Numerical simulation of fully saturated porous materials     

Boris Jeremić  Zhao Cheng  Mahdi Taiebat  Yannis Dafalias 《国际地质力学数值与分析法杂志》2008,32(13):1635-1660

Fully coupled, porous solid–fluid formulation, implementation and related modeling and simulation issues are presented in this work. To this end, coupled dynamic field equations with u?p?U formulation are used to simulate pore fluid and soil skeleton (elastic–plastic porous solid) responses. Present formulation allows, among other features, for water accelerations to be taken into account. This proves to be useful in modeling dynamic interaction of media of different stiffnesses (as in soil–foundation–structure interaction). Fluid compressibility is also explicitly taken into account, thus allowing excursions into modeling of limited cases of non‐saturated porous media. In addition to these features, present formulation and implementation models in a realistic way the physical damping, which dissipates energy. In particular, the velocity proportional damping is appropriately modeled and simulated by taking into account the interaction of pore fluid and solid skeleton. Similarly, the displacement proportional damping is physically modeled through elastic–plastic processes in soil skeleton. An advanced material model for sand is used in present work and is discussed at some length. Also explored in this paper are the verification and validation issues related to fully coupled modeling and simulations of porous media. Illustrative examples describing the dynamical behavior of porous media (saturated soils) are presented. The verified and validated methods and material models are used to predict the behavior of level and sloping grounds subjected to seismic shaking. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Ultraviolet Studies of Interacting Binaries     

Boris T. Gänsicke  Domitilla de Martino  Thomas R. Marsh  Carole A. Haswell  Christian Knigge  Knox S. Long  Steven N. Shore 《Astrophysics and Space Science》2006,306(3):177-177

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Venusian impact craters on Magellan images: View from Venera 15/16     

Ivanov  Boris A. 《Earth, Moon, and Planets》1990,(1):159-173

The review of the data of the analysis of images of Venera 15/16 mission is done. These data are used to make some predictions of how many impact craters the MAGELLAN space probe would see on Venus and how they would look. The possible trends of crater areal distribution and characteristic features of the size-frequency relationship are discussed.'Geology and Tectonics of Venus', special issue edited by Alexander T. Basilevsky (USSR Acad. of Sci. Moscow), James W. Head (Brown University, Providence), Gordon H. Pettengill (MIT, Cambridge, Massachusetts) and R. S. Saunders (J.P.L., Pasadena).  相似文献   

Crossing Filaments     

Boris Filippov  A. K. Srivastava 《Solar physics》2011,270(1):151-164

Solar filaments show the position of large-scale polarity-inversion lines and are used for the reconstruction of large-scale solar magnetic field structure on the basis of Hα synoptic charts for the periods that magnetographic measurements are not available. Sometimes crossing filaments are seen in Hα filtergrams. We analyze daily Hα filtergrams from the archive of Big Bear Solar Observatory for the period of 1999 – 2003 to find crossing and interacting filaments. A number of examples are presented and filament patterns are compared with photospheric magnetic field distributions. We have found that all crossing filaments reveal quadrupolar magnetic configurations of the photospheric field and presume the presence of null points in the corona.  相似文献   

Climate Change and Geochemistry May Explain the Finding of Marine Cyanobacteria in a Continental Saline Lake     

Zorigto NAMSARAEV  Vladimir GORLENKO  Boris KUZNETSOV  Bair NAMSARAEV 《《地质学报》英文版》2014,88(Z1):158-159

正1 Introduction Alkaline Lake Khilganta located in a steppe zone of South Siberia(N 50°42'535,E 115°06'086)is unique among adjacent lakes because of a development of a thick(up to 3 cm)cyanobacterial mat dominated by  相似文献   

A theory of the Trojan asteroids     

Boris Garfinkel 《Celestial Mechanics and Dynamical Astronomy》1976,14(3):301-306

The paper constructs a long-periodic solution for the case of 11 resonance in the restricted problem of three bodies. The solution is smoothed by the exclusion of the internal resonant terms arising from the near-commensurability between the long and the short periods of the asteroid.Although the Brown (1911) conjecture regarding the termination of the family of the tadpoles at the Lagrangian pointL ₃ is not supported by our analysis, the conjecture seems to hold in the limit asm0.  相似文献   

