Role of Feedback

In power supplies, we can either change the applied input voltage or increase the load (this may or may not be done suddenly). Either way, we always want the output to remain well regulated, and therefore, in effect, to reject the disturbance. 

But in practice, that clearly does not happen in a perfect manner, as we may have desired. For example, if we suddenly increase the input to a buck regulator, the output initially just 

We see that there are several such delays in the circuit before we can get the output to stabilize again. Minimizing these delays is clearly of great interest. Therefore, for example, using smaller filter components (L and C) will usually help the circuit respond faster. 

We see that an optimum feedback loop is neither too slow, nor too fast. If it is too slow, the output will exhibit severe overshoot (or undershoot). And if it is too fast (over-aggressive), the output may ring severely, and even break into full instability (oscillations). 

The study of how any disturbance propagates inside the converter, either getting attenuated or exacerbated in the process, is called feedback loop analysis. As mentioned, in practice, we test a feedback loop by deliberately injecting a small disturbance at an appropriate point inside it (cause), and then seeing at what magnitude and phase it returns to the same point (effect). If, for example, we find that the disturbance reinforces itself (at the right phase), cause-effect separation will be completely lost, and instability will result. 

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In the skill-based mode, recovery is usually rapid and efficient, because the individual will be aware of the expected outcome of his or her actions and will therefore get early feedback with regard to any slips that have occurred that may have prevented this outcome being achieved. This emphasizes the role of feedback as a critical aspect of error recovery. In the case of mistakes, the mistaken intention tends to be very resistant to disconfirming evidence. People tend to ignore feedback information that does not support their expectations of the situation, which is illustrated by case study 1.14. This is the basis of the commonly observed "mindset" syndrome. 

Based on a previously constructed model, two crucial questions with respect to dynamic properties were investigated [296] (i) What is the role of feedback regulation in maintaining the stability of the steady state. In particular, does the feedback regulation contribute to a stabilization of the in vivo metabolic state (ii) Is it possible to distinguish between different metabolic states That is, does knowledge of the metabolic state, characterized by the flux distribution and metabolite concentrations, indeed constrain the dynamic properties of the system ... 

The s terms in Eq. (80) contribute only the term E,2 in Eq. (97). Thus, the term represents the quantum diffusional. v-terms in the Fokker-Planck equation. The other terms in Eqs. (93)-(100) originate in the drift terms of the Fokker-Planck equation. The terms B12 and C in Eqs. (93)-(94) play the role of feedback terms that pump quantum fluctuations into the classical Bloembergen equations. If the s terms in Eq. (80) do not appear (the classical case), the term in Eq. (97) does not appear, either. In this case the subset (95)—(100) with zero initial conditions has zero solutions and in consequence leads to the first truncation [171]. 

The dependence of the control field e( , X) on the state could be quite complex, as a solution of Eqs. (2) and (3) would suggest. In general, this relation may only be revealed numerically. Furthermore, the dependence of the control field on the target deviation eigenvalue X emphasizes the inherent role of feedback in the control design process. This relation also indicates the nonlinear eigenvalue role of X. 

Here the central steady state at y k, 0.4... and the two extremal steady states with y 0.0... and 1.0... are stable, while the two remaining steady states at y k, 0.3... and 0.5... are of saddle type and therefore unstable. Of these, the central one gives the optimal concentration for component B. The unstable ones that are adjacent to the middle one give moderate concentrations for B, while the extremal steady states with y k 0.0... and 1.0... produce hardly any amount of B according to the bottom plot of xs y) in Figure 4.31. We shall return to this example in Figure 4.38 with further comments on the robustness of the optimal central steady state and on the beneficial role of feedback in chemical/biological systems. 

These results reflect the radical reorganization of the climate system that took place during comparatively short periods. The Holocene seemed (compared with these changes) a period of a comparatively stable climate. There is no doubt that without climatic feedbacks the growth in GHG concentration in the atmosphere should cause climate warming. However, the actual situation is much more complicated, and to understand it, it is necessary to reliably detect and estimate the role of feedbacks. Otherwise, it is impossible to reliably predict future climate change. Since peat bogs are one of the most important sources of such information, they should be protected. 

M.T. Sullivan and H.A. Stone, The role of feedback in microfluidic flow-foctrsing devices, Philosophical Transactiorrs of the Royal Society a-Mathematical Physical and Engineering Sciences, 366,2131-2143, (2008). 

Bliss, R.D., P.R. Painter A.G. Marr. 1982. Role of feedback inhibition in stabilizing the classical operon. J. Theor. Biol. 91 Vll-9i. 

FIGURE 23.22 The role of feedback inhibition in regulation of purine nucleotide biosynthesis. 

Recall Discuss the role of feedback inhibition in the anabolism of purine-containing nucleotides. 

A final observation is that, according to our model, only feedbacks able to reduce reputation produce effects. Hence, to save traffic, feedbacks with score 1 are not forwarded. The negative role of feedbacks (w.r.t. the reputation values) results in pushing node reputation towards low values. To contrast this effect, we introduce an aging mechanism producing a bonus the reputation of each node is increased (up to 1) by S each t time, where 6 and r are parameters suitably fixed. For example, setting d = 0.1 and t = 360 seconds, a node that has reputation score 0 (for example, because of a network problem occurred) and that does not interact with other nodes recovers a reputation score equal to 1 after 1 hour. 

The technological evidence from the instruments available suggests that until after the turn of the century there can have been little automatic on-line process control. The obstacles to be overcome were both practical and conceptual instrument manufacturers needed to solve both the transmission and amplification problems in order to produce viable industrial instruments and engineers needed to develop a ftill understanding of dynamics and the role of feedback in dynamic systems. 

A simple example that illustrates the roles of feedback and feedforward control in nature is the heat shock response exhibited by simple bacteria (El-Samad et al., 2006), as illustrated in Fig. 24.1. When the organism experiences an increase in temperature, it leads to the misfolding of protein, which disrupts a number of... 

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