The complex phenomena underlying mechanical contraction of cardiac cells and their influence in the dynamics of ventricular contraction are extremely important in understanding the overall function of the heart. In this paper we generalize previous contributions on the active strain formulation and propose a new model for the excitation-contraction coupling process. We derive an evolution equation for the active fiber contraction based on configurational forces, which is thermodynamically consistent. Geometrically, we link microscopic and macroscopic deformations giving rise to an orthotropic contraction mechanism that is able to represent physiologically correct thickening of the ventricular wall. A series of numerical tests highlights the importance of considering orthotropic mechanical activation in the heart and illustrates the main features of the proposed model.

Strain and composition distributions within wurtzite InGaN/GaN layers are investigated by high-resolution reciprocal space mapping (RSM). We illustrate the potential of RSM to detect composition and strain gradients independently. This information is extracted from the elongation of broadened reciprocal lattice points (RLP) in asymmetric x-ray reflections. Three InxGa12xN/GaN (nominal x50.25) samples with layer thickness of 60, 120, and 240 nm, were grown in a commercial metal-organic chemical vapor deposition reactor. The RSMs around the (105) reflection show that the strain profile is nonuniform over depth in InGaN. The directions of ''pure'' strain relaxation in the reciprocal space, for a given In content (isocomposition lines), are calculated based on elastic theory. Comparison between these directions and measured distributions of the RLP shows that the relaxation process does not follow a specific isocomposition line. The In mole fraction (x) increases as the films relax. At the start of growth all the films have x;0.2 and are coherent to GaN. As they relax, x progressively increases towards the nominal value (0.25). Compositional gradients along the growth direction extracted from the RSM analysis are confirmed by complementary Rutherford backscattering measurements

Abstract. This review is devoted to recent developments in blood flow modelling. It begins with the discussion of blood rheology and its non-Newtonian properties. After that we will present some modelling methods where blood is considered as a heterogeneous fluid composed of plasma and blood cells. Namely, we will describe the method of Dissipative Particle Dynamics and will present some results of blood flow modelling. The last part of this paper deals with onedimensional global models of blood circulation. We will explain the main ideas of this approach and will present some examples of its application.

The process of platelet activation and blood coagulation is quite complex and not yet completely understood. Recently, a phenomenological meaningful model of blood coagulation and clot formation in flowing blood that extends existing models to integrate biochemical, physiological and rheological factors, has been developed. The aim of this paper is to present results from a computational study of a simplified version of this coupled fluid-biochemistry model. A generalized Newtonian model with shearthinning viscosity has been adopted to describe the flow of blood. To simulate the biochemical changes and transport of various enzymes, proteins and platelets involved in the coagulation process, a set of coupled advection-diffusion -reaction equations is used. Three-dimensional numerical simulations are carried out for the whole model in a straight vessel with circular cross-section, using a finite volume semi-discretization in space, on structured grids, and a multistage scheme for time integration. Clot formation and growth are investigated in the vicinity of an injured region of the vessel wall. These are preliminary results aimed at showing the validation of the model and of the numerical code.

In this work, we investigate structural and optical properties of metalorganic chemical vapor deposition grown wurtzite InxGa1−xN/GaN epitaxial layers with thicknesses that are close to the critical layer thickness (CLT) for strain relaxation. CLT for InxGa1−xN/GaN structures was calculated as a function of the InN content, x, using the energy balance model proposed by People and Bean [Appl. Phys. Lett. 47, 322 (1985)]. Experimentally determined CLT are in good agreement with these calculations. The occurrence of discontinuous strain relaxation (DSR), when the CLT is exceeded, is revealed in the case of a 120 nm thick In0.19Ga0.89N layer by x-ray reciprocal space mapping of an asymmetrical reflection. The effect of DSR on the luminescence of this layer is clear: The luminescence spectrum shows two peaks centered at ∼2.50 and ∼2.67 eV, respectively. These two components of the luminescence of the sample originate in regions of different strain, as discriminated by depth-resolving cathodoluminescence spectroscopy. DSR leads directly to the emergence of the second, lower-energy, peak. Based on this experimental evidence, it is argued that the appearance of luminescence doublets in InGaN is not evidence of “quantum dotlike In-rich” or “phase separated” regions, as commonly proposed

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