Doctor of Philosophy, The Ohio State University, 2008, Astronomy

I analyze microlensing in gravitationally lensed quasars to yield measurements of the structure of their continuum emission regions. I first describe our lensed quasar monitoring program and RETROCAM, the auxiliary port camera I built for the 2.4m Hiltner telescope to monitor lensed quasars. I describe the application of our Monte Carlo microlensing analysis technique to SDSS 0924+0219, a system with a highly anomalous optical flux ratio. For an inclination angle cos(i)=0.5, I find an optical scale radius log[r_s/cm] = 14.8±0.4. I extrapolate the best-fitting light curves into the future to find a roughly 45% probability that the anomalous image (D) will brighten by at least an order of magnitude during the next decade. I expand our method to make simultaneous estimates of the time delays and structure of HE1104-1805 and QJ0158-4325, two doubly-imaged quasars with microlensing and intrinsic variability on comparable time scales. For HE1104-1805, I find a time delay of Delta t_{AB} = 162±6 days and estimate a scale radius of log[r_s/cm] = 15.7±0.5 at 200 nm in the rest frame. I am unable to measure a time delay for QJ0158-4325, but the scale radius is log[r_s/cm] = 14.9±0.3 at 300 nm in the rest frame. I then apply our Monte Carlo microlensing analysis technique to the optical light curves of 11 lensed quasar systems to show that quasar accretion disk sizes at 250 nm are strongly correlated with black hole mass. The resulting scaling relation is consistent with the expectation from thin disk theory, but it implies that black holes radiate with relatively low efficiency. These sizes are also larger, by a factor of approximately 3, than the size needed to produce the observed 800 nm quasar flux by thermal radiation from a thin disk with the same temperature profile. Finally, I analyze the microlensing of the X-ray and optical emission of the lensed quasar PG 1115+080. I find that the size of the X-ray emission region is approximately 1.3 dex smaller than that of the o (open full item for complete abstract)

Committee: Christopher Kochanek PhD (Advisor); Andrew Gould PhD (Committee Member); Darren DePoy PhD (Committee Member) Subjects: Astronomy; Astrophysics

Doctor of Philosophy (PhD), Ohio University, 2007, Physics (Arts and Sciences)

A time-dependent two-dimensional Monte Carlo/Fokker-Planck (MC/FP) code, which uses a Monte Carlo technique for Compton scattering and radiative transport, and a Fokker-Planck technique for electron evolution, has been fully parallelized with the Message Passing Interface (MPI) to take advantage of computers with multiple processors and decrease running time. This code has been successfully applied to the following astrophysically relevant scenario: it was coupled with the line transfer program XSTAR to simulate multiple Compton reflections within photon bubbles, making predictions for their X-ray spectral features. Predictions include a spectral feature at ~9 keV and hard power-law tails similar to those observed in X-ray binaries in the very high state. This dissertation also includes the results of an observational project to determine the redshifts of six BL Lac objects, (i.e., galaxies dominated by radiation from the jets emerging from their central black holes) with the 2.4 m Hiltner telescope at the MDM observatory on Kitt Peak, Arizona. The redshifts of these objects have been constrained in agreement with previous estimates in most cases; however, in one case (W Comae) the constraints and previous estimates were not in agreement.

Committee: Boettcher Markus (Advisor) Subjects: Physics, Astronomy and Astrophysics

Master of Science, Miami University, 2024, Mechanical and Manufacturing Engineering

A new method is proposed to mitigate ice accretions on wind turbine blades via the creation of a microstructural gradient surface geometry that facilitates spontaneous water droplet motion along the surface. The wettability gradients are formed by laser etching 35𝜇m wide, 35𝜇m deep channels into aluminum to form a surface with a gradually increasing solid area fraction. Different design permutations are then proposed and systematically evaluated on the merits of their performance. An analytical model is also derived based on a balance of hysteresis and drag forces to predict the critical airspeed necessary for droplet movement as a function of the droplet size and surface contact angle. Experimentation has shown good agreement with the model for both the baseline and fixed-pitch channel surfaces and has also demonstrated that, in certain cases, up to 70% lower critical airspeeds are needed to initiate droplet motion on these microstructured surfaces. Finally, the effects of frozen droplets on aerodynamic performance were studied via 3D-printed airfoil prototypes. This work demonstrated that at airspeeds under <15m/s and angles of attack between 0 – 20 degrees, frozen droplets on the top surface of the airfoil can be used to strengthen the lift-to-drag ratio by up to 184

