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991.
Rhian H. JONES 《Meteoritics & planetary science》2012,47(7):1176-1190
Abstract– Chondrules from different chondrite groups show characteristic properties, including abundances of different chondrule textural types, chondrule sizes, oxygen isotope compositions, chondrule bulk compositions, and petrographic properties of type I and type II chondrules, including abundances of relict grains. Overall, it can be argued that each chondrite group sampled a unique chondrule reservoir, and that chondrite groups may represent fractions of larger reservoirs that are represented by chondrite classes. These observations provide constraints for models of the early solar system, in which it is necessary to establish multiple separate chondrule reservoirs and maintain them over extended time periods. Models for accretion of chondrite parent bodies must be able to account for localized accretion of chondrules that were formed in spatially or temporally separated reservoirs. 相似文献
992.
Peter J. Wheatley Timothy R. Kallman 《Monthly notices of the Royal Astronomical Society》2006,372(4):1602-1606
We have re-analysed the ASCA X-ray spectrum of the bright symbiotic star CH Cyg, which exhibits apparently distinct hard and soft X-ray components. Our analysis demonstrates that the soft X-ray emission can be interpreted as scattering of the hard X-ray component in a photoionized medium surrounding the white dwarf. This is in contrast to previous analyses in which the soft X-ray emission was fitted separately and assumed to arise independently of the hard X-ray component. We note the striking similarity between the X-ray spectra of CH Cyg and Seyfert 2 galaxies, which are also believed to exhibit scattering in a photoionized medium. 相似文献
993.
994.
Transient sediment supply in a high‐altitude Alpine environment evidenced through a 10Be budget of the Etages catchment (French Western Alps) 下载免费PDF全文
Romain Delunel Peter A. van der Beek Didier L. Bourlès Julien Carcaillet Fritz Schlunegger 《地球表面变化过程与地形》2014,39(7):890-899
Although beryllium‐10 (10Be) concentrations in stream sediments provide useful synoptic views of catchment‐wide erosion rates, little is known on the relative contributions of different sediment supply mechanisms to the acquisition of their initial signature in the headwaters. Here we address this issue by conducting a 10Be‐budget of detrital materials that characterize the morphogenetic domains representative of high‐altitude environments of the European Alps. We focus on the Etages catchment, located in the Ecrins‐Pelvoux massif (southeast France), and illustrate how in situ 10Be concentrations can be used for tracing the origin of the sand fraction from the bedload in the trunk stream. The landscape of the Etages catchment is characterized by a geomorphic transient state, high topographic gradients, and a large variety of modern geomorphic domains ranging from glacial environments to scarcely vegetated alluvial plains. Beryllium‐10 concentrations measured in the Etages catchment vary from ~1 × 104 to 4.5 × 105 atoms per gram quartz, while displaying consistent 10Be signatures within each representative morphogenetic unit. We show that the basic requirements for inferring catchment‐wide denudation from 10Be concentration measurements are not satisfied in this small, dynamic catchment. However, the distinct 10Be signature observed for the geomorphic domains can be used as a tracer. We suggest that a terrestrial cosmogenic nuclide (TCN) budget approach provides a valuable tool for the tracing of material origin in basins where the ‘let nature do the averaging’ principles may be violated. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
995.
Non-linear response of the soil is investigated by comparing the spectral ratios (uphole/downhole) using weak and strong motions. Data from seven vertical arrays in Japan are analysed in this study. The frequency-dependent transfer function of soil is calculated as a ratio of the spectrum at uphole to the spectrum at downhole, considering the horizontal component of shear wave. In spectral ratio analysis auto- and cross-spectra are employed. The reduction in the predominant frequency of the transfer function with increases in excitation level reflects the non-linear response of the soil. Results of analysis demonstrate a significant non-linear ground response at six sites with surface PGA exceeding 90 gal. However, the results of one site show the linear response up to 130 gal surface PGA. Furthermore, the in situ strain-dependent soil behaviour is examined through the shear modulus – shear strain relationship. When compared, the actual and laboratory results of the shear strain – shear modulus relationship are in agreement. Additionally, a good consistency between the tendency of reduction in shear modulus ratio with shear strain increases, and reduction of predominant frequency with ground motion increases, confirms the significance of non-linearity in site effects study. 相似文献
996.
997.
B. J. Travis C. Anderson J. Baumgardner C. W. Gable B. H. Hager R. J. O'Connell 《地球物理与天体物理流体动力学》2013,107(3-4):137-160
Abstract A comparison is made between seven different numerical methods for calculating two-dimensional thermal convection in an infinite Prandtl number fluid. Among the seven methods are finite difference and finite element techniques that have been used to model thermal convection in the Earth's mantle. We evaluate the performance of each method using a suite of four benchmark problems, ranging from steady-state convection to intrinsically time-dependent convection with recurring thermal boundary layer instabilities. These results can be used to determine the accuracy of other computational methods, and to assist in the development of new ones. 相似文献
998.
999.
Generation, migration and accumulation of petroleum in a sedimentary basin is a function of geologic, hydrodynamic and thermodynamic development of the basin and the type and amount of organic matter. Temperature history not only determines rate of hydrocarbon generation, but also affects paleohydrodynamics and physical and thermal properties vs depth relationships. Therefore, paleotemperature is the most important parameter. Paleohydrodynamics together with geologic history of the basin is important in shaping secondary migration patterns and accumulation of hydrocarbons.Quantification of all the above processes is complicated. Steps in constructing a deterministic dynamic model for calculation of petroleum potential during a sedimentary basin development are stated and analyzed in this paper. The effect of paleotemperature variations on petroleum generation and on physical properties of sedimentary sequences are illustrated by numerical examples. Computer models will enable exploration geologists to make quantitative exploration predictions in sedimentary basins. 相似文献
1000.
A. T. M. Sakiur Rahman Takahiro Hosono Ozgur Kisi Boateng Dennis A. H. M. Rahmatullah Imon 《水文科学杂志》2020,65(12):1994-2006
ABSTRACT This study aimed to evaluate the potential of the recently introduced Prophet model for estimating reference evapotranspiration (ETo). A comparative study was conducted for benchmarking the model results with support vector regression (SVR) and temperature-based empirical models (Thornthwaite and Hargreaves) in southern Japan. The performance of the Prophet, SVR and temperature-based empirical models was evaluated by Nash–Sutcliffe efficiency (NSE) and coefficient of determination (R2). The results indicate that temperature-based Prophet and SVR models have greater accuracy than the empirical models. The Prophet model with sole input of relative humidity, sunshine hours or windspeed showed acceptable accuracy (NSE > 0.80; R2 > 0.80), while SVR models with similar inputs showed greater errors. Accuracy improved with increasing number of input parameters, giving excellent performance (NSE > 0.95; R2 > 0.95) with all input parameters. Hence, the Prophet model is a new promising approach for modelling ETo with limited input variables. 相似文献