Gas bubble growth and detachment under reduced gravity

Helium bubble growth and detachment are considered in liquid oxygen subject tc variations in acceleration and hole diameter.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 58, No. 2, pp. 190–196, February, 1990.     

A magnet system design for reduced gravity environment

Simulating a reduced gravity environment experienced in spaceships in a laboratory setting for studying different technical aspects (fluid transfer or propellant behavior, for example) is a primordial step prior to extraterrestrial explorations. We first present some results on boiling heat transfer in helium under reduced gravity using a commercial magnet and point out the limitations in volume and magnetic force homogeneity to perform reduced gravity experiments with such a non ad hoc magnet. Then, we present a new magnetic design to create a reduced gravity environment in large volume suitable for boiling test experiments in oxygen. Based on a modified design we present the magnetic configurations that allow compensating gravity for different elements such as hydrogen, water or helium but in smaller volumes. We detail the different aspects of winding techniques to achieve the requirements on magnetic force.     

A macroscopic solids-stabilized emulsion droplet model in reduced gravity

The presence of solid nano-scale particles affects the stability of emulsions but it is difficult to make direct observations of these particles because of their dimensions. By reducing the gravitational force exerted on the droplets and particles, it is possible to enlarge the emulsion droplet system and optically observe the particles on the interface. Such a macroscopic model of a solidsstabilized emulsion droplet has been developed using silicone oil, water and glass beads. The macroscopic system behaved similarly to colloidal scale emulsion systems in that beads protruding from the interface prevented coalescence. The behavior observed in the model system helps explain some previously published nanoscale solids-stabilized emulsion results and is consistent with the location of particles at fluid interfaces being influenced by: hydrophobicity, starting phase, line tension and van der Waals attraction.     

On the possible mechanism of crystal growth from melt under zero gravity conditions

A possible mechanism of the growth of semiconductor single crystals from melt under zero gravity conditions is considered. The results of computer simulation performed by the molecular dynamics method for a thin layer of melt on a single crystal surface are presented. The main characteristics of the melt component dynamics suggest a mechanism whereby the crystal grows to a significant extent due to the attachment of atoms or small atomic clusters, which accounts for the perfection of the crystal structure being grown.     

The flowability of fine powders in reduced gravity conditions

The extrapolation of Qian’s semi-theoretical relationship for the transition between cohesive and non-cohesive powder fluidization behavior into regions of low gravity is studied and a validation experiment employing fluidization is discussed. The fluidization experiment utilized fine glass and alumina powders in a fluidized bed and was flown onboard NASA’s reduced gravity aircraft. The transition region between cohesive and non-cohesive behavior is determined for the glass and alumina powders at gravity levels of 1.8, 1.0, 0.38, and 0.16 g. The results are compared to Qian’s model and show fair agreement. The fluidization experiment limitations are discussed and a rotating drum experiment that will reduce the experiment uncertainty, provide quantifiable results, and is suitable for flight onboard NASA’s reduced gravity aircraft is proposed. The rotating drum technique determines the characteristic frequency of the powder’s center of area to detect avalanching. The concept is validated by comparing the characteristic frequency obtained from analyzing a cohesive powder to the characteristic frequency obtained from analyzing a flowable powder.     

Failure processes of modeled recycled aggregate concrete under uniaxial compression

In order to investigate the failure processes of Recycled Aggregate Concrete (RAC), cracking behavior of modeled RAC specimens under compressive loading was investigated using Digital Image Correlation (DIC). Strain and displacement contour maps were produced to analyze the cracks’ initiation and propagation during loading. The testing results indicate that the discrepancy between the elastic moduli of coarse aggregates and mortar matrix significantly influences the mechanical properties and crack patterns of the modeled materials. It is found that the failure process is related to the relative strength of coarse aggregate and mortar matrix. For modeled RAC, the first bond cracks appear around both the old and new interfacial transition zones (ITZ), and then propagate into the old and new mortar matrix by connecting each other. The observation implies that the initiations and propagations of microcracks are different between RAC and Natural Aggregate Concrete (NAC). The findings in this investigation are useful to improve the mechanical properties of RAC by optimizing the mix proportion.     

