick the simplest - the one that requires least change to established science. In the case of ghosts - where there is absolutely zero solid evidence for them, we're left with two possibilities: (a) that there is an entire range of common, complex phenomena that science has somehow completely and utterly missed or (b) that some idiots are lying to us. Guess which we pick? SteveBaker (talk) 18:19, 6 October 2008 (UTC)

I choose (b), but how did the Bush administration creep into this discussion? (Hey, I gotta get my shots in while I still can.) If somebody from the Secret Service is reading this, I mean it figuratively. Clarityfiend (talk) 22:37, 6 October 2008 (UTC)

What about the coelacanth? Scientists regarded it as having been extinct for millions of years, based on the fossil record and the utter absence of any evidence - known to them - that it had survived. Then they discovered it had indeed survived, and had been regularly if infrequently caught by islanders since time immemorial. It was certainly no stranger to the people of the Comoros. It all depends on who you talk to and where you look when you're gathering your evidence. Not having looked in all possible places does not equal "it does not exist". -- JackofOz (talk) 23:18, 6 October 2008 (UTC)

There are innumerably many things that exist that we haven't discovered. As much as it is, it doesn't compare to the number of things that don't exist that we haven't discovered. Nobody claims that everything that we don't have evidence for is false. Quite the contrary, any scientist will tell you that we have no evidence for almost everything that's true. We also have no evidence for almost everything that's false. Because the number of things that we have no evidence for that are false astronomically exceeds the number that are true, it is reasonable to suppose that a given thing that we have no evidence for is false. For example: it is generally believed that the number of living species exceeds the number we have discovered by several orders of magnitude. Despite this, if you just made up a species, you could safely say it doesn't exist. By the way, the coelacanth is a bad example, as we at least knew it existed at one time. Every time we discover a new species of fish, until that point we had no reason whatsoever to believe that it existed. — DanielLC 23:41, 6 October 2008 (UTC)

Oh, I don't know. I agree with your last point, but in relation to the coelacanth, scientists confidently claimed "it no longer exists", when that was not true. They didn't just say "we know of no evidence that it has survived". -- JackofOz (talk) 00:03, 7 October 2008 (UTC)

Actually, the coelacanth is always a bad example, because its an aquatic species, and there are such vast areas of the earth;s oceans that have gone unstudied. Were scientists mildly intrigued to find one alive? Certainly, but its not like finding an extinct land-based animal alive. If someone found a live T. Rex, for example, it would be far more shocking... --Jayron32.talk.contribs 03:27, 7 October 2008 (UTC)

Mildly intrigued? That would be rather an understatement. This gets back to Steve Baker's options (a) and (b) above. They chose option (b) with the coelacanth, as they do with ghosts and other claimed phenomena - but option (a) turned out to be the one they should have chosen. It wasn't as if the evidence wasn't there for those with eyes to see it, but they based all their findings of non-existence on published research papers etc, none of which had ever looked in the numerous places where the coelacanth is now known to have thrived for millions of years after it supposedly became extinct. -- JackofOz (talk) 06:03, 7 October 2008 (UTC)

Before the discovery of a modern coelecanth, we have these two competing hypotheses:

1. The coelecanth is extinct.
2. Nobody has happened to catch one recently (or nobody who had ever caught one has ever come forward to mention it).

Using Occam's razor to choose between these two options is dubious at best. Neither of them breaks any extant scientific laws or principles or requires any rewriting of the rest of science. The existance or non-existance of this fish doesn't really change much of what we know about the remainder of the universe. Perhaps our notion of cuttlefish population densities and breeding rates off the coast of one small stretch of South African coastline may need tweaking - but that's hardly a big deal! This is a case where archeologists and marine biologists simply made an overly hasty assessment due to an understandable lack of evidence - science is not infallible and we can easily be wrong about the small details. But for ghosts to exist, huge swaths of biology, physics and chemistry would need to be rewritten - things that we've carefully measured and graphed and calculated for two hundred years or more would have to be proven wrong. The chances of that being the case (versus "a few idiots are lying to us") is close to zero. Hence the use of Occam's razor in that case is entirely appropriate. SteveBaker (talk) 11:06, 7 October 2008 (UTC)

And back to the original question; the reason scientists don't reliably believe that ghosts exist is that all paranormal experimentation lacks the one property that all true scientific proof requires: repeatability. In every case, independent verification of the results fails; it always depends on the the individual performing the experiment. That is why there is no scientific proof of ghosts; and why it is assumed they don't exist; any "proof" of their existance falls apart under controlled conditions... --Jayron32.talk.contribs 03:30, 7 October 2008 (UTC)

It's useful to understand the argument from ignorance fallacy (aka: lack of proof is not proof of lack) in any discussion of paranormal proof like this. --Shaggorama (talk) 05:48, 7 October 2008 (UTC)

"Proof" is too strong a term here. Let me state this very clearly and carefully: We do not have proof that ghosts don't exist. But proof isn't everything. What we must have (for sanity's sake) is the general principle that we don't go around believing in things just because there is no proof to the contrary. I don't believe that the Invisible pink unicorn (mhhnbs) exists - but I don't have a shred of proof for that non-belief (although the otherwise inexplicable existance of pineapple and ham pizza could certainly use some in-depth research). So, yes, User:Shaggorama is right: Absence of evidence is certainly not evidence of absence (ie it is not proof that something doesn't exist). But it is quite solid grounds for the only-slightly-weaker statement that we do not believe in something. The absence of evidence for ghosts is more than enough reason to disbelieve in them. There are quite literally an infinite number of things that we cannot prove do not exist. Does that mean that we should go around with the default hypothesis that those things do exist? Certainly not! That way lies madness. If you have to believe in a literally infinite number of improbable things until you have solid proof that they do not exist then your life becomes quite impossible to live. You can't get up in the morning for fear that an previously undiscovered species of mothball-scented purple velociraptor has been nesting in back of your sock drawer for the last 100 million years and is about to pounce...you can't prove that it hasn't, and this certainly explains all of those odd socks! SteveBaker (talk) 11:06, 7 October 2008 (UTC)

Just to clarify, I wasn't trying to say I beleive in ghosts :) --Shaggorama (talk) 20:36, 7 October 2008 (UTC)

I'm going to start checking for those mothball-scented purple velociraptors though. That provides an ideal explanation for my unmatched socks. The evidence is compelling - the only question now is whether those sock-eaters evolved or were created by God on Oct. 23, 4004 BC. Thanks Steve, for clearing that up! Franamax (talk) 02:17, 8 October 2008 (UTC)

This is why Occam's Razor shouldn't be paraphrased to "The simplest solution is usually the best". Simplest is a super subjective term. A velociraptor that instinctively steals socks seems like a pretty 'simple' solution to me. Even if it does involve needlessly multiplying entities it's a lot simpler than figuring out where the socks really go. APL (talk) 01:51, 9 October 2008 (UTC)

LCD Spectral Lines

I was curious one day so i got a pocket spectroscope and looked at my LCD monitor with it. Curiously, very defined spectral lines appeared. I can't find anything on this and i want to know why this happens. Can someone help? PS I don't know how to take a picture of these lines, sorry guys :) 31306D696E6E69636B6D (talk) 16:26, 6 October 2008 (UTC)

I think the backlight is a kind of fluorescent lamp. These can have sharp lines, depending on the design. See the article for examples. -- Coneslayer (talk) 16:48, 6 October 2008 (UTC)

The backlight is designed to produce pure colors when filtered through the LCD panel - so ideally it needs one spectral line at the center of each of the red, green and blue filters - putting out frequencies between those three colors would produce a 'muddy' display with all sorts of nasty colors and no decent, solid black. I don't know how they get it that good - but evidently, they do. SteveBaker (talk) 18:22, 6 October 2008 (UTC)

Fatigue relief

Is there any method whereby one may be relieved of fatigue and pain due to lactic acid deposition? Could ice packs be of any help?Leif edling (talk) 16:45, 6 October 2008 (UTC)

Rest would be best way to treat fatigue. If you want more of an answer than that, you'll need to ask a doctor, we can't medical advice here. (Ice could numb the area and reduce the pain, but then again it could give you frostbite or hypothermia or both, hence the need to ask someone more reliable than a random guy on the internet.) --Tango (talk) 17:00, 6 October 2008 (UTC)

Never place ice packs directly on the skin, no matter what you're trying to alleviate. Always put a towel or bandages between your skin and the ice. -- MacAddct1984 ^{(talk • contribs)} 18:44, 6 October 2008 (UTC)

We do have an article on Fatigue (medical), but it has no discussion on relief. --—— Gadget850 (Ed) ^talk - 18:54, 6 October 2008 (UTC)

Ice packs do help with pain caused by exercise, as do warm baths. Other than that, rest is your only other option without seeing a doctor. —Cyclonenim (talk · contribs · email) 23:02, 6 October 2008 (UTC)

Sounds like you're talking about post-exercise cramps. If so, check out Delayed onset muscle soreness. Being proactive with a warm-up, cool-down and stretching is believed to help alot. Also, cramping is usually the worst when beginning an exercise regimen: after a few weeks, your muscles become acclimated to the workout and your metabolism adjusts appropriately. --Shaggorama (talk) 05:42, 7 October 2008 (UTC)

Gauge>Alum foil?

The metallic scale GAUGE? 75.60.90.25 (talk) 16:58, 6 October 2008 (UTC)

The "gauge" of some aluminium foil is its thickness, is that what you wanted to know? According to Aluminium foil, it's usually between around 0.006mm and 0.2mm. --Tango (talk) 17:03, 6 October 2008 (UTC)

If you are wondering why metal thickness is measured in "gauge" units, this is a shorthand notation to make it easy for people in the metal industries to refer to their products. The development of the gauge system is rooted in the history of metalworking and lets everyone produce a series of standard products. For instance, 24-gauge mild steel is .024" thick and weighs 1 lb/sq.ft. Going by our Sheet metal gauge (redirected) article, aluminum foil thicknesses fall below the established "gauge" range - but the thickness is still referred to as the "gauge", even though it should be called "thickness". One reason might be that thicknesses are measured with a gauge instrument; another might be that the term "thickness" implies a definite number, whereas a metal "gauge" incorporates variations in thickness produced by the rolling mill, for instance 10-gauge mild steel has a "thickness" of .1345" but this can vary between .1285" and .1405".[3] Short answer: when we talk about metal thickness, we speak in terms of its "gauge". Don't know if that helps at all :) Franamax (talk) 21:45, 6 October 2008 (UTC)

finger print sensors

just like other sensors ,are there some finger print sensors that could be interfaced with some microcontrollers(like 8051).plz tell me the sources of information about it as well. 116.71.187.243 (talk) 19:25, 6 October 2008 (UTC)

Most seem to offer a Serial Peripheral Interface Bus interface, which can be spoken to as described here. Search for fingerprint sensor to see a bunch of them. --Sean 20:26, 6 October 2008 (UTC)

Zombie Newton is haunting me

I'm trying to understand how any why momentum, kinetic energy and mechanical work ... well, work in classical mechanics. I took a few courses of physics and mechanics years ago, but they all skirted the deep questions about exactly why they take the forms they do. Why should work be the dot product of displacement and force? Why is the first integral of mass relative to velicity momentum, and then why is the second integral kinetic energy? Is that something to do with the conservation of {energy, momentum, mass}, but why velocity?

I know these are rather open questions, but my curiosity keeps nagging away at me, and I don't seem to be able to find the answers without taking a physics degree myself. 79.72.138.94 (talk) 19:30, 6 October 2008 (UTC)

Also, I realise full well that the answer might be 'because it is, and that's just how it works', which would leave me feeling rather unfulfilled but sated. 79.72.138.94 (talk) 19:31, 6 October 2008 (UTC)

Actually, the answer is the exact opposite of what you expect. It is because that's the way we as people have organized our thinking. There's nothing fundemental about the concepts of "force" or "work" or "velocity". They are just convenient ways for us to organize our observations of motion. When we push something harder, it moves faster, so the concept of "force" was invented to explain this observation. When an effort is used to move something, that effort can no longer be used to move something else; thus the concept of energy is created. If you want to get beyond classical mechanics, physicists have been working on explaining it all, indeed a few different times but there are some fundemental flaws in all of these. Some show promise, others have run into dead ends. Maybe someone else wants to take a crack at this, but that's the best explanation I can come up with... --Jayron32.talk.contribs 19:41, 6 October 2008 (UTC)

Good point. I probably should have included that disclaimer as well, that it might just be an artifact of the analysis. I can accept the definition of force, velocity or acceleration as arbitrary artifacts, but energy and momentum seem to be more fundamental, because of the laws of conservation. Even if this is just the way they are organised, I still can't see the reaoning behind the patterns that form, so there is still something I'm missing. And GUTs and TOEs are altogether to visceral for me :) 79.72.138.94 (talk) 19:54, 6 October 2008 (UTC)

Noether's theorem (warning: article is extremely equation-heavy) basically boils down to "where you have symmetries, you have conserved quantities". As such, once you've defined positions, velocities and forces, under Newtonian mechanics you find that there are symmetries (e.g. time reversibility of a system) that are then associated with conserved quantities that happen to correspond to energy and momentum. Confusing Manifestation(Say hi!) 22:36, 6 October 2008 (UTC)

I have "answers" in some sense for you, as I've thought about these points myself.

1. Your question about work can be answered in two ways. You can identify force with the negative gradient of potential energy, which makes intuitive sense because we expect things on hills to be gravitationally accelerated down them and more quickly for steeper hills; then, using the chain rule, $dU=\sum _{i}dx_{i}{\frac {\partial U}{\partial x_{i}}}=d{\vec {x}}\cdot {\vec {\nabla }}U=-d{\vec {x}}\cdot {\vec {F}}$, and then (by conservation of energy) $U+E=C\Rightarrow dU+dE=0\Rightarrow dE=d{\vec {x}}\cdot {\vec {F}}$. (Note that nonconservative forces are a simplification of conservative ones; we need not treat them separately.) Alternatively, take the derivative of kinetic energy with respect to time: ${\frac {dE}{dt}}=m{\vec {v}}\cdot {\frac {d{\vec {v}}}{dt}}=m{\vec {a}}\cdot {\frac {d{\vec {x}}}{dt}}={\vec {F}}\cdot {\frac {d{\vec {x}}}{dt}}$ and $dE={\vec {F}}\cdot d{\vec {x}}$ immediately: in other words, when you apply a force in the opposite direction of displacement, you're slowing the object down, and when you apply it in the same direction, you're speeding it up, so the dot product is natural.
2. Momentum must be linear in velocity for the simple reason that otherwise small internal motions (like those due to heat) would affect the collective answer. But if heating (or cooling) an object reduces its momentum, what happens to a stationary object? Momentum must also be linear in mass so that inconsequential gossamer connections between objects sharing a velocity do not change their dynamics.
3. Energy's quadratic nature is the interesting part, and derives from the fact that it and momentum are conserved are a scalar and a vector respectively. Thus a change of frame of reference changes velocity but not energy (in Galilean relativity). (The reason for this is that any such changes must be linear functions of observer velocity, so that we can compose frame shifts without changing the answer. For changes in (measured) velocity, the identity function serves the purpose well, but the only isotropic scalar function is the zero function.) Now consider two observers who place a compressed (massless) spring between a pair of identical objects. Then one of the observers starts moving along the direction of the spring, and it fires. Choosing convenient numbers ($m=1,|v|=1$) and coordinates, the stationary observer records velocities of $({\vec {0}},{\vec {0}})$ and $(-{\hat {x}},{\hat {x}})$, for a total momentum before and after of $({\vec {0}},{\vec {0}})$ and a total energy before and after of $(0,2E(1))$. (I'm writing $E(v)$ for the "unknown" function that gives the energy per mass associated with speed v; we know it's linear in mass by the same argument as for momentum, and we know it's just speed because it has to be independent of direction.) The moving observer instead records $({\hat {x}},{\hat {x}})$ before and $({\vec {0}},2{\hat {x}})$ after, for a total momentum of $(2{\hat {x}},2{\hat {x}})$ before and after. This is good; our linear transform of velocity has preserved the conservation. But what of energy? In the moving frame, the construct already had $2E(1)$ kinetic energy, and the spring must still have added its own $2E(1)$; the one moving object must have kinetic energy $E(2)=2E(1)+2E(1)=4E(1)$; evidently it is quadratic. (The ½ is arbitrary; we could just as easily define ${\vec {F}}=-2{\vec {\nabla }}U$, for instance.)
4. Other arguments about energy include that it should be a smooth function of velocity (since observers with slightly different velocities should see much the same thing), and yet it must be a function only of speed. This rules out $E({\vec {v}})\propto |{\vec {v}}|$, because the magnitude of a vector is only continuous and not smooth at 0. (Consider the plot of $f(x,y)={\sqrt {x^{2}+y^{2}}}$; it's a cone and is sharp at the origin.) $E({\vec {v}})\propto v^{2}$ is the obvious choice. Finally, consider throwing an object into a potential energy barrier (like gravity): if the force is uniform, the object will slow down uniformly. Then throw it twice as fast: it takes it twice as long to stop, and was making twice as much progress per time all the while, so it made it four times as far into the barrier. The force being uniform means that, were we to push the object in rather than throwing it, we would certainly expect the effort involved to be linear in the distance, so kinetic energy is again quadratic in speed since it only took twice as much speed to effect four times as much progress.

There's a certain mathematical circularity that's inevitable here, and even appeals to intuition are subject to the objection that they are merely descriptions of our intuition's basis in physics rather than explanations of physics based in intuition. But I find it helpful to understand better the connection between the mathematics and my intuition even if neither has any external justification. Hope this helps. --Tardis (talk) 17:34, 7 October 2008 (UTC)

False or true?

The keratitis that can occur in a contact lens wearer caused by Pseudomonas aeruginosa is an ocular emergency, as if left untreated it could destroy an eye within 24 hours(four tildes). —Preceding unsigned comment added by 79.97.241.246 (talk) 20:03, 6 October 2008 (UTC)

We're not allowed to give medical advice here. The article on keratitis says that it can scar the eye and permanently damage vision. (Or worse : "loss of the eye"! ) If this question is more than hypothetical I strongly recommend that you get to a doctor or E.R. right away. Don't trust your eyesight to strangers on the internet. APL (talk) 20:13, 6 October 2008 (UTC)

I can't tell you how disturbed I am when a single question falls foul of both "we can't give medical advice" and "we won't do your homework for you". --Sean 20:30, 6 October 2008 (UTC)

At least we didn't have to explain how to sue the contact lens manufacturer! SteveBaker (talk) 22:39, 6 October 2008 (UTC)

Just using the information you gave in your question, "is an ocular emergency as if left untreated it could destroy an eye within 24 hours". If that's true, you're damn right it's an emergency. —Cyclonenim (talk · contribs · email) 23:07, 6 October 2008 (UTC)

We have an article on keratitis, which mentions "pseudomonas aeruginosa", "contact lens" and "loss of the eye". It also says that "[o]ne should consult a qualified Ophthalmologist or Optometrist for treatment of an eye condition". Take from that what you will. Plasticup ^T/C 02:04, 7 October 2008 (UTC)

BTW, your supposed to type out four tildes like this ~~~~ not type out the words four tildes. The tilde key would usyally be besides the 1 key on your keyboard. You probably have to hold down shift to get the tilde Nil Einne (talk) 15:34, 7 October 2008 (UTC)

Ha, I'm tempted to create a sockpuppet named User:Four Tildes! (But I won't.) —Tamfang (talk) 15:38, 8 October 2008 (UTC)

Thank you 79.97 for taking trouble to read the intro box at top of page even if it might be clearer in reverse viz "four tildes (~~~~)". ;) Julia Rossi (talk) 07:33, 11 October 2008 (UTC)

Electricity and magnetism

Is it possible to relate the positive and negative charges of protons and electrons and such to the north and south poles of a magnet? For example, does the north pole of a magnet act in a way that implies that it is positively (or possibly negatively) charged? Or are the similarities between electricity and magnetism, such as like repels like and opposites attract, explained in fundamentally different ways? Thank you. 86.74.122.84 (talk) 21:47, 6 October 2008 (UTC)

Magnetism is caused by a changing electric field, such as a moving charge. As such, two particles of opposite charge moving in the same direction will have opposite magnetic fields, so in that sense there is some similarity between north and south poles and positive and negative charges, but it's a little more complicated than that. Confusing Manifestation(Say hi!) 22:30, 6 October 2008 (UTC)

Umm, magnetism is an inherent property of matter, a changing electric field is not required. Variations in the electric field can induce a magnetic field perpendicular to the direction of charge motion, but you don't need current to have a magnet. Or at least, the electric field doesn't have to be changing. See magnetism. Franamax (talk) 00:40, 7 October 2008 (UTC)

Indeed, nuclei of atoms (which are for all intents and purposes "motionless") can display magnetic properties. Generally, the nucleons (protons and/or neutrons) will "match" magnetic poles so as to cancel out, but in nuclei with odd numbers of them (such as C-13) there is a net magnetic moment. Nuclear magnetic resonance and Magnetic resonance imaging use this property of the atomic nuclei. --Jayron32.talk.contribs 03:13, 7 October 2008 (UTC)

You may be interested in the "Gilbert Model" of magnetic behavior; just remember that it's not really physically accurate. --Tardis (talk) 15:43, 7 October 2008 (UTC)

The answer is that north and south "charges" behave like electric charges of ±i. Neither one is closer than the other to positive or negative charge. If you define F = E + iB, then Maxwell's equations

$\nabla \cdot E=\rho$

$\nabla \cdot B=0$

$\nabla \times E=-{\frac {\partial B}{\partial t}}$

$\nabla \times B={\frac {\partial E}{\partial t}}+J$

can be written

$\nabla \cdot F=\rho$

$\nabla \times F=i\left({\frac {\partial F}{\partial t}}+J\right)$

and in that form you can introduce magnetic charges by simply making ρ and J complex instead of real. You could also treat magnetic charge as real and electric charge as imaginary, or each as a mixture of the two (provided they're at right angles to each other). There's nothing special about the electric "direction" in the plane of possible charges except that, for unknown reasons, all known particles have purely electric charge. -- BenRG (talk) 10:00, 12 October 2008 (UTC)

Is THIS version understandable?

Still confusing, but a lot better IMRHO.

Sail Car Preliminary Description Our sail car is a trapezoid with two parallel sides, front and back. One side, the back, is longer than the other (hence a trapezoid), requiring two straws linked together (for the purposes of this description, they will be referred to as one straw). Two hypotenuses lie on the side of the trapezoid. They extend from the back to the front, where they bend and then meet to form the front side. They bend out on the back, creating two extensions outside of the trapezoid. These extensions are two straws deep with the back side straw in the rear and the hypotenuse straws immediately in front. On these extensions are two wheels. They are supported by two pins on each side of each wheel. On the front, there are two wheels as well. They lie near the bends of the front side.

At the midpoint of the back side, two straws extend diagonally frontwards towards the bends of the hypotenuse straws to give the frame extra support. Roughly halfway between the hypotenuse straws and the midpoint of the back side are two straws extending vertically upwards. Between the two straws is a sail. The sails is pinned to the straws for support. The sail is bent inwards and is thus also supported by a crossbeam at the top.

--hello, i'm a member | talk to me! 23:38, 6 October 2008 (UTC)

Member, a simple diagram would really help you out in this. Maybe the better strategy would be (assuming you want to create a new article) for you to start a page in your own user-space, let's say by clicking here: User:Member/Sailcar. You could put some external references in there for us to click on, so we could better understand what you are describing. You (or us others) could then have a shot at creating graphics to better describe your concept. Franamax (talk) 00:29, 7 October 2008 (UTC)

And as you can maybe see from Edison's comments below, put your text into the wiki-space and we will all slice-and-dice it into an encyclopedia article. The safest place is your own user-space per the redlink I gave above. Give us a link to an image or site that describes your concept, we can work with you to make it all work. Honest! Franamax (talk) 01:38, 7 October 2008 (UTC)

I will count the title as a sentence. In sentence 3, why not call the rear "straw" the rear axle? Your use of "hypotenuse" in the paragraph is inconsistent with Trapezoid and with Hypotenuse. Call them the "nonparallel sides of the trapezoid." In sentence 5 you refer to the "front" where the straws bend, and to a different "front side" which is formed by the meeting of the side straws. Eliminate the ambiguity. Sentence 6: Replace "They" with a more explicit description of the members you refer to. How about eliminating pronouns in such a terse yet confusing description? No idea what sentence 6 refers to. Sentence 7 is obscure and confusing. Sentence 8:Which extensions? Sentence 9: What does "They" refer to? Sentence 11: What is the "back line?" The "rear straw," which should probably be called the "rear axle?" Sentence 14 and 15: No idea of the shape or orientation of the sail. Edison (talk) 01:21, 7 October 2008 (UTC)

A diagram - or a photo - is needed here. There are some things that just don't work when put into words. It's possible we could come up with some better words - but because the words you have aren't working, we need the diagram/photo in order to understand what we're writing about! SteveBaker (talk) 10:16, 7 October 2008 (UTC)

I'm still stuck right at the start. A trapezoid is a 2D shape. Is your car a trapezoid cut out of cardboard and held vertical? Or is it a 3D solid shape, like a prism of a trapezoid? You need to make that clear before you start talking of front and back. Itsmejudith (talk) 11:07, 7 October 2008 (UTC)

There are lots of patented mechanical devices far more complex than this thing which have clear and unambiguous descriptions in the patent specifications. Instead of "two straws which will be called one straw" call it a freakin' "rear axle," for instance. From the description, it could be a structure made only of straws, or it could have a trapezoidal planar body made of some unspecified substance. It does not say what the vertical straws are attached to. Edison (talk) 18:18, 7 October 2008 (UTC)

Here is a (eui) sketch of what I see this thing as. Heaviest lines are the wheels, lightest are the pins, in the middle are the stiffeners and sail assembly. All are in the same plane except the cirlces and curved line representing the vertical sail. Franamax (talk) 02:44, 8 October 2008 (UTC)

And here is the elevation view. The U-shaped sail-straw is pinned through the two stiffener straws near the midpoint of the vehicle. Franamax (talk) 02:57, 8 October 2008 (UTC)

Momentum and photons

Gah such a simple question I've forgotten the answer to. How the hell do photons have momentum when they have no mass? Is it due to rest mass? Cheers! —Cyclonenim (talk · contribs · email) 23:05, 6 October 2008 (UTC)

They have no rest mass, but due to E=mc² they have mass which gives them momentum (m=E/c² so p=mv=E/c - there is a lot of hand waving required for that derivation, but it gets the right answer!). --Tango (talk) 23:15, 6 October 2008 (UTC)

Likewise, Electrons are dimensionless (they have no volume), yet they have a "spin". Try to figure that out using classical mechanics... --Jayron32.talk.contribs 03:07, 7 October 2008 (UTC)

How do you know that an electron has no volume? Ohanian (talk) 06:22, 7 October 2008 (UTC)

See Electron#Fundamental properties. Axl ¤ [Talk] 08:29, 7 October 2008 (UTC)

...which is not very helpful, because it says "for convenience, <the electron> is usually defined or assumed to be a point charge with no spatial extent; a point particle", and a point particle is "an idealized object". We know that the "point particle" model cannot be the whole story, because then the electron would be a singularity. In quantum field theory fundamental "particles" like the electron are not really particles at all - they are excitations of a quantum field, and they don't have a volume because the "volume" concept just doesn't apply to such things - any more than the colour red or the number seven has a volume. Fundamental particles might have some multi-dimensional equivalent of "spatial extent" in string theory, but I am not sure whether that could be made to correspond in any reasonable way to our macroscopic concept of "volume". So in simple terms, we might say that we don't think that an electron has a property that we could interpret as a volume - which is not the same as saying it has zero volume. Gandalf61 (talk) 09:30, 7 October 2008 (UTC)

Gandalf, your response is one interpretation. Axl ¤ [Talk] 10:31, 7 October 2008 (UTC)

If I understood (and/or remember) my Feynman, he described the paradox of infinite charge given zero volume for the electron vs. the impossibility of making accurate calculations without assuming zero volume. As I recall, he advised the whole matter was best swept under the desk. Franamax (talk) 03:06, 8 October 2008 (UTC)

It would be worse than that - being of zero volume but having a non-zero mass - the electron would exert enough gravity to form a micro-black hole with it's very own teeny-tiny event horizon. SteveBaker (talk) 02:28, 9 October 2008 (UTC)

They just do. We cannot demand that the universe conforms to our everyday notions, which require an object to have a non-zero rest mass in order to have momentum. Note also that photons are never at rest in any inertial frame.Martin Hogbin (talk) 09:44, 8 October 2008 (UTC)

Even if an electron does have volume, it doesn't have any component parts (i.e. it's not made of two smaller "half-electrons" or something), which still means that it's counterintuitive for one to have angular momentum; since _normally_ we think of angular momentum as being from the movement of something's component parts relative to one another. --Random832 (contribs) 13:44, 10 October 2008 (UTC)

Mars and Jupiter and Saturn's moon over sun's RGiant Stage

If Mars still exist, does anybody know what Mars surface will be like over sun's R Giant? Will it be yellow-orange molten lava like Earth was 4.6 billion years ago? What about Europa-Jupiter's moon. Europa's tan-gray ice will melt into water, then what will ahppen next. Will it scorch like Mercury. Titan's orange smog might bluen out. By 6 to 7 years from now, it is learnt Titan is the only place going to habitat for life. I wonder what will happen to Uranus' moon when sun enters a R Giant.--SCFReeways 23:44, 6 October 2008 (UTC)

• Will somebody be able to answer it?--SCFReeways 01:04, 7 October 2008 (UTC)

• Come on, do anybody know this?--SCFReeways 01:43, 7 October 2008 (UTC)

Have some patience, we don't know this off the top of our heads. Plasticup ^T/C 02:07, 7 October 2008 (UTC)

And we live in a variety of time zones... (yawwn) --140.247.11.55 (talk) 02:29, 7 October 2008 (UTC)

