Effect of convective disturbances induced by g-jitter on the periodic precipitation of lysozyme

Numerical simulations are carried out to investigate the crystallization process of a protein macromolecular substance under two different conditions: pure diffusive regime and microgravity conditions present on space laboratories. The configuration under investigation consists of a protein reactor and a salt chamber separated by an “interface”. The interface is strictly related to the presence of agarose gel in one of the two chambers. Sedimentation and convection under normal gravity conditions are prevented by the use of gel in the protein chamber (pure diffusive regime). Under microgravity conditions periodic time-dependent accelerations (g-jitter) are taken into account. Novel mathematical models are introduced to simulate the complex phenomena related to protein nucleation and further precipitation (or resolution) according to the concentration distribution and in particular to simulate the motion of the crystals due to g-jitter in the microgravity environment. The numerical results show that gellified lysozyme (crystals “locked” on the matrix of agarose gel) precipitates to produce “spaced deposits”. The crystal formation results modulated in time and in space (Liesegang patterns), due to the non-linear interplay among transport, crystal nucleation and growth. The propagation of the nucleation front is characterized by a wavelike behaviour. In microgravity conditions (without gel), g-jitter effects act modifying the phenomena with respect to the on ground gellified configuration. The role played by the direction of the applied sinusoidal acceleration with respect to the imposed concentration gradient (parallel or perpendicular) is investigated. It has a strong influence on the dynamic behaviour of the depletion zones and on the spatial distribution of the crystals. Accordingly the possibility to obtain better crystals for diffraction analyses is discussed.     

Compact laser light-scattering instrument for microgravity research

NASA has developed a compact laser light-scattering instrument that employs both static and dynamic light-scattering techniques for microgravity research. The first use of this instrument was to study the behavior of colloidal hard spheres in a reduced gravity environment during the Second United States Microgravity Laboratory space shuttle mission. We discuss the instrument design and possible improvements based on our observations of significant differences between hard-sphere behavior in Earth's gravity and microgravity.     

The effect of gravity on freely growing crystals

The effect of surface tensions and gravity on freely growing crystals has been formulated in simple mathematical expressions. This gives an opportunity to predict the shape of a crystal, freely grown in space under microgravity as well as in a gravity field. Limitations for crystal growth in a gravity field are also given.     

Convective Boiling Between 2D Plates: Microgravity Influence on Bubble Growth and Detachment

The experiment detailed in this paper presents results obtained on the nucleation, growth and detachment of HFE-7100 confined vapour bubbles. Bubbles are created on an artificial nucleation site between two-dimensional plates under terrestrial and microgravity conditions. The experiments are performed by varying the shear flow by changing the convective mass flow rate, and varying the bubble nucleation rate by changing the heat flux supplied. The experiments are performed under normal (1 g) and reduced gravity (μg). The distance between the plates is equal to 1 mm. The results of these experiments are related to the detachment diameters of bubbles on the single artificial nucleation site and to the associated effects on the heat transfer by the confinement influence. The experimental device allows the observation of the flow using both visible video camera and infrared video camera. Here, we present the results obtained concerning the influence of gravity on the bubble detachment diameter and the images of 2D bubbles obtained in microgravity by means of an infrared camera. The following parameters: nucleation site surface temperature, bubble detachment diameter and bubble nucleation frequency evidence modifications due to microgravity.     

Protein crystallization in space

The microgravity environment of space is an ideal place to study the complicated protein crystallization process and to grow good-quality protein crystals. A series of crystal growth experiments of 10 different proteins was carried out in space on a Chinese re-entry satellite FSW-2 in August, 1992. The experiments were performed for about two weeks at a temperature of 18.5 +/- 0.5 degrees C using a tube-like crystallization apparatus made in the Shanghai Institute of Technical Physics, Academia Sinica. More than half of 48 samples from 6 proteins produced crystals, and the effects of microgravity on protein crystal growth were observed, especially for hen-egg white lysozyme and an acidic phospholipase A2 from the venom of Agkistrodon halys Pallas. Analyses of the crystallization of these two enzymes in this mission showed that the microgravity environment in space may be beneficial to improve size, external perfection, morphology, internal order, and nucleation of protein crystals. Some of these positive microgravity effects were also demonstrated by the growth of protein crystals in gelled solution with the above two enzymes. A structural analysis of the tetragonal lysozyme crystal grown in space is in progress.     

