Stochastic Excitation of Gravity Waves by Overshooting Convection in Solar-Type Stars     

Boris Dintrans  Axel Brandenburg  Åke Nordlund  Robert F. Stein 《Astrophysics and Space Science》2003,284(1):237-240

The excitation of gravity waves by penetrative convective plumes isinvestigated using 2D direct simulations of compressible convection.The oscillation field is measured by a new technique based on theprojection of our simulation data onto the theoretical g-modes solutionsof the associated linear eigenvalue problem. This allows us to determineboth the excited modes and their corresponding amplitudes accurately.  相似文献   

The Need for Ultraviolet to Understand the Chemical Evolution of the Universe and Cosmology.     

Willem Wamsteker  Jason X. Prochaska  Luciana Bianchi  Dieter Reimers  Nino Panagia  Andrew C. Fabian  Claes Fransson  Boris M. Shustov  Patrick Petitjean  Phillipp Richter  Eduardo Battaner 《Astrophysics and Space Science》2006,303(1-4):69-84

We identify an important set of key areas where an advanced observational Ultraviolet capability would have major impact on studies of cosmology and Galaxy formation in the young Universe. Most of these are associated with the Universe at z < 3–4. We address the issues associated with Dark matter evidence in the local Universe and the impact of the Warm-Hot Intergalactic Medium WHIM on the local Baryon count. The motivations to make ultraviolet (UV) studies of supernovae (SNe) are reviewed and discussed in the light of the results obtained so far by means of IUE and HST observations. It appears that UV studies of SNe can, and do lead to fundamental results not only for our understanding of the SN phenomenon, such as the kinematics and the metallicity of the ejecta, but also for exciting new findings in Cosmology, such as the tantalizing evidence for “dark energy” that seems to pervade the Universe and to dominate its energetics. The need for additional and more detailed UV observations is also considered and discussed.Finally we show the enormous importance of the UV for abundance evolution in the Intergalactic Medium (IGM), and the importance of the He II studies to identify re-ionization epochs, which can only be done in the UV.  相似文献   

On the Stability of Planar Oscillations and Rotations of a Satellite in a Circular Orbit     

Anatoliy P. Markeev  Boris S. Bardin 《Celestial Mechanics and Dynamical Astronomy》2003,85(1):51-66

We deal with the stability problem of planar periodic motions of a satellite about its center of mass. The satellite is regarded a dynamically symmetric rigid body whose center of mass moves in a circular orbit.By using the method of normal forms and KAM theory we study the orbital stability of planar oscillations and rotations of the satellite in detail. In two special cases we investigate the orbital stability analytically by introducing a small parameter. In the general case, numerical calculations of Hamiltonian normal form are necessary.  相似文献   

Cosmological weak lensing with the HST GEMS survey     

Catherine Heymans  Michael L. Brown  Marco Barden  John A. R. Caldwell  Knud Jahnke  Chien Y. Peng  Hans-Walter Rix  y Taylor  Steven V. W. Beckwith  Eric F. Bell  rea Borch  Boris Häußler  Shardha Jogee  Daniel H. McIntosh  Klaus Meisenheimer  Sebastian F. Sánchez  Rachel Somerville  Lutz Wisotzki  Christian Wolf 《Monthly notices of the Royal Astronomical Society》2005,361(1):160-176

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Launch of martian meteorites in oblique impacts   总被引：1，自引：0，他引：1  

Natalia Artemieva  Boris Ivanov 《Icarus》2004,171(1):84-101

A high-velocity oblique impact into the martian surface accelerates solid target material to escape velocity. A fraction of that material eventually falls as meteorites on Earth. For a long time they were called the SNC meteorites (Shergotty, Nakhla, and Chassigny). We study production of potential martian meteorites numerically within the frame of 3D hydrodynamic modeling. The ratio of the volume of escaping solid ejecta to projectile volume depends on the impact angle, impact velocity and the volatile content in the projectile and in the target. The size distribution of ejected fragments appears to be of crucial importance for the atmosphere-ejecta interaction in the case of a relatively small impact (with final crater size <3 km): 10-cm-sized particles are decelerated efficiently, while 30-50% of larger fragments could escape Mars. The results of numerical modeling are compared with shock metamorphic features in martian meteorites, their burial depth, and preatmospheric mass. Although it is impossible to accelerate ejected fragments to escape velocity without substantial compression (above 10 GPa), the maximum temperature increase in dunite (Chassigny) or ortopyroxenite (ALH84001) may be lower than 200 degree. This result is consistent with the observed chaotic magnetization of ALH84001. The probability of microbes' survival may be rather high even for the extreme conditions during the ejection process.  相似文献   

Tensor visualizations in computational geomechanics     

Boris Jeremi&#x;  Gerik Scheuermann  Jan Frey  Zhaohui Yang  Bernd Hamann  Kenneth I. Joy  Hans Hagen 《国际地质力学数值与分析法杂志》2002,26(10):925-944

