Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Physics, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 37-38). / The Casimir energy is the change in energy of a configuration of objects due to second quantization of the electromagnetic field. The Casimir energy of a dielectric object inside a perfectly conducting sphere was recently analyzed [1]. Building on this result, I calculate the changes in energy levels of a quantum top inside a cavity after promoting the Casimir energy to a quantum Hamiltonian. I apply the result to a diatomic molecule and find the changes in the spectroscopy induced by the Casimir effect. This can potentially provide an additional experimental probe into the Casimir effect. / by Eric Andrew Vitus Fitzgerald. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2002. / Includes bibliographical references (p. 261-279). / A prismless Cr4+:YAG laser was used to generate 20 fs pulses at 1450 nm with a bandwidth of 190 nm FWHM. Intracavity group velocity dispersion was compensated with double-chirped mirrors. Pulse spectrum was observable from 1140 to >1700 nm. Broadband saturable Bragg reflectors were designed and used to ensure self-starting of 35 fs pulses in the ultrafast Cr4+:YAG laser or to generate picosecond pulses tunable from 1400 to 1525 nm. The mirrors were a 7-pair GaAs/AlxOy quarter-wave dielectric stack, and the absorber consisted of a InGaAs quantum well centered in a half-wave InP layer. Transmission was measured through a photonic bandgap crystal microcavity resonant near 1550 nm. Cavity quality factors as high as 360 were observed for cavities with a modal volume of only 2([lambda]/2n)3. Photonic crystals were used to enhance the total emission of a light emitting diode at 980 nm by 8-fold. At particular wavelengths, collected photoluminescence enhancements larger than 100 were observed. / by Daniel Jacob Ripin. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2004. / Includes bibliographical references (p. 33-34). / When a jet of water is in free fall, it rapidly breaks up into drops, since a cylinder of water is unstable. This and other problems involving the form of a volume of water bound by surface tension have yielded a wealth of theoretical and experimental results, and given insight into such phenomena as the shape of the Earth. Particularly interesting behaviors tend to emerge when the fluid in question is rotating; a drop may, for example, form a toroidal or ellipsoidal shape or even stretch out into some multi-lobed, non-axisymmetric form. In this paper, we investigate the properties of a rotating jet of water, and determine what regime of the parameter space are dominated by the various forms of instability. This is both predicted theoretically and demonstrated to be accurate experimentally. If we watch a jet of water as the rotation rate is gradually increased from zero, the drop size will start shrinking gradually, and then suddenly, rather than a single row of drops, we will see the jet breaking up into two-lobed, bar shaped forms, like the rung of a ladder. The point at which this transition occurs is characterized in terms of the rotational Bond number, B₀ = ... . The critical B₀ may be as low as 6, if there is a strong bias imparted by vibration of the table at an appropriate frequency, but for a perfectly quiescent rotating jet the second mode does not become dominant until a higher B₀. As the rotation rate is increased above this, the instability grows gradually more dramatic, and eventually the two lobes of each drop are breaking apart and flying outward. Then a transition to a third mode will occur, with three lobes in each drop; this is possible from a B₀ of 12, and dominant above a B₀ slightly higher than that. In general, mode m may occur whenever / (cont.) B₀ > m(m + 1). / by Russell Zahniser. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1995. / Includes bibliographical references (p. 91-95). / by Susan Mary Gascon-Shotkin. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 59). / In this thesis, we wish to test the hypothesis that scattering by a random potential causes localization of wave functions, and that this localization is governed by the Born postulate of quantum mechanics. We begin with a simple model system: a one-dimensional Gaussian wave packet incident from the left onto a delta function potential with a single scattering center. Then we proceed to study the more complicated models with double and triple scattering centers. Chapter 1 briefly describes the motivations behind this thesis and the phenomenon related to this research. Chapter 2 to Chapter 4 give the detailed calculations involved in the single, double and triple scattering