Alteration of structure and mobility of erythrocyte aggregates under normal- to microgravity conditions

An experimental analysis of the aggregates structure and their mobility under normal- and micro-g conditions is carried out. Fresh well mixed erythrocyte suspensions in plasma at 8.0% hematocrit are placed in a glass chamber and on-line video microscopic recording of the aggregation process under microgravity condition is carried out. The analysis of aggregate structure and mobility are carried out by an IBM-PC/AT based image processing system. The results show that (a) under normal gravity conditions the velocity of the formed aggregates depend on their sizes which tend to grow further by interacting with single cells and small aggregates, (b) under microgravity conditions the mobility of the aggregates reduces to zero and an alteration in their structural parameters is observed.     

Numerical Simulation of Condensation of Bubbles under Microgravity Conditions by Moving Mesh Method in the Double-staggered Grid

A numerical 2D method for simulation of two-phase flows including phase change under microgravity conditions is presented in this paper, with a level set method being coupled with the moving mesh method in the double-staggered grid systems. When the grid lines bend very much in a curvilinear grid, great errors may be generated by using the collocated grid or the staggered grid. So the double-staggered grid was adopted in this paper. The level set method is used to track the liquid–vapor interface. The numerical analysis is fulfilled by solving the Navier–Stokes equations using the SIMPLER method, and the surface tension force is modeled by a continuum surface force approximation. A comparison of the numerical results obtained with different numerical strategies shows that the double-staggered grid moving-mesh method presented in this paper is more accurate than that used previously in the collocated grid system. Based on the method presented in this paper, the condensation of a single bubble in the cold water under different level of gravity is simulated. The results show that the condensation process under the normal gravity condition is different from the condensation process under microgravity conditions. The whole condensation time is much longer under the normal gravity than under the microgravity conditions.     

Photoperiod-controlling Guttation and Growth of Rice Seedlings Under Microgravity on Board Chinese Spacelab TG-2

Guttation has been shown to play a crucial role in controlling plant growth and development by involvement of the transport of water, but how does this water transport in plant from roots to leaves work against pull of gravity is still unknown. The aim of the present study was to evaluate the influence of microgravity on photoperiod-controlling guttation and growth of rice (Oryza sativa L.) seedlings on board the Chinese Spacelab TongGong-2(TG-2). The growth rate of rice seedlings was closely correlated with guttation under both the microgravity and the ground conditions, which was increased by microgravity under both a 16-h long-day (LD) and an 8-h short-day (SD) photoperiod conditions. In addition, guttation of the TG-2 grown rice under the LD condition was more significant in comparison with that under the SD condition. These results indicated that microgravity affected the photoperiod-controlling growth of rice seedlings could be related to the enhanced guttation in space.     

微重力场下金属材料制备的发展现状

近年来微重力下制备金属材料的研究越来越引起人们的重视。简述了形成微重力的几种实验方法，综述了微重力下制备金属材料的发展现状。     

Performance of droplet generator and droplet collector in liquid droplet radiator under microgravity

The Liquid Droplet Radiator (LDR) has an advantage over comparable conventional radiators in terms of the rejected heat power-weight ratio. Therefore, the LDR has attracted attention as an advanced radiator for high-power space systems that will be prerequisite for large space structures. The performance of the LDR under microgravity condition has been studied from the viewpoint of operational space use of the LDR in the future. In this study, the performances of a droplet generator and a droplet collector in the LDR are investigated using drop shafts in Japan: MGLAB and JAMIC. As a result, it is considered that (1) the droplet generator can produce uniform droplet streams in the droplet diameter range from 200 to 280 [μm] and the spacing range from 400 to 950 [μm] under microgravity condition, (2) the droplet collector with the incidence angle of 35 degrees can prevent a uniform droplet stream, in which droplet diameter is 250 [μm] and the velocity is 16 [m/s], from splashing under microgravity condition, whereas splashes may occur at the surface of the droplet collector in the event that a nonuniform droplet stream collides against it.     

