Search

In this work, the role of convective flux in the solar nonradial oscillation is investigated. Although the adiabatic treatment is a good first order approximation of some physical process in the solar nonradial oscillations, a nonadiabatic analysis is needed to explain or compute other important aspects, especially the excitation and damping mechanisms. Since the nonadiabatic effects may rise to a significant level in the region that ranges from the outer part of the convection zone to the photosphere, an accurate description of the convective flux is required. Due to a lack of accurate and reliable theory of time dependent convection, previous works on nonadiabatic analysis simply neglected the perturbation of convective flux, or adopted the mixing length theory (MLT). We find the theory of time dependent turbulent convection developed by Xiong has many of the desired properties. We tried and tested many alternative ways of mathematical formulation and numerical computation to find a practical and reliable way to incorporate Xiong's work with our nonadiabatic analysis. While the treatment in this work may not be completely satisfactory, some interesting results are obtained. The curves of intensity amplitude vs. frequency display unique patterns from which we may suggest that the long period modes can be detected. The positions of minima in plots of temperature amplitude vs. frequency for ℓ = 2, 3, 4 are consistent with the results of SCLERA observations. This agreement speaks to the credibility of both the low order g-mode observations obtained at SCLERA and the way we treat the nonadiabatic oscillations coupled with the convective flux. The curves of heat input vs. radius suggest that the hydrogen ionization zone does play an important role for the coupling of convective flux and the low order g-mode oscillations.

Dijet angular distributions provide a excellent look at the interactions between partons. The measurements performed by the DO detector are the most precise accomplished to date at pp colliders and cover a larger angular range than previously possible. Both leading order and next-to-leading order QCD calculations show agreement with the data over a large range in dijet invariant mass. This comparison is limited mainly by the large size of the theoretical uncertainties which are larger than the experimental uncertainties for some mass ranges. Additionally, a limit on quark compositeness of Λ(C) > 1.1 TeV has been obtained.

Structural, magnetic, and magneto-optical properties of Co/Pd and Co/Pd/Cu superlattices, ultra-thin Co films and MnSb alloys have been studied. The superlattices and Co films were grown by molecular beam epitaxy (MBE) while the MnSb alloy films were made by sputtering techniques. Several x-ray diffraction techniques were used to analyze the physical structure of the superlattices and alloys. Magnetometry techniques were used to determine some of the room temperature and temperature dependent magnetic properties of the films. In situ and ex situ measurements of the magneto-optical properties of the ultra-thin Co films and alloys also were made.

The exact scalar wave solution for light scattering from a general dielectric disk array is found. The exact solution as well as a numerical solution is also given for an array of three dielectric disks, whose centers are placed on the vertices of an equilateral triangle. The various (differential, total and averaged total) cross sections and the poles of the scattering matrix are given. These results are analyzed in part by considering the effects which arise from the geometry of the system, and in part by comparison with the results (cross sections and poles) for a system with an identical arrangement of three hard (perfectly conducting) disks and with a system of one dielectric disk. This analysis helps rule out structure that arise from the chaos, which is very likely to exist, in the classical (geometric) limit of the three (or more) dielectric disk system. In the future after I study the geometric (classical) and physics (semiclassical) regimes of this system, I plan to reanalyse the exact wave solution in an attempt to discover the traces of the chaos present in the system. Time dependent Hartree-Fock theory (TDHF), with improved formulation and improved computer capabilities, is used to repeat the calculations of charge capture for the He²⁺ on He collision. The results of these calculations allow us to discuss the effects of various numerical truncations and to establish with certainty the viability and the accuracy of TDHF in its application to ion-atom collisions. Initially, we had hoped to find chaos in the TDHF problem, as it is nonlinear. However, due to the complexity and computational difficulties present in the TDHF problem, a simpler scattering system of light scattering from dielectric disk arrays was chosen for study.

In nonlinear optical waveguide structures, injection of an optical beam above a given threshold intensity can be theoretically shown to emit spatial solitons. An all-optical switch based on this phenomenon is designed and computer simulations show that the phenomenon persists despite detrimental effects such as saturation of the nonlinearity and nonlinear absorption. In the cylindrical geometry of an optical fiber, a soliton ring can be emitted from the core and fragment into filaments via a transverse modulational instability. The inclusion of temporal dispersion can destabilize spatially stable solutions, both for normal and anomalous group velocity dispersion. For a saturating nonlinearity, the temporal dispersion can be used to generate trains of nonlinearly self-bound light packets from a continuous sub-emission-treshold input field.

Optical properties of carbon are studied in bulk state from λ ∿ 0.05 to 100 μm for graphite, and from λ ∿ 0.05 to 1000 μm for glassy carbon; in small particle state, the optical studies cover the spectral range going from λ ∿ 0.1 to 100 μm for all the materials. A Kramers-Kronig analysis of near normal reflectance data and/or a reflectance data fit to a Drude-Lorentz model gave bulk optical constants. These optical constants are used in theoretical calculations of extinction and the results compared with experimental results obtained from measurements of a variety of carbon particles. It is inferred that the high experimentally observed extinction is mainly due to a shape effect.