SCN-Cam共晶合金的定向凝固研究

采用实时观测装置和定向凝固系统研究了SCN-Cam(Succinonitrile-wt%Camphor,wt%为质量分数)模型合金的凝固过程.实验结果表明,SCN-23.6%Cam共晶合金在常规条件下形成规则的共晶组织,共晶间距随界面推移速度的增大而减小;加入超声振动时,共晶合金生长出初生相;SCN-21%Cam亚共晶...     

Handling of particulate solids on the International Space Station

We present the principles of a particle-handling system for the International Space Station (ISS) with which experiments with astrophysical and planetological applications will be performed. The principle of dust deagglomeration and dispersion was successfully tested in short-duration microgravity experiments. The flight of the systems on the ISS is planned for 2012.     

Vicarious calibrations of HICO data acquired from the International Space Station

The Hyperspectral Imager for the Coastal Ocean (HICO) presently onboard the International Space Station (ISS) is an imaging spectrometer designed for remote sensing of coastal waters. The instrument is not equipped with any onboard spectral and radiometric calibration devices. Here we describe vicarious calibration techniques that have been used in converting the HICO raw digital numbers to calibrated radiances. The spectral calibration is based on matching atmospheric water vapor and oxygen absorption bands and extraterrestrial solar lines. The radiometric calibration is based on comparisons between HICO and the EOS/MODIS data measured over homogeneous desert areas and on spectral reflectance properties of coral reefs and water clouds. Improvements to the present vicarious calibration techniques are possible as we gain more in-depth understanding of the HICO laboratory calibration data and the ISS HICO data in the future.     

Radiation dosimetry for microbial experiments in the International Space Station using different etched track and luminescent detectors

The laboratory of Microbiology at SCK.CEN, in collaboration with different universities, participates in several ESA programmes with bacterial experiments that are carried out in the International Space Station (ISS). The main objective of these programmes is to study the effects of space flight conditions such as microgravity and cosmic radiation on the general behaviour of model bacteria. To measure the radiation doses received by the bacteria, different detectors accompanied the microbiological experiments. The results obtained during two space flight missions are discussed. This dosimetry experiment was a collaboration between different institutes so that the doses could be estimated by different techniques. For measurement of the high linear energy transfer (LET) doses (>10 keV microm(-1)), two types of etched track detectors were used. The low LET part of the spectrum was measured by three types of thermoluminescent detectors ((7)LiF:Mg,Ti; (7)LiF:Mg,Cu,P; Al(2)O(3):C) and by the optically stimulated luminescence technique using Al(2)O(3):C detectors.     

Biological dosimetry in the ENEIDE Mission on the International Space Station

Space radiation represents one of the major health hazards to crews of interplanetary missions. As the duration of space flight increases, according to International Space Station (ISS) and Mars mission programs, the risk associated with exposure to ionizing radiation also increases. Although physical dosimetry is routinely performed in manned space missions, it is generally accepted that direct measurement of biological endpoints (biological dosimetry) is necessary for a precise assessment of radiation risk in extraterrestrial activities. Chromosomal aberrations (CAs) in peripheral blood lymphocytes (PBLs) are particularly suitable to this purpose, as they can provide estimates of both equivalent radiation dose and risk. In this study, cytogenetic analysis was performed on PBL chromosomes of an Italian astronaut involved in two different 10-day missions on the ISS (Marco Polo, April 2002, and ENEIDE, May 2005). Blood samples were collected before and after flights. CAs were evaluated in either mitotic spreads or in prematurely condensed chromosomes (PCC) by Fluorescence in Situ Hybridization (FISH). In addition, blood samples were exposed to graded doses of X-rays in vitro before and after the flight and cytogenetic damage evaluated to investigate whether the space environment alters the sensitivity of human cells to ionizing radiation. The yield of baseline chromosomal aberrations was not modified following Marco Polo and ENEIDE mission. This is consistent with the low dose absorbed in these short-term space missions. Preliminary results from Marco Polo mission suggested a significant increase in intrinsic radiosensitivity of lymphocytes after landing compared to pre-flight and follow-up (6 months after landing) samples. However, this effect was not observed during the ENEIDE mission. The results suggest that intra-indi-vidual variations in radiosensitivity are significant, but they cannot be related to the space flight.     

