INFERRING A BIOPOLITICAL CONSENSUS VIEW OF STOCHASTIC DYNAMICS FOR MANAGEMENT OF A TRANSBOUNDARY FISHERY

ABSTRACT. Management of trans‐boundary fisheries is a complicated problem with biological, legal, economic and political implications. We propose a simple stochastic differential‐equation model to describe a biopolitical consensus view of fish stock dynamics. Estimates of the drift and diffusion terms of three stochastic differential equations are obtained using data from the southern bluefin tuna (SBT) fishery with a method based on the Kolmogorov‐Smirnov statistic. We refer to these estimated equations as alternative biopolitical consensus views of SBT stock dynamics. Each of these is used to generate a time series of optimal harvest that achieves the objective of maximizing the present value of expected fishery returns. These time series of optimal harvests are then compared to actual harvests for the period 1981 1997.     

Influence of external factors on the self-assembly of two structurally related antidepressant drugs: a thermodynamic study

Apparent molal volumes and adiabatic compressibilities of aqueous solutions of the amphiphilic antidepressant drugs imipramine and desipramine hydrochlorides have been determined from density and ultrasound velocity measurements in the temperature range 288.15—313.15 K in buffered solution of pH 3.0 and 5.5. Critical concentrations for aggregation of these drugs were obtained from inflections on the plots of the sound velocity against drug concentration. Positive deviation from the Debye—Hückel limiting law of the apparent molal volume of imipramine provides evidence of limited association at concentrations below the critical concentration over the temperature range studied. Apparent molal adiabatic compressibilities of the aggregates formed by the drugs, calculated by combining the ultrasound velocity and density data, were typical of those for a stacked aggregate. The critical concentration and energy involved in the aggregation process of these drugs have been evaluated using isothermal titration calorimetry. The solvent—aggregate interactions have been discussed from compressibility and calorimetry data.     

BUYING ECOLOGICAL SERVICES: FRAGMENTED RESERVES,CORE AND PERIPHERY NATIONAL PARK STRUCTURE,AND THE AGRICULTURAL EXTENSIFICATION DEBATE

Abstract Growing demand for cropland products has placed intense pressure on the ability of land resources to support nature, straining public budgets to purchase environmental goods. Fixing overall agricultural output, two environmental policy options are whether to (i) promote more agricultural extensification and nature‐friendly farming practices or (ii) produce intensively on some land and leave the rest wild. Microeconomic models of the topic have not accounted for widely recognized spatial externalities regarding fragmented reserves. This article does so, using Wirtinger's inequality to also identify a third policy possibility. This is that ecological services can follow a smoothly varying spatial path chararacterized by harmonic functions. We use the results to rationalize the core and periphery national park structure put in place around the world, that is, versions of our third policy possibility have been implemented.     

Thermal conductivity of fluids with steeply repulsive potentials

We consider the thermal conductivity of steeply repulsive inverse power fluids (SRP) in which the particles interact with a pair potential, φ(r) = ε(σ/r)ⁿ. The time correlation function for the heat flux, C_λ(t), and the time average, C_λ(0) are calculated numerically by molecular dynamics simulations, and accurate expressions for these are also derived for the SRP fluid. We show, by molecular dynamics simulations, that close to the hard-sphere limit this time correlation function has the same analytic form as for the shear and pressure correlation functions for the shear and bulk viscosity, i.e. C_λ(t)/C_λ(0) = 1 ?T* (nt*)² + 0((nt*)⁴), where T* = k _B T/ε, is the reduced temperature, k _B is Boltzmann's constant and t* = (ε/σ²)^1/2 t is the reduced time. The thermal conductivity for the limiting case of hard spheres is numerically very close to that given by the traditional Enskog relation. At low densities the normalized relaxation times are typically largest for the thermal conductivity, followed by shear and then bulk viscosity. Close to the maximum fluid density, the latter two increase rapidly with density (especially for the shear) but continue a monotonic decline for the thermal conductivity. This reflects the relative insensitivity of the thermal conductivity to the approach to the fluid-solid phase boundary.     

Computer simulations of soft repulsive spherocylinders

Computer simulations of systems of soft repulsive spherocylinders (SRS) of aspect ratio (L/D) equal to 4 have been carried out using the parallel molecular dynamics program GBMOLDD. At sufficiently high densities the system forms stable nematic and smectic-A liquid crystalline phases. Results are presented for a series of seven isochores in the NVE ensemble, and for isobars at T? = kT/?= 0.5, 1.0, 1.5 in the NpT ensemble.     

Eigenvalues,integer discontinuities and NMR shielding constants in Kohn—Sham theory

Kohn—Sham eigenvalues are determined from coupled cluster electron densities. The calculated HOMO—LUMO eigenvalue differences are compared with those from conventional generalized gradient approximation (GGA) exchange-correlation functionals for a range of small molecules. In all cases, GGA HOMO—LUMO differences are smaller than those calculated from the coupled cluster densities. When the GGA HOMO—LUMO differences are explicitly corrected—such that they equal those calculated from electron densities—significant improvements in NMR shielding constants are obtained. The eigenvalues calculated from electron densities are also used to approximate the magnitude of the integer discontinuity in the exact exchange-correlation potential. The value of the Kohn—Sham HOMO eigenvalue is then considered. Although HOMO eigenvalues from high quality, asymptotically vanishing, exchange-correlation potentials are close to the negative of the ionization potential, HOMO eigenvalues from the GGA functionals are shifted upwards by approximately 50% of the calculated integer discontinuity. An alternative approach for correcting NMR shielding constants is investigated.     

QUANTUM SUPERGROUPS I. FOUNDATIONS

In this part one of a series of papers, we introduce a new version of quantum covering and super groups with no isotropic odd simple root, which is suitable for the study of integrable modules, integral forms, and the bar involution. A quantum covering group involves parameters q and π with π²?=?1, and it specializes at π?=??1 to a quantum supergroup. Following Lusztig, we formulate and establish various structural results of the quantum covering groups, including a bilinear form, quasi- $ \mathcal{R} $ -matrix, Casimir element, character formulas for integrable modules, and higher Serre relations.     

PIGS,PARTIES, AND NOISE: HOW STOCHASTICITY IMPACTS THE ROBUSTNESS OF THE TSEMBAGA CULTURAL PRACTICES

Abstract We present a probabilistic perspective on sustainable resource usage. A mathematical model is introduced to describe the interplay between a population and its renewable resource base. The amount of effort a society chooses to exert in harvesting its resource is formalized in the model. Using an indigenous population of slash and burn farmers as a case study, we derive a system of stochastic differential equations from a system of ordinary differential equations introduced by another author. The cultural mechanisms that help to stabilize the population in the deterministic system actually decrease the expected survival time in the stochastic system.