VSX J074727.6 + 065050: A dwarf nova with a non-radially pulsating white dwarf primary     

Patrick A. Woudt  Brian Warner 《Astrophysics and Space Science》2011,333(1):119-123

High speed photometric observations of the dwarf nova VSX J074727.6 + 065050 made in December 2009 during quiescence show an orbital modulation at P _orb =85.6 min. They also show that the star is a member of the relatively rare CV/ZZ group, i.e. the accreting white dwarf primary has non-radial pulsations. The two regions of oscillating power are at 684 s and 238 s. There is some evidence for hidden ∼1 μHz fine structure splitting, which has been seen in three other CV/ZZ stars.  相似文献   

Electron transport and precipitation at Mercury during the MESSENGER flybys: Implications for electron-stimulated desorption     

David Schriver  Pavel Trávní?ek  Maha Ashour-Abdalla  Robert L. Richard  Petr Hellinger  James A. Slavin  Brian J. Anderson  Daniel N. Baker  Mehdi Benna  Scott A. Boardsen  Robert E. Gold  George C. Ho  Haje Korth  Stamatios M. Krimigis  William E. McClintock  Jason L. McLain  Thomas M. Orlando  Menelaos Sarantos  Ann L. Sprague  Richard D. Starr 《Planetary and Space Science》2011,59(15):2026-2036

To examine electron transport, energization, and precipitation in Mercury's magnetosphere, a hybrid simulation study has been carried out that follows electron trajectories within the global magnetospheric electric and magnetic field configuration of Mercury. We report analysis for two solar-wind parameter conditions corresponding to the first two MESSENGER Mercury flybys on January 14, 2008, and October 6, 2008, which occurred for similar solar wind speed and density but contrasting interplanetary magnetic field (IMF) directions. During the first flyby the IMF had a northward component, while during the second flyby the IMF was southward. Electron trajectories are traced in the fields of global hybrid simulations for the two flybys. Some solar wind electrons follow complex trajectories at or near where dayside reconnection occurs and enter the magnetosphere at these locations. The entry locations depend on the IMF orientation (north or south). As the electrons move through the entry regions they can be energized as they execute non-adiabatic (demagnetized) motion. Some electrons become magnetically trapped and drift around the planet with energies on the order of 1–10 keV. The highest energy of electrons anywhere in the magnetosphere is about 25 keV, consistent with the absence of high-energy (>35 keV) electrons observed during either MESSENGER flyby. Once within the magnetosphere, a fraction of the electrons precipitates at the planetary surface with fluxes on the order of 10⁹ cm⁻² s⁻¹ and with energies of hundreds of eV. This finding has important implications for the viability of electron-stimulated desorption (ESD) as a mechanism for contributing to the formation of the exosphere and heavy ion cloud around Mercury. From laboratory estimates of ESD ion yields, a calculated ion production rate due to ESD at Mercury is found to be on par with ion sputtering yields.  相似文献   

The IAU 2009 system of astronomical constants: the report of the IAU working group on numerical standards for Fundamental Astronomy     

Brian Luzum  Nicole Capitaine  Agn??s Fienga  William Folkner  Toshio Fukushima  James Hilton  Catherine Hohenkerk  George Krasinsky  G??rard Petit  Elena Pitjeva  Michael Soffel  Patrick Wallace 《Celestial Mechanics and Dynamical Astronomy》2011,110(4):293-304

In the 2006?C2009 triennium, the International Astronomical Union (IAU) Working Group on Numerical Standards for Fundamental Astronomy determined a list of Current Best Estimates (CBEs). The IAU 2009 Resolution B2 adopted these CBEs as the IAU (2009) System of Astronomical Constants. Additional work continues to define the process of updating the CBEs and creating a standard electronic document.  相似文献   

Impact cratering in sandstone: The MEMIN pilot study on the effect of pore water     

Thomas KENKMANN  Kai WÜNNEMANN  Alexander DEUTSCH  Michael H. POELCHAU  Frank SCHÄFER  Klaus THOMA 《Meteoritics & planetary science》2011,46(6):890-902

Abstract– Planetary surfaces are subjected to meteorite bombardment and crater formation. Rocks forming these surfaces are often porous and contain fluids. To understand the role of both parameters on impact cratering, we conducted laboratory experiments with dry and wet sandstone blocks impacted by centimeter‐sized steel spheres. We utilized a 40 m two‐stage light‐gas gun to achieve impact velocities of up to 5.4 km s^?1. Cratering efficiency, ejection velocities, and spall volume are enhanced if the pore space of the sandstone is filled with water. In addition, the crater morphologies differ substantially from wet to dry targets, i.e., craters in wet targets are larger, but shallower. We report on the effects of pore water on the excavation flow field and the degree of target damage. We suggest that vaporization of water upon pressure release significantly contributes to the impact process.  相似文献   

