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Article

Aitor Bilbao‐Guillerna, Manuel de la Sen and Santiago Alonso‐Quesada

The purpose of this paper is to improve the transient response and the inter‐sample behavior of a model reference adaptive control system by an appropriate selection of…

Abstract

Purpose

The purpose of this paper is to improve the transient response and the inter‐sample behavior of a model reference adaptive control system by an appropriate selection of the fractional order hold (FROH) gain β and the multirate gains used in the control reconstruction signal through a fully freely chosen reference model even when the continuous plant possesses unstable zeros.

Design/methodology/approach

A multiestimation adaptive control scheme for linear time‐invariant continuous‐time plant with unknown parameters is presented. The set of discrete adaptive models is calculated from a different combination of the correcting gain β in a FROH and the set of gains to reconstruct the plant input under multirate sampling with fast input sampling. Then the scheme selects online the model with the best continuous‐time tracking performance which includes a measure of the inter‐sample ripple, which is improved. The estimated discrete unstable zeros are avoided through an appropriate design of the multirate gains so that the reference model might be freely chosen with no constraints on potential unstable zeros.

Findings

The scheme is able to select online the discretization model with the best continuous‐time tracking performance without an appropriate initialization.

Research limitations/implications

The switching mechanism among the different models should maintain in operation the active discretization model at least for a minimum residence time in order to guarantee closed‐loop stability. The inter‐sample behavior is improved, but it is not always completely removed.

Practical implications

The transient response and the inter‐sample behavior are improved by using this multiestimation‐based discrete controller compared with a single estimation‐based one. The implementation of discrete controllers makes it easier and cheaper to implement and also more reliable than continuous‐time controllers.

Originality/value

The main innovation of the paper compared with previous background work is that the reference output is supplied by a stable continuous transfer function. Then the scheme is able to partly regulate the continuous‐time tracking error while the controller is essentially discrete‐time and operated by a FROH in general.

Details

Kybernetes, vol. 37 no. 6
Type: Research Article
ISSN: 0368-492X

Keywords

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Article

M. De la Sen

This purpose of this paper is to discuss a linear fractional representation (LFR) of parameter‐dependent systems which are linear in the parameters but uncertain, being…

Abstract

Purpose

This purpose of this paper is to discuss a linear fractional representation (LFR) of parameter‐dependent systems which are linear in the parameters but uncertain, being eventually time‐varying real‐rational nonlinear parameterizations, and dynamics with constant point delays.

Design/methodology/approach

The formulation is made in terms of Lyapunov's second method whereby the Lyapunov function candidate is confirmed to be a Lyapunov function by testing a finite number of linear‐matrix inequalities when the uncertain parameter vector, which might be time‐varying, lies within a known polytope which characterizes the uncertainties. The tests are performed only on the set of vertices associated with polytopes.

Findings

Sufficient conditions for global asymptotic stability are obtained. Conditions constraining the system to be slowly time‐varying around a stable nominal parameterization are not imposed in order to guarantee the stability.

Research limitations/implications

The formulation is applied to a class of systems whose uncertainties might be parameterized through time‐varying real‐rational nonlinear parameterizations and which include point‐delayed dynamics with constant delays. However, such a class includes certain classes of neural networks with delays, systems with switched parameterizations and systems whose uncertain dynamics evolve arbitrarily in regions defined by known polytopes.

Practical implications

The stability tests are less involved than usual for time‐varying systems since only a finite number of them is necessary to investigate the stability.

Originality/value

LFR descriptions of linear time‐varying systems are extended to a wide class of systems with constant point delays. Also, the real‐rational nonlinear parameterizations of the uncertainties are admitted in both the delay‐free and delayed dynamics.

Details

Engineering Computations, vol. 24 no. 6
Type: Research Article
ISSN: 0264-4401

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Article

Manuel De la Sen

The purpose of this paper is to discuss the properties of transparency and excitability of positive linear time‐invariant systems under internal point delays.

