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881.
Haimovich A.M. Yosko J. Greenberg R.J. Parisi M.A. Becker D. 《IEEE transactions on aerospace and electronic systems》1993,29(1):245-250
The case of data fusion of sensors dissimilar in their measurement/tracking errors is considered. It is shown that the fused track performance is similar whether the sensor data are fused at the track level or at the measurement level. The case of a cluster of targets, resolved by one sensor but not the other, is also considered. Under certain conditions the fused track may perform worse than the worst of the sensors. A remedy to this problem through modifications of the association algorithm is presented 相似文献
882.
J C Guillemin S El Chaouch A Bouayad T Janati 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2001,27(2):245-253
The photolysis of mixtures of gases containing NH3 or PH3 presents important differences mainly due to the strength of the X-H bond. On some examples, these differences are evidenced and the consequences for mixtures of gases containing these two compounds are shown: the photolysis of ammonia and ethylene mainly gives ethyl-, butyl- and hexylamine whereas the photolysis of phosphine and ethylene leads to ethyl- and vinylphosphine. When gaseous mixtures of NH3, PH3 and ethylene are photolyzed together, the presence of phosphine dramatically decreases the formation of nitrogen derivatives. The relevance of such lab studies to the atmospheres of Jupiter and Saturn is discussed. 相似文献
883.
Sustained research and development at Memorial University of Newfoundland has led to an operational High Frequency Ground Wave Radar (HF-GWR) system for coastal surveillance. This radar system has demonstrated over-the-horizon detection of targets such as vessels, ice hazards and low-flying aircraft, and performed ocean parameter measurements over a large area. The industrial developers of offshore hydrocarbon reserves in ice infested regions have an urgent requirement for the long range detection and tracking of icebergs from their production platforms. However, due to space restrictions, a rig- or ship-based system can only accommodate a compact antenna array. The uniform trajectory and low velocity of icebergs is ideal for Reciprocal Synthetic Aperture Radar (RSAR) processing with long target dwell times. The proven ice detection capability of HF-GWR systems, coupled with the compact antennas suggested by the RSAR technique, can be used to develop a rig- or ship-based all-weather surveillance device for ice hazards. It is also anticipated that the results of this research will allow the use of shorter antenna arrays for many other applications. Preliminary results using real data from the operational HF-GWR system are presented 相似文献
884.
S I Ramirez R Navarro-Gonzalez P Coll F Raulin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2001,27(2):261-270
A quantitative comparison of the products arising from the irradiation of a Titan's simulated atmosphere is presented. The energy sources used represent some of the main events that occur in the satellite's atmosphere. All of the compounds identified are classified in the hydrocarbon and nitrile chemical families. Almost all of the detected compounds in Titan's atmosphere are produced by one or more energy sources. The compounds with the highest energy yields include the C2 hydrocarbons, methanonitrile and ethanonitrile. The possibility of using some of the produced organics as tracer compounds during the Huygens descend to identify the leading energy form in the different atmospheric levels remains open. 相似文献
885.
V. Formisano V.I. Moroz H. Hirsch P. Orleanski G. Michel J. Lopez-Moreno E. Amata G. Bellucci G. Piccioni G. Chionchio A. Carusi A. Coradini P. Cerroni M.T. Capria F. Capaccioni A. Adriani M. Vitterbini F. Angrilli G. Bianchini B. Saggin S. Fonti E. Bussoletti D. Mancini L. Colangeli A. Grigoriev B. Moshkin V. Gnedykh I.A. Matsygorin D. Patsaev Yu.V. Nikolsky D.V. Titov L.V. Zasova I. Khatuntsev A. Kiselev G. Arnold H. Driesher M.I. Blecka R. Rodrigo J. Rodriguez-Gomez 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,17(12):61-64
Thin films containing a mixture of aliphatic (glycine) and aromatic (tryptophan or tyrosine) amino acids were exposed to a vacuum ultraviolet radiation (VUV) with wavelenghts 100–200 nm. Dipeptides (glycyl-tryptophan and glycyl-tyrosine) were synthesized in these conditions. We compared the actions of VUV and γ-radiation. Polymerization is an essential step in prebiological evolution and we have shown that this stage probably occured over an early Solar system history. 相似文献
886.
C H Yang L M Craise M Durante M Mei 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(10):373-382
On Moon and Mars, there will be more galactic cosmic rays and higher radiation doses than on earth. Our experimental studies showed that heavy ion radiation can effectively cause mutation and chromosome aberrations and that high-LET heavy-ion induced mutants can be irreversible. Chromosome translocations and deletions are common in cells irradiated by heavy particles, and ionizing radiations are effective in causing hyperploidy. The importance of the genetic changes in the evolution of life is an interesting question. Through evolution, there is an increase of DNA content in cells from lower forms of life to higher organisms. The DNA content, however, reached a plateau in vertebrates. By increasing DNA content, there can be an increase of information in the cell. For a given DNA content, the quality of information can be changed by rearranging the DNA. Because radiation can cause hyperploidy, an increase of DNA content in cells, and can induce DNA rearrangement, it is likely that the evolution of life on Mars will be effected by its radiation environment. A simple analysis shows that the radiation level on Mars may cause a mutation frequency comparable to that of the spontaneous mutation rate on Earth. To the extent that mutation plays a role in adaptation, radiation alone on Mars may thus provide sufficient mutation for the evolution of life. 相似文献
887.
An approach for fusing offboard track-level data at a central fusion node is presented. The case where the offboard tracker continues to update its local track estimate with measurement and system dynamics models that are not necessarily linear is considered. An algorithm is developed to perform this fusion at a central node without having access to the offboard measurements, their noise statistics, or the location of the local estimator. The algorithm is based on an extension of results that were originally established for linear offboard trackers. A second goal of this work is to develop an inequality constraint for selecting the proper sampling interval for the incoming state estimates to the fusion node. This interval is selected to allow use of conventional Kalman filter algorithms at the fusion node without suffering error performance degradation due to processing a correlated sequence of track state estimates 相似文献
888.
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
889.
The Indian Space Program is described. The main objectives of the program are to provide operation space services to the nation, especially in the fields of communications and remote sensing, and to use modern space technology for the benefit of the Indian people. Some applications of the Indian Space Program are remote sensing, imagery, communications, broadcasting, and surveys of natural resources for water, crop, forest, land, minerals, and ocean. The emphasis is on the development and operation of indigenous satellites and launch vehicles for providing these space services 相似文献
890.