Physics Theses and Dissertations

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Vapor Pressures of Saturated Aqueous Salt Solutions of Selected Inorganic Salts
(1965) Acheson, Donald Theodore; Mason, Edward A.; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
The vapor pressure of saturated aqueous salt solutions as functions of temperature have been measured for lithium bromide, lithium iodide, sodium bromide, potassium hydroxide, cesium fluoride, and zinc bromide. The temperature range is about plus s 0 c. to 70°c., with this range extended from minus 10°c. to plus 105°c. for lithium bromide and restricted to plus s 0 c. to 35°c. for sodium bromide. Vapor pressures, water 0 activities, and heats of vaporization and solution are tabulated at 5 C. intervals except in the vicinities of changes of hydration of the solid phase, where pressures and activities are plotted with sufficient frequency to show details. The experimental uncertainty in pressure is + 10 x 10-3 millibars and that in the heat of solution is+ 2 percent.
Almost Symmetric Spaces and Gravitational Radiation
(1967) Matzner, Richard Alfred; Misner, Charles W.; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
Gravitational Radiation in the Limit of High Frequency
(1967) Isaacson, Richard Allen; Misner, Charles W.; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
This dissertation deals with a technique for obtaining approximate radiative solutions to the Einstein equations of general relativity in situations where the gravitational fields of interest are quite strong. In the first chapter, we review the history of the problem and discuss previous work along related lines. In the second chapter, we assume the radiation to be of high frequency and expand the field equations in powers of the small wavelength this supplies. This assumption provides an approximation scheme valid for all orders of 1/r, for arbitrary velocities up to that of light, and for arbitrary intensities of the gravitational field. To lowest order we obtain a gauge invariant linear wave equation for gravitational radiation, which is a covariant generalization of that for massless spin-two fields in flat space, This wave equation is then solved by the W.K.B. approximation to show that gravitational waves travel on null geodesics with amplitude and frequency modified by gravitational fields in exactly the same way as are those of light waves, and with their polarization parallel transported along the geodesics, again as is the case for light. The metric containing high frequency gravitational waves is shown to be type N to lowest order, and some limits to the methods used are discussed. In the third chapter we go beyond the linear terms in the high frequency expansion, and consider the lowest order non-linear terms. They are shown to provide a natural, gauge invariant, averaged effective stress tensor for the energy localized in the high frequency radiation. By assuming the W.K.B. form for the field, this tensor is found to have the same structure as that for an electromagnetic null field. A Poynting vector is used to investigate the flow of energy and momentum in the gravitational wave field, and it is seen that high frequency waves propagate along null hypersurfaces and are not backscattered off by the curvature of space. Expressions for the total energy and momentum carried by the field to flat null infinity are given in terms of coordinate independent integrals valid within regions of strong field strength. The formalism is applied to the case of spherical gravitational waves where a news function is obtained, and where the source is found to lose exactly the energy and momentum contained in the radiation field.
