Living systems temporal periodicity

Time is the particular instant at which a structure exists or a process occurs, or the measured or measurable period over which a structure endures or a process continues. For the study of all aspects of living systems as we know them, for the measurement of durations, speeds, rates, and accelerations, the usual absolute scales of time—seconds, minutes, days, years—are adequate. A concrete system can move in any direction on the spatial dimensions, but only forward— never backward—on the temporal dimension. 

Chemical systems with complex kinetics exhibit a fascinating range of dynamical phenomena. These include periodic and aperiodic (chaotic) temporal oscillation as well as spatial patterns and waves. Many of these phenomena mimic similar behavior in living systems. With the addition of global feedback in an unstirred medium, the prototype chemical oscillator, the Belousov-Zhabotinsky reaction, gives rise to clusters, i.e., spatial domains that oscillate in phase, but out of phase with other domains in the system. Clusters are also thought to arise in systems of coupled neurons. 

Some degree of temporal resolution of emission may be obtained by incorporating a phosphoroscope attachment in the simple apparatus described above. A mechanical or electronic device is used to allow periodic and out-of-phase excitation and detection of luminescence. In the simplest case a mechanical shutter interrupts the excitation beam periodically and the detection system is gated so that emission is observed only after a fixed interval of time has elapsed after excitation. Under these conditions short-lived processes such as prompt fluorescence will have decayed to zero intensity and only longer-lived emission will be recorded. For mechanical devices the limit of measurable lifetime is of the order of 1 ms, thus allowing time resolved studies to be made of certain phosphorescence and delayed emission procesres (see ... 

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