Stochastic reliable control of a class of uncertain time-delay systems with unknown nonlinearities

Copyright [2001] IEEE. This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of Brunel University's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. By choosing to view this document, you agree to all provisions of the copyright laws protecting it.This paper investigates the robust reliable control problem for a class of nonlinear time-delay stochastic systems. The system under study involves stochastics, state time-delay, parameter uncertainties, possible actuator failures and unknown nonlinear disturbances, which are often encountered in practice and the sources of instability. Our attention is focused on the design of linear state feedback memoryless controllers such that, for all admissible uncertainties as well as actuator failures occurring among a prespecified subset of actuators, the plant remains stochastically exponentially stable in mean square, independent of the time delay. Sufficient conditions are proposed to guarantee the desired robust reliable exponential stability despite possible actuator failures, which are in terms of the solutions to algebraic Riccati inequalities. An illustrative example is exploited to demonstrate the applicability of the proposed design approac

The causes of full ocean depth interannual variability in Drake Passage

In recent years a number of large scale modes of Southern Hemisphere climate variability have been observed, most notably the Southern Annular Mode (SAM, e.g. Thompson and Solomon, 2002), the Pacific South American modes (PSA, e.g. Mo and Peagle, 2001), the Antarctic Dipole (e.g. Martinson and Ianuzzi, 2003), the Antarctic Circumpolar Wave (e.g. White and Peterson, 1996), and of course the El Niño Southern Oscillation (ENSO). All have pronounced effects over or in the Southern Ocean, and may be expected to account for a significant part of the interannual variability observed there. Most studies analyse these phenomena from a large-scale point of view, often by extracting modes from Southern Hemisphere atmospheric and oceanic fields using various mathematical techniques. In this study we have taken an alternative approach, and tried to understand the causes of the full ocean depth variability in Drake Passage observed in the WOCE SR1b repeat hydrographic sections (Cunningham et al. 2003)

Modified Baryonic Dynamics: two-component cosmological simulations with light sterile neutrinos

In this article we continue to test cosmological models centred on Modified Newtonian Dynamics (MOND) with light sterile neutrinos, which could in principle be a way to solve the fine-tuning problems of the standard model on galaxy scales while preserving successful predictions on larger scales. Due to previous failures of the simple MOND cosmological model, here we test a speculative model where the modified gravitational field is produced only by the baryons and the sterile neutrinos produce a purely Newtonian field (hence Modified Baryonic Dynamics). We use two component cosmological simulations to separate the baryonic N-body particles from the sterile neutrino ones. The premise is to attenuate the over-production of massive galaxy cluster halos which were prevalent in the original MOND plus light sterile neutrinos scenario. Theoretical issues with such a formulation notwithstanding, the Modified Baryonic Dynamics model fails to produce the correct amplitude for the galaxy cluster mass function for any reasonable value of the primordial power spectrum normalisation.Comment: 11 pages, 2 figures. Submitted to JCA

Specifying ODP computational objects in Z

The computational viewpoint contained within the Reference Model of Open Distributed Processing (RM-ODP) shows how collections of objects can be configured within a distributed system to enable interworking. It prescribes certain capabilities that such objects are expected to possess and structuring rules that apply to how these objects can be configured with one another. This paper highlights how the specification language Z can be used to formalise these capabilities and the associated structuring rules, thereby enabling specifications of ODP systems from the computational viewpoint to be achieved

Encoding of Marginal Utility across Time in the Human Brain

Marginal utility theory prescribes the relationship between the objective property of the magnitude of rewards and their subjective value. Despite its pervasive influence, however, there is remarkably little direct empirical evidence for such a theory of value, let alone of its neurobiological basis. We show that human preferences in an intertemporal choice task are best described by a model that integrates marginally diminishing utility with temporal discounting. Using functional magnetic resonance imaging, we show that activity in the dorsal striatum encodes both the marginal utility of rewards, over and above that which can be described by their magnitude alone, and the discounting associated with increasing time. In addition, our data show that dorsal striatum may be involved in integrating subjective valuation systems inherent to time and magnitude, thereby providing an overall metric of value used to guide choice behavior. Furthermore, during choice, we show that anterior cingulate activity correlates with the degree of difficulty associated with dissonance between value and time. Our data support an integrative architecture for decision making, revealing the neural representation of distinct subcomponents of value that may contribute to impulsivity and decisiveness

