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31.
Paul A. Crowther Joanne L. Bibby James P. Furness J. Simon Clark 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
We highlight how the downward revision in the distance to the star cluster associated with SGR 1806–20 by Bibby et al. (2008) reconciles the apparent low contamination of BATSE short GRBs by intense flares from extragalactic magnetars without recourse to modifying the frequency of one such flare per 30 years per Milky Way galaxy. We also discuss the variety in progenitor initial masses of magnetars based upon cluster ages, ranging from ∼50 M⊙ for SGR 1806–20 and AXP CXOU J164710.2–455216 in Westerlund 1 to ∼17 M⊙ for SGR 1900+14 according to Davies et al. (2009) and presumably also 1E 1841–045 if it originated from one of the massive RSG clusters #2 or #3. 相似文献
32.
A consistent tactical picture requires data fusion technology to combine and propagate information received from diverse objects and usually vague situations. The information may be contained in two types of data; numerical data received from sensor measurements, and linguistic data obtained from human operators and domain experts. In real world situations, the numerical data may be noisy, inconsistent, and incomplete, and the linguistic information is imprecise and vague. To deal with these two types of data simultaneously, fuzzy sets and fuzzy logic provide a methodology to obtain an approximate but consistent tactical picture in a timely manner for very complex or ill-defined engineering problems. A functional paradigm for fuzzy data fusion is presented. It consists of four basic elements: (1) fuzzification of crisp elements, (2) fuzzy knowledge base derived from numerical input/output relations and humans, (3) fuzzy inference mechanism based on a class of fuzzy logic, (4) defuzzification of fuzzy outputs into crisp outputs for use by a plant. For real-time practical systems, the on-line determination of a fuzzy membership function from a given set of crisp inputs is vital. To this end, a methodology for estimating an optimal membership function from crisp input data has been implemented. This is based on the possibility/probability consistency principle as proposed by L.A. Zadeh. A relationship between the fuzzy membership function and the confidence level of statistical input data has been developed and it serves as a design parameter for fuzzification. This technique has been applied to a two-dimensional multisensor-multitarget tracking system. Fuzzy system performance evaluations have been presented. With simulated data in the laboratory environment, the simulation has been performed to evaluate the Mission Avionics Sensor Synergism (MASS) Systems. These results show better performance for the data correlation function using the fuzzy logic techniques. 相似文献
33.
A conceptual system is proposed and described for the control of a multiplicity of drone aircraft. Each target (drone) aircraft is controlled, during a given mission, over a separate preprogrammed path comprised of straight line and circular arc segments. Full control of each target's altitude, plan position, and velocity is available. Position measurement can be obtained by use of either a radar or a bilateration method where altitude is measured in either case by each aircraft and telemetered to a central control point. Velocity is obtained by smoothing position data in a central computer, which also controls the entire mission complex. 相似文献
34.
P. C. Frisch 《Space Science Reviews》2007,130(1-4):355-365
The properties of interstellar matter at the Sun are regulated by our location with respect to a void in the local matter
distribution, known as the Local Bubble. The Local Bubble (LB) is bounded by associations of massive stars and fossil supernovae
that have disrupted dense interstellar matter (ISM), driving low density intermediate velocity ISM into the void. The Sun
appears to be located in one of these flows of low density material. This nearby interstellar matter, dubbed the Local Fluff,
has a bulk velocity of ∼19 km s−1 in the local standard of rest. The flow is coming from the direction of the gas and dust ring formed where the Loop I supernova
remnant merges into the LB. Optical polarization data suggest that the local interstellar magnetic field lines are draped
over the heliosphere. A longstanding discrepancy between the high thermal pressure of plasma filling the LB and low thermal
pressures in the embedded Local Fluff cloudlets is partially mitigated when the ram pressure component parallel to the cloudlet
flow direction is included. 相似文献
35.
TMA from bearings and multipath time delays 总被引:2,自引:0,他引:2
Blanc-Benon P. Jauffret C. 《IEEE transactions on aerospace and electronic systems》1997,33(3):813-824
A novel approach for target motion analysis (TMA), which uses conventional passive bearing together with multipath time-delay measurements is examined. This so-called "Multipath TMA" offers two tactical advantages over the classical bearings-only TMA: no requirement for any ownship maneuver, and a good performance in terms of estimation error achieved in a shorter time. Both known and unknown multipath cases are addressed. Finally, Monte-Carlo simulations and at-sea trials demonstrate the practical efficiency of such a multipath TMA. 相似文献
36.
