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Title: 21F Higher Spin Structures in ²⁵Na and ²¹F.
Creator: Vonmoss, Justin Matthew, Tabor, Samuel Lynn, Plewa, Tomasz, Bonesteel, N. E., Riley, Mark A., Volya, Alexander, Florida State University, College of Arts and Sciences,...
Show moreVonmoss, Justin Matthew, Tabor, Samuel Lynn, Plewa, Tomasz, Bonesteel, N. E., Riley, Mark A., Volya, Alexander, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Two experiments have been performed at Florida State University using the FSU Compton- Suppressed HPGe Array and associated particle telescope. The first experiment used the 9Be(18O, pnγ) reaction at 35 MeV to study the nuclear structure of 25Na. The second experiment used the 9Be(14C, pnγ) reaction at 30, 35, and 45 MeV to study the nuclear structure of 21F. Particle-γ and particle-γ-γ coincidence data were analyzed resulting in the discovery of several new gamma rays and states for both...
Show moreTwo experiments have been performed at Florida State University using the FSU Compton- Suppressed HPGe Array and associated particle telescope. The first experiment used the 9Be(18O, pnγ) reaction at 35 MeV to study the nuclear structure of 25Na. The second experiment used the 9Be(14C, pnγ) reaction at 30, 35, and 45 MeV to study the nuclear structure of 21F. Particle-γ and particle-γ-γ coincidence data were analyzed resulting in the discovery of several new gamma rays and states for both nuclei; this includes resolving a doublet in 25Na which has caused significant confusion in previous works. Angular distributions, lifetimes, and transition strengths have been measured for both nuclei. Shell model calculations have been performed using the USDA and WBP interactions; in addition to 0-particle-0-hole states, 1p1h states have been calculated for both nuclei and, in 21F, 2p2h states have been calculated as well.
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Date Issued: 2015
Identifier: FSU_migr_etd-9478
Format: Thesis

Title: Alternating Current Loss Characteristics in (Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀ and YBa₂Cu₃O[subscript 7-δ] Superconducting Tapes.
Creator: Nguyen, Hau T. B., Schwartz, Justin, Boebinger, Gregory, Logan, Timothy M., Hirst, Linda, Vafek, Oskar, Department of Physics, Florida State University
Abstract/Description: Alternating current (AC) loss and current carrying capacity are two of the most crucial considerations in large-scale power applications of high temperature superconducting (HTS) conductors. AC losses result in an increased thermal load for cooling machines, and thus increased operating costs. Furthermore, AC losses can stimulate quenching phenomena or at least decrease the stability margin for superconducting devices. Thus, understanding AC losses is essential for the development of HTS AC...
Show moreAlternating current (AC) loss and current carrying capacity are two of the most crucial considerations in large-scale power applications of high temperature superconducting (HTS) conductors. AC losses result in an increased thermal load for cooling machines, and thus increased operating costs. Furthermore, AC losses can stimulate quenching phenomena or at least decrease the stability margin for superconducting devices. Thus, understanding AC losses is essential for the development of HTS AC applications. The main focus of this dissertation is to make reliable total AC loss measurements and interpret the experimental results in a theoretical framework. With a specially designed magnet, advanced total AC loss measurement system in liquid nitrogen (77 K) has been successfully built. Both calorimetric and electromagnetic methods were employed to confirm the validity of the measured results and to have a more thorough understanding of AC loss in HTS conductors. The measurement is capable of measuring total AC loss in HTS tapes over a wide range of frequency and amplitude of transport current and magnetic field. An accurate phase control technique allows measurement of total AC loss with any phase difference between the transport current and magnetic field by calorimetric method. In addition, a novel total AC loss measurement system with variable temperatures from 30 K to 100 K was successfully built and tested. Understanding the dependence of AC losses on temperature will enable optimization of the operating temperature and design of HTS devices. As a part of the dissertation, numerical calculations using Brandt's model were developed to study electrodynamics and total AC loss in HTS conductors. In the calculations, the superconducting electrical behavior is assumed to follow a power-law model. In general, the practical properties of conductors, including field-dependence of critical current density Jc, n-value and non-uniform distribution of Jc, can be accounted for in the numerical calculations. The numerical calculations are also capable of investigating eddy current loss in the stabilizer and ferromagnetic loss in the substrate of YBa2Cu3O7 (YBCO) coated conductor. AC loss characteristics and electrodynamics in several (Bi,Pb)2Sr2Ca2Cu3Ox (Bi-2223) and YBCO tapes were studied experimentally and numerically. It was found that AC loss behavior in HTS tapes is strongly affected by the sample parameters such as cross-section, structure, dimensions, critical current distribution as well as by operation parameters including temperature, frequency, the phase difference between transport current and magnetic field, the orientation of magnetic field. The Ni-5%W substrate in YBCO conductors generates some ferromagnetic loss but this loss component is significantly reduced by a small parallel DC magnetic field. At a given AC magnetic field B0, there is a temperature Tmax at which the magnetization loss is maximum. The design of HTS devices needs to be optimized to avoid operating at that temperature. In general, the total AC loss in HTS tapes is still high for many power device applications, especially for those that present a rather high AC applied magnetic field. The development of low loss conductors is therefore crucial for HTS large-scale applications.
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Date Issued: 2007
Identifier: FSU_migr_etd-2624
Format: Thesis

Title: Analyzing Powers for the 12C(7Li, t/d/p) Reactions.
Creator: Weintraub, William D., Kemper, Kirby W., Robson, Donald, Cottle, Paul, Schlottmann, Pedro, Safron, Sanford A., Department of Physics, Florida State University
Abstract/Description: The first, second, and third rank analyzing powers tT10, tT20, tT30, and tT20 as well as cross section angular distributions for 12C(7Li, t/d/p) at 34 MeV were measured. The experimental results gave nonzero values for tT10 and tT30 which is indicative of a non-statistical compound nucleus reaction mechanism according to Hauser-Feshbach predictions. The experimental results were compared to finite-range distorted wave Born approximation calculations are discussed along with previous results....
Show moreThe first, second, and third rank analyzing powers tT10, tT20, tT30, and tT20 as well as cross section angular distributions for 12C(7Li, t/d/p) at 34 MeV were measured. The experimental results gave nonzero values for tT10 and tT30 which is indicative of a non-statistical compound nucleus reaction mechanism according to Hauser-Feshbach predictions. The experimental results were compared to finite-range distorted wave Born approximation calculations are discussed along with previous results. The main goal of this work is to determine the reaction mechanism; do these reactions proceed via direct transfer or statistical compound nucleus formation, and if direct, did it occur in one step or multiple steps? The results indicate that all the reactions studied are direct to some degree. There is evidence for direct transfer of a 4,5 He cluster but not a 6He cluster.
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Date Issued: 2003
Identifier: FSU_migr_etd-1214
Format: Thesis

Title: Angular Momentum Induced Shape Changes in the Rare-Earth Nuclei ¹⁵²,¹⁵³Gd and ¹⁵⁹,¹⁶⁰Yb.
Creator: Campbell, David B., Riley, Mark A., Steinbock, Oliver, Weidenhover, Ingo, Coa, Jianming, Piekarewicz, Jorge, Department of Physics, Florida State University
Abstract/Description: The technique of studying nuclear structure under the rigors of high angular momentum through the examination of γ-ray cascades has recently undergone an explosion in productivity. These advances have been brought on primarily by the development of new detection systems, such as GAMMASPHERE, which are comprised of numerous individual elements. When these Compton-suppressed Ge detectors are operated in unison, a remarkable ability to distinguish weak and exotic changes in structure emerges....
Show moreThe technique of studying nuclear structure under the rigors of high angular momentum through the examination of γ-ray cascades has recently undergone an explosion in productivity. These advances have been brought on primarily by the development of new detection systems, such as GAMMASPHERE, which are comprised of numerous individual elements. When these Compton-suppressed Ge detectors are operated in unison, a remarkable ability to distinguish weak and exotic changes in structure emerges. The current generation of spectrometers have allowed dramatic insight into the nucleus and are eclipsed only by the promises of arrays currently on the horizon. The fundamentals of employing γ-ray spectroscopic techniques to examine the fascinating behavior of rapidly rotating nuclei using these arrays will be discussed. The rare earth region of the nuclear landscape is a significant expanse of heavy nuclei with varying degrees of shell occupation. The region has proven to be a rich environment for studying nuclear structure at high spin. For example, superdeformation, identical bands, and backbending were all discovered in this region. This work explores the advances made on four nuclei from this region: 152,153Gd and 159,160Yb. Extensive additions to the previously known structure were made for each nucleus, exposing an unexpected similarity between 152Gd and 154Dy. Long sought after evidence of an angular momentum induced change in nuclear shape was found for each of the nuclei. This shift, from prolate collective rotation at low spin to oblate single particle behavior at high spin, represents a dramatic change in the method employed by the nucleus to generate angular momentum.
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Date Issued: 2004
Identifier: FSU_migr_etd-4512
Format: Thesis

Title: Anomalous Metallic Behavior in Strongly Correlated Electron Systems with Disorder.
Creator: Tanaskovic, Darko, Dobrosavljevic, Vladimir, Dalal, Naresh, Manousakis, Efstratios, Capstick, Simon, Xiong, Peng, Department of Physics, Florida State University
Abstract/Description: We study several aspects of the behavior of strongly correlated electron systems with disorder. First we examine the influence of strong electron-electron interactions on the impurity dominated resistivity. In the weak-coupling limit, the resistivity is reduced by the screening effect which is determined by the charge compressibility, which is proportional to the inverse screening length. We show that when strong correlations are present, although the compressibility is reduced, the screening...
Show moreWe study several aspects of the behavior of strongly correlated electron systems with disorder. First we examine the influence of strong electron-electron interactions on the impurity dominated resistivity. In the weak-coupling limit, the resistivity is reduced by the screening effect which is determined by the charge compressibility, which is proportional to the inverse screening length. We show that when strong correlations are present, although the compressibility is reduced, the screening effect is nevertheless strongly enhanced. This phenomenon is traced to the non-perturbative Kondo-like processes captured by dynamical mean field theory, but which are absent in weak coupling approaches. We discuss a possible relevance of our results for the physics of high mobility MOSFETs. In the second part of the thesis we study possible mechanisms of disorder-driven non-Fermi liquid behavior in heavy fermion systems. We present simple analytical arguments explaining the universal emergence of electronic Griffiths phases as precursors of disorder-driven metal-insulator transitions in correlated electronic systems. Then we examine the interplay of the Kondo effect and the RKKY interactions in electronic Griffiths phases using extended dynamical mean-field theory methods. We find that sub-Ohmic dissipation is generated for sufficiently strong disorder, leading to suppression of Kondo screening on a finite fraction of spins, and giving rise to universal spin-liquid behavior.
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Date Issued: 2005
Identifier: FSU_migr_etd-1718
Format: Thesis

Title: Applications of Effective Field Theories to the Many-Body Nuclear Problem and Frustrated Spin Chains.
Creator: Felline, Cosimo, Piekarewicz, Jorge, Krishnamurti, Ruby, Capstick, Simon, Tabor, Samuel, Schlottmann, Pedro, Department of Physics, Florida State University
Abstract/Description: Modern effective-theory techniques are applied to the many-body nuclear problem and frustrated quantum spin chains. A novel approach is proposed for the renormalization of nucleon-nucleon operators in a manner consistent with the construction of the effective potential. To test this approach a one-dimesional, yet realistic, nucleon-nucleon potential is introduced. An effective potential is then constructed by tuning its parameters to reproduce the exact effective range expansion and a variety...
Show moreModern effective-theory techniques are applied to the many-body nuclear problem and frustrated quantum spin chains. A novel approach is proposed for the renormalization of nucleon-nucleon operators in a manner consistent with the construction of the effective potential. To test this approach a one-dimesional, yet realistic, nucleon-nucleon potential is introduced. An effective potential is then constructed by tuning its parameters to reproduce the exact effective range expansion and a variety of bare operators are renormalized in a fashion compatible with this construction. Predictions for the expectation values of these operators in the ground state reproduce the results of the exact theory with remarkable accuracy (at the 0.5% level). We illustrate the main ideas of this work using the elastic form factor of the deuteron as an example. We also apply th COntractor REnormalizator technique to the study of frustrated anti-ferromagnetic zig-zag spin chains with arbitrary half-integer spin. A basis is employed in which three neighboring spins are coupled to a well-defined value of the total angular momentum. The basis is then truncated to retain only the lowest lying energy states, and the Hamiltonian renormalized to reproduce the low-lying spectrum of the original system. We prove the necessity of retaining two, rather than one, lowest energy eigenstates as frustration is increased. A finite size scaling approach is used to extract ground state energy densities in good agreement with DMRG calculations and spin gaps in qualitative agreement with the disappearance of the Haldane phase around a=0.3. Moreover, we are able to develop a renormalization group equation that predicts accurately the ground state energy density of the chain in the thermodynamic limit.
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Date Issued: 2004
Identifier: FSU_migr_etd-4481
Format: Thesis

Title: Automated One-Loop QCD and Electroweak Calculations with NLOX.
Creator: Honeywell, Steven Joseph, Reina, Laura, Aluffi, Paolo, Owens, Joseph F., Roberts, Winston, Yohay, Rachel, Florida State University, College of Arts and Sciences, Department of...
Show moreHoneywell, Steven Joseph, Reina, Laura, Aluffi, Paolo, Owens, Joseph F., Roberts, Winston, Yohay, Rachel, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: We introduce a new framework, NLOX, in which one-loop QCD and electroweak corrections to Standard Model processes can be automatically calculated. Within this framework, we calculate the first order of electroweak corrections to the hadronic production of Z + 1b-jet and discuss some of the most relevant theoretical issues related to this process.
Date Issued: 2017
Identifier: FSU_2017SP_Honeywell_fsu_0071E_13868
Format: Thesis

Title: Bayesian Neural Networks for Classification.
Creator: Saucedo, Skyler Richard, Prosper, Harrison B., Adams, Todd, Hagopian, Vasken, Department of Physics, Florida State University
Abstract/Description: We study a model for classification based upon Bayesian statistics. The model, called Bayesian Neural Networks (BNN), is based on a function that is a weighted sum of hyperbolic tangent functions. To illustrate this method, we apply it to the task of separating Supersymmetric (SUSY) events from Standard Model proton-proton events at the LHC. Unlike conventional Neural Networks, the BNN model is an average over networks, which is done by integrating over a high dimensional parameter space....
Show moreWe study a model for classification based upon Bayesian statistics. The model, called Bayesian Neural Networks (BNN), is based on a function that is a weighted sum of hyperbolic tangent functions. To illustrate this method, we apply it to the task of separating Supersymmetric (SUSY) events from Standard Model proton-proton events at the LHC. Unlike conventional Neural Networks, the BNN model is an average over networks, which is done by integrating over a high dimensional parameter space. Since integrating over the parameter space is analytically impossible, the BNN method uses Hybrid Markov Chain Monte Carlo techniques to sample the desired probability densities while preserving a high acceptance rate. In this thesis we study the correlation properties of a sequence of Neural Networks. The results of this study are of great importance because validate the strategy currently used by the D0 collaboration, in the search for single top quarks at Fermilab.
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Date Issued: 2007
Identifier: FSU_migr_etd-2069
Format: Thesis

Title: Beta Decay Studies of Neutron-Rich ³⁰,³¹Al and in-Beam Studies of Neutron-Rich ³⁰Al.
Creator: Hinners, Trisha, Tabor, Samuel L., Aldrovandi, Ettore, Blessing, Susan, Riley, Mark, Piekarewicz, Jorge, Department of Physics, Florida State University
Abstract/Description: Low-spin states were studied in 30Al following the β decay of 30Mg produced in the fragmentation of 140 MeV/AMU 48Ca. Analysis of the β-γ and β-γ-γ coincidences revealed a new 1+ state at 2413 keV, confirmation of the level scheme, and a more accurate half life measurement of 315(6)ms for the 30Mg ground state. Higher-spin states were investigated in the reaction of 14C on 18O at 22 MeV. Protons and deuterons were detected in a segmented E-Δ E Si telescope in coincidence with one or two gamma...
Show moreLow-spin states were studied in 30Al following the β decay of 30Mg produced in the fragmentation of 140 MeV/AMU 48Ca. Analysis of the β-γ and β-γ-γ coincidences revealed a new 1+ state at 2413 keV, confirmation of the level scheme, and a more accurate half life measurement of 315(6)ms for the 30Mg ground state. Higher-spin states were investigated in the reaction of 14C on 18O at 22 MeV. Protons and deuterons were detected in a segmented E-Δ E Si telescope in coincidence with one or two gamma rays in the FSU Ge detector array. A comparison of the resulting level and decay scheme with predictions of the sd shell model shows good agreement with all but 6 of the states in both excitation energy and γ decay branching ratios. The RMS deviations in energy of these states using the older USD and newer USDA and USDB interactions were 265, 176, and 173 keV respectively. The remaining 6 states are well described as 4-to 7- states, similar in relative energy to those in 28Al but shifted down by about 1200 keV. These states also agree well with the predictions of shell model calculations using the WBP interaction. A comparison of the lowest 4- states in even A Na, Al, and P isotopes shows a systematic decrease in energy with increasing N and with decreasing Z. The energies of the 4- states are almost identical in nuclei with the same N - Z values. In addition to the study of 30Al, 31Al was also produced following the β decay of 31Mg in the fragmentation of 140 MeV/AMU 48Ca. The β-γ and β-γ-γ coincidences were able to show all previously known work. However, no new transitions were observed.
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Date Issued: 2008
Identifier: FSU_migr_etd-4033
Format: Thesis