The Stability of the Schwarzschild Metric
(1968) Vishveshwara, C. V.; Misner, Charles W.; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
The stability of the Schwarzschild exterior metric against small perturbations is investigated. The exterior extending from the Schwarzschild radius r =2m to spatial infinity is visualized as having been produced by a spherically symmetric mass distribution that collapsed into the Schwarzschild horizon in the remote past. As a preamble to the stability analysis, the phenomenon of spherically symmetric gravitational collapse is discussed under the conditions of zero pressure, absence of rotation and adiabatic flow. This is followed by a brief study of the Kruskal coordinates in which the apparent singularity at r = 2m is no longer present; the process of spherical collapse and the consequent production of the Schwarzschild empty space geometry down to the Schwarzschild horizon are depicted on the Kruskal diagram. The perturbations superposed on the Schwarzschild background metric are the same as those given by Regge and Wheeler consisting of odd and even parity classes, and with the time dependence exp(-ikt), where k is the frequency. An analysis of the Einstein field equations computed to first order in the perturbations away from the Schwarzschild background metric shows that when the frequency is made purely imaginary, the solutions that vanish at large values of r, conforming to the requirement of asymptotic flatness, will diverge near the Schwarzschild surface in the Kruskal coordinates even at the initial instant t = 0. Since the background metric itself is finite at this surface, the above behaviour of the perturbation clearly contradicts the basic assumption that the perturbations are small compared to .the background metric. Thus perturbations with imaginary frequencies that grow exponentially with time are physically unacceptable and hence the metric is stable. In the case of the odd perturbations, the above proof of stability is made rigorous by showing that the radial functions for real values of k form a complete set, by superposition of which any well behaved initial perturbation can be represented so that the time development of such a perturbation is non-divergent, since each of the component modes is purely oscillatory in time. A similar rigorous extension of the proof of stability has not been possible in the case of the even perturbations because the frequency (or k2) does not appear linearly in the differential equation. A study of stationary perturbations (k = 0) shows that the only nontrivial stationary perturbation that can exist is that due to the rotation of the source which is given by the odd perturbation with the angular momentum £ = 1. Finally, complex frequencies are introduced under the boundary conditions of only outgoing waves at infinity and purely incoming waves at the Schwarzschild surface. The physical significance of this situation is discussed and its connection with phenomena such as radiation damping and resonance scattering, and with the idea of causality is pointed out.
The Li6(a,2a)d Reaction at 50 to 80 MeV
(1970) Watson, John W.; Pugh, Howel G.; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
The Li6(a,2a)d reaction was studied at 50.4, 59.0, 60.5, 70.3 and 79.6 MeV bombarding energy. For each bombarding energy, several coincident energy spectra of the two emitted a-particles were measured. Special emphasis was placed on measuring spectra at pairs of angles where zero momentum (in the laboratory frame of reference) was possible for the residual deuteron. Using the constraints on three body kinematics, events corresponding to an a+ a+ d final state were selected from the coincident energy spectra. The cross section for these events was projected onto the E1 energy axis of the coincident spectra. The projected energy spectra were analyzed with the Plane Wave Impulse Approximation. From those points in the projected spectra which corresponded to zero deuteron recoil momentum, off-mass-shell a-a scattering cross sections were extracted. These were found to be in excellent agreement with free a-a scattering cross sections, if free cross sections for the final state center of mass energy of the two a's in the Li6 (a,2a)d reaction were chosen for the comparison. Off- mass-shell a-a cross sections were also extracted for data where the residual deuteron had a momentum of 30 MeV/c. These cross sections were also found to agree with free a-a scattering, but it was necessary to introduce an ad hoc shift in the a-a scattering angle to produce this agreement. Predictions of off-mass-shell a-a cross sections were made using a potential model. These indicate that the off-mass-shell cross section should indeed be very similar to the on-mass-shell cross section at the final state energy. Using the Plane Wave Impulse Approximation a momentum distribution for a's in Li6 was extracted from the experimental data. A cluster model for Li6 was devised to fit the binding energy and r.m.s. charge radius of Li6, as well as the 3s1 a-d scattering phase shift. For comparison with the experimental data, the momentum wave function of the a-particle in Li6 was calculated by taking the Fourier transform of the a-d relative motion. The theoretical and experimental momentum distributions were found to be in serious disagreement, both in magnitude and width at half maximum. By introducing a cut-off radius into the theoretical wave function, the discrepancies between theory and experiment were accounted for. It was also found, that if the cut-off radius is used as an adjustable parameter, then this Li6 wave function and reaction model explains the magnitudes and widths of the a-d relative momentum distributions determined from a wide variety of other reactions.
Partially Covariant Quantum Theory of Gravitation
(1972) Moncrief, Vincent E.; Nutku, Yavuz; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
In this thesis it is argued that a strict law of conservation of probability is necessary for the unambiguous interpretation of any proposed quantum theory of gravitation. After a brief review of the current canonicnl methods for quantizing the gravitational field we conclude that they do not guarantee conservation of probability owing to the difficulty of finding a suitable intrinsic time coordinate. In an attempt to circumvent this problem we have proposed an alternative method of quantization which has a conventional Schrodinger equation and therefore a law of probability conservation. This result is achieved by imposing a weaker form of the quantum constraint equations than that of the conventional theory. In order to justify this approach it is necessary to show that, in spite of the weak form of the constraint equations, the Einstein theory is recovered in the classical limit . A partial proof of the desired result is given. The proposed quantum theory is developed somewhat by considering the interaction of matter and gravitational fields. Quantum analogs of the covariant conservation laws are derived for the special case of a massive spin-zero field. Charge conservation is also considered and an invariant scheme for defining the number of particles and anti-particles is developed.
