Modern seismic data acquisition and processing methods now enable scientists to extract information on both the stratigraphy and the physical properties of subsurface rocks. Laboratory acoustic measurementsa llow the physical conditions to be precisely measured and controlled. In the present study, P- and S-wave velocities (Vs, VS) and attenuations (1000/Qp, 1000/Qs) were measured in a range of sandstones using the ultrasonic pulse-echo technique, at effective pressures of 5 MPa to 60 MPa. The measurement accuracy is ±0.3 % for velocity and ±0.1 dB/cm for attenuation using this method. Velocities and quality factors( Q) fall with decreasinge ffectivep ressure,a nd the relationships are described by the empirical equationsV =A+KP-B C71' and Q=A-B e7DP , where P is the effective pressure and A, K, B, and D are the regression coefficients (D=0.115±0.016 and 0.048±0.010 for V and Q, respectively). Velocity and Q can therefore be extrapolated to pressures beyond the experimental range. The Biot, Gassmann, and unrelaxed pore-fluid models of seismic wave propagation in porous media fail to explain the pressure-dependenceo f the velocities. The difference between the experimental and Biot model predictions of the rate of change in P-wave velocity with pore fluid salinity (dVýdM) increases with percentage clay content (C) of the rock at the approximately linear rate of 0.95 m/s/mol. There is no clear relationship for dVs/dM. In clean sandstones there is a close agreement between the experimental results and Biot model predictions for dVP/dM, but the agreement breaks down when C>5%. This suggests that changes in the pore-fluid salinity alter the frame bulk and shear moduli of sandstones. Attenuation is generally independent of pore-fluid salinity. Attenuation and velocity are often strongly dependent on the degree of pore-fluid saturation. A study of nine samples shows that 1000/Qp exhibits a resonance peak at midrange saturations (SW av 30 % to SW = 70 %) in most samples, and 1000/Qs shows similar behaviour in several of these. For porosities greater than 13%, the normalised amplitudes of the peaks in P-wave and bulk attenuation are correlated to porosity; the latter increases at a linear rate of 0.98 per percentage increase in porosity. These data suggest that attenuation reaches a maximum when the gas/water mixture is neither too compressible nor too incompressible. The Biot/squirt (BISQ) theory inadequately models the saturation dependence of 1000/Qp and Vp in a sample at low confining pressure. Vp falls with decreasing saturation between SW =100 % to SW - 50 %; below SW = 50 %, the behaviour of Vp is dependent on the confining pressure. Vs generally increases with decreasing saturation over the entire saturation range in all samples. The unrelaxed pore-fluid model of Mavko and Nolen-Hoeksema (1994) describes the Vp data reasonably well in most samples using low wetting fractions (< 15 %), which indicates that the pore fluid is unrelaxed at both the grain and sample scales. The wetting pore fluid becomes unrelaxed at high frequencies and/or low permeabilities. The V. data are poorly described by the model, possibly due to matrix softening by the wetting fluid. The experimental data have indicated significant shortcomings in the mathematical models of seismic wave propagation in reservoir rocks. The data highlight important aspects of wave propagation that must be addressed in revised theories.

This thesis examines a single-stage barrel-less electromagnetic induction launcher, developed from an arrangement used previously for very high speed, low projectile mass accelerators. The projectile is placed on top of the launch coil, rather than inside the coil, as is more usually the case in both single and multi-stage launchers of this type. The examination is undertaken both theoretically and experimentally, with extensive experimental results being used to test the validity of the theoretical techniques used. The theoretical examination of the launcher is based on two distinct mathematical models, with results provided by the two approaches being compared. The first model uses a 2D electromagnetic finite-element approach, and does not include projectile motion or thermal effects. It is used to establish whether an analysis technique which does not take into account the projectile dynamics is a valid design tool for a single-stage launcher. The second model employs a coupled-circuit approach to take into account both projectile motion and thermal effects, and is used to obtain an accurate estimate of the overall launcher performance. With the aid of the two models the effects of varying many different launcher parameters are examined, including the size and shape of the stator coil and the size, shape and composition of the projectile. The launcher investigation could be based on a number of criteria but here it is primarily based on two; the highest average velocity over a given distance and the shortest time required to travel a given distance from the initial stationary position.

