Brownian dynamics simulations of colloidal hard spheres. Effects of sample dimensionality on self-diffusion

The self-diffusion coefficients of colloidal hard spheres were determined by Brownian dynamics (BD) computer simulations using a new efficient algorithm for treatment of the hard-sphere interactions. Calculations were done on an Apple PC type MacIIcx and on a Micro VAX 3000, considering samples in two and three dimensions at varying particle concentrations. Our results in three dimensions are compared with experimental results from our own group which were obtained by forced Rayleigh scattering (FRS), and with numerical results from a dynamical Monte Carlo simulation by Cichocki and Hinsen. Good agreement with the latter was found for particle volume fractions up to 0.40. Differences in the dynamical behavior of our numerically treated 2D and 3D samples are discussed using a simple geometrical model to enable comparison of particle concentrations in samples with different dimensionality.     

The Stress Response of Functionally Graded Isotropic Linearly Elastic Rotating Disks

The purpose of this research is to investigate the effects of material inhomogeneity on the response of linearly elastic isotropic solid circular disks or cylinders, rotating at constant angular velocity about a central axis. The work is motivated by the recent research activity on functionally graded materials (FGMs), i.e., materials with spatially varying properties tailored to satisfy particular engineering applications. The analog of the classic problem for a homogeneous isotropic rotating solid disk or cylinder is considered. The special case of a body with Young"s modulus depending on the radial coordinate only, and with constant Poisson"s ratio, is examined. For the case when the Young"s modulus has a power-law dependence on the radial coordinate, explicit exact solutions are obtained. It is shown that the stress response of the inhomogeneous disk (or cylinder) is significantly different from that of the homogeneous body. For example, the maximum radial and hoop stresses do not, in general, occur at the center as in the case for the homogeneous material. Furthermore, for the case where the Young"s modulus increases with radial distance from the center, it is shown that radially symmetric solutions exist provided the rate of growth of the Young"s modulus is, at most, cubic in the radial variable. It is also shown for the general inhomogeneous isotropic case how the material inhomogeneity may be tailored so that the radial and hoop stress are identical throughout the disk. This revised version was published online in August 2006 with corrections to the Cover Date.     

坚硬岩石在强冲击荷载作用近区的性状研究

根据坚硬岩石的性质,利用力学模型分析了在冲击荷载作用下的岩石破坏过程,经由弹性状态向内摩擦状态的转变,最终达到流体力学状态。通过对内摩擦状态的分析,认为在强冲击荷载区域的变形近似为一维变形状态。冲击荷载作用在岩石中产生的应力波可以看作类似于冲击波的短波,在波阵面附近的某个狭窄区域内将发生参数的急剧变化。根据近区变形状态与质量守恒导出了侵彻近区的速度场表达式。根据短波的研究,给出了近区应力波的衰减规律。     

一种不锈轴承钢离子束增强沉积表面的微观分析和摩擦学性能研究

利用离子束增强沉积技术，在将Ｔｉ用Ａｒ＾＋束溅沉积到淬火态９Ｃｒ１８Ｍｏ不锈轴承钢表面的同时，分别用Ａｒ＾＋，Ｎ＾＋和Ｃ＾＋轰击试样表面，制取了增强沉积的表面改性层     

Asymptotics of eigenfrequencies of an elastic body with a heavy and hard peak-shaped inclusion

A heavy and hard peak-shaped inclusion in an elastic body provokes to concentration of eigenvalues in the low-frequency range of the spectrum and localization of the corresponding eigenmodes near the peak tip. To cite this article: S.A. Nazarov, C. R. Mecanique 335 (2007).     

锐缘硬质轮在金属表面的滚动与滑动

在工程应用的很多摩擦对偶中，往往有一方是锐形的，因此，研究锐形滑块的滚动与滑动具有重要的实用意义。以锐缘硬质轮在挤压铝和软钢两种平面试样表面的滚动和滑动为研究对象，考察了两种摩擦过程中材料的受力状况和变形状况，结果表明，要在同种金属试样表面造成相同宽度的槽痕，滚动法所需要的垂直负荷比滑动法所需要的大，然而滚动法所需要的切向牵引力却比滑动法所需要的小．对两种摩擦过程中界面上的应力与材料的强度性能之关系的分析讨论指出，滚动试验中接触界面上的正应力相应于变形材料的屈服应力，因而滚动试验可以作为材料硬度的一种测量方法；滑动试验中接触界面上的剪应力相应于变形材料的流动剪应力；但滚动试验中界面剪应力与材料的流动剪应力之间，以及滑动试验中界面正应力与材料的屈服应力之间却都没有直线关系．     

高温硬焊料准连续半导体激光器巴条叠阵的性能研究

以巴条叠阵结构及封装方法为基础,研制了一组高温硬焊料准连续半导体激光器巴条叠阵,并研究了其相关的光电性能和寿命特征。结果表明,所研制的器件在200 A的工作电流下,重复频率250 Hz、脉宽200 μs时,单巴峰值功率>200 W,50%光谱宽度<3 nm,电光转换效率>50%,寿命达到4.71×10⁹ shots时的功率衰减<15%;当工作电流为150 A时,预期寿命高达1.5×10¹⁰ shots。     

Quo vadis,chemometrics?

Assessing current trends in chemometric publications reveals that most projects utilize known methodologies and fall into the category “application.” There seems to be worrying little of true innovation unless one counts “fashions” assimilated from other fields. The field may have reached a crossroad: One path leads to chemometrics becoming a fully mature but stagnant tool for analytical chemists; the other path, that is, maintaining chemometrics as an active and widely recognized research field, requires opening new research areas for chemometricians. It is argued that hard modeling as opposed to the ubiquitous soft modeling may become such a new direction. Hard modeling would focus on investigating chemical mechanisms that give raise to measured data as opposed to empirically analyzing data.Furthermore, chemometricians in academia are responsible for preparing the next generation of chemometricians. Despite the need for chemometricians in the workforce, the number of young chemometricians is low and will remain low unless changes in chemistry curricula happen. This remains a challenge because there are fundamental issues that need to be overcome. Copyright © 2014 John Wiley & Sons, Ltd.     

Quantitative estimates for a new complex Durrmeyer operator in compact disks

In the recent years the extension of linear positive operators from real to complex domain is one of the interesting area of research. In this context, we present the exact order of simultaneous approximation and Voronovskaja kind results with quantitative estimate for a new type of complex Durrmeyer operator (different from those previously studied), attached to analytic functions in compact disks. In this way, we put in evidence the overconvergence phenomenon for this kind of Durrmeyer operator, namely the extensions of approximation properties with exact quantitative estimates, from the real interval [1/3, 2/3] to compact disks in the complex plane.     

Tunneling of the hard‐core model on finite triangular lattices

We consider the hard‐core model on finite triangular lattices with Metropolis dynamics. Under suitable conditions on the triangular lattice sizes, this interacting particle system has 3 maximum‐occupancy configurations and we investigate its high‐fugacity behavior by studying tunneling times, that is, the first hitting times between these maximum‐occupancy configurations, and the mixing time. The proof method relies on the analysis of the corresponding state space using geometrical and combinatorial properties of the hard‐core configurations on finite triangular lattices, in combination with known results for first hitting times of Metropolis Markov chains in the equivalent zero‐temperature limit. In particular, we show how the order of magnitude of the expected tunneling times depends on the triangular lattice sizes in the low‐temperature regime and prove the asymptotic exponentiality of the rescaled tunneling time leveraging the intrinsic symmetry of the state space.