Structural studies of alkali aluminosilicate glasses using advanced scattering, resonance and computational techniques

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Development of a model for high precursor conversion efficiency pulsed-pressure chemical vapor deposition (PP-CVD) processing

A model of the movement of precursor particles in the unsteady Pulsed-Pressure Chemical Vapour Deposition (PP-CVD) process is developed to study the high conversion efficiencies observed experimentally in this process. Verification of the modelling procedures was conducted through a study of velocity persistence in an equilibrium gas and through Direct Simulation Monte Carlo (DSMC) simulations of unsteady self-diffusion processes. The model results demonstrate that in the PP-CVD process the arrival time for precursor particles at the deposition surface is much less than the reactor pump-down time, resulting in high precursor conversion efficiencies. Higher conversion efficiency was found to correlate with smaller size solvent molecules and moderate reactor peak pressure

Application of a meta-analysis of aortic geometry to the generation of a compliant phantom for use in particle image velocimetry experimentation

The evolution of pressure-flow geometry in the aortic arch is increasingly understood as a key element in the treatment of hemodynamic dysfunction in patients. However, little is known about the properties of the flow across the aortic geometry and thus the sensitivity of sensor placement is also unknown. Compliant models of the aortic path can be built to allow techniques such as particle image velocimetry to measure the velocity fields. This paper presents the justification and production methodology used to generate a compliant model of the aortic arch that represents the geometry and compliance of typical hemodynamics patients. The information from twenty papers was synthesized to generate a single model of the aortic arch. The model incorporates the three branching arteries at an apex of a tapering aortic path experimental that has been manufactured as a flexible thin-walled silicon model. Calculations were undertaken to ensure that the model matches the in vivo compliance of the arteries. The experimental setup uses the compliant silicone model of the aorta with variable flow pump to mimic the cardiac cycle, and a variable extramural pressure to mimic changes in intrathoracic pressure. This research was necessary for the development of an accurate experimental setup that would enable results that are immediately applicable to the research of cardiovascular therapy optimization

Implementation of Unsteady Sampling Procedures for the Parallel Direct Simulation Monte Carlo Method

accepted for publication 7th March 2008 JCOMP-D-07-00498R1An unsteady sampling routine for a general parallel Direct Simulation Monte Carlo method called PDSC is introduced, allowing the simulation of time-dependent flow problems in the near continuum range. A post-processing procedure called DSMC Rapid Ensemble Averaging Method (DREAM) is developed to improve the statistical scatter in the results while minimising both memory and simulation time. This method builds an ensemble average of repeated runs over small number of sampling intervals prior to the sampling point of interest by restarting the flow using either a Maxwellian distribution based on macroscopic properties for near equilibrium flows (DREAM-I) or output instantaneous particle data obtained by the original unsteady sampling of PDSC for strongly non-equilibrium flows (DREAM-II). The method is validated by simulating shock tube flow and the development of simple Couette flow. Unsteady PDSC is found to accurately predict the flow field in both cases with significantly reduced run-times over single processor code and DREAM greatly reduces the statistical scatter in the results while maintaining accurate particle velocity distributions. Simulations are then conducted of two applications involving the interaction of shocks over wedges. The results of these simulations are compared to experimental data and simulations from the literature where there these are available. In general it was found that ten ensembled runs of DREAM processing could reduce the statistical uncertainty in the raw PDSC data by 2.5-3.3 times, based on the limited number of cases in the present study

Evidence for the compensated continuous random network model for spodumene glass and analogues

We have combined X-ray and neutron scattering with solid state nuclear magnetic resonance (NMR) measurements on glasses of the spodumene and analogous compositions. These glasses LiAlSi2O6, NaAlSiO6 and KAlSi2O6 are fully compensated i.e. contain equal quantities of alkali and aluminium. Q-space and R-space representations for each probe suggest considerable similarity with the structure of silica and point to the crystalline analogue of P-spodumene, which has a stuffed quartz structure. Preliminary Reverse Monte Carlo (RMC) simulations have been made starting from a fully polymerised silica network model. Solid state Magic Angle Spinning NMR reveals that all aluminium retains tetrahedral coordination. This is indicative of fully compensated continuous random network (CCRN) structures for each glass. The chemical shift of Na-23 in NaAlSi2O6 glass indicates that sodium is associated with (AlO4)(-) tetrahedra. At the same time nearest neighbour oxygen distances from neutron scattering increase with size of alkali, suggesting reduction in charge transfer with alkali size together with the possibility of alkali clustering