Comparative Study Of The Influence Of Natural Convection On Directional Solidification Of Al-3.5 Wt% Ni And Al-7 Wt% Si Alloys

We present numerical simulations of thermosolutal convection for directional solidification of Al-3.5 wt% Ni and Al-7 wt% Si. Numerical results predict that fragmentation of dendrite arms resulting from dissolution could be favored in Al-7 wt% Si, but not in Al-3.5 wt% Ni. Corresponding experiments are in qualitative agreement with the numerical predictions. Distinguishing the two fragmentation mechanisms, namely dissolution and remelting, is critical during experiments on earth, when fluid flow is dominant. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

InAs0.3Sb0.7 films grown on (100) GaSb substrates with a buffer layer by liquid-phase epitaxy

The growth of InAsxSb1-x films on (100) GaSb substrates by liquid-phase epitaxy (LPE) has been investigated and epitaxial InAs0.3Sb0.7 films with InAs0.9Sb0.09 buffer layers have been successfully obtained. The low X-ray rocking curve FHWM values of InAs0.3Sb0.7 layer shows the high quality of crystal-orientation structure. Hall measurements show that the highest electron mobility in the samples obtained is 2.9 x 10(4) cm(2) V-1 s(-1) and the carrier density is 2.78 x 10(16)cm(-3) at room temperature (RT). The In As0.3Sb0.7 films grown on (10 0) GaSb substrates exhibit excellent optical performance with a cut-off wavelength of 12 mu m. (c) 2007 Elsevier B.V. All rights reserved.

第7届国际等离子体化学会议(ISPC-7)

<正> Ⅰ.概况 国际等离子体化学会议(ISPC)每两年举行一次,主要交流等离子体化学如下几方面的研究和发展情况:合成,诊断,等离子体刻蚀,等离子体沉积和聚合,模型,表面作用以及熔化、气化、等离子体喷涂等。ISPC-7由荷兰Ejndhoven技术大学负责组织,Philips公司支持,在Philips会议中心举行。会议期1985年7月1—5日。第一天样品展览,

材料在高速变形时的动力松弛性质和一维杆中的塑性波

材料在高速变形时,它的整个变形过程能不能只用一个状态方程来描写是值得讨论的。本文认为,状态方程只在x-t Lagrange平面的部分区域内才反映高速变形过程的力学规律。 本文讨论了函数g(σ,ε)在高速变形时的性质,并建议采用如下的形式:g(σ,ε)=A[1-e~-B(1-ε)(σ-f(ε))]. 本文认为横向惯性的存在是状态方程中应力提高项出现的原因或原因之一. 本文用应变率相关理论解释了等应变区的存在. 在每秒几十米的撞击速度范围内,撞击端面间的摩擦力对塑性波的形成和传播具有不可忽视的影响.但在速度高到100米/秒以上时,这种影响又可能予以忽略. 以上五点看法是给合了铬钢短试件和2S铝杆的高速变形分析得到的.

溶液热历史对蛋白质晶体生长影响的内在原因研究

从溶液中聚集体的角度研究了溶液的热历史改变生长出的蛋白质晶体的数目和尺寸的内在原因.将在281和309 K下保存1 d的两组溶菌酶溶液按不同比例混合,加入沉淀剂生长晶体.随着高温溶液的比例增加,生长出的晶体数目减少,同时溶液中生长基元的尺寸增大.在5周内,采用动态光散射对281,293和309K三种温度下保存的溶菌酶溶液中聚集体的变化情况进行监测,发现溶液中均存在大小不同的两部分聚集体,称之为小聚集体与多聚体.前者的尺寸基本不随保存时间而变化,而后者尺寸随保存时间增加而减小,减小的速度与保存温度有关.多聚体的尺寸经过5周后和小聚集体基本相同.研究结果表明,处于无序聚集阶段的溶液的均一化程度和成核阶段生长基元的尺寸受到了溶液热历史的影响,并最终对晶体的数目产生影响.

