Oscillator relay

In the first chapter, a very primitive radio transmitter was described, and it was mentioned that it was similar to the one on the famous ship Titanic. The transmitter shown in Fig. 19.2 is closer to the Titanic s radio, because it has a capacitor in parallel with the inductor, making a tuned resonant tank circuit (see index if necessary). This concentrates the transmissions at one particular frequency range. Also, the oscillating relay repeats those transmissions automatically. If an antenna were connected, as on page 181, the radio waves could be heard on an AM radio farther away. 

No a priori knowledge of the system time constants is needed. The method automatically results in a sustained oscillation at the critical frequency of the process. The only parameter that has to be specified is the height of the relay step. This would typically be set at 2 to 10 percent of the manipulated variable range. 

Numerical simulations indicate that relay of cAMP pulses represents a different mode of dynamic behavior, closely related to oscillations. Just before autonomous oscillations break out, cells in a stable steady state can amplify suprathreshold variations in extracellular cAMP in a pulsatory manner. Thus, relay and oscillations of cAMP are produced by a unique mechanism in adjacent domains in parameter space. The two types of dynamic behavior are analogous to the excitable or pacemaker behavior of nerve cells. 

Theoretical models shed light on additional aspects of pulsatile cAMP signaling in Dictyostelium. First, like Ca + spikes, cAMP pulses are frequency encoded. Only pulses delivered at 5-min intervals are capable of accelerating slime mold development after starvation. Simulations indicate that frequency encoding is based on reversible receptor desensitization [76]. The kinetics of receptor resensitization dictates the interval between successive pulses required for a maximum relay response [78]. Second, cAMP oscillations in... 

The bombing test is use to check the tightness of components which are already hermetically sealed and which exhibit a gas-filled, internal cavity. The components to be examined (e.g. transistors, 1C housings, dry-reed relays, reed contact sw/itches, quartz oscillators, laser diodes and the like) are placed in a pressure vessel which is filled with helium. Operating with the test gas at relatively high pressure (5 to 10 bar) and leaving the system standing over several hours the test gas (helium) will collect inside the... 

A somewhat different view is supported by a number of other studies. Behavioural rhythmicity persists in SCN-lesioned rodents under the influence of either periodically available food (Davidson Stephan 1999, Stephan et al 1979) or continuous treatment with methamphetamine (Honma et al 1992). Rhythmicity of at least some circadian genes persists in isolated peripheral tissues for periods of time ranging from several days to two or three weeks (Yamazaki et al 2000, our unpublished results). Removal of the retina (which is known to contain its own circadian oscillator Tosini Menaker 1996) changes the distribution of free-running periods of locomotor activity and the duration of active time (a) (Yamazaki et al 2002a). To pursue our metaphor, these results suggest that circadian signals may be relayed to the periphery by a baton rather than a whip the SCN may indeed be the conductor of an orchestra composed of dozens, if not thousands of potentially independent oscillators. 

The mechanism for ultrasonic emulsification is primarily that of cavitation. A typical sonicator for emulsification consists of a velocity transformer coupled to a transducer, capable of oscillating in a longitudinal mode, where the velocity transformer is immersed in the liquid. Figure 4 illustrates the basic parts of a sonicator with a continuous flow attachment, like the one used in this work. In this case, the flow cell is secured to the velocity transformer by a flange and a Teflon 0-ring. The intensity of cavitation depends on the power delivered to the velocity transformer, which is relayed to the transducer from a variable transformer or some other control device not shown in Fig. 4. 

Fig. 14 Schematic of the combined QCM-ECIS setup. In order to perform electrochemical impedance analysis of the adherent cell layer on the substrate electrode, an additional low impedance platinum dipping electrode is introduced into the measurement chamber. Impedance analysis of the cell layer (ECIS mode) is performed in the frequency range between 1 Hz and 1 MHz, whereas the shear oscillation is analyzed close to its fundamental resonance between 4.97 MHz and 5.04 MHz. A computer-controlled relay allows switching between both modes automatically...

In another method, called ATV (auto-tune variation), the controller is replaced by a relay of amplitude h%. The period is divided in each cycle by two up to the occurrence of oscillations. If a is the amplitude of oscillations, the ultimate gain can be calculated as ... 

The above observations account for the periodic secretion and relay of cAMP signals in the course of aggregation of amoebae on agar. The question which now arises is how to determine the molecular mechanism responsible for these two modes of dynamic behaviour. The theoretical study of experimentally based models clarifies the origin of relay and oscillations and permits us to explain why certain cells behave as centres while other cells act just as relays in the course of aggregation. 

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