空间微重力环境下蛋白质晶体生长的研究进展

空间微重力环境可消除或减弱常重力场下溶液中存在的对流和沉降,为蛋白质晶体生长提供一个相对均一和稳定的环境,有利于得到尺寸更大、衍射分辨率更高的蛋白质晶体。通过对这些高质量空间晶体进行X射线衍射分析,可获得多种蛋白质的精细三维结构。从空间蛋白质晶体生长的发展历史、研究成果、生长机理、存在的问题与对策等方面总结了空间微重力环境下蛋白质晶体生长的研究进展,展望了空间蛋白质结晶的未来。     

空间模拟条件下三元共晶合金凝固研究

三元共晶凝固过程涉及三个固相在同一液相中的竞争形核和协作生长,可以形成丰富多样的凝固组织,对发展原位复合材料制备技术和研究自发模式形成现象都具有重要的意义。空间环境中的微重力和无容器效应消除了重力引起的对流、沉降以及器壁引起的异质形核,为深入研究非平衡快速凝固规律提供了理想的实验条件。由于空间实验机会十分难得,人们发展了自由落体、悬浮、抛物飞行、探空火箭等多种空间环境的地面模拟方法,部分的或一定程度的实现空间的微重力和无容器效应。对国内外采用浸浮净化、落管、超声悬浮等地面模拟方法开展的三元共晶合金凝固研究工作进行了综述,并对未来发展趋势进行了展望。     

无容器凝固技术与新材料研究

无容器技术是新材料开发中新颖的超常技术。通过空间微重力或地面上的静电力、电磁力、声波力和气动力等来悬浮并稳定试样,实现新材料制备及其物性和结构的研究。无容器技术避免了器壁的异质形核,易获得深过冷和实现快速凝固,能制备常规技术无法获得的新型功能材料。由于无需容器,开辟了超高温熔体热物性测试的新方法。无容器技术和空间微重力、高能量精密结构分析和超级计算机模拟仿真相结合,必定为我国新材料的研发及设计理论的探索提供崭新的科学平台。     

垂直Bridgman法生长CaF2单晶传热过程的数值分析

采用有限元法对大尺寸氟化钙单晶的生长过程进行了传热分析,准稳态模型简化模拟计算过程.研究了梯度区不同的温度梯度对界面形状和晶体生长速度的影响,讨论了辐射传热对晶体生长过程传热的影响.研究表明:晶体生长过程中界面凸度发生变化;晶体生长速率与坩埚下降速率不一致;25 K/cm为合适的梯度区温度梯度;晶体内部辐射传热对单晶生长传热过程有重要影响.计算结果表明,3个时期的固相等温线的曲率小于液相的.根据数值模拟结果进行了晶体生长实验,生长出的晶体完整,透明,无宏观缺陷.     

基于磁补偿的液氧悬浮可视化验证实验研究

利用液氧的顺磁特性,以低温超导磁体为受控磁场发生器,设计了一套磁补偿低温液氧悬浮可视化验证性实验系统。通过改变超导线圈电流强度,实现了大小适当且持续稳定的磁场力用于补偿液氧重力,观察到氧气泡在最佳磁补偿点处的微重力悬浮现象,捕捉到微重力液氧气液界面处的气泡成型、脱离和相界面变化特征,展示出微重力下表面张力的主导作用,验证了通过磁场补偿实现地面研究液氧微重力环境下相关机制的可行性。     

多尺度晶体材料的原位表征技术与计算模拟研究进展

大尺寸晶体材料是半导体、激光、通讯等领域的基础原料,大尺寸、高品质晶体材料的制备已成为制约相关行业发展的瓶颈。我国面临的“卡脖子”技术中大多与关键基础材料相关。大尺寸晶体材料制备理论与技术是我国新材料产业高质量发展的一个重要方面,也是提升相应高技术产业的基础,突破大尺寸晶体材料的制备理论和技术是获得高品质大尺寸晶体材料的关键。探究并准确理解大尺寸晶体生长机理需要借助原位表征技术和多尺度计算模拟方法。单一的原位表征和模拟技术只能探究特定时间和空间范围内的结晶信息,为了准确反映结晶过程需要综合应用多种方法。本文综述了最新的多尺度晶体生长研究的原位表征方法、多尺度计算模拟技术以及机器学习方法,为发展结晶理论和控制晶体品质提供重要的实验和理论依据,并将为提升大尺寸晶体生长工艺的开发而服务。     

