Lampros K. Stergioulas

Simulation in manufacturing and business: A review

This paper reports the results of a review of simulation applications published within peer-reviewed literature between 1997 and 2006 to provide an up-to-date picture of the role of simulation techniques within manufacturing and business. The review is characterised by three factors: wide coverage, broad scope of the simulation techniques, and a focus on real-world applications. A structured methodology was followed to narrow down the search from around 20,000 papers to 281. Results include interesting trends and patterns. For instance, although discrete event simulation is the most popular technique, it has lower stakeholder engagement than other techniques, such as system dynamics or gaming. This is highly correlated with modelling lead time and purpose. Considering application areas, modelling is mostly used in scheduling. Finally, this review shows an increasing interest in hybrid modelling as an approach to cope with complex enterprise-wide systems.

An evaluation framework for Health Information Systems: human, organization and technology-fit factors (HOT-fit).

BACKGROUND AND PURPOSE The realization of Health Information Systems (HIS) requires rigorous evaluation that addresses technology, human and organization issues. Our review indicates that current evaluation methods evaluate different aspects of HIS and they can be improved upon. A new evaluation framework, human, organization and technology-fit (HOT-fit) was developed after having conducted a critical appraisal of the findings of existing HIS evaluation studies. HOT-fit builds on previous models of IS evaluation--in particular, the IS Success Model and the IT-Organization Fit Model. This paper introduces the new framework for HIS evaluation that incorporates comprehensive dimensions and measures of HIS and provides a technological, human and organizational fit. METHODS Literature review on HIS and IS evaluation studies and pilot testing of developed framework. The framework was used to evaluate a Fundus Imaging System (FIS) of a primary care organization in the UK. The case study was conducted through observation, interview and document analysis. RESULTS The main findings show that having the right user attitude and skills base together with good leadership, IT-friendly environment and good communication can have positive influence on the system adoption. CONCLUSIONS Comprehensive, specific evaluation factors, dimensions and measures in the new framework (HOT-fit) are applicable in HIS evaluation. The use of such a framework is argued to be useful not only for comprehensive evaluation of the particular FIS system under investigation, but potentially also for any Health Information System in general.

Robust Sliding Mode Control for Discrete Stochastic Systems With Mixed Time Delays, Randomly Occurring Uncertainties, and Randomly Occurring Nonlinearities

This paper investigates the robust sliding mode control (SMC) problem for a class of uncertain nonlinear stochastic systems with mixed time delays. Both the sectorlike nonlinearities and the norm-bounded uncertainties enter into the system in random ways, and such randomly occurring uncertainties and randomly occurring nonlinearities obey certain mutually uncorrelated Bernoulli distributed white noise sequences. The mixed time delays consist of both the discrete and the distributed delays. The time-varying delays are allowed in state. By employing the idea of delay fractioning and constructing a new Lyapunov-Krasovskii functional, sufficient conditions are established to ensure the stability of the system dynamics in the specified sliding surface by solving a certain semidefinite programming problem. A full-state feedback SMC law is designed to guarantee the reaching condition. A simulation example is given to demonstrate the effectiveness of the proposed SMC scheme.

Investigating evaluation frameworks for health information systems

BACKGROUND AND PURPOSE Evaluation of health information systems (HIS) enables the assessment of the extent to which HIS are fulfilling their objectives in supporting the services of healthcare delivery. This paper presents an overview of evaluation in health informatics and information systems. METHODS Literature review on discourses, dimensions and methods of HIS and IS evaluation. A critical appraisal of selected HIS and IS evaluation frameworks is undertaken in order to identify HIS evaluation dimensions and measures. The frameworks are compared based on their inclusion of human, organizational and technological factors. RESULTS We found that an increasing number of evaluation studies deal with two distinct trends of HIS: one considers human and organizational issues and the other is concerned with the employment of a subjectivist approach. Our review indicates that current evaluation methods complement each other in that they evaluate different aspects of HIS and they can be improved upon. CONCLUSIONS Evaluation is complex; it is easy to measure many things but not necessarily the right ones. Nevertheless, it is possible to consider, a HIS evaluation framework with more comprehensive and specific measures that would incorporate technological, human and organizational issues to facilitate HIS evaluation.

Extended Kalman filtering with stochastic nonlinearities and multiple missing measurements

In this paper, the extended Kalman filtering problem is investigated for a class of nonlinear systems with multiple missing measurements over a finite horizon. Both deterministic and stochastic nonlinearities are included in the system model, where the stochastic nonlinearities are described by statistical means that could reflect the multiplicative stochastic disturbances. The phenomenon of measurement missing occurs in a random way and the missing probability for each sensor is governed by an individual random variable satisfying a certain probability distribution over the interval [0,1]. Such a probability distribution is allowed to be any commonly used distribution over the interval [0,1] with known conditional probability. The aim of the addressed filtering problem is to design a filter such that, in the presence of both the stochastic nonlinearities and multiple missing measurements, there exists an upper bound for the filtering error covariance. Subsequently, such an upper bound is minimized by properly designing the filter gain at each sampling instant. It is shown that the desired filter can be obtained in terms of the solutions to two Riccati-like difference equations that are of a form suitable for recursive computation in online applications. An illustrative example is given to demonstrate the effectiveness of the proposed filter design scheme.

