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Feedback System (feedback + system)
Selected AbstractsDevelopment of sediment toxicity test with tropical peneid shrimpsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2000Rosane B. C. Moraes Abstract A methodology to test the toxicity of marine and estuarine sediments was developed using postlarval organisms of the marine shrimp Penaeus schmitti and P. paulensis. The tests were conducted in aquariums with a water feedback system and a sediment layer of 2 cm. The postlarvae exposure time to the sediments was 10, 28, and 52 d. The tested sediments were collected in contaminated sites of Guanabara and Sepetiba Bays and at the reference site of Ilha Grande inlet in Rio de Janerio, Brazil. The toxicity of the sediments was evidenced with exposures of 28 d or longer. The sediment from Saco do Engenho (Sepetiba Bay) was the most toxic, affecting the survival of both P. schmitti and P. paulensis. The sediment from Guanabara Bay was toxic to P. schmitti, affecting its survival after 28 d of exposure. [source] Improving the quality of clinical teaching in a restorative clinic using student feedbackEUROPEAN JOURNAL OF DENTAL EDUCATION, Issue 2 2008Callum Youngson Abstract Introduction:, A large proportion of the undergraduate curriculum is spent within Restorative Dentistry at the University of Liverpool. As well as supportive "phantom head" courses the undergraduates receive significant amounts of teaching within the clinics themselves. In 2004, to help inform the clinical tutors as to their areas of strengths and weaknesses, undergraduates were invited to complete an anonymous questionnaire on the quality of teaching they received from their clinical supervisors. This process has been repeated subsequently in 2005 and 2006. Method:, A 19 parameter questionnaire, employing a 5-point Likert scale and space for open comments, was circulated to every clinical undergraduate student. Questionnaires were returned anonymously and all data collected by one researcher. Descriptive statistical analysis was performed and the staff provided with individual feedback within the context of the overall departmental profile. The pooled data from each of the years was then compared to determine if any changes had occurred. Statistical analysis used Kruskal Wallis tests to determine whether these were statistically significant. Results:, Although the range varied, median scores of 4 (agree) were gained for each question each year. Following statistical analysis 18 of the parameters showed a statistically significant improvement (P < 0.05) between 2004 and 2006 with only one remaining constant throughout. Conclusion:, It would appear that the use of a questionnaire based feedback system can result in a tangible and demonstrable improvement in the delivery of clinical teaching. [source] Steady state and transient state behaviours analyses of TCP connections considering interactions between TCP connections and networkINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 7 2005Hiroyuki Hisamatsu Abstract The Internet uses a window-based congestion control mechanism in transmission control protocol (TCP). In the literature, there have been a great number of analytical studies on TCP. Most of those studies have focused on the statistical behaviour of TCP by assuming a constant packet loss probability in the network. However, the packet loss probability, in reality, changes according to the packet transmission rates from TCP connections. Conversely, the window size of a TCP connection is dependent on the packet loss probability in the network. In this paper, we explicitly model the interaction between the congestion control mechanism of TCP and the network as a feedback system. By using this model, we analyse the steady state and the transient state behaviours of TCP. We derive the throughput and the packet loss probability of TCP, and the number of packets queued in the bottleneck router. We then analyse the transient state behaviour using a control theoretic approach, showing the influence of the number of TCP connections and the propagation delay on the transient state behaviour of TCP. Copyright © 2005 John Wiley & Sons, Ltd. [source] New IQC for quasi-concave nonlinearitiesINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 7 2001Alexandre Megretski Abstract A new set of integral quadratic constraints (IQC) is derived for a class of ,rate limiters', modelled as a series connections of saturation-like memoryless nonlinearities followed by integrators. The result, when used within the standard IQC framework (in particular, with finite gain/passivity-based argiments, Lyapunov theory, structured singular values, etc.), is expected to be widely useful in nonlinear system analysis. For example, it enables ,discrimination' between ,saturation-like' and ,deadzone-like' nonlinearities and can be used to prove stability of systems with saturation in cases when replacing the saturation block by another memoryless nonlinearity with equivalent slope restrictions makes the whole system unstable. In particular, it is shown that the L2 gain of a unity feedback system with a rate limiter in the forward loop cannot exceed \sqrt{2}. In