Aggregates in Clay Bodies - A Research Project

An article outlining the origins of my current research. Featured in international ceramics magazine: Ceramics Technical. Originally published in 200

Patterns and rules for sensitivity and elasticity in population projection matrices

Sensitivity and elasticity analysis of population projection matrices (PPMs) are established tools in the analysis of structured populations, allowing comparison of the contributions made by different demographic rates to population growth. In some commonly used structures of PPM, however, there are mathematically inevitable patterns in the relative sensitivity and elasticity of certain demographic rates. We take a simulation approach to investigate these mathematical constraints for a range of PPM models. Our results challenge some previously proposed constraints on sensitivity and elasticity. We also identify constraints beyond those which have already been proven mathematically, and promote them as candidates for future mathematical proof. A general theme among these rules is that changes to the demographic rates of older or larger individuals have less impact on population growth than do equivalent changes among younger or smaller individuals. However, the validity of these rules in each case depends on the choice between sensitivity and elasticity, the growth rate of the population and the PPM structure used. If the structured population conforms perfectly to the assumptions of the PPM used to model it, the rules we describe represent biological reality, allowing us to prioritise management strategies in the absence of detailed demographic data. Conversely, if the model is a poor fit to the population (specifically; if demographic rates within stages are heterogeneous) such analyses could lead to inappropriate management prescriptions. Our results emphasise the importance of choosing a structured population model which fits the demographics of the population

Advance Production Duopolies and Posted Prices or Market-Clearing Prices

The paper reports the results of 39 laboratory duopoly markets for which pricing institution and participant experience are treatments. Duopolies in which producers with complete information about market demand make advance-production output decisions and sell their output at a clearing price (Cournot markets) are contrasted with comparable duopolies who post prices for sale through an efficient rationing mechanism (Kreps-Scheinkman or KS markets). Inexperienced participants in KS markets have much more difficulty selecting capacities consistent with the theoretical predictions than do those in Cournot markets. With experience, the differences disappear. If trading sessions last sufficiently long, it is likely that differences will disappear with inexperienced participants.

Counter-conditioning as an intervention to modify anti-fat attitudes

This study examined the effect of anti-fat attitude counter-conditioning using positive images of obese individuals participants completed implicit and explicit measures of attitudes towards fatness on three occasions: no intervention; following exposure to positive images of obese members of the general public; and to images of obese celebrities. Contrary to expectations, positive images of obese individuals did not result in more positive attitudes towards fatness as expected and, in some cases, indices of these attitudes worsened. Results suggest that attitudes towards obesity and fatness may be somewhat robust and resistant to change, possibly suggesting a central and not peripheral processing route for their formation

Quantity Precommitment with Price Competition versus Quantity Precommitment with Market Clearing Prices in the Laboratory

The paper reports the results of 39 laboratory duopoly markets for which pricing institution and participant experience are treatments. Cournot (C) duopolies (quantity precommitment and a price determined to clear the market) are contrasted with Kreps-Scheinkman (KS) duopolies (quantity precommitment and posted prices). Inexperienced participants in KS markets have much more difficulty selecting capacities consistent with the theoretical predictions than do those in C markets. With experience, the differences disappear.Duopoly; Laboratory experiment; Quantity precommitment; Posted prices; Price competition; Market-clearing prices; Experience