THE CONVECTIVE EFFECT ON THE MORPHOLOGICAL INSTABILITY OF KNbO3 CRYSTALS

Experimentally, it was observed that there were various morphologies of KNbO3 crystals in different regions of the melt of Li2B4O7 and KNbO3 mixture in Pt loop heater. Dendrites grew in the central area of the melt, the diffusive-advective region,in which the temperature gradient is negligible; whereas crystals with smooth sur face were observed in the marginal area, the diffusive-convective region, with large temperature gradient. Based on the solute concentration over the KNbO3 crystal surface examined by electronic probe analysis, it was proved that the combinative effect of buoyancy and surface tension convection induced by temperature gradient enhanced the homogeneity of the solute concentration around KNbO3 crystals and thus their morphological stability.     

EFFECTS OF CONVECTIVE FLUID MOTION UPON OXIDE CRYSTAL GROWTH IN HIGH TEMPERATURE SOLUTION

For understanding of the influence of convective flow on crystal growth, space high temperature in situ observation instrument (SHITISOI) is dedicated to visualize and record the whole growth process of oxide crystals in high temperature up to 1000°C. Model experiments using transparent liquids such as KNbO3 and a mix ture of Li2B4O7+KNbO3 were chosen to investigate effects on ground and in space.On the earth, an investigation of growth kinetics of KNbO3 crystal related to two different states of convection: diffusive-advective flow and diffusive-convective flow,has been performed. The per unit length of a step e is calculated from the exper imental data for two different states of convection. Analyses of these data show the effect of buoyancy convection is to enhance the sharpness of the interface. The growth of KNbO3 crystals from solution of KNbO3+Li2B4O7 was investigated in space. The streamlines of the steady thermocapillary convection in Li2B4O7 solvent was observed. Due to thermocapillary convection, KNbO3 crystal grains grew and filled the whole solution homogeneously. Earth-based quenching experiments are de signed in order to study polyhedral instability of KNbO3 crystal, which is controlled by diffusion mechanism limitation. In all cases, when the crystal was nucleated near air/solution surface, it lost its polyhedral stability and varied from polyhedrons to dedrites. The thickness of diffusion mechanism limitation layer is about 60μm.     

EXPERIMENTAL AND THEORETICAL STUDIES ON VELOCITY FIELD OF BUOYANCY CONVECTION IN KNbO3 MELT

The Schlieren technique coupling with a differential interference microscope was applied to visualize the KNbO3 melt motion in a loop-shaped Pt wire heater. The natural convection in KNbO3 melt was traced by observing the movement of the tiny KNbO3 crystals (～10μm) and the stream velocities of these tracer crystals were measured. In theoretical analysis, the Navier-Stokes equation was solved as a stable field. The general solution for this system of the differential equation was expressed by an approximate power series of azimuth and radius vector. The expression was substituted in the differential equation; a non-trivial solution was obtained exactly.The velocity distribution in the vertical section was obtained which is in qualitative agreement with the experimental result.     

INTERFACIAL MASS TRANSPORT IN OXIDE CRYSTAL GROWTH

A space high temperature in situobservation instrument (SHITISOI) is dedicated to visualize and record the whole growth process of oxide crystal in high temperature melts and solutions. Model experiments using transparent liquids such as KNbO3,Li2B4O7+KNbO3 were chosen to investigate effects of interracial mass transport in oxide crystal growth. For the scaling of the coupled velocity, heat and concentration fields in KNbO3 crystal growth, a rotating crystal growth process was performed and the widths of interfacial concentration, heat and momentum transition zones (The "boundary layers") are obtained, which are 7.5×10-a, 8.6×10-2 and 4.4×10-1 cm,respectively. Hence one can expect that interfacial concentration gradient will be confined to a narrow layer and in region of major concentration change at the in terface. In order to study a mechanism based on the interfacial mass transport resulting from hydrodynamics, the growth of KNbO3 grain in high temperature Li2B4O7 and KNbO3 solutin was studied. The result shows that the pivotal feature in the KNbO3 crystal growth is the initiated by KNbO3 solute surface tension gra dient which is caused by the slow diffusion of KNbO3 solutes. Direct comparison of the model predictions and experimental observed phenomena demonstrate the predictive capability of this model.     