And it says at the top of this page that we may need as much as four days to fully develop an answer. Anything that might be needed in less than four days is probably homework - which we don't do. The sun isn't going to do this for another 7 billion years - so this is hardly a time-critical answer. SteveBaker (talk) 09:58, 7 October 2008 (UTC)

It's tough to be patient though.--SCFReeways 02:48, 7 October 2008 (UTC)

The primary difficulty in answering your question is your poor grammar. Your first question appears to be "Does anybody know what will happen to Mars when the Sun turns into a red giant? It is not known. Mars may become superheated. It may escape the Sun since it will enlarge its orbit. So, no, nobody knows. Your next "questions" have leading assumptions that do not appear to be based on popular scientific evidence. Why do you assume Europa's surface will melt? Why do you believe that Titan will be the only habitat for life in 6 or 7 years? Uranus is very far from the Sun, why do you assume it will be heavily affected? Is this all based on an assumption that, as a red giant, the Sun will suddenly start producing so much heat that it burns up the Solar System? You must take into account how little heat reaches the outer planets right now and that they will move further from the sun when it loses mass. -- kainaw™ 03:34, 7 October 2008 (UTC)

They will move further out. Alot of sources said Titan might be habitatable at this time. I wonder about Uranus moon. Whole solar ssytem will heat up at this time. Mercury and possibly Venus and Earth will be engulf and destroy, then Mars will be the only inenr planets left. About Europa, after ice melt, even escaption Europa can be a little too hot. Uranus moon could get beenfit from sun's heating too.--SCFReeways 03:52, 7 October 2008 (UTC)

What about this?--SCFReeways 04:35, 7 October 2008 (UTC)

My understanding is that Titan may heat up to habitable temperature but it will lose its atmosphere so won't be habitable. The reason it can maintain such a dense atmosphere with its low mass is because it is very cold (cold gasses don't move around as much so are less likely to randomly achieve escape velocity). Once it warms up, the atmosphere will leak away into space pretty quickly. (That's just the theory I've heard, there are so many variables we can't pin down that it's difficult to say for sure.) --Tango (talk) 14:39, 7 October 2008 (UTC)

When you say "6 to 7 years" do you mean "6 to 7 billion years"? Plasticup ^T/C 15:19, 7 October 2008 (UTC)

I would guess so. It's still wrong, though, since by then the Sun will have gone past being a red giant and will be a white dwarf giving off very little heat. The red giant phase only lasts for a few million years, if that. --Tango (talk) 16:09, 7 October 2008 (UTC)

• This site said the tan-gray ice on Europa might melt into water, and possibly be warm enough.--SCFReeways 22:08, 7 October 2008 (UTC)

• THis site shows in 7 billion years, Europa's thick ice can melt into globe of liquid ocean, but artist say it's sky will still be black in 6 to 7 Gyrs when sun turns into giant star.--SCFReeways 22:15, 7 October 2008 (UTC)

  I question the reliability of those sites. For a start, it's 5 billion years, not 7. Secondly, Europa doesn't have the atmospheric pressure required for an ocean - the water would just boil away. --Tango (talk) 23:44, 7 October 2008 (UTC)

• you menat the ice will just boil away right? One source said only surface temperatu will be habitable. In about 1 to 2 billion year-time Mars can get bluer, possibly as the planet warm up the greenhouse effect will start to incrase, but after few billion year later, Mars could just black out right airless.--SCFReeways 00:17, 8 October 2008 (UTC)

  I'm afraid I don't understand. Mars is essentially airless now (from the point of view of liquids boiling and habitability) and I don't think it will get more air as it warms up. Likely less, in fact, since warm air escapes into space faster. --Tango (talk) 00:23, 8 October 2008 (UTC)

Mars has no magnetic field to speak of, so holding in an atmosphere is very difficult. Gasses need to increase in the atmosphere faster than they are lost into space. There is a theory that if it warms up enough a magnetic field will build up. Of course, this is all just theory. Give me any theory and it is trivial to find someone who disagrees. -- kainaw™ 00:22, 8 October 2008 (UTC)

I theorise that when I hold a pen about a metre off the ground away from any other objects and let go, it will fall. --Tango (talk) 00:25, 8 October 2008 (UTC)

I theorise that someone will come along and explain the difference between a validation experiment and a theory :) -- kainaw™ 00:27, 8 October 2008 (UTC)

It was a very restricted theory, but a theory nonetheless (ok, perhaps it was a law and I should have added some explanation to make it a theory). --Tango (talk) 14:16, 8 October 2008 (UTC)

This said Mars was once a blue planet, it just got too cold. In fact right now Mars is very cold. in about 1 to 2 Gyrs Mars might attain to the Earth surface temp today.--SCFReeways 00:39, 8 October 2008 (UTC)

At this time, Earth may be a greenhouse planet like Venus today.--SCFReeways 00:40, 8 October 2008 (UTC)

I think you are missing the point. It might turn blue again. It might not. It might get destroyed by a Vogon fleet to make way for an interstellar bypass. Whatever answer you want to get, there's a reference for it. That is why I stated that it is all theories. It is even possible that the sun may not turn into a red giant (though unlikely). -- kainaw™ 00:46, 8 October 2008 (UTC)

While it will probably heat up again that doesn't mean it will become Earth-like. It's already lost its atmosphere and warming up isn't going to bring it back. Without an atmosphere (and a significant one, not the few wisps of CO2 Mars has) you can't have liquids on the surface. Mars lost its atmosphere over millions, possibly billions of years due to its low mass and lack of an magnetic field (which allows solar wind to erode the atmosphere). --Tango (talk) 14:16, 8 October 2008 (UTC)

• Tango, let me backtrack a little bit. Europa is now white and smooth, and it's surface is like a crack eggshell. The problem with Europa is the planet is too small for an atmosphere, the sky is obviously black. I wonder if Europa ever had an atmospher later. Tango is right without an atmosphere we can't have a liquid atmosphere on the planet. So you menat when Europa heats up, it will just become a desert like Moon? Titan is known for it's orange-yellow color and it's sky is light orange. Titan's atmosph is 1.5 times thicker than Earth's. Tango, what you mean by when sun heats up it will drain it's atmosph?--SCFReeways 22:45, 8 October 2008 (UTC)

October 7

Quantum: Difference between an operator and a measurement

Suppose there is a qubit whose state is

$|\psi \rangle ={\frac {1}{\sqrt {3}}}|0\rangle +{\frac {\sqrt {2}}{\sqrt {3}}}|1\rangle ={\begin{bmatrix}{\tfrac {1}{\sqrt {3}}}\\{\tfrac {\sqrt {2}}{\sqrt {3}}}\end{bmatrix}}$

After we measure the qubit, the state of the qubit will change from $|\psi \rangle$ to $|1\rangle$ with probability

${\big |}\langle 1|\psi \rangle {\big |}^{2}=\left({\frac {\sqrt {2}}{\sqrt {3}}}\right)^{2}={\frac {2}{3}}\approx 0.666\dots$.

This process is called wave function collapse. If $|1\rangle$ is observed after the measurement, the qubit becomes

$|\psi \rangle =|1\rangle$

Instead of measuring the qubit, a Hadamard gate

$H={\frac {1}{\sqrt {2}}}{\begin{bmatrix}1&1\\1&-1\end{bmatrix}}$

operates on the qubit will be

$H|\psi \rangle ={\frac {1}{\sqrt {2}}}{\begin{bmatrix}1&1\\1&-1\end{bmatrix}}{\begin{bmatrix}{\tfrac {1}{\sqrt {3}}}\\{\tfrac {\sqrt {2}}{\sqrt {3}}}\end{bmatrix}}={\frac {1}{\sqrt {2}}}{\begin{bmatrix}{\tfrac {1+{\sqrt {2}}}{\sqrt {3}}}\\{\tfrac {1-{\sqrt {2}}}{\sqrt {3}}}\end{bmatrix}}={\frac {1+{\sqrt {2}}}{\sqrt {6}}}|0\rangle +{\frac {1-{\sqrt {2}}}{\sqrt {6}}}|1\rangle$

as I know, the process of the operation is 'not' a wave function collapse.

My problem is why an operator acts on a qubit doesn't cause a wave function collapse? As I know, any subtle interaction with the qubit will cause the wave function to collapse. The Hadamard gate operator, which should be an apparatus, when acts on the qubit should also interact with the qubit. So how an operator can circumvent the wave function collapse? - Justin545 (talk) 05:28, 7 October 2008 (UTC)

I'm a little rusty in my quantum theory, but if I remember correctly, it's not all interactions that cause wave-form collapse, only those actions that generate information. It is entirely possible to transform a wave-function without actually observing (i.e. gaining information from) said wave function. Take for example the most basic quantum experiment, the double-slit experiment. The slit certainly interacts with the beam of particles; as the beam hits the slits, an interference pattern immerges, this is a result of the slits "transforming" the beam of particles via interaction. The wave function collapse occurs only when you try to gain information about the particle's location, for example, by placing a charge detector at one of the slits. As long as no information is obtained on the system, it goes on behaving as an uncollapsed wave function. Once the detector is placed, information is extracted, and the wave function collapses, resulting in an uninterferred double beam... The Hadamard gate must operate in the same way; it performs a transformation on the qubit blindly (that is, without observing the state of the qubit). Such an action is not philosophically that hard to understand. Imagine a blind man turning coins over. You hand the man a coin, and he simply reverses the face of the coin. He can perform the operation (turning heads to tails and tails to heads) perfectly every time, even if he doesn't know which states the coins are in before he flips them. To take this on a quantum scale, he's able to perform a transformation on the wave function, without causing any waveform collapse. He's made no observations of the bits of information he's transforming, he's just doing the transformation. A Hadamard gate must work on this level. --Jayron32.talk.contribs 05:47, 7 October 2008 (UTC)

It could be difficult to define the term 'gaining information from'. Cite form the article Quantum computer:

One major problem is keeping the components of the computer in a coherent state, as the slightest interaction with the external world would cause the system to decohere. This effect causes the unitary character (and more specifically, the invertibility) of quantum computational steps to be violated. Decoherence times for candidate systems, in particular the transverse relaxation time T2 (terminology used in NMR and MRI technology, also called the dephasing time), typically range between nanoseconds and seconds at low temperature.

I think the 'decohere' is actually the wave function collapse. It seems that even the 'temperature' is also a way to interact with the qubit and it is not clear to me how an environmental temperature makes information gaining... maybe what you mean is that a measurement is an irreversible operation whereas a gate operation is a reversible operation. Indeed, the action of a Hadamard gate is a reversible operation since there is no information lost during the operation of the Hadamard gate. And saying that a measurement is an irreversible operation is just my suspicion since some information is lost and gained by the observer during a measurement. By thinking the gate operation as a transform as you said make it more understandable to me. And now I know there are some interactions don't collapse the wave function. - Justin545 (talk) 07:23, 7 October 2008 (UTC)

Unless the qubit is lost due to interaction with other particles; at high temperatures there are bound to be more particles moving faster and thus more interference on the qubit; there may be some threshold temperature where the system becomes so inefficient due to losses that it stops "working." --Jayron32.talk.contribs 11:29, 7 October 2008 (UTC)

Definitely some interactions don't collapse the wave function, otherwise a proton, for example, couldn't be a quantum particle since it consists of more fundamental particles constantly interacting with each other.

See quantum decoherence for more on that subject. It is effectively the same thing as wavefunction collapse and people are likely to use the terms interchangeably.

Measurement/decoherence is all about copying. An example of copying is a transition from $\alpha |0\rangle +\beta |1\rangle$ to $\alpha |0\rangle |0\rangle +\beta |1\rangle |1\rangle$. This is different from cloning, which would take $\psi$ to $\psi ^{2}$, e.g. $(\alpha |0\rangle +\beta |1\rangle )^{2}=\alpha ^{2}|0\rangle |0\rangle +\cdots$. Cloning isn't possible, but copying is possible. The key difference between them is that copying is basis-dependent. The example I gave above was copying with respect to the computational basis $\{|0\rangle ,|1\rangle \}$. Copying with respect to the dual basis $|{\pm }\rangle ={\tfrac {1}{\sqrt {2}}}(|0\rangle \pm |1\rangle )$ takes

$\alpha |{+}\rangle +\beta |{-}\rangle$ to $\alpha |{+}\rangle |{+}\rangle +\beta |{-}\rangle |{-}\rangle$,

which is the same as taking

$\alpha |{0}\rangle +\beta |{1}\rangle$ to ${\tfrac {\alpha }{\sqrt {2}}}(|00\rangle +|11\rangle )+{\tfrac {\beta }{\sqrt {2}}}(|01\rangle +|10\rangle )$,

if I calculated right—at any rate it's a different operation. If you copy a qubit (with respect to a basis) and put the copy somewhere where it's unavailable to you, the effect on the original qubit is exactly as though you'd measured it (with respect to that basis). But if the copy ever becomes accessible to you again, you can use it to "undo the measurement," so it's not a real measurement. Measurements only become definite when they can no longer be undone, e.g. because the copy has been amplified into a macroscopic thermodynamically irreversible state change like a flash from an LED.

Reply composed in a hurry and I may not be able to reply again for a few days. -- BenRG (talk) 11:44, 7 October 2008 (UTC)

A short mathematical answer: Self-adjoint operators correspond to measurements. Unitary operators correspond to state changes without any wave function collapse. Icek (talk) 21:32, 8 October 2008 (UTC)

Noisy laptop fan

Why do they (fans) do it (noise)? Is a silent laptop fan possible?Mr.K. (talk) 11:06, 7 October 2008 (UTC)

A (laptop) fan moves air, using an electric engine. Air flow creates sound, and the engine can't be perfectly silent either, so: no, a silent laptop fan isn't possible. There are however some new, interesting ways of cooling coming about, some of which may be silent. Someone please fill me in here :) -- Aeluwas (talk) 11:08, 7 October 2008 (UTC)

There is liquid cooling, but that would be for rack-mount mega-chips (stacked processors have a higher power density than a nuclear reactor), not laptops; and the liquid would still need cooling. See this Economist article (and I can email it if you can't see it). Franamax (talk) 22:13, 8 October 2008 (UTC)

Actually, there are ways of generating air flow without any moving parts, for example see Air ionizer; it operates similar to a mass spectrometer; air molecules can be ionized via say, a negatively charged plate, and accelerated via a pair of positively charged plates. Many air molecules will simply gain electrons at one plate and lose them back at the other (or visa-versa; I am not positive on the specific mechanics of the situation), however, some will "overshoot" the second plate, and also drag many "non-charged" molecules with them, resulting in net air flow. However, the method is quite innefficient, especially on a scale small enough to fit into a laptop, and I suspect that in terms of net air flow for, for both its size and wattage, a simple mechanical fan is far more efficient. --Jayron32.talk.contribs 11:24, 7 October 2008 (UTC)

The engine could be so silent like the HDD. Moving air doesn't have to be noisy. I suppose it is noisy only if it generates turbulence right? So, a silent laptop fan should be possible... Mr.K. (talk) 11:38, 7 October 2008 (UTC)

But laminar airflow may not be terribly efficient at moving heat around, as it may not move all the air and probably wouldn't move fast enough. 130.88.64.189 (talk) 12:29, 7 October 2008 (UTC)

The other common means of making a fan quieter is to spin it at a lower RPM. Of course, the direct consequence is that you move less air, reducing the cooling effectiveness. In a desktop system, that just means that you make the fan larger to compensate. With space at a premium in laptops, this solution is less effective. — Lomn 12:59, 7 October 2008 (UTC)

A related option is to reduce your CPU usage, which reduces the laptop's need for cooling, which should let the fan run slower and less frequently. Plasticup ^T/C 15:15, 7 October 2008 (UTC)

Often, reducing the CPU usage is not an option, since I use the laptop with a purpose. Mr.K. (talk) 15:24, 7 October 2008 (UTC)

Amen to that! Plasticup ^T/C 00:28, 8 October 2008 (UTC)

To remove a particular amount of heat per minute, you must move a particular amount of air per minute, often measured in CFM. A fan with a smaller diameter must spin faster for the same CFM. The higher speed results in a higher amount of vorticity at the blade ends, and this is where most of the noise is generated. A laptop cannot accomodate a large-diameter fan, so the fan must spin very fast and is therefore very noisy. The same is true for 1U rack-mount servers. As an example of the difference diameter makes, consider the difference between a 20" diameter window fan and a 3" diameter "muffin" fan in a desktop computer. The window fan at its lowest speed moves much more air than the muffin fan at its normal niosy speed, but is virtually silent.The motor contributes very little noise in either case. -Arch dude (talk) 00:41, 8 October 2008 (UTC)

Question (Goliath Beetle)

What is the main predator to the Goliath Beetle? —Preceding unsigned comment added by 204.210.238.42 (talk) 11:54, 7 October 2008 (UTC)

I'm not sure it has a main predator. There are more than enough predators and omnivores in tropical Africa that would not think twice before dining on a huge delicious beetle larva. Mandrill comes to mind as a very likely predator, but I couldn't find any specific data. Besides, Mandrill habitat extent is much smaller than that of Goliathus sp. . Sorry. --Dr Dima (talk) 17:13, 7 October 2008 (UTC)

How does fruit get "bruised"?

Just curious how fruits like apples and bananas get "bruised"? Aren't they dead? How does impact against the surface affect the fruit below the skin? --70.167.58.6 (talk) 16:00, 7 October 2008 (UTC)

I'm not sure it's accurate to say they're dead. They are still chemically active, otherwise they wouldn't be able to ripen after being picked. I think the bruising is caused by breaking the cell walls so the individual cells die, but I can't guarantee it. I'm sure a botanist will be along shortly. --Tango (talk) 16:07, 7 October 2008 (UTC)

Not a botanist, but Tango has the right idea. Inside of plant cells are chemicals which oxidize upon exposure to air. If the cell remains intact, nothing happens. However, cutting the fruit or striking it can cause the cell walls of the cells to break, exposing the chemicals to air, and causeing a change in both color and texture. Incidentally, bruised fruit is perfectly healthy and there's nothing at all wrong with eating it. You abuse the fruit much more when you chew and swallow the fruit anyways; the color change is not a sign of bacterial growth in any way, its merely a sign of physical damage. --Jayron32.talk.contribs 16:47, 7 October 2008 (UTC)

You may want to look at this. --Dr Dima (talk) 19:18, 7 October 2008 (UTC)

Fresh animal products consists of all dead cells when you buy them but fruits fruits and vegetables are all alive. The "bruise" consists of plant cells that are dead. Sjschen (talk) 03:51, 8 October 2008 (UTC)

So is it possible for bruises to grow? Will a bruise "infect" undamaged cells making it more unattractive? Do bruised areas rot faster? --71.158.222.207 (talk) 03:59, 8 October 2008 (UTC)

Yes, bruises will grow - the lysed cells burst in the original insult will release oxidizing enzymes which will continue to degrade the contents of the fruit, in part by lysing more cell membranes. And yes, as more cells contents are spilled out, they will be more susceptible to bacterial invasion. This is why the little bruise spot on your tomato when you bought it gets bigger and gets a grey mold at the centre. Franamax (talk) 05:54, 8 October 2008 (UTC)

Unquestionably the best resource on this is On Food and Cooking: The Science and Lore of the Kitchen H. McGee ISBN 978-0-684-80001-1.[4] It explains all this stuff and tells you how to get your eggs right! :) Franamax (talk) 06:18, 8 October 2008 (UTC)

Grass Seed Lifespan

I have had a bag of lawn grass seed in my garage for over 4 years. Over that time it has been exposed to -20C to +35C degrees. Would it still be alive and able to grow after all? —Preceding unsigned comment added by 151.123.128.250 (talk) 16:40, 7 October 2008 (UTC)

Quite possibly. Many kinds of seeds are quite resilient. There are some seeds that have been shown to germinate after hundreds of years of dormancy. The best thing to do is to run a little experiment. Take a cup of dirt, put a small pinch of seeds in it, keep it moist and in direct sunlight (like the windowsill) and see what happens. The seeds, if still viable, should germinate within a few days. If they do, you probably have good seed. If it just sits there for a week and nothing happens, then you probably need to pitch them. --Jayron32.talk.contribs 16:44, 7 October 2008 (UTC)

The normal rule is: If at least 75% of the seeds germinate, use as directed. If 50%-75% germinate, use double the normal amount. If less than 50% germinate, toss it and get a new bag. --Stephan Schulz (talk) 17:41, 7 October 2008 (UTC)

calorie consumption per hour/ mile (cycling)

Hello Everyone,

i've been trying to work out how many calories I burn on my cycle to work but i'm struggling to get some relevant info (i've been on a few forums but they use 40 year olds as reference points -i'm not even sure if one burns more or less calories as one ages so this is less than helpful.) Anyway, i'd be grateful if any one has any ideas - its about 4.7 miles (according to google maps anyway) each way, along reasonably flat terrain -stopping and starting for traffic lights often. It takes me about 30 minutes on average. Also i'm a (reasonably fit) 24 year old man... Any help, or even some starting data, would be great...

Thanks, 82.22.4.63 (talk) 19:09, 7 October 2008 (UTC)

While caloric intake is relatively easy to calculate, based on the nutritional content of the food in terms of ammounts of proteins, fats, and carbohydrates, its a different story for caloric output, in terms of exercise. Its going to vary WILDLY depending on how hard you are pedaling, your current body weight, your personal body chemistry and metabolism, the ambient temperature that day, your muscle mass, yada yada yada. The variables are almost too great to even think of all of them. Calculators that purport to determine how many calories you burn (for example, those found on treadmills or stationary bikes) are likely just WAGs. They may be based on, for example, the 50th percentile human, but variation from that ideal is likely so large that there is no way to assure they will be accurate for you. The easiest way to tell is to see if it has an effect on your own body: If you are losing body fat over time, you are likely burning more calories than you take in. If you are gaining body fat over time, you are likely consuming more than you burn. Take Michael Phelps for example. It is widely reported that he consumes 10,000 calories per day. That's roughly the amount of food 4 people would eat. And yet, he has almost no body fat, which means his level of activity has him burning at least that much. The funny thing is, another person, performing the same workout regimen as he does, may find himself gaining fat at that level of intake. Isolating WHICH activities are burning which calories is entirely a guessing game. The best thing that can be said is more activity always burns more calories, so more is always better. --Jayron32.talk.contribs 20:21, 7 October 2008 (UTC)

Human feet vs. Chimp feet

Chimps' feet have thumb like digits on them so they can grab objects with their feet in a similar way to how we can grab things with our hands correct? So I was curious if our feet which do not have that ability, have any advantages over their feet. 98.221.85.188 (talk) 19:51, 7 October 2008 (UTC)

Chimp feet are great for walking on branches, too. But they're lousy for running. (See achilles tendon not what I expected.) See Persistence hunting. Saintrain (talk) 20:07, 7 October 2008 (UTC)

Chimps are also not bipedal like humans. Like some other animals (bears, for example) they can, relatively easily walk on two legs, but their preferred method of ground locomotion is "knuckle walking" on all fours, generally as a sort of side-shuffle. Chimps are not very efficient at walking flat footed, however, as noted above, they are VERY efficient at traveling in trees, having evolved in a forested habitat. Modern humans largely evolved in a savannah habitat, with few trees, and thus flat-footed walking gave them an advantage in that environment. Thumbs are an impediment to flat-footed walking, and so proto-humans with "modern human" style feet tended to predominate in that environment. --Jayron32.talk.contribs 20:26, 7 October 2008 (UTC)

To expand on Jayron32, the human foot is specifically adapted to walking upright. The big advantage we have over chimps (for the bipedal environment) are the two arches of the foot which act --like springs-- as shock absorbers, distributing weight and allowing us to easily run upright. --Shaggorama (talk) 20:56, 7 October 2008 (UTC)

I was talking a while back to someone who lost their big toe in a lawnmower accident and they said the loss of the toe made walking quite bit more difficult. So it looks like the toe might have been actively evolved to help with walking. Dmcq (talk) 00:30, 8 October 2008 (UTC)

Fizzy drinks.

The aqueous carbon dioxide in fizzy drinks makes the drinks acidic (for some reason that I have forgotten), couldn't you just add an alkaline solution to the drink to neutralise it. Fizzy drinks are critisised for being bad for your teeth because they're acidic, this would get rid of that problem. Thanks.92.2.212.124 (talk) 20:02, 7 October 2008 (UTC)

Except that acidic compounds have a generally pleasant "sour" flavor. Alkali compounds have a bitter, soapy flavor. Eat a bar of soap, or drink some lemonade. Which do YOU prefer? --Jayron32.talk.contribs 20:31, 7 October 2008 (UTC)

Also, its not the acid in sodas that is damaging to your teeth per se since it does not remain in contact with your teeth for very long. However, bacteria, which DO remain in contact with your teeth for a long time, will feed on the sugar in the soda, and produce an acidic waste product. Since these bacteria are essentially always there, the more sugar you give them, the more acid they make. Its this acid, which is held directly against the tooth for a long period of time, and not the acid that washes over the tooth which causes decay. Its the sugars in the soda that cause the decay, not the acid inherent in the carbonic acid. --Jayron32.talk.contribs 20:31, 7 October 2008 (UTC)

Thanks92.2.212.124 (talk) 20:43, 7 October 2008 (UTC)

It is not carbonic acid that is responsible for the sour taste and the tooth weakening, it is phosphoric acid (Cola) or citric acid. Cacycle (talk) 03:28, 8 October 2008 (UTC)

From this article, it's due to a combination of acidity, buffering capacity (titratable acidity) and sugar content. Axl ¤ [Talk] 17:40, 8 October 2008 (UTC)

The grayed tip of a banana

As a child I was told to bite off the usually grayed tip of a banana before eating it. What is it, though? Thanks. Imagine Reason (talk) 20:03, 7 October 2008 (UTC)

Greyed tip? I assume this means pre-peeled bananas, but i wouldn't bite the peel of a banana. If this means a peeled banana, what grey tip? Anyway, I've never heard that.92.2.212.124 (talk) 20:30, 7 October 2008 (UTC)

I'm pretty sure it's banana. --Shaggorama (talk) 20:38, 7 October 2008 (UTC)

Yes, it's the tip of a just-peeled banana. It's usually not white. C'mon, I thought that were the common experience. Imagine Reason (talk) 21:19, 7 October 2008 (UTC)

See vascular bundle and, specifically for bananas, phloem bundle (What!? No article!?). What you are referring to is the part of the banana where the bundles (strings) join and invert into the center of the fruit. -- kainaw™ 21:49, 7 October 2008 (UTC)

You mean the dark bit at the far end from where you open it? I don't bite it off, it comes off very cleanly on its own if you push it sideways slightly. --Tango (talk) 23:17, 7 October 2008 (UTC)

Systemic bias! Seriously, you don't open a banana at the stem end? Weird. --Sean 22:43, 8 October 2008 (UTC)

This sounds like bruising as described not far above. When the cells are damaged, they release enyzmes which oxidize the surrounding tissue. Damage could occur at the stalk end due to wrenching when the banana bunch is pulled of the stem, at the bottom end when the bunch hits the container, and anywhere else the bananas get bumped in transit. If you're getting bananas with brown on them, consider yourself lucky, the only bananas I ever see are very far from ripe - thank you very much, modern commercial food distribution system. Franamax (talk) 03:33, 8 October 2008 (UTC)

My dad used to bite out the bruised bits of bananas before slicing them onto his breakfast cereal. (I don't know whether he still eats breakfast cereal.) The texture may be icky to some, but it won't hurt you, if that's what you're asking. —Tamfang (talk) 06:44, 8 October 2008 (UTC)

Nobel Prize winners

Have there been any Nobel Prize winners whose work has since been completely discredited or otherwise found to be useless/incorrect? -Elmer Clark (talk) 20:41, 7 October 2008 (UTC)

Interesting question! Since you posted in Science, I assume you're less interested in the Nobel Peace Prize, where Rigoberta_Menchú and Henry Kissinger come to mind. --Sean 21:45, 7 October 2008 (UTC)

If this were about Nobel laureates generally, I'd mention Paul Heyse, who won the 1910 Literature prize. One of the judges said "Germany has not had a greater literary genius since Goethe" - but history has been rather less kind to Heyse. -- JackofOz (talk) 01:12, 8 October 2008 (UTC)

Off the top of my head, the closest I could come up with is Neils Bohr, who won the Nobel Prize in Physics for devising the Bohr model of the atom. Its not that the Bohr model was wrong, in fact it is perfectly accurate for any two particle system. The problem is, in practical terms it means it predicts the electronic structure of the Hydrogen atom (which has an electron and the nucleus) and nothing else. The Bohr model breaks down for any atom with more than one electron in it; so while it works for the He⁺¹ ion, it doesn't work for the He atom. It was an important step in the modern understanding of the electronic structure of the atom, but other more recent models, such as the wave mechanical model of the atom as derived by Erwin Schrödinger, Paul Dirac, Louis de Broglie, and others is far more useful, and as a model it contains the Bohr model as a special case. Still, Bohr is important as a key step in our understanding of the atom, and his contributions should not be deminished merely because better models came along later. --Jayron32.talk.contribs 21:37, 7 October 2008 (UTC)

Bohr's idea of quantization of angular momentum also inspired de Broglie whose's work latter inspired Erwin Schrödinger so that he came up with Schrödinger equation. I believe that the modern quantum theory couldn't exist without Bohr's breakthrough. - Justin545 (talk) 00:35, 8 October 2008 (UTC)

Johannes Andreas Grib Fibiger is an interesting case, especially in light of this week's award to Harald zur Hausen. --Arcadian (talk) 09:47, 8 October 2008 (UTC)

Argh - the guy's name escapes me for the moment. There is at least one case where someone made a seemingly great discovery - and it was disproven shortly before the Nobel was awarded - so they gave him the prize anyway but changed the citation from that very specific discovery to some kind of vague lifetime-achievement award...but the guy's name escapes me right now. SteveBaker (talk) 13:55, 8 October 2008 (UTC)

In 1912 the swedes awarded the physics prize to one of their own, for the invention of an automatic lighthouse. Useful but trivial on the nobel scale. In 1949 the Nobel Prize in Medicine was awarded for an advance in Lobotomy. EverGreg (talk) 20:48, 8 October 2008 (UTC)

Times sure do change and science advances. Now, that 1949 choice seems unlikely, but at the time it was a no-brainer. DMacks (talk) 21:05, 8 October 2008 (UTC)

Ba-da-bomp! And the Nobel Prize for today's best joke goes to...DMacks. :) Franamax (talk) 22:00, 8 October 2008 (UTC)

Interesting answers, thanks - Fibiger at the very least certainly seems to qualify. -Elmer Clark (talk) 12:44, 9 October 2008 (UTC)

honey locust spines: poisonous?

