一类改进的气体静压轴承压力场分布有限差分算法(英文)

针对传统的静压气体轴承压力分布算法效率较低或收敛性较差等问题, 提出了一类改进的有限差分计算方法. 以小孔节流式的径向静压气体轴承的压力分布为对象, 采用有限差分法求解非线性雷诺气体润滑方程; 根据流量平衡原理, 提出了一种新型变步长逐步逼近迭代算法, 用于修正迭代过程中的供气口出口压力, 提高算法的效率和收敛性; 基于Matlab工具, 开发了一套通用的径向静压气体轴承的压力场分布计算软件. 算例结果表明: 所提出的改进有限差分法计算效率高, 稳定性好, 收敛快; 对于小间隙(小于2 μm)气膜, 此方法仍然有效并快速收敛.     

改进最大电流法的配电网损耗计算

针对配电网的实际情况,对传统的最大电流法进行了改进,考虑了三相不平衡问题的处理,基于现场能得到的的运行数据采用持续负荷曲线求损失因数,从而直接进行损耗计算。本方法从模型上比原有的方法要精确和符合实际情况,算例表明该方法的有效性和实用性,适用于配电网的网损计算。     

微分求积法求解不可压二阶粘弹性流体和热迁移模型中的稳态流动

1IntroductionAlthoughthe computation of the fluid mechanics hasgreat development during the last decades,due to themodel in nonlinear fluid mechanics is very complicat-ed,the more efficient techniques for solvingthis prob-lemstill attract the interest of many researchers.Thedifferential quadrature method(DQM)introduced byBell man,et al.[1,2]is an efficient numerical methodfor solving partial differential equations.In recentyears,the DQMhas been widely used for solving theproblems of enginee…     

傈僳族人口分布及形成原因分析

在对傈僳族人口分布的特点及变化进行详细描述的基础上,重点从战争与冲突、寻觅经济资源、宗教因素以及政府政策等四方面内容深入分析傈僳族人口分布格局形成的原因,进而揭示其人口地域分布的规律性。希望能够从理论上为实现这一民族人口的空间合理分布及全面发展提供科学依据与指导。     

扩招与限度——博士人才培养规模的测度

近年来,我国社会经济高速发展对于高层次人才的需求不断攀升,扩大博士培养规模成为大势所趋。根据已有文献,GDP总量、R&D投入力度等经济指标对于博士培养规模具有很强的预测作用。本文通过与西方发达五国在相关指标上的国际比较,并与我国的人才供求预测相结合,得出研究结论:我国目前一年的博士人才培养规模应保持在9万人左右为宜,其扩招幅度应与经济总量和R&D投入保持联动。同时,还提出了促进我国博士培养规模和质量同步提高的对策建议。     

A semi-analytical method for the analysis of pile-supported embankments

In this paper, a semi-analytical method for the analysis of pile-supported embankments is proposed. The mathematic model describes the cooperative behavior of pile, pile cap, foundation soil, and embankment fills. Based on Terzaghi??s 1D consolidation theory of saturated soil, the consolidation of foundation soil is calculated. The embankments with two different types of piles: floating piles and end-bearing piles are investigated and discussed. The results of axial force and skin friction distributions along the pile and the settlements of pile-supported embankments are presented. It is found that it takes a longer time for soil consolidation in the embankment with floating piles, compared with the case using end-bearing piles. The differential settlement between the pile and surrounding soil at the pile top is larger for the embankment with end-bearing piles, compared with the case of floating piles.     

Asymptotic solution for coupled heat and mass transfer during the solidification of high water content materials

This paper focuses on obtaining an asymptotic solution for coupled heat and mass transfer problem during the solidification of high water content materials. It is found that a complicated function involved in governing equations can be approached by Taylor polynomials unlimitedly, which leads to the simplification of governing equations. The unknown functions involved in governing equations can then be approximated by Chebyshev polynomials. The coefficients of Chebyshev polynomials are determined and an asymptotic solution is obtained. With the asymptotic solution, the dehydration and freezing fronts of materials are evaluated easily, and are consistent with numerical results obtained by using an explicit finite difference method.     

磁控法测定热发射电子速率分布实验的完善与优化

该文通过求解极坐标系下电子在径向电场和轴向磁场中的运动方程,建立了引入阳极电压条件下热电子初速度与磁控管中电磁场强度之间的关系,并提出一种以归一化阳极电流与励磁电流之间的关系验证热发射电子速率满足麦克斯韦分布的方法.实验结果定性证明了上述方法的可行性,同时表明阳极电压的引入可以有效抑制空间电荷.为了得到更精确的热发射电...     

