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<p> The process of star formation is an integral part of the new field of astrobiology, which studies the origins of life. Since the gas that collapses to form stars and their resulting protoplanetary disks is known to be weakly ionized and contain magnetic fields, star formation is governed by multifluid magnetohydrodynamics. In this thesis we consider two important problems involved in the process of star formation that may have strongly affected the origins of life, with the goal of determining the thermal effects of these flows and modeling the physical conditions of these environments.</p><p> We first considered the outstanding problem of how primitive bodies, specifically asteroids, were heated in protoplanetary disks early in their lifetime. Reexamining asteroid heating due to the classic unipolar induction heating mechanism described by Sonett et al. (1970), we find that this mechanism contains a subtle conceptual error. As original conceived, heating due to this mechanism is driven by a uniform, supersonic, fully-ionized, magnetized, T Tauri solar wind, which sweeps past an asteroid and causes the asteroid to experience a motional electric field in its rest frame. We point out that this mechanism ignores the interaction between the body surface and the flow, and thus only correctly describes the electric field far away from the asteroid where the plasma streams freely. In a realistic protoplanetary disk environment, we show that the interaction due to friction between the asteroid surface and the flow causes a shear layer to form close to the body, wherein the motional electric field predicted by Sonett et al. decreases and tends to zero at the asteroid surface. We correct this error by using the equations of multifluid magnetohydrodynamics to explicitly treat the shear layer. We calculate the velocity field in the plasma, and the magnetic and electric fields everywhere for two flows over an idealized infinite asteroid with varying magnetic field orientations. We show that the total electric field in the asteroid may either be of comparable strength to the electric field predicted by Sonett et al. or vanish depending on the magnetic field geometry. We include the effects of dust grains in the gas and calculate the heating rates in the plasma flow due to ion-neutral scattering and viscous dissipation. We term this newly discovered heating mechanism &ldquo;electrodynamic heating&rdquo;, use measurements of asteroid electrical conductivities to estimate the upper limits of the possible heating rates and amount of thermal energy that can be deposited in the solid body, and compare these to the heating produced by the decay of radioactive nuclei like Al²⁶.</p><p> For the second problem we modeled molecular line emission from time-dependent multifluid MHD shock waves in star-forming regions. By incorporating realistic radiative cooling by CO and H₂ into the numerical method developed by Ciolek &amp; Roberge (2013), we present the only current models of truly time-dependent multifluid MHD shock waves in weakly-ionized plasmas. Using the physical conditions determined by our models, we present predictions of molecular emission in the form of excitation diagrams, which can be compared to observations of protostellar outflows in order to trace the physical conditions of these environments. Current work focuses on creating models for varying initial conditions and shock ages, which are and will be the subject of several in progress studies of observed molecular outflows and will provide further insight into the physics and chemistry of these flows.</p>

The current gain of bipolar junction transistors is reduced due to ionizing radiation exposure or hot-carrier stressing. Radiation-induced degradation is particularly severe at the low dose rates encountered in space. In this work, the dose rate effect in lateral and substrate pnp bipolar transistors is rigorously quantified over the range of 0.001 to 294 rad(Si)/s. Gain degradation shows little dependence on dose rate below 0.005 rad(Si)/s, suggesting that degradation enhancement comparable to that expected from space-like dose rates was achieved. In addition, the effect of ambient temperature on radiation-induced gain degradation at 294 rad(Si)/s is thoroughly investigated over the range of 25 to 240°C. Degradation is enhanced with increasing temperature while simultaneously being moderated by in situ annealing such that, for a given total dose, an optimum irradiation temperature for maximum degradation results. Optimum irradiation temperature decreases logarithmically with total dose and is larger and more sensitive to dose in the substrate device than in the lateral device. Maximum high dose rate degradation at elevated temperature closely approaches low dose rate degradation in both of the devices. A flexible hardness assurance methodology based on accelerated irradiations at elevated temperatures is described. The influence of mechanical stress on the radiation hardness of single-crystalline emitter transistors is investigated using x-ray diffraction. Correlation of device radiation sensitivity and mechanical stress in the base supports previously reported observations that Si-SiO₂ interfaces exhibit increased susceptibility to radiation damage under tensile Si stress. Relaxation of processing-induced stress in the base oxide due to ionizing radiation is smaller than the stress induced by emitter contact metallization followed by a post-metallization anneal. Possible mechanisms for radiation-induced stress relaxation and their effect on the radiation sensitivity of bipolar transistors are discussed. The combined effects of ionizing radiation and hot-carrier stress on the current gain of npn transistors are investigated. The hot-carrier response of the transistors is improved by radiation damage, whereas hot-carrier damage has little effect on subsequent radiation stress. Characterization of the temporal progression of hot-carrier effects reveals that hot-carrier stress acts initially to reduce excess base current and improve current gain in irradiated transistors. Numerical simulations show that the magnitude of the peak electric-field within the emitter-base depletion region is reduced significantly by net positive oxide charges induced by radiation. The interaction of the two stress types is explained in a physical model based on the probability of hot-carrier injection and the neutralization and compensation of radiation damage in the base oxide. The results of this work further the understanding of stress-induced gain degradation in bipolar transistors and provide important insight for the use of bipolar transistors in stress environments.

High energy astrophysics is a relatively new discipline that has witnessed tremendous advancement in the past 25 years or so with the advent of space technology, which provides the field with an indispensable observational tool in the X-ray and $\gamma$-ray range previously unreachable by ground-based observations. Ongoing discoveries in this field demand new theories to explain new phenomena. In this thesis, I summarize my work on one of these topics in high energy astrophysics, the theory of accretion disks around black holes. Accretion disk models are applied to the dynamics of compact objects surrounded by material with organized angular momentum. The disk forms due to the process by which differentially rotating fluid layers interact with each other and transport angular momentum outwards with the gas spiraling into the central object, a black hole in this case. This process, known as accretion, is a very effective way to tap the energy of the gravitational field. In fact, for a non-rotating black hole, the conversion rate from mass to energy is about six percent. This is about ten times as effective as the sun, while for an extreme rotating black hole, as much as forty percent of the rest mass of the accreted gas is converted into energy. Based on the X-ray spectra and time variability of black hole candidates, I have developed a so-called radial-zoned thermal accretion disk model by dividing the disk radially into three zones. The outer zone is optically thick and the inner and middle zones are optically thin, with the latter being irradiated by the outer part of the disk. This model can produce a composite spectrum of black body radiation from the outer zone, optically thin comptonized thermal bremsstrahlung radiation from the inner zone, and inverse comptonized soft photon radiation from the middle. In this work, I have studied both the linear and nonlinear dynamic evolution and stability of this accretion disk model by solving the whole set of partial differential equations numerically. Spectral fitting and time series analysis to high energy satellite data have been done based on the steady disk model to fix parameters and to cross-examine the results from other methods.