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排序方式: 共有610条查询结果,搜索用时 15 毫秒
521.
C. J. Loupasakis B. G. Christaras G. Ch. Dimopoulos T. N. Hatzigogos 《Geotechnical and Geological Engineering》2009,27(1):71-80
The selection of the constitutive laws reproducing the response of geomaterials usually becomes a very complicated procedure;
especially during the analysis of geostructures containing coarse grained materials. The objective of this study, is the evaluation
of models based on the perfect and hardening plasticity theory, regarding their ability to analyze the behaviour of soil materials,
used for the construction of earth dams. The evaluated constitutive laws are the elastic–perfect plastic model based on the
Mohr–Coulomb failure criterion and the isotropic hardening CAP model based on the same criterion. The data used for the evaluation
of the models, originate from the body of the Sfikia earth dam. This dam is considered suitable, because of the specialized
laboratory tests’ available data, regarding the materials of every zone. The availability of those data, as well as the variety
of the construction geomaterials, allows the deduction of generalized conclusions, concerning the ability of the specific
models to simulate a variety of similar earth constructions. 相似文献
522.
St. Raetz M. Vako M. Mugrauer T.O.B. Schmidt T. Roell T. Eisenbeiss M. M. Hohle A. Koeltzsch Ch. Ginski C. Marka M. Moualla N. Tetzlaff Ch. Broeg R. Neuhuser 《Astronomische Nachrichten》2009,330(5):504-510
We report on observations of the eclipsing binary 2MASS 19090585+4911585 with the 25 cm auxiliary telescope of the University Observatory Jena. We show that a nearby brighter star (2MASS 19090783+4912085) was previously misclassified as the eclipsing binary and find 2MASS 19090585+4911585 to be the true source of variation. We present photometric analysis of VRI light curves. The system is an overcontact binary of W UMa type with an orbital period of (0.288374 ± 0.000010) d (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
523.
Telemachos Ch. Mouschovias Matthew W. Kunz Duncan A. Christie 《Monthly notices of the Royal Astronomical Society》2009,397(1):14-23
We numerically follow the nonlinear evolution of the Parker instability in the presence of phase transitions from a warm to a cold H i interstellar medium in two spatial dimensions. The nonlinear evolution of the system favours modes that allow the magnetic field lines to cross the galactic plane. Cold H i clouds form with typical masses ≃105 M⊙ , mean densities ≃20 cm−3 , mean magnetic-field strengths ≃4.3 μG (rms field strengths ≃6.4 μG ), mass-to-flux ratios ≃0.1–0.3 relative to critical, temperatures ≃50 K , (two-dimensional) turbulent velocity dispersions ≃1.6 km s−1 and separations ≃500 pc , in agreement with observations. The maximum density and magnetic-field strength are ≃103 cm−3 and ≃20 μG , respectively. Approximately 60 per cent of all H i mass is in the warm neutral medium. The cold neutral medium is arranged into sheet-like structures both perpendicular and parallel to the galactic plane, but it is also found almost everywhere in the galactic plane, with the density being highest in valleys of the magnetic field lines. 'Cloudlets' also form whose physical properties are in quantitative agreement with those observed for such objects by Heiles. The nonlinear phase of the evolution takes ≲30 Myr, so that, if the instability is triggered by a nonlinear perturbation such as a spiral density shock wave, interstellar clouds can form within a time suggested by observations. 相似文献
524.
We present a set of gas-phase Planck mean and Rosseland mean opacity tables applicable for simulations of star and planet formation, stellar evolution and disc modelling at various metallicities in hydrogen-rich environments. The tables are calculated for gas temperatures between 1000 and 10 000 K and total hydrogen number densities between 102 and 1017 cm−3 . The carbon-to-oxygen ratio is varied from 0.43 to well above 2.0, the nitrogen-to-oxygen ratio between 0.14 and 100.0. The tables are calculated for a range of metallicities down to [M/H]'= log N M / N H =−7.0 . We demonstrate how the mean opacities and the abundances of the opacity species vary with C/O, N/O and [M/H]' . We use the element abundances from Grevesse et al., and we provide additional tables for the oxygen abundance value from Caffau et al. All tables will be available online at http://star-www.st-and.ac.uk/~ch80/datasources.html . 相似文献
525.
526.
The aim of the present investigation has been to investigate numerically the orbits of particles in the gravitational field of barred galaxies for different models of such formations; with special attention to the families of direct periodic orbits in the co-rotating frame. 相似文献
527.
528.
H. Wieseneder K. Becherer J. Zemann E. Schroll Ch. Exner 《Mineralogy and Petrology》1969,13(3-4):293-298
Ohne Zusammenfassung 相似文献
529.
B. Ammann A. F. Lotter U. Eicher M.-J. Gaillard B. Wohlfarth W. Haeberli G. Lister M. Maisch F. Niessen Ch. Schlüchter 《第四纪科学杂志》1994,9(2):119-125
A synthesis is provided of Late-glacial (14-9 ka BP) environmental changes in lowland Switzerland (the ‘Swiss Plateau’). The chronology of deglaciation and subsequent developments in vegetation cover in the area are summarised. The sequence of climatic variations experienced in the region during the Late-glacial is then described and a curve representing the main palaeotemperature variations is presented. 相似文献
530.
Seismic ground motion in central Mexico is amplified relative to ground motion observed at the same epicentral distance along the Pacific Coast in a frequency band that includes destructive ground motion at Mexico City. Although several hypothesis have been advanced, at present there is no generally accepted explanation of such amplification. We have analyzed coda-length magnitude data reported by Servicio Sismológico Nacional (SSN) for events recorded during 1993 to increase our understanding of the spatial distribution of this phenomenon. Our results indicate that regional amplification: (a) is detected by magnitude residual computed at each station, relative to the average of SSN network;and (b) is likely related to the crustal structure under the central portion of the Transmexican Volcanic Belt (TMVB). Finally, preliminary wave propagation modelling (using SH wave, finite difference method) suggests that crustal heterogeneity is a possible cause of regional amplification. However, if this is so, it is required that both geometry and velocity distribution vary between the coast and Mexico City. 相似文献