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961.
P. R. Goode L. V. Didkovsky K. G. Libbrecht M. F. Woodard 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,29(12):1-1898
Solar oscillations provide the most accurate measures of cycle dependent changes in the sun, and the Solar and Heliospheric Observatory/Michelson Doppler Imager (MDI) data are the most precise of all. They give us the opportunity to address the real challenge — connecting the MDI seismic measures to observed characteristics of the dynamic sun. From inversions of the evolving MDI data, one expects to determine the nature of the evolution, through the solar cycle, of the layers just beneath the sun's surface. Such inversions require one to guess the form of the causal perturbation — usually beginning with asking whether it is thermal or magnetic. Matters here are complicated because the inversion kernels for these two are quite similar, which means that we don't have much chance of disentangling them by inversion. However, since the perturbation lies very close to the solar surface, one can use synoptic data as an outer boundary condition to fix the choice. It turns out that magnetic and thermal synoptic signals are also quite similar. Thus, the most precise measure of the surface is required.
We argue that the most precise synoptic data come from the Big Bear Solar Observatory (BBSO) Solar Disk Photometer (SDP). A preliminary analysis of these data implies a magnetic origin of the cycle-dependent sub-surface perturbation. However, we still need to do a more careful removal of the facular signal to determine the true thermal signal. 相似文献
962.
E. Möbius 《Space Science Reviews》1996,78(1-2):375-386
Over the last 10 years the experimental basis for the study of the very local interstellar medium (VLISM) has been substantially broadened by the direct detection of pickup ions and of neutral helium. The strength of these methods lies in the local measurement of the particles. By scanning the gravitational focusing cone of the interstellar wind, a consistent set of interstellar helium parameters, neutral density, temperature and relative velocity, has been derived. However, the accuracy of these parameters is still hampered by uncertainties in some of the crucial ionization rates and in the pickup ion transport. Recent observations have shown that the scattering mean free path of pickup ions is comparable with the large scale variation of the interplanetary magnetic field (IMF) in the inner heliosphere. This requires a substantial modification in the modeling of the ion distribution and more detailed measurements, tasks that can be addressed in the near future. 相似文献
963.
J. B. Blake M. C. McNab J. E. Mazur 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2001,28(12):1753-1757
The entry of energetic solar protons to the polar caps offers an interesting way to test models of the geomagnetic field. In this brief report, we present a comparison between SAMPEX observations of solar-particle intensity structure during a polar cap traversal with numerical trajectory calculations using the IGRF + T96 field model. 相似文献
964.
An adaptive array architecture is described which has improved convergence speed over the conventional Applebaum array when the eigenvalue spread of the input signal covariance matrix is large. The architecture uses N+1 Applebaum adaptive arrays in a two-layer cascaded configuration. The gain constants in the first layer are set so that large interfering sources are quickly nulled, but small interfering sources are suppressed more slowly. Since the first layer removes the large interfering signals, the gain constant for the second layer can be set to a large value to quickly null the smaller interferers. The adaptation time is examined for several combinations of signal levels and array sizes. It is shown that, in many signal environments, the computational requirements for the cascaded array compare favorably with those of conventional sample matrix inversion (SMI) methods for large arrays 相似文献
965.
Extensive research has been conducted in the design and manufacture of very long life sealed maintenance free nickel-cadmium aircraft batteries. This study presents data on a 100% depth of discharge (DOD) life test performed on a nominal capacity 42-Ah battery. The purpose of this study is to validate design concepts, determine the life characteristics of the newly designed sealed Ni-Cd batteries, and develop baseline information on failure rates and mechanisms. The data from this experiment can be used to compare depth of discharge versus battery life with similar tests such as the lower DOD experiments performed on spacecraft batteries. This information is important in the ongoing development of long life batteries and in developing failure models for life prediction 相似文献
966.
Scoles D.L. Hayden J.W. Pickett D.F. Jr. Rao G.M. 《Aerospace and Electronic Systems Magazine, IEEE》1996,11(7):27-30
A nickel cadmium cell system which utilizes a polypropylene separator impregnated with polybenzimadazole, and which shows promise of providing an aerospace battery with performance equivalent to Super NiCd, and yet is more cost effective, is described. Background information, cell construction information, detailed test program information and data, and status of qualification are given 相似文献
967.
The authors consider the effects of single event upsets (SEUs) on digital systems, and show techniques for designing reliable systems with current levels of SEU protection. Three main systems are discussed: main memory, logic, and cache memory. A design for the main and cache memory subsystems that are SEU protected is also described. With SEU defined in bit days p , and using single error correction, it is shown that for all subsystems considered, an effective upset rate which is proportional to the product of p 2 and the time between corrections, or scrub time, can be obtained. Data for memory chip size and performance derived from the gallium-arsenide (GaAs) pilot lines funded by the Defense Advanced Research Projects Agency (DARPA) throughout the 1980s are used 相似文献
968.
969.
H Houben R M Haberle R E Young A P Zent 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,19(8):1233-1236
The current Martian water cycle is extremely asymmetric, with large amounts of vapor subliming off a permanent north polar water ice cap in northern summer, but with no apparent major source of water vapor in the southern hemisphere. Detailed simulations of this process with a three-dimensional circulation model indicate that the summertime interhemispheric exchange (Hadley cell) is very much stronger than transport by eddies in other seasons. As a result, water ice would be distributed globally were it not for the buffering action of regolith soil adsorption which limits the net flux of water vapor off the north polar cap to amounts that are insignificant even on the scale of thousands of years. It has been suggested that the polar layered deposits are the result of exchange on these long time scales, driven by changes in Martian orbital parameters. We therefore are conducting simulations to test the effect of varied orbital parameters on the Martian water cycle. We find that when the perihelion summer pole is charged with a polar water ice cap, large quantities of water are quickly transfered to the aphelion summer pole, setting up an annual cycle that resembles the present one. Thus, the adsorptivity of the Martian regolith may be in the narrow range where it can limit net transport from the aphelion but not the perihelion pole. 相似文献
970.
Bhanu B. Das S. Roberts B. Duncan D. 《IEEE transactions on aerospace and electronic systems》1996,32(3):875-897
An airborne vehicle such as a rotorcraft must avoid obstacles like antennas, towers, poles, fences, tree branches, and wires strung across the flight path. Automatic detection of the obstacles and generation of appropriate guidance and control actions for the vehicle to avoid these obstacles would facilitate autonomous navigation. The requirements of an obstacle detection system for rotorcraft in low-altitude Nap-of-the-Earth (NOE) flight based on various rotorcraft motion constraints is analyzed here in detail. It is argued that an automated obstacle detection system for the rotorcraft scenario should include both passive and active sensors to be effective. Consequently, it introduces a maximally passive system which involves the use of passive sensors (TV, FLIR) as well as the selective use of an active (laser) sensor. The passive component is concerned with estimating range using optical flow-based motion analysis and binocular stereo. The optical flow-based motion analysis that is combined with on-board inertial navigation system (INS) to compute ranges to visible scene points is described. Experimental results obtained using land vehicle data illustrate the particular approach to motion analysis 相似文献