Title: Biophysical Studies of Protein Folding and Binding Stability.
Creator: Batra, Jyotica, Zhou, Huan-Xiang, Blaber, Michael, Xiong, Peng, Rikvold, Per Arne, Dobrosavljevic, Vladimir, Department of Physics, Florida State University
Abstract/Description: Interactions between charged residues are known to have significant effects on protein folding stability and binding properties. The contributions of different types of non-covalent interactions are altered by mutating one or more residues, resulting in change in the protein stability to considerable extent. The main goal of this dissertation is to understand contributions, specifically from electrostatic interactions, to the protein folding stability and also, to devise strategies in order...
Show moreInteractions between charged residues are known to have significant effects on protein folding stability and binding properties. The contributions of different types of non-covalent interactions are altered by mutating one or more residues, resulting in change in the protein stability to considerable extent. The main goal of this dissertation is to understand contributions, specifically from electrostatic interactions, to the protein folding stability and also, to devise strategies in order to enhance protein stability. We have introduced single and double mutations in FKBP12 (FK506 binding protein) modeled after its close homolog FKBP12.6, and later accumulated the most stabilizing mutations in order to create a hyper stable mutant. Similar experimental study was carried out, where insertion, deletion and systematic introduction of ion-pair clusters in FKBP12 were modeled after the thermophilic homolog MtFKBP17 and the results suggest that charge residues can modulate the folding stability significantly. This experimental study has allowed rigorous testing of computational models developed by our group for predicting electrostatic contributions to protein folding stability, which does not match closely and need further refinement. To further broaden our research in understanding biophysical properties of proteins in living cells, we have investigated the effects of macromolecular crowding on the folding stability of one of the less stable mutant of FKBP. We show that there is an optimal size of crowder at which stability increase is maximum and also, the stabilization effect of mixture (different crowders) is greater than the sum of constituent crowding agents. These findings may have profound implications for understanding crowding effects inside cells. The main aim of my dissertation is to understand protein folding and stability, which are the fundamental problems in biophysics. Experiments are underway to understand effects of crowding on protein binding and their quantitative information will provide key insights to the biological relevance of experimental results obtained in vitro. Overall my research aims for understanding fundamental study on protein folding stability and binding which will serve as a valuable tool for designing therapies for human diseases.
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Date Issued: 2009
Identifier: FSU_migr_etd-1129
Format: Thesis

Title: Braiding and Berry's Phases in Non-Abelian Quantum Hall States.
Creator: Zikos, Georgios, Bonesteel, Nicholas, Aldrovandi, Ettore, Schlottmann, Pedro, Reina, Laura, Chiorescu, Irinel, Department of Physics, Florida State University
Abstract/Description: If one could be built, a quantum computer would be capable of storing and manipulating quantum states with sufficient accuracy to carry out computations that no classical computer can do (most notably factoring integers in polynomial time). The greatest obstacle to building such a device is the problem of error and decoherence. Classical computers can exploit the physical robustness of ordered states to protect classical information (as in, for example, the magnetically ordered state of a...
Show moreIf one could be built, a quantum computer would be capable of storing and manipulating quantum states with sufficient accuracy to carry out computations that no classical computer can do (most notably factoring integers in polynomial time). The greatest obstacle to building such a device is the problem of error and decoherence. Classical computers can exploit the physical robustness of ordered states to protect classical information (as in, for example, the magnetically ordered state of a hard drive). Remarkably, a type of quantum order known as topological order can, in principle, play the same role for quantum information. The best studied topologically ordered states are quantum Hall states. These states arise when a two-dimensional electron gas is placed in a strong magnetic field and cooled to low temperatures. Under the right conditions, the electrons condense into an incompressible quantum liquid whose excitations are particle-like objects with fractional charge (quasiparticles). Certain quantum Hall states are thought to be non Abelian. This means that when a finite number of quasiparticles are present and fixed in space there is a low energy Hilbert space with finite dimension, rather than a unique state. Unitary operations can then be carried out on this Hilbert space by adiabatically dragging quasiparticles around one another so that their world-lines sweep out braids in 2+1 dimensional space time. A quantum computer which stores quantum information in this Hilbert space and computes by braiding is known as a topological quantum computer. In this thesis I review our work on determining precisely how one would carry out a computation on a topological quantum computer. I focus on the so-called Fibonacci anyons--quasiparticles which may exist in the experimentally observed quantum Hall state at Landau level filling fraction ν = 12/5. I give explicit prescriptions for encoding qubits (quantum bits) using Fibonacci anyons, and show how one would carry out a universal set of quantum gates (the quantum analogs of Boolean logic gates) by braiding them. I then focus in particular on my work developing algorithms for performing brute force searches over the space of braids to find braids which produce unitary operations close to any desired operation. These brute force searches are a crucial part of our quantum gate construction, and I show that by using a so-called "load balanced" bidirectional search I can find braids which approximate any desired operation to an accuracy of 1 part in 10 5 . I then turn to my work calculating the Berry's phase obtained when quasiparticles are moved around one another in the Moore-Read state, a non Abelian state generally believed to describe the ν = 5/2 quantum Hall effect. This work is done using variational Monte Carlo, a method which allows one to numerically evaluate the Berry's phase for finite size systems. By exploiting certain properties of the Moore-Read state I have been able to study systems consisting of as many as 150 electrons. In so doing I have verified the conjectured connection between the Berry's phase produced by physically moving quasiparticles around one another and the mathematical phase one obtains by simply analytically continuing the quasiparticle coordinates. An added benefit of these calculations is that we can deduce the length scale which determines the size of the quasiparticles. This length scale dictates how far apart the quasiparticles must be in order to prevent errors when they are used for topological quantum computation.
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Date Issued: 2009
Identifier: FSU_migr_etd-0503
Format: Thesis

Title: The Changing Geomagnetic Field from the Ionosphere to the Core-Mantle Boundary.
Creator: Mozzoni, David T. (David Theodore), Van Winkle, David, Cunningham, Philip, Berg, Bernd, Cain, Joseph, Riley, Mark, Department of Physics, Florida State University
Abstract/Description: In this study two aspects of the geomagnetic field have been investigated. The first part focuses on perturbations of the external field, as seen by the CHAMP satellite and predicted by the Thermosphere-Ionosphere Electrodynamic General Circulation Model, for the purpose of helping to separate out ionospheric sources from the ambient geomagnetic field using a physics based approach. Part two looks at variations of the internal field through an examination of the South Atlantic Anomaly. The...
Show moreIn this study two aspects of the geomagnetic field have been investigated. The first part focuses on perturbations of the external field, as seen by the CHAMP satellite and predicted by the Thermosphere-Ionosphere Electrodynamic General Circulation Model, for the purpose of helping to separate out ionospheric sources from the ambient geomagnetic field using a physics based approach. Part two looks at variations of the internal field through an examination of the South Atlantic Anomaly. The NCAR Thermosphere-Ionosphere Electrodynamic General Circulation Model (TIE-GCM) is a self-consistent, global, atmospheric model that can be used to estimate magnetic perturbations at satellite altitude. These computed perturbations can then be compared with the magnetic vector data provided by low-earth orbiting satellites. Analogous CHAMP magnetic vector residuals were computed for these intervals using the CHAOS model to remove the core and crustal geomagnetic contributions. Under various input parameters, the TIE-GCM predictions were compared with the CHAMP residuals on an orbit by orbit basis demonstrating a reasonable agreement between the TIE-GCM estimates and the CHAMP residuals in non-polar, dayside regions (±50° magnetic latitude). Although no clear component or temporal correlation was discerned, evidence showing overall residual decrease in the comparisons presents the possibility of using the TIE-GCM to preprocess geomagnetic data for main field modeling purposes. A group of spherical harmonic field test models, developed utilizing this correction, verify the feasibility of this application. Variations of the internal field are investigated through study of the South Atlantic Anomaly, a region of low geomagnetic field measured at the Earth's surface. The time evolution of this feature is tracked at the surface over the last 400 years. Subsequently, its associations with the axial dipole moment and radial geomagnetic flux are examined at the core-mantle boundary, revealing in the process, a possible link between total unsigned flux and geomagnetic jerks.
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Date Issued: 2007
Identifier: FSU_migr_etd-2213
Format: Thesis

Title: Characterization, Fabrication, and Application of Molecularly Modified Semiconductor Nano-Devices.
Creator: Chen, Kan-Sheng, Xiong, Peng, Stiegman, Albert, Bonesteel, Nicholas, Chiorescu, Irinel, Crede, Volker, Department of Physics, Florida State University
Abstract/Description: The integration of soft (organic, biological) and hard (semiconducting, metallic) materials is of central importance in a host of emerging areas in materials research and nanoscience. Micro- and nano-scale hybrid soft/hard condensed matter structures are necessary components for such diverse applications as molecular electronics, biological and chemical sensing, directed assembly of functional nanostructures, and controlled solution-chemistry synthesis of nanomaterials. Organic molecules have...
Show moreThe integration of soft (organic, biological) and hard (semiconducting, metallic) materials is of central importance in a host of emerging areas in materials research and nanoscience. Micro- and nano-scale hybrid soft/hard condensed matter structures are necessary components for such diverse applications as molecular electronics, biological and chemical sensing, directed assembly of functional nanostructures, and controlled solution-chemistry synthesis of nanomaterials. Organic molecules have been employed not only as pathways for molecular recognition (e.g., in biosensing and directed assembly), but also as means to produce novel electronic functionality and even as active electronic components (e.g., in molecular junctions and single molecule transistors). In recent years, the scientific and engineering community has expended unprecedented effort on fundamental research in this area of nanotechnology, in hope of finding new paradigms of nanoelectronics and biomedical sensors. Inspired by this concept, this dissertation research explores the fabrication and characterization of several diverse types of solid-state/molecular hybrid nanostructures. The objectives of the research are two-fold: 1) to investigate directed self-assembly of semiconductor nano devices using molecular templates and examine molecular modification of the electronic characteristics of such devices, and 2) to study molecular functionalization of semiconductor micro/nano devices and the utilization of the functionalized devices for biomolecular sensing. Carbon nanotubes are a class of quasi-one-dimensional nanomaterials which have received extensive interest. Single-walled carbon nanotubes (SWNTs) exhibit excellent electrical properties suitable for high performance nanoelectronics. Individual SWNT field-effect transistors (FETs) have been shown to outperform state-of-the-art silicon counterparts. However, the integration of the SWNT devices into high-density architectures remains a challenge. Through the bottom-up approach, utilizing directed assembly of solvent suspended SWNTs onto a molecular template, we demonstrated the fabrication of high performance SWNT-FETs. Furthermore, selective functionalization of the metal electrodes with various polar molecules patterned by dip-pen nanolithography (DPN) gave rise to molecularly modified SWNT-FETs comprising of s-SWNT/molecule/Au heterojunction and resulted in pronounced modification to the key electrical characteristics of the SWNT-FETs, including subthreshold swing, ON/OFF ratio, and threshold voltage. By replacing the semiconducting SWNT to a metallic one, the same strategy produced m-SWNT/molecule/Au heterojunction, where the m-SWNT serves a metallic nanoprobe to study the tunneling properties of electrical current through the molecular SAM. The extraordinary precision and high spatial registry of DPN were also used to selectively functionalize active regions of micro-Hall magnetometers fabricated from an InAs quantum well heterostructures, as a necessary step towards using the μ-Hall devices for biomolecular sensing. To demonstrate detection of protein binding, the submicron molecular SAM functionalized region was subsequently attached with biotin molecules. The streptavidin coated superparamagnetic nanobeads were specifically assembled onto the biotinylated region of μ-Hall device through the biotin-streptavidin linkage and detected by the ac-phase sensitive Hall magnetometry at room temperature. The same sensing scheme was employed for label-free discrimination of a 35 base pair (bp) single strand (ss) DNA target, as a demonstration for point of care (POC) pathogenic DNA detection. An independent study of fluorescence microscopy based on arrays of mimic μ-Hall crosses showed that the platform is feasible for discriminating target DNA at a concentration of 36 pM and < 10 ppm in the presence of extraneous DNA. Binary oxide nanobelts, synthesized through a catalyst-free physical vapor deposition growth method, have emerged as a class of useful quasi-one-dimensional nanomaterials with unique "belt" like morphology. We have fabricated high-performance channel-limited SnO2 nanobelt FETs and utilized them as high sensitivity electrochemical transducers to detect various biomolecules by molecularly modifying the surface of the nanobelt with specific molecular receptors. We first demonstrated the efficacy of the sensing scheme and platform via detection of streptavidin protein using biotinylated SnO2 nanobelt FETs. The same platform was then modified to detect cardiac troponin I (cTnI) antigen, a biomedically significant marker that has been widely considered to be an effective indicator of cardiac damage upon trauma to the heart. A systematic effort was placed on optimizing and extending the capabilities of the platform. The procedures for functionalizing the oxide surface of nanobelts were modified to improve the contact transparency between the molecularly functionalized nanobelt channel and the metal electrodes to increase the yield in obtaining channel-limited SnO2 FETs for sensing applications. The versatility of the sensing scheme was finally extended by the successful attachment of DNA aptamer to the surface of the oxide nanobelts, which provides a potential general pathway to the binding of a broad variety of biomolecules, such as small molecules, proteins, nucleic acids, and even cells, tissues, and organisms. With the DNA aptamer functionalized SnO2 nanobelt FET devices, we successfully demonstrated the detection of thrombin molecules.
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Date Issued: 2011
Identifier: FSU_migr_etd-3833
Format: Thesis

Title: Charge and Spin Processes in Anisotropic Materials.
Creator: Jobiliong, Eric, Brooks, James S., Dalal, Naresh, Dobrosavljevic, Vladimir, Xiong, Peng, Piekarewicz, Jorge, Department of Physics, Florida State University
Abstract/Description: Several materials have been investigated in order to study charge and spin processes in anisotropic materials, particularly in high magnetic fields. The behavior of charge carriers in graphite based material, such as bulk graphite, mesoscopic graphite and graphite intercalated compound is studied. In novel spin systems, a dense Kondo system, CeAgSb2 which has ferro- and antiferro-magnetic ordering depending on the direction of the magnetic field has been selected, in order to study the...
Show moreSeveral materials have been investigated in order to study charge and spin processes in anisotropic materials, particularly in high magnetic fields. The behavior of charge carriers in graphite based material, such as bulk graphite, mesoscopic graphite and graphite intercalated compound is studied. In novel spin systems, a dense Kondo system, CeAgSb2 which has ferro- and antiferro-magnetic ordering depending on the direction of the magnetic field has been selected, in order to study the behavior of the spin in this system. Here, I present briefly an explanation of each part of this work. The nature of the magnetic field dependent metal-insulator behavior has been investigated in bulk highly oriented pyrolytic graphite at low temperatures by electronic transport. The metal-insulator behavior has been examined by applying uniaxial stress to our sample up to 8 kbar and found that the temperature dependence of the resistivity for different magnetic fields is the same as that in ambient pressure. The temperature dependence of the resistivity in mesoscopic graphite (called as few layer graphene or FLG) has a strong dependence on the thickness of the sample. The effect of electric field in FLG has been studied in both magnetic fields and zero field. The Shubnikov-de Haas (SdH) oscillations frequency increases with absolute value of the gate voltage. I do not observe the field induced charge density wave transition, which is observed in bulk graphite. The intercalated graphite superconductor CaC6 with Tc ~ 11.5 K has been synthesized and characterized with magnetoresistance measurements. By using the McMillan formula, the electron-phonon coupling constant is estimated to be Ê = 0.85 which places this material in the intermediate-coupling regime. The angular dependence of the upper critical field parallel and perpendicular to the superconducting planes suggests that this material is a quasi-2D superconductor. Of the dense Kondo materials in the class CeTSb2 (where T = Au, Ag, Ni, Cu, or Pd), CeAgSb2 is special due to its complex magnetic ground state, which exhibits both ferro- and anti-ferromagnetic character below an ordering temperature TO ~ 9.8 K. To further elucidate a description this magnetic ground state, I have carried out a systematic study of single crystalline CeAgSb2 by magnetic, electrical magneto-transport, and SdH studies. At zero field the temperature dependent resistivity below TO is most consistent with antiferromagnetic order, based on transport theory which includes magnon scattering.
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Date Issued: 2006
Identifier: FSU_migr_etd-3657
Format: Thesis

