<p> Presented here is a detailed study of electron transport in highly disordered insulating materials (HDIM). Since HDIMs do not lend themselves to a lattice construct, the question arises: How can we describe their electron transport behavior in a consistent theoretical framework? In this work, a large group of experiments, theories, and physical models are coalesced into a single formalism to better address this difficult question. We find that a simple set of macroscopic transport equations--cast in a new formalism--provides an excellent framework in which to consider a wide array of experimentally observed behaviors. It is shown that carrier transport in HDIMs is governed by the transport equations that relate the density of localized states (DOS) within the band gap and the occupation of these states through thermal and quantum interactions. The discussion is facilitated by considering a small set of simple DOS models. This microscopic picture gives rise to a clear understanding of the macroscopic carrier transport in HDIMs. We conclude with a discussion of the application of this theoretical formalism to four specific types of experimental measurements employed by the Utah State University space environments effects Materials Physics Group.</p>

<p> The NPDGamma Experiment is measuring the parity-violating correlation A_&gamma; between neutron spin and gamma momentum in the radiative capture of a polarized cold neutron beam on a cryogenic liquid parahydrogen target. This measurement is expected to give insight into theories that incorporate the weak interaction into what is primarily a strongly interacting system. This dissertation discusses the operation and characterization of the liquid hydrogen target, including the calibration of the instrumentation that monitors the state of the hydrogen. An important consideration is the fact that for safety reasons the instrumentation in direct contact with the hydrogen is limited, and so a detailed understanding of the target design and of the properties of hydrogen is required in order to interpret the state of the system. For this experiment, it is essential that the hydrogen be kept mostly in the para state in order to prevent the beam from being significantly depolarized before capture. Since the uncatalyzed conversion rate is slow, an ortho-para conversion loop is used to promote conversion from the room temperature orthohydrogen fraction to the fraction associated with the temperatures of the cryogenic vessel. In addition to the calibration and characterization studies, a method is introduced for placing an empirical limit on the deviation of the orthohydrogen fraction inside the vessel from the desired level associated with the temperature of the ortho-para conversion catalyst and vessel. This method, which does not require precise knowledge of the parahydrogen cross section, involves observing the transmission of the beam through the target while the rate of flow of hydrogen through the ortho-para conversion loop is changed. In addition to the studies of the hydrogen target, this dissertation discusses a calibration of some ³He ion chambers that monitor the flux of the neutron beam and that are used to perform beam transmission measurements. This calibration, which involves a study of the noise inherent in the signal due to neutron capture, does not involve comparison to a separate calibrated detector.</p>

<p> Laser cooling and trapping are central to modern atomic physics. It has been roughly three decades since laser cooling techniques produced ultracold atoms, leading to rapid advances in a vast array of fields and a number of Nobel prizes. Prior to the work presented in this thesis, laser cooling had not yet been extended to molecules because of their complex internal structure. However, this complexity makes molecules potentially useful for a wide range of applications. The first direct laser cooling of a molecule and further results we present here provide a new route to ultracold temperatures for molecules. In particular, these methods bridge the gap between ultracold temperatures and the approximately 1 kelvin temperatures attainable with directly cooled molecules (e.g. with cryogenic buffer gas cooling or decelerated supersonic beams). Using the carefully chosen molecule strontium monofluoride (SrF), decays to unwanted vibrational states are suppressed. Driving a transition with rotational quantum number <i>R</i>=1 to an excited state with <i> R'</i>=0 eliminates decays to unwanted rotational states. The dark ground-state Zeeman sublevels present in this specific scheme are remixed via a static magnetic field. Using three lasers for this scheme, a given molecule should undergo an average of approximately 100,000 photon absorption/emission cycles before being lost via unwanted decays. This number of cycles should be sufficient to load a magneto-optical trap (MOT) of molecules. In this thesis, we demonstrate transverse cooling of an SrF beam, in both Doppler and a Sisyphus-type cooling regimes. We also realize longitudinal slowing of an SrF beam. Finally, we detail current progress towards trapping SrF in a MOT. Ultimately, this technique should enable the production of large samples of molecules at ultracold temperatures for molecules chemically distinct from competing methods.</p>

