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781.
    
For pt. I see ibid., vol. 37, no. 4, pp. 1194-1206 (2001).This paper presents the derivation of a polarimetric coherent adaptive scheme to detect a radar target against a non-Gaussian background. This completes the results presented in Part I for the Gaussian background. A Texture Free-Generalized Likelihood Ratio Test (TF-GLRT) detector is derived that exploits the polarimetric characteristics of the received radar echoes to improve the detection performance. The proposed polarimetric detector is shown to have Constant False Alarm Rate (CFAR) when operating against compound-Gaussian clutter with unknown parameters. Its performance is fully characterized by both theoretical analysis and simulation. Moreover, the application to recorded radar data demonstrates the performance improvement achievable in practice  相似文献   
782.
    
On January 20, 2005 there was an X 7.1 solar flare at 0636 UT with an accompanied halo coronal mass ejection (CME). The resultant interplanetary shock impacted earth ∼36 h later. Near earth, the Advanced Composition Explorer (ACE) spacecraft observed two impulses with a staircase structure in density and pressure. The estimated earth-arrival times of these impulses were 1713 UT and 1845 UT on January 21, 2005. Three MINIature Spectrometer (MINIS) balloons were aloft on January 21st; one in the northern polar stratosphere and two in the southern polar stratosphere. MeV relativistic electron precipitation (REP) observed by all three balloons is coincident (<3 min) with the impulse arrivals and magnetospheric compression observed by both GOES 10 and 12. Balloon electric field data from the southern hemisphere show no signs of the impulse electric field directly reaching the ionosphere. Enhancement of the balloon-observed convection electric field by as much as 40 mV/m in less than 20 min during this time period is consistent with typical substorm growth. Precipitation-induced ionospheric conductivity enhancements are suggested to be (a) the result of both shock arrival and substorm activity and (b) the cause of rapid (<6 min) decreases in the observed electric field (by as much as 40 mV/m). There is poor agreement between peak cross polar cap potential in the northern hemisphere calculated from Super Dual Auroral Radar Network (SuperDARN) echoes and horizontal electric field at the MINIS balloon locations in the southern hemisphere. Possible reasons for this poor agreement include (a) a true lack of north–south conjugacy between measurement sites, (b) an invalid comparison between global (SuperDARN radar) and local (MINIS balloon) measurements and/or (c) radar absorption resulting from precipitation-induced D-region ionosphere density enhancements.  相似文献   
783.
  总被引:1,自引:0,他引:1  
A typical ecosystem is composed of three compartments: photosynthetic producer (anabolizing processes), consumer and decomposer (catabolizing processes). It is still far too much complex, however, to form the basis on which establishing an engineered artificial ecosystem, dedicated to support life (of the consumer) in space. A simpler, two compartments, pilot model to start with has been selected. It is based on a symbiotic Chlorella (strain 241.80), which can be tuned, at low pH, to produce maltose. This feature prevents the accumulation of useless biomass, not readily edible by the consumer. Being excreted, maltose is easily recoverable, and constitutes a direct source of carbon suitable for many consumers. Since they will totally catabolize it back to CO2, the necessity for a decomposer compartment is avoided. The present status of the technological concept designed to support life of small consumers (animals, microorganisms) will be presented, taking into account the space compatibility of the technologies developed.  相似文献   
784.
Heavy ions are a hazard in manned deep space missions. It has been theoretically postulated that when they interact with cells, localized damage in the forms of \"microlesions\" may occur. Purported morphological evidence of these lesions, however, has not been confirmed in the most extensively studied tissue so far, the cornea. Recent morphological evidence from rat corneas demonstrated that holes in membranes do not form as consequence of heavy ion irradiation. This does not mean, however, that some other form of damage is excluded. For example such damage may be physiological in nature, impairing the ability of cells or tissues to function properly. In order to uncover any physiological effects, we investigated the microlesion question by monitoring the electrical potential difference across the endothelium of rat corneas in vitro before, during, and after irradiation. When the corneas were exposed to 1 Gy of 56Fe ions (450 and 600 MeV/a.m.u.), we detected no effect on this parameter. These results suggest that direct physical damage to cell membranes, as predicted by the microlesion theory, does not take place.  相似文献   
785.
    
