Modeling, simulation, and analysis of permanent-magnet motordrives. II. The brushless DC motor drive

For pt.I see ibid., vol.25, no.2, p.265-73 (1989). The authors develop a phase variable model of the BDCM (brushless DC motor) and use it to examine the performance of a BDCM speed servo drive system when fed by hysteresis and pulsewidth-modulated (PWM) current controllers. Particular attention was paid to the motor large-signal and small-signal dynamics and motor torque pulsations. The simulation included the state-space model of the motor and speed controller and real-time model of the inverter switches. Every instance of a power device turning on or off was simulated to calculate the current oscillations and resulting torque pulsations. The results indicate that the small- and large-signal responses are very similar. This result is only true when the timing of the input phase currents with the back EMF (electromotive force) is correct. The large-signal and small-signal speed response is the same whether PWM or hysteresis current controllers are used. This is because, even though the torque pulsations may be different due to the use of different current controllers, the average value which determines the overall speed response is the same     

Enhancement of multimodal biometric segregation using unconstrained cohort normalisation

This paper presents an investigation into the effects, on the accuracy of multimodal biometrics, of introducing unconstrained cohort normalisation (UCN) into the score-level fusion process. Whilst score normalisation has been widely used in voice biometrics, its effectiveness in other biometrics has not been previously investigated. This study aims to explore the potential usefulness of the said score normalisation technique in face biometrics and to investigate its effectiveness for enhancing the accuracy of multimodal biometrics. The experimental investigations involve the two recognition modes of verification and open-set identification, in clean mixed-quality and degraded data conditions. Based on the experimental results, it is demonstrated that the capabilities provided by UCN can significantly improve the accuracy of fused biometrics. The paper presents the motivation for, and the potential advantages of, the proposed approach and details the experimental study.     

Informing strategic IS change: Towards a ‘meta-learning’ framework

This paper combines theoretical models on organisational and Information Systems (ISs) change with the experiential theorising of practitioners from a case study site. Contemporary strands of IS and organisational change literature were reviewed, grouping common themes into planning, leadership, learning and culture approaches. This theoretical basis was extended through a case analysis of an IS organisation in the banking industry which had undergone wide ranging and successful strategic change. Twenty in-depth interviews were conducted with senior experienced change practitioners from across the organisation. Three propositions on IS and organisational change theory were developed from the finding for this research. Firstly, IS change is a subset of organisational change which is frequently noted and argued through existing academic or ‘espoused’ change theories. Secondly, whether successful or unsuccessful, strategic change is in itself a rich learning experience which may be leveraged through experience, intuition and self-reflexion. Thirdly, managers develop their own ‘theories in use’ of change based on experiential learning and apply them in a highly context specific ‘informed’ way. The main contribution of the research is a ‘meta-learning’ framework for informing IS strategic change which suggests valuable theoretical insights, a practitioner implementation process and proposals for further research directions and limitations.     

A Review of the Engineering Properties of Concrete with Paper Mill Waste Ash — Towards Sustainable Rigid Pavement Construction

Silicon - The drastic surge in urbanisation and construction-related activities is increasing the demand for cement and aggregates, especially for concrete production. Concrete is utilised for a...     

Prediction of electromagnetic forces and vibrations in SRMs operating at steady-state and transient speeds

Although some research has been conducted on vibrations in switched reluctance motors (SRMs), the response during transients, which may occur during sudden load changes or braking, has not received much investigation. In this paper, a simulation model to predict the transient vibration of SRMs is developed. The vibration prediction model is built based on the detailed normal force versus phase current and rotor position lookup table using finite-element calculations. The model is then verified by a running motor test, which shows acceptable accuracy. The results reveal that there are abundant harmonics of transient force during transients and, thus, resonance may be excited. This model allows the possibility of improved design of SRMs from a vibration and acoustic noise point of view.     

Modeling, simulation, and analysis of permanent-magnet motordrives. I. The permanent-magnet synchronous motor drive

The application of vector control to the PMSM (permanent-magnet synchronous motor) is described, and complete modeling, simulation, and analysis of the drive system are presented. State-space models of the motor and speed controller and real-time models of the inverter switches and vector controller are included. Performance differences due to the use of pulsewidth-modulation (PWM) and hysteresis current controllers are also examined. Particular attention is paid to the motor torque pulsations and speed response. Some experimental verification of the drive performance is also given     

An insight into power quality disturbances using wavelet multiresolution analysis

The wavelet transform is beginning to be used widely in power engineering. Its effectiveness for analyzing transients with time localized information is now well known. Multiresolution analysis is especially suitable for feature enhancement of transients and thus makes it possible for power disturbances to be classified. In addition, the wavelet transform works well where the Fourier transform fails. A graphical insight is demonstrated in this letter.     

Modifying and managing the surface properties of polymers

An ongoing challenge in polymer science is the preparation of materials with bespoke surface properties which differ from that of the bulk, for example hydrophobicity, wettability, chemical resistance, adhesion or biocompatibility. We highlight here recent efforts in the design, development and application of (multi)end‐functionalized polymers as additives for the efficient modification of polymer surface properties. Aryl‐ether moieties bearing up to eight functional groups have been used as initiators for the controlled polymerization of both styrene and methyl methacrylate by atom transfer radical polymerization (ATRP) and of lactide by ring opening polymerization (ROP). The resulting polymers have been used as additives to modify the surfaces of the corresponding bulk polymers. Fluorinated polymer surfaces are particularly appealing in terms of their liquid repellence, chemical inertness and low coefficient of friction. When an additive consisting of a low molecular weight polystyrene chain, end‐capped with four C₈F₁₇ groups, is present in a matrix of polystyrene at levels as low as 0.1%, near polytetrafluoroethylene‐like surface properties result. Copyright © 2007 Society of Chemical Industry     

Idiopathic CSF rhinorrhoea presenting with tension pneumocephalus and hemiparesis

A case of non-traumatic/non-iatrogenic CSF rhinorrhoea, presenting with tension pneumocephalus and hemiparesis is described. The possible pathological processes involved in this rare case are discussed. Cases in the literature of idiopathic CSF rhinorrhoea and also those of spontaneous pneumocephalus are reviewed.     

Diffuse cystic glandular malformation of the stomach associated with adenocarcinoma: Case report and review of the literature

A 60-year-old man was found to have diffuse cystic glandular malformation and adenocarcinoma of the stomach. Review of the literature revealed one similar reported case and five others with diffuse heterotopic cystic malformation only. Clinically, the lesion is associated with gastrointestinal symptoms, and radiologically, it can mimic diffuse gastric carcinoma, lymphoma, and polyposis.