Committee: Andrew Sommers (Advisor); Medhi Zanjani (Committee Member); Edgar Caraballo (Committee Member) Subjects: Alternative Energy; Energy; Engineering; Fluid Dynamics; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2021, Astronomy

In the basic core-collapse supernova problem, cold gas free-falls onto a standing accretion shock. Through some mechanism, the material below the shock is heated, reviving the shock and leading to the supernova explosion. The exact details of this heating mechanism is unclear. Pejcha & Thompson (2012) found an "antesonic" critical condition that limits the regime of stable accretion to cT2/vesc2≤ 3/16, where cT is the isothermal sound speed and vesc is the escape velocity at the shock radius. Above this limit, the accretion flow cannot conserve momentum across the standing shock at any radius, and the shock moves outwards without limit, forcing the system to a wind solution. This antesonic condition gives a fundamental physical explanation for the critical core neutrino luminosity observed in simulations of core-collapse. The first part of this dissertation concerns my extentions of this result. First, I extend the antesonic condition to time-dependent, spherically symmetric, polytropic models. I derive analytically the form the antesonic condition takes for this equation of state and confirm that it matches the results of my simulations, showing that models with sound speeds above the critical antesonic ratio drive transonic winds and models with lower sound speeds exhibit steady accretion. I also consider the degree to which the spatial resolution of my simulations affects my ability to properly measure the critical antesonic ratio, and find that lower resolution simulation systematically underpredict both this ratio and the shock radius. Furthermore, I explore the physical connection between the mass accretion rate at explosion and the mass loss rate of the transonic wind: the two are directly proportional at criticality, implying that, at criticality, the wind kinetic power is tied directly to the accretion power. Finally, I find that the value of the post-shock adiabatic index Γ has a large effect on the length and time scales of the post-b (open full item for complete abstract)

Committee: Todd Thompson (Advisor); Chris Kochankek (Committee Member); Marc Pinsonneault (Committee Member) Subjects: Astronomy; Astrophysics

Master of Science, University of Toledo, 2020, Civil Engineering

This thesis examines the influence of ice accretion on the bridge stay cables on the vortex shedding frequency and the lift and drag coefficient of the cables. Vibration of the stay cables due to wind is observed in many cable-stayed bridges. This vibration of stay cable may lead to fatigue in the cables and damage to the cable attachments. Therefore, it is important to understand the vortex shedding and aerodynamic behavior of iced stay cables. The present work explores the two-dimensional approach to study the aerodynamic coefficients and vibration frequency of the cable with ice accretion where the iced cable is simplified as a two-dimensional cross-section with ice profile and roughness applied on the iced area of cable while the remaining part of the cable is smooth. In the current study, the k-ω SST turbulent model in ANSYS-Fluent is used to solve the transient 2D Navier-Stokes equation. PISO is selected as a solution algorithm for pressure-velocity coupling equation. The first part of this thesis deals with the study of vortex shedding and lift and drag coefficients of cable sections with seven different ice accretion profiles. Due to icing, the vortex shedding frequency of the cable decreases by up to 15%. The drag coefficient of the iced cable section increases by up to 61% from smooth cable. The lift coefficient of iced cable increases by up to 58%. When ice accretion is not symmetrical about y=0, the lift coefficient oscillates in the direction of the side of the cable where ice accretion present. In the second part of this thesis, the influence of the thickness of ice accretion is studied; it is found that both the value of the drag coefficient and the range of the lift coefficient decreases with an increase in ice accreted thickness with the drag coefficient decreases by up to 20% and lift coefficient decreases by up to 58%. However, the ice accretion thickness causes little change in the vibration frequency. The final part deals with the a (open full item for complete abstract)

Committee: Douglas Nims (Committee Chair); Ahmed Abdelaal (Committee Member); Alex Spivak (Committee Member) Subjects: Civil Engineering

