• Panel adjustment and error analysis for a large active main reflector antenna by using the panel adjustment matrix

      Lian, Peiyuan; Wang, Congsi; Xue, Song; Xu, Qian; Wang, Na; xiang, Binbin; Shi, Yu; Jia, Yu; Xidian University; University of Chester; Aston University; Chinese Academy of Sciences
      Active panels are generally applied in large aperture and high frequency reflector antennas, and the precise calculation of the actuator adjustment value is of great importance. First, the approximation relationship between the adjustment value and panel elastic deformation is established. Subsequently, a panel adjustment matrix for the whole reflector is derived to calculate the reflector deformation caused by the actuator adjustment. Next, the root mean square (rms) error of the deformed reflector is expressed as a quadratic form in the matrix form, and the adjustment value can be derived easily and promptly from the corresponding extreme value. The solution is expected to be unique and optimal since the aforementioned quadratic form is a convex function. Finally, a 35 m reflector antenna is adopted to perform the panel adjustments, and the effect of the adjustment errors is discussed. The results show that compared to the traditional model, where the panel elastic deformation is not considered, the proposed method exhibits a higher accuracy and is more suitable for use in large reflectors with a high operation frequency. The adjustment errors in different rings exert different influences on the gain and sidelobe level, which can help determine the actuator distribution with different precisions.
    • Parametric model of human body shape and ligaments for patient-specific epidural simulation

      Vaughan, Neil; Dubey, Venketesh N.; Wee, Michael Y. K.; Isaacs, Richard; Bournemouth University; Poole Hospital NHS Foundation Trust (Elsevier, 2014-09-04)
      Objective: This work builds upon the concept of matching a person’s weight, height and age to their overall body shape to create an adjustable three-dimensional model. A versatile and accurate predictor of body size and shape and ligament thickness is required to improve simulation for medical procedures. A model which is adjustable for any size, shape, body mass, age or height would provide ability to simulate procedures on patients of various body compositions. Methods: Three methods are provided for estimating body circumferences and ligament thicknesses for each patient. The first method is using empirical relations from body shape and size. The second method is to load a dataset from a magnetic resonance imaging scan (MRI) or ultrasound scan containing accurate ligament measurements. The third method is a developed artificial neural network (ANN) which uses MRI dataset as a training set and improves accuracy using error back-propagation, which learns to increase accuracy as more patient data is added. The ANN is trained and tested with clinical data from 23088 patients. Results: The ANN can predict subscapular skinfold thickness within 3.54mm, waist circumference 3.92cm, thigh circumference 2.00cm, arm circumference 1.21cm, calf circumference 1.40cm, triceps skinfold thickness 3.43mm. Alternative regression analysis method gave overall slightly less accurate predictions for subscapular skinfold thickness within 3.75mm, waist circumference 3.84cm, thigh circumference 2.16cm, arm circumference 1.34cm, calf circumference 1.46cm, triceps skinfold thickness 3.89mm. These calculations are used to display a 3D graphics model of the patient’s body shape using OpenGL and adjusted by 3D mesh deformations. Conclusions: A patient-specific epidural simulator is presented using the developed body shape model, able to simulate needle insertion procedures on a 3D model of any patient size and shape. The developed ANN gave the most accurate results for body shape, size and ligament thickness. The resulting simulator offers the experience of simulating needle insertions accurately whilst allowing for variation in patient body mass, height or age.
    • Parametric Study of Environmental Conditions on The Energy Harvesting Efficiency for The Multifunctional Composite Structures

      Wen, Tao; Ratner, Alon; Jia, Yu; Shi, Yu; University of Chester;University of Warwick; Aston University
      This paper presents a parametric study of the efficacy of an integrated vibration energy harvesting device under the environmental condition representative of an offshore wind turbine. A multifunctional glass fibre composite with an integrated Micro Fibre Composite (MFC) energy harvesting device was tested by swept sine vibration under environmental conditions that ranged from – 40°C to 70°C in temperature and 10%RH to 90%RH in humidity in order to characterise the sensitivity and dependence of energy harvesting on environmental conditions. Experimental vibration testing was complemented with theoretical analysis to investigate the relative contributions to the temperature dependence of energy harvesting. This included mechanical properties of the stiffness and strength of the cantilever structure and the electrical properties of the MFC transducer, including its dielectric constants and charge coefficients. An inverse proportionality was observed between the magnitude of harvested energy and the climatic temperature. The efficiency of energy harvesting was dominated by the stiffness of the cantilever, which displayed viscoelastic temperature dependence. The sample was also tested with a vibration profile obtained from a wind turbine in order to validate the temperature influence under typical service conditions. Numerical modal analysis was used to determine the shapes of resonance modes, the frequencies of which were temperature dependent. Humidity was observed to have a secondary influence on energy harvesting, with no significant short-term effect on the structural properties of the samples within the limits of the experimental method.
    • ParaVR: A Virtual Reality Training Simulator for Paramedic Skills maintenance

