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991.
Removal of the mechanical pressure gradient on the soles leads to physiological adaptations that ultimately result in neuromotor degradation during spaceflight. We propose that mechanical stimulation of the soles serves to partially restore the afference associated with bipedal loading and assists in attenuating the negative neuromotor consequences of spaceflight. A dynamic foot stimulus device was used to stimulate the soles in a variety of conditions with different stimulation locations, stimulation patterns and muscle spindle input. Surface electromyography revealed the lateral side of the sole elicited the greatest neuromuscular response in ankle musculature, followed by the medial side, then the heel. These responses were modified by preceding stimulation. Neuromuscular responses were also influenced by the level of muscle spindle input. These results provide important information that can be used to guide the development of a “passive” countermeasure that relies on sole stimulation and can supplement existing exercise protocols during spaceflight. 相似文献
992.
Objective: To evaluate the cardiac, arterial and venous effect of a venotonic drug (Cirkan "Ck") administrated orally daily to 6 subjects in HDT position during 5 days. These subjects underwent a second 5d HDT without Ck treatment one month later. Pre and post HDT the subjects were submitted to a stand test. Method: The cardiovascular parameters were measured by echography and Doppler. Results and discussion: The Cirkan treatment contributed to reduce the increase in cerebral resistance, and to maintain the lower limb resistance at a higher level than on controls. It reduces the vein section at the extremities (Jugular, femoral) and in the central vein system connected to the right heart (sub hepatics). On the other hand it increases the portal vein section which means that the blood stagnation at the splanchnic level is increased. Despite these arterial and venous significant modifications the clinical and ECG and Blood pressure response to the Stand test was similar in both groups. 相似文献
993.
H K Charles T J Beck H S Feldmesser T C Magee T S Spisz V L Pisacane 《Acta Astronautica》2001,49(3-10):447-450
An advanced, multiple projection, dual energy x-ray absorptiometry (AMPDXA) scanner system is under development. The AMPDXA is designed to make precision bone and muscle loss measurements necessary to determine the deleterious effects of microgravity on astronauts as well as develop countermeasures to stem their bone and muscle loss. To date, a full size test system has been developed to verify principles and the results of computer simulations. Results indicate that accurate predictions of bone mechanical properties can be determined from as few as three projections, while more projections are needed for a complete, three-dimensional reconstruction. 相似文献
994.
This paper considers the detection of a sinusoidal or chirp signal imbedded in wideband FM interference (as might be generated by some types of active jamming), such that after pulse compression or other integration, the interference can be approximated by a sum of sinusoids of independent phase. The detection probability in such non-Gaussian noise is compared to that for Gaussian noise, with the Gaussian result approached, as required, in the limit that the number of sinusoids in the sum increases without bound. For detection using a comparison of the envelope with a threshold which yields a given false-alarm probability (CFAR detection), the detection probability is improved over the case of Gaussian noise, so that the usual approach basing the design on Gaussian noise would be conservative. Using a threshold determined from the envelope mean, the FM interference yields a lower false-alarm probability than for Gaussian noise, with detection probability only slightly degraded. 相似文献
995.
P. Groza A. Bordeianu S. Cananu A. Boca A. Petrescu D. Lungu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(14):179-185
Rats on board the Soviet Cosmos 936 satellite for 18 days showed a decreased glycoprotein secretion from the salivary mucous glands, stomach and intestine, and an increased leucine aminopeptidase and acid phosphatase content from the small intestine. Grimelius positive cells were activated. One group of rats were centrifuged at 1 g during the flight to simulate terrestrial gravity. Some investigations have suggested that under these conditions muscular and cardiac disorders diminished. In the digestive tract the benefits of centrifugation at 1 g are minimal and limited to a few glycoprotein components. The digestive changes are probably the expression of a stress response, unrelated to weightlessness. Similar changes, concomitant with a glycocorticoid hypersecretion, were found in rats after 15 days of hypokinesia on Earth. These digestive changes persisted even in adrenalectomized rats. 相似文献
996.
E. Zanrosso J. L. Long A. D. Zych R. S. White 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(13):235-238
Preliminary results are reported for gamma ray observations of the galactic center region made during a 15 hour balloon flight from Alice Springs, Australia on April 18, 1979. The observations were carried out with the UCR double-scatter gamma-ray telescope at energies of 1 to 30 MeV. The observations are compatible with a galactic source of approximately equal brightness along the region 300°<ℓII<60°. The energy distribution joins smoothly to previous spark chamber results at energies above 30 MeV and to scintillator results below 1 MeV. It appears to be a combination of nuclear gamma ray lines superimposed on a bremsstrahlung spectrum with a power law (1.3±.7) × 10−3 E−(1.7±.2). The 12C* line at 4.4 MeV appears to be present with a significance of about 16σ. The flux in the line is (6±3) × 10−4photons cm−2s−1rad−1. The oxygen line at 6.1 MeV does not seem to appear significantly above background. 相似文献
997.
