Thesis (Ph.D.) Massachusetts Institute of Technology. Dept. of Physics, 1954. / Vita. / Bibliography: leaves 105-106. / by Lawrence Gould. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 147-158). / Higher organisms, such as humans, have an adaptive immune system that usually enables them to successfully combat diverse (and evolving) microbial pathogens. The adaptive immune system is not preprogrammed to respond to prescribed pathogens, yet it mounts pathogen-specific responses against diverse microbes, and establishes memory of past infections (the basis of vaccination). Although major advances have been made in understanding pertinent molecular and cellular phenomena, the mechanistic principles that govern many aspects of an immune response are not known. In this thesis, I illustrate how complementary approaches from the physical and life sciences can help confront this challenge. Specifically, I describe work that brings together statistical mechanics and cell biology to shed light on how key regulators of the adaptive immune system, T cells, are selected to enable pathogen-specific responses. A model of T cell development is introduced and analyzed (computationally and analytically) by employing methods from statistical physics, such as extreme value distributions and Hamiltonian minimization. Results show that selected T cell receptors are enriched in weakly interacting amino acids. Such T cell receptors recognize (i.e. bind sufficiently strongly to) pathogens through several contacts of moderate strength, each of which makes a significant contribution to overall binding. Disrupting any contact by mutating the pathogen is statistically likely to abrogate T cell recognition of the mutated pathogen. We propose that this is the mechanism for the specificity of T cells for unknown pathogens. The T cell development model is also used to discuss one way in which host genetics can influence the selection of T cells and concomitantly the control of HIV infection. A model of the T cell selection process as diffusion in a random field of immobile traps that intermittently turn "on" and "off" is developed to estimate the escape probability of dangerous T cells that could cause autoimmune disease. Finally, and importantly, throughout this thesis, I describe, how the theoretical studies are closely synergistic/complementary with biological experiments and human clinical data. / by Andrej Košmrlj. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2009. / Includes bibliographical references (leaf 52) and index. / We analyze data associated with the coronal mass ejections of March 1991, with emphasis on a remarkable double-streaming proton event observed at 35 AU. The plasma data used in our analysis were collected by three spacecraft: Voyager 2 near 35 AU, Ulysses near 3 AU, and IMP-8 at 1 AU. The observations of the same CME events by three spacecraft over such a wide range of radii gives insight into the evolution of CMEs as they propagate from the Sun to 1 AU and then into the outer heliosphere. Of the many characteristics observed, we are especially interested in the double-streaming proton events seen at Voyager 2 in June 1991 over a two day period. Such pronounced double-streaming has not previously been reported to be a feature of CMEs at any distance, much less at distances of 35 AU, with its 120 day transit time from the Sun. The double streaming events show a remarkably large separation between the two peaks that is close to the Alfvén speed and much greater than the thermal spread of either peak. These double streaming events were followed a day later by a large scale polarity reversal in the interplanetary magnetic field at Voyager 2. This reversal is thought to be a site of magnetic reconnection, where energy in the field is being converted into particle energy. We speculate that the free energy involved in the earlier double streaming events is somehow related to this magnetic reconnection process, although we have found as yet no direct causal connection. / by Thanasin V. Nampaisarn. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1989. / GRSN 406579 / Includes bibliographical references (p. 209-213). / by Eric Leslie Kronenberg. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1992. / Includes bibliographical references (leaves 101-104). / by Tomás Alberto Arias. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1994. / Includes bibliographical references (p. 143-146). / by Ching-Hua Tan. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2005. / Includes bibliographical references (p. 169-175). / Basic electron transport phenomena observed in single-electron transistors (SETs) are introduced, such as Coulomb-blockade diamonds, inelastic cotunneling thresholds, the spin-1/2 Kondo effect, and Fano interference. With a magnetic field parallel to the motion of the electrons, single-particle energy levels undergo Zeeman splitting according to their spin. The g-factor describing this splitting is extracted in the spin-flip inelastic cotunneling regime. The Kondo splitting is linear and slightly greater than the Zeeman splitting. At zero magnetic field, the spin triplet excited state energy and its dependence on gate voltage are measured via sharp Kondo peaks superimposed on inelastic cotunneling thresholds. Singlet-triplet transitions and an avoided crossing are analyzed with a simple two-level model, which provides information about the exchange energy and the orbital mixing. With four electrons on the quantum dot, the spin triplet state has two characteristic energy scales, consistent with a two-stage Kondo effect description. The low energy scale extracted from a nonequilibrium measurement is larger than those extracted in equilibrium. / by Ghislain Granger. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1947. / Vita. / Includes bibliographical references (leaves 106-111). / by Herbert B. Callen. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1994. / Title as it appears in the Feb. 1994 MIT Graduate List: Laser gain studies in plasmas produced by a small zig-zag slab laser. / Includes bibliographical references (p. 187-191). / Martin Heinrich Muendel. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 69-70). / In this thesis we present an optical and electronic setup that is capable of performing coherent state tomography. We fully characterize it in order to verify whether or not it will be capable to perform non-demolition homodyne detection of squeezed light in a high-finesse cavity QED setup with an ensemble of Cesium atoms coupled to the cavity. After quantifying sources of noise, the photodiode efficiency, we perform a series of measurements of low photon number coherent states and compare them against the standard quantum limit. We discuss a variety of technical challenges encountered in such systems and some methods to overcome them. Lastly, we test the apparatus' ability to do quantum state tomography and quantum state reconstruction by reconstructing the density matrix and Wigner functions for low photon-number coherent states. / by Olivia L. Mello. / S.B.