A morphological investigation of marine transgression in estuaries     

Ian Townend  Zeng Zhou  Leicheng Guo  Giovanni Coco 《地球表面变化过程与地形》2021,46(3):626-641

The landscape setting of estuaries varies widely and is an important aspect of determining how they evolve. This paper focusses on alluvial estuaries in river valleys and how they respond to sea level rise. We examine the implications of marine transgression, as a response to sea level rise, where the estuary moves upwards and landwards to maintain its position in the tidal frame (so-called stratigraphic rollover). Here we encapsulate such kinematic movement of the estuary morphology using a ‘morphokinematic’ model, to assess the potential response to sea level rise and sediment supply. The model of the estuary form includes a single convergent channel, intertidal and surrounding floodplains (the valley) and allows the relative importance of the space available for deposition of sediments, the accommodation space, to be investigated as a function of rates of sea level rise and sediment supply. The transgression of the system is determined using a sediment mass balance, taking account of any supply from the river and marine environment. Model results confirm that the transgression distance, measured as the distance the entity moves landward, varies in proportion to the change in accommodation space, which mainly depends on the floodplain area. As the size of the floodplain reduces, the transgression distance is less and the system becomes much more sensitive to changes in the rate of sea level rise or changes in sediment supply. The greater demand for sediment when a floodplain is present results in greater cannibalization of the estuary form (i.e. greater landward movement) to meet the sediment demand. When the floodplain is disconnected from the estuary, the synergistic relationship is lost and the accommodation space increases. The capacity for restoration will depend on the availability of sediment and the prevailing rate of sea level rise.  相似文献   

The STAROX stellar evolution code     

Ian W. Roxburgh 《Astrophysics and Space Science》2008,316(1-4):75-82

This paper describes the STAROX stellar evolution code for the calculation of the evolution of a model of a spherical star. The code calculates a model at time t _k , that is the run of pressure, density, temperature, radius, energy flux and related variables on a mesh in mass M _i , given the distribution of chemical elements X _j (i) at t _k and the model at the previous time step t _k?1. It then advances the chemical composition to the next time step t _k+1 and calculates a new model at time t _k+1. This process is iterated to convergence. The model equations are solved by Newton–Raphson relaxation; the chemical equations are solved by an iterative procedure, each element being advanced in turn, and the process repeated to convergence. Convection is modelled by a mixing length model and convective mixing is treated as a diffusive process; chemical overshooting can be incorporated in parametric form. The equation of state is taken from OPAL tables and the opacity from a blend of OPAL and Alexander tables. Nuclear reaction rates are from NACRE but only cover the p–p chain and CNO cycle. The atmospheric layers are incorporated in the model by applying the surface boundary condition at small optical depth (τ≈0.001). The mesh in mass M _i is usually taken as fixed except that there is a moveable mesh point at the boundary of a convective core. Results are given for models of mass 0.9 and 5.0M _⊙ with initial composition X=0.7,Z=0.02 evolved to a state where the central hydrogen abundance is X _c =0.35, and for a model of mass 2.0M _⊙ with initial X=0.72,Z=0.02, evolved to X _c =0.01 and with core overshooting. In this latter case we compute two models one with and one without a moveable mesh point at the boundary of the convective core to illustrate the importance of having such a moveable mesh point for the determination of the Brunt–Väisälä frequency in the layers outside the core.  相似文献   

CoRoT/ESTA–TASK 1 and TASK 3 comparison of the internal structure and seismic properties of representative stellar models     

Yveline Lebreton  Josefina Montalbán  Jørgen Christensen-Dalsgaard  Ian W. Roxburgh  Achim Weiss 《Astrophysics and Space Science》2008,316(1-4):187-213

We compare stellar models produced by different stellar evolution codes for the CoRoT/ESTA project, comparing their global quantities, their physical structure, and their oscillation properties. We discuss the differences between models and identify the underlying reasons for these differences. The stellar models are representative of potential CoRoT targets. Overall we find very good agreement between the five different codes, but with some significant deviations. We find noticeable discrepancies (though still at the per cent level) that result from the handling of the equation of state, of the opacities and of the convective boundaries. The results of our work will be helpful in interpreting future asteroseismology results from CoRoT.  相似文献   

