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Existing Results (existing + result)
Selected AbstractsCytomegalovirus in inflammatory bowel disease: Pathogen or innocent bystander?INFLAMMATORY BOWEL DISEASES, Issue 9 2010Garrett Lawlor MD Abstract The role of cytomegalovirus (CMV) in exacerbations of inflammatory bowel disease (IBD) remains a topic of ongoing debate. Current data are conflicting as to whether CMV worsens inflammation in those with severe colitis, or is merely a surrogate marker for severe disease. The interpretation of existing results is limited by mostly small, retrospective studies, with varying definitions of disease severity and CMV disease. CMV colitis is rare in patients with Crohn's disease or mild-moderate ulcerative colitis. In patients with severe and/or steroid-refractory ulcerative colitis, local reactivation of CMV can be detected in actively inflamed colonic tissue in about 30% of cases. Where comparisons between CMV+ and CMV, steroid-refractory patients can be made, most, but not all, studies show no difference in outcomes according to CMV status. Treatment with antiviral therapy has allowed some patients with severe colitis to avoid colectomy despite poor response to conventional IBD therapies. This article reviews the immunobiology of CMV disease, the evidence for CMV's role in disease severity, and discusses the outcomes with antiviral therapy. (Inflamm Bowel Dis 2010) [source] Robust absolute stability criteria for uncertain Lur'e systems of neutral typeINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 3 2008Qing-Long Han Abstract This paper is concerned with robust absolute stability of uncertain Lur'e systems of neutral type. Some delay-dependent stability criteria are obtained and formulated in the form of linear matrix inequalities. The criteria cover some existing results as their special cases. Neither model transformation nor bounding technique for cross terms is involved through derivation of the stability criteria. Numerical examples show the effectiveness of the criteria. Copyright © 2007 John Wiley & Sons, Ltd. [source] Constrained robust sampled-data control for nonlinear uncertain systemsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 5 2002Li-Sheng Hu Abstract In industrial process control, computer control, which makes the closed-loop system a sampled-data one containing both continuous- and discrete-time signals, is widely used. In contrast with traditional approximation methods, sampled-data synthesis, a direct digital controller design procedure without approximation, has received increasing attention during the past few years. However, many of the existing results cannot be applied to sampled-data control design for the uncertain systems. In this paper, a result of robust asymptotic stability of sampled-data systems with constraints on the state is presented based on a result on practical stability for these systems. Then the robust sampled-data control for a class of uncertain nonlinear systems with constraints on the output is developed. The problem is formulated from vehicle steering control with constraint on the side slip angle of body. The result is described by some matrix inequalities which could be solved by an iterative algorithm based on the linear matrix inequality technique. Finally, a numerical example is presented to demonstrate the result. Copyright © 2002 John Wiley & Sons, Ltd. [source] Some conditions which make the constantly scaled H, control synthesis problems convexINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 1 2002Toru Asai Abstract In this paper, we present some computationally tractable conditions which make the constantly scaled H, control synthesis problem convex. If one of the conditions proposed in this paper holds, the constantly scaled H, control synthesis problem can be solved efficiently as an LMI problem. The results presented here include the existing results such as the state feedback and the full information problems as special cases. In addition, the results are generalized to the case that some of state variables are exactly available. Owing to this generalization, a larger class of problems can be reduced to convex problems, while reduced order controllers can be obtained. Copyright © 2001 John Wiley & Sons, Ltd. [source] A further result of the nonlinear mixed H2/H, tracking control problem for robotic systemsJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 1 2002C. Q. Huang The design objective of a mixed H2/H, control is to find the H2 optimal tracking control law under a prescribed disturbance attenuation level. With the help of the technique of completing the squares, a further result of the mixed H2/H, optimal tracking control problem is presented, by combining it with standard LQ optimal control technique. In this paper, only a nonlinear time-varying Riccati equation is required to solve the problem in the design procedure,instead of two coupled nonlinear time-varying Riccati equations, or two coupled linear algebraic Riccati-Iike equations,with some assumptions made regarding the weighting matrices in the existing results. A closed-form controller for the mixed H2/H, robotic tracking problem is simply constructed with a matrix inequality check. Moreover, it shows that the existing results are the special cases of these results. Finally, detailed comparison is performed by numerical simulation of a two-link robotic manipulator. © 2002 John Wiley & Sons, Inc. [source] General energy decay estimates of Timoshenko systems with frictional versus viscoelastic dampingMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 16 2009Aissa Guesmia Abstract In this paper we consider the following Timoshenko system: with Dirichlet boundary conditions and initial data where a, b, g and h are specific functions and ,1, ,2, k1, k2 and L are given positive constants. We establish a general stability estimate using the multiplier method and some properties of convex functions. Without imposing any growth condition on h at the origin, we show that the energy of the system is bounded above by a quantity, depending on g and h, which tends to zero as time goes to infinity. Our estimate allows us to consider a large class of functions h with general growth at the origin. We use some examples (known in the case of wave equations and Maxwell system) to show how to derive from our general estimate the polynomial, exponential or logarithmic decay. The results of this paper improve and generalize some existing results in the literature and generate some interesting open problems. Copyright © 2009 John Wiley & Sons, Ltd. [source] HETEROGENEOUS RISK ATTITUDES IN A CONTINUOUS-TIME MODEL,THE JAPANESE ECONOMIC REVIEW, Issue 3 2006CHIAKI HARA We prove that every continuous-time model in which all consumers have time-homogeneous and time-additive utility functions and share a common probabilistic belief and a common discount rate can be reduced to a static model. This result allows us to extend some of the existing results of the representative consumer and risk-sharing rules in static models to continuous-time models. We show that the equilibrium interest rate is lower and more volatile than in the standard representative consumer economy, and that the individual consumption growth rates are more dispersed than in the absence of uncertainty. [source] CONTROLLABILITY OF A CLASS OF SINGULAR SYSTEMSASIAN JOURNAL OF CONTROL, Issue 4 2006Guangming Xie ABSTRACT In this paper, several different concepts of controllability are investigated for a class of linear singular systems which system parameters are piecewise constant. Necessary and sufficient geometric criteria for C-controllability and R-controllability of such systems are established, respectively. These conditions can be easily transformed into algebraic form. By applying the principle of duality, C-observability is discussed as well. Furthermore, the intrinsic relationship between these results and existing results are also discussed. Then, a novel necessary, and sufficient criterion for C-controllability of linear time-invariant singular systems is derived as a byproduct. [source] A New Delay-Dependent Stability Criterion For Neutral Delay-Differential SystemsASIAN JOURNAL OF CONTROL, Issue 3 2003Bin Yang ABSTRACT This paper investigates the problem of asymptotic stability for neutral delay-differential systems. Using the Lyapunov method, we derive a new delay-dependent sufficient condition for the stability of systems in terms of the linear matrix inequality (LMI). Numerical examples show that the results obtained in this paper significantly improve the estimate of stability limit over some existing results reported previously in the literature. [source] Gamma-convergence of gradient flows with applications to Ginzburg-LandauCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 12 2004Etienne Sandier We present a method to prove convergence of gradient flows of families of energies that ,-converge to a limiting energy. It provides lower-bound criteria to obtain the convergence that correspond to a sort of C1 -order ,-convergence of functionals. We then apply this method to establish the limiting dynamical law of a finite number of vortices for the heat flow of the Ginzburg-Landau energy in dimension 2, retrieving in a different way the existing results for the case without magnetic field and obtaining new results for the case with magnetic field. © 2004 Wiley Periodicals, Inc. [source] | |||||||||||||