VictorJuiz/thesis huggingface dataset:
Semiconductors and their heterostructures: Contributions to the theory of electronic and optical properties
Keywords: Physics

We introduce a new scheme to study semiconductor heterostructure electronic states that is more general than common envelope function approaches, allowing full-zone dispersions and often-neglected material differences to be described. This modal scattering formalism offers a “best choice” flux conserving interface connection rule at each energy by identifying a relevant unitary scattering matrix. Calculations of T — A' scattering in GaA s/AlAs structures illustrates the technique. We then construct an efficient twelve mode/eight-band k • p theory that exposes a light and heavy-particle coupling absent in m any other schemes, as well as new transfer matrix contributions; the latter describe interfacial spin-orbit coupling effects and finite basis corrections. This model is employed to predict new transmission resonances in InA s/G aSb interband tunnel structures. We also offer a novel interpretation of the popular envelope function approximation, which emerges from our theory after simplifying assumptions. We then present a simple prescription for a “length gauge” derivation of the electronic contributions to nonlinear optical susceptibilities of crystals. This provides expressions free from the unphysical zero frequency divergences which often plague susceptibility calculations of clean, cold semiconductors. In contrast to a recently presented alternative formalism, the transparent mathematical details of our approach facilitates physical in tempretatio n and analysis; for example, we can easily identify corrections to the commonly quoted noninteracting- electron semiconductor Bloch equations. We also derive the general second and third order semiconductor susceptibilities, whose zero frequency limits can now reveal novel effects not previously discussed. Further, we present a model calculation of third order semiconductor nonlinearities that corrects previously published dispersions, clarifies various zero frequency limits, and corresponds with several known results. Finally, we offer preliminary considerations of the consequences of our results on theoretical descriptions of semiconductor heterostructure optical properties. This includes describing the advantages of a heterostructure analog to our bulk crystal optical response scheme, as well as the benefits of our heterostructure electronic state formalism.
Measurement of the top quark mass with in situ jet energy scale calibration using hadronic W boson decays at CDF-II
Keywords: Physics

We report a measurement of the top quark mass with the upgraded Collider Detector at Fermilab (CDF-II). The top quarks are produced in pairs (tt) in proton-antiproton collisions with a center-of-mass energy of 1.96 TeV. Each top quark decays to a W boson and a bottom quark. We select candidate events in which one W boson decays hadronically and the other decays to an electron or a muon and its associated neutrino. The data sample, which corresponds to an integrated luminosity of 318 pb-1, contains 138 tt candidates. A top quark mass is reconstructed for each event by placing energy and momentum constraints on the top quark pair decay products. We also employ the reconstructed mass of the hadronic W boson decays W —> jj to constrain in situ the largest systematic uncertainty of the top quark mass measurement, the jet energy scale. Monte Carlo tem plates of the reconstructed top quark and W boson mass are produced as a function of the top quark mass and the jet energy scale. The distribution of reconstructed top quark and W boson mass in the data are compared to the Monte Carlo tem plates using a likelihood fit to obtain M top = 173.5 +3.9/-3.8 GeV This constitutes the most precise measurement of the top quark mass to date. This measurement can be used to constrain the mass of the Higgs boson, a central particle in the Standard Model of particle physics that has yet to be observed. We also demonstrate that this new technique reduces naturally the jet energy scale uncertainty as more d a ta is accumulated and thus provides the capability to measure M top with an uncertainty of 2 G eV /c2 or better by the end of the CD F-II experiment.
A surface distortion decomposition for vector CSAMT data over one-dimensional earth
Keywords: Physics

