• An approach to construct higher order time discretisation schemes for time fractional partial differential equations with nonsmooth data

      Ford, Neville J.; Yan, Yubin; University of Chester (De Gruyter, 2017-10-31)
      In this paper, we shall review an approach by which we can seek higher order time discretisation schemes for solving time fractional partial differential equations with nonsmooth data. The low regularity of the solutions of time fractional partial differential equations implies standard time discretisation schemes only yield first order accuracy. To obtain higher order time discretisation schemes when the solutions of time fractional partial differential equations have low regularities, one may correct the starting steps of the standard time discretisation schemes to capture the singularities of the solutions. We will consider these corrections of some higher order time discretisation schemes obtained by using Lubich's fractional multistep methods, L1 scheme and its modification, discontinuous Galerkin methods, etc. Numerical examples are given to show that the theoretical results are consistent with the numerical results.
    • Assessment of Multi-Domain Energy Systems Modelling Methods

      Stewart, M.; Counsell, John M.; Al-Khaykan, A.; University of Chester (World Academy of Science, Engineering and Technology, 2017-06-06)
      Emissions are a consequence of electricity generation. A major option for low carbon generation, local energy systems featuring Combined Heat and Power with solar PV (CHPV) has significant potential to increase energy performance, increase resilience, and offer greater control of local energy prices while complementing the UK’s emissions standards and targets. Recent advances in dynamic modelling and simulation of buildings and clusters of buildings using the IDEAS framework have successfully validated a novel multi-vector (simultaneous) control of both heat and electricity approach to integrating the wide range of primary and secondary plant typical of local energy systems designs including CHP, solar PV, gas boilers, absorption chillers and thermal energy storage, and associated electrical and hot water networks, all operating under a single unified control strategy. Results from this work indicate through simulation that integrated control of thermal storage can have a pivotal role in optimizing system performance well beyond the present expectations. Environmental impact analysis and reporting of all energy systems including CHPV LES presently employ a static annual average carbon emissions intensity for grid supplied electricity. This paper focuses on establishing and validating CHPV environmental performance against conventional emissions values and assessment benchmarks to analyze emissions performance without and with an active thermal store in a notional group of non-domestic buildings. Results of this analysis are presented and discussed in context of performance validation and quantifying the reduced environmental impact of CHPV systems with active energy storage in comparison with conventional LES designs.
    • Assisting Serious Games Level Design with an Augmented Reality Application and Workflow

      Beever, Lee; John, Nigel W.; Pop, Serban R.; University of Chester (Eurographics Proceedings, 2019-09-13)
      With the rise in popularity of serious games there is an increasing demand for virtual environments based on real-world locations. Emergency evacuation or fire safety training are prime examples of serious games that would benefit from accurate location depiction together with any application involving personal space. However, creating digital indoor models of real-world spaces is a difficult task and the results obtained by applying current techniques are often not suitable for use in real-time virtual environments. To address this problem, we have developed an application called LevelEd AR that makes indoor modelling accessible by utilizing consumer grade technology in the form of Apple’s ARKit and a smartphone. We compared our system to that of a tape measure and a system based on an infra-red depth sensor and application. We evaluated the accuracy and efficiency of each system over four different measuring tasks of increasing complexity. Our results suggest that our application is more accurate than the depth sensor system and as accurate and more time efficient as the tape measure over several tasks. Participants also showed a preference to our LevelEd AR application over the depth sensor system regarding usability. Finally, we carried out a preliminary case study that demonstrates how LevelEd AR can be successfully used as part of current industry workflows for serious games level design.
    • Associating Colours with Emotions Detected in Social Media Tweets

      Harvey, Robert; Muncey, Andrew; Vaughan, Neil; University of Chester (The Society for the Study of Artificial Intelligence and Simulation for Behaviour (AISB), 2018-04-06)
      This project involves two major areas of work, the detection of emotions in text from Twitter posts (tweets), and the association of that emotion with colour. Emotion mining is the field of natural language processing which is concerned with the detection and classification. It is a subfield of semantic analysis which contains both emotion and opinion mining. Both tasks depend on an emotion model to classify detected emotions and to associate a colour depending on the location of the emotion in the model. This research paper demonstrates preliminary results from classification of tweets to assign emotion labels. Also designs are presented for a prototype web interface for displaying the assigned colour and emotion associated with tweets.
    • Atomic and vibrational origins of mechanical toughness in bioactive cement during setting