<p> Superconducting qubits and resonators with quality factors exceeding 10⁷ are of great interest for quantum information processing applications. The improvement of present devices necessarily involves the consideration of participation ratios, which budget the influence of each physical component in the total energy decay rate. Experiments on compact resonators in which participation ratios were varied has demonstrated the validity of this method, yielding a two-fold improvement in quality factor. Similar experiments on compact transmon qubit devices led to a three-fold improvement over previous transmons, validating the method of participation ratios for qubits as well. Through the use of a 3D cavity, a further minimization of the participation of surface components combined with the removal of unnecessary components, produced an additional ten-fold increase in coherence times. Finally, the fluxonium qubit was redesigned in a similar minimalist environment with an improved superinductance, thus combining the advantages of the 3D architecture with the natural insensitivity to dissipation of the fluxonium, resulting in <i>another</i> tenfold increase in relaxation times. This large increase in relaxation and coherence times enables experiments that were previously impossible, thus preparing the field of quantum information to advance on other fronts.</p>

<p>Quantum chromodynamics (QCD) is the theory that concerns how the strong force interacts with subatomic particles. Topological configurations that interpolate between vacuum states have been shown to play an important role in the quark-gluon plasma (QGP), believed to be created in heavy ion collisions. The possible existence of [special characters omitted]-odd domains in the QGP combined with an external magnetic field that is produced in mid-central collisions may be the ingredients necessary for the so-called chiral magnetic effect (CME). The CME is the consequence of topological features called sphalerons (that are created in the hot QCD matter) in the presence of a strong magnetic field, and it induces a separation of negatively and positively charged particles along the direction of the field. This separation varies its orientation from event to event, resulting in the expectation value of any [special characters omitted]-odd observable to vanish, making it necessary to measure the variation in fluctuations. Any indication of a real charge dipole moment could be evidence for local parity violation (LPV), which would have profound implications on our understanding of the natural world.</p><p> In this dissertation, charge dependent azimuthal correlations are used to measure the charge separation fluctuations in gold ion collisions at STAR. There are three primary analyses: measuring charge distributions as a function of beam energy, by selecting specific hadron species to filter background effects, and for uranium ion collisions. The beam energy analysis shows that a small charge separation shrinks with diminishing beam energy, eventually vanishing at the lowest energies. The kaon-pion correlations are performed to eliminate specific background effects unrelated to the CME, and behave consistently with results using all types of hadrons. The uranium analysis attempts to distinguish how much of the azimuthal correlations are influenced by elliptic anisotropy, suggesting the signal is coming from a mixture of CME and strong interaction backgrounds. From the evidence gathered from these analyses, we conclude that there are signs of small charge separations congruous to predictions from the CME, however, much of the signal is obscured by other strong interaction backgrounds. The effective contribution strengths are calculated and suggestions for improvements are made in the conclusion.</p>

<p> Collective magnetic behavior in nanostructures is a phenomenon commonly observed in various magnetic systems. It arises due to competing inter/intra&ndashparticle; interactions and size distribution and can manifest in phenomena like magnetic freezing, magnetic aging, and exchange bias (EB) effect. In order to probe these rather complex phenomena, conventional DC and AC magnetic measurements have been performed along with radio&ndashfrequency; transverse susceptibility (TS) measurements. We also demonstrate the magnetic entropy change as a parameter sensitive to subtle changes in the magnetization dynamics of nanostructures. The focus of this dissertation is to study the collective magnetic behavior in core-shell nanostructures of Fe/&gamma;&ndashFe;₂O₃ and Co/CoO, La_0.5Sr_0.5MnO₃ nanowires, and LaMnO₃ nanoparticles.</p><p> In the case of core/shell Fe/&gamma;&ndashFe;₂O₃, we found the particles to critically slow down below the glass transition temperature, below which they exhibit aging effects associated with a superspin glass (SSG) state. We demonstrate that it is possible to identify individual magnetic responses of the Fe core and the &gamma;&ndashFe;₂O₃ shell. Consistently, a systematic study of the magnetocaloric effect (MCE) in the Fe/&gamma;&ndashFe;₂O₃ system reveals the development of inverse MCE with peaks associated with the individual magnetic freezing of the core and the shell. From these obtained results, we establish a general criterion for EB to develop in core/shell nanostructures, that is when the core is in the frozen state and the magnetic moments in the shell begin to block. This criterion is shown to be valid for both ferromagnetic/ferrimagnetic (FM/FIM) Fe/&gamma;&ndashFe;₂O₃ and ferromagnetic/antiferromagnetic (FM/AFM) Co/CoO core&ndashshell; nanostructures. We also elucidate the physical origin of the occurrence of asymmetry in field-cooled hysteresis loops and its dependence on magnetic anisotropy in the Co/CoO system by performing a detailed TS study.</p><p> We have performed a detailed magnetic study on hydrothermally synthesized single crystalline La_0.5Sr_0.5MnO₃ nanowires. The temperature and field dependent evolution of the different magnetic phases leading to development of the inverse MCE and EB in the nanowires is discussed. Finally, we have studied the collective magnetic behavior of LaMnO₃ nanoparticles synthesized by the sol&ndashgel; technique. The nanoparticle ensemble shows the unusual co&ndashexistence; of super-ferromagnetism (SFM), as well as the SSG state, which we term the &lsquoferromagnetic; superglass&rsquo; (FSG) state. The existence of FSG and the characteristics of its magnetic ground state are discussed.</p>

