2,666 research outputs found
Exact results and mean field approximation for a model of molecular aggregation
We present a simple one-dimensional model with molecular interactions
favouring the formation of clusters with a defined optimal size. Increasing the
density, at low temperature, the system goes from a nearly-ideal gas of
independent molecules to a system with most of the molecules in optimal
clusters, in a way that resembles the formation of micelles in a dilution of
amphiphilic molecules, at the critical micellar concentration. Our model is
simple enough to have an exact solution, but it contains some basic features of
more realistic descriptions of amphiphilic systems: molecular excluded volume
and molecular attractions which are saturated at the optimal cluster. The
comparison between the exact results and the mean field density functional
approximation suggests new approaches to study the more complex and realistic
models of micelle formation; in particular it addresses the long-standing
controversy surrounding separation of internal degrees of freedom in the
formulation of cluster association phenomena.Comment: 7 pages, 5 figures, some minor correction
On a nonlocal degenerate parabolic problem
Conditions for the existence and uniqueness of weak solutions for a class of
nonlinear nonlocal degenerate parabolic equations are established. The
asymptotic behaviour of the solutions as time tends to infinity are also
studied. In particular, the finite time extinction and polynomial decay
properties are proved
Detecting groundwater discharge dynamics from point-to-catchment scale in a lowland stream : Combining hydraulic and tracer methods
Acknowledgements. We would like to thank members of the Northern Rivers Institute, Aberdeen University, for helpful discussions of data. We also thank Lars Rasmussen, Jolanta Kazmierczak and Charlotte Ditlevsen for help in the field. This study is part of the Hydrology Observatory, HOBE (http://www.hobe.dk), funded by the Villum Foundation and was as well funded by the Aarhus University Research Foundation.Peer reviewedPublisher PD
Convergence of the Crank-Nicolson-Galerkin finite element method for a class of nonlocal parabolic systems with moving boundaries
The aim of this paper is to establish the convergence and error bounds to the
fully discrete solution for a class of nonlinear systems of reaction-diffusion
nonlocal type with moving boundaries, using a linearized
Crank-Nicolson-Galerkin finite element method with polynomial approximations of
any degree. A coordinate transformation which fixes the boundaries is used.
Some numerical tests to compare our Matlab code with some existing moving
finite elements methods are investigated
Feeding Selectivity of Anchovia clupeoides (Pisces: Engraulidae) in the Ciénaga Grande de Santa Marta, Colombian Caribbean
Food selection by fishes is an important piece of information for modeling food webs in aquatic ecosystem. Monthly collections were made over a twenty-four hour period between October 1995 and June 1996 to examine the feeding selectivity of the zabaleta anchovy (Anchovia clupeoides) in the coastal lagoon Ciénaga Grande de Santa Marta, NE Colombia. A total of 4,389 specimens were collected, and the abundances and weights of the stomach food items were compared with similar measures calculated from samples obtained in nearby habitats. Our results indicate that the zabaleta anchovy is planktophagous, actively selecting copepods and detritus throughout the year. Individuals also exhibit positive selectivity of fish eggs and crab zoea on a seasonal basis and at different times of the day. This species avoids cyanobacteria, diatoms, and rotifers most of the year and during most of the day and always avoids copepod nauplii, polychaete larvae, and cladocerans. It seems that selection and avoidance of the food items by the zabaleta anchovy is due mainly to its preference for prey over 125 µm
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