硅酸铋(BSO)晶体的空间生长

BSO晶体首次在飞船上进行了空间晶体生长.本文对空间和地面生长的BSO晶体进行了X射线摇摆曲线、位错腐蚀和透过率的测试.实验结果表明:在微重力环境下能明显提高BSO晶体的光学质量.     

磁场力非均匀度对液氧磁补偿微重力自由界面的影响

利用液氧在磁场环境下的顺磁特性和超导磁体产生的强磁场,可以实现液氧的磁补偿,从而能够在地面进行长时间、低成本的流体受控微重力实验。为了能够准确合理设计液氧磁补偿系统,通过多场耦合数值模拟,研究了在超导磁体产生的磁场中,不同磁场力非均匀度条件下液氧在容器内的自由液面流动过程,并与在空间真实微重力环境(均匀10~(-6)g)下的结果进行了比较。结果表明:0.1%的非均匀度条件初步具备了模拟空间微重力环境的能力,在更低的非均匀度条件下(0.05%),液氧在磁补偿环境下的箱内流动能够得到很高程度的天地一致性还原;0.3%的非均匀度已经对液氧在箱内的流动过程造成了明显的偏差;在1%的非均匀度条件下,液氧在箱内的自由界面流动则基本脱离了空间真实特征,氧气气枕区无法稳定。     

半导体材料的微重力生长

空间微重力环境提供了一个独特平台,以改进地面材料性能、深入理解被地面重力掩盖的晶体生长现象。半导体空间材料科学的主要进展有:(1)基于对组分均匀的完美半导体的追求,人们对于晶体生长机理,特别是对流、溶质传输及组分分凝的相互作用,有了更加深入的理解;(2)基于空间实验结果,人们澄清了非接触Bridgman生长的内在机理,并将之用于指导空间及地面实验;(3)提出了新的微重力晶体生长技术并成功用于组分均匀半导体合金材料的制备。回顾了以上方面的研究进展,并对半导体空间材料科学的未来挑战进行了展望。     

ACRT技术对大尺寸ZnTe晶体溶液法制备及其性能影响

太赫兹(Terahertz,THz)技术在工业无损检测、科学研究和军事领域发挥着越来越重要的作用。作为太赫兹产生和探测最常用的电光晶体材料,ZnTe晶体在生长中依然面临众多挑战。为了制备大尺寸、均匀性好、高性能的ZnTe单晶,本研究在温度梯度溶液法生长ZnTe晶体过程中引入坩埚旋转加速技术,制备具有高结晶质量的ZnTe晶体。模拟计算得到不同坩埚旋转速度下生长界面处对流场和溶质分布,研究了坩埚旋转对晶体生长过程中的固液界面稳定性和晶体内Te夹杂分布的影响规律,证明坩埚旋转加速技术可以有效地促进熔体流动,改善溶质传质能力,稳定溶液法晶体生长的固液界面,不仅避免出现尾部混合相区,也减少了ZnTe晶体内Te夹杂相的数量并减小其尺寸。通过进一步优化坩埚旋转参数,制备出具有较高结晶质量的大尺寸ZnTe晶体(?60 mm)。同时,得益于晶体良好的均匀性,晶体对太赫兹的高响应区域超过90%,边缘效应小,满足太赫兹成像要求。研究表明,引入坩埚旋转加速技术为制备大尺寸ZnTe基电光晶体提供了新的思路。     

JAXA-GCF project - high-quality protein crystals grown under microgravity environment for better understanding of protein structure

