Utilization of the magnetogranulometric analysis to estimate the thermal conductivity of magnetic fluids

In this study, the semi-empirical equation for the effective thermal conductivity of the Holotescu-Stoian model was applied to a set of four dilutions of a transformer oil based magnetic fluid with magnetite nanoparticles as magnetic phase, using the results obtained for the size distributions from the magnetogranulometry analysis, followed by a comparison with the measured values of the effective thermal conductivity obtained by the hot ball method. The link between the size distribution by number and by volume used in the magnetogranulometry analysis and the Holotescu-Stoian model adaptation to the lognormal distribution were presented. The comparison between the results given by the model and the corresponding experimental data showed that by using the approximated size distribution to calculate the effective thermal conductivity the analytical results much closer to the experimental ones are obtained, compared to those given by the Maxwell classical model.     

Critical parameters influencing the material distribution produced by pulsed laser deposition

The parameters that control the thickness distribution of thin films produced by pulsed laser deposition are investigated. It is found that highly asymmetric material distribution profiles can be obtained in vacuum when high energy densities are used and the target surface is positioned at the lens focus. The asymmetries are due to asymmetries in the spatial distribution of the beam. Under Ar gas pressure, the profile becomes symmetric and the distribution narrows as a consequence of collisions between the ejected species and the gas. In vacuum, decreasing the energy density, by decreasing the laser energy output or by moving the lens to defocus the beam, leads to symmetric distribution profiles. Nevertheless, in the first case a quite broad distribution and a low deposition rate are obtained, whereas in the second case the distribution is narrow and the deposition rate increases.     

用磁致旋光效应估测二维磁场分布

为了克服现有测量磁场方法只能单点测量的局限性,基于法拉第磁光效应原理,提出利用磁致旋光估测磁场的方法,提高了磁场测量的效率,获得了磁场的直观分布.建立磁致旋光估测磁场的实验装置,测量了永磁体的磁场,用CCD采集了偏振光通过磁场的图像,通过程序处理可获得磁铁产生的局部磁场二维分布图,并可求得二维分布图上任意点的磁感应强度.     

The boundary between the spin-glass and ferromagnetic states of the bond-random Ising model in the square lattice at T = 0

The bond-random (±J) Ising model in the square lattice is considered in the square cluster approximation. The boundary between the ferromagnetic and spin-glass states at T = 0 is obtained as the transition point from the asymmetric distribution of the effective fields to the symmetric distribution. The concentration of this transition, P_FG is obtained by solving the integral equation for the distribution function of the effective fields.     

Two-dimensional imaging by the continuous-wave EPR

To be able to perform a two-dimensional study of free radical distribution by the continuous-wave electron paramagnetic resonance method in the X-band, special coils producing a magnetic gradient of 8 G/mm have been designed and constructed. The EPR spectra recorded for this gradient were subjected to the procedure of deconvolution in order to elicit information on the concentration of the radical distribution. The data obtained were used as the source file of the program reconstructing the image. The reconstruction was based on the iterative simultaneous algebraic reconstruction technique (Andersen A.H., Kak A.C.: Ultrason. Imag. 6, 81–94, 1984). The quality of the generated images depends on the angle of the sample axis to the gradient direction set by a goniometer and on the deconvolution procedures applied. The first tests on artificially generated phantoms indicated a dependence of the obtained images on the magnetic field gradients applied. The determined spatial distribution of radicals has confirmed their uniform distribution in the sample. The preliminary tests were performed for diphenyl-picrylhydrazyl. Having proved the reliability of the method, analogous measurements were also performed for plyphenylene sulphide PPS-V1 and indicated a homogeneous distribution of radicals in the whole volume of the sample. The images obtained confirmed the uniform distribution of the radicals.     

On the connection of the formulas for entropy and stationary distribution

As is well known in statistical physics, the stationary distribution can be obtained by maximizing entropy. We show how one can reconstruct the formula for entropy knowing the formula for the stationary distribution. A general case is discussed and some concrete physical examples are considered.     

Exact calculation of the mass distribution in the collision process of32S on medium-weight nuclei

This work deals with the exact integration of a Fokker-Planck equation for the mass distribution in heavy ion collisions. The results are compared to those obtained in a previous calculation in which the distribution is approximated by its two lowest moments.     

基于气溶胶光学厚度反演大气气溶胶尺度分布

介绍一种基于气溶胶光学厚度测量反演大气气溶胶尺度分布的新方法. 从实测气溶胶光学厚度出发，依据严格的Mie散射理论，将气溶胶尺度分布函数离散，采用线性回归法确定气溶胶尺度分布. 还通过对多重共线性的讨论，确定了用于反演气溶胶尺度分布的光谱波段.     

轴对称流场干涉条纹折射率的模拟计算

提出一种获取流场干涉条纹折射率分布的新方法。该方法首先采用不等间隔的环带分割轴对称流场,使折射率变化大的地方获得的数据点密,然后通过对Abel变换进行离散数值计算来获取流场的折射率分布。通过模拟轴对称流场的实时全息干涉条纹证明了该方法不仅简单易行,而且所获取的折射率分布精度高。     

Local field distribution and configuration of CO molecules adsorbed on the nanostructure platinum surface

This paper shows that the local electric field distribution near the nanostructure metallic surface is obtained by solving the Laplace equation, and furthermore, the configuration of CO molecules adsorbed on a Pt nanoparticle surface is obtained by using Monte Carlo simulation. It is found that the uneven local electric field distribution induced by the nanostructure surface can influence the configuration of carbon monoxide (CO) molecules by a force, which drags the adsorbates to the poles of the nanoparticles. This result, together with our results obtained before, may explain the experimental results that the nanostructure metallic surface can lead to abnormal phenomena such as anti-absorption infrared effects.     