Investigation of Vanishing of a Horizon for Bianchi Type IX (the Mixmaster) Universe
(1972) Chitre, D.M.; Misner, Charles W.; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
In this dissertation, the generic, non-rotating, homogeneous closed model universe ( the "Mixmaster Universe", Bianchi Type IX) is studied to gain some insight into how the broad-scale homogeneity of the universe may have been produced at very early times. We begin our discussion by sketching the development of relativistic cosmology until the last decade. In the second chapter we discuss particle horizons in the Robertson-Walker models. These standard models of the universe possess particle horizons. Thus, only a finite part of such a universe could have been causally connected; while the isotropy of 2.7°K microwave radiation implies the universe to be homogeneous on a much larger scale than the size of the horizon. The third chapter discusses in detail the evolution of the Mixmaster Universe near the singularity using the Hamiltonian techniques developed by Misner for these models . At a fixed time (or volume) epoch Ω0, a Mixmaster Universe is specified by initial conditions' β+, β- (shape anisotropy) and p+ , p- (expansion rate anisotropy). In the fourth chapter we derive the equations for rays of high-frequency sound waves and light waves. When these equations are applied in the Mixmaster Universe, we find that for certain subsets of initial conditions, some of these sound rays and light rays would circumnavigate the corresponding universes in certain directions. Our results for light rays parallel those of Doroshkevich and Novikov, however we use entirely different methods (Hamiltonian methods) for treating the Einstein equations. In the last chapter the evolution of the Mixmaster Universe is shown equivalent to a geodesic flow within a bounded region of the Lobatchewsky plane. The boundary shape makes this flow Ergodic. The ergodicity is proved by invoking a certain group of conformal transformations, G, which makes this flow of broken geodesics on the Lobatchewsky plane, D, into a continuous one on D/G. The Einstein equations in this problem lead to a natural measure on initial conditions related to β+, p+. The measure of the circumnavigation sets depends upon the epoch and it goes to zero as the volume of the universe shrinks to zero. Finally, we compute the probability for circumnavigation along any one axis of the universe, It turns out to be roughly 1% for an empty universe and it decreases to 0.02% for realistic models containing radiation and matter in them.
A Direct Measurement of the Relativistic Effect of the Gravitational Potential on the Rats of Atomic Clocks Flown in an Aircraft
(1976) Williams, Ralph Emerson; Alley, C . O.; Physics and Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
General relativity predicts that standard clocks placed at differing gravitational potentials will run at different rates. Although experiments confirming the gravitational redshift have been done, they involve frequency and not time, and need not appeal to general relativity for explanation. Therefore, considerable interest exists as to the result of an accurate experiment in which real macroscopic clocks are brought together for comparison before and after separation to differing potentials. This experiment consists of flying an ensemble of atomic clocks in a military aircraft and comparing them before and after flight to another clock ensemble remaining on the ground. The ground ensemble included several Hewlett-Packard Cesium Beam clocks, three Efratom optically pumped Rubidium clocks, and two hydrogen masers. The flying ensemble included at least three Hewlett-Packard Cesium clocks and three Efratom Rubidium clocks. Five of the Cesium clocks were new models delivered with a high beam current option resulting in higher stability than standard models. The clocks were maintained under stringent environmental controls to protect against vibration, magnetic fields, and changes in temperature, pressure, and power supply voltage. Five main flights were ma de, each at approximately 30,000 feet altitude for fifteen hours. The aircraft was continuously tracked by a theodolite calibrated radar which obtained position and velocity measurements for every second of flight. This allowed an accurate calculation of a theoretical prediction to compare to experiment. The flying clocks gained approximately 45 nanoseconds (45 x 10-9 s) with respect to the ground clocks. The normalized results (measured effect divided by predicted effect) and the experimental standard deviations of the mean for each of the five flights were as follows: .999 + .016 .977 + .026 .963 + .013 1.002 + .026 .991 + .037 The result for the entire experiment, with standard deviation of the mean, was .987 ±. .011. The statistically expected standard deviation of the mean based on knowledge of clock quality was approximately .015. Considering this result as well as systematic errors, a final result is established of Measured value/ Predicted value = 0.987 ± .016
