Preface     

L. M. Green  T. Sakurai  L. van Driel-Gesztelyi 《Solar physics》2012,277(1):1-2

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Dynamical attitude model for Gaia     

D. Risquez  F. van Leeuwen  A. G. A. Brown 《Experimental Astronomy》2012,34(3):669-703

The Dynamical Attitude Model (DAM) is a simulation package developed to achieve a detailed understanding of the Gaia spacecraft attitude. It takes into account external physical effects and considers internal hardware components controlling the satellite. The main goal of the Gaia mission is to obtain extremely accurate astrometry, and this necessitates a good knowledge of Gaia’s behaviour as a spinning rigid body under the influence of various perturbations. This paper describes these perturbations and how they are modelled in DAM.  相似文献   

Radio-continuum study of the Nearby sculptor group galaxies. Part 1: NGC 300 at λ=20 cm     

Timothy J. Galvin  Miroslav D. Filipović  Evan J. Crawford  Graeme Wong  Jeff L. Payne  Ain De Horta  Graeme L. White  Nick Tothill  Danica Drašković  Thomas G. Pannuti  Caleb K. Grimes  Benjamin J. Cahall  William C. Millar  Seppo Laine 《Astrophysics and Space Science》2012,340(1):133-142

A series of new radio-continuum (λ=20 cm) mosaic images focused on the NGC?300 galactic system were produced using archived observational data from the VLA and/or ATCA. These new images are both very sensitive (rms?=60 μJy) and feature high angular resolution (<10?″). The most prominent new feature is the galaxy’s extended radio-continuum emission, which does not match its optical appearance. Using these newly created images a number of previously unidentified discrete sources have been discovered. Furthermore, we demonstrate that a joint deconvolution approach to imaging this complete data-set is inferior when compared to an immerge approach.  相似文献   

Dynamical and collisional evolution of Halley-type comets     

E. van der Helm  S.V. Jeffers 《Icarus》2012,218(1):448-458

The number of observed Halley-type comets is hundreds of times less than predicted by models (Levison, H.F., Dones, L., Duncan, M.J. [2001]. Astron. J. 121, 2253–2267). In this paper we investigate the impact of collisions with planetesimals on the evolution of Halley-type comets. First we compute the dynamical evolution of a sub-set of 21 comets using the Mercury integrator package over 100 Myr. The dynamical lifetime is determined to be of the order of 10⁵–10⁶ years in agreement with previous work. The collisional probability of Halley-type comets colliding with known asteroids, a simulated population of Kuiper-belt objects, and planets, is calculated using a modified, Öpik-based collision code. Our results show that the catastrophic disruption of the cometary nucleus has a very low probability of occurring, and disruption through cumulative minor impacts is concluded to be negligible. The dust mantle formed from ejected material falling back to the comet’s surface is calculated to be less than a few centimeters thick, which is insignificant compared to the mantle formed by volatile depletion, while planetary encounters were found to be a negligible disruption mechanism.  相似文献   

Stardust impact analogs: Resolving pre‐ and postimpact mineralogy in Stardust Al foils     

Penelope J. WOZNIAKIEWICZ  Hope A. ISHII  Anton T. KEARSLEY  Mark J. BURCHELL  John P. BRADLEY  Mark C. PRICE  Nick TESLICH  Martin R. LEE  Mike J. COLE 《Meteoritics & planetary science》2012,47(4):708-728

