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Adaptive Method (adaptive + method)
Selected AbstractsAn Adaptive Method for Indirect Illumination Using Light VectorsCOMPUTER GRAPHICS FORUM, Issue 3 2001Xavier Serpaggi In computer graphics, several phenomema need to be taken into account when it comes to the field of photo-realism. One of the most relevant is obviously the notion of global, and more precisely indirect, illumination. In "classical" ray-tracing if you are not under the light, then you are in a shadow. A great amount of work has been carried out which proposes ray-tracing based solutions to take into account the fact that "there is a certain amount of light in shadows". All of these methods carry the same weaknesses: high computation time and a lot of parameters you need to manage to get something out of the method. This paper proposes a generic computation method of indirect illumination based on Monte Carlo sampling and on the sequential analysis theory, which is faster and more automatic than classical methods. [source] Demographic and clinical characteristics of motor vehicle accident victims in the community general health outpatient clinic: a comparison of PTSD and non-PTSD subjectsDEPRESSION AND ANXIETY, Issue 4 2007Marina Kupchik M.D. Abstract Motor vehicle accidents (MVAs) are the leading cause of posttraumatic stress disorder (PTSD) in the general population, often with enduring symptomatology. This study details epidemiological and clinical features that characterize PTSD among MVA victims living in a nonhospitalized community setting long after the MVA event, and includes exploration of premorbid and peritraumatic factors. MVA victims (n=60; 23 males, 37 females) identified from the registry of a community general health outpatient clinic during a 7-year period were administered an extensive structured battery of epidemiological, diagnostic and clinical ratings. Results indicated that 30 subjects (50%; 12 males, 18 females) had MVA-related PTSD (MVAR-PTSD). Among those with PTSD, 16 individuals exhibited PTSD in partial remission, and six, in full remission. There were no significant demographic or occupational function differences between PTSD and non-PTSD groups. The most common comorbid conditions with MVAR-PTSD were social phobia (20%), generalized anxiety disorder (7.8%) and obsessive,compulsive disorder (0.5%). Previous MVA's were not predictive of PTSD. Subjects with MVAR-PTSD scored worse on the Clinician-Administered Posttraumatic Stress Disorder Scale, Part 2 (CAPS-2), Impact of Event Scale, Hamilton Depression Rating Scale, Hamilton Anxiety Rating Scale, Impulsivity Scale, and Toronto Alexithymia Rating Scale. Study observations indicate a relatively high rate of PTSD following an MVA in a community-based sample. The relatively high rate of partially remitted MVAR-PTSD (N=16) underscores the importance of subsyndromal forms of illness. Alexithymia may be an adaptive method of coping with event stress. The development of PTSD appears not to be associated with the severity of MVA-related physical injury. Depression and Anxiety 24:244,250, 2007. © 2006 Wiley,Liss, Inc. [source] Adaptive bang,bang control for the vibration control of structures under earthquakesEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 13 2003C. W. Lim Abstract An adaptive method based on the modified bang,bang control algorithm is proposed for the vibration control of structures subjected to unexpected severe seismic loads greater than the design loads. A hydraulic-type active mass damper was made and experiments were carried out in the laboratory using a one-story test structure and a five-story test structure with the active mass damper. Through numerical simulations and experiments it was confirmed that the proposed method works well to suppress the vibration of structures subjected to unexpected severe seismic loads greater than the design loads without causing any unstable situations. Copyright © 2003 John Wiley & Sons, Ltd. [source] Parametric enrichment adaptivity by the extended finite element methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2008Haim Waisman Abstract An adaptive method within the extended finite element method (XFEM) framework which adapts the enrichment function locally to the physics of a problem, as opposed to polynomial or mesh refinement, is presented. The method minimizes a local residual and determines the parameters of the enrichment function. We consider an energy form and a ,strong' form of the residual as error measures to drive the algorithm. Numerical examples for boundary layers and solid mechanics problems illustrate that the procedure converges. Moreover, when only the character of the solution is known, a good approximation is obtained in the area of interest. It is also shown that the method can be used to determine the order of singularities in solutions. Copyright © 2007 John Wiley & Sons, Ltd. [source] Adaptive finite elements with large aspect ratio for mass transport in electroosmosis and pressure-driven microflowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 9 2010Virabouth Prachittham Abstract A space,time adaptive method is presented for the numerical simulation of mass transport in electroosmotic and pressure-driven microflows in two space dimensions. The method uses finite elements with large aspect ratio, which allows the electroosmotic flow and the mass transport to be solved accurately despite the presence of strong boundary layers. The unknowns are the external electric potential, the electrical double layer potential, the velocity field and the sample concentration. Continuous piecewise linear stabilized finite elements with large aspect ratio and the Crank,Nicolson scheme are used for the space and time discretization of the concentration equation. Numerical results are presented showing the efficiency of this approach, first in a straight channel, then in crossing and multiple T-form configuration channels. Copyright © 2009 John Wiley & Sons, Ltd. [source] Adaptive backstepping control for a class of time delay systems with nonlinear perturbationsINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 3 2008Chang-Chun Hua Abstract The sliding mode control method has been extensively employed to stabilize time delay systems with nonlinear perturbations. Although the resulting closed-loop systems have good transient and steady-state performances, the designed controllers are dependent on the time delays. But one knows that it is difficult to obtain the precise delay time in practical systems, especially when it is time varying. In this paper, we revisit the problem and use the backstepping method to construct the state feedback controller. First, a coordinate transformation is used to obtain a cascade time delay system. Then, a linear virtual control law is designed for the first subsystem. The memoryless controller is further constructed based on adaptive method for the second subsystem with the uncertainties bounded by linear function. By choosing new Lyapunov,Krasovskii functional, we show that the system state converges to zero asymptotically. Via the proposed approach, we also discuss the case that the uncertainties are bounded by nonlinear functions. Finally, simulations are done to verify the effectiveness of the main results obtained. Copyright © 2007 John Wiley & Sons, Ltd. [source] Speed-up and performance evaluation of piecewise-linear DC analysisINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 4 2007Janne RoosArticle first published online: 29 NOV 200 Abstract The good convergence properties of piecewise-linear (PWL) DC analysis have been thoroughly discussed in many papers. This paper, in turn, concentrates on the speed of PWL DC analysis, where the boundary crossing of linear regions plays a crucial role. Fast methods are presented for performing the following boundary-crossing computations: LU-decomposition update, matrix-equation solution, boundary-crossing direction, and damping-factor determination. Special attention is given to those PWL DC analysis methods that perform PWL modelling of the non-linear components on the fly; an adaptive method is proposed for controlling the accuracy of PWL modelling and speeding up simulation. The computational efficiency of the accelerated PWL DC analysis is discussed and compared with that of conventional, Newton,Raphson iteration-based, DC analysis. Finally, the performance evaluation is completed with realistic simulation examples: it is demonstrated that the speed of the accelerated PWL DC analysis is comparable with that of the conventional DC analysis. Copyright © 2006 John Wiley & Sons, Ltd. [source] An adaptive displacement/pressure finite element scheme for treating incompressibility effects in elasto-plastic materialsNUMERICAL METHODS FOR PARTIAL DIFFERENTIAL EQUATIONS, Issue 4 2001Franz, Theo SuttmeierArticle first published online: 13 AUG 200 Abstract In this article, a mixed finite element formulation is described for coping with (nearly) incompressible behavior in elasto-plastic problems. In addition to the displacements, an auxiliary variable, playing the role of a pressure, is introduced resulting in Stokes-like problems. The discretization is done by a stabilized conforming Q1/Q1 -element, and the corresponding algebraic systems are solved by an adaptive multigrid scheme using a smoother of block Gauss,Seidel type. The adaptive algorithm is based on the general concept of using duality arguments to obtain weighted a posteriori error bounds. This procedure is carried out here for the described discretization of elasto-plastic problems. Efficiency and reliability of the proposed adaptive method is demonstrated at (plane strain) model problems. © 2001 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 17:369,382, 2001 [source] | ||||||||||