Nucleation in Metallic Melt on the Ground and under Elevated Gravity

The expressions for nucleation rate in metallic melt on the ground and under elevated gravity have been derived theoretically and the effects of gravity and elevated gravity on nucleation rate have been discussed. A comparison of nucleation rate under microgravity with those on the ground and under elevated gravity has also been made     

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。     

A Review on InGaSb Growth under Microgravity and Terrestrial Conditions Towards Future Crystal Growth Project Using Chinese Recovery Satellite SJ-10

The paper reviewed the previous microgravity experiment using Chinese recovery satellite, the in-situ measurement of composition profile in the solution by X-ray penetration method and homogeneous growth of InGaSb by temperature freezing method under terrestrial condition for making clear the effect of gravity on the growth of InGaSb ternary alloy semiconductor crystals. The previous experimental results showed that the shape of solid/liquid interfaces and composition profile in the solution were significantly affected by gravity. Based on the previous microgravity experimental results, experimental conditions were investigated to grow homogeneous In _xGa _1?xSb with higher indium composition at Chinese recovery satellite SJ-10 in near future.     

Vapour phase crystal growth under microgravity environment

Vapour phase crystal growth experiments performed in the Skylab and ASTP missions are reviewed. The basic vapour phase crystal growth technique is described and effect of gravity is discussed. The multipurpose furnace specially designed to carry out various experiments in flight conditions is described. Ge Se, Ge Te and GeS as well as ternary GeSe_0·99 Te_0·01 and GeS_0·98 Se_0·02 crystals have been grown in space showing improvement over similarly grown crystals on ground as determined by x-ray diffraction, chomical homogeneity and surface morphology studies. Mass flux rates under microgravity conditions have been found to be up to 10 times larger than expected indicating need for better theoretical and experimental understanding of the effect of gravity on crystal growth.     

A New Paradigm of Crystallization Arising from Non-standard Nucleation Pathways

There is increasing evidence that large classes of colloid materials crystallize via a non-standard nucleation mechanism involving intermediate metastable phases. In this paper recent work on the microscopic derivation of the phase diagram and free energy barriers in the nucleation of protein crystals, and on the kinetics of growth of solid particles in the post-nucleation regime is reviewed. The extent to which combined structural and density fluctuation give rise to favourable crystallization pathways involving an intermediate fluid phase is assessed and the connection with experiments in microgravity at ISS (PROMISS-2 and NANOSLAB-2) is discussed.     

Effects of Gravity on Soot Formation in a Coflow Laminar Methane/Air Diffusion Flame

Simulations of a laminar coflow methane/air diffusion flame at atmospheric pressure are conducted to gain better understanding of the effects of gravity on soot formation by using detailed gas-phase chemistry, complex thermal and transport properties coupled with a semiempirical two-equation soot model and a nongray radiation model. Soot oxidation by O₂, OH and O was considered. Thermal radiation was calculated using the discrete ordinate method coupled with a statistical narrow-band correlated-K model. The spectral absorption coefficient of soot was obtained by Rayleigh’s theory for small particles. The results show that the peak temperature decreases with the decrease of the gravity level. The peak soot volume fraction in microgravity is about twice of that in normal gravity under the present conditions. The numerical results agree very well with available experimental results. The predicted results also show that gravity affects the location and intensity for soot nucleation and surface growth.     