      Rees, Nigel; Dorrington, Keith; Rees, Lloyd; Day, Thomas W; Vaughan, Neil; John, Nigel W; Welsh Ambulance Services NHS Trust, University of Chester
      Background, Virtual Reality (VR) technology is emerging as a powerful educational tool which is used in medical training and has potential benefits for paramedic practice education. Aim The aim of this paper is to report development of ParaVR, which utilises VR to address skills maintenance for paramedics. Methods Computer scientists at the University of Chester and the Welsh Ambulance Services NHS Trust (WAST) developed ParaVR in four stages: 1. Identifying requirements and specifications 2. Alpha version development, 3. Beta version development 4. Management: Development of software, further funding and commercialisation. Results Needle Cricothyrotomy and Needle Thoracostomy emerged as candidates for the prototype ParaVR. The Oculus Rift head mounted display (HMD) combined with Novint Falcon haptic device was used, and a virtual environment crafted using 3D modelling software, ported (a computing term meaning transfer (software) from one system or machine to another) onto Oculus Go and Google cardboard VR platform. Conclusion VR is an emerging educational tool with the potential to enhance paramedic skills development and maintenance. The ParaVR program is the first step in our development, testing, and scaling up of this technology.
    • Part-load performance of direct-firing and co-firing of coal and biomass in a power generation system integrated with a CO2 capture and compression system

      Ali, Usman; Akram, Muhammad; Font Palma, Carolina; Ingham, Derek B.; Pourkashanian, Mohamed; University of Sheffield; University of Chester; University of Engineering and Technology (Elsevier, 2017-09-18)
      Bioenergy with Carbon Capture and Storage (BECCS) is recognised as a key technology to mitigate CO2 emissions and achieve stringent climate targets due to its potential for negative emissions. However, the cost for its deployment is expected to be higher than for fossil-based power plants with CCS. To help in the transition to fully replace fossil fuels, co-firing of coal and biomass provide a less expensive means. Therefore, this work examines the co-firing at various levels in a pulverised supercritical power plant with post-combustion CO2 capture, using a fully integrated model developed in Aspen Plus. Co-firing offers flexibility in terms of the biomass resources needed. This work also investigates flexibility within operation. As a result, the performance of the power plant at various part-loads (40%, 60% and 80%) is studied and compared to the baseline at 100%, using a constant fuel flowrate. It was found that the net power output and net efficiency decrease when the biomass fraction increases for constant heat input and constant fuel flow rate cases. At constant heat input, more fuel is required as the biomass fraction is increased; whilst at constant fuel input, derating occurs, e.g. 30% derating of the power output capacity at firing 100% biomass compared to 100% coal. Co-firing of coal and biomass resulted in substantial power derating at each part-load operation.
    • The past, present and future of indoor air chemistry

      Bekö, Gabriel; Carslaw, Nicola; Fauser, Patrick; Kauneliene, Violeta; Nehr, Sascha; Phillips, Gavin; Saraga, Dikaia; Schoemaecker, Coralie; Wierzbicka, Aneta; Querol, Xavier; et al. (Wiley, 2020-04-25)
      This is an editorial contribution to the Journal Indoor Air on the future direction of indoor air chemistry research.
    • Pencil It In: Exploring the Feasibility of Hand-drawn Pencil Electrochemical Sensors and their Direct Comparison to Screen-printed Electrodes