Vadher V.V. Smith I.R. Fanthome B.A. 《IEEE transactions on aerospace and electronic systems》1986,(1):64-70
Permanent magnet generators are often used as the pilot exciters of three-stage generating units to provide an efficient and reliable source of electrical power. No external power supply is then necessary, and the problems associated with brushwear and with arcing at the rubbing contacts are eliminated. A technique is presented here by which the performance of a permanent magnet generator, when combined with a rectifier-fed d.c. load at its output terminals, may be accurately and efficiently computed. The machine model takes into account the magnetization characteristic of the permanent magnet rotor and involves only parameters which can be determined from terminal measurements on the machine at standstill. Both computed and measured characteristics for an experimental machine are presented, and a comparison of these characteristics shows that the model can predict accurately all the major characteristics of the machine, as well as its detailed internal performance, when supplying a typical resistiveinductive load. 相似文献
37.
Krishna M. V. Apparao 《Space Science Reviews》1994,69(3-4):255-329
Observations of X-ray emission from Be star/X-ray binaries are reviewed. Some optical characteristics of these binaries are also presented. Theoretical aspects pertaining to the X-ray emissions are given. 相似文献
38.
A.V. Bruns G.M. Grechko A.A. Gubarjev P.I. Klimuk V.I. Sevastjanov A.B. Severny N.V. Steshenko 《Acta Astronautica》1977,4(11-12)
The orbiting solar telescope on Salyut-4 (F = 2,5 m, d = 250 mm) produces images of the Sun on the entrance slit of a stigmatic two-grating spectrograph (R1 = 1 m, N1 = 1200 lines/mm; R2 = 0.5 m, N2 = 2400 lines/mm, dispersion 16 Å/mm, spectral resolution 0,3 Å). The automatic system keeps the observed solar features on the slit of the spectrograph with an accuracy of 3–4 arc sec. The far UV-spectra (970–1400 Å) of solar flares, brightenings, flocculi and prominences were photographed and fresh coatings of mirrors were made during the flight. 相似文献
39.
R. P. Lin K. A. Anderson S. Ashford C. Carlson D. Curtis R. Ergun D. Larson J. McFadden M. McCarthy G. K. Parks H. Rème J. M. Bosqued J. Coutelier F. Cotin C. D'Uston K. -P. Wenzel T. R. Sanderson J. Henrion J. C. Ronnet G. Paschmann 《Space Science Reviews》1995,71(1-4):125-153
This instrument is designed to make measurements of the full three-dimensional distribution of suprathermal electrons and ions from solar wind plasma to low energy cosmic rays, with high sensitivity, wide dynamic range, good energy and angular resolution, and high time resolution. The primary scientific goals are to explore the suprathermal particle population between the solar wind and low energy cosmic rays, to study particle accleration and transport and wave-particle interactions, and to monitor particle input to and output from the Earth's magnetosphere.Three arrays, each consisting of a pair of double-ended semi-conductor telescopes each with two or three closely sandwiched passivated ion implanted silicon detectors, measure electrons and ions above 20 keV. One side of each telescope is covered with a thin foil which absorbs ions below 400 keV, while on the other side the incoming <400 keV electrons are swept away by a magnet so electrons and ions are cleanly separated. Higher energy electrons (up to 1 MeV) and ions (up to 11 MeV) are identified by the two double-ended telescopes which have a third detector. The telescopes provide energy resolution of E/E0.3 and angular resolution of 22.5°×36°, and full 4 steradian coverage in one spin (3 s).Top-hat symmetrical spherical section electrostatic analyzers with microchannel plate detectors are used to measure ions and electrons from 3 eV to 30 keV. All these analyzers have either 180° or 360° fields of view in a plane, E/E0.2, and angular resolution varying from 5.6° (near the ecliptic) to 22.5°. Full 4 steradian coverage can be obtained in one-half or one spin. A large and a small geometric factor analyzer measure ions over the wide flux range from quiet-time suprathermal levels to intense solar wind fluxes. Similarly two analyzers are used to cover the wide range of electron fluxes. Moments of the electron and ion distributions are computed on board.In addition, a Fast Particle Correlator combines electron data from the high sensitivity electron analyzer with plasma wave data from the WAVE experiment (Bougeretet al., in this volume) to study wave-particle interactions on fast time scales. The large geometric factor electron analyzer has electrostatic deflectors to steer the field of view and follow the magnetic field to enhance the correlation measurements. 相似文献