Open Access. Powered by Scholars. Published by Universities.®
- Discipline
- Publication Year
Articles 1 - 30 of 99
Full-Text Articles in Entire DC Network
Aristotle's Account Of Time: A Moderate Realism, Pierre-Luc Boudreault
Aristotle's Account Of Time: A Moderate Realism, Pierre-Luc Boudreault
Electronic Thesis and Dissertation Repository
This dissertation proposes an interpretation of Aristotle’s theory of time as a whole from a study of Physics IV. 10-14. It addresses interpretive issues and objections pertaining to Aristotle’s view about the nature of time, its existence, as well as its unity and universality. In response to these problems, the interpretation of some ancient and medieval commentators – Themistius, Simplicius, Philoponus, Albert the Great and in particular, Thomas Aquinas – is by and large defended against recent interpretations. It is argued that by defining time as “the number of movement with respect to the “before” and “after” (Phys. IV. …
Emergence And Reduction In Science. A Case Study, Alexandru Manafu
Emergence And Reduction In Science. A Case Study, Alexandru Manafu
Electronic Thesis and Dissertation Repository
The past decade or so has witnessed an increase in the number of philosophical discussions about emergence and reduction in science. However, many of these discussions (though not all) remain too abstract and theoretical, and are wanting with respect to concrete examples taken from the sciences. This dissertation studies the topics of reduction and emergence in the context of a case study. I focus on the case of chemistry and investigate how emergentism can help us secure the autonomy of this discipline in relation to the underlying microphysics. I develop an account of emergence (called functional emergence) that is, …
Convective Properties Of Farley-Buneman Waves At High Latitude E-Region, Donglei Chen
Convective Properties Of Farley-Buneman Waves At High Latitude E-Region, Donglei Chen
Digitized Theses
The convective properties of the propagation of electrostatic Farley-Buneman waves in the high-latitude E-region have been studied using fluid theory based on their non-local character. This case is particularly useful for HF radar echoes. A principal objective of this thesis is to develop a new approach to solving the non-local problem of the Farley-Buneman waves in the high latitude E-region, and to explore the convective properties of wave propagation.;We first discussed the traditional treatment of the non-local problem and related approaches to solving such a non-local problem. Based on these, a new formulation of the non-local problem for the Farley-Buneman …
Large And Medium-Scale Dynamics In The Mesosphere And Lower Thermosphere Measured By Mf And Meteor Vhf Radars, Thayananthan Thayaparan
Large And Medium-Scale Dynamics In The Mesosphere And Lower Thermosphere Measured By Mf And Meteor Vhf Radars, Thayananthan Thayaparan
Digitized Theses
This thesis focuses on the experimental investigation of large- and medium-scale dynamics in the 70-100 km height range measured with MF (2.219 MHz) and meteor VHF (40.68 MHz) radar systems located at London (43{dollar}\sp\circ{dollar} N, 81{dollar}\sp\circ{dollar} W) Ontario, Canada. The MF radar uses the spaced antenna method by means of partial reflections to determine the horizontal winds. The VHF radar determines the horizontal wind velocity by means of radio reflections from meteor trails.;The major studies in this thesis include the following: (1) development of a numerical model to simulate the spaced antenna method, (2) validation of both radars, (3) studies …
Quantum Theory Of Spin-Wave Excitations In Ferromagnetic Layered Structures, Linjie Jiang
Quantum Theory Of Spin-Wave Excitations In Ferromagnetic Layered Structures, Linjie Jiang
Digitized Theses