I just tore an enormous (23 centimeter long) spine off of a honey locust near here and in the process my left hand got jabbed. It didn't break the skin or draw any blood, but there's a small, red raised bump there like an insect bite that itches a little and the area around it is somewhat red and feels sore. I heard that honey locusts have some sort of toxin in their thorns that can be dangerous, but I can't find any information on it at all. Is this true? If so, do I need to seek medical attention? Can this get infected?

Any help is appreciated. Thanks. 63.245.144.77 (talk) 20:44, 7 October 2008 (UTC)

Sorry, we can't give medical advice. Please contact your doctor's office. The nurses there will be able to tell you what sort of medical attention (if any) you need. Also, note that some locations have a poison control telephone number - they are usually staffed with medically trained people, and are very helpful with "is this plant poisonous" type questions. -- 128.104.112.147 (talk) 23:39, 7 October 2008 (UTC)

Holt Biology

What is a phospholipid layer that covers a cell`s surface and acts as a barrier between the inside of a cell and the cell`s environment? —Preceding unsigned comment added by 75.68.106.206 (talk) 21:14, 7 October 2008 (UTC)

Your Holt Biology book should have the answer. Please post all your homework questions at once so we don't have to repeat multiple times that we are not here to do your homework. -- kainaw™ 21:22, 7 October 2008 (UTC)

See comments below on the plant cells. Be aware that while Wikipedia has an article on Cells, which I recommend that you read, your Holt Biology book is likely much easier to follow, and if you read it, it will give you the answer. --Jayron32.talk.contribs 21:23, 7 October 2008 (UTC)

Hearing

Hi all,

Hypothetically, and I do mean hypothetically because I’m not asking for medical advice, how does one increase the results of a hearing test (only a temporary basis, not permanently).

I’ve heard that: 1. One’s hearing is better in the morning (so take the hearing test in the morning) – there will be a slight benefit. 2. Wear headphones (like the headphones for ear protection with firearms) prior to the hearing test. This will allow one to “rest” the ear drums so they’ll be more “sensitive” during the hearing test.

Any other thoughts (again, not seeking medical advice). Thx! Rangermike (talk) 21:15, 7 October 2008 (UTC)

I had an uncle (until my aunt divorced him) who was practically deaf from working on jet aircraft. He needed to pass a hearing test to stay in the Navy Reserve or National Guard (don't remember which). What he did was wear ear plugs for a week or two before the test. Then, he would barely pass. He never tried it without the earplugs before the test, so I can't make a claim that it actually helped. -- kainaw™ 23:39, 7 October 2008 (UTC)

Fully off-topic - what is that guy called now? Ex-uncle? Uncle infinitely-removed? Former uncle (is this one best)? And for that matter, how do I refer to events that occured when my ex-wife was still just my girlfriend? SciRefDesk is probably not the best place to ask, I suppose... Franamax (talk) 05:45, 8 October 2008 (UTC)

Um - he is called "the ass who tried to stay in the reserves so he could spend one weekend a month in another city where he married another woman and, eventually, couldn't keep the two wives apart, got caught, and got dumped by both of them", or "the ass" for short. -- kainaw™ 13:16, 8 October 2008 (UTC)

Wait, seriously? Plasticup ^T/C 04:20, 10 October 2008 (UTC)

I was thinking that too - good God man, two wives? I had enough trouble with just the one. OTOH man in unhappy marriage meets woman fresh out of unhappy marriage - Franamax results and mummy/daddy live happily together 'til death do them part. I suppose that "the ass" is always a relative term (though Kainaw seems to have identified the type specimen). Franamax (talk) 07:25, 10 October 2008 (UTC)

Holt Biology

what is an organelle found in plant and algae cells where photosynthesis occurs? —Preceding unsigned comment added by 75.68.106.206 (talk) 21:17, 7 October 2008 (UTC)

You know, if you read your Holt Biology book, you may find the answer very easily. I bet you wouldn't have to look for more than 2 or 3 minutes. As an aside, you should also read the disclaimer at the top of this page, where it mentions that we aren't here to answer your homework questions. If reading your textbook is too much, you may want to read the Wikipedia article on Plant cells. Toodles. --Jayron32.talk.contribs 21:20, 7 October 2008 (UTC)

Really you'd get a much faster answer by typing photosynthesis into the search box than we could ever provide, I just don't get it. -- Mad031683 (talk) 22:07, 7 October 2008 (UTC)

What is, "I'll take chloroplast for 200, Alex"? - Nunh-huh 06:47, 8 October 2008 (UTC)

An acceptable phrasing for choosing a 200 dollar question on the subject of chloroplasts on the show Jeopardy? —Preceding unsigned comment added by 82.120.232.170 (talk) 19:56, 8 October 2008 (UTC)

And always remember, google is your friend. Sjschen (talk) 03:51, 9 October 2008 (UTC)

steam rockets

I am interested in steam rockets. What can you tell me about them? I specifically wanted to know about heating the steam. The small steam rockets I've seen are preheated with a torch and then released. Is it possible to have an onboard heating system on a relatively small rocket? What would that be? Any additional information would be very helpful. Thank you.Wizardh2o (talk) 22:43, 7 October 2008 (UTC)

We have an article on hot water rockets. While it's possible to do an onboard heating device, it's inefficient -- you're burning fuel to heat water not just to "steam" but to "very hot steam" (to ensure sufficient pressure) when you could just be burning fuel for the pressure of the initial combustion and leaving the weight of the water out. So while it's possible, it's going to be rare. — Lomn 23:09, 7 October 2008 (UTC)

One exception occurs in science-fiction: fusion reactors produce heat, but nothing much you could expell directly, so the writer imagines a tiny super-storng nozzle through TINY amounts of insanely super-heated water are expelled. (This is a space ship). Can't remember who the writer was, someone famous like Asimov... —Preceding unsigned comment added by 82.120.232.170 (talk) 18:00, 8 October 2008 (UTC)

This is the basic idea behind the nuclear thermal rocket, except that for an NTR, Very Bad Things can happen if you expel the fuel. --Carnildo (talk) 21:50, 8 October 2008 (UTC)

I think you mean Nuclear salt-water rocket, and the rocket doesn't expell fuel, it expells propellent (aka reaction mass). 98.221.85.188 (talk) 04:21, 9 October 2008

I meant nuclear thermal. A nuclear salt-water rocket *does* expel the fuel -- that's what the uranium salts in the water are. --Carnildo (talk) 20:05, 9 October 2008 (UTC)

No, you meant Nuclear salt-water. And what the salt-water rocket expells is reaction mass. Sometimes fuel can be used as reaction mass, but if it's being expelled, it's called reaction mass, not fuel. 98.221.85.188 (talk) 14:44, 10 October 2008 (UTC)

No, I mean "nuclear thermal". As in a solid-state nuclear reactor ("nuclear") that heats ("thermal") water, expelling it out the back of the rocket at high velocity. --Carnildo (talk) 22:17, 10 October 2008 (UTC)

Isn't that what the ip is talking about? You mentioned fuel being expelled as uranium salts in the water, so presumably, you indeed are talking about what he is saying. ScienceApe (talk) 00:12, 11 October 2008 (UTC)

What about those new racing motorcycles that have rockets? they must have on board heating. How do they work? And what about those mini helicopters with rockets on their blades? Or that car that went 260 mph for a quarter mile? It had rockets also, that I'm pretty sure were steam. I really could use the information. 74.71.203.132 (talk) 17:54, 9 October 2008 (UTC)

Putting car in park

Is it a good idea to shift my car (a 2004 automatic) into park when I'm at a long light or waiting for a left turn? Can doing this alot damage my car? Does it save any gas?97.118.170.250 (talk) 23:08, 7 October 2008 (UTC)

For an automatic? It's not likely to affect the car negatively, though in many cases it'll burn more gas -- my auto, and most I've driven, idle faster in park/neutral than in drive. There's an advantage to shifting to neutral in a stick shift so as to reduce wear on the clutch. — Lomn 23:11, 7 October 2008 (UTC)

Is there much wear on a clutch when it's fully disengaged? --Tango (talk) 23:19, 7 October 2008 (UTC)

According to the Car Talk guys, keeping the clutch pedal fully in causes wear on the throw-out bearing. They recommend shifting to neutral. — Lomn 00:02, 8 October 2008 (UTC)

The only advantage of shifting to park that I can think of is to avoid putting your foot on the brake. The disadvantage is that you'll need to ensure you shift into drive (not neutral and definitely not reverse) when the light turns green. As for the transmission (it's automatic, so you aren't manually messing with the clutch), each car I've owned has run just fine for at least 10 years without transmission problems. From my experience, people I know with automatic transmission problems are those who gun it and race from light to light - which has nothing to do with sitting at a light. My sister-in-law has two foot settings: all the way down or all the way up. She goes through a transmission a year. -- kainaw™ 23:36, 7 October 2008 (UTC)

But will it save me any gas?97.118.170.250 (talk) 23:41, 7 October 2008 (UTC)

Did you read Lomn's response above? He states that his experience is that it will burn more gas, not less. -- kainaw™ 23:45, 7 October 2008 (UTC)

Re Lomm's observation: isn't the idling speedup due to removing the transmission load from the engine rather than increasing the fuel supply? -hydnjo talk 00:40, 8 October 2008 (UTC)

It is difficult to say in modern vehicles where a computer controls the fuel supply. In the good old days, shortly after we had to use our feet to make the car move, the gas pedal actually increased/decreased the amount of fuel to the engine. So, regardless of what else was happening, not having your foot on the pedal would make it consume fuel at the idling rate at all times. The OP said this was a 2004 car, so it is one of those newfangled computer-controlled ones. -- kainaw™ 01:53, 8 October 2008 (UTC)

In re the above:

• Switching an automatic transmission into Park should alert the computer to select the most economical fuel mode possible. At certain times, it could select "curb idle", which is a higher idle rate to maintain alternator output. If you aren't running your A/C, there's no particular reason I can think of that the computer would choose to send more fuel to the engine. However, given the same amount of fuel, shifting to Park would stop your motor from pumping liquid around the transmission torque converter, so I'd expect the engine to rev a little higher without that load.
• And for a manual transmission, shifting to neutral is always good, not least because your leg doesn't get tired. However, I think Lomn's Car Guys link is a piece of semi-crap. Their piece ends with an appeal to send them $3 to find out the rest of the mysteries, which is a little suspicious. Keeping your clutch depressed means there is a constant load on the throw-out bearing, but there is no other load - the bearing is not rotating, it's just sitting there with the incredibly hard steel of the bearing-balls and bearing-races subject to the pressure of - your foot! Contrast keeping the clutch fully disengaged though with riding the clutch, or keeping your foot lazily off the floor, so that the throw-out bearing is under pedal pressure and is rotating the partially-engaged clutch - that's definitely not good! But I've gotten 14 years and 440,001 km out of a single clutch (1992 VW Golf), and I never worried that much about shifting to neutral. The Car Guys might be right though, maybe the clutch would have blown at 600,000 km... :) Franamax (talk) 04:08, 8 October 2008 (UTC)

Keeping your foot on the clutch in a stick-shift car does indeed wear out that bearing prematurely (it's sometimes called the "thrust washer"...same thing). But in a modern car, with a typical driver, it's pretty unlikely that that'll wear out before the clutch itself - so while it's a good idea to shift into neutral and take your foot off the clutch when stopped - it's not a really critical thing. On an automatic, it's irrelevant because there is a fluid coupling clutch. There are many cases though where it's DANGEROUS to leave the car in gear with your foot on the clutch - for example, if you are stopped at a junction and you get rear-ended, your foot will almost certainly slip off of the clutch and you'll be launched forward into oncoming traffic - turning a minor fender-bender into a life-threatening situation. If you are in neutral with your foot on the brake (either in an automatic or a manual, then if your foot should happen to slip (eg as a result of a rear-ending or wet shoes or something) then at least you'll only roll rather gently forwards. Best of all is to put the car in neutral and put on the parking brake. In an automatic, putting it in park should have the same effect - but I have heard that the pin that slips into the transmission when you put the car in park can get worn out from excessive use...so I'm still going to say "Neutral with the parking brake on" is the best option and "In park" as the second best. I would be very surprised indeed to discover any difference whatever in gas consumption with any of the above techniques so long as you aren't revving your engine to keep your turbo spooled up in preparation for an impending burn-out when the light turns green!

Rather the contrary, if you're sitting in (manual transmission) neutral and get rear-ended, you will be launched into the intersection if your foot slips off the brake. If you're in gear with the clutch down, when your foot slips off the car will stall and engine braking will prevent you from being shoved into the intersection. Neutral with parking brake on would be best though. Franamax (talk) 21:31, 8 October 2008 (UTC)

I disagree about the stalling thing. I know of one person who had this happen - the car didn't stall and she ended up being side-swiped by a Jeep that was going about 40 to 50mph - which rolled the Jeep - totalled her car and might have killed her had it not been for her side-impact airbag and door reinforcement. If you think about it, that's not surprising. The engine stalls when you are at a dead stop and dump the clutch too suddenly - but if you've just been propelled forwards by the force of a rear-ending, the RPM may well be efficiently matched to the speed of the wheels when the clutch bites - and far from stalling - the car may actually accellerate into the intersection. A lot will depend on the car - my MINI Cooper'S is pretty hard to stall like that - it has a pretty flat torque curve so you tend to get a bit of tyre squeak and then it's perfectly happy. Personally - I don't recommend taking that bet. If that's your driving style - you should change it ASAP. In neutral with the parking brake on - or possibly in gear with the clutch down AND the parking brake on - are the only safe possibilities with a stickshift car. SteveBaker (talk) 02:14, 9 October 2008 (UTC)

Steve, I quail at the thought of ever disagreeing with you, what with you being pretty much completely always right and all (I mean that!) - but I have to disagree here. Yes of course using the parking brake is always the best solution, and by that we probably both mean the handbrake available to hand in a small car. Even then, most people will not engage the handbrake at a common driving stop. Consider now a traffic stop where the parking brake is not engaged, and the only variable is whether or not the manual transmission is engaged in gear, or in neutral (the driver's feet disengage from all pedals on impact). In the neutral case, the car will accept the momemtum transferred on impact (minus energy of deformation) and (almost) immediately adopt a forward velocity. In the case where the transmission is engaged, regardless of whether or not the engine stalls, the rotating/translating mass of the engine will participate in the collision energetics. Unless you were sitting there revving the engine, including the inertial moment of the engine elements into the energy equation can only slow the car down. Remember that you are not feeding extra fuel to the engine - whacking the car from behind may cause the auto with an engaged gear to move slowly forward making a "putt-putt" sound from the idling engine, but I see no possible way it would cause sufficient velocity to participate in an intersection crash. Smacking a car in neutral gear though - think about billiard balls, and the pocket is on the other side of the intersection.

As far as changing my driving style, I'll let you know when I've completed ny second million kilometres, the first has gone pretty well. (FD - 2 accidents - early 20's [age, not year!] - one, making a U-turn without looking back, the other looking for something in my back seat) I've in the past read advice about sitting still in a manual auto, it's uniformly to stay in gear with the clutch down. You are absolutely right that the parking brake is the way to go, but in abeyance of that advice - keep it in gear. Franamax (talk) 03:28, 9 October 2008 (UTC)

Actually, I'm not sure - there may be no pockets in billiards. So instead, think of it as a snooker ball or a pool ball. I know how to play and lose at both of those. :) Franamax (talk) 03:33, 9 October 2008 (UTC)

When the engine is idling, there is fuel going into it. You put a car in gear and take your feet of all the pedals it will move forwards (assuming it doesn't stall, and the fact that it's already moving slightly from the impact will help there as Steve says). I'm not sure the velocity imparted by the impact would be enough to prevent the car stalling, but it could well be - remember the engine is disengaged at the time of the impact (since your foot is on the clutch) so there is no engine braking in that first fraction of a second. I guess it all depends on how quickly your foot falls off the clutch pedal. That said, I don't think I know anyone that puts their car in neutral every time they stop at lights, and my driving instructor never told me to. Of course, if you have your feet on both the clutch and the foot brake, you should be fine - the brake will stop you moving forwards from the impact even if your foot does then fall off it, so then the engine will stall when you lift the clutch. --Tango (talk) 20:50, 9 October 2008 (UTC)

Just think about the dynamics. You've been rear-ended and your feet have been knocked off all the pedals. If you're in neutral, your car is free to move forward with all the imparted momentum. If the car is in gear, part of the momentum is dissipated into accelerating the engine. The idle fuel feed is immaterial - how fast does your car go when your foot's not on the gas pedal? Chugging forward into the intersection is not the problem, getting shoved forward is. If you get rear-ended hard enough to knock your feet off the pedals, you want every possible means to stay out of that intersection.

If I take my car out of gear whilst sitting on the active road area, I pull the handbrake - always. But usually I hold the clutch in, with the other foot on the brake pedal. I also do the left-turn thing where you pull out and crank the wheel left to get a good sight-line, then turn the wheel back so you don't get rammed into oncoming traffic. And the left-turn thing where you hang back until at least one other car is behind you, then move forward a bit. There's also the best practice thing where you stop 20 feet behind the next car at a stop-light, wait 'til at least one other car stops behind you, then move up - I don't do that though, since I've paid for an airbag I didn't ask for, meant to save the life of an overweight American male who isn't using his seatbelt. :) I actually spend most of my driving time evaluating threats - and enjoying my machine. Franamax (talk) 07:17, 10 October 2008 (UTC)

I've never actually measured the speed a car goes when idling, but I heard 8mph given as a figure once, which is plenty fast enough to cause a problem at a junction. --Tango (talk) 21:15, 10 October 2008 (UTC)

And if you're sitting in neutral and get rear-ended by a car moving at 30 mph, what is your resulting velocity? More or less than 8 mph? Franamax (talk) 01:06, 11 October 2008 (UTC)

Difficult to say, but probably about the same. If we assume your cars are of similar masses, then the maximum you could be going is 15mph, but quite a lot of energy will be absorbed by deformation (cars have crumple zones which can and do absorb a lot of energy). Also, most cars rear-ending you will be going slower than that, since they will have just started braking too late rather than not at all. --Tango (talk) 11:36, 12 October 2008 (UTC)

October 8

Headset to hear dictations

What are the technical specifications that we have to look in a head phone to get maximum efficiency to hear dictations and comfort for wearing long hours?

As far as comfort goes, that's not likely to be a question of technical specifications. Your head and ears are pretty unique in their shape, and what is comfortable for one person may not be comfortable for you, and vice versa. -- Captain Disdain (talk) 01:17, 8 October 2008 (UTC)

For example, I switched from earmuffs (which I otherwise prefer) to plugs after I got new glasses whose shafts stand out further from my head than before. —Tamfang (talk) 05:34, 8 October 2008 (UTC)

Sensory Integration Disorder and its Impact on Potty Training

I have a 4 yr old daughter who has SID and is very hypersensitive. She has been working with OT and PT since she was 5 mths old. No one has any clear information to give me on how to potty train! The developmental specialist states to give her time- the uroligists states she must get it done b/c of the severe negative side effects it has had on her (kidney infections that have led to hospitalizations). She is very fearful of even sitting on the toilet much less wanting to be in the bathroom when it flushes! I have read all I can find on SID and own numerous books on potty training. Are there methods used for children with SID to help with this issue??

Thank you- —Preceding unsigned comment added by 12.202.108.191 (talk) 03:25, 8 October 2008 (UTC)

Have you asked the medical professionals for locations of appropriate support groups? Have you tried searching on the web for support groups that address this specific issue? There are lots of parents here, but we're really not allowed to give medical advice on specific issues. Franamax (talk) 05:01, 8 October 2008 (UTC)

And there's no particular reason the child must be in the bathroom when the toilet flushes. She can be standing just outside the door watching when you flush the toilet, and then she can hold a long stick to help you flush the toilet, and then she can use the stick herself. But that's starting to be medical advice... Franamax (talk) 05:07, 8 October 2008 (UTC)

Strange gender inequality in the dental industry

I've been to numerous dentists. Why are the dentists always only men and the assistants always only women? Are you ready for IPv6? (talk) 03:49, 8 October 2008 (UTC)

That's an interesting question. Have you tried to seek out dental clinics where the dentists are female? As far as the gender split goes:

• Dentist does seem to be a male-dominated field. A discussion on possible gender-bias can be found here. Stand-alone professional fields such as dentistry would seem good ground for women to avoid gender bias, since they have only to fulfill the qualifications. I would speculate that those women so inclined might gravitate instead to pharmacology or in particular physiology (M.D.-type doctor rather than D.D.S-doctor). Perhaps those women inclined to a medical field either go big or go home (pace to any dentists who might think I denigrate their important field - but it does rank just a little under M.D.).
• As far as dental assistants or dental hygienists, I would speculate that the field offers a good way for women of child-bearing age to acquire a valuable transferable skill that offers them maximum flexibility as to hours worked, balanced with a good income. Also, women are probably just better as dental assistants, since they're more empathetic, interact naturally with children, etc. You can read that as a sexist statement, but I mean it as a statement of great admiration.
• And the factor of bearing and caring for children must always be considered in choice of training and work for women - they're the ones making them after all. :) In the case you question though, the balance does seem somewhat skewed. Franamax (talk) 04:55, 8 October 2008 (UTC)

My current dentist is female, my former dentist was female. Of the 4 dentists over my life-time 2 have been female. Of course that's my perspective and so statistics might not back this up. Just throwing that in there. 194.221.133.226 (talk) 10:32, 8 October 2008 (UTC)

Could it be the case that greater (on average) physical strength and large hands are an advantage when pulling teeth? Or that the general wisdom is such - thus discouraging some women from taking up dentistry? A personal observation - the only time a female dentist tried to remove one of my teeth (I've had a lot of teeth removed), she wasn't strong enough to budge it and had to go fetch a male colleague. --Kurt Shaped Box (talk) 10:59, 8 October 2008 (UTC)

Personal observation #2 - my lower wisdom teeth had twisted roots and the (male) dentist couldn't pull them no-how. He ended up jack-hammering them into pieces (which I still have). As well as the pain from the extraction site, I had a bruise on my jaw from where he braced his hand trying to pull. The point about physical strength may have some merit. Franamax (talk) 21:24, 8 October 2008 (UTC)

This site has some numbers. It says there is an 83%/17% male/female split among all private practice dentists in the US. It's interesting to note that at a prestigious veterinarian school in my area there is a similar split in the other direction. --Sean 14:51, 8 October 2008 (UTC)

It's probably the same reason that most Doctors (traditionally) have been male, and most Nurses female. "Dentist is to Doctor as Dental hygienist is to Nurse" (FWIW, my current dentist is female, and I know of male hygienists, just like I know female doctors and male nurses) -- 128.104.112.147 (talk) 15:40, 8 October 2008 (UTC)

A dental hygienist is different from a dental nurse. --Tango (talk) 23:23, 8 October 2008 (UTC)

I'm a male and I don't work out very well and probably every woman in the miitary is stronger than me so I don't think it's strength. As for pregnancy, dentists often share a practice with another dentist and dentists themselves generally see the patient for two minutes during checkup. I also have noticed there's a lot of female vets. I'm not really quite sure how to really search for lots of dentists. I usually call 800-DENTIST when I move, but my last move within about 50 miles only one dentist was registered. That dentist had a nice office with fancy machines so I thought he'd be good. It turns out that he pays for it all by not just charging 4 times more for an exam, but will give false diagnosis and tell people they need expensive things done that only harm their teeth. I wasn't certain until I searched on the internet about this. There's countless cases of people who moved to a new location, got a new dentist, and despite having no cavities or other problems for 10-15+ years their new dentist claims to find 5-12 cavities that don't exist just so he can mutilate a person's body to make extra money. It's rather common. I take it dentists don't have to take the hipocratic oath. Are you ready for IPv6? (talk) 01:39, 9 October 2008 (UTC)

Well, if you just wanted to rant about how evil dentists are, you could have saved us some time and effort answering what looked like a legitimate question. How's this then? Dentists are a male-dominated caste placed on this earth solely to suck away our cash and destroy our bodies. There you go, you read it here on Wikipedia, so it must be true. Can we close this thread now? Franamax (talk) 02:51, 9 October 2008 (UTC)

That wasn't reason for the question. I just bought it up along with a lot of othe things because I saw a lot of people discussing this. Are you ready for IPv6? (talk) 03:41, 9 October 2008 (UTC)

OK, I'll retract any suggestion that you posed an improper question in the first place. However, the later post you made strays over the line into our striction that the RefDesk is not a forum for opinions, nor is it a soapbox to put forth your own opinions. If you have a specific follow-up question, we can consider it. Franamax (talk) 03:47, 9 October 2008 (UTC)

It seems that over-servicing is not an article here though Google attests dentistry is rife with it. Dentistry may not have the hippocratic oath as such, but its national professional association would have an ethical code and is the body to complain to usually. On wiki, entering "Dental ethics" gives you Michele Aerden who instigated the first Dental Ethics Manual and "Dentistry ethics" comes up with stuff worth sifting if you're keen. Julia Rossi (talk) 10:45, 12 October 2008 (UTC)

immume system

types of immumoglobine —Preceding unsigned comment added by Ksneyhaa (talk • contribs) 06:37, 8 October 2008 (UTC)

WIth regard to the immune system, we discuss immunoglobulins IgA, IgD, IgE, IgG, and IgM. - Nunh-huh 06:43, 8 October 2008 (UTC)

chemistry

two flasks A & B have equal volumes .flask A contains Hydrogen maintained at 300K while B contains methane gas maintained at 600K. 1.which flask contain greater number of molecules & hwmany times more —Preceding unsigned comment added by Bhuwanntl (talk • contribs) 07:55, 8 October 2008 (UTC)

"Do your own homework. The reference desk will not give you answers for your homework, although we will try to help you out if there is a specific part of your homework you do not understand. Make an effort to show that you have tried solving it first." -- Aeluwas (talk) 08:53, 8 October 2008 (UTC)

Your question is unanswerable, because you have not specified whether the two flasks have equal pressures. Take a look at combined gas laws. If we specify that pressure is equal, you're looking at Charles's law. - Nunh-huh 09:00, 8 October 2008 (UTC)

Aflatoxin in raw peeled peanuts

How can I know if raw peeled peanuts are contaminated by Aspergillus flavus and Aspergillus parasiticus? Is it possible to see it like mold on bread? Mr.K. (talk) 12:14, 8 October 2008 (UTC)

Peanuts in general are susceptible to aflatoxin contamination. You wouldn't see the aflatoxin itself (except under blacklight), but you might see the fungus that produces it. Cooking doesn't really affect it, since the toxins are heat stable (the fungus that produces them, however, is not). Fungus doesn't imply aflatoxin (not all fungi produce it), but lack of fungus doesn't guarantee safety. Like most toxins, a really small dose (i.e. one dubious peanut eaten per year) isn't going to kill you. If in doubt, don't eat it (no surprise there), but probably best to avoid the whole group if you see some fungus growing on anything in it. SDY (talk) 13:01, 8 October 2008 (UTC)

Sleep injuries

I'm failing to find the medical term for injuries that occur while sleeping, such as pulling a muscle or separating a joint. Is there a term to classify those injuries? -- kainaw™ 13:18, 8 October 2008 (UTC)

They don't happen often enough, and aren't intrinsically different from similar injuries occurring while awake, for there to be a common medical name for them. - Nunh-huh 15:22, 8 October 2008 (UTC)

Semen and Enzymes

Do the enzymes in washing detergent break down the proteins ect, that are in semen? i always wash my underwear seperately, because i worry that im simply spreading it all evenly on my clothes, and that microscopic amounts will rub off on where i sit ect. Zakbrak341 (talk) 13:56, 8 October 2008 (UTC)

If they're only microscopic amounts, what difference does it make? Also, why do you have so much semen in your underwear? You're meant to remove your clothes for that kind of thing... --Tango (talk) 14:10, 8 October 2008 (UTC)

Its not loads, just very small amounts of precum before i take them off ect, if got lots on them i'd just throw them away, but the thought of any amount of semen on anything bothers me, for a while i was doing a hot wash, so it would denature the protiens but then i worried that the heat would denature the enzymes in the powder, and if the enzymes break down the protiens into amino acids, then thats better than simply unfolding the protien into its secondary of primary structure, then i started worrying, what if these enzymes in the washing powder are specfic to protiens in common food stains only and have no effect on the protiens in semen, so now im just wash them in serveral changes on water with lots of detergent. —Preceding unsigned comment added by Zakbrak341 (talk • contribs) 14:31, 8 October 2008 (UTC)

Tango, two things. First, some people are kinda clean freaks when it comes to everything, so it's not really unusual to be concerned over whether semen is contaminating other clothes in the washing machine. Secondly, it's not really your place to ask him why he has semen in his underwear, you should only address his questions. 98.221.85.188 (talk) 14:35, 8 October 2008 (UTC)

Your detergent should emulsify fats, which means that it wraps little bubbles of detergent around your semen and stops it from sticking to any of your clothes. Plasticup ^T/C 15:08, 8 October 2008 (UTC)

Except that semen is essentially fat-free. No emulsification. For the original questioner: the enzymes in washing detergents are designed to be as non-specific as possible in breaking down proteins, and should have no trouble with semen. - Nunh-huh 15:19, 8 October 2008 (UTC)

Even if someone can get something which is soiled physically clean, meaning that the offending sunstance cannot be seen or even detected by CSI, they still remember it was once there. It can get more into ritual purification, like the concept of a ritual bath removing some iniquity or moral stain. I read a housewife's complaint to an advice column that her husband had soaked his sore toe in warm salt water (at the doctor's advice) in one of her expensive gourmet cooking pots, and that she had to throw the pot away because she would never afterward feel that it was "clean" regardless of scrubbing or dishwasher cleansing. If the questioner gets a reference to an authoritative laundering site which says a wash of some temperature on some cycle with certain cleaning products will render the garment as clean as it was when it came out of the package, then he might be saved the expense of frequently throwing garments away and buying replacements. Some people, even in this era of "cold water" energy-saving detergents wash a load of white cotton washcloths, towels, and underwear in the "hot" wash cycle with detergent and chlorine bleach, with an extra rinse, Not saying this is the authoritative answer to the original question, and there is also the question of enzymes versus bleach and hot versus cold water to eliminate biological stains. Interestingly there are loads of book references dealing with semen stains[[5]] though few specifically address their removal. (Not to be confused with the mythical character "Seaman Staines" on the Captain Pugwash children's program). Edison (talk) 15:23, 8 October 2008 (UTC)

You can check how good a job your selected detergent is doing by taking a look at your unmentionables under a black light before and after the wash. 71.178.135.144 (talk) 02:15, 9 October 2008 (UTC)

Not a great method. While semen does fluroesce under a black light, it is not the only thing that does. Lots of detergents and fabric softeners do, as well. When you see, on crime shows, them use a black light to look for semen and/or blood, it's not the black light that proves its presence; the black light merely lets them know where the most likely places to test are. Its only after they have done a positive chemical test can they know that the stain that glows under black light is semen, or blood, or any of a number of other agents that also glow... --Jayron32.talk.contribs 02:24, 9 October 2008 (UTC)

If it makes the questioner feel any better, the sperm in semen dies after the semen dries, so no matter what, there is no sperm spreading around your clothes or to any other surfaces.--el Aprel (^facta-_facienda) 20:20, 11 October 2008 (UTC)

E=mc^2...Whatever that means.

