Influence of liquid bridge volume on the onset of oscillation in floating-zone convection .1. Experiments

The onset of oscillation in the floating zone convection driven by the gradient of surface tension was experimentally studied, and discussions were concentrated on the influence of liquid bridge volume on the onset of oscillation. Distributions of critical applied temperature difference and frequency depending on the volume of the liquid bridge were obtained, and there was a gap range of liquid volume which separated the curve of marginal stability into two parts for fixed rod diameter and aspect ratio. The results imply that the volume of the liquid bridge is a sensitive critical parameter for the onset of oscillation. The implication on the instability is also discussed in the present paper.

Influence of liquid bridge volume on the onset of oscillation in floating-zone convection .2. Numerical-simulation

The onset of oscillation in the floating zone convection driven by the gradient of surface tension was studied numerically for an unsteady and two-dimensional model, and studies were concentrated on the influence of liquid bridge volume on the onset of oscillation in comparison with the experimental results in the Paper I. The numerical results agree with the experimental ones presented in the previous paper, in which the distributions of critical applied temperature difference depending on the volume of liquid bridge and a gap range of liquid volume in marginal stability curve were obtained.

Coupling of melting-solidification phase-change convection with floating-zone convection under microgravity

A finite element algorithm is used to analyze the process of floating zone crystal growth under microgravity. The effect of phase change convection coupled with surface tension convection is considered. The results show that the rate of crystal growth is very important. The single-crystal-melt interface is steeper than the feed-melt interface during the process of crystal growth. When the rate exceeds a critical value, the Marangoni vortex near the feed-melt interface will become so large that a secondary vortex will exist.

分子间相互作用对蛋白质晶体生长的影响

采用原子力显微镜对溶菌酶和刀豆蛋白A的分子间相互作用力的情况进行了研究,并用动态光散射研究了此二种分子间相互作用力有较大差异的蛋白质在晶体生长条件和非生长条件下,溶液中的聚集体的状态(大小和分散度)随浓度和温度的变化情况.实验结果表明,范德华力强的刀豆蛋白A在成核前,溶液中的聚集体不能很快转变为生长基元,导致晶体生长时间长;而范德华力弱的溶菌酶,溶液中的聚集体可以很快转变成生长基元,晶体生长时间也较短.

气相扩散法生长溶菌酶晶体的动态光散射研究

首次采用动态光散射研究了气相扩散法生长溶菌酶晶体 .实验中采用了两种溶解溶菌酶的方法，所得实验结果是有区别的 .这种区别表明了 NaCl对溶菌酶分子间相互作用产生十分重要的影响 .实验结果表明，晶体生长过程中，溶液中溶菌酶始终保持单分子与两分子聚集体的状态，这种状态是生长晶体的基础 .

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.

微小晶体生长过程的光学诊断实验研究

将光学干涉技术与显微技术相结合，应用计算机技术、图像处理技术发展形成一种实时细观诊断的实验方法——光学细观干涉诊断技术；实时观测了KCl晶体在容积为3mm * 3mm * 4.5mm的生长池内的结晶过程，得到了该过程的晶体的表面形貌、生长速率、以及晶体生长尺寸与时间、浓度与时间的定量的关系，观测到由重力引起的浮力对流现象，它直接影响晶体的生长。实验表明重力对晶体生长形态有很大的影响；生长速率与浓度存在很大的依赖关系。

气相扩散速率对溶菌酶晶体生长的影响

为研究气相扩散速率对溶菌酶晶体生长的影响,特设计了一种可方便调节气相扩散速率的晶体生长样品池,并用动态光散射法对不同气相扩散速率下晶体生长过程进行了研究.实验结果表明,随着气相扩散速率的增加,晶体生长过程中的成核阶段缩短.气相扩散速率通过影响溶菌酶溶液形成过饱和的速率来影响生长出的晶体的数量和大小.

Oscillatory Instability of Rayleigh-Marangoni-Benard Convection in Two-Layer System

The convective instabilities in two or more superposed layers heated from below were studied extensively by many scientists due to several interfacial phenomena in nature and crystal growth application. Most works of them were performed mainly on the instability behaviors induced only by buoyancy force, especially on the oscillatory behavior at onset of convection (see Gershuni et. Al.(1982), Renardy et. Al. (1985,2000), Rasenat et. Al. (1989), and Colinet et. Al.(1994)) . But the unstable situations of multi-layer liquid convection will become more complicated and interesting while considering at the same time the buoyancy effect combined with thermocapillary effect. This is the case in the gravity reduced field or thin liquid layer where the thermocapillary effect is as important as buoyancy effect. The objective of this study was to investigate theoretically the interaction between Rayleigh-Bénard instability and pure Marangoni instability in a two-layer system, and more attention focus on the oscillatory instability both at the onset of convection and with increasing supercriticality. Oscillatory behavious of Rayleigh-Marangoni-Bénard convective instability (R-M-B instability) and flow patterns are presented in the two-layer system of Silicon Oil (10cSt) over Fluorinert (FC70) for a larger various range of two-layer depth ratios (Hr=Hupper/Hdown) from 0.2 to 5.0. Both linear instability analysis and 2D numerical simulation (A=L/H=10) show that the instability of the system depends strongly on the depth ratio of two-layer liquids. The oscillatory instability regime at the onset of R-M-B convection are found theoretically in different regions of layer thickness ratio for different two-layer depth H=12,6,4,3mm. The neutral stability curve of the system displaces to right while we consider the Marangoni effect at the interface in comparison with the Rayleigh-Bénard instability of the system without the Marangoni effect (Ma=0). The numerical results show different regimes of the developing of convection in the two-layer system for different thickness ratios and some differences at the onset of pure Marangoni convection and the onset of Rayleigh-Bénard convections in two-layer liquids. Both traveling wave and standing wave were detected in the oscillatory instability regime due to the competition between Rayleigh-Bénard instability and Marangoni effect. The mechanism of the standing wave formation in the system is presented numerically in this paper. The oscillating standing wave results in the competition of the intermediate Marangoni cell and the Rayleigh convective rolls. In the two-layer system of 47v2 silicone oil over water, a transition form the steady instability to the oscillatory instability of the Rayleigh-Marangoni-Bénard Convection was found numerically above the onset of convection for ε=0.9 and Hr=0.5. We propose that this oscillatory mechanism is possible to explain the experimental observation of Degen et. Al.(1998). Experimental work in comparison with our theoretical findings on the two-layer Rayleigh-Marangoni-Bénard convection with thinner depth for H<6mm will be carried out in the near future, and more attention will be paid to new oscillatory instability regimes possible in the influence of thermocapillary effects on the competition of two-layer liquids