Latest Results on Complex Plasmas with the PK-3 Plus Laboratory on Board the International Space Station

Complex plasmas are low temperature plasmas that contain microparticles in addition to ions, electrons, and neutral particles. The microparticles acquire high charges, interact with each other and can be considered as model particles for effects in classical condensed matter systems, such as crystallization and fluid dynamics. In contrast to atoms in ordinary systems, their movement can be traced on the most basic level, that of individual particles. In order to avoid disturbances caused by gravity, experiments on complex plasmas are often performed under microgravity conditions. The PK-3 Plus Laboratory was operated on board the International Space Station from 2006 – 2013. Its heart consisted of a capacitively coupled radio-frequency plasma chamber. Microparticles were inserted into the low-temperature plasma, forming large, homogeneous complex plasma clouds. Here, we review the results obtained with recent analyzes of PK-3 Plus data: We study the formation of crystallization fronts, as well as the microparticle motion in, and structure of crystalline complex plasmas. We investigate fluid effects such as wave transmission across an interface, and the development of the energy spectra during the onset of turbulent microparticle movement. We explore how abnormal particles move through, and how macroscopic spheres interact with the microparticle cloud. These examples demonstrate the versatility of the PK-3 Plus Laboratory.     

Miscible Fluids in Microgravity (MFMG): A zero-upmass investigation on the International Space Station

Miscible Fluids in Microgravity (MFMG) was a zero-upmass investigation performed on the International Space Station. The goal of MFMG was to determine if interfacial phenomena seen with immiscible fluids could be seen with miscible fluids. The experiments had to be performed with existing materials on the ISS. Honey and water were chosen as the fluids, and urine collection syringes were used as the vessels in which the experiments were performed. In March 2004 (Increment 8) Dr. Michael Foale performed four experiments under isothermal conditions to determine: If a stream of honey injected into water would exhibit the Rayleigh-Tomotika instability and break into small drops. If an aspherical drop of water in honey would spontaneously assume a spherical shape. The experiments were performed successfully. During Increment 9, Mike Fincke performed two runs in which a stream of honey was injected into water while the syringe was attached to the surface of the Commercial Generic Bioprocessing Apparatus (CGBA) at approximately 31° C. No change in the stream shape was observed. Two more runs were performed on Increments 10 and 11 but no additional phenomena were observed. No behavior beyond simple diffusion was observed. We performed simulations with the Navier-Stokes equations plus a Korteweg stress term. We estimated that the maximum possible value of the square gradient parameter was 10⁻¹² N for the honey-water system.     

Effect of cooling rate on the 3D morphology of the proeutectic Al_3Ni intermetallic compound formed at the Al/Ni interface after solidification

Effect of cooling rate on the 3 D morphology and the growth mechanism of the proeutectic Al_3Ni intermetallic compound(IMC) that forms at the Al/Ni interface after solidification was investigated by synchrotron X-ray microtomography in combination with EBSD analysis. The proeutectic Al_3Ni phase that forms under an average cooling rate of 0.1 Ks~(-1) shows a characteristic faceted growth behavior and presents a typical 3 D morphology as partially hollow quadrangular prisms. On the contrary, that forms under an average cooling rate of 10 Ks~(-1) shows complicated dendritic morphology with asymmetrically distributed arms and faceted V-shape groove at the distal end, indicating a gradual transition of the growth behavior from non-faceted to faceted during the solidification process. These results reveal that the morphology of the proeutectic Al_3Ni is highly sensitive to the solidification condition so that fine control of the desired morphology may be achieved by carefully manipulating the cooling profile.     

Thermodiffusion in Ternary Mixtures of Water/Ethanol/Triethylene Glycol: First Report on the DCMIX3-Experiments Performed on the International Space Station