Hey...what unit is the E in $E=mc^{2}$? Is it calories, Joules, tons, or what? I have been wondering about this for a while and saw the article on E=mc^2 with its handy list of how much energy is contained in a dollar bill. It lists several units of measuring energy, which got me confused. When you convert mass to energy, is the mass converted to Joules or calories or another type of energy? 31306D696E6E69636B6D (talk) 16:36, 8 October 2008 (UTC)

Well, it defaults to kg·m²/s² (Joules), which it does say in the intro :)

In the formula, c2 is the conversion factor required to convert from units of mass to units of energy. The formula does not depend on a specific system of units. In the International System of Units, the unit for energy is the joule, for mass the kilogram, and for speed meters per second. Note that 1 joule equals 1 . In unit-specific terms, E (in joules) = m (in kilograms) multiplied by (299,792,458 m/s)2.

-- MacAddct1984 ^{(talk &#149; contribs)} 16:42, 8 October 2008 (UTC)

(ec) :Joules and calories are units of measurement, not different "type[s] of energy". Just like you can measure speed as miles per hour or kilometers per hour or feet per second and can convert a speed from one to the other but it's still the "same speed". So whatever units you use for c and for m determines the units of E. If that's not the unit you want, you can convert. Or you can choose what units of energy you want and then convert the mass and speed of light to use them. DMacks (talk) 16:43, 8 October 2008 (UTC)

As long as you're consistent, you can use any unit system (for example, you could use ergs, but then you would have to measure the mass in grams and the speed of light in cm/s - see cgs). Usually scientists use SI units, where energy is measured in joules. It's also common to see energy measured in electron volts. --Tango (talk) 16:46, 8 October 2008 (UTC)

You're wrong: you can use any units that measure the same thing. For example, instead of asking how many 'joules' a certain number of 'kilograms' would result in according to e=mc^2, you can ask Google how many "horsepower-hours" (which measures the same thing joules do) a "pound" of stuff results in. Just google "1 pound * c^2 in horsepower*hours". You get "1 pound * (c^2) = 1.51859015 × 1010 horsepower * hours". In other words, if you had a magic reactor in your room that completely turned matter into energy, then with 1 pound of fuel you could output one horsepower (745 watts) for

15000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 hours.

You haven't used the same equation, though, you've added a conversion factor (or, you've absorbed the conversion factor into the constant by measuring the speed of light in obscure units). You have to use consistent units, otherwise you quite clearly get nonsense. If I use kg for the mass and m/s for the speed, plug it in and I get joules for the energy, I can't just choose for that to be ergs or electron volts or horsepower hours, since that would be assuming they are all the same thing. To get to another unit I had to multiply by a conversion factor so then I'm actually using E=kmc² where k conversion factor. --Tango (talk) 21:12, 8 October 2008 (UTC)

No, you're just wrong. Take something simple: distance = speed * time. So, 60 miles per hour for two minutes = distance = 60 m/h * 2 minute = 120 minutes * m/h, ie "120 mile-per-hour minutes". And look 120 mile per hour * minutes = 3.218688 kilometers is a perfectly good answer. You can ask for it in feet, inches, anything. It's just a unit conversion, it's not solving an equation. —Preceding unsigned comment added by 82.120.232.170 (talk) 12:26, 11 October 2008 (UTC)

yeah, just remember that the CONSTANT in the equation, C, isn't just a number, like a million. Instead, it's a "million miles per hour" (for example). So, if you take a pound, or a kilogram, or any unit of mass you want, and mulitply it by a million miles per hour squared, you get a certain amount of energy. I don't have an intuitive conception for why a million miles per hour squared times 1 pound should be an amount of energy though... —Preceding unsigned comment added by 82.120.232.170 (talk) 17:54, 8 October 2008 (UTC)

Lets take it in terms of the metric system, for symplicity. Energy is defined, in one instance, as the measure of the change of speed of object of a defined mass over a defined distance. From a unit-based analysis, that means that energy is measured as kilograms times meters squared divided by seconds squared, ( kg*m²/s² ). That is the inherent definition of energy. The deal is, if you do ANY other combination of measurements, and arrive at the same final units, that is a measure of energy. For example, air pressure*volume is a unit of energy (air pressure can be expressed as force per unit area, and force is mass * acceleration, and volume is displacement cubed, so the if we express pressure as (kg) * (m/s²) / (m²) * (m³) we get, kg*m²/s², which is energy. How we calculate energy, as electron-volts or as newton-meters, or as joules, or as liter-atmosphere (these are all energy measurments) is largely dependent on the particlar application. --Jayron32.talk.contribs 18:18, 8 October 2008 (UTC)

I've thought of an analogy that might help you: if you could increase your gas mileage by 20% for every 10% under the speed limit that you go (just made that up!!!) you can use that without knowing units for EITHER mileage OR speed limit -- and indeed, our British readers would translate that "tip" into different actual numbers than the Americans...

So if m is kilograms then E would have to be in Joules? 31306D696E6E69636B6D (talk) 18:29, 8 October 2008 (UTC)

No, you're confused by the mistake the poster above made. See my correction of him above. (The poster above is lazy and wants to just cross out units that are the same, for example, when you multiply 55 miles per hour by 2 hours you figure out what units the answer will be by going: [m/h]*[h], ie crossing out the two h's. But you can just as easily ask what distance you go in a minute at that speed).

The easiest thing to do is play around. Into google put "c=" . Then try "1 lb * c^2". And put "1 kilo * c^2". Then you can ask for the results in different units by saying "in" as I did above ("1 pound * c^2 in horsepower*hours").

If m is in kg and c is in m/s, the E will be in joules. If you chose different units for c, you'll get different units for E. --Tango (talk) 21:14, 8 October 2008 (UTC)

Energy is dimensionally equivalent to Force*Distance, which is equivalent to Mass*Speed*Speed. (See Dimensional analysis for a better grounding on the subject.) The exact units that Energy comes out in is dependent on the units that you use both for mass and for speed. $E=mc^{2}$ is always valid, regardless of choice of units for any two of the quantities, however, the units of the third may end up not to be a "conventional" measure (e.g. $stone*furlong^{2}/fortnight^{2}$ is a unit of energy, albeit not one that has much use/respect). SI, however, is designed to be self-consistent, so if you stick to the standard SI units, things tend to work out well, unit-wise. Kilograms, meters, and seconds are all base SI units, so for mass in kg, and speed in m/s, the units of energy work out to the SI unit of energy (joule), because the joule is defined as equal to $1kg*m^{2}/s^{2}$ (See joule#Description). -- 128.104.112.147 (talk) 22:27, 8 October 2008 (UTC)

safe dough?

I live with an Italian, and she's making pizza in four days -- but she's started today. She mixed a spoonful of honey with oil into flour and water and is letting it rise at room temperature, keeping it moist under a moist cloth (which she will keep remoistening over the next four days). This "mother" dough she will use over the course of several pizzas, the first one Saturday, until she's done with it.

My question is: how does this work? I'm not sure what role the "mother" dough has, is it like yeast?

In fact I heard that "sourdough" was created by accident more than a hundred years ago, and since then they have alwyas been reusing the same starter -- they always saved a little to make more. But she's not adding a "starting" piece, she's just starting from honey and oil! So, isn't it just a random toss-up what microbes will start growing? Why is it even safe?

Obviously I'm not asking for any medical or legal advice... —Preceding unsigned comment added by 82.120.232.170 (talk) 17:14, 8 October 2008 (UTC)

Actually, the invention of having isolated yeast which you add to the dough to make it rise is a relatively recent invention. For thousands of years, bread was made the same way: You mixed flour, water, and a few seasonings, you sat the mixture on the window sill, and it picked up whatever yeast cultures blew in on the wind, and the bread rose and you baked that. The problem is that some cultures don't taste particularly good. Someone a long time ago figured out that if you find a particularly tasty piece of dough, rather than let future batches of dough get cultured randomly, if you innoculate it with your good-tasting culture, you get equally good tasting bread. This is often accomplished by reserving a "starter" or "mother" culture from each batch of bread, and using it to innoculate the next batch. However, you can also control which cultures take hold in your bread by carefully controling the chemistry of the dough. Cultures are highly sensitive to variations in pH and salinity and other factors, so the specific ratios of say, honey to salt to flour will basically be highly favorable to a single variety of microorganism, and not so much to the others. Once you find a recipe that attracts the right yeast, if you use the same recipe each time, you will end up with the same yeast each time, and thus a fairly consistent bread. --Jayron32.talk.contribs 18:04, 8 October 2008 (UTC)

(EC) See sourdough, which is exactly what she's making; it should be delicious! The reason it's not a toss-up is that whatever incidental microbes might be hanging around get their asses kicked by the massive amounts of good yeast and bacteria already in the flour. It's only if they run out of food (the honey) that those agents will start to die off and bad ones can take over. Sourdough has been around for thousands of years, and while it is indeed possible to keep a starter going indefinitely, most people just start one from scratch. --Sean 18:15, 8 October 2008 (UTC)

if I get you right, your response implies 1) flour you buy has lots of good yeast and bacteria in it (and not bad ones), it's made that way? How's that work? 2) if you added honey forever the good ones would always have enough to eat, you could keep it going a month and then bake it... —Preceding unsigned comment added by 82.120.232.170 (talk) 19:45, 8 October 2008 (UTC)

Actually, most of the yeast is present in the air, or on the flour itself. The yeast is just there, it isn't added or anything. It may grow on the grain naturally, or it may just alight on the flour from the air. The determining factor as to which microbe predominates is the local chemistry in the dough. The good yeast, if correctly encouraged to grow, will simply crowd out any nasty critters. --Jayron32.talk.contribs 20:09, 8 October 2008 (UTC)

In fact, the use of "ambient" yeast and bacteria in lambic beer rather than pure yeast cultures is the reason for the rich complex taste of Belgian beer. - Nunh-huh 21:03, 8 October 2008 (UTC)

1) Correct. It's only natural that microbes that can live on wheat will be found on it in the wild. 2) No, just adding honey won't do it. You also need to add more flour, and water, and keep the bacteria/yeast balance correct. I seem to remember Harold McGee's magisterial On Food and Cooking covering the details, but I'm sure many baking books do, too. FYI, some cooks have kept starters going for *decades*, though refrigeration makes that a lot easier. --Sean 22:32, 8 October 2008 (UTC)

We cannot rule out that "wild" yeast or fungus might make the dough taste bad or even become toxic. Edison (talk) 03:53, 9 October 2008 (UTC)

An archived Ref Desk answer describes some undesirables which might grow in a dough culture : "I suppose we could add a disclaimer about "Ask a baker" or "Ask a mycologist" for bread mold advice. I claim no expertise in this area and only cite info found on the net or from general reading, including a baking textbook, and from baking various types of bread in the home. The surface of fresh-baked bread is generally free of microorganisms because of the heat of baking, but ropy mold may survive in the interior of bread. The surface can become contaminated while the bread is cooling or being wrapped, while it is sliced, or while it is stored. [6]. Bread can be attacked by various types of mold. There are over 600 varieties of bread mold. Some of them are listed at [7]. Note that the same mold may grow on bread and other substances, and some of these are toxic to humans. In general, some spores are just part of nature. But if mold from bread or other sources has left a high concentration of spores in an area such as your kitchen or your breadbox, it stands to reason that a loaf of bread placed there subsequently might get moldy quicker than if the mold spores were not drifting around. See Black bread mold, [8] at Madsci.org. Edison 14:59, 14 August 2007 (UTC)" Edison (talk) 18:49, 9 October 2008 (UTC)

and, of course, once you've made a few loaves of bread in a kitchen it's pretty thoroughly inoculated with enough yeast on a permanent basis. fungi are remarkably tenacious. I worked in a lab with the fungus neurospora crassa 20 years ago; i'm still seeing random colonies of neurospora appear around the house where i haven't hit it with the lysol lately, along with the usual household mildew and random gunk. mind you, i didn't grow the fungus at home, that's just from spores which hitched home with me; and moreover, I've moved twice since then. for another example, microbreweries which make beer for on premises consumption but subcontract the bottled product to big breweries (often the case) can specify their recipe, but can't specify their particular strain of yeast, as one particular strain of yeast will colonize a brewery, and you just can't make a batch with a different strain in that premises. (so i've been told at the local microbrewery). see also lambic for another example of trusting in airborne yeast to produce a palatable and nontoxic product, rather than adding a defined yeast (oh, somebody said that already). Gzuckier (talk) 06:03, 11 October 2008 (UTC)

Erronious definition

I found this definition for Hyperthyroidism. I don't believe this is the real definition. I couldn't figure out how to correct it so I am sending it to you.

<obvious bit of vandalism removed ... no need to keep that around for posterity --98.217.8.46 (talk) 03:13, 9 October 2008 (UTC)> —Preceding unsigned comment added by 152.130.7.64 (talk) 18:27, 8 October 2008 (UTC)

Yes, that's a bit of vandalism in our hyperthyroidism article. It's fixed now, thanks for pointing it out. - Nunh-huh 19:09, 8 October 2008 (UTC)

Perhaps it's an alternate definition? --Sean 22:38, 8 October 2008 (UTC)

Perhaps in an alternative universe. - Nunh-huh 23:32, 8 October 2008 (UTC)

Do gas giant even have a flowing water?

Do Jupiter, Saturn, Uranus, and Neptune even have a flowing water in it's mantle or it's just a hot dense white-hot vapor if human touch it they will instantly get electricute and roast. All their core is very white-hot, hotter than the surface of the sun.--SCFReeways 23:13, 8 October 2008 (UTC)

To be honest, I'm not sure. Any water in the mantle would be extremely hot, but the pressure may be enough for it to stay liquid. I think it would be all mixed in with everything else rather than flowing, though. A human at those temperatures would be instantly killed, yes, although I don't know why you think they would be electrocuted... --Tango (talk) 23:20, 8 October 2008 (UTC)

• metallic hydrogen for jupiter and Saturn, certainly they conduct electricity, even Uranus and Neptune the ice to me actually means electronic stuff, hot gluey vapours similar to lightning and molten comets. I don't think is true water the water we use and drink. Those planets is total gas, and landing to me is like going to hell. No solid surface no place to land, from what I've learnt when I was elementary student, if we try to land on it we will just keep sinking trough their interior, until we get to it's nucleus, and even prior to getting to it's center, the strong heat will instantly kill humans, even those dense vapours. Does your saying of liquid mean vapours from the burnt rockets?--SCFReeways 23:36, 8 October 2008 (UTC)

To answer Tango's question, I presume the OP is concerned about that big-ass storm that's been circling Jupiter for at least the last 300 years. And there's plenty of lightning on Jupiter (at least) and presumably the other gas giants. Matt Deres (talk) 23:42, 8 October 2008 (UTC)

• Even Uranus and Neptune's mantle I beleive is made of deadly "junks" possibly liquid, eelctrical wastes, vapors, perhaps anything.--SCFReeways 23:51, 8 October 2008 (UTC)

I think we can all agree that anyone standing in the core of a gas giant would be killed instantly. The heat and pressure would be extraordinarily deadly. I'm pretty sure you would not live long enough to be electrocuted by a lightning bolt.

Does that answer your question? APL (talk) 01:35, 9 October 2008 (UTC)

Heat, pressure AND radiation. The gas giants are certainly pretty nasty places. Given that there must be a more or less continuous gradient from the low temperature and pressure of space down to the metallic hydrogen at the center - you'd imagine that there would be some altitude at which liquid water could exist - whether there actually is enough water at that level to form flows is much harder to determine. Probing the conditions deep into that atmosphere is very hard. SteveBaker (talk) 01:53, 9 October 2008 (UTC)

Are you saying gas giants have a core that is just gas? Not rock? I'd assume enough asteroids fell into them to give them a rocky core, though I hear Saturn is very light. Though I also would assume then that the sun must swallow a lot of asteroids, though why this doesn't make the sun die with iron going into its core, who knows. Are you ready for IPv6? (talk) 03:39, 9 October 2008 (UTC)

Talking about Earth or gas giant? While Earth have "Greenhouse" or "Icehouse" have nothing to do with gas giants. Earth had icehouse in the past, and once it was cooler when all the continenets is at the South Pole. 100 to 200 million years later, Earth will likely to be greenhouse or hot again. I don't know why you ask this becasue this have nothing to do with the question.--Freeway91 19:58, 9 October 2008 (UTC)

Gas giants have a solid core, but not because they swallow asteroids, it's because of the immense pressure. 98.221.85.188 (talk) 04:17, 9 October 2008 (UTC)

I don't think the core is rock as we know it. In Jupiter's case, at least, it's rather exotic matter (metallic hydrogen and similar), due to the intense pressure. Regular rock would probably be destroyed long before it reached the core. --Tango (talk) 10:23, 9 October 2008 (UTC)

Well, the elements that make up the rock (iron, etc) have to be there somewhere. In these cases, though, it's a matter of scale. Neither Jupiter nor the Sun consume enough asteroids to be relevant when analyzing their overall composition. — Lomn 13:01, 9 October 2008 (UTC)

Sure, the elements will be there, but not in the forms we're used to. They had plenty of the components of rock from the start, they don't need asteroids for that (well, they make have formed by aggregation of what were essentially asteroids, but that was a long time ago), but those components can't make rock at those temperatures and pressures. --Tango (talk) 13:36, 9 October 2008 (UTC)

I wonder if consumered rock has anything to do with the sun cycles like the sun is supposed to go in cycles where it varies from stronger and weaker to what it puts out. I know that the earth while it did go into cycles of hot to freezing, did used t average a lot hotter but in the last tens of millions of years it gradually really cooled down and then the recent ice age was pretty much its lowest point and then it started warming back up a bit, but still lower than the average. Mars was also supposedly warmer at one time, too. Are you ready for IPv6? (talk) 13:46, 9 October 2008 (UTC)

Highly unlikely, again as a matter of scale. There's just not enough foreign material entering the sun to affect things, even if things would be affected in the first place. With that caveat, it's worth noting that even dropping a planet-sized chunk of iron into the sun would likely have no effect. Iron is the fusion stage at which stars quit, yes -- but the presence of iron should have no effect on the hydrogen fusion process currently ongoing, or the helium fusion that will follow once the hydrogen is exhausted, or the lithium or beryllium or whatever follows that. Iron isn't exothermically fusible, but neither does it poison other fusion reactions. — Lomn 14:08, 9 October 2008 (UTC)

Metallicity does affect how a star behaves, but I agree that on the scale we're talking about the effect would be negligible. I'm not sure much even falls into the sun - to do so it would need to shed almost all its angular momentum, which is pretty difficult to do. --Tango (talk) 14:18, 9 October 2008 (UTC)

Time-independent Schrödinger equation: "If $\psi$ is a solution then $\psi$* is also a solution."

In an Introductory Quantum Mechanics book I'm reading, the author often claims that if $\psi$ is a solution then so is its conjugate, and this is stated as being self-evident (leaving me to suspect I'm missing something obvious). Previously, I've only ever encountered complex conjugates when related to an actual complex number, whereas $\psi$ is actually a function $\psi (x)$, hence my confusion.

The equation is as follows:

$E\psi =-{\frac {\hbar ^{2}}{2m}}{d^{2}\psi \over dx^{2}}+V(x)\psi \,$

This forms part of a question that asks to show that a time-independent wave function $\psi (x)$ can always be taken to be real, because if a solution isn't real it can just be expressed as a linear combination. Quote: "if $\psi (x)$ satisfies [the above equation], for a given E, so too does its complex conjugate, and hence also the real linear combinations $(\psi +\psi *)$ and $i(\psi -\psi *)$."

So I basically have two questions: 1) Why can we say $\psi *$ is a solution because $\psi$ is? 2) What else is this question looking for, since it basically gives the answer away when it talks about the linear combinations?

I have the feeling I'm mis-interpreting something here, so I'd be grateful for any clarification or help. Leucippus89 (talk) 23:54, 8 October 2008 (UTC)

Edit: Just to be clear, this question is about $\psi (x)$ and not $\Psi (x,t)$. I know that when you solve the Schrödinger equation by separation of variables, the time-dependent function always has complex components which are dependent on t and so could be safely ignored (?) in an equation that's just concerned with x. But that's not what this question's about, and I think that's what's confused me, because I'm not used to seeing complex terms in $\psi (x)$. Leucippus89 (talk) 00:39, 9 October 2008 (UTC)

I suppose $E$, $V$ and $m$ are all real? If so, it's pretty easy to see that $E\psi ^{*}=(E\psi )^{*}$ and $-{\frac {\hbar ^{2}}{2m}}{d^{2}\psi ^{*} \over dx^{2}}+V(x)\psi ^{*}=\left(-{\frac {\hbar ^{2}}{2m}}{d^{2}\psi \over dx^{2}}+V(x)\psi \right)^{*}$. —Ilmari Karonen (talk) 02:45, 9 October 2008 (UTC)

October 9

Sending Sound Wave or Voice Messages to the Past?

Is it possible to send sound waves or voice messages to the past? For example, sending sound through time where the sound could be picked up by a local telephone. Can we build a technology to do this? 72.136.111.205 (talk) 00:19, 9 October 2008 (UTC)

No. --98.217.8.46 (talk) 00:29, 9 October 2008 (UTC)

Currently, humans have absolutely no ability to send anything through time. It's possible we never will.CalamusFortis 01:17, 9 October 2008 (UTC)

Backwards through time...no. Forwards...yes. Relativity allows 'fast-forwarding' of time. From everything we know about the nature of time, there is absolutely no way to send anything back in time. SteveBaker (talk) 01:47, 9 October 2008 (UTC)

If Extrasensory perception worked, you might send the voice message by "mental telepathy" to someone in the past who had the right "gift," by some means beyond the knowledge of present science. Sending a sound vibration to an eardrum or making a voice frequency currents flow in phone wires or sending a telegraph message or affecting a computer circuit would require a transfer of energy, which would seem to violate the conservation of mass and energy in the universe both at the present and in the past. Jumping into the realm of science fiction, I suppose a way around this would be if the person 100 years ago left a message that he would send a message to the future, amounting to a certain amount of energy, and you sent a message with an identical amount of energy to the past, and somehow the messages cancelled, conserving mass and energy. That notion would work for letters or for time travellers of equal mass. Of course, any influence from the present to the past would alter the course of events, meaning that things might proceed a little differently in that time space continuum than turned out in ours. Edison (talk) 03:51, 9 October 2008 (UTC)

The whole idea of time travel is logically inconsistant anyways. If someone could travel in time as freely as in space, it would presuppose some "meta-time" that itself behaved exactly like real time is supposed to behave, but doesn't cuz you are traveling through it. There's a database of causality, and if it isn't time, its something that behaves exactly like it... --Jayron32.talk.contribs 04:13, 9 October 2008 (UTC)

There can be an almost infinite number of parallel universes, with every possible outcome of each quantum choice-point oiccurring, so there is no problem of causality. If I send a message to Kennedy to duck when Oswald shoots, then only that time-space continuum has a second Kennedy term as president, and ours is not affected. If the bread falls jelly side up in one continuum, it falls jelly side down in another. I doubt time travel being possible, because to the best of my knowledge, no chrononaut from the future has ever held a press conference. Edison (talk) 05:42, 9 October 2008 (UTC)

Well, never had a reliable press conference. (There have been claimed chrononauts, e.g. John Titor). --98.217.8.46 (talk) 11:30, 9 October 2008 (UTC)

(undent) Well, WRT the parallel universe problem, that still presupposes a "branching" causality, which can still only be traced in a forward direction. That forward moving coordinate is still behaving exactly like time. --Jayron32.talk.contribs 18:10, 9 October 2008 (UTC)

I suppose that in branching causality, a choice point would be whether or not the chrononaut arrived at a certain time and place. Edison (talk) 18:46, 9 October 2008 (UTC)

There is a problem with the branching 'many worlds' hypothesis for time travellers (I've been thinking a lot about this recently because I've been geeking-out on the latest Neil Stephenson book "Anathem"). So let's review what is generally said about this:

The theory says that in every possible instant in which a quantum event happens (Schrodinger's cat either dies or doesn't die - to pick a typical example), then the universe splits into two copies that are identical in every way except for that one event. So now there are two universes - one with a live cat in the box and another with a dead one. OK - so now, the "future-you" builds a time machine - goes back in time and yanks the cat out of the box when nobody is looking 10 minutes BEFORE the experiment is started. The idea is that your arrival into the past caused another fork in the universe back before the cat did or did not die - so now there is a third path...that the cat was never in the box in the first place. The future-you who jumped back in time didn't come from the "cat not in the box at all" future - but from...oh - but wait...from BOTH the cat-is-dead and cat-isn't-dead universes? Since those two universes are identical in all other respects - it's pretty reasonable to assume that both of you make identical time machines and jump back to an identical past...at a time when there were VASTLY fewer copies of the universe. Since an insanely large number of quantum events have happened throughout the universe between the cat experiment and the time machine being turned on - there are an insanely large number of time travellers all jumping back to the exact same copy of the universe at (typically) the exact same point in space and time. Only very few potential time travellers would fail to make it back because (through random quantum effects) were too grief-stricken by the pointless death of the kitty - or were just ABOUT to turn on their time machines when a cat leaps onto it and destroys it just seconds before launch.

But the fact remains that an almost infinite number of universes have been 'forked' from what was a single universe in the past at the moment in time to which the time machine is aimed. Hence a nearly infinite number of almost identical time travellers would pop into existance at more or less the same instant!

This is a big problem for the 'branching' many worlds concept. The reason I mentioned Anathem is because Stephenson has proposed in it an alternative means for the 'many worlds' thing to happen. I haven't finished thinking my way through the implications of it yet (and all the heavy thinking it requires is slowing my reading of the book to a crawl!) - but essentially he envisages an infinite number of universes proceeding down every possible path through "configuration space" - requiring them to converge as well as diverge! So two universes that have differed only in some very subtle manner could 'collide' and become one universe in which those past differences have quite utterly ceased to matter. This eliminates my complaint rather neatly. But it's not (I think) quite what most many-world-theorists had in mind.

SteveBaker (talk) 04:37, 10 October 2008 (UTC)

So...In Stephenson's book (which, we must emphasise, is fiction) - he proposes that we look at the multiverse in "configuration space". Imagine plotting a graph of (say) the cost of gasoline versus (say) the number of sunspots visibile on the sun...two totally unrelated things. Each point on your graph paper represents one possible combination of price and sunspot count - and if you plot these two things over time - you get a curve that traces around in some bizarre shape - looping back on itself, etc. Well, if you didn't limit yourself to 2D graph paper - you could plot more properties of more things - on 3D graph paper, you could plot price of gas against sunspots against the Dow Jones index. With 4D graph paper, you could add the popularity of the current US president...and if you had a truly INSANE number of dimensions for your hypothetical graph "paper" - you could plot the position, mass, spin, momentum, etc for every single fundamental particle in the entire universe. Since every possible configuration of the universe would be represented by a point somewhere in our bazillion-dimensional graph paper, we can draw a line on that graph that represents the progress of our universe through time...one of Stephensons' characters calls this a "Narrative". We could also plot the narratives of other possible universes through configuration space. OK - so that's Stephenson's idea of configuration space.

When you look at a classical (non-quantum) view of the universe - in which every event is entirely deterministic - the Narrative for our universe would be a L-O-N-G wiggly line snaking it's way through configuration space - looping around a region that's somewhat compact on the bazillion-dimensional graph because so much of the universe is relatively stable. But in a quantum universe like ours where events that are truly random happen and weird superposition phenomena exist - that line branches...just as in the many-worlds interpretation of quantum theory. But viewed in configuration space, it's also possible for two of these Narrative branches to merge back together - if two versions of the universe that differ only by the location of one fundamental particle happen to arrive at the same point in configuration space because that particle ended up in the same place in both of them - making the two universes identical in every respect. This is rather nicer than the conventional "many worlds" picture where universe split into copies of themselves - but never come back together again.

