Clock phenomena

The absence of purely kinetic oscillations in the case of a network of first-order reactions does not exclude the possibility of periodic phenomena in chemically reacting systems. Indeed many such phenomena are known and their study has exerted a particular fascination on chemical kineticists from the early days of physical chemistry. With the rapid development of kinetics in biochemistry and biophysics, the interest in periodic phenomena is rapidly increasing, especially in connection with the study of photoperiodism in plants and animals, of rhythmic processes in living organisms and of clock phenomena in general. 

Clock-type induction periods occur in the spontaneous ignition of hydrocarbon-oxygen mixtures [2], in the setting of concrete and the curing of polymers [3]. A related phenomenon is the induction period exhibited... 

Synchronization.—This phenomenon apparently was observed for the first time by Huyghens (1629-1695) who reported the following curious observation. Two clocks fixed on a wall exhibited a certain lack of synchronization (one clock was going faster than the other). However, when the same clocks were fastened on a thin wooden board, they were found to be in synchronism. 

Other chemical changes can be much faster than the RNA conformational changes illustrated here. Photodissociation of sodium iodide (Nal) in the gas phase occurs on the time scale of a few picoseconds (10-12 seconds). To measure this phenomenon, Nal molecules are irradiated by a sub-picosecond ultraviolet pulse of radiation, and the subsequent events are clocked by another short light pulse that detects the newborn... 

Glycolytic oscillations in yeast cells provided one of the first examples of oscillatory behavior in a biochemical system. They continue to serve as a prototype for cellular rhythms. This oscillatory phenomenon, discovered some 40 years ago [36, 37] and still vigorously investigated today [38], was important in several respects First, it illustrated the occurrence of periodic behavior in a key metabolic pathway. Second, because they were soon observed in cell extracts, glycolytic oscillations provided an instance of a biochemical clock amenable to in vitro studies. Initially observed in yeast cells and extracts, glycolytic oscillations were later observed in muscle cells and evidence exists for their occurrence in pancreatic p-cells in which they could underlie the pulsatile secretion of insulin [39]. 

Loros Of course, Synecococcus doesn t have a nucleus but it displays perfectly functional rhythms. There may be something there. Who has replicated the Acetahularia work Another perfectly reasonable explanation of the. Acetabularia phenomenon is that parts of the clock requiring daily transcription are encoded for in the chloroplast. It could be a plastid clock. 

A rare but especially intriguing experience reported from some d-ASCs is that the direction of flow of time seems to change. An event from the future happens now the experiencer may even know it does not belong in the now but will happen later. An effect seems to precede the cause. Our immediate reaction, resulting from our deeply ingrained belief in the total reality of clock time, is that this cannot be "true," and we see the phenomenon as some confusion of time perception or possibly a hallucination. 

Fluctuations are inherent to any experimental chemical system. Even if these fluctuations are infinitesimally small, they are sufficient to drive the system away from an unstable state. The optically active state is characterized by two equivalent options starting from an unstable racemic situation, the system can evolve into either an R configuration or into an S one. However, each individual experiment remains unpredictable as to which of the optically active states the system will move towards. For a large number of experiments an equal and random distribution between R and S dominance is expected if the initial conditions do not involve any preferences. Due to this unpredictability of the chiral configuration, the phenomenon of mirror-symmetry breaking introduces another element of stochastic behavior into chemical reactions different from that occurring in clock reactions [38,39]. 

Another important feature of mass transfer processes is related to the very physical nature of the phenomenon. As such it is easily quantifiable and predictable. Thus the rate of mass transfer to and from an electrode may be determined a priori for a given electrochemical system. As a result this rate may be used as natural built-in clock by which the rate of other electrochemical processes may be measured. Such a property was apparent in our earlier discussions related to electrode kinetics (electron transfer and coupled chemical reactions). Basically it proceeds from the same idea as that frequently used in organic chemistry for relative rate constant determinations, when opposing a chemical reaction of known (or taken as the reference in a series of experiments) rate constant against a chemical reaction whose rate constant (or relative rate constant) is to be determined. Many such examples exist in the organic literature, among which are the famous radical-clocks ... 

If excess iodic acid solution is added to aqueous sulfurous acid it is well known that iodine separates from the mixture. The reaction occurs immediately if the liquids are concentrated however, if the same liquids are used in dilute form it leads to the remarkable phenomenon that such a mixture treated with a little starch initially remains completely clear, and only after the passage of a certain amount of time suddenly becomes blue, which may require a few seconds up to minutes. Using the same amounts of the two solutions and maintaining a specific temperature, the time interval from the moment of mixing to the appearance of the blue color is entirely constant, with a value that can easily be determined with a clock. 

In models with several ground states (3 state Potts model, clock models etc.) a further wetting phenomenon may occur at interfaces between coexisting domains e.g., in a model with an interface between domains in states 1 and 2 the third phase may intrude in the interface (Selke, 1984 Sega et al., 1985 Dietrich, 1988). 

Synchronization is a fundamental phenomenon found in nonlinear oscillatory systems [12]. The most prominent example, known since long time ago (Huygens, 1665), is the adjustment to a common frequency of two pendulum clocks with slightly different frequencies, coupled via a common support. This type of synchronization between two coupled systems is called mutual synchronization. In the following we are interested in the synchronization of a system to a periodic driving, called forced synchronization. In a synchronized state the systems dynamics is entrained to the signal, i.e. the system inherits the very same frequency of the signal (1 1 synchronization) or the frequencies are locked with some rational n m relation. This... 

As a certain concentration of CHBr (C02H)2 is needed for reaction 9 to occur long induction period for oscillations is expected, a phenomenon, which is also observed experimentally. During this induction period, the concentration of Br" is small and mechanism II dominates due to the slow conversion of Ce4+ into Ce3+ and the accumulation of brommalonic acid (reaction 8). Step 9 (8.71) results in the change of the blue color of solution to red resetting the chemical clock for the next oscillation. In fact, the oxidized form of the catalyst can also react directly with malonic acid, so there may be less than one bromide ion per cerium (III) ion produced. 

In spite of everything, the station personnel continued to believe that the reactor core was covered by water, but at the same time, by some unknown phenomenon, that it had been damaged. The station superintendent would later say ... I don t think that in my mind I was really convinced that the core had remained completely uncovered or uncovered in a substantial measure at that time (eight o clock in the morning) . 

The time difference t in IS is therefore always larger than the time difference r in IS, where the clock is at rest, i.e., a moving clock loses time as compared to a clock at rest. This phenomenon is called relativistic time dilation and might briefly be summarized by the statement that "proper time is always the shortest time between two events". 

---