Doctor of Philosophy, The Ohio State University, 2017, Astronomy

I present the initial results of characterizing moderate redshift (z > 2) quasars in the Dark Energy Survey (DES) by their variability. As the scales associated with supermassive black holes (SMBHs) are too small to be resolved directly, alternative methods are necessary to learn about their structure, how they grow, and how they impact their environments. One such method is through variability. Quasars are naturally variable objects, and by measuring the time delay to different emitting regions as they respond to changes in the extreme ionizing UV photons produced at the inner edge of the disk, we can estimate normally inaccessible size scales associated with SMBHs. This technique is known as reverberation mapping. I first apply this technique to probe accretion disk sizes. Only a handful of such measurements exist in the literature, sampled through reverberation mapping or gravitational microlensing. I measure time delays between the DES photometric bands to place constraints on accretion disk sizes, and then present a software extension to the JAVELIN code that provides a Bayesian framework for fitting a thin accretion disk model directly to the data rather than the individual lags themselves. This is tested on fake data as well as the highest quality dataset available for a local active galaxy, NGC 5548, before being applied to a sample of DES quasars. This new framework, under our thin disk assumption, gives competitive accretion disk sizes for quasars with our survey quality data alone, and adds over a dozen objects to the relatively small number of quasars with measured disk properties. Next, I present the serendipitous discovery of a z=0.65 low-ionization broad absorption line (LoBAL) quasar in a post-starburst galaxy in the DES data, spectroscopically confirmed with the Australian Dark Energy Survey (OzDES) project. LoBAL quasars are a minority of all BALs, and rarer still is that this object also exhibits broad FeII (an FeLoBAL) and Balme (open full item for complete abstract)

Committee: Paul Martini (Advisor); Christopher Kochanek (Committee Member); Bradley Peterson (Committee Member) Subjects: Astronomy; Astrophysics

Doctor of Philosophy, The Ohio State University, 2017, Earth Sciences

Plate spreading at mid-ocean ridges (MOR) is responsible for the creation of most of the crust on earth. The ridge system is very complex and many questions remain unresolved. Among these are the controls on the architecture of magma plumbing systems beneath mid-ocean ridges of different spreading rates and in proximity to transform faults. Previous studies have called into question the hypothesis that a decrease in magma flux and increase in conductive cooling along transforms faults promotes higher pressures of partial crystallization, and that this also explains the higher partial pressures of crystallization inferred for magmas erupted along slow spreading ridges compared to magmas erupted along faster spreading ridges. To test these hypothesis, I undertook a detailed analysis of pressures of partial crystallization (PPC) for magmas erupted along the slow spreading Reykjanes Ridge (RR), indeterminate spreading Juan de Fuca Ridge (JdF), 3 transforms along the fast to intermediate spreading East Pacific Rise (Blanco, Clipperton, and Siqueiros), and 5 transforms along the slow spreading Mid Atlantic Ridge (Oceanographer, Famous Transform A & B, Kane, and 15°20'N). PPC were calculated from the compositions of glasses (quenched liquids) lying along the P (and T) dependent olivine, plagioclase, and augite cotectic using the method described by Kelley and Barton (2008). Published analyses of MOR basalt glasses sampled from the ridges and transforms were used as input data. Samples with anomalous chemical compositions and samples that yielded pressures associated with unrealistically large uncertainties were filtered out of the database. The calculated pressures for the remaining 459 samples for the RR, 564 samples for the JdF, and 1056 samples for the transforms were used to calculate the depths of partial crystallization and to identify the likely location of magma chambers. The RR results indicate that the pressure of partial crystallization decreases from 102 ± 37 (open full item for complete abstract)

Committee: Michael Barton Dr. (Advisor); W. Berry Lyons Dr. (Committee Member); Thomas Darrah Dr. (Committee Member); Derek Sawyer Dr. (Committee Member); Daniel Kelley Dr. (Committee Member) Subjects: Geology; Petrology

