Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Compensation of timing jitter-induced distortion of sampledwaveforms

The presence of timing jitter between the trigger signal and the sampling strobe in an equivalent-time sampling oscilloscope causes distortion of the recorded waveform. Two methods exist to estimate the waveform from the jittered measurements. One method, called the median method, is based on the calculation of the point-by-point median of a large set of waveform measurements. It is shown here that this method is asymptotically biased if noise is present and if the waveform is nonmonotonic. Another method, called the pdf deconvolution method, is based on an estimation of the jitter probability density function and on a technique to deconvolve this density function from the average of all recorded waveforms. To estimate the jitter probability density function, it is assumed that the waveform has a part which can very well be approximated by a ramp during a time span which is smaller than the standard deviation. It is shown that a significant asymptotic bias is introduced by the method when this assumption is violated. A novel approach is proposed, based on a parametric model of the jitter probability density function, which results in an asymptotic unbiased estimate of the jitter probability density function. The method is experimentally verified, and it is explained why this method is especially useful when one is interested in the Fourier spectrum of the recorded waveform     

太平洋牡蛎(Crassostrea gigas)鳃氯细胞的超微形态研究

利用透射电子显微镜研究了太平洋牡蛎鳃氯细胞的超微结构。氯细胞主要分布于鳃小叶的基部,呈口袋状,细胞个体较大,在鳃表面有一凹隐的分泌腔。细胞中,细胞核多位于基部,体积较小;具有发达的微细小管系统,但小管的分支程度低;线粒体数量较少且结构不够发达;可见少量的高尔基体,未见内质网。鳃氯细胞是太平洋牡蛎鳃渗透压调节的重要细胞系统。     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

装甲材料侵彻试验仿真

采用显式动力学算法对装甲材料侵彻试验的过程进行数值仿真研究。介绍了冲击动力学的基本理论，对侵彻试验中装甲材料的破坏进行了数值模拟，校核了试验靶架的强度，仿真结果和试验值进行了比较。研究结果表明。装甲材料侵彻试验过程的数值仿真是有效可行的。与侵彻试验相比，数值仿真具有可重复性好、周期短、成本低的优点，对物理试验具有重要指导意义。     

Measurements of the thermal magnetoresistance of aluminum

The transverse thermal magnetoresistance of single-crystal plates of pure aluminum has been measured at liquid helium temperatures. It is shown that the high field Lorentz ratio is practically independent of field in agreement with theoretical predictions, and the value of the Lorentz ratio in high fields is discussed in terms of thermal and electrical relaxation times. It is also shown that the previously observed linear increase of the electrical resistivity in high fields is reflected in the thermal resistivity, and the origin of this effect is discussed. It is believed that the linear behavior is not caused by a magnetic breakdown effect in this case, but is due to other intrinsic or nonintrinsic effects.     

One method of reception of the exact analytical decision of the hyperbolic equation of heat conductivity on the basis of use of orthogonal methods

On the basis of use of a method of separation of variables and the orthogonal method of Bubnov-Galerkin, the exact analytical solution of the hyperbolic equation of heat conductivity for an infinite plate under boundary conditions of the first sort is obtained. It is shown that heating of the body (cooling) is deter-mined by movement of the thermal shock wave on which there is a temperature jump. The front of the thermal wave divides the investigated area into two subareas splitting where the temperature changes from the wall temperature (a boundary condition of the first sort) to the temperature at the front waves and not splitting when the temperature is equal to the reference temperature.     

具多件内装物的瓦楞纸箱尺寸优化设计

跳出传统的设计思路，提出装多件内装物的瓦楞纸箱尺寸优化设计方法，建立优化设计模型，编写程序用于生产，节省纸用量，降低成本。     

Dissipative heating under conditions of shear flow of liquid in a flat channel of finite length in view of temperature dependence of viscosity

A steady-state process of heat transfer is considered under conditions of Couette-type shear flow in a flat channel of finite length. The problem is solved in view of dissipation of mechanical energy and of temperature dependence of viscosity under symmetric boundary conditions of the third kind on the channel walls. A number of simplifying assumptions are made, and approximate solutions are obtained within two formulations of the initial problem. In the first case, the constant velocity of the moving channel wall is assigned. This problem is conventional and leads to quite predictable results. In the second case, it is assumed that it is the resultant force applied to the moving channel wall which is assigned. The wall velocity in the steady-state mode is not known in advance. It is found that, in this case, the dependence of kinematic and thermal characteristics of the process on Froude number exhibits a hysteretic pattern.     

Formulation of non-standard dissipative behavior of geomaterials

In this paper, fundamental mathematical concepts for modeling the dissipative behavior of geomaterials are recalled. These concepts are illustrated on two basic models and applied to derive a new form of the evolution law of the modified Cam-clay model. The aim is to discuss the mathematical structure of the constitutive relationships and its consequences on the structural level. It is recalled that non-differentiable potentials provide an appropriate means of modeling rate-independent behavior. The Cam-clay model is revisited and a standard version is presented. It is seen that this standard version is non-dissipative, which at the same time explains why a non-standard version is needed. The partial normality is exploited and an implicit variational formulation of the modified Cam-clay model is derived. As a result, the solution of boundary-value problems can be replaced by seeking stationary points of a functional.An erratum to this article can be found at .     

