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Rgis Guinvarc'h Marc Lesturgie Rmi Durand Anil Cheraly 《Oceanic Engineering, IEEE Journal of》2006,31(4):894-903
In this paper, we assess the capability of a high-frequency surface wave radar (HFSWR) to detect a small fast boat moving behind a ship, the dimensions of which are comparable to the wavelength. We show that, in the HF-band, the scattered field in the shadow region of the large ship is significant enough to induce strong coupling between the two vessels. This results in fluctuations in the radar cross section (RCS) values of the small boat of about 12 dB at 10 MHz, for instance. We also introduce a complete simulation tool to account for the environment and, thus, to be able to simulate real scenes. We have validated these results through anechoic chamber measurements, with two different masking vessels and three different masked ships. The measurements have shown both the low-attenuation results and the RCS fluctuations 相似文献
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Daniel J. BOMBARDIERI Marc D. NORMAN Vadim S. KAMENETSKY Leonid V. DANYUSHEVSKY 《Meteoritics & planetary science》2005,40(5):679-693
Abstract— Major element and sulfur concentrations have been determined in experimentally heated olivine‐hosted melt inclusions from a suite of Apollo 12 picritic basalts (samples 12009, 12075, 12020, 12018, 12040, 12035). These lunar basalts are likely to be genetically related by olivine accumulation (Walker et al. 1976a, b). Our results show that major element compositions of melt inclusions from samples 12009, 12075, and 12020 follow model crystallization trends from a parental liquid similar in composition to whole rock sample 12009, thereby partially confirming the olivine accumulation hypothesis. In contrast, the compositions of melt inclusions from samples 12018, 12040, and 12035 fall away from model crystallization trends, suggesting that these samples crystallized from melts compositionally distinct from the 12009 parent liquid and therefore may not be strictly cogenetic with other members of the Apollo 12 picritic basalt suite. Sulfur concentrations in melt inclusions hosted in early crystallized olivine (Fo75) are consistent with a primary magmatic composition of 1050 ppm S, or about a factor of 2 greater than whole rock compositions with 400–600 ppm S. The Apollo 12 picritic basalt parental magma apparently experienced outgassing and loss of S during transport and eruption on the lunar surface. Even with the higher estimates of primary magmatic sulfur concentrations provided by the melt inclusions, the Apollo 12 picritic basalt magmas would have been undersaturated in sulfide in their mantle source regions and capable of transporting chalcophile elements from the lunar mantle to the surface. Therefore, the measured low concentration of chalcophile elements (e.g., Cu, Au, PGEs) in these lavas must be a primary feature of the lunar mantle and is not related to residual sulfide remaining in the mantle during melting. We estimate the sulfur concentration of the Apollo 12 mare basalt source regions to be ~75 ppm, which is significantly lower than that of the terrestrial mantle. 相似文献
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Marc Hemsendorf 《Astrophysics and Space Science》2003,284(2):561-564
Collapsing collisionless particle systems form gravitational bound halos with cuspy density profiles. Also hierarchical merging
of these systems produce remnants with cuspy central density profiles. These results lead to the assumption of cuspy NFW (Navarro
et al., 1996) profiles for the density distribution in dark matter halos. However, observed rotation curves in disk galaxies
suggest dark matter halos with isothermal cores. The same kind of problem can be found for globular clusters, which show cores
in their density profiles but should be cuspy if they where formed through a cold collapse(King, 1962; Jenkins et al., 1998).
We are showing how small, massive, and compact objects can efficiently transform cuspy stellar systems into density profiles
with an isothermal core.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
848.
Emmanuel Chapron Fabien Arnaud HERVÉ Noël Marie Revel Marc Desmet Laurent Perdereau 《Boreas: An International Journal of Quaternary Research》2005,34(4):404-416
The Holocene evolution of Rhone River clastic sediment supply in Lake Le Bourget is documented by sub-bottom seismic profiling and multidisciplinary analysis of well-dated sediment cores. Six high-amplitude reflectors within the lacustrine drape can be correlated to periods of enhanced inter- and underflow deposition in sediment cores. Based on the synthesis of major environmental changes in the NW Alps and on the age-depth model covering the past 7500 years in Lake Le Bourget, periods of enhanced Rhone River flood events in the lake can be related to abrupt climate changes and/or to increasing land use since c. 2700 cal. yr BP. For example, significant land use under rather stable climate conditions during the Roman Empire may be responsible for large flood deposits in the northern part of Lake Le Bourget between AD 966 and 1093. However, during the Little Ice Age (LIA), well-documented major environmental changes in the catchment area essentially resulted from climate change and formed basin-wide major flood deposits in Lake Le Bourget. Up to five 'LIA-like' Holocene cold periods developing enhanced Rhone River flooding activity in Lake Le Bourget are documented at c. 7200, 5200, 2800, 1600 and 200 cal. yr BP. These abrupt climate changes were associated in the NW Alps with Mont Blanc glacier advances, enhanced glaciofluvial regimes and high lake levels. Correlations with European lake level fluctuations and winter precipitation regimes inferred from glacier fluctuations in western Norway suggest that these five Holocene cooling events at 45°N were associated with enhanced westerlies, possibly resulting from a persistent negative mode of the North Atlantic Oscillation. 相似文献
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