Thesis (Ph. D.)--University of Iowa, 2007. / Supervisor: Shaoping Xiao.. Includes bibliographical references (leaves 174-182).

Atmospheric mixing is a problem of exceptional importance and difficult to study. The anelastic approximation is the accepted fluid system governing the atmosphere over large vertical scales (about 8 km). The anelastic equations, unlike the Navier-Stokes equations, incorporate a nontrivial spatial divergence constraint on the velocity field. This yields a weakly compressible fluid flow. The basis of this study is to use numerical analysis to explore the effects of weak compressibility in the evolution of fluid governed by the anelastic equations, and the effects of incompressibility governed by the Navier-Stokes equation. The analysis then goes on to investigate the difference between three different initial conditions. Within each initial condition different density profiles are observed while varying parameters are investigated. Numerical results show that comparisons of incompressible Navier-Stokes equations to the anelastic fluid flow equations do not produce similar results. The weakly compressible flow creates a mixing barrier, stopping vertical fluid exchange. The perturbed middle region / US Navy (USN) author

This thesis describes an investigation by computer simulation of the performance of two semiconductor device types at the heart of optical high speed data communications, namely the PIN photodiode and the electroabsorption modulator. Both device types operate by light absorption and are therefore likely to have similar factors that limit their performance at high speed. In order to have high speed detection, the PIN photodiode has been investigated through varying the materials, and used a photodiode structure to improve its bandwidth. If output signals beyond the 3dB frequency limit can be well detected by the photodiode, then significant improvements in the detection speed can be achieved. This possibility is a motivation of this thesis. In this study the InP /InGaAs/InP PIN photodiode is chosen because the light at 1.55 urn wavelength can be absorbed by InGaAs. At 1.55J.lm, the fibre is on low dispersion and low loss. A numerical model of a PIN photodiode has been written in C. Comprehensive modelling ofthe PIN photodiode requires a self-consistent solution of the Poisson's equation for calculating the electrostatic potential and the continuity equations for the electron and hole currents. The PIN photo diode model has included the therm ionic current over the hetero-junction, drift current and diffusion current that other models often ignore. After completing an extensive study of the large signal performance of PIN photodiodes at data rates much higher than the conventional 3dB bandwidth, the model was extended to investigate InP/InGaAsP/lnGaAs MQW -EAM under high speed applied bias pulses. The numerical modelling of the MQW-EAM requires a self-consistent solution of the Poisson's equation, the Schrcdinger 's equation and the current continuity equation. The Schrodinger 's equation is for the estimation of carrier concentration in the quantum wells. The MQW-EAM numerical model has applied a special technique for adding the carrier concentration in the quantum wells to the charge density. 11 Large performance has been successfully analysed on PIN photodiode to reveal that optical pulses at repetition frequencies are substantially higher than the conventional 3dB limit can detect (1 ps FWHM and up to 240Gb/s repetition rate) to give photocurrent pulses with an open eye diagram even in the presence of simulated noise, however, these output current pulses tend to spread and merge together sometimes. This tendency can be counteracted to a reasonable extent by using a suitable repetition time, and a large input average power. Similar Gaussian shaped applied bias pulses have also applied to the MQW-EAM, in order to generate fast Gaussian shaped light power, however; the output light pulses spread out nearly 3 times compared with its applied bias pulses under 5ps FWHM and 48Gb/s repetition rate. Thinner l-layer and less quantum wells in the MQW-EAM might be the solution. iii

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by Moshe Dubiner. / Ph.D.

The conventional techniques of manufacturing large-size structures in a very large plate pose severe challenges in making microstructures. In contrast, semiconductor process that employs lithographic processes to form micro scale features is limited in its wafer size. In ordre to modify the defeat of shadow mask. This thesis propose to use TMAH anisotropic wet etching process and 2D- joining technique to fabricate silicon shadow mask. The potential of this technique would be significant for a very large plate beyond a wafer size with microstructures, and provides a new approach with a high replication and potentially low cost. In the numerical analysis, this study uses the finite element software, ANSYS, to simulate shadow mask with different size, material, and temperature displacement situation. The results shows the feasibility of silicon shadow mask used in the thermal evaporation process. It indicates that this design could have smoother pattern and reduce the limitation of Organic Light-Emitting Diode resolution.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 142-156). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Hong Kong, 1989.

Thesis (Ph. D. in Mechanical Engineering)--Naval Postgraduate School, June 2003. / Dissertation supervisor: Ashok Gopinath. Includes bibliographical references (p. 162-164). Also available online.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

published_or_final_version / Physics / Doctoral / Doctor of Philosophy