So what we have in Stephenson's rather clever model is that every conceivable point in configuration space (even some crazy, impossible-seeming ones) "exist" in some sense - and each one changes over time by threading a line through that bazillion-dimensional graph - sometimes splitting into two because of quantum randomness - other times merging together because two universes that have (potentially) very different origins and history happen to wind up with identical configurations. (One might argue that this would mess with the memories of living creatures in those universes - but if they have different memories to start with then the two universes can't merge because they are different. Only if every record of past history is somehow erased could two universes join back together. But because configuration space is 100% full of these snaking "narratives" - there are (paradoxically) exactly as many rejoinings as there are splits!

Now - what about time-travel? Well, when a creature who is in a universe that's winding through its narrative line decides to jump "back in time" - they take themselves to a point in configuration space where the universe has a bunch of particles representing the time traveller. That's close (in configuration space) to the narrative that the time traveller's universe passed along - but it's not the same. If the time traveller is super-careful not to kill his grandfather or do anything else to "change the future" (a very tough proposition!) then when he finally leaves the past to return to the present, the universe with the narrative that contains his particles in the past will eventually merge with the narrative of the universe he came from - and he will truly have "done no damage" to the present. If, however (much more likely!) he displaces an air molecule and that has a "butterfly" effect that causes greater and greater divergence of the narrative of this universe from the one he remembers - then perhaps the two narratives will never be able to rejoin.

It could also happen though that he could kill his own grandfather - thereby causing the "new" narrative to diverge still more from our own - but in a million years, the consequences of the time traveller never having lived might be utterly erased by the passage of time such that the original time-line and the new one would become identical in every respect - and rejoin.

But in this peculiar interpretation of the multiverse (which I find exceedingly compelling) - time travel not only might exist - but it definitely does exist - in the sense that somewhere in configuration space, there must be a universe where I suddenly pop into existance for no obvious reason with memories of being a time-traveller. Since all possible configurations "exist" - then for all practical purposes, time travel can happen even if the laws of physics prohibit it. Of course there are also versions of the universe where I pop back into a nearly identical narrative - but my ears have turned to lime jello...or the world of the "past" is entirely populated by giant intelligent pink rabbits.

This is a very weird view of the multiverse - but it's kinda compelling.

SteveBaker (talk) 12:51, 10 October 2008 (UTC)

true, an interesting model. and as you say, if all possible universes exist, then there must be an infinity of universes where time travel was invented, and the travelers spilled over into the neighboring universes. but that comes up against the next problem: the chances of us living in a universe where nobody pops up from a parallel where they invented time travel would seem to be close to zero; yet that's where we are. (inspired by the logic that since model universes can be created inside computers or such so much more easily and go through their life cycle so much more quickly that there must be so many more of them, that in all probability we would have to be in one of those, not in the "real" universe.)Gzuckier (talk) 05:48, 11 October 2008 (UTC)

I don't know that we can conclude that time travel "must" be common enough in the infinity of universes to say that we should expect to have seen time travellers. Also, I'm not suggesting that time travel can actually exist - it can't - the laws of physics don't allow that. What I'm suggesting is that the APPEARANCE of there being time travellers is perfectly possible - in the sense that (due to some quantum weirdness - or because Stephenson's model of configuration space is true) people could pop into existance with a complete set of memories that are clearly from the future and may indeed perfectly predict who will win the superbowl for the next 20 years. Such an event would be totally indistinguishable from real time travel. The John Titor incident is somewhat chilling though - he was pretty convincing as a time-traveller. This raises two difficult questions: Firstly, perhaps we HAVE been visited by a time traveller. Secondly, we didn't believe him - what makes you think we'd believe anyone who was a genuine time traveller? SteveBaker (talk) 01:45, 12 October 2008 (UTC)

Sterling Silver Allergy

If I were allergic to sterling silver jewelry, how long would I have to wear a ring around my finger to find out? 98.223.89.7 (talk) 02:32, 9 October 2008 (UTC)

I can't comment on sterling silver per se, but I can anecdotally report that my wife is allergic to gold. Its not the impurities in, say, 14K gold, its the gold itself. She's been tested an everything. The higher the Karats of the gold, the worse her reaction is. Even a few second contact with 24 karat gold gives her hives. So it is at least possible to be allergic to a metal like that. As far as how long YOU would take to break out, well, that depends entirely on YOU. Such facts of body chemistry are unique to each individual, and individual reactions cannot be predicted, especially over the internet. If you have questions about possible allergies you may have (and metal allergies are very real), you should see a dermatologist or an allergist and get tested. That is the only way to really know. --Jayron32.talk.contribs 02:43, 9 October 2008 (UTC)

This is interesting. How can an inert metal like gold (especially higher purity) trigger an allergic reaction? Sjschen (talk) 03:47, 9 October 2008 (UTC)

No idea on the mechanics, and if I had never seen it myself, I would not have believed it. We are both chemists by training, and understand the chemistry of gold. Gold is not entirely inert, and there is something there that triggers an allergic reaction in my wife. This is partially a wag, but there may be something about the surface texture of the gold that triggers the reaction; it may not need to actually dissolve into the skin, but the contact triggers a histamine response in my wife. Like I said, it shouldn't work that way, but I can only say that something about gold (and not the alloyants in lower purity gold jewlery, but the gold itself) that triggers the response in my wife. --Jayron32.talk.contribs 04:08, 9 October 2008 (UTC)

That's really interesting, especially as you can both take a scientific view on it. Have you tried double-blind experiments? Have you tried the experiment with and without her using whatever soap or lotion she uses on her hands? The latter to examine if the gold somehow acts as a catalyst. There apparently exist gold-based room-temperature catalysts for the oxidation of CO, for instance. EverGreg (talk) 08:28, 9 October 2008 (UTC)

I know that Gold can be ionized by a strong oxidizer such as conc. nitric acid, but I doubt sweat and lotions can do anything close to that. Maybe the gold catalyzed rxns in the lotion or soap is indeed the answer. Sjschen (talk) 22:28, 9 October 2008 (UTC)

Just as a totally apocryphal story, I once met a woman with a similar problem, but in her case it was lupus and not an allergy (she had a ring tattooed on her finger instead of wearing a wedding band because of a similar problem). My guess is that's more an issue of skin sensitivity and not the metal in itself. One option to test if it's a true allergic symptom is to see if it responds to antihistamines (i.e. diphenhydramine or somesuch), but it's more likely to be Contact dermatitis or some other sort of hypersensitivity than a true allergy. SDY (talk) 12:41, 9 October 2008 (UTC)

Yeah, your terminology is probably more correct than mine. I was probably using the term "Allergy" too broadly. The fact is that she has a reaction to gold (she has a platinum wedding band, and that causes no problems for her, and neither does silver or other costume jewlery), and whatever that reaction is is unpleasant for her, as gold causes an itchy rash. The solution for me is I just buy her cheap jewlery. Its a win-win situation for all of us!--Jayron32.talk.contribs 13:10, 9 October 2008 (UTC)

The original question actually asked how long to wear a ring until they find out. Well pure silver or gold is very weak and usually have alloys in it. Some people are very allergic and can only wear stainless steel, titanium, platinum, palladium, or tungsten, though sometimes I've read forum posts of people who're allergic to those, except I've never heard of a tungsten allergy. Also, there are some online sellers (often in China) who sell what they claim are sterling silver rings and they turn out not to be. Are you ready for IPv6? (talk) 13:53, 9 October 2008 (UTC)

(Not a RefDesk-quality answer...) Jayron, does this happen with other forms of gold, and on other parts of the body? Has she, for instance, "merely" set a gold coin on her arm and got the same reaction? Just curious. Maybe this should be moved to a talk page somewhere. --DaHorsesMouth (talk) 22:25, 9 October 2008 (UTC)

Jayron: I really think that if you are both scientists then a double-blind experiment is called for - and I'm very surprised you haven't already tried it. Too many scientists think that science ends at the laboratory door. A while back, my wife was spending a small fortune on bottled water - I maintained that she couldn't tell the difference between the cheap stuff and the expensive stuff - so we did a double-blind experiment. It turned out that not only could she not tell the difference between brands - but she couldn't even tell the difference between the good stuff and tap-water. That experiment saved us a fortune! In your wife's case, I think it's highly likely to be some kind of psychosomatic thing. Gold is just too inert to be a true culprit here. You need two similar sized rings - one gold, one of something else. It should be easy to figure out a double-blind methodology here - have one person take two small boxes labelled "A" and "B" and put one ring into each box - using a coin toss to decide which goes into which box and noting which was which - but not letting the other person know. Then the second person secretly does a coin flip and either swaps over the labels or does not (without looking inside). Then, both of you close your eyes - you pick out the ring from the box marked "A" and rub it onto her skin on her left arm - take the one from "B" and rub it onto her right arm - each time putting the ring back into the same box and closing the lid. Neither of you knows which ring was in which box until the results are in - then you can look into the box to find out - you should really do the experiment several times to be sure the result wasn't a flook. SteveBaker (talk) 04:10, 10 October 2008 (UTC)

Yeah, try this conversation on for size "Hey honey, you know that festering rash you get everytime you wear gold? Yeah, that really itchy shit that gets all pusy and nasty? Say, lets do that on purpose". I'll stick to buying her sterling silver jewlery and keep marital harmony going, thanks... --Jayron32.talk.contribs 04:22, 10 October 2008 (UTC)

I may have mentioned this before. I have a friend who has a weird reaction to gold, but only when she drinks alcohol. The skin around her wedding ring goes quite markedly blue. The whole ring finger and that side of her hand is affected. The skin touching her other jewellery or any other material does not do this. To prove the gold is playing some part, she once held a gold chain in the palm of her other hand while she was drinking wine, and her palm also went blue. She removed the chain, and the blue gradually receded, but the ring hand was still blue. It never happens when she's not drinking. I was spooked the first time I saw it. -- JackofOz (talk) 04:37, 10 October 2008 (UTC)

I have seen that before. That is generally due to the formation of copper compounds (which are blue) due to the presense of copper (as a hardener) in most gold jewelery alloys. Apparently, some people have skin chemistry capable of dissolving the copper out of these alloys. My wife has a very different reaction, which is distinctly either allergy, or dermatitis. --Jayron32.talk.contribs 04:45, 10 October 2008 (UTC)

I know you maintained that it was gold alone that caused your wife's allergy, but is she also allergic to nickel? a two-factor effect with gold + nickel could be one hypothesis. EverGreg (talk) 21:11, 10 October 2008 (UTC)

Perpetuating genes

Are there any known ways I can perpetuate my genetic stock without myself reproducing? Any that won't contribute to overpopulation? Also, are there any known ways of determining whether my genetic stock is above-average and worth making an effort to perpetuate? I have Asperger Syndrome, if that makes any difference. NeonMerlin 03:20, 9 October 2008 (UTC)

You could store your own semen. There are many sperm banks and other services that will do this for you. If you are female, you could also have eggs extracted and stored, but that involves invasive surgery, and is far riskier and less pleasant than the male method for extraction of reproductive genetic information. --Jayron32.talk.contribs 03:22, 9 October 2008 (UTC)

Note that the technology for long-term storage of unfertilized eggs is very new and has resulted in very few live births (I think I read about a first within the last year, but most IVF clinics don't do it yet). The exact reason why is not all that clearly understood, but freezing and the fertilization process don't work all that well together. Fertilized eggs can be stored easily, as can semen. SDY (talk) 08:47, 9 October 2008 (UTC)

You're asking some pretty tough questions, and it's hard to give suggestions here without bias. I suggest looking at genetic diversity, natural selection, and genetic testing to start you on the path to finding your own answers. Sjschen (talk) 04:01, 9 October 2008 (UTC)

An alternative is to support one's extended family as they have much the same genes as yourself. This is a tried and tested way of propagating genes in the animal world, with examples ranging from insects to mammals. EverGreg (talk) 08:34, 9 October 2008 (UTC)

This was what I was going to recommend. If your sister reproduces (if you have a sister), it's pretty similar genetic stock as your own, so at times it might be worth (from an evolutionary point of view) working to enhance her reproductive fitness even at the detriment of your own. See kin selection. --98.217.8.46 (talk) 11:20, 9 October 2008 (UTC)

As for "above average"... what do you really mean by that? You'd need to define your system of genetic worth first. It's not intuitive, and frankly we would probably disagree on what traits were most "desirable" and even some that were less "desirable". In the long run though your individual concerns about the worth of your genetics will play little role in the overall gene pool unless your reproduction rate is significantly differential from the average (either you produce more or they produce less). See eugenics. --98.217.8.46 (talk) 11:20, 9 October 2008 (UTC)

Although encouraging your relatives to reproduce will perpetuate your stock without your reproducing, it will still contribute to overpopulation. Theoretically, you could try to prevent other people from reproducing, but that would have a negligible effect on the portion of people who are related to you. Your only real solution is to go ahead and reproduce, and counter the effect on overpopulation by preventing others from having kids, or by increasing the capacity of the world. Because people in poverty reproduce more, I suggest donating to a charity that helps stop poverty, such as microcredit. If you donate a significant amount of money, it will be overkill, but I recommend that you do so anyway. — DanielLC 14:43, 9 October 2008 (UTC)

"Goodness" for a gene is really determined only by it's ability to spread and continue. Genes which don't make it into the next generation for some reason are "bad". So there is no way to indirectly measure goodness or badness of someone's genes. If they succeed in reproducing (preferably as many times as possible - and continuing for as many generations as possible) - then they are functioning well. A decision to not have children (no matter how socially good that is) is an indication that your genes have already failed in their goal to reproduce. Sooner or later, someone will come along with a higher sex drive or a higher maternal/paternal instinct that manages to overpower any hint of a desire to keep the earth's population in check. When that happens, their genes will spread faster than yours and your genes have failed and were therefore not as "good" as the ones that wiped them off the face of the gene pool. However, humans are (IMHO) gradually seeing more influence from memetic evolution than genetics. Memes are also able to propagate, evolve and reproduce - and in humans, a meme can have a greater role in driving us than our genes do. So perhaps the 'meme' that's telling us to save the planet is more powerful than the gene that's telling us to fill the planet from edge to edge with human beings. It is arguable, therefore, that you are doing a better job of passing on your best memes to the next generation than you are at passing on genes. So - become a teacher, or a writer or a musician - or merely answer questions on the ref desk in a way that reinforces the ideas (memes) that are worth passing on. SteveBaker (talk) 03:53, 10 October 2008 (UTC)

You might find Nature versus nurture an interesting read as well. SDY (talk) 15:05, 10 October 2008 (UTC)

in the Big Picture, you in all probability do not carry any genes which are not represented in the entire human gene pool at least several million times. and furthermore, if you did carry any rare mutations, the vast majority of them would be deleterious. so you can rest assured that even if you die without issue, your genetic components will not be lost to humanity. Gzuckier (talk) 05:41, 11 October 2008 (UTC)

Is our planet's core mostly iron because of boyancy?

?? 98.221.85.188 (talk) 04:18, 9 October 2008 (UTC)

Inner core is a pretty good read. One of the main driving forces behind the assumption that the core is mostly iron is that we know what everything else in the solar system is made of, and we know what our planet should be made of, and there's not nearly enough iron anywhere else on the planet to match the rest of the solar system. Ergo, the iron has to be somewhere, so its gotta be in the core. At least, that's how our article explains it. Its a fairly logical analysis of the situation. --Jayron32.talk.contribs 04:33, 9 October 2008 (UTC)

However, from the article Earth's magnetic field: Citing oceanic basalt 3He/4He ratios [5] and other evidence, J. Marvin Herndon et al contend that the inner core of the Earth is not iron but much denser atoms. --Ayacop (talk) 18:27, 9 October 2008 (UTC)

That's not what our articles say though. Our articles claim that the core is mostly Iron. And besides, what would these denser atoms be? 98.221.85.188 (talk) 14:37, 10 October 2008 (UTC)

Balancing equations

I can't for the life of me balance this equation: H₂S + SO₂ ---> S₈ + H₂O . The S₈ in the product's side is throwing me off! I thought I knew how to do this, until I attempted this problem. Can someone explain to me how to do this? I've been at it for far too long! —Preceding unsigned comment added by 134.241.222.116 (talk) 05:16, 9 October 2008 (UTC)

Note that that there must be twice as much H as O on the right. The S is just along for the ride. The coefficients are not low. I guarantee the equation will balance. Edison (talk) 05:30, 9 October 2008 (UTC)

In other words, if the left hand side of the balanced equation is AH₂S + BSO₂ where A and B are integers, then you must have A=2B in order to get the hydrogen and oxygen to balance, and also A+B must be a multiple of 8 so that you have a whole number of S₈ molecules on the right hand side. Gandalf61 (talk) 09:06, 9 October 2008 (UTC)

I still can't get it! Can you just tell me what it is? —Preceding unsigned comment added by 69.16.88.147 (talk) 11:15, 9 October 2008 (UTC)

Also note that, since A=2B, A+B=2B+B=3B. Since 8 is not divisible by 3, the fact that 3B must be a multiple of 8 implies that B itself must be a multiple of 8. In particular, the smallest value that could possibly be a solution is B=8. Why not try plugging it in and see if it works out? —Ilmari Karonen (talk) 11:45, 9 October 2008 (UTC)

To restate the above, since the water/SO₂ ratio requires there to be 3 sulfurs on the left side of the equation, and the S₈ is on the right, the answer must involve a number of sulfurs that is divisible BOTH by 3 and by 8. The lowest number that works for that is 24, so try to work out a solution that involves 24 sulfurs. That should put you in the right direction. An alternative method would involve solving this via the half-cell method. The reaction is a Synproportionation reaction, where sulfur in 2 oxidation states react to form a third oxidation state of sulfur. Track the oxidation numbers and see for yourself. You could try setting up two half-cell equations and balancing each and recombing them. This method is described here and an example is put forward here. If the brute force method using 24 sulfurs doesn't work, try the half-cell method.--Jayron32.talk.contribs 13:03, 9 October 2008 (UTC)

My recommendation to my students - ignore the requirement for integers until the end. After balancing the oxygen and hydrogen, you have 3 sulfur atoms on the left, with S₈ on the right. So you require 3/8ths of S₈. At the end, you can't have fractions, so then multiply everything all the coefficients by 8. I find this method a lot more intuitive than some of the above. --Bennybp (talk) 14:56, 9 October 2008 (UTC)

I think I got it! Is it 16-8-3-16? If so, thanks for all your help! If not, then I give up. —Preceding unsigned comment added by 69.16.88.147 (talk) 15:50, 12 October 2008 (UTC)

Ovulation

Why does the human body temperature increase whilst ovulating?90.210.162.166 (talk) 08:20, 9 October 2008 (UTC)

You may want to read Wikipedia's article on Ovulation. Having read it myself, I could posit an educated guess that ovulation is controlled by pituitary hormones, as mentioned in that article. The pituitary gland also controls metabolism and homeostasis in the body, and one of its main jobs is the regulation of your body temperature via metabolic control. My guess is that changes in body temperature are an indication that the pituitary is firing up in some way, which is a likely indication that it has released whatever the pre-ovulatory hormones are. This is largely a guess based on some intuitive readings of the articles on Ovulation and the Pituitary gland, but it makes sense to me. Does anyone else have a more concrete answer? --Jayron32.talk.contribs 12:52, 9 October 2008 (UTC)

From "Review of Medical Physiology" (William Ganong), the temperature rise at ovulation is probably due to the increase in progesterone secretion. Progesterone is thermogenic (i.e. increases metabolic rate and generates more heat). Axl ¤ [Talk] 18:03, 9 October 2008 (UTC)

True or False? Attack of the mutant 6 foot man eating catfist?

There is this story about a scientist who found a man eating catfish. As reported in the Newspaper.

http://www.thesun.co.uk/sol/homepage/news/weird/article1784470.ece

Is this story scientifically true? Ohanian (talk) 10:50, 9 October 2008 (UTC)

Well it certainly doesn't seem scientifically supported. All evidence given seems to be from what local natives and one reporter say—which generally means it is anecdotal evidence, the stuff of legend (no matter whether your locals are in India or Missouri). Personally I would want to see why the reporter fellow ruled out animals better known to have attacked humans in the past (crocodiles, snakes, etc.) before jumping to a new theory. --98.217.8.46 (talk) 11:10, 9 October 2008 (UTC)

Ha ha I read that as a scientist finding a man who was eating a catfish, rather than a man-eating catfish. I'd go with 98.217's reasoning, though a man eating a catfish would be pretty plausible - if not exactly newsworthy. 194.221.133.226 (talk) 12:29, 9 October 2008 (UTC)

The Sun isn't really world renowned for its fact-checking. APL (talk) 12:48, 9 October 2008 (UTC)

If you see the cover of The Sun at supermarkets, it's usually hypin some biblical prophecy that it says is about to happen. Are you ready for IPv6? (talk) 13:58, 9 October 2008 (UTC)

You should have put an "NSFW" warning on that. ;-) Axl ¤ [Talk] 18:07, 9 October 2008 (UTC)

I have seen catfish which weighed 50 pounds, and reliable witnesses have told of seeing larger ones living at the bottom of U.S. rivers just downstream from hydroelectric dams, eating the chopped fish who went through the turbines. As bottom feeders, catfish would certainly eat human bodies which had been placed in a river. All in all, it seems plausible but certainly not proved by a photo in a tabloid. I would have no trouble believing a report of one half the weight they claim. I could place a minnow that large in someone's hands in a Photoshopped picture. Seeing is not believing.

I don't know that much about catfish in general, but I can't quite imagine one eating a live human. I know that they would eat dead meat, so a dead human body wouldn't be that unlikely, but the live human...nonetheless, we could have a story about three 6 foot men eating a catfish, judging by that picture :-) Nyttend (talk) 22:01, 9 October 2008 (UTC)

6-foot and 161 lbs may be a record for that species of catfish but some species get much larger. The record Mekong giant catfish was "9 feet in length and weighing 293 kg (646 lb)." Rmhermen (talk) 23:42, 9 October 2008 (UTC)

Snopes has a couple of stories about huge catfish that may be of interest. Matt Deres (talk) 00:28, 10 October 2008 (UTC)

Quantum: why for entangled state but not separable states

I think there should be no difference between the entangled states and separable states (entangled states are just quantum states with special "pattern" and nothing else), so I speculate: if we measure one of the two entangled particle, the other will collapse instantly (just like this experiment), then how about measuring one of the two separated (non-entangled) particle? If we measure one of the two particle in separable state, does the other separated particle also collapse instantly? do whole of the other separated particles in our unverse collapse together with it (as the distance doesn't matter) simutaniously simultaneously and instantly? Can I say that all the other separated particles in our universe will actually collapse but just our sensor/device can't distinguish wheather whether they have collasped or not since they are in separable state? - Justin545 (talk) 12:07, 9 October 2008 (UTC)

Don't take too seriously the stuff about "the other particle collapsing instantly across arbitrary reaches of time and space." That's not something you can experimentally detect, it's just a feature of one particular mathematical formulation of quantum mechanics, and probably it should be taken to mean that that formulation doesn't correspond very well to reality. -- BenRG (talk) 21:34, 11 October 2008 (UTC)

Wave Function Collapse of Entangled Separable State

Suppose we have two particles $A$ and $B$ their respective states are

$|\psi \rangle _{A}={\sqrt {0.2}}|0\rangle _{A}+{\sqrt {0.8}}|1\rangle _{A}$

$|\psi \rangle _{B}={\sqrt {0.3}}|0\rangle _{B}+{\sqrt {0.7}}|1\rangle _{B}$

The state of the composite system of $A$ and $B$ is

$|\psi \rangle _{A}\otimes |\psi \rangle _{B}=({\sqrt {0.2}}|0\rangle _{A}+{\sqrt {0.8}}|1\rangle _{A})\otimes ({\sqrt {0.3}}|0\rangle _{B}+{\sqrt {0.7}}|1\rangle _{B})$

$|\psi \rangle _{A}|\psi \rangle _{B}={\sqrt {0.06}}|0\rangle _{A}|0\rangle _{B}+{\sqrt {0.14}}|0\rangle _{A}|1\rangle _{B}+{\sqrt {0.24}}|1\rangle _{A}|0\rangle _{B}+{\sqrt {0.56}}|1\rangle _{A}|1\rangle _{B}$

If we try to measure the state of particle $A$ of $|\psi \rangle _{A}|\psi \rangle _{B}$ and get state $|1\rangle _{A}$, it means $|\psi \rangle _{A}|\psi \rangle _{B}$ collapses to either $|1\rangle _{A}|0\rangle _{B}$ or $|1\rangle _{A}|1\rangle _{B}$. Besides, the probability of finding particle $B$ in state $|1\rangle _{B}$ is

$P\left(|1\rangle _{B}{\Big |}|1\rangle _{A}\right)={\frac {P(|1\rangle _{A}\cap |1\rangle _{B})}{P(|1\rangle _{A})}}$ (according to conditional probability $P(B\mid A)={\frac {P(A\cap B)}{P(A)}}$)

where

$P(|1\rangle _{A}\cap |1\rangle _{B})=P(|1\rangle _{A}|1\rangle _{B})=|{\sqrt {0.56}}|^{2}=0.56$

$P(|1\rangle _{A})=|{\sqrt {0.24}}|^{2}+|{\sqrt {0.56}}|^{2}=0.8$

therefore,

$P\left(|1\rangle _{B}{\Big |}|1\rangle _{A}\right)={\frac {0.56}{0.8}}=0.7=|{\sqrt {0.14}}|^{2}+|{\sqrt {0.56}}|^{2}=P(|1\rangle _{B})$

Similarly, if we try to measure the state of particle $A$ of $|\psi \rangle _{A}|\psi \rangle _{B}$ and get state $|0\rangle _{A}$, it means $|\psi \rangle _{A}|\psi \rangle _{B}$ collapses to either $|0\rangle _{A}|0\rangle _{B}$ or $|0\rangle _{A}|1\rangle _{B}$. Besides, the probability of finding particle $B$ in state $|1\rangle _{B}$ is

$P\left(|1\rangle _{B}{\Big |}|0\rangle _{A}\right)={\frac {0.14}{0.06+0.14}}=0.7=P(|1\rangle _{B})$

The above illustration shows that we are not able to distinguish whether the state of particle $B$ has collapsed or not, because no matter the state of particle $A$ we measured is $|0\rangle _{A}$ or $|1\rangle _{A}$, the state of particle $B$ always collapses to $|1\rangle _{B}$ with probability $0.7$. Therefore, we can say the particle $B$ DOSE collapse instantly (and so do all other particles in the universe) when we measure particle $A$, but we just have no way to emphasize that.

- Justin545 (talk) 06:06, 10 October 2008 (UTC)

what is the best way to structure a case study presentation on a medical patient ?

I have to present a case study to a large, mixed group of medical and allied-medical professionals. I have chosen my subject (the patient) and would like opinions on how best to structure and present the information and how to encourage discussion.Mollyisthedog1 (talk) 13:21, 9 October 2008 (UTC)

Are you planning to use Powerpoint? See "Medical history". Start with age & sex. Presenting complaint. History of presenting complaint. Past medical history. Drugs & allergies. Occupation. Social circumstances. Smoking & alcohol. Clinical examination findings. Relevant investigations. Treatment. Information about the specific disease. In smaller groups, I often invite individuals to comment on differential diagnosis and proposed management during the presentation. Axl ¤ [Talk] 18:16, 9 October 2008 (UTC)

Have you seen House (TV series)?

Just a thought, it may be worthwhile to present a brief abstract and overview before you plunge into details. Much of your audience will likely be used to reading journal articles, so following that structure (summary->methods->data->interpretation) will make the talk easier to follow for those familiar with the format. If the case study involves several cycles of "let's try this test, no that didn't work" it may make sense to have an overall summary, then do methods/data/discussion for each angle considered. SDY (talk) 15:03, 10 October 2008 (UTC)

solar power roof installations and having to do roof maintenance

Hi,

When you install a solar panel on your roof, and then have to replace the roof shingles for routine maintenance, how do the solar panels get in the way? Do you have to take the solar panels off, replace the shingles, and then reinstall the solar panels? What's the deal?

I feel irritated that all the solar roof websites I've read don't discuss this issue.

Thanks

--InverseSubstance (talk) 18:31, 9 October 2008 (UTC)

Hm. I don't know much about this, but perhaps calling one of the companies directly may get you a live person, who could answer any specific questions that you have? Its a start... --Jayron32.talk.contribs 19:20, 9 October 2008 (UTC)

Asphalt shingles are now available with rated lifetimes of forty years or more; steel roofing is often good for a hundred years. A properly designed and built roof that doesn't use low-quality shingles will almost certainly outlast the photovoltaic system on top. Proper installation of the solar panels may even slightly increase the lifespan of the roof by providing a small amount of extra protection from the elements. What type of 'routine maintenance' are you expecting to have to do that would require removal and replacement of shingles?

