• A Tablet-based Virtual Environment for Neurosurgery Training

      John, Nigel W.; Phillips, Nicholas I.; ap Cenydd, Llyr; Coope, David; Carleton-Bland, Nick; Kamaly-Asl, Ian; Grey, William P.; University of Chester, Leeds General Infirmary, Bangor University, University of Manchester, Cardiff University (MIT Press, 2015-10-15)
      The requirement for training surgical procedures without exposing the patient to additional risk is well accepted and is part of a national drive in the UK and internationally. Computer-based simulations are important in this context, including neurosurgical resident training. The objective of this study is to evaluate the effectiveness of a custom built virtual environment in assisting training of a ventriculostomy procedure. The training tool (called VCath) has been developed as an app for a tablet platform to provide easy access and availability to trainees. The study was conducted at the first boot camp organized for all year one trainees in neurosurgery in the UK. The attendees were randomly distributed between the VCath training group and the Control group. Efficacy of performing ventriculostomy for both groups was assessed at the beginning and end of the study using a simulated insertion task. Statistically significant changes in performance of selecting the burr hole entry point, the trajectory length and duration metrics for the VCath group, together with a good indicator of improved normalized jerk (representing the speed and smoothness of arm motion), all suggest that there has been a higher level cognitive benefit to using VCath. The app is successful as it is focused on the cognitive task of ventriculostomy, encouraging the trainee to rehearse the entry point and use anatomical landmarks to create a trajectory to the target. In straight-line trajectory procedures such as ventriculostomy, cognitive task based education is a useful adjunct to traditional methods and may reduce the learning curve and ultimately improve patient safety.
    • Talos: a prototype Intrusion Detection and Prevention system for profiling ransomware behaviour

      Wood, Ashley; Eze, Thaddeus; Speakman, Lee; University of Chester
      Abstract: In this paper, we profile the behaviour and functionality of multiple recent variants of WannaCry and CrySiS/Dharma, through static and dynamic malware analysis. We then analyse and detail the commonly occurring behavioural features of ransomware. These features are utilised to develop a prototype Intrusion Detection and Prevention System (IDPS) named Talos, which comprises of several detection mechanisms/components. Benchmarking is later performed to test and validate the performance of the proposed Talos IDPS system and the results discussed in detail. It is established that the Talos system can successfully detect all ransomware variants tested, in an average of 1.7 seconds and instigate remedial action in a timely manner following first detection. The paper concludes with a summarisation of our main findings and discussion of potential future works which may be carried out to allow the effective detection and prevention of ransomware on systems and networks.
    • A Taylor-Surrogate-Model-Based Method for the Electrical Performance of Array Antennas Under Interval Position Errors

      Wang, Congsi; Yuan, Shuai; Gao, Wei; Jiang, Chao; Zhu, Cheng; Li, Peng; Wang, Zhihai; Peng, Xuelin; Shi, Yu; Xidian University; University of New South Wales; Hunan University; Nanjing Research Institute of Electronics Technology; University of Chester
      In this letter, a Taylor-surrogate-model-based method (TSMBM) is proposed to predict the bounds of power pattern of array antennas with interval position errors of antenna elements. The advantage of TSMBM is that it provides the approximate analytical solution of the problem with high precision and free of “wrapping effect.” First, the integral form of the Taylor surrogate model (IFTSM) of the distorted power pattern of array antennas is deduced. Then, the extrema point vector of IFTSM can be readily calculated within a set composed of bounds, –1 and 1. Finally, the bounds of the distorted power pattern are determined by submit- ting the extrema point vector of IFTSM to the distorted power pattern. Representative examples are presented to demonstrate the accuracy and effectiveness of the method.
    • Terahertz Characterisation of UV Offset Lithographically Printed Electronic-Ink

      Zeng, Yang; Edwards, Marc R.; Stevens, Robert; Bowen, John; Donnan, Robert S.; Yang, Bin; University of London; National University of Defense Technology; University of Chester; Nottingham Trent University; University of Reading (Elsevier, 2017-06-10)
      Inkjet-printed electronics are showing promising potential in practical applications, but methods for real-time, non-contact monitoring of printing quality are lacking. This work explores Terahertz (THz) sensing as an approach for such monitoring. It is demonstrated that alterations in the localised dielectric characteristics of inkjet-printed electronics can be qualitatively distinguished using quasi-optically-based, sub-THz reflection spectroscopy. Decreased reflection coefficients caused by the sintering process are observed and quantified. Using THz near-field scanning imaging, it is shown that sintering produces a more uniform spatial distribution of permittivity in the printed carbon patterns. Images generated using THz-TDS based imaging are presented, demonstrating the combination of high resolution imaging with quantification of complex permittivities. This work, for the first time, demonstrates the feasibility of quality control in printed electronic-ink with THz sensing, and is of practical significance to the development of in-situ and non-contact commercial-quality characterisation methods for inkjet-printed electronics.
    • Terahertz Probing Irreversible Phase Transitions Related to Polar Clusters in Bi0.5Na0.5TiO3-based Ferroelectric

