Shear stress and alterations in blood flow within a stenosed artery promote platelet-dependent thrombosis. Using the Folts model of coronary thrombosis, we evaluated morphology, histology, and the hemodynamic properties of the stenosed vessel in 18 animals. The average stenosis created was 58 +/- 8%, with stenosed vessel diameters ranging from 0.084 to 0.159 cm. Histological examination of the stenosed vessel demonstrated that thrombi were composed primarily of platelets and formation occurred 1.0 mm downstream from the apex of the constriction, propagating distally. Peak shear stress occurred just upstream from the apex of the stenosis and varied from 520 to 3,349 dyn/cm2. Only small differences in shear forces were noted when blood viscosity was calculated using Newtonian and non-Newtonian properties. In contrast, shear stress computed for Poiseuille flow with use of the stenosis diameter underestimated the apical shear stress. Blood flow remained laminar within the stenosis with a Reynolds number range of 292-534. Our data indicate that the geometry of the stenosis inflow region must be considered in the evaluation of platelet activation and thrombus formation within a stenosed artery.

AbstractÐStress±strain responses of single and polycrystals of Had®eld steel were modeled using a viscoplastic self-consistent approach. A unique hardening formulation was proposed in the constitutive model incorporating length scales associated with spacing between twin lamellae and grain boundaries. TEM observations lend further support to the length scales incorporated into the constitutive model. Many of the experimental ®ndings were made on " 111 and " 144 crystal orientations deformed in tension, displaying ®ne twin lamellae at small strains in addition to slip in intra-twin regions. A natural outcome of the model was the small deformation activity inside the twinned regions and higher deformations between the twins. The model utilized dislocation density as a state variable and predicted the stress±strain responses and texture evolution in single crystals accurately over a broad range of strains. The responses of polycrystals with three grain sizes (100, 300, and 1000 mm) were also captured closely with the model in addition to the twin volume fraction evolution with increasing deformation. Based on the simulations, it was possible to explain unequivocally the upward curvature in stress±strain curves in the single crystals and in coarse grained polycrystals of Had®eld steel. Overall, the combined experimental and modeling e orts provide a reliable tool to characterize slip±twin interaction in low stacking fault energy f

No abstract

No abstract

An explicit Galerkin/least-squares formulation is introduced for a quasilinear transport equation in field dislocation mechanics (FDM) and applied to the study of the kinematics of dislocation density evolution in the following physical contexts: annihilation of dislocations, expansion of a polygonal dislocation loop and simulation of a Frank–Read source. Stability analysis is carried out for the corresponding linear one-dimensional (1D) case. The formulation reduces to the Lax–Wendroff finite difference scheme for the 1D equation when equal weighting is used for the Galerkin and least-squares terms and the shape functions are linear. This conditionally stable method leads to a symmetric well-conditioned system of equations with constant coefficients, making it attractive for large-scale problems.It is shown that the transport equation, in the contexts mentioned above simplifies to the Hamilton–Jacobi equations governing geometrical optics and level-set methods. The weak solutions to these equations are not unique, and the numerical method is able to capture solutions corresponding to shock as well as rarefraction waves by appropriate algorithmic modifications.