VictorJuiz/thesis huggingface dataset:
Paleointensity determinations on basaltsfrom the Emperor Seamounts and testingthe properties of FORC diagrams usingmicromagnetic modelling and measurements

The intensity of the geomagnetic field recorded in rocks from the Emperor Seamounts was measured. Paleolatitudes determined from thermal demagnetization in the Thellier experiments support the hypothesis of a moving Hawaiian hotspot. Because of thermal alteration and the presence of titanomaghemite, the Thellier success rate was only 5%. The virtual axial dipole moment at 56 Ma was (7.2 ± 0.2) x 1022 Am2 , about 60% higher than the average value for the 300-0.3 Ma time period, although still within the error bounds of this average. First-order reversal curve (FORC) diagrams give the coercivity and interaction field distributions of magnetic minerals and could be used to pre-select samples for paleointensity experiments. Micromagnetic modelling shows that non-interacting particles are manifested by a symmetrical single peak. When particles interact, splitting of the central peak on the interaction field (Hu) axis might explain the vertical spread observed on FORC diagrams. I measured FORC diagrams on elongated SD particles at temperatures ranging from 20 K to 853 K. The median field of the profile through the FORC peak along the coercivity field (Hu) axis varies in proportion to the bulk coercive force. The half-width of a profile through the FORC peak parallel to the Hu axis is similar to independent measures of local interaction fields Hi. These properties support the interpretation of the FORC variables He and Hu as being equivalent to microcoercivity He and interaction field Hi, respectively, and validate the FORC method. In nature, magnetic minerals usually occur as mixtures. The linear additivity of FORC diagrams was investigated, in order to study the possibility of separating magnetic mixtures into their components. Micromagnetic models of mixtures of magnetite and hematite and mixtures of magnetite with bimodal grain size distributions, as well as experimental measurements, yield linearly additive FORC diagrams. I compared FORC and Preisach diagrams measured on a range of natural and synthetic samples. I find a good agreement between both diagrams in the main features. Contours that are very close to the Hu axis are not imaged on a Preisach diagram. As a first approximation, FORC and Preisach diagrams are equivalent. However, the level of detail offered by FORC diagrams makes them more attractive to use than Preisach diagrams.

Keywords: Physics
Advisor: Dunlop, David
High Field Magnetic Properties Of Iron-Platinum Alloys In The Context Of The Invar Problem

The magnetic properties of a series of f.c.c. Fe-Pt alloys, near Fe3Pt, have been investigated at low temperatures as a function of composition and atomic ordering. This thesis describes two aspects of such study. First, the design and construction of a new type of orbiting sample magnetometer of high sensitivity (Δx/x=4x10-3 ). This magnetometer permits the direct comparison of two samples (the ordered and disordered states at a given concentration) and a standard in a wide range of temperatures and magnetic fields. Second, the behaviour of Fe-Pt is characterized relative to that of the other Invars. In particular the similarities and differences with the classical Fe-Ni Invar are stressed. Central to the design of the magnetometer has been the development of bearings which can operate under the combined effects of high speed and low temperature in the presence of a high magnetic field. The sample holder consist of a horizontal wheel which is rotated in a vertical magnetic field. The three samples are passed successively through detection coils at a fixed frequency achieved by means of a phase sensitive feedback loop. The output signal contains all the information of the flux changes due to all three samples; this signal is processed by a signal averaging system...

Keywords: Physics
Baryons In A Relativized Quark Model With QCD

The three quark system is studied in a 'relativized' version of the quark model which incorporates the important features of quantum chromodynamics. These include a universal one-gluon exchange potential and a string picture confining potential. A good description is obtained of the masses and compositions of all the known baryons known baryons from the nucleon to the ∑e, with parameters similar to those of an analogous study of the qq system. The inclusion of relativistic effects leads to a natural explanation of the apparent absence of spin-orbit interactions in baryons, and is crucial to the success of the model. The results indicate that a well-founded and successful quark model can be built on the basis of the effects expected from QCD and from a relativistic treatment of the quark dynamics.