Title: Charge density waves and superconductivity in alpha-uranium.
Creator: VanGennep, Derrick, Department of Physics
Abstract/Description: We have measured the electrical resistivity and magnetoresistance of several α-uranium single crystals under pressure. The residual resistivity ratios (RRRs) of these samples ranged from 158 to 265 and the pressure dependence is discussed. Superconductivity was observed at temperatures varying from approximately 20 mK at ambient pressure to 3 K at 16 kBar and critical fields were observed up to 0.5 T at 16 kBar. Sharp features were seen at each of the three charge density wave (CDW)...
Show moreWe have measured the electrical resistivity and magnetoresistance of several α-uranium single crystals under pressure. The residual resistivity ratios (RRRs) of these samples ranged from 158 to 265 and the pressure dependence is discussed. Superconductivity was observed at temperatures varying from approximately 20 mK at ambient pressure to 3 K at 16 kBar and critical fields were observed up to 0.5 T at 16 kBar. Sharp features were seen at each of the three charge density wave (CDW) transitions starting near 40 K. The magnetic field and pressure dependences of the CDWs as well as superconductivity are presented and discussed.
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Date Issued: 2012
Identifier: FSU_migr_uhm-0132
Format: Thesis

Title: Charge Glassiness and Magnetotransport in Lightly Doped Cuprates.
Creator: Raičević, Ivana, Popović, Dragana, Dobrosavljević, Vladimir, Dalal, Naresh, Brooks, James, Wahl, Horst, Department of Physics, Florida State University
Abstract/Description: Magnetotransport and resistance noise have been studied in high quality singlecrystals of La2Cu1−xLixO4 and La2−xSrxCuO4 with x=0.03. The detailed measurements are performed at temperatures ranging from 0.03 to 190K and in magnetic fields of up to 18T parallel and perpendicular to the c axis of the crystals. Two specific problems have been addressed: the emergence of both the charge glassiness and positive magnetoresistance at very low temperatures in both materials, and the formation of...
Show moreMagnetotransport and resistance noise have been studied in high quality singlecrystals of La2Cu1−xLixO4 and La2−xSrxCuO4 with x=0.03. The detailed measurements are performed at temperatures ranging from 0.03 to 190K and in magnetic fields of up to 18T parallel and perpendicular to the c axis of the crystals. Two specific problems have been addressed: the emergence of both the charge glassiness and positive magnetoresistance at very low temperatures in both materials, and the formation of skyrmions at moderate temperatures in Li doped La2CuO4. The signatures of charge glassiness have been observed for the first time in lightly doped cuprates in this study. It is shown that the magnetoresistance exhibits features of glassy systems such as hysteresis, history dependence and memory effects at temperatures far below the spin-glass transition temperature. The resistance noise spectroscopy has also revealed that the charge dynamics becomes increasingly slow and correlated, i.e. glassy, as temperature goes to 0. All our results support the picture of the spatial segregation of holes into the hole-rich regions in the presence of the hole-poor antiferromagnetic (AF) domains in CuO2 planes, as inferred from other studies and different experimental techniques. However, for the first time, we have disclosed that these hole-rich regions are dynamic at such low temperatures. Furthermore, in the same temperature regime, we have observed that the magnetoresistance becomes positive. Our data strongly indicate that the onset of this positive sign strongly correlates to the emergence of the charge glass dynamics. The complicated behavior of the cuprates, as strongly correlated electron systems, is once again manifested through our observation of the emergence of the skyrmion texture in La2Cu0.97Li0.03O4. Our work, described in Chapter 5, presents the first experimental evidence for quantum (T = 0) skyrmions in the ground state of a doped antiferromagnet. The skyrmions are topologically nontrivial magnetic excitations that can be detected using the magnetoresistance measurements. In particular, we demonstrate that the skyrmions make a clear signature in the magnetotransport, since their formation is responsible for the change in the monotonic increase of the magnetoresistance step size with decreasing temperature.
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Date Issued: 2009
Identifier: FSU_migr_etd-2175
Format: Thesis

Title: The Cluster Structure of Oxygen Isotopes.
Creator: Johnson, Eric D., Rogachev, Grigory V., Humayun, Munir, Blessing, Susan K., Tabor, Samuel L., Volya, Alexander S., Department of Physics, Florida State University
Abstract/Description: The alpha-cluster structure of two oxygen isotopes, 17O and 18O, was studied using two experimental techniques. The first technique measured resonance elastic scattering of alpha particles and the second used the direct alpha-transfer reactions (6Li,d) and (7Li,t) to determine resonance properties. Motivation for this study was two-fold. First, the alpha-cluster structure of N not equal Z nuclei is poorly known and is a subject of intense theoretical discussion . Historically, the alpha...
Show moreThe alpha-cluster structure of two oxygen isotopes, 17O and 18O, was studied using two experimental techniques. The first technique measured resonance elastic scattering of alpha particles and the second used the direct alpha-transfer reactions (6Li,d) and (7Li,t) to determine resonance properties. Motivation for this study was two-fold. First, the alpha-cluster structure of N not equal Z nuclei is poorly known and is a subject of intense theoretical discussion . Historically, the alpha-particle model of the atomic nucleus was the leading model of nuclear structure. As it became clear that nuclei consist of protons and neutrons this model was replaced. The Pauli principle forbids nucleons from different alpha particles to be in the same state since the total wave function of an atomic nucleus must be antisymmetric. However, alpha clusters have been used to explain various nuclear effects including quasi-rotational bands of states with large alpha-particle widths which were observed in light 4N nuclei, 8Be, 12C, 16O and so on. Included here is a report on the observation of the alpha-cluster structure in the N not equal Z nucleus 18O. We measured the alpha-cluster structure of 18O using the Thick Target Inverse Kinematics (TTIK) technique . We found that 18O has a very elaborate alpha-cluster structure, including two unusual states with alpha widths larger than the single particle limit (the Wigner limit ). A comparison of the observed 18O alpha-cluster structure with the predictions of modern theoretical approaches is given. The peculiar nature of the two very broad states is discussed. Second, the alpha-cluster structure of near alpha-threshold excited states in 17O and 18O plays a crucial role in the field of nuclear astrophysics as it determines the rates of the 13C(alpha,n) and 14C(alpha,gamma) reactions. These reactions are thought to play important roles in stellar evolution of Asymptotic Giant Branch (AGB) stars. Unfortunately, direct measurement of these reactions is currently impractical. This has led to the development of indirect methods to determine reaction rates. One such method is the Asymptotic Normalization Coefficient (ANC) technique. We determined the alpha-cluster structure of several near alpha-threshold states in 17O and 18O using this ANC technique. Using this alpha-cluster information we were able to determine the 13C(alpha,n) reaction rate and reduce its uncertainty from approximately 300% to 25%. Also we were able to calculate the 14C(alpha,gamma) reaction rate. Accurately knowing the 13C(alpha,n) reaction rate is crucial to the modeling of AGB stars, and a reliable determination of the 14C(alpha,gamma) reaction rate is needed in order to help understand the unexplained abundance of 19F in the universe.
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Date Issued: 2008
Identifier: FSU_migr_etd-3494
Format: Thesis

Title: Clustering in ¹⁸O and ANC Measurements Using (⁶Li,D) Reactions.
Creator: Avila, Melina, Rogachev, Grigory, Humayun, Munir, Hoeﬂich, Peter, Volya, Alexander, Wiedenhover, Ingo, Department of Physics, Florida State University
Abstract/Description: Clustering in atomic nuclei is an interesting phenomenon that has been studied extensively in the past. However, most studies were related to clustering in α-like 4N nuclei. This work is focused on clustering in N≠Z non-self-conjugate nuclei. Two experimental approaches are applied. Properties of resonances above the α-decay threshold in 18O are studied using resonance elastic scattering of α-particles on 14C. Asymptotic Normalization Coefficients (ANCs) of near-threshold resonances in 16O,...
Show moreClustering in atomic nuclei is an interesting phenomenon that has been studied extensively in the past. However, most studies were related to clustering in α-like 4N nuclei. This work is focused on clustering in N≠Z non-self-conjugate nuclei. Two experimental approaches are applied. Properties of resonances above the α-decay threshold in 18O are studied using resonance elastic scattering of α-particles on 14C. Asymptotic Normalization Coefficients (ANCs) of near-threshold resonances in 16O, 17O and 20Ne are measured using sub-Coulomb α-transfer (6Li,d) reaction. To investigate the α-cluster states of 18O the α+14C elastic scattering reaction was studied using the Thick Target Inverse Kinematics (TTIK) technique. An exhaustive analysis of the 14C+α excitation functions using multi-channel, multi-level R-matrix approach has been performed. This analysis led to a more complete picture of α-cluster states in 18O. The excitation function was studied in an excitation energy range of 8 MeV-15 MeV. The most remarkable feature found in this analysis is the presence of states with high degree of clustering throughout the whole excitation energy range, including two states with pure α-cluster configuration. To provide a more detailed description of these two broad states, potential model calculations were preformed. These calculations reproduced rather well the excitation energy and width of these states. The Asymptotic Normalization Coefficient (ANC) technique can be used as an effective method to determine the astrophysical S-factor. Combination of the sub-Coulomb α-transfer reaction and application of the ANC technique in the analysis of the experimental data practically eliminates dependence of the result on model parameters, making this approach a very valuable tool for studies of astrophysically important reaction rates. In this study we report the ANC measurements of near threshold states for the reactions: 16O(6Li,d20Ne, 13C(6Li,d)17O and 12C(6Li,d)16O. Two astrophysically important reactions, 13C(α,n) and 12C(α,γ) were studied. The 13C(α,n) reaction is considered to be the main source of neutrons for the s-process in Asymptotic Giant Branch (AGB) stars and the 12C(α,γ) reaction is often regarded as the "holy grail"of nuclear astrophysics, because it enters as a crucial parameter for so many stellar processes. The ANCs of the near α-threshold states were used to calculate astrophysical S-factors and corresponding reaction rates.
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Date Issued: 2013
Identifier: FSU_migr_etd-8525
Format: Thesis

Title: Clustering Phenomena in the a = 10 T = 1 Isobaric Multiplet.
Creator: Kuchera, Anthony N., Rogachev, Grigory, Tabor, Samuel, Aldrovandi, Ettore, Prosper, Harrison, Volya, Alexander, Department of Physics, Florida State University
Abstract/Description: Clustering of α particles plays an important role in light atomic nuclei. For example, multicenter structures built on the well-known low-lying states of 8Be can be formed. The addition of nucleons to the system may result in covalent-like bonding between the two α-cores. These structures have been called ''nuclear molecules" because of their analog to atomic molecules. Investigation of these exotic nuclear structures is the main subject of this experimental work. Much of the experimental and...
Show moreClustering of α particles plays an important role in light atomic nuclei. For example, multicenter structures built on the well-known low-lying states of 8Be can be formed. The addition of nucleons to the system may result in covalent-like bonding between the two α-cores. These structures have been called ''nuclear molecules" because of their analog to atomic molecules. Investigation of these exotic nuclear structures is the main subject of this experimental work. Much of the experimental and theoretical work for molecular-like states has been done within the Be isotopes, however, despite of significant effort, our knowledge and understanding of molecular-like structures is still deficient. This is due to limited experimental information on the states of interest. The main goal of this work is to provide this information for the unbound T=1 states in A=10 systems and look for signatures of the exotic α:2N:α configurations. The T=1 states in 10B between Ex = 8.7- 12.1 MeV were studied using the 1H(9Be,α)6Li*(T=1, 0+, 3.56 MeV) reaction. An R-matrix analysis was used to extract parameters for the five resonances observed. The widths of the known 2+ resonance at 8.9 MeV have been measured and support the theoretical predictions that it is a highly clustered state and can be identified as a member of the α-np-α rotational band. The 4+ member was not observed in this reaction channel. In a second experiment, 6He+4He elastic scattering was used to probe resonances in 10Be in search of α-2n-α structures. Using the active target detector system, ANASEN, the excitation function was measured from Ex = 9.6 - 15.4 MeV. This was the first experiment in which the new active target detector, ANASEN, was used in filled (active target) mode. The excitation function shows a strong resonance at 10.2 MeV which was identified as 4+ and assigned to the extremely stretched α:2n:α configuration. A broad structure centered at 13.5 MeV was also observed and it may possibly be the 6+ member of this rotational band.
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Date Issued: 2013
Identifier: FSU_migr_etd-8585
Format: Thesis

Title: Cold Nuclear Matter Effects on J/ψ → e+e̅ and ψ́ → e+e̅ Production in d + Au Collisions at 200 GeV.
Creator: McGlinchey, D. (Darren), Frawley, Anthony, Eugenio, Paul, Humayun, Munir, Capstick, Simon, Adams, Todd, Department of Physics, Florida State University
Abstract/Description: Mesons composed of heavy quark-antiquark pairs, known as quarkonia, provide the only direct probe of the screening length in the deconfined state of quarks and gluons, known as the quark gluon plasma (QGP), which is believed to be produced in high energy heavy ion collisions. However, the observation of suppression of quarkonia production in heavy ion collisions at high energies is complicated by the modification of quarkonia production in normal nuclear matter. Measuring the modification of...
Show moreMesons composed of heavy quark-antiquark pairs, known as quarkonia, provide the only direct probe of the screening length in the deconfined state of quarks and gluons, known as the quark gluon plasma (QGP), which is believed to be produced in high energy heavy ion collisions. However, the observation of suppression of quarkonia production in heavy ion collisions at high energies is complicated by the modification of quarkonia production in normal nuclear matter. Measuring the modification of quarkonia production due to the effects of normal nuclear matter, often termed cold nuclear matter (CNM) effects, provide a critical baseline for understanding the properties of the QGP. Measurements of CNM effects on quarkonia production are also interesting in their own right, and can be measured independently in proton-nucleus (p+A) collisions. The modification of quarkonia production in p+A collisions provides insight into quarkonia production mechanisms unavailable through the study of proton-proton collisions alone. The study of quarkonia production in p+A collisions over a wide range of kinematic variables can also provide constraints on the modification of parton distribution functions in nuclei. In order to quantify the CNM effects present at the Relativistic Heavy Ion Collider (RHIC), the PHENIX experiment has recorded data on d+Au collisions at \sqsn=200 GeV. The analysis of J/psi→e+e-and psi'→e+e-production from that data set is presented here. Both J/psi and psi' production are found to be suppressed in d+Au relative to p+p collisions, with the suppression increasing for collisions with small impact parameters. The psi' production is found to be much more suppressed than J/psi production, a result which is unexpected based on measurements at lower collision energy and present theoretical pictures. A parametrization of the J/psi modification measured by PHENIX in terms of two CNM effects is also presented. One is the nuclear breakup of the forming quarkonium state through collisions with nucleons during the d+Au collision. The other is the modification of the gluon distribution in the Au nucleus. It is found that the two effects can be separated due to the very different impact parameter dependencies. A strongly non-linear geometric dependence on the modification of the gluon distribution function is observed, with the modification found to be concentrated near the center of the Au nucleus. This parametrization is also used to estimate the modification of J/psi production in Au+Au collisions due to CNM effects. This modification is compared to PHENIX measurements of J/psi production in Au+Au collisions. Suppression of J/psi production in Au+Au collisions beyond CNM effects is observed. This excess suppression is interpreted as suppression of J/psi production due to the formation of a QGP.
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Date Issued: 2012
Identifier: FSU_migr_etd-5399
Format: Thesis

