有限弹塑性变形的几何模型

以连续介质力学内变量理论为基础，建立了一个以材料内部微结构变量为底流形，材料外部变形状为对应纤维的材料状态纤维丛模型，使材料的力学特性与模型的几何性质自然对应起来。在模型上讨论和分析了有限弹塑性变形中变形梯度的Lee和Clifton的分解和联系，并证明了塑性变形为沿内变量演化在纤维丛的水平空间的运动。由此获得了塑性变形随内变量演化的变化方程和塑性梯度与内变演化的协调关系。

扩散处理热浸镀铝钢高温抗氧化行为的研究

Effect of diffusion on coating microstructure and oxidation resistance of aluminizing steel

The effect of diffuse treatment on coating microstructure and oxidation resistance at high-temperature of hot-dip aluminum were studied by means of TEM, SEM and XRD. The results show that, the diffusion temperature has significant effect on structure of coatings and its oxidation resistance. After diffusion at 750 degreesC, the coating consists of thick outer surface layer (Fe2Al5+ FeAl2), thin internal layer (FeAl + stripe FeAl2), and its oxidation resistance is poor. After diffusion at 950 degreesC, the outer surface layer is composed of single FeAl2 phase, the internal layer is composed of FeAl phase, and its oxidation resistance declines due to the occurrence of early stage internal oxidation cracks in the coating. After diffusion at 850 degreesC, the outer surface layer becomes thinner and consists of FeAl2 Fe2Al5(small amount), the internal layer becomes thicker and consists of FeAl+spherical FeAl2, and the spheroidized FeAl2 phase in the internal layer and its existing in FeAl phase steadily improve the oxidation resistance of the coating.

Direct Numerical Simulation Of Hypersonic Boundary-Layer Transition Over A Blunt Cone

Direct numerical simulation of transition How over a blunt cone with a freestream Mach number of 6, Reynolds number of 10,000 based on the nose radius, and a 1-deg angle of attack is performed by using a seventh-order weighted essentially nonoscillatory scheme for the convection terms of the Navier-Stokes equations, together with an eighth-order central finite difference scheme for the viscous terms. The wall blow-and-suction perturbations, including random perturbation and multifrequency perturbation, are used to trigger the transition. The maximum amplitude of the wall-normal velocity disturbance is set to 1% of the freestream velocity. The obtained transition locations on the cone surface agree well with each other far both cases. Transition onset is located at about 500 times the nose radius in the leeward section and 750 times the nose radius in the windward section. The frequency spectrum of velocity and pressure fluctuations at different streamwise locations are analyzed and compared with the linear stability theory. The second-mode disturbance wave is deemed to be the dominating disturbance because the growth rate of the second mode is much higher than the first mode. The reason why transition in the leeward section occurs earlier than that in the windward section is analyzed. It is not because of higher local growth rate of disturbance waves in the leeward section, but because the growth start location of the dominating second-mode wave in the leeward section is much earlier than that in the windward section.

Atomistic investigation of the effects of temperature and surface roughness on diffusion bonding between Cu and Al

Molecular dynamics (MD) simulations are carried out to analyze the diffusion bonding at Cu/Al interfaces. The results indicate that the thickness of the interfacial layer is temperature-dependent, with higher temperatures yielding larger thicknesses. At temperatures below 750 K, the interface thickness is found to increase in a stepwise manner as a function of time. At temperatures above 750 K, the thickness increases rapidly and smoothly. When surface roughness is present, the bonding process consists of three stages. In the first stage, surfaces deform under stress, resulting in increased contact areas. The second stage involves significant plastic deformation at the interface as temperature increases, resulting in the disappearance of interstices and full contact of the surface pair. The last stage entails the diffusion of atoms under constant temperature. The bonded specimens show tensile strengths reaching 88% of the ideal Cu/Al contact strength. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

星系密度波的非线性不稳定性

<正> 星系密度波理论成功地解释了螺旋结构的缠卷困难。为了克服有限群速度引起的维持困难,人们研究了各种线性波的不稳定增长模式解。线性波的不稳定性分析只能适用于短的时间发展,所以应该进一步讨论非线性密度波的稳定性。徐遐生等用星系激波方程计算恒星的非线性密度波时发现,解极敏感地依赖于初值的选择,可能在物理上不稳定。许多数

The effects of coil current distribution in a cylindrical electron-cyclotron-resonance reactor

Using a 2-D hybrid model, the authors have found that external currents play an important role in the plasma parameters in the reactor. The plasma density, temperature and electrostatic potential would be significantly influenced by the applied external currents.

