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461.
G. Nagel K.W. Benz 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(5):23-26
Single crystals of binary III-V-semiconductors, e.g. GaAs or InP, are important basic materials for optoelectronic devices, e.g. LED's and lasers. Device production needs highly perfect substrate crystals with low defect densities and homogeneous dopant distributions. In our experiment we applied the Travelling-Heater-Method to grow the III-V compound GaSb. The aim of this research project was to improve the crystal quality by investigating convective transport phenomena and the origins of dopant inhomogeneities under earth and space conditions. Earth grown crystals show strong dopant variations mainly due to convective flow phenomena. The preliminary result of our SPACELAB 1 experiment reveals an increase of dopant homogeneity in the space grown crystal because of the absence of natural convection under reduced gravity. 相似文献
462.
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464.
W R Schwingel J C Sager 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,18(1-2):293-297
An anaerobic reactor seeded with organisms from an anaerobic lagoon was used to study the degradation of inedible crop residues from potato and wheat crops grown in a closed environment. Conversion of this biomass into other products was also evaluated. Degradation of wheat volatile solids was about 25% where that of potato was about 50%. The main product of the anaerobic fermentation of both crops was acetic acid with smaller quantities of propionate and butyrate produced. Nitrate, known to be high in concentration in inedible potato and wheat biomass grown hydroponically, was converted to ammonia in the anaerobic reactor. Both volatile fatty acid and ammonia production may have implications in a crop production system. 相似文献
465.
L.W. Esposito 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(9):85-90
Pioneer Venus data from the first 5 years of operation show a decline by more than a factor of ten in SO2 at the cloud tops. A consistent decline has also recurred in the amount of sub-micron haze above the clouds. The correlation between these two observables is 0.8 over this period. A plausible explanation is injection of SO2 from episodic volcanism. The episodic behavior implies that steady state models of the Venus cloud chemistry and dynamics may be of limited use. 相似文献
466.
Birk R. Camus W. Valenti E. McCandless W. Jr. 《Aerospace and Electronic Systems Magazine, IEEE》1995,10(11):15-23
This paper presents profiles of 12 airborne and spaceborne Synthetic Aperture Radar (SAR) imaging systems. This information is intended to help potential users evaluate the systems for specific applications. The systems profiled in this article can be used for commercial purposes; some have been built specifically for commercial use while others also serve as science and research tools, Both domestic and foreign systems designed for government agencies and private industry are profiled. Nine of these systems are currently operational; two systems are scheduled to begin service in the near future. A third system is no longer active, but archive data are commercially available 相似文献
467.
W Schimmerling J W Wilson J E Nealy S A Thibeault F A Cucinotta J L Shinn M Kim R Kiefer 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,17(2):31-36
Ions of galactic origin are modified but not attenuated by the presence of shielding materials. Indeed, the number of particles and the absorbed energy behind most shield materials increases as a function of shield thickness. The modification of the galactic cosmic ray composition upon interaction with shielding is the only effective means of providing astronaut protection. This modification is intimately connected with the shield transport properties and is a strong function of shield composition. The systematic behavior of the shield properties in terms of microscopic energy absorption events will be discussed. The shield effectiveness is examined with respect to conventional protection practice and in terms of a biological endpoint: the efficiency for reduction of the probability of transformation of shielded C3H10T1/2 mouse cells. The relative advantage of developing new shielding technologies is discussed in terms of a shield performance as related to biological effect and the resulting uncertainty in estimating astronaut risk. 相似文献
468.
E F Wheeler J Kossowski E Goto R W Langhans G White L D Albright D Wilcox 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,18(1-2):233-236
A Linear Programming model has been constructed which aids in selecting appropriate crops for CELSS (Controlled Environment Life Support System) food production. A team of Controlled Environment Agriculture (CEA) faculty, staff, graduate students and invited experts representing more than a dozen disciplines, provided a wide range of expertise in developing the model and the crop production program. The model incorporates nutritional content and controlled-environment based production yields of carefully chosen crops into a framework where a crop mix can be constructed to suit the astronauts' needs. The crew's nutritional requirements can be adequately satisfied with only a few crops (assuming vitamin mineral supplements are provided) but this will not be satisfactory from a culinary standpoint. This model is flexible enough that taste and variety driven food choices can be built into the model. 相似文献
469.
Phase accuracy and simplicity advantages of a direct-sampling coherent detection (DCD) system were demonstrated by computer simulation in earlier correspondence. This correspondence reviews the DCD approach and reports the results of experiments involving digitized samples of analog signals taken by a high-quality, off-the-shelf A/Dconverter. IF signals near 10, 20, and 30 MHz were sampled at 5 MHzresulting in rms DCD phase errors generally below 0.50 compared witherrors less than 0.20 computed in the earlier simulations. 相似文献
470.
L W Townsend F A Cucinotta 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,17(2):59-68
It has been known for some time that adequate assessment of spacecraft shield requirements and concomitant estimates of astronauts radiation exposures from galactic cosmic radiation requires accurate, quantitative methods for characterizing these radiation fields as they pass through thick absorbers. The main nuclear interaction processes involved are (1) nuclear elastic and inelastic collisions, and (2) nuclear breakup (fragmentation) and electromagnetic dissociation (EMD). Nuclear fragmentation and EMD are important because they alter the elemental and isotopic composition of the transported radiation fields. At present, there is no suitably accurate theory for predicting nuclear fragmentation cross sections for all collision pairs and energies of interest in space radiation protection. Typical cross-section differences between theory and experiment range from about 25 percent to a factor of two. The resulting errors in transported flux, for high linear energy transfer (LET) particles, are comparble to these cross-section errors. In this overview, theoretical models of heavy ion fragmentation currently used to generate input data bases for cosmic-ray transport and shielding codes are reviewed. Their shortcomings are discussed. Further actions needed to improve their accuracy and generality are presented. 相似文献