Title: Comparing the Poisson-Boltzmann Equation to Alternative Electrostatic Theories and Improving Stochastic Techniques for Implicit Solvent Models.
Creator: Harris, Robert C., Fenley, Marcia O., Blaber, Michael, Berg, Bernd A., Van Winkle, David, Dobrosavljevic, Vladimir, Department of Physics, Florida State University
Abstract/Description: The Poisson-Boltzmann equation, PBE, the linearized PBE, LPBE, and generalized Born, GB, model are implicit solvent methods that accelerate biophysical calculations by eliminating the need to integrate across the solvent's degrees of freedom. This thesis compares the predictions of the Poisson-Boltzmann equation, PBE, to those of another electrostatic theory, the counterion condensation theory, CCT. It demonstrates that the CCT's predictions of the salt dependence of the electrostatic binding...
Show moreThe Poisson-Boltzmann equation, PBE, the linearized PBE, LPBE, and generalized Born, GB, model are implicit solvent methods that accelerate biophysical calculations by eliminating the need to integrate across the solvent's degrees of freedom. This thesis compares the predictions of the Poisson-Boltzmann equation, PBE, to those of another electrostatic theory, the counterion condensation theory, CCT. It demonstrates that the CCT's predictions of the salt dependence of the electrostatic binding free energy agree with those of the PBE, but its predictions of the electrostatic binding free energy itself do not. This observation is explained by deriving a simple analytical expression for the salt dependence of the electrostatic binding free energy from the GB model. This expression indicates that essentially any electrostatic theory with the same long-distance predictions will predict the same salt dependence, it explains the observed correlations between this salt dependence and various empirical quantities, and it provides a rapid method for predicting its change upon mutation of the charged residues of the binding partners. Implicit solvent models do include several approximations whose validity should be evaluated to determine the reliability of their estimates of experimental quantities. In this thesis the effect of finite ion sizes upon PBE solutions is examined with the size-modified PBE, SMPBE. These findings show that the SMPBE predicts different dependences of electrostatic energies upon ion size than the PBE, but whether these changes lead to different predictions for observable quantities is not clear. Additionally, the ion-exclusion layer does not match the dependences on ion size given by the SMPBE, and combined with the superior physical basis of the SMPBE, the use of the ion-exclusion layer is called into question. Additionally, this thesis improves stochastic solvers of the LPBE and presents a new stochastic solver of the GB model. By optimizing the bias-generating parameters in a walk-on-spheres, WOS, LPBE solver, dividing the variance evenly across the atoms of the molecule, and using an approximate nearest-neighbor solver, WOS solvers can solve the LPBE in times comparable to deterministic solvers. The stochastic GB solver has the advantage over traditional analytical solvers of the GB in that analytical solutions to the GB model must approximate a set of parameters called the Born radii, and the error due to this approximation cannot usually be evaluated. The stochastic solver, on the other hand quantifies this error and converges to the exact GB model with additional computation time. This behavior allows the validity of the Born approximation itself to be evaluated, and the results presented here indicate that the GB model gives different estimates of the electrostatic binding free energy than the LPBE. More research will be required to refine the GB approximation to better compute the electrostatic binding free energy, and that the radii in the stochastic method are arbitrarily precise indicates that the stochastic solver will be useful in this endeavor.
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Date Issued: 2012
Identifier: FSU_migr_etd-5687
Format: Thesis

Title: Computational and Analytical Studies of Magnetization Switching in Iron Nanopillars.
Creator: Thompson, Sam Hill, Rikvold, Per Arne, Ye, Ming, Brown, Gregory, Van Moln´ar, Stephan, Berg, Bernd, Department of Physics, Florida State University
Abstract/Description: In this dissertation we study the behavior of several computational models of a magnetic nanopillar. We first compare the effect that coarse-graining the computational lattice has on the magnetization switching for three degrees of discretization. Bimodal switching-time distributions are found for all three models, however the underlying mechanism is different for each one. In the lowest-resolution, single-spin model, a bimodal distribution is the result of spin precession which sometimes...
Show moreIn this dissertation we study the behavior of several computational models of a magnetic nanopillar. We first compare the effect that coarse-graining the computational lattice has on the magnetization switching for three degrees of discretization. Bimodal switching-time distributions are found for all three models, however the underlying mechanism is different for each one. In the lowest-resolution, single-spin model, a bimodal distribution is the result of spin precession which sometimes crosses the threshold defining a switching event early or in the next precession period, depending on thermal fluctuations. For the medium-resolution, stack-of-spins model, the presence of either one or two propagating domain walls during the switching event determines the total switching time, leading to the observed bimodal distribution. The most realistic model, which employs a high-resolution computational lattice, permits multiple switching paths, some of which are characterized by their visitation to a metastable free-energy well and consequently longer lifetimes. It is also notable that the medium-resolution model exhibits reentrant behavior for reversal fields that are applied close to the easy axis. The highest-resolution model is studied in detail, due to its complexity, which precludes a simple description of the mechanism resulting in bimodal switching-time behavior. Phase-space portraits of components of the total energy indicate that the metastable free-energy basin is circumvented for short-lived trials. Sufficient statistics are gathered to allow Markov matrices describing the average behavior of each mode to be investigated. Eigenvectors of these matrices provide estimates of the probability distribution of the largest transient for each mode in the energy space, while the projective dynamics technique identifies the location of the free-energy saddle point. The hypothesis that the visitation of the metastable well underlies the bimodal behavior is further reinforced by comparing the long-lived trials to simulations that are constrained to start in the metastable state. Finally, exploratory results for thermally-assisted magnetization reversal of the highest-resolution model are provided to test the assumption that it is only necessary to increase the temperature at the endcaps of the pillar, since this the site of nucleation. By introducing additional thermal energy to the pillar, the coercive field might be lowered, relaxing the required field of the write head of a hard disk drive. We find that varying the maximum temperature of a narrow pulse, centered at the top of the pillar, results in a very modest change in the coercivity when the maximum temperature is kept close to, or below, the Curie temperature. This effect is largely limited by the added heat diffusing quickly to the constant-temperature substrate. Switching fields were significantly reduced for pulse widths that were large enough to elevate the temperature of the entire pillar. However, using such large pulses stretch the approximations of the model. Another approach is attempted, tuning the parameter that controls energy exchange between the temperature bath and the spins. This also results in only a minimal reduction of the coercive field. Some suggestions are given for future computational studies of thermally-assisted magnetization reversal.
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Date Issued: 2009
Identifier: FSU_migr_etd-1359
Format: Thesis

Title: Computational Studies of Equilibrium and Non-Equilibrium Phase Diagrams and Critical Properties of Two Physical and Chemical Model Systems with Both Short-Range and Long-Range Interactions or Reactivities.
Creator: Chan, Chor-Hoi, Rikvold, Per Arne, Shanbhag, Sachin, Brown, Gregory, Capstick, Simon, Xiong, Peng, Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: In this dissertation, we introduce long-range interactions into one equilibrium model (Ising model) and one non-equilibrium system (Ziff-Gulari-Barshad model), and study their phase diagrams and critical properties. A new approach to do Wang-Landau simulation: macroscopically constrained Wang-Landau, is proposed in connection with the former system. Our macroscopically constrained Wang-Landau method breaks a multidimensional random walk process in phase space into many separate, one...
Show moreIn this dissertation, we introduce long-range interactions into one equilibrium model (Ising model) and one non-equilibrium system (Ziff-Gulari-Barshad model), and study their phase diagrams and critical properties. A new approach to do Wang-Landau simulation: macroscopically constrained Wang-Landau, is proposed in connection with the former system. Our macroscopically constrained Wang-Landau method breaks a multidimensional random walk process in phase space into many separate, one-dimensional random walk processes in the energy space. Each of these random walks is constrained to a different value of the macroscopic order parameters. By knowing the distribution of these constrained variables, we can deduce the multi-variable density of states. When the multi-variable density of states for one set of external parameters is obtained, the density of states at any point in the phase diagram can be obtained by simple transformations. After that, all thermodynamic quantities can be obtained. We apply this method to an antiferromagnetic Ising model with a ferromagnetic long-range interaction. The addition of the long-range interaction induces metastable regions in the phase diagram, and a mean-field class critical point emerges for sufficiently strong long-range interaction. We demonstrate how to use the multi-variable density of states obtained to sketch out the complicated phase diagrams for different values of the long-range interaction. We also give free-energy plots, and plots of the distributions of the order parameters of the system for different special points in these phase diagrams. The Ziff-Gulari-Barshad (ZGB) model, a simplified description of the oxidation of carbon monoxide (CO) on a catalyst surface, is widely used to study properties of nonequilibrium phase transitions. Instead of restricting the CO and atomic oxygen (O) to react to form carbon dioxide (CO₂) only when they are adsorbed in close proximity, we consider a modified model that includes an adjustable probability for adsorbed CO and O atoms located far apart on the lattice to react. We employ large-scale Monte Carlo simulations to study the critical properties of this system. We find that the nonequilibrium critical point changes from the two-dimensional Ising universality class to the mean-field universality class upon introducing even a weak long-range reactivity mechanism.
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Date Issued: 2016
Identifier: FSU_FA2016_Chan_fsu_0071E_13552
Format: Thesis

Title: Computational Studies of Lattice Gas Models.
Creator: Juwono, Tjipto, Rikvold, Per Arne, Steinbock, Oliver, Capstick, Simon, Van Winkle, David, Brown, Gregory, Department of Physics, Florida State University
Abstract/Description: We have studied the effect of diffusion on the dynamics of desorption on a lattice-gas model The chemical potential during the adsorption phase was varied in order to vary the initial size distribution for the desorption phase. The effect of diffusion on the size distribution dynamics during the desorption process was observed by turning the diffusion on and off while keeping the chemical potential during desorption constant. We study the effect of diffusion on correlation length during the...
Show moreWe have studied the effect of diffusion on the dynamics of desorption on a lattice-gas model The chemical potential during the adsorption phase was varied in order to vary the initial size distribution for the desorption phase. The effect of diffusion on the size distribution dynamics during the desorption process was observed by turning the diffusion on and off while keeping the chemical potential during desorption constant. We study the effect of diffusion on correlation length during the desorption process. We also compare size distribution dynamics without and with the application of diffusion and study the effect of diffusion on the size distributions at given coverages. During the desorption process, the correlation length increased up to a maximum and then decreased. We found that diffusion tends to increase correlation length at any given coverage. However diffusion increase correlation length by very small percentage in the regime where correlation length is decreasing, and increase it more significantly when the correlation length is increasing. When the correlation length of the initial configuration is large, the correlation length during the desorption only increase slightly at initial coverages and decrease for the most part. As a result, diffusion only increase correlation length insignificantly during the whole process. When the correlation length of the initial configuration is small, the correlation length increase during a significant part of the process. As a result, diffusion increase correlation length significantly during the process. By studying the size distributions at some coverages during the process -before and after diffusion- we found that diffusion tends to shrink large clusters and grow or create small clusters. When the clusters growth or creating of new clusters by diffusion is small, the increase of correlation length by diffusion is small and large otherwise. We also study Bromine and Chlorine chemisorption on a Ag(100) surface, using a lattice-gas model and the quantum-mechanical Density Functional Theory (DFT) method. In this model the Br and Cl ions adsorb at the fourfold hollow sites of the Ag(100) surface, which can be represented by a square lattice of adsorption sites. Five different coverages were used for each kind of adsorbate. For each adsorbate and coverage, we obtained the minimum-energy configuration, its energy, and its charge distribution. From these data we calculated dipole moments, lateral interaction energies, and binding energies. Our results show that for Br the lateral interactions obtained by fitting to the adsorption energies obtained from the DFT calculation are consistent with long-range dipole-dipole lateral interactions obtained using the dipole moments calculated from the DFT charge distribution. For Cl we found that, while the long-range dipole-dipole lateral interactions are important, short-range attractive interactions are also present. Our results are overall consistent with parameter estimates previously obtained by fitting room-temperature Monte Carlo simulations to electrochemical adsorption isotherms [I. Abou Hamad et al., J. Electroanal. Chem. 554 (2003), 211; Electrochim. Acta 50 (2005), 5518].
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Date Issued: 2012
Identifier: FSU_migr_etd-4937
Format: Thesis

Title: A Configuration Space Monte Carlo Algorithm for Solving the Nuclear Pairing Problem.
Creator: Lingle, Mark, Volya, Alexander, Kopriva, David A., Capstick, Simon, Wiedenhöver, Ingo, Manousakis, Efstratios, Florida State University, College of Arts and Sciences, Department...
Show moreLingle, Mark, Volya, Alexander, Kopriva, David A., Capstick, Simon, Wiedenhöver, Ingo, Manousakis, Efstratios, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Nuclear pairing correlations using Quantum Monte Carlo are studied in this dissertation. We start by defining the nuclear pairing problem and discussing several historical methods developed to solve this problem, paying special attention to the applicability of such methods. A numerical example discussing pairing correlations in several calcium isotopes using the BCS and Exact Pairing solutions are presented. The ground state energies, correlation energies, and occupation numbers are compared...
Show moreNuclear pairing correlations using Quantum Monte Carlo are studied in this dissertation. We start by defining the nuclear pairing problem and discussing several historical methods developed to solve this problem, paying special attention to the applicability of such methods. A numerical example discussing pairing correlations in several calcium isotopes using the BCS and Exact Pairing solutions are presented. The ground state energies, correlation energies, and occupation numbers are compared to determine the applicability of each approach to realistic cases. Next we discuss some generalities related to the theory of Markov Chains and Quantum Monte Carlo in regards to nuclear structure. Finally we present our configuration space Monte Carlo algorithm starting from a discussion of a path integral approach by the authors [2, 3]. Some general features of the Pairing Hamiltonian that boost the effectiveness of a configuration space Monte Carlo approach are mentioned. The full details of our method are presented and special attention is paid to convergence and error control. We present a series of examples illustrating the effectiveness of our approach. These include situations with non-constant pairing strengths, limits when pairing correlations are weak, the computation of excited states, and problems when the relevant configuration space is large. We conclude with a chapter examining some of the effects of continuum states in 24O.
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Date Issued: 2015
Identifier: FSU_migr_etd-9383
Format: Thesis

Title: Constraining Type Ia Supernovae Progenitor Parameters via Light Curves.
Creator: Sadler, Benjamin, H¨oﬂich, Peter, Chicken, Eric, Gerardy, Chris, Piekarewicz, Jorge, Prosper, Harrison, Department of Physics, Florida State University
Abstract/Description: I study thermonuclear explosions of White Dwarf (WD) stars, or so-called Type Ia supernovae (SNe Ia). A WD is the final stage of stellar evolution of a star with an initial mass of less than 8 Solar masses, and the thermonuclear explosion occurs either when the WD is in a close binary system where mass overflows from a companion star in a red-giant or asymptotic-branch giant phase, or when two WDs merge. SNe Ia are as bright as their entire host galaxy, which allows their use as long-range...
Show moreI study thermonuclear explosions of White Dwarf (WD) stars, or so-called Type Ia supernovae (SNe Ia). A WD is the final stage of stellar evolution of a star with an initial mass of less than 8 Solar masses, and the thermonuclear explosion occurs either when the WD is in a close binary system where mass overflows from a companion star in a red-giant or asymptotic-branch giant phase, or when two WDs merge. SNe Ia are as bright as their entire host galaxy, which allows their use as long-range cosmic beacons. Although their maximum brightness may vary by a factor of 20, an empirical correlation between their primary parameters of light curve (LC) shape and their intrinsic brightness allows us to account for the majority of this dispersion, with a residual uncertainty of roughly 20%. This calibration has led to their use as standardizable candles, which led to the discovery of the dark energy. Higher precision is needed to determine the nature of the dark energy, however, and to accomplish this we turn to secondary parameters of LC variation. I have devised a general scheme and developed a code to analyze large sets of LC data for these secondary parameter variations which is based on a combination of theoretical model template fitting and Principal Component Analysis. Novel methods for finding statistical trends in sparsely-sampled and non-coincidental light curve data are explored and utilized. In practice, data sets for different supernovae are inhomogeneous in time, time coverage and accuracy, but I have developed a method to remap these inhomogeneous data sets of large numbers of individual objects to a homogeneous data set centered in time and magnitude space from which we can obtain the external, primary, and secondary LC parameters of individual objects. The set of external parameters of a given SN include the time of its maximum light in various bands, its distance modulus, the extinction along the light path, and redshift corrections (K-corrections) due to cosmic expansion. I investigate the intrinsic primary parameter variation of SNe Ia via template fitting, and then probe the secondary LC variations using monochromatic differential analysis in the (UBV) bands. We use photometry from 25 SNe Ia which were recently and precisely observed by the Carnegie Supernova Project to analyze the presence of theoretical model-based differential LC signatures of Main-Sequence mass variation of the progenitor stars when they formed, central density variation of the WD at the time of the explosion, and metallicity Z variation the in the progenitors. The light curves in the V band are found to provide the highest accuracy in determining the distance modulus, K-corrections, extinction, main-sequence mass and central density of the WD progenitor, and also the V-band LCs are insensitive to metallicity. Moreover, the V-band appears to be the band which is most stable for differential creation due to the stability of the differentials with respect to uncertainties in the SNe pairs' primary parameters. The B-band's larger K-correction uncertainties and dependence on progenitor metallicity and primary parameter uncertainties discourages its use in secondary parameter differential analysis. As with B, the U-band also suffers large uncertainties in extinction and K-corrections, but this band is a good indicator of metallicity, because the effects of metallicity variation on differential LCs are larger by an order of magnitude than the Main-Sequence mass and central density effects combined. Our sample includes three SN1991T-like objects, but we find no evidence of secondary parameter variation among them, and conclude that this class of object may be identified by its primary LC parameter as well as its lack of secondary parameter features. Accounting for these secondary parameters reduces the residuals in the fiducial LC fits from 0.2 magnitude to approximately 0.02 magnitude, a requirement for high-precision cosmology based on SNe Ia. I also reconstruct the distributions of Main-Sequence mass, central density, and metallicity for the progenitors of the 25 SNe in our sample. I find that most SNe in our sample originate from stars close to the upper limit of the range of possible Main-Sequence masses, indicating that most SNe Ia explode relatively soon after the progenitor star's formation. However, the reconstructed progenitor mass distribution displays a long tail down to lower-mass objects of about 1.5 Solar masses. The central density secondary parameter distribution is much flatter, and shows SNe originate from WD progenitors of a wide range of central densities, from as low as 1.5E9 grams per cubic centimeter, and up to the limit of accretion-induced collapse, suggesting that some potential SNe Ia progenitors become neutron stars instead. Although our sample size is small, all SN1991bg-like objects in it come from progenitors with low reconstructed central density and metallicity secondary parameters. Because SN1991bg-like objects are only found in local samples and not in high-redshift searches, our findings suggest that these progenitor systems are formed at high redshifts but exhibit long delay times before the explosion.
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Date Issued: 2012
Identifier: FSU_migr_etd-5156
Format: Thesis