Doctor of Philosophy, The Ohio State University, 2017, Astronomy

I present results from a monitoring campaign of 11 active galactic nuclei (AGN) conducted in Spring of 2014. I use the reverberation mapping method to probe the interior structures of the AGN, specifically the broad line regions (BLRs) and accretion disks. One of these AGN, NGC~5548, was also subject to multi-wavelength (X-ray, UV, optical, and near-IR) monitoring using 25 ground-based telescopes and four space-based facilities. For NGC~5548, I detect lags between the continuum emission at different wavelengths that follow a trend consistent with the prediction for continuum reprocessing by an accretion disk with temperature profile $T \propto R^{-3/4}$. However, the lags imply a disk radius that is 3 times larger than the prediction from standard thin-disk models. The lags at wavelengths longer than the {\it V} band are also equal to or greater than the lags of high-ionization-state emission lines (such as He\,{\sc ii}\,$\lambda 1640$ and $\lambda 4686$), suggesting that the continuum-emitting source is of a physical size comparable to the inner broad-line region. Using optical spectra from the Large Binocular Telescope, I estimate the bias of the interband continuum lags due to BLR emission observed in the filters, and I find that the bias for filters with high levels of BLR contamination ($\sim\! 20\%$) can be important for the shortest continuum lags. This likely has a significant impact on the {\it u} and {\it U} bands owing to Balmer continuum emission. I then develop a new procedure for the internal (night-to-night) calibration of time series spectra that can reach precisions of $\sim\! 1$ millimagnitude and improves traditional techniques by up to a factor of 5. At this level, other systematic issues (e.g., the nightly sensitivity functions and Fe{\sc ii} contamination) limit the final precision of the observed light curves. Using the new calibration method, I next present the data and first results from the op (open full item for complete abstract)

Committee: Brad Peterson (Advisor); Chris Kochanek (Committee Member); Richard Pogge (Committee Member); Timothy Plageman Jr (Committee Member) Subjects: Astronomy; Astrophysics

Doctor of Philosophy (PhD), Ohio University, 2016, Physics and Astronomy (Arts and Sciences)

This dissertation focuses on placing observational constraints on outflows and accretion disks in active galactic nuclei (AGN) for the purpose of better understanding the physics of super-massive black holes (SMBHs) and their evolution with the host galaxy over cosmic time. Quasar outflows and their importance in SMBH–host galaxy co-evolution can be further understood by analyzing broad absorption lines (BALs) in rest-frame UV spectra that trace a range of wind conditions. We quantify the properties of the flows by conducting BAL variability studies using multiple-epoch spectra acquired primarily from MDM Observatory and from the Sloan Digital Sky Survey. Iron low-ionization BALs (FeLoBALs) are a rare type of outflow that may represent a transient phase in galaxy evolution, and we analyze the variations in 12 FeLoBAL quasars with redshifts between 0.7 < z < 1.9 and rest frame timescales between 10 d to 7.6 yr. We investigate BAL variability in 71 quasar outflows that exhibit P V absorption, a tracer of high column density gas (i.e. NH > 1022 cm-2), in order to quantify the energies and momenta of the flows. We also characterize the variability patterns of 26 quasars with mini-BALs, an interesting class of absorbers that may represent a distinct phase in the evolution of outflows. Low-luminosity AGN (LLAGN) are important objects to study since their prominence in the local Universe suggest a possible evolution from the quasar era, and their low radiative outputs likely indicate a distinct mode of accretion onto the SMBH. We probe the accretion conditions in the LLAGN NGC 4203 by estimating the SMBH mass, which is obtained by modeling the 2-dimensional velocity field of the nebular gas using spectra from the Hubble Space Telescope. We detect significant BAL and mini-BAL variability in a subset of quasars from each of our samples, with measured rest-frame variability time-scales from days to years and over multiple years on average. Variable wavelength intervals a (open full item for complete abstract)

Committee: Joseph Shields (Advisor); Douglas Clowe (Committee Member); Douglas Green (Committee Member); Madappa Prakash (Committee Member) Subjects: Astronomy; Astrophysics

Doctor of Philosophy (Ph.D.), Bowling Green State University, 2015, Biological Sciences

Abstract: Lake Vostok (Antarctica) is the 4th deepest lake on Earth, the 6th largest by volume, and 16th largest by area, being similar in area to Ladoga Lake (Russia) and Lake Ontario (North America). However, it is a subglacial lake, constantly covered by more than 3,800 m of glacial ice, and has been covered for at least 15 million years. As the glacier slowly traverses the lake, water from the lake freezes (i.e., accretes) to the bottom of the glacier, such that on the far side of the lake a 230 m thick layer of accretion ice collects. This essentially samples various parts of the lake surface water as the glacier moves across the lake. As the glacier enters the lake, it passes over a shallow embayment. The embayment accretion ice is characterized by its silty inclusions and relatively high concentrations of several ions. It then passes over a peninsula (or island) and into the main basin. The main basin accretion ice is clear with almost no inclusions and low ion content. Metagenomic/metatranscriptomic analysis has been performed on two accretion ice samples; one from the shallow embayment and the other from part of the main lake basin. Ice from the shallow embayment contains a variety of Bacteria as well as a few Archaea and several types of Eukarya. Most are related to species that are psychrophilic, marine, aquatic, or live in lake/ocean sediments, or a combination of these. However, sequences identified as originating from many different thermophiles were found, suggesting the presence of hydrothermal activity in the lake. In contrast to the embayment ice, the ice from the main basin yielded only about 5-6% of the number of sequences. Here again, molecular signatures of psychrophiles, marine, aquatic, a few sediment-dwelling organisms, and a few thermophiles were found. Because of the extreme conditions, it has been hypothesized that Lake Vostok is sterile, or that very few types of organisms inhabit the lake. Our results indicate that it contains a diverse (open full item for complete abstract)