Floating zone convection

The microgravity research, as a branch of the advanced sciences and a spe- cialized field of high technology, has been made in China since the late 1980's. The research group investigating microgravity fluid physics consisted of our col- leagues and the authors in the Institute of Mechanics of the Chinese Academy of Sciences (CAS), and we pay special attention to the floating zone convection as our first research priority. Now, the research group has expanded and is a part of the National Microgravity Laboratory of the CAS, and the research fields have been extended to include more subjects related to microgravity science. Howev- er, the floating zone convection is still an important topic that greatly holds our research interests.

溶菌酶晶体生长过程中的扩散传质问题

采用Mach-Zehnder干涉测量系统与图象处理系统相结合实时观测溶菌酶蛋白质晶体生长过程中的流体动力学现象,对汽相扩散法溶菌酶蛋白质晶体生长过程进行了研究,观测到溶菌酶晶体生长时晶体周围存在的干涉条纹.分析了晶体生长时的重力沉降效应和溶质扩散过程.实验结果表明,该生长过程中的流体物理特征直接影响了生长晶体的晶面.根据实验结果,给出对蛋白质晶体生长过程流体物理现象的讨论。 

Direct observation of adsorption sites of protein impurities and their effects on step advancement of protein crystals

We measured noninvasively step velocities of elementary two-dimensional (2D) islands on {110} faces of tetragonal lysozyme crystals, under various supersaturations, by laser confocal microscopy combined with differential interference contrast microscopy. We studied the correlation between the effects of protein impurities on the growth of elementary steps and their adsorption sites on a crystal surface, using three kinds of proteins: fluorescent-labeled lysozyme (F-lysozyme), covalently bonded dimers of lysozyme (dimer), and a 18 kDa polypeptide (18 kDa). These three protein impurities suppressed the advancement of the steps. However, they exhibited different supersaturation dependencies of the suppression of the step velocities. To clarify the cause of this difference, we observed in situ the adsorption sites of individual molecules of F-lysozyme and fluorescent-labeled dimer (F-dimer) on the crystal surface by single-molecule visualization. We found that F-lysozyme adsorbed preferentially on steps (i.e., kinks), whereas F-dimer adsorbed randomly on terraces. Taking into account the different adsorption sites of F-lysozyme and F-dimer, we could successfully explain the different effects of the impurities on the step velocities. These observations strongly suggest that 18 kDa also adsorbs randomly on terraces. Seikagaku lysozyme exhibited a complex effect that could not alone be explained by the two major impurities (dimer and 18 kDa) present in Seikagaku lysozyme, indicating that trace amounts of other impurities significantly affect the step advancement.

硅生长过程中尖形磁场对流场及提拉速率的影响

通过使用基于非正交网格有限体积法的FLUTRAPP(fluid flow and transport phenomena pro-gram)程序模拟了工业8 in单晶硅提拉法生长过程.数值模拟结果表明,流场及提拉速率在单晶硅生长过程中具有振荡特性,提拉速率的振荡周期大约为2 min.尖形磁场的引入能够抑制坩埚中熔体流动的振荡,减小提拉速率的振幅,从而有利于提高所生长单晶的质量.

用半导体激光器对 Yb3+:LYSO 晶体的高效率激光特性的研究

本文报导了采用半导体激光器泵浦的高效连续可调谐Yb:LYSO激光器的输出特性。LYSO晶体同时具有LSO晶体良好的激光性能和YSO晶体易于生长且成本低廉的优点，实验中我们采用5at%掺杂的Yb:LYSO晶体进行研究，获得了最大输出功率2.84W、输出波长1085nm、光-光转换效率54.5%的高效输出。并且得到了1030-1111nm，一共81nm的波长调谐范围，这是目前我们所知道的从Yb:LYSO激光器获得的最宽的调谐输出。

Effect of PbO on precipitation of laser-induced gold nanoparticles inside silicate glasses

We report on three-dimensional precipitation of Au nanoparticles in gold ions-doped silicate glasses by a femtosecond laser irradiation and further annealing. Experimental results show that PbO addition plays the double roles of inhibiting hole-trapped centers generation and promoting formation and growth of gold nanoparticles. Additionally, glass containing PbO shows an increased non-linear absorption after femtosecond laser irradiation and annealing. The observed phenomena are significant for applications such as fabrications of three-dimensional multi-colored images inside transparent materials and three-dimensional optical memory, and integrated micro-optical switches. (c) 2007 Elsevier B.V. All rights reserved.