Single source CSAMT data, also known as vector CSAMT data, has been routinely collected in recent years and processed using the conventional 2-D induction model which does not incorporate galvanic distortion effects, although the importance of these has been widely recognized. The small number of data available in vector CSAMT though, does not allow models that simultaneously incorporate both 2-D induction and local galvanic distortion. Either the 2-D inductive model with no distortion or alternatively a 1-D model with up to two distortion parameters can be used. Two 1-D distortion models were tested that are specialized cases of the general Groom and Bailey’s (1989) M T decomposition method, (A) one which assumes the distortion parameter splitting (s) can be made zero choosing an appropriate coordinate system, and (B) other in terms of polarization ellipses that assumes the distortion parameter shear (e) can be zeroed by rotating the principal axes to the measurement axes. The former produces the distortion parameters twist and shear while the later generates twist and splitting. Computer algorithms were implemented and a data set was used to test the models and later compared with the classical 2- D model. Except for the magnitudes which differ by a scaling factor, the apparent resitivities computed with the three different approaches show very similar electrical distributions but the phases show discrepancies. The distortion parameters distribution of the distortion model (A) for the used data set has a complicated pattern and are frequency dependent. Distortion parameters obtained using model (B) define better the conductive structure and are approximately constant in a reasonable frequency interval. The results of the test suggest that the zero-split assumption is likely not valid while the zero-shear approach is a more realistic one, although further testing is necessary to confirm this.
Influence of the quasi-biennial oscillation on interannual variability in the Northern Hemisphere winter stratosphere.
Keywords: Physics

Observations show that the interannual variability of the Northern Hemisphere (NH) extratropical winter stratosphere is strongly correlated with the quasi-biennial oscillation (QBO) of tropical stratospheric winds, particularly during early winter. Most current general circulation models (GCMs) do not exhibit a QBO and therefore do not represent this important mode of tropical-extratropical interaction. In this study we examine the QBO-extratropical correlation using a 150-year GCM simulation in which a QBO occurs. Since no external forcings or interannual variations in sea surface temperatures are imposed, the modelled tropical-extratropical interactions represent an internal mode of atmospheric variability. The QBO itself is spontaneously forced by a combination of resolved and parameterized waves. The effects of this QBO on the climatological mean state and its interannual variability are considered, both by comparison with a control simulation (also 150 years in length, but with no QBO) and by compositing winters according to the phase of the QBO. Careful attention is given to the definition of QBO phase. Comparisons of the model results with observations (reanalysis data) are also made. QBO-induced changes in the climatological state of the model are found to have high statistical significance above the tropopause. In the extratropical winter stratosphere, these mean-state changes arise predominantly from the influence of the QBO on the propagation and dissipation of planetary-scale waves. This behaviour is shown to depend on the seasonal cycle, which argues for the usefulness of considering tropical-extratropical interactions in a GCM context. QBO influence on the interannual variability of the extratropical winter stratosphere is also seasonal, and the tropical-extratropical interaction is sensitive to the phase alignment of the QBO with respect to the annual cycle. This phase alignment is strongly affected by the seasonality of QBO phase transitions, which – due to the QBO being spontaneously generated, rather than having an imposed period – is somewhat realistic in the model. This leads to fluctuations in the strength of the modelled tropical-extratropical interaction occurring on a decadal timescale as an internal mode of atmospheric variability.
Coherent of excitons and continuum excitations in Indium Phosphide
Keywords: Physics

