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791.
Experiments of prolonged bedrest in antiorthostatic position are conducted in order to simulated cardio-circulatory modifications observed in weightlessness. Until now, no studies of r.C.B.F. have been effected in these conditions. Six young, healthy volunteers (average age 23.8) were placed in strict bedrest and in antiorthostatic position -4 degrees for 7 days. The r.C.B.F. measurements were studied by 133Xe inhalation method using a 32 detectors system. Studies were made first in basal conditions, then between the 6th and 12th hr, and finally between the 72nd and the 78th hr after the beginning of the experiment. Three of the subjects received 0.450 mg of Clonidine daily during the experiment. In the subjects having taken no Clonidine, we observed a constant increase in r.C.B.F. (12, 17 and 16% respectively) in the first 12 hr; at the 72nd hour, all values had returned to basal state. This findings agrees with the well known notion of a rapid correction of hemodynamic disturbances observed in the first days of weightlessness. In the subjects treated with Clonidine, the increase of r.C.B.F. did not occur. Several mechanisms of action are possible; the Clonidine affecting either the heart by inhibiting volemic atrial receptors or the brain by direct vasoconstriction. 相似文献
792.
793.
Many simple radars use fact-risetime pulses, but wide bandwidth does not translate into corresponding high resolution since the spectrum is far from flat. A scheme for enhancing down- and cross-range resolution of multiple targets through a two-step partial equalization of the spectrum is illustrated by detailed computer simulation, with emphasis on the tradeoffs between resolution and signal-to-noise ratios. Three examples are treated: two equal scattering centers, two unequal scattering centers, and compound target 相似文献
794.
Severns J.G. Hobbs R.M. Elliott N.P. Towsley R.H. Conway R.W. Virshup G.F. 《Aerospace and Electronic Systems Magazine, IEEE》1989,4(12):8-12
The LIPS III satellite, which was launched into a 1100-km circular orbit of 60° inclination in the spring of 1987, is discussed. LIPS III is a member of the living-plume-shield class of spacecraft, all of which were built around a simple sheet metal plume deflector. The purpose of LIPS III was to provide a testbed for space power sources. An overview of the LIPS III system is given, and the experiments submitted for it, all but one of which were photovoltaic in nature, are described 相似文献
795.
796.
B. Nebeling K. Roessler G. Schmitz 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1986,6(12):207-210
The redox properties of irradiated liquid and frozen H2O, NH3 and H2O/NH3 mixtures at 298 K and 77 K, resp., towards some simple organic molecules have been checked by injecting carrierfree 11C atoms and analyzing their chemical state by means of radiochromatography. The reactions and the stability of organic products versus radiation dose (in this study by MeV protons) depend on temperature, phase state, mobility of radicals, their concentration and reactivity. Especially dangerous are the reactive OH and O2H radicals which oxidize organic material to inorganic CO2. Highest stability has been found at low temperatures (solid state, reduced mobility of radicals) and for systems containing H-donors (H2O/NH3 mixtures), which reduce the concentration of oxidizing radicals. The fact that many bodies in space consist of H2O-ice with NH3 and CH4 additives at temperatures between 10 and 150 K is promising in view of the survival of organic matter under high doses of radiation. 相似文献
797.
798.
H.A. Taylor H.G. Mayr R.E. Hartle L. Kramer R. Stirling 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(4):41-45
During January–August 1978, the global atmospheric angular momentum (M) exhibits distinct patterns of short term momentum interchange across latitudes. In the northern hemisphere winter-spring season, 30–50 day modulations of M are present in which momentum at mid-latitudes (20–30°) are closely matched by momentum at high latitudes (50–60°). During the same interval there are no corresponding variations in M evident in the southern hemisphere. Conversely, during southern hemisphere fall-winter, similar anticorrelations in monthly scale momentum excursions are evident between mid and high latitudes. In the northern hemisphere, the winter-spring momentum signatures are detected throughout the atmosphere, from the lower troposphere to the stratosphere. During the southern hemisphere fall-winter, the modulation patterns are not evident at the higher altitudes. Structural details of the momentum signatures indicate that the coupling is sometimes effective on very short time scales, e.g. 1–2 days, or less. The evidence of distinct anti-correlation between large regions has interesting implications for studies of global atmospheric circulation, and also for studies of the excitation of variations in earth rotation in response to short term modulations of M. 相似文献
799.
J. Fertig G.H. Schwehm 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(9):213-216
In March 1985 ESA's GIOTTO spacecraft will fly by P/Halley's nucleus at a distance of a few hundred kilometres. The near nucleus dust environment the probe will traverse poses a hazard with respect to physical damage as well as to attitude disturbance with the possible loss of ground station contact. To predict S/C survivability and dust impact rates for the experiments, a model of the spatial distribution of the dust in the nucleus' vicinity is required. In the ‘dynamic’ model, the local spatial dust density is derived from exact expressions for the dust particle dynamic motion. The model has been implemented in a software system which allows for fast simulations of a cometary fly-by. 相似文献
800.
J O Kessler 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(1):33-42
The orientation of a body which has an anisotropic distribution of mass and which is suspended in water is biased by gravitational torque, so that the center of gravity lies below the center of buoyancy. Many species of unicellular swimming algae are gravitationally oriented in this manner. Their axis of propulsion is essentially fixed within their bodies, so that when the cells swim, they swim upwards. Gravitaxis is an exotaxis, which requires no sensory processing. Nevertheless, gravity affects the lives of these cells both individually and collectively. For single cells, gravity intervenes in the execution and mechanism of sense-dependent taxes, such as phototaxis, it provides for fail-safe locomotion toward the upper interface of their habitat, the source of light and air, and it may cause up-accumulation. Populations of single cells, swimming in the presence of gravity, are coupled through fluid-mechanical interactions which cause spatial and temporal patterns of fluid convection and cell concentration. These patterns modify the cell's environmental interactions, by facilitating downward migrations of cell populations, by mixing the embedding fluid and its contents, and by providing a collective mechanism for controlling light intensity at the individual cell level. Summarizing, gravity modulates the interaction of algal cells with each other and with their environment. 相似文献