We report on thermodiffusion experiments conducted on the International Space Station ISS during fall 2016. These experiments are part of the DCMIX (Diffusion and thermodiffusion Coefficients Measurements in ternary Mixtures) project, which aims at establishing a reliable data base of non-isothermal transport coefficients for selected ternary liquid mixtures. The third campaign, DCMIX3, focuses on aqueous systems with water/ethanol/triethylene glycol as an example, where sign changes of the Soret coefficient have already been reported for certain binary subsystems. Investigations have been carried out with the SODI (Selectable Optical Diagnostics Instrument) instrument, a Mach-Zehnder interferometer set up inside the Microgravity Science Glovebox in the Destiny Module of the ISS. Concentration changes within the liquids have been monitored in response to an external temperature gradient using phase-stepping interferometry. The complete data set has been made available in spring 2017. Due to additionally available measurement time, it was possible to collect a complete data set at 30^°C and an almost complete data set at 25^°C, which significantly exceeds the originally envisaged measurements at a single temperature only. All samples could be measured successfully. The SODI instrument and the DCMIX experiments have proven reliable and robust, allowing to extract meaningful data even in case of unforeseen laser instabilities. First assessments of the data quality have revealed six out of 31 runs with some problems in image contrast and/or phase step stability that will require more sophisticated algorithms. This publication documents all relevant parameters of the conducted experiments and also events that might have an influence on the final results. The compiled information is intended to serve as a starting point for all following data evaluations.     

Determination of interface properties from experiments on the fragmentation process in single-fiber composites

This paper attempts to quantify the fracture properties (strength and toughness) of the fiber–matrix interface in composites, using the fragmentation process and debonding growth for HI-Nicalon™ SiC single-fiber and T300 carbon single-fiber epoxy (Bisphenol-A type epoxy resin with triethylenetetramine (TETA) as curing agent) composite systems. This method is based on the numerical modeling for the microscopic damage and fragmentation process in single-fiber composite (SFC) tests, with a cohesive zone model (CZM). For the HI-Nicalon™ SiC single-fiber epoxy composite in which the major damage near a fiber break is interfacial debonding, interface properties were reasonably determined as (T_II,max, G_IIc) = (75 MPa, 200 J/m²). In contrast, for T300 carbon single-fiber epoxy composite, we could not determine unique interfacial properties, since the variation of the cohesive parameters hardly affects the microscopic damage process due to the transition to the damage pattern dominated by matrix cracking.     

Influence of directional solidification variables on the microstructure and crystal orientation of AM3 under high thermal gradient

Solid–liquid interface morphologies of a nickel-base single crystal superalloy AM3 were investigated under high thermal gradient. The critical velocities of planar–cellular and cellular–dendritic transition were greatly increased by high thermal gradients. A high thermal gradient was of great benefit to dendrite refinement. Experimental results showed that the primary and secondary dendrite arm spacings decreased with increasing cooling rate. As expected, the segregation of elements was suppressed and the size of the gamma prime (γ′) phase decreased significantly with increasing withdrawal rates. The shape of γ′ in interdendritic region kept cuboidal at higher withdrawal rate. It was found that the withdrawal rates had little influence on the crystallographic orientation in high thermal gradient directional solidification.     

Study on the solidification cracking behaviour of high strength aluminum alloy welds: Effects of alloying elements and solidification behaviours

The solidification cracking susceptibility of the 7000 series Al-Zn-Mg high strength aluminum alloy has been studied. The cracking behaviour of the specimens were evaluated by a Tig-a-Ma-Jig Varestraint test process under various augmented strain conditions. It has been experimentally observed that the addition of copper decreased the solidification cracking resistivity of the high strength aluminum alloy weld metal by increasing the total crack length (TCL). The effect of the addition of manganese on the solidification cracking behaviour is found to be beneficial by markedly decreasing the solidification cracking susceptibility as the manganese content increases from 0.3 to 0.7%. This enhancement by manganese is understood to be attributed to the reduction of the mushy zone size during the solidification process. The effects of chromium and zirconium additions are also investigated. The weld metal containing zirconium is less sensitive to the solidification cracking than the weld metal containing chromium. In addition, the solidification behaviours of the tested alloys are also investigated and it is found that as the solidification temperature range (T) becomes narrow, the solidified structure becomes more dendritic in its features which is believed to create higher solidification cracking resistance.     

Dynamics of the3He A-B interface in the velocity range of second sound

The movingA-B interface emits second sound which extracts the latent heat from the transition region. The amplitude is calculated for all interface velocities . A pronounced maximum is found if is close to the second sound velocity.     