Keywords: Physics
Moist potential vorticity generation in extratropical cyclones

The mechanism of moist potential vorticity (MPV) generation in a three-dimensional moist adiabatic and frictionless flow is investigated. It is found that MPV generation is governed by baroclinic vectors and moisture gradients. Negative (positive) MPV can be generated in the region where baroclinic vectors have a component along (against) the direction of moisture gradients. Numerical simulations of extratropical cyclones with different moisture distributions show that at the different stages of cvclogenesis, negative MPV usually appears in the warm sector near the north part of the cold front, the bent-back warm front, the warm core and the cold front. The effects of the Boussinesq approximation on the distribution of vorticity and M PV are examined. The Boussinesq approximation neglects several components of the solenoidal term in the vorticity equation. As a result, it underestimates the thermally direct circulations in the cold front and the bent-back warm front by 25% to 30%. This effect is more pronounced when latent heat release is taken into account. Consequently, the influence of the Boussinesq approximation on the M PV field is very significant. Evidence of the presence of conditional symmetric instability in the negative MPV region of the extratropical cyclone is also presented.

Keywords: Physics
Advisor: Cho, Han-Run
Compact stars in the Nonsymmetric gravitational theory

Stable white dwarfs and neutron stars are shown to exist in the Nonsymmetric Gravitational Theory (NGT). They are modelled as static spherically symmetric bodies of charge-neutral perfect fluid matter, with standard equations of state. The particle number model for the NGT conserved current, S* , is used. The effects of NGT reduce the stability of these compact stars compared to similar stars modelled using General Relativity or Newtonian gravity. There is a decrease in the maximum mass of both white dwarfs and neutron stars. The central densities are greater and the radii are smaller. In all these ways, NGT acts as if it were softening the equation of state. NGT also decreases the surface gravitational redshift, allowing even the possibility of a blueshift. From examination of the solutions for compact stars, constraints are placed on the l2 charges, (f2/p + f 2/e) and f2/n , of protons, neutrons and electrons. If matter composed only of these particles is considered, the constraints keep the l2 charge of the Sun so small that the NGT effects it produces in the solar system are unobservable at present. Similarly, the NGT terms in the periastron precession of eclipsing binary star systems, such as DI Herculis, would be so small that NGT could not explain the anomalies found there. Extended models for are considered. One of these, based on cosmions (wimps), might allow l2 charges for the Sun and DI Herculis to be large enough to be interesting while keeping the l2 charges of compact stars small.

Keywords: Physics
Development of a short-baseline transient EM marine system and its application in the study of the TAG hydrothermal mound

Seafloor hydrothermal mounds are accumulations of polymetallic sulfides that are produced by hydro thermal processes along active plate boundaries. While surficial rocks and fluids of such mounds have been extensively sampled, few geophysical methods are capable of resolving their structure at depth. Consequently, little is known of the resource value of individual deposits. Electrical conductivity is a parameter sensitive to variations in rock porosity, pore fluid salinity and temperature. Perhaps now here on Earth are these parameters more variable than in a hydrothermal environment, suggesting that conductivity measurements made with an appropriate technique are a method of choice for imaging the internal features of these deposits. Innovative transient electric dipole-dipole instruments have been developed for this purpose. The instruments are compact, autonomous, and have dual transmitter/receiver capability. When transmitting, the instruments generate a 3 A bipolar square wave of variable base frequency. When receiving, the instruments act as recording voltmeters which measure the horizontal components of the seafloor electric field. The instruments were deployed in their first trial in a survey of the Trans-Atlantic Geo traverse (TAG) hydrothermal mound on the mid -Atlantic ridge using the Alvin submersible. One instrument was configured as a transmitter and another as a receiver. Alvin carried the instruments to the seafloor where the receiver was deployed near the center of the mound. The transmitter was then carried through a survey path which circled the receiver at a range of ~ 70 m. providing measurements of axial variations in the mound's conductivity. The survey lasted 3.5 hours. One receiver component was damaged during deployment. Measurements made a t 12 sites on the second receiver component are interpreted in terms of a uniform seafloor model and a two-layered seafloor model. Results from the layered seafloor interpretation are rejected on the basis of eigenparameter error analysis. Apparent conductivities for the uniform seafloor model rang e from 1.4 to 15.9 S /m . being generally higher than the 3.2 S /m of seawater. Sensitivity analysis indicates that these values primarily reflect structure over a depth interval of 10 to 30 meters below the seafloor. T h e results are discussed in term s o f know n geology of the TAG mound.