The study of low-dimensional magnetic microstructures has become increasingly active and important because of the recent advances in sample growth techniques and the potential applications of structures to technology. The theoretical study of the spin-wave excitations in these magnetic structures is important to understand many physical properties of these structures. The aim of this thesis is to study the exchange-dominated spin waves in ferromagnetic layered structures, especially those structures with one-dimensional (1D) translational symmetry.;The general method used in this thesis is a quantum-mechanical Green function theory formulated within a microscopic approach. However, a particular matrix diagonalization technique is developed to …
Langevin Simulations Of First-Order Phase Transitions In Fluids And Materials, Yanan Wu
Langevin Simulations Of First-Order Phase Transitions In Fluids And Materials, Yanan Wu
Digitized Theses
In this thesis, we study dynamical aspects associated with (a) phase separation in binary mixtures, which involve their time evolution and time-dependent correlation behaviour, and (b) pattern formation in martensitic transformations. Using a Langevin model, we show for the first time how the predictions of scaling the dimensional arguments for two and three dimensional binary mixtures may be validated numerically within the context of a single model. In particular, we show how domain growth exponents result by an appropriate choice of the crossover lengths in the diffusive, viscous and inertial regimes. We also find that the small-wavenumber-scaling of the structure …
Relativistic Variational Calculations For Helium-Like Systems, Alicja (Alice) Kolakowska
Relativistic Variational Calculations For Helium-Like Systems, Alicja (Alice) Kolakowska
Digitized Theses
Ab initio relativistic variational calculations are performed to obtain the 1{dollar}\sp1{dollar}S{dollar}\sb0{dollar}, 2{dollar}\sp1{dollar}S{dollar}\sb0{dollar}, 2{dollar}\sp1{dollar}P{dollar}\sb0{dollar}, 2{dollar}\sp3{dollar}S{dollar}\sb1{dollar}, 2{dollar}\sp3{dollar}P{dollar}\sb0{dollar}, 2{dollar}\sp3{dollar}P{dollar}\sb1{dollar} and 2{dollar}\sp3{dollar}P{dollar}\sb2{dollar} terms of helium and helium-like argon, krypton, xenon and mercury. The variational approach is formulated for the stationary problem for the Dirac-Coulomb-Breit Hamiltonian. The approximate solutions to the problem are sought in the form of variational expansions in terms of products of normalizable variational one-electron bi-spinors. Then the variational approach based on the minimax formulation of Talman generalized to the two-electron system is applied. The minimax formulation is discussed in the context of the variational approach to the one-electron Dirac-Coulomb problem and …
Using The Quantum Mechanical Path Integral In Quantum Field Theory, Siu Kwan Wong
Using The Quantum Mechanical Path Integral In Quantum Field Theory, Siu Kwan Wong
Digitized Theses
Matrix elements of the form {dollar}\langle x\vert\exp({lcub}-{rcub}iHt)\vert y\rangle{dollar} arise when operator regularization, a symmetry-preserving regulating procedure that avoids explicit occurrence of divergences, is employed to do perturbative calculations in quantum field theory. In recent years, it is shown that this matrix element can be evaluated using a path integral encountered in single particle quantum mechanics. This technique has the advantage of eliminating loop momentum integrals and algebraically complicated vertices in gauge theories. We develop this technique to handle various problems. Our approach is similar to but distinct from the one of Polyakov and Strassler which is related to the string …
Dynamics And Thermodynamics Of The Quasi-Two Dimensional Magnetic Systems, Igor V. Rojdestvenski
Dynamics And Thermodynamics Of The Quasi-Two Dimensional Magnetic Systems, Igor V. Rojdestvenski
Digitized Theses
In recent years a considerable research effort has been put into the understanding of the physical properties of quasi-two-dimensional magnetic systems. Theoretical investigations help to explain many current experimental results. The aim of this thesis is to study dynamic and critical properties of certain quasi-two-dimensional magnetic systems.;In the first part of the thesis (Chapters 2 and 3) the Handscomb Monte-Carlo method is applied to investigate the critical behavior of the S = {dollar}1\over 2{dollar} Heisenberg ferromagnetic film with the number of monolayers L {dollar}\le{dollar} 3. We confirm the renormalization group results for the two-dimensional model for a wide range of …