Tunable morphology from 2D to 3D in the formation of hierarchical architectures from a self-assembling dipeptide: thermal-induced morphological transition to 1D nanostructures

Construction of complex three-dimensional (3D) architectures through hierarchical self-assembly of peptide molecules has become an attractive approach of fabricating multifunctional advanced materials due to their various potential applications in bionanotechnology. This paper describes the tunable formation of flower-like 3D hierarchical architectures of intricate morphology from a simple self-assembling dipeptide phenylalanine–tyrosine with a facile preparative method by applying a range of voltages through a drop of peptide solution. The fine-tuning of voltages and their application time enable to produce morphological changes of the microstructures from 2D to 3D and also control their formation. The morphology has been characterized by the gradual change in the height-to-diameter ratio of the microstructures with change in the applied voltages. Moreover, these microstructures show significant thermal stability over a wide range of temperatures, whereas adequately high temperature promotes the morphological transformation of the microstructures into different types of ultrathin 1D nanostructures such as nanowires, nanofibrils, etc. Furthermore, we have suggested a possible growth model for the fabrication of unique hierarchical architectures through diffusion-limited aggregation mechanism.     

ARGES: Radial segregation and helical instabilities in metal halide lamps studied under microgravity conditions in the International Space Station

HID lamps (High-Intensity Discharge) are gaining ground in the lighting industry because of their very high energy efficiency (up to 40%). In these lamps, which are operated in the arc regime and which are contained in a ceramic balloon, filled with argon or xenon, mercury, and salts of various rare earth metals and iodine), de-mixing occurs. This de-mixing is driven by differences in diffusion velocities of molecules and atoms. Furthermore, helical instabilities might occur in the lamp. Both phenomena are severely modified under 1 G conditions: convection will bend a horizontally burning arc channel upwards, and a vertically burning arc channel will exhibit convective cells. This makes it impossible to study these phenomena on the ground. If a proper understanding of these phenomena is to be gained, experiments under microgravity are necessary. The main objectives of the experiment are: (1) determination of the critical factors for the onset of helical instabilities in HID lamps and (2) characterisation of the radial de-mixing processes by radially resolved high-resolution emission spectroscopy. To this end, special hardware has been designed and built which houses a very compact high-resolution spectrometer, a video camera and a caroussel with 20 lamps in it. The lamps are measured consecutively. The experiments have been performed successfully by the Dutch astronaut André Kuipers on board the International Space Station during the Dutch Soyuz Mission “DELTA” on 24 and 25 April 2004. Especially the helical instabilities part yielded immediate and surprising results: the arc channel does bend, but does not rotate under microgravity. This fact is very important in improving the performance of the lamps, especially since the instabilities occur mainly in the most efficient lamps.     

在三维CAD软件中建立空间几何元素模型的研究

在三维CAD软件中对空间几何元素建立模型是解决工程领域空间问题的基础,本文对各种空间几何元素提供了多种建立模型的方法.每种三维CAD软件对于建立空间平面、空间直线、空间曲线的模型都提供了简单方便的方法,但是建立空间曲面的模型则要比建立其它空间几何元素的模型更加复杂和困难.CAXA实体设计是国产的三维CAD软件,在该软件...     

Wetting behaviour and mullite formation at the interface of inviscid melt-spun CaO-Al2O3 fibre-reinforced Al-Si alloy (4032) composite

Inviscid melt-spun calcia-alumina fibre-reinforced aluminium-silicon alloy (4032) composites were produced using a melt-infiltration technique. Scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were used to investigate interfacial wetting and interphase formation, and identify the crystalline phase of the interphase of these composites. The composites processed at 700°C showed a good interfacial wetting and silicon accumulation at the interface. The composites processed at 927°C showed formation of an interphase region of about 10–20 m thick, as well as excellent interfacial wetting. EDS analysis gave averaged compositions of this interphase region at 74 wt % Al and 26 wt % Si, which corresponds to the composition of mullite (3Al₂O₃ · 2SiO₂). The formation of mullite at the interface was confirmed by XRD analysis.     

Lattice Dynamics of 2D Monoatomic Crystals: Application to 3He on Graphite

The dynamics of a two-dimensional rare gas crystal with triangular lattice is investigated theoretically. Phonon spectra of the 2D crystal are calculated within the model which takes into account the interaction between nearest neighbours in the layer and interaction of layer atoms with the substrate. On the basis of obtained results the temperature dependence of lattice heat capacity has been calculated and a comparison is made with experimental data.