Sequential virtual motion camouflage method for nonlinear constrained optimal trajectory control

Nonlinear constrained optimal trajectory planning is a challenging and fundamental area of research. This paper proposes bio-inspired fast-time approaches for this type of problems based on the inspiration drawn from the natural phenomenon known as the motion camouflage. Two algorithms are proposed: the virtual motion camouflage (VMC) subspace method and the sequential VMC method. As a hybrid approach, the sequential VMC method works through a two-step structure in each iteration. First, the VMC subspace method will solve for an optimal solution over a selected subspace. Second, an algorithm consisting of a linear programming and a line search will vary the subspace so that the next VMC subspace result will be guaranteed not to be worse than that of the current step. The dimension and time complexities of the algorithms will be analyzed, and the optimality of the solution via the sequential VMC approach will be studied. Through the VMC approaches, the state and control variables in the kinematics or dynamics models of vehicles in the selected subspace can be represented by a single degree-of-freedom vector, called the path control parameter vector. The reduction in dimension and no involvement of equality constraints will in practice make the convergence faster and easier, and a much smaller computational cost is expected. Two simulation examples, the Breakwell problem and a minimum time robot obstacle avoidance problem with different numbers of obstacles, are used to demonstrate the capabilities of the algorithms.     

Robust method for identifying material parameters based on virtual fields in elastodynamics

We develop an inverse method with the purpose of extracting elastic properties of materials in the framework of transient dynamics. To this end, we create a small linear system based on a set of well-chosen time-dependent virtual fields (VF) and measurement data. The parameters are the solutions of this system and can be quickly extracted. We compare this new method with the classical finite element model updating (FEMU) method for different case studies. In our study, the measurements are synthetic, i.e, they are calculated using a fine finite element (FE) model. Uniform white noise is added to model measurement uncertainties. Results, based on Monte Carlo simulations, show that our method is more robust and accurate than the FEMU method for an acceptable noise level. Our new method appears well-adapted to linear elasticity in transient dynamics.     

A mixed virtual element method for a nonlinear Brinkman model of porous media flow

In this work we introduce and analyze a mixed virtual element method for the two-dimensional nonlinear Brinkman model of porous media flow with non-homogeneous Dirichlet boundary conditions. For the continuous formulation we consider a dual-mixed approach in which the main unknowns are given by the gradient of the velocity and the pseudostress, whereas the velocity itself and the pressure are computed via simple postprocessing formulae. In addition, because of analysis reasons we add a redundant term arising from the constitutive equation relating the pseudostress and the velocity, so that the well-posedness of the resulting augmented formulation is established by using known results from nonlinear functional analysis. Then, we introduce the main features of the mixed virtual element method, which employs an explicit piecewise polynomial subspace and a virtual element subspace for approximating the aforementioned main unknowns, respectively. In turn, the associated computable discrete nonlinear operator is defined in terms of the \(\mathbb {L}^2\)-orthogonal projector onto a suitable space of polynomials, which allows the explicit integration of the terms involving deviatoric tensors that appear in the original setting. Next, we show the well-posedness of the discrete scheme and derive the associated a priori error estimates for the virtual element solution as well as for the fully computable projection of it. Furthermore, we also introduce a second element-by-element postprocessing formula for the pseudostress, which yields an optimally convergent approximation of this unknown with respect to the broken \(\mathbb {H}(\mathbf {div})\)-norm. Finally, several numerical results illustrating the good performance of the method and confirming the theoretical rates of convergence are presented.     

扩展风险性滤波算法的修正方法

针对非线性系统扩展风险性滤波(ERSF)估计精度较低的缺点,提出一种基于二阶Taylor展开对其进行高阶修正的算法.该算法利用高阶项对一阶扩展卡尔曼滤波(EKF)的状态估计向量及协方差阵进行适当修正,并由新息滤波方法得到修正的扩展风险性滤波(MERSF).高度非线性的仿真研究表明,所提出的算法在计算量增加不多的情况下,滤波精度有明显的提高.     

The utility of a virtual reality locomotion interface for studying gait behavior

OBJECTIVE: To investigate the effect of optic flow on gait behavior during treadmill walking using an immersive virtual reality (VR) setup and compare it with conventional treadmill walking (TW) and overground walking (OW). BACKGROUND: Previous research comparing TW with OW speculated that a lack of optic flow (relative visual movement between a walker and the environment) during TW may have led to perceptual cue conflicts, resulting in differences in gait behavior, as compared with OW. METHOD: Participants walked under three locomotion conditions (OW, TW, and TW with VR [TWVR]) under three walking constraint conditions (no constraint, a temporal/pacing constraint, and a spatial/path-following constraint). Presence questionnaires (PQs) were administered at the close of the TWVR trials. Trials were subjected to video analysis to determine spatiotemporal and kinematics variables used for comparison of locomotion conditions. RESULTS: ANOVA revealed gait behavior during TWVR to be between that of OW and TW. Speed and cadence during TWVR were significantly different from those of TW, whereas knee angle was comparable to that of OW. Correlation analysis of PQ scores with gait measures revealed a positive linear association of the distraction subfactor of the PQ with walking speed during TWVR, suggesting an increase in the sense of presence in the virtual environment led to increases in walking speed. CONCLUSION: The results demonstrate that providing optic flow during TW through VR has an impact on gait behavior. APPLICATION: This study provides a basis for developing simple VR locomotion interface setups for gait research.     

