Digital Commons Network^™

Rocket Observations Of The Hf Heated Ionosphere, William James Peria

Doctoral Dissertations

Measurements of the ion distribution function, electron density, wave activity, and convection electric field have been made in situ by a sounding rocket flown through the artificially heated F layer ionosphere over Arecibo, Puerto Rico. The ion distributions show the effect of the HF heater through elevated effective temperatures, superthermal fluctuation level, and a plume-like population of energetic ions drifting out of the HF reflection region. The electron density, from a Langmuir probe, shows meter-scale depletions of $\sim$10% in the immediate vicinity of the reflection height, both above and below (Kelley et al., 1995). A shear in the convection electric …

Magneto-Optical Properties Of Cubic Ferromagnetic Metals., Neeraj Arvind Mainkar

LSU Historical Dissertations and Theses

I present a first principles, all electron, linear combination of Gaussian orbitals calculation of a comprehensive collection of magneto-optical properties of the cubic ferromagnetic metals nickel, iron and cobalt based on density functional theory. Among the many magneto-optical effects, this is the first ab initio study of the equatorial Kerr effect for absorption in the optical as well as the X-ray region, where it is called the X-ray magnetic linear dichroism. I find that in the optical region, this effect is of the order of 2% while in the X-ray region, it is of the order of 1% for the …

Amorphization And Fracture In Silicon Selenium(2) Nanowires: Molecular-Dynamics Simulations On Parallel Computer Architectures., Wei Li

LSU Historical Dissertations and Theses

The primary goal of this dissertation is to investigate the structural and mechanical properties and dynamical fracture in SiSe$\sb2$ nanowires using the molecular-dynamics (MD) simulation technique. The present work is the first study of SiSe$\sb2$ nanowires. Large-scale simulations reported in this thesis are carried out with parallel multiresolution schemes for the long-range Coulomb and the three-body covalent potentials. The multiresolution scheme reduces the computational complexity from O(N$\sp2$) to O(N). Using an effective interatomic potential containing both 2- and 3-body interactions, MD simulations are performed for SiSe$\sb2$ nanowires composed of finite (1-64) number of chains. Under small uniaxial strain, the nanowires …

Cross-Tail Current Carriers In A Two-Dimensional Equilibrium Magnetotail Model, Douglas Johnston Larson

Doctoral Dissertations

The purpose of this study is to gain physical insight into how charged particles, that violate the guiding center approximations, contribute to cross-tail current in a self-consistent plasma sheet. A technique to generate self-consistent two-dimensional (2D) current sheets is described. Groups of monoenergetic protons are followed in a model magnetic field. The sample current sheets are characterized by resonant quasiadiabatic and stochastic orbits. Several ion and electron groups are combined to produce a plasma sheet in which the charged particles carry the currents needed to generate the magnetic field in which the orbits are traced. An electric field also is …

Aspects Of Particle Acceleration In Solar Flares, Yuri Eduardovich Litvinenko

Doctoral Dissertations

This is a theoretical study of the acceleration of charged particles during solar flares. An attempt is made to trace the relationship between the processes of acceleration and primary flare energy release.

Motion of charged particles in a reconnecting current sheet (RCS) is considered, including both the electric field and the magnetic field with nonzero transverse (perpendicular to the RCS plane) and longitudinal (parallel to the electric current) components. An analytical technique is developed to calculate particle trajectories and energy gain. The solution predicts a critical value of the longitudinal field beyond which it counteracts the effect of the transverse …

Global Terrestrial Biogeochemistry: Perturbations, Interactions, And Time Scales, Bobby H. Braswell

Doctoral Dissertations

Global biogeochemical processes are being perturbed by human activity, principally that which is associated with industrial activity and expansion of urban and agricultural complexes. Perturbations have manifested themselves at least since the beginning of the 19th Century, and include emissions of CO$\sb2$ and other pollutants from fossil fuel combustion, agricultural emissions of reactive nitrogen, and direct disruption of ecosystem function through land conversion. These perturbations yield local impacts, but there are also global consequences that are the sum of local-scale influences.

