Using a group support system to aid input-output identification in DEA

In data envelopment analysis (DEA), operating units are compared on their outputs relative to their inputs. The identification of an appropriate input-output set is of decisive significance if assessment of the relative performance of the units is not to be biased. This paper reports on a novel approach used for identifying a suitable input-output set for assessing central administrative services at universities. A computer-supported group support system was used with an advisory board to enable the analysts to extract information pertaining to the boundaries of the unit of assessment and the corresponding input-output variables. The approach provides for a more comprehensive and less inhibited discussion of input-output variables to inform the DEA model. © 2005 Operational Research Society Ltd. All rights reserved.

Emulation of random output simulators

Computer models, or simulators, are widely used in a range of scientific fields to aid understanding of the processes involved and make predictions. Such simulators are often computationally demanding and are thus not amenable to statistical analysis. Emulators provide a statistical approximation, or surrogate, for the simulators accounting for the additional approximation uncertainty. This thesis develops a novel sequential screening method to reduce the set of simulator variables considered during emulation. This screening method is shown to require fewer simulator evaluations than existing approaches. Utilising the lower dimensional active variable set simplifies subsequent emulation analysis. For random output, or stochastic, simulators the output dispersion, and thus variance, is typically a function of the inputs. This work extends the emulator framework to account for such heteroscedasticity by constructing two new heteroscedastic Gaussian process representations and proposes an experimental design technique to optimally learn the model parameters. The design criterion is an extension of Fisher information to heteroscedastic variance models. Replicated observations are efficiently handled in both the design and model inference stages. Through a series of simulation experiments on both synthetic and real world simulators, the emulators inferred on optimal designs with replicated observations are shown to outperform equivalent models inferred on space-filling replicate-free designs in terms of both model parameter uncertainty and predictive variance.

Autonomic dysfunction in unselected and untreated primary open angle glaucoma patients:A pilot study

Purpose: To investigate the presence of silent cardiac ischaemic episodes and the status of autonomic function in consecutive, newly diagnosed and untreated primary open-angle glaucoma patients. Methods: Twenty-four consecutively diagnosed glaucoma patients and 22 age-matched controls were subjected to ambulatory 24-h blood pressure (BP) and electrocardiogram (ECG) monitoring by using Cardiotens-01 (Meditech Ltd). Based on the ECG recordings, heart rate variability (HRV) frequency domain parameters [low-frequency (LF), high-frequency (HF) and LF/HF ratio] were calculated and analysed in the two study groups. Results: Glaucoma patients demonstrated higher LF and LF/HF values than normal subjects for both the active period (p = 0.020 and 0.029) and the passive period (p = 0.044 and 0.049 respectively). HRV parameters were similar in patients and controls suffering from silent cardiac ischaemia (p > 0.05); however, glaucoma patients with normal ECG demonstrated higher LF and LF/HF values during the active period of the 24-h measurement period than control subjects characterized by the same cardiac activity (p = 0.010 and 0.021 respectively). Conclusion: Independent of a history and/or clinical signs of cardiovascular disease, glaucoma patients exhibit abnormal autonomic function. © 2007 The Authors.

Effect of β-adrenoceptor antagonists on autonomic control of ciliary smooth muscle

Purpose: Pharmacological intervention with peripheral sympathetic transmission at ciliary smooth muscle neuro-receptor junctions has been used against a background of controlled parasympathetic activity to investigate the characteristics of autonomic control of ocular accommodation. Methods: A continuously recording infrared optometer was used to measure accommodation on a group of five visually normal emmetropic subjects under open- and closed-loop conditions. A double-blind protocol between saline, timolol and betaxolol was used to differentiate between the localised action on ciliary smooth muscle and effects induced by changes in stimulus conditions. Data were collected before and 45 min following the instillation of saline, timolol or betaxolol. Open-loop post-task decay was investigated following 3 min sustained near fixation of a stimulus placed 3 D above the subject's pre-task tonic accommodation level. Closed-loop dynamic responses were recorded for each treatment condition while subjects viewed sinusoidally (0.05-0.6 Hz) or stepwise vergence-modulated targets over a 2 D range (2-4 D). Results: Open-loop data demonstrate a rapid post-task regression to pre-task tonic accommodation levels for saline and betaxolol control conditions. A slow positive post-task shift was induced by timolol indicating that sympathetic inhibition contributes to accommodative adaptation during sustained near vision. Closed-loop accommodation responses to temporally modulated sinusoidal stimuli showed characteristic features for both saline and betaxolol control conditions. Timolol induced a reduced gain for low- and mid-temporal frequencies (< 0.3 Hz) but did not affect the response at higher temporal frequencies. Response times to stepwise stimuli increased following the instillation of timolol for the near-to-far fixation condition compared with the controls and was related to the period of sustained prior fixation. Conclusions: Modulation of accommodation under open- and closed-loop conditions by a non-selective β-blocker is consistent with the temporal and inhibitory features of sympathetic innervation to ciliary smooth muscle. Although parasympathetic innervation predominates there is evidence to support a role for sympathetic innervation in the control of ocular accommodation. © 2002 The College of Optometrists.