Abstract

Purpose

The purpose of this paper is to discuss the properties of transparency and excitability of positive linear time‐invariant systems under internal point delays.

Design/methodology/approach

The problem is solved by combining the algebraic conditions for positivity, excitability, and transparency for the case of linear and time‐invariant dynamic systems in the presence of discrete lags.

Findings

It is shown that the excitability independent of delay is guaranteed if an auxiliary delay‐free system is excitable. Necessary and sufficient conditions for excitability and transparency are formulated in terms of the parameterization of the dynamics and control matrices, and equivalently, in terms of strict positivity of a matrix of an associate system obtained from the influence graph of the original system. Such conditions are testable through simple algebraic tests involving moderate computational effort.

Practical implications

The practical implications mainly rely on some biological and medical problems where delays are present by nature, excitability means the activation of all the state components under positive controls after a short time in the sense that it cannot remain identically zero. In the same way, it relays on the activation of all the output components under zero controls and non‐negative initial conditions.

Originality/value

The paper extends the concepts of excitability and transparency to dynamic systems with point time‐lags which are very common in nature and some practical problems.

Details

Kybernetes, vol. 38 no. 9
Type: Research Article
ISSN: 0368-492X

Keywords

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Article

M. De la Sen and C.F. Alastruey

The stability of linear time‐delay systems with point internal delays is difficult to deal with in practice because of the fact that their characteristic equation is…

Abstract

The stability of linear time‐delay systems with point internal delays is difficult to deal with in practice because of the fact that their characteristic equation is usually of transcendent type rather than of polynomial type. This feature causes usually the system to possess an infinite number of poles. In this paper, stability tests for this class of systems are obtained either based on extensions of classical tests applicable to delay‐free systems or on approaches within the framework of two‐dimensional digital filters. Some of those two‐dimensional stability tests are also proved to be useful for stability testing of a common class of linear hybrid systems which involve coupled continuous and digital substates after a slight “ad‐hoc” adaptation of the tests for that situation.

Details

Engineering Computations, vol. 21 no. 7
Type: Research Article
ISSN: 0264-4401

Keywords

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Article

Abstract

Details

Kybernetes, vol. 41 no. 1/2
Type: Research Article
ISSN: 0368-492X

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Article

Yamna Ghoul

An identification scheme to identify interconnected discrete-time (DT) varying systems.

Abstract

Purpose

An identification scheme to identify interconnected discrete-time (DT) varying systems.

Design/methodology/approach

The purpose of this paper is the identification of interconnected discrete time varying systems. The proposed technique permits the division of global system to many subsystems by building a vector observation of each subsystem and then using the gradient method to identify the time-varying parameters of each subsystem. The convergence of the presented algorithm is proven under a given condition.

Findings

The effectiveness of the proposed technique is then shown with application to a simulation example.

Originality/value

In the past decade, there has been a renewed interest in interconnected systems that are multidimensional and composed of similar subsystems, which interact with their closest neighbors. In this context, the concept of parametric identification of interconnected systems becomes relevant, as it considers the estimation problem of such systems. Therefore, the identification of interconnected systems is a challenging problem in which it is crucial to exploit the available knowledge about the interconnection structure. For time-varying systems, the identification problem is much more difficult. To cope with this issue, this paper addresses the identification of DT dynamical models, composed by the interconnection of time-varying systems.

Details

Engineering Computations, vol. 37 no. 3
Type: Research Article
ISSN: 0264-4401

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Article

George K. Chacko

Gives an in depth view of the strategies pursued by the world’s leading chief executive officers in an attempt to provide guidance to new chief executives of today…

Abstract

Gives an in depth view of the strategies pursued by the world’s leading chief executive officers in an attempt to provide guidance to new chief executives of today. Considers the marketing strategies employed, together with the organizational structures used and looks at the universal concepts that can be applied to any product. Uses anecdotal evidence to formulate a number of theories which can be used to compare your company with the best in the world. Presents initial survival strategies and then looks at ways companies can broaden their boundaries through manipulation and choice. Covers a huge variety of case studies and examples together with a substantial question and answer section.

