Effects of a Rotating Magnetic Field on Gas Transport during Detached Crystal Growth in Space

During the detached Bridgman growth of semiconductor crystals, the melt has a short free surface, which is detached from the ampul wall near the crystal–melt interface, thus eliminating the crystal defects caused by contact with the ampul wall. Recent modeling has indicated that initiation and continuation of detached growth depends on the rate of transport of dissolved gas from the crystal–melt interface, where gas is rejected into the melt, to the detached free surface, where evaporating gas maintains the pressure on the free surface. Here we use numerical modeling to investigate whether the application of a rotating magnetic field increases or decreases the transport of rejected gas to the detached free surface. Unfortunately, the results show that a rotating magnetic field almost always decreases the evaporation rate at the detached free surface. The exception is an insignificant increase for a short period at the beginning of crystal growth for a few circumstances. The evaporation rate decreases as the strength of the rotating magnetic field is increased.     

Enhancement of recombinant β‐D‐glucuronidase production under low‐shear modeled microgravity in Pichia pastoris

BACKGROUND: The effects of low‐shear modeled microgravity (LSMMG) on the production of recombinant proteins in a eukaryotic expression host have been investigated. The gene (GenBank Accession No.EU095019) derived from Penicillium purpurogenum Stoll (CGMCC 3. 3708) encoding β‐D ‐glucuronidase (EC 3.2.1.31, PGUS) was expressed in Pichia pastoris GS115. The behavior of P. pastoris growth and recombinant PGUS production during the methanol induction stage were examined in a high‐aspect ratio vessel (HARV) that could model the microgravity environment. RESULTS: The recombinant P. pastoris showed better growth under LSMMG than normal gravity (NG) during the methanol induction phase. It was also found that the efficiencies of PGUS production were enhanced 1.51 to 2.21‐fold under LSMMG compared with NG control at four different rotary speeds (P < 0.05), and 15 rpm was found to be the optimal for PGUS expression. Furthermore, the efficiency of PGUS secretion was also enhanced under LSMMG (all values above 30%). CONCLUSIONS: The LSMMG environment significantly enhances production and secretion of the recombinant PGUS expressed in P. pastoris GS115. Results suggest that simulated microgravity techniques could be used for the efficient production of recombinant proteins by microbial hosts. Copyright © 2010 Society of Chemical Industry     

Scalable Microgravity Simulator Used for Long-Term Musculoskeletal Cells and Tissue Engineering

We introduce a new benchtop microgravity simulator (MGS) that is scalable and easy to use. Its working principle is similar to that of random positioning machines (RPM), commonly used in research laboratories and regarded as one of the gold standards for simulating microgravity. The improvement of the MGS concerns mainly the algorithms controlling the movements of the samples and the design that, for the first time, guarantees equal treatment of all the culture flasks undergoing simulated microgravity. Qualification and validation tests of the new device were conducted with human bone marrow stem cells (bMSC) and mouse skeletal muscle myoblasts (C2C12). bMSC were cultured for 4 days on the MGS and the RPM in parallel. In the presence of osteogenic medium, an overexpression of osteogenic markers was detected in the samples from both devices. Similarly, C2C12 cells were maintained for 4 days on the MGS and the rotating wall vessel (RWV) device, another widely used microgravity simulator. Significant downregulation of myogenesis markers was observed in gravitationally unloaded cells. Therefore, similar results can be obtained regardless of the used simulated microgravity devices, namely MGS, RPM, or RWV. The newly developed MGS device thus offers easy and reliable long-term cell culture possibilities under simulated microgravity conditions. Currently, upgrades are in progress to allow real-time monitoring of the culture media and liquids exchange while running. This is of particular interest for long-term cultivation, needed for tissue engineering applications. Tissue grown under real or simulated microgravity has specific features, such as growth in three-dimensions (3D). Growth in weightlessness conditions fosters mechanical, structural, and chemical interactions between cells and the extracellular matrix in any direction.     

Numerical study on onset of oscillatory thermocapillary flow in rectangular liquid pool

Thermocapillary flow in a rectangular liquid pool of large Prandtl fluid(Pr=105.6) is numerically studied in microgravity.Oscillatory thermocapillary flow arises when the imposed temperature difference between the sidewalls exceeds a critical value.The fluctuations of the oscillatory flow,accompanied by the propagation of the hydrothermal wave from the cold sidewall to the hot one,are much smaller than the time-averaged velocity and temperature fields.The corresponding disturbance cells arise in the centre ...     

Effects of low-shear modeled microgravity on a microbial community filtered through a 0.2-μm filter and its potential application in screening for novel microorganisms

The effects of low-shear modeled microgravity (LSMMG) on a microbial community filtered through a 0.2-μm filter were investigated, and the potential application of LSMMG in the screening of microorganisms was evaluated. Pond water was passed through a 0.2-μm filter and the filtrate inoculated into two kinds of media (Schneider's insect medium, and ten-times-diluted Schneider's insect [0.1-Sch] medium). The cultures were incubated under LSMMG and normal-gravity and the microbial cell growth rates compared. Cell growth rates, final cell concentrations, and substrate consumption rates were higher in the LSMMG culture than in the normal-gravity culture. The microbial communities obtained under the various culture conditions were subjected to denaturing gradient gel electrophoresis (DGGE), revealing three different groups of microorganisms: (i) microorganisms whose growth rates were increased by LSMMG; (ii) microorganisms whose growth rates were suppressed or inhibited by LSMMG; and (iii) microorganisms whose growth rates were not affected by LSMMG. Sequence analysis of the microorganisms whose growth rates were increased by LSMMG showed that some had high similarity with unculturable microorganisms. When these microorganisms that displayed similarity with unculturable microorganisms were cultivated on agar plates, some of the DGGE bands present in the LSMMG culture were also present. We show that it is possible to isolate and cultivate uncultured microorganisms by using combinations of LSMMG, normal-gravity, and agar plate culturing techniques.     