Abstract– The grains returned by NASA’s Stardust mission from comet 81P/Wild 2 represent a valuable sample set that is significantly advancing our understanding of small solar system bodies. However, the grains were captured via impact at ～6.1 km s^?1 and have experienced pressures and temperatures that caused alteration. To ensure correct interpretations of comet 81P/Wild 2 mineralogy, and therefore preaccretional or parent body processes, an understanding of the effects of capture is required. Using a two‐stage light‐gas gun, we recreated Stardust encounter conditions and generated a series of impact analogs for a range of minerals of cometary relevance into flight spare Al foils. Through analyses of both preimpact projectiles and postimpact analogs by transmission electron microscopy, we explore the impact processes occurring during capture and distinguish between those materials inherent to the impactor and those that are the product of capture. We review existing and present additional data on olivine, diopside, pyrrhotite, and pentlandite. We find that surviving crystalline material is observed in most single grain impactor residues. However, none is found in that of a relatively monodisperse aggregate. A variety of impact‐generated components are observed in all samples. Al incorporation into melt‐derived phases allows differentiation between melt and shock‐induced phases. In single grain impactor residues, impact‐generated phases largely retain original (nonvolatile) major element ratios. We conclude that both surviving and impact‐generated phases in residues of single grain impactors provide valuable information regarding the mineralogy of the impacting grain whilst further studies are required to fully understand aggregate impacts and the role of subgrain interactions during impact.  相似文献   

Interferometric observations of rapidly rotating stars     

Gerard T. van Belle 《Astronomy and Astrophysics Review》2012,20(1):1-49

Optical interferometry provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Through direct observation of rotationally distorted photospheres at sub-milliarcsecond scales, we are now able to characterize latitude dependencies of stellar radius, temperature structure, and even energy transport. These detailed new views of stars are leading to revised thinking in a broad array of associated topics, such as spectroscopy, stellar evolution, and exoplanet detection. As newly advanced techniques and instrumentation mature, this topic in astronomy is poised to greatly expand in depth and influence.  相似文献   

Preface     

V. M. Nakariakov  M. K. Georgoulis  S. Poedts  L. van Driel-Gesztelyi  C. H. Mandrini  J. Leibacher 《Solar physics》2012,280(2):295-297

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Investigating Ionospheric Scintillation Effects on Multifrequency GPS Signals     

Salles  Lucas A.  Vani  Bruno C.  Moraes  Alison  Costa  Emanoel  de Paula  Eurico R. 《Surveys in Geophysics》2021,42(4):999-1025

Surveys in Geophysics - Over the last 15&nbsp;years, the satellite constellation of the global positioning system (GPS) has been modernized for more precise applications, with the introduction...  相似文献   

Water Availability of Sub-Basins with Restrictions on Use under Climate Change Scenarios in Brazil     

Redivo  Polyana Comino  Sanches  Luciana  de Carvalho Alves  Marcelo  Barbosa da Silva  Jhonatan 《Water Resources》2021,48(6):905-913

Water Resources - The Queima Pé Stream Basin (QPSB) and Ararão River Basin (ARB) in central Brazil have had recurrent problems with water scarcity. This may get worse under anthropogenic...  相似文献   

Late Holocene flood magnitudes in the Lower Rhine river valley and upper delta resolved by a two-dimensional hydraulic modelling approach     

Bas van der Meulen  Anouk Bomers  Kim M. Cohen  Hans Middelkoop 《地球表面变化过程与地形》2021,46(4):853-868

Palaeoflood hydraulic modelling is essential for quantifying ‘millennial flood’ events not covered in the instrumental record. Palaeoflood modelling research has largely focused on one-dimensional analysis for geomorphologically stable fluvial settings because two-dimensional analysis for dynamic alluvial settings is time consuming and requires a detailed representation of the past landscape. In this study, we make the step to spatially continuous palaeoflood modelling for a large and dynamic lowland area. We applied advanced hydraulic model simulations (1D–2D coupled set-up in HEC-RAS with 950 channel sections and 108 × 10³ floodplain grid cells) to quantify the extent and magnitude of past floods in the Lower Rhine river valley and upper delta. As input, we used a high-resolution terrain reconstruction (palaeo-DEM) of the area in early mediaeval times, complemented with hydraulic roughness values. After conducting a series of model runs with increasing discharge magnitudes at the upstream boundary, we compared the simulated flood water levels with an inventory of exceeded and non-exceeded elevations extracted from various geological, archaeological and historical sources. This comparison demonstrated a Lower Rhine millennial flood magnitude of approximately 14,000 m³/s for the Late Holocene period before late mediaeval times. This value exceeds the largest measured discharges in the instrumental record, but not the design discharges currently accounted for in flood risk management.  相似文献