Electrons and Spin Waves in Itinerant Ferromagnets
(1976) Murray, Joanne; Korenman, Victor; Physics and Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
Though it is accepted that the 3-d magnetic electrons of transition metals such as nickel are itinerant, at high temperature these itinerant ferromagnets act as if the electrons were localized at lattice sites. In particular, three experimental results conflict with the Stoner itinerant model: 1) The spin band gap does not decrease with temperature as the average magnetization, but much more slowly. 2) Spin waves of short wavelength propagate above the Curie temperature. 3) Magnetic degrees of freedom play a role in determining thermodynamic properties n ear and above TC. The source of these discrepancies is the failure of Stoner theory to take into account magnetization fluctuations. In this paper, I do calculations of single particle and spin wave properties in a generalization of Stoner theory devised by R. E. Prange and V. Korenman to take account of fluctuations. In Stoner theory, electrons interact with an effective magnetic field proportional to the average magnetization, which becomes zero at the phase transition. The basic idea of the generalization of Stoner theory is that electrons are sensitive to their local environment and therefore that electronic and spin wave properties should be calculated in the presence of a local slowly fluctuating magnetization configuration. Only after calculating these properties should the fluctuations be thermally averaged. As a result, electrons interact with an effective magnetic field which is basically proportional to the magnitude of the local magnetization vector and which need not become zero at TC. Single particle properties are calculated by making a transformation to the spatially varying frame of reference of the local magnetization and doing perturbation theory with the magnetization gradients as the small perturbation parameter. We find that the spin eigenstates are approximately in or opposite to the direction of the local magnetization. Even when there is no longer a macroscopic magnetization, an energy gap is maintained between spin-split bands, the bands now being defined in terms of the local magnetization direction. The change in the energy gap from its zero temperature value is proportional only to the average square o f a magnetization gradient, a quantity which may be small even above TC. Thus we can understand that the gap changes only slowly with temperature and that the spin wave does not decay into Stoner single particle excitations even at high temperature. A free energy is found which is very similar in form to the free energy used to compute thermodynamic properties in localized models; thus we find that magnetic degrees of freedom are still important in computing thermodynamic properties above TC. It is the existence of a population difference and energy gap, rather than a macroscopic average magnetization that permits the existence of a spin flip collective excitation. We find a secular equation for the spin wave frequency in the presence of fluctuations which is very similar to the usua1 RPA secular equation, except for small perturbations proportional to the square of magnetization gradients. The corrections to the spin wave frequency and lifetime include the effect of the perturbation of single electron energies by the background, and also of the scattering of the spin wave from single particle spin-conserving excitations and from other spin waves. These corrections are quite small and allow for propagation even above TC. Thus it is a prediction of our theory that one see spin waves even above the critical temperature, so long as an appropriate Population difference maintains a locally ordered magnetization.
Gravitational Radiation Detection
(1976) Rydbeck, Gustaf H. B.; Weber, Joseph; Physics and Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
This dissertation studies resonant gravitational wave detectors and related data analysis. Different forms (strain amplitude) of the equation of motion for a medium responding to a gravitational wave are discussed in relation to the detection of such waves. Utilizing "Bayesian techniques" an optimal method for data analysis is developed. Noise and filter theory is reviewed. It is seen that the “Bayesian techniques" integrates filter theory and data analysis, providing both filter properties and optimal methods for integrating the data.(In particular the method leads to a non threshold type of analysis, and "looks for" correlation between two detectors without the use of time delay). Expressions for optimal sensitivity (and filters) of detector systems are given, including the limit of perfect sensors and electronics. The signal to noise ratio in terms of the spectral power of the gravitational radiation is derived. Long baseline interferometry is discussed. A computer program simulating a pair of Weber type detectors is developed to study different approaches to data analysis.
