A numerical method for computing the structured singular value

This article suggests a new approach to computing Doyle's structured singular value (SSV) of a matrix. The SSV is a notion important in robust control and several iteration schemes exist for approximation a solution [1,2,4,-8,10,11].Our idea is to pick a special case of the general problem, which we believe to be natural and give an algorithm for studying it based on ‘off the shelf’ packages. Once we are committed to this ‘special case’ we discuss a very general plant uncertainty problem; it embraces real as well as complex plant perturbations of many kinds. The idea is simple and we believe very natural to the problem.     

Computation of the robustness margin with the skewed μ tool

Methods for the direct computation of the maximal structured singular value (s.s.v.) over the frequency range require a recursive application of μ analysis. Introducing the v measure as a skewed s.s.v., we point out the problem can be solved by a single application of the v tool. A mixed v upper bound is then proposed, which provides a direct solution to the problem. The relationship between the mixed μ and v upper bounds is moreover clarified. The nonnegativity of the sensitivity of the mixed μ upper bound is finally obtained as a corollary.     

Comparing computer-supported dynamic modeling and ‘paper & pencil’ concept mapping technique in students’ collaborative activity

This study aims at highlighting the collaborative activity of two high school students (age 14) in the cases of modeling the complex biological process of plant growth with two different tools: the ‘paper & pencil’ concept mapping technique and the computer-supported educational environment ‘ModelsCreator’. Students’ shared activity in both cases is carried out in the presence of a facilitator providing technical as well as cognitive support when necessary. The objective of the study is to highlight the ways in which the collaborating students are engaged in the plant growth modeling activity in the two cases and also identify the activity’s similar and different aspects in each one. Our analysis is carried out on two complementary axes, the first of which concerns the process of collaboratively creating a plant growth model with each different tool, while the second has to do with the students’ conceptualizations of the biological aspect of the modeling task in each case. A two-level analytic tool for the modeling process has been derived within the theoretical framework of ‘activity theory’ on the basis of the OCAF scheme for basic modeling operations and the scheme of Stratford et al. [Stratford, S. J., Krajcik, J., & Soloway, E. (1998). Secondary students’ dynamic modeling processes: analyzing, reasoning about, synthesizing, and testing models of stream ecosystems. Journal of Science Education and Technology, 7(3), 215–234.] for higher-order modeling actions. According to our results, four major modeling actions (analysis, synthesis, testing-interpreting, technical and cognitive support) performed through a plethora of modeling operations define the steps of the modeling process in both cases, while specific qualitative differences can be actually identified. Finally, the students’ conceptualizations of the biological aspect of the modeling task in the two-case activity is analyzed in regard with their capability of shifting reasoning between macro- and micro-levels, while educational implications are also discussed.     

‘Light’ and ‘heavy’ work in the housekeeping service of a hospital

Work is organized based in part on the perceptions, by managers and workers, of workers, their abilities and the characteristics of the work to be done. Physical tasks in factories and services have often been divided into ‘light’ and ‘heavy’, a division that often corresponds formally or informally to gender. We have observed the work of cleaners on wards and in offices in an acute-care hospital, using several indicators of workload to identify and characterize typical work situations. ‘Heavy’ work was characterized by neutral postures, walking, repetitive movements involving the articulations of the upper limb pushing a 1-6 kg (wet or dry) mop, with occasional more intense effort. ‘Light’ work was characterized by flexed postures, walking, rapid repetitive movements involving the articulations of the upper limb and light weights (dusting) or 1-3 kg weights (emptying wastebaskets), with more occasional intense effort. We did not discover any compelling reason to divide cleaning into ‘light’ and ‘heavy’ work. Task assignment by sex may appear to be a solution to excessive job demands which would be better addressed by job re-design.     