万家寨引黄工程7~#土质引水隧洞变形的有限元分析

在山西省万家寨引黄入晋工程总干线 7#隧洞的开挖和衬砌的应力应变分析中 ,为确定土体c、Φ值和邓肯 -张模型参数 ,分别进行了加载试验和卸载试验 ,本文对用两种试验获得的模型参数进行有限元变形分析的结果进行比较。

非转移弧层流等离子体射流铸铁表面熔凝强化

用大气压非转移弧层流等离子体射流,对W-Mo-Cu铸铁表面进行熔凝相变强化处理,观察和测试了试样经不同弧电流处理后的表面层组织、硬度、耐磨性.结果表明,层流等离子体射流对铸铁表面的局部快速加热熔化和冷却凝固,明显改变了表面层的微观组织,提高了硬度和抗磨损性能.

给定井眼方向的修正轨道设计方法

在定向钻进过程中，井眼方向及其变化规律是井眼轨道监测与控制的关键参数。修正轨道设计作为井眼轨道监控的重要组成部分，对修正设计目标点的井眼方向往往有一定的要求。根据定向钻井工艺技术的特点，构造出了具有两个圆弧段和一个直线段的三段式剖面，从而解决了给定井眼方向条件下的修正轨道设计问题，为井眼轨道的有效监控奠定了基础。该设计方法避开了求解约束方程组，使得求解过程是一致收敛的，并且所有计算公式在理论上都是精确解，因此其普遍适用性、精确性、稳定性和收敛性得到了保证，可广泛应用于定向井、水平井、大位移井、多目标井的修正轨道设计。

ANSYS 7.0分析实例与工程应用

Effects of wall temperature on boundary layer stability over a blunt cone at Mach 7.99

Effects of wall temperature on stabilities of hypersonic boundary layer over a 7-degree half-cone-angle blunt cone are studied by using both direct numerical simulation (DNS) and linear stability theory (LST) analysis. Four isothermal wall cases with Tw/T0= 0.5, 0.7, 0.8 and 0.9, as well as an adiabatic wall case are considered. Results of both DNS and LST indicate that wall temperature has significant effects on the growth of disturbance waves. Cooling the surface accelerates unstable Mack II mode waves and decelerates the first mode (Tollmien–Schlichting mode) waves. LST results show that growth rate of the most unstable Mack II mode waves for the cases of cold wall Tw/T0=0.5 and 0.7 are about 45% and 25% larger than that for the adiabatic wall, respectively. Numerical results show that surface cooling modifies the profiles of rdut/dyn and temperature in the boundary layers, and thus changes the stability haracteristic of the boundary layers, and then effects on the growth of unstable waves. The results of DNS indicate that the disturbances with the frequency range from about 119.4 to 179.1 kHz, including the most unstable Mack modes, produce strong mode competition in the downstream region from about 11 to 100 nose radii. And adiabatic wall enhances the amplitudes of disturbance according to the results of DNS, although the LST indicates that the growth rate of the disturbance of cold wall is larger. That because the growth of the disturbance does not only depend on the development of the second unstable mode.

Laser action from 1,3,5,7-tetramethyl-2,6-diethyl-8-n-propyl pyrromethene-BF2

We measured spectroscopic and laser action properties of a novel 8-position substituted pyrromethene-BF2, namely 1,3,5,7-tetramethyl-2,6-diethyl-8-n-propyl pyrromethene-BF2 complex. The laser action was performed with the corresponding dye solution in ethanol, which was placed in a Littman-type laser cavity pumped by the second harmonic of a Q-switched Nd:YAG laser. The spectroscopic measurements clearly indicated that the corresponding dye solution in ethanol exhibited intense absorption in the visible spectral region with large fluorescence quantum yield. It possesses rather low triplet-triplet absorption in the spectral region 460-550 nm and almost negligible triplet-triplet absorption in the lasing spectral region. As a consequence, it lases nearly as efficiently as commercially available benchmark laser dyes such as Rhodamine-6G and outperformed them in wavelength tunability in our laser cavity and pump geometry. (C) 2002 Optical Society of America.

7 fs超快强激光驱动Ar原子产生支持单个阿秒脉冲的高次谐波连续谱

采用脉冲宽度为7 fs，脉冲能量为0．4mJ的超快强激光脉冲与气体盒子中Ar原子作用获得了高次谐波截止区连续谱，并发现当驱动激光稳定在不同的载波包络相位时，高次谐波的谱结构、谱调制深度和连续谱的带宽都有很大区别。在某些载波包络相位时获得了平滑的连续谱，调制深度小于17％，连续带宽达10eV，从而支持时域上获得变换极限500as的单个阿秒脉冲。