Computational and experimental modeling of a univentricular circulation with systemic-topulmonary shunt and aortic coarctation.

Circulation in a univentricular physiology, palliated with a systemic-to-pulmonary shunt, is highly dependent on the hemodynamic behavior of the shunt and presence of an aortic coarctation (AC). Both local (shunt and AC) and peripheral (pulmonary and systemic, arranged in parallel) impedances need to be properly described to evaluate this unique circulation. One approach is based on in-vitro experiments, testing a threedimensional (3D) phantom in a mock circulatory system. Similarly, this may be achieved in-silico, coupling a 3D model to a lumped parameter network (LPN), requiring substantial computational cost. In this study the results obtained by applying the two methodologies are compared, enabling a mutual validation when matching each other, and using their differences to better understand single-ventricle hemodynamics. A patient-specific aortic arch model with AC and proximal shunt anastomosis was inserted into a mock loop with several resistive and compliant elements representing the downstream circulation. Pressures and flows were measured during pulsatile flow. A computational analogue was developed, coupling a 3D model to a LPN, and a pulsatile simulation with the same boundary conditions as in-vitro was performed. Comparison of the experimentally measured hemodynamic variables with those calculated in-silico suggested that typical in-vitro resistive components should be modeled as non-linear terms, although they do not reproduce the linear behavior of peripheral vascular resistances in-vivo. Moreover, pipe connections are likely to give a non-negligible contribution to the resistances downstream the 3D phantom. Computational modeling of complex hemodynamics is an important tool that can improve the understanding of invitro experiments. At the same time, validating the computational model against experimental data can result in a more flexible tool for further investigating complex hemodynamics

A grinding-based manufacturing method for silicon wafers: decomposition analysis of wafer surfaces

It is difficult for the lapping-based manufacturing method currently used to manufacture the majority of silicon wafers to meet the ever-increasing demand for flatter wafers at lower costs. A grinding-based manufacturing method for silicon wafers has been investigated. It has been demonstrated that the site flatness on the ground wafers (except for a few sites at the wafer center) could meet the stringent specifications for future silicon wafers. The generation mechanisms of the dimples and bumps in the central areas on ground wafers have also been studied. This paper reports another study on the grinding-based method, aiming to reduce the cost of chemical-mechanical polishing – the final material removal process in manufacturing of silicon wafers. Using design of experiments, investigations were carried out to understand the influences of grinding process variables on the peak-to-valley values of the polished wafer surfaces. It was found that the peak-to-valley values over the entire wafer surfaces did not show any relationship with grinding process variables. However, after analyzing the surface profiles by decomposing them into different frequencies, it was observed that there is a correlation between grinding process variables and certain surface feature components. Based on this finding, it is recommended to optimize the grinding process variables by minimizing the peak-to-valley values for each surface feature component, one at a time. This methodology has not been published for wafer grinding and is of practical use to the wafer industry

Particle image velocimetry in the investigation of flow past artificial heart valves

10.1007/BF02368237Annals of Biomedical Engineering223307-318ABME