Committee: Scott O. Rogers Dr. (Advisor); Paul F. Morris Dr. (Committee Member); Vipaporn Phuntumart Dr. (Committee Member); Robert Michael McKay Dr. (Committee Member); Rober W. Midden Dr. (Other) Subjects: Bioinformatics; Biology; Ecology; Limnology; Molecular Biology

MARCH, University of Cincinnati, 2014, Design, Architecture, Art and Planning: Architecture

Second-tier American cities are the new target for urban transformation and in turn require critical responses in architecture and planning. Time has shown that traditional planning instruments have become tools incapable of directing projects for redevelopment - master plans often derail leaving their results incoherent or irrelevant and the quality struggles to be controlled. Contrary to the use of long-term master plans, accretionary responses to the specific qualities and conditions of urban sites have begun to emerge as a means of acting consciously to the demands of the city. Conditions define how and where a response formulates. As a reaction to the conditions surrounding the development of any city: How can tactical development critically enable sites and in turn impact the territorial scale? A thorough understanding of the site's context - the consequential significances of the environmental, social, political and economic - is key to responding to this question. Acting tactically to the strategies set forth by the municipality while keeping in tune with the complexities of the everyday promotes a contingent and accretionary approach to urban development. It is crucial to recognize conjunctions between public policy and contemporary society in order to achieve environments of flexibility; ones capable of evolving in non-linear directions and allowing for productive futures. This document acts as a summary to an in-depth study of the intersections of public policy and urban design, of the way in which the city has positioned itself and its subsequent spatial manifestations. It targets Jacksonville, Florida, which has recently been referred to as America's most average city. The city's historical identity as a `port city' frames the contemporary issues of global society and in turn is considered to be a major contributor to evolving the identity of downtown. Encouraged by recent revitalization efforts and intended as an extension (open full item for complete abstract)

Committee: Aarati Kanekar Ph.D. (Committee Chair); Michael McInturf M.Arch. (Committee Member) Subjects: Architecture

Master of Science, The Ohio State University, 2011, Geological Sciences

Plate spreading at the mid-ocean ridges is accompanied by intrusion of dikes and eruption of lava along the ridge axis. It has been suggested that the depth of magma chambers that feed the flows and dikes is related to the heat flux – the higher the heat flux the shallower the magma chamber. To examine this hypothesis, I determined the depths of magma chambers beneath the intermediate spreading Juan de Fuca Ridge (JdF) in the northeast Pacific and the slow spreading Reykjanes Ridge (RR) south of Iceland. Pressures of partial crystallization were determined by comparing the compositions of natural liquids (glasses) with those of experimental liquids in equilibrium with olivine, plagioclase, and clinopyroxene at different pressures and temperatures using the method described by Kelley and Barton (2008). Chemical analyses mid-ocean ridge basalts glasses sampled from along the RR and JdF were used as liquid compositions. Samples with anomalous chemical compositions and samples that yielded pressures associated with unrealistically large uncertainties were filtered out of the database. The calculated pressures for the remaining 519 for the RR and 479 samples for the JdF were used to calculate the depths of partial crystallization and to identify the likely location of magma chambers. The RR results indicate that the pressure of partial crystallization decreases from 102 ± 33 MPa at the Charlie Gibbs Fracture Zone to 21 ± 12 MPa at 56°N, then increases to 367 ± 68 MPa as Iceland is approached. Four magma lenses were identified at depths of 2.5±.8km, 5.2±.8km , 5.9±1km, and 6.7±1. The magma lens at 2.46±.83 km agrees very well with seismically imaged sill at 2.5 km (Peirce et al 2007). The JDF results indicate that the pressure of partial crystallization decreases from 200 to100±50 MPa from the Blanco fracture zone to the north along the Cleft segment of the ridge. Calculated pressures remain approximately constant at 87±.53MPa along ridge segments to the north of the Clef (open full item for complete abstract)