Mycological evidence of coprophagy from the feces of an Alaskan Late Glacial mammoth     

Bas van Geel  R. Dale Guthrie  Jens G. Altmann  Peter Broekens  Ian D. Bull  Fiona L. Gill  Boris Jansen  Aline M. Nieman  Barbara Gravendeel 《Quaternary Science Reviews》2011,30(17-18):2289-2303

Dung from a mammoth was preserved under frozen conditions in Alaska. The mammoth lived during the early part of the Late Glacial interstadial (ca 12,300 BP). Microfossils, macroremains and ancient DNA from the dung were studied and the chemical composition was determined to reconstruct both the paleoenvironment and paleobiology of this mammoth. Pollen spectra are dominated by Poaceae, Artemisia and other light-demanding taxa, indicating an open, treeless landscape (‘mammoth steppe’). Fruits and seeds support this conclusion. The dung consists mainly of cyperaceous stems and leaves, with a minor component of vegetative remains of Poaceae. Analyses of fragments of the plastid rbcL gene and trnL intron and nrITS1 region, amplified from DNA extracted from the dung, supplemented the microscopic identifications. Many fruit bodies with ascospores of the coprophilous fungus Podospora conica were found inside the dung ball, indicating that the mammoth had eaten dung. The absence of bile acids points to mammoth dung. This is the second time that evidence for coprophagy of mammoths has been derived from the presence of fruit bodies of coprophilous fungi in frozen dung. Coprophagy might well have been a common habit of mammoths. Therefore, we strongly recommend that particular attention should be given to fungal remains in future fossil dung studies.  相似文献   

Self-Regulating Supernova Heating in Interstellar Medium Simulations     

Graeme R. Sarson  Anvar Shukurov  Åke Nordlund  Boris Gudiksen  Axel Brandenburg 《Astrophysics and Space Science》2004,292(1-4):267-272

Numerical simulations of the multi-phase interstellar medium have been carried out, using a 3D, nonlinear, magnetohydrodynamic, shearing-box model, with random motions driven by supernova explosions. These calculations incorporate the effects of magnetic fields and rotation in 3D; these play important dynamical roles in the galaxy, but are neglected in many other simulations. The supernovae driving the motions are not arbitrarily imposed, but occur where gas accumulates into cold, dense clouds; their implementation uses a physically motivated model for the evolution of such clouds. The process is self-regulating, and produces mean supernova rates as part of the solution. Simulations with differing mean density show a power law relation between the supernova rate and density, with exponent 1.7; this value is within the range suggested from observations (taking star formation rate as a proxy for supernova rate). The global structure of the supernova driven medium is strongly affected by the presence of magnetic fields; e.g. for one solution the filling factor of hot gas is found to vary from 0.19 (with no field) to 0.12 (with initial mid-plane field B ₀ = 6 μG).  相似文献   

A potentiometric study of the stability of aqueous yttrium-acetate complexes from 25 to 175 °C and 1-1000 bar     

Boris Tagirov  Alexander Zotov  Oleg Suleimenov 《Geochimica et cosmochimica acta》2007,71(7):1689-1708

The stability of yttrium-acetate (Y-Ac) complexes in aqueous solution was determined potentiometrically at temperatures 25-175 °C (at P_s) and pressures 1-1000 bar (at 25 and 75 °C). Measurements were performed using glass H⁺-selective electrodes in potentiometric cells with a liquid junction. The species YAc²⁺ and were found to dominate yttrium aqueous speciation in experimental solutions at 25-100 °C (log [Ac⁻] < −1.5, pH < 5.2), whereas at 125, 150 and 175 °C introduction of into the Y-Ac speciation model was necessary. The overall stability constants β_n were determined for the reaction