基于Cosserat理论的平面等参元

为解释材料在微尺度下的尺度效应,基于Cosserat理论,从势能泛函驻值条件出发提出构造8节点Serendipity平面等参元,并建立平面有限元法．每个节点拥有3个独立节点自由度,分别为2个方向的线位移和1个逆时针方向的角位移．用该方法分析含中心小孔的无限平板在单轴拉伸情况下的应力集中问题．数值计算结果与Cosserat理论的解析解非常符合,表明应力集中因数k受泊松比μ,常数c及a／l值的影响很大;由于偶应力的存在,小孔周围的应力分布明显小于经典弹性力学理论的预测．通过对材料常数c的调节可以将该方法推广应用于基于Mindlin偶应力理论的数值分析中．     

An integration scheme for electromagnetic scattering using plane wave edge elements

Finite element techniques for the simulation of electromagnetic wave propagation are, like all conventional element based approaches for wave problems, limited by the ability of the polynomial basis to capture the sinusoidal nature of the solution. The Partition of Unity Method (PUM) has recently been applied successfully, in finite and boundary element algorithms, to wave propagation. In this paper, we apply the PUM approach to the edge finite elements in the solution of Maxwell’s equations. The electric field is expanded in a set of plane waves, the amplitudes of which become the unknowns, allowing each element to span a region containing multiple wavelengths. However, it is well known that, with PUM enrichment, the burden of computation shifts from the solver to the evaluation of oscillatory integrals during matrix assembly. A full electromagnetic scattering problem is not simulated or solved in this paper. This paper is an addition to the work of Ledger and concentrates on efficient methods of evaluating the oscillatory integrals that arise. A semi-analytical scheme of the Filon character is presented.     

A Monte Carlo program for the simulation of scintillation camera characteristics

There is a need for mathematical modelling for the evaluation of important parameters for photon imaging systems. A Monte Carlo program which simulates medical imaging nuclear detectors has been developed. Different materials can be chosen for the detector, a cover and a phantom. Cylindrical, spherical, rectangular and more complex phantom and source shapes can be simulated. Photoelectric, incoherent, coherent interactions and pair production are simulated. Different detector parameters, e.g. the energy pulse-height distribution and pulse pile-up due to finite decay time of the scintillation light emission, can be calculated. An energy resolution of the system is simulated by convolving the energy imparted with an energy-dependent Gaussian function. An image matrix of the centroid of the events in the detector can be simulated. Simulation of different collimators permits studies of spatial resolution and sensitivity. Comparisons of our results with experimental data and other published results have shown good agreement. The usefulness of the Monte Carlo code for the accurately simulation of important parameters in scintillation camera systems, stationary as well as SPECT (single-photon emission computed tomography) systems, has been demonstrated.     

A numerical model of propagation of waves from complex-shape emitters in an inhomogeneous medium

At present physical optics still calls for effective numerical solutions of diffraction problems. The main difficulty is a large amount of computation needed to perform integral conversions with rapidly oscillating cores. There are studies [1, 2] that offer effective algorithms of solving this kind of problems, yet these algorithms aim at determining amplitude-phase distributions in the detector’s plane only. The approach like that is barely suitable for computing the field at all points of the propagation medium between the emitter and detector. The necessity of such computations arises when one tries to model scattering of short waves on intricate-shape objects [3] in an inhomogeneous medium. The paper considers the application of algorithm [1] when visible light experiences scattering on plane triangular polygons in propagation through an inhomogeneous medium. The consideration of plane triangular apertures is important because of wide use of polygonal models for approximating real intricately shaped objects with a various degree of accuracy.     