      Tian, Kun V.; Yang, Bin; Yue, Yuan-Zheng; Bowron, Daniel T.; Mayers, Jerry; Donnan, Robert S.; Dobo-Nagy, Csaba; Nicholson, John W.; Greer, A. Lindsay; Chass, Gregory A.; et al. (Nature Publishing Group, 2015-11-09)
      Bioactive glass ionomer cements (GICs) have been in widespread use for ~40 years in dentistry and medicine. However, these composites fall short of the toughness needed for permanent implants. Significant impediment to improvement has been the requisite use of conventional destructive mechanical testing, which is necessarily retrospective. Here we show quantitatively, through the novel use of calorimetry, terahertz (THz) spectroscopy and neutron scattering, how GIC’s developing fracture toughness during setting is related to interfacial THz dynamics, changing atomic cohesion and fluctuating interfacial configurations. Contrary to convention, we find setting is non-monotonic, characterized by abrupt features not previously detected, including a glass–polymer coupling point, an early setting point, where decreasing toughness unexpectedly recovers, followed by stress-induced weakening of interfaces. Subsequently, toughness declines asymptotically to long-term fracture test values. We expect the insight afforded by these in situ non-destructive techniques will assist in raising understanding of the setting mechanisms and associated dynamics of cementitious materials.
    • Atomic-layer-deposited aluminum and zirconium oxides for surface passivation of TiO 2 in High-Efficiency Organic Photovoltaics

      Vasilopoulou, Maria; Georgiadou, Dimitra G.; Soultati, Anastasia; Boukos, Nikos; Gardelis, Spyros; Palilis, Leonidas C.; Fakis, Mihalis; Skoulatakis, Georgios; Kennou, Stella; Botzakaki, Martha A.; et al. (Wiley, 2014-06-23)
      The reduction in electronic recombination losses by the passivation of surfaces is a key factor enabling high-efficiency solar cells. Here we investigate a strategy to passivate surface trap states of TiO 2 films used as cathode interlayers in organic photovoltaics (OPVs) through applying alumina (Al2O3) or zirconia (ZrO2) insulating nanolayers by thermal atomic layer deposition (ALD). Our results suggest that the surface traps in TiO 2 are oxygen vacancies, which cause undesirable recombination and high electron extraction barrier, reducing the open-circuit voltage and the short-circuit current of the complete OPV device. It was found that the ALD metal oxides enable excellent passivation of the TiO2 surface followed by a downward shift of the conduction band minimum. OPV devices based on different photoactive layers and using the passivated TiO2 electron extraction layers exhibited a significant enhancement of more than 30% in their power conversion efficiencies (PCEs) as compared to their reference devices without the insulating metal oxide nanolayers as a result of significant suppression of charge recombination and enhanced electron extraction rates at the TiO2/ALD metal-oxide/organic interface.
    • An Augmented Reality Tool to aid Radiotherapy Set Up implemented on a Tablet Device

      Cosentino, Francesco; Vaarkamp, Japp; John, Nigel W.; University of Chester, North Wales Cancer Treatment Centre (International Conference on the use of Computers in Radiation Therapy, 2016-06)
      The accurate daily set up of patients for radiotherapy treatment remains a challenge for which the development of new strategies and solutions continues to be an area of active research. We have developed an augmented reality tool to view the real world scene, i.e. the patient on a treatment couch, combined with computer graphics content, such as planning image data and any defined outlines of organ structures. We have built this on widely available hand held consumer tablet devices and describe here the implementation and initial experience. We suggest that, in contrast to other augmented reality tools explored for radiotherapy[1], due to the wide availability and low cost of the hardware platform the application has further potential as a tool for patients to visualize their treatment and demonstrate to patients e.g. the importance of compliance with instructions around bladder filling and rectal suppositories.
    • Avoiding ambient air and light induced degradation in high-efficiency polymer solar cells by the use of hydrogen-doped zinc oxide as electron extraction material

      Polydorou, Ermioni; Sakelis, Elias; Soultati, Anastasia; Kaltzoglou, Andreas; Papadopoulos, Theodoros A.; Briscoe, Joe; Tsikritzis, Dimitris; Fakis, Mihalis; Palilis, Leonidas C.; Kennou, Stella; et al. (Elsevier, 2017-02-24)
      Polymer solar cells have undergone rapid development in recent years. Their limited stability to environmental influence and during illumination, however, still remains a major stumbling block to the commercial application of this technology. Several attempts have been made to address the instability issue, mostly concentrated on the insertion of charge transport interlayers in the device stack. Although zinc oxide (ZnO) is one of the most common electron transport materials in those cells, the presence of defects at the surface and grain boundaries significantly affects the efficiency and stability of the working devices. To address these issues, we herein employ hydrogen-doping of ZnO electron extraction material. It is found that devices based on photoactive layers composed of blends of poly(3-hexylthiophene) (P3HT) with electron acceptors possessing different energy levels, such as [6,6]-phenyl-C70butyric acid methyl ester (PC70BM) or indene-C60 bisadduct (IC60BA) essentially enhanced their photovoltaic performance when using the hydrogen-doped ZnO with maximum power conversion efficiency (PCE) reaching values of 4.62% and 6.65%, respectively, which are much higher than those of the cells with the pristine ZnO (3.08% and 4.51%). Most significantly, the degradation of non-encapsulated solar cells when exposed to ambient or under prolonged illumination is studied and it is found that devices based on un-doped ZnO showed poor environmental stability and significant photo-degradation while those using hydrogen-doped ZnO interlayers exhibited high long-term ambient stability and maintained nearly 80–90% of their initial PCE values after 40 h of 1.5 AM illumination. All mechanisms responsible for this enhanced stability are elucidated and corresponding models are proposed. This work successfully addresses and tackles the instability problem of polymer solar cells and the key findings pave the way for the upscaling of these and, perhaps, of related devices such as perovskite solar cells.
    • Bacillus Spores and Their Relevant Chemicals Studied by Terahertz Time Domain Spectroscopy

