A fast integration method for translating-pulsating source Green’s function in Bessho form简

The singularities and oscillatory performance of translating-pulsating source Green＇s function in Bessho form were analyzed. Relative numerical integration methods such as Gaussian quadrature rule, variable substitution method （VSM）, and steepest descent integration method （SDIM） were used to evaluate this type of Green＇s function. For SDIM, the complex domain was restricted only on the 0-plane. Meanwhile, the integral along the real axis was computed by use of the VSM to avoid the complication of a numerical search of the steepest descent line. Furthermore, the steepest descent line was represented by the B-spline function. Based on this representation, a new self-compatible integration method corresponding to parametric t was established. The numerical method was validated through comparison with other existing results, and was shown to be efficient and reliable in the calculation of the velocity potentials for the 3D seakeeping and hydrodynamic performance of floating struc- tures moving in waves.     

开放英语CD-ROM应用效率调查研究简

采取定量研究方法,对某电大208名开放英语CD—ROM使用者进行问卷调查。研究结果表明系统应用效率低下。这既有学习者本身的原因,如学习自主性不高、计算机辅助语言学习经验欠缺、语言水平不足以及投入学习时间少等;也有学校和教师的原因,如没有采取相关措施或政策以及支持、服务和对话互动不够。其中,最重要的原因是学习者自主学习能力不足。     

揭秘物质的变质简

CaO、NaOH、Ca（OH）2等物质放置在空气中,极易吸收空气中的水蒸气、二氧化碳气体而发生变质,这部分内容已成为近年来中考化学命题的热点,试题多以探究题为主.     

A study on the contraction joint element and damage constitutive model for concrete arch dams简

A new contraction joint element model for the interface in different meshes between the arch dam sections is con- structed. The study on the elastic-plastic damage constitutive model for concrete, which is applied to multi-axial stresses, is also taken. The models of the dam-foundation-reservoir system for Xingbiling and Jinping concrete arch dams, China are calculated using the proposed contraction joint elements and the elastic-plastic damage constitutive model to verify the proposed models. Results showed that the proposed contraction joint element model has a high precision in simulating the behavior of contraction joints and the elastic-plastic damage constitutive model has a high precision in simulating the behavior of the damage to the concrete.     

Mechanical Engineering and MechanicsA morphing machining strategy for artificial bone简

In this work, a novel morphing machining strategy （MMS） is proposed. In the method, the workpiece is progressively carved out from the stock. Pitfalls in conventional iso-height strategy, such as sharp edges and unevenly distributed left-over materials, are overcome. Moreover, to calculate different levels in the MMS, an energy-based morphing algorithm is proposed. Finally, the proposed strategy is employed in the machining of artificial bone represented by a T-spline surface. The excellent properties of T-spline, such as expressing complex shapes with a single surface, have been well adopted to artificial bone fabri- cation. Computer simulation and the actual machining of the middle finger bone show the feasibility of the proposed strategy.     

Node shift method for stiffness-based optimization of single-layer reticulated shells简

This paper presents a node shift method to find the optimal distribution of nodes in single-layer reticulated shells. The optimization process searches for the minimum strain energy configuration and this leads to reduced sensitivity in initial imper- fections. Strain energy sensitivity numbers are derived for free shift and restricted shift where nodes can move freely in the 3D space or have to move within a predefmed surface respectively. Numerical examples demonstrate the efficiency of the proposed approach. It was found that optimized structures achieve higher ultimate load and are less sensitive to imperfections than the initial structure. The configuration of the final structure is closely related to factors like the initial structural configuration, spatial conditions, etc. Based on different initial conditions, architects can be provided with diverse reasonable structures. Furthermore, by amending the defined shapes and nodal distributions, it is possible to improve the mechanical behavior of the structures.     

Target localization based on joint measurement of amplitude and frequency in a LOFAR field简

To estimate the motion parameters of a moving target before its passing by the closest point of approach （CPA） point in a low frequency analyzing and recording （LOFAR） field, an error-free theoretical method based on the joint measurement of target radiated noise＇s amplitude and frequency was presented. First, the error-free theoretical equations for target characteristic frequency, absolute velocity, the CPA, and amplitude of the radiation noise were derived by three equal interval measured values of the target amplitude and frequency. Then, the method to improve the calculation accuracy was given. Finally, the simulation and experiments were conducted in the air and showed the correctness of this method. By using one single piece of LOFAR, this method can calculate four target parameters and the relative error of each estimated parameter is less than 10%.     

