机房空调在变环境温度下的数值模拟与实验研究

文中对变环境温度下的机房空调进行研究,利用实验研究与Matlab编程模拟相结合的方法,比较了不同工况下性能参数的模拟值与实测值,其偏差控制在10%左右。从研究结果中得出,随着冷凝器进风温度从35℃降低到5℃,压缩机的压比、输入功率降低,制冷量增加,整个机组的制冷系数迅速升高,从2.23迅速升高到4.24,提高47%。以及所选模型中存在的问题,分析了出现问题的原因,为机组进一步优化打下良好基础。     

Formation of triblock copolymers via a tandem enhanced spin capturing—nitroxide‐mediated polymerization reaction sequence

The preparation of ABA‐type block copolymers via tandem enhanced spin capturing polymerization (ESCP) and nitroxide‐mediated polymerization (NMP) processes is explored in‐depth. Midchain alkoxyamine functional polystyrenes (M_n = 6200, 12,500 and 19,900 g mol^?1) were chain extended with styrene as well as tert‐butyl acrylate at elevated temperature NMP conditions (T = 110 °C) generating a tandem ESCP‐NMP sequence. Although the chain extensions and thus the block copolymer formation processes function well (yielding in the case of the chain extension with styrene number average molecular weights of up to 20,800 g mol^?1 (PDI = 1.22) when the 6200 g mol^?1 precursor is used and up to 67,500 g mol^?1 (PDI = 1.36) when the 19,900 g mol^?1 precursor is used and 21,600 g mol^?1 (PDI = 1.17) as well as 37,100 g mol^?1 (PDI = 1.21) for the tert‐butyl acrylate chain extensions for the 6200 and 12,500 g mol^?1 precursors, respectively), it is also evident that the efficiency of the block copolymer formation process decreases with an increasing chain length of the ESCP precursor macromolecules (i.e., for the 19,900 g mol^?1 ESCP precursor no efficient chain extension with tert‐butyl acrylate can be observed). For the polystyrene‐block‐tert‐butyl acrylate‐block‐polystyrene polymers, the molecular weights were determined via triple detection SEC using light scattering and small‐angle X‐ray scattering. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Laser Doppler vibrometer for real-time speech-signal acquirement

Laser Doppler vibrometer （LDV） has a potential application prospect in remote sensing. Based on the correlation theories of heterodyne detection, a LDV system with a configuration of all fiber and heterodyne techniques is developed to detect the sound signal through the vibration of glass. Experimental results show that the LDV system has an ability to acquire the real-time speech signal 25 m away through glass. While, the system signal-to-noise ratio （SNR） value decreases with the increase of the glass thickness and the detection distance.     

一阶完全非线性常微分方程的周期粘性解

本文在适当的自然结构条件下证明了完全非线性常微分方程F(t,u(t),u′(t))=0的周期粘性解的存在唯一性.     

克尔介质中瞬态热光非线性效应的作用

研究了介质中瞬态热光非线性效应对于克尔效应Z扫描测量结果的影响，观察到了Z扫描峰谷特性的转变，相应的数值模拟结果与实验结果很好地吻合.实验也发现，克尔效应和瞬态热光非线性效应相互抵消时Z扫描曲线呈现出新奇的单峰或平台状曲线.对于用纳秒脉冲激光进行的Z扫描测量结果的正确分析具有重要意义. 关键词： 瞬态热光非线性效应 克尔效应 Z扫描     

A higher-order boundary element method for three-dimensional potential problems

A method of eliminating the singularities involved in boundary element methods for three-dimensional potential problems is presented and the non-singular expressions of integrals on an element on which the singular point is situated are given for linear and quadratic interpolation functions. Numerical examples are compared with analytical solutions to show that the higher-order interpolations have better precision.     

Dissolution of metallic platinum as water soluble species by naturally occurring complexing agents

Platinum is released into the environment as a result of surface abrasion from automobile catalysts during operation. Previous investigations showed that this finely dispersed metallic platinum is dissolved in organic matrices, e.g. a humic soil to a significantly high degree, resulting in possibly bioavailable Pt species. In this work several natural complexing agents (adenosine, ADP, ATP, L-His, humic acid fraction, L-Met, pyrophosphate, and triphosphate) were treated with metallic platinum (as Pt black and as a Pt(0) containing tunnel dust) for 3–60 d. Some of the compounds used dissolved Pt(0) to a recognizable degree, whereas others were in the range of the aqueous blanks. Comparison of Pt black with a natural dust sample showed that L-methionine had in both cases the greatest effect after 60 d. Generally more Pt(0) was dissolved in the dust sample (finer dispersion and smaller particle size) than in the Pt-black used. By carrying out the experiment under natural conditions instead of in pure oxygen-, the amounts of dissolved platinum are about one order of magnitude lower.On leave from Liaoning University, Department of Chemistry, 110036 Shenyang, PR China     

Generalized arcwise-connected functions and characterizations of local-global minimum properties

In this paper, new classes of generalized convex functions are introduced, extending the concepts of quasi-convexity, pseudoconvexity, and their associate subclasses. Functions belonging to these classes satisfy certain local-global minimum properties. Conversely, it is shown that, under some mild regularity conditions, functions for which the local-global minimum properties hold must belong to one of the classes of functions introduced.Dedicated to R. BellmanThe authors are indebted to I. Kozma, N. Megiddo, and A. Tamir for valuable discussions and to S. Schaible for valuable remarks. This research was partially supported by the Fund for the Encouragement of Research at the Technion.     

Near field radiation pattern of tapered monomode optical waveguides

The Near Field radiation pattern of a tapered monomode planar waveguide is investigated for the first time. A theoretical technique is developed and the results obtained are shown to agree sufficiently well with experiments performed on tapered ion-exchanged glass guides to permit using this technique to predict taper performance.