Interestingly, one can also purchase 'solar shingles'—photovoltaic panels which replace shingles altogether. TenOfAllTrades(talk) 19:33, 9 October 2008 (UTC)

The questioner could be asking about a solar water heater, and the removal of shingles might not be for maintenance of the shingles but maintenance of the roof structure. It's going to be hard to answer the question without knowing a lot more about the structure of the roof, how large the panel is, how and where it is located. It's good practice always to get at least three quotations for any kind of building work and the companies should be asked whether they have encountered a similar situation before and how they dealt with it. Itsmejudith (talk) 13:35, 10 October 2008 (UTC)

Watch question

When was the jump hour function invented for clocks and watches? I imagine it must be quite old (here's a watch from the 1890s with the ability), but was curious. --140.247.42.160 (talk) 20:10, 9 October 2008 (UTC)

Unit of Measures

Would UOM KOhm be the same as kOhm —Preceding unsigned comment added by A01534 (talk • contribs) 20:27, 9 October 2008 (UTC)

I would think so. A lowercase k is the correct abbreviation for the SI prefix, "kilo-", but "K" is fairly common. I don't know anything else it could mean (in computing it sometimes means 1024 times, but that's non-standard). --Tango (talk) 20:54, 9 October 2008 (UTC)

I always found that slightly confusing. I had thought capitals were for "bigger" prefixes, and lower-case was for "smaller" prefixes. That seems to be the pattern most of the time - mega vs. milli, peta vs. pico, etc. But kilo, deca, and hecto don't. I guess it would be asking too much to be completely logical.... But yes, K probably means k in your question - there is no (SI) prefix for a capital K. --Bennybp (talk) 22:07, 9 October 2008 (UTC)

What you have to remember is that all the prefixes from milli- to kilo- are part of the original metric system while the ones from mega- upwards (and from micro- downwards) are later additions that have come in several batches over time. Presumably the forms "kg" and "km" were well established by the time that M- for mega- was introduced, and it wasn't until there were several more prefixes that the pattern of "higher prefixes get capitalized" was really established. So it makes sense that there was no pressure to change kilo- to be represented with a capital K. --Anonymous, 01:08 UTC, dekaOctober :-) 2008.

Along those same lines, the M- for mega- is also obviously influenced by the m- prefix already being in use. The next step there led to the use of μ- for micro-. Had more size prefixes started with k's, you'd likely see k-, K-, and κ- prefixes instead. Personally, I think using the Greek symbol was a dumb idea, but they no doubt didn't think of the hassle it was cause folks trying to use it on standard keyboards (and typewriters!). I would have gone with i- (for itsy-). ;-) Matt Deres (talk) 10:48, 10 October 2008 (UTC)

They probably rationalized it by assuming the letter 'u' could be used in place of the 'μ' without loss of clarity in typewritten documents. (No SI prefix uses upper- or lowercase 'u'.) Heck, I still use that shortcut—I've got Word set to autocorrect any instance of um to μm for me as I type.

I'd still say it's a better solution than the one adopted by some (mostly electrical) engineers. They use mm as a prefix (millimilli-) in lieu of mu, which is just asking for trouble. (Did you mean 1 mF or 1 mmF? Or do you want me to use a capacitor 1 mm long?) TenOfAllTrades(talk) 13:50, 10 October 2008 (UTC)

In fact the use of "u" in place of µ was officially approved by the ISO in 1974, but later withdrawn as character sets including µ became more commonly available. --Anonymous, 18:57 UTC, October 10, 2008.

See, all this confusion could have been avoided if they had just asked me in the first place! That way, at least I would have understood. (Of course I was only born in 1985, but that's what time machines are for!) :) --Bennybp (talk) 19:47, 10 October 2008 (UTC)

Then you'll appreciate what King Alfonso X of Castile (known as "Alfonso the Wise") said: Had I been present at the creation, I would have given some useful hints for the better ordering of the universe. -- JackofOz (talk) 20:28, 10 October 2008 (UTC)

"Ohm" as a unit of measure is not capitalized: hence "kohm". Axl ¤ [Talk] 18:57, 10 October 2008 (UTC)

Of course, if one were being pedantic, kohm is no more acceptable than kgram, kmeter, or kamp. It's either kΩ or kilohm. TenOfAllTrades(talk) 19:05, 10 October 2008 (UTC)

It would seem your spelling is correct, but what happened to the other 'o'? --Tango (talk) 19:10, 10 October 2008 (UTC)

It seems to be an arbitrary decision by the powers-that-be (I presume the BIPM). For ease of use, the doubled vowel was removed from kilohm and megohm (instead of using kiloohm and megaohm). A similar change was made with the are, giving us areas in hectares rather than hectaares. Not all double vowels are forbidden, however—kiloamperes and megaampere are cool. I imagine that there's a formal document spelling all this out somewhere, but I can't bring myself to hunt it down at the moment. TenOfAllTrades(talk) 20:14, 10 October 2008 (UTC)

Googling bipm.org reveals 3 instances of "kiloohm" and none of "kilohm". The SI brochure itself says nothing about removing vowels. It seems to me that the shortened forms, although widespread, are not sanctioned by the CGPM, but some national bodies like the NIST choose to define their own variants. --Heron (talk) 10:40, 11 October 2008 (UTC)

The SI standard only defines the symbols, not the spelling of the units (thus "m" is standard but corresponds to "meter" or "metre" in English, "mètre" in French, "Meter" in German, "metro" in Spanish, the Cyrillic equivalent of "metr" in Russian, etc.). National standards bodies may standardize the spelling of units, though. I don't know about the particular cases in question. --Anon, 21:48 UTC, October 11, 2008.

trying to remember the name of a certain stone

hi I have been trying to remember the name of a certain stone that we used to see alot of when we were kids. its a flacky stone that is black and foung in abundance in caves. i believed it was called "mika" but a search of it came up empty. the best way to describe it is that it usually comes in small or large chunks but can easily be split into little flakes and crumbles verry easily. If you could please get back to me it would be verry much apreciated. My email is [Redacted] —Preceding unsigned comment added by 99.241.82.198 (talk) 20:51, 9 October 2008 (UTC)

(I've removed your email address to protect you from spam - people will reply here.) I don't know much about rocks, so you'll have to wait for someone else to come along, but you can look through List of rock types and see if anything jumps out at you, if you like. --Tango (talk) 20:57, 9 October 2008 (UTC)

Mica? Saintrain (talk) 20:59, 9 October 2008 (UTC)

And if the variety you were seeing was black, Biotite. Deor (talk) 02:58, 10 October 2008 (UTC)

Another possibility is flint - but I was also thinking mica when I first read the question. Flint can be flaked, but mica is more "crumbly". Franamax (talk) 06:38, 10 October 2008 (UTC)

Venus axial tilt

Which one is right? Is Venus upside-down tilt axis of 177 degs, or normal upright of 2.6 degs. Old books say 2.6 degs axial tilt, but ewer study say Venus is upside down of 177 degs.--Freeway91 22:28, 9 October 2008 (UTC)

Either, they're the same thing. You can think of it as being tilted 177 degrees and rotating in the usual direction ("prograde"), or tilted 3 degrees and rotating backwards ("retrograde"). It doesn't really make any difference which you go with. (Although, interesting, our article says 177 degrees and retrograde, which doesn't sound right to me...) --Tango (talk) 22:36, 9 October 2008 (UTC)

Another way to view it is that "retrograde" means the axial tilt is greater than 90°, so "177° and retrograde" is a perfectly legitimate choice and in fact is probably the one I see most often. I don't know how professional astronomers describe it, though. --Anonymous, 01:11 UTC, October 10, 2008.

Then if Venus is rtro, then count it as 2.7 deg tilt. What about Pluto (which is no longer plnaet). If Pluto is rtro would it still be 120 deg. tilt?--Freeway91 22:51, 9 October 2008 (UTC)

Quantum Mechanics

Since quantum mechanics can't provide deterministic predictions, is it really falsifiable? And if it's not falsifiable, is it really a true science? 12.10.248.51 (talk) 19:02, 9 October 2008 (UTC)

The statistical predictions of QM are very much deterministic in the important ways, similar to Meteorology. In the place QM says things can not be determined (uncertainty principle) the theory puts a tight limit on the indeterminance(uncertainty) of its predictions. This aspect of the theory would easily be falsified by a theory being able to make a more accurate prediction. It might interest you to know that the prediction of QM explain many aspects of observations we make with chemical instrumentation. If we saw something different than what we do with NMR, EPR, UV-Vis, FTIR, Electroanalytical chemistry we would have to work on QM. This isn't to say QM is complete its just our best working theory. I've moved this to the reference desk since its a more appropriate place for the question and will receives explanations that far surpass this one.--OMCV (talk) 23:32, 9 October 2008 (UTC)

You can certainly falsify all sorts of aspects of it, even the stuff that appears almost purely philosophical at first glance. See, for example, the Bell test experiments. And the non-deterministic nature doesn't preclude testing or even predictions. Simple example: we have no way of making a "deterministic prediction" about when a single unstable atom will decay. But we can make statistical predictions which are easily testable (and thus come up with things like half-lives which are pretty iron-clad on the aggregate, even if they tell us nothing about the individual atom).

Note of course that Quantum Mechanics is the name of a field, not the name of a specific theory. Asking "can you test Quantum Mechanics?" is like asking "can you test Biology?" or "can you test Anthropology?" You wouldn't say a field was untestable unless the field's very definition excluded the possibility of naturalistic explanations (like Creationism). You can falsify all sorts of aspects to the theories that make up QM—it's been done since the 1930s, and is why we have the version of QM we have today and not many of the other versions that have been floated. (It's why we have something more like Bohr's version of QM rather than Einstein's, for example.)

There are some aspects of QM which are at the moment not falsifiable, in the realm of the metaphysical/philosophical interpretations of them. Whether those interpretations count as "science" would depend on who you asked and how you interpreted the term "science" in this case. But even then, sometimes they actually turn out to be falsifiable, like the issue of the EPR paradox, which was thought to be just a philosophical debate with no real testable content when it occurred in the 1930s, but in the 1970s it was discovered that there were very complicated but clever experimental setups that should be able to distinguish between some of the possible answers of it (the Bell tests I linked to earlier). --98.217.8.46 (talk) 23:58, 9 October 2008 (UTC)

October 10

Particle Physics

What is the difference between the Higg's boson and the graviton? They both are hypothesized to explain gravity, right? So how are they different? Ζρς ι'β' ^¡hábleme! 00:44, 10 October 2008 (UTC)

The Higgs boson is the unobserved member of the Standard Model that is supposed to explain inertial mass. The Standard Model does not deal with gravity at all. The graviton is the hypothetical force carrier for gravity within various theories of quantum gravity. Dragons flight (talk) 01:29, 10 October 2008 (UTC)

That's right. Sorry, I got the ideas cross for a second. Higgs deals with mass and the standard model, and graviton deals with gravity and hasn't anything to do with the standard model, really. Thanks, Ζρς ι'β' ^¡hábleme! 02:19, 10 October 2008 (UTC)

Turning off all electronic equipment during take-off and landing

Why are airline passengers instructed to turn off all electronic equipment during take-off and landing, even equipment that does not contain radio transmitters or receivers? I overheard a conversation recently, in which a fellow passenger claimed that it is done to ensure that people pay attention to what is being said over the loudspeakers, in case of emergencies during the most critical parts of a flight. Can anyone confirm this, or suggest other reasons for this requirement? --NorwegianBlue ^talk 11:07, 10 October 2008 (UTC)

I've heard the same reason (on numerous ocassions) as you suggest. LIke you say it ensures people are not distracted if there is a need to make an annoucement/emergency decisions. I have been told to stop reading my book before so I would suggest it is more about paying attention than it is about anything else. 194.221.133.226 (talk) 11:19, 10 October 2008 (UTC)

In the past it could have been do to with interference (even without transmitters any electronic equipment will emit some EM, I believe), but I'm pretty sure all critical systems on planes are shielded these days. As such, it is probably just to make sure people pay attention and, if not, at least don't make too much noise stopping other people from hearing announcements. On a related note, the reason you aren't allowed to use mobile phones in hospitals is simply because it annoys people, it's been a long time since medical equipment was sensitive to such things. --Tango (talk) 11:21, 10 October 2008 (UTC)

In general it's both. EM interference is a legitimate risk (though a much smaller one than when the rules were written in the 60s and 70s), and it is easier to swtich off all electronics than have flight attendents try to figure out which ones actually need to be disabled. At the same time, the FAA also cites the "possibility of missing important safety announcements during these important phases of flight" [9] as an additional reason to turn off electronics during takeoff and landing. Dragons flight (talk) 11:32, 10 October 2008 (UTC)

Note as well that handheld electronics represent dangerous projectiles in the cabin in the event of a crash. Headphone cables can present a tripping hazard. On takeoff and landing, the cabin crew want you to stow everything securely, not just electronics. TenOfAllTrades(talk) 13:30, 10 October 2008 (UTC)

The turning off electronics thing is just to "make sure", but realistically there's no point. If turning on an electronic device could really interfere with the cockpit's electronics, then terrorists would have a field day. 98.221.85.188 (talk) 14:41, 10 October 2008 (UTC)

The initial justification, Crossair Flight 498, was pretty lame since there were other confounding factors involved. That said, I can hear my speakers making odd noises when I point my cell phone at them the right way, and if I were talking to a control tower to avoid smacking into somebody at 400 knots, I think I'd rather the pilot have a clear signal. SDY (talk) 14:51, 10 October 2008 (UTC)

Your speakers (and the cables attached to them) aren't shielded from EM interference, I would hope the flight deck radio is. --Tango (talk) 15:10, 10 October 2008 (UTC)

How does that work with wireless communication, though? Then again, I'd imagine that the cell phone bands are all quite separate from the bands that aircraft use. SDY (talk) 15:18, 10 October 2008 (UTC)

Is anything in planes wireless? The computers they use for duty free transactions might be, but that's hardly a critical system! --Tango (talk) 15:27, 10 October 2008 (UTC)

Many planes have satellite radios, satellite TV, etc. for the passengers. Not to mention all of their telemetry equipment that is used to monitor where the plane is, how it is flying, etc. by flight control. --98.217.8.46 (talk) 15:49, 10 October 2008 (UTC)

The thinking is that if some of the electronic equipment onboard had been stripped of shielding (say, by shoddy maintenance) then your electronics could interfere. Of course, the plane has a high-voltage radio of its own, which would produce a thousand times more interference than your iPod. It is a dumb rule, but lots of these FAA rules are. They are rituals meant to make you feel safe, not actual safety measures. The lifejackets are a great example. How long do they spend teaching you how to put on a lifejacket? "Your life jacket is located under your seat, or under the arm rest between the seats. Pull the life jacket over your head and attach the strap. Infant life jackets will be distributed, if required. Do not inflate your jacket until you leave the aircraft. Pull the strap until the jacket is properly adjusted. If the life jacket does not inflate or needs more air, blow through the rubber tube." It's a nice image, you bobbing safely in the water with a bright yellow life jacket on. How many people have they actually saved? Zero. Meanwhile hundreds of people die from smoke inhalation which can be prevented by a lightweight mask. There is no rhyme or reason. Plasticup ^T/C 16:05, 10 October 2008 (UTC)

Are you sure of that number? I'm aware of several water landings where there were survivors; are you saying that in none of the cases were life vests used? --Carnildo (talk) 22:32, 10 October 2008 (UTC)

They shouldn't have been used if the evacuation went as planned since everyone would be in inflatable life rafts. Of course, if you're making a water landing, things aren't exactly going to plan, so... --Tango (talk) 23:14, 10 October 2008 (UTC)

Carnildo, for my interest, could you point to a water landing where there were survivors? My impression is that no commercial (large) jet passengers have ever survived a water impact. Skidding off runways, yes, but not "crashes". I'd be interested in the details. Franamax (talk) 00:58, 11 October 2008 (UTC)

See Ditching#Survival Rates of Passenger Plane Water Ditchings. From the article this crash] had 52 survivors. - Akamad (talk) 02:19, 11 October 2008 (UTC)

And more specifically, Ethiopian Airlines Flight 961, although I'm under the impression that life jackets actually killed more people than they saved in that particular incident. --antilived^{T | C | G} 05:12, 11 October 2008 (UTC)

Seen another way, improper use of life jackets caused loss of life, because people inflated them prior to exiting the plane, which is directly contrary to standard instruction. Maybe the relatively protracted training reflects the complexity of using these devices properly. Perhaps they should spend more time on when to inflate than how to inflate. --Scray (talk) 15:02, 12 October 2008 (UTC)

coincidentally, yesterday:

Safety investigators will now ask passengers if they were using any electronic equipment at the time of this latest incident. "Certainly in our discussions with passengers that is exactly the sort of question we will be asking - 'Were you using a computer?'," The Courier Mail quoted an Australian Transport Safety Bureau (ATSB) spokesman as saying. The ATSB said the pilots received messages about "some irregularity with the aircraft's elevator control system", before the plane climbed 300 feet and then nosedived. [10] but apparently they've decided laptops were innocent.

that article does contain the following surprising (to me) sentence, though: In July, a passenger clicking on a wireless mouse mid-flight was blamed for causing a Qantas jet to be thrown off course, according to the Australian Transport Safety Bureau's monthly report. Gzuckier (talk) 05:33, 11 October 2008 (UTC)

Thanks, everyone, for your responses! --NorwegianBlue ^talk 12:52, 11 October 2008 (UTC)

problem sum

a constant retarding force of 50 newtons is applied to a body of mass 20 kilograms moving initially with speed of 15 metres per second. how lomg does the body take to stop —Preceding unsigned comment added by 77.31.137.209 (talk) 16:22, 10 October 2008 (UTC)

Not that we should solve homework problems for you, but consider that a newton is a kilogram meter per second squared (kg*m/s²) and simple factor label cancelling (i.e. do the algebra with the units to figure out how to multiply and divide the numbers) should give you the answer. The article I linked shows the basic framework for solving problems like this. --Jayron32.talk.contribs 16:51, 10 October 2008 (UTC)

While I would probably do the same as you, the more standard approach is the learn the constant acceleration formulae. Pick the appropriate one of them along with F=ma and substitute in the numbers. --Tango (talk) 16:58, 10 October 2008 (UTC)

True, but that requires one to either memorize a list of formlas, or to be able to work the calculus on one formula to derive the rest. The nice thing about the factor-label method is that it requires learning a single method that is broadly applicable accross MANY fields. It will get you the right answer, for example, in any high school or introductory collegiate chemistry and/or physics class for, quite literally, 90% of the homework problems you will get. One method, 90% of the problems. The "learn every formula method" also works, but is, IMHO, more labor intensive and time consuming. --Jayron32.talk.contribs 17:33, 10 October 2008 (UTC)

Couldn't agree more, but it's generally best to help someone get to grips with the method they're being taught (which is almost certainly the memorise formulae method) rather than teaching them a whole new method. --Tango (talk) 19:01, 10 October 2008 (UTC)

You've all forgotten that the dimensional analysis, while certainly very useful, is no substitute for knowing why you're multiplying things in the first place--it's simply a way to check that you haven't combined units in a nonsensical way. For example, for energy stored in a spring, you may be tempted to use U = kx^2, when the formula is actually (1/2)kx^2. If you were to merely use dimensional analysis you would arrive at the wrong answer. Actually, the best way is to learn everything, including the calculus behind it. Then you'll never have any doubt as to whether the formula has a 1/2 or not; just do the integral. --M1ss1ontomars2k4 (talk) 21:03, 11 October 2008 (UTC)

Actually, you don't even need calculus to get the constant acceleration formulae, you can work them out geometrically from distance/time and velocity/time graphs (well, I guess you could say it's calculus because you need to know how to interpret the area under the curve, etc., but you don't actually need to integrate or differentiate anything). But you are correct that the method does mean you are occasionally out by a factor of two (it's always two...), but I generally ignore factors of two, they're rarely important! ;) --Tango (talk) 22:56, 11 October 2008 (UTC)

threshold logic synthesis

can anybody help me to know how to find the false vertices for threshold logic synthesis....... —Preceding unsigned comment added by Sveta rathi (talk • contribs) 19:04, 10 October 2008 (UTC)

Wikipedia has an article on Logic synthesis that also has a long list of referenes and other links at the end. This may be a good place to start. --Jayron32.talk.contribs 19:20, 10 October 2008 (UTC)

"Virgin birth" in a shark

http://ap.google.com/article/ALeqM5gV-UePymWuPU7HFxNgUXRUrakU1wD93NPTM80

How did this exactly happen? Can the same thing happen to humans? --Emyn ned (talk) 20:07, 10 October 2008 (UTC)

The process is called parthenogenesis. (Our article discusses the matter in some detail.) Briefly, there's never been a substantiated case of parthenogenesis in any mammal (including humans) in the wild. Induced parthenogenesis has apparently been demonstrated in rabbits and mice, producing viable offspring. Human parthenogenesis has been demonstrated to the extent of creating human embryonic stem cells from unfertilized eggs, though no human beings have been born via this method. TenOfAllTrades(talk) 20:22, 10 October 2008 (UTC)

it's not too hard to make an egg cell of any animal start to divide, even if not fertilized; it's all caused by a bunch of calcium entering, calcium being a handy ion in organisms for signals like that, it's not too scarce like magnesium and not too abundant like sodium. The chromosomes provided by the sperm actually don't have anything to do with triggering the egg's development, but the whole thing is set up that the arrival of the sperm triggers that calcium influx which starts the division, and the arrival of the chromosomes in the same package is basically a happy accident. but you can trigger the calcium influx via drugs and things in eggs of many species and away they go. once the cell starts the process of dividing and then duplicating chromosomes and dividing again, the fact that it only has one set of chromosomes instead of two gets fixed as that set gets duplicated after a cell division. (the other product of the division has no sets of chromosomes, and just sort of fades away, but that's not a problem; cells early in the division process aren't specialized yet, each one can produce a complete embryo if they're separated, that's where identical twins come from.) so at that point you've got a dividing egg cell with two sets of chromosomes, and you're on your way. the fact that both sets are identical isn't critical, but of course any undesirable recessive genes will pop up.

in sharks? well we're seeing a lot of it now, because we didn't look for it before, so it's likely that some mechanism has evolved which can trigger the egg reasonably frequently without the need for sperm. there are other species which don't have males at all, of course, so this is just a less emphatic version of that. might happen occasionally in other animals too; people for instance. it would be hard to prove, particularly if it was pretty rare. there is this one story about a virgin, a couple of thousand years ago.... Gzuckier (talk) 20:29, 10 October 2008 (UTC)

It could happen in humans, I believe. Unfortunately or fortunately, only females would be produced in such cases, due to the XY sex chromosome thing. Imagine Reason (talk) 04:15, 11 October 2008 (UTC)

i really should know this but

how do volumes add in a liquid solution? i know all about partial pressures, etc. but if 10 ml of alcohol is added to 90 ml of water, is the result 100 ml? how about when dissolving solids in a liquid? thanks. Gzuckier (talk) 20:18, 10 October 2008 (UTC)

Unfortunately, there's not a simple answer to this one. In general, the volume of a solution will not be equal to the sum of the separate volumes of its components. In other words, if you add 10 mL of ethanol to 90 mL of water, the final volume will come out to be slightly less than 100 mL (about 99.5 mL, actually). This discrepancy will depend on the compounds being mixed, and on their proportions. (If you add 40 mL of ethanol to 60 mL of water, the final solution will be a shade less than 98 mL volume.) Dissolving solids in liquids has similar problems.

Conceptually, you can think of the molecules of solute being able to at least partially occupy gaps left between the loosely-packed solvent molecules, but that's an awfully hand-waving description. TenOfAllTrades(talk) 20:44, 10 October 2008 (UTC)

As a more detailed description, consider that there is in the individual pure liquids, the macroscopic "volume" property is determined by a microscopic property we can call "intermolecular distance" that the molecules seperate themselves by. So, there is a water-water intermolecular distance and a ethanol-ethanol intermolecular distance. When you mix the two, you create a new interaction, the ethanol-water interaction, which is a shorter distance than either the ethanol-ethanol or water-water distance. This makes sense if you consider that in order to for two substances be miscable, the molecules of each substance must be more attracted to each other than to themselves.(if the water and ethanol were more attracted to themselves than to each other, then the two would merely aggregate seperately, and would not mix). More attractive force means shorter distance between them. So a solution of two substances should always occupy a smaller volume than the sum of their pre-mixed volumes. --Jayron32.talk.contribs 23:13, 10 October 2008 (UTC)

That's a completely different description. The first one is wrong, and just happens to partially explain a little. — DanielLC 16:22, 11 October 2008 (UTC)

What is the movement of a submarine called?

Sailing? Driving? —Preceding unsigned comment added by 87.165.220.170 (talk) 20:55, 10 October 2008 (UTC)

'Sailing' appears to be a widely-used, widely-accepted term. (Google submarine sailed or submarine sailing to see many, many examples of usage.) 'Driving' is definitely not. TenOfAllTrades(talk) 23:30, 10 October 2008 (UTC)

It's odd that, for ships, at one time "sailing" was updated to "steaming" but now seems to have reverted to "sailing" even though the technology has gone somewhere else entirely. I guess dieseling, electricking or nuclear reacting just don't roll off the tongue. SpinningSpark 12:41, 11 October 2008 (UTC)

So we sailed up to the sun . . . in our yellow submarine - Lennon-McCartney

Sudden moon

I am writing a story set on a planet that has suddenly acquired a moon. For the purposes of this question, just assume it suddenly appeared and that both the planet and moon are the same size as ours.

I'm trying to work out exactly the nature and scale of the disasters this would cause. All I've got so far are extreme tidal waves and flooding, but would there also be earthquakes? I think it would probably result in massive unbalancing and possibly death among nocturnal species, not to mention the probable extinction of a lot of tidal zone species. What else, though?

While I'm at it, what would a world be like that did not have a moon? It would have very small tides thanks to the sun, and would always be very dark at night... One of my friends claims that it wouldn't have seasons, but I find that dubious. Any thoughts? --Masamage ♫ 21:12, 10 October 2008 (UTC)

I don't think you would get anything more drastic that we get every day, since as the Earth rotates different parts of the Earth are affected by the moon's gravity (you might get some problems immeadiately after the arrival since you would have the effect of 6 hours worth of tidal change in an instant [although the magnitude of the tides would be the same as for the Earth], but that wouldn't last long, although the damage from it might). The fact that life wouldn't be used to the tides would be a problem, certainly, but I think that's about it (and remember, it's just increased tides, not new tides, because of the sun). As for a planet without a moon, it would probably affect the seasons, but it wouldn't preclude having them. Seasons are caused by the rotational axis being tilted with respect to the orbit, the moon may well have affected our axial tilt, but having a moon isn't a requirement to have one. The day would also be shorter, since the same tidal forces which mean the moon always shows the same face to Earth are gradually slowing the Earth's rotation, without the moon that wouldn't have happened so the day would be a few hours shorter (I'm not sure how many, but I believe it's been measured by looking at fossilised coral). I read somewhere that the moon has helped stabilise the Earth's rotational axis, but I'm not sure how, so the seasons may be more variable without a moon (although probably on the scale of centuries at least). --Tango (talk) 21:31, 10 October 2008 (UTC)

Instantaneous appearance? You'd get at least the following:

1. A sudden shock as the planet shifts from following a simple orbital path around its sun to the sine-wave pattern the Earth follows. (The center of gravity of the Earth-Moon system follows an elliptical path around the Sun; the Earth and Moon orbit that center of gravity with a period of one Lunar month).
2. Gradually-increasing tidal heights, with the final tidal range being about three times what it used to be. Timing of the high tides will also change. You won't get tidal waves because the water has a long way to flow to adapt to the new gravity patterns, and it doesn't move very fast. At a guess, it'll take a month or two for the tides to reach their final heights.
3. More earthquakes. They won't be stronger, and they might be weaker, because of increased tidal flexing of the crustal plates.
4. Disruption of activity for many species: some night-active species will have trouble being active during full moons; some day-active species will stay active at night during full moons.
5. Increased predation of day-active prey species. The increased night-time lighting means that camoflage patterns and sleeping habits are no longer adequate for protection. It'll take about five years for the resulting boom-and-bust of night-active predator species to settle out.

Over the long term, you'd see the following:

1. More reliable seasons. Adding a large moon will stabilize the planet's rotation axis, so the strength of the seasons won't change over time (millions to billion of years)
2. An increase in the number of night-active species. More light means it's easier to move around at night. (hundreds to tens of thousands of years)
3. A reduction in meteor impacts: the Moon provides some protection against meteors by variously blocking them, causing them to break up, or throwing them out of Earth-crossing orbits.
4. An increase in volcanism: the increase in tidal flexing will increase the temperature of the planet. (Hundreds of thousands to millions of years)

Hope this helps. --Carnildo (talk) 22:58, 10 October 2008 (UTC)

If you are interested in this subject, and want to see how another author has treated a similar situation (though not exactly the same), may I recommend Jack McDevitt's book Deepsix, it has some interesting descriptions of weird tidal effects caused by two large planets on a collision course. Its part of his "Priscilla Hutchins" series, and is an enjoyable read. --Jayron32.talk.contribs 23:05, 10 October 2008 (UTC)

Why would it take months for the tides to reach their maximum? The water doesn't need to move any faster than it does on Earth and it can go all the way round the Earth in 24 hours (well, individual bits of water don't, but you know what I mean). --Tango (talk) 23:13, 10 October 2008 (UTC)

On Earth, the tides have had billions of years to build up momentum. The Moon's gravity isn't very strong, so the water doesn't accelerate very fast. --Carnildo (talk) 23:29, 10 October 2008 (UTC)

That's utter nonsense.

