Browsing Faculty of Science and Engineering by Title
Now showing items 363382 of 607

Nanodiamond based surface modified screenprinted electrodes for the simultaneous voltammetric determination of dopamine and uric acid.The electroanalytical detection of the neurotransmitter dopamine (DA) in the presence of uric acid (UA) is explored for the first time using commercially procured nanodiamonds (NDs). These are electrically wired via surface modification upon screenprinted graphite macroelectrodes (SPEs). The surface coverage of the NDs on the SPEs was explored in order to optimize electroanalytical outputs to result in wellresolved signals and in low limits of detection. The (electro)analytical outputs are observed to be more sensitive than those achieved at bare (unmodified) SPEs. Such responses, previously reported in the academic literature have been reported to be electrocatalytic and have been previously attributed to the presence of surface sp2 carbon and oxygenated species on the surface of the NDs. However, XPS analysis reveals the commercial NDs to be solely composed of nonconductive sp3 carbon. The low/negligible electroconductivity of the NDs was further confirmed when ND paste electrodes were fabricated and found to exhibit no electrochemical activity. The electroanalytical enhancement, when using NDs electronically wired upon SPEs, is attributed not to the NDs themselves being electrocatalytic, as reported previously, but rather changes in mass transport where the inert NDs block the underlying electroactive SPEs and create a random array of graphite microelectrodes. The electrode was applied to simultaneous sensing of DA and UA at pH 5.5. Figures of merit include (a) low working potentials of around 0.27 and 0.35 V (vs. Ag/AgCl); and (b) detection limits of 5.7 × 107 and 8.9 × 107 M for DA and UA, respectively. Graphical abstract The electroanalytical enhancement of screenprinted electrodes modified with inert/nonconductive nanodiamonds is due to a change in mass transfer where the inert nanodiamonds facilitate the production of a random microelectrode array.

Neutral delay differential equations in the modelling of cell growthIn this contribution, we indicate (and illustrate by example) roles that may be played by neutral delay differential equations in modelling of certain cell growth phenomena that display a time lag in reacting to events. We explore, in this connection, questions involving the sensitivity analysis of models and related mathematical theory; we provide some associated numerical results.

New binary selfdual codes via a generalization of the four circulant constructionIn this work, we generalize the four circulant construction for selfdual codes. By applying the constructions over the alphabets $\mathbb{F}_2$, $\mathbb{F}_2+u\mathbb{F}_2$, $\mathbb{F}_4+u\mathbb{F}_4$, we were able to obtain extremal binary selfdual codes of lengths 40, 64 including new extremal binary selfdual codes of length 68. More precisely, 43 new extremal binary selfdual codes of length 68, with rare new parameters have been constructed.

A New Electrode Design Method in Piezoelectric Vibration Energy Harvesters to Maximize Output PowerA resonant vibration energy harvester typically comprises of a clamped anchor and a vibrating shuttle with a proof mass. Piezoelectric materials are embedded in locations of high strain in order to transduce mechanical deformation into electrical charge. Conventional design for piezoelectric vibration energy harvesters (PVEH) usually utilizes piezoelectric materials and metal electrode layers covering the entire surface area of the cantilever with no consideration provided to examine the tradeoff involved with respect to maximize output power. This paper reports on the theory and experimental verification underpinning optimization of the active electrode area in order to maximize output power. The calculations show that, in order to maximize the output power of a PVEH, the electrode should cover the piezoelectric layer from the peak strain area to a position, where the strain is a half of the average strain in all the previously covered area. With the proposed electrode design, the output power can be improved by 145% and 126% for a cantilever and a clampedclamped beam, respectively. MEMS piezoelectric harvesters are fabricated to experimentally validate the theory.

New Extremal binary selfdual codes of length 68 from generalized neighborsIn this work, we use the concept of distance between selfdual codes, which generalizes the concept of a neighbor for selfdual codes. Using the $k$neighbors, we are able to construct extremal binary selfdual codes of length 68 with new weight enumerators. We construct 143 extremal binary selfdual codes of length 68 with new weight enumerators including 42 codes with $\gamma=8$ in their $W_{68,2}$ and 40 with $\gamma=9$ in their $W_{68,2}$. These examples are the first in the literature for these $\gamma$ values. This completes the theoretical list of possible values for $\gamma$ in $W_{68,2}$.