‘Best’ for whom?: the tension between ‘best practice’ ERP packages and diverse epistemic cultures in a university context

The idea that so-called ‘best’ business practices can be transferred to organizations when they purchase enterprise resource planning (ERP) software packages is a major selling point of these packages. Yet recent research has illustrated a gap between the espoused theory of a best practice solution and the theory-in-use experienced by those who install software with such a design. As researchers begin to examine the difficult process by which organizations recast the best practices model handed down to them by consultancies and software vendors in an effort to make the software ‘work for them’ in practice, it is equally important that we begin to understand the reasons that such a gap exists. To this end, we analyze the strategic partnership between a multinational software vendor and a university who together designed a ‘best practice’ ERP package for the higher education industry. Through the theoretical lens of ‘epistemic cultures’ we argue that in organizational contexts made up of more than one epistemic culture, the use of a best practice model will be problematic because, by definition, the model mandates one epistemological position through the software design. This is counter to a university's loosely coupled organizational form.     

Geometric characterization, hydraulic behavior and upscaling of 3D fissured geologic media

In this article, we present numerical modeling and upscaling procedures for highly fissured and discontinuous geologic media, such as ‘karsts’. In particular, we propose a geomorphological generation model, and we address the ‘upscaling’ problem for flow in a highly fissured porous medium (‘what is the macroscale hydraulic behavior of the fissured porous medium?’). The morphological model is partly Boolean, based on statistical distributions of discrete objects (voids), combined with a (random) continuum representation for the underlying porous matrix. Various methods for constraining these two types of media are discussed (self-consistent thresholding; genetic dissolution). Hydraulic simulations are then conducted with the 3D finite volume code BIGFLOW, for the case of 3D composite media with constant matrix and high ‘fissure/matrix’ permeability contrast. The hydrodynamic equations are based on either Darcy’s linear head loss law, or on a linear/quadratic combination of Darcy and Ward–Forchheimer quadratic law (inertial effects). The numerical experiments are conducted for saturated steady flow under permeametric boundary conditions. They are used to analyze the equivalent macroscale behavior of fissured media, as well as quasi-percolation effects, in comparison with analytical results and bounds (Darcian case, low Reynolds). In addition, at moderate to large Reynolds numbers, the macroscale effects of non-Darcian (inertial) head losses are also analyzed.     

On the stable exact model matching problem

The stable exact model matching problem (SEMMP) is investigated. We state and prove a number of equivalent necessary and sufficient conditions for the existence of proper solutions to the exact model matching problem that are also Ω-stable, i.e. have no poles inside a symmetric ‘forbidden’ subset Ω of the finite complex plane . These results can be viewed as the counterpart of the results in [3] and [9] for the case of the ring of proper and Ω-stable rational functions.     

An observer-based set-point controller for robot manipulators with flexible joints

We present a globally asymptotically stable controller for point-to-point regulation of robot manipulators with flexible joints that uses only position measurement on the motor side. Existing asymptotically stable schemes for the set point regulation problem without velocity measurement address only the rigid robot case. Furthermore, these solutions ensure only local stability provided some bounds on the dynamic part of the robot model are known. Also, they require the injection of high gains into the loop to enlarge the equilibrium domain of attraction. In contrast, our solution is global, applies for robots with flexible joints and assumes only that the gravity forces are known. The underlying rationale of the design is to ‘shape’ the potential energy of the closed loop system so that it has an absolute minimum at the desired equilibrium, and add the required dampingto achieve asymptotic stability. This is attained by adding a (linear) observer that converges to the position required to compensate the gravity forces and injects the damping, and a ‘spring-like’ effect between the observer and the robot that ‘pulls’ the robot to the desired target. This approach to observer-based controller design differs from the classical certainly equivalent approach and effectively exploits the dynamic properties of the physical system.     

Assessing the ‘insider–outsider threat’ duality in the context of the development of public–private partnerships delivering ‘choice’ in healthcare services: A sociomaterial critique

Containing the ‘outsider’ threat to the information systems of organisations as well as recognising the disruptive potential of ‘insiders’ are fundamentals of security management. However, the recent development of public–private partnerships in the UK requires a reassessment of the continuing utility of such dualities. This paper draws upon a sociological understanding of the complexities of organisational practices as well as a grounded case study of the implementation of the NHS ‘Choose and book’ service across both public and private healthcare organisations in order to challenge these essentialist forms of sociotechnical analysis. The paper proposes a sociomaterial understanding of information systems and organisational dynamics that does not seek to separate out distinct ‘human’ and ‘technical’ information security risks. Rather, it asserts that the organisational outcomes of the introduction of new information systems are necessarily emergent and contingent, and it is with these indeterminate realities that security analysts have to engage.     