Two new analytic approximations of the Chandrasekhar's H function for isotropic scattering     

Dragomir M. Davidovi?  Jovan Vukani? 《Icarus》2008,194(1):389-397

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Low temperature (39-298 K) kinetics study of the reactions of the C₄H radical with various hydrocarbons observed in Titan's atmosphere     

Coralie Berteloite  Petre Birza  André Canosa  Ian R. Sims 《Icarus》2008,194(2):746-757

The reaction kinetics of the butadinyl radical, C₄H, with various hydrocarbons detected in the atmosphere of Titan (methane, ethane, propane, acetylene, ethene and methylacetylene) are studied over the temperature range of 39-298 K using the Rennes CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) apparatus. Kinetic measurements were made using the pulsed laser photolysis—laser induced fluorescence technique. The rate coefficients, except for the reaction with methane, all show a negative temperature dependence and can be fitted with the following expressions over the temperature range of this study: ; ; , , . These expressions are not intended to be physically meaningful but rather to provide an easy way to introduce experimental results in photochemical models. They are only valid over the temperature range of the experiments. Possible channels of these reactions are discussed as well as possible consequences of these results for the production of large molecules and hazes in the atmosphere of Titan. These results should also be considered for the photochemistry of Giant Planets.  相似文献   

A method to search for strong galaxy–galaxy lenses in optical imaging surveys     

Jeffrey M. Kubo  Ian P. Dell'Antonio 《Monthly notices of the Royal Astronomical Society》2008,385(2):918-928

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Exploring the infrared/radio correlation at high redshift     

Edo Ibar  Michele Cirasuolo  Rob Ivison  Philip Best  Ian Smail  y Biggs  Chris Simpson  Jim Dunlop  Omar Almaini  Ross McLure  Sebastien Foucaud  Steve Rawlings 《Monthly notices of the Royal Astronomical Society》2008,386(2):953-962

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Spitzer observations of M33 and the hot star, H ii region connection     

Robert H. Rubin  Janet P. Simpson  Sean W. J. Colgan  Reginald J. Dufour  Gregory Brunner  Ian A. McNabb  Adalbert W. A. Pauldrach  Edwin F. Erickson  Michael R. Haas  Robert I. Citron 《Monthly notices of the Royal Astronomical Society》2008,387(1):45-62

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Testing the evolutionary link between submillimetre galaxies and quasars: CO observations of QSOs at z∼ 2     

K. E. K. Coppin  A. M. Swinbank  R. Neri  P. Cox  D. M. Alexander  Ian Smail  M. J. Page  J. A. Stevens  K. K. Knudsen  R. J. Ivison  A. Beelen  F. Bertoldi  A. Omont 《Monthly notices of the Royal Astronomical Society》2008,389(1):45-62

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The long-term stability of a possible aqueous ammonium sulfate ocean inside Titan     

P.M. Grindrod  A.D. Fortes  D.L. Feltham  L. Vo?adlo 《Icarus》2008,197(1):137-151

We model the thermal evolution of a subsurface ocean of aqueous ammonium sulfate inside Titan using a parameterized convection scheme. The cooling and crystallization of such an ocean depends on its heat flux balance, and is governed by the pressure-dependent melting temperatures at the top and bottom of the ocean. Using recent observations and previous experimental data, we present a nominal model which predicts the thickness of the ocean throughout the evolution of Titan; after 4.5 Ga we expect an aqueous ammonium sulfate ocean 56 km thick, overlain by a thick (176 km) heterogeneous crust of methane clathrate, ice I and ammonium sulfate. Underplating of the crust by ice I will give rise to compositional diapirs that are capable of rising through the crust and providing a mechanism for cryovolcanism at the surface. We have conducted a parameter space survey to account for possible variations in the nominal model, and find that for a wide range of plausible conditions, an ocean of aqueous ammonium sulfate can survive to the present day, which is consistent with the recent observations of Titan's spin state from Cassini radar data [Lorenz, R.D., Stiles, B.W., Kirk, R.L., Allison, M.D., del Marmo, P.P., Iess, L., Lunine, J.I., Ostro, S.J., Hensley, S., 2008. Science 319, 1649-1651].  相似文献