The dynamics of optically generated, coherent electronic excitations in Indium P hosphide at a temperature of 5 K are investigated over a 140 meV energy range near the band gap, using the two-pulse, self-diffracted, degenerate four-wave mixing technique with 30-50 fs near-infra-red pulses and spectrally resolved detection. The coherent dynamics of excitons associated with the fundamental energy gap are investigated under conditions of simultaneous excitation of continuum transitions. Exciton-carrier scattering is shown to produce the dominant source of diffraction for excitons due to excitation-induced dephasing. The dephasing rate of continuum excitations is found to increase abruptly at the threshold energy for LO phonon emission by electrons. Below this threshold energy the dephasing rate is determined to be at least 8 ps-l, whereas above the threshold energy, the dephasing rate is at least 13 ps-'. Near the spin-orbit split-off valence to conduction band transition energy the diffracted spectrum is strongly affected by an interaction between split-off excitons and continuum excitations of heavy and light hole bands. A Fano-like spectral profile is observed in the coherent emission spectrum at the split-off transition and the coherent dynamics is dis- . * 11 cussed in terms of coupled exciton-continuum excitations. The Fano coupling parameter q. which characterizes the spectral profile. is found to decrease as excitation density increases. The interaction matnx elernent between split-off excitons and continuum excitations is determined to be approximately 5 meV, which corresponds to a 130 fs lifetime, over the density range investigated. Observation of the Fano interference phenornenom by fourwave mixing is found to depend on the relative orientation of the electric field polarization vectors. The Fano-like spectral profile is much less prominent for cross-polarized pulses than for CO-polarized pulses. Evidence for Fano interference is also observed by spectrally integrated four-wave mixing; there is no evidence of the interference in the cross-polarized case. At present, the polarization dependence is not understood: therefore, the interaction mechanism is not identified but possible interaction mechanisms that could give rise to Fano interference are discussed.
Reprocessing of High Resolution Crustal Seismic Reflection Data from the Abitibi Greenstone Belt
Keywords: Physics

Deep crustal reflection seismic data were collected in the Abitibi Greenstone Belt during the winter of 1987-8 as part of the Lithoprobe Project. Although much reflection energy was visible after initial processing, it was apparent that the stacked section could be improved. In particular, very little reflection energy was imaged in the upper 1 s, making it difficult to correlate deeper reflections with the mapped surface geology. The high resolution line 12A was reprocessed with a particular effort to obtaining a better image of the shallow data. Spectral equalisation of the upper 3 to 4 s and an accurate, complete static solution were found to be the most important steps in the reprocessing. Ground roll proved difficult to attenuate, with velocity filtering showing some promise, although not entirely satisfactory. Neax offset, low frequency vibrator noise was only partially attenuated through spectral equalisation, and may have been caused by subhaxmonic distortion in the vibrator signal. The dip moveout effect was substantial for shallow data in the southern part of the line. Reflection energy is apparent at all travel times in the unstacked data, although most of it does not stack coherently because its amplitude and phase characteristics vary with offset. Reflection energy above 100 Hz could not be imaged as coherent reflection energy after stacking. Reprocessing resulted in great improvement throughout the stacked section, with considerable reflection energy being imaged to 0.5 s. The results of this thesis illustrate the value of detailed processing of deep crusted reflection data in Archaean cratons.
Critical Pathways Towards Antiracism in an Elementary Knowledge Building Classroom
Keywords: critical knowledge
knowledge building
antiracism
classroom
autoethnography

This research project studies how a critical knowledge building environment might be created and sustained by taking into consideration several factors: (1) the dialogue and patterns of participation within this space; (2) whose knowledge is values and whose is silenced; and (3) the various forms of resistance in the classroom and school where this research takes place. It questions whether knowledge building can help to foster critical antiracism in the classroom, and also looks at how critical antiracism can inform the practice of knowledge building by explicitly recognizing, naming, and questioning the power that exists within the classroom, online and offline. Data was collected from a Knowledge Forum® database, focus group discussions, classroom observations, in-class discussions with the students and teacher, email, and an analysis of the revisions within the Ontario Social Studies curriculum documents from 1998 and 2004 in an attempt to understand the way in which both explicit and hidden curricula are mandated provincially. Also part of this study is the investigation of my role as an antiracist educator/researcher in this project and the various tensions, silencing, and resistance that I encountered throughout this journey. This role is recognized as one of power and powerlessness, depending on with whom, this role is negotiated. I investigate this role through the negotiations with various participants and their explanation of my role as well as through the reflexive process of autoethnography where I frame my role and my location as it is negotiated with the participants, my family, my work, and the process of coming to this project.
Electromagnetic decay of states of high spin and high isospin in fluorine-19
Keywords: Physics

