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941.
942.
943.
U Bork K Gartenbach C Koch A R Kranz 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1986,6(11):149-152
Irradiation of dry seeds of Arabidopsis with heavy ions (HZE-particles) produced by UNILAC-accelerator (GSI, Darmstadt) yielded aberrations in varied developmental endpoints such as survival rate and embryo vitality. The damage increased with particle density and charge. Cross sections in the range of 0.2-1.0 micrometer2 for Ne and Ar and 2.0-10.0 micrometers2 for Xe were estimated. Soaked seeds were more sensitive than dry seeds (cross-section 2.0-10.0 micrometers2 for Ar). The induced total damage in the irradiated seeds was estimated adding the different damages weighted by certain factors. These results will be used as base data for the interpretation and evaluation of spaceflight experiments on the biological effects of cosmic radiation. 相似文献
944.
W K Sinclair 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1986,6(11):335-343
Radiation protection standards for the individual exposed to ionizing radiation in his/her daily work have evolved over more than 50 years since the first recommendations on limits by the NCRP and the ICRP. Initial standards were based on the absence of observable harm, notably skin erythema, but have since been modified as other concerns, such as leukemia and genetic effects, became more important. More recently, the general carcinogenic effect of radiation has become the principal concern at low doses. Genetic effects are also of concern in the younger individual. Modern radiation protection practices take both of these risks into account. Quantification of these risks improves as new information emerges. The study of the Japanese survivors of the atomic bombs continues to yield new information and the recent revisions in the dosimetry are about to be completed. The special circumstances of space travel suggest approaches to limits not unlike those for radiation workers on the ground. One approach is to derive a career limit based on the risks of accident faced by many nonradiation workers in a lifetime. The career limit can be apportioned according to the type of mission. The NCRP is considering this and other approaches to the specification of radiation standards in space. 相似文献
945.
Importance sampling is a technique which can significantly reduce the number of Monte Carlos necessary to accurately estimate the probability of low-probability of occurrence events (e.g., the probability of false alarm PF associated with a given detection scheme). A new technique called the Chernoff Importance Sampling Method is introduced. It is shown that the number of required Monte Carlos can be reduced by a factor of a Chernoff-like bound on P F. In addition, techniques for choosing the multiplying factor of the distorted variance method (the most common method used in importance sampling) are presented 相似文献
946.
K. -I. Nishikawa S. Ohtani 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(12):2675-2681
This paper reports the spatial and temporal development of bursty bulk flows (BBFs) created by reconnection as well as current disruptions (CDs) in the near-Earth tail using our 3-D global electromagnetic (EM) particle simulation with a southward turning interplanetary magnetic field (IMF) in the context of the substorm onset. Recently, observations show that BBFs are often accompanied by current disruptions for triggering substorms. We have examined the dynamics of BBFs and CDs in order to understand the timing and triggering mechanism of substorms. As the solar wind with the southward IMF advances over the Earth, the near-Earth tail thins and the sheet current intensifies. Before the peak of the current density becomes maximum, reconnection takes place, which ejects particles from the reconnection region. Because of earthward flows the peak of the current density moves toward Earth. The characteristics of the earthward flows depend on the ions and electrons. Electrons flow back into the inflow region (the center of reconnection region), which provides current closure. Therefore the structure of electron flows near the reconnection region is rather complicated. In contrast, the ion earthward flows are generated far from the reconnection region. These earthward flows pile up near the Earth. The ions mainly drift toward the duskside. The electrons are diverted toward the dawnside. Due to the pile-up, dawnward current is generated near Earth. This dawnward current dissipates rapidly with the sheet current because of the opposite current direction, which coincides with the dipolarization in the near-Earth tail. At this time the wedge current may be created in our simulation model. This simulation study shows the sequence of the substorm dynamics in the near-Earth tail, which is similar to the features obtained by multisatellite observations. Identification of the timing and mechanism of triggering substorm onset requires further studies in conjunction with observations. 相似文献
947.
Influence of clinorotation and fettering stress on tail regeneration of Triturus vulgaris (Urodela).
