Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2005. / Includes bibliographical references (p. 145-159). / Nanoscale structures present both unique physics and unique theoretical challenges. Atomic-scale simulations can find novel nanostructures with desirable properties, but the search can be difficult if the wide range of possible structures is not well understood. Electrical response and other non-equilibrium transport phenomena are measured experimentally, but not always simulated accurately. This thesis presents four diverse applications that demonstrate how first-principles calculations can address these challenges. Novel boron nanotube structures with unusual elastic properties are presented. Internal degrees of freedom are identified that allow longitudinal stress to be dissipated without changing the tube's diameter, leading to high lateral stiffness. Self-trapped hole structures in amorphous silicon dioxide are investigated in order to connect the behavior of hole currents to atomic-scale structures. Calculations on a paired-oxygen analogue to the ... center show that such a configuration does not result in a metastable trapped-hole state. A novel method to enable first-principles mobility calculations in ultrathin silicon-on-insulator (UTSOI) structures is presented and applied to interface roughness scattering in transistor channels. Self-consistent potentials and accurate wavefunctions and band structures allow for a direct link between measured electrical response and atomic structure. Atomic-scale interface roughness is shown to be an important limit on mobility at high carrier densities. At low carrier densities, such short-wavelength roughness results in qualitatively different mobility behavior than gradual UTSOI channel thickness fluctuations. / (cont.) An effective Hamiltonian technique to calculate short-time, non-equilibrium fluctuations in quantum devices is developed. Applications to quantum dots and resonant tunneling diodes show that temporal fluctuations are reproduced well. / by Matthew Hiram Evans. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2007. / Includes bibliographical references (p. 99-106). / In this work, we present the results of a general search for periodicities and for time-variable modulation strength in X-ray sources using data from the All-Sky Monitor onboard the Rossi X-ray Timing Explorer. New findings, including a sharp increase in the modulation of the X-ray flux from the Galactic bulge low-mass X-ray binary GX 9+9 and the recent spin-down event of the pulsar in the high-mass X-ray binary X0114+650, are reported. These searches employed new methods of periodicity detection that employed an algorithm to reduce the effects of low frequency noise from X-ray sources. We discuss these methods and show how they can be used to enhance the signal-to-noise ratio in the Fourier domain for many sources. / by Robert J. Harris. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2007. / Includes bibliographical references (p. 81-89). / To produce motion, cells rely on the conversion of potential energy into mechanical work. One such example is the dramatic process involving the acrosome reaction of Limulus sperm, whereby a 60-im long bundle of actin filaments straightens from a coiled conformation to extend out of the cell in five seconds. This cellular engine and the motion it produces represent a third type of actin-based motility fundamentally different from polymerization or myosin-driven processes. The motive force for this extension originates from stored elastic energy in the overtwisted, pre-formed coilmuch like a compressed mechanical spring. When the actin bundle untwists, this energy is converted to mechanical work powering the extension. We investigate the behavior of this actin spring with the identification of an osmotic mechanism controlling the extension and retraction of a helical conformation of the spring. In addition, we measure the bending stiffness of the helical bundle to be 0 - 2.3+0.25 x 10-21 N-m2 and compare the stored elastic energy to the osmotic work. We stall the retraction of this bundle and find that the required stall force is nearly - 8 nN. Furthermore, we stall the acrosome reaction (true discharge) of this actin spring and calculate the maximum force generated by this spring to be nearly 2 nN. To verify this value, we subject cells to a viscous load and characterize the viscosity to independently arrive at a lower bound for the force generated during the true discharge extension. Finally, we detail a mechanism, consistent with experimental observations, which accounts for the role of calcium during extension of the actin spring. / by Barney Kwun-poo Tam. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1995. / Includes bibliographical references (p. 96-97). / by Kendall Bruce Davis. / Ph.D.

