Surface tension-driven flows in horizontal liquid metal layers

The problem of surface tension-driven flows in horizontal liquid layers has been studied experimentally, and theoretically by direct numerical simulation and small perturbation analysis. We focus our attention on situations in which the depth of the fluid (liquid tin; small Prandtl number, Pr=0.015) is small enough to ensure the predominance of the surface tension forces over those due to the buoyancy. The surface velocity has been experimentally obtained for liquid tin layer with various aspect ratio (length to height) in the range 5<A<83. The thermal gradients are ranged from 5 to 40°K/cm. In the numerical study, the Navier-Stokes and energy equations are solved by an efficient finite difference technique. The parameters governing the flow behaviour in the liquid are varied to determine their effects on thermocapillary convection: the Reynolds number 10<Re<210⁴ and the aspect ratio 2<A<25; with Pr kept constant at Pr=0.015. The linear eigenequation resulting from small spatial disturbances of the Couette flow solution is solved using an Tau-Chebyshev approximation. A notable feature of the theoretical study is the totally different end circulations. In the region near the cold wall a multicell structure is evident. This agrees with the eigensolution which is of complex type, indicating spatial periodicity. In the hot wall region the flow is accelerated to reach the velocity value for the fully-developed Couette flow which is reached under conditions such as Re/A<20. The transition from viscous to boundary layer regime occurs for a critical value (Re/A)_c of nearly about 200, as deduced from the numerical and experimental results.     

Marangoni convection when the surface tension increases with the temperature in normal and low gravity conditions

Thermocapillary convection has been studied in n-heptanol aqueous solutions whose surface tension is increasing with the temperature.

The fluid was confined in a parallelipipedic enclosure and a thermal gradient was imposed parallel to the free liquid/gas interface. The motions induced by the thermocapillary forces have been studied under low gravity conditions during Texus sounding rocket experiments and during the Spacelab D1 mission.

The combined thermocapillary and buoyancy convection have been extensively studied during ground based experiments.

The influence of the aspect ratio and of the alcohol concentration were investigated. Detailed velocity field was determined at the steady state under normal gravity conditions by Laser Doppler Anemometry (LDA).

The aspect ratio was of 0.3 and the temperatures imposed to the lateral sides of the cell were respectively 45°C and 60°C. With these experimental conditions, two superposed contrarotative cells were observed with rapid motions in the surface from the cold to the hot side. This convective pattern was also observed during the normal and high gravity periods of parabolic flights but during the low gravity period of the parabola the motions stopped everywhere in the fluid even in the surface and reappeared immediatly at the pull out of the parabola.     

Interaction of growth-determining systems with gravity

The experiments have been carried out with lettuce shoots on board the Salyut-7 orbital station, the Kosmos-1667 biological satellite and under ground conditions at 180° plant inversion. By means of the centrifuge Biogravistat-1M the threshold value of gravitational sensitivity of lettuce shoots has been determined on board the Salyut-7 station. It was found to be equal to 2.9 × 10⁻³g for hypocotyls and 1.5 × 10⁻⁴g for roots. The following results have been received in the experiment performed on board the Kosmos-1667 satellite: a) under microgravity the proliferation of the meristem cells and the growth of roots did not differ from the control; b) the growth of hypocotyls in length was significantly enhanced in microgravity; c) under microgravity transverse growth of hypocotyls (increase in cross sectional area) was significantly increased due to enhancement of cortical parenchyma cell growth. At 180° inversion in Earth's gravity root extension growth and rate of cell division in the root apical meristem were decreased. The determination of DNA-fuchsin value in the nuclei of the cell root apexes showed that inversion affected processess of the cell cycle preceeding cytokinesis.     

