Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, February 2007. / In title on t.p., "[sigma]" appears as the lower-case Greek letter. / Includes bibliographical references (p. 367-376). / The search for and the study of flavor oscillations in the neutral B,B, meson system is an experimentally challenging endeavor. This constitutes a flagship analysis of the Tevatron proton-antiproton collider physics program. In this dissertation we develop such an analysis of the time-dependent B, flavor oscillations using data collected with the CDF detector. The data samples are formed of both fully and partially reconstructed B meson decays, B, -+ D7r(irir) and B8 -- Dalv. A likelihood fitting framework is implemented and appropriate models and techniques developed for describing the mass, proper decay time, and flavor tagging characteristics of the data samples. The analysis is extended to samples of B+ and Bo mesons, which are further used for algorithm calibration and method validation. The B mesons lifetimes are extracted. The measurement of the Bo oscillation frequency yields Amd = 0.522 ± 0.017 ps-1. The search for B, oscillations is performed using an amplitude method based on a frequency scanning procedure. Applying a combination of lepton and jet charge flavor tagging algorithms, with a total tagging power ED2 of 1.6%, to a data sample of 355 pb-1, a sensitivity of 13.0 ps-1 is achieved. / (cont.) In a preliminary study, we develop a same side kaon tagging algorithm, which is found to provide a superior tagging power, of about 4.0% for the B, meson species. An evaluation of the dilution systematic uncertainties is not reported but after including the algorithm as is in the analysis the sensistivity is significantly increased to about 18 ps-'. An indication of a B, oscillation signal is seen at a frequency of about 17.5 ps-1. We show that the extension of the analysis to the increasing data samples with the inclusion of the same side tagging algorithm is capable of providing an observation of B, mixing beyond the standard model expectation. We show also that the improved knowledge of Am, has a considerable impact on constraining the CKM matrix elements. / by Nuno Teotónio Viegas Guerreiro Leonardo. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2001. / Includes bibliographical references (p. 145-157). / I have carried out several investigations of the long-term behavior of galactic X-ray sources using the 4.5-year database of the All Sky Monitor (ASM), and pointed observations made with the Proportional Counter Array (PCA) on board the Rossi X-ray Timing Explorer (RXTE). I have conducted a systematic search through the ASM data of all the 300 X-ray sources monitored for evidence of periodic behavior. Follow-up investigations are pursued on the discoveries I made in (1) the state transition and orbital modulation of the black hole candidate Cyg X-1; (2) a 4.4-d period in a previously poorly-known X-ray source X 1908+075; and (3) a 98-d period in another previously poorly known X-ray source XTE J1716-389. In Cyg X-1, I have detected its orbital period in the low-hard state but not in the high-soft state. I show that absorption of X-rays by a stellar wind from the companion star can reproduce the observed modulations in the hard state. To explain the low orbital modulation in the soft-state data, a reduction of the wind density during the soft state would be required. In addition, I have discovered an evolution of the correlation between the 1.5-12 keV X-ray count rate of Cyg X-1 and its spectral hardness during the 1996 spectral state transition. I present a quantitative study of this evolution using both the ASM and the PCA data. Implications of our findings are discussed. I have discovered a 4.4-d period in the ASM light curves of the X-ray source XTE J1716-389. I present the results of the investigations on this 98-d periodic modulation using both the ASM and the PCA data. The possible cause of this period and the nature of this system are discussed. / by Linqing Wen. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1954. / Includes bibliographical references. / by David Allen Hill. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Physics, 2004. / Includes bibliographical references (p. 45-46). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Actin polymerization plays a critical role in generating propulsive force to drive many types of cell motility. The discovery of actin based motility of the bacterial pathogen Listeria monocytogenes has lead to clearer understandings of the essential ingredients required for cell motility. The biophysical mechanisms by which these proteins generate forces is the subject of intense investigation. A novel system to study force generation by this polymerization engine is introduced by combining the well characterized mechanical properties of synthetic Giant Vesicles with the well understood biochemistry of actin polymerization. Giant Vesicles mimic the structural features of eukaryotic cell membranes. We find that Giant Vesicles coated with a protein that catalyzes actin polymerization form thick actin shells which produce a compressive force. The polymerization force directed at the membrane interface causes the membrane to rupture. In the resulting collapse we find that the shell thickens inward with a constant radial velocity and is characterized by radial lines of lipid and actin. We show that actin polymerization is the primary force driving the collapse. / by Hyman A. Carrel. / S.M.