Since 2003, Japan Aerospace Exploration Agency (JAXA, former NASDA) has been conducting a project on a semi-annual basis (JAXA-GCF) to obtain high-quality protein crystals in the microgravity environment using the Russian transportation system. For this project, protein samples were mostly provided by Japanese users for whom JAXA provided technical and clerical support for crystallization experiments in microgravity. For the project, JAXA has constructed a user-friendly support service for microgravity experiments and provided regular and frequent flight opportunities. To simplify and improve technological matters, JAXA devised a gel-tube method crystallization device, which is effective both in space and on ground, based on the counter-diffusion technique. JAXA also provided ground-based techniques for efficient preliminary optimization of crystallization conditions using a 1-dimensional simulation and for harvesting and cryoprotecting crystals before X-ray diffraction experiments. These improvements have significantly increased the success rate of obtaining useful results. In conclusion, JAXA has developed technologies for growing, in microgravity, high-quality protein crystals, which may diffract up to atomic resolution, for a better understanding of 3-dimensional protein structures through X-ray diffraction experiments.     

Aerodynamic Levitation and Inductive Heating – A New Concept for Structural Investigations of Undercooled Melts

The combined application of containerless techniques with X-ray diffraction and absorption at synchrotron sources as well as neutron diffraction enables structural investigations of high-melting-point and/or corrosive liquids above the melting point and in the undercooled state. A variety of containerless techniques are available including electromagnetic and aerodynamic levitation. In the framework of a bilateral project, a new hybrid system combining aerodynamic levitation with inductive heating is being developed. Advantages and concept of the setup are discussed. Different Helmholtz coils and cylindrical coils were used to heat levitated, solid samples. Melting and stable levitation in the liquid state were achieved for aluminum. The general problem of deformation of liquid samples by electromagnetic fields is discussed. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.     

Measurement of density,sound velocity,surface tension,and viscosity of freely suspended supercooled liquids

Noncontact methods have been implemented in conjunction with levitation techniques to carry out the measurement of the macroscopic properties of liquids significantly cooled below their nominal melting point. Free suspension of the sample and remote methods allow the deep excursion into the metastable liquid state and the determination of its thermophysical properties. We used this approach to investigate common substances such as water,v-terphenyl. succinonitrile, as well as higher temperature melts such as molten indium, aluminum, and other metals. Although these techniques have thus far involved ultrasonic, eletromagnetic, and more recently electrostatic levitation, we restrict our attention to ultrasonic methods in this paper. The resulting magnitude of maximum thermal supercooling achieved has ranged between 10% and 15% of the absolute temperature of the melting point for the materials mentioned above. The methods for measuring the physical properties have been mostly novel approaches, and the typical accuracy achieved has not yet matched the standard equivalent techniques involving contained samples and invasive probing. They are currently being refined, however, as the levitation techniques become more widespread and as we gain a better understanding of the physics of levitated liquid samples.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–34, 1994, Boulder, Colorado, U.S.A.     

Diamagnetic levitation enhances growth of liquid bacterial cultures by increasing oxygen availability

Diamagnetic levitation is a technique that uses a strong, spatially varying magnetic field to reproduce aspects of weightlessness, on the Earth. We used a superconducting magnet to levitate growing bacterial cultures for up to 18 h, to determine the effect of diamagnetic levitation on all phases of the bacterial growth cycle. We find that diamagnetic levitation increases the rate of population growth in a liquid culture and reduces the sedimentation rate of the cells. Further experiments and microarray gene analysis show that the increase in growth rate is owing to enhanced oxygen availability. We also demonstrate that the magnetic field that levitates the cells also induces convective stirring in the liquid. We present a simple theoretical model, showing how the paramagnetic force on dissolved oxygen can cause convection during the aerobic phases of bacterial growth. We propose that this convection enhances oxygen availability by transporting oxygen around the liquid culture. Since this process results from the strong magnetic field, it is not present in other weightless environments, e.g. in Earth orbit. Hence, these results are of significance and timely to researchers considering the use of diamagnetic levitation to explore effects of weightlessness on living organisms and on physical phenomena.     

