Robust model predictive controller with output feedback and target tracking

A model predictive controller (MPC) is proposed, which is robustly stable for some classes of model uncertainty and to unknown disturbances. It is considered as the case of open-loop stable systems, where only the inputs and controlled outputs are measured. It is assumed that the controller will work in a scenario where target tracking is also required. Here, it is extended to the nominal infinite horizon MPC with output feedback. The method considers an extended cost function that can be made globally convergent for any finite input horizon considered for the uncertain system. The method is based on the explicit inclusion of cost contracting constraints in the control problem. The controller considers the output feedback case through a non-minimal state-space model that is built using past output measurements and past input increments. The application of the robust output feedback MPC is illustrated through the simulation of a low-order multivariable system.

Infinite horizon MPC with non-minimal state space feedback

In the MPC literature, stability is usually assured under the assumption that the state is measured. Since the closed-loop system may be nonlinear because of the constraints, it is not possible to apply the separation principle to prove global stability for the Output feedback case. It is well known that, a nonlinear closed-loop system with the state estimated via an exponentially converging observer combined with a state feedback controller can be unstable even when the controller is stable. One alternative to overcome the state estimation problem is to adopt a non-minimal state space model, in which the states are represented by measured past inputs and outputs [P.C. Young, M.A. Behzadi, C.L. Wang, A. Chotai, Direct digital and adaptative control by input-output, state variable feedback pole assignment, International journal of Control 46 (1987) 1867-1881; C. Wang, P.C. Young, Direct digital control by input-output, state variable feedback: theoretical background, International journal of Control 47 (1988) 97-109]. In this case, no observer is needed since the state variables can be directly measured. However, an important disadvantage of this approach is that the realigned model is not of minimal order, which makes the infinite horizon approach to obtain nominal stability difficult to apply. Here, we propose a method to properly formulate an infinite horizon MPC based on the output-realigned model, which avoids the use of an observer and guarantees the closed loop stability. The simulation results show that, besides providing closed-loop stability for systems with integrating and stable modes, the proposed controller may have a better performance than those MPC controllers that make use of an observer to estimate the current states. (C) 2008 Elsevier Ltd. All rights reserved.

A Class of Channels Resulting in Ill-Convergence for CMA in Decision Feedback Equalizers

This paper analyzes the convergence of the constant modulus algorithm (CMA) in a decision feedback equalizer using only a feedback filter. Several works had already observed that the CMA presented a better performance than decision directed algorithm in the adaptation of the decision feedback equalizer, but theoretical analysis always showed to be difficult specially due to the analytical difficulties presented by the constant modulus criterion. In this paper, we surmount such obstacle by using a recent result concerning the CM analysis, first obtained in a linear finite impulse response context with the objective of comparing its solutions to the ones obtained through the Wiener criterion. The theoretical analysis presented here confirms the robustness of the CMA when applied to the adaptation of the decision feedback equalizer and also defines a class of channels for which the algorithm will suffer from ill-convergence when initialized at the origin.

Galerkin Method and Weighting Functions Applied to Nonlinear H(infinity) Control with Output Feedback

This paper considers two aspects of the nonlinear H(infinity) control problem: the use of weighting functions for performance and robustness improvement, as in the linear case, and the development of a successive Galerkin approximation method for the solution of the Hamilton-Jacobi-Isaacs equation that arises in the output-feedback case. Design of nonlinear H(infinity) controllers obtained by the well-established Taylor approximation and by the proposed Galerkin approximation method applied to a magnetic levitation system are presented for comparison purposes.

On the convergence of successive Galerkin approximation for nonlinear output feedback H(infinity) control

Although the formulation of the nonlinear theory of H(infinity) control has been well developed, solving the Hamilton-Jacobi-Isaacs equation remains a challenge and is the major bottleneck for practical application of the theory. Several numerical methods have been proposed for its solution. In this paper, results on convergence and stability for a successive Galerkin approximation approach for nonlinear H(infinity) control via output feedback are presented. An example is presented illustrating the application of the algorithm.

Some remarks on static-feedback linearization for time-varying systems

This work summarizes some results about static state feedback linearization for time-varying systems. Three different necessary and sufficient conditions are stated in this paper. The first condition is the one by [Sluis, W. M. (1993). A necessary condition for dynamic feedback linearization. Systems & Control Letters, 21, 277-283]. The second and the third are the generalizations of known results due respectively to [Aranda-Bricaire, E., Moog, C. H., Pomet, J. B. (1995). A linear algebraic framework for dynamic feedback linearization. IEEE Transactions on Automatic Control, 40, 127-132] and to [Jakubczyk, B., Respondek, W. (1980). On linearization of control systems. Bulletin del` Academie Polonaise des Sciences. Serie des Sciences Mathematiques, 28, 517-522]. The proofs of the second and third conditions are established by showing the equivalence between these three conditions. The results are re-stated in the infinite dimensional geometric approach of [Fliess, M., Levine J., Martin, P., Rouchon, P. (1999). A Lie-Backlund approach to equivalence and flatness of nonlinear systems. IEEE Transactions on Automatic Control, 44(5), 922-937]. (C) 2008 Elsevier Ltd. All rights reserved.