空间在轨流体输运双槽道微重力实验装置

空间在轨流体输运双槽道微重力实验装置通过在微重力环境下对开口槽道中的流动进行观察,可以分析研究微重力下流体输运的稳定特性.双槽道形式的实验装置在单次实验中可同时对两种不同截面,不同流量的槽道流动进行观测,同时可有效提升落塔实验效率,减少不同槽道对比实验中的不确定因素.针对双槽道流体实验装置设计的关键问题,例如密封、压力补偿、设备布局等,提出了实验装置的系统结构及落塔实验步骤.在落塔短时微重力环境中,采用氟化液（HFE7500）流体介质,利用本实验装置成功观测到槽道流体输运流动与失稳现象.      

微重力板式贮箱推进剂重定位的数值仿真

板式表面张力贮箱内推进剂重定位对确定推进剂分布情况、研究晃动影响、提高控制精度等具有重要意义．为研究板式贮箱内推进剂重定位的规律,对微重力下板式贮箱内液体重定位问题进行数值仿真．计算时使用三维非定常两相流动流体（VOF）模型,对某一板式贮箱寿命末期在不同微重力加速度情况下各种重定位过程进行数值仿真,得到各种工况下重定位的全过程,以及定位后推进剂的分布情况．数值仿真结果为板式贮箱的设计提供有利依据．     

热毛细效应对细丝薄膜流动不稳定性的影响

根据重力与热毛细力耦合作用薄膜在细丝上的流动情况,采用长波近似推导了界面的演化方程.通过色散关系分析热毛细作用对Rayleigh-Plateau稳定性的影响;通过时空模式的稳定性分析,研究了系统的绝对对流不稳定性特性;通过直接数值模拟,研究了薄膜破裂和绝对对流稳定性的关系.      

侧向微重力环境下板式表面张力贮箱内推进剂晃动行为分析

侧向微重力是航天器在轨飞行时在东西位置保持和南北位置保持状态时所处的加速度环境.由于航天器贮箱内推进剂在侧向加速度环境下的重定位过程易产生晃动，因此侧向加速度环境对贮箱内推进剂管理装置(PMD)的管理能力的要求更高.为确保板式贮箱对推进剂的在轨管理能力，需要开展一系列的数值仿真与试验对PMD的管理能力进行验证.本文以板式表面张力贮箱为研究对象，采用VOF两相流模型对侧向微重力环境下重定位过程中贮箱内推进剂的运动进行数值模拟，并对推进剂运动中的晃动行为进行分析.最终，通过数值模拟结果验证了板式表面贮箱的管理能力，为微重力落塔试验与空间站试验提供参考依据.     

微重力下两相控温型储液器内气液界面仿真分析

两相控温型储液器对机械泵驱动两相流体回路的稳定运行起到关键作用，而储液器内部气液分布状态是其控温性能的决定性因素之一。在轨微重力条件下，储液器内两相流动特性与地面状态差别巨大，这将给储液器的设计带来较大难度。针对两相控温型储液器在轨微重力下的两相工质分布特性，通过计算流体力学（CFD）方法对其内两相流动行为进行数值模拟。通过使用连续表面张力模型计算表面张力，使用多相流计算的流体体积分数方法对两相控温型储液器内气液界面形态的发展进行了追踪预测，并与理论解进行对比，结果吻合一致。通过对两相控温型储液器在不同Bond数、接触角、工质充灌量等参数下的仿真分析，得到了不同条件下储液器内气液运动及分布情况，结果表明:两相控温型储液器内气液界面状态与储液器尺寸、壁面浸润性、工质充灌量相关。研究结果可以为微重力下两相控温型储液器内气液界面的控制提供理论依据，并能指导储液器研制及在轨应用。      

Intensity profiles of the multiple scattering light near the cometary nucleus

The multiple scattering of solar radiation in the cometary atmosphere is treated with the method of successive scattering. Referring to in situ measurements of comet Halley about the size and spatial distributions of dust, the optical thickness τ₁ of dust has been estimated, i.e. τ₁=0.03 at wavelength λ=0.62μm in a quiet time, but τ₁=0.3 when the outbursts/jets occur. In the derivation of τ₁, optical properties of dust including a mixing ratio of absorbing to silicate grains, are determined based on the polarimetry of P/Halley at λ=0.62μm observed during the phase angles over Nov. 1985 to May 1986 at the Dodaira Station of Tokyo Astronomical Observatory.

