Stuart Townley
University of Exeter
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Featured researches published by Stuart Townley.
Systems & Control Letters | 1996
Hartmut Logemann; Stuart Townley
It is well-known that exponential stabilization of a neutral system with unstable difference operator is only possible by allowing for control laws containing derivative feedback. We show that closed-loop stability of a neutral system with unstable open-loop difference operator obtained by applying a derivative feedback scheme is extremely sensitive to arbitrarily small time delays in the feedback loop.
Journal of Differential Equations | 1989
A.J. Pritchard; Stuart Townley
Abstract In this paper we consider linear systems which are stable and examine the robustness of this property. The perturbations are assumed to have unbounded structure and we determine the smallest perturbation which destroys stability. We begin with an abstract analysis of the problem, but in later sections specialize to three types of systems: those whose mild solutions are given in terms of 1. (a) strongly continuous semigroups, 2. (b) resolvent operators-integrodifferential systems, 3. (c) evolution operators-time varying systems. For B a Banach space, L2(t0, T; B) denotes the space of all square integrable functions defined on [t0, T] with values in B. For B1, B2 Banach spaces, [t0, T] denotes the space of strongly measurable functions f(·):[t0, T]→L(B1, B2) with ess sup ∥f(·)∥⩽∞.B−1(t0, ∞;L(B1, B2)) denotes the space of strongly measurable functions f(·): [t0, ∞) → L(B1, B2) with ∥f(t)∥ 0 and k(·) ϵ L1(t0, ∞).
Ecology Letters | 2011
Iain Stott; Stuart Townley; David J. Hodgson
Empirical models are central to effective conservation and population management, and should be predictive of real-world dynamics. Available modelling methods are diverse, but analysis usually focuses on long-term dynamics that are unable to describe the complicated short-term time series that can arise even from simple models following ecological disturbances or perturbations. Recent interest in such transient dynamics has led to diverse methodologies for their quantification in density-independent, time-invariant population projection matrix (PPM) models, but the fragmented nature of this literature has stifled the widespread analysis of transients. We review the literature on transient analyses of linear PPM models and synthesise a coherent framework. We promote the use of standardised indices, and categorise indices according to their focus on either convergence times or transient population density, and on either transient bounds or case-specific transient dynamics. We use a large database of empirical PPM models to explore relationships between indices of transient dynamics. This analysis promotes the use of population inertia as a simple, versatile and informative predictor of transient population density, but criticises the utility of established indices of convergence times. Our findings should guide further development of analyses of transient population dynamics using PPMs or other empirical modelling techniques.
IEEE Transactions on Neural Networks | 1998
Antonio C. Ruiz; David H. Owens; Stuart Townley
A class of recurrent neural networks is shown to possess a stable limit cycle. A gradient type algorithm is used to modify the parameters of the network so that it learns and replicates autonomously a time varying periodic signal. The results are applied to controlling the repetitive motion of a two-link robot manipulator.
Siam Journal on Control and Optimization | 1997
Hartmut Logemann; Stuart Townley
It is well known that closing the loop around an exponentially stable, finite-dimensional, linear, time-invariant plant with square transfer-function matrix
European Journal of Control | 2000
Zbigniew Emirsjlow; Stuart Townley
\BG(s)
Siam Journal on Applied Dynamical Systems | 2007
Peter Ashwin; Gábor Orosz; John Wordsworth; Stuart Townley
compensated by a controller of the form
IEEE Transactions on Automatic Control | 1999
Hartmut Logemann; Eugene P. Ryan; Stuart Townley
(k/s)\Gamma_0
Siam Journal on Control and Optimization | 1999
Richard Rebarber; Stuart Townley
, where
Siam Journal on Control and Optimization | 1998
Hartmut Logemann; Eugene P. Ryan; Stuart Townley
k\in {\Bbb R}