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901.
J T Lett A B Cox A C Lee 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1986,6(11):295-303
Aspects of experiments on radiation-induced lenticular opacification during the life spans of two animal models, the New Zealand white rabbit and the rhesus monkey, are compared and contrasted with published results from a life span study of another animal model, the beagle dog, and the most recent data from the ongoing study of the survivors from radiation exposure at Hiroshima and Nagasaki. An important connection among the three animal studies is that all the measurements of cataract indices were made by one of the authors (A.C.L.), so variation form personal subjectivity was reduced to a minimum. The primary objective of the rabbit experiments (radiations involved: 56Fe, 40Ar and 20Ne ions and 60Co gamma photons) is an evaluation of hazards to astronauts from galactic particulate radiations. An analogous evaluation of hazards from solar flares during space flight is being made with monkeys exposed to 32, 55, 138 and 400 MeV protons. Conclusions are drawn about the proper use of animal models to simulate radiation responses in man and the levels of radiation-induced lenticular opacification that pose risks to man in space. 相似文献
902.
903.
Q-Flex quartz flexure suspension technology has evolved to produce a world class accelerometer with thousands of units delivered in 1991. The Sundstrand Model QA3000 Q-Flex design achieves a new level of inertial grade performance while maintaining a competitive market price. The specification for the QA3000, supported by actual performance data, depicts performance characteristics superior in both bias and scale factor. Long term measurements display bias and scale factor repeatability obtained across temperature over a period of three years. These data exhibit improved thermal behavior with reduced errors. Reaction time and radiation data highlight the performance of the hybrid position detector circuit 相似文献
904.
The commercialization status of Stirling machines varies from established niche market products to potential products that are in early stages of development. In other words, we are talking about a typical emerging technology. Many organizations are actively pursuing product development based on Stirling machine technology. Stirling machines offer significant performance advantages, but many obstacles remain to be fully resolved, including cost and demonstrated reliability. This article describes the technology upon which Stirling machines are based. Several application areas are then explored, including hot air engines, remote power, solar thermal power, sensor cooling, refrigeration, cogeneration and air-independent propulsion 相似文献
905.
Wei Huang Zhen-guo Wang Mohamed Pourkashanian Lin Ma Derek B. Ingham Shi-bin Luo Jing Lei Jun Liu 《Acta Astronautica》2011,68(11-12):1669-1675
The scramjet isolator, which is used to prevent the hypersonic inlet from disturbances that arise from the pressure rise in the scramjet combustor due to the intense turbulent combustion, is one of the most critical components in hypersonic airbreathing propulsion systems. Any engineering error that is possible in the design and manufacturing procedure of the experimental model, and the intense heat release in the scramjet combustor, may cause the performance of the isolator to decrease, leading to its lack of capability in supporting the back pressure. The coupled implicit Reynolds Averaged Navier–Stokes (RANS) equations and the two-equation standard k?ε turbulent model have been employed to numerically simulate the flow fields in a three-dimensional scramjet isolator. The effects of the divergent angle and the back pressure on the shock wave transition and the location of the leading edge of the shock wave train have been estimated and discussed. The obtained results show that the present numerical results are in very good agreement with the available experimental shadow-pictures, and the numerical method is more suitable for capturing the shock wave train and predicting the location of the leading edge of the shock wave train in the scramjet isolator than the present two-dimensional numerical methods. This is due to the small width-to-height ratio of the isolator and the intense three-dimensional flow structures. On increasing the divergent angle of the scramjet isolator, the static pressure along the central symmetrical line of the isolator decreases sharply. This is due to the strong expansion wave generated at the entrance of the isolator, and when the divergent angle of the isolator is sufficiently large, namely 1.5°, a zone of negative pressure is formed just ahead of the leading edge of the shock wave train. At the same time, the shock wave train varies from being oblique to being normal, and then back to oblique. With an increase in the prescribed back pressure at the exit of the scramjet isolator, the leading edge of the shock wave train moves forward towards the entrance of the isolator, and when the back pressure is sufficiently large, unstart conditions in the hypersonic inlet can take place if the shock train reaches the inlet. 相似文献
906.
The actual topic of optimization of multi-orbit low-thrust spacecraft inter-orbital transfers is considered. We have developed
an original approach to solving this problem, and it is described. 相似文献
907.
Armin Heinze Kerstin Eckert Marcus J.B. Hauser Stefan Odenbach 《Acta Astronautica》2011,68(7-8):707-716
We present a hybrid algorithm to analyse complex interferograms with significant fringe deformations without an a-priori given zero-phase image containing the optical aberration of the instrument. Situations of this type frequently appear in fluid physics experiments using lateral shearing interferometers. The algorithm proposed employs a wavelet transformation in parallel with an approximation of the phase field directly after the experimental container is filled applying Zernike polynomials. As a result the aberrations of the interferometer can be described by a few coefficients. The subtraction of these phase aberrations can be traced back to a complex multiplication in the wavelet space which strongly reduces the effort of the phase unwrapping using the Goldstein algorithm. We explain the performance of the algorithm, which is not restricted to a particular interferometer type, by applying it to interferograms captured during a recent microgravity experiment. 相似文献
908.