It is found that a temporary enhancement of τ₁ leads an increase of the upward reflected intensity when the surface albedo A of the nucleus is less than 0.04, but the reverse is true when A>0.04. On the other hand, the intensity of the downward radiation at the surface of the nucleus always decreases as an increase of τ₁.     

Growth of Prunus tree stems under simulated microgravity conditions.

Stem growth of Prunus trees under simulated microgravity conditions was examined using a three-dimensional clinostat. The stems elongated with bending under such conditions. Stem elongation and leaf expansion were both promoted, whereas the formation of xylem in the secondary thickening growth was inhibited under the simulated microgravity condition. In secondary xylem, sedimentable amyloplasts were observed in the 1g control. The present results suggest that stem elongation and leaf expansion may be inhibited at 1g, while growth direction and secondary xylem formation depend on a gravity stimulus. A space experiment is expected to advance research on thickening growth in trees.     

空间在轨流体输运稳定性落塔实验

空间流体管理是微重力流体科学的重要研究方向之一,而有外力驱动的开口流道毛细流动界面稳定性研究是其重要的内容.设计研制了一种微重力双流道流体输运实验装置,采用的两个流道分别为截面相同的对称内角和非对称内角,并有相同的开口长度,在百米微重力落塔进行了10次双舱实验.通过分析不同流量下的液面特性,判定流动的类别,将流动形态分为亚临界、临界和超临界三种,确定了两个流道的临界流量,并对两个流道毛细流动的特征进行了比较.      

环形液池热毛细对流的线性稳定性研究

对外壁加热的环形液池热毛细对流进行了线性稳定性分析.采用Chebyshev配点法对Pr=6.8、内外径之比为0.5、深宽比A范围为0.25～1.4的数值结果进行分析,发现流动的临界状态均为振荡形式,并且随着A的增大,临界雷诺数减小,相应的临界波数与振荡频率也呈减小趋势.能量分析结果表明,小扰动与基本流相互作用项较小,表面张力在径向做功与周向做功对小扰动的动能变化起主导作用.观察三者与液池深宽比的关系,发现A=0.8时表面张力在径向做功项达到极小值,周向做功项以及小扰动与基本流相互作用项达到极大值.      

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.     

X-ray measurements of the dark matter distribution in clusters of galaxies with Chandra

We investigate the dark matter distributions in the central region of two clusters of galaxies (A1835 and MKW3S) using Chandra data. N-body simulations in the standard cold dark matter (CDM) model predict the dark matter distribution shows a cuspy dark matter profile: ρ(r) ∝ r, with in the range 1–2, while observations of dwarf and low surface brightness galaxies seem to favor the presence of a relatively flat core: 0 <  < 1. To investigate the dark matter distributions in the central region of clusters of galaxies, we analyze the Chandra data of A1835 and MKW3S with a deprojection method. We derive the mass profiles without the assumption of analytical models. We examine the inner slope of derived mass profiles assuming the dark matter profile is described with a power-law expression. The values of the slope are 0.95 ± 0.10 for A1835 and 1.33 ± 0.12 for MKW3S within the radius of 200 kpc. These are consistent with the result of the CDM simulations. However, within the radius of 100 kpc, the value of is less than unity for A1835 (0.47 ± 0.31). Our result implies that the central dark matter profile of some clusters cannot be described by CDM halos.     

Two-dimensional convection in liquid layer related to crystal growth techniques in space

In this paper, the Marangoni convection including buoyancy convection in two-dimensional fluid model was investigated experimentally and theoretically. The transparent liquid in the test cell was heated and cooled under various conditions. The fluid flow driven by surface tension and by buoyancy force was visualized and measured. The flow patterns, velocity distributions and temperature field were obtained and they were compared with the results of the numerical solutions. The effect of the configuration and the convection in microgravity on crystal growth was discussed. The temperature field of the crystallizing surface was predicted.     