Title: Controlled Growth of Ultrathin Molecular Films of the P-Phenylene Oligomers on Alkali Halide Substrates.
Creator: Kintzel, Edward J., Safron, Sanford A., Van Winkle, David H., Bonesteel, Nicholas E., Lind, David M., Department of Physics, Florida State University
Abstract/Description: Controlled growth of the aromatic p-phenylene oligomer molecules of p-4P, p-5P, and p-6P adsorbed onto individual KBr(001), KCl(001), NaCl(001), and NaF(001) substrates, has been investigated primarily by x-ray diffraction (XRD) and to a lesser degree by atomic force microscopy (AFM). XRD analysis provides evidence that the temperature of the alkali halide substrate during deposition, substrate lattice constant, and molecular length affects the molecular orientations within these adsorbed...
Show moreControlled growth of the aromatic p-phenylene oligomer molecules of p-4P, p-5P, and p-6P adsorbed onto individual KBr(001), KCl(001), NaCl(001), and NaF(001) substrates, has been investigated primarily by x-ray diffraction (XRD) and to a lesser degree by atomic force microscopy (AFM). XRD analysis provides evidence that the temperature of the alkali halide substrate during deposition, substrate lattice constant, and molecular length affects the molecular orientations within these adsorbed ultrathin films. AFM images contribute independent evidence for a surface microstructure evolution that is consistent with the XRD results. An initial in-plane x-ray study suggests a possible explanation for the preferential orientation of p-6P crystallites, as observed in AFM images. This alignment is approximately along the [110] direction of the KCl(001) substrate. From this work, oriented films of the above mentioned p-phenylene oligomer molecules can therefore be grown with desired molecular orientations by careful selection of an appropriate combination of the above deposition parameters.
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Date Issued: 2002
Identifier: FSU_migr_etd-2903
Format: Thesis

Title: Coulomb Liquids: from Electron to Biology Systems.
Creator: Pramudya, Yohanes H. R., Dobrosavljevic, Vladimir, Dalal, Naresh, Manousakis, Efstratios, Berg, Bernd A., Engel, Lloyd, Department of Physics, Florida State University
Abstract/Description: We study the unusual transport behavior driven mostly by the correlations between the charge carriers in lattice and continuum systems. The strongly correlated systems are studied in the classical limit where the Coulomb interaction dominates the systems and brings the systems into the nearly frozen state that we call Coulomb Liquids. Theoretical description of the materials with the strongly interacting electron systems in the lattice or solid state physics and ions in biological systems or...
Show moreWe study the unusual transport behavior driven mostly by the correlations between the charge carriers in lattice and continuum systems. The strongly correlated systems are studied in the classical limit where the Coulomb interaction dominates the systems and brings the systems into the nearly frozen state that we call Coulomb Liquids. Theoretical description of the materials with the strongly interacting electron systems in the lattice or solid state physics and ions in biological systems or solutions are constantly challenging problems in condensed matter physics and biophysics. First we investigate the non-activated behavior of transport that observed near Wigner crystallization in two dimensions electron gas (2DEG) that is observed experimentally. The effect of Coulomb interaction in the system is studied with Monte Carlo (MC) simulation and extended dynamical mean field theory (EDMFT) in hypercubic lattice and pseudogap phase is found as a robust feature driven by long-range interaction. In the second part of the thesis we study the effect of geometrical frustration in pyrochlore lattice which competes with the interaction-driven frustration. The MC and EDMFT methods give pseudo-gap phase as found in cubic lattice that has no geometrical frustration and agree with the unusual transport property of ancient magnet/magnetite above the Verwey transition. The third part discusses the effect of strongly-correlated liquid (SCL) model by Shklovskii and the mean-field approach of Poisson-Boltzmann equation (PBE) describing the screening of macro-ions in solution or biological system. We compare those approximations with MC simulation and explain which approximation is good at different limit of temperature or ion density. And the last part describes the visualization for different type of interactions and the effect of filling, disordered, etc. from the study of Coulomb liquids.
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Date Issued: 2013
Identifier: FSU_migr_etd-8715
Format: Thesis

Title: Coulomb Pseudogaps and Their Role at Metal-Insulator Transitions.
Creator: Mahmoudian, Samiyeh, Dobrosavljević, Vladimir, Dalal, Naresh S., Balicas, Luis, Manousakis, Efstratios, Capstick, Simon, Florida State University, College of Arts and Sciences,...
Show moreMahmoudian, Samiyeh, Dobrosavljević, Vladimir, Dalal, Naresh S., Balicas, Luis, Manousakis, Efstratios, Capstick, Simon, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: We investigate various fundamental aspects of the metal insulator transition (MIT) by employing several theoretical approaches. Describing the novel features of interacting electronic systems remains one of the principle challenges to theoretical condensed matter physics. Therefore, any effort to provide a deep insight into understanding the nature of MITs opens a new avenue for development of modern technology. First, we present a complete analytical and numerical solution of the Typical...
Show moreWe investigate various fundamental aspects of the metal insulator transition (MIT) by employing several theoretical approaches. Describing the novel features of interacting electronic systems remains one of the principle challenges to theoretical condensed matter physics. Therefore, any effort to provide a deep insight into understanding the nature of MITs opens a new avenue for development of modern technology. First, we present a complete analytical and numerical solution of the Typical Medium Theory (TMT) for the metal-insulator transition. In this theory, we self-consistently calculate the typical amplitude of the electron wave-functions, representing the conceptually simplest order-parameter for the Anderson transition. We classify all possible universality classes for the critical behavior, that can be found within such a mean-field approach. This provides insights into how interaction-induced renormalizations of the disorder potential may produce qualitative modifications of critical behavior. We also formulate a simple description of the leading critical behavior of varies quantities, and then obtain an effective Landau theory for Anderson localization. We also develop an efficient numerical algorithm, "Cluster Typical Medium Theory" (CTMT) to capture both non-local effects and localization in disordered electronic systems. Our formalism utilizes the momentum-resolved typical density of states to characterize the localization transition. We apply this approach to the Anderson model of localization in one and two-dimensions. In one dimension, we find that the critical disorder strength scales inversely with the linear cluster size with a power-law, W[subscript c] ∼ (1/L[subscript c])[superscript 1/v]; whereas in two dimensions, the critical disorder strength decreases logarithmically with the linear cluster size. Our results are in agreement with the one-parameter scaling theory. Furthermore, we show how spatial correlations can also be captured analytically within such a self-consistent theory, by utilizing the standard Landau method of allowing for (slow) spatial fluctuations of the order parameter, and performing an appropriate gradient expansion. Our theoretical results provide insight into recent STM experiments, which were used to visualize the spatially fluctuating electronic wave functions near the metal insulator transition in Ga[subscript 1-x]Mn[subscript x]As.$ We show that, within our theory, all features of the experiment can be accounted for by considering a model of disorder renormalized by long-range Coulomb interactions. This includes the pseudogap formation, the C(R) ∼ 1/R form of the LDOS autocorrelations function, and the ζ ∼ 1/E energy dependence of the correlation length at criticality. In the second part of my Thesis, we show that introducing long-range Coulomb interactions immediately lifts the massive ground state degeneracy induced by geometric frustration for electrons on quarter-filled triangular lattices in the classical limit. Important consequences include the stabilization of a stripe-ordered crystalline (global) ground state, but also the emergence of very many low-lying metastable states with amorphous "stripe-glass" spatial structures. Melting of the stripe order thus leads to a frustrated Coulomb liquid at intermediate temperatures, showing remarkably slow (viscous) dynamics, with very long relaxation times growing in Arrhenius fashion upon cooling, as typical of strong glass formers. On shorter time scales, the system falls out of equilibrium and displays the aging phenomena characteristic of supercooled liquids above the glass transition. Our results show remarkable similarity with the recent observations of charge-glass behavior in ultra-clean triangular organic materials of the θ-(BEDT-TTF)₂ family.
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Date Issued: 2015
Identifier: FSU_2015fall_Mahmoudian_fsu_0071E_12817
Format: Thesis

Title: A Dalitz Plot Analysis and Extraction of Spin Density Matrix Elements for the Ω → 3Π Decay.
Creator: Zeoli, Christopher Paul, Crede, Volker, Sura, Philip, Eugenio, Paul Michael, Roberts, Winston, Adams, Todd, Florida State University, College of Arts and Sciences, Department of...
Show moreZeoli, Christopher Paul, Crede, Volker, Sura, Philip, Eugenio, Paul Michael, Roberts, Winston, Adams, Todd, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: At the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson National Laboratory (JLab), $\omega$ vector-mesons were photo-produced off a fixed, liquid-hydrogen target during the 2009 run-period via the reaction $\gamma p \rightarrow p \omega$. The charged final-state particles from the $\omega$~resonance decays were detected by the CEBAF Large Acceptance Spectrometer (CLAS). With a combination of measurements which involved the use of time and energy-deposit counters as well as...
Show moreAt the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson National Laboratory (JLab), $\omega$ vector-mesons were photo-produced off a fixed, liquid-hydrogen target during the 2009 run-period via the reaction $\gamma p \rightarrow p \omega$. The charged final-state particles from the $\omega$~resonance decays were detected by the CEBAF Large Acceptance Spectrometer (CLAS). With a combination of measurements which involved the use of time and energy-deposit counters as well as reconstructed drift chamber (DC) tracks, the 4-momenta and vertices of the initial- and charged final-state particles were determined. Subsequent to reconstruction, event selection, kinematic fitting, signal and background separation, and detector efficiency simulation of the data for the three-pion final-state, i.e. $\omega \rightarrow \pi^+~\pi^-~(\pi^0)$, the Florida State University (FSU) Experimental Hadronic Nuclear Group has extracted the differential production cross section.\\ \indent With such data and the measured differential cross section in hand, I have conducted a Dalitz plot analysis of the $\omega \rightarrow 3\pi$ decay in close cooperation with the Joint Physics Analysis Center (JPAC) at JLab. The decay probability density separates into angle-dependent and -independent factors: the Spin Density Distribution (SDD) which is proportional to the differential cross section, and the reduced decay distribution (RDD) which is proportional to the decay width, respectively. The Spin Density Matrix Elements (SDMEs) for an unpolarized beam were obtained from fitting the SDD. In addition, fits for two different RDDs, i.e. a Dalitz plot distribution and a JPAC distribution, have been underway. The former is a truncated polynomial expansion of Lorentz Invariant Dalitz plot variables. The latter was based on the isobar model of the $\omega$ decay. Having made use of sub-energy unitarity, this model accounts for both elastic and inelastic 3-body re-scattering effects. Plus, fitting this model to measured data is a first. A comparison through fit parameters of each reduced distribution is intended. Lastly, my results and as well as a discussion of future extensions to this study and the prospects for similar light-meson-decay analyses are concluded at the end of this thesis.\\
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Date Issued: 2016
Identifier: FSU_FA2016_Zeoli_fsu_0071E_13456
Format: Thesis

Title: Dark Matter Detection in Supersymmetric Models with Non-Universal Gaugino Masses.
Creator: Park, Eun-Kyung, Baer, Howard, Aldrovandi, Ettore, Reina, Laura, Prosper, Harrison, Volya, Alexander, Department of Physics, Florida State University
Abstract/Description: SUSY is one of the most promising new physics ideas, and will soon be tested at high energy accelerators like the CERN LHC. Moreover SUSY provides a good candidate for cold dark matter (CDM). In this dissertation, we investigated phenomenology of SUSY models with non-universal gaugino masses (NUGM) at colliding experiments using event generators such as ISAJET and examined direct and indirect detection rates of relic neutralino CDM in the universe. The motivation of these models is that in...
Show moreSUSY is one of the most promising new physics ideas, and will soon be tested at high energy accelerators like the CERN LHC. Moreover SUSY provides a good candidate for cold dark matter (CDM). In this dissertation, we investigated phenomenology of SUSY models with non-universal gaugino masses (NUGM) at colliding experiments using event generators such as ISAJET and examined direct and indirect detection rates of relic neutralino CDM in the universe. The motivation of these models is that in most of mSUGRA parameter space, the relic density $Omega_{ z_1}h^2$ is considerably larger than the WMAP measurement, and it is well known that if non-universal gaugino masses are allowed, then qualitatively new possibilities arise that are not realized in the mSUGRA model. Our first NUGM attempt is to allow a mixed wino-bino lightest SUSY particle (LSP) by lowering $SU(2)$ gaugino mass $M_2$ at the weak scale from its mSUGRA value while keeping the hypercharge gaugino mass $M_1$ fixed ({it Mixed Wino Dark Matter}). In this model, wino-like $ ilde{Z_1}$ with sufficiently low $M_2$ compared to $M_1$ enhances $ ilde{Z_1} ilde{Z_1} ightarrow W_{1}^{+} W_{1}^{-}$ annihilations to reach the WMAP measured relic density. The second attempt is study on the NUGM model with different signs of $M_1$ and $M_2$ ({it Bino-Wino Co-Annihilation Scenario}). In this case, there is little mixing, so that $ ilde{Z_1}$ remains nearly a pure bino or a pure wino. By increasing $M_1 simeq M_2$, enhanced bino-wino co-annihilation can achieve the relic neutralino abundance. The final attempt of NUGM models is lowering the $SU(3)$ gaugino mass to diminish the effect of the large top quark Yukawa coupling in the running of the higgs mass, so that the value of superpotential $mu$ parameter gets efficiently low to give rise to mixed higgsino dark matter ({it Mixed Higgsino Dark Matter}). Consequences of these NUGM model studies show us that relaxing universality of gaugino masses in SUSY models leads to enhanced direct and indirect dark matter detection rates and reduced $m_{ ilde{Z_2}}-m_{ ilde{Z_1}}$ mass gap so that the LHC and ILC can distinguish each NUGM model from others. Finally, we found that models with well-tempered neutralinos, where the composition of the neutralino is adjusted to give observed relic density, yield target cross sections which are detectable at proposed experiments.
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Date Issued: 2007
Identifier: FSU_migr_etd-2254
Format: Thesis

Title: DC Transport in Two-Dimensional Electron Systems under Strong Microwave Illumination.
Creator: Chakraborty, Shantanu, Engel, Lloyd W., Chiorescu, Irinel, Dalal, Naresh S., Cao, Jianming, Bonesteel, N. E., Volya, Alexander, Florida State University, College of Art and...
Show moreChakraborty, Shantanu, Engel, Lloyd W., Chiorescu, Irinel, Dalal, Naresh S., Cao, Jianming, Bonesteel, N. E., Volya, Alexander, Florida State University, College of Art and Sciences, Department of Physics
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Abstract/Description: At low temperature (T) and weak magnetic field (B), two dimensional electron systems (2DES) can exhibit strong 1/B-periodic resistance oscillations on application of sufficiently strong microwave radiation. These oscillations are known as microwave induced resistance oscillations (MIROs), MIROs appearing near cyclotron resonance (CR) and its harmonics involve single photon processes and are called integer MIROs while the oscillations near CR subharmonics require multiphoton processes and are...
Show moreAt low temperature (T) and weak magnetic field (B), two dimensional electron systems (2DES) can exhibit strong 1/B-periodic resistance oscillations on application of sufficiently strong microwave radiation. These oscillations are known as microwave induced resistance oscillations (MIROs), MIROs appearing near cyclotron resonance (CR) and its harmonics involve single photon processes and are called integer MIROs while the oscillations near CR subharmonics require multiphoton processes and are called fractional MIROs. Similar strong 1/B periodic resistance oscillations can occur due to strong dc current, and are known as Hall-field resistance oscillations (HIROs). Oscillations also occur for a combination of microwave radiation and strong dc current. In one prominent theory of MIROs, known as the displacement model , electrons make impurity-assisted transitions into higher or lower Landau levels by absorbing or emitting one or more (N) photons. In the presence of combined strong dc current and microwave radiation, electrons make transitions between Landau levels by absorbing or emitting photons followed by a space transition along the applied dc bias. The object of the dissertation is to explore how the different resistance oscillations are affected by strong microwave radiation when multiphoton processes are relevant. We used a coplanar waveguide (CPW) structure deposited on the sample, as opposed to simply placing the sample near the termination of a waveguide as is more the usual practice in this field. The CPW allows us to estimate the AC electric field (E_{AC}) at the sample. In much of the work presented in this thesis we find that higher $N$ processes supersede the competing lower N processes as microwave power is increased. We show this in the presence and in the absence of a strong dc electric field. Finally, we look at the temperature evolution of fractional MIROs to compare the origin of the fractional MIROs with that of integer MIROs.
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Date Issued: 2014
Identifier: FSU_migr_etd-9155
Format: Thesis

