排序方式： 共有37条查询结果，搜索用时 15 毫秒
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Philip Lah Jayaram N. Chengalur Frank H. Briggs Matthew Colless Roberto De Propris Michael B. Pracy W. J. G. de Blok Shinobu S. Fujita Masaru Ajiki Yasuhiro Shioya Tohru Nagao Takashi Murayama Yoshiaki Taniguchi Masafumi Yagi Sadanori Okamura 《Monthly notices of the Royal Astronomical Society》2007,376(3):1357-1366
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Prasun Dutta Ayesha Begum Somnath Bharadwaj Jayaram N. Chengalur 《Monthly notices of the Royal Astronomical Society》2009,398(2):887-897
We estimate the power spectrum of H i intensity fluctuations for a sample of eight galaxies (seven dwarf and one spiral). The power spectrum can be fitted to a power-law for six of these galaxies, indicating turbulence is operational. The estimated best-fitting value for the slope ranges from ∼−1.5 (AND IV, NGC 628, UGC 4459 and GR 8) to ∼−2.6 (DDO 210 and NGC 3741). We interpret this bi-modality as being due to having effectively 2D turbulence on length-scales much larger than the scale-height of the galaxy disc and 3D otherwise. This allows us to use the estimated slope to set bounds on the scale-heights of the face-on galaxies in our sample. We also find that the power-law slope remains constant as we increase the channel thickness for all these galaxies, suggesting that the fluctuations in H i intensity are due to density fluctuations and not velocity fluctuations, or that the slope of the velocity structure function is ∼0. Finally, for the four galaxies with '2D turbulence' we find that the slope α correlates with the star formation rate (SFR) per unit area, with larger SFRs leading to steeper power laws. Given our small sample size, this result needs to be confirmed with a larger sample. 相似文献
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Mineral compositions from cordierite-bearing metasedimentary enclaves adjacent to the Closepet granite in the Bangalore region of the South Indian Craton indicate peak metamorphism in the range 4.5–5.0 kb, 690–730°C. PH2O is found to decrease towards the south and those assemblages which lie south of the charnockite line are formed under conditions of PH2O < 0.3 Ptotal. 250 km north Bangalore, andalusite-bearing assemblages from the northern margin of the Closepet granite indicate peak metamorphic conditions in the range 2.6–3.8 kb, 520–620°C. The inferred piezotacrmic array is strongly convex towards the temperature axis and may represent a transient geotherm in the upper crust related to the emplacement of the Closepet granite or to volatile activity along the margins of the granite. 相似文献
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Nathaniel G. Plant Kacey L. Edwards James M. Kaihatu Jayaram Veeramony Larry Hsu K. Todd Holland 《Coastal Engineering》2009
Nearshore wave and flow model results are shown to exhibit a strong sensitivity to the resolution of the input bathymetry. In this analysis, bathymetric resolution was varied by applying smoothing filters to high-resolution survey data to produce a number of bathymetric grid surfaces. We demonstrate that the sensitivity of model-predicted wave height and flow to variations in bathymetric resolution had different characteristics. Wave height predictions were most sensitive to resolution of cross-shore variability associated with the structure of nearshore sandbars. Flow predictions were most sensitive to the resolution of intermediate scale alongshore variability associated with the prominent sandbar rhythmicity. Flow sensitivity increased in cases where a sandbar was closer to shore and shallower. Perhaps the most surprising implication of these results is that the interpolation and smoothing of bathymetric data could be optimized differently for the wave and flow models. We show that errors between observed and modeled flow and wave heights are well predicted by comparing model simulation results using progressively filtered bathymetry to results from the highest resolution simulation. The damage done by over smoothing or inadequate sampling can therefore be estimated using model simulations. We conclude that the ability to quantify prediction errors will be useful for supporting future data assimilation efforts that require this information. 相似文献
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Nissim Kanekar Ravi Subrahmanyan Jayaram N Chengalur Vicky Safouris 《Monthly notices of the Royal Astronomical Society》2003,346(4):L57-L61
We report high-spectral-resolution Australia Telescope Compact Array (ATCA) H i 21-cm observations resulting in the detection of the warm neutral medium (WNM) of the Galaxy in absorption against two extragalactic radio sources, PKS 1814−637 and PKS 0407−658. The two lines of sight were selected on the basis of the simplicity of their absorption profiles and the strength of the background sources; the high velocity resolution of the spectra then enabled us to estimate the kinetic temperatures of the absorbing gas by fitting multiple Gaussians to the absorption profiles. Four separate WNM components were detected towards the two sources, with peak optical depths τmax = (1.0 ± 0.08) × 10−2 , (1.4 ± 0.2) × 10−3 , (2.2 ± 0.5) × 10−3 and (3.4 ± 0.5) × 10−3 and kinetic temperatures T k = 3127 ± 300, 3694 ± 1595, 3500 ± 1354 and 2165 ± 608 K , respectively. All four components were thus found to have temperatures in the thermally unstable range 500 < T k < 5000 K ; this suggests that thermal equilibrium has not been reached throughout the WNM. 相似文献
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Risk assessment of spatially distributed building portfolios or infrastructure systems requires quantification of the joint occurrence of ground‐motion intensities at several sites, during the same earthquake. The ground‐motion models that are used for site‐specific hazard analysis do not provide information on the spatial correlation between ground‐motion intensities, which is required for the joint prediction of intensities at multiple sites. Moreover, researchers who have previously computed these correlations using observed ground‐motion recordings differ in their estimates of spatial correlation. In this paper, ground motions observed during seven past earthquakes are used to estimate correlations between spatially distributed spectral accelerations at various spectral periods. Geostatistical tools are used to quantify and express the observed correlations in a standard format. The estimated correlation model is also compared with previously published results, and apparent discrepancies among the previous results are explained. The analysis shows that the spatial correlation reduces with increasing separation between the sites of interest. The rate of decay of correlation typically decreases with increasing spectral acceleration period. At periods longer than 2 s, the correlations were similar for all the earthquake ground motions considered. At shorter periods, however, the correlations were found to be related to the local‐site conditions (as indicated by site Vs30 values) at the ground‐motion recording stations. The research work also investigates the assumption of isotropy used in developing the spatial correlation models. It is seen using the Northridge and Chi‐Chi earthquake time histories that the isotropy assumption is reasonable at both long and short periods. Based on the factors identified as influencing the spatial correlation, a model is developed that can be used to select appropriate correlation estimates for use in practical risk assessment problems. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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