A. Kiraga Z. K
os V. N. Oraevsky S. A. Pulinets V. C. Dokukin E. P. Szuszczewicz 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,15(12):143-146
Based on the dispersion relation of electron plasma, one can expect, that the waves excited in the frequency band (fp, fu=sqrt(fp*fp+fc*fc)) should persist in experimental spectra. For wave data from a spacecraft immersed in a cold plasma such an assumption may be misleading. In measurements performed on board the INTERCOSMOS-19, ACTIVE, APEX satellites and VC36.064CE rocket the most prominent spectral structure is centered around frequency fr fulfilling the relation fcrp and corresponds to resonant detection of Bernstein waves excited in the surrounding plasma by spacecraft systems. Input network mismatch at frequencies around fu significantly depresses natural plasma noise as well as that excited by the spacecraft. Plasma emissions in the band (fp, fu) are prominent if the electromagnetic excitation is preferential (topside sounders) or if the excitation introduces nonequilibrium components into the plasma e.g. particle beams or clouds. Experimental examples are presented and parameters of cold plasma spectra useful for electron density estimation are discussed. The application to other spacecraft-cold plasma configurations is suggested. 相似文献
998.
Gravitational force regulates elongation growth of Arabidopsis hypocotyls by modifying xyloglucan metabolism. 总被引:1,自引:0,他引:1
K Soga K Wakabayashi T Hoson S Kamisaka 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2001,27(5):1011-1016
Growth of dark-grown Arabidopsis hypocotyls was suppressed under hypergravity conditions (300 g), or was stimulated under microgravity conditions in space (Space Shuttle STS-95). The mechanical extensibility of cell walls decreased and increased under hypergravity and microgravity conditions, respectively. The amounts of cell wall polysaccharides (pectin, hemicellulose-I, hemicellulose-II and cellulose) per unit length of hypocotyls increased under hypergravity conditions, and decreased under microgravity conditions. The amount and the molecular mass of xyloglucans also increased under the hypergravity conditions, while those decreased under microgravity conditions. The activity of xyloglucan-degrading enzymes extracted from hypocotyl cell walls decreased and increased under hypergravity and microgravity conditions, respectively. These results indicate that the amount and the molecular mass of xyloglucans are affected by the magnitude of gravity and that such changes are caused by changes in xyloglucan-degrading activity. Modifications of xyloglucan metabolism as well as the thickness of cell walls by gravity stimulus may be the primary event determining the cell wall extensibility, thereby regulating the growth rate of Arabidopsis hypocotyls. 相似文献
999.
R.R. Rosa H.S. Sawant J.A. Valdivia A.S. Sharma 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,20(12):2303-2308
We have analysed, for the first time, the high resolution X-ray images of the solar corona, obtained by the Yohkoh Mission, as non-linear extended systems. To quantify the spatio-temporal complexity in this extended system, we use an asymmetric spatial fragmentation parameter computed from a matrix representing an image. Choosing different spatial scales on the same image, wave numbers are computed from the intensity contours and this yields a fragmentation spectrum. This spectrum is used to analyze the images of a complex transient event obtained by the Soft X-ray Telescope board the Yohkoh satellite. The dynamics of the fine structures of the contours suggests the origin of the observed fragmentation to be localized weak turbulence process occuring in an evolving coronal active region. 相似文献
1000.
Effect of HZE particles and space hadrons on bacteriophages. 总被引:2,自引:0,他引:2
S S Yurov I G Akoev G A Leont'eva 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(8):51-60
The effect of high energy (HZE) particles and high energy hadrons on T4Br+ bacteriophage was analyzed. The experiments were done in orbital flight, on high mountains, on an accelerator, and with an alpha particle source. We studied the survival rate of the bacteriophage, the mutation frequency, the mutation spectrum and the revertability under the action of chemical mutagens with a known mechanism of action on DNA. It was found that the biological efficiency of HZE particles and high energy hadrons is greater than that of gamma radiation. The spectra of mutations produced by these mutations and the mechanisms of their action are also different. These effects were local, because of the mode of interaction of the radiant energy with biological objects, and depended on the linear energy transfer (LET). The modes have now been experimentally defined. 相似文献