The Protein Crystallisation Diagnostics Facility (PCDF) on Board ESA Columbus Laboratory

Crystals of proteins or macromolecules are at the basis of X-ray crystallography to reveal structural information necessary for the understanding of their likely mode of action. However, the structural resolution is strongly dependent on the crystalline quality, which is known to be related to gravity dependent processes. The facilities and instruments used so far to grow crystals in space have mostly focused on the growing of crystals for detailed post-flight analysis on ground, and less on the understanding of phenomena associated to the crystallisation processes. The Protein Crystallisation Diagnostics Facility (PCDF), developed by Astrium under contract of the European Space Agency (ESA), allows to study with several diagnostics means in situ the crystallisation of macromolecules over long periods in microgravity. In addition, several ground models with PCDF similar capabilities were developed to allow scientists to prepare their experiments. The PCDF is installed in the European Drawer Rack (EDR), on board ESA’s Columbus Laboratory module launched in February 2008 to the International Space Station (ISS) for research in microgravity on protein nucleation and assembling sequences. The PCDF configuration for this first mission accommodates four reactors, using the batch crystallization technique. Individual process control for temperature and concentration will allow several crystallizations of solutions to be performed. Each reactor will be observed by several optical diagnostics, including video microscopy, dynamic light scattering, and Mach–Zehnder interferometry. This paper presents the overall PCDF design and details the different diagnostics allowing the scientific community to use the PCDF in orbit for microgravity research on molecule assemblies grown from solutions.     

重力对聚合物形成的影响

在聚合物合成过程和聚合物凝固过程中,聚合物分子量和聚合物颗粒尺寸的大小,分布和聚合物聚集态结构强烈依赖于重力,文中分增重力,减重力和微重力３部分了近年来重力对聚合物形成影响研究概况,重点介绍了微重力下聚合物的一些研究成果,并指出今后的发展方向。     

Evaluation of Simulated Microgravity Environments Induced by Diamagnetic Levitation of Plant Cell Suspension Cultures

Ground-Based Facilities (GBF) are essetial tools to understand the physical and biological effects of the absence of gravity and they are necessary to prepare and complement space experiments. It has been shown previously that a real microgravity environment induces the dissociation of cell proliferation from cell growth in seedling root meristems, which are limited populations of proliferating cells. Plant cell cultures are large and homogeneous populations of proliferating cells, so that they are a convenient model to study the effects of altered gravity on cellular mechanisms regulating cell proliferation and associated cell growth. Cell suspension cultures of the Arabidopsis thaliana cell line MM2d were exposed to four altered gravity and magnetic field environments in a magnetic levitation facility for 3 hours, including two simulated microgravity and Mars-like gravity levels obtained with different magnetic field intensities. Samples were processed either by quick freezing, to be used in flow cytometry for cell cycle studies, or by chemical fixation for microscopy techniques to measure parameters of the nucleolus. Although the trend of the results was the same as those obtained in real microgravity on meristems (increased cell proliferation and decreased cell growth), we provide a technical discussion in the context of validation of proper conditions to achieve true cell levitation inside a levitating droplet. We conclude that the use of magnetic levitation as a simulated microgravity GBF for cell suspension cultures is not recommended.     

Particle accumulation structures in time-dependent thermocapillary flow in a liquid bridge under microgravity

The formation of a dynamic spiral string of particles with larger density than the fluid was investigated for time-dependent thermocapillary flow in liquid bridges under various gravity conditions including microgravity. The dynamic spiral string forms after approximately 20–60 oscillation periods from the homogeneous dilute particle suspension. It was found that the action of gravity is not decisive in the process of the particle accumulation structure (PAS) but gravity influences the flow field for PAS-formation. We could realize and observe PAS with modal structure m=3 under μ-g but modal structure m=2 occurred only during a transient of the operating parameters in an aspect ratio-range different from that under normal gravity. The correlation of the optically observed PAS structure with the temperature structure of the azimuthally rotating hydrothermal wave on the free surface is the same under microgravity as under normal gravity indicating that PAS is a pure Marangoni effect.     