      Yang, Bin; University of Chester (Wiley-VCH, 2020-02-16)
      Electric-field-induced phase transitions in Bi0.5Na0.5TiO3 (BNT)-based relaxor ferroelectrics are essential to the controlling of their electrical properties and consequently in revolutionizing their dielectric and piezoelectric applications. However, the fundamental understanding of these transitions is a long-standing challenge due to their complex crystal structures. Given the structural inhomogeneity at the nanoscale or sub-nanoscale in these materials, dielectric response characterization based on terahertz (THz) electromagnetic-probe beam-fields, is intrinsically coordinated to lattice dynamics during DC-biased poling cycles. The complex permittivity reveals the field-induced phase transitions to be irreversible. This profoundly counters the claim of reversibility, the conventional support for which, is based upon the peak that is manifest in each of four quadrants of the current-field curves. The mechanism of this irreversibility is solely attributed to polar clusters in the transformed lattices. These represent an extrinsic factor which is quiescent in the THz spectral domain.
    • Terahertz reading of ferroelectric domain wall dielectric switching

      Zhang, Man; Chen, Zhe; Yue, Yajun; Chen, Tao; Yan, Zhongna; Jiang, Qinghui; Yang, Bin; Eriksson, Mirva; Tang, Jianhua; Zhang, Dou; et al.
      Ferroelectric domain walls (DWs) are important nano scale interfaces between two domains. It is widely accepted that ferroelectric domain walls work idly at terahertz (THz) frequencies, consequently discouraging efforts to engineer the domain walls to create new applications that utilise THz radiation. However, the present work clearly demonstrates the activity of domain walls at THz frequencies in a lead free Aurivillius phase ferroelectric ceramic, Ca0.99Rb0.005Ce0.005Bi2Nb2O9, examined using THz time domain spectroscopy (THz-TDS). The dynamics of domain walls are different at kHz and THz frequencies. At low frequencies, domain walls work as a group to increase dielectric permittivity. At THz frequencies, the defective nature of domain walls serves to lower the overall dielectric permittivity. This is evidenced by higher dielectric permittivity in the THz band after poling, reflecting decreased domain wall density. An elastic vibrational model has also been used to verify that a single frustrated dipole in a domain wall represents a weaker contribution to the permittivity than its counterpart within a domain. The work represents a fundamental breakthrough in understanding dielectric contributions of domain walls at THz frequencies. It also demonstrates that THz probing can be used to read domain wall dielectric switching.
    • Terahertz Signatures of Hydrate Formation in Alkali Halide Solutions

      Ligang, Chen; Ren, Guanhua; Liu, Liyuan; Guo, Pan; Wan, Endong; Zhou, Lu; Zhu, Zhonglie; Zhang, Jianbing; Yang, Bin; Zhang, Wentao; et al.
      We systematically studied the ability of 20 alkali halides to form solid hydrates in the frozen state from their aqueous solutions by terahertz time-domain spectroscopy combined with density functional theory (DFT) calculations. We experimentally observed the rise of new terahertz absorption peaks in the spectral range of 0.3-3.5 THz in frozen alkali halide solutions. The DFT calculations prove that the rise of observed new peaks in solutions containing Li+, Na+ or F‾ ions indicates the formation of salt hydrates, while that in other alkali halide solutions is caused by the splitting phonon modes of the imperfectly crystallized salts in ice. As a simple empirical rule, the correlation between the terahertz signatures and the ability of 20 alkali halides to form a hydrate has been established.
    • Theoretical and numerical analysis of unsteady fractional viscoelastic flows in simple geometries.

      Ferras, Luis L.; Ford, Neville J.; Morgado, Maria L.; Rebelo, Magda S.; McKinley, Gareth H.; Nobrega, Joao M.; University of Chester, University of Minho, UTAD, Universidade Nova de Lisboa (Elsevier, 2018-07-12)
      In this work we discuss the connection between classical and fractional viscoelastic Maxwell models, presenting the basic theory supporting these constitutive equations, and establishing some background on the admissibility of the fractional Maxwell model. We then develop a numerical method for the solution of two coupled fractional differential equations (one for the velocity and the other for the stress), that appear in the pure tangential annular ow of fractional viscoelastic fluids. The numerical method is based on finite differences, with the approximation of fractional derivatives of the velocity and stress being inspired by the method proposed by Sun and Wu for the fractional diffusion-wave equation [ Z.Z. Sun, X. Wu, A fully discrete difference scheme for a diffusion-wave system, Applied Numerical Mathematics 56 (2006) 193-209]. We prove solvability, study numerical convergence of the method, and also discuss the applicability of this method for simulating the rheological response of complex fluids in a real concentric cylinder rheometer. By imposing a torsional step-strain, we observe the different rates of stress relaxation obtained with different values of \alpha and \beta (the fractional order exponents that regulate the viscoelastic response of the complex fluids).
    • Theory and numerics for multi-term periodic delay differential equations, small solutions and their detection