A new method has been developed to incorporate particles with internal structure into the framework of the Variance Reduction method [17] for solving the discrete velocity Boltzmann Equation. Internal structure in the present context refers to physical phenomena like rotation and vibration of molecules consisting of two or more atoms. A gas in equilibrium has all modes of internal energy at the same temperature as the translational temperature. If the gas is in a non-equilibrium state, translational temperature and internal temperatures tend to proceed towards an equilibrium state during equilibration, but they all do so at different relaxation rates. In this thesis, rotational energy of a distribution of molecules is modeled as a single value at a point in a discrete velocity space; this represents the average rotational energy of molecules at that specific velocity. Inelastic collisions are the sole mechanism of translational and rotational energy exchange, and are governed by a modified Landau-Teller equation. The method is tested for heat bath simulations, or homogeneous relaxations, and one dimensional shock problems. Homogeneous relaxations demonstrate that the rotational and translational temperatures equilibrate to the correct final temperature, which can be predicted by conservation of energy. Moreover, the rates of relaxation agree with the direct simulation Monte Carlo (DSMC) method with internal energy for the same input parameters. Using a fourth order method for convecting mass along with its corresponding internal energy, a one dimensional Mach 1.71 normal shock is simulated. Once the translational and rotational temperatures equilibrate downstream, the temperature, density and velocity, predicted by the Rankine-Hugoniot conditions, are obtained to within an error of 0.5%. The result is compared to a normal shock with the same upstream flow properties generated by the DSMC method. Internal vibrational energy and a method to use Larsen Borgnakke statistical sampling for inelastic collisions is formulated in this text and prepared in the code, but remains to be tested. / text

The factors that influence gait velocity post-stroke are not clearly understood. This thesis sought to uncover the factors associated with gait velocity, particularly those related to maximum velocity. The first of two studies investigated the associations between physical factors and preferred and maximum gait velocity. Analysis revealed that individuals with stroke were able to increase gait velocity from preferred and that this increase, along with the achieved velocity, were related to functional balance. The second study characterized the strategy individuals used to increase gait velocity, and compared between the stroke and healthy population. It also probed the relationships between cadence, step length, strategy, and post-stroke impairment. This study demonstrated that individuals with stroke rely more on cadence than step length to increase gait velocity. These results revealed the role of balance control on limiting gait velocity and the need for specific measures of impairment in research to direct clinical practice.

The factors that influence gait velocity post-stroke are not clearly understood. This thesis sought to uncover the factors associated with gait velocity, particularly those related to maximum velocity. The first of two studies investigated the associations between physical factors and preferred and maximum gait velocity. Analysis revealed that individuals with stroke were able to increase gait velocity from preferred and that this increase, along with the achieved velocity, were related to functional balance. The second study characterized the strategy individuals used to increase gait velocity, and compared between the stroke and healthy population. It also probed the relationships between cadence, step length, strategy, and post-stroke impairment. This study demonstrated that individuals with stroke rely more on cadence than step length to increase gait velocity. These results revealed the role of balance control on limiting gait velocity and the need for specific measures of impairment in research to direct clinical practice.

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This work describes the design and development of a velocity map imaging apparatus that will be used to study the laser initiated photochemistry of water ice and other condensed phases. Experiments on methanol ice photolysis using a different apparatus at Kyoto University are described to give an appreciation of the photochemistry and the experimental parameters. Water deposited on a surface at temperatures below 140 K can form an amorphous solid. Amorphous solid water (ASW), which does not exhibit properties of a well-defined phase, is the most profuse phase of water found in astrophysical environments. Chemical characteristics of ASW - in particular its photochemistry - and the physical characteristics closely associated with the structure such as density and surface are reviewed. The correlations between the morphology and the growth conditions of ASW are also described. Methanol is also known to be a component on the icy mantle on interstellar grains. The effects of irradiating amorphous solid methanol by UV photons are discussed. Experiments at Kyoto University have been performed to detect state-selectively nascent OH and CH3 photofragments following photolysis at 157 nm. Information on the velocity distributions was obtained from time-of-flight measurements. At Queen’s University Velocity Map Imaging combined with resonance enhance multiphoton ionization (REMPI) will be used for quantum state-selective detection of the nascent photoproducts and their velocity distribution. To help automate the experiments “virtual instruments” have been created for the hardware components of the experiment using LabVIEW 8.6. The ion optics of the velocity map imaging spectrometer under construction at Queen’s have been characterized using the SIMION 7.0 software package, and the anticipated experimental image of nascent photoproducts has been simulated by a Monte-Carlo-type algorithm. / Thesis (Master, Chemistry) -- Queen's University, 2011-03-03 15:18:04.543

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