Performance of droplet generator and droplet collector in liquid droplet radiator under microgravity

The Liquid Droplet Radiator (LDR) has an advantage over comparable conventional radiators in terms of the rejected heat power-weight ratio. Therefore, the LDR has attracted attention as an advanced radiator for high-power space systems that will be prerequisite for large space structures. The performance of the LDR under microgravity condition has been studied from the viewpoint of operational space use of the LDR in the future. In this study, the performances of a droplet generator and a droplet collector in the LDR are investigated using drop shafts in Japan: MGLAB and JAMIC. As a result, it is considered that (1) the droplet generator can produce uniform droplet streams in the droplet diameter range from 200 to 280 [μm] and the spacing range from 400 to 950 [μm] under microgravity condition, (2) the droplet collector with the incidence angle of 35 degrees can prevent a uniform droplet stream, in which droplet diameter is 250 [μm] and the velocity is 16 [m/s], from splashing under microgravity condition, whereas splashes may occur at the surface of the droplet collector in the event that a nonuniform droplet stream collides against it.     

Effect of Gravity on Arc Shape in GTA Welding-for Low Electric Arc Current

Gas tungsten arc (GTA) welding was performed both in a microgravity environment and in a terrestrial environment,and the arc shapes in both environments were compared. A microgravity condition was obtained using the free fallsystem at the Japan Microgravi     

Thermophysical property measurements on molten semiconductors using 10-s microgravity in a drop shaft

The effectiveness of 10-s microgravity on thermophysical property measurements on molten materials, such as molten semiconductors, is discussed. The thermal conductivity of molten InSb was successfully measured under microgravity conditions on board the German sounding rocket TEXUS and in a drop shaft in Hokkaido, Japan. Surface tension measurements using an oscillating drop method was attempted in low gravity using a parabolic flight of the NASA KC-135 aircraft. Combined levitation and microgravity, which can provide a contamination-free and undercooled condition. is recommended as a novel approach to obtain missing thermophysical property data on undercooled melts of semiconductors.Paper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29. 1995. Köln, Germany.     

Flowering in space

The reproductive success of plants is often dependent on their flowering time being adapted to the terrestrial environment, in which gravity remain constant. Whether plants can follow the same rule to determine their flowering time under microgravity in space is unknown. Although numerous attempts have been made to grow a plant through a complete life cycle in space, apparently no published information exists concerning the flowering control of plants under microgravity in space. Here, we focused on two aspects. Firstly the environmental and intrinsic factors under microgravity related to flowering control. Secondly, the plant-derived regulators are involved in flowering control under microgravity condition. The potential environmental and intrinsic factors affect plant flowering under microgravity may include light, biological circadian clock as well as long-distance signaling, while the plant-derived flowering regulators in response to microgravity could include gibberellic acid, ethylene, microRNA and sugar. The results we have obtained from the space experiments on board the Chinese recoverable satellites (the SJ-8 and the SJ-10) and the experiment on the Chinese space lab TG-2 are also introduced. We conclude by suggesting that long-term space experiments from successive generations and a systematic analysis of regulatory networks at the molecular level is needed to understand the mechanism of plant flowering control under microgravity conditions in space.     

Numerical Investigation on Turbulence and Bubbles Distribution in Bubbly Flow Under Normal Gravity and Microgravity Conditions

Two-phase flows of gas and liquid are increasingly paid much attention to space application due to excellent properties of heat and mass transfer, so it is very meaningful to develop studies on them in microgravity. In this paper, gas-phase distribution and turbulence characteristics of bubbly flow in normal gravity and microgravity were investigated in detail by using Euler–Lagrange two-way model. The liquid-phase velocity field was solved by using direct numerical simulations (DNS) in Euler frame of reference, and the bubble motion was tracked by using Newtonian motion equations that took into account interphase interaction forces including drag force, shear lift force, wall lift force, virtual mass force and inertia force, etc. in Lagrange frame of reference. The coupling between gas–liquid phases was made with regarding interphase forces as a momentum source term in the momentum equation of the liquid phase. Under the normal gravity condition, a great number of bubbles accumulate near the walls under the influence of the shear lift force, and addition of bubbles reduces turbulence of the liquid phase. Different from the normal gravity condition, in microgravity, an overwhelming majority of bubbles migrate towards the centre of the channel driven by the pressure gradient force, and bubbles have little effect on the turbulence of the liquid phase.     