A generalization of Tyler’s M-estimators to the case of incomplete data

Many different robust estimation approaches for the covariance or shape matrix of multivariate data have been established. Tyler’s M-estimator has been recognized as the ‘most robust’ M-estimator for the shape matrix of elliptically symmetric distributed data. Tyler’s M-estimators for location and shape are generalized by taking account of incomplete data. It is shown that the shape matrix estimator remains distribution-free under the class of generalized elliptical distributions. Its asymptotic distribution is also derived and a fast algorithm, which works well even for high-dimensional data, is presented. A simulation study with clean and contaminated data covers the complete-data as well as the incomplete-data case, where the missing data are assumed to be MCAR, MAR, and NMAR.     

Automated High Throughput Screening of Fluorescent Imaging Plate Reader (FLIPR) Assays Using Assay Platform™ Integrated with Activity Base for ‘on the fly’ Compound Reconfirmation

Advances in the field of automation have meant hitherto complex manual cell-based assays can now be automated. These improvements have brought significant enhancements in throughput, data fidelity and consistency, and allowed a reallocation of constrained resources.Building upon these improvements, we have linked our automated cell-based screening system, Assay Platform™, to Activity Base (IDBS), a software package designed to automate the analysis of HTS data. Customisation of this package has resulted in software that can identify ‘active’ compounds and re-pick them ‘on the fly’ from the original compound plates for triplicate re-testing without operator intervention.Based on an operator initially defining ‘normal’ parameters for assay activity in Activity Base, combined with an automated quality control software module that checks data fidelity, wells containing ‘active’ compounds can be re-picked and re-tested at the end of an automated screening run. Automating cell-based assays has significantly improved productivity, and, with the synergism of Activity Base, has given us greater power to complete each screening run and report ‘active’ compounds to Chemistry more rapidly. This article presents our approach to the automation of cell-based Fluorescent Imaging Plate Reader (FLIPR) screening together with automated active re-test confirmation using Activity Base.     

Optimal diagonal scaling for infinity-norm optimization

A solution is presented for the previously unsolved diagonally scaled multivariable infinity-norm optimization problem of minimizing D(s)(A(s) + Ψ(s) X(s))D⁻¹(s)_∞ over the set of stable minimum-phase diagonal D(s) and stable X(s). This problem is of central importance in the synthesis of feedback control laws for robust stability and insensitivity in the presence of ‘structured’ plant uncertainty. The result facilitates the design of feedback controllers which optimize the ‘excess stability margin’ [3] (or, equivalently, the ‘structured singular value μ’ [4]) of diagonally perturbed feedback systems.     

The influence of self-esteem and locus of control on perceived email-related stress

Electronic mail has become an indispensable tool in business and academia, and personal use is increasing every day. However, there is also evidence that Email, unlike more traditional communication media, can exert a powerful hold over its users and that many computer users experience stress as a direct result of email-related pressure. This paper develops a three-fold typology of orientations to email: ‘relaxed’, ‘driven’ and ‘stressed’. It further investigates whether the personality traits of self-esteem and locus of control are associated with email-related stress. It finds that low self-esteem is associated with the ‘driven’ orientation. It further suggests that the ‘stressed’ orientation may be related to how distractive email is perceived to be, compared with other forms of communication.     

Singular H∞ Suboptimal Control for a Class of Nonlinear Cascade Systems

In the present paper singular state feedback _∞ suboptimal control for a class of nonlinear cascade systems is addressed. Under the assumption that a regular state feedback _∞ suboptimal control problem is solvable for a particular subsystem of the cascade system, an auxiliary nonlinear system is defined. It is shown that a state feedback solution to the singular _∞ suboptimal control problem for the auxiliary system also applies to the original problem. The advantage of the auxiliary problem to the original problem is that the auxiliary penalty variable has lower dimension than the original penalty variable. It is shown how this fact can simplify the problem considerably for the case when the auxiliary system can be strongly input-output decoupled. The theory is applied to a problem of a rigid spacecraft with actuator dynamics. Application to the special case when a subsystem of the nonlinear cascade system is passive is also considered.     