Compositional Analysis Of Gate Dielectric Films, Hongtao Tang
Compositional Analysis Of Gate Dielectric Films, Hongtao Tang
Digitized Theses
Oxynitride has recently drawn attention as a candidate gate dielectric material for deep sub-micron devices, e.g. MOSFET's. Since the oxide growth rates in pure oxygen are high, efforts to scale down device dimensions with high quality ultrathin ({dollar}<{dollar}100A) SiO{dollar}\sb2{dollar} films are encountering some difficulties. Recently, it has been found that oxynitride films fabricated directly by a N{dollar}\sb2{dollar}O-rapid thermal processing method exhibit improved electrical properties compared to SiO{dollar}\sb2{dollar} films. Structural analysis for such oxynitride films is necessary in order to understand the physical reasons behind the observed improvements.;Nuclear reaction analysis combined with a chemical step-etching method was performed to depth profile nitrogen quantitatively in N{dollar}\sb2{dollar}O-RTP grown oxynitride films. The oxynitride dielectric composition dependence on growth conditions in a rapid thermal processing system was also investigated by nuclear reaction analysis. It is found that most N in the oxynitride films accumulates in a region close to the interface (less than 25 A from the interface in the oxynitride). Both N concentration and film thickness increase with temperature. Furthermore, a UHV initial growth study of oxynitride films on a Si(100) substrate was carried out by nuclear reaction analysis and Auger electron spectroscopy. The results clearly confirm that the nitrogen involvement occurs primarily before an oxynitride film thickness of {dollar}\sim{dollar}25 A is developed, and the subsequent film growth is dominated by oxidation. For the first time, it is found that there is a special growth period at the very beginning during which nitridation (with no simultaneous oxidation) dominates the growth process. It is speculated that the phenomenon results from a competition between reactions of Si with O and N. The dependence of film growth on temperature is such that below 950{dollar}\sp\circ{dollar}C, there is little nitrogen incorporated in the oxide film.
Theory Of Spin Waves In Heisenberg Ferromagnetic And Antiferromagnetic Thin Films With Nonuniaxial Single-Ion Anisotropy, Paula R. Heron
Theory Of Spin Waves In Heisenberg Ferromagnetic And Antiferromagnetic Thin Films With Nonuniaxial Single-Ion Anisotropy, Paula R. Heron
Digitized Theses
This thesis describes the microscopic, quantum mechanical theory of exchange-dominated spin waves in Heisenberg ferromagnetic and antiferromagnetic thin films including the effects of nonuniaxial single-ion anisotropy. The results constitute a generalization of previous theoretical studies on spin waves in thin films with uniaxial anisotropy and in semi-infinite ferromagnets with nonuniaxial anisotropy.;A spin Hamiltonian containing nearest-neighbour exchange terms, Zeeman terms, and single-ion anisotropy terms is used. The films may be asymmetric with respect to surface exchange and anisotropy parameters which are also assured to be perturbed from the bulk values. The results apply both to cases in which the nonuniaxial anisotropy …
Interacting Scalar Fields On 2 + 1-Dimensional Manifolds, George Tsoupros
Interacting Scalar Fields On 2 + 1-Dimensional Manifolds, George Tsoupros
Digitized Theses
The unusually rich topological structure accommodated by three dimensional manifolds and their consequent importance to the exploration of fundamental realistic issues, has recently generated interest in 2+1-dimensional physics. The stated dimensionality offers, as a result, a challenging perspective to the fundamentally important issues of second quantization and renormalization. The present project explores the peculiar implications which this odd dimensionality has for the technique of dimensional regularization in whose context the perturbative evaluation of the renormalization group functions characterizing a renormalizable scalar field theory with self-interacting {dollar}\phi\sp6{dollar} and {dollar}\phi\sp4{dollar} couplings, is subsequently pursued in flat Euclidean space. The analysis is naturally …
