• Visualisation and analysis of interfacial instability in the co-extrusion of a LDPE melt

      Martyn, Michael T.; Coates, Philip D.; Spares, Robert; Zatloukal, M. (2004)
    • Visuomotor control of step descent: evidence of specialised role of the lower visual field

      Timmis, Matthew A.; Bennett, S.J.; Buckley, John G. (2009-05)
      We often complete step downs in the absence of visual feedback of the lower-limbs, and/or of the area on the ground where we intend to land (e.g. when descending a step whilst carrying a laundry basket). Therefore, the present study examined whether information from lower visual field (lvf) provides any advantage to the control of step descent. Ten healthy subjects (age 24.4 ± 9.4 years) completed repeated step downs over three-step heights with visual information available from either full or upper visual fields (lvf occluded), and for specific intervals relative to step initiation. Visuomotor control of step descent was assessed by determining pre-landing kinematic measures and landing mechanic variables for the initial landing period. Findings indicate that whilst there were only limited effects on pre-landing kinematic measures under lvf occlusion, individual’s ability to plan/control landing mechanics was significantly different in such conditions compared to when they had access to full field vision. These changes were consistent with participants being uncertain regarding precise floor height when access to lvf was restricted, and consequently led them to adapt their landing behaviour but without fundamentally altering their stepping strategy. Compared to when vision was available throughout, the occlusion of vision (full or upper visual field) from toe-off or mid-swing onwards caused very few differences in landing behaviour. This suggests that the contribution of information from lvf to the control of landing behaviour occurs predominantly prior to or during movement initiation and that ‘online’ vision is used only in the latter portion of the descent phase to subtly ‘fine tune’ landings.
    • Voltage Unbalance Mitigation in Low Voltage Distribution Networks using Time Series Three-Phase Optimal Power Flow

      Al-Ja'afreh, M.A.A.; Mokryani, Geev (IEEE, 2021)
      Due to high penetration of single-phase Photovoltaic (PV) cells into low voltage (LV) distribution networks, several impacts such as voltage unbalance, voltage rise, power losses, reverse power flow arise which leads to operational constraints violation in the network. In this paper, a time series Three Phase Optimal Power Flow (TPOPF) method is proposed to minimize the voltage unbalance in LV distribution networks with high penetration of residential PVs. TPOPF problem is formulated using the current injection method in which the PVs are modelled via a time-varying PV power profile with active and reactive power control. The proposed method is validated on a real LV distribution feeder. The results show that the reactive power management of the PVs helps mitigate the voltage unbalance significantly. Moreover, the voltage unbalance index reduced significantly compared to the case without voltage unbalance minimisation.
    • Vortices in Josephson arrays interacting with non-classical microwaves: The effect of dissipation.

      Konstadopoulou, Anastasia; Hollingworth, J.M.; Everitt, M.; Vourdas, Apostolos; Clark, T.D.; Ralph, J.F. (2003)
      Vortices circulating in a ring made from a Josephson array in the insulating phase are studied. The ring contains a `dual Josephson junction' through which the vortices tunnel. External non-classical microwaves are coupled to the device. The time evolution of this two-mode fully quantum mechanical system is studied, taking into account the dissipation in the system. The effect of the quantum statistics of the photons on the quantum statistics of the vortices is discussed. Entropic calculations quantify the entanglement between the two systems. Quantum phenomena in the system are also studied through Wigner functions. After a certain time (which depends on the dissipation parameters) these quantum phenomena are destroyed due to dissipation.
    • VPAStab: stabilised vector-Padé approximation with application to linear systems.