V D Kern A Rehm B Hock 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,21(8-9):1173-1178
Gravitropic bending of the winter mushroom Flammulina velutipes is achieved by differential growth of the apical part of the stem, the transition zone. Ultrastructural analysis revealed that bending is due to the relaxation of tissue tensions at the lower flank of the stem where hyphal extension growth is promoted in contrast to the upper flank. Extension of lower flank hyphae is preceded by a conspicuous accumulation of microvesicles in the cytosol and their subsequent fusion with the vacuolar compartment, leading to a large volume increase. The hypothesis is put forward that all hyphae in the transition zone are capable of gravisensing. It is derived from experiments with transition zone segments, which exhibit negative gravitropic response independent from their origin within the stem. A model is presented which connects individual gravisensing of the hyphae with a cooperative response within the stem or small segments of the stem. An essential step is the transmission of positional information, by each hypha with respect to the gravitational vector, to the surroundings. The existence of a soluble growth regulator, which is enriched at the lower flank of the stem, is discussed. A gradient could be formed which precedes the gradient of microvesicle formation, and thereby determines the change of growth direction. 相似文献
909.
B.R. Dennis A. Veronig R.A. Schwartz L. Sui A.K. Tolbert D.M. Zarro RHESSI Team 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,32(12):2459-2464
It is believed that a large fraction of the total energy released in a solar flare goes initially into acceleratedelectrons. These electrons generate the observed hard X-ray bremsstrahlung as they lose most of their energy by coulomb collisions in the lower corona and chromosphere. Results from the Solar Maximum Mission showed that there may be even more energy in accelerated electrons with energies above 25 keV than in the soft X-ray emitting thermal plasma. If this is the case, it is difficult to understand why the Neupert Effect — the empirical result that for many flares the time integral of the hard X-ray emission closely matches the temporal variation of the soft X-ray emission — is not more clearly observed in many flares. From recent studies, it appears that the fraction of the released energy going into accelerated electrons is lower, on average, for smaller flares than for larger flares. Also, from relative timing differences, about 25% of all flares are inconsistent with the Neupert Effect. The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is uniquely capable of investigating the Neupert Effec since it covers soft X-rays down to 3 keV (when both attenuators are out of the field of view) and hard X-rays with keV energy resolution, arcsecond-class angular resolution, and sub-second time resolution. When combined with the anticipated observations from the Soft X-ray Imager on the next GOES satellite, these observations will provide us with the ability to track the Neupert Effect in space and time and learn more about the relation between plasma heating and particle acceleration. The early results from RHESSI show that the electron spectrum extends down to as low as 10 keV in many flares, thus increasing the total energy estimates of the accelerated electrons by an order of magnitude or more compared with the SMM values. This combined with the possible effects of filling factors smaller than unity for the soft X-ray plasma suggest that there is significantly more energy in nonthermal electrons than in the soft X-ray emitting plasma in many flares. 相似文献
910.
G Horneck R Facius M Reichert P Rettberg W Seboldt D Manzey B Comet A Maillet H Preiss L Schauer C G Dussap L Poughon A Belyavin G Reitz C Baumstark-Khan R Gerzer 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,31(11):2389-2401
The European Space Agency has recently initiated a study of the human responses, limits and needs with regard to the stress environments of interplanetary and planetary missions. Emphasis has been laid on human health and performance care as well as advanced life support developments including bioregenerative life support systems and environmental monitoring. The overall study goals were as follows: (i) to define reference scenarios for a European participation in human exploration and to estimate their influence on the life sciences and life support requirements; (ii) for selected mission scenarios, to critically assess the limiting factors for human health, wellbeing, and performance and to recommend relevant countermeasures; (iii) for selected mission scenarios, to critically assess the potential of advanced life support developments and to propose a European strategy including terrestrial applications; (iv) to critically assess the feasibility of existing facilities and technologies on ground and in space as testbeds in preparation for human exploratory missions and to develop a test plan for ground and space campaigns; (v) to develop a roadmap for a future European strategy towards human exploratory missions, including preparatory activities and terrestrial applications and benefits. This paper covers the part of the HUMEX study dealing with lunar missions. A lunar base at the south pole where long-time sunlight and potential water ice deposits could be assumed was selected as the Moon reference scenario. The impact on human health, performance and well being has been investigated from the view point of the effects of microgravity (during space travel), reduced gravity (on the Moon) and abrupt gravity changes (during launch and landing), of the effects of cosmic radiation including solar particle events, of psychological issues as well as general health care. Countermeasures as well as necessary research using ground-based test beds and/or the International Space Station have been defined. Likewise advanced life support systems with a high degree of autonomy and regenerative capacity and synergy effects were considered where bioregenerative life support systems and biodiagnostic systems become essential. Finally, a European strategy leading to a potential European participation in future human exploratory missions has been recommended. 相似文献