The Reduction Of Concentration Values In A Contaminant Cloud In Environmental Flows, William Kenneth Heagy
The Reduction Of Concentration Values In A Contaminant Cloud In Environmental Flows, William Kenneth Heagy
Digitized Theses
This thesis considers the spread of contaminant after the release of a cloud of toxic gas into the atmosphere. A new measure, the Expected Mass Fraction (EMF), presents an improvement over the mean dosage as an indicator of the risk associated with the cloud release. The study shows that the variability of estimates of the EMF should be comparable to that of the dosage, so that reliable evaluation should be possible in many situations. The theory is based on the Chatwin-Sullivan {dollar}\alpha{dollar}-{dollar}\beta{dollar} formulation, which relates the mean concentration to the moments of the probability density function of the concentration. The …
Surface And Interfacial Alloys Of Palladium With Copper(100): Structure, Chemistry, And Kinematics, Timothy Daniel Pope
Surface And Interfacial Alloys Of Palladium With Copper(100): Structure, Chemistry, And Kinematics, Timothy Daniel Pope
Digitized Theses
The interaction between Pd and the Cu(100) surface has been studied by surface science techniques. When Pd is evaporated onto Cu(100) at 110 K, small Pd islands form on the surface. At substrate temperatures above approximately 180 K, mixed Pd-Cu interfacial layers form. For Pd deposition at 300 K, c(2x2) and p4g surface alloy structures form near 0.5 and 1.0 monolayer (ML) Pd coverage respectively. Above one ML, disordered Pd overlayers form. The surface alloy structures are metastable only, since heating irreversibly segregates Cu to the surface.;The chemistry of the Pd and Cu atoms in the interfacial layers is changed …
The Luminosity Function Of The Scorpius-Centaurus Ob Association, Robert William Slawson
The Luminosity Function Of The Scorpius-Centaurus Ob Association, Robert William Slawson
Digitized Theses
The Scorpius-Centaurus OB Association is, at 160 pc, the nearest of all regions where hot, 8-12 M{dollar}\sb\odot{dollar} B stars have formed within the last 10{dollar}\sp7{dollar} yr or so. Despite its relative nearness, the stellar content of intermediate mass hot stars, in the 3-7 M{dollar}\sb\odot{dollar} range, has never been fully explored. The purpose of this thesis is to identify and count those stars in the lower mass range of the B-type stars that are plausible members of the association and to construct the Luminosity Function, LF, of Sco-Cen. This is the distribution by luminosity of the numbers of stars that formed …
Self-Consistent Theory For Magnetic Properties In High-Temperature Superconductors, Ravi Prakash Singh
Self-Consistent Theory For Magnetic Properties In High-Temperature Superconductors, Ravi Prakash Singh
Digitized Theses
It is now widely known that the new high-temperature superconductors are antiferromagnetic insulators in their normal state. Experimental results indicate that layered cuprates such as {dollar}La\sb{lcub}2-x{rcub}Sr\sb{lcub}x{rcub}CuO\sb4{dollar} and {dollar}YBa\sb2Cu\sb3O\sb{lcub}6+x{rcub}{dollar} go from antiferromagnetic to superconducting state as x changes in the stoichiometry with doping. This suggests a possible correlation between the properties of antiferromagnetism and superconductivity in these materials. Also, the magnetic properties in the normal state such as Neel temperature, its dependence on doping, the sublattice magnetization etc. have an unusual behaviour which is not yet fully understood. The existing theories are not able to explain these magnetic properties. The aim …
A Quasiclassical Trajectory Study Of Impulsive Collisions Between Hydroxyl (Nu = 1--9, K = 1,2,5,10) And Molecular Oxygen In The Upper Mesophere, Kathleen L. Gilbert
A Quasiclassical Trajectory Study Of Impulsive Collisions Between Hydroxyl (Nu = 1--9, K = 1,2,5,10) And Molecular Oxygen In The Upper Mesophere, Kathleen L. Gilbert