We present NeV/MgV and MgVII/SiVII theoretical line intensity ratios as a function of electron density and temperature for physical conditions within the solar chromosphere-corona transition region. The electron pressure within the emission regions has been assumed to be a constant parameter. These line intensity ratios in addition could be useful for estimating relative element abundances Ne/Mg and Mg/Si. Line intensities of these ions have been computed using a model solar atmosphere and these have been compared with the available observed values for the quiet -Sun conditions. The analysis suggests the need for observations at higher spectral resolution. The successful launch of the SOHO satellite recently should provide such spectra.  相似文献   
786.
    
This paper presents a numerical analysis of the incompressible flow at Reynolds number 6.0×104 around the Selig–Donovan 7003 airfoil. The airfoil performances have been computed by the Reynolds averaged Navier–Stokes equations and large eddy simulations. The airfoil stall and preliminary post-stall have been obtained by both the methods. Some limitations of the RANS turbulence models for low-Reynolds number flows have been overcome by the κω SST-LR model, a recent modification of the well-known SST model. Large-eddy simulations have also been performed for a more detailed analysis of the results. The relevance in the stall mechanism of the laminar separation bubble arising on the airfoil is highlighted. The stall occurs when the laminar bubble present in the leading edge zone and a separated region forming on the central part of the airfoil join together. The κω SST-LR model returns the same stall mechanism as the large eddy simulation. Flows at low-Reynolds numbers can be simulated by the RANS methods, but the choice of the turbulence model is crucial. The κω SST-LR model has provided results in good agreement with the large eddy simulation and the available experimental data.  相似文献   
787.
The algorithms for calculating available overloads and maneuvers are presented. Nesterov’s loop maneuver is analyzed.  相似文献   
788.
A method is described to normalize the step parameter and perturbation amount used for gradient search adaptive algorithms. The step normalization assures rapid stable convergence. The perturbation normalization also assures rapid stable convergence and limits the output perturbation noise to a level below thermal noise. The normalizations are computationally simple and are consistent with the use of a single receiver at the adaptive array output. Results are presented to verify the robustness of the technique.<>  相似文献   
789.
Based upon the most efficient electron acceleration near the midplane of 3D non-neutral driven reconnecting current sheet (RCS) and the electrostatic wave excitation by the drift Maxwellian distribution of electrons in Vlasov simulation, we assume that the electrostatic waves mainly propagate opposite to the reconnecting electric field and investigated how these waves affect the electron acceleration. The main results are: (1) when the electron’s velocity equals to the phase speed of the waves, they will be trapped and have the different accelerating characteristics from the untrapped electrons through solving the momentum equations of electrons analytically; (2) the test particle simulations further prove that the number of the energetic electrons decreases with the increasing intensity of unstable waves, and the distribution of the energetic electrons takes on the double power-law.  相似文献   
790.
Did life begin on the beach?   总被引:2,自引:0,他引:2  
Water is one of the prerequisites of life. Further requirements are the existence of a system of interacting organic molecules capable of capturing and converting the supply of external energy and elaborating the replicating function that is needed for propagation. None of this would be possible without the existence of some means of concentrating, selecting, and then containing these mutually interacting substances in proximity to one another, i.e., a primitive cell. Starting from this hypothesis we propose a model for the development of life on Earth. Our model embodies the following new features: (1) rapid cycles of catalysis and transport of material, (2) desegregation (separation by tidal action and degradation by catalysis) as well as segregation (by chromatography on tidal beaches), (3) cross-catalysis instead of auto-catalysis, as well as (4) compartmentalization, although the latter idea is of course not new. But our "lipid first" model, in contrast to earlier "peptide first" or "RNA first" models, provides for the compartments needed to act as a cradle for the subsequent development of information- rich molecules like peptides and RNA. If anything, the earliest information-rich molecules were probably membrane-spanning peptides/proteins.  相似文献   
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