VELOCITY FIELD OF THERMOCAPILLARY CONVECTION IN HIGH-TEMPERATURE OXIDE SOLUTION

We have investigated experimentally and theoretically the thermocapillary convec tive flow phenomena in a loop-shaped Pt wire heater of KNbO3 (20wt.%) and Li2B4O7 solutions. Optical evaluations in connection with thermocouple measure ments made it possible to get a new type of thermocapillary convective flow in the considered system. To study the kinematical behaviour of thermocapillary convec tion, we have measured the stream flow velocities. In a theoretical analysis, the flow velocity due to the thermocapillary effect alone was estimated by balancing the sur face tension forces by viscous forces. The velocity distribution in the solution near the margin of the heater was obtained, which is in agreement with the experimental result.     

NUMERICAL MODELLING OF VELOCITY AND TEMPERATURE DISTRIBUTIONS OF THE BUOYANCY CONVECTION EFFECT IN KNbO3 MELT

Numerical modelling of velocity and temperature fields in high-temperature KNbO3 melt of a loop-shaped Pt wire heater is carried out by using the commercial com putational code ANSYS for the mathematical solution of the governing equations.Based on the experimental boundary conditions and the Boussinesq approximation,the numerical modelling of a steady and two-dimensional model is applied to study the process under consideration of the buoyancy-driven convection condition. The result is compared with the previous experimental and theoretical data obtained in our laboratory, and the former is in agreement with the latter. Thus a theoretical guide for reasonable growth conditions is provided by studying in depth the real fluid flow effects in the crystal growth from the melt.     

用国产装置进行的空间蛋白质结晶实验

使用国内研制的管式汽相扩散结晶装置,在我国返回式卫星上,成功地完成了两次空间蛋白质晶体生长实验,10种不同种类的蛋白质配制的48个样品在空间的出晶率分别达52%和80%,其中少数蛋白质生长出了较高质量的蛋白质晶体。结果表明,空间的微重力环境利于改善蛋白质晶体的生长,而且在结晶条件优化足够好的条件下,在空间里能生长出比地面晶体尺寸较大、形态较好和内部有序性较高的蛋白质晶体。本文还就微重力对蛋白质晶体生长的具体作用及其开发利用做了讨论。      

THE SPACE EXPERIMENT OF PROTEIN CRYSTALLIZATION ABOARD THE CHINESE SPACECRAFT SZ-3

Using a new flight hardware, a Chinese mission of space protein crystallization has been performed on the Chinese spacecraft SZ-3 for seven days from March 25 to Apr. 1, 2002. The rate of yielding crystals in the 60 samples is 75%, a little higher than the ground control experiment. Preliminary analysis of the experimental results have shown that among the 16 proteins involved in the mission, about 4 kinds of better diffraction-quality protein crystals were produced in space. At least one kind of protein crystals, i.e. crystals of cytochrome b5 mutant could diffract X ray beyond the highest resolution reported so far. In addition, some rules derived from our numerical studies of the liquid/liquid diffusion protein crystallization were proved by the crystallization of lysozyme as model protein in this space experiment,which also clearly showed the advantages and disadvantages of the gelled protein solution used in microgravity growth of protein crystals. In order to exploit this mission, more diffraction work with the grown crystals and detailed analysis of data to be obtained will be done in the next few months.     