addition, a new, more flexible version of the general IQC analysis framework is presented, which relaxes the homotopy and boundedness conditions, and is more aligned with the language of the emerging IQC software. Copyright © 2001 John Wiley & Sons, Ltd. [source] Effects of Climate Change and Shifts in Forest Composition on Forest Net Primary ProductionJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 11 2008Jyh-Min Chiang Abstract Forests are dynamic in both structure and species composition, and these dynamics are strongly influenced by climate. However, the net effects of future tree species composition on net primary production (NPP) are not well understood. The objective of this work was to model the potential range shifts of tree species (DISTRIB Model) and predict their impacts on NPP (PnET-II Model) that will be associated with alterations in species composition. We selected four 200 × 200 km areas in Wisconsin, Maine, Arkansas, and the Ohio-West Virginia area, representing focal areas of potential species range shifts. PnET-II model simulations were carried out assuming that all forests achieved steady state, of which the species compositions were predicted by DISTRIB model with no migration limitation. The total NPP under the current climate ranged from 552 to 908 g C/m2 per year. The effects of potential species redistributions on NPP were moderate (,12% to +8%) compared with the influence of future climatic changes (,60% to +25%). The direction and magnitude of climate change effects on NPP were largely dependent on the degree of warming and water balance. Thus, the magnitude of future climate change can affect the feedback system between the atmosphere and biosphere. [source] The role of cutaneous sensation in the motor function of the handJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2004Ayman M. Ebied Abstract We studied the effect of abolishing cutaneous sensation (by infiltrating local anaesthetic around the median nerve at the wrist) on the ability of 10 healthy volunteers (a) to maintain a submaximal isometric pinch-grip force for 30 s without visual feedback, and (b) to perform a fine finger-manipulation ,handwriting" task. Blocking cutaneous sensation had no effect on ability to maintain pinch force, suggesting that muscle afferents have the major role in force-control feedback. However, a near-linear fall in force, present with or without block (mean slope = ,1.3 ± 0.2% s,1), which cannot be attributed to motor fatigue, reveals a shortcoming of the afferent feedback system. Blocking cutaneous sensation did impair ability to perform the more demanding writing task, as judged by an 18 ± 6% increase in the length of the path between target points, a 22 ± 9% increase in the duration of the movement and a 63 ± 24% in ,normalised averaged rectified jerk", an averaged time-derivative of acceleration (all significantly nonzero, P < 0.04). These experiments demonstrate the relative importance of muscular and cutaneous afferent feedback on two aspects of hand performance, and provide a way to quantify the deficit resulting from the lack of cutaneous sensation. © 2003 Published by Elsevier Ltd. on behalf of Orthopaedic Research Society. All rights reserved. [source] Ethanol-Induced Increase of Agouti-Related Protein (AgRP) Immunoreactivity in the Arcuate Nucleus of the Hypothalamus of C57BL/6J, but not 129/SvJ, Inbred MiceALCOHOLISM, Issue 4 2010Inmaculada Cubero Background:, The melanocortin (MC) system is composed of peptides that are cleaved from the polypeptide precursor, pro-opiomelanocortin (POMC). Previous research has shown that MC receptor (MCR) agonists reduce, and MCR antagonists increase, ethanol consumption in rats and mice. Consistently, genetic deletion of the endogenous MCR antagonist, agouti-related protein (AgRP), causes reductions of ethanol-reinforced lever pressing and binge-like ethanol drinking in C57BL/6J mice. Ethanol also has direct effects on the central MC system, as chronic exposure to an ethanol-containing diet causes significant reductions of ,-melanocyte stimulating hormone (,-MSH) immunoreactivity in specific brain regions of Sprague-Dawley rats. Together, these observations suggest that the central MC system modulates neurobiological responses to ethanol. To further characterize the role of the MC system in responses to ethanol, here we compared AgRP and ,-MSH immunoreactivity in response to an acute injection of saline or ethanol between high ethanol drinking C57BL/6J mice and moderate ethanol drinking 129/SvJ mice. Methods:, Mice received an intraperitoneal (i.p.) injection of ethanol (1.5 g/kg or 3.5 g/kg; mixed in 0.9% saline) or an equivolume of 0.9% saline. Two hours after injection, animals were sacrificed and their brains were processed for AgRP and ,-MSH immunoreactivity. Results:, Results indicated that acute ethanol administration triggered a dose-dependent increase in AgRP immunoreactivity in the arcuate (ARC) of C57BL/6J mice, an effect that was not evident in the 129/SvJ strain. Although acute administration of ethanol did not influence ,-MSH immunoreactivity, C57BL/6J mice had significantly greater overall ,-MSH immunoreactivity in the ARC, dorsomedial, and lateral regions