Now showing items 448-467 of 626

• #### Oscillatory and stability of a mixed type difference equation with variable coefficients

The goal of this paper is to study the oscillatory and stability of the mixed type difference equation with variable coefficients $\Delta x(n)=\sum_{i=1}^{\ell}p_{i}(n)x(\tau_{i}(n))+\sum_{j=1}^{m}q_{j}(n)x(\sigma_{i}(n)),\quad n\ge n_{0},$ where $\tau_{i}(n)$ is the delay term and $\sigma_{j}(n)$ is the advance term and they are positive real sequences for $i=1,\cdots,l$ and $j=1,\cdots,m$, respectively, and $p_{i}(n)$ and $q_{j}(n)$ are real functions. This paper generalise some known results and the examples illustrate the results.
• #### Overcurrent relays coordination optimisation methods in distribution systems for microgrids: a review

Electric power networks connected with multiple distributed generations (microgrids) require adequate protection coordination. In this paper, the overcurrent relay coordination concept in distribution system has been presented with details. In this available literature, the previous works on optimisation methods utilised for the coordination of over current relays; classification has been made based on the optimisation techniques, non-standard characteristics, new constraints that have been proposed for optimal coordination and dual setting protection schemes. Then a comprehensive review has been done on optimisation techniques including the conventional methods, heuristic and hybrid methods and the relevant issues have been addressed.
• #### An overview of self-adaptive technologies within virtual reality training

This overview presents the current state-of-the-art of self-adaptive technologies within virtual reality (VR) training. Virtual reality training and assessment is increasingly used for five key areas: medical, industrial & commercial training, serious games, rehabilitation and remote training such as Massive Open Online Courses (MOOCs). Adaptation can be applied to five core technologies of VR including haptic devices, stereo graphics, adaptive content, assessment and autonomous agents. Automation of VR training can contribute to automation of actual procedures including remote and robotic assisted surgery which reduces injury and improves accuracy of the procedure. Automated haptic interaction can enable tele-presence and virtual artefact tactile interaction from either remote or simulated environments. Automation, machine learning and data driven features play an important role in providing trainee-specific individual adaptive training content. Data from trainee assessment can form an input to autonomous systems for customised training and automated difficulty levels to match individual requirements. Self-adaptive technology has been developed previously within individual technologies of VR training. One of the conclusions of this research is that while it does not exist, an enhanced portable framework is needed and it would be beneficial to combine automation of core technologies, producing a reusable automation framework for VR training.
• #### An overview of thermal necrosis: present and future

Introduction: Many orthopaedic procedures require drilling of bone, especially fracture repair cases. Bone drilling results in heat generation due to the friction between the bone and the drill bit. A high-level of heat generation kills bone cells. Bone cell death results in resorption of bone around bone screws. Materials and methods: We searched in the literature for data on parameters that influence drilling bone and could lead to thermal necrosis. The points of view of many orthopaedists and neurosurgeons based upon on previous practices and clinical experience are presented. Results: Several potential complications are discussed and highlighted that lead to thermal necrosis. Discussion: Even in the face of growing evidence as to the negative effects of heat-induction during drilling, simple and effective methods for monitoring and cooling in real-time are not in widespread usage today. For that purpose, we propose some suggestions for the future of bone drilling, taking note of recent advances in autonomous robotics, intelligent systems, and computer simulation techniques. Conclusions: These advances in prevention of thermal necrosis during bone drilling surgery are expected to reduce the risk of patient injury and costs for the health service.
• #### Oxidation processes in the eastern Mediterranean atmosphere: evidence from the modelling of HOx measurements over Cyprus

The Mediterranean is a climatically sensitive region located at the crossroads of air masses from three continents: Europe, Africa, and Asia. The chemical processing of air masses over this region has implications not only for the air quality but also for the long-range transport of air pollution. To obtain a comprehensive understanding of oxidation processes over the Mediterranean, atmospheric concentrations of the hydroxyl radical (OH) and the hydroperoxyl radical (HO2) were measured during an intensive field campaign (CYprus PHotochemistry EXperiment, CYPHEX-2014) in the northwest of Cyprus in the summer of 2014. Very low local anthropogenic and biogenic emissions around the measurement location provided a vantage point to study the contrasts in atmospheric oxidation pathways under highly processed marine air masses and those influenced by relatively fresh emissions from mainland Europe. The CYPHEX measurements were used to evaluate OH and HO2 simulations using a photochemical box model (CAABA/MECCA) constrained with CYPHEX observations of O3, CO, NOx, hydrocarbons, peroxides, and other major HOx (OH+HO2) sources and sinks in a low-NOx environment (<100pptv of NO). The model simulations for OH agreed to within 10% with in situ OH observations. Model simulations for HO2 agreed to within 17% of the in situ observations. However, the model strongly under-predicted HO2 at high terpene concentrations, this under-prediction reaching up to 38% at the highest terpene levels. Different schemes to improve the agreement between observed and modelled HO2, including changing the rate coefficients for the reactions of terpene-generated peroxy radicals (RO2) with NO and HO2 as well as the autoxidation of terpene-generated RO2 species, are explored in this work. The main source of OH in Cyprus was its primary production from O3 photolysis during the day and HONO photolysis during early morning. Recycling contributed about one-third of the total OH production, and the maximum recycling efficiency was about 0.7. CO, which was the largest OH sink, was also the largest HO2 source. The lowest HOx production and losses occurred when the air masses had higher residence time over the oceans.

• #### Parametric model of human body shape and ligaments for patient-specific epidural simulation

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

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

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

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

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

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

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

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

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

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

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

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

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.