New Extremal SelfDual Binary Codes of Length 68 via Composite Construction, F2 + uF2 Lifts, Extensions and NeighborsWe describe a composite construction from group rings where the groups have orders 16 and 8. This construction is then applied to find the extremal binary selfdual codes with parameters [32, 16, 8] or [32, 16, 6]. We also extend this composite construction by expanding the search field which enables us to find more extremal binary selfdual codes with the above parameters and with different orders of automorphism groups. These codes are then lifted to F2 + uF2, to obtain extremal binary images of codes of length 64. Finally, we use the extension method and neighbor construction to obtain new extremal binary selfdual codes of length 68. As a result, we obtain 28 new codes of length 68 which were not known in the literature before.

New QuinolineBased Heterocycles as Anticancer Agents Targeting Bcl2The Bcl2 protein has been studied as an anticancer drug target in recent years, due to its gatekeeper role in resisting programmed cancer cell death (apoptosis), and the design of BH3 domain mimetics has led to the clinical approval of Venetoclax (ABT199) for the treatment of chronic lymphocytic leukaemia. In this work we extend our previous studies on the discovery of indolebased heterocycles as Bcl2 inhibitors, to the identification of quinolin4yl based oxadiazole and triazole analogues. Target compounds were readily synthesized via a common arylsubstituted quinolin4carbonylNarylhydrazine1carbothioamide (5a⁻b) intermediate, through simple variation of the basic cyclisation conditions. Some of the quinolinebased oxadiazole analogues (e.g. compound 6i) were found to exhibit submicromolar antiproliferative activity in Bcl2expressing cancer cell lines, and submicromolar IC50 activity within a Bcl2Bim peptide ELISA assay. The Bcl2 targeted anticancer activity of 6i was further rationalised via computational molecular modelling, offering possibilities to extend this work into the design of further potent and selective Bcl2 inhibitory heteroaromatics with therapeutic potential.

New SelfDual and Formally SelfDual Codes from Group Ring ConstructionsIn this work, we study construction methods for selfdual and formally selfdual codes from group rings, arising from the cyclic group, the dihedral group, the dicyclic group and the semidihedral group. Using these constructions over the rings $_F2 +uF_2$ and $F_4 + uF_4$, we obtain 9 new extremal binary selfdual codes of length 68 and 25 even formally selfdual codes with parameters [72,36,14].

New SelfDual Codes of Length 68 from a 2 × 2 Block Matrix Construction and Group RingsMany generator matrices for constructing extremal binary selfdual codes of different lengths have the form G = (In  A); where In is the n x n identity matrix and A is the n x n matrix fully determined by the first row. In this work, we define a generator matrix in which A is a block matrix, where the blocks come from group rings and also, A is not fully determined by the elements appearing in the first row. By applying our construction over F2 +uF2 and by employing the extension method for codes, we were able to construct new extremal binary selfdual codes of length 68. Additionally, by employing a generalised neighbour method to the codes obtained, we were able to con struct many new binary selfdual [68,34,12]codes with the rare parameters $\gamma = 7$; $8$ and $9$ in $W_{68,2}$: In particular, we find 92 new binary selfdual [68,34,12]codes.