of the hypothalamus relative to the 129/SvJ strain. In contrast, C57BL/6J mice displayed significantly lower ,-MSH immunoreactivity in the medial amygdala. Conclusions:, The results show that acute ethanol exposure has direct effects on endogenous AgRP activity in ethanol preferring C57BL/6J mice. It is suggested that ethanol-induced increases in AgRP may be part of a positive feedback system that stimulates excessive binge-like ethanol drinking in C57BL/6J mice. Inherent differences in ,-MSH immunoreactivity may contribute to differences in neurobiological responses to ethanol that are characteristically observed between the C57BL/6J and 129/SvJ inbred strains of mice. [source] Towards a model of implicit feedback for Web searchJOURNAL OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE AND TECHNOLOGY, Issue 1 2010Xin Fu Abstract This research investigated several important issues in using implicit feedback techniques to assist searchers with difficulties in formulating effective search strategies. It focused on examining the relationship between types of behavioral evidence that can be captured from Web searches and searchers' interests. A carefully crafted observation study was conducted to capture, examine, and elucidate the analytical processes and work practices of human analysts when they simulated the role of an implicit feedback system by trying to infer searchers' interests from behavioral traces. Findings provided rare insight into the complexities and nuances in using behavioral evidence for implicit feedback and led to the proposal of an implicit feedback model for Web search that bridged previous studies on behavioral evidence and implicit feedback measures. A new level of analysis termed an analytical lens emerged from the data and provides a road map for future research on this topic. [source] Pilot clinical study of a novel minimally invasive bipolar microneedle radiofrequency device,LASERS IN SURGERY AND MEDICINE, Issue 2 2009Basil M. Hantash MD Abstract Background and Objectives Noninvasive bipolar and monopolar radiofrequency (RF) deep dermal heating devices have previously been described. A novel minimally invasive RF device employing a bipolar microneedle electrode system is introduced and its resultant thermal effects on human skin in vivo were characterized for the first time. Study Design/Materials and Methods An investigational 35 W RF device was configured to operate in bipolar mode delivering energy directly within the dermis using 5 microneedle electrode pairs with real-time feedback of tissue temperature for treatment control. Superficial cooling was achieved using a Peltier device. A range of pulse durations between 1 and 25 seconds, and lesion temperatures between 60 and 80°C were tested in vivo on 15 human subjects. Thermal effects were assessed histologically using either hematoxylin & eosin (H&E) or nitroblue-tetrazoliumchloride (NBTC) staining. Treatment effects and adverse events were also monitored clinically. Results The investigational bipolar RF device delivered controlled heating within dermal tissue. Histological staining with H&E revealed the presence of zones of denatured collagen within the reticular dermis. Lesions were generated at preselected temperatures between 60 and 80°C. Fractional lesions separated by zones of sparing as well as contiguous lesion patterns were demonstrated. Histological staining with H&E and NBTC revealed sparing of adnexal structures and adipose tissue. No major adverse events were observed. Conclusions A novel fractional RF device utilizing a minimally invasive bipolar microneedle delivery system for the treatment of human tissue was developed. Treatment of 15 human subjects illustrated the controlled creation of dermally located thermal coagulation zones, herein known as radiofrequency thermal zones. We discovered that varying the pulse length allowed for fractional sparing of dermal tissue. To our knowledge, this is the first report to describe use of a direct real-time temperature and impedance feedback system to control energy delivery during deep dermal heating. Lasers Surg. Med. 41:87,95, 2009. © 2009 Wiley-Liss, Inc. [source] Leptin and Insulin Action in the Central Nervous SystemNUTRITION REVIEWS, Issue 2002Daniel Porte Jr M.D. Body adiposity is known to be carefully regulated and to remain relatively stable for long periods of time in most mammalian species. This review summarizes old and recent data implicating insulin and leptin as key circulating signals to the central nervous system, particularly the ventral hypothalamus, in communicating thesizeand thedistribution of body fat stores. This input ultimately alters food intake and energy expenditure to maintain constancy of the adipose depot. The key primary neurons in the arcuate nucleus containing NPY/AgRP and POMC/CART appear be critical constituents of the CNS regulating system, and are shown to contribute to anabolic and catabolic signaling systems to complete the feedback loop. New data to indicate shared intracellular signaling from leptin and insulin is provided. The satiety system for meals, consisting of neural afferents to the hind-brain from the gastrointestinal tract, is described and its