      Graves-Morris, Peter R. (2003)
      An algorithm called VPAStab is given for the acceleration of convergence of a sequence of vectors. It combines a method of vector-Padé approximation with a successful technique for stabilisation. More generally, this algorithm is designed to find the fixed point of the generating function of the given sequence of vectors, analogously to the way in which ordinary Padé approximants can accelerate the convergence of a given scalar sequence. VPAStab is justified in the context of its application to the solution of a large sparse system of linear equations. The possible breakdowns of the algorithm are listed. Numerical experiments indicate that these breakdowns can be classified either as pivot-type (type L) or as ghost-type (type D).
    • Walking speed related joint kinetic alterations in trans-tibial amputees: impact of hydraulic 'ankle' damping

      De Asha, Alan R.; Munjal, R.; Kulkarni, J.; Buckley, John G. (2013)
      Passive prosthetic devices are set up to provide optimal function at customary walking speed and thus may function less effectively at other speeds. This partly explains why joint kinetic adaptations become more apparent in lower-limb amputees when walking at speeds other than customary. The present study determined whether a trans-tibial prosthesis incorporating a dynamic-response foot that was attached to the shank via an articulating hydraulic device (hyA-F) lessened speed-related adaptations in joint kinetics compared to when the foot was attached via a rigid, non-articulating attachment (rigF). Eight active unilateral trans-tibial amputees completed walking trials at their customary walking speed, and at speeds they deemed to be slow-comfortable and fast-comfortable whilst using each type of foot attachment. Moments and powers at the distal end of the prosthetic shank and at the intact joints of both limbs were compared between attachment conditions. There was no change in the amount of intact-limb ankle work across speed or attachment conditions. As speed level increased there was an increase on both limbs in the amount of hip and knee joint work done, and increases on the prosthetic side were greater when using the hyA-F. However, because all walking speed levels were higher when using the hyA-F, the intact-limb ankle and combined joints work per meter travelled were significantly lower; particularly so at the customary speed level. This was the case despite the hyA-F dissipating more energy during stance. In addition, the amount of eccentric work done per meter travelled became increased at the residual knee when using the hyA-F, with increases again greatest at customary speed. Findings indicate that a trans-tibial prosthesis incorporating a dynamic-response foot reduced speed-related changes in compensatory intact-limb joint kinetics when the foot was attached via an articulating hydraulic device compared to rigid attachment. As differences between attachment conditions were greatest at customary speed, findings indicate a hydraulic ankle-foot device is most effectual at the speed it is set-up for.
    • Wastewater Treatment by Spiral Wound Reverse Osmosis: Development and Validation of a Two Dimensional Process Model

      Al-Obaidi, M.A.; Kara-Zaitri, Chakib; Mujtaba, Iqbal M. (2017-01)
      Reverse osmosis (RO) has become a significant method for removing salts and organic compounds from seawater and wastewater in recent decades. Spiral-wound module has been widely used due to a number of special features such as high packing density, premium separation and low operating cost. In this paper, a two-dimensional mathematical model is developed for the transport of dilute aqueous solutions through a spiral-wound RO module and the operational characteristics of the process under steady state conditions are analysed. The model is based on the solution-diffusion model coupled with the concentration polarization mechanism. This model yields a set of Differential and Algebraic Equations (DAEs), which are solved using the gPROMS software. The model is validated using experimental data from the literature for the rejection of dimethylphenol as solute in aqueous solutions. The model is then used to simulate the process under steady state conditions to gain deeper insight of the process.
    • Water assisted injection moulding: development of insights and predictive capabilities through experiments on instrumented process in parallel with computer simulations.

      Polynkin, A.; Bai, L.; Pittman, J.F.T.; Sienz, J.; Mulvaney-Johnson, Leigh; Brown, Elaine C.; Dawson, A.; Coates, Philip D.; Brookshaw, B.; Vinning, K.; et al. (Maney Publishing, 2008)
      An idealised model of core-out in water assisted injection moulding (WAIM) is set up to isolate the effect of cooling by the water on the deposited layer thickness. Based on simulations, this is investigated for a specific case as a function of Pearson number and power law index. It is found that cooling significantly reduces the layer thickness to the extent that a change in the flow regime ahead of the bubble, from bypass to recirculating flow, is possible. For shear thinning melts with high temperature coefficient of viscosity, the simulations show very low layer thickness, which may indicate unfavourable conditions for WAIM. Although in the real moulding situation, other effects will be superimposed on those found here, the results provide new insights into the fundamentals of WAIM. Investigation of other effects characterised by Fourier and Reynolds numbers will be reported subsequently. Some early process measurement results from an experimental WAIM mould are presented. Reductions in residual wall thickness are observed as the water injection set pressure is increased and the duration of water bubble penetration through the melt is determined experimentally. The formation of voids within the residual wall is noted and observed to reduce in severity with increasing water injection pressure. The presence of such voids can be detected by the signature from an infrared temperatures sensor.
    • Wave-induced seabed residual response and liquefaction around a mono-pile foundation with various embedded depth

