J J Beech-Brandt

The University of Edinburgh, Edinburgh, SCT, United Kingdom

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Publications (9)6.21 Total impact

  • M X Li, J J Beech-Brandt, L R John, P R Hoskins, W J Easson
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    ABSTRACT: Hemodynamics factors and biomechanical forces play key roles in atherogenesis, plaque development and final rupture. In this paper, we investigated the flow field and stress field for different degrees of stenoses under physiological conditions. Disease is modelled as axisymmetric cosine shape stenoses with varying diameter reductions of 30%, 50% and 70%, respectively. A simulation model which incorporates fluid-structure interaction, a turbulence model and realistic boundary conditions has been developed. The results show that wall motion is constrained at the throat by 60% for the 30% stenosis and 85% for the 50% stenosis; while for the 70% stenosis, wall motion at the throat is negligible through the whole cycle. Peak velocity at the throat varies from 1.47 m/s in the 30% stenosis to 3.2m/s in the 70% stenosis against a value of 0.78 m/s in healthy arteries. Peak wall shear stress values greater than 100 Pa were found for > or =50% stenoses, which in vivo could lead to endothelial stripping. Maximum circumferential stress was found at the shoulders of plaques. The results from this investigation suggest that severe stenoses inhibit wall motion, resulting in higher blood velocities and higher peak wall shear stress, and localization of hoop stress. These factors may contribute to further development and rupture of plaques.
    Journal of Biomechanics 01/2007; 40(16):3715-24. · 2.72 Impact Factor
  • Journal of Biomechanics - J BIOMECH. 01/2006; 39.
  • Journal of Biomechanics - J BIOMECH. 01/2006; 39.
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    ABSTRACT: A method for segmentation of arteries in ultrasound B-mode images using a modified balloon model is presented. The external force which pulls the contour to the arterial boundary is the combination of the gradient and the second order derivative of the image. For 3D segmentation the contour of the first slice is found, and this is used as the initial position for the next slice. As the initial position of the contour may be outside the artery, the pressure term is decided by comparing the feature of texture inside and outside of the contour, allowing the contour to expand or shrink. The model has been tested on 55 images from carotid arteries. The 'gold standard' boundary drawn by a radiologist and the segmented boundary showed an average difference of 0.40±0.30mm. 3D data was obtained using an anatomically correct carotid bifurcation flow phantom and gridded ready for CFD.
    Biomedical Imaging: Nano to Macro, 2004. IEEE International Symposium on; 05/2004
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    ABSTRACT: A 3D Ultrasound (US) phantom scanning device has been developed to provide calibration data for image processing and computational fluid dynamics (CFD) as part of a study into the biomechanical status of diseased arteries in vivo. The cartesian scanning system moves a conventional US probe from a Philips HDI5000 US scanner over the upper surface of the phantom. The device can scan phantoms of up to 150 mm long and 75 mm wide. The transducer can be rotated about two axes and translated in one axis manually. X and Y planar movements are made automatically. Control is provided by a labVIEW based control program and a Parker L25i stepper motor driver system. scalar and rotary positional accuracies are ±50μm and ±0.1° respectively.
    Engineering in Medicine and Biology Society, 2003. Proceedings of the 25th Annual International Conference of the IEEE; 10/2003
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    J J Beech-Brandt, N F Smyth
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    ABSTRACT: The effect of fiber loss, amplification, and sliding-frequency filters on the evolution of optical pulses in nonlinear optical fibers is considered, this evolution being governed by a perturbed nonlinear Schrödinger (NLS) equation. Approximate ordinary differential equations (ODE's) governing the pulse evolution are obtained using conservation and moment equations for the perturbed NLS equation together with a trial function incorporating a solitonlike pulse with independently varying amplitude and width. In addition, the trial function incorporates the interaction between the pulse and the dispersive radiation shed as the pulse evolves. This interaction must be included in order to obtain approximate ODE's whose solutions are in good agreement with full numerical solutions of the governing perturbed NLS equation. The solutions of the approximate ODE's are compared with full numerical solutions of the perturbed NLS equation and very good agreement is found.
    Physical Review E 06/2001; 63(5 Pt 2):056604. · 2.31 Impact Factor
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    W. Gawronski, J.J. Beech-Brandt, H.G. Ahlstrom Jr, E. Maneri
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    ABSTRACT: Measurements at the drives of the NASA Deep Space Network (DSN) antennas indicated that the small gap between gear teeth was causing backlash at the gearboxes and elevation bullgear. Left uncorrected, backlash will deteriorate the antenna's pointing precision. At DSN, the backlash was eliminated by implementing two identical drives that impose two nonidentical torques (a.k.a. torque bias, or counter-torque). The difference between these two torques depends on the antenna load, and is shaped by the drive's electronic circuits. The paper explains the shaping principles of the circuit, and shows how the circuits can be modified to improve the antenna dynamics under external disturbances
    IEEE Antennas and Propagation Magazine 01/2001; · 1.18 Impact Factor
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    K H Fraser, P R Hoskins, W J Easson, J J Beech-Brandt, M Li
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    Jason J. (Jason James) Beech-Brandt
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    ABSTRACT: Thesis (Ph. D.)--University of Edinburgh, 2002.