H J Anton E N Grigoryan K Krupp-Beyerlein H Pitzer V I Mitashov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,21(8-9):1159-1162
Tail-amputated adult Triturus vulgaris, fettered in cuvettes of a fast-rotating clinostat were exposed to simulated weightlessness (60 rpm; equiv. to 10(-3)-10(-4) g), during a 14-day period. To feed and clean the animals rotation was stopped once a day for approx. 10 min. To test the influence of the fettering stress, a second series of animals was kept separately under normal earth conditions without rotation. A further control series was kept in a dark container without any handicap. While tail regeneration of the rotated animals was markedly accelerated, the fettered-only animals showed a considerably less marked acceleration effect. At the end of the 14-day period, all regenerates were reamputated together with an additional 5 mm of the tail stump. Although this second level of amputation was distant from the first, the regenerative growth rate of the rotated series was accelerated 123% in contrast to both the control and the fettered-only series. Our results demonstrate that the growth acceleration is induced by clinorotation. Fettering stress has no comparable influence. The growth promoting effect is not limited to the regenerating area. 相似文献
948.
K. Clausen H. Sainct 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(12):189-195
The mission of the Huygens Probe is to enter into the Titan atmosphere and to descend in a controlled manner to the surface such that scientific measurements can be taken and transmitted to earth via the Orbiter. The entry is the most challenging phase of the mission. The deceleration is achieved by an aeroshell. Thermal protection against entry heat fluxes is achieved by an ablator rejecting heat mainly by radiation. The descent profile in terms of descent velocity, spin rate and attitude stability is designed to allow imaging, sampling and measurements at the various atmospheric layers within the overall time and energy constraints. The Huygens system has to operate in an autonomous and fault tolerant manner, as no ground control and failure recovery during the descent phase is feasible. This autonomy and fault tolerance is the main driver for the chosen architecture of the on-board system. 相似文献
949.
J. M. Cassanto H. I. Ziserman D. K. Chapman Z. R. Korszun P. Todd 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1988,8(12):141-146
Microgravity experiments designed for execution in Get-Away Special canisters, Hitchhiker modules, and Reusable Re-entry Satellites will be subjected to launch and re-entry accelerations. Crew-dependent provisions for preventing acceleration damage to equipment or products will not be available for these payloads during flight; therefore, the effects of launch and re-entry accelerations on all aspects of such payloads must be evaluated prior to flight. A procedure was developed for conveniently simulating the launch and re-entry acceleration profiles of the Space Shuttle (3.3 and 1.7 × g maximum, respectively) and of two versions of NASA's proposed materials research Re-usable Re-entry Satellite (8 × g maximum in one case and 4 × g in the other). By using the 7 m centrifuge of the Gravitational Plant Physiology Laboratory in Philadelphia it was found possible to simulate the time dependence of these 5 different acceleration episodes for payload masses up to 59 kg. A commercial low-cost payload device, the “Materials Dispersion Apparatus” of Instrumentation Technology Associates was tested for (1) integrity of mechanical function, (2) retention of fluid in its compartments, and (3) integrity of products under simulated re-entry g-loads. In particular, the sharp rise from 1 g to maximum g-loading that occurs during re-entry in various unmanned vehicles was successfully simulated, conditions were established for reliable functioning of the MDA, and crystals of 5 proteins suspended in compartments filled with mother liquor were subjected to this acceleration load. 相似文献
950.
Sofya A. Ushakova Alexander A. Tikhomirov Valentin N. Shikhov Jean-Bernard Gros Tamara K. Golovko Igor V. Dal’ke Ilya G. Zakhozhii 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
The main objective of a life support system for space missions is to supply a crew with food, water and oxygen, and to eliminate their wastes. The ultimate goal is to achieve the highest degree of closure of the system using controlled processes offering a high level of reliability and flexibility. Enhancement of closure of a biological life support system (BLSS) that includes plants relies on increased regeneration of plant waste, and utilization of solid and liquid human wastes. Clearly, the robustness of a BLSS subjected to stress will be substantially determined by the robustness of the plant components of the phototrophic unit. The aim of the present work was to estimate the heat resistance of two plants (wheat and lettuce) grown on human wastes. Human exometabolites mineralized by hydrogen peroxide in an electromagnetic field were used to make a nutrient solution for the plants. We looked for a possible increase in the heat tolerance of the wheat plants using changes in photosynthetically active radiation (PAR) intensity during heat stress. At age 15 days, plants were subjected to a rise in air temperature (from 23 ± 1 °C to 44 ± 1 °С) under different PAR intensities for 4 h. The status of the photosynthetic apparatus of the plants was assessed by external СО2 gas exchange and fluorescence measurements. The increased irradiance of the plants during the high temperature period demonstrated its protective action for both the photosynthetic apparatus of the leaves and subsequent plant growth and development. The productivity of the plants subjected to temperature changes at 250 W m−2 of PAR did not differ from that of controls, whereas the productivity of the plants subjected to the same heat stress but in darkness was halved. 相似文献