Fatigue analysis of the surface EMG signal in isometric constant force contractions using the averaged instantaneous frequency

The averaged instantaneous frequency (AIF) is proposed as an alternative method for the frequency analysis of surface electromyography (EMG) in the study of muscle fatigue during sustained, isometric muscle contractions. Results from performance analysis using experimental EMG signals demonstrate the low variability of the proposed frequency variable. Indeed, the AIF measure is shown to perform significantly better than the widely used mean and median frequency variables, in terms of robustness to the length of the analysis window.

Impact phase kinematics of instep kicking in soccer

Abstract The purpose of this study was to capture the lower limb kinematics before during and after ball impact of soccer kicking by examining the influence of both sampling rate and smoothing procedures. Nine male soccer players performed maximal instep kicks and the three-dimensional leg movements were captured at 1000 Hz. Angular and linear velocities and accelerations were determined using four different processing approaches: processed using a modified version of a time-frequency filtering algorithm (WGN), smoothed by a second-order low-pass Butterworth filter at 200 Hz cut-off (BWF), re-sampled at 250 Hz without smoothing (RSR) and re-sampled at 250 Hz but filtered by the same Butterworth filter at 10 Hz cut-off (RSF). The WGN approach appeared to establish representative kinematics, whereas the other procedures failed to remove noisy oscillation from the baseline of signal (BWF), lost the peaks of rapid changes (RSR) or produced totally distorted movement patterns (RSF). The results indicate that the procedures used by some previous studies may have been insufficient to adequately capture the lower limb motion near ball impact. We propose a new time-frequency filtering technique as a better way to smooth data whose frequency content varies dramatically.

Probability-guaranteed H∞ finite-horizon filtering for a class of nonlinear time-varying systems with sensor saturations

In this paper, the probability-guaranteed H∞ finite-horizon filtering problem is investigated for a class of nonlinear time-varying systems with uncertain parameters and sensor saturations. The system matrices are functions of mutually independent stochastic variables that obey uniform distributions over known finite ranges. Attention is focused on the construction of a time-varying filter such that the prescribed H∞ performance requirement can be guaranteed with probability constraint. By using the difference linear matrix inequalities (DLMIs) approach, sufficient conditions are established to guarantee the desired performance of the designed finite-horizon filter. The time-varying filter gains can be obtained in terms of the feasible solutions of a set of DLMIs that can be recursively solved by using the semi-definite programming method. A computational algorithm is specifically developed for the addressed probability-guaranteed H∞ finite-horizon filtering problem. Finally, a simulation example is given to illustrate the effectiveness of the proposed filtering scheme.

Robust H∞ sliding mode control for discrete time-delay systems with stochastic nonlinearities

Abstract This paper is concerned with the robust H ∞ sliding mode control (SMC) problem for a general class of discrete time-delay uncertain systems with stochastic nonlinearities. The time-varying delay is unknown with given lower and upper bounds, and the stochastic nonlinearities are described by statistical means. The purpose of the problem addressed is to integrate the SMC method with the H ∞ technique such that, for all admissible parameter uncertainty, unmatched stochastic nonlinearities, time-varying delay and unmatched external disturbance, the closed-loop system is asymptotically mean-square stable while achieving a prescribed disturbance attenuation level. Sufficient conditions are presented to ensure the desired performance of the system dynamics in the specified sliding surface by solving a semi-definite programming problem. Moreover, a discrete-time SMC law is synthesized to ensure the reaching condition. A simulation example is given to illustrate the validity of the proposed SMC scheme.

Towards a Framework for Health Information Systems Evaluation

The evaluation of Health Information Systems (HIS) is crucial to ensure their effective implementation and positive impact on healthcare delivery. A review of HIS evaluation studies was carried out which indicated that the improvement of current methods is required. In order to satisfy this requirement, a new framework is introduced for the evaluation of Information Systems (IS) in healthcare settings. The proposed HOT-fit framework (Human, Organization and Technology-fit) was developed after having critically appraised the existing findings of HIS evaluation studies. It also builds on previous models of IS evaluation, in particular, the IS Success Model and the IT-Organization Fit Model. HOT-fit incorporates the concept of fit between technology, human and organization. The paper outlined the proposed methodology of a Fundus Imaging Systems in a primary care in the UK. The framework can be potentially used as a tool to conduct better and comprehensive HIS evaluation.