      Bernalte, Elena; Foster, Christopher W.; Brownson, Dale A. C.; Mosna, Morgane; Smith, Graham C.; Banks, Craig E.; Manchester Metropolitain University (Foster, Brownson, Mosna, Banks), Universidad de Extremadura, Badajoz (Bernalte), University of Chester (Smith) (MDPI, 2016-08-29)
      We explore the fabrication, physicochemical characterisation (SEM, Raman, EDX and XPS) and electrochemical application of hand-drawn pencil electrodes (PDEs) upon an ultra-flexible polyester substrate; investigating the number of draws (used for their fabrication), the pencil grade utilised (HB to 9B) and the electrochemical properties of an array of batches (i.e, pencil boxes). Electrochemical characterisation of the PDEs, using different batches of HB grade pencils, is undertaken using several inner- and outer-sphere redox probes and is critically compared to screen-printed electrodes (SPEs). Proof-of-concept is demonstrated for the electrochemical sensing of dopamine and acetaminophen using PDEs, which are found to exhibit competitive limits of detection (3 ) upon comparison to SPEs. Nonetheless, it is important to note that a clear lack of reproducibility was demonstrated when utilising these PDEs fabricated using the HB pencils from different batches. We also explore the suitability and feasibility of a pencil-drawn reference electrode compared to screen-printed alternatives, to see if one can draw the entire sensing platform. This article reports a critical assessment of these PDEs against that of its screen-printed competitors, questioning the overall feasibility of PDEs’ implementation as a sensing platform.
    • Performance Comparison of Protonic and Sodium Phosphomolybdovanadate Polyoxoanion Catholytes Within a Chemically Regenerative Redox Cathode Polymer Electrolyte Fuel Cell

      Ward, David B.; Gunn, Natasha; Uwigena, Nadine; Davies, Trevor J.; University of Chester (Elsevier, 2017-11-23)
      The direct reduction of oxygen in conventional polymer electrolyte fuel cells (PEFCs) is seen by many researchers as a key challenge in PEFC development. Chemically regenerative redox cathode (CRRC) polymer electrolyte fuel cells offer an alternative approach via the indirect reduction of oxygen, improving durability and reducing cost. These systems substitute gaseous oxygen for a liquid catalyst that is reduced at the cathode then oxidised in a regeneration vessel via air bubbling. A key component of a CRRC system is the liquid catalyst or catholyte. To date, phosphomolybdovanadium polyoxometalates with empirical formula H3+nPVnMo12-nO40 have shown the most promise for CRRC PEFC systems. In this work, four catholyte formulations are studied and compared against each other. The catholytes vary in vanadium content, pH and counter ion, with empirical formulas H6PV3Mo9O40, H7PV4Mo8O40, Na3H3PV3Mo9O40 and Na4H3PV4Mo8O40. Thermodynamic properties, cell performance and regeneration rates are measured, generating new insights into how formulation chemistry affects the components of a CRRC system. The results include the best CRRC PEFC performance reported to date, with noticeable advantages over conventional PEFCs. The optimum catholyte formulation is then determined via steady state tests, the results of which will guide further optimization of the catholyte formulation.
    • Periodic solutions of discrete Volterra equations

      Baker, Christopher T. H.; Song, Yihong; University College Chester ; Suzhou University (Elsevier, 2004-02-25)
      This article investigates periodic solutions of linear and nonlinear discrete Volterra equations of convolution or non-convolution type with unbounded memory. For linear discrete Volterra equations of convolution type, we establish Fredholm’s alternative theorem and for equations of non-convolution type, and we prove that a unique periodic solution exists for a particular bounded initial function under appropriate conditions. Further, this unique periodic solution attracts all other solutions with bounded initial function. All solutions of linear discrete Volterra equations with bounded initial functions are asymptotically periodic under certain conditions. A condition for periodic solutions in the nonlinear case is established.
    • Perovskite Srx(Bi1-xNa0.97-xLi0.03)0.5TiO3 ceramics with polar nano regions for high power energy storage