Investigating culture-related aspects of behavior for virtual characters

In this paper, culture-related behaviors are investigated on several channels of communication for virtual characters. Prototypical behaviors were formalized in computational models based on a literature review as well as a corpus analysis, exemplifying the German and Japanese cultures. Therefore, aspects of verbal behavior, communication management and nonverbal behavior were taken into account. In evaluation studies conducted in the targeted cultures, each aspect’s impact on human observers was tested. With it, we investigated for which of the aspects, observers prefer agent behavior that was designed to resemble their own cultural background.     

Modal representation of geometrically nonlinear behavior by the finite element method

A method is described for representing mild geometrically nonlinear static behavior of thin-type structures, within the finite element method, in terms of the solution of a certain eigenvalue problem. This eigenvalue problem, commonly known as the linear or bifurcation buckling problem for a restricted class of so-called “perfect” structural situations, is thus seen to have a broader significance. The applied loading nonlinearly amplifies the contributions of each mode (eigenvector) present in the linear finite dement solution, and the amplification factors are easily computable functions of the eigenvalues. Computational results for braced frames and arches under asymmetric loading are presented.     

Series solution of nonlinear differential equations by a novel extension of the Laplace transform method

A technique for extending the Laplace transform method to solve nonlinear differential equations is presented. By developing several theorems, which incorporate the Adomian polynomials, the Laplace transformation of nonlinear expressions is made possible. A number of well-known nonlinear equations including the Riccati equation, Clairaut's equation, the Blasius equation and several other ones involving nonlinearities of various types such as exponential and sinusoidal are solved for illustration. The proposed approach is analytical, accurate, and free of integration.     

Image-based virtual exhibit and its extension to 3D

In this paper we introduce an image-based virtual exhibition system especially for clothing product.It can provide a powerful material substitution function,which is very useful for customization clothing-built.A novel color substitution algorithm and two texture morphing methods are designed to ensure realistic substitution result.To extend it to 3D,we need to do the model reconstruction based on photos.Thus we present an improved method for modeling human body.It deforms a generic model with shape details extracted from pictures to generate a new model.Our method begins with model image generation followed by silhouette extraction and segmentation.Then it builds a mapping between pixeis inside every pair of silhouette segments in the model image and in the picture.Our mapping algorithm is based on a slice space representation that conforms to the natural features of human body.     

一种虚拟社区信任机制模型的构建方法

虚拟社区是网络社会化的重要产物,在众多网络应用中发展极为迅速.虚拟社区以现实社区为原型,社区成员间的交互行为很大程度上依赖于信任关系,稳定良好的信任环境对于虚拟社区的健康发展十分重要.通过分析虚拟社区的特性,结合现有实现机制的相关经验,在课题信任模型研究的基础上提出了一种基于结构化P2P网络环境的虚拟社区的信任模型构建方法.通过分析现实社会社区与虚拟社区的层次关系和映射关系,结合结构化P2P网络环境的特点和优势,使得社区构建更为真实合理,从而有效地提高了虚拟社区的运作性能.     

A lightweight method for virtual machine introspection

A method for the introspection of virtual machines is proposed. The main distinctive feature of this method is that it makes it possible to obtain information about the system operation using the minimum knowledge about its internal organization. The proposed approach uses rarely changing parts of the application binary interface, such as identifiers and parameters of system calls, calling conventions, and the formats of executable files. The lightweight property of the introspection method is due to the minimization of the knowledge about the system and by its high performance. The introspection infrastructure is based on the QEMU emulator, version 2.8. Presently, monitoring the file operations, processes, and API function calls are implemented. The available introspection tools (RTKDSM, Panda, and DECAF) get data for the analysis using kernel structures. All the data obtained (addresses of structures, etc.) is written to special profiles. Since the addresses and offsets strongly depend not only on the version of the operating system but also on the parameters of its assembly, these tools have to store a large number of profiles. We propose to use parts of the application binary interface because they are rarely modified and it is often possible to use one profile for a family of OSs. The main idea underlying the proposed method is to intercept the system and library function calls and read parameters and returned values. The processor provides special instructions for calling system and user defined functions. The capabilities of QEMU are extended by an instrumentation mechanism to enable one to track each executed instruction and find the instructions of interest among them. When a system call occurs, the control is passed to the system call detector that checks the number of the call and decides to which module the job should be forwarded. In the case of an API function call, the situation is similar, but the API function detector checks the function address. An introspection tool consisting of a set of modules is developed. These modules are dynamic libraries that are plugged in QEMU. The modules can interact by exchanging data.     

