Transiting exoplanets provide the best opportunity for planetary characterization, and thus the search for life outside the Solar System. These planets orbit such that they pass in front ("transit'') and behind ("eclipse'') their host star, and a spectrum of the lost flux constrains the atmospheric properties of the planet. In transits, the flux modulation scales with the cross-sectional area of the planet, and the spectrum includes signatures of molecules in the upper atmosphere of the planet's terminator, which the host star's light passes through on the way to the observer. With eclipses, the lost flux is the direct emission of the planet, a spectrum of which contains emission and absorption features of molecules in the atmosphere depending on atmospheric thermal structure. These signals scale with the size and brightness of the planet and are so dwarfed by the brightness of the host star that only > 1000 K Jupiter-sized planets are observable with current instrumentation. In this work, I develop new techniques and compare existing data analysis methods to extract weak planetary signals. Chapter 2 describes a new elliptical photometry data analysis approach to disentangle exoplanet observations from telescope vibrations. Chapter 3 describes an analysis of Spitzer Space Telescope observations of eclipses of the planet WASP-29b using elliptical photometry and two different light curve modeling methods, and addresses the differences between results. In Chapter 4, I analyze two similar observations of WASP-34b using a grazing eclipse light-curve model. Finally, in Chapter 5 I reanalyze all Spitzer eclipse observations of the Neptune-sized GJ 436b, applying the lessons learned from my earlier works, and comparing my results with the literature.

This thesis investigates techniques for prototyping and evaluation of medium voltage (MV) power module packages. Specific focus will be given to the utilization of silver sintering as a bonding method for high temperature, high density power modules. Nano-silver paste and preform will be examined in detail as enabling technologies for a new generation of power electronics. To accomplish this task, analysis and characterization of the metal-ceramic substrate and its structure is performed. First, finite element models are created to evaluate the fatigue behavior of the large area bonds in the substrate structure. Prototypes of these multi-layer substrates have also been fabricated and will be subjected to thermal cycling tests for experimental verification of the efficacy of their sintered silver bonds. Stacked direct-bonded aluminum (DBA) substrates have been found to withstand up to 1000 thermal cycles of –40 °C to 200 °C when attached with low pressure-assisted silver sintering. The thermal performance of 10 kV SiC power module utilizing multi-layer DBA substrates bonded with a large-area, low pressure-assisted sintered silver bond will also be examined to ensure the sintered bond is viable for the harsh operating conditions of MV modules. A junction-to-case thermal resistance of 0.142 °C/W is measured on a module prototype utilizing stacked DBA substrates. Finally, analysis of a double-sided cooling scheme enabled by large area sintering is simulated and prototyped to demonstrate a 6.5 kV package for a MV power device. Residual stress failures induced by a highly rigid structure have been examined and mitigated through implementation of a 5 MPa pressure-assisted, double-sided silver sintering approach. / Master of Science / Power modules are the building blocks of the electrical grid of the future. As society transitions to renewable energy to fight the crisis presented by climate change, the structure of the energy grid will have to change to accommodate the increase in solar, wind, geothermal, and other renewable sources of energy generation. A clean energy grid structure will contain ubiquitous opportunities to use power modules for medium-voltage (MV) applications, like managing the flow of electricity from solar panels and wind turbines to neighborhoods and office buildings. However, these MV power modules will need to be resilient to extreme temperature and electrical stresses inherent to these applications. Current technology must be improved in both performance and reliability to match the needs of this future grid. This thesis investigates, through both experiment and computer simulation, techniques for improving the reliability of MV power modules without sacrificing thermal or electrical performance. Techniques presented in this work have the potential to transform power modules, so they may operate at higher temperatures and efficiencies for a longer lifetime than the current state-of-the-art.

