Adaptive meshing for two-dimensional thermoelastic problems using Hermite boundary elements

In the present work, error indicators for the potential and elastostatic problems are used in a combined fashion to implement an adaptive meshing scheme for the solution of two-dimensional steady-state thermoelastic problems using the Boundary Element Method. These error indicators exploit in their formulation the possibility of generating two different numerical solutions from just one analysis using Hermite elements. The first solution is the standard one obtained from an analysis using Hermite elements. The second is a “reduced” solution obtained representing the field variables inside an element using some of the degrees of freedom of the Hermite element together with Lagrangian shape functions. The basic idea behind the computation of the error indicator is to compare these two solutions, on an element by element basis, to obtain an estimate of the magnitude of the error in the numerical solution corresponding to the Hermite elements. In this sense, it is assumed that the bigger the difference between these two solutions, the bigger the error in the original solution with Hermite elements. Since the thermoelastic problem in its uncoupled fashion is considered, the former approach is applied to both problems, heat conduction and thermoelastic. Since both numerical solutions for each one of these problems are obtained from just one analysis, the computational cost of the proposed error indicators is very low.     

Adaptive hierarchical image segmentation technique

In the report a technique of multiple adaptive image segmentation is outlined. Three hierarchy-to-hierarchy transforms for primary digital data ordering and filtration are introduced. To optimize the approximation of observed object with image segments the 22 algorithms of sequential segmentation are tested. The required standard deviation value depending on segment number is estimated. The prototypes are reviewed.     

Adaptive testing for hierarchical student models

This paper presents an approach to student modeling in which knowledge is represented by means of probability distributions associated to a tree of concepts. A diagnosis procedure which uses adaptive testing is part of this approach. Adaptive tests provide well-founded and accurate diagnosis thanks to the underlying probabilistic theory, i.e., the Item Response Theory. Most adaptive testing proposals are based on dichotomous models, where he student answer can only be considered either correct or incorrect. In the work described here, a polytomous model has been used, i.e., answers can be given partial credits. Thus, models are more informative and diagnosis is more efficient. This paper also presents an algorithm for estimating question characteristic curves, which are necessary in order to apply the Item Response Theory to a given domain and hence must be inferred before testing begins. Most prior estimation procedures need huge sets of data. We have modified preexisting procedures in such a way that data requirements are significantly reduced. Finally, this paper presents the results of some controlled evaluations that have been carried out in order to analyze the feasibility and advantages of this approach. This paper (or a similar version) is not currently under review by a journal or conference, nor will it be submitted to such within the next three months.     

Adaptive hierarchical tuning of fuzzy controllers

Fuzzy controller design includes both linear and non-linear dynamic analysis. The knowledge base parameters associated within the fuzzy rule base influence the non-linear control dynamics while the linear parameters associated within the fuzzy output signal influence the overall control dynamics. For distinct identification of tuning levels, an equivalent linear controller output and a normalized non-linear controller output are defined. A linear proportional-integral-derivative (PID) controller analogy is used for determining the linear tuning parameters. Non-linear tuning is derived from the locally defined control properties in the non-linear fuzzy output. The non-linearity in the fuzzy output is then represented in a graphical form for achieving the necessary non-linear tuning. Three different tuning strategies are evaluated. The first strategy uses a genetic algorithm to simultaneously tune both linear and non-linear parameters. In the second strategy the non-linear parameters are initially selected on the basis of some desired non-linear control characteristics and the linear tuning is then performed using a trial and error approach. In the third method the linear tuning is initially performed off-line using an existing linear PID law and an adaptive non-linear tuning is then performed online in a hierarchical fashion. The control performance of each design is compared against its corresponding linear PID system. The controllers based on the first two design methods show superior performance when they are implemented on the estimated process system. However, in the presence of process uncertainties and external disturbances these controllers fail to perform any better than linear controllers. In the hierarchical control architecture, the non-linear fuzzy control method adapts to process uncertainties and disturbances to produce superior performance.     

Adaptive hierarchical control for output feedback systems

In this paper, we address the problem of adaptive hierarchical control for a class of so-called uncertain output feedback systems. The proposed approach is to design an adaptive output interface dynamic by estimating the uncertainties. With the interface connected to the uncertain nonlinear system and a linear abstract system, the system could track approximately the abstraction. Finally, two examples are presented to illustrate our approach.     

Adaptive hierarchical vector quantization for image coding

In this paper an adaptive hierarchical algorithm of vector quantization for image coding is proposed. First the basic codebook is generated adaptively, then the codes are coded into higher-level codes by creating an index codebook using the redundance presented in the codes. This hierarchical scheme lowers the bit rate significantly and causes little more computation and no more distortion than the single-layer adaptive VQ algorithm does which is used to create the basic codebook.     