cases; for each case, we work out the exact expressions of wave functions, write computer programs to numerically calculate the behavior of the wave packets, and use graphs to illustrate the results of the calculations. In Chapter 5, we study the parameters that determine how much the wave function shrinks, including the initial width, the initial position and the momentum of the Gaussian wave packet, and the strength of and the spacing between the delta functions; then we examine different combinations of the parameters in order to find a pattern to achieve maximum shrinking. Chapter 6 concludes the thesis with the essential results of this research as well as its implications and potentials. / by Fei Sun. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 65-66). / The fluid/gravity correspondence describes an map from relativistic fluid dynamics to general relativity in an anti de Sitter (AdS) background in one more dimension. This is a specific example of a more general principle known as holographic duality, in which a quantum field theory (QFT) is dual to a gravitational theory with the QFT defined on the boundary. Since we can regard hydrodynamics as a low-energy description of many QFTs, the fluid/gravity correspondence lets us probe holographic duality for QFTs at low energy. In this thesis, we will discuss holographic duality, hydrodynamic theory and turbulence, numerical implementations of hydrodynamics, black branes in AdS, the fluid/gravity correspondence, and numerically testing the fluid/gravity correspondence. / by Nathan S. Benjamin. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 77-78). / The GEANT4 physics simulation program is known to have errors in how hadronic interactions are implemented. This has the potential to cause errors in the Monte Carlos used to determine the expected neutron backgrounds in the MiniCLEAN single phase liquid argon WIMP detector. Elastic and inelastic collisions between neutrons and argon nuclei as well as neutron captures were simulated independently in order to characterize the accuracy of the implementation by GEANT4.9.3.pOl and GEANT4.9.5. The effective cross sections, angular distributions, photons, decay schemes, energy conservation, and momentum conservation were determined through analysis of the neutron tracks created by GEANT4. A large proportion of the interactions behave as expected, however energy and momentum are not conserved by varying degrees of severity with some GEANT4.9.3.pOl inelastic collisions resulting in over twice the correct amount of energy. / by Kathleen M. Harrington. / S.B.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 143-147). / Large-scale numerical simulations are key to studying the complex physical systems that surround us. Simulations provide the ability to perform simplified numerical experiments to build our understanding of large-scale processes which cannot be controlled and examined in the laboratory. This dissertation develops a new open-source computational framework, Dedalus, for solving a diverse range of equations used to model such systems and applies the code to the study of stellar and oceanic fluid flows. In the first part, the spectral algorithms used in Dedalus are introduced and the design and development of the code are described. In particular, the code's symbolic equation specification, arbitrary-dimensional parallelization, and sparse spectral discretization systems are detailed. This project provides the scientific community with an easy-to-use tool that can efficiently and accurately simulate many processes arising in geophysical and astrophysical fluid dynamics. In the second part, Dedalus is used to study the turbulent boundary layers that form at the interface between marine-terminating glaciers and the ocean. A simplified model considering the heat transfer from a heated or cooled wall in a stratified fluid is investigated. We find new scaling laws for the turbulent heat transfer from the wall as a function of the imposed thermal forcing, with potential implications for the sensitivity of glacier melting to warming ocean temperatures. In the third part, Dedalus is used to study the stability of the tidal deformations experienced by binary neutron stars as they inspiral. We develop a numerical workflow for determining the weakly nonlinear stability of a tidally forced plane-parallel atmosphere and verify the results using fully nonlinear simulations. This framework may help determine whether tidal instabilities can be observed in gravitational wave signatures of binary neutron stars, which could provide observational constraints on the equation of state of matter above nuclear densities. / by Keaton James Burns. / Ph. D.