面向数字化技术支援的数字样机逐层轻量化技术

直观的三维模型有助于提高民用飞机远程维修支援的效率和准确度,但由于计算机辅助设计系统产生的模型数据量通常比较巨大,三维数字样机的轻量化成为了很大的挑战.基于对格式转换与模型简化这两种轻量化方法的分析,提出了基于单元数据量的数字样机逐级轻量化的方法,将全机的三维模型进行不同简化程度的轻量化处理,并且提出了基于失真度判据的层级化管理方法,按照模型结构树对简化率高的失真模型与具有细节特征的无损模型进行逐级的加载与使用.实例验证表明所提出的方法有效减小了网络传输的数据量并保留了模型必要的细节特征,使在互联网中快速访问全机三维模型得以实现.     

高频随机响应分析中的一种有限元网格细化标准

根据波动理论,满足随机响应工程计算精度要求的有限元网格大小与待求高频随机响应问题的频率范围上限有关。提出了一种新的有限元网格细化标准———三分之一波动细化标准。以简支板高频加速度响应分析为例,通过NASTRAN分析结果与解析解的对比验证了其有效性。     

一个高性能单反射面紧缩场

介绍了一个单反射面紧缩场,其反射面实体由多块面板拼装而成.单块面板成形基于"点阵钉模、真空负压、金属蜂窝"精密成形工艺,平均精度达到25μm(rms),拼装后总体形面精度达到40μm(rms).通过优化电气布局、边缘设计和馈源设计,该紧缩场具有优良电性能.给出了该紧缩场在39GHz时电性能实测曲线.      

微重力下胶原蛋白纤维化及羟基磷灰石结晶的初步研究

在长期空间飞行过程中, 骨质丢失是一个严重问题. 羟基磷灰石(HAP)晶体是骨骼的主要成分, 骨骼中的胶原蛋白纤维在HAP生长结晶过程中起到关键作用. 研究了胶原蛋白纤维化过程在模拟微重力和常重力条件下的变化, 对以胶原 蛋白纤维作为模板生长出的HAP晶体形貌进行了观察. 结果表明, 不同浓度胶原蛋白溶液中形成的胶原蛋白纤维, 其内部孔隙数量和尺寸在模拟微重力条件下要明显大于常重力条件下, 胶原蛋白纤维内部孔隙的分布也不同于常重力条 件下的结果. 以模拟微重力条件下形成的胶原蛋白纤维为模板生长出的HAP 晶体主要为立方体状, 而以常重力条件下形成的胶原蛋白纤维为模板生长出的 HAP晶体形貌主要为板状. 该结果有助于未来进一步阐明空间骨质丢失的机理.      

臭氧9.6μ带总吸收比的实验测定

在室温(约18℃)下测定了臭氧(O₃)9.6μ带的总吸收比,O₃含量在0.0188-0.5atmcm,压力在17—760mmHg之间。实验中使用了十字型吸收池,其一支通过紫外线,用以测量臭氧含量;另一支通过红外线,用以测量臭氧9.6μ带的总吸收比。对实验数据应用光谱模式理论进行了分析和处理,结果表明本实验资料与统计模式符合。最后给出了适用于统计模式的带参数。      

基于非参数假设检验的程序缺陷定位方法

调查了西门子测试集中的程序失败用例的规模和谓词评估偏差的分布.结果表明,中心极限定理的前提和参数假设检验的假设条件无法得到普遍满足.所以,已有的基于参数假设检验的方法存在潜在的问题.针对这一现象,提出了基于非参数假设检验定位程序缺陷的方法.实验结果表明,该方法在非正态分布的样本集上仍具有较好的适用性,且在缺陷定位效率上优于已有的基于程序谓词的缺陷定位技术.同时比较了基于2种常用的非参数假设检验模型的缺陷定位方法的效率.一种方法基于Kolmogorov-Smirnov检验,另一种方法基于Cramér-von-Mises准则.比较结果表明,在西门子测试集上,基于Kolmogorov-Smirnov检验的方法在缺陷定位效率上优于基于Cramér-von-Mises准则的方法.     

