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771.
Purpose of the work is to analyze and to summarize the data of investigations into human hemodynamics performed over 20 years aboard orbital stations Salyut-7 and Mir with participation of 26 cosmonauts on space flights (SF) from 8 to 438 days in duration. The ultrasonic techniques and occlusive plethysmography demonstrated dynamics of changes in the cardiovascular system during SF of various durations. The parameters of general hemodynamics, the pumping function of the heart and arterial circulation in the brain remained stable in all the space flights; however, there were alterations in peripheral circulation associated with blood redistribution and hypovolemie in microgravity. The anti-gravity distribution of the vascular tone decayed gradually as unneeded. The most considerable changes were observed in leg vessels, equally in arteries (decrease in resistance) and veins (increase in maximum capacity). The lower body negative pressure test (LBNP) revealed deterioration of the gravity-dependent reactions that changed for the worse as SF duration extended. The cardiovascular deconditioning showed itself as loss of descent acceleration tolerance and orthostatic instability in the postflight period. 相似文献
772.
Gustavo A. Mansilla 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
This paper reports the global response of the mid high and low latitude ionosphere in four longitudinal sectors to two moderate geomagnetic storms that occurred during 2007 (the more intense storms occurred that year). The results obtained during these storms show that the ionospheric effects in general are not moderate in magnitude, showing an important degree of complexity as during intense storms. The outstanding features produced during the storms are significant positive storm effects at mid-high latitudes during the main phase/first part of the recovery, positive effects after the onset of the storm followed by negatives effects at middle latitudes and delayed positive effects during the night-time hours in the trough of the equatorial anomaly (“dusk” effect). Possible physical mechanisms for controlling the morphology of the ionosphere during these events are considered. 相似文献
773.
Nicole D. Buckley Claude P. Champagne Adriana I. Masotti Lisa E. Wagar Thomas A. Tompkins Julia M. Green-Johnson 《Acta Astronautica》2011,68(7-8):731-738
Astronauts face numerous health challenges during long-duration space missions, including diminished immunity, bone loss and increased risk of radiation-induced carcinogenesis. Changes in the intestinal flora of astronauts may contribute to these problems. Soy-based fermented food products could provide a nutritional strategy to help alleviate these challenges by incorporating beneficial lactic acid bacteria, while reaping the benefits of soy isoflavones. We carried out strain selection for the development of soy ferments, selecting strains of lactic acid bacteria showing the most effective growth and fermentation ability in soy milk (Streptococcus thermophilus ST5, Bifidobacterium longum R0175 and Lactobacillus helveticus R0052). Immunomodulatory bioactivity of selected ferments was assessed using an in vitro challenge system with human intestinal epithelial and macrophage cell lines, and selected ferments show the ability to down-regulate production of the pro-inflammatory cytokine interleukin-8 following challenge with tumour necrosis factor-alpha. The impact of fermentation on vitamin B1 and B6 levels and on isoflavone biotransformation to agluconic forms was also assessed, with strain variation-dependent biotransformation ability detected. Overall this suggests that probiotic bacteria can be successfully utilized to develop soy-based fermented products targeted against health problems associated with long-term space travel. 相似文献
774.
775.
Previous attempts to identify aircraft stability and control derivatives from flight test data, using three-degrees-of-freedom (3-DOF) longitudinal or lateral-directional perturbation equation-of-motion models, suffer from the disadvantage that the coupling between the longitudinal and lateral-directional dynamics has been ignored. In this paper, the identification of aircraft stability parameters is accomplished using a more accurate 6-DOF model which includes this coupling. Hierarchical system identification theory is used to reduce the computational effort involved. The 6-DOF system of equations is first decomposed into two 3-DOF subsystems, one for the longitudinal dynamics and the other for the lateral-directional dynamics. The two subsystem parameter identification processes are then coordinated in such a way that the overall system parameter identification problem is solved. Next, a six-subsystem decomposition is considered. Computational considerations and comparison with the unhierarchically structured problem are presented. 相似文献
776.
