A simulator for the electro-chemical dynamics of the human cardiac cell
ABSTRACT A simulator of the ionic dynamics in the human cardiomyocyte (E-C coupling process) is developed in this work using Matlab® v 6.5. It contains three different mathematical models, namely the models by Tang and Othmer, Luo and Rudy and Roche et al. Its user-friendly interface allows the comparison between the three models, the modification of the model parameters in correspondence with different cellular elements, and hence the testing of the sensibility of the E-C process to drugs and inhibitors. The simulator also features a graphics builder for the visualization of the results, and facilities to export data to other formats such as Excel®, or import experimental data from files. The simulator is compiled in a binary executable program and therefore is fully transportable.
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ABSTRACT: We consider $2d$ sigma models with a $D=2+N$ - dimensional Minkowski signature target space metric having a covariantly constant null Killing vector. These models are UV finite. The $2+N$-dimensional target space metric can be explicitly determined for a class of supersymmetric sigma models with $N$-dimensional `transverse' part of the target space being homogeneous K\"ahler. The corresponding `transverse' sub-theory is an $n=2$ supersymmetric sigma model with the exact $\gb$-function coinciding with its one-loop expression. For example, the finite $D=4$ model has $O(3)$ supersymmetric sigma model as its `transverse' part. Moreover, there exists a non-trivial dilaton field such that the Weyl invariance conditions are also satisfied, i.e. the resulting models correspond to string vacua. Generic solutions are represented in terms of the RG flow in `transverse' theory. We suggest a possible application of the constructed Weyl invariant sigma models to quantisation of $2d$ gravity. They may be interpreted as `effective actions' of the quantum $2d$ dilaton gravity coupled to a (non-conformal) $N$-dimensional `matter' theory. The conformal factor of the $2d$ metric and $2d$ `dilaton' are identified with the light cone coordinates of the $2+N$ - dimensional sigma model. Comment: 24 pages, harvmac, Imperial/TP/92-93/7Physical review D: Particles and fields 11/1992;
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ABSTRACT: We present a maximally supersymmetric IIB string background. The geometry is that of a conformally flat lorentzian symmetric space G/K with solvable G, with a homogeneous five-form flux. We give the explicit supergravity solution, compute the isometries, the 32 Killing spinors, and the symmetry superalgebra, and then discuss T-duality and the relation to M-theory. Comment: 17 pages10/2001;
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ABSTRACT: The ryanodine-sensitive calcium channels are pivotal to signal transduction and cell function in many cell types, including cardiac myocytes. In this paper a kinetic model is proposed for these channels. In the model there are two Ca regulatory sites on the channel protein, one positive and the other negative. Cytoplasmic Ca binds to these regulatory sites independently It is assumed that the binding of Ca to the positive site is a much faster process than binding to the negative site. At steady state, the channel opening as a function of the Ca concentration is a bell-shaped curve. The model predicts the adaptation of channels to constant Ca stimulus. When this model is applied to cardiac myocytes, it predicts excitability with respect to Ca perturbations, smoothly graded responses, and Ca oscillations in certain pathological circumstances. In a spatially distributed system, traveling Ca waves in individual myocytes exist under certain conditions. This model can also be applied to other systems where the ryanodine-sensitive channels have been identified.Biophysical Journal 01/1995; 67(6):2223-35. · 3.67 Impact Factor