The lowest Jπ =11/2+ state and the lowest two T = 3/2 states In 19F have been located among a number of new resonances in the 15 N(α,γ)19F reaction. The spins and radiative widths of these three new levels have been established by measurements of angular distribution and yield of γ-radiation. Their isospin is inferred from their spins, excitation energies, radiative widths and decay schemes. Measured transition matrix elements are compared with those calculated from shell-model wavefunctions which Include all (sd)3 configurations. Disagreements between 3 experiment and theory indicate that the (sd) description is inadequate for some of the positive parity states in 19F above about 4 MeV in excitation. Arguments are presented for the inclusion of (p) -2 (sd) 5 configurations to account for the properties of these states. The new 11/2+ level and the 7/2+ level at 4.38 MeV (whose spin has been definitely established in the course of this work) are discussed also in terms of a simple adiabatic rotational model for 19F. This model is found to account reasonably well for the excitation energies and transition probabilities of the lowest levels of spins 1/2 to 13/2.
In Vivo Neutron Activation Analysis and Associated Dosimetry
Keywords: Physics

The use of neutron activation analysis in-vivo for the measurement of calcium in the human body has proved to be a more accurate and less hazardous technique than many other methods currently used. The health hazard associated with this technique is determined in this study by a method of neutron dosimetry based on the radiation damage in plastics caused by neutron induced fission fragments. The lower legs of a phantom were irradiated for 10 minutes with four 23Q 49 Pu-Be neutron sources immersed in water. The 3.1 MeV Ca gamma rays from the legs were counted by two 8" dia. by 4" Nal(Tl) scintillation detectors in the Whole Body Counter at the Toronto General Hospital. The activity was such that there was a statistical error of 2%. The reproducibility of the results was determined from a series of 10 irradiations and the standard deviation was found to be +/- 2.3%. The expected interference from the 3.1 MeV peak in 37S produced by the 37Cl(n,p)37S reaction was estimated to be about 2% and an experimental assessment of this interference showed that the contribution made by 37S to the 49Ca peak was about 4% . For the neutron dosimetry, the plastic damaged by the fission fragments was etched in a 6N solution of NaOH, and the resulting holes counted by an electrical sparking method. Experiments were carried out to find optimum processing procedures and to check the range of linearity of the system. It was found that 232th foils were adequate for determining the significant neutron dose, which was about 0.8 rem during the irradiation of the legs. If required, 235U foils may also be used to monitor thermal fluences. A comparison of fast neutron doses measured by this technique with a completely independent method at Brookhaven National Laboratories showed very good agreement.
Magnetic and transport properties of FeGe2
Keywords: Physics

We have measured the electrical resistivity and the elastic and inelastic neutron scattering cross-sections of the itinerant antiferromagnets FeGe2 and Fe(Ge.96Ga.04)2. FeGe2 has a tetragonal structure with a collinear antiferromagnetic phase below TC-IC = 263 K, and an incommensurate spin density wave (SDW) phase between TC-IC and the Néel temperature (289 K). The ordering wavevector is along the a-axis and the moments are ferromagnetically aligned along the c-axis. We determined the phase diagram of FeGe2 for basal plane fields up to 16 T using resistivity measurements. The incommensurate phase is much more stable (up to ~30 T) in a magnetic field than theory predicts (1 T). Quantum oscillations appeared in the resistivity below 4 K for a c-axis magnetic field above 7 T. The resulting effective carrier mass is 0.45 ± .05 me, and the frequency is 190 ± 10 T. We used elastic neutron scattering to study the magnetic phases of Fe(Ge .96Ga.04)2. TC -IC = 183 K and this transition is clearly first-order. The low-temperature phase consists of a commensurate SDW with a long-wavelength modulation along the a-axis with weaker magnetic scattering reflections which are not displaced along the a-axis. Resistivity measurements show that the low-field commensurate phase is destroyed at temperatures below 20 K by a 12 T basal-plane magnetic field. Inelastic neutron scattering on FeGe2 at 11 K up to energy transfer (E = 540 meV shows magnon dispersion that is well described by a classical Heisenberg spin-wave model. The exchange constant along the c-axis, SJFM = 68 ± 5 meV, is 15 times higher than along the a-axis, ' SJAFM' = 4.4 ± 1.0 meV, making FeGe2 a unique example of a quasi-one-dimensional itinerant magnet. Up to 350 meV the c-axis magnon linewidth can be described by Γ( E) = (2.7 ± .6) * 10-3 MeV -1E2 (E2 dependence of a hydrodynamic model). We measure Γ values several orders of magnitude larger than localised models predict, presumably due to itinerant effects which also lead to a continuum of scattering above ~350 meV. At higher temperatures the peak height and lifetime of the c-axis magnons decrease, changing rapidly between TC-IC and TN. Magnon-like excitations persist to 600 or 700K as might be expected for a 1-D system without long-range order.
Interpretation of EM Sounding Data for a Stratified Earth by Means of Non-Linear Regression
Keywords: Geophysics