Star formation is an inherently multi-scale process, connecting scales from the kiloparsecs of the galactic disk to the single AU scale of a protostar. In the middle of these scales are star clusters and molecular clouds, the structures in which most stars form. The clouds and clusters are connected via the interstellar medium, the gas and dust making up the matter between stars. In the cold phases of this medium rests the first steps of star formation, the formation of molecular gas and networks of filaments. This cold, neutral medium (CNM) hosts a handful of physical mechanisms, all contributing to the structures that feeds star formation. In this thesis work, we present a suite of simulations using the magneto-hydrodynamical code Ramses to investigate the role of turbulence, magnetic fields and cooling on the formation of filaments and clusters in the CNM. Through 9 different models we find that velocity dispersions in the CNM play a significant role in the formation of structure, requiring a balance between turbulence, self gravity and cooling to form filaments. We find magnetic fields, initialized at strengths of 7 muG, affect the formation of filaments, creating higher percentages of star-forming dense gas and lower percentages of molecular gas. Both magnetic fields and velocity dispersion in the gas affect the formation rate of clusters early in the simulation. Our 8 km/s simulations present a good initial condition for star formation that can include multiple scales of the process and recreate accurate clouds and filamentary structure. / Thesis / Master of Science (MSc)

The Almahata Sitta meteorites produced from the breakup of 2008 TC3 were highly unusual, as the stones contained various meteorite types, with stones spanning almost every meteorite petrologic type. This was considered a remarkable event at the time since meteorites of different types had never been found among the same fall before. However, new discoveries of exogenous material on (4) Vesta, (101955) Bennu, and (162173) Ryugu in subsequent years imply that this event may be more common than initially thought. This is unexpected due to the high average collisional velocity in the asteroid belt of ~5 km/s. High velocity impacts are more likely to have low impact retention efficiencies, which lowers the likelihood of xenoliths surviving the collision. Our understanding of this material and the mechanisms by which it is delivered can give insights into the dynamic histories of these asteroids and even the greater dynamic history of the asteroid belt.

The effect of culture media and mycotoxin on porcine preimplantation embryonic development has been investigated. In the first experiment, porcine embryonic cleavage rates were similar in NCSU-23 and PZM-3 culture media, while more blastocysts were produced in PZM-3 (P<0.05). BAX and BCL2L1 transcription levels were similar in blastocysts cultured in both media. Cleavage rates were significantly decreased in the presence of cycloheximide (P<0.05), and both á-amanitin and cycloheximide completely inhibited blastocyst formation. In the mycotoxin experiment, porcine embryonic cleavage rates decreased in 10 ìM á-ZEA group, while blastocyst rates decreased in 30 ìM á-ZEA group (P<0.05). Total cell numbers of blastocysts were significantly lower in the 10 µM á-ZEA group (P<0.05). The transcription levels of POU5F1 and BCL2L1 were similar, while that of BAX and the ratio of BAX/BCL2L1 significantly increased in 3 ìM and 10 ìM á-ZEA groups compared to control group.

Thesis (Ph.D.)--Boston University / This dissertation studies the interstellar medium (ISM) in dwarf galaxies. Dwarf galaxies are important because: 1) they constitute the largest fraction of extragalactic systems, and 2) they provide templates for primordial galaxies. Indeed, local active dwarf galaxies resemble primitive systems, since they are poor in dust and heavy elements and they are profusely forming massive stars. Because dwarf galaxies are nearby, however, they can be observed in much greater detail than distant primordial systems. Therefore studies of the ISM in nearby dwarf galaxies can be used to understand the processes at work in primitive galaxies. This work focuses on the effects of low heavy element abundances (i.e., low metallicities) on the star-forming ISM. Low metallicities are known to drastically affect the ISM. With decreasing metallicity, an increasingly large fraction of the molecular ISM is photodissociated into atoms and ions. We modeled and observed the emission of a sample of low metallicity dwarf galaxies in the millimeter, submillimeter, and far-infrared wavebands. The submillimeter waveband allows us to observe the mid-J rotational transitions of carbon monoxide (CO), the usual tracer of the molecular ISM, and the fine structure transit ions of neutral carbon ([C I]), a tracer of translucent and photodissociated material. We studied regions in the Large and Small Magellanic Clouds and the Northern Hemisphere dwarf galaxy IC 10. We find that the preponderant mechanism producing neutral carbon inside molecular clouds is photodissociation. We observe a moderate increase in the ratio of [C I] to CO emission for decreasing metallicity. Our models of clumpy, unresolved photo dissociation regions explain these observations as the natural result of an augmented fraction of photo dissociated material. Finally, our observations of the submillimeter thermal dust continuum in IC 10 find an abnormally low emissivity exponent for its graybody emission. We conclude that the unusual dust continuum is caused by the selective destruction of small grains, brought about by the combined effects of low metallicities and high radiation fields.

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