M A Atherton

Publications (10)3.14 Total impact

• Article: Non-newtonian and flow pulsatility effects in simulation models of a stented intracranial aneurysm.

  M Cavazzuti, M A Atherton, M W Collins, G S Barozzi
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  ABSTRACT: Three models of different stent designs implanted in a cerebral aneurysm, originating from the Virtual Intracranial Stenting Challenge '07, are meshed and the flow characteristics simulated using commercial computational fluid dynamics (CFD) software in order to investigate the effects of non-Newtonian viscosity and pulsatile flow. Conventional mass inflow and wall shear stress (WSS) output are used as a means of comparing the CFD simulations. In addition, a WSS distribution is presented, which clearly discriminates in favour of the stent design identified by other groups. It is concluded that non-Newtonian and pulsatile effects are important to include in order to avoid underestimating wss, to understand dynamic flow effects, and to discriminate more effectively between stent designs.
  Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine 06/2011; 225(6):597-609. · 1.21 Impact Factor
• Article: Effects of stents under asymmetric inflow conditions.

  M A Atherton, K Tesch, M W Collins
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  ABSTRACT: Patient-to-patient variations in artery geometry may determine their susceptibility to stenosis formation. These geometrical variations can be linked to variations in flow characteristics such as wall shear stress through stents, which increases the risk of restenosis. This paper considers computer models of stents in non-symmetric flows and their effects on flow characteristics at the wall. This is a fresh approach from the point of view of identifying a stent design whose performance is insensitive to asymmetric flow. Measures of dissipated energy and power are introduced in order to discriminate between competing designs of stents.
  Biorheology 02/2002; 39(3-4):501-6. · 1.93 Impact Factor
• Article: Molecular mechanisms of the bleaching actions associated with commercially-available whitening oral health care products.

  E Lynch, A Sheerin, D Y Samarawickrama, M A Atherton, A W Claxson, J Hawkes, P Haycock, D Naughton, K G Seymour, F M Burke
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  ABSTRACT: An increased public awareness in dental aesthetics has resulted in the wide availability of techniques of tooth bleaching, both in the dental chair and at home. This article reviews the aetiology of tooth discolouration both at the clinical and the molecular level, together with methods of alleviating such discolouration. Much of the therapeutic and aesthetic actions of commercially-available tooth whiteners, gels, oral rinses and other dentifrices are predominantly dependent on their ability to act as oxidants. A novel method of evaluating these aspects of dentifrice activity is also described: high resolution proton nuclear magnetic resonance (NMR) spectroscopy is a virtually non-invasive, multi component bioanalytical technique that can be employed to study oxidation/reduction reactions at the molecular level and is utilised here to investigate the mechanisms of action of a newly developed dentifrice (Ultrawhite Opal, Janina International). Such methodology also offers much potential for studies concerning the numerous chemical reactions occurring within the oral environment.
  Journal of the Irish Dental Association 02/1995; 41(4):94-102.
• Article: Heat transfer coefficient calibrations by means of evolutionary algorithms

  K Tesch, M A Atherton, T G Karayiannis, M W Collins, P Edwards
• Source

  Available from: brunel.ac.uk

  Article: Section properties of palm petioles, part 2: The relationship of petiole histology with the torsional rigidity of the palm, Trachycarpus fortunei

  A G Windsor-Collins, M A Atherton, M W Collins, D F Cutler
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  ABSTRACT: The Trachycarpus fortunei palm is a good example of a palm with a large leaf blade supported by a correspondingly large petiole. The interaction of the material and functional properties of the petiole was analysed using engineering and botanical methods with a view to understanding how the petiole functions from a structural standpoint. The histological aspects of the petiole were analysed from sections taken at regular intervals along the petiole axis, in order to determine the density and position of the vascular bundles. A modified torsion rig was then used to acquire torsion readings and calculate the rigidity modulus variation along the petiole. To supplement this, shape factor derived data from the Trachycarpus fortunei palm petiole were calculated and then compared with the empirical results and the differences analysed.
• Article: Modelling the interaction of haemodynamics and the Artery Wall: Current status and future prospects