We consider the problem of a spacecraft subjected to constant body-fixed forces and moments about all three axes during a spinning-up, thrusting maneuver. In applications, undesired forces and moments can arise due to thruster imbalances and misalignments and to center-of-mass offset. In previous works, approximate analytical solutions have been found for the attitude motion, and for the change in inertial velocity and inertial position. In this paper we find asymptotic and limiting-case expressions which we derive from the analytic solutions, in order to obtain simplified, practical formulas that lend insight into the motion. Specifically, we investigate how the motion evolves (1) as time grows without bound and (2) for geometric cases of the sphere, the thin rod, and the thin plate. Closed-forms or upper-bound limits are provided for angular velocities, Eulerian angles, angular momentum pointing error, transverse and axial velocities, and transverse and axial displacements. Summaries for the asymptotic limits (for zero initial conditions) are provided in tabular form. Results are verified by numerical simulations. 相似文献
777.
Shtessel Yuri B. Shkolnikov Ilya A. Levant Arie 《IEEE transactions on aerospace and electronic systems》2009,45(1):110-124
A new smooth second-order sliding mode control (SSOSM) is proposed and proved for a system driven by uncertain sufficiently smooth disturbances. The main target application of this technique, the missile interceptor guidance-control system against targets performing evasive maneuvers, is considered to demonstrate benefits of this design for a two-loop integration of guidance and flight control systems. The designed guidance-control system performance is verified via computer simulations using a miniature hypervelocity kinetic energy endo-atmospheric interceptor planar model. 相似文献
778.
Compact antennas for UWB applications 总被引:1,自引:0,他引:1
Taeyoung Yang Seong-Youp Suh Nealy R. Davis W.A. Stutzman W.L. 《Aerospace and Electronic Systems Magazine, IEEE》2004,19(5):16-20
A report on an investigation of spherical, disc, and half-disc antennas in the frequency and time domains with the objective of developing small planar versions of the antennas. These antennas have an omni-directional impulse response in azimuth and pulse duration of 0.5-0.65 nanoseconds. In addition, the measured data show a reasonable peak received signal in a pulse communication link using two identical antennas. 相似文献
779.
J.L. Hall D. Fairbrother T. Frederickson V.V. Kerzhanovich M. Said C. Sandy J. Ware C. Willey A.H. Yavrouian 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
This paper describes the design, fabrication and testing of a full scale prototype balloon intended for long duration flight in the upper atmosphere of Venus. The balloon is 5.5 m in diameter and is designed to carry a 45 kg payload at an altitude of 55 km. The balloon material is a 180 g/m2 multi-component laminate comprised of the following layers bonded together from outside to inside: aluminized Teflon film, aluminized Mylar film, Vectran fabric and a polyurethane coating. This construction provides the required balloon functional characteristics of low gas permeability, sulfuric acid resistance and high strength for superpressure operation. The design burst superpressure is 39,200 Pa which is predicted to be 3.3 times the worst case value expected during flight at the highest solar irradiance in the mission profile. The prototype is constructed from 16 gores with bi-taped seams employing a sulfuric acid resistant adhesive on the outside. Material coupon tests were performed to evaluate the optical and mechanical characteristics of the laminate. These were followed by full prototype tests for inflation, leakage and sulfuric acid tolerance. The results confirmed the suitability of this balloon design for use at Venus in a long duration mission. The various data are presented and the implications for mission design and operation are discussed. 相似文献
780.
Howard G. Levine A.D. Krikorian 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
We present results on the analysis of 100 mL medium samples extracted from sterilized foam (Smithers-Oasis, Kent OH) used to support the growth of a representative dicotyledon (Haplopappus gracilis) and a representative monocotyledon (Hemerocallis cv Autumn Blaze) in NASA’s Plant Growth Unit (PGU) during a 5-day Space Shuttle flight and ground experiments. At recovery, the media remaining within replicate (n = 5) foam blocks (for both the spaceflight and ground experiments) were extracted under vacuum, filtered and subjected to elemental analyses. A unique aspect of this experiment was that all plants were either aseptically-generated tissue culture propagated plantlets or aseptic seedling clones. The design of the PGU facilitated the maintenance of asepsis throughout the mission (confirmed by post-flight microbial sampling) and thus any possible impact of microorganisms on medium composition was eliminated. Concentration levels of some elements remained the same, while some decreased and others increased. There was a significant two-fold difference between the final concentrations of potassium when the Earth-based and microgravity experiments were contrasted. 相似文献