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941.
Prolonged exposure to microgravity in space flight missions (days) impairs the mechanisms responsible for defense of arterial blood pressure (ABP) and cardiac output (CO) against orthostatic stress in the post-flight period. The mechanisms responsible for the observed orthostatic intolerance are not yet completely understood. Additionally, effective counter measures to attenuate this pathophysiological response are not available. The aim of this study was to investigate the ability of our proposed system identification method to predict closed-loop dynamic changes in TPR induced by changes in mean arterial pressure (MAP) and right atrial pressure (RAP). For this purpose we designed and employed a novel experimental animal model for the examination of arterial and cardiopulmonary baroreceptors in the dynamic closed-loop control of total peripheral resistance (TPR), and applied system identification to the analysis of beat-to-beat fluctuations in the measured signals. Grant numbers: NAG5-4989. 相似文献
942.
943.
M Kliss C Blackwell A Zografos M Drews R MacElroy R McKenna A G Heyenga 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,31(1):263-270
As part of the NASA Advanced Life Support Flight Program, a Controlled Ecological Life Support System (CELSS) Test Facility Engineering Development Unit has been constructed and is undergoing initial operational testing at NASA Ames Research Center. The Engineering Development Unit (EDU) is a tightly closed, stringently controlled, ground-based testbed which provides a broad range of environmental conditions under which a variety of CELSS higher plant crops can be grown. Although the EDU was developed primarily to provide near-term engineering data and a realistic determination of the subsystem and system requirements necessary for the fabrication of a comparable flight unit, the EDU has also provided a means to evaluate plant crop productivity and physiology under controlled conditions. This paper describes the initial closed operational testing of the EDU, with emphasis on the hardware performance capabilities. Measured performance data during a 28-day closed operation period are compared with the specified functional requirements, and an example of inferring crop growth parameters from the test data is presented. Plans for future science and technology testing are also discussed. 相似文献
944.
Steven R. Cranmer 《Space Science Reviews》2002,101(3-4):229-294
Coronal holes are the lowest density plasma components of the Sun's outer atmosphere, and are associated with rapidly expanding magnetic fields and the acceleration of the high-speed solar wind. Spectroscopic and polarimetric observations of the extended corona, coupled with interplanetary particle and radio sounding measurements going back several decades, have put strong constraints on possible explanations for how the plasma in coronal holes receives its extreme kinetic properties. The Ultraviolet Coronagraph Spectrometer (UVCS) aboard the Solar and Heliospheric Observatory (SOHO) spacecraft has revealed surprisingly large temperatures, outflow speeds, and velocity distribution anisotropies for positive ions in coronal holes. We review recent observations, modeling techniques, and proposed heating and acceleration processes for protons, electrons, and heavy ions. We emphasize that an understanding of the acceleration region of the wind (in the nearly collisionless extended corona) is indispensable for building a complete picture of the physics of coronal holes. 相似文献
945.
L Y Popova T I Lobova T Y Krylova T V Kargatova E E Maksimova A N Boyandin N S Pechurkin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2001,27(9):1571-1579
The role of key environmental factors in adaptation of spore-forming and non-spore-forming transgenic microorganisms (TM) have been studied in model ecosystems. Model TM Escherichia coli Z905 (bearing plasmid genes of bacterial luminescence Ap (r) Lux+) has been found to have a higher adaptation potential than TM Bacillus subtilis 2335/105 (bearing genes of human alpha 2-interferon Km (r) Inf+), planned for employment as a living vaccine under varying environmental conditions. Effects of abiotic factors on migration of natural and recombinant plasmids between microorganisms under model ecosystem conditions has been estimated. The transgenic microorganisms with low copy number survived better under introduction conditions in the microcosms studied. This trend has been shown to be independent of the microcosm type and its complexity. Grant numbers: 99-04-96017, 25, 00-07-9011. 相似文献
946.
This is a brief overview on what we know and do not know about the low-latitude boundary layer (LLBL) at the flanks of the magnetotail. On the basis of recent observations, simulations and theories we conclude that reconnection is the dominant process in generating the LLBL and its structure probably even under northward IMF conditions. Part of the LLBL always seems to be on open field lines. Possibly the LLBL possesses a double structure with its outer part open and inner part closed. Anomalous diffusive processes cannot sustain the LLBL but provide sufficient diffusivity for reconnection. Strong diffusion is only expected in narrow localized regions and can make the transition to superdiffusion. Kelvin-Helmholtz instability (KHI) is favoured for northward IMF, producing vortices at the tail flanks. Its contribution to efficient mass transport still remains questionable. Coupling of the LLBL to the ionosphere can strongly affect the internal structure of the LLBL, causing turbulent eddies and detachments of plasma blobs as also field-aligned currents and electron heating. The structure and dynamics of the LLBL are affected by field-aligned electric potentials that decouple the LLBL from the ionosphere. Non-ideal coupling simulations suggest that the dusk flank is decoupled, favouring KHI, while the dawn flank is dominated by currents and turbulence. 相似文献
947.
A ceramic material having a large dielectric constant at 77 K, ε=8000-12000, has been developed for capacitive energy storage at this temperature. A large matrix of multilayer ceramic capacitors were fabricated using conventional tape-casting methods to optimize the dielectric breakdown strength at 77 K, and measured energy storage values on these capacitors range up to 6 J/cm3 at 77 K. An unfused bank of these capacitors was voltage-cycled 105 times at 77 K without failure, and the heating effects during cycling were immeasurably small (i.e., nitrogen boiloff was monitored). An electrocaloric effect on discharge (ΔT~1 K) contributes to the thermal stability. Measurements of the frequency dependence of the dielectric properties of the ceramic at 77 K indicate a fundamental limit of about 8 μs for the switching repetition rate. Improved capacitor-manufacturing methods are discussed which can increase the energy density to the 20-30 J/cm3 range 相似文献
948.
Reed I.S. Gagliardi R.M. Stotts L.B. 《IEEE transactions on aerospace and electronic systems》1990,26(3):434-440
A recursive track-before-detect algorithm, producing potentially large signal-to-noise ratio (SNR) gains under realizable conditions, is described. The basic relation has the form of a linear, constant-coefficient difference equation with a unity magnitude damping factor. Known as recursive moving-target-indication (RMTI), this procedure adapts easily to digital processing and achieves SNR gains comparable to those from other robust track-before-detect algorithms. Examples are given to demonstrate the performance of the moving target indicator (MTI) procedure 相似文献
949.
The practical implementation of adaptive Doppler filters requires estimates of clutter parameters to determine the adaptive weights. A method of deriving the estimate via the sample matrix inversion (SMI) algorithm using multiple data snapshots from adjacent range cells is presented. For homogeneous clutter environments, the results of this technique asymptotically approach the optimum (a priori known covariance matrix) as the number of snapshots approaches infinity; this asymptotic behavior does not occur for heterogeneous clutter environments. An equation for the decrease in improvement factor is derived. To promote understanding, the simplified special case of narrowband clutter is considered in detail. In almost all cases, the loss is small 相似文献
950.
Two methods for constructing robust polarimetric constant-false-alarm-rate (CFAR) detectors that use elements of the scattering matrix are discussed. Both methods use robust estimators to recognize outliers and exclude them from further calculations. The first method weighs each sample of the surrounding vectors, and vectors that appear to be outliers are weighted with lower values than the others. The second method uses cluster algorithms to arrange the data in different clusters; some clusters contain the outliers, and others contain observations assumed to come from the main body of the data. The detectors are intended to be used in multitarget and nonhomogeneous-clutter environments 相似文献