云计算的可信性

云计算是一种新兴的商业计算模型,同时又是一种能够动态伸缩的虚拟化资源。云计算的安全问题其实就是一种对可信的挑战。     

反应堆堆芯围筒结构热流固耦合热变形分析

针对反应堆堆芯围筒热流固耦合问题,采用三维有限元法研究堆芯围筒的热变形.考察ANSYS的三维实体热单元SOLID 70,三维实体单元SOLID 45,三维表面热效应单元SURF 152和三维热-流耦合管单元FLUID 116等单元类型的特点和实用性.建立堆芯围筒、吊篮和冷却剂的温度分析有限元模型：堆芯围筒和吊篮采用SOLID 70,结构表面与冷却剂的对流传热表面采用SURF152,堆芯围筒与吊篮之间冷却剂采用FLUID 116.采用SOLID 45建立堆芯围筒有限元模型,根据得到的堆芯围筒、吊篮和冷却剂的温度场结果分析堆芯围筒热变形.结果表明,在考虑堆芯围筒及吊篮固体和流体的交叉耦合的基础上,采用三维有限元法能比较客观地模拟反应堆堆芯处的复杂运行环境.     

Correlation of high-pressure thermal conductivity,viscosity, and diffusion coefficients for n-alkanes

Thermal conductivity, viscosity, and self-diffusion coefficient data for liquid n-alkanes are satisfactorily correlated simultaneously by a method based on the hard-sphere theory of transport properties. Universal curves are developed for the reduced transport properties ^*, ^*, and D ^* as a function of the reduced volume. A consistent set of equations is derived for the characteristic volume and for the parameters R , R , and R _D, introduced to account for the nonsphericity and roughness of the molecules. The temperature range of the above scheme extends from 110 to 370 K, and the pressure range up to 650 MPa.     

一种测量工业环境感应传导干扰的方法

针对采用干扰测量仪或频谱分析仪只能测量工业环境中干扰源的辐射干扰强度的问题,提出了一种测量工业环境感应传导干扰的方法。该方法采用HBYV非双绞2芯线作为干扰接收体,采用数字示波器记录干扰波形的最大幅值和单个脉冲的最大强度,通过与标准干扰发生器感应到HBYV非双绞2芯线上的干扰信号大小进行比较,确定干扰强度。以瞬变脉冲群干扰强度和浪涌干扰强度的测量为例,详细介绍了该方法的具体实现。     

Influence of base resistance on extracting thermal resistance for SiGe HBTs

In this article, the influence of base resistance on extracting thermal resistance for SiGe heterojunction bipolar transistors is studied and an improved approach for determining the junction temperature and thermal resistance is presented. The proposed method for extracting thermal resistance is based on the temperature sensitivity of the base–emitter (B–E) voltage when the device is biased with a fixed emitter current density. This approach not only takes into account the self‐heating during the different ambient temperature measurement but also revises the empirical equation of B–E voltage due to the influence of base resistance during the power dissipation increment measurement. Results are obtained for devices with different emitter lengths and fingers. Compared with the conventional method, the thermal resistance is about up to 15% improvement for the device with 0.3 × 1.9 μm² emitter area and 13.8% for the device with 0.3 × 13.9 μm² emitter area. The accurate thermal resistance implemented in HICUM model has resulted in better fit for transistor output characteristics. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

DTA measurements of normal-incommensurate phase transition in (NH4)2ZnCl4 and K2ZnCl4 crystals

Differential thermal analysis (DTA) was applied to determine the changes in enthalpy and entropy of (NH₄)₂ZnCl₄ and K₂ZnCl₄ crystals at their phase transition from the orthorhombic normal phase to the incommensurate phase. The temperature of this transition, T _i , is 406 K for (NH₄)₂ZnCl₄ and 555 K for K₂ZnCl₄ and the entropy changes (S/R) are 0.053 and 0.035, respectively. The low value obtained for S/R is characteristic of incommensurate phase transitions. The results were compared with the data reported for other crystals of the A₂BX₄ family. Thermal properties of the crystals of the A₂ZnCl₄ subgroup were found to the correlated with the length of A-Cl bonds.     

Thermal conductivity of a dendritic ice layer

Measurements of the thermal conductivities of the frozen layer of aqueous binary solutions have been performed using the transient hot-wire method. Solutions of ethylene glycol and sodium chloride were utilized as the testing fluids, and they were frozen up in the test section in which the platinum wires 40 m in diameter and 170 mm in length were strung. Measurements were carried out under equilibrium at a variety of both the initial concentration of the solution and the temperature of the frozen layer. The expressions of the thermal conductivity of the frozen layer were determined. It was found that the thermal conductivity of the dendritic ice layer was favorably assessed with the Lichteneker's model by introducing the solid fraction under an assumption of the equililbrium within the range of parameters examined.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

On the determination of the thermal diffusion factor from column measurements

A new method for experimental determination of the thermal diffusion factor _T for binary gas mixtures with a thermal diffusion column (TDC) is developed, based on A. M. Rozen's equation of TDC. The experimental results for _T are obtained in a reduced form in this approximation. An experimental reference point, determined in the same TDC with a standard gas mixture, is used for the transformation of the results for _T in absolute units. The proposed method is applicable for arbitrary gas mixtures, irrespective of the mass difference of the components.     

Thermal conductivity of liquid n-alkanes

The thermal conductivity of liquids has been shown in the past to be difficult to predict with a reasonable accuracy, due to the lack of accurate experimental data and reliable prediction schemes. However, data of a high accuracy, and covering wide density ranges, obtained recently in laboratories in Boulder, Lisbon, and London with the transient hot-wire technique, can be used to revise an existing correlation scheme and to develop a new universal predictive technique for the thermal conductivity of liquid normal alkanes. The proposed correlation scheme is constructed on a theoretically based treatment of the van der Waals model of a liquid, which permits the prediction of the density dependence and the thermal conductivity of liquid n-alkanes, methane to tridecane, for temperatures between 110 and 370 K and pressures up to 0.6 MPa, i.e., for 0.3T/T _c0.7 and 2.4P/P _c3.7, with an accuracy of ±1%, given a known value of the thermal conductivity of the fluid at the desired temperature. A generalization of the hard-core volumes obtained, as a function of the number of carbon atoms, showed that it was possible to predict the thermal conductivity of pentane to tetradecane±2%, without the necessity of available experimental measurements.     

机器人三维路径规划问题的一种改进蚁群算法

本文研究移动机器人三维空间路径规划问题,针对三维空间的复杂地形特点,提出了一种基于改进蚁群算法的路径规划算法。文中首先描述了一种简单有效的环境建模方法,然后给出了算法在信息素呈现、路径点选取、信息素更新以及启发式函数设计等方面的改进方法。仿真结果证明了算法的可行性和可靠性。