Jerry Gao, Peng Du, Rosalind Archer, Greg O'Grady, Simon J. Gibbons, Gianrico Farrugia, Leo K. Cheng, Andrew J. PullanIEEE Trans. Biomed. Engineering. 01/2011; 58:3451-3455.
Article: Radius-dependent decline of performance in isolated cardiac muscle does not reflect inadequacy of diffusive oxygen supply.June-Chiew Han, Andrew J Taberner, Robert S Kirton, Poul M F Nielsen, Rosalind Archer, Nari Kim, Denis S Loiselle[show abstract] [hide abstract]
ABSTRACT: The study of cardiac energetics commonly involves the use of isolated muscle preparations (papillary muscles or trabeculae carneae). Their contractile performance has been observed to vary inversely with thickness. This inverse dependence has been attributed, almost without exception, to inadequate diffusion of oxygen into the centers of muscles of large diameter. It is thus commonly hypothesized that the radius-dependent diminution of performance reflects the development of an anoxic core. We tested this hypothesis theoretically by solving a modification of the diffusion equation, in which the rate of oxygen consumption is a sigmoidal function of the partial pressure of oxygen. The model demonstrates that sufficiently thick muscles, operating at sufficiently high rates of oxygen demand or sufficiently low ambient partial pressures of oxygen, will indeed show diminished energetic performance, whether indirectly indexed as stress (force per cross-sectional area) development or as the rate of heat production. However, such simulated behavior requires the adoption of extreme parameter values, often differing by an order of magnitude from their experimental equivalents. We thus conclude that the radius-dependent diminution of muscle performance in vitro cannot be attributed entirely to an insufficient supply of oxygen via diffusion.AJP Heart and Circulatory Physiology 01/2011; 300(4):H1222-36. · 3.71 Impact Factor
Rosalind A. Archer[show abstract] [hide abstract]
ABSTRACT: To use pressure transient test data in computerised methods for integrated reservoir charcterisation numerical simulations of the well tests are typically required. Numerical artifacts occurring in the simulation must be avoided as much as possible so that they do not adversely a#ect the reservoir characterisation. This work explores the advantages of a hybrid boundary element method known as the Green element method for modeling pressure transient tests. Boundary element methods are a natural choice for the problem because they are based on Green's functions, which are an established part of well test analysis. The classical boundary element method is limited to single phase flow in homogeneous media. This works presents formulations which give computationally efficient means to handle heterogeneity. The accuracy of the scheme is further enhanced by incorporating singularity programming. Comparisons of the proposed Green element approach to standard finite di#erence simulation show t...06/2000;
Article: Flow Simulation in Heterogeneous Reservoirs using the Dual Reciprocity Boundary Element Method and the Green Element MethodRosalind Archer[show abstract] [hide abstract]
ABSTRACT: Green's functions are established tools for solving petroleum engineering flow problems. Their utility and rigor was extended to arbitrarily shaped reservoirs using the Boundary Element Method (BEM). Traditional BEMs are limited to single-phase flow in homogeneous reservoirs. Earlier authors have developed techniques to handle heterogeneity. These methods are perturbationbased and computation-intensive. The current work adapted the most recent developments in boundary element methods to reservoir engineering problems. The transient pressure (diffusion) and convection-diffusion equations were solved in heterogeneous media using the Dual Reciprocity Boundary Element Method (DRBEM) and the Green Element Method (GEM). Numerical experiments showed that DRBEM is more accurate than a standard finite difference method. However like finite difference methods, DRBEM is subject to spurious oscillation at high Peclet numbers. DRBEM also requires the solution of a dense system of equations. GEM, wh...07/1998;
[show abstract] [hide abstract]
ABSTRACT: This work illustrates the optimization of thermoacoustic systems, while taking into account thermal losses to the surroundings that are typically disregarded. A simple thermoacoustic engine is used as an example for the methodology. Its driving component, the thermoacoustic regenerator (also referred to as the stack), is modeled with a finite element method and its dimensions are varied to find an optimal design with regard to thermal losses. Thermoacoustic phenomena are included by considering acoustic power, and viscous and capacitive losses that are characteristic for the regenerator. The optimization considers four weighted objectives and is conducted with the Nelder–Mead Simplex method. When trying to minimize thermal losses, the presented results show that the regenerator should be designed to be as short as possible. It was found that there is an optimal regenerator diameter for a given length. The results are presented for a variety of materials and weights for each objective.International Journal of Thermal Sciences.