  P V Lawford, Y Ventikos, A Khir, M A Atherton, D Evans, D R Hose, C M Care, P N Watton, I Halliday, D C Walker, A P Hollis, M W Collins
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  ABSTRACT: The arterial wall is exposed to mechanical forces associated with the flowing blood. In vivo the artery is subject to an axial load, a wall stress in the circumferential direction due to the internal pulsatile pressure and a frictional stress, the wall shear stress, generated by the moving blood. The cells are sensitive to changes in the magnitude and frequency of these stresses which are important modulators of cell function. Deviation of the mechanical environment of the cells from homeostatic levels stimulates vessel wall remodeling, increasing the production of structural proteins and degradative enzymes until a new homeostatic state is achieved. The haemodynamic environment can give rise to deleterious remodeling, for example, atherosclerosis or aneurysms. Clinical research has historically focused on the two main strategies of in vivo and in vitro experimentation. The concept of applying scientific theory to direct clinical applications is relatively recent. In this paper we focus on the interaction of wall shear stress with the endothelium and discuss how ‘state of the art’ computer modeling techniques can provide valuable data to aid understanding. Such data may be used to inform experiment and further, may help identify the key features of this complex system.
• Article: Determining heat transfer coefficients using evolutionary algorithms

  K Tesch, M A Atherton, T G Karayiannis, M W Collins, P Edwards
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  ABSTRACT: This article presents a way of determining heat transfer calibrations for multi-objective and single-objective optimization by means of genetic algorithms. The need for optimization arises from the necessity for mathematical model validation and is very relevant to practical applications. The SPEA algorithm is used for multi-objective optimization. Scalarization of the fitness function is also addressed in combination with a small population size in order to keep the computational cost of the problem to a minimum. This is because of the time spent for a fitness function evaluation which comes from numerical solution of the nonlinear partial differential equations. The result is that a value of the heat transfer coefficient is determined that produces minimal difference between experimental results and numerical predictions.
• Source

  Available from: brunel.ac.uk

  Article: Section properties of palm petioles, Part 1: The influence of section shape on the flexural and torsional properties of selected palm petioles

  A G Windsor-Collins, M A Atherton, M W Collins, D F Cutler
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  ABSTRACT: Shape factors have been used to calculate the shape efficiency of palm leaf petiole sections in order to understand how palms compensate for the torsional and bending forces put upon them by their environment. That part of the palm leaf that is similar in form to the leaf stalk (petiole) in dicot leaves will be referred to as a petiole in this paper, whilst recognising that it is probably not an exact homologue. Wind and rain on the blade generate combined flexural and torsion loads on the petiole and a question arises as to how the section properties of the petiole deal with this loading. By isolating the shape from the size of the sections through the use of shape factors, the effects of the petiole section shape can be analysed on its own. Thus micro structural and material factors become a separate issue and will be discussed in a later paper. Cross section profiles from seven palm petioles are modelled, independent of their sizes, in order to calculate and plot the flexural and torsional coupling efficiencies for comparison with other plants and typical engineering cross sections.
• Source

  Available from: cnrs.fr

  Article: Heat and mass transfer in air-fed pressurised suits

  K Tesch, M W Collins, T G Karayiannis, M A Atherton, P Edwards
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  ABSTRACT: Air-fed pressurised suits are used to protect workers against contamination and hazardous environments. The specic application here is the necessity for regular clean-up maintenance within the torus chamber of fusion reactors. The current design of suiting has been developed empirically. It is, therefore, very desirable to formulate a thermofluids model, which will be able to define optimum designs and operating parameters. Two factors indicate that the modelling should be as comprehensive as possible. Firstly, the overall thermofluids problem is three-dimensional and includes mass as well as heat transfer. The fluid field is complex, bounded on one side by the human body and on the other by what may be distensible, porous and multi-layer clothing. In this paper, we report firstly the modelling necessary for the additional mass and heat transport processes. This involves the use of Fick's and Fourier's laws and conjugate heat transfer. The results of an initial validation study are presented. Temperatures at the outlet of the suits were obtained experimentally and compared with those predicted by the overall CFD model. Realistic three-dimensional geometries were used for the suit and human body. Calculations were for turbulent flow with single- and two-component (species) models.
• Source

  Available from: Ashraf Khir

  Article: Multi-scale interaction of flow and the artery wall

  I Halliday, S V Lishchuk, M A Atherton, C Care, M W Collins, D Evans, P C Evans, D R Hose, A Khir, R Krams, P Lawford, V Ridger, Y Ventikos, D C Walker, P N Watton
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  ABSTRACT: We discuss, from the perspective of basic science, the physical and biological processes which underlie atherosclerotic (plaque) initiation at the vascular endothelium, identifying their widely separated spatial and temporal scales which participate. We draw on current, related models of vessel wall evolution, paying particular attention to the role of flow, and proceed to propose, then validate (in practical, qualitative terms, at least) a multiply coupled, multi-scale modeling strategy, which, eventually, aims at a quantitative, patient-specific understanding of the coupling between the flow and the endothelial state.