We present a novel technique for visualizing tensors in three dimensional (3D) space. Of particular interest is the visualization of stress tensors resulting from 3D numerical simulations in computational geomechanics. To this end we present three different approaches to visualizing tensors in 3D space, namely hedgehogs, hyperstreamlines and hyperstreamsurfaces. We also present a number of examples related to stress distributions in 3D solids subjected to single and load couples. In addition, we present stress visualizations resulting from single‐pile and pile‐group computations. The main objective of this work is to investigate various techniques for visualizing general Cartesian tensors of rank 2 and it's application to geomechanics problems. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Template elastic‐plastic computations in geomechanics     

Boris Jeremi&#x;  Zhaohui Yang 《国际地质力学数值与分析法杂志》2002,26(14):1407-1427

In this paper we present a new approach to computations in elasto‐plastic geomechanics. The approach is based on the object oriented design philosophy and observations on similarity of most incremental elastic–plastic material models. This new approach to elastic–plastic computations in geomechanics allows for creation of template material models. The analysis of template material models will in turn allow for an easy implementation of other elastic–plastic material models based on the object oriented design principles. Furthermore we present some illustrative implementation details. Finally we present analysis results that emphasize features of template elastic–plastic computations in geomechanics. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Experimental and Numerical Modelling of Flow over Complex Terrain: The Bolund Hill     

Boris Conan  Ashvinkumar Chaudhari  Sandrine Aubrun  Jeroen van Beeck  Jari Hämäläinen  Antti Hellsten 《Boundary-Layer Meteorology》2016,158(2):183-208

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An Investigation of the Reliability of HF Acid Mixtures in the Bomb Digestion of Silicate Rocks for the Determination of Trace Elements by ICP‐MS          下载免费PDF全文

Olga Okina  Sergey Lyapunov  Mariya Avdosyeva  Boris Ermolaev  Vladimir Golubchikov  Anatoly Gorbunov  Victor Sheshukov 《Geostandards and Geoanalytical Research》2016,40(4):583-597

The influence of the mixtures HF‐HNO₃ and HF‐NH₄F‐HNO₃ in bomb digestion for trace element determination from different rock types was studied using ICP‐MS. It is shown that the HF concentration, not the ratio of reagents in the decomposing mixture, controls the digestion process of a rock. Data for Zr in the granite G‐2 as a function of HF concentration gave the same results as reaction mixtures of various compositions. A complete digestion in 50‐mg sample bombs was achieved by 1.0 ml of HF alone, or with a mixture of other acids at a HF concentration of at least 35% m/m at 196 °C over 18 h. The results of the analysis of basalts BCR‐1, BIR‐1, mica schist SDC‐1, shale SBC‐1, granites G‐2, SG‐1A, garnet‐biotite plagiogneiss GBPg‐1, rhyolite RGM‐1, granodiorite GSP‐1, trachyandesite MTA‐1 and rhyolite MRh‐1 are given and compared against available data. The reproducibility of the element determinations by ICP‐MS and XRF as an independent non‐destructive analysis for a quality check in the range of concentrations typical for routine rock samples is given.  相似文献   

A geomorphological seabed classification for the Weddell Sea,Antarctica     

Kerstin Jerosch  Gerhard Kuhn  Ingo Krajnik  Frauke Katharina Scharf  Boris Dorschel 《Marine Geophysical Researches》2016,37(2):127-141

Sea floor morphology plays an important role in many scientific disciplines such as ecology, hydrology and sedimentology since geomorphic features can act as physical controls for e.g. species distribution, oceanographically flow-path estimations or sedimentation processes. In this study, we provide a terrain analysis of the Weddell Sea based on the 500 m × 500 m resolution bathymetry data provided by the mapping project IBCSO. Seventeen seabed classes are recognized at the sea floor based on a fine and broad scale Benthic Positioning Index calculation highlighting the diversity of the glacially carved shelf. Beside the morphology, slope, aspect, terrain rugosity and hillshade were calculated and supplied to the data archive PANGAEA. Applying zonal statistics to the geomorphic features identified unambiguously the shelf edge of the Weddell Sea with a width of 45–70 km and a mean depth of about 1200 m ranging from 270 m to 4300 m. A complex morphology of troughs, flat ridges, pinnacles, steep slopes, seamounts, outcrops, and narrow ridges, structures with approx. 5–7 km width, build an approx. 40–70 km long swath along the shelf edge. The study shows where scarps and depressions control the connection between shelf and abyssal and where high and low declination within the scarps e.g. occur. For evaluation purpose, 428 grain size samples were added to the seabed class map. The mean values of mud, sand and gravel of those samples falling into a single seabed class was calculated, respectively, and assigned to a sediment texture class according to a common sediment classification scheme.  相似文献