Stability of linear difference and differential inclusions

Any given n X n matrix A is shown to be a restriction, to the A-invariant subspace, of a nonnegative N x N matrix B of spectral radius p(B) arbitrarily close to p(A). A difference inclusion x(k+1) is an element of Ax(k), where A is a compact set of matrices, is asymptotically stable if and only if A can be extended to a set B of nonnegative matrices B with \ \B \ \ (1) < 1 or \ \B \ \ (infinity) < 1. Similar results are derived for differential inclusions.

Estimates of the real structured radius of stability of linear dynamic systems

A question is examined as to estimates of the norms of perturbations of a linear stable dynamic system, under which the perturbed system remains stable in a situation R:here a perturbation has a fixed structure.

Noise-free scattering of the quantized electromagnetic field from a dispersive linear dielectric

We study the scattering of the quantized electromagnetic field from a linear, dispersive dielectric using the scattering formalism for quantum fields. The medium is modeled as a collection of harmonic oscillators with a number of distinct resonance frequencies. This model corresponds to the Sellmeir expansion, which is widely used to describe experimental data for real dispersive media. The integral equation for the interpolating field in terms of the in field is solved and the solution used to find the out field. The relation between the ill and out creation and annihilation operators is found that allows one to calculate the S matrix for this system. In this model, we find that there are absorption bands, but the input-output relations are completely unitary. No additional quantum-noise terms are required.

Linear models of simple cells: Correspondence to real cell responses and space spanning properties

Despite their limitations, linear filter models continue to be used to simulate the receptive field properties of cortical simple cells. For theoreticians interested in large scale models of visual cortex, a family of self-similar filters represents a convenient way in which to characterise simple cells in one basic model. This paper reviews research on the suitability of such models, and goes on to advance biologically motivated reasons for adopting a particular group of models in preference to all others. In particular, the paper describes why the Gabor model, so often used in network simulations, should be dropped in favour of a Cauchy model, both on the grounds of frequency response and mutual filter orthogonality.

Lexical decision in Parkinson's disease: A reply to Brown, McDonald, and Spicer (1999)

Recent semantic priming investigations in Parkinsons disease (PD) employed variants of Neelys (1977) lexical decision paradigm to dissociate the automatic and attentional aspects of semantic activation (McDonald, Brown, Gorell, 1996; Spicer, Brown, Gorell, 1994). In our earlier review, we claimed that the results of Spicer, McDonald and colleagues normal control participants violated the two-process model of information processing (Posner Snyder, 1975) upon which their experimental paradigm had been based (Arnott Chenery, 1999). We argued that, even at the shortest SOA employed, key design modifications to Neelys original experiments biased the tasks employed by Spicer et al. and McDonald et al. towards being assessments of attention-dependent processes. Accordingly, we contended that experimental procedures did not speak to issues of automaticity and, therefore, Spicer, McDonald and colleagues claims of robust automatic semantic activation in PD must be treated with caution.

The Napster decision : implications for copyright law in the digital age

Challenges posed to copyright law in the digital age is most evident in A and M Records Inc v Napster Inc - the various court rulings indicate that Napster is likely to be held responsible for massive copyright infringement should the case come to a full trial - implications for Australian copyright law, the recording industry and individual artists - globalisation may hinder the ability of the recording industry to prevent mass copyright infringement.

A decision support process to compare Riparian revegetation options in Scheu Creek catchment in North Queensland

While riparian vegetation can play a major role in protecting land, water and natural habitat in catchments, there are high costs associated with tree planting and establishment and in diverting land from cropping. The distribution of costs and benefits of riparian revegetation creates conflicts in the objectives of various stakeholder groups. Multicriteria analysis provides an appropriate tool to evaluate alternative riparian revegetation options, and to accommodate the conflicting views of various stakeholder groups. This paper discusses an application of multicriteria analysis in an evaluation of riparian revegetation policy options for Scheu Creek, a small sub-catchment in the Johnstone River catchment in north Queensland, Australia. Clear differences are found in the rankings of revegetation options for different stakeholder groups with respect to environmental, social and economic impacts. Implementation of a revegetation option will involve considerable cost for landholders for the benefits of society. Queensland legislation does not provide a means to require farmers to implement riparian revegetation, hence the need for subsidies, tau incentives and moral suasion. (C) 2001 Academic Press.

Determination of breeding strategies for beef cattle bull breeders selling bulls into two competing markets on a non-linear price grid

Computer simulation was used to suggest potential selection strategies for beef cattle breeders with different mixes of clients between two potential markets. The traditional market paid on the basis of carcass weight (CWT), while a new market considered marbling grade in addition to CWT as a basis for payment. Both markets instituted discounts for CWT in excess of 340 kg and light carcasses below 300 kg. Herds were simulated for each price category on the carcass weight grid for the new market. This enabled the establishment of phenotypic relationships among the traits examined [CWT, percent intramuscular fat (IMF), carcass value in the traditional market, carcass value in the new market, and the expected proportion of progeny in elite price cells in the new market pricing grid]. The appropriateness of breeding goals was assessed on the basis of client satisfaction. Satisfaction was determined by the equitable distribution of available stock between markets combined with the assessment of the utility of the animal within the market to which it was assigned. The best goal for breeders with predominantly traditional clients was a CWT in excess of 330 kg, while that for breeders with predominantly new market clients was a CWT of between 310 and 329 kg and with a marbling grade of AAA in the Ontario carcass pricing system. For breeders who wished to satisfy both new and traditional clients, the optimal CWT was 310-329 kg and the optimal marbling grade was AA-AAA. This combination resulted in satisfaction levels of greater than 75% among clients, regardless of the distribution of the clients between the traditional and new marketplaces.

ReoPro rules: results from the 'DoTirofiban and ReoPro give similar efficacy trial' (TARGET) - A Key Paper Evaluation (Topol, Ej et al)

In the treatment of atherosclerotic disease, stenting in the presence of a glycoprotein (GP) IIb/IIIa antagonist is becoming an increasingly common procedure. The ‘Do Tirofiban and ReoPro Give Similar Efficacy Trial’ (TARGET) was designed to determine whether the cheaper tirofiban was as effective and safe as abciximab in the prevention of ischaemic events with stenting. Unexpectedly, abciximab was shown to be superior to tirofiban. Tirofiban is a selective GP IIb/IIIa antagonist whereas abciximab has additional anti-inflammatory actions, which may contribute to its superiority.