溶胶凝胶基质修饰的磺胺嘧啶电极简

制备一种以四（十二烷基）碘化铵为定域体试剂,利用二氧化钛溶胶凝胶技术研制的磺胺嘧啶电极．该电极以溶胶凝胶为载体,线性范围为4．Ox10^-6-1．0x10^-2mol／L,检测下限为2．0×10^-6mol／L,平均斜率为61．0mV／dec．适宜的pH范围为1．1-5．3．电极用作测定药物含量及其回收率测定,结果令人满意．     

Design and analysis of bidirectional deployable parabolic cylindrical antenna简

A bidirectional deployable parabolic cylindrical reflector for an L-band synthetic aperture radar is presented in this study, in which a self-deployed antenna with low weight was designed. The antenna consists of four curved surfaces formed from thin sheets of composite materials connected by hinges along the edges, and the reflective surface is provided by the front surface. The edge profiles of connecting lines were obtained through geometric analysis. A scaled model, including design and manufac- ture, was demonstrated to validate the process from the folded state to the fully deployed state. The non-contact synchronous vision measuring method was used to test the basic frequency of the scaled model, and the test results gave the verification of the analyses. Compared with the existing unidirectional deployable antenna, this new type of bidirectional deployable antenna can be applied to larger-size antennas and has better performance because the glass-woven tape connections were substituted with more reliable hinges. Static, modal, harmonic response, and transient response analyses of the full-sized reflector structure were mod- eled with the commercial finite element （FE） package ABAQUS. The modeling techniques were developed to predict the struc- tural dynamic behavior of the reflector and the results showed that the first natural frequency was 0.865 Hz, and the reflector structure had good stiffness in three directions. This proposed structure has very high stiffness-to-mass ratio because of its hollow solid construction. A preliminary simulation of radiation properties of the parabolic cylindrical antenna, fed by an off-set linear feed horn array, was conducted to obtain the radiation pattern of the feed and the reflector.     

小学数学课堂中情境的创设简

《全日制义务教育数学课程标准（实验稿）》明确指出：“数学教学,要紧密联系学生的生活实际,从学生的生活经验和已有知识出发,创设生动有趣的情境。”生动有趣的情境能充分调动学生的学习积极性和创造性,从而激发学习的内在动力,接下来笔者就小学数学教学情境的创设谈谈自己的看法。     

An adaptive finite element procedure for crack propagation analysis

INTRODUCTION The finite element method (FEM) has proved to be very well suited for the study of fracture mechanics. Nevertheless, modelling the propagation of a crack through a finite element mesh turns out to be difficult because of the modification of the mesh topology. Use of crack propagation laws based on stress inten-sity factor range is the most successful engineering application of fracture mechanics. The stress intensity factors are a very important parameter in fracture analys…     

An improved axisymmetric wilson nonconforming finite element method for stress analysis

The Wilson and Taylor elements Q6 and QM6, the representative nonconforming finite element method (FEM), have been successfully developed and implemented in the finite element code SAP for improved displacement and stress analysis. This paper formulates an improved convergent nonconforming axisymmetric element AQM6 over the corresponding axisymmetric Q6 and QM6 elements. The proposed modified nonconforming axisymmetric element AQM6 satisfies the engineering patch test condition for convergence, and also meets the condition for suppression of spurious shear stress by using a special remedying procedure. The numerical test results are in agreement with the element performance. Project supported by CAO Guangbiao High-Tech F. of Zhejiang Univ. (No. U19902), Zhejiang Edu. Committee SRF for Outstanding Returned Overseas Scholars (No. G59990), US NSF (No. DDM-9313204) and Seiko Epson-Rutgers Univ. Project (No. 4-27365).     

Dynamic crack propagation analysis using scaled boundary finite element method

The prediction of dynamic crack propagation in brittle materials is still an important issue in many engineering fields. The remeshing technique based on scaled boundary finite element method（SBFEM） is extended to predict the dynamic crack propagation in brittle materials. The structure is firstly divided into a number of superelements, only the boundaries of which need to be discretized with line elements. In the SBFEM formulation, the stiffness and mass matrices of the super-elements can be coupled seamlessly with standard finite elements, thus the advantages of versatility and flexibility of the FEM are well maintained. The transient response of the structure can be calculated directly in the time domain using a standard time-integration scheme. Then the dynamic stress intensity factor（DSIF） during crack propagation can be solved analytically due to the semi-analytical nature of SBFEM. Only the fine mesh discretization for the crack-tip super-element is needed to ensure the required accuracy for the determination of stress intensity factor（SIF）. According to the predicted crack-tip position, a simple remeshing algorithm with the minimum mesh changes is suggested to simulate the dynamic crack propagation. Numerical examples indicate that the proposed method can be effectively used to deal with the dynamic crack propagation in a finite sized rectangular plate including a central crack. Comparison is made with the results available in the literature, which shows good agreement between each other.     