effectiveness is shown to vary with the strength of the insulin and leptin signals. This provides anefferent mechanism that plays a key role in a complex feedback system that allows intermittent meals to vary from day to day, but provides appropriate long-term adjustment to need. Recently described contributions of this system to obesity are described and potential therapeutic implications are discussed. [source] Nonimmersive Virtual Reality Mirror Visual Feedback Therapy and Its Application for the Treatment of Complex Regional Pain Syndrome: An Open-Label Pilot StudyPAIN MEDICINE, Issue 4 2010Kenji Sato MD Abstract Objective., Chronic pain conditions such as phantom limb pain and complex regional pain syndrome are difficult to treat, and traditional pharmacological treatment and invasive neural block are not always effective. Plasticity in the central nervous system occurs in these conditions and may be associated with pain. Mirror visual feedback therapy aims to restore normal cortical organization and is applied in the treatment of chronic pain conditions. However, not all patients benefit from this treatment. Virtual reality technology is increasingly attracting attention for medical application, including as an analgesic modality. An advanced mirror visual feedback system with virtual reality technology may have increased analgesic efficacy and benefit a wider patient population. In this preliminary work, we developed a virtual reality mirror visual feedback system and applied it to the treatment of complex regional pain syndrome. Design., A small open-label case series. Five patients with complex regional pain syndrome received virtual reality mirror visual feedback therapy once a week for five to eight sessions on an outpatient basis. Patients were monitored for continued medication use and pain intensity. Results., Four of the five patients showed >50% reduction in pain intensity. Two of these patients ended their visits to our pain clinic after five sessions. Conclusion., Our results indicate that virtual reality mirror visual feedback therapy is a promising alternative treatment for complex regional pain syndrome. Further studies are necessary before concluding that analgesia provided from virtual reality mirror visual feedback therapy is the result of reversing maladaptive changes in pain perception. [source] Functions of corticotropin-releasing hormone in anthropoid primates: From brain to placentaAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 4 2006Michael L. Power Corticotropin-releasing hormone (CRH) is an ancient regulatory molecule. The CRH hormone family has at least four ligands, two receptors, and a binding protein. Its well-known role in the hypothalamic-pituitary-adrenal (HPA) axis is only one of many. The expression of CRH and its related peptides is widespread in peripheral tissue, with important functions in the immune system, energy metabolism, and female reproduction. For example, CRH is involved in the implantation of fertilized ova and in maternal tolerance to the fetus. An apparently unique adaptation has evolved in anthropoid primates: placental expression of CRH. Placental CRH stimulates the fetal adrenal zone, an adrenal structure unique to primates, to produce dehydroepiandrosterone sulfate (DHEAS), which is converted to estrogen by the placenta. Cortisol induced from the fetal and maternal adrenal glands by placental CRH induces further placental CRH expression, forming a positive feedback system that results in increasing placental production of estrogen. In humans, abnormally high placental expression of CRH is associated with pregnancy complications (e.g., preterm labor, intrauterine growth restriction (IUGR), and preeclampsia). Within anthropoid primates, there are at least two patterns of placental CRH expression over gestation: monkeys differ from great apes (and humans) by having a midgestational peak in CRH expression. The functional significance of these differences between monkeys and apes is not yet understood, but it supports the hypothesis that placental CRH performs multiple roles during gestation. A clearer understanding of the diversity of patterns of placental CRH expression among anthropoid primates would aid our understanding of its role in human pregnancy. Am. J. Hum. Biol. 18:431,447, 2006. © 2006 Wiley-Liss, Inc. [source] PKS1 plays a role in red-light-based positive phototropism in rootsPLANT CELL & ENVIRONMENT, Issue 6 2008MARIA LIA MOLAS ABSTRACT Aerial parts of plants curve towards the light (i.e. positive phototropism), and roots typically grow away from the light (i.e. negative phototropism). In addition, Arabidopsis roots exhibit positive phototropism relative to red light (RL), and this response is mediated by phytochromes A and B (phyA and phyB). Upon light stimulation, phyA and phyB interact with the phytochrome kinase substrate (PKS1) in the cytoplasm. In this study, we investigated the role of PKS1, along with phyA and phyB, in the positive phototropic responses to RL in roots. Using a high-resolution feedback system, we studied the phenotypic responses of roots of phyA, phyB, pks1, phyA pks1 and phyB pks1 null mutants as well as the PKS1- overexpressing line in response to