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Natalia Orlova Vladimir Korchagin Nobuhiro Kikuchi Shoken. M. Miyama Aleksei Moiseev 《Astrophysics and Space Science》2003,284(2):739-742
We have tested the applicability of the global modal approach in the density wave theory of spiral structure for a sample
of spiral galaxies with measured axisymmetric background properties. We report here the results of the simulations for four
galaxies: NGC 488, NGC 628, NGC 1566, and NGC 3938. Using the observed radial distributions for the stellar velocity dispersions
and the rotation velocities we have constructed the equilibrium models for the galactic disks in each galaxy and implemented
two kinds of stability analyses - the linear global analysis and 2D-nonlinear simulations. In general, the global modal approach
is able to reproduce the observed properties of the spiral arms in the galactic disks. The growth of spirals in the galactic
disks can be physically understood in terms of amplification by over-reflection at the corotation resonance. Our results support
the global modal approach as a theoretical explanation of spiral structure in galaxies.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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Genetic diversity and differentiation of the oyster Crassostreaplicatula populations from China's coast were studied basedon seven microsatellite loci.All loci showed high polymorphism for all five C.plicatula populations,with an average number of alleleper locus of 19.3-27.9 and an average expected heterozygosity of 0.889-0.952.Significant departures from Hardy-Weinberg equilib-rium and deficits of heterozygotes were observed over most populations at each locus,which were fully explained by null alleles.Microsatellite analysis revealed significant subdivision in the C.plicatula populations.According to the neighbor-joining tree con-structed on the basis of the D,A distance,the five populations fell into three regional groups,showing a relatively homogeneous geneticstructure in geographically close populations.Assignation tests correctly assigned high percentages of individuals to their originalpopulations and groups,and also confirmed the existence of genetic differentiation among C.plicatula populations.The results ob-tained in this study will facilitate the formulation of appropriate fisheries management programs,stock identification and conservationof biodiversity for the species. 相似文献
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I.IN~crIOXLocatedinthecoddlepatofTallmBasin,withanareaof33.76X104klnZ,theTaldirnakan~isinthehinterlandofEurasia.Blockedbythehighmountainsaround,vapourofoceancanhardlyreachthedesert.APartfromthis,asthedeSertisinthesinkingcompensationareaoftheascensionalaircurrentaamstheQinghal-XIZangPlateau,itSprecipitationisrareandtheevaporationcapacityisintensealltheyearround.Allthesecontributetotheformationsofthetypifydrydesertclimate.Theacidityindexofthedesertandthearoundregionisashighasmorethan50,w… 相似文献
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Based on the Germany Koldwey Station's 1994-2003 conventional observation hourly data, this paper conducts a statistical analysis on the short-term climate characteristics for an arctic tundra region (Ny-(A)lesund island) where our first arctic expedition station (Huanghe Station) was located. Affected by the North Atlantic warming current, this area has a humid temperate climate, and the air temperature at Ny-(A)lesund rose above 0 ℃ even during deep winter season during our research period. The wind speed in this area was low and appeared most at southeast direction. We find that the temperature at Ny-(A)lesund rose in the faster rate (0.68 ℃/10 a) than those at the whole Arctic area. Compared with the floating ices where our expedition conducted in the Arctic, Ny-(A)lesund was warmer and more humid and had lower wind speed. Comparison of the near surface air temperature derived by NCEP/NCAR reanalysis to the conventional measurements conducted at the Koldwey site in Ny-(A)lesund area shows a good agreement for winter season and a significant difference for summer season. 相似文献