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101.
X-ray data obtained by the Prognoz 5,6,7 and 8 hard X-ray photometers are compared with the measurements carried out by similar instruments aboard the Solrad 11, ISEE 3, SMM and Hinotori satellites. Using the method of relative amplitude analysis, the apparent disagreement in the energy discrimination level calibration between the instruments is pointed out. The results of the comparison and the possible sources of disagreement are given. We suggest an international effort be made to develop a system of uniform pre-launch calibration of photometers based on a reference calibration source.  相似文献   
102.
The 100 meter high drop tube at the Marshall Space Flight Center has proven to be a viable facility for studies of containerless solidification. Advantages are that experiments are inexpensive and large numbers of specimens can be processed rapidly. It would not be unusual to run ten specimens in a day. Another significant advantage is that the undercooling behavior can be followed with sufficient sensitivity to easily detect the onset of recalescence and subsequent events.Disadvantages are the restrictions on specimen sizes and types of alloys that can be run in a microgravity environment. Practical specimen sizes range between 50 mg and 500 mg depending on the type of furnace being used. Refractory alloys can be processed in a vacuum (about 10?5 torr) and therefore at microgravity. Non-refractory alloys demand an atmosphere (about 200 torr) to obtain appreciable undercooling before impact at the bottom of the tube. Under these conditions significant g forces result.Because of the present limitations of the 100 meter drop tube, the most definitive work has been done on niobium based alloys. Large amounts of undercooling have been observed routinely and the effects of undercooling on microstructure have been characterized in detail. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy have been used to determine types of phases, amounts of phases, and compositions of phases. It is clear, as would be expected, that the results bear some resemblance to rapid solidification processing by quenching. However, there are dissimilarities due to the uniqueness of solidification by deep undercooling without quenching in long drop tubes and accompanying recalescence effects.  相似文献   
103.
The effects of gravity waves on OH and 5577 0I emissions have been used to investigate (1) the possible production of “secondary” waves or “ripples” by a “primary” wave; (2) the possible application of such observed optical emissions for computing atmospheric parameters such as turbulence viscosity in the mesospheric regions.  相似文献   
104.
In order to prepare infrared sounding of comet Halley from the flyby VEGA probes, we have computed the synthetic spectrum between 2.5 and 15 μ of a typical comet at a heliocentric distance of ~ 0.8 AU. The present paper is particularly devoted to the contribution from the cometary gases. For a selection of 20 possible parent molecules, the most efficient excitation process is resonant fluorescence by the solar radiation field. The H2O, CO, CO2, CH4, NH3 and H2CO molecules are the best candidates for detection by the IKS infrared spectrometers aboard the VEGA probes. For the water molecule, collisions are too rare to ensure thermal equilibrium in the whole coma ; therefore a limited number of fluorescence lines are expected to be present in the H2O vibrational bands.  相似文献   
105.
An overview is given of the Productivity, Reliability, Availability, and Maintainability (PRAM) Project 00-256, which aims to integrate the Digital Multimedia Information System (DMIS) into the Reconnaissance Module Automatic Test System (RMATS). Benefits to be derived from the incorporation of the DMIS and return on investment for the US Air Force are discussed. The process used to obtain approval and funding support for this advanced maintenance aiding and data collection system is described  相似文献   
106.
107.
We investigated the effect of substratum adhesiveness on stimulated lymphocyte blastogenesis by reducing and blocking cell adhesion with poly (2-hydroxyethyl methacrylate) (poly-HEMA) in a simple on-ground system. Cells grown on medium-thick and thick poly-HEMA films were rounded in shape and displayed no signs of spreading. By contrast, on tissue culture plastic and very thin poly-HEMA films, they showed clear signs of spreading. The mitogenic response of lymphocytes grown on thick poly-HEMA films was reduced by up to 68% of the control (tissue culture plastic). Interferon-gamma production was near zero when the cells were grown on the least adhesive substratum. On uncoated plastic, activated lymphocytes subjected to high gravity (20g) exhibited an increased proliferation rate (40%) compared with 1g. By contrast, on poly-HEMA, high gravity did not improve lymphocyte responsiveness. These results show that activated lymphocytes need to anchor and spread prior to achieving an optimal proliferation response. We conclude that decreased lymphocyte adhesion could contribute to the depressed in vitro lymphocyte responsiveness found in the microgravity conditions of space flight.  相似文献   
108.
Some preliminary new results are presented of the keV plasma experiment on GEOS-1. Electrons and ions have been observed to stream along the magnetic field lines in the dayside magnetosphere from the ionospheric side of the satellite towards the equatorial plane during magnetic storms, with streaming velocities corresponding to a kinetic energy of the order of a keV. The opposite streaming velocity has also been seen, but primarily in the ions only and with a smaller flux ratio for the two opposite directions along the field lines. The transition between the two opposite streaming directions, as seen by the satellite, has been found to occur even in a fraction of a second.In magnetic storm conditions azimuthal asymmetries in ion fluxes corresponding to electric field intensities of several tens of millivolts per meter have been observed.  相似文献   
109.
    
Titan, the largest satellite of Saturn, with a dense atmosphere very rich in organics, and many couplings in the various parts of its \"geofluid\", is a reference for studying prebiotic chemistry on a planetary scale. New data have been obtained from experiments simulating this organic chemistry (gas and aerosol phases), within the right ranges of temperature and a careful avoiding of any chemical contamination. They show a very good agreement with the observational data, demonstrating for the first time the formation of all the organic species already detected in Titan atmosphere including, at last, C4N2, together with many other species not yet detected in Titan. This strongly suggests the presence of more complex organics in Titan's atmosphere and surface, including high molecular weight polyynes and cyanopolyynes. The NASA-ESA Cassini-Huygens mission has been successfully launched in October 1997. The Cassini spacecraft will reach the Saturn system in 2004 and become an orbiter around Saturn, while the Huygens probe will penetrate into Titan's atmosphere. In situ measurements, in particular from Huygens GC-MS and ACP instruments, will provide a detailed analysis of the organics present in the air, aerosols, and surface. This very ambitious mission should yield much information of crucial importance for our knowledge of the complexity of Titan's chemistry, and, more generally for the field of exobiology.  相似文献   
110.
    
Thermodynamic conditions suggest that clathrates might exist on Mars. Despite observations which show that the dominant condensed phases on the surface of Mars are solid carbon dioxide and water ice, clathrates have been repeatedly proposed to play an important role in the distribution and total inventory of the planet’s volatiles. Here we review the potential consequences of the presence of clathrates on Mars. We investigate how clathrates could be a potential source for the claimed existence of atmospheric methane. In this context, plausible clathrate formation processes, either in the close subsurface or at the base of the cryosphere, are reviewed. Mechanisms that would allow for methane release into the atmosphere from an existing clathrate layer are addressed as well. We also discuss the proposed relationship between clathrate formation/dissociation cycles and how potential seasonal variations influence the atmospheric abundances of argon, krypton and xenon. Moreover, we examine several Martian geomorphologic features that could have been generated by the dissociation of extended subsurface clathrate layers. Finally we investigate the future in situ measurements, as well as the theoretical and experimental improvements that will be needed to better understand the influence of clathrates on the evolution of Mars and its atmosphere.  相似文献   
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