Equivalence relationships between stage-structured population models.

Matrix population models are widely applied in conservation ecology to help predict future population trends and guide conservation effort. Researchers must decide upon an appropriate level of model complexity, yet there is little theoretical work to guide such decisions. In this paper we present an analysis of a stage-structured model, and prove that the model's structure can be simplified and parameterised in such a way that the long-term growth rate, the stable-stage distribution and the generation time are all invariant to the simplification. We further show that for certain structures of model the simplified models require less effort in data collection. We also discuss features of the models which are not invariant to the simplification and the implications of our results for the selection of an appropriate model. We illustrate the ideas using a population model for short-tailed shearwaters (Puffinus tenuirostris). In this example, model simplification can increase parameter elasticity, indicating that an intermediate level of complexity is likely to be preferred

In vivo and in vitro diagnosis of latex allergy at Groote Schuur Hospital

No Abstract

Determining the race structure of Leptosphaeria maculans in western Canada

Non-Peer ReviewedEach year blackleg disease of canola (Brassica napus L.), caused by Leptosphaeria maculans (Desmaz.) Ces. & De Not., is responsible for significant yield loss of Brassica napus L., oilseed rape and canola worldwide. In western Canada, blackleg disease has been managed using a combination of four-year rotations and resistant canola varieties. To determine the current race structures present in western Canada, isolates were collected from eight locations across Alberta, Saskatchewan, and Manitoba in 2007 and 2008. These isolates were inoculated onto eight different canola varieties containing different resistant genes: ‘Westar’, ‘Quinta’, ‘Glacier’, ‘MT29’, ‘Samourai’, ‘Quantum’, ‘Falcon’ and ‘Darmor’. Using the gene-for-gene theory, race structure was determined based on variety resistance to L. maculans. A scale of 0 (no disease symptoms) to 9 (severely diseased) (Newman 1980) was implemented to assess plant resistance, with a score of 5 and above suggesting susceptibility. Preliminary results have identified 18 different races, nine of which contain the majority of isolates. These results have also shown that the frequency of L. maculans avirulent alleles greatly varies between the different sites in western Canada

Review of potential fisheries and marine management impacts on the south-western Australian white shark population

Following five fatal incidents involving white sharks (Carcharodon carcharias) off the lower west coast of Western Australia between September 2011 and July 2012, as well as other highly-publicised non-fatal encounters with this species, in 2012 the State Government funded several new initiatives to better understand white sharks in Western Australia and the likely effectiveness of any community safety interventions in Western Australian waters

Quantized charge transport through a static quantum dot using a surface acoustic wave

We present a detailed study of the surface acoustic wave mediated quantized transport of electrons through a split gate device containing an impurity potential defined quantum dot within the split gate channel. A new regime of quantized transport is observed at low RF powers where the surface acoustic wave amplitude is comparable to the quantum dot charging energy. In this regime resonant transport through the single-electron dot state occurs which we interpret as turnstile-like operation in which the traveling wave amplitude modulates the entrance and exit barriers of the quantum dot in a cyclic fashion at GHz frequencies. For high RF powers, where the amplitude of the surface acoustic wave is much larger than the quantum dot energies, the quantized acoustoelectric current transport shows behavior consistent with previously reported results. However, in this regime, the number of quantized current plateaus observed and the plateau widths are determined by the properties of the quantum dot, demonstrating that the microscopic detail of the potential landscape in the split gate channel has a profound influence on the quantized acoustoelectric current transport.Comment: 9 page

On pure-strategy Nash equilibria in a duopolistic market share model

This paper develops a duopolistic discounted marketing model with linear advertising costs and advertised prices for mature markets still in expansion. Generic and predatory advertising effects are combined together in the model. We characterize a class of advertising models with some lowered production costs. For such a class of models, advertising investments have a no-free-riding strict Nash equilibrium in pure strategies if discount rates are small. We discuss the entity of this efficiency at varying of parameters of our advertising model. We provide a computational framework in which market shares can be computed at equilibrium, too. We analyze market share dynamics for an asymmetrical numerical scenario where one of the two firms is more effective in generic and predatory advertising. Several numerical insights on market share dynamics are obtained. Our computational framework allows for different scenarios in practical applications and it is developed, thanks to Mathematica software

A parallel implementation of an off-lattice individual-based model of multicellular populations

As computational models of multicellular populations include ever more detailed descriptions of biophysical and biochemical processes, the computational cost of simulating such models limits their ability to generate novel scientific hypotheses and testable predictions. While developments in microchip technology continue to increase the power of individual processors, parallel computing offers an immediate increase in available processing power. To make full use of parallel computing technology, it is necessary to develop specialised algorithms. To this end, we present a parallel algorithm for a class of off-lattice individual-based models of multicellular populations. The algorithm divides the spatial domain between computing processes and comprises communication routines that ensure the model is correctly simulated on multiple processors. The parallel algorithm is shown to accurately reproduce the results of a deterministic simulation performed using a pre-existing serial implementation. We test the scaling of computation time, memory use and load balancing as more processes are used to simulate a cell population of fixed size. We find approximate linear scaling of both speed-up and memory consumption on up to 32 processor cores. Dynamic load balancing is shown to provide speed-up for non-regular spatial distributions of cells in the case of a growing population

The Volume of some Non-spherical Horizons and the AdS/CFT Correspondence

We calculate the volumes of a large class of Einstein manifolds, namely Sasaki-Einstein manifolds which are the bases of Ricci-flat affine cones described by polynomial embedding relations in C^n. These volumes are important because they allow us to extend and test the AdS/CFT correspondence. We use these volumes to extend the central charge calculation of Gubser (1998) to the generalized conifolds of Gubser, Shatashvili, and Nekrasov (1999). These volumes also allow one to quantize precisely the D-brane flux of the AdS supergravity solution. We end by demonstrating a relationship between the volumes of these Einstein spaces and the number of holomorphic polynomials (which correspond to chiral primary operators in the field theory dual) on the corresponding affine cone.Comment: 25 pp, LaTeX, 1 figure, v2: refs adde