Influence of visual feedback on pelvic floor muscle strength

Objective: The objective of this study is to evaluate the visual feedback influence on pelvic floor muscle contraction. Study design: Seventeen nulliparous, urinary-continent women participated in this study. Pelvic floor muscle strength with and without the use of visual feedback was measured with a dynamometric speculum in two directions (anteroposterior and left-right). To compare the mean strength values with and without the use of visual feedback, the t test was applied. Results: There was no significant difference between the pelvic floor muscle anteroposterior strength values with and without the use of visual feedback (p = 0.30), and no significant difference for the left-right strength (p = 0.37). Conclusion: There was no difference between the pelvic floor muscle strength values with and without the use of visual feedback. (C) 2010 Elsevier Ireland Ltd. All rights reserved.

Noradrenaline Involvement in the Negative-Feedback Effects of Ovarian Steroids on Luteinising Hormone Secretion

Noradrenaline has been shown to modulate the ovarian-steroid feedback on luteinising-hormone (LH) release. However, despite the high amount of evidence accumulated over many years, the role of noradrenaline in LH regulation is still not clearly understood. The present study aimed to further investigate the involvement of noradrenaline in the negative-feedback effect of oestradiol and progesterone on basal LH secretion. In experiment 1, ovariectomised (OVX) rats received a single injection of oil, oestradiol, or progesterone at 09.00-10.00 h and were decapitated 30 or 60 min later. Levels of noradrenaline and its metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG), were determined in microdissections of the preoptic area (POA) and medial basal hypothalamus-median eminence (MBH-ME) and correlated with LH secretion. Basal LH levels were decreased 30 and 60 min after oestradiol or progesterone injection, and this hormonal response was significantly correlated with a reduction in POA MHPG levels, which reflect noradrenaline release. In addition, noradrenaline levels in the POA were increased, whereas noradrenaline turnover (MHPG/noradrenaline ratio) was decreased 60 min after the injection of both hormones. No effect was found in the MBH-ME. In experiment 2, i.c.v. administration of noradrenaline (60 nmol), performed 15 min before oestradiol or progesterone injection in jugular vein-cannulated OVX rats, completely prevented the ovarian steroid-induced inhibition of LH secretion. The data obtained provide direct evidence that LH secretion in OVX rats is positively regulated by basal noradrenergic activity in the POA, and its reduction appears to play a role in the negative-feedback effect of ovarian steroids on LH secretion in vivo.

Vitamina D e doenças endocrinometabólicas

Atualmente, a insuficiência/deficiência de vitamina D tem sido considerada um problema de saúde pública no mundo todo, em razão de suas implicações no desenvolvimento de diversas doenças, entre elas, o diabetes melito tipo 2 (DMT2), a obesidade e a hipertensão arterial. A deficiência de vitamina D pode predispor à intolerância à glicose, a alterações na secreção de insulina e, assim, ao desenvolvimento do DMT2. Esse possível mecanismo ocorre em razão da presença do receptor de vitamina D em diversas células e tecidos, incluindo células-β do pâncreas, no adipócito e no tecido muscular. Em indivíduos obesos, as alterações do sistema endócrino da vitamina D, caracterizada por elevados níveis de PTH e da 1,25(OH)2D3 são responsáveis pelo feedback negativo da síntese hepática de 25-OHD3 e também pelo maior influxo de cálcio para o meio intracelular, que pode prejudicar a secreção e a sensibilidade à insulina. Na hipertensão, a vitamina D pode atuar via sistema renina-angiotensina e também na função vascular. Há evidências de que a 1,25(OH)2D3 inibe a expressão da renina e bloqueia a proliferação da célula vascular muscular lisa. Entretanto, estudos prospectivos e de intervenção em humanos que comprovem a efetividade da adequação do status da vitamina D sob o aspecto "prevenção e tratamento de doenças endocrinometabólicas" são ainda escassos. Mais pesquisas são necessárias para se garantir o benefício máximo da vitamina D nessas situações.