RL. PKS1 emerged as an intermediary in the signalling pathways and appears to promote a negative curvature to RL in roots. In addition, phyA and phyB were both essential for a positive response to RL and act in a complementary fashion. However, either photoreceptor acting without the other results in negative curvature in response to red illumination so that the mode of action differs depending on whether phyA and phyB act independently or together. Our results suggest that PKS1 is part of a signalling pathway independent of phyA and phyB and that PKS1 modulates RL-based root phototropism. [source] Spatial separation of light perception and growth response in maize root phototropismPLANT CELL & ENVIRONMENT, Issue 9 2002J. L. Mullen Abstract Although the effects of gravity on root growth are well known and interactions between light and gravity have been reported, details of root phototropic responses are less documented. We used high-resolution image analysis to study phototropism in primary roots of Zea mays L. Similar to the location of perception in gravitropism, the perception of light was localized in the root cap. Phototropic curvature away from the light, on the other hand, developed in the central elongation zone, more basal than the site of initiation of gravitropic curvature. The phototropic curvature saturated at approximately 10 µmol m,2 s,1 blue light with a peak curvature of 29 ± 4°, in part due to induction of positive gravitropism following displacement of the root tip from vertical during negative phototropism. However, at higher fluence rates, development of phototropic curvature is arrested even if gravitropism is avoided by maintaining the root cap vertically using a rotating feedback system. Thus continuous illumination can cause adaptation in the signalling pathway of the phototropic response in roots. [source] Approximate Pole Placement with Dominance for Continuous Delay Systems by PID ControllersTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2007Qing-Guo Wang Abstract It is well known that a continuous-time feedback system with time delay has infinite spectrum and it is not possible to assign such infinite spectrum with a finite-dimensional controller. In such a case, only the partial pole placement may be feasible and hopefully some of the assigned poles are dominant. But there is no easy way to guarantee dominance of the desired poles. In this paper, an analytical PID design method is proposed for continuous-time delay systems to achieve approximate pole placement with dominance. Its idea is to bypass continuous infinite spectrum problem by converting a delay process to a rational discrete model and getting back continuous PID controller from its discrete form designed for the model with pole placement. Simulation results are included to illustrate the effectiveness of this method. Il est bien établi qu'un système de rétroalimentation continu dans le temps avec retard a un spectre infini et qu'il n'est pas possible d'assigner un tel spectre à un contrôleur à dimensions finies. Dans un tel cas, seul le placement de pôles partiels peut être réalisable, et heureusement, certains des pôles assignés sont dominants. Mais il n'y a pas de manière facile de garantir la dominance des pôles désirés. Dans cet article, on propose une méthode de conception PID analytique pour les systèmes avec retard continu dans le temps, afin d'effectuer le placement de pôles approximatif avec dominance. L'idée est de contourner le problème des spectres infinis continus en convertissant le procédé de retard en un modèle discret rationnel et de récupérer le contrôleur PID continu de sa forme discrète conçue pour le modèle avec placement de pôles. Les résultats des simulations sont inclus pour illustrer l'efficacité de cette méthode. [source] Twitch and nontwitch motoneuron subgroups in the oculomotor nucleus of monkeys receive different afferent projectionsTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 2 2004Richard Wasicky Abstract Motoneurons in the primate oculomotor nucleus can be divided into two categories, those supplying twitch muscle fibers and those supplying nontwitch muscle fibers. Recent studies have shown that twitch motoneurons lie within the classical oculomotor nucleus (nIII), and nontwitch motoneurons lie around the borders. Nontwitch motoneurons of medial and inferior rectus are in the C group dorsomedial to nIII, whereas those of inferior oblique and superior rectus lie near the midline are in the S group. In this anatomical study, afferents to the twitch and nontwitch subgroups of nIII have been anterogradely labeled by injections of tritiated leucine into three areas and compared. 1) Abducens nucleus injections gave rise to silver grain deposits over all medial rectus subgroups, both twitch and nontwitch. 2) Laterally placed vestibular complex injections that included the central superior vestibular nucleus labeled projections only in twitch motoneuron subgroups. However, injections into the parvocellular medial vestibular nucleus (mvp), or Y group, resulted in labeled terminals over both twitch and nontwitch motoneurons. 