      Sui, T.; Zhang, C.; Jeng, D-S.; Guo, Yakun; Zheng, J.; Zhang, W.; Shi, J. (Elsevier, 2019-01)
      Wave-induced seabed instability caused by the residual liquefaction of seabed may threaten the safety of an offshore foundation. Most previous studies have focused on the structure that sits on the seabed surface (e.g., breakwater and pipeline), a few studies investigate the structure embedded into the seabed (e.g. a mono-pile). In this study, by considering the inertial terms of pore fluid and soil skeleton, a three-dimensional (3D) integrated model for the wave-induced seabed residual response around a mono-pile is developed. The model is validated with five experimental tests available in the literature. The proposed model is then applied to investigate the spatial and temporal pattern of pore pressure accumulation as well as the 3D liquefaction zone around a mono-pile. The numerical simulation shows that the residual pore pressure in front of a pile is larger than that at the rear, and the seabed residual response would be underestimated if the inertial terms of pore fluid and soil skeleton are neglected. The result also shows that the maximum residual liquefaction depth will increase with the increase of the embedded depth of the pile.
    • Wavelet based MIMO-multicarrier system using forward error correction and beam forming

      Asif, Rameez; Ali, N.T.; Migdadi, Hassan S.O.; Abd-Alhameed, Raed A.; Hussaini, Abubakar S.; Ghazaany, Tahereh S.; Naveed, S.; Noras, James M.; Excell, Peter S.; Rodriguez, Jonathan (2013)
      Wavelet based multicarrier systems have attracted the attention of the researchers over the past few years to replace the conventional OFDM systems in the next generation communication systems. In this paper we have investigated the performance of such wavelet based systems using forward error correction with covolutional coding and interleaving in a Wavelet-SISO system and then in a Wavelet multicarrier modulation (WMCM) multiple input multiple output (MIMO) system using Convolutional coding and beamforming to reduce the source bit rate and overall system error and increase the data rate. Results show outstanding Bit Error Rate vs. Signal to Noise Ratio Performance. Other than better performance the proposed systems keep the computational burden off the receiver that has more cost and power constraints.
    • Wavelet Packet Transform Modulation for Multiple Input Multiple Output Applications

      Jones, Steven M.R.; Noras, James M.; Abd-Alhameed, Raed A.; Anoh, Kelvin O.O. (2013)
      An investigation into the wavelet packet transform (WPT) modulation scheme for Multiple Input Multiple Output (MIMO) band-limited systems is presented. The implementation involves using the WPT as the base multiplexing technology at baseband, instead of the traditional Fast Fourier Transform (FFT) common in Orthogonal Frequency Division Multiplexing (OFDM) systems. An investigation for a WPT-MIMO multicarrier system, using the Alamouti diversity technique, is presented. Results are consistent with those in the original Alamouti work. The scheme is then implemented for WPT-MIMO and FFTMIMO cases with extended receiver diversity, namely 2 ×Nr MIMO systems, where Nr is the number of receiver elements. It is found that the diversity gain decreases with increasing receiver diversity and that WPT-MIMO systems can be more advantageous than FFT-based MIMO-OFDM systems.
    • Weakest Bus Identification Based on Modal Analysis and Singular Value Decomposition Techniques.