The influence of film structure on the interfacial friction in annular two-phase flow under microgravity and normal gravity conditions

Results for the interfacial friction factor and relative interfacial roughness on the gas-liquid interface are reported for an air-water annular flow in a small inner diameter tube (9.53 mm i.d.). The film structure was obtained through processing the time trace signal of film thickness measurements using conductance probes. The interfacial friction factor and the wave height were altered through changing the gravity level and gas Reynolds number. It was found that the wave height decreased with increasing the gas Reynolds number. The wave height in microgravity is less than half of that in normal gravity, while the friction factor was about 10% smaller in microgravity than that in normal gravity. It was shown that the annular two-phase flow friction factor decreased less dramatically as the relative interfacial roughness decreased compared to the single-phase case. It is interesting to note that the interfacial shear stress values at microgravity were very close (or even larger than) those at normal gravity. This was attributed to the thicker substrate at microgravity.     

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.     

The effects of gravity on the features of the interfacial waves in annular two-phase flow

A physical model of interfacial waves in annular two-phase flow was studied in both microgravity and normal gravity. The wave structure was obtained for local film thickness and velocity measurements using a conductance probe technique. It was found that the wave height, and not its width, is strongly affected by changing the gravity level. In fact, the wave height in normal gravity is more than twice that in microgravity. Using an analogous approach to a turbulent, single-phase flow in a rough tube, a preliminary mathematical model was proposed to calculate the wave amplitude. The model fits well with the experimental data and shows that the wave height in normal gravity is approximately 1.7 times the combined thickness of the viscous sublayer and transition zones in the turbulent gas stream. The wave height in microgravity was estimated to be approximately 80% of the total thickness.     

Effect of magnetic field on metallurgical structure of magnetostrictive alloys solidified unidirectionally in microgravity

TbFe₂ alloy solidification experiments were conducted in a static magnetic field in microgravity using a 10 m drop tower. When TbFe₂ melt was solidified in a magnetic field from 0 to 0.12T in microgravity, a [111] crystallographic alignment dominated with an increased magnetic field, but the planar macrostructure was random. The magnetostrictive constant of TbFe₂ solidified in magnetic field of 0.12T in microgravity was 2000 ppm at the external 1. 6T magnetic field. When TbFe₂ melt was solidified unidirectionally in a 0. 1 T magnetic field in microgravity, a [111] crystallographic alignment dominated, and the planar structure grew and oriented along the solidification direction. The magnetostrictive constant of TbFe₂ solidified unidirectionally in a 0. 1 T magnetic field in microgravity was 4500 ppm at the external 1. 6T static magnetic field. For all solidification in normal gravity, the maximum magnetostrictive constant remained at 2000 ppm at the external 1. 6T static magnetic field. TbFe₂ crystals grew predominantly along the same direction as the magnetic field, and the planar structure oriented along the solidification direction in microgravity.     

Effect of microgravity on crystallization in heavy metal fluoride glasses processed on the CSAR-I sounding rocket

Gravity-driven density segregation in viscous glass is believed to trigger homogeneous nucleation during the high-temperature processing of heavy metal fluoride (HMF) glasses. Processing of HMF glasses in microgravity could, therefore, minimize commonly observed micro-crystal formation in these glasses during their heat treatment for fibre drawing. Although, preliminary experiments on parabolic flight aircraft had earlier indicated that gravity enhances and microgravity suppresses crystallization during the processing of HMF glasses, these results were considered inconclusive due to the short processing time of 20 seconds. The CSAR-I sounding rocket provided an opportunity to process HMF glasses over a longer duration of five minutes in microgravity. These experiments indicated that microgravity helps in reducing crystallization in HMF glasses during their heat treatment at 325°C, which is very close to their fibre drawing temperature range of 300–320°C.