一种融合加权策略及分布估计的蚁群优化算法

通过对蚁群算法、加权策略、分布估算算法等进行研究和分析,首先提出将加权策略应用于蚁群算法的信息素更新,有效地提高了算法的全局收敛速度,然后将蚁群算法与分布估算算法进行融合,从而避免了由于信息素的正反馈机制而陷入局部最优的问题,仿真实验表明该算法在收敛速度及最优路径求解方面有较好的改进。     

溴化锂溶液热物理性及传质性能实验装置

介绍一套多功能溴化锂吸收式制冷实验装置的设计。通过设计的多功能模块,该装置可以进行传热功能实验、传质功能实验以及溴化锂溶液工程热物理特性研究实验。实验时可以任选装置内部不同功能模块组合进行不同目的的实验。实验装置能够提供高度稳定的温度和压力环境。经过优化设计,该装置具有操作灵活、运行方便、功能多样化、热工参数自动数字监测和控制等特点,可以为开发改良型H2O-LiBr溶液、研发新型吸收式制冷空调设备提供服务。     

轻偶偶核电荷分布的一个统一描述

应用唯象模型结合原子核的电子散射实验结果,研究了轻偶偶核的电荷分布,给出了一个能很好地统一描述轻偶偶核的电荷分布的解析模型。该模型可以很好地给出原子核^4He,^12C,^16O,^24Mg,^28Si和^32S的电荷密度分布,电荷密度分布的均方根半径及电荷形状因子。     

A fast commonly-used algorithm of P-Ⅲ distribution curve and its application

Based on theoretical analysis and studying other methods, P-Ⅲ curve is transformed into an incomplete Γ function by means of mathematical expression transformation, thus the mathematical model of the fast commonly-used algorithm is drawn out. Algorithm comparison and practices demonstrate that the mathematical model has an easy algorithm, agile resolution process, very good commonality, faster convergence rate and better calculation accuracy, and can be applied to other respects.     

波纹板表面凝结传热的数学模型与计算

基于波纹板表面与液膜之间的表面张力作用能减薄液膜厚度而强化传热的机理,建立了竖直波纹板表面的凝结过程的数学模型．计算了波纹板对应于当量平板的凝结传热增强系数．分析了波纹的主要几何参数如波纹节距、波纹板高度、波纹角、波纹倾斜角、波纹圆角半径等对强化传热的影响效应以指导波纹结构的优化．提出了一种能兼顾强化传热效果和适当的流动截面积的双尺度波纹,其凝结传热系数可比当量平板增强1～2倍．     

Numerical study on heat transfer enhancement for use of corrugated,nodal and horizontal grain tubes

With isopentane as working fluid, the heat transfer performances for corrugated, nodal and horizontal grain tubes are simulated. The structural parameters of the three kinds of tubes are compared with those of the plain tube. The numerical results using computational fluid dynamics are validated with theoretical values. For the corrugated, nodal and horizontal grain tubes, the heat transfer enhancements(HTEs) are 2.31—2.53, 1.18—1.86 and 1.02—1.31 times of those of the plain tube, respectively. However, the improved HTEs are at the expense of pressure losses. The drag coefficients are 6.10—7.09, 2.06—11.03 and 0.53—1.83 higher, respectively. From the viewpoint of comprehensive heat transfer factor, the corrugated tube is recommended for engineering applications, followed by the horizontal grain tube.     

供配电计算机模拟演示系统的设计与实现

提出一种供配电计算机模拟演示系统,通过设计系统的硬件和软件,给出演示功能和监控功能的实现方法,并说明了系统的特点。     

中小学网管人员能力移转模式探析

本研究主要在于探讨能力移转理论,分析情境再现、内在动力与能力移转之关系。以中小学内从事网络管理的教师或工作人员为研究对象,采用皮尔森（Pearson）积差相关与复回归分析。以分层抽样方式获得有效问卷129份。所得结果如下：①不同性别的网管人员基本能力没有显着差异。情境再现与能力移转程度呈现正相关：②个人内在动力对能力移转的程度有预测作用。其中以成就感、兴趣与自我效能最具代表性,而以自我效能为最重要因素;③个人应内在动力而产生能力移转的程度较大,亦即情境再现与内在动力两者相较,内在动力的相关因素是较能预测能力移转的项目。     

Coupled models of heat transfer and phase transformation for the run-out table in hot rolling

Mathematical models are been proposed to simulate the thermal and metallurgical behaviors of the strip occtLrring on the run-out table （ROT） in a hot strip mill. A variational method is utilized for the discretization of the governing transient conduction-convection equation, with heat transfer coefficients adaptively determined by the actual mill data. To consider the thermal effect of phase transformation during cooling, a constitutive equation for describing austenite decomposition kinetics of steel in air and water cooling zones is coupled with the heat transfer model. As the basic required inputs in the numerical simulations, thermal material properties are experimentally measured for three carbon steels and the least squares method is used to statistically derive regression models for the properties, including specific heat and thermal conductivity. The numerical simulation and experimental results show that the setup accuracy of the temperature prediction system of ROT is effectively improved.     

高职院校专科毕业生就业问题分析

本文分析了当前我国高职毕业生就业难现状的形成原因,提出了突破高职毕业生就业“困境”的对策思路。     

非独立不同分布随机变量序列的弱大数定律

本文讨论非独立不同分布情况下随机变量序列的弱大数定律的存在条件,将I.I.D情形下的弱大数定律进行了推广.     

The demand for student loans in higher education: A study of preferences and attitudes

This empirical study examined postsecondary-student attitudes and preferences regarding five discrete student loan plans and loan plan features. Certain demographic variables were examined for their relationship to student attitudes toward the various loan plans. The study addressed the following questions: What debt ceiling do students identify as acceptable? Are students willing to indebt themselves over an extended time span? What percent of annual income do they feel reasonably can be applied to loan repayment? Will students alter their repayment plan choices given additional and more detailed information about loan options? A random sample of 218 recipients of federal higher education loans during the 1973–74 academic year was drawn from the population of 6,765 undergraduate borrowers at the University Park Campus of the Pennsylvania State University.