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-05, Section: B, page: 3041. Adviser: Douglas H. Beck. Includes bibliographical references (leaves 182-185) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-11, Section: B, page: 6636. Adviser: Taekjip Ha. Includes bibliographical references (leaves 241-254). Available on microfilm from Pro Quest Information and Learning.

This thesis considers various aspects of general relativity in more than four spacetime dimensions. Firstly, I review the generalization to higher dimensions of the algebraic classification of the Weyl tensor and the Newman-Penrose formalism. In four dimensions, these techniques have proved useful for studying many aspects of general relativity, and it is hoped that their higher dimensional generalizations will prove equally useful in the future. Unfortunately, many calculations using the Newman-Penrose formalism can be unnecessarily complicated. To address this, I describe new work introducing a higher-dimensional generalization of the so-called Geroch-Held-Penrose formalism, which allows for a partially covariant reformulation of general relativity. This approach provides great simplifications for many calculations involving spacetimes which admit one or two preferred null directions. The next chapter describes the proof of an important result regarding algebraic classification in higher dimensions. The classification is based upon the existence of a particular null direction that is aligned with the Weyl tensor of the geometry in some appropriate sense. In four dimensions, it is known that a null vector field is such a multiple Weyl aligned null direction (WAND) if and only if it is tangent to a shearfree null geodesic congruence. This is not the case in higher dimensions. However, I have formulated and proved a partial generalization of the result to arbitrary dimension, namely that a spacetime admits a multiple WAND if and only if it admits a geodesic multiple WAND.Moving onto more physical applications, I describe how the formalism that we have developed can be applied to study certain aspects of the stability of extremal black holes in arbitrary dimension. The final chapter of the thesis has a rather different flavour. I give a detailed analysis of the properties of a particular solution to the Einstein equations in five dimensions: the Pomeransky-Sen'kov doubly spinning black ring. I study geodesic motion around this black ring and demonstrate the separability of the Hamilton-Jacobi equation for null, zero energy geodesics. I show that this unexpected separability can be understood in terms of a symmetry described by a conformal Killing tensor on a four dimensional spacetime obtained by a Kaluza-Klein reduction of the original black ring spacetime.

The goal of this dissertation is to broaden our understanding of interactive teaching strategies, in the context of the introductory physics classroom at the undergraduate level. The dissertation is divided into four main projects, each of which investigates a specific aspect of teaching physics interactively. All four projects look towards improving the effectiveness of interactive teaching by understanding how pre-course student characteristics affect the way students learn interactively. We first discuss lecture demonstrations in the context of an interactive classroom using Peer Instruction. We study the role of predictions in conceptual learning. We examine how students' predictions affect what they report having seen during a demonstration. We also examine how student predictions affect what they recall as the outcome of the demonstration at the end of the semester. We then analyze student response patterns to conceptual questions posed during Peer Instruction. We look at the relationship between a student's tendency to switch their answer and pre-course student characteristics like science self-efficacy. Next we elucidate response timing to conceptual questions posed over the course of the semester, in two introductory physics classes taught using Peer Instruction. We look at the relationship between student response times and student characteristics like pre-course physics knowledge, science self-efficacy and gender. We study response times as a way of gaining insight into students thinking in Peer Instruction environments as well as to improve the implementation of Peer Instruction. Finally, we present work on the role of NB, an online collaborative textbook annotation tool, in a flipped, project based, physics class. We analyze the relationship between students' level of online engagement and traditional learning metrics to understand the effectiveness of NB in the context of flipped classrooms. We also report the results of experiments conducted to explore ways to steer discussion forums to produce high-quality learning interactions.