Recent advances in nanotechnology offer a new platform for the label free detection of biomolecules at ultra-low concentrations. Nano biosensors are emerging as a powerful method of improving device performance whilst minimizing device size, cost and fabrication times. Nanogap capacitive biosensors are an excellent approach for detecting biomolecular interactions due to the ease of measurement, low cost equipment needed and compatibility with multiplex formats. This thesis describes research into the fabrication of a nanogap capacitive biosensor and its detection results in label-free aptamer-based protein detection for proof of concept. Over the last four decades many research groups have worked on fabrication and applications of these type of biosensors, with different approaches, but there is much scope for the improvement of sensitivity and reliability. Additionally, the potential of these sensors for use in commercial markets and in everyday life has yet to be realized. Initial work in the field was limited to high frequency (>100 kHz) measurements only, since at low frequency there is significant electronic thermal noise (< V2 > = 4kBTR) from the electrical double layer (EDL). This was a significant drawback since this noise masked most of the important information from biomolecular interactions of interest. A novel approach to remove this parasitic noise is to minimize the EDL impedance by reducing the capacitor electrode separation to less than the EDL thickness. In the case of aptamer functionalized electrodes, this is particularly advantageous since device sensitivity is increased as the dielectric volume is better matched to the size of the biomolecules and their binding to the electrode surface. This work has demonstrated experimentally the concepts postulated theoretically. In this work we have fabricated a large area (100 x 5 μm x 5 μm) vertically oriented capacitive nanogap biosensor with a 40 nm electrode separation between two gold electrodes. A silicon dioxide support layer separates the two electrodes and this is partially etched (approximately 800 nm from both sides of each 5 μm x 5 μm capacitor), leaving an area of the gold electrodes available for thiol-aptamer functionalization. AC impedance spectroscopy measurements were performed with the biosensor in the presence of air, D.I. water, various ionic strength buffer solutions and aptamer/protein pairs inside the nanogap. Applied frequencies were from 1Hz to 500 kHz at 20 mV AC voltage with 0 DC. We obtained relative permittivity results as a function of frequency for air (ɛ=1) and DI water (ɛ~80) which compares very favorably with previous works done by different research groups. The sensitivity and response of the sensors to buffer solution (SSC buffer) with various ionic strengths (0.1x SSC, 0.2x SSC, 0.5x SSC and 1x SSC) was studied in detail. It was found that in the low frequency region (< 1 kHz) the relative permittivity (capacitance) was broadly constant, that means it is independent from the applied frequency in this range. With increasing buffer concentration, the relative permittivity starts to increase (from ɛ=170 for 0.1x SSC to ɛ=260 for 1x SSC). The sensor performance was further investigated for aptamer-based protein detection, human alpha thrombin aptamers and human alpha thrombin protein pairs were selected for proof of concept. Aptamers were functionalized into the gold electrode surface with the Self-Assembly-Monolayer (SAM) method and measurements were performed in the presence of 0.5x SSC buffer solution (ɛ=180). Then the hybridization step was carried out with 1 μM of human alpha thrombin protein followed by measurements in the presence of the same buffer (ɛ=130). The response of the sensors with different solutions inside the nanogap was studied at room temperature (5 working devices were tested for each step). The replacement of the buffer solution (ɛ=250) with lower relative permittivity biomolecules (aptamer ɛ=180) and further binding proteins to immobilized aptamer (ɛ=130) was studied. To validate these results, a control experiment was carried out using different aptamers, in this case which are not able to bind to human alpha thrombin protein. It was found that the relative permittivity did not change after the hybridization step compared to the aptamer functionalization step, which indicates that the sensors performance is highly sensitive and reliable. This work serves as a proof of concept for a novel nanogap based biosensor with the potential to be used for many applications in environmental, food industry and medical industry. The fabrication method has been shown to be reliable and consistent with the possibility of being easily commercialized for mass production for use in laboratories for the analysis of a wide range of samples.

<p> Acoustic parameters (velocity and attenuation-coecient) are known to be sensitive to the Degree of Sensitization (DoS) in aluminum alloys. The attenuation coecient has been shown to be more sensitive to DoS than transverse and longitudinal wave velocities. There is a need to investigate ways of improving the precision (reducing the error bars) in the attenuation coecient. In this thesis, two methods for generating source signals, and two techniques for analyzing the received signals, both using the Pulse{Echo ultrasonic technique, were investigated. The two techniques of analysis (time- and frequency-domain correlation) were compared with the scope of observing the variation in the precision of the attenuation coecient, with the frequency-domain correlation technique found to be slightly more precise. In addition, a comparison was made between the frequency-domain correlation technique developed in this thesis and the technique previously used by the group to obtain the acoustic parameters. The frequency-domain correlation technique was found to be comparable, in terms of errors, with the current technique. Most importantly, it was also found to be much faster (480 times faster than the current technique), less tedious, since it is automated. A conclusion that the frequency-domain correlation technique would be suitable for analyzing very large data sets (e.g in material health monitoring), with less eort, can be drawn. Further, because of the ease-of-use, large sets of data can be analyzed quickly to allow for proper statistics, making frequency dependent measurements of acoustic parameters of interest an easier task.</p><p>