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61.
K O'Brien H H Sauer 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,32(1):73-80
High-energy solar particles, produced in association with solar flares and coronal mass ejections, occasionally bombard the earth's atmosphere. resulting in radiation intensities additional to the background cosmic radiation. Access of these particles to the earth's vicinity during times of geomagnetic disturbances are not adequately described by using static geomagnetic field models. These solar fluxes are also often distributed non uniformly in space, so that fluxes measured by satellites obtained at great distances from the earth and which sample large volumes of space around the earth cannot be used to predict fluxes locally at the earth's surface. We present here a method which uses the ground-level neutron monitor counting rates as adjoint sources of the flux in the atmosphere immediately above them to obtain solar-particle effective dose rates as a function of position over the earth's surface. We have applied this approach to the large September 29-30, 1989 ground-level event (designated GLE 42) to obtain the magnitude and distribution of the solar-particle effective dose rate from an atypically large event. The results of these calculations clearly show the effect of the softer particle spectra associated with solar particle events, as compared with galactic cosmic rays, results in a greater sensitivity to the geomagnetic field, and, unlike cosmic rays, the near-absence of a "knee" near 60 degrees geomagnetic latitude. 相似文献
62.
H. Ben Hadid B. Roux P. Laure P. Tison D. Camel J. J. Favier 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1988,8(12):293-304
The problem of surface tension-driven flows in horizontal liquid layers has been studied experimentally, and theoretically by direct numerical simulation and small perturbation analysis. We focus our attention on situations in which the depth of the fluid (liquid tin; small Prandtl number, Pr=0.015) is small enough to ensure the predominance of the surface tension forces over those due to the buoyancy. The surface velocity has been experimentally obtained for liquid tin layer with various aspect ratio (length to height) in the range 5<A<83. The thermal gradients are ranged from 5 to 40°K/cm. In the numerical study, the Navier-Stokes and energy equations are solved by an efficient finite difference technique. The parameters governing the flow behaviour in the liquid are varied to determine their effects on thermocapillary convection: the Reynolds number 10<Re<2104 and the aspect ratio 2<A<25; with Pr kept constant at Pr=0.015. The linear eigenequation resulting from small spatial disturbances of the Couette flow solution is solved using an Tau-Chebyshev approximation. A notable feature of the theoretical study is the totally different end circulations. In the region near the cold wall a multicell structure is evident. This agrees with the eigensolution which is of complex type, indicating spatial periodicity. In the hot wall region the flow is accelerated to reach the velocity value for the fully-developed Couette flow which is reached under conditions such as Re/A<20. The transition from viscous to boundary layer regime occurs for a critical value (Re/A)c of nearly about 200, as deduced from the numerical and experimental results. 相似文献
63.
Some comparisons of orbit determination and parameter estimation based on LAGEOS 1 and LAGEOS 2 data
H. Montag 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,16(12):149-154
The modelling accuracy of the LAGEOS 1 orbit was continously improved since its launch in 1976. In spite of these experiences the modelling accuracy of LAGEOS 2 is still about 20 per cent worse. Considering e. g. only the influence of different gravity field models it has been shown that the orbital fits for arc lengths of one month is generally about 25 mm for LAGEOS 1 and more than 30 mm for LAGEOS 2. This is mainly due to the fact that LAGEOS 2 has not yet been used for the determination of most gravity field models. The influences of different model parameters on the estimation of station coordinates, Earth rotation parameters, the geogravitational coefficient, the radiation pressure coefficient, and the empirical acceleration has been studied. The differences and peculiarities of both satellites are discussed. Although the analysis of LAGEOS 2 data still does not reach the high level of LAGEOS 1 combination solutions using both satellites allow new insights, higher accuracies, and a higher time resolution for the parameters and phenomena investigated. 相似文献
64.
