Modelling of sediment dynamics in a laboratory‐scale experimental catchment     

G. R. Hancock  J. Nuake  S. G. Fityus 《水文研究》2006,20(1):67-84

The variability of hillslope form and function is examined experimentally using a simple model catchment in which most landscape development parameters are either known or controlled. It is demonstrated that there is considerable variability in sediment output from similar catchments, subjected to the same hydrological processes, and for which the initial hillslope profiles are the same. The results demonstrate that, in the case of catchments with a linear initial hillslope profile, the sediment output is initially high but reduces through time, whereas for a concave initial profile the sediment output was smaller and relatively constant. Concave hillslope profiles also displayed reduced sediment output when compared with linear slopes with the same overall slope. Using this experimental model catchment data, the SIBERIA landscape evolution model was tested for its ability to predict temporal sediment transport. When calibrated for the rainfall and erodible material, SIBERIA is able to simulate mean temporal sediment output for the experimental catchment over a range of hillslope profiles and rainfall intensities. SIBERIA is also able to match the hillslope profile of the experimental catchments. The results of the study provide confidence in the ability of SIBERIA to predict temporal sediment output. The experimental and modelling data also demonstrate that, even with all geomorphic and hydrological variables being known and/or controlled, there is still a need for long‐term stream gauging to obtain reliable assessments of field catchment hydrology and sediment transport. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

The metallicities of luminous, massive field galaxies at intermediate redshifts     

M. Mouhcine †  S. P. Bamford ‡  A. Aragón-Salamanca  O. Nakamura  B. Milvang-Jensen 《Monthly notices of the Royal Astronomical Society》2006,369(2):891-908

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Resonance trapping and evolution of particles subject to poynting-robertson drag: Adiabatic and non-adiabatic approaches     

R.S. Gomes 《Celestial Mechanics and Dynamical Astronomy》1995,61(1):97-113

The problem of resonance trapping for particles subject to Poynting-Robertson drag is approached initially from an adiabatic regime theory. A simplified Hamiltonian system is presented for simple eccentricity-type resonances up to order 3, and expressions related to the trapping process are deduced. The fast dissipation provoked by Poynting-Robertson leads to the employment of a numerical approach for the computation of resonance capture probabilities, for particles in the size range of practical importance. Some aspects of the dynamical evolution of a particle after capture are noticed from results of numerical integrations. Analytical methods are used in order to confirm the numerical results.  相似文献   

Poincarè Chaos and the Dynamical Evolution of Systems of Gravitating Bodies     

A. D. Chernin  M. Valtonen  L. P. Ossipkov  Q.-J. Zheng  S. Wiren 《Astrophysics》2002,45(2):240-247

Some general laws of evolution of a system of a large number of gravitating bodies are discussed. If in the initial stage the dynamics of the system is determined by large-scale perturbations of the gravitational potential associated with excitations of a few collective degrees of freedom, then one can assume, by analogy with chaos in the several-body problem (Poincarè chaos), that randomization will occur in the system over several average crossing times. In the next stage of evolution, the energy of collective modes should be transferred by the cascade mechanism to ever smaller scales, down to invididual particles. Numerical experiments and gross-dynamical considerations that could verify this picture and bring out details are discussed.  相似文献   

The Butcher–Oemler effect at z∼ 0.35: a change in perspective     

S. Andreon  H. Quintana  M. Tajer  G. Galaz  J. Surdej 《Monthly notices of the Royal Astronomical Society》2006,365(3):915-928

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Mass transfer in eccentric binary stars     

Enikö Regös  Vernon C. Bailey  Rosemary Mardling 《Monthly notices of the Royal Astronomical Society》2005,358(2):544-550

The concept of Roche lobe overflow is fundamental to the theory of interacting binaries. Based on potential theory, it is dependent on all the relevant material corotating in a single frame of reference. Therefore if the mass losing star is asynchronous with the orbital motion or the orbit is eccentric, the simple theory no longer applies and no exact analytical treatment has been found. We use an analytic approximation whose predictions are largely justified by smoothed particle hydrodynamic simulations (SPH). We present SPH simulations of binary systems with the same semi-major axis   a = 5.55 R_⊙  , masses   M ₁= 1 M_⊙, M ₂= 2 M_⊙  and radius   R ₁= 0.89 R_⊙  for the primary star but with different eccentricities   e = 0.4, 0.5, 0.6  and 0.7. In each case the secondary star is treated as a point mass. When   e = 0.4  no mass is lost from the primary while at   e = 0.7  catastrophic mass transfer, partly through the L₂ point, takes place near periastron. This would probably lead to common-envelope evolution if star 1 were a giant or to coalescence for a main-sequence star. In between, at   e ≥ 0.5  , some mass is lost through the L₁ point from the primary close to periastron. However, rather than being all accreted by the secondary, some of the stream appears to leave the system. Our results indicate that the radius of the Roche lobe is similar to circular binaries when calculated for the separation and angular velocity at periastron. Part of the mass loss occurs through the L₂ point.  相似文献   