Title: Deconfinement Transition in Equilibrium Lattice Gauge Theory with Realistic Boundary Conditions.
Creator: Wu, Hao, Berg, Bernd A., Brüschweiler, Rafael, Adams, Todd, Piekarewicz, Jorge, Reina, Laura, Department of Physics, Florida State University
Abstract/Description: Heavy-ion collision experiments carried out at the Brookhaven National Laboratory, or BNL, and at the European Organization for Nuclear Research, or CERN, provide evidence that matter can be driven from a confined, low-temperature phase into a deconfined high temperature phase of liberated quarks and gluons. Understanding of the deconfinement transition can bring our knowledge of strongly-interacting matter to a deeper level. Ab initio equilibrium studies of the thermodynamic equation of...
Show moreHeavy-ion collision experiments carried out at the Brookhaven National Laboratory, or BNL, and at the European Organization for Nuclear Research, or CERN, provide evidence that matter can be driven from a confined, low-temperature phase into a deconfined high temperature phase of liberated quarks and gluons. Understanding of the deconfinement transition can bring our knowledge of strongly-interacting matter to a deeper level. Ab initio equilibrium studies of the thermodynamic equation of state in the deconfined phase are possible in the framework of lattice gauge theory. It is often desired in such studies to approach the infinite volume thermodynamic limit. To accomplish it quickly, most studies have implemented lattices with periodic boundary conditions. However, the physical volumes created at the Brookhaven National Laboratory are small and exploratory work for pure SU(3) lattice gauge theory suggests that boundary effects cannot be neglected. In this work we study the SU(3) deconfined equilibrium phase in small volumes with inside and outside temperatures in the SU(3) scaling region, using a lattice geometry of the double-layered torus. Our results show substantial finite size effects on the deconfining transition temperature under realistic boundary conditions.
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Date Issued: 2012
Identifier: FSU_migr_etd-5461
Format: Thesis

Title: The Deconfining Phase Transition in and out of Equilibrium.
Creator: Bazavov, Oleksiy, Berg, Bernd A., Mascagni, Michael, Capstick, Simon, Frawley, Anthony, Reina, Laura, Department of Physics, Florida State University
Abstract/Description: Recent experiments carried out at the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory provide strong evidence that a matter can be driven from a confined, low-temperature phase, observed in our every day world into a deconfined high-temperature phase of liberated quarks and gluons. The equilibrium and dynamical properties of the deconfining phase transition are thus of great theoretical interest, since they also provide an information about the first femtoseconds of the...
Show moreRecent experiments carried out at the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory provide strong evidence that a matter can be driven from a confined, low-temperature phase, observed in our every day world into a deconfined high-temperature phase of liberated quarks and gluons. The equilibrium and dynamical properties of the deconfining phase transition are thus of great theoretical interest, since they also provide an information about the first femtoseconds of the evolution of our Universe, when the hot primordial soup while cooling has undergone a chain of phase transitions. The aspects of the deconfining phase transition studied in this work include: the dynamics of the SU(3) gauge theory after the heating quench (which models rapid heating in the heavy-ion collisions), equilibrium properties of the phase transition in the SU(3) gauge theory with boundaries at low temperature (small volumes at RHIC suggest that boundary effects cannot be neglected and periodic boundary conditions normally used in lattice simulations do not correspond to the experimental situation), and a study of the order of the transition in U(1) gauge theory.
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Date Issued: 2007
Identifier: FSU_migr_etd-1166
Format: Thesis

Title: Detailed Spectroscopic Study of the High-Spin Structures in ¹⁶⁸,¹⁶⁹,¹⁷⁰,¹⁷¹W and ¹⁹⁶Hg and a Systematic Examination of Nuclear Structure Behavior of Rare-Earth Isotopes in the A≈160−180 Region.
Creator: Miller, Scott, Riley, Mark A., Plewa, Tomasz, Tabor, Samuel Lynn, Volya, Alexander, Van Winkle, David H., Florida State University, College of Arts and Sciences, Department of...
Show moreMiller, Scott, Riley, Mark A., Plewa, Tomasz, Tabor, Samuel Lynn, Volya, Alexander, Van Winkle, David H., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: High-spin states in the rare-earth nuclei $^{168,169,170,171}$W (Z=74) were produced via fusion evaporation reactions carried out at Argonne National Laboratory (ANL) using the Argonne Tandem Linear Accelerator System (ATLAS). An additional experiment probing the high-spin structure of $^{196}$Hg was conducted at the Florida State University (FSU) tandem-linac facility. The $\gamma$ rays from these experiments were detected and recorded using the Gammasphere spectrometer at ANL and the FSU $...
Show moreHigh-spin states in the rare-earth nuclei $^{168,169,170,171}$W (Z=74) were produced via fusion evaporation reactions carried out at Argonne National Laboratory (ANL) using the Argonne Tandem Linear Accelerator System (ATLAS). An additional experiment probing the high-spin structure of $^{196}$Hg was conducted at the Florida State University (FSU) tandem-linac facility. The $\gamma$ rays from these experiments were detected and recorded using the Gammasphere spectrometer at ANL and the FSU $\gamma$-ray Array system, respectively. As a result of the analysis, well over 500 new decay transitions and over 300 new energy levels were observed in these nuclei. Whenever possible, the intensities, angular correlations, spins, parities, and rotational behaviors of these newly discovered states were analyzed. Theoretical analysis of the observed structures, including spin, parity, and quasiparticle configurations, was carried out within the framework of the Cranked Shell Model (CSM). Due in part to results obtained from the aforementioned analysis, new systematic data in the A $\approx$ 160 region is also discussed, with an emphasis on the role that pair-blocking effects play during the rotation of the nucleus.
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Date Issued: 2015
Identifier: FSU_migr_etd-9410
Format: Thesis

Title: Determining Spin Polarization of Ferromagnets Using Superconducting Spectroscopy.
Creator: Braden, Jazcek Guy, Xiong, Peng, Chase, P. Byrant, Van Molnar, Stephan, Schlottmann, Pedro, Wiedenhover, Ingo, Department of Physics, Florida State University
Abstract/Description: The tremendous interest in using the spin degree of freedom in electronic devices has led to an extensive endeavor to investigate the intrinsic spin polarization of various magnetic materials. The work done here expands upon existing methods to develop a more general technique of precise electrical determination of spin polarization using superconducting spectroscopy with or without the presence of a magnetic field. As part of this effort, the use of Andreev reflection in planar junction...
Show moreThe tremendous interest in using the spin degree of freedom in electronic devices has led to an extensive endeavor to investigate the intrinsic spin polarization of various magnetic materials. The work done here expands upon existing methods to develop a more general technique of precise electrical determination of spin polarization using superconducting spectroscopy with or without the presence of a magnetic field. As part of this effort, the use of Andreev reflection in planar junction configuration was explored on several ferromagnetic materials including the dilute magnetic semiconductor (DMS) Ga1−xMnxAs and the concentrated magnetic semiconductor EuS. This work also led to the exploration of the effects of barrier strength on the measured spin polarization. Traditionally, using superconducting spectroscopy to measure spin polarization (P) was limited to the case of a tunnel junction in a magnetic field or Andreev reflection measurements in point contact structures in zero-field. This project aimed to develop a method that bridged these two regimes to allow for determination of spin polarization in more practical device structures, such as planar junctions, with arbitrary barrier strength. This work led to the first direct electrical determination of P on the representative DMS Ga1−xMnxAs by measuring GaMnAs/Ga structures using Andreev reflection in planar configuration. The analysis of the conductance spectra on highly transparent junctions consistently yielded P values of at least 85%. These experiments also revealed an extreme sensitivity of P to the interfacial properties. Another major part of this work was the measurement of the P of doped EuS using zerofield and Zeeman-split Andreev reflection spectroscopy (ARS) on EuS/Al planar junctions are reported. The zero-field ARS spectra can be fit straightforwardly to a spin-polarized BTK model, which consistently yield P on the order of 80% regardless of the barrier strength. Moreover, we performed ARS in the presence of a Zeeman-splitting of the quasiparticle density of states in Al. The Zeeman-split ARS spectra are well described theoretically by combining the solution to the Maki-Fulde equations with the spin-polarized BTK analysis. The results have provided an independent verification of the validity of the zero-field ARS, and helped demonstrate the utility of field-split superconducting spectroscopy on Andreev junctions of arbitrary barrier strengths. Additionally the effect of barrier thickness on the measured spin polarization was explored in Al/Al2O3/Ni79Fe21 tunnel junctions. Planar tunnel junction structures were formed by natural oxidation of Al; by varying the oxidation time the barrier thickness could be controlled. The measured spin polarization increased with increasing barrier thickness which is attributed to the interplay of both the sp and d electronic states of the NiFe.
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Date Issued: 2006
Identifier: FSU_migr_etd-3418
Format: Thesis

$Development of Femtosecond Electron Diffraction for Direct Measurements of Ultrafast Atomic Motions$

Title: The Development of Femtosecond Electron Diffraction for Direct Measurements of Ultrafast Atomic Motions.
Creator: Park, Hyuk, Cao, Jianming, Safron, Sanford A., Bonesteel, Nicholas, Piekarewicz, Jorge, Xiong, Peng, Department of Physics, Florida State University
Abstract/Description: The evolution of material structures is governed by the making and breaking of chemical bonds and the rearrangement of atoms, which occurs on the time scale of an atomic vibrational period, hundreds of femtoseconds. Atomic motion on this time scale ultimately determines the course of phase transitions in solids, the kinetic pathways of chemical reactions, and even the function of biological processes. Direct observation and understanding these ultrafast structural dynamics at the time and...
Show moreThe evolution of material structures is governed by the making and breaking of chemical bonds and the rearrangement of atoms, which occurs on the time scale of an atomic vibrational period, hundreds of femtoseconds. Atomic motion on this time scale ultimately determines the course of phase transitions in solids, the kinetic pathways of chemical reactions, and even the function of biological processes. Direct observation and understanding these ultrafast structural dynamics at the time and length scales of atomic motions represent an important frontier in scientific research and applications. We have developed a femtosecond electron diffraction system (FED) capable of directly measuring the atomic motions in sub-picosecond temporal resolution and sub-milli-angstrom spatial resolution. In the path of the development of FED various technical challenges have been overcome and an unprecedented capability has been achieved. These advancements allow us to study a range of ultrafast structural dynamics directly on the fundamental level of atomic motions for the first time. With FED we measured laser-induced ultrafast structural dynamics in a 20-nm Al film by taking real-time snapshots of transmission electron patterns. The damped single-mode breathing motion of the Al film along the surface normal was recorded as coherent and in-phase oscillations of all the Bragg peak positions. The concurrent lattice heating was measured by tracking the associated Bragg peak intensity attenuation. This acoustic phonon can be well fitted with a classical harmonic oscillator model using a driving force which includes both electronic and lattice contribution. The pressure of the free electrons contributes significantly in driving the coherent acoustic phonons under nonequilibrium conditions when electrons and phonons are not thermalized. In addition, by using a pair of optical excitation pulses and varying their time delay and relative pulse intensities, we demonstrated successful control of coherent lattice motions.
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Date Issued: 2006
Identifier: FSU_migr_etd-2265
Format: Thesis

Title: Dielectric and Conducting Properties of the Spinel Structures FeV₂O₂, MnV₂O₂ and CoV₂O₂ in High Magnetic Field and under Very High Pressure.
Creator: Kismarahardja, Ade Wijaya, Brooks, James S., Zhang, Mei, Dobrosavljevic, Vladimir, Xiong, Peng, Credé, Volker, Department of Physics, Florida State University
Abstract/Description: It is always very nice when a new discovery found in an old material. The spinel vanadate has become one of the hot topics in the condensed matter physics both experimentally and theoretically. It shows many interesting behaviors due to the interaction among spin, orbital and lattice degrees of freedom. The AV2O4 structure with A is a transition metal ion (Fe2+, Mn2+ and Co2+) exhibits several structural transitions and a magnetic ordering from paramagnetic to ferrimagnetic. Some theoretical...
Show moreIt is always very nice when a new discovery found in an old material. The spinel vanadate has become one of the hot topics in the condensed matter physics both experimentally and theoretically. It shows many interesting behaviors due to the interaction among spin, orbital and lattice degrees of freedom. The AV2O4 structure with A is a transition metal ion (Fe2+, Mn2+ and Co2+) exhibits several structural transitions and a magnetic ordering from paramagnetic to ferrimagnetic. Some theoretical approaches have been made in order to explain the physics of spinels. There are four main factors that contribute to the complexity of spinel system, e.g, spin, orbital, crystal structure and charge. Kugel and Khomskii first proposed a physical model combining spin and orbit degrees of freedom followed by Tsunetsugu and Motome who combined the super exchange and Jahn-Teller effect[2,3]. On the other hand, Tchernyshyov proposed a physical model based on the interplay of spin, orbital and Jahn-Teller effect[4]. Many discoveries from the experiments were also found in this type of material; memory effect in the polycrystal FeV2O4[5], the magnetic switching of the crystal structure in MnV2O4[7] and the magnetic structure of MnV2O4 using neutron study[7]. The modern techniques of x-ray and neutron scattering have brought important knowledge of the crystal and its magnetic structure. However, these techniques require a very good apparatus and a very high accuracy. I used much simpler technique to examine the physical properties of single crystals FeV2O4, MnV2O4 and CoV2O4. Firstly, I did the capacitance and dissipation measurements in high magnetic field on single crystals FeV2O4, MnV2O4 and CoV2O4 in our laboratory (NHMFL) at Tallahassee, Florida and secondly, I did the electrical transport measurements under very high pressure on single crystals FeV2O4 and CoV2O4 in Institute for Solid State Physics (ISSP), the University of Tokyo, Japan. Single crystals MnV2O4 and FeV2O4 are insulators and their resistivity can be higher than 200 Ω cm at room temperature but single crystal CoV2O4 is a semiconductor with the resistivity is around 60 x 10-3 Ω cm at room temperature. However, these single crystals become more insulating at low temperatures so the capacitance measurement is a good tool to investigate their electrical properties. It turned out that the capacitance and dissipation measurements in high magnetic field were very interesting measurements in order to study the interaction between the spin, orbital and lattice in these spinels. The capacitance of a material is related to the dielectric constant and also the geometrical factors of the material, i.e, the distance between the electrodes and the area of the electrodes. In addition, the magnetic field creates magnetostriction effect that changes the dimension of crystal. This situation can be very interesting in order to investigate dielectric properties of these compounds in high magnetic field. FeV2O4, MnV2O4 and CoV2O4 have a magnetic ordering from paramagnetic to ferrimagnetic at 110 K, 56 K and 152 K respectively. Furthermore, the interaction between the tetrahedral site and the octahedral site in the spinel structure also creates structural distortions. I observed the changes of the crystal structure in single crystal FeV2O4 by measuring the capacitance and dissipation under high magnetic field. I discovered that there was a significant amount of heat released at low temperature as the magnetic moment changes its orientation. This effect was observed from a sharp peak in the temperature, the capacitance and the dissipation versus magnetic field data at the field where the magnetic moment changes its orientation. This was not observed in the previous measurements on polycrystal FeV2O4 done by Takei, et al.[5] and in the field dependence of capacitance of the other spinels, MnV2O4 and CoV2O4. Moreover, from the magnetization and capacitance measurements on single crystal FeV2O4, a small plateau at low temperature was observed in the vicinity of 0 Tesla. This is the evidence that there are two magnetic moments exist in single crystal FeV2O4. In single crystal MnV2O4, I also observed the changes of the crystal structure and the magnetic ordering. I applied the magnetic field at different temperatures and measured the capacitance and dissipation of single crystal MnV2O4. From the field dependence of the capacitance and dissipation of single crystal MnV2O4, I confirmed that there is a structural transition at 52 K and a magnetic ordering at 56 K. However, at low temperature, the field dependence of the capacitance of single crystal MnV2O4 behaves differently compared to FeV2O4. This is most likely due to the ratio between lattice constant c in tetragonal phase and lattice constant a in cubic phase, ct/ac . For single crystal FeV2O4 ct/ac, > 1, but ct/ac < 1 for single crystal MnV2O4. The third one, single crystal CoV2O4, is the most conducting among three spinels and I could not measure the capacitance from room temperature down to 30 K. However, below 30 K this crystal becomes more insulating and I could measure its capacitance. As I swept the field below 10 K, the field dependence of the dielectric constant showed a time dependent behavior. Moreover, I observed a dipole like behavior in single crystal CoV2O4 although it was not very pronounced. Another good tool to probe the electrical properties of spinels is the resistivity measurement under very high pressure. I did resistivity measurements on single crystals CoV2O4 and FeV2O4 under very high pressure up to 8 GPa using cubic anvil system in ISSP. In general, the resistivity of these compounds decreased with increasing pressure. I could not observe the magnetic ordering of FeV2O4 under ambient pressure because it was very insulating. The magnetic ordering could be observed above 2 GPa and the magnetic ordering temperature increased linearly with increasing pressure. The effect was similar with CoV2O4. More interestingly, CoV2O4 showed a metallic behavior and a metal to insulator transition under high pressure. This is a new observation in this type of material. The interesting aspect of spinel vanadate is that the system approaches the itinerant electron limit with decreasing distance between vanadium ions. J.B Goodenough predicted a critical distance between vanadium ions in the spinel vanadate system, 2.94 Å. If the distance between vanadium ions (V-V distance) is smaller than this critical distance, the system becomes metallic. The V-V distance of single crystal CoV2O4 is close to this critical value. The resistivity data of single crystal CoV2O4 under very high pressure confirmed that CoV2O4 is sitting at the boundary between the insulator and the metal regime. Finally, Variable Range Hopping (VRH) model and Arrhenius model were used to fit the resistivity data of single crystals FeV2O4 and CoV2O4. I found that the energy barrier parameter T0 and the activation energy Ea decreased with increasing pressure.
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Date Issued: 2010
Identifier: FSU_migr_etd-2882
Format: Thesis