Direct inversion methods for electromagnetic soundings have not been used widely for routine interpretation of field data, even though they provide more useful information to the interpreter than do indirect methods, because existing inversion routines require large amounts of computer time and are relatively difficult to use. In an attempt to make direct inverse methods accessible for routine use, a study was made of the various available methods and a new computer program was written. This program solves for conductivity on a layering specified by the user, and uses the Fast Hankel transform with Anderson’s (1979) filter coefficients, a quintic spline approximation, and improvements in the Marquardt-Fletcher nonlinear regression algorithm to reduce the computer time required for convergence. The routine was tested with numerically generated sounding data which includes some random noise, as well as with several sets of field data. The results indicate that the routine solves easily for simple structures with moderate (≤ 10:1) conductivity contrasts, while larger contrasts in the conductivity structure require some care in setting up the starting model. Resistive structures are not resolved well, but the depth to conductive features in the stratigraphy can be determined accurately. Results from the inversion of five sets of field data are given: they were found to compare well with geophysical information from well logs or with interpretations made by other means.
A Short Baseline Transient Electromagnetic Method for Use on the Sea Floor
Keywords: Geophysics

A towed electromagnetic system capable of mapping the electrical conductivity of the sea floor over a large area has many possible applications, including mapping Quaternary geology, and understanding the physical properties of midocean ridge hydrothermal systems in association with massive sulphide deposits. However, the electrical conductivity of seawater is usually much greater than that of the sea floor, rendering the majority of electromagnetic systems presently employed on land unsuitable for marine use. A theoretical study of the transient step-on responses of some common controlled source, electromagnetic systems to adjoining conductive half-spaces shows that for two systems, the horizontal, in-line, electric dipole-dipole (ERER) and horizontal, coaxial, magnetic dipole-dipole (HRHR), the position in time of the initial portion of the transient indicates the conductivity of the sea floor, while at distinctly later time, a second characteristic of the transient is a measure of the larger seawater conductivity. The diagnostic separation between the two parts of the transient response does not occur for many other systems, including several commonly used for exploration on land. The concept of apparent conductivity is defined for the transient system in terms of the time of the first arrival of the transient signal. This apparent conductivity is used to produce characteristic curves of the HRHR system response for different layered earth models. A prototype HRHR system operating on a 100 m scale has been designed and constructed. A successful test of the system in shallow water was conducted in the coastal waters of Vancouver Island. The survey yielded 37 conductivity measurements along three lines. The instruments were towed by a ship along the sea floor. The tow cable carried both current to the transmitter coil and the received signal back to the ship for processing. Both the shape and amplitude of the received signal are indicative of the conductivity of the bottom sediments. Inversion of the data suggest that a varying thickness of 1.2 S·m-1mud overlies rock or sediment with a conductivity of about .1 S·m-1 . Improvements in equipment design might allow the production in real time of a continuous map of the conductivity structure of the sea floor.