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 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.     

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).     

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.     

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 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.     

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 boundary layer meshing for viscous flow simulations

A procedure for anisotropic mesh adaptation accounting for mixed element types and boundary layer meshes is presented. The method allows to automatically construct meshes on domains of interest to accurately and efficiently compute key flow quantities, especially near wall quantities like wall shear stress. The new adaptive approach uses local mesh modification procedures in a manner that maintains layered and graded elements near the walls, which are popularly known as boundary layer or semi-structured meshes, with highly anisotropic elements of mixed topologies. The technique developed is well suited for viscous flow applications where exact knowledge of the mesh resolution over the computational domain required to accurately resolve flow features of interest is unknown a priori. We apply the method to two types of problem cases; the first type, which lies in the field of hemodynamics, involves pulsatile flow in blood vessels including a porcine aorta case with a stenosis bypassed by a graft whereas the other involves high-speed flow through a double throat nozzle encountered in the field of aerodynamics.     

The use of continuous boundary elements in the boundary elements method for domains with non-smooth boundaries via finite difference approach

A numerical method is presented in this article to deal with the drawback of boundary elements method (BEM) at corner points. The use of continuous elements instead of the discontinuous ones has been recommended in the BEM literature widely because of the simplicity and accuracy. However the continuous elements lead to certain difficulties for problems where their domains contain corners. In this paper the finite difference method (FDM) has been applied to obtain some constraints for boundary points near the corners to deal with this drawback. Because of its simplicity and capability, the new scheme is applicable on BEM problems for all geometries, all governing equations and general boundary conditions, easily. Since the Dirichlet boundary condition is more critical than the other ones, we will focus on it in the numerical implementation. The numerical results show that the new treatment improves the accuracy of BEM significantly.     

WSN中基于能量和距离的自适应分层路由算法

针对无线传感器网络中能量受限的问题,提出了节能的、负载均衡的分层路由算法EDUC（energy-based and distance-based unequal clustering algorithm）。EDUC用基于能量和距离的概率模型产生候选簇头;同时,EDUC利用定时器,使局部区域内剩余能量多的候选簇头成为簇头,并且根据能量和距离计算簇的半径。普通节点根据能量和距离计算候选节点的权值,加入权值最大的簇头。在构建多跳路由时,簇头根据候选节点的剩余能量、簇内和簇间通信代价选择最优的中继节点。在OMNet＋＋平台上的仿真结果表明,与其他算法相比,EDUC能够有效地均衡能量消耗,降低节点死亡速度,从而延长网络生命周期。     

Adaptive searching and replication of images in mobile hierarchical peer-to-peer networks

Due to the limitation of resources in mobile handheld devices and bandwidth constraints in wireless networks, it is important to efficiently manage image content and traffic to improve network throughput and response time. The efficient distribution of images in wireless networks is based on many parameters like the quality of service requirement, available bandwidth, restricted memory and diverse user profiles. We consider digital images as data objects accessed in a hierarchical mobile ad-hoc peer-to-peer network, referred as M-P2P. Our objective is to optimize the number of replicas of images in such a network architecture based on the resource limitations of the requesting peers equipped with miniature mobile devices as well as of wireless constraints in mobile ad-hoc networks (MANET). While replicating images, fragments of different resolution and their residues are used to optimize the traffic in the network and to decrease the search turnaround time. We call this replication algorithm as Ada-Rep. Performance evaluation is done by simulating Ada-Rep, base replication and uniform replication methods to evaluate parameters such as response time, failure rate, memory usage, traffic etc. Our results prove the efficiency and better performance of Ada-Rep.     

Adaptive boundary control of a flexible marine installation system

In this paper, boundary control of a marine installation system is developed to position the subsea payload to the desired set-point and suppress the cable’s vibration. Using Hamilton’s principle, the flexible cable coupled with vessel and payload dynamics is described as a distributed parameter system with one partial differential equation (PDE) and two ordinary differential equations (ODEs). Adaptive boundary control is proposed at the top and bottom boundaries of the cable, based on Lyapunov’s direct method. Considering the system parametric uncertainty, the boundary control schemes developed achieve uniform boundedness of the steady state error between the boundary payload and the desired position. The control performance of the closed-loop system is guaranteed by suitably choosing the design parameters. Simulations are provided to illustrate the applicability and effectiveness of the proposed control.     

A posteriori error estimate for the symmetric coupling of finite elements and boundary elements

In this note we study a posteriori error estimates for a model problem in the symmetric coupling of boundary element and finite elements methods. Emphasis is on the use of the Poincaré-Steklov operator and its discretization which are analyzed in general for both a priori and a posteriori error estimates. Combining arguments from [6] and [9, 10] we refine the a posteriori error estimate obtained in [9, 10]. For quasi-uniform meshes on the boundary, we prove some inequality of a reverse type using techniques from [5] and [36]. This indicates efficiency of the new estimate as illustrated in a numerical example.     

Adaptive mesh redistribution for the boundary element in elastostatics

An adaptive mesh redistribution strategy based on the grading function method is employed to solve the two dimensional elastostatic problem with the boundary element method. Three benchmark problems, one of which involves a crack or singularity, are treated to verify the overall procedure. The results are quite satisfactory, pointing to the fact that mesh redistribution can be used effectively along with the boundary element technique.