Accuracy assessment to applying 20-node solid elements to pressurized composite shells

A factorial analysis is conducted to explore the impact of five factors — aspect ratio, radius-to-thickness ratio, material anisotropy, fiber angle and integration order on the finite element accuracy, with regard to the application of 20-node isoparametric solid elements to clamped composite cylindrical shells subjected to internal pressure. The maximum radial displacement at the central cross-section is employed as the indicator of accuracy. Results from finite element methods were compared with closed-form solutions. Aspect ratio, radius-to- thickness ratio, and integration order are significant main effects as predicted for isotropic materials. Material anisotropy shows no significant main effect, while the fiber angle does have strong impact on the finite element accuracy. In addition to four influential main effects, some multiple-factor interactions are shown to have significant influences on the finite element accuracy. The analysis is limited to the linear elastic range.     

B邻接片错误定位码的译码

针对两类Ｂ邻接片错误定位码进行了分析，并给出了其译码方案．     

一类线性回归模型中核估计的渐近性质

考虑固定设计下具有一阶非参数自回归误差的线性模型,构造了参数和非参数函数的N-W核估计,在适当的条件下,证明了参数估计的强相合性,同时给出了非参数函数估计的渐近正态性.     

Chapter 7 DEA multiplier analytic center sensitivity with an illustrative application to independent oil companies

The setE of extreme points which are also efficient are of basic importance in defining the efficiency frontier, from which the observations for all other DMUs are evaluated in DEA. A significant question which we address is “What variations in the data can be tolerated before the membership inE is changed?” This topic is explored using (1) a simple illustrative example, and (2) production data for 30 independent oil companies during the period 1983–1985. Data were allowed to vary simultaneously for all observations and in different subsets determined by random drawings of data for points both inE and not inE. The results were found to be robust in this study, thereby lending further support to earlier studies which also found these classifications into efficient and inefficient performers to be robust in DEA. Technical developments for these new methods of sensitivity analysis are supplied. These developments feature an application of analytic center (interior point) algorithms which ensure that the Strong Complementary Slackness Condition (SCSC) is fulfilled. The solutions satisfy a mathematical condition called “centrality”. Generally, the solutions are at interior points calledanalytic centers. At these interior points, continuity of the input-output ratios ensures that DMUs inE remain inE for at least small relative variations in the data, while empirically these properties have been found to extend to much larger variations in the data sets.     

JM-2/JM-3转动惯量仪的改进

本对JM-2／JM-3转动惯量仪进行了改进，减小了实验误差。     

An O(k2 + kh2 + h4) arithmetic average discretization for the solution of 1‐D nonlinear parabolic equations

This article develops a new two‐level three‐point implicit finite difference scheme of order 2 in time and 4 in space based on arithmetic average discretization for the solution of nonlinear parabolic equation ε u_xx = f(x, t, u, u_x, u_t), 0 < x < 1, t > 0 subject to appropriate initial and Dirichlet boundary conditions, where ε > 0 is a small positive constant. We also propose a new explicit difference scheme of order 2 in time and 4 in space for the estimates of (?u/?x). The main objective is the proposed formulas are directly applicable to both singular and nonsingular problems. We do not require any fictitious points outside the solution region and any special technique to handle the singular problems. Stability analysis of a model problem is discussed. Numerical results are provided to validate the usefulness of the proposed formulas. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007     

Propagation of round-off errors and the role of stability in numerical methods for linear and nonlinear PDEs

It is shown that the customary assumption on the propagation of round-off errors in numerical methods for PDEs is unrealistic, as it yields a convergence result which is better than the best possible similar convergence result for ODEs. A solution is suggested by which round-off errors can be modelled by smooth functions, with consequent weakening of overall stability conditions and improvement of convergence conditions.     

Searching and exploring properties of geometric configurations using dynamic software

The decline in enrolments and interest in advanced mathematics studies is of growing concern internationally. Previous research suggests that a range of factors can influence students' academic decisions. The focus of the paper is on one of these potential sources of influence— students' perceptions of the tertiary mathematics learning environment. Data from two large-scale surveys (N = 1883) and from a smaller number of interviews (N = 71) with students enrolled in tertiary mathematics courses at five Australian universities are presented and discussed. Collectively, the survey results and the interview data reveal considerable variations in the quality of the teaching and student support available in different mathematics departments. Students' comments were constructive and offered valuable ideas for improving the existing situation, retaining current students and attracting others to mathematics.     

Sensitivity analysis for a type of statically stable sailcrafts

Two types of sensitivities are proposed for statically stable sailcrafts.One type is the sensitivities of solar-radiation-pressure force with respect to position of the center of mass,and the other type is the sensitivities of solar-radiation-pressure force with respect to attitude.The two types of sensitivities represent how the solar-radiationpressure force changes with the position of mass center and the attitude.Sailcrafts with larger sensitivities undergo larger error of the solar-radiation-pressure force,leading to larger orbit error,as demonstrated by simulation.Then as a case study,detailed formulas are derived to calculate the sensitivities for sailcrafts with four triangular sails.According to these formulas,in order to reduce both types of sensitivities,the angle between opposed sails should not be too large,and the center of mass should be as close to the axis of symmetry of the four sails as possible and as far away from the center of pressure of the sailcraft as possible.     

The structure of 11,12-bis[spiro(cyclopropyl)]-1,4,4a,5,8,8a,9a,10a-octahydro-1,4∶5,8-dimethano-9,10-anthraquinone

In the solid state the 21 Diels-Alder adduct between spiro[4.2]hepta-1,3-diene and p-benzoquinone has a planar cyclohexadione ring with a center of symmetry. Both planar and boat conformations have been observed in similar systems, and the relative stability of the two conformers is of interest. The adduct in the gas phase should contain a mirror plane perpendicular to the cyclohexadione ring; however, a data set collected on a crystal in a capillary resulted in a structure where some bond lengths related by this mirror plane differed by more than 4 in the solid state. Molecular mechanics, MOPAC, and the Cambridge Structural Data Base were used to investigate the factors influencing the conformation of the cyclohexadione ring and the asymmetry across the noncrystallographic mirror plane. The energy differences between the planar and nonplanar ring system is small, and the conformation is determined by crystal packing. No reason for the bond length asymmetry could be found, and a recollection of data on a crystal exposed to the environment led to a structure with statistically equivalent bond lengths.