Radar observations and the shape of near-Earth asteroid 2008 EV5     

Michael W. Busch  Steven J. Ostro  Lance A.M. Benner  Jon D. Giorgini  Daniel J. Scheeres  Michael C. Nolan  Patrick A. Taylor  Walter Brisken 《Icarus》2011,212(2):649-660

We observed the near-Earth ASTEROID 2008 EV5 with the Arecibo and Goldstone planetary radars and the Very Long Baseline Array during December 2008. EV5 rotates retrograde and its overall shape is a 400 ± 50 m oblate spheroid. The most prominent surface feature is a ridge parallel to the asteroid’s equator that is broken by a concavity about 150 m in diameter. Otherwise the asteroid’s surface is notably smooth on decameter scales. EV5’s radar and optical albedos are consistent with either rocky or stony-iron composition. The equatorial ridge is similar to structure seen on the rubble-pile near-Earth asteroid (66391) 1999 KW4 and is consistent with YORP spin-up reconfiguring the asteroid in the past. We interpret the concavity as an impact crater. Shaking during the impact and later regolith redistribution may have erased smaller features, explaining the general lack of decameter-scale surface structure.  相似文献   

Shock fragmentation model for gravitational collapse     

Michael Wilkinson  Bernhard Mehlig  Michael A.Morgan 《中国天文和天体物理学报》2011,11(5)

A cloud of gas collapsing under gravity will fragment.We present a new theory for this process,in which layers of shocked gas fragment due to their gravitational instability.Our model explains why angular momentum does not inhibit the collapse process.The theory predicts that the fragmentation process produces objects which are significantly smaller than most stars,implying that accretion onto the fragments plays an essential role in determining the initial masses of stars.This prediction is also consistent...  相似文献   

Comparison of two different approaches for computing the gravitational effect of a tesseroid     

Marotta  Anna Maria  Seitz  Kurt  Barzaghi  Riccardo  Grombein  Thomas  Heck  Bernhard 《Studia Geophysica et Geodaetica》2019,63(3):321-344

Studia Geophysica et Geodaetica - Forward modelling in the space domain is a very important task in geodesy and other geosciences. From topographical or isostatic information in the form of digital...  相似文献   

Nano-mechanical Properties and Pore-Scale Characterization of Different Rank Coals   总被引：1，自引：0，他引：1  

Zhang  Yihuai  Lebedev  Maxim  Smith  Gregory  Jing  Yu  Busch  Andreas  Iglauer  Stefan 《Natural Resources Research》2020,29(3):1787-1800

Characterization of coal micro-structure and the associated rock mechanical properties are of key importance for coal seam exploration, coal bed methane development, enhanced coal bed methane production and CO₂ storage in deep coal seams. Considerable knowledge exists about coal chemical properties, but less is known about the nanoscale to the micro-scale structure of coals and how they change with coal strength across coal ranks. Thus, in this study, 3D X-ray micro-computed tomography (with a voxel size of 3.43 µm) and nano-indentation tests were conducted on coal samples of different ranks from peat to anthracite. The micro-structure of peats showed a well-developed pore system with meso- and micro-pores. The meso-pores essentially disappear with increasing rank, whereas the micro-pores persist and then increase past the bituminous rank. The micro-fracture system develops past the peat stage and by sub-bituminous ranks and changes into larger and mature fracture systems at higher ranks. The nano-indentation modulus showed the increasing trend from low- to high-rank coal with a perfect linear relationship with vitrinite reflectance and is highly correlated with carbon content as expected.

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The effect of fluid compressibility on the simulation of sloshing impacts     

Bernhard Godderidge  Stephen Turnock  Chris Earl  Mingyi Tan 《Ocean Engineering》2009,36(8):578-587

Resonant and near-resonant sway-induced sloshing flow in a rectangular container is used to compare various combinations of compressibility models for air and water. The numerical model is implemented in a commercial RANS computational fluid dynamics (CFD) code. A criterion based on wave propagation is developed to assess the importance of including fluid compressibility. For sloshing flows with low levels of fluid impact, this can be simulated with incompressible fluid models for both air and water. When modelling sloshing at low-filling levels with a travelling wave, which generates large air bubble entrainment, the choice of fluid compressibility model is shown to have a significant influence on pressure magnitude and frequency of oscillation required for structural assessment. Further comparisons with theoretical models show that a full thermal energy compressibility model is also required.  相似文献   

Benthic foraminifera living in Gulf of Mexico bathyal and abyssal sediments: Community analysis and comparison to metazoan meiofaunal biomass and density     

Joan M. Bernhard  Barun K. Sen Gupta  Jeffrey G. Baguley 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(24-26):2617

Benthic foraminiferal biomass, density, and species composition were determined at 10 sites in the Gulf of Mexico. During June 2001 and 2002, sediment samples were collected with a GoMex box corer. A 7.5-cm diameter subcore was taken from a box core collected at each site and sliced into 1-cm or 2-cm sections to a depth of 2 or 3 cm; the >63-μm fraction was examined shipboard for benthic foraminifera. Individual foraminifers were extracted for adenosine triphosphate (ATP) using a luciferin–luciferase assay, which indicated the total ATP content per specimen; that data was converted to organic carbon. Foraminiferal biomass and density varied substantially (2–53 mg C m⁻²; 3600–44,500 individuals m⁻², respectively) and inconsistently with water depth: although two 1000-m deep sites were geographically separated by only 75 km, the foraminiferal biomass at one site was relatively low (9 mg C m⁻²) while the other site had the highest foraminiferal biomass (53 mg C m⁻²). Although most samples from Sigsbee Plain (>3000 m) had low biomass, one Sigsbee site had >20 mg foraminiferal C m⁻². The foraminiferal community from all sites (i.e. bathyal and abyssal locales) was dominated by agglutinated, rather than calcareous or tectinous, species. Foraminiferal density never exceeded that of metazoan meiofauna at any site. Foraminiferal biomass, however, exceeded metazoan meiofaunal biomass at 5 of the 10 sites, indicating that foraminifera constitute a major component of the Gulf's deep-water meiofaunal biomass.  相似文献   

Thermal history and source rock characterization of a Paleozoic section in the Awbari Trough,Murzuq Basin,SW Libya     

Abdulmonem Belaid  Bernhard M. KroossRalf Littke 《Marine and Petroleum Geology》2010

In some areas of the Murzuq Basin, SW Libya, the lower Silurian member comprises highly radioactive shales (Hot Shale), which are regarded as the most significant factor controlling petroleum generation in the basin. In this context, it was the goal of our project to study the distribution and maturity of the Hot Shale in the framework of basin evolution. Organic geochemical, organic petrological and basin modelling methods were used to obtain a more thorough understanding. Four wells from the northern and central part of the Awbari Trough have been selected for this study.  相似文献   

Estuarine nitrifiers: New players,patterns and processes   总被引：1，自引：0，他引：1  

Anne E. Bernhard  Annette Bollmann 《Estuarine, Coastal and Shelf Science》2010

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