基于激光器输出模式的离轴激光雷达重叠因子计算及近场信号校正

基于几何分析,将离轴激光雷达在近距离范围内望远镜视场与发射激光分布的交叠区分为三种形状,并给出了计算离轴激光雷达重叠因子的解析计算公式.基于该公式和发射激光的高斯分布得到了本实验室Mie散射激光雷达重叠因子随高度的变化曲线.利用该曲线对成都地区在不同天气状况下的雷达回波信号进行了校正.在此基础上,利用Klett算法对校正后的回波信号进行了反演,得到了532 nm波长大气消光系数随高度的变化曲线.结果表明,基于文中校正方法得到的大气消光系数能反映实际的天气情况. 关键词： 离轴雷达 重叠因子 高斯模式     

Scaling in the structure of directory trees in a computer cluster

We describe the topological structure and the underlying organization principles of the directories created by users of a computer cluster. Users create trees with a scale-free degree distribution whose properties are reproduced by a growth and preferential attachment mechanism with a single parameter. The degree distribution has a nonuniversal exponent associated with different values of the parameter. However, the distribution of branch sizes has a universal exponent analytically obtained from the model.     

Determination of strain and stress distribution on shearwalls by using the speckle photography technique

Speckle photography (SP) is a powerful tool that is adequate to determine small displacements in micrometer range. This information shows other characteristics of structure deformation under loads and can be determined as stress and strain distribution. In this paper we present the results of the application of the SP technique used to study the behaviour of discontinuities in a shearwall model. These structural elements are very important to the stability of buildings. The displacement whole field around the discontinuities and loading points was determined using the pointwise method. This allows us to determine stress distribution at the point of interest by means of the suitable equations. We also present the stress distribution obtained through the finite element method in order to compare the results obtained by means of these two techniques. Good correspondence was found between the displacements determined by both techniques (r=0.982) and also between the stress values we obtained.     

Correlations between the electric charging properties and the optically determined structure of non-woven fabrics

The aim of this paper is to determine the degree of correlation between the electrostatic potential distribution on the surface of non-woven fabrics and the material structure as obtained by optical means. The potential distribution on the material surface was monitored for several samples of two types of fabrics that were electrically charged using corona discharge. The results show that the charge distribution on the samples surface significantly correlates with the spreading and the third centered moment of the gray-scale pictures of the samples.     

Longitudinal intensity distribution near the focus produced by light through scattering media

Speckle pattern is formed when coherent light passes through scattering media. It has been demonstrated that after appropriately optimizing the phase of the incident light, a bright focal spot in the target point can be obtained for the case that the light passes through the scattering medium. However, until now the focused intensity distribution near the focus seems unclear. In this paper we experimentally investigate some factors influencing the longitudinal intensity distribution near the focus in details. It is shown that the desired longitudinal focused intensity distribution can be obtained by optimizing the incident light. The results may have potential applications in particle manipulation and laser processing, etc.     

键合界面阻抗对VCSEL的电、热学特性的影响

采用一电阻层来表征键合界面处的阻抗.通过求泊松方程、电流密度方程、载流子扩散方程以及有源层结压降方程自洽解的方法，计算了VCSEL的电势分布，进而求解热传导方程，得到VCSEL的温度分布.详细分析了键合界面阻抗对晶片键合结构垂直腔面发射激光器内部的电势分布、温度分布以及有源层中的注入电流密度、载流子浓度、结压降和温度沿径向分布的影响.     

Theory of the Ionization Equilibrium in Nonideal Alkali Plasmas

With the help of local pseudopotentials and binary distribution functions bound and scattering state parts of the thermodynamic functions of nondegenerate nonideal alkali plasmas with a large interaction parameter are calculated. The one-particle distribution functions for the atomic levels are obtained by reinterpretation from the bound state part of the binary distribution functions. The ionization equilibrium is described by a Saha equation which is evaluated for certain ranges of temperature and density. The transition to high conducting states is discussed.     

Detection of the difference between two images: An improved method

The method for the detection of the difference between two images, proposed by the authors, can be modified to improve the signal/noise ratio. An amplitude distribution proportional to cos²? is obtained in the Fourier plane using three exposures in the ratio 1 : 2 : 1. In the neighbourhood of ? = Π/2 the gradient of this distribution is one order of magnitude inferior to that of cos? obtained with two equal exposures. Consequently a wider slit can be used as a filter. A further improvement can be obtained if the number of exposures is increased.     

Exact solution of the Boltzmann equation in the homogeneous color conductivity problem

An exact solution of the Boltzmann equation for a binary mixture of colored Maxwell molecules is found. The solution corresponds to a nonequilibrium homogeneous steady state created by a nonconservative external force. Explicit expressions for the moments of the distribution function are obtained. By using information theory, an approximate velocity distribution function is constructed, which is exact in the limits of small and large field strengths. Comparison is made between the exact energy flux and the one obtained from the information theory distribution.     

利用4400系统构造具有光学多道分析功能的信号处理系统

基于4400系统,通过引入光电二极管列阵作为传感器,构造了具有光学多道分析功能的信号处理系统。利用该系统对实际的激光空间分布进行了描绘,给出了高斯场分布的相应参数。通过进一步观测p偏振光在K9玻璃上下表面反射光强比(γ)的角度调制曲线,获得了玻璃表面层的光学参数。实验结果表明,该系统测量精度高,可应用在激光时间信号及空间场分布的表征与测量领域。