一种虚拟现实建模的新方法

介绍了OpenGL和Matlab2009a各自的特点,在结合各自特点基础上,建立了基于二者的虚拟现实三维建模开发平台;以建立的虚拟现实建模开发平台为例,对比已有的使用Matlab外部接口的方法,证明了基于OpenGL和Matlab开发方法的优越性和有效性.     

面向虚拟维修训练的自抓取虚拟手交互行为构建

针对当前维护训练模拟器（MTD）不能很好地向受训者展示飞机维修过程中的具体维修动作的问题,构建一种自抓取的虚拟手与相应的交互行为,以提高机务培训质量。通过分析维修的基本动作要素,定义与构建基于蒙皮骨骼的虚拟手动作库;在场景漫游阶段,实时获取视角位置来驱动虚拟手运动,减轻场景漫游下的虚拟手控制负荷;在具体维修操作阶段,利用所提的交互行为算法,将虚拟手的位置自调节与骨骼动画osgCal相结合,通过调取动作库中的相应动作,完成具体的维修任务。实验结果表明,所提出的方法能较好地展现具体的维修操作,对于虚拟维修训练具有良好可用性。     

The method of particular solutions for solving nonlinear Poisson problems

Based on the recent development in the method of particular solutions, we re-exam three approaches using different basis functions for solving nonlinear Poisson problems. We further propose to simplify the solution procedure by removing the insolvency condition when the radial basis functions are augmented with high order polynomial basis functions. We also specify the deficiency of some of these methods and provide necessary remedy. The traditional Picard method is introduced to compare with the recent proposed methods using MATLAB optimization toolbox solver for solving nonlinear Poisson equations. Ranking on these three approaches are given based on the results of numerical experiment.     

浏览器扩展行为监控系统的设计与实现*

浏览器扩展是一种允许为浏览器添加个性化功能的机制。然而,这一机制在极大地增强了浏览器表现能力的同时,也使浏览器暴露在更多的攻击之下。为有效缓和浏览器扩展机制给用户带来的安全威胁,设计并实现了针对浏览器扩展的行为监控系统,通过一组安全策略来控制扩展对关键接口的访问;最后对该系统的有效性及性能进行了分析和测试。实验结果表明,系统可有效降低用户在使用浏览器扩展时所带来的安全风险。     

A nonlinear extension of the Generalized Hebbian learning

In this letter, we introduce a nonlinear hierarchic PCA type neural network with a simple architecture. The learning algorithm is a kind of nonlinear extension of the well-known Sanger's Generalized Hebbian Algorithm (GHA). It is derived from a nonlinear optimization criterion. Experiments with sinusoidal data show that the neurons become sensitive to different sinusoids. Standard linear PCA algorithms don't have such a separation property.     

基于裂缝中心线方向的土遗址裂缝宽度计算方法

针对现存的大量具有历史和科学研究价值的土遗址受到裂缝病害的影响,而现常用的裂缝宽度测量方法耗时、耗力、成本高,并且对土遗址本身具有一定的损害等问题.提出了一种以数字图像处理技术为基础,基于裂缝中心线方向的土遗址裂缝宽度计算方法.该方法首先对裂缝图像进行除燥和形态学处理,利用骨架化的方法求得裂缝的中心线,再基于中心线上每一点的方向,求其法线与裂缝左右边界交点间的距离,并以此作为此处裂缝的宽度.实验表明:该裂缝宽度计算方法具有较高的准确性和通用性.     

Simple saturated designs for ANCBC systems and extension to feedforward nonlinear systems

This article re-examines the robust stabilisation of the asymptotically null-controllable with bounded controls (ANCBC) systems, and extends the established algorithm to a wide class of feedforward nonlinear systems whose nominal dynamics contains both multiple integrators and multiple oscillators. Based on the notion of ‘converging-input bounded-state’ (CIBS) rather than ‘small-input small-state’ (SISS), the computation burden in Sussmann et al. (Sussmann, H.J., Sontag, E.D., and Yang, Y. (1994), ‘A General Result on the Stabilization of Linear Systems using Bounded Controls’, IEEE Transactions on Automatic Control, 39, 2411–2425) is reduced and a class of simple saturated control laws is presented for the CIBS stabilisation of ANCBC systems. Then, by combining the technique of dealing with higher-order terms, the algorithm for ANCBC systems is extended to feedforward nonlinear systems.     

Multigrid method for nonlinear poroelasticity equations

In this study, a nonlinear multigrid method is applied for solving the system of incompressible poroelasticity equations considering nonlinear hydraulic conductivity. For the unsteady problem, an additional artificial term is utilized to stabilize the solutions when the equations are discretized on collocated grids. We employ two nonlinear multigrid methods, i.e. the “full approximation scheme” and “Newton multigrid” for solving the corresponding system of equations arising after discretization. For the steady case, both homogeneous and heterogeneous cases are solved and two different smoothers are examined to search for an efficient multigrid method. Numerical results show a good convergence performance for all the strategies.