A magnetic levitation rotating plate model based on high-Tc superconducting technology

With the wide requirements of the training aids and display models of science, technology and even industrial products for the public like schools, museums and pleasure grounds, a simple-structure and long-term stable-levitation technology is needed for these exhibitions. Opportunely, high temperature superconducting (HTS) technology using bulk superconductors indeed has prominent advantages on magnetic levitation and suspension for its self-stable characteristic in an applied magnetic field without any external power or control. This paper explores the feasibility of designing a rotatable magnetic levitation (maglev) plate model with HTS bulks placed beneath a permanent magnet (PM) plate. The model is featured with HTS bulks together with their essential cryogenic equipment above and PMs below, therefore it eliminates the unclear visual effects by spray due to the low temperature coolant such as liquid nitrogen (LN₂) and additional levitation weight of the cryogenic equipment. Besides that, a matched LN₂ automation filling system is adopted to help achieving a long-term working state of the rotatable maglev plate. The key low-temperature working condition for HTS bulks is maintained by repeatedly opening a solenoid valve and automatically filling LN₂ under the monitoring of a temperature sensor inside the cryostat. With the support of the cryogenic devices, the HTS maglev system can meet all requirements of the levitating display model for exhibitions, and may enlighten the research work on HTS maglev applications.     

Measurement of Density and Structural Short-Range Order of Levitated Liquid Metals

The determination of thermophysical properties and structure of undercooled metallic melts must be accomplished by contactless methods due to the high reactivity of the material. It has been shown that electromagnetic levitation provides high-purity conditions to allow deep undercooling. The density and thermal expansion of a levitated drop can be derived from volume measurements using a charge-coupled device (CCD) camera and a digital image processing system. Combining levitation with extended x-ray absorption fine structure (EXAFS) spectroscopy leads to the possibility of studying the local structure of the liquid in a wide temperature range including the deeply undercooled regime.     

高温超导磁悬浮测试系统

介绍一种高温超导磁悬浮测试系统,该系统主要包括液氮低温容器,永磁体轨道,数据采集和处理,机械传动和自动控制四部分,采用了能放量高温超导体块材的薄底液氮低温容器（杜瓦容器）,解决了将高温超导体块材置于永久磁体之上的磁悬浮测量问题,能实时检测多块或单块高温超导体块材的各种高温超导磁悬浮性能。     

Nd3+/Yb3+共掺La2O3-TiO2-ZrO2微晶玻璃的制备及上转换发光研究

利用气悬浮方法制备了Nd³⁺/Yb³⁺共掺La₂O₃-TiO₂-ZrO₂前驱体玻璃, 通过热处理获得了微晶玻璃。通过DTA对前驱体玻璃的热稳定性进行了研究。利用光致发光谱, TEM和EDS对微晶玻璃进行了表征分析, 并研究了热处理对上转换发光的影响。结果表明: 玻璃转变温度和析晶起始温度分别为799℃和880℃. 在980 nm激光激发下, 样品发射出中心位于497, 523, 545, 603和657 nm处的五条发光带。热处理后样品上转换发光强度提高, 经过880℃保温50 min热处理的微晶玻璃显示了最强的上转换发光, 在545 nm处的发光强度是前驱体玻璃的11倍, 这是由于在微晶玻璃基质中存在致密柱状晶和Nd³⁺离子在晶体中富集造成的。     

基于磁悬浮技术建筑物振动测量研究

针对大型基建设备工作时产生的振动对周围建筑和环境的影响,设计了利用磁悬浮技术进行振动测量系统。建立了振子的动力学方程,证明了磁悬浮技术可实现绝对振动测量;对磁悬浮技术振动测量系统的自振和外加振动仿真及功率谱进行了分析;并实测了大型设备工作时产生的振动,得到其振动主频为5 Hz左右的低频分量。分析表明,利用磁悬浮技术测振易于实现绝对式低频振动测量且灵敏度高。