Deep plant-derived carbon storage in Amazonian podzols

Equatorial podzols are soils characterized by thick sandy horizons overlying more clayey horizons. Organic matter produced in the topsoil is transferred in depth through the sandy horizons and accumulate at the transition, at a depth varying from 1 to more than 3 m, forming deep horizons rich in organic matter (Bh horizons). Although they cover great surfaces in the equatorial zone, these soils are still poorly known. Studying podzols from Amazonia, we found out that the deep Bh horizons in poorly drained podzol areas have a thickness higher than 1m and store unexpected amounts of carbon. The average for the studied area was 66.7 +/- 5.8 kgCm(-2) for the deep Bh and 86.8 +/- 7.1 kgCm(-2) for the whole profile. Extrapolating to the podzol areas of the whole Amazonian basin has been possible thanks to digital maps, giving an order of magnitude around 13.6 +/- 1.1 PgC, at least 12.3 PgC higher than previous estimates. This assessment should be refined by additional investigations, not only in Amazonia but in all equatorial areas where podzols have been identified. Because of the lack of knowledge on the quality and behaviour of the podzol organic matter, the question of the feedback between the climate and the equatorial podzol carbon cycle is open.

AVERAGE CONTINUOUS CONTROL OF PIECEWISE DETERMINISTIC MARKOV PROCESSES

This paper deals with the long run average continuous control problem of piecewise deterministic Markov processes (PDMPs) taking values in a general Borel space and with compact action space depending on the state variable. The control variable acts on the jump rate and transition measure of the PDMP, and the running and boundary costs are assumed to be positive but not necessarily bounded. Our first main result is to obtain an optimality equation for the long run average cost in terms of a discrete-time optimality equation related to the embedded Markov chain given by the postjump location of the PDMP. Our second main result guarantees the existence of a feedback measurable selector for the discrete-time optimality equation by establishing a connection between this equation and an integro-differential equation. Our final main result is to obtain some sufficient conditions for the existence of a solution for a discrete-time optimality inequality and an ordinary optimal feedback control for the long run average cost using the so-called vanishing discount approach. Two examples are presented illustrating the possible applications of the results developed in the paper.

Synchronization of Discrete-Time Chaotic Systems in Bandlimited Channels

Over the last couple of decades, many methods for synchronizing chaotic systems have been proposed with communications applications in view. Yet their performance has proved disappointing in face of the nonideal character of usual channels linking transmitter and receiver, that is, due to both noise and signal propagation distortion. Here we consider a discrete-time master-slave system that synchronizes despite channel bandwidth limitations and an allied communication system. Synchronization is achieved introducing a digital filter that limits the spectral content of the feedback loop responsible for producing the transmitted signal. Copyright (C) 2009 Marcio Eisencraft et al.

Spontaneous symmetry breaking in amnestically induced persistence

We investigate a recently proposed non-Markovian random walk model characterized by loss of memories of the recent past and amnestically induced persistence. We report numerical and analytical results showing the complete phase diagram, consisting of four phases, for this system: (i) classical nonpersistence, (ii) classical persistence, (iii) log-periodic nonpersistence, and (iv) log-periodic persistence driven by negative feedback. The first two phases possess continuous scale invariance symmetry, however, log-periodicity breaks this symmetry. Instead, log-periodic motion satisfies discrete scale invariance symmetry, with complex rather than real fractal dimensions. We find for log-periodic persistence evidence not only of statistical but also of geometric self-similarity.

Rotation curve bifurcations as indicators of close recent galaxy encounters

Context. Rotation curves of interacting galaxies often show that velocities are either rising or falling in the direction of the companion galaxy. Aims. We seek to reproduce and analyse these features in the rotation curves of simulated equal-mass galaxies suffering a one-to-one encounter as possible indicators of close encounters. Methods. Using simulations of major mergers in 3D, we study the time evolution of these asymmetries in a pair of galaxies during the first passage. Results. Our main results are: (a) the rotation curve asymmetries appear right at pericentre of the first passage, (b) the significant disturbed rotation velocities occur within a small time interval, of similar to 0.5 Gyr h(-1), and, therefore, the presence of bifurcation in the velocity curve could be used as an indicator of the pericentre occurrence. These results are in qualitative agreement with previous findings for minor mergers and flybys.

An analytical approach to the dwarf galaxies cusp problem

Aims. An analytical solution for the discrepancy between observed core-like profiles and predicted cusp profiles in dark matter halos is studied. Methods. We calculate the distribution function for Navarro-Frenk-White halos and extract energy from the distribution, taking into account the effects of baryonic physics processes. Results. We show with a simple argument that we can reproduce the evolution of a cusp to a flat density profile by a decrease of the initial potential energy.