Keywords: Physics
Advisor: Edwards, Nigel R.
Convection in earth's mantle: Impacts of solid-solid phase transformations and crystalline rheology

I first present a detailed analysis of the linear stability of an intern al thermal boundary layer. In the absence of effects due to convective motion, this boundary layer is shown to be extremely unstable. When effects due to the background flow are parameterized through a Peclet number and an endothermic phase transition is present, it is shown that the boundary layer is stabilized to the extent seen in numerical simulations of mantle convection. A series of detailed numerical calculations are presented in which I perform a broad survey of the effects of internal heating, depth-dependent viscosity, and differing Clapeyron slopes of the endothermic phase transition. The size distribution of mass flux events that cross the 660-km depth horizon is examined. It is determined that as the degree of layering increases, the number of small mass flux events increases while the number of large events decreases. I also determine that when the core-mantle boundary temperature is set such as to be in accord with high pressure experiments, the calculated surface heat flow is significantly greater than that of the real Earth. Earth-like surface heat flows were calculated only when convection was very strongly layered or when the mean viscosity was significantly greater than the viscosity inferred on the basis of post-glacial rebound. I also derive a simple parameterized model of convection and demonstrate that its predictions are very close to those of the full dynamical model. This parameterized model is further used to calculate possible Earth thermal histories. It is determined that for models which have a constant degree of layering, the Earth’s initial core temperature must be improbably high in order to match the constraint of the observed surface heat flow today. If the degree of layering is allowed to vary with the system Rayleigh number, a novel mechanism occurs which buffers the upper mantle temperature allowing for long periods of time with constant, Earth-like, surface heat flow with reasonable initial core temperatures. All acceptable models also require high viscosities which argues that the viscosity of the mantle that controls convection may be greater than that for post-glacial rebound.

Keywords: Physics
Advisor: Peltier, Richard
Cyclogenesis in the atmosphere and Gulf Stream ring formation in the ocean

A particularly engaging and appealing aspect of geophysical fluid dynamics is the similitude that may exist between flows in different media. Through exploitation of this fundamental fact, laboratory experiments have been performed to mimic a broad spectrum of geophysical motions. Such experiments have been augmented by the recent and rapid expansion in the methods of computational fluid dynamics (CFD). The work presented herein is an attempt to explore, through the application of such CFD methodology, the extent of the long-proposed but previously unfocused analogy between synoptic-scale atmospheric cyclogenesis and the process of “ring” formation in the western boundary currents of oceanic gyre circulations. The exploration of atmospheric cyclogenesis begins with direct numerical simulations of three mid-latitude zonal jets as determined by the three-dimensional aneiastic equations of motion in a zonally periodic channel. Each jet is perturbed by the structure of the fastest growing normal mode of linear theory. The ensuing evolution of the synoptic-scale baroclinic waves is examined in detail with emphasis placed on the generic process of tropopause folding and its implications for stratosphere-troposphere exchange. The degree to which such a nonlinearly developing baroclinic wave may be adequately described by a set of Balance Equations appropriate to synoptic-scale motion is thereafter explored through the development of a diagnostic analysis procedure. The nonlinear evolution of two oceanic jets, one of which is modeled on observations of the Gulf Stream, is explored using a substantially modified version of the model in a three-dimensional channel configuration with inflow/outflow boundary conditions in the streamwise direction. The early time evolution of the jets is compared to the predictions of linear stability analyses. Study of the late time flow. Evolution encompasses such aspects as eddy pinch-off, propagation, and demise; the strongly dipolar nature of these oceanic eddies and the effect such structures have on eddy characteristics is explored in detail. Implications for both cross-stream and vertical mixing by these eddies are noted. The culmination of this research is presented in the conclusions, wherein the atmospheric and oceanic simulations are compared and contrasted in order to make specific the degree to which these two geophysical flows may be considered analogous. It is concluded that a fundamental asymmetry exists between these two baroclinically unstable jet flows which undercuts the utility of the analogy that has often been drawn between them.

