Coincidence

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Coincidence (from Latin con , 'common', and incidere , 'to fall') is a temporal and / or spatial coincidence of events or objects.

To infer a causal (causal) connection from the coincidence of two or more events is logically a fallacy , which is called cum hoc ergo propter hoc (Latin).

Sensory perception

In physiological perception , two signals are perceived as one (and are then called coincident) if their time difference is less than a period of time that is dependent on the sense organ. When seeing , this period is 20–30 ms. While listening, stimuli that are more than 3–4 ms apart can be separated. The sequence, however, can only be determined for each sense organ when the stimuli are at least 30–40 ms apart.

organization

In organizational science, coincidence is a criterion for fulfilling an assignment or a service. The determination of coincidence takes place in several related steps:

  • The identity of the objects or people in question is established.
  • The identities are compared with the known specifications.
  • The time of collapse is determined.
  • The place of the meeting is documented.

These determinations can be made fully automatically with appropriate aids. If there is no connection in place, time or if the identities deviate from the specifications, or if such a connection is not recognized, then there is no coincidence and the order is not fulfilled or the service is not performed. This applies accordingly, for example, in healthcare or logistics.

Radiation measurements

Experimental physics

In physical measurements, coincidence denotes the "simultaneous" occurrence of signals from two (or more) particle or radiation detectors (more precisely: the case that their time difference is below a given resolution time ). If only those signals are registered that meet such a coincidence condition, then the events of a specific, interesting type can be separated from the "background" of non-interesting, but possibly much more frequent events. With this method, Bothe and Geiger were the first to demonstrate the Compton effect (detailed description: see coincidence measurement ).

The coincidence events sought in each case are referred to as true coincidences in contrast to possible random coincidences. In the case of a true coincidence, a single physical process is the cause of both detector signals; in the case of a coincidental one, two different processes that occur independently of one another. Therefore, the two detector signals of the true coincidence are correlated in time, i. H. at a certain time interval from each other; at other time intervals, only random coincidences are found. This is used to differentiate the two types of coincidence, so that the separately measured background can be subtracted from the measurement result at random coincidences.

In some cases, the events of interest are identified by anticoincidence rather than by coincidence . The condition for the registration is then, for example, that a signal in detector 1 is not accompanied by a signal in detector 2.

Positron emission tomography

The positron emission tomography (PET), an imaging examination method of the medicine, also uses coincidence detection to suppress undesirable events and at the same time for the accurate location of the radiation source. With a large number of detectors working simultaneously, the spatial distribution of a radioactive substance in the examination volume is measured by determining which detectors respond in coincidence and how often.

Color television technology

In (analog) color television technology , coincidence denotes the temporal correspondence between the signal edges in the luminance signal and in the color difference signals .

Because of the lower bandwidth in the color difference signal channels, the edges there are less steep and are more delayed. On the transmitter side, the luminance signal is delayed to such an extent that the edges recognizable in the modulated color difference signal match those of the luminance signal in the transmitted signal. On the receiver side, the correspondence of the signal edges in the luminance signal and in the color difference signals is achieved by a transit time compensation of the order of magnitude of 1000 ns.

The spatial correspondence of the three color channels is known as convergence , especially in the case of picture tubes .

See also

Web links

Wiktionary: coincidence  - explanations of meanings, word origins, synonyms, translations