Title: Direct and Indirect Detection of Neutralino Dark Matter.
Creator: O’Farrill, Jorge A., Baer, Howard, Aldrovandi, Ettore, Prosper, Harrison, Hagopian, Vasken, Kemper, Kirby, Department of Physics, Florida State University
Abstract/Description: This dissertation examines the observability of neutralino dark matter in the context of supersymmetric models constrained constrained by the recent WMAP data on the relic density of cold dark matter. The neutralino-nucleon scattering cross-section is calculated and used to derive the rate of interaction for neutralinos scattering from nuclei as well as different modes of indirect detection. Indirect detection of neutralinos is made possible through the annihilation of neutralino pairs into...
Show moreThis dissertation examines the observability of neutralino dark matter in the context of supersymmetric models constrained constrained by the recent WMAP data on the relic density of cold dark matter. The neutralino-nucleon scattering cross-section is calculated and used to derive the rate of interaction for neutralinos scattering from nuclei as well as different modes of indirect detection. Indirect detection of neutralinos is made possible through the annihilation of neutralino pairs into Standard Model (SM) particles. Four different avenues of indirect detection will be covered, including: neutralino annihilation to positrons in the galactic halo, antiprotons from neutralino annihilation in the halo, gamma rays from neutralino annihilation near the core of the galaxy and neutrinos from neutralino annihilation in the core of the sun and the earth. The reaches of various proposed collider experiments will also be calculated. There are many viable supersymmetric models and this dissertation will cover only a few. Most of the rates will be calculated for the mSUGRA model. Results for direct detection will also be given for Yukawa unified SO(10) models with non-universal scalar masses, and 5-dimensional gauge mediated SUSY GUTS. Results for indirect detection will be given for mSUGRA as well as mSUGRA with non-universal gaugino masses. These results will be compared to the sensitivities of ongoing as well as proposed dark matter experiments. Given the precision of the WMAP data, it will be shown that nearly all of the mSUGRA parameter space satisfying the WMAP constraints can be covered by a combination of direct, indirect and collider searches for neutralinos.
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Date Issued: 2004
Identifier: FSU_migr_etd-2311
Format: Thesis

Title: Direct Photon Production in Association with a Heavy Quark.
Creator: Stavreva, Tzvetalina P., Owens, Joseph F., Dewar, William, Reina, Laura, Wahl, Horst, Fenley, Marcia, Department of Physics, Florida State University
Abstract/Description: In this Thesis we present the Next-To-Leading-Order calculation, O(ααs2), of the inclusive cross section for a photon and a heavy quark (charm or bottom), p bar p / pp γ + Q +X, (Q=c,b) at hadron colliders. We include fragmentation effects through the Next-To-Leading-Order. This calculation is performed with the use of a phase space slicing technique so that the effects of experimental cuts can be easily included. We study in detail the characteristics of this process at both the Tevatron and...
Show moreIn this Thesis we present the Next-To-Leading-Order calculation, O(ααs2), of the inclusive cross section for a photon and a heavy quark (charm or bottom), p bar p / pp γ + Q +X, (Q=c,b) at hadron colliders. We include fragmentation effects through the Next-To-Leading-Order. This calculation is performed with the use of a phase space slicing technique so that the effects of experimental cuts can be easily included. We study in detail the characteristics of this process at both the Tevatron and the LHC. Results for the ratios of the charm and bottom cross sections are presented and the systematics of the various subprocesses are compared and contrasted. The theory predictions are compared to experimental measurements from the DO collaboration at Fermilab. A brief overview of the LO massive calculation is also presented, and compared to the NLO massless case. We predict that the investigation of this process and our results will be relevant in the study of heavy quark PDFs at the LHC.
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Date Issued: 2009
Identifier: FSU_migr_etd-1572
Format: Thesis

Title: Direct Reactions with Exotic Beams and Polarized Lithium Beams.
Creator: Roeder, Brian T., Kemper, Kirby, Keel, Brooks, Wiedenhoever, Ingo, Piekarewicz, Jorge, Myers, Edmund, Department of Physics, Florida State University
Abstract/Description: In the first two chapters of this dissertation, the total cross sections for 38 different reaction products produced in the interaction of 48Ca, 40S and 42S beams at energies around 100 MeV/nucleon with a liquid deuterium target are reported. The cross sections for the 48Ca+d products are compared to those with 48Ca incident on the commonly used fragmentation targets 9Be and 181Ta, and also to global calculations for fragmentation reaction cross sections based on the EPAX parameterization...
Show moreIn the first two chapters of this dissertation, the total cross sections for 38 different reaction products produced in the interaction of 48Ca, 40S and 42S beams at energies around 100 MeV/nucleon with a liquid deuterium target are reported. The cross sections for the 48Ca+d products are compared to those with 48Ca incident on the commonly used fragmentation targets 9Be and 181Ta, and also to global calculations for fragmentation reaction cross sections based on the EPAX parameterization performed with the program LISE. The sizes of the measured reaction cross sections for the deuterium target were comparable to the cross sections measured on the heavier targets indicating that both nucleon addition and removal from a deuterium target can be carried out for comparative "stripping" and "pickup" reaction studies. It was also found that the charge exchange cross sections were large enough so that it should be possible to obtain nuclear structure information from these reactions. Calculations using the Johnson-Soper adiabatic model and Eikonal nucleon knockout theory were performed to study the reaction mechanisms for the "stripping" and "pickup" reactions studied in the experiment. It was found that the magnitude of the cross sections for both the single nucleon "stripping" and single nucleon "pickup" reactions were consistent with the assumption that they proceeded as direct, single step reactions. In the third chapter of this dissertation, the recent upgrade to the Florida State University Optically Pumped Polarized Lithium Ion Source (OPPLIS) is summarized. A new laser system was installed, and the laser optics were modified to increase the laser power available for optically pumping the lithium atomic beam from about 40 mW to nearly 200 mW. This improvement, along with proper alignment of the laser beam divergence to the atomic beam divergence, increased the vector polarization t10 of the beam on-target from about 40% to about 60%.
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Date Issued: 2006
Identifier: FSU_migr_etd-1941
Format: Thesis

Title: Disordered Strongly Correlated Electronic Systems.
Creator: Javan Mard, Hossein, Dobrosavljević, Vladimir, Salters, Vincent J. M., Von Molnar, S. (Stephan), Yang, Kun, Piekarewicz, Jorge, Florida State University, College of Arts and...
Show moreJavan Mard, Hossein, Dobrosavljević, Vladimir, Salters, Vincent J. M., Von Molnar, S. (Stephan), Yang, Kun, Piekarewicz, Jorge, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Disorder can have a vast variety of consequences for the physics of phase transitions. Some transitions remain unchanged in the presence of disorder while others are completely destroyed. In this dissertation we study the effects of quenched disorder on electronic systmens at zero temperature. First, we perform variational studies of the interaction-localization problem to describe the interaction-induced renormalizations of the effective (screened) random potential seen by quasiparticles....
Show moreDisorder can have a vast variety of consequences for the physics of phase transitions. Some transitions remain unchanged in the presence of disorder while others are completely destroyed. In this dissertation we study the effects of quenched disorder on electronic systmens at zero temperature. First, we perform variational studies of the interaction-localization problem to describe the interaction-induced renormalizations of the effective (screened) random potential seen by quasiparticles. Here we present results of careful finite-size scaling studies for the conductance of disordered Hubbard chains at half-filling and zero temperature. While our results indicate that quasiparticle wave functions remain exponentially localized even in the presence of moderate to strong repulsive interactions, we show that interactions produce a strong decrease of the characteristic conductance scale g* signaling the crossover to strong localization. This effect, which cannot be captured by a simple renormalization of the disorder strength, instead reflects a peculiar non-Gaussian form of the spatial correlations of the screened disordered potential, a hitherto neglected mechanism to dramatically reduce the impact of Anderson localization (interference) effects. Second, we formulate a strong-disorder renormalization-group (SDRG) approach to study the beta function of the tight-binding model in one dimension with both diagonal and off-diagonal disorder for states at the band center. We show that the SDRG method, when used to compute transport properties, yields exact results since it is identical to the transfer matrix method. The beta function is shown to be universal when only off-diagonal disorder is present even though single-parameter scaling is known to be violated. A different single-parameter scaling theory is formulated for this particular (particle-hole symmetric) case. Upon breaking particle-hole symmetry (by adding diagonal disorder), the beta function is shown to crossover from the universal behavior of the particle-hole symmetric case to the conventional nonuniversal one in agreement with the two-parameter scaling theory. We finally draw an analogy with the random transverse-field Ising chain in the paramagnetic phase. The particle-hole symmetric case corresponds to the critical point of the quantum Ising model, while the generic case corresponds to the Griffiths paramagnetic phase. Finally, we implement an efficient strong-disorder renormalization-group (SDRG) procedure to study disordered tight-binding models in any dimension and on the Erdos- Renyi random graphs, which represent an appropriate infinite dimensional limit. Our SDRG algorithm is based on a judicious elimination of most (irrelevant) new bonds generated under RG. It yields excellent agreement with exact numerical results for universal properties at the critical point without significant increase of computer time, and confirm that, for Anderson localization, the upper critical dimension duc = infinite. We find excellent convergence of the relevant 1/d expansion down to d = 2, in contrast to the conventional 2 + ε expansion, which has little to say about what happens in any d [greater than] 3. We show that the mysterious mirror symmetry of the conductance scaling function is a genuine strong-coupling effect, as speculated in early work. This opens an efficient avenue to explore the critical properties of Anderson transition in the strong-coupling limit in high dimensions.
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Date Issued: 2015
Identifier: FSU_2015fall_JavanMard_fsu_0071E_12907
Format: Thesis

Title: DNA Electrophoresis in Agarose Gels: A New Mobility vs. DNA Length Dependence.
Creator: Beheshti, Afshin, Van Winkle, David H., Rill, Randolph L., Cao, Jianming, Bonesteel, Nicholas E., Riley, Mark A., Department of Physics, Florida State University
Abstract/Description: Separations were performed on double stranded DNA (dsDNA) using electrophoresis. Electrophoresis is the steady transport of particles under the influence of an external electric field. Double stranded DNA fragments ranging in length from 200 base pairs (bp) to 194,000 bp (0.34 nm = 1 bp) were electrophoresed at agarose gel concentrations T = 0:4%¡1:5%. The electric field was varied from 0.62 V/cm to 6.21 V/cm. A wide range of electric fields and gel concentrations were used to study the...
Show moreSeparations were performed on double stranded DNA (dsDNA) using electrophoresis. Electrophoresis is the steady transport of particles under the influence of an external electric field. Double stranded DNA fragments ranging in length from 200 base pairs (bp) to 194,000 bp (0.34 nm = 1 bp) were electrophoresed at agarose gel concentrations T = 0:4%¡1:5%. The electric field was varied from 0.62 V/cm to 6.21 V/cm. A wide range of electric fields and gel concentrations were used to study the usefulness of a new interpolation equation, 1¹(L) =1¹L¡(1¹L¡1¹s)e¡L=°, where ¹L, ¹s, and ° are independent free fitting parameters. The long length mobility limit is interpreted as ¹L, the short length mobility limit is ¹s, and ° is the crossover between the long length limit and the short length limit. This exponential relation fit very well (Â2 ¸ 0:999) when there are two smooth transitions observed in the "reptation plots" (plotting 3¹L=¹± vs. L) (J. Rousseau, G. Drouin, and G. W. Slater, Phys Rev Lett. 1997, 79, 1945-1948). Fits deviate from the data when three different slopes were observed in the reptation plots. Reptation plots were used to determine a phase diagram for dsDNA migration regimes. The phase diagrams define different regions where mechanisms for molecular transport affect the migration of dsDNA in agarose gels during electrophoresis. The parameters from the equation have also been interpreted to provide a physical description of the structure of the agarose gel by calculating the pore sizes. The relations between the values for the pore sizes and the phase diagrams are interpreted to better understand the migration of the DNA through agarose gels.
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Date Issued: 2002
Identifier: FSU_migr_etd-1207
Format: Thesis

Title: Domain Coarsening in the Hyperbolic Plane.
Creator: Raffield, Jesse, Department of Physics
Abstract/Description: Since the simplest case was solved exactly by Onsager in 1944, the two-dimensional Ising model has become one of the most studied models in statistical physics. Despite its simplicity, it has found applications in research ranging from condensed matter physics to biology. Our research focused on an interesting variant of this model that lives within an area of negative Gaussian curvature instead of traditional Euclidean space. Specifically, a series of Monte-Carlo simulations were conducted...
Show moreSince the simplest case was solved exactly by Onsager in 1944, the two-dimensional Ising model has become one of the most studied models in statistical physics. Despite its simplicity, it has found applications in research ranging from condensed matter physics to biology. Our research focused on an interesting variant of this model that lives within an area of negative Gaussian curvature instead of traditional Euclidean space. Specifically, a series of Monte-Carlo simulations were conducted to analyze how domains within the model coarsen as a function of time. In the Euclidean model, the feature size goes as t1/3<\sup>, which is close to our results on two of the Euclidean lattices, but for our model on a hyperbolic lattice the characteristic growth exponent was found to be much lower, approximately 0.13.
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Date Issued: 2013
Identifier: FSU_migr_uhm-0199
Format: Thesis

Title: Doping Effects on the Kondo Lattice Materials: FeSi, CeCoin5, and YbInCu4.
Creator: Yeo, Sunmog, Fisk, Zachary, Dalal, Naresh, Molnar, Stephan von, Bonesteel, Nicholas, Piekarewicz, Jorge, Department of Physics, Florida State University
Abstract/Description: Three doping studies on Kondo lattices are investigated in this thesis: FeSi1-xGex, Ce1-xLaxCoIn5, and Yb1-xYxInCu4. For FeSi1-xGex, we constructed the phase diagram through the analysis of magnetic, thermal and transport measurements on single crystals. The phase diagram shows a first-order transition from a Kondo insulator (exponentially activated properties) to a ferromagnetic metal at a critical concentration, xc ~ 0:25. The field dependence of the magnetization (M(H)) shows that the...
Show moreThree doping studies on Kondo lattices are investigated in this thesis: FeSi1-xGex, Ce1-xLaxCoIn5, and Yb1-xYxInCu4. For FeSi1-xGex, we constructed the phase diagram through the analysis of magnetic, thermal and transport measurements on single crystals. The phase diagram shows a first-order transition from a Kondo insulator (exponentially activated properties) to a ferromagnetic metal at a critical concentration, xc ~ 0:25. The field dependence of the magnetization (M(H)) shows that the saturation moment of x = 0:27 is 10 times larger than that of x = 0:24. The spin gap of x = 0:24, 167K, is quite close to the transition temperature of x = 0:27, 150K, indicating that the characteristic energies of the two competing phases, i.e. the Curie temperature and the spin gap of the Kondo insulator, are essentially equal at the critical concentration. For x c, spin gap, transport gap and resistivity minimum systematically decrease with increasing x. Saturation moments and specific heat coefficients are almost zero for x c. The temperature dependence of magnetic susceptibility (X(T)) for x = 0:2 shows a broad maximum around 200K, indicating that the broad maximum temperature decreases with x for x c. The variable range hopping analysis suggests the existence of the localized state for this region. For x > x xc, the data break into two distinct regimes: xc» 0:5 and » 0:5 · 1. For xc 0:5, X(T) does not displays a sharp transition at Tc and M(H) increases with increasing fields. The temperature dependence of the resistivity (ρ(T)) shows metallic behavior. However, it does not have any kink at Tc. In contrast, for ~ 0:5 · 1, X(T) displays a sharp transition at Tc and M(H) saturates at H ~ 0:3T. ρ (T) has a kink at Tc. Based on the Kondo insulator picture, we can explain the specific heat coefficient y evolution with x. The transition from a Kondo insulator to a ferromagnetic metal can be explained as the consequence of the changes in hybridization between Fe 3d electrons and Si/Ge p conduction electrons in conjunction with disorder on the Si/Ge ligand site. For Ce1-xLaxCoIn5, we studied antiferromagnetic intersite correlations for the Kondo lattice by comparison with data on the single Kondo impurity. All the magnetic susceptibility per mole Ce for H || ab plane and H || c axis collapse onto one curve above 100K in Ce1-xLaxCoIn5, indicating the same high T Kondo temperature (~ 35K) for all concentrations. Further, the magnetic part of the resistivity shows the same -logT dependence above 50K for all concentrations, again indicating that the high T Kondo temperature is essentially independent of Ce concentration. The magnetic part of the heat capacity for Ce1-xLaxCoIn5 alloys has a peak around 70K, suggesting the same crystalline field splittings occurs the alloy series Ce1-xLaxCoIn5. Based on these experimental findings, the scaling laws for the susceptibility and the heat capacity reveal that the screening of the magnetic moments in this Kondo lattice involves antiferromagnetic intersite correlations and this intersite correlation has a larger energy scale compared to the Kondo impurity case. In addition, a Fermi liquid ground state appears in the La rich region while the specific heat and inelastic part of ρm show non-Fermi liquid behavior for Ce rich region. For Yb1-xYxInCu4, measurements using cantilever torque magnetometry discover the new phase above Hv for x = 0 and x = 0:1. With proper scaling of the critical fields and temperatures, data for all alloys collapse onto the same curve, representing a common phase above Hv. The magneto-resistance does not change at the new phase boundary. Due to the crystalline electric field, there is anisotropy of the valence transition in applied magnetic field in different directions. For x = 0:2, the specific heat and the resistance indicate the appearance of a spin glass state below 4K for H > 5T. Since Ytterbium occupies the corners of a tetrahedron in the F43m structure, the spin glass state is not unexpected.
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Date Issued: 2003
Identifier: FSU_migr_etd-0646
Format: Thesis