Toolkit design for interactive structured graphics

Here, we analyze toolkit designs for building graphical applications with rich user interfaces, comparing polylithic and monolithic toolkit-based solutions. Polylithic toolkits encourage extension by composition and follow a design philosophy similar to 3D scene graphs supported by toolkits including JavaSD and Openlnventor. Monolithic toolkits, on the other hand, encourage extension by inheritance, and are more akin to 2D graphical user interface toolkits such as Swing or MFC. We describe Jazz (a polylithic toolkit) and Piccolo (a monolithic toolkit), each of which we built to support interactive 2D structured graphics applications in general, and zoomable user interface applications in particular. We examine the trade offs of each approach in terms of performance, memory requirements, and programmability. We conclude that a polylithic approach is most suitable for toolkit builders, visual design software where code is automatically generated, and application builders where there is much customization of the toolkit. Correspondingly, we find that monolithic approaches appear to be best for application builders where there is not much customization of the toolkit.     

Nonlinear finite element analysis for composite structures of axisymmetric geometry and loading

A linear strain, axisymmetric, triangular finite element is formulated for the modeling of materials which are generally orthotropic in the plane of the fibers and loaded axisymmetrically. The fibers may be oriented in planes other than the symmetric plane.This necessitates the use of three displacement degrees of freedom at each node.The element is also formulated to include geometric nonlinearity to take into account any stiffening or weakening of the structure due to deformation.The element is programmed into a finite element code, which is validated using a well-known isotropic nonlinear problem. It shows very good agreement with the results of other programs.The unique application of the element is shown in the analysis of a pneumatic tire.     

A Toolkit for Generating Sentences from Context-Free Grammars

Producing sentences from a grammar, according to various criteria, is required in many applications. It is also a basic building block for grammar engineering. This paper presents a toolkit for context-free grammars, which mainly consists of several algorithms for sentence generation or enumeration and for coverage analysis for context-free grammars. The toolkit deals with general context-free grammars. Besides providing implementations of algorithms, the toolkit also provides a simple graphical user interface, through which the user can use the toolkit directly. The toolkit is implemented in Java and is available at http://lcs.ios.ac.cn/~zhiwu/toolkit.php. In the paper, the overview of the toolkit and the major algorithms implemented in the toolkit are presented, and experimental results and preliminary applications of the toolkit are also contained.     

HgCdTe焦平面探测器热应力有限元分析

为降低HgCdTe焦平面探测器的内热应力、提高其可靠性,在MSC Patran和MSC Nastran 中对HgCdTe焦平面探测器进行热-力耦合分析.借助MSC Patran的参数化建模方法建立焦平面探测器的有限元模型,对该模型进行热分析,将结果作为温度载荷进行静力分析,得出HgCdTe芯片热应力分布情况.通过分析5...     

Geant4 hadron elastic diffuse model

Differential elastic hadron-nucleus cross-sections are discussed in the framework of the optical approach. The model predictions implemented in the Geant4 toolkit are compared with the experimental data for protons and pions. The contribution of Coulomb scattering is discussed for charged hadrons.     

New software developments for quality mesh generation and optimization from biomedical imaging data

In this paper we present a new software toolkit for generating and optimizing surface and volumetric meshes from three-dimensional (3D) biomedical imaging data, targeted at image-based finite element analysis of some biomedical activities in a single material domain. Our toolkit includes a series of geometric processing algorithms including surface re-meshing and quality-guaranteed tetrahedral mesh generation and optimization. All methods described have been encapsulated into a user-friendly graphical interface for easy manipulation and informative visualization of biomedical images and mesh models. Numerous examples are presented to demonstrate the effectiveness and efficiency of the described methods and toolkit.     

高职院校计算机硬件方向的Linux操作系统课程教学改革

对高职院校计算机硬件方向的Linux操作系统课程的教学模式和教学内容进行了探讨和改进。吸取了＂案例教学法＂、＂问题驱动法＂、＂互动教学法＂的理念,提出了＂类比＂的概念。通过与其他操作系统类比的方法实施教学,对知识的传授从点到面,再到应用。改进后的教学模式取得了较好的教学效果。     

A coordinate transformation approach for efficient repeated solution of Helmholtz equation pertaining to obstacle scattering by shape deformations