      Wu, Jiyue; Mahajan, Amit; Riekehr, Lars; Zhang, Hangfeng; Yang, Bin; Meng, Nan; Zhang, Zhen; Yan, Haixue; Queen Mary University of London; Uppsala University; University of Chester (Elsevier, 2018-06-06)
      Dielectric capacitors are very attractive for high power energy storage. However, the low energy density of these capacitors, which is mainly limited by the dielectric materials, is still the bottleneck for their applications. In this work, lead-free single-phase perovskite Srx(Bi1-xNa0.97-xLi0.03)0.5TiO3 (x=0.30 and 0.38) bulk ceramics, prepared using solid-state reaction method, were carefully studied for the dielectric capacitor application. Polar nano regions (PNRs) were created in this material using co-substitution at A-site to enable relaxor behaviour with low remnant polarization (Pr) and high maximum polarization (Pmax). Moreover, Pmax was further increased due to reversible electric field induced phase transitions. Comprehensive structural and electrical studies were performed to confirm the PNRs and the reversible phase transitions. And finally a high energy density (1.70 J/cm3) with an excellent efficiency (87.2%) was achieved using the contribution of PNRs and field-induced transitions in this material, making it among the best performing lead-free dielectric ceramic bulk material for high energy storage.
    • Perturbation of Volterra difference equations

      Song, Yihong; Baker, Christopher T. H.; Suzhou University ; University College Chester (2004)
      A fixed point theorem is used to investigate nonlinear Volterra difference equations that are perturbed versions of linear equations. Sufficient conditions are established to ensure that the stability properties of linear Volterra difference equations are preserved under perturbation. The existence of asymptotically periodic solutions of perturbed Volterra difference equations is also proved.
    • The physicochemical investigation of hydrothermally reduced textile waste and application within carbon-based electrodes

      Randviir, Edward P.; Kanou, Omar; Liauw, Christopher M.; Miller, Gary; Andrews, Hayley; Smith, Graham C.; Manchester Metropolitan University; University of Chester (Royal Society of Chemistry, 2019-04-10)
      Textile waste is on the rise due to the expanding global population and the fast fashion market. Large volumes of textile waste are increasing the need for new methods for recycling mixed fabric materials. This paper employs a hydrothermal conversion route for a polyester/cotton mix in phosphoric acid to generate carbon materials (hydrochars) for electrochemical applications. A combination of characterization techniques revealed the reaction products were largely comprised of two major components. The first is a granular material with a surface C : O ratio of 2 : 1 interspersed with phosphorous and titanium proved using energy dispersive X-ray spectroscopy, and the other is a crystalline material with a surface C : O ratio of 3 : 2 containing no phosphorous or titanium. The latter material was found via X-ray diffraction and differential scanning calorimetry to be terephthalic acid. Electrochemical experiments conducted using the hydrochar as a carbon paste electrode demonstrates an increase in current response compared to carbon reference materials. The improved current responses, intrinsically related to the surface area of the material, could be beneficial for electrochemical sensor applications, meaning that this route holds promise for the development of a cheap recycled carbon material, using straightforward methods and simple laboratory reagents.
    • Piezoelectric vibration energy harvesting: A connection configuration scheme to increase operational range and output power

      Du, Sijun; Jia, Yu; Seshia, Ashwin A.; University of Cambridge; University of Chester (SAGE, 2016-12-12)
      For a conventional monolithic piezoelectric transducer (PT) using a full-bridge rectifier, there is a threshold voltage that the open-circuit voltage measured across the PT must attain prior to any transfer of energy to the storage capacitor at the output of the rectifier. This threshold voltage usually depends on the voltage of the storage capacitor and the forward voltage drop of diodes. This article presents a scheme of splitting the electrode of a monolithic piezoelectric vibration energy harvester into multiple (n) equal regions connected in series in order to provide a wider operating voltage range and higher output power while using a full-bridge rectifier as the interface circuit. The performance of different series stage numbers has been theoretically studied and experimentally validated. The number of series stages (n≥1n≥1) can be predefined for a particular implementation, which depends on the specified operating conditions, to achieve optimal performance. This enables the system to attain comparable performance compared to active interface circuits under an increased input range while no additional active circuits are required and the system is comparatively less affected by synchronized switching damping effect.
    • Pitfalls in fast numerical solvers for fractional differential equations

      Diethelm, Kai; Ford, Judith M.; Ford, Neville J.; Weilbeer, Marc (Elsevier, 2006-02-15)
      This preprint discusses the properties of high order methods for the solution of fractional differential equations. A number of fractional multistep methods are are discussed.
    • Policing the Cyber Threat: Exploring the threat from Cyber Crime and the ability of local Law Enforcement to respond