热毛细对流模式转换及温度振荡特征

研究了矩形液池中由于两端温差引起的热毛细对流的温度振荡临界条件.在实验室中,设计了一个高分辨率的温度测量系统,用于实时观测并记录流体的温度.该系统主要由热电偶温度传感器、纳伏表和数据采集电脑3部分组成.得到了各种实验条件下温度振荡的临界条件,并且讨论了它与Prandtl数和Bond数之间的关系.利用flow3d软件数值模拟了微重力条件下的热毛细对流,发现了一种由于自由面变形和液层流场相互作用导致的晃荡的现象.     

UV photobiochemistry of anhydrobiotic organisms at extremely low temperatures

Spores of Bacillus subtilis (TKJ 3412), cells of Deinococcus radiodurans R₁ (wild type) and conidia of Aspergillus ochraceus (strain 3174) have been UV irradiated (254 nm) in the dry state (3% relative humidity, argon) or in aqueous suspension at room temperature, at −55°C to −70°C and at −165°C to −170°C. The following effects have been analyzed: decrease in viability, occurrence of DNA strand breaks (pulsed-field gel electrophoresis) and production of DNA-protein cross-links (membrane filter method). The loss in viability is usually more pronounced at around −70°C than at room temperature, but it is lowest around −170°C. The kind of prevailing DNA damage varies from organism to organism. The amount of UV induced DNA-protein cross-link products steadily decreases with the temperature and is lowest at −170°C. The decrease in highly polymeric DNA by double strand breaks follows no universal pattern. The observed hypersensitivity of the three very different species at −70°C can therefore not be simply explained on the basis of the number of DNA lesions analyzed in the course of this work. We suggest that also the changing state of cellular water below and above about −130°C significantly contributes to the change in photosensitivity.     

Capillary brazing under microgravity (TEXUS-II) and 1g conditions

Experiments of vacuum brazing under both microgravity and 1-g conditions show the effect of hydrostatic pressure on ga-filling. The absence of buoyancy forces under microgravity affects the microstructure of the solidified braze in the joint.     

Study of the Marangoni convection around a surface tension minimum under microgravity conditions

At equilibrium, aqueous fatty alcohol solutions presents a surface tension minimum versus temperature. The influence of such an extremum on the Marangoni convection is studied. Two experiments have been performed under microgravity conditions (Texus 8 (1983) and Texus 9 (1984) flights). The velocity fields are determined by following the paths of tracer particles and furthermore, in the Texus 9 experiment, differential interferograms have been recorded.     

Auroral signatures of transient processes in the outer magnetosphere

We present an analysis of sporadic and recurrent injections of magnetospheric ions in the midnight auroral oval during substorms and of the associated ionospheric ion outflows. The source of plasma sheet precipitating ions is determined using a simple method, based on the measured relation between the ion inverse velocity and time (l = v × t). This method is applied here to two typical passes of the Interball-Auroral (IA) satellite at distances of 3 R_E above the auroral regions. Substorm related ion injections are shown to be mainly due to time of flight effects. In contrast with particle trajectory computations (Sauvaud et al., 1999), the inverse velocity method does not require magnetic and electric field models and can thus be used systematically for the detection of time of flight dispersed ion structures (TDIS). This allowed us to build a large database of TDIS events and to perform a statistical analysis of their spatial distribution. For the cases presented here the source region of the injected ions is found at radial distances from 18 to 30 R_E near the equatorial magnetosphere. At Interball altitudes ( 3 R_E), ion injections detected at the poleward boundary of the nighside auroral oval are associated with shear Alfvén waves superimposed over large-scale quasi-static current structures. We show that the most poleward TDIS are collocated with a large outflow of ionospheric H⁺ and O⁺ displaying pitch-angle distributions peaked in the pitch-angle range 90°–120°. These ions are thus accelerated perpendicularly to the magnetic field not only in the main auroral acceleration region but also up to at least 3 R_E. The expanding auroral bulge thus constitutes a significant source of H⁺ and O⁺ ions for the mid-tail magnetosphere.