Development of a unidirectional cooling technique for synthesizing compound semiconductors in 10 m drop tower

The solidification process and structures of CdTe solidified in microgravity were studied using the unidirectional cooling apparatus in a 10 m drop tower. Since the drop tower provides 1.4 seconds of microgravity, the unidirectional cooling apparatus cools samples rapidly by cooling gas. The system adopts a Pt heater, which accurately heats samples to a maximum of 1300°C. The sample is placed in an ampoule under vacuum conditions. A flat wall in the ampoule divides the inner sealed sample from the outer open side. A nozzle blowing cooling gas is directed on to the outer wall, and cools the sample until solidification. The cooling properties were measured during CdTe solidification in microgravity. The result shows that solidification occurred between 0.9 and 1.3 seconds after release, so solidification is completed in microgravity. Optical microscope (OM) observation of the sample solidified in microgravity revealed that it produces CdTe and Te phases with segregation patterns, and the structures are ordered along the cooling direction, whereas no order is observed in the structures of the terrestrial sample solidified under 1 g.     

Enhancing effects of simulated microgravity on Agrobacterium-infected frequency of tobacco callus

Under the condition of rotation-induced gravity compensation, the time course of interaction between Agrobacteriun tumefaciens and tobacco callus was investigated by means of a scanning electronic microscope. Resulted from repeated experiments, it was found that callus induced from tobacco leaves under simulated microgravity was easier to be infected by A. tumefaciens than controls. Analyses with a scanning electronic microscope indicated that A. tumefaciens were instantly detected on the surface of cell in the first 5 min, that is, A. tumefaciens are liable to interrecognize with callus cell upon contact with each other. With the proceeding of co-culture, the infection efficiency of A. tumefaciens was correspondingly increased. When the time reached 6 h, the fiber was formed between A. tumefaciens and callus cell. In our experiment, the erecting rotating state was taken as the control to exclude the interference of rotating. In this case, A. tumefaciens did not adsorb on calli until 3 h of co-culture, and fiber was only observed as late as 16 h. Statistic data showed that A. tumefaciens-infected frequency of the callus under the action of microgravity was elevated to 176% over that of control.     

Germination of Arabidopsis Seed in Space and in Simulated Microgravity: Alterations in Root Cell Growth and Proliferation

Changes have been reported in the pattern of gene expression in Arabidopsis on exposure to microgravity. Plant cell growth and proliferation are functions that are potentially affected by such changes in gene expression. In the present investigation, the cell proliferation rate, the regulation of cell cycle progression and the rate of ribosome biogenesis (this latter taken to estimate cell growth) have been studied using morphometric markers or parameters evaluated by light and electron microscopy in real microgravity on the International Space Station (ISS) and in ground-based simulated microgravity, using the Random Positioning Machine and the Magnetic Levitation Instrument. Results showed enhanced cell proliferation but depleted cell growth in both real and simulated microgravity, indicating that the two processes are uncoupled, unlike the situation under normal gravity on Earth in which they are strictly co-ordinated events. It is concluded that microgravity is an important stress condition for plant cells compared to normal ground gravity conditions.     

Biochemical and molecular biological analyses of space-flown nematodes in Japan, the first international caenorhabditis elegans experiment (ICE-First)

The first International Caenorhabditis elegans Experiment (ICE-First) was carried out using a Russian Soyuz spacecraft from April 19–30, 2004. This experiment was apart of the program of the DELTA (Dutch Expedition for Life science Technology and Atmospheric research) mission, and the space agencies that participate in the International Space Station (ISS) program formed international research teams. A Japanese research team that conducted by Japan aerospace Exploration Agency (JAXA) investigated the following aspects of the organism: (1) whether meiotic chromosomal dynamics and apoptosis in the germ cells were normal under microgravity conditions, (2) the effect of the space flight on muscle cell development, and (3) the effect of the space flight on protein aggregation. In this article, we summarize the results of these biochemical and molecular biological analyses.     

