Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2005. / Includes bibliographical references (leaf 35). / Oscillons are localized solutions of nonlinear field theories that oscillate without dissipation. We have numerically found a family of very long-lived oscillons the spherical ansatz of the SU(2) gauged Higgs model -the standard model of the weak interactions without electromagnetism and fermions. In this thesis, we study the stability of these objects. We do this by adding a massless mode to the model and coupling it to the oscillating fields contained in the Higgs doublet. Such a mode is expected to provide a decaying mechanism for the oscillons. However, numerical investigation shows that our oscillons do not decay if the massless mode is sufficiently weakly coupled and suggests that our oscillons are stable long-lived solutions that could substantially influence the dynamics of this theory. / by Ruza Markov. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 57). / In this thesis, I present a new technique for measuring the optical aberrations produced by a telescope, with an eye towards future use of these aberration measurements to align wide-field telescopes. This method determines the aberrations by simultaneously fitting a pair of oppositely defocused images to a mostly analytic model. I develop the model and describe its software implementation in detail, and then report on the results of tests with simulated and real data. This technique is able to extract the aberrations from simulated data rapidly and accurately, and it has been used with mixed success to analyze data from the VISTA telescope. With the VISTA data, the algorithm is unable to match small-scale brightness variations in the images. However, it was able to determine aberrations with median accuracies of 0.08 um for coma, 0.08 um for astigmatism, 0.9 um for tilt, and 0.3 um for defocus. It was also quite fast, with an average of 34 iterations until convergence. / by Ryan J. Janish. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1994. / Includes bibliographical references (p. 91-94). / by Long Hsu. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1995. / Vita. / Includes bibliographical references (p. 139-142). / by Jens-Ole Hansen. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 41). / I implemented event reconstruction of a Monte Carlo simulation using neural networks. The OLYMPUS Collaboration is using a Monte Carlo simulation of the OLYMPUS particle detector to evaluate systematics and reconstruct events. This simulation registers the passage of particles as 'hits' in the detector elements, which can be used to determine event parameters such as momentum and direction. However, these hits are often obscured by noise. Using Geant4 and ROOT, I wrote a program that uses artificial neural networks to separate track hits from noise and reconstruct event parameters. The classification network successfully discriminates between track hits and noise for 97.48% of events. The reconstruction networks determine the various event parameters to within 2-3%. / by Emma Elizabeth Tolley. / S.B.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Since Einstein proposed the theory of general relativity (GR) as a theory of gravity, it has passed all experimental checks and tests. Until recently, all of these tests have been done in the weak gravity limit. The first test of strong-field GR came just a few months ago, when the LIGO collaboration directly detected gravitational waves for the first time. Using gravitational waves as a tool to test the validity of GR requires us to know the waveforms that GR predicts from various sources. The ultimate goal of the research described in this thesis is to compute the waveform generated by a stellar mass Kerr black hole as it inspirals into a much more massive black hole (SMBH). To compute this waveform, we must first compute the inspiral trajectory of the stellar mass black hole. The trajectory of the smaller black hole differs from the geodesic structure taught in GR textbooks due to the influence of this body's mass and spin. In this thesis, I examine these two effects separately. Later work will need to consider the two effects simultaneously, but the separate impact of these effects provides insight which helps us to understand how to model these sources. The small body's mass perturbs the spacetime and pushes its trajectory away from textbook geodesic motion. I show how to compute the dissipative part of this "self force," whose average impact is equivalent to the loss of energy and angular momentum due to gravitational wave emission. I study in particular how the self force's averaged behavior changes near orbital resonances, quantifying the impact that such resonances will have on the small body's inspiral. The small body's spin couples to spacetime curvature. This coupling leads to a force which also pushes the small body's trajectory away from the geodesic. This force is comparable in magnitude to the self force associated with the small body's mass, indicating that future work will need to assess the impact of these effects together in a self consistent way in order to make accurate inspiral waveforms. / by Uchupol Ruangsri. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1996. / Includes bibliographical references (p. 121-126). / by Anton Andreev. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 53). / Black holes and compact objects are often surrounded by structures known as accretion disks which consist of ionized plasma. Due to the immense forces present in the disk, interesting and complex magnetic field structures can be set up within the disk. The influence of gravity on these structures is explored via a higher-order expansion of the gravitational potential. We consider several cases: the case when the Lorentz force is negligible and the case when the Lorentz force becomes significant in the dynamics of the disk. When the Lorentz force is negligible, we find using the Ferraro Co-rotation Theorem that the strength of the magnetic field increases near the event horizon. As the strength of the Lorentz force increases and it is included in our analysis, we discover that it leads to a periodic "crystal" structure of concentric rings of current. This structure is significantly affected by gravitational forces: we find a solution to the equations of motion that shows a composite structure within the disk. We discuss the general relativistic effects near the event horizon using the Pseudo- Newtonian potential in this limit. In addition, we consider an alternate derivation of the equation of motion describing the behavior of the magnetic field and discuss its consequences. / by Kristiana E. Schneck. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2004. / Includes bibliographical references (p. 67-72). / We present the results of five Chandra observations of the normal galaxy NGC 3877. A total of 27 X-ray sources are detected, including SN 1998S. We find 15 sources to be variable during the 646-day period covered by the observations. We use two methods to determine source color and find no apparent correlation between color and brightness in our population sample. We provide flux and luminosity estimates for every source and construct cumulative X-ray luminosity functions (XLFs) for each observation. We find a higher density of luminous ([approximately] 10³⁷ erg s⁻¹) sources in NGC 3877 than we see in two other galaxies. We tentatively identify some sources as X-ray binaries. / by Edgar Raul Gonzalez. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 119-124). / Recent stellarator experiments have been designed with one of two types of neoclassical optimization: quasisymmetry or quasi-isodynamism. Both types of stellarator have perfectly confined collisionless particle orbits as well as one additional feature. Quasisymmetric plasmas have minimal flow damping, which may lead to reduced turbulent transport. Quasi-isodynamic plasmas can have vanishing bootstrap current, implying less variation in the magnetic configuration as the pressure changes and also implying greater stability. Analytical expressions for neoclassical transport in a general stellarator are complicated, so it is desirable to find reduced expressions for ideal limiting cases to provide insight. Here, new neoclassical expressions are derived for a quasi-isodynamic plasma. The Pfirsch-Schliiter flow and current can be written concisely as an integral of B. The remaining components of the flow and bootstrap current are identical to those in a quasi-poloidally symmetric device. A compact expression is derived for the radial electric field Er which is largely independent of the details of the magnetic field. Another issue in the neoclassical theory of stellarators which has not been fully resolved is the validity of the so-called monoenergetic approximation, in which ad-hoc changes are made to Er terms in the kinetic equation to expedite numerical computations. Here we show that at least in a quasisymmetric plasma, this approximate treatment of Er leads to a significant and systematic underestimation of the trapped particle fraction. This distortion of the collisionless orbits is independent of any approximations made to the collision operator. For ideal quasisymmetric and quasi-isodynamic plasmas, new neoclassical expressions are derived in which this problematic monoenergetic approximation is avoided. In the quasisymmetric case, results are presented in both the banana regime and plateau regime for the ion flow, ion radial heat flux, and bootstrap current. The bootstrap current is found to be enhanced. For the quasi-isodynamic case, new Er-driven contributions to the distribution function are obtained. The flow and bootstrap current turn out to be modified by the same numerical coefficient as in the quasisymmetric case. / by Matthew Joseph Landreman. / Ph.D.