Semi‐analytical integration of the 8‐node plane element stiffness matrix using symbolic computation

The semi‐analytical integration of an 8‐node plane strain finite element stiffness matrix is presented in this work. The element is assumed to be super‐parametric, having straight sides. Before carrying out the integration, the integral expressions are classified into several groups, thus avoiding duplication of calculations. Symbolic manipulation and integration is used to obtain the basic formulae to evaluate the stiffness matrix. Then, the resulting expressions are postprocessed, optimized, and simplified in order to reduce the computation time. Maple symbolic‐manipulation software was used to generate the closed expressions and to develop the corresponding Fortran code. Comparisons between semi‐analytical integration and numerical integration were made. It was demonstrated that semi‐analytical integration required less CPU time than conventional numerical integration (using Gaussian‐Legendre quadrature) to obtain the stiffness matrix. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2006     

Glass transition measurements of asphalts by DSC

The glass transition temperature (T_g), measured by Modulated Differential Scanning Calorimetry (MDSC), is related to the flow characteristics of asphalt at low temperatures as is the rate of change of the creep stiffnessm. This study compared the glass transition temperature of different asphalts (neat, chemically modified, and crumb rubber modified asphalts) with the creep stiffness, the rate of change of creep stiffness, and the low specification temperature of the continuous PG grading of those asphalts.From the rheological data (BBR) and the thermal data (MDSC) for the virgin and the modified asphalts, the modified products had the same variations of values ofm, S, and T_g at lower temperatures as those of their corresponding virgin asphalts. A correlation between the T_g andm value was observed for both the modified and unmodified asphalts. Since DSC measurements for asphalt low temperature properties use less operator time, less sample, and have less measurement and operator error than rheological methods, T_g has promise to be considered as a fast and easy laboratory method to obtain the low temperature useful range of asphalts in pavements.The authors would like to acknowledge Susan P. Needham for her work in conducting rheological testing for the modified and unmodified asphalts.     

Prostaglandin D2 synthase and its post-translational modifications in neurological disorders

Prostaglandin D2 synthase (PGDS) (beta-trace protein) is a highly abundant cerebrospinal fluid (CSF) glycoprotein. A number of studies have been performed to determine the potential value of this protein for the diagnosis of various neurological disorders. The measurement of total PGDS levels in CSF has proved marginally useful for this purpose, but promising results were obtained while investigating changes in the posttranslational modifications (PTM) pattern. Using 2-DE analysis, we previously showed that PGDS is differentially expressed in ante- and post mortem CSF samples. In the present study, we examined whether the PGDS isoforms may help to distinguish stroke and neurodegenerative disease patients from healthy subjects. The pattern of PGDS PTM was analyzed in CSF from patients with various neurological disorders (n = 44) using IEF/immunoblotting techniques. Strong alterations of this pattern were detected in patients with different forms of degenerative dementia. These findings are consistent with PGDS being altered in some neurological diseases and provide new opportunities for clinical applications.     

Multiple polypeptide forms observed in two-dimensional gels of Methylococcus capsulatus (Bath) polypeptides are generated during the separation procedure

We have examined two-dimensional electrophoresis (2-DE) gel maps of polypeptides from the Gram-negative bacterium Methylococcus capsulatus (Bath) and found the same widespread trains of spots as often reported in 2-DE gels of polypeptides of other Gram-negative bacteria. Some of the trains of polypeptides, both from the outer membrane and soluble protein fraction, were shown to be generated during the separation procedure of 2-DE, and not by covalent post-translational modifications. The trains were found to be regenerated when rerunning individual polypeptide spots. The polypeptides analysed giving this type of trains were all found to be classified as stable polypeptides according to the instability index of Guruprasad et al. (Protein Eng. 1990, 4, 155-161). The phenomenon most likely reflects conformational equilibria of polypeptides arising from the experimental conditions used, and is a clear drawback of the standard 2-DE procedure, making the gel picture unnecessarily complex to analyse.     