The water oscillates back and forth twice per day. So the momentum builds up slowly over about six hours then back the other way over the next six. It doesn't "build up" over millions of years. The tides would settle into their regular pattern in about a day or two. I think there could be no earthquakes or anything because the earth too squeezes and stretches in a cycle over 12 hours and we don't see particular problems because of that. I agree though that the SUDDEN arrive of a few gigatons of stuff in orbit would very abruptly jerk the planet in it's orbit - and that would be utterly disasterous - all of the oceans and atmosphere would slosh violently - possibly flying off the planet completely...it's hard to imagine any life surviving that. But if the moon somehow slowly spiralled into position over decades - then I think it would have fairly benign effects (well, crazy weather - tides where they'd never been before - flooding, rivers running backwards...but definitely something you could survive). You'd also have to consider the consequences of the moon suddenly being dumped into the much stronger gravity well of the planet. Since we have no knowledge of the "magic" that makes the moon suddenly teleport into place - we can't guess what forces that entails - but it might well break up, ending up as a truly spectacular ring system...or possibly raining death and destruction onto the surface. SteveBaker (talk) 01:12, 11 October 2008 (UTC)

hydrogen reaction

Will a balloon filled with pure hydrogen and pierced with a needle made of palladium explode/combust? —Preceding unsigned comment added by Kaufmann1 (talk • contribs) 21:57, 10 October 2008 (UTC)

Not unless the palladium is particularly hot. Palladium can act as a catalyst for certain reactions involving hydrogen, however as far as I am aware, it does not lower the activation energy of the combustion reaction enough to cause it to become spontaneous. --Jayron32.talk.contribs 22:56, 10 October 2008 (UTC)

Pure hydrogen? What would it react with? --Carnildo (talk) 22:58, 10 October 2008 (UTC)

The oxygen in the atmosphere outside the balloon, presumably. Algebraist 23:05, 10 October 2008 (UTC)

Our article on palladium says it can absorb large amounts of hydrogen. I'm not sure if that reaction releases energy, but I doubt it would do so to the extent of causing an explosion. --Tango (talk) 23:10, 10 October 2008 (UTC)

Where can I get a palladium needle, to try the experiment? Edison (talk) 19:30, 11 October 2008 (UTC)

You would probably have to turn it into a needle yourself, but you could buy a palladium coin here (for about $200, although they're out of stock apparently...). --Tango (talk) 22:51, 11 October 2008 (UTC)

However, a needle or other solid form is just about the worst you can do if you're trying to get a rapid reaction. The reaction between a gas and a metal (or "chemical adsorbed or absorbed onto/into the metal" happens at the metal surface, so the bulk of the solid metal below the surface is useless. Much better to use powdered Pd (or Pd coated on some other powder) or a porous matrix. The large surface area allows much more rapid reaction. I've seen active metals like Pd and Pt supported on powdered charcoal--the form commonly used for lab-scale catalytic hydrogenation reactions--lead to combustion with atmospheric oxygen even without substantial hydrogen present (I'm sure helped by the charcoal being flammable). DMacks (talk) 18:46, 12 October 2008 (UTC)

Mars climate

How does climates on Mars work?Does temperats range by latitudes, seasons or night-and day. Ithouhgt Mars is a very cold planet, often colder than a freezer, and the average planet temp is around minus 67 F. Is that the mid-latitude average surface temp? I thought only tropical zones of Mars or low latitudes get temp range from +10 to +69 F.--Freeway91 22:15, 10 October 2008 (UTC)

Interestingly, we have an article on that: Climate of Mars. --Jayron32.talk.contribs 22:58, 10 October 2008 (UTC)

The variation of temperature with latitude, seasons and day/night don't really depend on the planet so much as how it moves around the sun. Pretty much all of the planets have all of those things (with the sole exception of Mercury which keeps the same face pointing towards the sun all the time - so it doesn't have day/night cycles).

• Variation by latitude is because the planet is round and the sun's rays spread out more at the poles than at the equator.
• Variation by season is because most planets are doing their daily rotation about an axis that's tipped over somewhat. This means that the suns rays are more spread out at some times of the year than others. For planets with very elliptical orbits, there is a variation due to distance from the sun too.
• Variation between night and day is because the sun isn't shining on the surface at night.

So all of those things vary on all planets that are round, have an axial tilt and rotate on their axis...and that includes Mars.

SteveBaker (talk) 00:47, 11 October 2008 (UTC)

Actually, Mercury isn't tidally locked (although astronomers did think it was at one time). See Mercury (planet)#Spin–orbit resonance. --Tango (talk) 00:55, 11 October 2008 (UTC)

Seconded. Apparently Steve is stuck in 1964;-) --Stephan Schulz (talk) 01:01, 11 October 2008 (UTC)

In more ways than you can imagine! SteveBaker (talk) 01:20, 11 October 2008 (UTC)

So isn't temperate zone on Mars lattide of 30+ always or often below 0, and lattitude of 50+ alwas colder than Greenland? Generally, Mars I thought is very cold.--Freeway91 01:04, 11 October 2008 (UTC)

Because of its thin atmosphere it doesn't retain heat well, so at night it is going to be extremely cold regardless of your latitude. During the day, it will be warmer the nearer the equator you are (well, not quite the equator due to the axial tilt). I don't know any numbers off the top of my head, but they shouldn't be too difficult to find with a bit of googling. --Tango (talk) 13:53, 11 October 2008 (UTC)

gas constant?

why should we use a constant for gas equations?where does the universal gas constant come from?i couldn't find any information about history of gas constant(R)? —Preceding unsigned comment added by 88.242.106.180 (talk) 00:57, 11 October 2008 (UTC)

You may want to have a look at gas constant and Boltzmann constant for a more detailed treatment of the topic. Briefly, the gas constant (R) is a proportionality constant which describes how much energy is stored in a mole of (ideal) gas molecules per degree of temperature. (The related Boltzmann constant, k_B, describes the quantity of energy per molecule.) TenOfAllTrades(talk) 01:40, 11 October 2008 (UTC)

A pity nothing is said in the articles about experiments like in de:Universelle_Gaskonstante#Ein Experiment zur Ermittlung einer Näherung der Gaskonstante, or how the constant was measured to this accuracy. --Ayacop (talk) 09:26, 11 October 2008 (UTC)

If you can translate from the german, the English Wikipedia articles could probably benefit from your help. --Jayron32.talk.contribs 12:46, 11 October 2008 (UTC)

Back to the gas constant. The SI system was carefully constructed to in general, avoid these sort of proportionality constants. Many calculations would require them, except that the units are defined to be compatable in ways that generate proprotionality constants of "1". The situation with "R" is because the SI unit for temperature, kelvin, is created not to be compatable with other SI units, but be compatable with the Celsius scale. Since the size of a Celsius unit is arbitary (there's nothing inherently useful about being 1/100th the difference between the sea-level freezing and boiling points of water), the size of the kelvin is arbitrary as well. One could define a temperature scale where 1 degree was equal to the the amount of energy contained by 1 mole of molecules, and under THAT scale, R would be equal to 1. However, for other reasons of convenience and history, we use the Kelvin scale, so we are stuck with a non-unitary R values. --Jayron32.talk.contribs 13:00, 11 October 2008 (UTC)

I'm not entirely sure I'd agree with that. While interconversion among SI units is very straightforward and generally avoids weird proportionality constants, such constants are almost always necessary in calculations which describe physical processes in the real world. (The energy of a photon is equal to its frequency multiplied by 6.626x10^-34: the Planck constant; the gravitational attraction between two bodies is the product of their masses divided by the square of their separation distance, multipied by 6.674x10^-11: the gravitational constant. And so forth.)

The seven base SI units trace their roots to essentially arbitrary roots which don't have any universal scientific or physical significance. (The meter was originally based on a rough measure of the Earth's circumference; the second on arbitrary divisions in the length of Earth's day; the kilgram tied to the density of water.)

To get rid of arbitrary constants of proportionality, physicists will resort to systems of so-called natural units which peg most physical constants to be exactly 1. Under (for example) Planck units, the speed of light, the gravitational constant, the reduced Planck's constant, Boltzmann's constant, and the Coulomb force constant are all set to be 1, and other units defined from there. Such systems can make calculations dramatically 'neater' and eliminate the risk of 'losing' a constant in a complicated expression. The downside of such systems is that they generate base units which aren't convenient for 'everyday' usage. (The base unit of temperature in Planck units is about 10³² kelvin, and the base unit of time is about 10^-44 seconds.) TenOfAllTrades(talk) 14:51, 11 October 2008 (UTC)

Use of Oil

Generally what percentage of a barrel of oil is used strictly for fuels such as gasoline and diesel? How much is used for plastics and other products? I had heard that oil used for fuels was low - around 20% - and the bulk of every oil pumped out of the ground was for other products like plastic. Is this true142.68.216.154 (talk) 02:35, 11 October 2008 (UTC)

You might want to look at this link [11]. Which deals with oils use for energy. Only 20-30% of the energy we use goes to transportation but almost all of that energy comes from oil. I know that doesn't answer you question but it is probably the origin of you mangled statistic. What comes out of a barrel of oil depends on what the oil is like (where it was found) and how you crack it but this link gives you and idea of how an average barrel gets fractioned [12]. The key chunks of plastics are mostly derived from natural gas. The other components are derived from side products in process of refining oil for gasoline/diesel. Transportation fuel is the largest and most powerful market for oil, plastic just removes 4.7% of the barrel of what would other wise be a waste stream to burn for heat/electcity or maybe converted into hydrogen. In addition consumers can afford to pay more for natural gas to heat their homes and produce electricity than chemical producers can afford to pay for natural gas as a feed stock. The price of natural gas in North America has forced many chemical producers to close up shop and move to places with cheaper natural gas like the Middle East and Africa. I think BASF cited this when they closed plants around 2005 among other companies. I hope that helps.--OMCV (talk) 03:28, 11 October 2008 (UTC)

yeah, the demand for gasoline/fuel oil basically requires economically to "crack" as much of the petroleum that can possibly be used into the proper weights. In addition, the advent of fuel injection and the associated in-tank fuel pumps have made it possible to add the lighter petroleum fractions into gasoline which would have created a lot of vapor lock in the carbureted engines with the fuel pump on the engine, and used to be disposed of. In fact, (according to what i read) the vapor pressure on gasoline has risen enough even just in a decade or two to saturate the vapor capture systems on cars from the 80s. basically, any oil that goes into plastics is leftovers that would otherwise be waste. Gzuckier (talk) 05:22, 11 October 2008 (UTC)

Plants with edible stems

Are there plants other than Rhubarb with edible stems?74.50.200.72 (talk) 06:41, 11 October 2008 (UTC)

Cattails Ζρς ι'β' ^¡hábleme! 07:18, 11 October 2008 (UTC)

Leeks and spring onions are commonly eaten in the UK. Axl ¤ [Talk] 07:20, 11 October 2008 (UTC)

The pedia does it again -- try Edible plant stems for a nice list of munchies. (It doesn't mention mushroom stems/stalks which are not notable but edible.) Julia Rossi (talk) 07:25, 11 October 2008 (UTC)

Mushrooms are also not plants. —Ilmari Karonen (talk) 07:33, 11 October 2008 (UTC)

(ec) A lot of herbs are edible in the whole (or at least their above-ground parts are), so I guess they count. At the other end of the scale, pine phloem is edible (if not very nutritious), though the whole trunk isn't. —Ilmari Karonen (talk) 07:31, 11 October 2008 (UTC)

Rhubarb's culinary cousin Celery certainly qualifies, doesn't it?--Jayron32.talk.contribs 12:44, 11 October 2008 (UTC)

Noisy faucet

My kitchen faucet, which works well otherwise, makes a high pitched whine when running hot water through it. Why? Dismas|^(talk) 15:19, 11 October 2008 (UTC)

There is some air in the pipes. As the air flows through the the narrow opening, it makes a sound. Axl ¤ [Talk] 18:50, 11 October 2008 (UTC)

As water flows through your faucet, there may be regions of turbulent flow; there may also be areas of lower pressure created by the flowing water. (See Bernoulli's principle for more details on how that might arise.)

Turbulence and low pressure can generate noise in at least a couple of ways that would be more dramatic with hot water than cold. First, the solubility of air (mostly oxygen and nitrogen) drops with increasing temperatures. In other words, cold water that left the treatment plant or well saturated with air will be supersaturated after being heated in your water heater. The reduction in pressure and increase in turbulence as the water approaches your faucet will encourage that air to come out of solution and form bubbles; turbulent movement of bubbles generates noise.

Even in the absence of dissolved air, you might still see effects due to cavitation. Hot water has a higher vapor pressure than cold, and hot water may actually boil in regions of low pressure within the plumbing. The formation and subsequent collapse of bubbles of water vapor can generate noise as well. TenOfAllTrades(talk) 19:06, 11 October 2008 (UTC)

Quote identification

With regard to the Fermi paradox: "If there are so many alien civilizations, why haven't they visited us? I decided to do an experiment. I wanted lobsters for dinner. I put a plate on my table, sat down, opened the front door, and waited for a lobster to crawl onto my plate. Three hours later, no lobster came. I ended the experiment, concluding there are no lobsters in the world."

This "quote", which is obviously not word-for-word, is from a show that aired on Discovery Channel a few years ago. --99.237.96.81 (talk) 16:34, 11 October 2008 (UTC)

Lobsters are not a highly intelligent species in an advanced technological civilization with a desire to explore the universe. Axl ¤ [Talk] 18:56, 11 October 2008 (UTC)

If they were, is it a given that we would even notice? ;) --Kurt Shaped Box (talk) 02:01, 12 October 2008 (UTC)

A bad analogy is like a pickle playing chess. TenOfAllTrades(talk) 19:12, 11 October 2008 (UTC)

A quick web search indicates that the story is variously attributed to "a SETI offical", and Timothy Ferris (who is not a SETI official). Ferris is a science popularizer, though, so he may be quoting someone else (or he could be the originator - it's hard to tell). I can't find anything that looks like an "original" source. (Most web hits for "lobster Fermi Paradox" are for Accelerando (book).) -- 128.104.112.147 (talk) 19:42, 11 October 2008 (UTC)

Well, the other issue is that we may be the only advanced civilization in our galaxy, but our galaxy is such an isignificant fraction of the whole universe its hard to say definately we are the only ones. Back to the lobster analogy, imagine putting out your plate and waiting for a lobster to crawl on it from the moon. There universe may be teeming with advanced civilization, but we lack the ability to detect evidence of it because its too far away. --Jayron32.talk.contribs 20:17, 11 October 2008 (UTC)

The Fermi paradox is really a pretty shakey proposition. We are a civilisation - have we visited any alien species? Could we even if we knew which star system thay lived at? Even if they lived on Proxima Centauri (the closest star to the Sun) - we currently have no clue whatever how we could get to them. Why would we expect that other civilisations would have any better ideas than we do?

Even if they are smarter than we are - or have simply been around a lot longer...if travel between the stars is impossible for us right now - maybe it's impossible, period. Worse still - how do they know we're here? Our SETI detectors are unable to detect a signal unless it's either beamed on a narrow-beam directly at us - or a broadcast signal that's VASTLY more powerful than the most powerful signal we've ever sent into space. We don't routinely beam narrow-beam signals at stars - so they would need much more powerful radio receivers than we currently have in order to hear us...and again - if we don't know how to do that, why should we assume that the aliens do?

Also, we've only been transmitting radio signal with any strength out into space for less than a hundred years - so only aliens within 100 light years could possibly know we're here - and only those within 50 light years could possibly have gotten here after hearing us...if it took them a while to plan the mission and get it funded and launched - they might have to be much closer to have gotten here yet. There are only 1000 stars within 50 light years - and only 50 or so within 20 light years. It's perfectly possible that none of those 50 stars have planets suitable for life.

From what we know - even if aliens are REALLY common around our galaxy - and even if they have close to light-speed travel and radio receivers that are vastly more sensitive than ours, it would STILL be quite surprising if they were able to get here to visit us. Far from being a paradox, Fermi's claim is just wrong.

SteveBaker (talk) 01:28, 12 October 2008 (UTC)

That's assuming that they'd even be interested in contacting us. What's to say that they wouldn't view us as savage, warlike, power-hungry carnivorous beasts with just enough brainpower to be a potential threat to *their* peace-loving civilization should an encounter occur - and decide to steer well clear? Either that, or they see that we're just lumps of meat restricted to 3-dimensional space with no subspace hivemind capability and think 'bleh - who cares about that?'. ;) --Kurt Shaped Box (talk) 02:14, 12 October 2008 (UTC)

Perhaps they're preparing an application for a hyperspatial express route? Axl ¤ [Talk] 09:49, 12 October 2008 (UTC)

Or they've seen what we do to the lobsters whenever they venture forth from the ocean in an attempt to engage in peaceful communication with us... --Kurt Shaped Box (talk) 19:13, 12 October 2008 (UTC)

We are very young on an astronomical scale, and we are advancing at a significant rate. For the purposes of the Fermi paradox, we are not advanced. We have never left this solar system, but we currently emit very large amounts of radio waves, and have even done so with the intent of contacting aliens. We are currently quite capable of interstellar travel, as can be seen by Project Daedalus. Unless advanced civilizations stop sending stop sending out signals, there would logically be roughly spherical areas around where each one began where all, or at least many, of the stars are emitting suspiciously large amounts of a small band of electromagnetic waves. — DanielLC 16:07, 12 October 2008 (UTC)

I've got to disagree.

Project Daedalus is a joke - it requires Helium-3 as a fuel. Which they propose to mine from Jupiter over a 20 year period using robotic probes...we are SO far from even being able to start making the robots that would autonomously mine the fuel for the darned thing - we're nowhere CLOSE to being able to do that. The craft itself weighs 50,000 tons...getting that into orbit would require 2,000 shuttle launches! And all of that to get a small number of teeny-tiny robotic probes to one of the nearest stars. Worse still - those probes would shoot past the star at 12% of the speed of light - leaving only a very short period for observation and science! It's also true that this is not just a matter of science. There is also the matter of politics. There is no conceivable way of getting a government to fund a massive 20 program to mine fuel for a 50 year program which would take another 6 years to report back results. Worse still - nobody who was alive at the start of the program would be alive at the end. The cost of launching the components into orbit alone would be 160 times the cost of the ISS! With present funding levels, NASA would be doing nothing else for a thousand years! Politicians will never allocate that amount of funding to achieve a goal that not one of their voters will live to see through to completion. All of this for at most a couple of hours of science data captured at such a high speed that detailed photography would be impossible! A thousand years of funding for a probe that might just fail when it gets there? I don't think so.

No - we REALLY don't know how to do interstellar travel...not in any kind of practical manner. If aliens managed to build a Daedalus - it would pass us by so quickly that we'd never notice it passing.

You say that we're pushing out a lot of radio waves - but not on an interstellar scale. Recall that the very best radio telescopes we have would be unable to detect broadcast signals of the strength we're putting out from a distance of the nearest star.

You say that we're young on an astronomical scale - perhaps we are - but perhaps we're already pushing the outer limits of what's possible? Because we can't know that there are vast improvements in space technology out there - it's perfectly possible that we're already close to hitting the limits. You can't claim that it's paradoxical that we haven't seen any alien visitors - it's perfectly reasonable given what we know. More to the point - I could claim that because we haven't seen any aliens (and the math makes it seem like there must be lots of them out there) then it must be that we're close to the limits of the technologically possible.

SteveBaker (talk) 20:56, 12 October 2008 (UTC)

Isn't there a theory doing the rounds that radio waves of the strength we tend to emit will peter out into the background radiation after a couple of light years? I seem to remember reading about that a while back. --Kurt Shaped Box (talk) 19:09, 12 October 2008 (UTC)

would you freeze in space with nothing on

if i went into outer space without a suit would i freeze instantly? why? is there no oxygen or something?--Majorcolors1 (talk) 17:59, 11 October 2008 (UTC)

You wouldn't freeze very quickly, if at all. In a vacuum (ie. when there's no air) the only way to lose heat it by radiation, which is very slow. You would suffocate long before you froze. We have an article on it: Human adaptation to space#Unprotected effects. --Tango (talk) 19:00, 11 October 2008 (UTC)

Well, it also depends on how you were exposed to the vacuum. If your space suit just suddenly disappeared and all the gas surrounding your body expanded rapidly, the gas would cool so rapidly that the outer layers of your body would be chilled to below freezing. If on the other hand, there was only a slow leak in your space suit until there was no air left, you probably would not freeze, unless your spacesuit was conductive. --M1ss1ontomars2k4 (talk) 20:59, 11 October 2008 (UTC)

Yeah, the gas would cool, but it would be nowhere near your body after a fraction of a second, so how would if affect you? And your spacesuit being conductive won't make any difference since there is nowhere for the heat to go, it still has to be radiated. --Tango (talk) 22:46, 11 October 2008 (UTC)

Well, it depends on the temperature of your spacesuit, I suppose. If it were colder than you (it wouldn't be unless you were in the shadow of something, right?), then you might have a problem. But I'd assume that spacesuits are very insulating, or they'd be conducting heat to/from you all the time. --M1ss1ontomars2k4 (talk) 23:14, 11 October 2008 (UTC)

Your spacesuit is in contact with you and nothing else, so it's almost certainly the same temperature as you. --Tango (talk) 23:25, 11 October 2008 (UTC)

I think the most horrifying thing is that without external pressure your bodily fluids begin to boil, starting with the water on your tongue. Plasticup ^T/C 03:28, 12 October 2008 (UTC)

Your skin is able to provide enough pressure to prevent most bodily fluids from boiling - but your eyes, the interior of your nose, lungs and mouth would certainly have problems with that. For water to boil at body temperature, the pressure has to be down below 100mm of mercury - that's about one eighth of an atmosphere. That's about the pressure at 40,000' - but people have successfully flown unpressurized aircraft at higher altitudes than that. Supermarine_Spitfire#Speed_and_altitude_records - for example, shows a flight up to 51,000' at which air pressure is down to about 76mm of mercury - where the boiling point of water would have dropped to 32 degC - 90 degF. SteveBaker (talk) 03:51, 12 October 2008 (UTC)

Perhaps in those instances the gradual pressure change allowed the liquids to boil off more subtly, but there is no doubt that suddenly being thrust into a near-zero pressure environment makes your tongue boil. It actually happened to one unfortunate gentleman. Plasticup ^T/C 05:48, 12 October 2008 (UTC)

While the plane may not have been pressurised they would almost certainly have been wearing an oxygen mask so the pressure on their mouth and nose would be much greater, and wearing a full face mask wouldn't surprise me. They would probably also have had a pressure suit to apply pressure to the rest of their body (although that wouldn't be vital, since skin can do the job in a pinch, as you say). --Tango (talk) 11:43, 12 October 2008 (UTC)

You would certainly freeze, Tango, although not before you suffocated. Heat loss by radiation is given by the Stefan-Boltzmann law: $P=\sigma (T^{4}-T_{0}^{4})A$

where

σ is the Stefan-Boltzmann constant, about 5.7e-8 W/m2K4

T is the body temperature, normally about 310 K

$T_{0}$ is the cosmic background temperature, about 3 K

A is the body surface area, about 1.7 m2

(I'm ignoring the emissivity of skin which is, to my surprise, close to unity. [13])

The result is about P = 879 watts, dropping to about 528 watts at freezing point. That is a significant rate of heat loss. Let's see how quickly you would freeze.

Energy to cool a 75 kg body from 310 K to 273 K: 75 kg x (310 K - 273 K) x 4000 J/kg.K = 11.1 MJ

Energy to freeze a 75 kg body at 273 K: 75 kg x 333 kJ/kg = 25.0 MJ

At an average 700 watts rate of cooling, it would take (11.1 MJ + 25.0 MJ) / 700 W = 14 hours to freeze you solid. But I imagine that, if you were losing heat at 879 W, you would start getting frostbite quite soon after exposure.

--Heron (talk) 15:47, 12 October 2008 (UTC)

That 3K figure is for deep space away from any heat source. If you are in Earth orbit and not in the shadow of the Earth you are more likely to burn than freeze (the average daytime temperature on the moon is 107°C according to our article and that's pretty much the same as being in space at the same distance from the sun). Space suits have sophisticated refrigeration units in them. You would get very cold in the shadow of the Earth, though, so in LEO you would be going from over 100 degrees above to over 100 degrees below every hour and a half or so. Of course, you lose conciousness in about 15 seconds from hypoxia, so it doesn't really matter. --Tango (talk) 17:09, 12 October 2008 (UTC)

Damn Interesting has a great article on exposure in space here

In the absence of atmospheric pressure water will spontaneously convert into vapor, which would cause the moisture in a victim's mouth and eyes to quickly boil away. The same effect would cause water in the muscles and soft tissues of the body to evaporate, prompting some parts of the body to swell to twice their usual size after a few moments. This bloating may result in some superficial bruising due to broken capillaries, but it would not be sufficient to break the skin. -- Within seconds the reduced pressure would cause the nitrogen which is dissolved in the blood to form gaseous bubbles, a painful condition known to divers as "the bends." Direct exposure to the sun's ultraviolet radiation would also cause a severe sunburn to any unprotected skin. Heat does not transfer out of the body very rapidly in the absence of a medium such as air or water, so freezing to death is not an immediate risk in outer space despite the extreme cold. -- For about ten full seconds– a long time to be loitering in space without protection– an average human would be rather uncomfortable, but they would still have their wits about them. Depending on the nature of the decompression, this may give a victim sufficient time to take measures to save their own life. But this period of "useful consciousness" would wane as the effects of brain asphyxiation begin to set in. In the absence of air pressure the gas exchange of the lungs works in reverse, dumping oxygen out of the blood and accelerating the oxygen-starved state known as hypoxia. After about ten seconds a victim will experience loss of vision and impaired judgement, and the cooling effect of evaporation will lower the temperature in the victim's mouth and nose to near-freezing. Unconsciousness and convulsions would follow several seconds later, and a blue discoloration of the skin called cyanosis would become evident.

-- MacAddct1984 ^{(talk &#149; contribs)} 16:08, 12 October 2008 (UTC)

I don't believe you'll get the bends - and I don't believe that your blood would boil. You are making the mistake of assuming that the pressure inside your body drops to zero. It doesn't because your skin is able to exert a force to keep your innards under pressure (to some degree at least). So pressure inside your body will remain at some fraction of an atmosphere. As I explained before - for water at body temperature to boil, you need the pressure to be below one eighth of an atmosphere - and I'd certainly expect your skin to be able to do that...at least for short periods...in the longer term, you're dead anyway. The liquid on the surface of your eyes, inside your mouth and near other orifices will boil because they WILL fall to zero pressure - but not your blood.

As for getting the bends - I'm not sure what the threshold for getting the bends is - but remember that your body is pressurised to one atmosphere when you are just 32 feet underwater - you can happily snorkel to that depth and come up quickly without getting the bends - and that's the same pressure differential as going from normal air pressure into a vacuum. Note also that astronauts have their space suits pressurised at only half an atmosphere anyway (to keep them flexible apparently) - so the drop is more like coming up from 16 feet to the surface...which I can do in any decent swimming pool with a diving board. How many people get the bends in a swimming pool?

SteveBaker (talk) 20:11, 12 October 2008 (UTC)

The above sounds kind of like what was posited in one sci-fi book I read once (set in 2017, astronauts thought they were in space, trapped underground, to get out had to get through this place w/no pressure & properly fitting suit caused some nasty bulging/bruising; someone might know what I mean). But, I always thought that the lack of pressure in space was so huge that one would literally "pop" instantly. I'll have to read that article on exposure to space when i have more time. I guess it wouldn't be as instnat as I thought.Somebody or his brother (talk) 17:00, 12 October 2008 (UTC)

The classic scene is the one in 2001 (movie) when Bowman is forced to cross from the 'pod' into the main spacecraft without a helmet. SteveBaker (talk) 20:11, 12 October 2008 (UTC)

Robotics - what is static stability?

