A J-Spectral Factorization Approach to ℋ∞ Control

Necessary and sufficient conditions for the existence of suboptimal solutions to the standard model matching problem associated with ℋ∞ control, are derived using J-spectral factorization theory. The existence of solutions to the model matching problem is shown to be equivalent to the existence of solutions to two coupled J-spectral factorization problems, with the second factor providing a parametrization of all solutions to the model matching problem. The existence of the J-spectral factors is then shown to be equivalent to the existence of nonnegative definite, stabilizing solutions to two indefinite algebraic Riccati equations, allowing a state-space formula for a linear fractional representation of all controllers to be given. A virtue of the approach is that a very general class of problems may be tackled within a conceptually simple framework, and no additional auxiliary Riccati equations are required

A Characterization of all Solutions to the Four Block General Distance Problem

All solutions to the four block general distance problem which arises in H^∞ optimal control are characterized. The procedure is to embed the original problem in an all-pass matrix which is constructed. It is then shown that part of this all-pass matrix acts as a generator of all solutions. Special attention is given to the characterization of all optimal solutions by invoking a new descriptor characterization of all-pass transfer functions. As an application, necessary and sufficient conditions are found for the existence of an H^∞ optimal controller. Following that, a descriptor representation of all solutions is derived

Ondansetron interferes with the establishment and expression of lithium-induced conditioned rejection reactions

Conditioned rejection reactions displayed in the taste reactivity test may reflect conditioned nausea in rats because they are exclusively produced by emetic agents. The present experiments demonstrated that pretreatment with the anti-nausea agent, ondansetron, interfered with the establishment of conditioned rejection reactions (Experiment 1) and interfered with the expression of previously established conditioned rejection reactions (Experiment 2). Ondansetron selectively interfered with conditioned nausea as reflected by conditioned rejection reactions because it did not modify the unconditioned rejection reactions elicited by unpalatable quinine solution (Experiment 2). Although ondansetron blocked the expression of the selective taste reactivity reaction of conditioned rejection, it did not modify the nonselective reactions of conditioned taste or place avoidance (Experiment 3). The results suggest that conditioned rejection reactions reflect conditioned nausea in rats that is attenuated by pretreatment with the anti-nausea agent, ondansetron

Some significant South African contributions to engineering

Significance:To mark the centenary of the University of the Witwatersrand (Wits), we review several major engineering achievements made over the last century by South African citizens, or individuals educated in South Africa – several of these contributions were made by Wits graduates and academic staff members. Equally significant are some outstanding contributions to engineering education. There is no sense in which this review is exhaustive but is more a reflection of the authors’ personal interests and expertise

Motorcycle steering oscillations due to road profiling

Published versio

Nausea: Current knowledge of mechanisms, measurement and clinical impact

AbstractNausea is a subjective sensation, which often acts as a signal that emesis is imminent. It is a widespread problem that occurs as a clinical sign of disease or as an adverse effect of a drug therapy or surgical procedure. The mechanisms of nausea are complex and the neural pathways are currently poorly understood. This review summarises the current knowledge of nausea mechanisms, the available animal models for nausea research and the anti-nausea properties of commercially available anti-emetic drugs. The review also presents subjective assessment and scoring of nausea. A better understanding of the underlying mechanisms of nausea might reveal potential clinically useful biomarkers for objective measurement of nausea in species of veterinary interest

Nonlinear steering oscillations of motorcycles

Published versio

A descriptor solution to a class of discrete distance problems

Published versio

Advances in the modelling of motorcycle dynamics

Published versio