Title: Dynamical Studies of Antiferromagnetic Exchange Interactions in Low Dimensional Quantum Spin Systems.
Creator: De Lia, Anthony F., Dagotto, Elbio, Heil, Wolfgang, Moreo, Adriana, Piekarewicz, Jorge, Riley, Mark, Department of Physics, Florida State University
Abstract/Description: Various forms of antiferromagnetic exchange interaction among quantized spins in one-dimensional and quasi-one-dimensional lattices are examined. Primary results are reported in two real compounds, the sodium vanadate NaV2O5 and the copper germanate CuGeO3, and in a class of compounds of real materials modeled as dimerized antiferromagnetically coupled spin-1/2 chains susceptible to spin-1 impurity doping and that include such examples as the strontium cuprate Sr14Cu24O41 and vanadium...
Show moreVarious forms of antiferromagnetic exchange interaction among quantized spins in one-dimensional and quasi-one-dimensional lattices are examined. Primary results are reported in two real compounds, the sodium vanadate NaV2O5 and the copper germanate CuGeO3, and in a class of compounds of real materials modeled as dimerized antiferromagnetically coupled spin-1/2 chains susceptible to spin-1 impurity doping and that include such examples as the strontium cuprate Sr14Cu24O41 and vanadium pyrophosphate (VO)2P2O7. Sodium vanadate, NaV2O5, a quarter-filled two-leg ladder compound that was originally thought to be composed of magnetic legs and nonmagnetic legs was subsequently shown to be a charge ordered system below room temperature. Initial models of the material as isolated antiferromagnetically coupled spin-1/2 chains can be mapped to the subsequently resolved magnetic system of the charge ordered state with the spins on molecular orbitals of V-O-V rungs antiferromagentically coupled between neighboring rungs either on the same ladder or on neighboring ladders. Comparing the model's dynamic structure factor to inelastic neutron scattering data could distinguish between the proposed spin coupling schemes and consequently reveal the details of the interaction between the lattice and the "zig-zag" charge density as well as the magnetic stabilization of the low temperature phase. Copper germanate, the first and only known inorganic spin-Peierls compound, exhibits a strong temperature dependent exchange coupling pattern among the spin-1/2 Cu2+ chains. Above the spin-Peierls transition temperature an unmodulated antiferromagnetic nearest neighbor exchange interaction J1 competes with an antiferromagnetic next nearest neighbor interaction J2. The next nearest neighbor exchange represents an effective coupling equivalent to the net effect of all longer range exchange interactions. This frustration to the nearest neighbor spin exchange produces a distinctive magnetic susceptibility χ (T) much different from the Bonner-Fisher susceptibility of the spin-1/2 Heisenberg chain with nearest neighbor antiferromagnetic exchange only. The ratio of the second to first nearest neighbor couplings α = J2/J1 ≈ 0.36 is sufficient to open a spontaneous gap in the spin-wave excitation spectrum at low temperatures. Below TSP = 14K, the dynamical structure factor is used to fit the dimerization δ and the exchange interactions J1 and J2 to the inelastic neutron scattering data of CuGeO3 at T = 10K. It is found that both δ and α increase significantly at lower temperatures, relative to the values obtained in the high temperature phase and at the onset of dimeration at 14 K. Static structure factor calculations how Scattering inconsistent with the δâJ1âJ2 model and can be attributed primarily to the phonon degrees of freedom but possibly also to the couplings between chains in the b and a directions of the crystal lattice. Structurally dimerized compounds of antiferromagnetic spin-1/2 chains possess dynamic structure factor and magnetic susceptibility features that are very sensitive to doping with magnetic and nonmagnetic impurities. It is shown that the effects of spin-1 impurities are very similar to those of nonmagnetic (S = 0) impurities if the coupling between impurity and native spin is about the same magnitude as or larger than between native S = 1/2 spins. The microscopic origins of the similarity can be appreciated with the consideration that neighboring spins to the impurity find it more energetically favorable to couple to the impurity than the other spins of the lattice. Thus the spin-1 impurity and its neighboring S = 1/2 spins decouple from the lattice, creating a nonmagnetic break in the chain. The spins that now observe a nonmagnetic cluster on one side can couple to the S = 1/2 spins on the other side with a higher AF correlation than in the pure compound since they do not have to have a ï¬uctuating dimer resonating between two neighbors. Such enhancements to the local correlations can stabilize the global AF order in one dimensional compounds as shown in theoretical and experimental studies of CuGeO3. ED calculations of the dynamic structure factor show that S(q, ω) developes states with ω = 0 in the gap at q = π. Magnetic susceptibilites in the presense of spin-1 impurities were obtained for 80 site chains by QMC simulations and for 16 site chains by ED calculations. An impurity concentration-dependent second peak in the low temperature region reveals an increasing second maximum with T as observed in doped copper germanates and suggests that the results of the study are applicable even to phonon mediated dimerization. This is not immediately apparent because spin-phonon coupling could distort the dimerization patterns. However, experimental and theoretical results show that elastic coupling between chains can stabilize the dimerization pattern due to the impurities and the results will still apply.
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Date Issued: 2003
Identifier: FSU_migr_etd-0058
Format: Thesis

Title: Dynamics of Biomolecules, Ligand Binding & Biological Functions.
Creator: Yi, Myunggi, Zhou, Huan-xiang, Logan, Timothy M., Berg, Bernd A., Xiong, Peng, Nymeyer, Hugh, Department of Physics, Florida State University
Abstract/Description: Proteins are flexible and dynamic. One static structure alone does not often completely explain biological functions of the protein, and some proteins do not even have high resolution structures. In order to provide better understanding to the biological functions of nicotinic acetylcholine receptor, Diphtheria toxin repressor and M2 proton channel, the dynamics of these proteins are investigated using molecular modeling and molecular dynamics (MD) simulations. With absence of high resolution...
Show moreProteins are flexible and dynamic. One static structure alone does not often completely explain biological functions of the protein, and some proteins do not even have high resolution structures. In order to provide better understanding to the biological functions of nicotinic acetylcholine receptor, Diphtheria toxin repressor and M2 proton channel, the dynamics of these proteins are investigated using molecular modeling and molecular dynamics (MD) simulations. With absence of high resolution structure of alpha 7 receptor, the homology models of apo and cobra toxin bound forms have been built. From the MD simulations of these model structures, we observed one subunit of apo simulation moved away from other four subunits. With local movement of flexible loop regions, the whole subunit tilted clockwise. These conformational changes occurred spontaneously, and were strongly correlated with the conformational change when the channel is activated by agonists. Unlike other computational studies, we directly compared our model of open conformation with the experimental data. However, the subunits of toxin bound form were stable, and conformational change is restricted by the bound cobra toxin. These results provide activation and inhibition mechanisms of alpha 7 receptors and a possible explanation for intermediate conductance of the channel. Intramolecular complex of SH3-like domain with a proline-rich (Pr) peptide segment in Diphtheria toxin repressor (DtxR) is stabilized in inactive state. Upon activation of DtxR by transition metal binding, this intramolecular complex should be dissociated. The dynamics of this intramolecular complex is investigated using MD simulations and NMR spectroscopy. We observed spontaneous opening and closing motions of the Pr segment binding pockets in both Pr-SH3 and SH3 simulations. The MD simulation results and NMR relaxation data suggest that the Pr segment exhibits a binding ¡ê unbinding equilibrium. Despite a wealth of experimental validation of Gouy-Chapman (GC) theory to charged lipid membranes, a test of GC theory by MD simulations has been elusive. Here we demonstrate that the ion distributions at different salt concentrations in anionic lipid bilayer systems agree well with GC predictions using MD simulations. Na+ ions are adsorbed to the bilayer through favorable interactions with carbonyls and hydroxyls, reducing the surface charge density by 72.5%. The interactions of amantadine, an antiinfluenza A drug, with DMPC bilayers are investigated by an MD simulation and by solid-state NMR. The MD simulation results and NMR data demonstrate that amantadine is located within the interfacial region with upward orientation and interacts with the lipid headgroup and glycerol backbone, while the adamantane group of amantadine interacts with the glycerol backbone and much of fatty acyl chain, as it wraps underneath of the drug. The lipid headgroup orientation is influenced by the drug as well. The recent prevalence of amantadine-resistant mutants makes a development of new drug urgent. The mechanism of inhibition of M2 proton channel in influenza virus A by amantadine is investigated. In the absence of high resolution structure, we model the apo and drug bound forms based on NMR structures. MD simulations demonstrate that channel pore is blocked by a primary gate formed by Trp41 helped by His37 and a secondary gate formed by Val27. The blockage by the secondary gate is extended by the drug bound just below the gate, resulting in a broken water wire throughout the simulation, suggesting a novel role of Val27 in the inhibition by amantadine. Recent X-ray structure validates the simulation results.
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Date Issued: 2008
Identifier: FSU_migr_etd-0661
Format: Thesis

Title: The Dynamics of DNA Electrophoresis in Lyotropic Polymer Liquid Crystals.
Creator: You, Seungyong, Van Winkle, David H., Shanbhag, Sachin, Brooks, James, Manousakis, Efstratios, Wiedenhover, Ingo, Department of Physics, Florida State University
Abstract/Description: Electrophoresis is one of the most powerful tools used to separate biological molecules by size in a supporting medium under the influence of an electric field. Pluronic F127 gel, introduced as a new sieving medium for electrophoresis in the late 1990s, has potential promise, but the transport and separation of DNA molecules in Pluronic gel are not fully understood among scientists. This dissertation research conducts three experiments to investigate the dynamics of DNA electrophoresis in...
Show moreElectrophoresis is one of the most powerful tools used to separate biological molecules by size in a supporting medium under the influence of an electric field. Pluronic F127 gel, introduced as a new sieving medium for electrophoresis in the late 1990s, has potential promise, but the transport and separation of DNA molecules in Pluronic gel are not fully understood among scientists. This dissertation research conducts three experiments to investigate the dynamics of DNA electrophoresis in Pluronic gel. First, a direct observation study examines how DNA molecules move through the Pluronic gel on a microscopic scale using fluorescence microscopy. Evidence is presented that in some cases DNA molecules electrophorese directly through gel crystallites and in other cases along grain boundaries between gel crystallites. Next, two dimensional electrophoresis is performed in order to understand the size dependence of the mobility of DNA molecules ranging from 20 bp to 3500 bp in Pluronic gels. Small DNA molecules (<125 >bp) became slower as their molecular size decreased, while large DNA molecules (>175 bp) became exponentially slower as their molecular size increased. DNA molecules of intermediate sizes showed a sinusoidal pattern in their mobility. Based on the experimental results, we developed a phenomenological model to fit the size dependence of the DNA mobility, and discussed the separation mechanisms of the DNA molecules in the Pluronic gels. In the final experiment, DNA molecules of the same length, which moved together and formed a single band in the agarose gel, were split into two bands in the Pluronic gel. This indicates that the Pluronic gel is possibly able to separate the DNA molecules according to their sequence. We expect that this study will contribute to an enhanced understanding of the dynamics of DNA molecules in Pluronic gel and facilitation of Pluronic gel as an alternative sieving medium for electrophoresis in the fields of molecular biology and biotechnology.
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Date Issued: 2009
Identifier: FSU_migr_etd-0863
Format: Thesis

Title: Edge Spin Excitations and Reconstructions of Quantum Hall Liquids.
Creator: Zhang, Yuhui, Yang, Kun, Aldrovandi, Ettore, Piekarewicz, Jorge, Engel, Lloyd W., Bonesteel, N. E., Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: In this dissertation, we investigate the edge spin excitations and reconstructions of quantum Hall (QH) liquids. Edge spin reconstructions reflect the interplay of confining potential, electron-electron interaction, and Zeeman splitting at the edges of QH liquids. The main method used in this dissertation is the exact diagonalization calculation for finite size systems. The QH liquids studied in this dissertation are classified into three kinds, based on their topological properties and...
Show moreIn this dissertation, we investigate the edge spin excitations and reconstructions of quantum Hall (QH) liquids. Edge spin reconstructions reflect the interplay of confining potential, electron-electron interaction, and Zeeman splitting at the edges of QH liquids. The main method used in this dissertation is the exact diagonalization calculation for finite size systems. The QH liquids studied in this dissertation are classified into three kinds, based on their topological properties and statistics of quasiparticles (quasiholes). The first kind of QH liquids is spin-polarized QH liquids. The QH liquids with filling factors ν = 1 and 1/3 are studied in this kind. We find the low-energy excitations of the ν = 1 and 1/3 are bosonic edge spin waves. Instabilities of these ferromagnetic state with altering confinement strength result from the softening of these spin waves and formation of edge spin textures. A microscopic trial wave function is used to study the edge instabilities of larger systems with particle number up to 40, and the obtained results are consistent to the ones calculated by exact diagonalization. The second kind of QH liquids is spin-unpolarized QH liquids. The liquids with ν = 2, 2/5 and 2/3 are studied in this kind. When ν = 2, exact diagonalization on edge electron systems indicates that compact Hartree-Fock states with different total spin always become ground states in some regions of parameter space, and the ground states appearing between two compact states are their edge spin waves. The initial ν = 2 instability is toward the compact state with total spin 1. At ν = 2/5, the edge instabilities is also triggered by softening of the edge spin waves with smoother confinement. The situation of ν = 2/3 unpolarized QH liquids is a little different, because it has one backward-moving edge spin wave mode and one forward-moving magnetoplasmon mode. There is no mystery about what kind of instability would occur with stronger or smoother confinement. The exact diagonalization calculation of finite systems can reproduce the instability induced by edge spin wave at the stronger confinement side and gives an estimate about the critical value of confining potential. But instability due to edge magnetoplasmon mode can not be realized in small size systems because of the high velocity of this mode. The last kind is the non-Abelian QH liquid (at ν = 5/2). Its edge instability triggered by softening of edge magnetoplasmon excitations with smoother confinement. Three different confinements are compared in the study of integer QH liquids in finite size systems. And some quantitative predictions on the edge instabilities for a certain type of confining potential are reached in the thermodynamic limit. The effect of Zeeman splitting to the edge instabilities is also considered in this dissertation.
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Date Issued: 2014
Identifier: FSU_migr_etd-9274
Format: Thesis

Title: Effective R-Matrix Parameters of the Woods-Saxon Potential.
Creator: Abrahamsen, Dylan, Department of Physics
Abstract/Description: The phenomenological R-matrix approach is one of the most practical tools for the study of multi-channel resonant scattering data. This approach, however, has been subject to criticism for the relatively unconstrained phenomenological parameters. In this study the objective is to observe the connection between effective square well radius, the limiting case of the R-matrix channel radius, and the parameters of the actual potential model. In this work the effective channel radius is determined...
Show moreThe phenomenological R-matrix approach is one of the most practical tools for the study of multi-channel resonant scattering data. This approach, however, has been subject to criticism for the relatively unconstrained phenomenological parameters. In this study the objective is to observe the connection between effective square well radius, the limiting case of the R-matrix channel radius, and the parameters of the actual potential model. In this work the effective channel radius is determined by comparing the scattering observables of the Woods-Saxon potential and the square well.
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Date Issued: 2014
Identifier: FSU_migr_uhm-0289
Format: Thesis

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