      Jalboub, Mohamed K.; Rajamani, Haile S.; Abd-Alhameed, Raed A.; Ihbal, Abdel-Baset M.I. (02/12/2010)
      Voltage instability problems in power system is an important issue that should be taken into consideration during the planning and operation stages of modern power system networks. The system operators always need to know when and where the voltage stability problem can occur in order to apply suitable action to avoid unexpected results. In this paper, a study has been conducted to identify the weakest bus in the power system based on multi-variable control, modal analysis, and Singular Value Decomposition (SVD) techniques for both static and dynamic voltage stability analysis. A typical IEEE 3-machine, 9-bus test power system is used to validate these techniques, for which the test results are presented and discussed.
    • What you see is what you step: the horizontal-vertical illusion increases toe clearance in older adults during stair ascent.

      Foster, Richard J.; Whitaker, David J.; Scally, Andy J.; Buckley, John G.; Elliott, David B. (2015-05)
      Purpose.: Falls on stairs are a significant cause of morbidity and mortality in elderly people. A simple safety strategy to avoid tripping on stairs is increasing foot clearance. We determined whether a horizontal–vertical illusion superimposed onto stairs to create an illusory perceived increase in stair-riser height would increase stair ascent foot clearance in older participants. Methods.: Preliminary experiments determined the optimum parameters for the horizontal–vertical illusion. Fourteen older adults (mean age ± 1 SD, 68.5 ± 7.4 years) ascended a three-step staircase with the optimized version of the horizontal–vertical illusion (spatial frequency: 12 cycles per stair riser) positioned either on the bottom or top stair only, or on the bottom and top stair simultaneously. These were compared to a control condition, which had a plain stair riser with edge highlighters positioned flush with each stair-tread edge. Foot clearance and measures of postural stability were compared across conditions. Results.: The optimized illusion on the bottom and top stair led to a significant increase in foot clearance over the respective stair edge, compared to the control condition. There were no significant decreases in postural stability. Conclusions.: An optimized horizontal–vertical visual illusion led to significant increases in foot clearance in older adults when ascending a staircase, but the effects did not destabilize their postural stability. Inclusion of the horizontal–vertical illusion on raised surfaces (e.g., curbs) or the bottom and top stairs of staircases could improve stair ascent safety in older adults.
    • Wheel movement during braking

      Klaps, J.; Day, Andrew J. (2002)
      An experimental study of wheel movement arising from compliance in the front suspension and steering system of a passenger car during braking is presented. Using a Kinematic and Compliance (K&C) test rig, movement of the front wheels and the suspension sub-frame, together with corresponding changes in suspension / steering geometry under simulated braking conditions, were measured and compared with dynamic measurements of the centre points of the front wheels. The resulting knowledge of front wheel deflections has enabled the causes and effects of steering drift during braking to be better understood in the design of front suspension systems for vehicle stability.
    • Which prosthetic foot to prescribe? Biomechanical differences found during a single session comparison of different foot types hold true one year later