      Eze, Thaddeus; Hull, Matthew; Speakman, Lee; University of Chester (Proceedings of the IEEE, 2019-07-01)
      The landscape in which UK policing operates today is a dynamic one, and growing threats such as the proliferation of cyber crime are increasing the demand on police resources. The response to cyber crime by national and regional law enforcement agencies has been robust, with significant investment in mitigating against, and tackling cyber threats. However, at a local level, police forces have to deal with an unknown demand, whilst trying to come to terms with new crime types, terminology and criminal techniques which are far from traditional. This paper looks to identify the demand from cyber crime in one police force in the United Kingdom, and whether there is consistency in the recording of crime. As well as this, it looks to understand whether the force can deal with cyber crime from the point of view of the Police Officers and Police Staff in the organisation.
    • A Posteriori Analysis for Space-Time, discontinuous in time Galerkin approximations for parabolic equations in a variable domain

      Antonopoulou, Dimitra; Plexousakis, Michael; University of Chester; University of Crete (ECP sciences, 2019-04-24)
      This paper presents an a posteriori error analysis for the discontinuous in time space-time scheme proposed by Jamet for the heat equation in multi-dimensional, non-cylindrical domains [25]. Using a Cl ement-type interpolant, we prove abstract a posteriori error bounds for the numerical error. Furthermore, in the case of two-dimensional spatial domains we transform the problem into an equivalent one, of parabolic type, with space-time dependent coe cients but posed on a cylindrical domain. We formulate a discontinuous in time space{time scheme and prove a posteriori error bounds of optimal order. The a priori estimates of [19] for general parabolic initial and boundary value problems are used in the derivation of the upper bound. Our lower bound coincides with that of Picasso [36], proposed for adaptive, Runge-Kutta finite element methods for linear parabolic problems. Our theoretical results are verified by numerical experiments.
    • A posteriori error estimates for fully discrete fractional-step ϑ-approximations for parabolic equations

      Karakatsani, Fotini; University of Chester (Oxford University Press, 2015-07-22)
      We derive optimal order a posteriori error estimates for fully discrete approximations of initial and boundary value problems for linear parabolic equations. For the discretisation in time we apply the fractional-step #-scheme and for the discretisation in space the finite element method with finite element spaces that are allowed to change with time.
    • A posteriori error estimates for fully discrete schemes for the time dependent Stokes problem

      Baensch, Eberhard; Karakatsani, Fotini; Makridakis, Charalambos; University of Erlangen; University of Chester; University of Crete; Foundation for Research & Technology, Greece; University of Sussex (Springer, 2018-05-02)
      This work is devoted to a posteriori error analysis of fully discrete finite element approximations to the time dependent Stokes system. The space discretization is based on popular stable spaces, including Crouzeix–Raviart and Taylor–Hood finite element methods. Implicit Euler is applied for the time discretization. The finite element spaces are allowed to change with time steps and the projection steps include alternatives that is hoped to cope with possible numerical artifices and the loss of the discrete incompressibility of the schemes. The final estimates are of optimal order in L∞(L2) for the velocity error.
    • The power of VNA-driven quasi-optics to sense group molecular action in condensed phase systems

      Donnan, Robert S.; Tian, Kun V.; Yang, Bin; Chass, Gregory A.; University of Chester (2014-12-08)
      The versatility for quasi-optical circuits, driven by modern vector network analysers, is demonstrated for the purpose of low energy (meV) coherent spectroscopy. One such example is shown applied to the curing dynamics of a non-mercury-based dental cement. This highlights the special place the methodology holds as a `soft-probe' to reveal the time-resolved energetics of condensed phased systems as they self-organise to adopt their low energy state.
    • Power System with Variable Speed Wind Turbine and Diesel Generation Units

      Hu, Yanting; Chen, Zhe; Glyndwr; Aalborg University (EER, 2014-01-20)
      Thispaper presents a power system consisting of wind turbines, diesel generation units, and energy storage system. Both wind turbines and diesel engine adopt variable speed operation mode;and power electronic interface are used for the generation units which provide flexible and wide range of control on the power. The system configuration, characteristics, operation principles are presented. The controller and control strategies are discussed. The simulation studies have been performed and the results are presented.