A computational model is developed for efficient solutions of electromagnetic scattering from obstacles having random surface deformations or irregularities (such as roughness or randomly-positioned bump on the surface), by combining the Monte Carlo method with the principles of transformation electromagnetics in the context of finite element method. In conventional implementation of the Monte Carlo technique in such problems, a set of random rough surfaces is defined from a given probability distribution; a mesh is generated anew for each surface realization; and the problem is solved for each surface. Hence, this repeated mesh generation process places a heavy burden on CPU time. In the proposed approach, a single mesh is created assuming smooth surface, and a transformation medium is designed on the smooth surface of the object. Constitutive parameters of the medium are obtained by the coordinate transformation technique combined with the form-invariance property of Maxwell’s equations. At each surface realization, only the material parameters are modified according to the geometry of the deformed surface, thereby avoiding repeated mesh generation process. In this way, a simple, single and uniform mesh is employed; and CPU time is reduced to a great extent. The technique is demonstrated via various finite element simulations for the solution of two-dimensional, Helmholtz-type and transverse magnetic scattering problems.     

The um toolkit for cooperative user modelling

This paper gives an overview of the um toolkit: the philosophy underlying its design, examples of its use and discussion of the way it deals with some major issues in creating user modelling shells. The um toolkit has been developed to provide support for a variety of cooperative agents. An important element of its cooperativeness is due to its capacity to give users an understanding of their own user models. This paper describes two substantial but very different uses of the toolkit. The first involves a collection of coaching systems that help users learn more about their text editor. Experimental results suggest that the user model is associated with users learning more. The second is a movie advisor that uses a range of tools to construct and refine the user model and to filter a database of movies. Both these systems are built from combining tools in um. The paper describes several of the tools for constructing and refining user models. In addition it describes the user-model viewing tools and the way that these help users ensure their user models are correct. The paper also discusses the two central themes of the um work, the application of a tools approach to the design of a user modelling toolkit and the implications of making the user model accessible to its owner, the person modelled.     

Computer programs for application of equations describing elastic and electromagnetic wave scattering from planar interfaces

MATLAB programs are presented which solve equations describing the scattering of plane elastic and electromagnetic waves from a planar interface separating homogenous, isotropic, and semi-infinite geologic media. The PSHSV program calculates and plots amplitude (reflection and refraction/transmission) coefficients, square root energy ratios, energy coefficients, and phase changes for elastic waves of P-, SH- or SV-type incident on an interface between elastic media. The EHEV program calculates and plots amplitude coefficients, square root energy ratios, energy coefficients, and phase changes for electromagnetic waves of EH- or EV-type incident on an interface between dielectric media. The applicability of the programs is demonstrated through the presentation of solutions (plotted as a function of incidence angle) obtained for geologic environments commonly encountered in seismic and ground penetrating radar applications.     

Cutoff wave numbers for energy-orthogonal six-node triangular plane-strain elements

This paper studies the propagation of plane harmonic waves in unbounded media discretized by the standard six-node triangular finite element. The element stiffness matrix is split into basic and higher order components which are obtained from mean and deviatoric strain fields, respectively. This decomposition is applied to the elastic energy. Based on the properties of the higher order energy, two values of the wave number are selected. Depending on the desired precision one of those values can be used as optimum cutoff wave number to properly capture a wave field.     

Physics-based subsurface visualization of human tissue

In this paper, we present a framework for simulating light transport in three-dimensional tissue with inhomogeneous scattering properties. Our approach employs a computational model to simulate light scattering in tissue through the finite element solution of the diffusion equation. Although our model handles both visible and nonvisible wavelengths, we especially focus on the interaction of near infrared (NIR) light with tissue. Since most human tissue is permeable to NIR light, tools to noninvasively image tumors, blood vasculature, and monitor blood oxygenation levels are being constructed. We apply this model to a numerical phantom to visually reproduce the images generated by these real-world tools. Therefore, in addition to enabling inverse design of detector instruments, our computational tools produce physically-accurate visualizations of subsurface structures.     