Massachusetts Institute of Technology. Dept. of Physics. Thesis. 1965. Sc.D. / Sc.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2009. / In title on title page, [psi][phi] appears as lower case Greek letter italic and double underscored "s" appears as subscript. Cataloged from PDF version of thesis. / Includes bibliographical references (p. 193-200). / In this dissertation, we present the results of a time-dependent angular analysis of Bs -+ J/,0 decays performed with the use of initial-state flavor tagging. CP violation is observed in this mode through the interference of decay without net mixing and decay with net mixing, that is, Bs -- J/0 and Bs -+ B, -+ J/q0. The time-dependent angular analysis is used to extract the decay widths of the heavy and light B, eigenstates and the difference between these decay widths AF, - FL - FH. Initial-state flavor tagging is used to determine the matter-antimatter content of the B. mesons at production time. We combine flavor tagging with the angular analysis, which statistically determines the contributions of the CP-even and CP- odd components at decay time, to measure the CP-violating phase 0,. The phase 3, is expressed in terms of elements of the Cabibbo-Kobayashi-Maskawa matrix as s - arg (-VtsV4/VcsV*b), and is predicted by the Standard Model to be close to zero, O3SM = 0.02. In the measurement of AF,, we use a dataset corresponding to 1.7 fb- of luminosity, collected at the CDF experiment from proton-antiproton collisions at a center of mass energy f = 1.96 TeV. In the measurement of Ps, we use a dataset corresponding to 1.3 fb-1 of collected luminosity. We measure AF, = (0.071+0.064 ± 0.007) ps-1 using the time-dependent angular analysis. Combining the angular analysis with flavor-tagging, we find that assuming the Standard Model predictions of p/ and AF,, the probability of a deviation as large as the level of the observed data is 33%. We obtain a suite of associated results which are discussed in detail in this dissertation alongside the main results. / by Khaldoun Makhoul. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 275-288). / Measurements of the ratio of the proton elastic form factors ([mu]pGe/Gm) using Rosenbluth separation and those using polarization-based techniques show a strong discrepancy, which has persisted both in modern experimental results and in re-analyses of previous data. The most widely accepted hypothesis to explain this discrepancy is the treatment of the contributions from hard two-photon exchange (TPE) to elastic electron-proton scattering in the radiative corrections applied to the Rosenbluth separation measurements. Calculations of the hard TPE contribution are highly model dependent, but the effect may be measured experimentally with a precise determination of the ratio of the positron-proton and electron-proton elastic scattering cross sections. The OLYMPUS experiment collected approximately 4 fb-1 of e+p and e-p scattering data at the DORIS storage ring at DESY in 2012, with the goal of measuring the elastic [sigma]e+p/[sigma]e-p ratio over the kinematic range (0.4 < c < 0.9), (0.6 < Q2 < 2.2) GeV2 /c 2 at a fixed lepton beam energy of 2.01 GeV. The detector for the OLYMPUS experiment consisted of refurbished elements of the Bates Large Acceptance Spectrometer Toroid (BLAST) surrounding an internal gaseous hydrogen target, with the addition of multiple systems for the monitoring of the luminosity collected by the experiment. A detailed simulation of the experiment was developed to account for both radiative corrections and various systematic effects. This work presents preliminary results from the OLYMPUS data, demonstrating that the elastic [sigma]e+p/[sigma]e-p ratio rises to several percent at [epsilon] ~~ 0.4 and indicating a significant contribution from TPE to e± p scattering. Additionally, the value of [sigma]e+p/[sigma]e-p has been measured to unprecedented precision at [epsilon] = 0.98, which provides a valuable normalization point for other experimental data. / by Brian Scott Henderson. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2005. / Includes bibliographical references (P. 201-206). / Nuclear structure and the underlying internucleon (NN) interaction are central to the understanding of how nucleons interact. However, despite decades of research, Quantum Chromodynamics, which governs the interactions of quarks making up nucleons, continues to evade a fully tractable solution. As a result, understanding of the nucleon and how it interacts with other nucleons is not complete. Due to its simple composition, the deuteron has long been important in understanding the structure of the NN potential. In particular, the tensor asymmetry, Ad, and beam-vector asymmetry, Al, from deuteron electrodisintegration, ... , are sensitive to the existence of a tensor component in the NN interaction. The Bates Large Acceptance Spectrometer Toroid (BLAST) provides a unique opportunity to measure deuteron electrodisintegration asymmetries at low momentum transfer. BLAST combines a high-duty polarized electron beam, an Atomic Beam Source (ABS) target of highly-polarized deuterium atoms, and a large-acceptance spectrometer detector. This work reports on measurements of A.4 and Aid for Q2 ranges between 0.1 and 0.5 (GeV/c)2. Comparisons with Monte Carlo simulations based on the current understanding of the deuteron are made, and conclusions are drawn. / by Aaron J. Maschinot. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1986. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographies. / by Joyce Anne Peetermans. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2003. / Includes bibliographical references (leaves 121-124). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / This thesis describes the demonstration of a new technique that allows masses to be compared with fractional uncertainty at or below 1 x 10-11, an order of magnitude improvement over our previous results. By confining two different ions in a Penning trap we can now simultaneously measure the ratio of their two cyclotron frequencies, making our mass comparisons insensitive to many sources of fluctuations (e.g. of the magnetic field). To minimize the systematic error associated with the Coulomb interaction between the two ions, we keep them about 1 mm apart from each other, on a common magnetron orbit. We have developed novel techniques to measure and control all three normal modes of motion of each ion, including the two strongly coupled magnetron modes. With the help of a new computer control system we have characterized the electric field anharmonicities and magnetic field inhomogeneities to an unprecedented level of precision. This allows us to optimize the trap so that our measurement of the cyclotron frequency ratio is to first order insensitive to the field imperfections. Using the ions 13C2H2+ and 14N2+, we performed many tests of our understanding of the ions dynamics and of the various sources of errors in this technique. From these we conclude that there should be no systematic error in our measurements at the level of 5 x 10-12. Thus we feel confident reporting a value for the mass ratio of these ions with an uncertainty of 10-11. / (cont.) In this thesis, we also report measurements of the two mass ratios m[33S+]/m[32SH+] and m[29Si+]/m[28SiH+] with a relative uncertainty of less than 10-1l, which makes them the best known mass ratios to date. These can be combined with precise measurements of high-energy gamma-rays to provide a direct test of the relation E = mc2. This is a test of special relativity which does not rely on the assumption of a preferred reference frame. The uncertainty on the atomic mass of 29Si is also reduced by about an order of magnitude. / by Simon Rainville. / Ph.D.