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931.
A general analysis of the effect of an arbitrary power-series nonlinear amplifier followed by a coherent mixing device on signal-to-noise ratio (SNR) is performed. An expression is derived for the improvement factor which is defined as the logarithm of the ratio of the output SNR to the input SNR. This expression is applicable to the coherent amplitude detector and phase locked loop as well as noncoherent amplifier by appropriate selections of the detection angle. Moreover, the improvement factor can be obtained for noise with an arbitrary amplitude distribution. To demonstrate the applicability of this analysis, the improvement factors of the nonlinear amplifiers such as a power-law amplifier and a power-series amplifier with positive and negative discriminations are numerically calculated for the cases where the input noise amplitude distributions are Rician and triangular. 相似文献
932.
K. Kecskeméty S. Pintér 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(3):101-104
Flux variations of 1 – 5 MeV protons are studied in energetic storm particle events with respect to the preshock solar wind plasma parameters and to the thickness of the collisionless interplanetary shock wave. It is found that the peak intensity in ESP events depends on pre-shock plasma density and on the thickness of the transition region. These relations predict, in agreement with recent observations, the increase of ESP events at larger heliocentric distances. 相似文献
933.
A. DasGupta D.N. Anderson J.A. Klobuchar 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(10):199-202
Ionospheric total electron content and the F-region maximum electron density at a number of stations in the equatorial region, during the recent solar activity maximum period 1979 to 1980, show significant differences between the two equinoctial periods. Ionization during the month of March is higher than in September, irrespective of the station location both in northern and southern hemispheres, and in different longitude sectors. The observed pattern is compared with those predicted by different models, in particular with one of the authors which includes processes such as ionization production, loss, electrodynamic drifts, winds and global composition changes involved in the equatorial ionosphere. It is found that a change in the neutral composition is primarily responsible for the observed F-region density differences between March and September. 相似文献
934.
M K Wallis N C Wickramasinghe F Hoyle 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(4):281-285
Comet Halley studies indicate most of the nucleus is covered by an insulating crust, presumed of pyrolysed organic material. The subcrust is warmed and percolated by gases within 2AU, so provides one habitat for primitive replicating organisms. Cracks and crevices within contaminated ice in the craters provides a habitat for photosynthesising organisms. Subsurface lakes on the Europa model, though insulated by some metres of ice, would require a trigger (perhaps meteorite impact and energy source (chemical or metabolic energy) to initiate and maintain a suitable-habitat on short period comets. Constraints on transfer between comets and other planetary bodies implies that radiation-resistant species with lengthy hibernation potential would be expected. 相似文献
935.
B.N. Swanenburg 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(4):71
The NASA Gamma-Ray Observatory, GRO, will carry two instruments for low energy gamma-ray astronomy. The ‘Oriented Scintillation Spectrometer Experiment - OSSE’ represents the latest step in the evolution of collimated detectors. A large detection area, simultaneous source and background observation and rigorous control over systematic errors yield significant improvements in sensitivity over earlier instruments. The ‘Imaging Compton Telescope - COMPTEL’ brings the proven concept of the Compton telescope to the state of the art level. Position sensitive scintillation detectors make it possible to generate sky images with a resolution of about 2° over a f.o.v. of about 1 sr. The complementary nature of these two experiments promises a first in-depth exploration of the sky in a wavelength range which covers the transition from the X-ray sky to the apparently unrelated high energy gamma-ray sky. Possible directions of further evolution of these experiments will be discussed. 相似文献
936.
Shats S. Bobrovsky B.Z. Shaked U. 《IEEE transactions on aerospace and electronic systems》1988,24(6):670-677
The problem of minimum variance discrete-time state estimation of a continuous-time double integrator via noisy continuous-time measurements is considered. The error covariance matrices of this estimation are calculated and analyzed. The relations between these covariance matrices and the error covariance matrix of the optimal continuous-time filter are obtained, and a way for determining the required sampling period is proposed. A commonly used approximated model is investigated; it is shown to be inappropriate unless a specific improvement is introduced in the model 相似文献
937.
Knox S. Long 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(9):177-188
An extensive program to study nearby normal galaxies was carried out by various observers using the imaging instruments on the Observatory; more than 50 such galaxies were detected with 0.5 – 3.0 keV luminosities ranging from 2 × 1038 ergs s?1 to 3 × 1041ergs s?1. The X-ray luminosity of normal galaxies is ~2 × 10?4 of the optical luminosity and shows no strong correlation with morphological type. For the nearest galaxies, (the Large and Small Magellanic Clouds, M31 and M33,) studies, performed with the Observatory, were comparable to the survey of the Galaxy. Approximately 30 new SNR were recognized in the Magellanic Clouds as a result. Over 90 sources were detected in M31 of which at least 20 are identified with globular cluster. The numbers of luminous (>1037 ergs s?1) sources detected in the nearest galaxies per unit mass are similar to that found in our own galaxy. Individual X-ray sources in the arms of nearby spirals can be very luminous; seven with luminosities in excess of 1039ergs s?1 have been discovered. The nuclei of some, but not all, normal galaxies are luminous X-ray sources; X-ray activity is not presently predictable from the radio or optical properties of the nucleus. 相似文献
938.
939.
Bhat A.K.S. Biswas A. Iyengar B.S.R. 《IEEE transactions on aerospace and electronic systems》1995,31(3):1186-1193
A series-parallel resonant converter employing (LC)(LC)-type tank circuit operating in lagging power factor (PF) mode is presented and analyzed using complex ac circuit analysis. Design curves are obtained and the converter is optimized under certain constraints. Detailed Space Integrated Control Experiment (SPICE) simulation results are presented to evaluate the performance of the designed converter under varying load conditions. Results obtained from an experimental converter are also presented. The results obtained from the theory, SPICE simulation, and the experimental converter are compared. The proposed converter has high efficiency from full load to very light load (<10%). Switching frequency variation required for a wide change in the load (near load open circuit to full load) is narrow compared with the series resonant converter (SRC) 相似文献
940.
S.A. Bowhill 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(11):13-16
During the Middle Atmosphere Program, 1982–1985, balloons will play a central role in gathering stratospheric, chemical, and dynamical data. This paper discusses some of the unique aspects of balloons as tools for probing the middle atmosphere, and suggests some directions for future projects and enhanced capabilities that would improve their utility in future investigations. 相似文献