A noble gas and cosmogenic radionuclide analysis of two ordinary chondrites from Almahata Sitta     

Matthias M. M. MEIER  Kees C. WELTEN  Marc W. CAFFEE  Jon M. FRIEDRICH  Peter JENNISKENS  Kunihiko NISHIIZUMI  Muawia H. SHADDAD  Rainer WIELER 《Meteoritics & planetary science》2012,47(6):1075-1086

Abstract– We present the results of a noble gas (He, Ne, Ar) and cosmogenic radionuclide (¹⁰Be, ²⁶Al, ³⁶Cl) analysis of two chondritic fragments (#A100, L4 and #25, H5) found in the Almahata Sitta strewn field in Sudan. We confirm their earlier attribution to the same fall as the ureilites dominating the strewn field, based on the following findings: (1) both chondrite samples indicate a preatmospheric radius of approximately 300 g cm^?2, consistent with the preatmospheric size of asteroid 2008 TC₃ that produced the Almahata Sitta strewn field; (2) both have, within error, a ²¹Ne/²⁶Al‐based cosmic ray exposure age of approximately 20 Ma, identical to the reported ages of Almahata Sitta ureilites; (3) both exhibit hints of ureilitic Ar in the trapped component. We discuss a possible earlier irradiation phase for the two fragments of approximately 10–20 Ma, visible only in cosmogenic ³⁸Ar. We also discuss the approximately 3.8 Ga (⁴He) and approximately 4.6 Ga (⁴⁰Ar) gas retention ages, measured in both chondritic fragments. These imply that the two chondrite fragments were incorporated into the ureilite host early in solar system evolution, and that the parent asteroid from which 2008 TC₃ is derived has not experienced a large break‐up event in the last 3.8 Ga.  相似文献   

Finite element methods for variable density flow and solute transport     

T. J. Povich  C. N. Dawson  M. W. Farthing  C. E. Kees 《Computational Geosciences》2013,17(3):529-549

Saltwater intrusion into coastal freshwater aquifers is an ongoing problem that will continue to impact coastal freshwater resources as coastal populations increase. To effectively model saltwater intrusion, the impacts of increased salt content on fluid density must be accounted for to properly model saltwater/freshwater transition zones and sharp interfaces. We present a model for variable density fluid flow and solute transport where a conforming finite element method discretization with a locally conservative velocity post-processing method is used for the flow model and the transport equation is discretized using a variational multiscale stabilized conforming finite element method. This formulation provides a consistent velocity and performs well even in advection-dominated problems that can occur in saltwater intrusion modeling. The physical model is presented as well as the formulation of the numerical model and solution methods. The model is tested against several 2-D and 3-D numerical and experimental benchmark problems, and the results are presented to verify the code.  相似文献   

Seabirds as monitors of the marine environment   总被引：15，自引：1，他引：15  

Furness  R. W.; Camphuysen  Kees 《ICES Journal of Marine Science》1997,54(4):726-737

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Balancing exploitation and conservation of the eastern Scotian Shelf ecosystem: application of a 4D ecosystem exploitation index     

Bundy  Alida; Fanning  Paul; Zwanenburg  Kees C.T. 《ICES Journal of Marine Science》2005,62(3):503-510

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An ELLAM approximation for advective–dispersive transport with nonlinear sorption     

Matthew W. Farthing  Christopher E. Kees  Thomas F. Russell  Cass T. Miller 《Advances in water resources》2006

We consider an Eulerian–Lagrangian localized adjoint method (ELLAM) applied to nonlinear model equations governing solute transport and sorption in porous media. Solute transport in the aqueous phase is modeled by standard advection and hydrodynamic dispersion processes, while sorption is modeled with a nonlinear local-equilibrium model. We present our implementation of finite volume ELLAM (FV-ELLAM) and finite element (FE-ELLAM) discretizations to the reactive transport model and evaluate their performance for several test problems containing self-sharpening fronts.  相似文献   

Wavefield extrapolation and amplitude-variation-with-angle migration in highly discontinuous media   总被引：4，自引：0，他引：4  

Jianfeng Zhang  Kees Wapenaar 《Geophysical Journal International》2003,155(1):327-339

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Versatile Two-Level Schwarz Preconditioners for Multiphase Flow     

C.E. Kees  C.T. Miller  E.W. Jenkins  C.T. Kelley 《Computational Geosciences》2003,7(2):91-114

Numerically modeling groundwater flow on finely discretized two- and three-dimensional domains requires solution algorithms appropriate for distributed memory multiprocessor architectures. Multilevel and domain decomposition algorithms are appropriate for preconditioning or solving linear systems in parallel and have, therefore, been applied to linear models for saturated groundwater flow. These algorithms have also been incorporated into more complex nonlinear multiphase flow models in the context of a linearization procedure such as Newton's method. In this work, we study a class of parallel preconditioners based on two-level Schwarz domain decomposition applied in a nonlinear two-phase flow numerical model. The restriction and interpolation operators are based on an aggregation approach that has a straightforward implementation for a variety of applications arising in subsurface modeling: structured and unstructured discretizations, finite elements and finite differences, and multicomponent model equations. We present model formulations, results from numerical experiments, and a comparison of a standard one-level Schwarz method to three two-level aggregation-based methods.  相似文献   

Inexact Newton methods and the method of lines for solving Richards' equation in two space dimensions     

Michael D. Tocci  C.T. Kelley  Cass T. Miller  Christopher E. Kees 《Computational Geosciences》1998,2(4):291-309

Richards' equation (RE) is often used to model flow in unsaturated porous media. This model captures physical effects, such as sharp fronts in fluid pressures and saturations, which are present in more complex models of multiphase flow. The numerical solution of RE is difficult not only because of these physical effects but also because of the mathematical problems that arise in dealing with the nonlinearities. The method of lines has been shown to be very effective for solving RE in one space dimension. When solving RE in two space dimensions, direct methods for solving the linearized problem for the Newton step are impractical. In this work, we show how the method of lines and Newton-iterative methods, which solve linear equations with iterative methods, can be applied to RE in two space dimensions. We present theoretical results on convergence and use that theory to design an adaptive method for computation of the linear tolerance. Numerical results show the method to be effective and robust compared with an existing approach.  相似文献   

Progress in Geodynamics: (Proceedings of the national symposium on Geodynamics held in Amsterdam,April 3–4, 1975). G.J. Borradaile,A.R. Ritsema,H.E. Rondeel and O.J. Simon (editors). North-Holland,Amsterdam, 1975, 245 pp., US$ 24.95     

Kees A. De Jong 《Tectonophysics》1977,37(4):364-366

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Colonial auks and eiders as potential indicators of oil pollution     

Kees Vermeer 《Marine pollution bulletin》1976,7(9):165-167

Colonial auk (Alcid) populations can be used as indicators of the effects of oil pollution on the seabirds of Canada's coastal zones. Of approximately 11 million breeding colonial alcids in Canada and in adjacent West Greenland waters, 87% are murres. Common Eiders may serve as the best indicators of the effects of oil pollution in Canada's western Arctic where colonial alcids are scarce.  相似文献