Details

Asia Pacific Journal of Marketing and Logistics, vol. 11 no. 2/3
Type: Research Article
ISSN: 1355-5855

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Article

Yaw A. Debrah and Ian G. Smith

Presents over sixty abstracts summarising the 1999 Employment Research Unit annual conference held at the University of Cardiff. Explores the multiple impacts of…

Abstract

Presents over sixty abstracts summarising the 1999 Employment Research Unit annual conference held at the University of Cardiff. Explores the multiple impacts of globalization on work and employment in contemporary organizations. Covers the human resource management implications of organizational responses to globalization. Examines the theoretical, methodological, empirical and comparative issues pertaining to competitiveness and the management of human resources, the impact of organisational strategies and international production on the workplace, the organization of labour markets, human resource development, cultural change in organisations, trade union responses, and trans‐national corporations. Cites many case studies showing how globalization has brought a lot of opportunities together with much change both to the employee and the employer. Considers the threats to existing cultures, structures and systems.

Details

Management Research News, vol. 23 no. 2/3/4
Type: Research Article
ISSN: 0140-9174

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Article

Brian H. Kleiner

Presents a special issue, enlisting the help of the author’s students and colleagues, focusing on age, sex, colour and disability discrimination in America. Breaks the…

Abstract

Presents a special issue, enlisting the help of the author’s students and colleagues, focusing on age, sex, colour and disability discrimination in America. Breaks the evidence down into manageable chunks, covering: age discrimination in the workplace; discrimination against African‐Americans; sex discrimination in the workplace; same sex sexual harassment; how to investigate and prove disability discrimination; sexual harassment in the military; when the main US job‐discrimination law applies to small companies; how to investigate and prove racial discrimination; developments concerning race discrimination in the workplace; developments concerning the Equal Pay Act; developments concerning discrimination against workers with HIV or AIDS; developments concerning discrimination based on refusal of family care leave; developments concerning discrimination against gay or lesbian employees; developments concerning discrimination based on colour; how to investigate and prove discrimination concerning based on colour; developments concerning the Equal Pay Act; using statistics in employment discrimination cases; race discrimination in the workplace; developments concerning gender discrimination in the workplace; discrimination in Japanese organizations in America; discrimination in the entertainment industry; discrimination in the utility industry; understanding and effectively managing national origin discrimination; how to investigate and prove hiring discrimination based on colour; and, finally, how to investigate sexual harassment in the workplace.

Details

Equal Opportunities International, vol. 17 no. 3/4/5
Type: Research Article
ISSN: 0261-0159

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Article

Li‐teh Sun

Man has been seeking an ideal existence for a very long time. In this existence, justice, love, and peace are no longer words, but actual experiences. How ever, with the…

Abstract

Man has been seeking an ideal existence for a very long time. In this existence, justice, love, and peace are no longer words, but actual experiences. How ever, with the American preemptive invasion and occupation of Afghanistan and Iraq and the subsequent prisoner abuse, such an existence seems to be farther and farther away from reality. The purpose of this work is to stop this dangerous trend by promoting justice, love, and peace through a change of the paradigm that is inconsistent with justice, love, and peace. The strong paradigm that created the strong nation like the U.S. and the strong man like George W. Bush have been the culprit, rather than the contributor, of the above three universal ideals. Thus, rather than justice, love, and peace, the strong paradigm resulted in in justice, hatred, and violence. In order to remove these three and related evils, what the world needs in the beginning of the third millenium is the weak paradigm. Through the acceptance of the latter paradigm, the golden mean or middle paradigm can be formulated, which is a synergy of the weak and the strong paradigm. In order to understand properly the meaning of these paradigms, however, some digression appears necessary.

Details

International Journal of Sociology and Social Policy, vol. 25 no. 6/7
Type: Research Article
ISSN: 0144-333X

Keywords

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