AN INDIVIDUAL‐BASED MODEL FOR FERAL HOGS IN GREAT SMOKY MOUNTAINS NATIONAL PARK

The expansion of feral hog (Sus scrofa) populations in the United States has resulted in increased efforts to develop and implement control strategies designed to minimize the impacts done by this invasive species. We describe an individual‐based model for feral hogs in Great Smoky Mountains National Park (GSMNP). The objectives of the model are to provide an understanding of the population dynamics of this feral hog population and to determine the efficacy of the annual harvest as a population control method. Results suggest that the dynamics of the population are driven by fall hard mast production and the GSMNP harvests currently limit growth of the population, but these control efforts have not reduced the population.     

Summation of electrostatic interactions in quasi-two-dimensional simulations

An error in our previous paper (Clark, A. T., Madden, T. J. and Warren, P. B., 1996 Molec. Phys., 87, 1063) is corrected. This brings the results into agreement with the recent work of Grønbech-Jensen et al. (Grønbech-Jensen, N., Hummer, G. and Beardmore, K. M., Molec. Phys., 1997, 92, 941).     

Models of environmental effects on anion polarizability

This paper deals with three different approaches to the representation of environmental effects on anion polarizability in cubic crystals of the stoichiometry MX, where M is an alkali metal and X is a halogen. Ab initio embedded cluster calculations of the variation in anion polarizability with pressure in a fixed crystal type are presented and compared with experiment. The results are then used in a scaled ab initio model used to predict further values for the pressure dependence of the in-crystal anion polarizability. This scaled model is compared with a fully empirical ‘universal’ model due to Batana et al. based on polarizability change with ionic radius [1997, Molec. Phys., 92, 1029]. The assumptions of the two models differ substantially and the central purpose of this paper is to contrast these differences and highlight their consequences for prediction. Although the empirical model typically overestimates the experimental pressure derivatives, and the ab initio calculations somewhat underestimate them, it is shown that the assumption of incompressible cations in the scaled ab initio-derived model has a firmer physical basis than the empirical picture in which all ions are compressible.     

A unified description of MCI3 systems with a polarizable ion simulation model

Computer simulations of a range of ionic systems of stoichiometry MX₃ using a polarizable, formal charge ionic interaction model are described. The objective of the present work is to describe the optimization of the interaction potentials in the light of new structural information which has become available from neutron scattering studies of the liquid. As well as substantially improving the agreement with experiment for LaC1₃, TbC1₃, YC1₃ and A1C1₃, simulation results are presented for the first time for ScC1₃, which is shown to exhibit a fascinating crosslinked network structure. The optimization of potentials for the crystal structures is also considered. It is shown that the C1^? ion must be considered as of smaller size in the crystal than in the liquid in order to successfully reproduce the properties of both phases.     

Theoretical calculation of the structure of a polarizable-ionic fluid

Much theory of the structures of fluids depends on the assumption of pair-additive forces between the particles. Simulations and experiments have shown that many molten salts, molecular fluids and other systems have structures that depend sensitively on polarization of their electron clouds, or on other internal distortions. In such cases, the forces are not pair additive and the theoretical calculation of structure, expressed as a radial distribution function, g(r), is not possible using the ordinary methods. Part of the problem is that the internal structure is quantum mechanical. A theoretical method for the calculation of the structure of a fluid of polarizable particles is presented here, in a form that may be applied to any one of many structure theories in common use. The method is inspired by work on the simulation of polarizable fluids. It is applied to a simple model of a molten salt with polarizable ions. The theory is applicable to particles carrying any combination of induced electrical multipole moments, along with charges and permanent moments.     

Cation polarization and the crystal structure of SnO

Tin(II) oxide has an unusual crystal structure (litharge) which exhibits numerous ‘non-ionic’ features, such as nearest neighbour ions of like charge and a large lattice energy compared with other oxides of similar cation radius. It is shown that a generic ionic interaction model for oxides, with an ab initio based representation of such many-body effects as ionic polarization and the compression of the oxide ion by its environment, predicts litharge as the lowest energy structure. Cation polarization is found to play the dominant role.     

A transferable representation of the induced multipoles in ionic crystals

Electronic structure calculations of the induced dipole and quadrupole moments on a fluoride ion at low symmetry sites in a model crystalline environments are described. The results are used to characterize the short range contributions to the induced multipoles on the F^? ion that arise from overlap between the wavefunctions of the ions. These are represented by general functions of the positions of the surrounding ions, suitable for use in a computationally tractable simulation model. The present calculations are designed to test the transferability to other classes of materials of this representation which, to date, largely has been deduced from calculations on distorted alkali halide crystals. First, the induced multipoles in mixed crystals of the alkali halides are considered, in order to check that they are predicted reliably by combining the representations deduced for the corresponding pure materials. Second, polarization effects in the alkaline earth fluorides MgF₂, and CaF₂, in a locally distorted fluorite crystal structure are examined. It is found that the material-specific parameters in the representation are related through simple functions of the ionic radii. This relationship holds between MgF₂, and CaF₂, in the fluorite structure, but also extends to the alkali fluorides previously studied. In order to illustrate the significance of polarization effects, the polarization model for CaF₂ is combined with an ab initio pair potential for the repulsion and dispersion interactions and used in a molecular dynamics simulation. Inclusion of the polarization term improves greatly the calculated phonon frequencies in the crystal.     

A METAPOPULATION MODEL FOR FERAL HOGS IN GREAT SMOKY MOUNTAINS NATIONAL PARK

Feral Hogs (Sus scrofa) are an invasive species that have occupied the Great Smoky Mountains National Park since the early 1900s. Recent studies on vegetation, mast, and harvest history were important for our work. Using these data, a model with discrete time and space was formulated to represent the feral hog dynamics in the Park. Management strategies and key characteristics of the population were investigated. The model uses observed mast variation to help govern population dynamics and results indicate that Park control efforts have limited the growth of the population.     

Ligand Substituent Effects on Ruthenium (III/II) Redox Properties: An Advanced Inorganic Laboratory Experiment

A convenient inorganic laboratory exercise is presented that exposes the student to the influences of ligand substituents on a metal centers redox properties. Students prepare a series of compounds with the general formula [Ru(bpy)₂(R¹,R²mal)](PF₆), where bpy is 2,2-bipyridine and R¹,R²mal is an anionic -diketone ligand with various R¹ and R² substituents. Each complex is prepared in a single synthetic step, and the Ru(III)/Ru(II) couple is characterized by cyclic voltammetry. The potential of the Ru(III)/Ru(II) couple shifts upon varying R¹ and R² from 0.64 to 1.10 volts vs. SSCE in the following order: (R¹ = R² = Me) < (R¹ = R² = Ph) < (R¹ = Me, R² = CF₃) < (R¹ = R² = CF₃). The inductive effects of the R substituents on the Ru(III)/Ru(II) couple are consistent with their electron-donating and electron-withdrawing properties. Hammett constants for the substituents provide an approximate measure of these effects. A linear relationship is observed when the Hammett constants are plotted against the Ru(III)/Ru(II) potential. This laboratory exercise applies a versatile electroanalytical method, cyclic voltammetry, to measure the substituent effects on a metal centers electron density. Student results of the syntheses and redox characterizations of a series of [Ru(bpy)₂(R¹,R²mal)]⁺ complexes are presented and discussed.