Several approaches to understanding the global-scale implications of chemical perturbations to the Earth system are discussed. The lifetime of …

Pseudospin Symmetry In Heavy Deformed Nuclei., Andrey L. Blokhin

LSU Historical Dissertations and Theses

The origin and validity of pseudospin symmetry, which is characteristic for heavy atomic nuclei ($A \ge 100$), are discussed. The transformation to the pseudospin representation for physically significant operators is performed by means of specially designed analytical techniques. The many-particle helicity operator is found to accomplish the transformation to the pseudospin basis in the scope of realistic nuclear models. Estimates based on both nonrelativistic mean-field and relativistic Dirac-Brueckner results show that in the helicity-transformed space nucleons move in a finite-depth, strongly nonlocal, potential with an effectively reduced spin-orbit strength. Since the chirality operation is the limiting case of the helicity …

The Study Of High Energy Heavy Nucleus Interactions In Nuclear Emulsion Chambers Using Digital Image Processing., Philip Vern Deines-Jones

LSU Historical Dissertations and Theses

Nuclear emulsion chambers with lead targets have been exposed to a 158 GeV per nucleon beam of $\sp{208}$pb nuclei, by far the heaviest ion accelerated to such a high energy to date. These interactions frequently produce more than 1000 charged particles. In order to measure multiplicities and secondary particle trajectories in these extremely large events, an automatic CCD-based microscope system has been developed to analyze images, count secondary tracks, measure their trajectories, and estimate their charge. Based on the analysis of 40 high-multiplicity Pb-Pb events measured using this system, we assess the degree to which these interactions can be described …

Gravitational Radiation From And Instabilities In Compact Stars And Compact Binary Systems., Kimberly C. B New

LSU Historical Dissertations and Theses

We have examined three types of compact astrophysical systems that are possible sources of detectable gravitational wave radiation (GWR): nonaxisymmetric pulsars; rapidly rotating compact stars undergoing the bar-mode instability; and coalescing compact binaries. Our analysis of nonaxisymmetric pulsars, based on the assumption that any equatorial asymmetries present in these objects were rotationally induced, indicates that nearby millisecond pulsars are generally better candidates for the detection of GWR than the Crab pulsar, which has been the object of an ongoing search for GWR (Tsubono 1991). Our finite difference hydrodynamics (FDH) simulation of an object encountering the rotationally induced bar-mode instability results …

Large And Medium-Scale Dynamics In The Mesosphere And Lower Thermosphere Measured By Mf And Meteor Vhf Radars, Thayananthan Thayaparan

Digitized Theses

This thesis focuses on the experimental investigation of large- and medium-scale dynamics in the 70-100 km height range measured with MF (2.219 MHz) and meteor VHF (40.68 MHz) radar systems located at London (43{dollar}\sp\circ{dollar} N, 81{dollar}\sp\circ{dollar} W) Ontario, Canada. The MF radar uses the spaced antenna method by means of partial reflections to determine the horizontal winds. The VHF radar determines the horizontal wind velocity by means of radio reflections from meteor trails.;The major studies in this thesis include the following: (1) development of a numerical model to simulate the spaced antenna method, (2) validation of both radars, (3) studies …

Convective Properties Of Farley-Buneman Waves At High Latitude E-Region, Donglei Chen

Digitized Theses

The convective properties of the propagation of electrostatic Farley-Buneman waves in the high-latitude E-region have been studied using fluid theory based on their non-local character. This case is particularly useful for HF radar echoes. A principal objective of this thesis is to develop a new approach to solving the non-local problem of the Farley-Buneman waves in the high latitude E-region, and to explore the convective properties of wave propagation.;We first discussed the traditional treatment of the non-local problem and related approaches to solving such a non-local problem. Based on these, a new formulation of the non-local problem for the Farley-Buneman …