A new visualisation and measurement technology for water continuous multiphase flowsThis paper reports the performance of a research prototype of a new multiphase flow instrument to noninvasively measure the phase flow rates, with the capability to rapidly image the flow distributions of two and threephase (gas and/or oil in water) flows. The research prototype is based on the novel concepts of combining vector Electrical Impedance Tomography (EIT) sensor (for measuring dispersedphase velocity and fraction) with an electromagnetic flow metre (EMF, for measuring continuousphase velocity with the EIT input) and a gradiomanometer flowmixture density metre (FDM), in addition to online water conductivity, temperature and absolute pressure measurements. EIT–EMF–FDM data fusion embedded in the research prototype, including online calibration/compensation of conductivity change due to the change of fluids' temperature or ionic concentration, enables the determination of mean concentration, mean velocity and hence the mean flow rate of each individual phase based on the measurement of dispersedphase distributions and velocity profiles. Results from first flowloop experiments conducted at Schlumberger Gould Research (SGR) will be described. The performance of the research prototype in flowrate measurements are evaluated by comparison with the flowloop references. The results indicate that optimum performance of the research prototype for threephase flows is confined within the measuring envelope 45–100% WaterinLiquid Ratio (WLR) and 0–45% Gas Volume Fraction (GVF). Within the scope of this joint research project funded by the UK Engineering & Physical Sciences Research Council (EPSRC), only vertical flows with a conductive continuous liquid phase will be addressed.

Next Generation Additive Manufacturing: Tailorable Graphene/Polylactic(acid) Filaments Allow the Fabrication of 3D Printable Porous Anodes for Utilisation within LithiumIon BatteriesHerein, we report the fabrication and application of Liion anodes for utilisation within Liion batteries, which are fabricated via additive manufacturing/3D printing (fused depo sition modelling) using a bespoke graphene/polylactic acid (PLA) filament, where the graphene content can be readily tailored and controlled over the range 1–40 wt. %. We demon strate that a graphene content of 20 wt. % exhibits sufficient conductivity and critically, effective 3D printability for the rapid manufacturing of 3D printed freestanding anodes (3DAs); simplifying the components of the Liion battery negating the need for a copper current collector. The 3DAs are physicochemcally and electrochemically characterised and possess sufficient conductivity for electrochemical studies. Critically, it is found that if the 3DAs are used in Liion batteries the specific capacity is very poor but can be significantly improved through the use of a chemical pretreatment. Such treatment induces an increased porosity, which results in a 200fold increase (after anode stabilisation) of the specific capacity (ca. 500 mAhg1 at a current density of 40 mAg1). This work significantly enhances the field of additive manufacturing/3D printed graphene based energy storage devices demonstrating that useful 3D printable batteries can be realised

NextGeneration Additive Manufacturing of Complete Standalone SodiumIon Energy Storage ArchitecturesThe first entirely AM/3Dprinted sodiumion (fullcell) battery is reported herein, presenting a paradigm shift in the design and prototyping of energy storage architectures. AM/3Dprinting compatible composite materials are developed for the first time, integrating the active materials NaMnO2 and TiO2 within a porous supporting material, before being AM/3D printed into a proofofconcept model based upon the basic geometry of commercially existing AA battery designs. The freestanding and completely AM/3Dfabricated device demonstrates a respectable performance of 84.3 mAh g1 with a current density of 8.43 mA g1; note that the structure is typically comprised of 80% thermoplastic, but yet, still works and functions as an energystorage platform. The AM/3Dfabricated device is critically benchmarked against a battery developed using the same active materials, but fabricated via a traditional manufacturing method utilizing an inkbased/doctorbladed methodology, which is found to exhibit a specific capacity of 98.9 mAh m2 (116.35 mAh g1). The fabrication of fully AM/3Dprinted energystorage architectures compares favorably with traditional approaches, with the former providing a new direction in battery manufacturing. This work represents a paradigm shift in the technological and design considerations in battery and energystorage architectures

Noise induced changes to dynamic behaviour of stochastic delay differential equationsThis thesis is concerned with changes in the behaviour of solutions to parameterdependent stochastic delay differential equations.

Noiseinduced changes to the behaviour of semiimplicit Euler methods for stochastic delay differential equations undergoing bifurcationThis article discusses estimating parameter values at which bifurcations occur in stochastic delay differential equations. After a brief review of bifurcation, we employ a numerical approach and consider how bifurcation values are influenced by the choice of numerical scheme and the step length and by the level of white noise present in the equation. In this paper we provide a formulaic relationship between the estimated bifurcation value, the level of noise, the choice of numerical scheme and the step length. We are able to show that in the presence of noise there may be some loss of order in the accuracy of the approximation to the true bifurcation value compared to the use of the same approach in the absence of noise.