改性聚酰亚胺复合材料的电导机理分析

首先,选用半导电的微米级和纳米级改性剂粉料对玻璃布补强聚酰亚胺基复合材料进行改性.共制备了5种试样,其中包括4种使用无碱玻璃布补强的聚酰亚胺试样,分别是未改性、纳米改性、微米改性和微/纳米改性和一种使用微碱玻璃布补强的试样.其次,研究改性剂粒径和玻璃布含碱量对复合材料介电性能及电导率特性的影响.试验结果表明改性剂粒径对复合材料的介电性能影响不显著,但是微米粒径的改性剂能显著提高复合材料的体电导率并赋予复合材料一定的非线性电导率特性,而纳米粒径的改性剂会小量地降低复合材料的电导率.与无碱玻璃布补强的试样相比,采用微碱玻璃布改性和补强的复合材料试样有较高的非线性电导阈值电场.      

Remote sensing of clouds

The extraction of information on cloud cover from present-day multispectral satellite images poses a challenge to the remote sensing specialist. When approached one pixel at a time, the derived cloud cover parameters are inherently nonunique. More information is needed than is available in the radiances from each channel of an isolated pixel. The required additional information can be obtained for each scene, however, by analyzing the distribution of pixels in the multi-dimensional space of channel radiances. The cluster patterns in this space yield statistical information that points to the most likely solution for that scene. The geostationary and polar orbiting meteorological satellites all have, at a minimum, a solar reflection channel in the visible spectrum and a thermal infrared channel in the 8–12 micron window. With the information from the cluster patterns and application of the equations of radiative transfer, the measurements in those channels will yield cloud cover fraction, optical thickness, and cloud-top temperature for an assumed microphysical model of the cloud layer. Additional channels, such as the 3.7 micron channel on the AVHRR of the polar orbiting meteorological satellites, will will yield information on the microphysical model—e.g., distinguishing small liquid liquid droplets (typical of low level clouds) from large ice particles (typical of cirrus and the tops of cumulonimbus). New channels to be included in future satellite missions will provide information on cloud height, independent of temperature, and on a particle size and thermodynamic phase, independently of each other. A proposed STS mission using lidar will pave the way for the use of active sensors that will provide more precise information on cloud height and probe the structure of thin cirrus and the top layer of of the thicker cloud.     

资源卫星CCD多光谱扫描仪系统的像质评价

综述了资源卫星ＣＣＤ多光谱扫描仪系统像质评价的重要性。内容和影响像质的主要因素;还综述了ＳＰＯＴ和ＴＭ使用的评价准则、评价方法以及卫星发射前的图像质量预估和在卫星发射后的像质评估结果。     

γ-TiAl合金的显微组织对其蠕变性能的影响

讨论了γ-TiAl合金显微组织与蠕变性能的关系,并用PST(Polysynthetically Twinned Crystal,简称PST晶体)晶体研究了片层界面相对于外力轴取向对TiAl合金蠕变性能的影响.认为影响该合金蠕变性能的主要显微组织参数是片层取向,γ体积分数,晶粒尺寸,片层宽度以及晶界形貌,并分析了它们与蠕变性能的关系.提出了如何控制以上显微组织参数,使得该合金具有最佳蠕变抗力.     

神舟七号微小卫星伴随飞行技术试验

神舟七号 (SZ-7) 载人航天任务中释放的一颗微小伴随卫星 (BX-1), 首次开展了卫星在轨释放、对飞船观测和对轨道舱接近及绕飞等技术试验. 该卫星首次进行了GaInP2/GaAs/Ge 中国产太阳电池阵、锂离子蓄电池、微型液氨推进模块、小型化姿态跟踪控制模块、双焦距一体化可见光相机及小型化USB 测控应答机等技术验证. 本文介绍了SZ-7 微小卫星的设计方案, 讨论了形成稳定伴随飞行的轨道设计等技术, 并根据卫星在轨运行情况对试验任务进行了评价.