MS, University of Cincinnati, 2009, Engineering : Electrical Engineering

Electron spin, alone or in conjunction with charge, can be used to process information and build up quantum computers because it is a natural quantum bit. In this work, a Java simulator has been constructed and a 3D display has been created using Java 3D API to animate the motion of a qubit or spinor based on the Bloch sphere and Bloch ball concepts. The simulator is capable of illustrating the Larmor precession of a qubit, the Rabi formula which calculates the probability of spin flip in a time dependent magnetic field, and the density matrix concept where the time evolution of an ensemble of spinors can be examined. Control panels are constructed on the user interface to allow manipulation of qubits and adjustment of simulation parameters such as external time-independent and time-dependent magnetic fields. The simulator provides a user friendly software package useful for teaching and self-learning in the field of spintronics.

Committee: Marc Cahay PhD (Committee Chair); Punit Boolchand PhD (Committee Member); Carla Purdy PhD (Committee Member) Subjects:

Master of Science, The Ohio State University, 2012, Physics

As the power requirements of computation for large scale and mobile applications increase and the fundamental limits of current technology are being approached, the development of novel computational schema is required to continue the meteoric improvements in processing. One such schema, spintronics, relies on manipulation of the magnetic state of electrons in computation. Such approaches to computation would be facilitated by the development of high-quality ferromagnetic semiconductors capable of room temperature operation and by controlled injection of magnetically polarized electrons into conventional semiconductors. The first part of this work explores the utility of gadolinium doped GaN/AlGaN heterojunctions as a magnetic semiconductor system. The extremely large magnetization per magnetic dopant atom observed in gadolinium doped gallium nitride is also observed in some, but not all, of these heterojunctions. The second part of this work involves the fabrication of spin valve devices on undoped GaN/AlGaN heterojunctions. Such devices present one potential avenue for the control of magnetically polarized current within conventional semiconductor systems.

Committee: Ezekiel Johnston-Halperin (Advisor); Roberto Myers (Advisor) Subjects: Condensed Matter Physics; Physics

Master of Science, Miami University, 2012, Physics

Since its discovery in 1949, Nereid's photometric variations, orbit, and mass have been well established, however knowledge of its spin, orientation, and shape is lacking. We simulate Nereid's orbital and rotational motion, dependent on these unknown characteristics, in an attempt to match observations. We show how a time-dependent gravitational torque can cause the body to precess on a timespan as small as ~ 17 years, following a complicated coning nutation. Modeled as a uniformly reflecting body, we find that if the photometric variations are to be solely explained by geometry, Nereid cannot be either prolate or oblate. We have produced large amplitude, intra-night variations similar to those presented in Schaefer et al. (2008), but are unable to fully match their observations. Our study shows our strongest candidate to have an initial obliquity of 60 degrees, a spin rate of 144 hours, and semi-axial ratios of c/a ~ 0.5, b/a ~ 0.6.

Committee: Stephen Alexander PhD (Advisor); Michael Pechan PhD (Committee Member); Paul Urayama PhD (Committee Member) Subjects: Applied Mathematics; Astronomy; Astrophysics; Physics; Theoretical Physics

Master of Science, University of Akron, 2010, Geology

The West African monsoon is an important component of the Earth's atmospheric system because the monsoon redistributes heat and moisture in the tropics. In addition, West Africa is densely populated and has an ecosystem controlled by monsoon rainfall. Therefore, a better understanding of past monsoon variability has social relevance. The hydrologically-closed Lake Bosumtwi occupies a 1.07 Ma meteorite impact crater located in Ghana, West Africa. The lake lies beneath the seasonal passage of the ITCZ; hence, the lake's sediment record is well suited for studies of past monsoon variability. This thesis research identifies down-core mineralogic variations in a 291-m long sediment core from Lake Bosumtwi using X-Ray diffraction (XRD). Scanning electron microscope and calcium carbonate measurements were also performed to support the XRD results. X-ray diffraction measurements were performed on more than 410 samples at a 1-meter spacing; and at a resolution of 50-cm or less, above 67 m.Lake Bosumtwi mineralogy is shown to provide an interpretable proxy of paleoclimate variability. During several well-documented lake level lowstands (at 3.2 kyr and 16.3 to 20 kyr when the lake was 30 m and 60 m below the present lake level, respectively), increases in calcite, Mg-calcite and total carbonate content indicate carbonate precipitation by evaporative enhancement during arid climate conditions. During the lake-level highstand of the Holocene African Humid Period, calcite is completely absent and Mg-calcite is present in low abundance reflecting the diluted lake water during this moist climate period. In general, detrital (i.e., quartz), carbonate (i.e., calcite, Mg-calcite, ankerite, dolomite) and diagenetic (i.e., analcime) minerals are more abundant during times of low boreal summer insolation when the West Africa summer monsoon is weak. The source of quartz to Lake Bosumtwi include both the bedrock of the crater walls and wind-blown dust from the Sahel, both of which increase (open full item for complete abstract)

Committee: John A. Peck Dr. (Advisor) Subjects: Environmental Science; Geology; Mineralogy; Oceanography

Doctor of Philosophy, The Ohio State University, 2013, Physics

Ultrafast laser optics is becoming a powerful tool in materials research. The interaction between femtosecond laser pulses with electrons and the subsequent relaxation process is an active research topic in recent years. In the time scale of femtoseconds to nanoseconds, several interesting physics take place. The laser pulses are short that they can be used to probe these very short time scale interactions, for example, the spin precession in GHz range. The laser can be easily focused using an objective lens, thus providing a micron-scale spatial resolution. In this dissertation, I will start by discussing the dynamics of electron, lattice and spin after a sample absorbs focused femtosecond laser pulses and the information can be used for measurement of elastic constants and saturation magnetization. The micron-scale spatial resolution and picosecond temporal resolution of our ultrafast laser pump-probe system allows us to measure elastic, magnetic and thermal properties of materials locally. By performing such measurements on diffusion couple/multiple samples with composition gradients, we can more effectively establish composition dependent property databases than conventional ways of making single uniform alloys and measuring them one at a time. Absorption of low power focused femtosecond laser pulses by sample surface leads to localized thermal expansion, which launches Surface Acoustic Waves (SAW) that can be used to measure elastic modulus. Such measurements must be supplemented by theoretical calculations since there are complications related to pseudo-SAWs and skimming longitudinal waves in addition to regular SAWs. It is a bit surprising that a mathematical solution to the surface response induced by a thermally expansion source on an arbitrary bulk surface (half space) of an isotropic crystal/solid is not available in the literature. By convolving the strain Green's function with the thermal stress field created by an ultrafast Gaussian laser illuminat (open full item for complete abstract)

Committee: Peter Hammel (Committee Chair); Zhao Ji-Cheng (Advisor); John Wilkins (Committee Member); Yuri Kovchegov (Committee Member) Subjects: Physics