Study on Prefire Phenomena of Wire Insulation at Microgravity

The experimental hardware was developed to perform the experiments of prefire characteristics of wire insulation caused by overload on board the SJ-8 China recoverable satellite. In the experiments, the prefire characteristics including the temperature and radiation characteristics of the wire insulations were presented. The temperature histories of the wire insulation in microgravity and the low-pressure environment in normal gravity were obtained. Effects of overloaded currents on the fire initiation were investigated for different wire coiled states. The results indicate that the natural convection almost vanished and the heat loss of the electric components decreased in the microgravity environment. It might cause overheating of the electric components and then results in fire, and thus the fire risks of wire in the microgravity condition are much more dangerous than that in normal gravity under the condition of overload.     

Development of a 3He Refrigerator for Possible Experiments of Solid 4He on a Small Jet Plane

The gravity on the Earth (g _E) has not been taken seriously to mask the fundamental phenomena on quantum solids, though there are some important studies on the critical phenomena of superfluid ⁴He under microgravity. We are planning to investigate the effect of gravity on the equilibrium shape of solid ⁴He. Since we had a chance to do such an experiment on a small jet plane through the ground based program by JAXA, we got started to construct a cryostat which could cool down as low as 500?mK and meet severe restrictions of experiments on a jet plane. The main part of the refrigerator was a usual ³He-evaporator pumped by a scroll pump. A?small GM refrigerator was installed to provide 4?K stage. 1?K pot was also put in which was also pumped by another scroll pump to condense ³He gas and sample ⁴He. The cryostat was designed to have two optical windows to be able to observe solid ⁴He under microgravity. In the test flight for the refrigerator, the minimum temperature of 690?mK was kept during the entire flight of two hours in which 7 to 8 times parabolic flight was performed. Each parabolic flight includes about 20?seconds microgravity and 20?seconds 1.5 to 2.0?g _E period before and after the microgravity. We did some preliminary experiments with bcc solid ⁴He under microgravity. The crystal remained stuck to the bottom of the sample cell even in the 20 seconds microgravity condition.     

Development of a small He II cryostat with optical windows for a microgravity experiment

In order to study film-boiling phenomena in saturated superfluid helium (He IIs) under a microgravity environment, a very compact visualization setup was designed and fabricated at High Energy Accelerator Research Organization (KEK). It consists of a cryostat, a vacuum pump, a high-speed video camera and electrical circuits for measurement. The cryostat in the setup is equipped with optical windows for the visualization of film boiling in He IIs. The setup was tested to verify its thermal and safety performance under a microgravity environment using a 10 m free-drop tower at the Hokkaido Center of the National Institute of Advanced Industrial Science and Technology (AIST). Successful system operation from 1.94 to 2.05 K under microgravity conditions below 1 × 10⁻³ g was confirmed. The design and test results are described in this technical note.     

The 2.5 s Microgravity Drop Tower at National Centre for Combustion Research and Development (NCCRD), Indian Institute of Technology Madras

Space missions involving humans require a better understanding of various phenomena happening in space environments. A number of experiments need to be conducted in microgravity for addressing various issues encompassing safety (primarily fire) and better understanding of fluid and material behaviour. Of the various methods used for obtaining microgravity conditions, drop towers offer ground based microgravity platform. They provide a cost effective platform for doing short duration, repeatable, high quality microgravity experiments. This paper describes key factors that influence the design of a drop tower. The salient features of 2.5 s microgravity tower set up at National Centre for Combustion Research and Development (NCCRD), IIT Madras (IITM) are discussed. Primary features of the three critical elements, namely the drop capsule, the release unit and the decelerator unit are described along with review of these elements in existing drop towers. The IITM drop tower operates in ambient atmospheric conditions to minimise the cost of operation. In order to achieve good quality microgravity levels, a dual capsule configuration is adopted. The shape of the outer capsule is arrived at by detailed transient computational fluid dynamic analysis of the drag shield under free fall condition over the drop height. A pneumatic mechanism is used for capsule release and brought to rest at the end of fall in a carefully designed decelerator unit. The decelerator unit consists of an airbag with controlled air outflow for smooth deceleration.     