Arc-length technique for nonlinear finite element analysis

INTRODUCTION Complete investigation of the nonlinear be-havior of structures must follow the equilibriumpath; identify and compute the singular points likelimit or bifurcation points, whose secondary bran-ches in the equilibrium path must be examined andfollowed. Several techniques to achieve the solu-tion pattern on the equilibrium path were presentedin literature. Load controlled Newton-Raphson me-thod was the earliest method in this regard; but itfails near the limit point. To overcom…     

Arc-length technique for nonlinear finite element analysis

Nonlinear solution of reinforced concrete structures, particularly complete load-deflection response, requires tracing of the equilibrium path and proper treatment of the limit and bifurcation points. In this regard, ordinary solution techniques lead to instability near the limit points and also have problems in case of snap-through and snap-back. Thus they fail to predict the complete load-displacement response. The arc-length method serves the purpose well in principle, Received wide acceptance in finite element analysis, and has been used extensively. However modifications to the basic idea are vital to meet the particular needs of the analysis. This paper reviews some of the recent developments of the method in the last two decades, with particular emphasis on nonlinear finite element analysis of reinforced concrete structures.     

Large eddy simulation for wind field analysis based on stabilized finite element method

In this paper, a stabilized finite element technique, actualized by streamline upwind Petrov-Galerkin (SUPG) stabilized method and three-step finite element method (FEM), for large eddy simulation (LES) is developed to predict the wind flow with high Reynolds numbers. Weak form of LES motion equation is combined with the SUPG stabilized term for the spatial finite element discretization. An explicit three-step scheme is implemented for the temporal discretization. For the numerical example of 2D wind flow over a square rib at Re=4.2×10⁵, the Smagorinsky’s subgrid-scale (SSGS) model, the DSGS model, and the DSGS model with Cabot near-wall model are applied, and their results are analyzed and compared with experimental results. Furthermore, numerical examples of 3D wind flow around a surface-mounted cube with different Reynolds numbers are performed using DSGS model with Cabot near-wall model based on the present stabilized method to study the wind field and compared with experimental and numerical results. Finally, vortex structures for wind flow around a surface-mounted cube are studied by present numerical method. Stable and satisfactory results are obtained, which are consistent with most of the measurements even under coarse mesh.     

An efficient algorithm for mining closed itemsets

This paper presents a new efficient algorithm for mining frequent closed itemsets. It enumerates the closed set of frequent itemsets by using a novel compound frequent itemset tree that facilitates fast growth and efficient pruning of search space. It also employs a hybrid approach that adapts search strategies, representations of projected transaction subsets, and projecting methods to the characteristics of the dataset. Efficient local pruning, global subsumption checking, and fast hashing methods are detailed in this paper. The principle that balances the overheads of search space growth and pruning is also discussed. Extensive experimental evaluations on real world and artificial datasets showed that our algorithm outperforms CHARM by a factor of five and is one to three orders of magnitude more efficient than CLOSET and MAFIA.     

An efficient algorithm for mining closed itemsets

INTRODUCTIONMiningfrequentitemsetsisafundamentalandessentialprobleminmanydataminingapplica tionsincludingthediscoveryofassociationrules,strongrules,correlations,sequentialrules,epi sodes,multi dimensionalpatterns,andmanyoth erimportantdiscoverytasks (AgarwalandSri kant,1994;Wangetal.,2 0 0 2 ) .Mostalgo rithmsproposedsofarworkwellondatasetswherethesizesofitemsetsarerelativelysmall.Howev er,theyusuallycrashwithdensedatasetswheretheitemsetsizesarelarge.Suchdatasetsincludethosecomposedofque…     

关于一类Crouzeix-Raviart型非协调有限元误差分析的不等式

关于一类Crouzeix—Raviart型非协调单元,本文给出了从边界积分到单元积分的一个不等式 ∫δkv^2ds≤C（hk）∫kv^2dxdy 中C（hk）的具体值、它在相应的有限元误差分析中将起到关键的作用．     

非均匀材料有限元分析刚度阵实现的两种方法——积分法和中点材料法

用积分法和中点材料法形成单元刚度阵对非均匀材料进行结构分析。用函数形式表达材料参数,通过在每个三角形区域里对弹性系数进行积分,得到单元刚度矩阵,从而真实地反映了材料的非均匀性;另一种简化方法是用三角形中心处的材料参数代替整个三角形单元的材料参数,使每一个三角形单元为均匀单元。文章比较了两种方法的计算结果和时间,同时用COMSOL对这两种方法进行了验证。