Lattice dynamical study of body-centred tetragonal indium

The phonon dispersion curves, phonon frequency distribution function as well as the lattice specific heat of body-centred tetragonal indium have been deduced using a lattice dynamical model which includes central, angular and volume forces. Six elastic constants, four zone boundary frequencies and an equilibrium condition were used in the evaluation of the force constants. It is shown that this model is elastically consistent and satisfies the symmetry requirements of the lattice, the phonon frequencies of indium deduced from it are in very good agreement with the experimental values of Reichardt and Smith and the theoretical values of Garrett and Swihart, and theθ _D values compare well with the experimental values over a wide temperature range. The apparent discrepancies in the phonon dispersion curves and theθ _D-T curves obtained from deficient models, importance of umklapp processes and the significance of angular forces in the lattice dynamical models are discussed.     

基于永磁体间的磁性负刚度的分析与优化

为了有效地降低磁性负刚度结构的非线性程度,从简单三磁体结构出发,引入新型负刚度结构模型——五磁体对称结构,运用MATLAB建立新型负刚度结构的磁力学模型并应用Ansoft Maxwell进行仿真验证.研究永磁体间的相对位置参数对五磁体对称结构的负刚度曲线走势的影响,在微幅振动下对基于磁引力的负刚度曲线拟合后使用谐波平衡...     

考虑收缩徐变影响的新旧混凝土叠合梁单元刚度矩阵改进

混凝土自身的收缩徐变会在新旧混凝土叠合梁中使应力重分布.为了计算重分布应力,首先推导以挠度表达的叠合梁非线性微分方程,然后通过求解该微分方程,引入位移形函数、刚度形函数和等效节点载荷形函数,最后得出新混凝土梁、旧混凝土梁和Goodman弹性夹层三合一的叠合梁改进型单元刚度矩阵和等效节点载荷,从而为收缩徐变影响下的混凝土的内力计算提供了一种有效的新方法.文中还进行了实例验证分析,并从中得出了一些有益的结论.     

运输类飞机机身大开口结构加强方式理论研究

为了对运输类飞机机身大开口结构进行加强,满足刚度连续变形协调的设计要求,本文对机身大开口结构和完整机身结构的刚度进行了深入研究,首先简化了计算模型,对刚度进行了计算,提出了刚度比的定义,得出刚度比与大开口角度、机身半径、蒙皮厚度以及边梁面积之间的关系表达式,得到运输类飞机机身大开口结构加强的原则和方法,在型号上成功得到了应用,用于指导初期的结构设计.     

浅议梁的强度与刚度的关系1)

本文提出了梁的强刚比的定义,用无量纲的形式定量地表达了梁的强度与刚度之间的关系,以期充分发挥材料的潜力并促进材料力学的课堂教学。强刚比与载荷大小无关,其数值可以通过有限元方法或者通过梁的载荷试验来获得。结合工程实际,从设计和试验两个方面对梁的强刚比 及其影响因素进行了简要地探讨和分析。     

Rate sensitivity and deformation mechanism of semi-crystalline polymers during instrumented indentation

Instrumented indentation tests using both constant loading rate (CLR) and continuous stiffness measurement (CSM) operation modes were performed to investigate the deformation mechanism and their sensitivity to the deformation rate in semi-crystalline polymers through the quantitative analysis of load-depth loading and unloading curves. The strain rate was constant during the CSM tests, while the strain rate decreased with the increasing of loading time in CLR tests. The mechanical response mechanism of the semi-crystalline polymers to these tests was very complicated because of the combined effects of strain-hardening in the crystal phase and strain-softening in the amorphous phase. Results show that the loading index m reflects the strain-hardening or strain-softening response during indentation. When m > 2, the mechanical response was due to the strain-hardening, and when m < 2, the response was due to strain-softening. A method based on the measured contact hardness was proposed to obtain the unloading stiffness, and the other mechanical parameters could then be determined according to the unloading stiffness.