An experimental study of surface-tension induced convection at reduced gravity

Fluid motions are induced by surface-tension gradients on the free surface of a liquid in a cylindrical container which is in free fall in a drop tower. Identical experiments are conducted in a normal gravitational environment. The motion in that case is due to natural convection. The ratio of surface-tension to buoyancy forces in the tests is of the order of 10⁴ at reduced gravity conditions and 0·13 under normal gravity. In each case a two way flow occurs throughout most of the liquid. Comparison of the results from the two types of experiments is made in order to indicate differences in the flow details.     

Effect of gravity on InGaSb crystal growth

The effect of gravity on dissolution of GaSb in InSb melt and growth of InGaSb was experimentally investigated. Experiments were carried out in a GaSb(seed)/InSb/GaSb(feed) sandwich system under an imposed temperature gradient. In the experiments, the GaSb feed crystal dissolved into the InSb melt to supply the required GaSb component for the growth of In_0.1Ga_0.9Sb crystal. Two parameters were considered: (1) the inclination angle (θ) of the sample for gravity as 0° and 53°, and (2) the sample diameter (D) as 9 mm and 5mm. When θ was 0°, the interface was almost flat, indicating that convection was axisymmetric and stable. Whereas the interface was distorted towards gravitational direction when θ was 53°, indicating that solutal convection was dominant. The decrease of growth temperature and sample diameter reduced the distortion of interface and the dissolution amount of GaSb feed. The homogeneous crystals were grown at the initial growth stage by supplying the GaSb component during growth.     

Escherichia coli genosensor based on polyaniline

Avidin-modified polyaniline (PANI) electrochemically deposited onto a Pt disk electrode has been utilized for direct detection of Escherichia coli by immobilizing a 5'-biotin-labeled E. coli probe (BdE) using a differential pulse voltammetric technique in the presence of methylene blue as a DNA hybridization indicator. Depending on the target sample and the sonication time, this BdE-avidin-PANI bioelectrode can be utilized to electrochemically detect a complementary target probe (0.009 ng/microL), E. coli genomic DNA (0.01 ng/microL) and 11 E. coli cells/mL in 60 s to 14 min (hybridization time) without using PCR and can be used 5-7 times at temperatures of 30-45 degrees C.     

Convection phenomena at reduced gravity of importance in space processing of materials

The basic aspects of convection processes are delineated. It is shown that even in weak gravitational fields buoyancy can induce fluid motions. Furthermore, at reduced-gravity other non-gravity forces such as surface or interfacial tensions,g-jitter, thermal-volume expansions, density differences due to phase changes, and magnetic and electric fields can induce fluid motions. The various types of flow possible with these various driving forces are described and criteria for determining the extent and nature of the resulting flows and heat transfer are presented. The various physical mechanisms that can occur separately and in combination are indicated and the present state of knowledge of each of the phenomena is outlined.     

牙鲆生长激素基因的克隆及其在大肠杆菌中的融合表达

采用逆转录聚合酶链式反应(RT-PCR)方法,从牙鲆(Paralichthys olivaceus)脑垂体总RNA中扩增出编码牙鲆生长素(GH)成熟肽基因序列。重组至融合表达载体pGEX-4T-3中,构建成牙鲆GH基因融合表达载体pGEX-gh,转化大肠杆菌BL21(DF3),筛选阳性克隆,IVIG诱导表达。经SDS-PAGE电泳显示在45kD处有特异的蛋白条带出现,该蛋白的表达量随诱导时间的延长而增加,3h达最高值,达到细胞总蛋白的18．3％。该融合蛋白在胞内主要以包涵体状态存在,经优化表达条件,成功地获得了可溶性的融合蛋白,经Glutathione Sepharase 4B凝胶纯化后用Western-blotting检测表明其为牙鲆生长激素,并通过酶联免疫吸附受体法证实其具有生物学活性。     

Influences of support fibers on shapes of heptane/hexadecane droplets in reduced gravity

This paper describes analytical and experimental results related to the effects of support fibers on shapes of heptane/hexadecane mixture droplets (both burning and evaporating) in reduced gravity. The experimental results were obtained from large droplets (a few mm) investigated during the MSL-1 Flight of Spacelab. Theoretical (asymptotic) analyses are developed to predict droplet shapes. These analyses, which predict droplet shapes very well, illustrate important aspects of droplet shapes in a transparent fashion. The asymptotic theory shows that for small droplet-fiber contact angles, two spatial zones exist where droplet shapes behave differently. Away from a fiber, a droplet is essentially spherical. As the fiber is approached, however, deviations from spherical symmetry are significant. Previously developed analytical theory to predict macroscopic droplet shapes also compares well with experimental results. In addition, the experiments indicate that thin liquid films can form on support fibers. In the present experiments, these films apparently lead to transient formation of small droplets/bubbles on the support fibers at locations near the surface of a droplet.     