自供电的同步电荷提取电路的优化设计

利用压电元件的压电效应将外界振动产生的机械能转化为电能是当前一种有效的俘能方法。将压电元件表面累积的电荷进行有效提取是这种俘能方法的关键。因此,高效的电荷提取电路的设计显得特别重要。本文提出了一种自供电同步电荷提取电路SP-OSCE（Self-Powered Optimized Synchronous Charge Extraction Circuit）,使用两个无源的极值检测电路检测压电元件输出信号的正负极值并在极值点进行能量提取。所提出的SP-OSCE电路采用整流电路、极值检测电路元件复用的方法,从而避免了传统的整流桥结构;电路不但提取了压电元件受夹电容中的电荷,而且将检测电容中所积累的电荷提取到电感上,提高了能量的转换效率。通过Multisim建模仿真验证了所设计电路的有效性,进而进行了物理验证,实验表明与仿真结果相吻合。     

Design and Evaluation of a Team Mutual Awareness Toolkit for Digital Interfaces of Nuclear Power Plant Context

In the teamwork of nuclear power plants (NPPs), the maintenance of mutual awareness enables the operators to have an up-to-the-moment understanding of each other’s work and makes the collaboration more efficient. Providing interface support for mutual awareness is proven to be an effective way to enhance the operators’ mutual awareness in digital systems. What mutual awareness-relevant information to provide and how to present the information on the display are two questions worth studying. This research focused on the above two questions and provided a newly designed mutual awareness toolkit on the context of digital interfaces in NPPs. The usability of the designed toolkit was evaluated through a laboratory experiment. The influence of the mutual awareness toolkit on team performance and its interaction effect with task complexity was further examined under incident scenarios. The results showed that the designed mutual awareness toolkit improved the operators’ mutual awareness, while it did not decrease their individual situation awareness (SA) or impose extra mental workloads. In team diagnosis tasks, the teams using the mutual awareness toolkit more thoroughly discussed the incident scenarios and identified more key points of the incidents. The diagnosis correctness, perhaps moderated by other factors besides mutual awareness, was not significantly improved.     

A simple mixed finite element for static limit analysis

In this paper, we investigate the behavior of a simple mixed finite element for the limit analysis of plane structures. In particular, its ability to overcome incompressibility locking in plane strain situations is investigated. The element is constructed from a piecewise constant displacement field and a piecewise bilinear stress field, and is used within a mathematical programming based discrete representation of the classical static formulation. Several benchmark examples of both plane stress and plane strain situations are solved to illustrate the predictive accuracy and to assess the large-scale capability of the element. The results are compared with those obtained by a recent sophisticated enhanced strain mixed element formulation.     

8- and 12-node plane hybrid stress-function elements immune to severely distorted mesh containing elements with concave shapes

By simply improving the first version of hybrid stress element method proposed by Pian, several 8- and 12-node plane quadrilateral elements, which are immune to severely distorted mesh containing elements with concave shapes, are successfully developed. Firstly, instead of the stresses, the stress function ? is regarded as the functional variable and introduced into the complementary energy functional. Then, the fundamental analytical solutions (in global Cartesian coordinates) of ? are taken as the trial functions for 2D finite element models, and meanwhile, the corresponding unknown stress-function constants are introduced. Thus, the resulting stress fields must be more reasonable because both the equilibrium and the compatibility relations can be satisfied. Thirdly, by using the principle of minimum complementary energy, these unknown stress-function constants can be expressed in terms of the displacements along element boundaries, which can be interpolated directly by the element nodal displacements. Finally, the complementary energy functional can be rewritten in terms of element nodal displacement vector, and thus, the element stiffness matrix of such hybrid stress-function (HS-F) element is obtained. This technique establishes a universal frame for developing reasonable hybrid stress elements based on the principle of minimum complementary energy. And the first hybrid stress element proposed by Pian is just a special case within this frame. Following above procedure, two 8-node and two 12-node quadrilateral plane elements are constructed by employing different fundamental analytical solutions of Airy stress function. Numerical results show that, the 8-node and 12-node models can produce the exact solutions for pure bending and linear bending problems, respectively, even the element shape degenerates into triangle and concave quadrangle. Furthermore, these elements do not possess any spurious zero energy mode and rotational frame dependence.