      De Asha, Alan R.; Barnett, C.T.; Struchkov, Vasily; Buckley, John G. (2017)
      Introduction: Clinicians typically use findings from cohort studies to objectively inform judgements regarding the potential (dis)advantages of prescribing a new prosthetic device. However, before finalising prescription a clinician will typically ask a patient to ‘try out’ a change of prosthetic device while the patient is at the clinic. Observed differences in gait when using the new device should be the result of the device’s mechanical function, but could also conceivably be due to patient related factors which can change from day-to-day and can thus make device comparisons unreliable. To determine whether a device’s mechanical function consistently has a more meaningful impact on gait than patient-related factors, the present study undertook quantitative gait analyses of a trans-tibial amputee walking using two different foot-ankle devices on two occasions over a year apart. If the observed differences present between devices, established using quantitative gait analysis, were in the same direction and of similar magnitude on each of the two occasions, this would indicate that device-related factors were more important than patient-related factors. Methods: One adult male with a unilateral trans-tibial amputation completed repeated walking trials using two different prosthetic foot devices on two separate occasions, 14 months apart. Walking speed and sagittal plane joint kinematics and kinetics for both limbs were assessed on each occasion. Clinically meaningful differences in these biomechanical outcome variables were defined as those with an effect size difference (d) between prosthetic conditions of at least 0.4 (i.e. ‘medium’ effect size). Results: Eight variables namely, walking speed, prosthetic ‘ankle’ peak plantar- and dorsi- flexion and peak positive power, and residual knee loading response flexion, peak stance-phase extension and flexion moments and peak negative power, displayed clinically meaningful differences (d > 0.4) between foot devices during the first session. All eight of these showed similar effect size differences during the second session despite the participant being heavier and older. Conclusions: Findings suggest that a prosthetic device’s mechanical function consistently has a more meaningful impact on gait than patient-related factors. These findings support the current clinical practice of making decisions regarding prosthetic prescription for an individual, based on a single session evaluation of their gait using two different devices. However, to confirm this conclusion, a case series using the same approach as the present study could be undertaken.
    • Whole life cost performance of domestic rainwater harvesting systems in the United Kingdom

      Roebuck, R.M.; Oltean-Dumbrava, Crina; Tait, Simon J. (2011)
      Rainwater harvesting (RWH) can be used to reduce the demand for potable mains water. At the single-building scale, previous research has focused on water-saving potential, while financial assessment has either been omitted or considered in an ad hoc manner. This paper reports on the application of a more rigorous financial analysis of domestic RWH systems than had been conducted previously. Whole life costing was selected as the most appropriate financial assessment technique. A total of 3840 domestic system configurations were assessed at a daily time step, taking into account various stakeholder perspectives and future cost scenarios. In each case, it was found that harvesting rainwater was significantly less cost effective than relying solely on mains-only water. The domestic RWH systems generally resulted in financial losses approximately equal to their capital costs. Without significant financial support, domestic RWH is unlikely to be cost effective for all reasonably foreseeable scenarios.
    • Why Do Users Accept Innovative Technologies? A Critical Review of Models and Theories of Technology Acceptance in The Information System Literature

      Alkhwaldi, A.F.A.; Kamala, Mumtaz A. (2017-08)
      Earlier literature illustrates that the selection of the appropriate theoretical model has always prescribed as a crucial task for the research community in the information systems (IS) field. According to the authors' knowledge, there are few articles aims to review IT acceptance theories and models at the individuals' level. Thus, this paper aims to bridge this gap by presenting a critical review of ten of the most influential models/theories that have been employed in predicting and explaining the human acceptance behavior of different technologies at the individuals' level. This paper also provides a summary of their evolution, pointed out the main constructs, strengths, related fields, and criticisms based on a selected published literature appeared in IS research. This review offers a holistic view for future scholars to select appropriate constructs/models owing to their strengths and criticisms as well explanatory or predictive power. This paper concluded that the well-established and comprehensive theoretical model should consider the parsimony in the term of simplifying the model with the least constructs and the highest predictive power, also the ability to integrate the relevant context's factors (e.g., UTAUT2).
    • Wideband G-Shaped Slotted Printed Monopole Antenna for WLAN and WiMAX Applications

      Abd-Alhameed, Raed A.; Abidin, Z.Z. (2014-09)
      A novel wideband printed monopole antenna is proposed covering frequency spectrum of wireless local area network (WLAN) and the Worldwide Interoperability for Microwave Access (WiMAX). The total antenna size is 30 × 48 × 1.6 mm³ in which it consists of a G-shaped slotted printed antenna and a defected ground plane. Theoretical and experimental characteristics are presented and compared. The antenna yields an achieved impedance bandwidth of 95.1% between 2.374 GHz and 6.682 GHz at a reflection coefficient |S11| ≤ -10 dB.The results including S-parameters, surface current distribution, VSWR, radiation patterns and antenna gains; in addition to a reasonable and stable radiation pattern and power gain.