EDGE PERMEABILITY AND POPULATION PERSISTENCE IN ISOLATED HABITAT PATCHES

ABSTRACT. Population persistence in isolated habitat fragments is investigated using integrodifference equations. The propensity of individual dispersers encountering the boundary of the patch to emigrate is defined by edge permeability. A dispersal model incorporating movement, settlement and edge permeability defines dispersal success as a function of a disperser's starting location. This dispersal model is used to generate dispersal kernels for integrodifference equation models, analysis of which gives a condition for population persistence in terms of edge permeability, patch size and average dispersal distance. An approximation reduces the spatial problem to a simple nonspatial model that can be easily analyzed.     

AN IMPLICIT SURFACE TENSION ALGORITHM FOR PICARD SOLVERS OF SURFACE–TENSION–DOMINATED FREE AND MOVING BOUNDARY PROBLEMS

One of the methods for solving a free or moving boundary problem is the use of Picard solvers which solve the geometry and the velocity field successively. When, however, the kinematic condition is used for updating the geometry in this technique, numerical stability problems occur for surface-tension-dominated flow. These problems are shown here to originate from the unstable integration of the local smoothing of the surface by surface tension. By an extension of the surface tension contribution to the flow field an implicit treatment of surface tension is obtained which overcomes these stability problems. The algorithm is applicable to both free and moving boundary problems, as will be shown by examples in this paper.     

Molecular and electronic structure of zwitterionic diamino-meta-quinonoid molecules

Quantum chemical calculations using molecular orbital (HF, CASSCF) and density functional theory (B3LYP) methods, in conjunction with the 6–311 + + G(d,p) basis set, have been applied to investigate the molecular and electronic structure of two diamino-meta-quinonoid molecules 1a and 2a, each containing a six-membered ring coupled with two exocyclic C = O bonds situated in a meta position, along with two amino substituents (NH₂ and NH-CH₃). It is confirmed that these substituted meta-quinone systems exhibit a zwitterionic structure in which the positively charged N-C-C(H)-C-N subunit, containing the two amino-groups, forms two chemical bonds with the negatively charged O-C-C(H)-C-O subunit. The negative charge amounts to about half of an electron. The charge separation has been approached in terms of geometries, vibrational frequencies, and electronic distribution. The ionization energy for molecule 1a is about 7.8±0.3eV. The quinonoid systems are essentially non-aromatic characterized by the NICS(+1) values of around 1.2 ppm.     

Applications of Commuting Difference Operators to Orthogonal Polynomials in Several Variables

Elementary properties of the Koornwinder--Macdonald multivariable Askey--Wilson polynomials are discussed. Studied are the orthogonality, the difference equations, the recurrence relations, and the orthonormalization constants for these polynomials. Essential in our approach are certain commuting difference operators simultaneously diagonalized by the polynomials.     

An Approximate Solution for Fluid Infiltration near a Circular Opening in Unsaturated Media

A regular perturbation technique is employed to approximate the solution for fluid infiltration from a circular opening into an unsaturated medium. Introducing two empirical constitutive relations and relating the permeability k and water content with pore fluid pressure p, a nonlinear diffusion equation in terms of pore pressure is established. After rearranging the nonlinear diffusion equation, a parameter perturbation on is performed and an approximate solution with an error of is obtained, which correlate to a condition in which = . This approximate solution is verified by a finite difference solution and compared also with a linear solution in which the diffusivity is constant. It is shown that the perturbation solution with terms up to and including first-order can give a reasonably accurate solution for the parameter range for p ₀ selected in this paper. The solution procedure provided in this paper also avoids the numerical problem normally encountered for a small time solution. The solution may also be used to overcome difficulties arising in solution procedure by the similarity transformation (Boltzmann), commonly conducted on diffusion equation, which cannot be applied for a finite wellbore problem.     

Evidence for a Second Transport Porosity for the Diffusion of Tritiated Water (HTO) in a Sedimentary Rock (Opalinus Clay - OPA): Application of Through- and Out-Diffusion Techniques

The diffusion of tritiated water (HTO) in Opalinus clay (OPA) samples from bore cores from the Benken area (Northern Switzerland) was studied using the radial through- and out-diffusion technique. Results from inverse modelling of out-diffusion data for HTO indicated the presence of two preferential diffusion pathways: a fast and a slow one. Analysing through-diffusion data, however, provides hardly any information concerning a second transport-relevant porosity. Only by also analysing the out-diffusion phase can finer details of the diffusion process and information on sample heterogeneity be recognised. The extracted values for the effective diffusion coefficient are in the order of 3 × 10^–11 m² s^–1 for the faster transport porosity and roughly an order of magnitude smaller for the slower type of porosity. We had to account for tritium sorption on the clay minerals by a small but non-zero K_d-value in the order of 10^–5 m³ kg^–1 in order to reproduce the data with acceptable precision. In the model applied both porosities are considered as being independent from each other. Roughly 30% of the tracer diffused through the second, slower porosity; such a fact might be interesting for future performance assessments for radioactive waste repositories hosted by clay formations. Based on our present picture from water-saturated OPA, on a microscopic scale three different kind of waters can be discriminated: free water, double layer water and interlayer water. However, using HTO as tracer only, it could not be deduced which type of water-filled pores finally account for the transport-relevant porosity.Author for correspondence: Tel.: +41-56-3102257; Fax: +41-56-3104438; E-mail: luc.vanloon@psi.ch     

ASSESSING UNCERTAINTY IN A MULTISPECIES AGE‐STRUCTURED ASSESSMENT FRAMEWORK: THE EFFECTS OF DATA LIMITATIONS AND MODEL ASSUMPTIONS

Performance of a multispecies age‐structured assessment (MSASA) model in the Gulf of Alaska (GOA) relative to changes in data and model assumptions was examined through simulation exercises. Species included arrowtooth flounder (Atheresthes stomias), Pacific cod (Gadus macrocephalus), walleye pollock (Theragra chalcogramma), Pacific halibut (Hippoglossus stenolepis), and Steller sea lion (Eumetopias jubatus). Age‐specific predation mortality was estimated as a flexible function of predator and prey abundances and fitted to diet data. Simulated data sets were constructed by applying random error to estimates of catch, survey, and diet data from an operating model, whose structure was identical to that of the estimating model. Simulations explored the effects of data variability, mismatched assumptions regarding model structure, and lack of diet data on model performance. Model misspecification and uninformative diet data had the greatest influence on model performance. Given the current emphasis on the development of ecosystem‐based models and management, prioritizing the rigorous sampling of diet data would best facilitate the development of predation models useful to management agencies.