A Field Theory of Extended Particles Based on Covariant Harmonic Oscillator Wavefunctions
(1976) Karr, Thomas John; Kim, Young Suh; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
We attempt to combine the covariant harmonic oscillator (CHO) quark model with second quantized field theory. We review the CHO formalism for a system of two quarks (meson). We introduce a mesonic field Φ(x1 ,x2) that depends on the position of both quarks, and then derive the field equations from a covariant lagrangian L(x1, x2). The CHO equation allows a complete separation of the average meson coordinate X from the relative quark coordinate ξ. The CHO wavefunction in the field expresses the extended size and internal structure of the meson. Φ, describes mesons in the ground state and any excited state , with angular momentum ∞ mass^2. From Φ we construct conserved tensors like P^μ the meson momentum. We second quantize Φ in the X variable only and discuss the extended particle commutation relations. We investigate a Φ^3-type meson interaction where the vertex function is an overlap integral of the wavefunctions entering the interaction region. We derive a nonlinear integrodifferential equation for the U matrix , linearize and solve it by perturbation theory. The result is simple diagramatic rules for the S matrix. The S matrix is covariant and unitary. We do not find any contradiction between the principles of QFT and the CHO quark model. The Φ field theory includes scalar meson(point particle)theory as a special case, while its greater generality illuminates the difference between point and extended particles.
Topics in Nonlinear Wave Theory With Applications
(1984) Tracy, Eugene Raymond; Chen, Hsing Hen; Physics; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
Selected topics in nonlinear wave theory are discussed and applications to the study of modulational instabilities are presented. A historical survey is given of topics relating to solitons and modulational problems. A method is then presented for generating exact periodic and quasiperiodic solutions to several nonlinear wave equations which have important physical applications. The method is then specialized for the purposes of studying the modulational instability of a plane wave solution of the nonlinear Schrodinger equation, an equation with general applicability in one dimensional modulational problems. Some numerical results obtained in conjunction with the analytic study are presented. The analytic approach explains the recurrence phenomena seen in our numerical studies, and the numerical work of other authors. The method of solution (related to the Inverse Scattering Method) is then analyzed within t􀀏e context of Hamiltonian dynamics where we show that the method can be viewed as simply a pair of canonical transformations. The Abel Transformation which appears here and in the work of other authors is shown to be a special form of Liouville's Transformation to action-angle variables. The construction of closed form solutions of these nonlinear wave equations, via the solution of Jacobi's Inversion Problem, is surveyed briefly.
Lie Algebraic Methods for Treating Lattice Parameter Errors in Particle Accelerators
(1986) Healy, Liam Michael; Dragt, Alex J.; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
Orbital dynamics in particle accelerators, and ray tracing in light optics, are examples of Hamiltonian systems. The transformation from initial to final phase space coordinates in such systems is a symplectic map. Lie algebraic techniques have been used with great success in the case of idealized systems to represent symplectic maps by Lie transformations. These techniques allow rapid computation in tracking particles while maintaining complete symplecticity, and easy extraction of analytical quantities such as chromaticities and aberrations. Real accelerators differ from ideal ones in a number of ways. Magnetic or electric devices, designed to guide and focus the beam, may be in the wrong place or have the wrong orientation, and they may not have the intended field strengths. The purpose of this dissertation is to extend the Lie algebraic techniques to treat these misplacement, misalignment and mispowering errors. Symplectic maps describing accelerators with errors typically have first-order terms. There are two major aspects to creating a Lie algebraic theory of accelerator errors: creation of appropriate maps and their subsequent manipulation and use. There are several aspects to the manipulation and use of symplectic maps. A first aspect is particle tracking. That is, one must find how particle positions are transformed by a map. A second is concatenation, the combining of several maps into a single map including nonlinear feed-down effects from high-order elements. A third aspect is the computation of the fixed point of a map, and the expansion of a map about its fixed point. For the case of a map representing a full turn in a circular accelerator, the fixed point corresponds to the closed orbit. The creation of a map for an element with errors requires the integration of a Hamiltonian with first-order terms to obtain the corresponding Lie transformation. It also involves a procedure for the complete specification of errors, and the generation of the map for an element with errors from the map of an ideal element. The methods described are expected to be applicable to other electromagnetic systems such as electron microscopes, and also to light optics systems.