A factor graph description of deep temporal active inference

Active inference is a corollary of the Free Energy Principle that prescribes how self-organizing biological agents interact with their environment. The study of active inference processes relies on the definition of a generative probabilistic model and a description of how a free energy functional is minimized by neuronal message passing under thatmodel. This paper presents a tutorial introduction to specifying active inference processes by Forney-style factor graphs (FFG). The FFG framework provides both an insightful representation of the probabilistic model and a biologically plausible inference scheme that, in principle, can be automatically executed in a computer simulation. As an illustrative example, we present an FFG for a deep temporal active inference process. The graph clearly shows how policy selection by expected free energy minimization results from free energy minimization per se, in an appropriate generative policy model

Metabolic flexibility as a major predictor of spatial distribution in microbial communities

A better understand the ecology of microbes and their role in the global ecosystem could be achieved if traditional ecological theories can be applied to microbes. In ecology organisms are defined as specialists or generalists according to the breadth of their niche. Spatial distribution is often used as a proxy measure of niche breadth; generalists have broad niches and a wide spatial distribution and specialists a narrow niche and spatial distribution. Previous studies suggest that microbial distribution patterns are contrary to this idea; a microbial generalist genus (Desulfobulbus) has a limited spatial distribution while a specialist genus (Methanosaeta) has a cosmopolitan distribution. Therefore, we hypothesise that this counter-intuitive distribution within generalist and specialist microbial genera is a common microbial characteristic. Using molecular fingerprinting the distribution of four microbial genera, two generalists, Desulfobulbus and the methanogenic archaea Methanosarcina, and two specialists, Methanosaeta and the sulfate-reducing bacteria Desulfobacter were analysed in sediment samples from along a UK estuary. Detected genotypes of both generalist genera showed a distinct spatial distribution, significantly correlated with geographic distance between sites. Genotypes of both specialist genera showed no significant differential spatial distribution. These data support the hypothesis that the spatial distribution of specialist and generalist microbes does not match that seen with specialist and generalist large organisms. It may be that generalist microbes, while having a wider potential niche, are constrained, possibly by intrageneric competition, to exploit only a small part of that potential niche while specialists, with far fewer constraints to their niche, are more capable of filling their potential niche more effectively, perhaps by avoiding intrageneric competition. We suggest that these counter-intuitive distribution patterns may be a common feature of microbes in general and represent a distinct microbial principle in ecology, which is a real challenge if we are to develop a truly inclusive ecology

Investigating green supply chain management practices and performance: the moderating roles of supply chain ecocentricity and traceability

Sustainable supply chain management has become an increasingly important driver of business performance. Understanding the contingent nature of how performance is improved in this context is therefore a critical task for management. We explore the moderating effects of two practices unique to sustainable supply chain - ecocentricity and supply chain traceability - on a firm’s environmental and operating cost performance. Design: Survey data were collected from 248 UK manufacturing firms and analyzed using moderated hierarchical regression. Findings: The results suggest that green supply chain management practices are associated with improvements in both environmental and cost-based performance. Further, higher levels of ecocentricity and supply chain traceability are associated with stronger relationships between green supply chain management practices and cost performance. Contrary to expectations, high levels of supply chain traceability were found to negatively moderate the relationship between green supply chain management practices and environmental performance. Limitations: Our research design was survey-based and cross-sectional. Future studies would benefit from longitudinal research designs that capture the effects of GSCM practices on performance over an extended period. Our survey data is also perceptual; using secondary data to capture environmental performance outcomes, for example, would be another opportunity for future research. Practical Implications: We provide additional support to findings that green supply chain management practices benefit both environmental and cost performance dimensions. In this context, we show that investments by firms in working with a broader set of eco-system partners (ecocentricity) and building supply chain traceability and leads to improved environmental sustainability outcomes. We encourage managers to carefully consider how they conceptualize and monitor their supply chains. Not applicable. Originality: This paper offers several contributions to the research in this area. First, we develop and validate a measurement scale for ecocentricity and supply chain traceability. Second, we show how these two variables – unique to sustainable supply chains – can positively influence firm and environmental performance