Letter from the Editor     

Klaus G. Strassmeier 《Astronomische Nachrichten》2012,333(1):3-3

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LAMOST Experiment for Galactic Understanding and Exploration （LEGUE） The survey＇s science plan     

Li-Cai Deng  Heidi Jo Newberg  Chao Liu  Jeffrey L. Carlin  Timothy C. Beers  Li Chen  Hsu-Tai Lee  Carl J. Grillmair  Puragra Guhathakurta  Zhan-Wen Han  Jin-Liang Hou  Sebastien Lepine  Jing Li  Xiao-Wei Liu  Kai-Ke Pan  J. A. Sellwood  Bo Wang  Hong-Chi Wang  Fan Yang  Brian Yanny  Hao-Tong Zhang  Yue-Yang Zhang  Zheng Zheng  Zi Zhu 《天体物理学报》2012,(7):735-754

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An algorithm for preferential selection of spectroscopic targets in LEGUE     

Jeffrey L. Carlin  Sebastien Lepine  Heidi Jo Newberg  Li-Cai Deng  Timothy C. Beers  Yu-Qin Chen  Norbert Christlie  Xiao-Ting Fu  Shuang Gao  Carl J. Grillmair  PuragraGuhathakurta  Zhan-Wen Han  Jin-Liang Hou  Hsu-Tai Lee  Jing Li  Chao Liu  Xiao-Wei Liu  Kai-Ke Pan  J. A. Sellwood  Hong-Chi Wang  Fan Yang  Brian Yanny  Yue-Yang Zhan  Zheng Zheng  Zi Zhu 《天体物理学报》2012,(7):755-771

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A resurgence in urban living? Trends in residential location patterns of young and older adults since 2000     

Evelyn Blumenberg  Anne Brown  Kelcie Ralph  Brian D. Taylor  Carole Turley Voulgaris 《Urban geography》2013,34(9):1375-1397

ABSTRACT

Some have heralded a resurgence of urban living in the U.S., particularly among young adults. Are Americans abandoning suburbs in favor of more urban lifestyles? What is the scope and scale of this urban resurgence? We develop a typology of neighborhoods to analyze the residential location of young and older U.S. adults from 2000 to 2011–15. Census and national travel survey data reveal that suburban population growth continues to outpace that in urban neighborhoods. Although young adults are more likely than older adults to live in urban neighborhoods, recent urban population growth is neither associated with suburban decline, nor being led by young adults. Significant recent population growth in the newest, suburban neighborhoods suggests that greenfield development remains the primary means to increase American housing supply. Shifting metropolitan growth from the suburban fringe would likely require expanding housing supply in urban neighborhoods, and bringing urban amenities to established inner-ring suburbs.  相似文献   

Peter Alan Burrough     

Peter Fisher  Brian Lees 《International journal of geographical information science》2013,27(4)

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A porosity-gradient replacement approach for computational simulation of chemical-dissolution front propagation in fluid-saturated porous media including pore-fluid compressibility   总被引：1，自引：0，他引：1  

Chongbin Zhao  Lynn B. Reid  Klaus Regenauer-Lieb  Thomas Poulet 《Computational Geosciences》2012,16(3):735-755

In dealing with chemical-dissolution-front propagation problems in fluid-saturated porous media, the chemical dissolution front represented by the porosity of the medium may have a very steep slope (i.e., a very large porosity gradient) at the dissolution front, depending on the mineral dissolution ratio that is defined as the equilibrium concentration of the dissolved minerals in the pore-fluid to the solid molar density of the dissolvable minerals in the solid matrix. When the mineral dissolution ratio approaches zero, the theoretical value of the porosity gradient tends to infinity at the chemical dissolution front. Even for a very small value of the mineral dissolution ratio, which is very common in geochemical systems, the porosity gradient can be large enough to cause the solution hard to converge when the conventional finite element method is used to solve a chemical dissolution problem in a fluid-saturated porous medium where the pore-fluid is compressible. To improve the convergent speed of solution, a porosity-gradient replacement approach, in which the term involving porosity-gradient computation is replaced by a new term consisting of pore-fluid density-gradient and pressure-gradient computation, is first proposed and then incorporated into the finite element method in this study. Through comparing the numerical results obtained from the proposed approach with the theoretical solutions for a benchmark problem, it has been demonstrated that not only can the solution divergence be avoid, but also the accurate simulation results can be obtained when the proposed porosity-gradient replacement approach is used to solve chemical-dissolution-front propagation problems in fluid-saturated porous media including pore-fluid compressibility.  相似文献