Digitized Theses
Observations of the hydroxyl airglow are widely used as a remote sensing tool in the study of middle atmosphere dynamics. To assess the validity of this technique, a comprehensive understanding of the excitation and emission processes is required. The effect of collisional quenching of vibrationally excited OH by {dollar}\rm O\sb2{dollar} remains an outstanding problem in interpreting OH airglow intensity variations. Impulsive collisions between {dollar}\rm OH\sp\*(\nu{dollar} = 1-9, K = 1,2,5,10) and {dollar}\rm O\sb2{dollar} are modelled using quasiclassical trajectories to investigate the distribution of product {dollar}\rm OH\sp\*{dollar} states. The mode of vibrational deactivation depends on whether the O or H atom …
Nonperturbative Fermion Propagator, The Axial Ward Identity And Dynamical Electroweak Symmetry Breaking, Mong Tong
Digitized Theses
In this thesis, we present a field-theoretical derivation of the nonperturbative fermion propagator in configuration space and construct its momentum space representation, which leads to the relevant Feynman rules. We also present an argument for the vanishing of such a propagator in Euclidean space via its contour integral representation.;We demonstrate that the nonperturbative fermion propagator contributions to the VVA and VVP triangle diagrams uphold the anomalous axial Ward identity to leading and next-to-leading order in the expansion parameter {dollar}m\sbsp{lcub}quark{rcub}{lcub}2{rcub}/p\sp2{dollar}, as well as in the expansion parameter {dollar}m\sbsp{lcub}\pi{rcub}{lcub}2{rcub}/m\sbsp{lcub}quark{rcub}{lcub}2{rcub}{dollar} appropriate for {dollar}\pi\sp0 \to \ \gamma\gamma{dollar} kinematics. We also utilize the "Feynman-rule" approach …
Unsteady Rotational Shear Flow Of Power Law Fluids, Jean-Paul Pascal
Unsteady Rotational Shear Flow Of Power Law Fluids, Jean-Paul Pascal
Digitized Theses
In this thesis we have investigated unsteady circular Couette flow for Non-Newtonian fluids of power law behaviour. We considered two specific problems: (1) A solid cylinder rotating in a power law fluid of infinite extent and (2) A power law fluid filling the gap between two concentric rotating cylinders.;Due to the nonlinearity of Non-Newtonian constitutive equations, velocity disturbances from a rotating cylinder propagate through the fluid with finite speed. The existence of this moving velocity disturbance front was observed in the analytic similarity solutions and numerical solutions. For the problem with one cylinder two numerical methods were used to determine …
Dynamics Of The Envelopes Of Be Stars In The Equatorial Plane, Haiqi Chen
Dynamics Of The Envelopes Of Be Stars In The Equatorial Plane, Haiqi Chen
Digitized Theses
In this thesis, I shall investigate the dynamics of the envelopes of Be stars in the equatorial plane. Currently there is no general agreement as to what are the most important forces controlling the dynamics in and near the equatorial plane. I expect that my research will yield a significant improvement in the knowledge of the forces which are most important in controlling the dynamics of the circumstellar matter, and thus lead to a major advance in the understanding of Be stars. Recently, observations of the continuous energy distribution of several Be stars from infrared to radio wavelengths have been …
High Resolution Gas-Phase Silicon 2p Core-Level Spectroscopy Using Synchrotron Radiation, Douglas George Sutherland
High Resolution Gas-Phase Silicon 2p Core-Level Spectroscopy Using Synchrotron Radiation, Douglas George Sutherland
Digitized Theses
High resolution (0.05 eV) Si 2p pre-edge photoabsorption spectra of SiH{dollar}\sb4{dollar}, SiD{dollar}\sb4{dollar}, Si{dollar}\sb2{dollar}H{dollar}\sb6{dollar} and Si{dollar}\sb3{dollar}H{dollar}\sb8{dollar} show a large number of peaks due to Si 2p {dollar}\to{dollar} Rydberg transitions, along with rich vibrational structure. The SiD{dollar}\sb4{dollar} spectrum has been very useful in distinguishing between Rydberg states and vibrational excitations. The spectra of Si{dollar}\sb2{dollar}H{dollar}\sb6{dollar} and Si{dollar}\sb3{dollar}H{dollar}\sb8{dollar} are very similar to each other, exhibiting excitation of asymmetric Si-H vibrations.;The Si L- and K-edge XANES spectra of Si(OCH{dollar}\sb3)\sb{lcub}\rm X{rcub}{dollar}(CH{dollar}\sb3)\sb{lcub}\rm 4-X{rcub}{dollar} (X = 0-4) are reported and the two end members of the series, Si(OCH{dollar}\sb3)\sb4{dollar} and Si(CH{dollar}\sb3)\sb4{dollar}, are compared to the spectra of SiO{dollar}\sb2{dollar} and …