Finite elements with boundary interpolation

Finite elements for which an interpolation scheme is postulated on the boundary only are potentially more accurate. An efficient and easy technique for generating such elements from classical displacement element-types is presented. The method is applied to the Poisson problem using rectilinear triangles with quadratic interpolation. Suitable error measures are defined and convergence is discussed. A benchmark demonstrates the computational efficiency of the proposed method.     

WSN自适应负载均衡集簇分层路由协议

结合考虑传统无线传感器网络(wireless sensor networks,WSN)路由协议特点以及实际应用中节点的不对等性,提出了一种自适应负载均衡集簇分层路由协议——ALBCH.该协议在簇头选举时引入剩余能量等相关因子,将贪婪算法成链机制分别引入分层路由协议的簇内通信和簇头间通信,对贪婪算法成链机制进行了一些改进.仿真结果表明,ALBCH能更有效地均衡网络负载,具有更好的健壮性和更高的实时性能,同时解决了传统协议在处理异构网络时的局限性.     

Complex boundary elements for contaminant transport

Recent numerical advances in the Complex Variable Boundary Element Method (CVBEM) provide easier-to-use analysis procedures in the study of advection-dominated contaminant transport of conservative specie migration in a steady groundwater flow field. In this paper, the CVBEM is applied to groundwater advection contaminant transport problems, and the CVBEM numerical error is evaluated by use of the approximate boundary graphical technique. Besides providing actual solutions to many groundwater flow and advective contaminant transport problems, the CVBEM can be used to develop analytic test cases to be used in numerically calibrating other groundwater and contaminant transport numerical models for other classes of problems. In this paper, the CVBEM model is developed by use of a coupled L²/Collocation fit to prescribed boundary conditions.     

Adaptive r and h — r algorithms for boundary elements

The techniques of mesh redistribution (r) and mesh refinement-redistribution (h – r) have been proven to be of considerable practical importance in the numerical solution of boundary value problems. In this paper, the implementation of these techniques in the boundary element formulation is considered. To assess the validity of the proposed algorithms, two model problems are employed. These problems are the potential equation and the equations of linear elasticity in two dimensions, both containing boundary singularities (cracks).     

Contribution to free boundary problems using boundary elements: Trefftz approach

There are two main approaches to the formulation of boundary methods, these are boundary integral equations and approximations by complete systems of solutions (Trefftz method). The latter has been the subject of extensive studies by one of the authors oriented to clarifying the foundations of the method and increasing its versatility. The present paper is devoted to explain the application of this procedure to free boundary problems such as Signorini and friction problems in elasticity.     

Adaptive optimal hierarchical control of nonstationary nonlinear large systems

An adaptive approach for closed-loop coordinated hierarchical control of large-scale, nonlinear, interconnected dynamic systems with time varying parameters is presented. Viability of the approach is established with simulation results.     

Adaptive hierarchical scheduling policy for enterprise grid computing systems

In an enterprise grid computing environments, users have access to multiple resources that may be distributed geographically. Thus, resource allocation and scheduling is a fundamental issue in achieving high performance on enterprise grid computing. Most of current job scheduling systems for enterprise grid computing provide batch queuing support and focused solely on the allocation of processors to jobs. However, since I/O is also a critical resource for many jobs, the allocation of processor and I/O resources must be coordinated to allow the system to operate most effectively. To this end, we present a hierarchical scheduling policy paying special attention to I/O and service-demands of parallel jobs in homogeneous and heterogeneous systems with background workload. The performance of the proposed scheduling policy is studied under various system and workload parameters through simulation. We also compare performance of the proposed policy with a static space–time sharing policy. The results show that the proposed policy performs substantially better than the static space–time sharing policy.     

Beam and plate stability by boundary elements

The direct boundary element method is used for the linear elastic stability analysis of Bernoulli-Euler beams and Kirchhoff thin plates. The formulation is based on the reciprocal work theorem of Betti and utilizes either fundamental solutions which incorporate the effect of axial and in-plane forces on bending, or fundamental solutions which correspond to pure flexure. In the former case. only a boundary discretization of the structure is required, while in the latter case discretization of the boundary as well as of the interior is necessary. However, the fundamental solutions in the latter case are less complicated than the ones in the former case. Numerical examples are subsequently presented to illustrate the methodology. The basic conclusion is that the simpler fundamental solutions are adequate and, by virtue of being more general, greatly expand the versatility of the boundary element method.     

Adaptive boundary concentration control using Zakai equation

A mean-variance control problem is formulated with respect to a partially observed nonlinear system that includes unknown constant parameters. A physical prototype of the system is the cathode surface reaction in an electrolysis cell, where the controller aim is to keep the boundary concentration of species in the near vicinity of the cathode surface low but not zero. The boundary concentration is a diffusion-controlled process observed through the measured current density and, in practice, controlled through the applied voltage. The former incomplete data control problem is converted to complete data–to the so-called separated control problem whose solution is given by the infinite-dimensional Zakai equation. In this article, the separated control problem is solved numerically using pathwise integration of the Zakai equation. This article demonstrates precise tracking of the target trajectory with a rapid convergence of estimates to unknown parameters, which take place simultaneously with control.     