Emulation of dynamic computer models with multivariate output

This preliminary report describes work carried out as part of work package 1.2 of the MUCM research project. The report is split in two parts: the ?rst part (Sections 1 and 2) summarises the state of the art in emulation of computer models, while the second presents some initial work on the emulation of dynamic models. In the ?rst part, we describe the basics of emulation, introduce the notation and put together the key results for the emulation of models with single and multiple outputs, with or without the use of mean function. In the second part, we present preliminary results on the chaotic Lorenz 63 model. We look at emulation of a single time step, and repeated application of the emulator for sequential predic- tion. After some design considerations, the emulator is compared with the exact simulator on a number of runs to assess its performance. Several general issues related to emulating dynamic models are raised and discussed. Current work on the larger Lorenz 96 model (40 variables) is presented in the context of dimension reduction, with results to be provided in a follow-up report. The notation used in this report are summarised in appendix.

Autonomic correlates of ocular accommodation and cardiovascular function

PURPOSE: To evaluate the hypothesis that objective measures of open- and closed-loop ocular accommodation are related to systemic cardiovascular function, and ipso facto autonomic nervous system activity. METHODS: Sixty subjects (29 male; 31 female) varying in age from 18 to 33 years (average: 20.3 +/- 2.9 years) with a range of refractive errors [mean spherical equivalent (MSE): -7.12 to +1.82 D] participated in the study. Five 20-s continuous objective recordings of the accommodative response, measured with an open-view IR autorefractor (Shin-Nippon SRW-5000), were obtained for a variety of open- and closed-loop accommodative demands while simultaneous continuous measurement of heart rate was recorded with a finger-mounted piezo-electric pulse transducer for 5 min. Fast Fourier Transformation of cardiovascular function allowed the absolute and relative power of the autonomic components to be assessed in the frequency-domain, whereas heart period gave an indication of the time-domain response. RESULTS: Increasing closed-loop accommodative demand led to a concurrent increase in heart rate of approximately 2 beats/min for a 4.0 D increase in accommodative demand. The increase was attributable to a reduction in the absolute (p < 0.05) and normalised (p < 0.001) input of the systemic parasympathetic nervous system, and was unaffected by refractive group. The interaction with refractive group failed to reach significance. CONCLUSIONS: For sustained accommodation effort, the data demonstrate covariation between the oculomotor and cardiovascular systems which implies that a near visual task can significantly influence cardiovascular behaviour. Accommodative effort alone, however, is not a sufficient stimulus to induce autonomic differences between refractive groups. The data suggest that both the oculomotor and cardiovascular systems are predominantly attributable to changes in the systemic parasympathetic nervous system.

Pulse tail suppression in laser diode output by tunable notch filter

Efficient suppression of relaxation oscillations in the output signal from an overdriven gain-switched laser diode was demonstrated. Several quantum-well distributed feedback laser diodes from different manufacturers were used for experimental analysis. A five-fold increase in the peak power was achieved for the tail-free operation. It was found that spectral filtering removed the nonlinearly chirped components resulting in pulse shortening by a factor of three.