What Is Normal Among The A-Type Stars?, Grant Michael Hill
What Is Normal Among The A-Type Stars?, Grant Michael Hill
Digitized Theses
Abundances of 15 elements have been determined for 16 early A-type stars, 14 of which are classified as normal. Abundances have been determined for Sirius, a hot Am star, and {dollar}\lambda{dollar} Boo, the prototypical member of its class. These stars range in vsini from 6 to 114 km s{dollar}\sp{lcub}-1{rcub}.{dollar} Spectrum synthesis has been used to determine the abundances. It is shown to be reliable and capable of application to even broader lined stars. Despite the fact that most of the stars studied are classified as normal, they exhibit a considerable range of abundances. The abundances of most elements scale (at …
The Formation Of Massive Stars: A 30 Mo Case Study, Martin Beech
The Formation Of Massive Stars: A 30 Mo Case Study, Martin Beech
Digitized Theses
I have used a generalized Naur and Osterbrock (1953) criterion to investigate the manner in which a convective core develops. Stars more massive than {dollar}\sim{dollar}30 Mo can develop convective cores before the onset of central hydrogen burning. It is estimated that stars more massive than {dollar}\sim{dollar}95 Mo will have a convective core throughout the whole of their pre-main sequence phase.;Pre-main sequence evolution has been calculated under the accretion paradigm: beginning with a collapsed core, mass is accreted until a final stellar mass is reached. The calculations begin with a one solar mass core.;The initial 1 Mo model was fully convective …
Dynamical Symmetry Breaking And Electroweak Processes, Nicholas Christopher Hill
Dynamical Symmetry Breaking And Electroweak Processes, Nicholas Christopher Hill
Digitized Theses
The on-mass-shell renormalization prescription of electroweak theory is extended to account for shifts in the mass-shell. These shifts arise from dynamical contributions generated by the nonperturbative content of the vacuum to the quark self-energies. Upper limits for the value of the dimension-3 fermion-antifermion condensate are found by considering its contribution to the u-d mass difference and the strangeness-changing nonleptonic decays of the kaon. Dynamical generation of fermion masses under chiral gauge interactions is also examined by considering the coupling of light fermions to a heavy fermion-antifermion condensate.
The Response Of An Hyperpure Germanium Detector To Ionizing Radiation, Shao Ying Tong
The Response Of An Hyperpure Germanium Detector To Ionizing Radiation, Shao Ying Tong
Digitized Theses
A basic understanding of the response of semiconductor detectors to ionizing radiation is important for their proper usage and their further development. Such devices may also be used to explore the energy deposition process in semiconductors.;The detailed response of an HPGe detector ({dollar}\sim{dollar}1 cm{dollar}\sp3{dollar} hyperpure Ge with an ion-implanted front contact) to ionizing radiation has been studied with regard to the radiation ionization energy ratio, {dollar}\varepsilon\sb{lcub}\rm ion{rcub}{dollar}/{dollar}\varepsilon\sb0{dollar}, using radioactive {dollar}\alpha{dollar} and {dollar}\gamma{dollar} sources and accelerated ion beams ({dollar}\sp1{dollar}H, {dollar}\sp{lcub}3,4{rcub}{dollar}He, {dollar}\sp7{dollar}Li). The data span the energy range of a few hundred keV to a few MeV. Effects of temperature and bias …
Heat Flow And Collisional Energy Exchange In Farley-Buneman Waves, Randy Steven Kissack
Heat Flow And Collisional Energy Exchange In Farley-Buneman Waves, Randy Steven Kissack
Digitized Theses
