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431.
Daeipour E. Blair W.D. Bar-Shalom Y. 《IEEE transactions on aerospace and electronic systems》1997,33(3):863-882
The problem of tracking targets in the presence of reflections from sea or ground is addressed. Both types of reflections (specular and diffuse) are considered. Specular reflection causes large peak errors followed by an approximately constant bias in the monopulse ratio, while diffuse reflection has random variations which on the average generate a bias in the monopulse ratio. Expressions for the average error (bias) in the monopulse ratio due to specular and diffuse reflections and the corresponding variance in the presence of noise in the radar channels are derived. A maximum maneuver-based filter and a multiple model estimator are used for tracking. Simulation results for five scenarios, typical of sea skimmers, with Swerling III fluctuating radar cross sections (RCSs) indicate the significance and efficiency of the technique developed in this paper-a 65% reduction of the rms error in the target height estimate. 相似文献
432.
K. J. Meech M. F. A’Hearn Y. R. Fernández C. M. Lisse H. A. Weaver N. Biver L. M. Woodney 《Space Science Reviews》2005,117(1-2):297-334
Prior to the selection of the comet 9P/Tempel 1 as the Deep Impact mission target, the comet was not well observed. From 1999 through the present there has been an intensive world-wide observing
campaign designed to obtain mission critical information about the target nucleus, including the nucleus size, albedo, rotation
rate, rotation state, phase function, and the development of the dust and gas coma. The specific observing schemes used to
obtain this information and the resources needed are presented here. The Deep Impact mission is unique in that part of the mission observations will rely on an Earth-based (ground and orbital) suite of complementary
observations of the comet just prior to impact and in the weeks following. While the impact should result in new cometary
activity, the actual physical outcome is uncertain, and the Earth-based observations must allow for a wide range of post-impact
phenomena. A world-wide coordinated effort for these observations is described. 相似文献
433.
A Takahashi N Kondo H Inaba K Uotani Y Kiyohara K Ohnishi T Ohnishi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,31(6):1569-1573
To assess the radioadaptive response of the whole body system in mice, we examined the temporal effect of low dose priming as an indicator of challenging irradiation-induced apoptosis through a p53 tumor suppressor protein- mediated signal transduction pathway. The p53 protein also plays an important role both in cell cycle control and DNA repair through cellular signal transduction. Using severe combined immunodeficiency mice defective in DNA-dependent protein kinase catalytic subunit, we examined the role of DNA-dependent protein kinase activity in radioadaptation induced by low dose irradiation. Specific pathogen free 5-week-old female severe combined immunodeficiency mice and the parental mice (CB- 17 Icr +/+) were irradiated with X-ray at 3.0 Gy at 1, 2, 3 or 4 weeks after the conditioning irradiation at 0.15, 0.30, 0.45 or 0.60 Gy. The mice spleens were fixed for immunohistochemistry 12 h after the challenging irradiation. The p53-dependent apoptosis related Bax proteins on formalin-fixed paraffin-embedded sections were stained by the avidin-biotin peroxidase complex method. The apoptosis incidence in the sections was measured by hematoxylin-eosin staining. The frequency of Bax- and apoptosis-positive cells increased up to 12 h after the challenging irradiation in the spleen of both mice. However, these cells were not observed after a low dose irradiation at 0.15-0.60 Gy. When pre-irradiation at 0.45 Gy 2 weeks before the challenging irradiation at 3.0 Gy was performed, Bax accumulation and apoptosis induced by challenging irradiation were depressed in the spleens of CB-17 Icr +/+ mice, but not in severe combined immunodeficiency mice. These data suggest that DNA-dependent protein kinase might play a major role in radioadaptation induced by pre-irradiation with a low dose in mice spleen. We expect that the present findings will provide useful information in the health care of space crews. 相似文献
434.
H. Kishida S. Taguchi T. Mukai Y. Saito 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(12):2781-2786
A detailed analysis of Geotail observations on June 1, 1997 provides evidence for the appearance of the plasma mantle at low-latitudes, ZGSM 3 RE for southward interplanetary magnetic field (IMF), and clarifies the characteristics of the plasma flow in the low-latitude mantle. The tailward flow speed in the mantle is 80 160 km/s, smaller than the flow speed (300 km/s) in the adjacent magnetosheath. The component of the velocity perpendicular to the magnetic field lines is predominantly poleward at speeds up to 60 km/s, and the convection tends to be stronger for |;BY|<|;BZ| than for IMF |BY|>|BZ|;. This polewardconvection can be interpreted as being driven by a J × B force operating on the field lines. 相似文献
435.