K Kobayashi T Kasamatsu T Kaneko J Koike T Oshima T Saito T Yamamoto H Yanagawa 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,16(2):21-26
Cometary ices are believed to contain water, carbon monoxide, methane and ammonia, and are possible sites for the formation and preservation of organic compounds relating to the origin of life. Cosmic rays, together with ultraviolet light, are among the most effective energy sources for the formation of organic compounds in space. In order to study the possibility of the formation of amino acids in comets or their precursory bodies (interstellar dust grains), several types of ice mixtures made in a cryostat at 10 K ("simulated cometary ices") were irradiated with high energy protons. After irradiation, the volatile products were analyzed with a quadrupole mass spectrometer, while temperature of the cryostat was raised to room temperature. The non-volatile products remaining in the cryostat at room temperature were collected with water. They were acid-hydrolyzed, and analyzed by ion-exchange chromatography. When an ice mixture of carbon monoxide (or methane), ammonia and water was irradiated, some hydrocarbons were formed, and amino acids such as glycine and alanine were detected in the hydrolyzate. These results suggest the possible formation of "amino acid precursors" (compounds yielding amino acids after hydrolysis) in interstellar dust grains by cosmic radiation. We previously reported that amino acid precursors were formed when simulated primitive planetary atmospheres were irradiated with cosmic ray particles. It will be of great interest to compare the amount of bioorganic compounds that were formed in the primitive earth and that brought by comets to the earth. 相似文献
65.
余建祖 《北京航空航天大学学报》1998,24(2):212-215
针对我国军用电子设备吊舱载机电源紧张,国产电子元器件耐温性能相对较差,对环境控制系统要求较高的特点,本文提出了一种新型用冲压空气驱动的环境控制系统.该系统采用"蓄冷节能"的设计思想和逆升压回冷技术,并配备具有智能功能的测控子系统.为克服冲压空气压头低的困难,利用空气动力学理论,提高进气道总压恢复系数,扩大系统进出口压差,从而获得较大涡轮膨胀比.试验结果证明所设计的吊舱环控系统具有良好的制冷性能和经济性. 相似文献
66.
钱翼稷 《北京航空航天大学学报》1993,(1):42-51
本文直接从音速线出发计算了一个旋成体跨音速绕流超音速泡中的特征线网。提出了从音速线开拓到一条超音速线的方法,计算了无旋轴对称流的特征线网,发现其特点是不能跨越对称轴线,并对其原因作了初步的讨论。本文的计算结果可应用于物面修形。 相似文献
67.
68.
Spectral emission lines created in the solar chromosphere — corona transition region show net red-shifts. It has been proposed that this may be the result of the return of spicular material. We simulate a spicule numerically using the rebound shock model and find that the resulting hydrodynamic evolution leads to a perceived up-flow in transition region spectral lines even though the average velocity in the line forming region is directed downward. The explanation for this apparent paradox is found in the correlation between density and velocity in the waves generated by the rebound shock spicule. 相似文献
69.
Timothy G. Hawarden Robert Crane Harley A. Thronson Jr. Alan J. Penny Anna H. Orlowska Thomas W. Bradshaw 《Space Science Reviews》1995,74(1-2):45-56
The designs of cold space telescopes, cryogenic and radiatively cooled, are similar in most elements and both benefit from orbits distant from the Earth. In particular such orbits allow the anti-sunward side of radiatively-cooled spacecraft to be used to provide large cooling radiators for the individual radiation shields. Designs incorporating these features have predictedT
tel near 20 K. The attainability of such temperatures is supported by limited practical experience (IRAS, COBE). Supplementary cooling systems (cryogens, mechanical coolers) can be advantageously combined with radiative cooling in hybrid designs to provide robustness against deterioration and yet lower temperatures for detectors, instruments, and even the whole telescope. The possibility of such major additional gains is illustrated by the Very Cold Telescope option under study forEdison, which should offerT
tel5 K for a little extra mechanical cooling capacity. 相似文献
70.
Miller RH 《Acta Astronautica》1995,36(8-12):581-587
Human productivity during assembly operations in-orbit is dependent on limits set by fatigue, metabolic rates, learning, and assembly techniques. In order to quantify these effects, tests were conducted in the NASA MSFC Neutral Buoyancy Simulator, in the NASA KC-135 in parabolic flight, and in space with the EASE program during the Shuttle Atlantis mission 61-B. A separate program attempted to relate productivity to system costs. Because of the surprisingly high productivity which had been demonstrated in orbit, it was shown that assembly operations would have only a small effect on system costs at the present level of launch costs. The results of these continuing studies have been reported in a recent paper(1). They will be briefly summarized here and the results updated to include additional cost elements and to examine the effects of reductions in transportation costs, resulting from advances in technology and from increased demand, on system costs. It is shown that, as launch costs are reduced, the assembly costs could become an increasingly important component of the total system costs. 相似文献