Noiseinduced changes to the bifurcation behaviour of semiimplicit Euler methods for stochastic delay differential equationsWe are concerned with estimating parameter values at which bifurcations occur in stochastic delay differential equations. After a brief review of bifurcation, we employ a numerical approach and consider how bifurcation values are influenced by the choice of numerical scheme and the step length and by the level of white noise present in the equation. In this paper we provide a formulaic relationship between the estimated bifurcation value, the level of noise, the choice of numerical scheme and the step length. We are able to show that in the presence of noise there maybe some loss of order in the accuracy of the approximation to the true bifurcation value compared to the use of the same approach in the absence of noise.

NonLocal Partial Differential Equations for Engineering and Biology: Mathematical Modeling and AnalysisThis book presents new developments in nonlocal mathematical modeling and mathematical analysis on the behavior of solutions with novel technical tools. Theoretical backgrounds in mechanics, thermodynamics, game theory, and theoretical biology are examined in details. It starts off with a review and summary of the basic ideas of mathematical modeling frequently used in the sciences and engineering. The authors then employ a number of models in bioscience and material science to demonstrate applications, and provide recent advanced studies, both on deterministic nonlocal partial differential equations and on some of their stochastic counterparts used in engineering. Mathematical models applied in engineering, chemistry, and biology are subject to conservation laws. For instance, decrease or increase in thermodynamic quantities and nonlocal partial differential equations, associated with the conserved physical quantities as parameters. These present novel mathematical objects are engaged with rich mathematical structures, in accordance with the interactions between species or individuals, selforganization, pattern formation, hysteresis. These models are based on various laws of physics, such as mechanics of continuum, electromagnetic theory, and thermodynamics. This is why many areas of mathematics, calculus of variation, dynamical systems, integrable systems, blowup analysis, and energy methods are indispensable in understanding and analyzing these phenomena. This book aims for researchers and upper grades students in mathematics, engineering, physics, economics, and biology.

A nonpolynomial collocation method for fractional terminal value problemsIn this paper we propose a nonpolynomial collocation method for solving a class of terminal (or boundary) value problems for differential equations of fractional order α, 0 < α < 1. The approach used is based on the equivalence between a problem of this type and a Fredholm integral equation of a particular form. Taking into account the asymptotic behaviour of the solution of this problem, we propose a nonpolynomial collocation method on a uniform mesh. We study the order of convergence of the proposed algorithm and a result on optimal order of convergence is obtained. In order to illustrate the theoretical results and the performance of the method we present several numerical examples.

A note on finite difference methods for nonlinear fractional differential equations with nonuniform meshesWe consider finite difference methods for solving nonlinear fractional differential equations in the Caputo fractional derivative sense with nonuniform meshes. Under the assumption that the Caputo derivative of the solution of the fractional differential equation is suitably smooth, Li et al. \lq \lq Finite difference methods with nonuniform meshes for nonlinear fractional differential equations\rq\rq, Journal of Computational Physics, 316(2016), 614631, obtained the error estimates of finite difference methods with nonuniform meshes. However the Caputo derivative of the solution of the fractional differential equation in general has a weak singularity near the initial time. In this paper, we obtain the error estimates of finite difference methods with nonuniform meshes when the Caputo fractional derivative of the solution of the fractional differential equation has lower smoothness. The convergence result shows clearly how the regularity of the Caputo fractional derivative of the solution affect the order of convergence of the finite difference methods. Numerical results are presented that confirm the sharpness of the error analysis.

A Note on the WellPosedness of Terminal Value Problems for Fractional Differential Equations.This note is intended to clarify some im portant points about the wellposedness of terminal value problems for fractional di erential equations. It follows the recent publication of a paper by Cong and Tuan in this jour nal in which a counterexample calls into question the earlier results in a paper by this note's authors. Here, we show in the light of these new insights that a wide class of terminal value problems of fractional differential equations is well posed and we identify those cases where the wellposedness question must be regarded as open.