3) Pretectal injections that included the nucleus of the optic tract (NOT), and the olivary pretectal nucleus (OLN), labeled terminals only over nontwitch motoneurons, in the contralateral C group and in the S group. Our study demonstrates that twitch and nontwitch motoneuron subgroups do not receive identical afferent inputs. They can be controlled either in parallel, or independently, suggesting that they have basically different functions. We propose that twitch motoneurons primarily drive eye movements and nontwitch motoneurons the tonic muscle activity, as in gaze holding and vergence, possibly involving a proprioceptive feedback system. J. Comp. Neurol. 479:117,129, 2004. © 2004 Wiley-Liss, Inc. [source] Is peripheral locomotor muscle fatigue during endurance exercise a variable carefully regulated by a negative feedback system?THE JOURNAL OF PHYSIOLOGY, Issue 7 2008Samuele Marcora No abstract is available for this article. [source] Is It Time for Clinicians to Routinely Track Patient Outcome?CLINICAL PSYCHOLOGY: SCIENCE AND PRACTICE, Issue 3 2003A Meta-Analysis Empirically supported psychotherapies, treatment guidelines, best practices, and treatment manuals are methods proposed to enhance treatment outcomes in routine practice. Patient-focused research systems provide a compatible and contrasting methodology. Such systems monitor and feed back information about a patient's progress during psychotherapy for the purpose of enhancing outcomes. A meta-analytic review of three large-scale studies is summarized and suggests that formally monitoring patient progress has a significant impact on clients who show a poor initial response to treatment. Implementation of this feedback system reduced deterioration by 4% to 8% and increased positive outcomes. Our interpretation of these results suggests that it may be time for clinicians routinely and formally to monitor patient treatment response. [source] Global output regulation for output feedback systems with an uncertain exosystem and its applicationINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 15 2010Dabo Xu Abstract This paper presents the solvability conditions for the global robust output regulation problem for a class of output feedback systems with an uncertain exosystem by using output feedback control. An adaptive control technique is used to handle the unknown parameter vector in the exosystem. It is shown that this unknown parameter vector can be exactly estimated asymptotically if a controller containing a minimal internal model is employed. The effectiveness of our approach has been illustrated by an asymptotic tracking problem of a generalized fourth-order Lorenz system. Copyright © 2009 John Wiley & Sons, Ltd. [source] A test for stability robustness of linear time-varying systems utilizing the linear time-invariant ,-gap metricINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 9 2009Wynita M. Griggs Abstract A stability robustness test is developed for internally stable, nominal, linear time-invariant (LTI) feedback systems subject to structured, linear time-varying uncertainty. There exists (in the literature) a necessary and sufficient structured small gain condition that determines robust stability in such cases. In this paper, the structured small gain theorem is utilized to formulate a (sufficient) stability robustness condition in a scaled LTI ,-gap metric framework. The scaled LTI ,-gap metric stability condition is shown to be computable via linear matrix inequality techniques, similar to the structured small gain condition. Apart from a comparison with a generalized robust stability margin as the final part of the stability test, however, the solution algorithm implemented to test the scaled LTI ,-gap metric stability robustness condition is shown to be independent of knowledge about the controller transfer function (as opposed to the LMI feasibility problem associated with the scaled small gain condition which is dependent on knowledge about the controller). Thus, given a nominal plant and a structured uncertainty set, the stability robustness condition presented in this paper provides a single constraint on a controller (in terms of a large enough generalized robust stability margin) that (sufficiently) guarantees to stabilize all plants in the uncertainty set. Copyright © 2008 John Wiley & Sons, Ltd. [source] Robust and efficient quantization and coding for control of multidimensional linear systems under data rate constraintsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 10-11 2007K. Li Abstract Recently, we reported results on coding strategies for scalar feedback systems with data-rate-limited feedback channels in which the data-rate constraints are time varying. Such rate-varying channels are typically encountered in communication networks in which links between nodes are subject to noise, congestion, and intermittent disruption. The present paper describes results of extending this research into the multidimensional domain. An important consideration is that for systems of dimension greater than one, many classical feedback designs cannot be realized for operation near the theoretical minimum possible data rate. A novel control coding scheme will be presented, and in terms of this, it will be shown that the advantages of coarse signal