It is commonly accepted in the literature that the phase speed of Farley-Buneman waves in the E-region electrojets saturates at approximately the instability threshold phase speed (or ion-acoustic speed) of traditional linear theory. The formula often quoted, viz{dollar}{dollar}C\sbsp{lcub}s{rcub}{lcub}2{rcub} = {lcub}\gamma\sb{lcub}i{rcub}T\sb{lcub}i{rcub}+\gamma\sb{lcub}e{rcub}T\sb{lcub}e{rcub}\over m\sb{lcub}i{rcub}{rcub},{dollar}{dollar}customarily assumes isothermal behaviour({dollar}\gamma\sb{lcub}e,i{rcub} = 1),{dollar} or adiabatic behaviour ({dollar}\gamma\sb{lcub}e,i{rcub} = 5/3{dollar}) for the electrons and ions. As neither assumption is true in general, we have improved the traditional approach by including the effects of electron energy exchange and heat flow through the use of Grad's 8-moment method, with collision terms derived from the Boltzmann collision integral. The ions are …
Flow In Tubes Of Non-Circular Cross-Sections, Raushan Ara Quadir
Flow In Tubes Of Non-Circular Cross-Sections, Raushan Ara Quadir
Digitized Theses
In this thesis steady, laminar, viscous, incompressible flow in tubes of non-circular cross sections is investigated. The specific aims of the investigation are (a) to look at the problems of both developing flow and fully developed flow, (b) to consider non-circular cross sections in a more systematic manner than has been done in the past, and (c) to develop a relatively simple finite element technique for producing accurate numerical solutions of flow in tubes of fairly arbitrary cross sections.;Fully developed flow in tubes is governed by a Poisson type equation for the mainstream velocity. Both analytical and numerical solutions are …
Recrystallisation Of Strontium Titanate, Todd William Simpson
Recrystallisation Of Strontium Titanate, Todd William Simpson
Digitized Theses
The recrystallisation rate of amorphous strontium titanate is dramatically enhanced by thermal annealing in water vapour as compared with a dry ambient. Time resolved optical reflectivity (TRR) has been combined with Rutherford backscattering spectrometry (RBS) and ion channelling to investigate this effect. Thin amorphous films were produced on single crystal substrates of (100) strontium titanate by ion bombardment. Specimens were annealed under controlled ambient conditions and the solid phase epitaxial recrystallisation monitored in situ by TRR. The TRR data were calibrated ex situ by RBS measurements. Isotope substitution, nuclear reaction analysis and secondary ion mass spectrometry were utilised to reveal …
Some New Results In Topological Field Theories, Weidong Zhao
Some New Results In Topological Field Theories, Weidong Zhao
Digitized Theses
We report two results in topological field theories. Using the Hamiltonian approach, we reinterpret the partition functions of cohomology models as various character-valued indices. Secondly, we also show that, in the presence of Gribov zero modes, the topological field theories without regulating terms permit spontaneous symmetry breaking. The relation to reducible configurations is discussed.
Positron Annihilation Studies Of Defects In Silicon, Peter J. Simpson
Positron Annihilation Studies Of Defects In Silicon, Peter J. Simpson
Digitized Theses
Measurements of Doppler-broadening of annihilation radiation from variable-energy positrons have been applied to examine the nature and distribution of defects in ion-irradiated silicon. Positron measurements were supplemented by ion backscattering/channeling to determine displaced atom distributions, and infrared absorption measurements to determine divacancy concentrations. Silicon (100) wafers were irradiated at 300K with helium ions at energies from 0.25 to 4.0 MeV and fluences from 10{dollar}\sp{lcub}13{rcub}{dollar} to 10{dollar}\sp{lcub}16{rcub}{dollar} cm{dollar}\sp{lcub}-2{rcub},{dollar} and with silicon ions at energies from 0.5 to 5.0 MeV and fluences from 10{dollar}\sp{lcub}11{rcub}{dollar} to 10{dollar}\sp{lcub}15{rcub}{dollar} cm{dollar}\sp{lcub}-2{rcub}.{dollar} Defect annealing was observed through the divacancy annealing stage {dollar}(\sim{dollar}470 to 570K). He-irradiated silicon was …