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2009. / Includes bibliographical references (leaves 67-70). / The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a network of long-arm interferometers designed to directly measure gravitational-wave strain. Direct observation of gravitational waves would provide a test of general relativity, as well as new insight into high-energy astrophysics. As of yet there have been no confirmed direct observations of gravitational waves, the largest of which are expected to be near the limit of LIGO's sensitivity. Analyses of LIGO data face the challenge of distinguishing small gravitational-wave signals from noise. This thesis presents a blind analysis of data from LIGO's fifth science run (November 2005-October 2007), searching for high-frequency gravitational-wave bursts coincident in data from the two LIGO interferometers located in Hanford, WA. The search for high-frequency gravitational-wave bursts is motivated by potential astrophysical sources such as supernovae and neutron stars, and enabled by the improvement of LIGO's sensitivity and the extension of the LIGO calibration up to 6 kHz. This analysis searches for gravitational-wave candidates with a duration under 1 second and central frequency from 1 to 6 kHz, of unspecified signal shape, during times when LIGO's two Hanford detectors were in science mode but its detector in Livingston, LA was not in science mode. The search is a blind analysis, developed using a set of background data that was previously established not to contain any gravitational-wave candidates. / (cont.) The background data are the data from the two Hanford detectors during times when the Livingston detector was in science mode. These background data are used to set requirements for identifying a gravitational-wave candidate in the foreground data, which are the data from the two Hanford detectors when the Livingston detector was not in science mode. The analysis identifies no gravitational-wave candidates. However, the analysis does set an upper limit on the rate of high-frequency gravitational-wave bursts as a function of signal strength and frequency. The upper limits converge to an upper limit of 0.018 events per day, or 6.5 events per year, at the 90% confidence level, for bursts at or above a characteristic strain amplitude of 10-19 strain/JH. This work does not reflect the scientific opinion of the LIGO Scientific Collaboration and its results have not been reviewed by the collaboration. / by Jacqueline Rose Villadsen. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1994. / Includes bibliographical references (leaves 263-265). / by Stephen G. Rowley, II. / Ph.D.

Thesis (Ph.D.) Massachusetts Institute of Technology. Dept. of Physics, 1947. / Vita. / Bibliography: leaves [71-72]. / by Joaquin Mazdak Luttinger. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1963. / Includes bibliographical references (leaves 41-43). / by Richard Kumeo Yamamoto. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 218-226). / The thesis presents results from experiments in which ultracold Sodium-6 and Lithium-23 atomic gases were studied near a Feshbach resonance at high magnetic fields. The enhanced interactions between atoms in the presence of a molecular state enhance collisions, leading to inelastic decay and loss, many-body dynamics, novel quantum phases, and molecule formation. Experimental data is presented alongside relevant theory and numerical models. Results are presented for both homonuclear Na 2 and Li 2 molecules, as well as heteronuclear NaLi resonances, although we were unable to isolate and measure NaLi molecules. Furthermore, experiments and theories related to strongly-correlated quantum phases such as Stoner model ferromagnetism, Bose mediated Fermi interactions, and Bose-Fermi mixtures are presented as applicable to Na and Li gases. Conclusions are presented regarding the feasibility of producing deeply bound, dipolar NaLi molecules, as well as future prospects for strongly interacting atomic gases of Na and Li. / by Caleb A. Christensen. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 189-205). / Entanglement is a special form of quantum correlation that exists among quantum particles and it has been realized that surprising things can happen when a large number of particles are entangled together. For example, topological orders emerge in condensed matter systems where the constituent 1023 particles are entangled in a nontrivial way; moreover, quantum computers, which can perform certain tasks significantly faster than classical computers, are made possible by the existence of entanglement among a large number of particles. However, a systematic understanding of entanglement in many-body systems is missing, leaving open the questions of what kinds of many-body entanglement exist, where to find them and what they can be used for. In this thesis, I present my work towards a more systematic understanding of many-body entanglement in systems where the particles interact with each other locally and the ground state of the system is separated from the excited states by a finite energy gap. Under such physically realistic locality and gap constraints, I am able to obtain more understanding concerning the efficient representation of many-body entangled states, the classification of such states according to their universal properties and the application of such states in quantum computation. More specifically, this thesis is focused on the tensor network representation of many-body entangled states and studies how the tensors in the representation reflect the universal properties of the states. An algorithm is presented to extract the universal properties from the tensors and certain symmetry constraints are found necessary for the tensors to represent states with nontrivial topological order. Classification of gapped quantum states is then carried out based on this representation. An operational procedure relating states with the same universal properties is established which is then applied to systems in one and higher dimensions. This leads not only to the discovery of new quantum phases but also to a more systematic understanding of them. A more complete understanding of possible many-body entanglement structures enables us to design an experimentally more feasible many-body entangled state for application in measurement-based quantum computation. Moreover, the framework of measurement-based quantum computation is generalized from spin to fermion systems leading to new possibilities for experimental realization. / by Xie Chen. / Ph.D.