Synthesis and characterisation of epoxy-novolac/bismaleimide networks

Epoxy-novolac resin was modified with 1,1^′-(methylenedi-4,1-phenylene) bismaleimide (BMI), and cured with an aromatic amine. Cure behaviour of these blends was studied using differential scanning calorimetry (DSC). The thermograms indicated a unimodal exothermic peak for blends containing lower percentage of BMI. The cured blends showed much higher glass transition temperatures than that of the unmodified epoxy. Thermal stability of the cured epoxy resin was also improved with BMI addition. A homogeneous structure (with no phase separation) of the blends was confirmed both by DSC analysis and scanning electron microscopy (SEM).     

Continuous time random walks and heat transfer in porous media

An approach to describe heat transfer in porous media is presented on the basis of the continuous time random walk (CTRW) framework. CTRW is capable of quantifying both local equilibrium and non-equilibrium heat transfer in heterogeneous domains, and is shown here to match published experimental data of non-equilibrium thermal breakthrough. It is argued that CTRW will be particularly applicable to the quantification of heat transfer in naturally heterogeneous geological systems, such as soils and geothermal reservoirs.     

超大规模集成电路互连电迁移自由体积电阻模型

将晶核析出的Avrami 方程应用于描述超大规模集成电路中金属Al薄膜互连电迁移过程中电阻的演变. 根据电子散射理论，晶界电阻主要起源于晶界处空位或者空洞对电子的散射. 为了描述这些离子的特征，引入了自由体积的概念，将晶界处电子散射这个复杂的过程简化用自由体积的有效散射截面来描述，从而建立了自由体积与电阻变化的定量关系，统一描述了电迁移过程中不同阶段的电阻变化. 数值模拟结果表明，在第一个空洞成核时刻电阻会发生急剧变化，这一结果已被实验所证实. 关键词： 电迁移 Al互连 电阻变化     

Inverse heat conduction problem in a thin circular plate and its thermal deflection

An inverse problem of transient heat conduction in a thin finite circular plate with the given temperature distribution on the interior surface of a thin circular plate being a function of both time and position has been solved with the help of integral transform technique and also determine the thermal deflection on the outer curved surface of a thin circular plate defined as 0 ? r ? a, 0 ? z ? h. The results, obtained in the series form in terms of Bessel’s functions, are illustrated numerically.     

La2CuO4+δ和La2-xSrxCuO4系统中的电子输运性质

 本文解释了La₂CuO_4+δ（0≤δ≤0.09）和La_2-xSr_xCuO₄（0≤x≤0.3）两种p型系统含铜稀土氧化物中的电阻和Seebeck系数与温度的依赖关系，在室温以上，一氧大气压下的La₂CuO_4+δ系统趋于失氧；在500 K以上，超导样品显示出失氧的一级相变，并且恢复到反铁磁相。在转变温度T₁≈300 K以下，对0<δ<0.05成份的样品，相分离成反铁磁相和超导相；而在T_cρ≈100 K的温度范围内，超导相进一步分离成富空穴和贫空穴畴。在0.04≤δ≤0.09范围内，T_c处的电阻陡降出现了台阶；我们认为，它反映了电子成对的起伏。在La_2-xSr_xCuO₄系统中，对于成分为01≈300 K以上，空穴的运动是弥散的，但是ΔH_m=0；而对于x≥0.22的样品，经历了从平滑到Fermi液态的转变。成份为0c1范围（其中空穴继续以弥散方式运动）是亚稳的，但是，在T_cρ≤150 K范围，出现了电荷起伏。当样品冷却通过T₁时，对于成份为0.15≤x≤0.2的样品，经历了由弥散到强质量增强巡游电子状态的转变；在T_c处，从均匀的修饰电子的正常态凝聚成超导的载流子对。在超导成份样品的正常态中，不寻常的电子-晶格相互作用，可以归结为在CuO₂面上从更离子性的到共价性的Cu:3d_x²-r²─O:P_σ键合的转变；通过这种转变，轨道杂化和Hubbard U参量随Cu─O键长和Cu原子上的外表局域氧化态都产生灵敏的变化。     

车用潜热贮热器的流动与换热实验研究

本文通过对车用潜热贮热器流动与换热实验研究，获得了该相变过程的流动、传热特性，为修正该装置的设计提供了可靠的数据．     

Changes in electrical resistance of carbon‐black‐filled silicone rubber composite during compression

We studied the changes in the electrical resistance of carbon black filled silicone rubber composite, which is the sensitive element of the flexible force sensor, as a function of time during compression. The experimental results show that there is a sudden increase of the electrical resistance along with the sudden increase of the stress immediately after the compression. When the sample strain is kept constant, the electrical resistance and the stress both decay with time. The data of the stress relaxation and the resistance relaxation both can be fitted by the linear combination of two exponential functions. Based on the shell structure theory, the experimental phenomena are explained from the view that the uniaxial pressure induces the changes in the effective conductive paths. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2700–2706, 2007     

Experiment determination of after-operating gas compositions in a transverse-flow CW high power CO2 laser

For a high-power CO₂ laser with a close-confined structure, the compositions and ratios of gas mixtures are changed due to electron impacts during the laser-operating period. As a result, the laser performance is gradually degraded, even to non-lasing output. In this paper, three different methods (a chemiluminescence, a titration analysis and a thermal conductivity measurement) are utilized to determine both the compositions and the ratios, according to different thermal and chemical characteristics of the gases. Corresponding experiments are implemented to a typical transverse-flow high-power CO₂ laser after a long-term discharge (around 15 h) with the output power decreased from an initial 3 kW to final 2 kW. There is evidence in the experiments to indicate that CO₂ decreases by 13.2% comparing with an initially optimal content. Also, the produced impurities are mostly CO and O₂ molecules with noticeable concentrations, while nitrogen–oxygen complexes are little in the gas mixtures.     

非线性晶体内腔倍频的温度模式分布

为了提高谐波转换效率和消除温升引起的晶体走离效应，对于非线性晶体温度场分布特点进行了分析与计算.同时研究了基波偏心辐射对KTP晶体温度场的影响.通过对腔内倍频KTP晶体工作特点的分析，建立了方形非线性晶体热模型并首次引入了方形晶体辐射偏心度的定义.基于热传导方程，得到了温度场分布的一般解析表达式.     

Influence of surface modification adopting thermal treatments on dispersion of detonation nanodiamond

In order to improve the dispersion of detonation nanodiamonds (ND) in aqueous and non-aqueous media, a series of thermal treatments have been conducted in air ambient to modify ND surface. Small angle X-ray scattering (SAXS) technique and high resolution transmission electron microscopy (HRTEM) were introduced to observe the primary size of ND. Differential thermal analysis (DTA), X-ray diffraction (XRD) methodology, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy were adopted to analyze the structure, bonds at surfaces of the treated ND. Malvern instrument Zetasizer3000HS was used for measuring the surface electric potential and the size distribution of ND. As thermal treatments can cause graphitization and oxidization of functional groups at the surface, ND treated at high temperature is correspondingly more negatively charged in an aqueous medium, and the increased absolute value of zeta potential ensures the electrostatic stability of ND particles. Specially, after being treated at a temperature more than 850 K, ND can be well dispersed in various media.