Energy Dependence of the Effective Interaction for Nucleon-Nucleus Scattering
(1990) Seifert, Helmut; Kelly, James J.; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
We have measured cross sections and analyzing powers for 40, 42, 44, 48Ca and 16O at IUCF using the new high-resolution K600 spectrometer for 100 and 200 MeV protons. Measurements at 318 MeV for 40, 42, 44 ,48Ca and 32 ,34S were done at LAMPF using the HRS spectrometer. In this work, we obtain empirical effective interactions by fitting inelastic scattering data for many low-lying normal-parity isoscalar excitations of the self-conjugate nuclei 16O and 40Ca, assuming a local tp folding model. One-nucleon transition densities are from (e, e') . The fitted interactions are iterated to generate optical potentials self-consistently. We find that the fitted parameters are essentially target independent, which supports the validity of the local density hypothesis. Elastic scattering is predicted by extracting the rearrangement factor (1 + pd/dp) from the fitted in elastic interactions. Below 300 MeV the strength of the empirical interaction is reduced at zero density and the general density dependence is weaker compared to the theoretical interaction. Above 300 MeV we find the density dependence is stronger than expected. The empirical interactions provide better descriptions of elastic and inelastic data than IA calculations or LDA calculations using theoretical G-matrices, and can be used for nuclear structure studies of other nuclei . Fitted optical potentials above 300 MeV are comparable to equivalent Schrödinger potentials from the relativistic IA2 model.
Continuous Imaginary Time Histories Representing Black Hold Nucleation in Desitter Spacetime
(2000) Branoff, Paul M.; Brill, Dieter R.; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
We address the issues involved in finding and constructing continuous imaginary time histories (CITHs) representing black hold nucleation in a background de Sitter spacetime. Such rates are often calculated by adopting the instanton methods used to calculate ordinary particle-antiparticle production rates in background fields. Unlike the particle production case, there are certain instances of black hole nucleation described by two separate and distinct solution to the Euclidean Einstein's equations, i.e., the instanton is disconnected. Hence, one must justify including such histories in a path integral. We first discuss the existence of continuous imaginary time histories for black hole nucleation in theories consisting of modifications to Einstein's equations. First, we consider adding powers of the Ricci scalar to Einstein-Hilbert gravity with a cosmological constant. When the higher curvature coupling constants are negative, we find continuous instantons describing a background de Sitter to de Sitter transition characterized by a periodic, non-singular scale factor α (τ). Negative coupling constants imply an equivalent theory of Einstein gravity coupled to a negative energy density scalar field. This motivates our exploration of Einstein gravity coupled to Narlikar's negative energy density C-field. We again find a continuous background instanton, but such a solution exists only when small violations of the Hamiltonian constraint are allowed. Because of the unattractive features of the above solutions, we explore how one can construct CITHs by surgically altering the disconnected instanton. In the spirit of the path integral, we claim that one should sum over all possible geometries which can connect the instanton. We limit attention to connections with topology S^3 and S^1 x S^2. We find that the S^3 connection is preferred in the context of "no-boundary" quantum cosmology. However, we believe that the S^1 x S^2 connection may be more preferred for two reasons. First, the S^1 x S^2 connection allows two of its dimensions to-be large, implying via holography, that information from the initial state can "survive" the near-annihilation, recreation process. Second, Planck sized perturbations on the S^2 portion of the connection give rise to more histories over which to sum in the path integral.
