A numerical panel method based on the potential flow theory has been refined and applied to the simulations of steady and unsteady cavitating flows inside water-jet pumps. The potential flow inside the water-jet is solved simultaneously in order to take the interaction of all geometries (blades, hub and casing) into account. The integral equation and boundary conditions for the water-jet problem are formulated and solved by distributing constant dipoles and sources on blades, hub and shroud surfaces, and constant dipoles in the trailing wake sheets behind the rotor (or stator) blades. The interaction between the rotor and stator is carried out based on an iterative procedure by considering the circumferentially averaged velocities induced on each one by the other. The present numerical scheme is coupled with a 2-D axisymmetric version of the Reynolds Averaged Navier-Stokes (RANS) solver to evaluate the pressure rise on the shroud and simulate viscous flow fields inside the pump. A tip gap model based on a 2-D orifice equation derived from Bernoulli’s obstruction theory is implemented in the present method to analyze the clearance effect between the blade tip and the shroud inner wall in a global sense. The reduction of the flow from losses in the orifice can be defined in terms of an empirically determined discharge coefficient (CQ) representing the relationship between the flow rate and the pressure difference across the gap because of the viscous effect in the tip gap region. The simulations of the rotor/stator interaction, the prediction of partial and super cavitation on the rotor blade and their effects on the hydrodynamic performance including the thrust/torque breakdown of a water-jet pump are presented. The predicted results, including the power coefficient (P*), head coefficient (H*), pump efficiency (η), thrust and torque coefficients (KT and KQ), as well as the cavity patterns are compared and validated against the experimental data from a series of on the ONR AxWJ-2 pump at NSWCCD. / text

Current research into L2 motivation addresses all aspects of language learning. However, there is a paucity of research into students’ L2 motivations to improve their speaking skills. Specifically, research on pronunciation issues is very rare. This report sheds light on factors that relate to pronunciation issues and their facilitating or hindering effects on L2 motivation. It starts by reviewing research that informs about students’ social-psychological and utilitarian motivations to acquire a second language. Interestingly, these general L2 motivations are mostly affected by factors related to students’ pronunciation skills. The second section discusses the negative factors, which have been found to hinder students’ motivations to learn, and in particular to improve their pronunciation. Based on these research findings, the third section of the report offers recommends pronunciation-teaching strategies to motivate and empower students. This report makes a case for Multi-competence that focuses on increased intelligibility through suprasegmentals and sociopragmatic awareness. / text

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The thesis constitutes a systematic theoretical and experimental investigation into impulse breakdown voltage-time curves of coaxial-cylinder gaps in SF(,6) and a 50% SF(,6) - 50% N(,2) mixture. The breakdown time delay probability is treated as a bivariate distribution in statistical and formative time lags. A method is developed to deduce the marginal breakdown voltage probability curve from statistics of time delay. The experimental work was performed on 2.54/7.0-cm diameter, 60-cm long coaxial-cylinder electrodes using SF(,6) or SF(,6)-N(,2) mixtures at pressures of 0.1 - 0.3 MPa subjected to 0.5/50-(mu)s and 1.2/50-(mu)s impulses of both polarities. The effect of a spherical conducting particle attached to the central electrode of the coaxial-cylinder gap on the voltage-time characteristics is also investigated.

In this thesis, current driven domain-wall motion is studied using atomistic simulations with the exchange coupling modeled by the Heisenberg Hamiltonian under the nearest-neighbor approximation. The investigations may be divided into two parts, each concerned with how different aspects of the systems affect the domain-wall motion. The first part deals with domain-wall width dependence of the velocity in a three dimensional geometry with simple cubic crystal structure and uniaxial anisotropy. Results from this part showed that the velocity has a minor domain-wall width dependence. For a fixed current density, the velocity increased with domain-wall width, though only from 61.5 a/ns to 64.5 a/ns as the domain-wall width was increased from 3 to 25 atoms. The second part of the investigations deals with phenomena involving mixed cubic and uniaxial anisotropy, the non-adiabaticity parameter as well as the geometry of the system. The discussion includes an account of how the spin-transfer and cubic anisotropy torques contribute to the motion for different values of the non-adiabaticity parameter. In comparing a one dimensional atomic chain and a three dimensional system with simple cubic crystal structure, but otherwise with the same material properties, results showed a difference in how the two systems responded to currents. This difference is not accounted for by the micromagnetic theory, and its origin was unable to be determined.

Superconductivity Centennial Conference 2011- EUCAS–ISEC–ICMC (18-23 Sep 2011, The Hague, The Netherlands)

Temporal and wavelet characteristics of initial breakdown pulses are meticulously studied especially during the earliest moment of lightning events. Any possible features during the earliest moment that may exist which lead to either negative cloud-to-ground (CG), positive cloud-to-ground, cloud or isolated breakdown flashes in Sweden are investigated. Moreover, the occurrence of narrow bipolar pulses (NBPs) as part of a CG event that has been recorded from tropical thunderstorms are also included in the investigation. Electric field signatures selected from a collection of waveforms recorded using fast electric field broadband antenna system installed in Uppsala, Sweden and Skudai, South Malaysia are then carefully analyzed in order to observe any similarities or/and differences of their features. Temporal analysis reveals that there are significant distinctions within the first 1 ms among different types of lightning flashes. It is found that a negative CG flash tends to radiate pulses more frequently than other flashes and a cloud flash tends to radiate shorter pulses than other flashes but less frequently when compared to negative CG and isolated breakdown flashes. Perhaps, the ionization process during the earliest moment of negative CG flashes is more rapid than other discharges. Using a wavelet transformation, it can be suggested that the first electric field pulse of both negative CG and cloud flashes experiences a more rapid and extensive ionization process compared to positive CG and isolated breakdown flashes. Further temporal analysis on NBPs found to occur as part of CG flashes show the disparity of the normalized electric field amplitude between the NBPs prior to and after the first return stroke. This indicates that the NBPs intensities were influenced by the return stroke events and they occurred in the same thundercloud. The similarity between the temporal characteristics of NBPs as part of CG flashes and isolated NBPs suggests that their breakdown mechanisms might be similar.

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2007. / Title from Web page (viewed on Mar. 24, 2008). "September 2007." Includes bibliographical references.

Universiẗat, Diss.--Bremen, 2007.

Zugl.: Aachen, Techn. Hochsch., Diss., 2008.