Many biological oscillators have a cyclic structure consisting of negative feedback loops. In this paper, we analyze the impact that the addition of a positive or a negative self-feedback loop has on the oscillatory behavior of the three negative feedback oscillators proposed by Tsai et al. (Science 231:126-129, 2008) where, in contrast with numerous oscillator models, the interactions between ...

Positive feedback is a process that occurs in a feedback loop in which the effects of a small disturbance on a system include an increase in the magnitude of the perturbation.[1] That is, A produces more of B which in turn produces more of A.[2] In contrast, a system in which the results of a change act to reduce or counteract it has negative feedback.[1][3] Mathematically, positive feedback is...

Our computational model of the circadian clock comprised the feedback loop between LATE ELONGATED HYPOCOTYL (LHY), CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and TIMING OF CAB EXPRESSION 1 (TOC1), and a predicted, interlocking feedback loop involving TOC1 and a hypothetical component Y. Experiments based on model predictions suggested GIGANTEA (GI) as a candidate for Y. We now extend the model to incl...

Technical reports from the Automatic Control group in Linkk oping are available by anonymous ftp at the Abstract A new method for closed-loop identiication that allows tting the model to the data with arbitrary frequency weighting is described and analyzed. Just as the direct method this new method is applicable to systems with arbitrary feedback mechanisms. This is in sharp contrast with other...

Recent research has shown that control of the oxygen content in the catalyst has potential to further reduce the emissions from spark ignited engines. This gives rise to a cascade structure where an outer loop influences an inner loop. Different ways of augmenting the inner loop, a traditional PI-feedback controller based on feedback from the binary oxygen sensor, are studied. The SI-engine con...

This literature provided a basis for SD model building. Additional experiences in Indonesia maintained model realism. One SD corruption overview is based on the oft cited idea that 'amount of corruption' is part of reinforcing loops linked to 'amount of bureaucratic red tape.' In this view, corruption is imbedded in positive feedback loops also linking it to lowered economic openness, a weak le...

In this paper we consider an atomic system with a narrow transition probed with a usercontrolled electromagnetic radiation, the basis of atomic clocks. We propose a simple feedback-loop in order to lock automatically the probe frequency on the atomic transition, allowing continuous clock operation without any preparation steps. The proof of the convergence of the feedback-loop is based on avera...

Control input-output contact systems are the representation of open irreversible Thermodynamic systems whose geometric structure is defined by Gibbs’ relation. These systems are called conservative if furthermore they leave invariant a particular Legendre submanifold defining their thermodynamic properties. In this paper we address the stabilization of controlled input-output contact systems. F...

Negative feedback control is used in switched-mode power supplies to regulate the output at a desired value. The optimum design of the feedback control loop starts with understanding the characteristics of the power stage, which can be analyzed using small-signal modeling. This paper explains the fundamental idea and meaning of small-signal modeling for power supplies and explores the small-sig...

In this paper, the authors present a linear matrix inequality (LMI) approach to the strictly positive real (SPR) synthesis problem: find an output feedback K such that the closed-loop system T (s) is SPR. The authors establish that if no such constant output feedback K exists, then no dynamic output feedback with a proper transfer matrix exists to make the closed-loop system SPR. The existence ...