COHERENT DYNAMICS IN ATOM-FIELD INTERACTIONS
(2003-10-15) Shresta, Sanjiv; Hu, Bei-Lok; Physics
This dissertation treats quantum open system dynamics, focusing on the coherent evolution of a two-level atom (as the system) interacting with an electromagnetic field (as the bath), for purposes relevant to quantum computing. In order to maintain the quantum correlations that develop between the system and bath throughout the evolution path integral formalisms such as the influence functional and closed time path formalisms are used. Predictions of effects due to the quantum correlations in the composite interacting system are computed. Conventional treatments using Schr\"odinger-master equation and Heisenberg-Langevin approaches usually ignore system+bath quantum correlations as a technical simplification. It is argued that although neglect of system+bath correlations is generally a good approximation when the bath has a large continuous set of degrees of freedom, a residual coherence effect remains due to the non-zero bath correlation time. Though small, these effects are becoming more relevant as, with the advent of ultra cold atom sources, atom optics experiments are reaching levels at which such residual effects are becoming measurable. Three specific problems are investigated in this thesis: First is a self-dressing rederivation of the Casimir-Polder retardation force. The well known stationary atom result is reproduced and a result for a slowly moving atom is obtained which is up to twice the stationary atom correction. Second is the entangled evolution of a qubit with an initially thermal low temperature bath. The diagonal matrix elements are found to thermalize and the off-diagonal elements to decohere as expected, however they do so non-exponentially due to the quantum correlations that develop between the qubit and bath. Third is a calculation of qubit dynamics in the presence of quantized atomic motion as well as zero point fluctuations of the electromagnetic field. The decoherence rate of the qubit is found to increase slightly in that case due to the additional degree of freedom.
Charge Form Factor of the Neutron Through d vector(e vector, e'n) at Q(2) = 1.0(GeV/c)2
(2003-11-24) Savvinov, Nikolai; Kelly, James J.; Physics
Elastic electromagnetic form factors of the nucleon are of fundamental importance for our understanding of its internal structure. Experiment E93-026 at the Thomas Jefferson National Accelerator Facility (JLab) determined the electric form factor of the neutron, $G_E^n$, through quasielastic ${\vec{d}(\vec{e},e'n)p}$ scattering using a longitudinally polarized electron beam and a frozen polarized $^{15}ND_3$ target. The knocked out neutrons were detected in a segmented plastic scintillator detector in coincidence with the scattered electrons, which were tracked in High Momentum Spectrometer of the Hall C. The form factor was extracted by comparing the experimental beam--target asymmetry with full theoretical calculations based on different values of $G_E^n$. The dissertation discusses the experimental setup, data acquisition and analysis for the $Q^2=1.0~(\mathrm{GeV}/c)^2$ point, and implications of the experimental results for our understanding of the nucleon electromagnetic structure.
Superfluidity in a Degenerate Atomic Fermi Gas
(2003-11-25) Nygaard, Nicolai; Alexander, Millard H; Clark, Charles W; Chemical Physics
Dilute atomic gases have become a powerful tool for studying many-body quantum mechanics. The best example of this is the achievement of Bose-Einstein condensation in 1995 in a gas of Bose atoms, a discovery which has invoked a confluence of ideas from condensed matter, atomic and nuclear physics. Now a concerted research effort is focused on creating and studying a BCS superfluid in an atomic Fermi gas. In the work presented here we study in detail pairing superfluidity in a Fermi gas of atoms, by self-consistently solving the Bogoliubov-de Gennes equations, both for bulk systems, and for atoms in a harmonic confining potential. A critical part of this work is the derivation of a regularized theory, which is formulated entirely in terms of physically measurable quantities, such that a quantitative comparison between theory and experiment is possible with no adjustable parameters. The resulting equations form a non-linear problem, and the accurate numerical solution of this poses a formidable challenge. A major component of this thesis is the development of efficient computational approaches to overcome these difficulties. Based on the linear response of the gas to a twisting of the order parameter phase, the superfluid density can be defined as a generalized elasticity of the system. Using finite temperature perturbation theory we calculate the superfluid density in an inhomogeneous system. We investigate the structure and thermodynamic properties of a singly quantized vortex line in a gas of superfluid fermionic atoms, making the first quantitative determination the critical rotation frequency for thermodynamic stability of the vortex state, and study the nature of the bound states in the vortex core. These excitations fill the core, making direct imaging of the vortex unlikely. Instead, we propose an experiment to indirectly probe the vortex density of states with laser fields, in a scheme analogous to Scanning Tunneling Microscopy. Furthermore, it is shown that the vortex state causes a shift of the superfluid transition temperature, which can be understood as a finite size effect.
