Multiple clocks

Circadian Rhythms. Figure 1 Mammalian circadian system is organized as a hierarchy of multiple clocks thatfunction to synchronize timing of internal processes between each other and with the environment. See details in the text. 

What happens in the above case if we switch the order of the statements around In this case, since the value of Temp is used before its assignment, its value needs to be retained across multiple clock cycles, thereby inferring flip-flops for Temp. Temp models the internal state of the always statement. This is shown in the following example, where Temp is used before its assignment. 

It is possible to have a single module that has multiple clocked always statements. Here is such an example of multiple clocks used in a single model. 

Figure 2-50 Multiple clocks within an always statement.

Even the tiniest inaccuracies in the measurement of the time interval between when the signal is sent and when it is received can cause substantial errors— differences of several feet or more— in the triangulation calculation that determines the user s physical location. As a result, GPS receivers rely heavily on standard atomic frequency references. Each satellite has a small handful of local atomic clocks onboard (multiple clocks are used to provide a system of redundancies, a way to ensure reliability and accuracy). Each clock is calibrated to a master atomic clock measuring UTG and managed by the U.S. Naval Observatory. In general, each clock on a GPS receiver, no matter where on Earth it is located, will be no more than 500 nanoseconds to 1 millisecond out of sync with UTG. Time measurement not only facilitates the movement of cars, boats, and airplanes on the earth... 

In designs where there are multiple clock domains and datapaths between the clock domains, TC will place clocks in separate capture clock groups, provided they are independent clocks sources in the testmode and not multiplexed to one test clock. Further, the clock skew must be accounted for in the clock waveforms. 

The code fragment is now finished after the eighth clock cycle. Note that there are stiU three clock cycles during which there are idle stages in the multiplication pipeline. The compiler would look for other statements in the code that could be overlapped with those already in process. 

Banked Memory. Another characteristic of many vector supercomputers is banked memory. The main memory is usually divided into a small number of electronically separate banks. A given memory bank can absorb or supply operands at a much slower rate than the rate at which the central processing unit (CPU) can produce or use data. If the data can be spread across multiple memory banks, the effective memory bandwidth, or rate at which memory can absorb or supply data, is increased. For example, if a single memory bank can supply one operand every 16 clock cycles, then 16 memory banks would enable the entire memory subsystem to deflver one operand per clock cycle, assuming that the data come sequentially from different memory banks. 

Time-Triggered Actions. In addition to explicit stimulus from exemal actors, a system may need to respond on its own to the passage of time. Model this also as an external input to the system, driven by a clock of arbitrarily precise frequency. Pick a suitable name for this action e g. end of day, or tick. For clarity, separately define named effects to specify what happens at that time e.g. clear outdated reservations. As always, you can have multiple specifications for the action. 

Further extensions of the model are required to address the dynamical consequences of these additional regulatory loops and of the indirect nature of the negative feedback on gene expression. Such extended models have been proposed for Drosophila [112, 113] and mammals [113]. The model for the circadian clock mechanism in mammals is schematized in Fig. 3C. The presence of additional mRNA and protein species, as well as of multiple complexes formed between the various clock proteins, complicates the model, which is now governed by a system of 16 or 19 kinetic equations. Sustained or damped oscillations can occur in this model for parameter values corresponding to continuous darkness. As observed in the experiments on the mammalian clock. Email mRNA oscillates in opposite phase with respect to Per and Cry mRNAs [97]. The model displays the property of entrainment by the ED cycle... 

Rosbash You could back off the specifics of PAS domains in BMAL and White Collar. The more general question is whether we are in a position to say with confidence that these things did evolve multiple times, or are there very strong molecular connectors between systems Ravi Allada and I have recently published a paper on CK2, a kinase and a new clock mutant (Lin et al 2002). CK2 is implicated in plant clocks, Neurosopora clocks and now in animal clocks. My feeling is that the jury is still out as to whether we have hit on the key common proteins or whether it is independent evolution. 

Garceau NY, Liu Y, Loros JJ, Dunlap JC 1997 Alternative initiation of translation and time-specific phosphorylation yield multiple forms of the essential clock protein FREQUENCY. Cell 89 469-476... 

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