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 …

Photometric Studies Of Cygnus X-1 From 322-473 Kev With The Solar Maximum Mission, Benjamin Vaughn Augustine Hersh

Doctoral Dissertations

We present results from three years of observations from Cygnus X-1 and the Crab Nebula using the Gamma Ray Spectrometer onboard the Solar Maximum Mission satellite. We show that using a neural network based background model, it is possible to predict the terrestrial component of the gamma-ray background to a $<$1% level. We also show that the flux from the Crab is steady over a three year period at level of 0.024 $\pm$ 0.002 $\gamma$ cm$\rm\sp{-2}\ s\sp{-1}\ MeV\sp{-1}$. Similarly, the flux from Cygnus X-1 was consistent with the flux measured in 1979 with HEAO-3 and in 1991 with BATSE. We measured a flux of 0.013 $\pm$ 0.003 $\gamma\rm\ cm\sp{-2}\ s\sp{-1}\ MeV\sp{-1}$. We discuss the electron lifetimes within the Crab Nebula and limits on temperature variations from the Cygnus X-1 accretion disk.

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 …

Time Evolution Of The Chiral Phase Transition During A Spherical Expansion, Melissa Anne Lampert

Doctoral Dissertations

We examine the nonequilibrium time evolution of the hadronic plasma produced in a relativistic heavy ion collision, assuming a spherical expansion into the vacuum. We study the O(4) linear $\sigma$ model to leading order in a large-N expansion. Starting in the high temperature unbroken chiral symmetry phase, the system expands and cools, finally settling into the broken symmetry vacuum state. We consider the proper time evolution of the effective pion mass, the order parameter $\langle\sigma\rangle,$ and the particle number distribution. We examine several different initial conditions and look for instabilities (exponentially growing long wavelength modes) which can lead to the …

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 …