Reconfigurable service-oriented architecture for autonomic computing

Almost a decade has passed since the objectives and benefits of autonomic computing were stated, yet even the latest system designs and deployments exhibit only limited and isolated elements of autonomic functionality. In previous work, we identified several of the key challenges behind this delay in the adoption of autonomic solutions, and proposed a generic framework for the development of autonomic computing systems that overcomes these challenges. In this article, we describe how existing technologies and standards can be used to realise our autonomic computing framework, and present its implementation as a service-oriented architecture. We show how this implementation employs a combination of automated code generation, model-based and object-oriented development techniques to ensure that the framework can be used to add autonomic capabilities to systems whose characteristics are unknown until runtime. We then use our framework to develop two autonomic solutions for the allocation of server capacity to services of different priorities and variable workloads, thus illustrating its application in the context of a typical data-centre resource management problem.

Using quantitative analysis to implement autonomic IT systems

The software underpinning today’s IT systems needs to adapt dynamically and predictably to rapid changes in system workload, environment and objectives. We describe a software framework that achieves such adaptiveness for IT systems whose components can be modelled as Markov chains. The framework comprises (i) an autonomic architecture that uses Markov-chain quantitative analysis to dynamically adjust the parameters of an IT system in line with its state, environment and objectives; and (ii) a method for developing instances of this architecture for real-world systems. Two case studies are presented that use the framework successfully for the dynamic power management of disk drives, and for the adaptive management of cluster availability within data centres, respectively.

General-purpose autonomic computing

The success of mainstream computing is largely due to the widespread availability of general-purpose architectures and of generic approaches that can be used to solve real-world problems cost-effectively and across a broad range of application domains. In this chapter, we propose that a similar generic framework is used to make the development of autonomic solutions cost effective, and to establish autonomic computing as a major approach to managing the complexity of today’s large-scale systems and systems of systems. To demonstrate the feasibility of general-purpose autonomic computing, we introduce a generic autonomic computing framework comprising a policy-based autonomic architecture and a novel four-step method for the effective development of self-managing systems. A prototype implementation of the reconfigurable policy engine at the core of our architecture is then used to develop autonomic solutions for case studies from several application domains. Looking into the future, we describe a methodology for the engineering of self-managing systems that extends and generalises our autonomic computing framework further.

Resource-definition policies for autonomic computing

The paper introduces a framework for the formal specification of autonomic computing policies, and uses it to define a new type of autonomic computing policy termed a resource-definition policy. We describe the semantics of resource-definition policies, explain how they can be used as a basis for the development of autonomic system of systems, and present a sample data-centre application built using the new policy type.

Implementation of a generic autonomic framework

Based on insights from the implementation of commercial products for data-centre resource management, we identified key challenges in the development of cost-effective autonomic solutions, and best practices for overcoming these challenges. In a related paper, we proposed a generic autonomic framework that complies with these best practices, and suggested ways in which existing technologies could be used to realise this framework. In this paper, we describe the actual implementation of our autonomic framework as a service-oriented architecture, and we show how the universal policy engine at its core can be configured to manage the allocation of server capacity to services of different priorities. This case study demonstrates the effectiveness of our generic approach to autonomic solution development in an area of great interest for commercial data centres, research laboratories and application service providers.

Towards a generic autonomic architecture for legacy resource management

Half a decade has passed since the objectives and benefits of autonomic computing were stated, yet even the latest system designs and deployments exhibit only limited and isolated elements of autonomic functionality. From an autonomic computing standpoint, all computing systems – old, new or under development – are legacy systems, and will continue to be so for some time to come. In this paper, we propose a generic architecture for developing fully-fledged autonomic systems out of legacy, non-autonomic components, and we investigate how existing technologies can be used to implement this architecture.

Run-time connector synthesis for autonomic systems of systems

A key objective of autonomic computing is to reduce the cost and expertise required for the management of complex IT systems. As a growing number of these systems are implemented as hierarchies or federations of lower-level systems, techniques that support the development of autonomic systems of systems are required. This article introduces one such technique, which involves the run-time synthesis of autonomic system connectors. These connectors are specified by means of a new type of autonomic computing policy termed a resource definition policy, and enable the dynamic realisation of collections of collaborating autonomic systems, as envisaged by the original vision of autonomic computing. We propose a framework for the formal specification of autonomic computing policies, and use it to define the new policy type and to describe its application to the development of autonomic system of systems. To validate the approach, we present a sample data-centre application that was built using connectors synthesised from resource-definition policies.