The emergence of COVID-19 has recently dominated public discourse given its serious impact on vulnerable patient groups. Advice in relation to reducing risk of contamination has justifiably been circulated widely during the COVID-19 crisis. Contamination fear is a common obsessional theme in patients with obsessive–compulsive disorder (OCD), and there is a need for increased research on how infectious disease epidemics affect patients with OCD. We present the case of a lady in her 30s with a history of well-controlled contamination OCD who presented acutely with a significant exacerbation of OCD symptoms precipitated by media reports of COVID-19. The case highlights the potential psychological impacts of infectious disease epidemics on individuals with mental illness. We also highlight some of the risks posed to such patients in response to epidemics such as the COVID-19 crisis.

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This paper presents the conditions necessary to sustain a limit cycle in hydraulic position control systems with displacement feedback. The limit cycle performance of the system is then examined when the temperature of the working fluid varies between 283K(10°C) to 343K(70°C). Results are presented for an electrohydraulic system driving a load comprising inertia, viscous friction, and coulomb friction.

This article introduces non‐linear dynamics to assess the interactions in duopoly competition between two rivals. The generic competition is considered here to be the competition for quality between two consumer durable products. The authors have used a system dynamics approach to develop the model of interactions and simulate the behaviour over time. The outcomes of several hundred simulations have shown that the recognition and implementation lags in quality improvement strongly influence the qualitative behaviour of the system. When the speed of adaptation to customer demand reaches a certain value, a Hopf bifurcation occurs and the system converges into a limit cycle. Quasi‐periodicity and chaos emerge when further increasing the speed of the response. Instead of tending to equilibrium around an optimal quality value the model exhibits complex counter‐intuitive behaviours. Copyright © 2000 John Wiley & Sons, Ltd.

PurposeTo outline a philosophical system of inquiry that may be used as a frame‐of‐reference for modelling social systems.Design/methodology/approachThe paper draws on insights from cognitive science, autopoiesis, management cybernetics and non‐linear dynamics.FindingsThe outcome of this paper is an outline of a frame‐of‐reference to be used as a starting point (or a frame of orientation) for any problem solving/modelling intent or act. The framework highlights the importance of epistemological reflection and the need to avoid any separation of the process of knowing from that of modelling. It also emphasises the importance of inquiry into the assumptions that underpin the methods, tools and techniques that we employ, and into the tacit beliefs of the human actors who use them.Research limitations/implicationsThe presented frame‐of‐reference should be regarded as an evolving system of inquiry, one that seeks to incorporate contemporary human insight.Practical implicationsExactly, how the frame‐of‐reference presented in this paper should be exploited within an organisational or educational context, is a question to which there is no single “correct” answer. What is primarily important, however, is that it should be used to raise the profile of, and disseminate the benefits that accrue from, inquiry which goes beyond the simple application of tools and methods.Originality/valueThis paper proposes a new framework‐of‐reference for modelling social systems that draws on insights from cognitive science, autopoiesis, management cybernetics and non‐linear dynamics.