Electron Transport Simulations and Band Structure Calculations of New Materials for Electronics: Silicon Carbide and Carbon Nanotubes.
(2003-12-03) Pennington, Gary Wayne; Goldsman, Neil; Physics
Silicon carbide (SiC) and carbon nanotubes (CNTs) are two materials which have promising potential in electronics. Due to its large bandgap and large thermal conductivity, SiC is targeted as a potential material for use in high-power high-temperature electronics. Carbon nanotubes are at the forefront of current research in nanoelectronics, and field-effect nanotube transistors have already been developed in research laboratories. The small dimensions of these materials suggests their possible use in densely packed CNT-integrated circuits. Carbon nanotubes also appear to have very large electron mobilities, and may have applications in high-speed electronic devices. In this work the properties of the electronic structure and electron transport in silicon carbide and in semiconducting zig-zag carbon nanotubes are studied. For SiC, a new method to calculate the bulk band structure is developed. The conduction band minimum is found to lie at the $L$ and $M$ points in the Brillouin zones of 4H and 6H-SiC respectively. The quasi-2D band structure of hexagonal SiC is also determined for a number of lattice orientations. Electron transport in SiC is investigated in the bulk and at the SiC/oxide interface. The dependence of transport on the lattice temperature, applied field, and crystal orientation is studied. A methodology for semiclassical transport of electrons in semiconducting carbon nanotubes is also developed. Monte Carlo simulations predict large low-field mobilities (4000-13000 cm*cm/Vs) agreeing with experiments. The simulations also predict high electron drift velocities (500 km/s) and negative differential resistance.
SOLAR NEUTRINOS AT SUPER-KAMIOKANDE: SOLVING THE SOLAR NEUTRINO PUZZLE VIA NEUTRINO FLAVOR OSCILLATIONS
(2003-12-04) Turcan, Dusan; Sullivan, Gregory W; Physics
The Super-Kamiokande neutrino detector was built with the intent to explain the long-standing apparent solar neutrino flux deficit through signatures of neutrino flavor oscillations, such as a distortion in the energy spectrum and an asymmetry in the day and night fluxes. With the absence of any such ``smoking-gun'' evidence, an oscillation analysis of solar neutrinos was performed using the data sample from Super-Kamiokande I (SK), Sudbury Neutrino Observatory (SNO), and all other neutrino detectors. A model-independent analysis of SK's total solar neutrino rate and SNO's solar electron-neutrino rate showed at $3.7\,\sigma$ level that the apparent deficit is due to the effects of neutrino flavor oscillations. This analysis was possible because for a careful choice of energy thresholds, SK and SNO have virtually the same response to $^8$B solar neutrinos, whose energy spectrum is undistorted, as demonstrated by the data. By utilizing the full data sets of SK and SNO, however, the oscillation scenario is favored at $6.0\,\sigma$ level, with the best-fit oscillation parameters of $\Delta m^2=6.3\times10^{-5}\rm\,eV^2$ and $tan^2\theta=0.44$ (in the LMA region). The measured $^8$B neutrino flux is $\Phi_\nu=5.45^{+0.64}_{-0.69} \times10^6\rm\,cm^{-2}s^{-1}$, which confirms its theoretical prediction from the Standard Solar Model. With the addition of the neutrino rates from the radiochemical experiments (gallium and chlorine), and the anti-neutrino oscillation result from KamLAND, the LMA solution is further constricted, the $^8$B neutrino flux is again confirmed ($\Phi_\nu=5.66^{+0.62}_{-0.59} \times10^6\rm\,cm^{-2}s^{-1}$), and the no-oscillation scenario is ruled out at more than $10\,\sigma$ level.