This thesis is a computational study of circumstellar gas disks, with a special focus on modeling techniques and on numerical methods not only as scientific tools but also as a target of study. In particular, in-depth discussions are included on the main numerical strategy used, namely the moving-mesh method for astrophysical hydrodynamics. In this work, the moving-mesh approach is used to simulate circumstellar disks for the first time. / Astronomy

What processes are responsible for the dispersal of protoplanetary disks? In this dissertation, beginning with a brief Introduction to planet detection, disk dispersal and high-contrast imaging in Chapter 1, I will describe how ground-based adaptive optics (AO) imaging can help to inform these processes. Chapter 2 presents Polarized Differential Imaging (PDI) of the transitional disk SR21 at H-band taken as part of the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS). These observations were the first to show that transition disk cavities can appear markedly different at different wavelengths. The observation that the sub-mm cavity is absent in NIR scattered light is consistent with grain filtration at a planet-induced gap edge. Chapter 3 presents SEEDS data of the transition disk Oph IRS 48. This highly asymmetrical disk is also most consistent with a planet-induced clearing mechanism. In particular, the images reveal both the disk cavity and a spiral arm/divot that had not been imaged previously. This study demonstrates the power of multiwavelength PDI imaging to verify disk structure and to probe azimuthal variation in grain properties. Chapter 4 presents Magellan visible light adaptive optics imaging of the silhouette disk Orion 218-354. In addition to its technical merits, these observations reveal the surprising fact that this very young disk is optically thin at H-alpha. The simplest explanation for this observation is that significant grain growth has occurred in this disk, which may be responsible for the pre-transitional nature of its SED. Chapter 5 presents brief descriptions of several other works-in-progress that build on my previous work. These include the MagAO Giant Accreting Protoplanet Survey (GAPlanetS), which will probe the inner regions of transition disks at unprecedented resolution in search of young planets in the process of formation. Chapters 6-8 represent my educational research in quantitative literacy, beginning with an introduction to the literature and study motivation in Chapter 6. Chapter 7 describes the development and validation of the Quantitative Reasoning for College Science (QuaRCS) Assessment instrument. Chapter 8 briefly describes the next steps for Phase II of the QuaRCS study.

I investigate the emission properties of the molecular interstellar medium in protoplanetary disks and galaxy mergers, though focus largely on the latter topic. I utilize both numerical models as well as observations to relate the emission characteristics to physical models for the formation and evolution of gas giant planets and galaxies. The main results of this thesis follow. (1) Gas giant protoplanets may be detectable via self-absorption signatures in molecular emission lines with sufficiently high critical density. Given the spatial resolution of e.g. ALMA, gas giant planets in formation may be directly imageable. (2) Starburst and AGN feedback-driven winds in galaxies can leave imprints on the molecular line emission properties via morphological outflows and high velocity peaks in the emission line spectra. Methods for distinguishing between high velocity peaks driven by dynamics versus those driven by winds are discussed. (3) CO line widths on average trace the virial velocity of z ∼ 6 quasar host halos. Thus, if the earliest quasars formed in ∼1013 M ⊙ halos, they are predicted to have broad molecular line widths. Selection effects may exist which tend quasars selected for optical luminosity toward molecular line widths narrower than the slightline-dependent mean. (4) Using the SMT, I observe a roughly linear relation between infrared luminosity and CO (J=3-2) luminosity in local galaxies confirming the results of recently observed L(IR)-HCN (J=1-0) relations. Subsequent modeling shows that observed SFR-molecular line luminosity relations owe to the average fraction of subthermally excited gas in galaxies, and are simply reflective of the assumed Schmidt law governing the SFR.

The number of extrasolar planet discoveries has increased dramatically over the last 15 years. Nearly 700 exoplanets have currently been observed through a variety of observation techniques. Most of the currently documented exoplanets differ greatly from the planets in our own Solar System, with various combinations of eccentric orbits, short orbital periods, and masses many times that of Jupiter. More recently, planets belonging to a new class of `distant gas giants' have also been discovered with orbits of 30 to 100 times that of Jupiter. The wide variety of different planet formation outcomes stem from a complex interplay between gravitational interactions, hydrodynamic interactions and competitive accretion among the planets that is not yet fully understood. Simulations performed using a series of modifications to an existing, widely used hydrodynamic code (FARGO) are presented. The main goal is to develop a more rigorous and robust gas accretion scheme that is valid and consistent for the ranges of exolanetary gas giant masses, eccentricities and semimajor axes that have been observed to better understand the mechanisms involved in their formation. The resulting scheme is a more robust and accurate prescription for gas accretion onto planetary cores in a manner that is mostly resolution independent and valid over a large range of masses (less than an Earth mass to multiple Jupiter masses). The modified scheme accounts for multiple, competing, dynamic accretion mechanisms (including atmospheric effects) and their associated time scales between an arbitrary number of protoplanets. This updated accretion scheme provides a means for exploring the entire formation process of gas giants out of a variety of initial conditions in a self-consistent manner. The modifications made to the code as well as simulation results will be discussed and explored.

The search for extraterrestrial life begins with understanding how life developed and evolved on our own planet. Earth's polar regions provide a unique setting conducive to developing the methodologies and techniques that will be needed to find new life forms either as living organisms or as some biological signal in a sedimentary record. / The highest latitude perennial spring system in a region of thick, continuous permafrost resides in the Arctic archipelago of northern Canada. At Expedition Fiord on Axel Heiberg Island there are two sets of springs that provide useful analogs to liquid water habitats that may have existed on Mars. The springs occur in a region with a mean annual air temperature of -15.5° C. Spring flow rates and discharge temperatures are constant throughout the year. Filamentous bacteria, biofilms and mineral precipitates occur in association with the emergent, anoxic brine flowing from the springs. / Preliminary data on the microbial composition of the spring water has been obtained by applying the culture-independent approach. The majority (76%) of the fifty-five environtaxa showed high sequence similarity to Thiomicrospira species (sulfur-oxidizing organism). Other sequences show high similarity to sulfate-reducing members of the delta (Desulfocapsa sp.) and epsilon (Sulfurospirillum sp.) proteobacterium groups. A single sequence was found to have 99% sequence similarity to species of the genus Haloanaerobium a group of low G+C Gram positive, anaerobic, halophiles (Rainey et al. 1995). / A combined flow and thermal model of the Axel Heiberg springs has demonstrated how such springs are able to persist throughout the year despite temperatures that fall to below -50°C during the winter darkness. Dissolved gases emanating from the springs provide evidence of the origin of the water for the springs as well as placing constraints upon the residence time. The gas is composed primarily of N2 with relative concentrations of Ar, Kr, and Xe almost identical to air. No O2 is detectable and Ne is 60% of air values. We believe that ~50% of this gas originates from the direct release of air by nearby alpine glaciers and local ice sheets into groundwater that infiltrates sub-ice sedimentary deposits.

Stuttgart, Univ., Diss., 2007.

Thesis (Ph.D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Dr. Paul G. Steffes; Committee Member: Dr. Gregory D. Durgin; Committee Member: Dr. Robert D. Braun; Committee Member: Dr. Thomas K. Gaylord; Committee Member: Dr. Waymond R. Scott

Thesis (M.S. in Astronautical Engineering)--Naval Postgraduate School, Dec. 2004. / Thesis Advisor(s): Sherif Michael. Includes bibliographical references. Also available online.

Konstanz, FH, Diplomarb., 2005.

Thesis--Zürich. / Vita. Includes bibliographical references.