静态法和动态法测量乙醇饱和蒸气压的比较

物质的蒸气压是化学、化工、冶金、医药等领域的重要基础数据。测量饱和蒸气压是大学物理化学实验教学中的一个基础实验,测量方法主要有静态法和动态法,但两种方法的比较尚未见报道。本文通过比较,得出了两种方法的优缺点以及注意事项。     

粉喷桩单桩承载力确定方法的比较

粉喷桩在高速公路软土地基处理中得到了广泛的应用,但其承载力的合理确定是工程实际中关心的一个重要问题。通过对工程中常用的几种粉喷桩单桩承载力确定方法的比较,分析了各自存在的问题和适用条件,提出了在实际工程应用中确定水泥搅拌桩单桩承载力的选用建议。     

Variance of the virtual displacement

We show that the affine structure of the 3-dimensional space is deeply enmeshed with the static laws expression. The relevance of tensorial rules for calculus in mechanics is thus enhanced. The virtual work principle is stated precisely but a little twist is given to the usual statements: the tensorial nature of the so-called virtual displacement vector is asserted to be covariant. To cite this article: C. Vallée et al., C. R. Mecanique 332 (2004).

Résumé

Nous montrons que la structure affine de l'espace tridimensionnel est fortement imbriquée avec l'expression des lois de la statique. La pertinence de l'application des règles du calcul tensoriel à la mécanique est ainsi renforcée. Le principe des travaux virtuels est établi précisément avec une seule entorse aux exposés classiques : la nature tensorielle de l'habituel vecteur déplacement virtuel est affirmée covariante. Pour citer cet article : C. Vallée et al., C. R. Mecanique 332 (2004).     

Topic tracking with Bayesian belief network

The task of topic tracking is to monitor a stream of stories and find all subsequent stories that discuss the same topic. Using Bayesian belief network we give three topic tracking models: a static topic model BSTM and two dynamic topic models BDTM-I, BDTM-II. BDTM-II merges the advantages of BSTM and BDTM-I, has better tracking performance than the former two, and effectively alleviates topic drift phenomenon. Applying unrelated coming stories to update BDTM-I and BDTM-II can filter noises existed in topics. Experiments on TDT corpora show that BSTM decreases (C_det)_norm by 5.5% comparing to VSM, BDTM-II decreases (C_det)_norm by 6.3% and 6.0% comparing to BSTM and BDTM-I respectively, using unrelated stories can improve the tracking performance.     

FULLY SYMBOLIC GENERATION OF COMPLEX MULTIBODY MODELS*

Abstract

In this paper, a quasistatic finite element model of a spur gear pair is developed. A node-to-target contact formulation is given, where calculations of initial gaps are based upon the actual geometry of the gear flanks rather than upon a contact node and a facet or a line segment. By using a special contact search algorithm, profile modifications and mounting errors are easily incorporated in the analysis. The problem, which also includes friction, is solved by using a nonsmooth Newton method. The static transmission error can be calculated with accuracy with a relatively small number of nodes along the gear flanks. Several examples are given in order to demonstrate the model.     

Conditions of stability and instability for a pair of arbitrarily stratified compressible fluids in an arbitrary non-uniform gravity field

The work continues and develops authors’ previous investigation of stability in the small for a two-layer system of inhomogeneous compressible fluids in the uniform gravity field. Here we present a solution of a similar problem in the case of arbitrary non-uniform potential gravity field. The equilibrium stratification of both density and elastic properties of the fluids is supposed arbitrary, as well as the shape of open on top reservoir filled by the fluids. The problem of stability of equilibrium is analyzed as the corresponding problem for the non-linearly elastic bodies, basing on the static energy criterion with regard for the boundary conditions at all parts of the boundary. The crucial element of the analysis is conversion of the quadratic functional of second variation of total potential energy of the system into a “canonical” form that enables to determine its sign. Making use of this canonical form, we obtain almost coinciding with each other necessary and sufficient conditions for stability (those being valid also for an arbitrary number of layers).     

Totally umbilic null hypersurfaces in generalized Robertson–Walker spaces

We show that there is a correspondence between totally umbilic null hypersurfaces in generalized Robertson–Walker spaces and twisted decompositions of the fibre. This allows us to prove that nullcones are the unique totally umbilic null hypersurfaces in the closed Friedmann Cosmological model. We also apply this kind of ideas to static spaces, in particular to Reissner–Nordström and Schwarzschild exterior spacetimes.     

光静态散射测试系统的研究与实现

随着科学技术的发展,对粒子的大小、浓度及其他特性的探测已经发展成为一个专门的研究领域和现代测量学中的一个重要分支,而光散射法已经成为一种常用的粒子测量方法。为了满足应用需求,文中提出了一种基于C8051F500单片机的光静态散射测试系统方案,详细介绍了该测试系统的设计理论原理、硬件电路的设计依据、固件程序的设计思想和测试系统的具体实现。选取一定浓度的样品溶液,运用该系统进行光散射的角度依赖性测试,实际测量值与理论依据基本相符;在不同激光功率下,对同一角度的散射光强进行测试,将测量得到的数据分析,线性度良好,满足设计要求。     

A model of nonlinear electrodynamics

A new model of nonlinear electrodynamics with two parameters is investigated. We also consider a model with one dimensional parameter. It was shown that the electric field of a point-like charge is not singular at the origin and there is the finiteness of the static electric energy of point-like charged particle. We obtain the canonical and symmetrical Belinfante energy–momentum tensors and dilatation currents. It is demonstrated that the dilatation symmetry and dual symmetry are broken in the models suggested. We have calculated the static electric energy of point-like particles.