Convection under low gravity: Correctness of mathematical models

The alternative mathematical models of convective fluids flows (the microconvection model of isothermally incompressible fluid, the model of convection of weakly compressible fluid) and the classical Oberbeck-Boussinesq model with temperature dependent viscosity are applicable to investigation of many applied problems of convection: convection under low gravity, in small scales and at fast changes of the boundary thermal regimes. A characteristic property of the alternative mathematical models is the nonsolenoidality of the velocity fields. Principal issues relating to well/ill posed initial boundary value problems for the mathematical models of convection are considered. For the convection equations of weakly compressible fluid the initial boundary value problem with general temperature condition on the boundary is studied. The analytical result concerning the correctness of this problem is presented: the local theorem of existence of a smooth solution in the classes of the Hoelder functions is proved.     

Quasi-universality in the packing of uniform spheres under gravity

A hypothesis that packing fraction alone can be used to characterize the structure of a sphere packing, known as the quasi-universality in the literature, is tested. The analysis, conducted in terms of coordination number, radial distribution function, and structural properties from the Voronoi/Delaunay tessellation, is based on the packing results generated under different conditions, covering a wide packing fraction range. The results show strong similarities in these properties for a given packing fraction, indicating that although not generally valid, the quasi-universality approximately holds for the packing of spheres formed when the gravity is the driving force. The usefulness of this finding is also demonstrated through representative examples.     

Bacteriorhodopsin crystal growth in reduced gravity - Results under the conditions, given in CPCF on board of a space shuttle, versus the conditions, given in DCAM on board of the Space Station Mir

For the purpose of bio-electronics, bacteriorhodopsin was crystallized into two habits through liquid-liquid-diffusion, namely individual needles of up to 1.9 mm in length and needle bunch-like clusters of up to 4.9 mm in total length. In both the reduced gravity experiments performed, the morphology of the individual needles (crystal form A) had improved in terms of sharp needle edges and compact needle packing, compared to the parallel ground controls. For the long duration wide range low gravity condition in the "Diffusion-controlled Crystallization Apparatus for Microgravity (DCAM)" on Mir (STS-89 up), needle bunches on average were longer there than on the ground, while the compactness of the clusters, i.e. the average ratio of clustered length to clustered width was the reverse. Some exceptionally large individual needles were grown in DCAM. For the "Commercial Protein Crystallization Facility (CPCF)" in short duration high definition microgravity condition during a science mission of the Space Shuttle Discovery (STS-95), size and shape of the individual needles were homogeneous and superior to those of both the parallel ground controls and the results in DCAM. In CPCF, the average volume of the individual needles in suspension was increased by 50 % in microgravity compared to those in the ground control.     

Bacteriorhodopsin crystal growth in reduced gravity - Results under the conditions,given in CPCF on board of a space shuttle,versus the conditions,given in DCAM on board of the Space Station Mir

For the purpose of bio-electronics, bacteriorhodopsin was crystallized into two habits through liquid-liquid-diffusion, namely individual needles of up to 1.9 mm in length and needle bunch-like clusters of up to 4.9 mm in total length. In both the reduced gravity experiments performed, the morphology of the individual needles (crystal form A) had improved in terms of sharp needle edges and compact needle packing, compared to the parallel ground controls. For the long duration wide range low gravity condition in the "Diffusion-controlled Crystallization Apparatus for Microgravity (DCAM)" on Mir (STS-89 up), needle bunches on average were longer there than on the ground, while the compactness of the clusters, i.e. the average ratio of clustered length to clustered width was the reverse. Some exceptionally large individual needles were grown in DCAM. For the "Commercial Protein Crystallization Facility (CPCF)" in short duration high definition microgravity condition during a science mission of the Space Shuttle Discovery (STS-95), size and shape of the individual needles were homogeneous and superior to those of both the parallel ground controls and the results in DCAM. In CPCF, the average volume of the individual needles in suspension was increased by 50 % in microgravity compared to those in the ground control.