      Tang, Jianhua; Yang, Bin; Llewellyn, Ian; Cutler, Ronald R.; Donnan, Robert S.; Queen Mary University of London; University of Bolton (Elsevier, 2013-12-28)
      Terahertz Time Domain Spectroscopy has been used to investigate 0.2 to 2.2 terahertz (THz) transmission responses of Bacillus spores and their related chemical components. Whilst no THz signatures could be clearly associated with either sporulated cells or their chief chemical components, differing degrees of signal attenuation and frequency-dependent light scattering were observed depending on spore composition and culture media. The observed monotonic increase in absorption by spores over this THz spectral domain is mainly from Mie scattering and also from remnant water bound to the spores.
    • A barrier and techno-economic analysis of small-scale bCHP (biomass combined heat and power) schemes in the UK.

      Wright, Daniel G.; Dey, Prasanta K.; Brammer, John G.; Aston University (Elsevier, 2014-05-17)
      bCHP (Biomass combined heat and power) systems are highly efficient at smaller-scales when a significant proportion of the heat produced can be effectively utilised for hot water, space heating or industrial heating purposes. However, there are many barriers to project development and this has greatly inhibited deployment in the UK. Project viability is highly subjective to changes in policy, regulation, the finance market and the low cost fossil fuel incumbent. The paper reviews the barriers to small-scale bCHP project development in the UK along with a case study of a failed 1.5 MWel bCHP scheme. The paper offers possible explanations for the project’s failure and suggests adaptations to improve the project resilience. Analysis of the project’s: capital structuring; contract length and bankability; feedstock type and price uncertainty, and; plant oversizing highlight the negative impact of the existing project barriers on project development. The research paper concludes with a discussion on the effects of these barriers on the case study project and this industry more generally. A greater understanding of the techno-economic effects of some barriers for small-scale bCHP schemes is demonstrated within this paper, along with some methods for improving the attractiveness and resilience of projects of this kind.
    • Benchmarking of a micro gas turbine model integrated with post-combustion CO2 capture

      Usman, Ali; Font Palma, Carolina; Nikpey Somehsaraei, Homam; Mansouri Majoumerd, Mohammad; Akram, Muhammad; Finney, Karen N.; Best, Thom; Mohd Said, Nassya B.; Assadi, Mohsen; Pourkashanian, Mohamed; et al. (Elsevier, 2017-03-19)
      The deployment of post-combustion CO2 capture on large-scale gas-fired power plants is currently progressing, hence the integration of the power and capture plants requires a good understanding of operational requirements and limitations to support this effort. This article aims to assist research in this area, by studying a micro gas turbine (MGT) integrated with an amine-based post-combustion CO2 capture unit. Both processes were simulated using two different software tools –IPSEpro and Aspen Hysys, and validated against experimental tests. The two MGT models were benchmarked at the nominal condition, and then extended to part-loads (50 and 80 kWe), prior to their integration with the capture plant at flue gas CO2 concentrations between 5 and 10 mol%. Further, the performance of the MGT and capture plant when gas turbine exhaust gases were recirculated was assessed. Exhaust gas recirculation increases the CO2 concentration, and reduces the exhaust gas flowrate and specific reboiler duty. The benchmarking of the two models revealed that the IPSEpro model can be easily adapted to new MGT cycle modifications since turbine temperatures and rotational speeds respond to reaching temperature limits; whilst a detailed rate-based approach for the capture plant in Hysys resulted in closely aligned simulation results with experimental data.
    • Bifurcations in approximate solutions of stochastic delay differential equations

      Baker, Christopher T. H.; Ford, Judith M.; Ford, Neville J.; University College Chester/UMIST ; UMIST; University College Chester (World Scientific Publishing Company, 2004)
    • Bifurcations in numerical methods for volterra integro-differential equations