I find definition of "static stability" as it relates to missiles and whatnot, but not as it relates to robotics. It sounds like it means just the concept that when a robot is at rest it should be stable, but I don't know for sure so I decided to query the WP community. Smaug 18:01, 11 October 2008 (UTC)

Ack nevermind. Just found the answer: "A statically stable robot can stand still without falling over." So I was right. Smaug 18:02, 11 October 2008 (UTC)

Stability is a slightly more subtle thing. With very great care, you can balance a coin on it's edge - but it's not stable - the slightest knock or jolt and it'll fall over. When you leave the coin lying on it's side - then it's very stable - it takes a HUGE jolt to make it flip over. That's "static stability". A statically stable robot would not only be able to stand still - but it would be able to do that with the power turned off - and it wouldn't fall over if you knocked it hard. SteveBaker (talk) 01:05, 12 October 2008 (UTC)

There is also a strange condition between stable and unstable called astable, where the system is in an unstable state, but if disturbed merely goes to another similarly unstable state. Our article redirects to multivibrator which is certainly an example of a device in an astable condition, but not the most informative one. A ball lying on a flat surface is in astable equilibrium, the slightest force on it will change its state, but only to another one exactly the same. A cone has all three types of stabilty: stable if on its base, unstable if on its apex, and astable if lying on its side. In terms of robotics, walking is a challenge to the designer because it requires astable equilibrium. A walker is continually falling, but never does so as he/she immediately moves to another falling state on the other leg. The mechanical equilibrium article appears only to cover static equilibrium. SpinningSpark 12:01, 12 October 2008 (UTC)

Jobs in the private spaceflight industry

It seems that private-sector spaceflight is really taking off (pun not intended) these days. I'm really excited about what's happening with it lately, and I really want to be a part of it all. I'm preparing to go into college starting next semester and I still haven't made up my mind on what I want to specialize in. My question is, what sort of degrees would be useful to the private spaceflight industry? My goal is to collect skills that would make me indispensable to a company in this field. I'm not particularly good at anything as it is. I have some very basic computer programming skills (I could get better, though) and I'm extremely bad at math (I'm aware that this is a huge drawback for what I seek). Does anyone have any suggestions for the career I should choose and what I should learn about in school? Thanks. 63.245.144.77 (talk) 20:11, 11 October 2008 (UTC)

My goal is to collect skills shows you are very wise, that is exactly what will make you indispensable in any field. I'm literally doing the same thing right now. I'm already "competing" against future neurologists(m.d.) who are still in their undergrad. Just think of the bell curve. You have to compete to be in the top 5, in whatever you genuinely want to excel at. The problem is you don't know who the other top four are. You have to be extremely motivated, and (possibly even more importantly) you have to know where to direct your efforts. Its just that (if you live in U.S.A.) most teachers who are great at teaching math, all conspire to make sure that they aren't your math teacher. Math is a dealbreaker, and you need to be an expert at quantitative reasoning. Specific advice: study rigorously and take the LSAT (its a puzzles test mainly), make yourself better at math (ask questions on the math ref desk anytime--always glad to help aspiring rocket scientists), and become a master of metacognition as that's the only way to change your brain's wiring about motivation. Sentriclecub (talk) 21:05, 11 October 2008 (UTC)

There are certain jobs that exist in any industry - personnel (aka human resources), accounts, etc., which you could go for. Jobs specifically related to space flight would be physics and engineering related, most likely, with some mathematicians as well. All of those involve quite a lot of maths, unfortunately... They will certainly need programmers to do simulations and things, but you would need the maths and physics knowledge in order to know what to program. I think, in short, you can't be a rocket scientist without maths! If you're interested in the space tourism side of the industry, you could try studying hospitality and tourism. While you would be learning about land based hotels rather than space hotels, there would be transferable skills. There will be lots of new legal issues with the new sector opening up, so I'm sure they'll need lots of lawyers - working out what jurisdiction a space hotel or moon base falls under could be quite interesting, as would extraterrestrial real estate. Really, they're going to need people from all disciplines, so just pick something that sounds interesting as a degree and then apply for whatever jobs you're suitable for (a lot of jobs just require a degree and it doesn't matter what it's in). --Tango (talk) 20:52, 11 October 2008 (UTC)

Learn Mandarin and business. If by "private spaceflight" you mean space tourism, it's likely many of the punters will be the Chinese nouveau riche showing off their wealth. If you mean it to include privately launched spacecraft in general (including satellites) then a lot of that business will be Chinese entrepreneurs blanketing the middle kingdom with cheap video messaging services and such. -- Finlay McWalter | Talk 21:21, 11 October 2008 (UTC)

There are really a vast range of skills that are going to be needed when private spaceflight really takes off - I would start with a solid grounding in math and science - probably physics, electronics and computer science would be good places to concentrate your efforts. But if you can learn as much breadth of science as possible - and enjoy doing it - then I think your speciality can be almost any science-related subject and you'll find jobs are available. But that wide knowledge base is critical. No small rocketry company can afford to have an extreme specialist in a very narrow field on their staff - they need generalists. SteveBaker (talk) 00:57, 12 October 2008 (UTC)

Obviously you'll want to master all of the intellectual disciplines enumerated by my venerable RefDesk colleagues, but you shouldn't neglect your physical health. Competition for the jobs of first generation space pilots will be nothing short of astronomical, and you will need to be in peak physical condition to remain in contention. Plasticup ^T/C 05:42, 12 October 2008 (UTC)

You're assuming "job in private space travel" means being a pilot - the vast majority of the jobs will be ground based. I didn't even discuss becoming a pilot because the competition is so great it's barely worth considering - you would need to already be an experienced aeroplane pilot, it's not a job you can get straight out of college. --Tango (talk) 11:46, 12 October 2008 (UTC)

Oh - sure. Forget being a pilot. They won't need many pilots and EVERYONE who ever dreamed of being Buck Rogers is going to be after that job. Supply and demand means that that's going to become an increasingly low-grade job. These space-planes are going to be automated to death and you won't need any more skills than (say) an airline pilot needs to fly one. I'm assuming that the interesting, high-dollar jobs are on the ground. Design, test, construction, launch. SteveBaker (talk) 15:10, 12 October 2008 (UTC)

I'd expect the spaceship pilots themselves to be recruited exclusively from the pool of experienced military test pilots anyway... --Kurt Shaped Box (talk) 19:07, 12 October 2008 (UTC)

I think Virgin Galactic are recruiting experienced commercial pilots, not just military. You need a lot of experience, though. While SteveBaker is right about the automation, that only applies to routine flights - if something goes wrong you need to be able to take manual control and know what to do. While lots of people will want the job, there won't be many people qualified, so the supply is actually very low and I would expect them to be extremely well paid (there will be equally well paid jobs on the ground and probably a few better paid jobs, though). --Tango (talk) 20:20, 12 October 2008 (UTC)

Organisms living inside crude oil

Just out of curiosity, are there any organisms that live in oil deposits in the ground? Surely there's at least some kind of bacteria that have taken advantage of the energy in the oil. 63.245.144.77 (talk) 20:14, 11 October 2008 (UTC)

Check out entropy, oil has less usable energy than the stuff it started out as. Then again, evolution is more a model to fit past data, and it really doesn't hold any prediction ability. (The evolution sentence was a joke. -sorry) If that dream organism existed, it sure would have a monopoly and would propogate very quickly. I'm guessing that biology doesn't work that deep below ground, its sequestered by too much rock. Any organism fit for glycolysis surely would have a field day down there! All those C-H bonds, maybe cockroaches could live down there? Good question, I am very curious myself and hope someone can explain this better. Sentriclecub (talk) 20:46, 11 October 2008 (UTC)

You are incorrect. Evolution is a testable theory that has significant prediction ability. Organisms that are fit for glycolysis are essentially all organisms (yes, including humans). Oil is not sugar. It doesn't matter how good we are at glycolysis; we will in no way be able to digest oil. Cockroaches can't live down there because there's no oxygen. Evolution theory essentially tells us that if there were a way for life forms to get down there and adapt, they would (organisms will adapt to fill open niches). However, they'd have to pass through the intermediate layers of rock, which do not support any life whatsoever. Obviously things cannot live in an area that supports no life, so it's pretty much impossible for any organisms to end up down there. Entropy is also not related to any of this, because entropy has little to do with how much chemical potential energy something has. The amount of useful work that can be done with a given amount of enthalpy is decreased by the temperature times the change in entropy (see Gibbs free energy). Oil has less usable energy (per unit mass, probably) than the organic matter it started out as due to inefficiencies in converting organic material to oil. --M1ss1ontomars2k4 (talk) 20:57, 11 October 2008 (UTC)

Endoliths have been found 3 km down in rock (ref). It seems the only limit on how deep these guys can go is increasing temperature, so it's possible they go down a lot deeper (this article claims maybe 7 km). -- Finlay McWalter | Talk 21:11, 11 October 2008 (UTC)

And there are places where oil literally oozes from the surface of the earth at sea level. No - the remoteness of oil from bacteria isn't a reason they might not have evolved to use oil as an energy source. SteveBaker (talk) 00:52, 12 October 2008 (UTC)

It's hard to find a niche on Earth that doesn't have some kind of life living in it, so I wouldn't be at all surprised if there is something living in oil deposits underground. I know nothing about it, though. --Tango (talk) 20:54, 11 October 2008 (UTC)

Note there are (a rather small minority of) oil geologists who subscribe to the abiogenic petroleum origin theory, wherein oil deposits are not only inhabited by microorganisms (particularly thermophiles, both bacteria and archaea), but are actually made by them. -- Finlay McWalter | Talk 21:03, 11 October 2008 (UTC)

Read Ananda Mohan Chakrabarty to learn about one scientist who created and patented organisms which eat oil. Not sure about the "in the ground" part. It might be undesirable to release bacteria which consumed all the oil under the ground. Edison (talk) 00:03, 12 October 2008 (UTC)

In order to extract usable energy from oil (which is essentially hydrocarbons), one would need be able to create compounds with lower internal energy (enthalpy, or H) than the hydrocarbons. This is generally accomplished via oxidation. However, in order to oxidize these compounds, a source of some usable oxidizing agent needs be present. The most likely source of this is oxygen itself, and underground oil has no access to this. From a purely chemical point of view, that oil underground is safe from nearly any biological organism that might be able to "eat it". There may be some that exist that can consume oil at the surface, but that is because of the availibility of free oxygen. --Jayron32.talk.contribs 11:48, 12 October 2008 (UTC)

Strange thermodynamics question

Say we have some ideal gas. It undergoes an adiabatic expansion from 1 Liter to 2 Liters and does no work. What are ΔU and ΔH for this process? I already know ΔU (ΔU = ΔQ + ΔW, all of which are zero), but I don't quite get ΔH. So far, we have that dH = dU + PdV + VdP. dU is zero, PdV is zero (no work done). But what's VdP? Since no work is done, can we say that the external pressure is zero and constant, and thus VdP is zero? --M1ss1ontomars2k4 (talk) 20:30, 11 October 2008 (UTC)

Your question is self-contradictory, I'm afraid. If you let the ideal (or any) gas expand adiabatically from V₁ = 1 L to V₂ = 2 L, it will perform work equal to integral of PdV from V₁ to V₂. On the other hand, if you put external pressure to zero, the gas will not do any work, but the expansion will not be adiabatic. The only way to stay adiabatic AND to have zero pressure is to have initial pressure = 0. That implies either an ideal gas at initial T=0, or ideal gas with zero particles in the volume considered. Hope this helps. --Dr Dima (talk) 03:58, 12 October 2008 (UTC)

Why would it not be adiabatic, if external pressure were zero? Reversible adiabatic processes are isentropic but this is not really reversible, if the external pressure were zero. --M1ss1ontomars2k4 (talk) 04:04, 12 October 2008 (UTC)

Intelligent Life in the Universe/Voyager Golden Record

I have been interested in the Golden Record that is on Voyager 1 and 2. I learned about how it is there in case Voyager encounters intelligent extraterrestrial life on its journey. If other intelligent extraterrestrial life created something similar and it went through our solar system, would we have any way of knowing? —Preceding unsigned comment added by 75.169.21.144 (talk) 21:28, 11 October 2008 (UTC)

It would probably be difficult to spot unless it passed very close to Earth. I expect any radio transmissions would be pointed back towards where it's come from, if there even are any (the Voyager craft will stop transmitting millennia before they reach other stars). Because they operate so far from the sun, they use nuclear power rather than solar panels, which means they don't have a particularly large reflective area so would be very bright. You would probably only see one if it passed close to Earth and you happened to point a large telescope in the right direction at the right time. --Tango (talk) 22:39, 11 October 2008 (UTC)

if such a device entered the solar system, it might have a circuit to trigger a beacon which would send radio sugnals to get our attention. When Voyager was launched, we did not know how to build a device which would "wake up" and send out signals after tens of thousands of years. Edison (talk) 23:56, 11 October 2008 (UTC)

It's probably safe to say that we still don't know how to build such a device. We have no idea what happens to our spacecraft after tens of thousands of years, since we've only had most of the supporting technology and advanced materials for less than a century. We could design a system to be "very reliable" and develop some system (software?) to wake it up in a few millenia, but there is no way we could test the reliability of it over thousands of years. HALT testing only goes so far in estimating certain types of failure. Nimur (talk) 00:37, 12 October 2008 (UTC)

Most of it doesn't need to be operational for 10,000 years, it just needs to sit there, so there isn't a whole lot that can go wrong (you would want some good shielding from radiation, etc, but that's about it). I think the real problem isn't the time, it's the cold, electronics break pretty quickly if they get too cold and the power requirements of keeping the probe warm for 10,000 years are most likely beyond us at the moment. --Tango (talk) 11:51, 12 October 2008 (UTC)

The point is that once Voyager gets away from the Oort cloud, there is no reason why it shouldn't keep moving off into the galaxy for millions or even billions of years. Over all that time - it is perhaps possible that some alien species would find it. It seems unlikely that they'd be able to decypher it though. The plaque and record are really poorly designed IMHO. SteveBaker (talk) 03:30, 12 October 2008 (UTC)

I think the likelihood of anything finding it is probably less than the likelihood of making any sense of it. Assuming something beyond dumb and impossible luck, any species that had the technology to locate that particular need in the interstellar haystack should be able to figure out the technology without too much difficulty, I'd imagine. --98.217.8.46 (talk) 03:33, 12 October 2008 (UTC)

That doesn't diminish how undeniably cool it is. We recorded the fundamentals of our species in a (hopefully) universal format and sent it careening into the depths of space. That has an intrinsic value to our species, even if it never facilitates communication with another. Plasticup ^T/C 05:23, 12 October 2008 (UTC)

I agree that it's an interesting statement, one that says more about the act of creating it than it does about its potential discovery. But it's worth noting that the selection of content says more about the people who created it than it does about the human species. Not all members of our species would agree on what the fundamentals were. For example, from what I can tell via Voyager Golden Record, there were no religious texts included whatsoever. No doubt Sagan may have thought that "Johnnie B. Goode" was more fundamental to understanding US culture than the Bible, but I'm sure there would be those who would vehemently disagree. ;-) --98.217.8.46 (talk) 13:33, 12 October 2008 (UTC)

It's about putting our best foot forward, I suppose. Plasticup ^T/C 16:14, 12 October 2008 (UTC)

There don't seem to have been any texts included at all, religious or otherwise. It looks like among the vocal music there was none with a religious text, but it's not as though an extraterrestrial could tell what the words meant anyway. -- BenRG (talk) 19:15, 12 October 2008 (UTC)

Well if we were really a space-faring society, i.e. one with personal and commercial inter-planetary travel, then I suspect that Space Traffic Control would monitor every rock much bigger than a ping-pong ball and fairly quickly notice a new metallic object entering the solar system. Obviously that makes assumptions about what the distant future of space travel might be like, but there is no reason to assume that ET will be as primitive as us. Dragons flight (talk) 06:03, 12 October 2008 (UTC)

If Voyager I ever travels through a planetary system similar to our solar system then it will be moving very fast indeed by the time it reaches the vicinity of an Earth-like planet's orbit. At the moment it is about 100 AU from the Sun and is travelling at about 17 km/s. If it fell into the gravity well of a star similar in mass to the Sun then at 1 AU from that star it would be travelling 10 times as fast, so 170 km/s. At this speed it covers a distance equal to the diameter of the Earth's orbit in about 20 days. So not much time to detect it, and quite difficult to catch it if it is detected. Gandalf61 (talk) 10:31, 12 October 2008 (UTC)

Ummm, your numbers are off. Falling into the sun's gravity well would only give you ~42 km/s at Earth's orbit. Dragons flight (talk) 16:51, 12 October 2008 (UTC)

42 km/s is escape velocity from the solar system starting from the Earth's orbit. But Voyager I is going much faster than escape velocity, mainly due to gravity assists from Jupiter and Saturn on its way out of the solar system. In the absence of interactions with planets, velocity of a free-falling spacecraft is inversely proportional to the square root of distance from the Sun (by conservation of energy), so 17 km/s at a distance of 100 AU becomes 170 km/s at a distance of 1 AU. Gandalf61 (talk) 20:19, 12 October 2008 (UTC)

I don't follow your calculation. Falling adds to the velocity, it doesn't multiply it by something (what it adds is dependant on initial velocity, but I can't see how you end up that result). --Tango (talk) 20:38, 12 October 2008 (UTC)

No, 17 km/s approximately goes to ${\sqrt {17^{2}+42^{2}}}\approx 45$. The energies, which are proportional to velocity squared, will add not multiply. You seem to just multiplying by 10 since that is the sqrt of 100, which is wildly wrong. Dragons flight (talk) 21:15, 12 October 2008 (UTC)

What does Radioactive Waste look like?

I read the article on radioactive waste, but I'm still not sure what the final "stuff" looks like. In popular culture, it's usually depicted as this glowing green stuff, but I have a feeling that's not really what it looks like. I guess in other words, what does the radioactive waste inside of those containers look like? ScienceApe (talk) 22:37, 11 October 2008 (UTC)

Radioactive waste can be unprocessed, in which case it's just raw fuel rods (containing fuel pellets). So that's just thin shiny cylinders filled with little metal cylinders the size of short stacks of coins. For reprocessed waste, high-level waste can be encapsulated in a number of ways; one is in glass blocks (or disks). -- Finlay McWalter | Talk 22:48, 11 October 2008 (UTC)

Radioactive waste (low level) can be clothing, rags, mops, cardboard, bottles, and many other materials which could become contaminated with radioactive materisl, as when there is a fluid leak in a power plant which releases radioactive materials that must be cleaned up. It goes in drums and gets stored. Edison (talk) 23:54, 11 October 2008 (UTC)

What's the fluid usually? ScienceApe (talk) 01:13, 12 October 2008 (UTC)

My understanding is that most high-level radioactive waste is produced in reprocessing plants—acids and washes used to separate out plutonium from other fission products and things like that. Probably just looks like sludge. If you google "hanford waste tanks" you can find images of a lot of liquid waste—nothing very interesting. Certainly not glowing green goo. --98.217.8.46 (talk) 03:16, 12 October 2008 (UTC)

So it would look like just some thick brown fluid? ScienceApe (talk) 14:42, 12 October 2008 (UTC)

For the record, the Cerenkov radiation in nuclear reactors causes them to glow blue, not green. Radioactive waste stored in water could also glow blue if there was enough of it, but more likely it would be broken up into small enough portions that there would not be a human perceptible glow. Dragons flight (talk) 04:13, 12 October 2008 (UTC)

Image licensing

HI,I AM DOING THIS PROJECT ABOUT NORTH AND SOUTH POLE AND I JUST WANT TO ASK YOU THAT IF I CAN PRINT SOME PICUTER THANKYOU VERY MUCH FROM MEENAKSHI —Preceding unsigned comment added by 68.183.31.96 (talk) 00:18, 12 October 2008 (UTC)

Yes

SpinningSpark 11:23, 12 October 2008 (UTC)

Smallprint for lawyers to read

Almost every photo on Wikipedia is freely licensed. This means that you may re-use or modify the photos (including printed copies). For any specific image, check its license information, which will provide details on what the image owner requires regarding re-use. Also see Wikipedia:Image copyright tags for general information. In general, if you are using these photos for a school project, that would be permissible under most of the image licenses on Wikipedia. Nimur (talk) 00:32, 12 October 2008 (UTC)

I have no idea what cutting pie has to do with the North and South poles....--el Aprel (^facta-_facienda) 00:36, 12 October 2008 (UTC)

Hi! It's OK to print most pictures that are on Wikipedia - but there are a few exceptions. All of the photos at our South pole, Antarctica, North pole and Arctic are OK to copy. You can also go to our sister site "WikiCommons" - and type "North pole" or "South pole" into the search box...you'll find also that there are "categories" of photos: Category:South_Pole and Category:North_Pole. There is also a bunch of photos of the Amundsen-Scott south pole station. All of those photos are OK to print.

If you need to know about other pictures on Wikipedia, what you need to do is to click on the photo you are interested in and when the image's own page pops up, it should look a bit like this one: HERE. Now you need to scroll down and look where it says either: "Licensing" or "Permission (Reusing this image)" - if it says something about "Fair use" then it's not OK.

SteveBaker (talk) 00:47, 12 October 2008 (UTC)

Though honestly if you are using it in an elementary school assignment I don't think anybody cares about the copyright status. --98.217.8.46 (talk) 03:29, 12 October 2008 (UTC)

You mean ANY school project? Who's going to sue you because you used, say, Coca-Cola's logo in a school assignment? That would just make the copyright owner look bad. --M1ss1ontomars2k4 (talk) 04:06, 12 October 2008 (UTC)

Well, I left out "any" because I could imagine some school projects in some scenarios where stuff like that could matter. (A dissertation is a "school project", in a sense, and you have to be mindful of copyrights with those.) But yeah. Really not worth worrying about for run-of-the-mill assignments. Falls under fair use pretty solidly. --98.217.8.46 (talk) 13:25, 12 October 2008 (UTC)

It is important to teach a respect for the copyright law. If kids get the idea that they can copy anything anytime - they are going to get into a lot of trouble in later life. Copyright laws are annoying and a big pain in the butt - but they are laws - and it's important that kids realise that. The idea that copyright holders don't "care" about little things like school projects is likely true - but that's not true of trademark law - where if you don't actively pursue infringements you can lose your ownership of them. Hence, CocaCola may well be forced to pursue even "irrelevant" infringement at the level of a high school project. SteveBaker (talk) 14:58, 12 October 2008 (UTC)

Oh yeah, sorry, I was forgetting about all those CocaCola billboards at the North Pole and the pictures of them in Wikipedia to catch out the unwary. Context! please. SpinningSpark 18:24, 12 October 2008 (UTC)

Large corporations will most certainly sue schools over misues of their trademarks: Disney has done it to day care centers and most other companies will as well. They will also always win, and it isn't only because they have lots of high powered lawyers. Under intellectual property law, there is a concept known as "trademark dilution"; once a trademark (be it a word, logo, or character, basically any symbol of your company) has entered the common lexicon, you can no longer use it as a trademark. Basically, if Disney did NOT aggressively defend its trademark, and was shown to allow, say, a day care center in Florida to use Mickey Mouse in their logos without proper permission, then it would set a precedent for anyone to use it. Disney cannot be selective in allowing infringements of its trademarks; it either has to expressly require that all uses are licenced, or it has to allow all uses by anyone for any purpose. As a result, large corporations can and do pursue these cases... --Jayron32.talk.contribs 18:35, 12 October 2008 (UTC)

What colour would you say best describes the upper mandible of a male Eclectus?

Question as topic. A user has suggested that 'candy-corn-coloured' (as stated in the article at present) is less than ideal. I'm inclined to agree.

Any suggestions? I'm thinking 'saffron' - though I'll readily admit that colour naming is not my strong point... --Kurt Shaped Box (talk) 02:52, 12 October 2008 (UTC)

It looks like scarlet (or orange) with a bright yellow tip, though I see what the phrase "candy-corn-coloured" means when I look at the photograph of the parrot. Just "candy corn", without the "coloured", might work for those who have seen candy corn (and for those who haven't, click here [14]) but candy corn has a white tip. ៛ Bielle (talk) 03:09, 12 October 2008 (UTC)

I agree. When writing for Wikipedia, one should strive to keep specific cultural references like "candy-corn" out of articles like that. We are read in dozens of countries around the world - most of whom will never have seen or heard of candy-corn. Most people in the USA know what it is - and what color it typically is - but I doubt whether people from other countries would know. Sure, you can provide a link to the article candy corn - but it would be much better to use a proper description of the color rather than to send people off on hunts for obscure references like that. Better still - just put a nice color picture in there. SteveBaker (talk) 03:26, 12 October 2008 (UTC)

People who don't know candy corn? My God, man! I don't believe it. I won't believe it! Plasticup ^T/C 05:15, 12 October 2008 (UTC)

Well, I've never heard of it. But I wouldn't want to interfere with your deeply held beliefs. Algebraist 09:08, 12 October 2008 (UTC)

Looks orange-yellow to me. [By the way, I have no idea what "candy-corn" is. ;-) ] Axl ¤ [Talk] 11:04, 12 October 2008 (UTC)

Candy corn is little multi-colored globs of sugar, usually served at Halloween in the U.S. I've never had a taste for it... --Jayron32.talk.contribs 13:00, 12 October 2008 (UTC)

Nobody has tasted it. None have been produced since 1934. The entire supply at that time has simply been recycled each year. -- kainaw™ 17:08, 12 October 2008 (UTC)

Yeah, every year the entire supply is melted down to make Circus peanuts. Interestingly, every year the entire suply of Circus peanuts is melted down to make candy corns, resulting in a never ending cycle of recycling inedible "candy". --Jayron32.talk.contribs 18:01, 12 October 2008 (UTC)

I think you've all forgotten that the sole purpose of candy corn is to insert two of them - pointy-end-down - between teeth and upper lip for the purpose of scaring little sisters into thinking you have turned into a vampire on all-hallows evening. Subsequent consumption of these objects can only be accidental. SteveBaker (talk) 19:46, 12 October 2008 (UTC)

I'd never seen, nor heard of 'candy corn' until yesterday. When I saw the term used in the article, I was imagining something like toffee popcorn - or maybe candyfloss. --Kurt Shaped Box (talk) 19:28, 12 October 2008 (UTC)

...which is PRECISELY why we shouldn't use it. SteveBaker (talk) 19:48, 12 October 2008 (UTC)

Copper(II) Sulfate Crystal

Hello. Are there any catalysts or fancy methods to make a solution of CuSO₄ • 5H₂O and water crystallize faster, clearer, and with clean cuts? Thanks in advance. --Mayfare (talk) 04:08, 12 October 2008 (UTC)

The problem is that speed and quality are exactly competing factors in crystalization. Any method used to make crystals quickly (such as rapidly dropping solution temperature, or "scratching", or adding seed crystals) will cause LOTS of small, imperfect crystals to form. If you want faster, then create a hot supersaturated solution of CuSO₄, and let it cool to below the precipitation temperature. Drop a small "seed crystal" of CuSO₄ • 5H₂O into the mixture, and viola, you'll get crystals, but they will likely be small and imperfect. If you want high quality crystals, you should aim for making them AS SLOW as possible. You should start with the same hot, supersaturated solution (this is generally made by boiling a saturated solution of CuSO₄ until the volume reduces, but there are ABSOLUTELY NO crystals in the solution) and then place it in some insulation, and let it cool VERY SLOWLY. After several days, crystals should form, and they should be nice and big and well defined. --Jayron32.talk.contribs 11:38, 12 October 2008 (UTC)

1876 Supplement to Harper's Bazar, No.13 and No. 25

I recently discovered two tapestry patterns from 1876 each are double sided on one side clothing patterns on the other side maybe embordry prints/designs. The patterns and instructions are printed on old newspaper and folded in half twice. The paper is very fragile to handle or measure without causing damage. I want to know more about these documents and how to share them? —Preceding unsigned comment added by Yma99 (talk • contribs) 09:35, 12 October 2008 (UTC)

I copied this question from the new users page as how to handle old newspapers is bit beyond a question on how to use Wikipedia. SpinningSpark 09:47, 12 October 2008 (UTC)

photographic chemicals

Up to the 1940's photographers knew various chemical formula for making black & white negatives and prints. Where can I find this chemistry? —Preceding unsigned comment added by 122.111.64.194 (talk) 09:58, 12 October 2008 (UTC)

A good place to start looking is History of photography and follow the links there. Timeline of photography technology may also link to useful articles. SpinningSpark 11:06, 12 October 2008 (UTC)

electron configuration of Barium

Hi is the following electron configuration for I have come up with for the element barium correct?

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2. Thanks. —Preceding unsigned comment added by 139.222.240.110 (talk) 12:43, 12 October 2008 (UTC)

Looks right to me. Barium is in period 6, group IIA, which should have the configuration "...6s2" and it doesn't look like you missed any core orbitals either. --Jayron32.talk.contribs 12:57, 12 October 2008 (UTC)

Yeah, that's right. Source: Clicky —Cyclonenim (talk · contribs · email) 13:58, 12 October 2008 (UTC)

thanks :) —Preceding unsigned comment added by 139.222.240.66 (talk) 17:50, 12 October 2008 (UTC)

Using nuclear weapons as a propulsion system for spacecrafts

I'm reading Neal Stephenson's new book Anathem and in it he describes a rather unusual propulsion system for spacetravel (this isn't a big spoiler at all, feel free to read on even if you haven't read the book yet).

The idea is this: a spaceship would have one side on it that is covered by a so-called "pusher plate", which acts as a big shield, capable of withstanding a nuclear blast. A nuclear weapon is deployed on the other side of it and detonated, and thus the spaceship would fly off with enourmous velocity (essentially rocket jumping, but with nuke instead of a rocket and a spaceship instead of a player).

I've thought a little bit about this, and it seems to me that this wouldn't work. The reason a nuclear weapon will blow everything around it to smithereens (like that famous exploding house that we've all seen), is that it has an enourmous shockwave. But space is essentially a vacuum, there's no medium for a shockwave to propagate through. So it wouldn't impart basically any momentum to anything near it. The only thing that would happen (I imagine) is that it releases lots and lots of energy through electromagnetic radiation, which would barbeque any organic material nearby, but it wouldn't actually have a shockwave. I don't know if electromagnetic radiation departs any momentum on the things it hits, but even if it does, it's not all that much, is it?

Look at the sun: the sun is basically a mindnumbingly big nuclear reaction, much much bigger than any nuclear weapon, yet it doesn't "propel" it's satellites to enourmous speeds. The earth isn't flying off into space because of the sun. So why would this system work? 195.58.125.56 (talk) 17:51, 12 October 2008 (UTC)

See Project Orion (nuclear propulsion). Its "performance" section explains how they intended to design special bombs such that they'd maximise the kinetic yield of the nuclear explosive, which they'd then impart to the spacecraft itself by collision. -- Finlay McWalter | Talk 17:56, 12 October 2008 (UTC)

(e/c) Neal stephenson is just one in a long line of science fiction authors who have used the idea proposed by Stanislaw Ulam in or about the late 1950s. See Nuclear pulse propulsion.--Fuhghettaboutit (talk) 17:58, 12 October 2008 (UTC)

Yep - project Orion is famous in Sci.Fi. circles - lots of books have used it. I'd argue that the rather subtle manouvering that's implied would be impossible for such a craft - you've only got an all-or-nothing thrust mechanism. You can't do a "three second orbital injection burn" with a motor that either kicks you up the backside with 20 megatons or does nothing at all. But with such a large craft - you'd need something pretty powerful. SteveBaker (talk) 19:39, 12 October 2008 (UTC)

If I were building such a craft I would include a conventional rocket engine as well for the subtle stuff. Just use the nukes for simple acceleration. You need to be able to get a safe distance from anything you don't want to blow up/irradiate anyway, which requires some kind of propulsion. --Tango (talk) 20:40, 12 October 2008 (UTC)

What good an anal probe?

I've just thinking about all those personal accounts of (supposed) abduction and experimentation upon humans by aliens. How much useful data would one actually be able to collect on a human subject by probing its anus? Can anyone think of what it is that the prober might actually be trying to discover about the probee by doing this?

The taking of skin, blood, sperm and tooth samples at least kinda makes sense from a 'research into the species' viewpoint. --Kurt Shaped Box (talk) 19:24, 12 October 2008 (UTC)

It's a particularly unpleasant and degrading experience which elicits sympathy from those the abductee tells about it. --Tango (talk) 19:35, 12 October 2008 (UTC)

Apparently aliens are fascinated by cows (e.g. cattle mutilation). Perhaps they are looking for evidence of beef consumption? Dragons flight (talk) 19:50, 12 October 2008 (UTC)

Temperature and eating habits come to mind. —Cyclonenim (talk · contribs · email) 20:53, 12 October 2008 (UTC)

how much gas?

How much gas would an average human be able to pass in his or her lifetime? ("Would" because normally we don't try to maximize this. I mean if they were to eat a lot of beans all their life -- nothing chemical/artifical). —Preceding unsigned comment added by 82.120.232.170 (talk) 21:41, 12 October 2008 (UTC)