الثلاثاء، 23 مايو، 2017

تعبير بالانجليزي عن صدفه

عبير بالانجليزي عن صدفه

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coincidence

Is a temporal and / or spatial coincidence of events or interactions of objects.

To conclude from the coincidence of two or more events to a causal (causal) connection logically represents a fallacy which is called cum hoc ergo propter hoc (lat.). Nonetheless, the term language is sometimes used to indicate a suspected causal connection of coincident events.

Table of Contents

• 1Sinneswahrnehmung

• 2Organisation

• 3Strahlungsmessungen

o 3.1Experimentalphysik

o 3.2Positronen emission tomography

• 4Farbfernsehtechnik

• See also

• 6Weblinks

Sensory perception

In physiological perception, two signals are perceived as one (and are called coincident) when their temporal difference is less than a time-dependent period. When viewed, this period is 20-30 ms. When listening, stimuli that are more than 3-4 ms apart can be separated. The order of succession, on the other hand, can only be determined in each sense organ if the stimuli are at least 30-40 ms apart.

organization

In organizational science, coincidence is a criterion for fulfilling an order or service. In this case, the determination of coincidence takes place in a plurality of contiguous steps:

• The identity of the objects or persons concerned is determined.

• The identities are compared with the known specifications.

• The time of the coincidence is determined.

• The location of the meeting is documented.

These findings can be carried out automatically with the help of appropriate tools. If there is no connection in place, time, or if the identities deviate from the specifications, or if such a connection is not recognized, there is no coincidence and the order is not fulfilled or the service is not performed. This applies, for example, to health care or logistics.

radiation measurements

experimental Physics

In the case of physical measurements, coincidence means the "simultaneous" occurrence of the signals from two (or more) particle or radiation detectors (more precisely, their time difference is below a predetermined resolution time). If one only accepts those signals which satisfy such a coincidence condition, then the events of a particular, interesting type can be separated from the "background" of events which are not more interesting but possibly much more frequent. With this method, Bothe and Geiger first demonstrated the Compton effect (detailed representation: see coincidence measurement).

The coincidence events sought are referred to as true coincidences, in contrast to eventual coincidences. In the case of a true coincidence, a single physical process is the cause of both detector signals, in the case of a random two different and independent processes. Therefore, the two detector signals of the true coincidence are temporally correlated, i.e., at a certain time interval from each other; At other intervals, only coincident coincidences are found. This is used to distinguish the two coincident types, so that the separately measured background can be subtracted from coincident coincidences by the measurement result.

In some cases, the events of interest are identified by coincidence, 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

Positron emission tomography (PET), a medical imaging technique, also uses coincidences to suppress unwanted detection events, but also to accurately determine the location of the radiation source. With a large number of detectors operating at the same time, the spatial distribution of a radioactive substance in the examination volume is measured by determining which detectors respond as often to coincidence.

Color television technology

In (analog) color television technology, coincidence refers to the temporal coincidence of the signal edges in the luminance signal and in the color difference signals.

Because of the smaller bandwidth in the color difference signal channels, the edges are less steep and are delayed more. The luminance signal is delayed so far that the flanks recognizable in the modulated color difference signal coincide with those of the luminance signal in the transmitted signal. On the receiver side, the matching of the signal edges in the luminance signal and in the color difference signals is achieved by a delay compensation of the order of 1000 ns.

The spatial correspondence of the three color channels is referred to as convergence, in particular in the case of picture tubes.


See also

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