      Ford, Neville J.; Lumb, Patricia M.; University of Chester (University of Chester, 2006)
      We summarise a theoretical treatment that analyses whether the equation has small solutions. We consider discrete equations that arise when a numerical method with fixed step size is applied to approximate the solution to (†) and we develop a corresponding theory. Our results show that small solutions can be detected reliably by the numerical scheme. We conclude with some numerical examples.
    • Thermodynamic Analysis and Process System Comparison of the Exhaust Gas Recirculated, Steam Injected and Humidified Micro Gas Turbine

      Ali, Usman; Font Palma, Carolina; Hughes, Kevin J.; Ingham, Derek B.; Ma, Lin; Pourkashanian, Mohamed; University of Leeds (ASME Proceedings, 2015-08-12)
      Stringent environmental emission regulations and continuing efforts to reduce carbon dioxide (CO2) from the energy sector, in the context of global warming, have promoted interest to improve the efficiency of power generation systems whilst reducing emissions. Further, this has led to the development of innovative gas turbine systems which either result in higher electrical efficiency or the reduction of CO2 emissions. Micro gas turbines are one of the secure, economical and environmentally viable options for power and heat generation. Here, a Turbec T100 micro gas turbine (MGT) is simulated using Aspen HYSYS® V8.4 and validated through experimental data. Due to the consistency and robustness of the steady state model developed, it is further extended to three different innovative cycles: (i) an exhaust gas recirculated (EGR) cycle, in which part of the exhaust gas is dried and re-circulated to the MGT inlet; (ii) a steam injected (STIG) cycle, and (iii) a humid air turbine (HAT) cycle. The steam and hot water are generated through the exhaust of the recuperator for the STIG and HAT cycle, respectively. Further, the steam is directly injected into the recuperator for power augmentation, while for the HAT cycle; the compressed air is saturated with water in the humid tower before entering the recuperator. This study evaluates the impact of the EGR ratio, steam to air ratio, and water to air ratio on the performance and efficiency of the system. The comparative potential for each innovative cycle is assessed by thermodynamic properties estimation of process parameters through the models developed to better understand the behavior of each cycle. The thermodynamic assessment indicates that CO2 enrichment occurs for the three innovative cycles. Further, the results indicate that the electrical efficiency increases for the STIG and HAT cycle while it decreases for the EGR cycle. In conclusion, the innovative cycles indicates the possibilities to improve the system performance and efficiency.
    • Thermophoresis effect on the free convective flow in a differentially heated square cavity

      Pop, Serban R.; Grosan, Teodor; University of Chester; Babes-Bolyai University of Cluj Napoca (Begell House, 2015)
      A numerical analysis is made for thermophoretic transport of small particles through the convective flow in a differentially heated square cavity. The governing gas-particle partial differential equations are solved numerically for some values of the considered parameters to investigate their influence on the flow, heat, and mass transfer patterns. It is found that the effect of thermophoresis can be quite significant in appropriate situations.
    • Throwing sheep in the bandroom: Visualising a social and economic network of musicians in Cheshire and North Wales

      Southall, Helen; University of Chester (2012-07-25)
      The aim of this session is to apply some of the visual and technological tools of 21st-Century online social networking, e.g. network visualisation using "friend wheels", to a densely interconnected network of jazz and dance band musicians active in the Chester (UK) area in the 1950s, as revealed by research on the "hidden history" of live music in the area. Over 30 interviews with musicians, dancers and promoters have been collected, plus more than 200 photographs from personal collections, and an M.U. diary/address book belonging to local bandleader Wilf Field. The recent dramatic growth of online social networks such as Facebook, LinkedIn and MySpace has led to a revival of interest in the economic importance of social networks; Fraser and Dutta’s "Throwing Sheep in the Boardroom" provides an interesting survey of the issues, and was an inspiration for this session. But working musicians have long known the importance of knowing (and impressing) the "right people" in order to get work. Have social networks changed fundamentally since the advent of Web 2.0, or were they always there, and just a little harder to visualise when held in a pocket diary, rather than displayed on a Facebook wall?
    • A time discretization scheme for a nonlocal degenerate problem modelling resistance spot welding