Orbital spaceflight during pregnancy shapes function of mammalian vestibular system.

Pregnant rats were flown on the NASA Space Shuttle during the early developmental period of their fetuses' vestibular apparatus and onset of vestibular function. The authors report that prenatal spaceflight exposure shapes vestibular-mediated behavior and central morphology. Postflight testing revealed (a) delayed onset of body righting responses, (b) cardiac deceleration (bradycardia) to 70° head-up roll, (c) decreased branching of gravistatic afferent axons, but (d) no change in branching of angular acceleration receptor projections with comparable synaptogenesis of the medial vestibular nucleus in flight relative to control fetuses. Kinematic analyses of the dams' on-orbit behavior suggest that, although the fetal otolith organs are unloaded in microgravity, the fetus' semicircular canals receive high levels of stimulation during longitudinal rotations of the mother's weightless body. Behaviorally derived stimulation from maternal movements may be a significant factor in studies of vestibular sensory development. Taken together, these studies provide evidence that gravity and angular acceleration shape prenatal organization and function within the mammalian vestibular system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of constrained growth on defect structures in microgravity grown CdZnTe boules

In a microgravity environment obtainable in an orbiting space shuttle, it is possible to virtually eliminate gravity related effects such as buoyancy driven convection and hydrostatic forces thus providing an ideal environment for diffusion-controlled, containerless crystal growth processes. Under such conditions, it is possible to investigate the effects of gravity independent growth parameters on crystal growth. Studies of CdZnTe boules grown on space shuttle mission USML-1 revealed that regions of the boules grown with wall contact were associated with a higher defect density than regions grown with partial or no wall contact. Defect densities in certain regions grown without wall contact were as low as 5 × 10²/cm² to 1.2 × 10³/cm². More detailed studies on the effects of wall contact were sought in the USML-2 mission. Two CdZnTe boules (GCRC-1 and GCRC-2) were grown by the seeded Bridgman-Stockbarger method. Boule GCRC-1 was grown under constrained conditions to force full wall contact while boule GCRC-2 had a tapered geometry designed to minimize wall contact. Defect distributions in the boules were investigated by synchrotron white beam x-ray topography. The sample GCRC-1 was characterized by the presence of large inhomogeneous strains, numerous grains and twins, all of which are caused by effects related to wall contact. On the other hand, a part of the boule GCRC-2 that grew free from wall contact revealed minimum surface strains, the absence of twins and a very high structural uniformity. Results clearly verify that ampoule wall contact plays an important role in determining the incidence of crystal imperfections.     

微重力流动沸腾气泡脱离机制

为了研究微重力条件下的流动沸腾换热过程气泡脱离的特点,研究了气泡在脱离过程中的受力情况,推导并给出了气泡在切向方向和垂直方向上的粘滞力、浮力、附加压力、惯性力的表达式,并在此基础上提出了气泡从加热表面脱离特性的分析模型。研究结果表明,在微重力下气泡的长大时间明显比常重力下大,对应的气泡脱离直径比常重力下也大。随着工质流速的增加,气泡的脱离直径逐步变小,当工质流速达到一定值后,常重力和微重力下气泡的脱离半径差别可以忽略不计。     

微重力蜡烛火焰特征数值模拟

建立了微重力蜡烛火焰的数学模型。计算与分析表明，火焰的形状由空气动力学特征决定，火焰的温度取决于化学反应动力学特征和火焰的热损失。在静止微重力环境中，自然对流的消失使火焰为半球形。辐射热损失对蜡烛火焰温度（颜色）特征的形成有重要贡献，在静止微重力环境下，化学反应放热速率受氧气扩散速率控制，辐射热损失的冷却使火焰温度低于正常重力温度值。但当环境气体的流动速度加大时，辐射热损失的影响逐渐减小，蜡烛火焰的温度逐渐接近正常重力蜡烛火焰的温度。当氧浓度较小时，火焰峰值温度小于烟黑形成的阈值温度（1300k）；当氧浓度较大时，火焰温度大于黑烟形成的阈值温度。     

Space Tourism: Waiting for Ignition

Space tourism is in its infancy, having been launched a little over a decade ago by billionaire businessman Dennis Tito's venture into Space. Ondřej Doule , Assistant Professor of Human-Centered Design and Aerospace Engineering at the Florida Institute of Technology, and Chair of the Space Architecture Technical Committee at the AIAA, considers the shift that will have to be made in designing Space Architecture as space shuttles and stations transition from being ostensibly high-security labs into floating hotels.