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931.
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
932.
J.K. Alexander 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(3):17-24
The Planetary Radio Astronomy instruments on Voyager 1 and 2 provided new, highly detailed measurements of several different kinds of strong, nonthermal radiation generated in the inner magnetospheres and upper ionospheres of Jupiter and Saturn. At Jupiter, an intense decameter-wavelength component (between a few tenths of a MHz and 39.5 MHz) is characterized by complex, highly organized structure in the frequency-time domain and by a strong dependence on the longitude of the observer and, in some cases, of Io. At frequencies below about 1 MHz there exists a (principally) kilometer-wavelength component of emission that is bursty, relatively broadbanded (typically covering 10 to 1000 kHz), and strongly modulated by planetary rotation. The properties of this component are consistent with a source confined to high latitudes on the dayside hemisphere of Jupiter. A second kilometric component is narrow-banded, relatively weak and exhibits a spectral peak near 100 kHz. The narrowband component also occurs periodically but at a repetition rate that is a few percent slower than that corresponding to the planetary rotation rate. This component is thought to originate at a frequency near the electron plasma frequency in the outer part of the Io plasma torus (8 to 10 RJ) and to reflect the small departures from perfect corotation experienced by plasma there.The Voyager instruments also detected intense, low frequency, radio emissions from the Saturn system. The Saturnian kilometric radiation is observed in a relatively narrow frequency band between 3 kHz and 1.2 MHz, is elliptically or circularly polarized, and is strongly modulated in intensity at Saturn's 10.66-hr rotation period. This emission is believed to be emitted in the right-hand extraordinary mode from regions near or in Saturn's dayside, polar, magnetospheric cusps. Variations in intensity at Saturn's rotation period may correspond to the rotation of a localized magnetic anomaly into the vicinity of the ionospheric footprint of the polar cusp. Variations in activity on time scales of a few days and longer seem to indicate that both the solar wind and the satellite Dione can also influence the generation of the radio emission. 相似文献
933.
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
934.
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
935.
T.H. Vonder Haar G.G. Campbell E.A. Smith A. Arking K. Coulson J. Hickey F. House A. Ingersoll H. Jacobowitz L. Smith L. Stowe 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(4):285-297
Two special measurements of the energy exchange between earth and space were made in connection with the FGGE. A global monitoring program using wide-field-of-view and scanner detectors from NASA's NIMBUS-7 satellite successfully returned measurements during the entire FGGE. This experiment system also used a black cavity detector to measure the total energy output of the sun to very high precision. A second set of high frequency time and space estimates of the radiation budget were determined from selected geostationary satellite data. Preliminary results from both radiation budget data sets and the solar “constant” measurements will be presented. 相似文献
936.
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
937.
V. N. Oraevsky Yu. Ya. Ruzhin V. G. Korobeinikov A. S. Volokitin V. S. Skomarovsky 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(12):131-134
The paper presents the results and discussion of VLF wave measurements carried out in the course of two rocket experiments on injection of a dense cesium ion beam into the ionosphere at the heights of 165–240 km. The injection was accompanied by enhancement of the broad-band noise by several orders of magnitude. The wave measurements in the frequency range of 1–11 kHz revealed two pronounced frequencies somewhat exceeding that of the lower-hybrid resonance oscillations in the background plasma and the cesium beam. The oscillations were modulated by frequencies close to the ion-cyclotron frequencies of the background plasma. 相似文献
938.
S.G. Ungar S.N. Goward 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(2):291-295
Improvements in crop discrimination can be realized by using mid-IR bands (1.55–1.75 μm and 2.08–2.35 μm) which are sensitive to canopy moisture content. Analyses of data from two growing seasons in Webster County, Iowa clearly indicate that corn and soybeans are highly separable in the mid-IR from early season through harvest. This contrasts sharply with visible and near-IR bands where corn and soybeans are confused throughout much of the growing season. The mid-IR temporal reflectance behavior appears to result from differences between C4 monocot and C3 dicot internal leaf structure. If this hypothesis holds, mid-IR observations should improve discrimination in other instances where similar differences in internal leaf structure are present. 相似文献
939.
Y Ishikawa K Kuriki 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(9):35-38
The chemistry in a supersonic plasma source flow was studied as a laboratory model for interstellar chemical evolution. It is important to match the similarity parameters for cosmic and laboratory conditions, which connect the temporal and spatial scales of the two cases. The apparatus simulated the conditions in a molecular cloud with respect to molecular-ionic reaction fraction, temperature, and non-equilibrium kinetics. The plasma flow was found to be cold enough, by the radical expansion, to produce polyatomic molecules. From the simple atomic plasma as reactant, cyanopolyyne and unsaturated hydrocarbons were synthesized in the present experiment. These molecules are also inherent in molecular clouds. The reaction mechanism is discussed. 相似文献
940.
Shing-Tung Yau Yau S.S.-T. 《IEEE transactions on aerospace and electronic systems》1997,33(4):1277-1294
We consider the Duncan-Mortensen-Zakai (DMZ) equation for the Kalman-Bucy filtering system and Benes filtering system. We show that this equation can be solved explicitly with an arbitrary initial condition by solving a system of ordinary differential equations and a Kolmogorov-type equation, Let n be the dimension of state space. We show that we need only n sufficient statistics in order to solve the DMZ equation. 相似文献