      Kavallaris, Nikos I.; Yan, Yubin; University of Chester (Cambridge University Press, 2015-10-02)
      In the current work we construct a nonlocal mathematical model describing the phase transition occurs during the resistance spot welding process in the industry of metallurgy. We then consider a time discretization scheme for solving the resulting nonlocal moving boundary problem. The scheme consists of solving at each time step a linear elliptic partial differential equation and then making a correction to account for the nonlinearity. The stability and error estimates of the developed scheme are investigated. Finally some numerical results are presented confirming the efficiency of the developed numerical algorithm.
    • Titanium Dioxide Engineered for Near-dispersionless High Terahertz Permittivity and Ultra-low-loss

      Chuying, Yu; Zeng, Yang; Yang, Bin; Donnan, Robert S.; Huang, Jinbao; Xiong, Zhaoxian; Mahajan, Amit; Shi, Baogui; Ye, Haitao; Binions, Russell; et al. (Nature Publishing Group, 2017-07-26)
      Realising engineering ceramics to serve as substrate materials in high-performance terahertz(THz) that are low-cost, have low dielectric loss and near-dispersionless broadband, high permittivity, is exceedingly demanding. Such substrates are deployed in, for example, integrated circuits for synthesizing and converting nonplanar and 3D structures into planar forms. The Rutile form of titanium dioxide (TiO2) has been widely accepted as commercially economical candidate substrate that meets demands for both low-loss and high permittivities at sub-THz bands. However, the relationship between its mechanisms of dielectric response to the microstructure have never been systematically investigated in order to engineer ultra-low dielectric-loss and high value, dispersionless permittivities. Here we show TiO2 THz dielectrics with high permittivity (ca. 102.30) and ultra-low loss (ca. 0.0042). These were prepared by insight gleaned from a broad use of materials characterisation methods to successfully engineer porosities, second phase, crystallography shear-planes and oxygen vacancies during sintering. The dielectric loss achieved here is not only with negligible dispersion over 0.2 - 0.8 THz, but also has the lowest value measured for known high-permittivity dielectrics. We expect the insight afforded by this study will underpin the development of subwavelength-scale, planar integrated circuits, compact high Q-resonators and broadband, slow-light devices in the THz band.
    • Torsion Units for a Ree group, Tits group and a Steinberg triality group

      Gildea, Joe; University of Chester (Springer, 2015-12-28)
      We investigate the Zassenhaus conjecture for the Steinberg triality group ${}^3D_4(2^3)$, Tits group ${}^2F_4(2)'$ and the Ree group ${}^2F_4(2)$. Consequently, we prove that the Prime Graph question is true for all three groups.
    • Torsion Units for Some Almost Simple Groups

      Gildea, Joe; University of Chester (Springer, 2016-06-25)
      We prove that the Zassenhaus conjecture is true for $Aut(PSL(2,11))$. Additionally we prove that the Prime graph question is true for $Aut(PSL(2,13))$.
    • Torsion Units for some Projected Special Linear Groups

      Gildea, Joe; University of Chester (2015-12-31)
      In this paper, we investigate the Zassenhaus conjecture for $PSL(4,3)$ and $PSL(5,2)$. Consequently, we prove that the Prime graph question is true for both groups.
    • Torsion units for some untwisted exceptional groups of lie type

      Gildea, Joe; O'Brien, Killian; University of Chester ; Manchester Metropolitan University (Bolyai Institute, University of Szeged, 2016)
      In this paper, we investigate the Zassenhaus conjecture for exceptional groups of lie type $G_2(q)$ for $q=\{3,4\}$. Consequently, we prove that the Prime graph question is true for these groups.
    • Torsion units in the integral group ring of PSL(3,4)

      Gildea, Joe; Tylyshchak, Alexander; University of Chester ; Uzhgorod State University (World Scientific Publishing, 2015-08-31)
      We investigate the Zassenhaus Conjecture for the integral group ring of the simple group PSL(3,4).
    • Total war and its effects on the live music industry in Cheshire and North Wales

      Southall, Helen; University of Chester (University of Chester, 2014-10-03)
      Given the profound effect which World War II had on the economy of the UK as a whole, it would be surprising if specific areas of that economy – such as live music in the provinces – were not affected as well. How did ‘total war’ affect the live music industry on a local level? Evidence I have collected for a study of musicians active in and around Chester during the period suggests that the large number of military bases in the area, combined with the effects of other wartime factors such as conscription, rationing and the need to maintain both military and civilian morale, did indeed affect the size and nature of the market for live dance music locally. For instance, the large US Air Force base at Burtonwood was a source of work for local musicians, as well as an opportunity to mix with American musicians and music fans. As well as presenting information obtained through interviews with musicians and their relatives, I will also look briefly at what happened to the musicians and the bands after the war, when economic and social conditions changed again, at the same time as advances occurred in music-related technology.