HF化学激光放大器的交叉弛豫动力学研究

在低气压超声速cwHF化学激光放大器中，假设平动和转动非平衡交叉弛豫同时起作用。对于气流介质的层流和湍流扩散混合两类流动模型，分别导出了饱和增益谱的表示式，并进行了数值计算。计算结果表明，湍流扩散混合模型与实验结果符合得更好。

扩散处理热浸镀铝钢高温抗氧化行为的研究

对经不同扩散工艺处理的热浸镀铝层高温抗氧化性进行了研究,通过SEM、TEM、XRD分析了经扩散处理后,热浸镀铝层高温氧化过程中组织结构的变化情况,分析了热浸镀铝层高温抗氧化性能和微观结构的关系,确定了提高热浸镀铝层高温抗氧化性的适宜扩散温度。结果表明,经750℃扩散处理,热浸镀铝层结构由较厚的外表层(Fe2Al5+FeAl2)及内层(FeAl+条状:FeAl2)组成,条状FeAl2的形成为氧提供了扩散通道,其抗氧化性较差;经950℃扩散处理,镀层外表层变薄,外表层转为单一FeAl2、内层为FeAl,并出现早期内氧化裂纹,其抗氧化性较差:当扩散处理温度为850℃时,镀层外表层变薄,结构转为FeAl2+少量Fe2Al5,而内层增厚,其结构为FeAl+球状FeAl2,而内层FeAl2球化,增强了氧由内层向基体扩散的阻碍作用,使氧只能逐层形成Al2O3+Fe2O3的氧化膜,提高了镀层的高温抗氧化性。

水蒸气对氧化钙脱氯效率影响的实验研究

本文采用实验方法,在一个流化床反应器中研究160～750℃下水蒸气的存在对HCl脱除效率(RE)的影响.实验结果表明:在低温区,水蒸气对RE的影响不明显;380℃时水蒸气的存在抑制反应进行;580℃和750℃时,脱除效率先下降,当水蒸气含量达到15%时,又呈现上升趋势.对于水蒸气含量为5%、10%和15%情况下,580℃的脱氯效率最高.最后通过对暴露的反应物表面积和HCl气体穿越产物层扩散过程的分析解释实验得到的规律.

双套管密相气力输运过程的数值模拟和能耗分析

基于计算流体力学理论,提出一种可用于预测双套管密相气力输送系统能耗的新方法.与以往依靠经验的计算方法不同,本工作将输送管道分为起始段与充分发展段两部分,分别进行详细的计算流体力学模拟后汇总得出整个系统的总能耗.压力梯度为750 Pa/m的情况下,计算所得物料输送速率为10 t/h,耗气量为290 m~3/h,实验所得物料输送速率为8.0 t/h,耗气量240 m~3/h,证明本数模方法是可靠的.

飞秒激光对氟化镁烧蚀机理研究

用扫描电镜（SEM）研究了氟化镁在800nm超短脉冲激光作用下的单枪表面烧蚀形貌．根据烧蚀斑面积与激光脉冲能量间的对数关系，测得烧蚀阈值与激光脉宽的关系曲线（55—750fs）．计算了导带电子的双光子吸收，改进了多速率方程模型．很好地解释了实验结果．

Active phase control and frequency chirp effects on supercontinuum generation in high birefringence photonic crystal fiber

An acoustic-optics programmable dispersive filter (AOPDF) was first employed to actively control the linearly polarized femtosecond pump pulse frequency chirp for supercontinuum (SC) generation in a high birefringence photonic crystal fiber (PCF). By accurately controlling the second order phase distortion and polarization direction of incident pulses, the output SC spectrum can be tuned to various spectral energy distributions and bandwidths. The pump pulse energy and bandwidth are preserved in our experiment. It is found that SC with broader bandwidth can be generated with positive chirped pump pulses except when the chirp value is larger than the optimal value, and the same optimal value exists for the pump pulses polarized along the two principal axes. With optimal positive chirp, more than 78% of the pump energy can be transferred to below 750 nm. Otherwise, negative chirp will weaken the blue-shift broadening and the SC bandwidth. (C) 2007 Elsevier B.V. All rights reserved.