EPS: An ‘elementary’ programming system for the Delft Parallel Processor

A programming system for synchronous parallel processors, like the DPP-84 working in synchronous mode, is proposed. In EPS a program consists of a collection of well-defined and separate units, described in a conventional procedure-oriented language like PASCAL or MODULA-2. The connection between the ‘elementary’ program units is laid in a supervisory ‘configuration’ program, which defines both the spatial and time relations between the units. The concept of ‘virtual’ parallel processing is introduced, which enables the construction of logical parallel programs, independent of the number of processing elements actually available.     

A sensitivity formula for risk-sensitive cost and the actor–critic algorithm

We propose for risk sensitive control of finite Markov chains a counterpart of the popular ‘actor–critic’ algorithm for classical Markov decision processes. The algorithm is based on a ‘sensitivity formula’ for the risk sensitive cost and is shown to converge with probability one to the desired solution. The proof technique is an adaptation of the ordinary differential equations approach for the analysis of two time-scale stochastic approximation algorithms.     

∞ guaranteed cost control for uncertain continuous-time linear systems

This paper deals with the _∞ guaranteed cost control problems for continuous-time uncertain systems. It consist of the determination of a stabilizing state feedback gain which imposes on all possible closed-loop models an _∞ -norm upper bound γ > 0. Assuming that the uncertain domain is convex-bounded and the uncertain system is quadratic-stabilizable with γ disturbance attenuation, it is shown how to determine, by means of a convex programming problem, the global minimum of γ. As a particular and important case, for precisely known linear systems, the last problem reduces to the classical _∞ optimal control problem. The results follow from the definition of a special parameter space on which the above-mentioned problems are convex.     

Sontag's ‘input to state stability condition’ and global stabilization using state detection

This paper deals with the global stabilization problem for nonlinear system using state detection. Sufficient algebraic conditions for stabilization and detectability concerning particular classes of systems are included. These conditions are based to a version of a Lyapunov-like condition proposed by Sontag, which guarantees ‘input to state stability’.     

An extension of singular value analysis for assessing manipulated variable constraints

A new approach called feasible output radius analysis for linear or linearised models is introduced to address the problem of scaling dependency. This problem arises when assessing the effect of manipulated variable constraints (MVCs) on the closed-loop performance of chemical processes prior to carrying out control designs. The new indicators, and can be used to rank alternative control schemes on the basis that the larger and , the better the closed-loop performance in the presence of control constraints. These indicators are determined from extending the concept of the ‘feasible output amplitude region’ and are independent of the input scaling chosen. Theoretical analysis shows that this method is an extension of the more traditional singular value analysis approach and is more flexible in dealing with various kinds of manipulated variable constraints. A case study, i.e. a two-CSTR process, is investigated using the new method. Via the case study, some superior characteristics of the new technique are demonstrated, such as ease of calculation, and flexibility in coping with different kinds of constraints.     

A New Concept for the On-line Storage of Sample Plates, Integrated with Plate Preparation for High-Throughput Screening and ‘Cherry-Picking’

Recently Organon installed automated screening and plate preparation systems for its research facilities in Oss (The Netherlands) and Newhouse (UK). These robotic systems have been developed in close collaboration between Organon and Scitec Laboratory Automation (Lausanne, Switzerland), now part of the Zymark corporation.Each of the systems consists of three linear track robots, one of which performs the screening process using standard peripherals. The other two robots take care of the plate preparation and ‘cherry-picking’ procedures. To this end, copies of our total mother plate collection are stored under controlled conditions in Scitec plate stackers (AutoStack) that can be addressed by one of the two robots. The system is designed in such a way that the loading and refreshment of the on-line storage, screening-plate preparation, and ‘cherry-picking’ can be executed automatically in 24 hours operation.