Keywords: Physics
Advisor: Peltier, Richard
Nonperturbative aspects of B meson decays

In this thesis we study a number of decay modes of the B meson. First we discuss the rare inclusive leptonic decay B —> Xs l +l- , where Xs denotes any hadronic state containing an s-quark. This decay is interesting primarily because it is potentially sensitive to new physics at a higher energy scale. Previous theoretical studies of this decay have calculated the nonperturbative corrections up to O(Λ2QCD/ m2b); we calculate the O(Λ3QCD/ m3b) corrections to the lepton invariant mass spectrum, the forward-backward asymmetry, and the hadronic invariant mass spectrum. The values of the nonperturbative parameters entering at this order are unknown, resulting in uncertainties in the Standard Model prediction. We estimate the size of these uncertainties by varying the nonperturbative parameters in a range suggested by dimensional analysis. We study how the uncertainties depend on experimentally motivated phase space cuts. We also discuss the rare inclusive semileptonic decay B ̅ —> Xu lv, where Xu is any hadronic final state resulting from the weak b —>u transition. We study the hadronic invariant mass spectrum as a means of measuring the CKM parameter |Vub|. Experimental backgrounds restrict the accessible phase space to a region where the spectrum is very sensitive to nonperturbative physics, and the spectrum is written in terms of nonperturbative functions called shape functions. We calculate the subleading shape function contributions, and estimate the uncertainty they induce in a measurement of |Vub|. We reduce the uncertainty by relating the spectrum to the photon energy spectrum of the radiative decay B —)■ X sj , and we compare the uncertainties to those found when using the lepton energy spectrum to extract |Vub|. Finally, we study two-body exclusive nonleptonic decays of the form B —» D W L, where L is a light meson (L =π, K, p). We consider these decay modes in a theoretical framework, called ‘QCD factorization’, which has attracted much interest in recent years. This framework provides no systematic way to calculate nonperturbative corrections to decay amplitudes. We estimate the parametric size of a class of nonperturbative corrections to these decays by partially summing the amplitudes to all orders in perturbation theory.

Keywords: Physics
Advisor: Luke, Michael
A measurement of the total photon-proton cross section in the center of mass energy range 167 to 194 GeV

The thesis is a complete presentation of a total photon-proton (ϒp) cross section measurement using the ZEUS detector at the recently commissioned HERA electron-proton (ep) collider. A measurement of yp interactions using the exchanged virtual photon of ep collisions is shown to be justified and the correct flux of photons is determined. HERA and ZEUS are introduced, with an emphasis on the components used in the measurement. The data was collected during the fall of 1992 for which the experimental conditions are described, including the determination of the 13 nb-1 of integrated ep luminosity which provided the event sample. The treatment of background events is described, as are event losses due to inefficiencies in their identification by the trigger and in their subsequent analysis. The observed number of events is corrected for the acceptance of the experiment using Monte Carlo simulations of ϒp interactions tuned to match characteristics of the observed events. Radiative corrections to the measurement are shown to be small and the calculation is corroborated by a measurement of the number of radiative events. In the yp center of mass energy range 167 < W < 194 GeV, the total ϒp cross section is ϒp/tot = 143 ± 3 (stat.) ± 18 (syst.) μb.