汽车电子部件振动疲劳试验规范设计

本文根据汽车电子部件加速度振动试验要求 ,设计了与实际载荷作用等价的正弦激振载荷幅度与试验时间的关系 ,制定了一套完整的加速振动试验方案并完成了相关实验 ,得到了强化系数K ;对直接采用道路谱信号应用于UD振动台上的试验进行了设计。整个振动试验设计可指导汽车电子产品试验规范工作 ,具有实际意义和应用价值。     

Formulation of non-standard dissipative behavior of geomaterials

In this paper, fundamental mathematical concepts for modeling the dissipative behavior of geomaterials are recalled. These concepts are illustrated on two basic models and applied to derive a new form of the evolution law of the modified Cam-clay model. The aim is to discuss the mathematical structure of the constitutive relationships and its consequences on the structural level. It is recalled that non-differentiable potentials provide an appropriate means of modeling rate-independent behavior. The Cam-clay model is revisited and a standard version is presented. It is seen that this standard version is non-dissipative, which at the same time explains why a non-standard version is needed. The partial normality is exploited and an implicit variational formulation of the modified Cam-clay model is derived. As a result, the solution of boundary-value problems can be replaced by seeking stationary points of a functional.     

鲍鱼壳珍珠层无机文石片的层状微结构研究

贝壳珍珠层是软体动物壳的最内层,经过若干世纪的自然进化,贝壳珍珠层形成了优良的微结构,并使贝壳具有了相当高的强度、刚度及断裂韧性.本文利用扫描电镜(SEM)观察了鲍鱼贝壳珍珠层的主要微结构特征,发现其是由层状的无机文石片和有机胶原蛋白质组成的生物陶瓷复合材料.根据发现的贝壳珍珠层层状微结构特征,建立贝壳珍珠层三维有限元模型,并用此模型分析了珍珠层的拉伸屈服极限与无机文石片拉伸屈服极限及其厚度的关系,研究表明珍珠层的屈服极限随无机文石片屈服极限的增加和无机文石片厚度的减小而增加.     

轧辊辊型曲线的评定方法

提出把轧辊辊型测量曲线评定转换为对形状曲线w(x)的构造和噪声曲线y(x)的评定这两个过程。其中，形状曲线w(x)作为噪声曲线y(x)评定的基准曲线，可采用递归神经网络(GRNN)来进行构造。中不但分析了此法的优点，还指出用递归神经网络能够捕捉局部高点。噪声曲线y(x)的评定采用的是基于控制线旋转的最小区域法。最后通过仿真试验证明了整个过程的可行性。     

复合材料层合板力学性质分析及角铺设层优化设计

基于Kirchhoff经典理论,用样条有限元法以三次B样条函数构成的样条基对反对称多层角铺设层合板的三个独立位移进行插值,推导了复合材料层合板刚度阵,质量阵列式,阻尼阵列式,并由Lagrange方程导出了层合板的动力学方程,通过瑞利一李兹法建立了特征方程。分析了层合板的固有频率及不同层数和不同约束条件下的基频变化等力学特性,在Kirchhoff假设的基础上,对层合板的非线性弯曲的力学特性进行了探讨。基于样条有限元法和遗传算法进行复合材料层合板的角铺设层的优化设计,数值算列验证了算法的有效性。     

Evaluation of the mechanical properties of multicomponent materials of stochastic structure

A new algorithm for simulating the mechanical behavior of a composite material of stochastic structure is proposed. The use of a model material, which is composed according to the parameters of the shape, size, and orientation distributions of the components in the real composite, as a standard medium is proposed. A procedure is proposed for determining the bounds of the interval of microvolume sizes in the model material which ensure that it is locally representative. The possibility of preliminarily estimating these bounds from the parameters of the distributions of geometric characteristics of the microvolumes, which does not require the solution of a sequence of inverse problems, is demonstrated. Pis’ma Zh. Tekh. Fiz. 25, 89–94 (June 26, 1999)     

Solutions of some problems of vibration of inhomogeneous bodies

The object of the paper is to solve the problems of vibrations of thick elastic cylindrical and spherical shells when only Young's modulus E varies from point to point on the region according to certain rules. Here Cinelli's method is applied for obtaining the solutions in general form. The general rules for variation of E for which the above method is applicable, is expressed.     

Theory of hydrogen embrittlement of metals

The present state of the theory of hydrogen embrittlement of metals is analyzed and the shortcoming of several vanants of this theory are discussed. A new hypothesis of hydrogen embrittlement is presented; the hypothesis is based on concepts of dynamic strain aging and makes it possible to overcome certain difficulties of the theory of this phenomenon.This article is published as part of a discussion of the theory of hydrogen embrittlement of metals.     

杀爆战斗部装药能量对破片动能的转化率

针对典型柱形装药,通过理论推导,建立了战斗部装药能量对破片动能转化率ξ的计算模型,其计算结果与试验结果吻合较好。在此模型的基础上,构建了战斗部破片动能最大化的优化设计方程组,发现破片获得最大动能的充分条件是:在限定战斗部总质量时,装填比为2;在限定装药长径比时,装填比为[η+(η~2+48η)~(1/2)]/4;其中,η为装药与壳体的密度之比。     

液氧贮槽增压管线冻堵故障分析

由于没有将液氧贮槽升压后再向槽车充装液氧,在充装过程中使贮槽内形成负压,导致外界空气被倒吸入放空管线,长期积累使增压管线结冰冻堵。通过吹扫增压管线排除了故障。为防止同类故障再次发生,改进了向槽车充装液氧的操作规程。