quantization that had been reported earlier for scalar systems remain in the multidimensional case. The key is to allocate the communication bandwidth efficiently among faster and slower modes. We discuss various strategies that allocate bandwidth by scheduling the time slots assigned to each mode. In particular, we propose a ,robust attention varying' technique, whose merit will be discussed in terms of its robustness with respect to time-varying communication channel capacity and also in terms of how well it operates when the feedback channel capacity is near the theoretical minimum data rate. Copyright © 2006 John Wiley & Sons, Ltd. [source] Improvements on the computation of boundaries in QFTINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 12 2006José Carlos Moreno Abstract Quantitative feedback theory (QFT) is an engineering design technique of uncertain feedback systems that uses frequency domain specifications. A key step in QFT is the mapping of these specifications into regions of the Nichols plane, whose borders are usually referred to as boundaries. Boundaries computation is a key design step, thus a precise and efficient computation is critical for both obtaining low bandwidth feedback compensators and simplification of the design process. In this work, the problem of boundaries computation is analysed, introducing a new algorithm based on the computation of level curves of a three-dimensional surface. Besides magnitude boundaries, associated with some specification over the magnitude of a closed-loop transfer function, phase boundaries are also considered. In addition, comparison with previous published algorithms is done in terms of precision and computational efficiency. Copyright © 2006 John Wiley & Sons, Ltd. [source] The Liapunov's second method for continuous time difference equationsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 15 2003P. PepeArticle first published online: 10 OCT 200 Abstract Among many other cases such as economic and lossless propagation models, continuous time difference equations are encountered as the internal dynamics in a class of non-linear time delay systems, when controlled by a suitable state feedback which drives the output exponentially to zero. The Liapunov's second method for these infinite dimensional systems has not been extensively investigated in the literature. This paper has the aim of filling this gap. Liapunov's second method theorems for checking the stability and the asymptotic stability of this class of infinite dimensional systems are built up, in both a finite and an infinite dimensional setting. In the finite dimensional setting, the Liapunov function is defined on finite dimensional sets. The conditions for stability are given as inequalities on continuous time. No derivatives are involved, as in the dynamics of the studied systems. In the infinite dimensional setting, the continuous time difference equation is transformed into a discrete time system evolving on an infinite dimensional space, and then the classical Liapunov theorem for the system in the new form is written. In this paper the very general case is considered, that is non-linear continuous time difference equations with multiple non commensurate delays are considered, and moreover the functions involved in the dynamics are allowed to be discontinuous, as well as the initial state. In order to study the stability of the internal dynamics in non-linear time delay feedback systems, an exogenous disturbance is added, which goes to zero exponentially as the time goes to infinity. An example is considered, from non-linear time delay feedback theory. While the results available in the literature are inconclusive as far as the stability of that example is concerned, such stability is proved to hold by the theorems developed in this paper, and is validated by simulation results. Copyright © 2003 John Wiley & Sons, Ltd. [source] Generalization of the Nyquist robust stability margin and its application to systems with real affine parametric uncertaintiesINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 15 2001Charles T. Baab The critical direction theory for analysing the robust stability of uncertain feedback systems is generalized to include the case of non-convex critical value sets, hence making the approach applicable for a much larger class of relevant systems. A redefinition of the critical perturbation radius is introduced, leading to the formulation of a Nyquist robust stability measure that preserves all the properties of the previous theory. The generalized theory is applied to the case of rational systems with an affine uncertainty structure where the uncertain parameters belong to a real rectangular polytope. Necessary and sufficient conditions for robust stability are developed in terms of the feasibility of a tractable linear-equality problem subject to a set of linear inequalities, leading ultimately to a computable Nyquist robust stability margin. A systematic and numerically tractable algorithm is proposed for computing the critical perturbation radius needed for the calculation of the stability margin, and the approach is illustrated via examples. Copyright © 2001 John Wiley & Sons, Ltd. [source] Integrated