Finite Element Analysis of Osteocytes Mechanosensitivity Under Simulated Microgravity

It was found that the mechanosensitivity of osteocytes could be altered under simulated microgravity. However, how the mechanical stimuli as the biomechanical origins cause the bioresponse in osteocytes under microgravity is unclear yet. Computational studies may help us to explore the mechanical deformation changes of osteocytes under microgravity. Here in this paper, we intend to use the computational simulation to investigate the mechanical behavior of osteocytes under simulated microgravity. In order to obtain the shape information of osteocytes, the biological experiment was conducted under simulated microgravity prior to the numerical simulation The cells were rotated by a clinostat for 6 hours or 5 days and fixed, the cytoskeleton and the nucleus were immunofluorescence stained and scanned, and the cell shape and the fluorescent intensity were measured from fluorescent images to get the dimension information of osteocytes The 3D finite element (FE) cell models were then established based on the scanned image stacks. Several components such as the actin cortex, the cytoplasm, the nucleus, the cytoskeleton of F-actin and microtubules were considered in the model. The cell models in both 6 hours and 5 days groups were then imposed by three magnitudes (0.5, 10 and 15 Pa) of simulating fluid shear stress, with cell total displacement and the internal discrete components deformation calculated. The results showed that under the simulated microgravity: (1) the nuclear area and height statistically significantly increased, which made the ratio of membrane-cortex height to nucleus height statistically significantly decreased; (2) the fluid shear stress-induced maximum displacements and average displacements in the whole cell decreased, with the deformation decreasing amplitude was largest when exposed to 1.5Pa of fluid shear stress; (3) the fluid shear stress-induced deformation of cell membrane-cortex and cytoskeleton decreased, while the fluid shear stress-induced deformation of nucleus increased. The results suggested the mechanical behavior of whole osteocyte cell body was suppressed by simulated microgravity, and this decrement was enlarged with either the increasing amplitude of fluid shear stress or the duration of simulated microgravity. What’s more, the mechanical behavior of membrane-cortex and cytoskeleton was suppressed by the simulated microgravity, which indicated the mechanotransduction process in the cell body may be further inhibited. On the contrary, the cell nucleus deformation increased under simulated microgravity, which may be related to either the decreased amount of cytoskeleton or the increased volume occupied proportion of nucleus in whole cell under the simulated microgravity. The numerical results supported our previous biological experiments, and showed particularly affected cellular components under the simulated microgravity. The computational study here may help us to better understand the mechanism of mechanosensitivity changes in osteocytes under simulated microgravity, and further to explore the mechanism of the bone loss in space flight.     

Two-phase Flow in Fuel Cells in Short-term Microgravity Condition

A visual observation of liquid–gas two-phase flow in anode channels of a direct methanol proton exchange membrane fuel cells in microgravity has been carried out in a drop tower. The anode flow bed consisted of 2 manifolds and 11 parallel straight channels. The length, width and depth of single channel with rectangular cross section was 48.0 mm, 2.5 mm and 2.0 mm, respectively. The experimental results indicated that the size of bubbles in microgravity condition is bigger than that in normal gravity. The longer the time, the bigger the bubbles. The velocity of bubbles rising is slower than that in normal gravity because buoyancy lift is very weak in microgravity. The flow pattern in anode channels could change from bubbly flow in normal gravity to slug flow in microgravity. The gas slugs blocked supply of reactants from channels to anode catalyst layer through gas diffusion layer. When the weakened mass transfer causes concentration polarization, the output performance of fuel cells declines.