Morphological evolution of discs in clusters     

Chiara Mastropietro  Ben Moore  Lucio Mayer  Victor P. Debattista  Rocco Piffaretti  Joachim Stadel 《Monthly notices of the Royal Astronomical Society》2005,364(2):607-619

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A Statistical Model for Predicting the Average Abundance Patterns of Heavier Elements in Metal-Poor Stars     

Bo Zhang  Yan-Xia Zhang  Ji Li  Qiu-He Peng Department of Physics  Hebei Normal University  Shijiazhuang Center of Theoretical Nuclear Physics  National Laboratory of Heavy Ion Accelerator  Lanzhou National Astronomical Observatories  Chinese Academy of Sciences  Beijing Department of Astronomy  Nanjing University  Nanjing 《中国天文和天体物理学报》2002,2(5):429-440

We have collected nearly all the available observed data of the elements from Ba to Dy in halo and disk stars in the metallicity range -4.0 <[Fe/H]< 0.5. Based on the observed data of Ba and Eu, we evaluated the least-squares regressions of [Ba/Fe] on [Fe/H], and [Eu/H] on [Ba/H]. Assuming that the heavy elements (heavier than Ba) are produced by a combination of the main components of s- and r-processes in metal-poor stars, and choosing Ba and Eu as respective representative elements of the main s- and the main r-processes, a statistical model for predicting the Galactic chemical evolution of the heavy elements is presented. With this model, we calculate the mean abundance trends of the heavy elements La, Ce, Pr, Nd, Sm, and Dy with the metallicity. We compare our results with the observed data at various metallicities, showing that the predicted trends are in good agreement with the observed trends, at least for the metallicity range [Fe/H]> -2.5. Finally, we discuss our results and deduce some importa  相似文献   

Determination of the Ages of Close Binary Stars on the Main Sequence from Evolutionary Model Stars of Claret and Gimenez     

G. N. Dryomova  M. A. Svechnikov 《Astrophysics》2002,45(3):342-357

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Spatially resolved spectroscopy of the E+A galaxies in the z= 0.32 cluster AC 114   总被引：1，自引：0，他引：1  

Michael B. Pracy  Warrick J. Couch  Chris Blake  Kenji Bekki  Craig Harrison  Matthew Colless  Harald Kuntschner  Roberto de Propris 《Monthly notices of the Royal Astronomical Society》2005,359(4):1421-1432

We present spatially resolved intermediate-resolution spectroscopy of a sample of 12 E+A galaxies in the   z = 0.32  rich galaxy cluster AC 114, obtained with the FLAMES multi-integral field unit system on the Very Large Telescope (VLT) of the European Southern Observatory. Previous integrated spectroscopy of all these galaxies by Couch & Sharples had shown them to have strong Balmer line absorption and an absence of [O  ii ]λ3727 emission – the defining characteristics of the 'E+A' spectral signature, indicative of an abrupt halt to a recent episode of quite vigorous star formation. We have used our spectral data to determine the radial variation in the strength of Hδ absorption in these galaxies and hence map out the distribution of this recently formed stellar population. Such information provides important clues as to what physical event might have been responsible for this quite dramatic change in star formation activity in the recent past of these galaxies. We find a diversity of behaviour amongst these galaxies in terms of the radial variation in Hδ absorption: four galaxies show little Hδ absorption across their entire extent; it would appear they were misidentified as E+A galaxies in the earlier integrated spectroscopic studies. The remainder show strong Hδ absorption, with a gradient that is either negative (Hδ equivalent width decreasing with radius), flat or positive . By comparison with numerical simulations we suggest that the first of these different types of radial behaviour provides evidence for a merger/interaction origin, whereas the latter two types of behaviour are more consistent with the truncation of star formation in normal disc galaxies with the Hδ gradient becoming increasingly positive with time after truncation. It would seem therefore that more than one physical mechanism is responsible for E+A formation in the same environment.  相似文献