      Edwards, John T.; Ford, Neville J.; Roberts, Jason A. (World Scientific Publishing Company, 2003)
      This article discusses changes in bifurcations in the solutions. It extends the work of Brunner and Lambert and Matthys to consider other bifurcations.
    • Bioinspired bactericidal surfaces with polymer nanocone arrays

      Hazell, Gavin; Fisher, Leanne E.; Murray, Andrew W.; Nobbs, Angela H.; Su, Bo; University of Chester; University of Bristol (Elsevier, 2018-05-28)
      Infections resulting from bacterial biofilm formation on the surface of medical devices are challenging to treat and can cause significant patient morbidity. Recently, it has become apparent that regulation of surface nanotopography can render surfaces bactericidal. In this study, poly(ethylene terephthalate) nanocone arrays are generated through a polystyrene nanosphere-mask colloidal lithographic process. It is shown that modification of the mask diameter leads to a direct modification of centre-to-centre spacing between nanocones. By altering the oxygen plasma etching time it is possible to modify the height, tip width and base diameter of the individual nanocone features. The bactericidal activity of the nanocone arrays was investigated against Escherichia coli and Klebsiella pneumoniae. It is shown that surfaces with the most densely populated nanocone arrays (center-to-center spacing of 200 nm), higher aspect ratios (>3) and tip widths <20 nm kill the highest percentage of bacteria (∼30%).
    • A black box at the end of the rainbow: Searching for the perfect preconditioner

      Ford, Judith M.; Chester College of Higher Education (Royal Society, 2003-11-03)
    • Blending low-order stabilised finite element methods: a positivity preserving local projection method for the convection-diffusion equation

      Barrenechea, Gabriel; Burman, Erik; Karakatsani, Fotini; University of Strathclyde; UCL; University of Chester (Elsevier, 2017-01-20)
      In this work we propose a nonlinear blending of two low-order stabilisation mechanisms for the convection–diffusion equation. The motivation for this approach is to preserve monotonicity without sacrificing accuracy for smooth solutions. The approach is to blend a first-order artificial diffusion method, which will be active only in the vicinity of layers and extrema, with an optimal order local projection stabilisation method that will be active on the smooth regions of the solution. We prove existence of discrete solutions, as well as convergence, under appropriate assumptions on the nonlinear terms, and on the exact solution. Numerical examples show that the discrete solution produced by this method remains within the bounds given by the continuous maximum principle, while the layers are not smeared significantly.
    • Bordered Constructions of Self-Dual Codes from Group Rings and New Extremal Binary Self-Dual Codes

      Dougherty, Steven; Gildea, Joe; Kaya, Abidin; Korban, Adrian; Tylyshchak, Alexander; Yildiz, Bahattin; University of Scranton; University of Chester; Sampoerna Academy; Uzhgorod State University; Northern Arizona University (Elsevier, 2019-02-22)
      We introduce a bordered construction over group rings for self-dual codes. We apply the constructions over the binary field and the ring $\F_2+u\F_2$, using groups of orders 9, 15, 21, 25, 27, 33 and 35 to find extremal binary self-dual codes of lengths 20, 32, 40, 44, 52, 56, 64, 68, 88 and best known binary self-dual codes of length 72. In particular we obtain 41 new binary extremal self-dual codes of length 68 from groups of orders 15 and 33 using neighboring and extensions. All the numerical results are tabulated throughout the paper.
    • Boundedness and stability of solutions to difference equations

      Edwards, John T.; Ford, Neville J. (Elsevier Science, 2002-03-01)
      This article discusses the qualitative behaviour of solutions to difference equations, focusing on boundedness and stability of solutions. Examples demonstrate how the use of Lipschintz constants can provide insights into the qualitative behaviour of solutions to some nonlinear problems.
    • Boundness and stability of differential equations

      Edwards, John T.; Ford, Neville J. (Manchester Centre for Computational Mathematics, 2003-05-23)
      This paper discusses the qualitative behaviour of solutions to difference equations, focusing on boundedness and stability of solutions. Examples demonstrate how the use of Lipschintz constants can provide insights into the qualitative behaviour of solutions to some nonlinear problems.
    • Building Immersive Data Visualizations for the Web

      Butcher, Peter; Ritsos, Panagiotis D.; University of Chester; Bangor University (IEEE Conference Publications, 2017-09)
      We present our early work on building prototype applications for Immersive Analytics using emerging standards-based web technologies for VR. For our preliminary investigations we visualize 3D bar charts that attempt to resemble recent physical visualizations built in the visualization community. We explore some of the challenges faced by developers in working with emerging VR tools for the web, and in building effective and informative immersive 3D visualizations.