Keywords: Physics
Advisor: Martin, John F.
Ultrafast memory loss and energy redistribution in the hydrogen bond network of liquid water

Using two-dimensional infrared spectroscopy, this work has dissected the intermolecular dynamics in the fully resonant hydrogen-bonded network of liquid H₂0. This work involved the development of new infrared laser sources with sufficient (µJ) pulse energies, as well an experimental apparatus suitable for performing phase sensitive infrared (IR) spectroscopy. In particular, the development of a diffractive optics based experimental setup for use in the IR, as well as nanofluidics for handling the strong absorption of pure H₂0, were found to be necessary for extracting the relevant water dynamics, and are described in detail. Resonant energy transfer on a 100 fs time scale is observed in H₂0, as well as extremely fast spectral diffusion that results in a spectral sweep in the OH frequencies on a 50 fs time scale. There is an equally fast dephasing process observed in the system, leading to a near complete loss of inhomogeneity within 50 fs. The net effect is a very efficient redistribution of energy in liquid water. These results are in dramatic contrast to studies of isotopic water and clearly illustrate the importance of studying pure liquid H₂0 directly. These findings lead to new appreciation of the significance of fully resonant conditions for energy exchange and coupling among different degrees of freedom that can only be probed for pure H₂0.

Keywords: Physics
Advisor: Miller, Dwayne
Specific Heat Measurements Of Some Solid Gases In A Helium-3 Cryostat

The specific heats of solid CO, NO, 0₂, N₂, and some dilute mixtures of 0₂ in CO and N₂ in the temperature range 0.6⁰ to 4⁰K are reported. The measurements were made in a mechanical heat switch calorimeter in a He⁴ cryostat to which had been added a He³ stage. A commercial germanium resistance thermometer was used which was calibrated against the He³ and He⁴ vapor pressure scales. The specific heats of CO and NO were measured in an attempt to settle the question as to the origin of the residual entropy of these two substances. For these cases, there exists a discrepancy between the entropy calculated from spectroscopic data (Sspec) and that calculated from specific heat data (Scal); the difference Spec‐s cal being called the residual entropy. For many years, the usually accepted explanation for the appearance of a positive, finite value of the residual entropy in the cases of CO and NO has been in terms of ‘frozen-in’ non-equilibrium states of the crystal. For these cases, it was assumed that the orientation of the molecules becomes frozen—in at a high temperature because the forces tending to produce orientational order are insufficient to overcome the high potential barriers to molecular rotation in the crystal. In this way, the disorder persists to the absolute zero, resulting in the observed value of the residual entropy. Recently, considerable doubt as to the validity of this kind of argument has been raised, especially because molecular rotation in solid CH₄ has been demonstrated even at 1.8⁰K from a recent spin—lattice relaxation study. In an attempt to find a specific heat anomaly which could remove the residual entropy, this study of CO and NO was undertaken. No anomalous behavior in either case was revealed down to 0.6⁰K. It is pointed out that our present incomplete knowledge of molecular rotation in solids at low temperatures needs to be improved by extensive infrared absorption, spin—lattice relaxation, and other studies in order to be in a better position to understand the origin of the residual entropy in those few simple substances for which such an effect persists. During the course of this work, a sample of CO was found to have been contaminated with CO₂ and air. The specific heat measurements on this sample revealed a rather broad anomaly, not accounted for by the Debye theory. A subsequent experiment in which more oxygen was deliberately added to the sample showed that the anomaly was caused by the oxygen impurity. A further experiment in this series in which oxygen was added to a nitrogen host was performed and the results allowed certain conclusions to be made regarding the origin of the anomaly. The concentrations of oxygen were very low, generally a few tenths percent. The results may be interpreted in terms of a model consistent with the low-lying rotational energy levels of the oxygen molecule. The observed anomaly was in excellent agreement with the Schottky anomaly for a system containing two levels with a degeneracy ratio, upper to lower, of 2:1, and an energy spacing of 5.14⁰.

Keywords: Physics
Advisor: Graham, G.N.