O Iversen T-HRasmussen F Gmünder C Baggerud E L Kordyum V V Lozovaya M Tairbekov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(1):123-131
An experiment using plant protoplasts has been accepted for the IML-1 Space Shuttle mission scheduled for 1991. Preparatory experiments have been performed using both fast and slow rotating clinostats and in orbit to study the effect of simulated and real weightlessness on protoplast regeneration. Late access to the space vehicles before launch has required special attention since it is important to delay cell wall regeneration until the samples are in orbit. On a flight on Biokosmos 9 ("Kosmos-2044") in September 1989 some preliminary results were obtained. Compared to the ground control, the growth of both carrot and rapeseed protoplasts was decreased by 18% and 44% respectively, after 14 days in orbit. The results also indicated that there is less cell wall regeneration under micro-g conditions. Compared to the ground controls the production of cellulose in rapeseed and carrot flight samples was only 46% and 29% respectively. The production of hemicellulose in the flight samples was 63% and 67% respectively of that of the ground controls. In both cases all samples reached the stage of callus development. The peroxidase activity was also found to be lower in the flight samples than in the ground controls, and the number of different isoenzymes was decreased in the flight samples. In general, the regeneration processes were retarded in the flight samples with respect to the ground controls. From a simulation experiment for IML-1 performed in January 1990 at ESTEC, Holland, regenerated plants have been obtained. These results are discussed and compared to the results obtained on Biokosmos 9. Protoplast regeneration did not develop beyond the callus stage in either the flight or the ground control samples from the Biokosmos 9 experiment. 相似文献
436.
F. Ahmed Y.A. Hagaz A.S. Andrawis 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(11):123-131
The region of Nuba Mountains is largely dominated by Precambrian crystalline basement rocks, and often experiences acute shortage of water for domestic and irrigation purposes especially during the dry season (February – May). A Landsat model essentially based on lineament and drainage analysis is proposed to delineate potential target zones for groundwater prospecting. Target zones are indicated by the overlap of the high-intensity lineament contours and the low-intensity drainage contours, and by intersection of a stream channel and lineament structure. Most wells lying within the defined targets are successful. 相似文献
437.
Chen D.Y. Lee F.C. Blackburn D.L. Berning D.W. 《IEEE transactions on aerospace and electronic systems》1983,(6):840-847
The reverse-bias second breakdown (RBSB) characteristics of high power Darlington transistors are discussed. The Darlingtons investigated are rated at 400 V maximum voltage and 100 A maximum current. Devices with and without speed-up diodes (connected between the bases of the input and output transistors) were studied. A nondestructive system for characterizing the RBSB behavior of these devices is described. The RBSB behavior was found to vary unpredictably with varying reverse base current magnitude. It was also found that the RBSB behavior of the Darlingtons was a function of the forward base current magnitude. This is in marked contrast to what has been found for discrete devices. The presence of a speed-up diode also influenced the RBSB behavior of these devices. 相似文献
438.
A.Y. Wong J. Santoru J.G. Roederer G. Sivjee 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(2):225-228
Laboratory experiments in which high power, pulsed electromagnetic waves interact with an inhomogeneous plasma indicate that the generated nonlinear plasma phenomena depend on peak incident power and not on pulse length. The electromagnetic waves can penetrate beyond the cutoff and produce large, enhanced electrostatic fields at the critical layer within 100 electron plasma periods. The enhanced electric field pressure can be comparable to the thermal pressure and can accelerate ions and electrons to velocities much greater than their thermal speed. Large density cavities (with δn/n ? 10%) can be created in a time shorter than the usual ion response time because of the accelerated ion dynamics. These laboratory results have been extended to create a new and generalized concept to actively stimulate space plasmas with high power pulses of short duration. A field experiment will be used for the stimulation of auroral ionospheric plasma. The ground-based system is modular, each module consisting of a 2 MW pulsed HF transmitter designed at UCLA and a crossed-dipole antenna element. Incoherent scatter radar and optical diagnostic methods are discussed. 相似文献
439.
P.Y. Deschamps M. Herman J. Lenoble D. Tanre 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(5):171-176
A simple modelization of the earth atmosphere system including tropospheric and stratospheric aerosols has been derived and tested. Analytical expressions are obtained for the albedo variation due to a thin stratospheric aerosol layer. Also outlined are the physical procedures and the respective influence of the main parameters: aerosol optical thickness, single scattering albedo and asymmetry factor, and sublayer albedo. The method is applied to compute the variation of the zonal and planetary albedos due to a stratospheric layer of background H2SO4 particles and of volcanic ash. 相似文献
440.
Y. Boudon F. Barlier A. Bernard R. Juillerat A.M. Mainguy J.J. Walch 《Acta Astronautica》1979,6(11):1387-1398
The Cactus accelerometer, developed at ONERA and making up the payload of the Castor satellite, has been operating continuously and normally for 40 months. Thanks to the great quantity of data acquired and to a well adapted processing technique, acceleration measurements were in fact obtained with a better sensitivity than that expected before launch.This paper presents a synthesis of the work carried out in the past year and concerning the measurement of very low accelerations. These are due, for the most part, to the Earth IR radiation pressure when the satellite is in the Earth's shadow, and to the thrust it is subjected to under the influence of the anisotropy of its own radiation. 相似文献