分层特征模板筛选的维吾尔语韵律边界预测

韵律边界的正确预测是连续语音合成系统中首要解决的关键问题。针对维吾尔语分层韵律结构,通过基于条件随机场（CRF）的分层自底向上方法预测了维吾尔语的韵律词和韵律短语边界,并将维吾尔语形态特征作为韵律边界预测模型的重要特征。根据不同韵律边界层次的特点,对分层韵律边界预测方法进行了改进,针对分层方法的不同层次进行独立特征模板筛选,从而进一步提高韵律边界预测性能。通过对不同的特征模板和不同韵律边界预测模型进行反复实验,得到了最好的预测性能。实验结果表明,该方法明显提高了韵律边界预测结果。     

Lead field computation for the electrocardiographic inverse problem--finite elements versus boundary elements

In order to be able to solve the inverse problem of electrocardiography, the lead field matrix (transfer matrix) has to be calculated. The two methods applied for computing this matrix, which are compared in this study, are the boundary element method (BEM) and the finite element method (FEM). The performance of both methods using a spherical model was investigated. For a comparable discretization level, the BEM yields smaller relative errors compared to analytical solutions. The BEM needs less computation time, but a larger amount of memory. Inversely calculated myocardial activation times using either the FEM or BEM computed lead field matrices give similar activation time patterns. The FEM, however, is also capable of considering anisotropic conductivities. This property might have an impact for future development, when also individual myocardial fiber architecture can be considered in the inverse formulation.     

Adaptive refinement analysis using hybrid-stress transition elements

In this paper, 4-node to 7-node hybrid-stress transition elements are developed for automatic adaptive refinement analysis of plane elasticity problems. The displacement-based transition quadrilateral elements are first adopted and applied to refinement analysis using both full and reduced integration schemes. As the stress field over the displacement-based transition elements is not continuous, a more smooth stress pattern is desirable and could enhance the performance of the element. Indeed, continuous stress field of various orders can be easily introduced into a displacement-based element through a variational procedure based on the Hellinger–Reissner functional. Of the same kinematics and displacement pattern, the resulting hybrid-stress transition elements are more superior to the displacement-based elements in possessing a more continuous high quality stress field within the element. The hybrid-stress transition elements are tested with classical benchmark examples, and the results indicate that hybrid-stress transition elements are consistently more efficient than the displacement-based counterparts in adaptive refinement analysis. A more economical rank-deficient version of hybrid-stress transition elements is also available. While they are less expensive to evaluate, they enjoy a very similar convergence rate as the rank-sufficient hybrid-stress transition elements.     

Adaptive remeshing process with quadrangular finite elements

Since the quality of FEM analysis directly depends on the quality of meshes, various mesh adaptation schemes have been researched. There are two stages on adaptive finite element analysis; to derive error measure and to control meshes based on error measure. The former has been well researched among applied mathematicians. However, the importance of the latter aspect wasn't considered enough. Even if the error measures were well estimated, the total performance of mesh adaptation might be poor with a poor mesh control. This paper proposes an effective mesh control scheme for h-adaptation, or adaptive remeshing scheme with the explicit relation between interpolation theory based on error measure and desirable mesh size. Total mesh adaptation is controlled by introducing Quality Index, or the ratio between the total error norm and the total energy norm which represents the quality of the total meshes; specifying the desirable value of Quality Index, then the adaptive remeshing process can handle it and Quality Index is almost converged to the given value. Since the full automatic feature of the mesh generator is a prerequisite for adaptive remeshing, the author also discusses the algorithm of the quadrangular mesh generator for arbitrary domains. After evaluation on a linear problem, it's confirmed that the proposed mesh control scheme and the proposed error measure-mesh size relations are acceptable. The incompatible case for mesh adaptation is also discussed in this paper.     

基于错误学习的自适应等级可搜索加密方案

针对现有分等级可搜索加密方案存在不能有效抵抗量子攻击以及不能灵活添加与删除等级的问题,提出一种基于错误学习的自适应等级可搜索加密（AHSE）方案。首先,利用格的多维特点并基于格上错误学习（LWE）问题,使该方案能有效抵抗量子攻击;其次,构造条件键对用户进行明确的等级划分,使用户只能搜索其所属等级下的文件,实现有效的等级访问控制;同时,设计一种分段式索引结构,其等级能够灵活添加与删除,具有良好的自适应性,可以满足不同粒度访问控制的需求,并且,该方案中所有用户仅共享一张分段式索引表即可实现搜索,从而有效提高搜索效率;最后,理论分析表明,该方案中用户和文件的更新、删除以及等级变动简单、易于操作,适用于动态的加密数据库、云医疗系统等环境。