medical feedback systems for drug delivery,AICHE JOURNAL, Issue 4 2005Adam Heller Drugs are now administered at frequencies and doses based on averages optimized for large populations. Because the optimal frequency and dose for an individual differs, transiently or permanently, from that of a population's average, the dosing is necessarily suboptimal. Feedback loop-based individualized integrated medical systems, comprising an implanted sensor, battery, amplifier, processor, and actuator are now in use in cardiac pacemakers and defibrillators. Drug-delivering medical feedback loops, comprising miniature sensors and drug pumps, would individualize, and thereby improve the effectiveness and safety of drugs. Their sensor would continuously or frequently monitor the effect of the drug and adjust, through a medical control algorithm, its flow to the minimum necessary for effectiveness, reducing thereby side effects and improving the success rate of experimental drugs. The pace of integration of the drug delivering feedback loops depends on the availability of proven miniature components and of medical control algorithms. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source] Latent errors and adverse organizational consequences: a conceptualizationJOURNAL OF ORGANIZATIONAL BEHAVIOR, Issue 7 2003Rangaraj Ramanujam We develop the concept of latent errors,uncorrected deviations from procedures and policies that have no direct adverse consequences,and examine the complex relationships between organizational antecedents, latent errors, and adverse consequences. Latent errors, with varying levels of frequency, are present in all organizations whereas extreme adverse outcomes are rare. Thus, all organizations become potential objects of study in research on errors. Latent errors enable the design of ex ante studies of errors that avoid sampling on the dependent variable. The basic elements of our framework focus on two critical linkages. First is the role of antecedent factors such as incentives and goals in contributing to the presence of latent errors. Second, we explore how positive and negative feedback systems and external triggers link an acceleration of latent errors with adverse organizational outcomes. We also discuss how variations in context (e.g., whether work activities are co-located or distributed) may affect these factors. Implications for research on high-reliability organizations are discussed. Copyright © 2003 John Wiley & Sons, Ltd. [source] The impact of multiple source feedback on management development: findings from a longitudinal studyJOURNAL OF ORGANIZATIONAL BEHAVIOR, Issue 7 2002Caroline Bailey Despite the rapid uptake of multi-source multi-rater (MSMR) feedback systems by UK organizations, comparatively little research exists describing the actual impact on participant managers, in terms of changes in management competence. Ratings of 104 target managers (by self assessments, bosses-, first- and second-level subordinates) were investigated within the context of a developmental feedback programme in operation within an organization. The study compared ratings over two administrations (with two years between administrations) to determine: (1) changes in co-workers' perceptions of their target manager's competence, (2) changes in target managers' development needs over time, (3) factors influencing a target manager's revised self-assessment and co-workers ratings, (4) changes in congruence between self and co-workers ratings and (5) the relationship of feedback to the organization's formal performance appraisal process. Significant increases in managers' competence were perceived by the managers' themselves and by their subordinates, development needs were seen to reduce and self and co-workers ratings were largely seen to become more congruent. However, polynomial regression analyses revealed co-workers feedback at Time One was not predictive of targets' self-assessments at Time Two. The implications of these findings with regard to the utility of MSMR feedback as a tool for management development are discussed. Copyright © 2002 John Wiley & Sons, Ltd. [source] Recursive Back-Stepping Design of An Adaptive Fuzzy Controller for Strict Output Feedback Nonlinear SystemsASIAN JOURNAL OF CONTROL, Issue 3 2002Wei-Yen Wang ABSTRACT In this paper, a back-stepping adaptive fuzzy controller is proposed for strict output feedback nonlinear systems. The unknown nonlinearity and external disturbances of such systems are considered. We assume that only the output of the system is available for measurement. As a result, two filters are constructed to estimate the states of strict output feedback systems. Since fuzzy systems can uniformly approximate nonlinear continuous functions to arbitrary accuracy, the adaptive fuzzy control theory combined with a tuning function scheme is developed to derive the control laws of strict output feedback systems that possess unknown functions. Moreover, the H, performance condition is introduced to attenuate the effect of the modeling error and external disturbances. Finally, an example is simulated in order to confirm the applicability of the proposed method. [source] | ||||||||||||||||||||||