Committee: Michael Barton Ph.D. (Advisor); W. Berry Lyons Ph.D. (Committee Member); Wendy Panero Ph.D. (Committee Member) Subjects: Geology; Petrology

Doctor of Philosophy, The Ohio State University, 2009, Astronomy

We attempt to identify all microlensing parallax events for which the parallax fit improves ΔΧ2 > 100 relative to a standard microlensing model. We outline a procedure to identify three types of discrete degeneracies and find many new degenerate solutions in 16 previously published and 6 unpublished events. The lens of event OGLE-2003-BLG-84 may be a Jupiter-mass free-floating planet candidate based on a weak 3σ detection of finite-source effects. These events were examined for xallarap, which can mimic parallax. We find that 23% of these events are strongly affected by xallarap. The mid-IR flux ratios of the two images of the gravitationally lensed quasar HE 1104-1805 show no wavelength dependence to within 3% across 3.6-8.0 microns, no time dependence over 6 months and agree with the broad emission line flux ratios. This indicates that the mid-IR emission likely comes from scales large enough to be little affected by microlensing and that there is little differential extinction between the images. We measure a revised time-delay between these two images. We also observed uncorrelated variations of ~ 0.05 mag/yr-1 which we attribute to microlensing of the optical emission from the accretion disk. The optical colors have also changed significantly in the sense that image A is now redder than image B, rather than bluer as it was in 1993. Based on the microlensing variability of the two-image gravitational lens HE 1104-1805 observed between 0.4 and 8 microns, we have measured the size and wavelength-dependent structure of the quasar accretion disk. Modeled as a power law in temperature, we measure a B-band half-light radius of R = 6.7(+6.2)(-3.2)x10^15 cm (68% CL) and a logarithmic slope of 0.61(+0.21)(-0.17) (68% CL) for our standard model with a logarithmic prior on the disk size. Both the scale and the slope are consistent with simple thin disk models. The observed fluxes favor a slightly shallower temperature profile. Using 11-years of OGLE V-band photometry of Q2 (open full item for complete abstract)

Committee: Christopher Kochanek PhD (Advisor); Andrew Gould PhD (Committee Member); Bradley Peterson PhD (Committee Member) Subjects: Astronomy

Doctor of Philosophy, The Ohio State University, 2006, Physics

After reviewing the pillars of the concordance cosmology, which serves as the framework of this thesis, I describe how the accretion history of the Universe is revealed by thermal X-ray emission from the stellar sytems and nuclear regions of galaxies. I then go on to discuss how my collaborators and I have used this information to trace the formation of stars and the growth of supermassive black holes over the last ~ 8 Gyrs, i.e., from z ~ 1 to the present. It is of great importance for our understanding of galaxy evolution to determine whether there is a break or a continuum in these processes from the powerful quasars and starbursts of the past, to the seemingly dormant, "normal" galaxies more typical of the present epoch. To help settle the question, we combined optical data from the NOAO Deep Wide-Field Survey (NDWFS), X-ray data from the XBootes survey, and spectral information from the AGN and Galaxy Evolution Survey (AGES) in order to simultaneously obtain deep and wide coverage of the normal galaxy population. In this manner, my collaborators and I were able to bridge the gap in normal galaxy X-ray coverage between large-area local surveys and high redshift, small volume deep fields. Our findings suggest the accretion history of the Universe plays out as a continuum, with the growth of stellar populations and supermassive black holes steadily tailing off rather than abruptly ceasing as we move toward the faint end of the luminosity function.

Committee: Terry Walker (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy (Ph.D.), Bowling Green State University, 2008, Biological Sciences

Lake Vostok, located below the 4000 m thick Antarctic Ice Sheet, is the largest subglacial lake in Antarctica. The lake water has not been sampled due to concerns of forward contamination. However, ice cores available from the Vostok 5G well of depths greater than 3538 m represent lake water that has accreted to the overhead glacier from various regions across Lake Vostok. Here, we report the characterization of bacteria and fungi from ten accretion ice sections (15,000 to 18,000 years old), and two deep glacial ice sections (1 to 2 million years old) from the Vostok, Antarctica 5G ice core. Fungi, as well as bacteria, were characterized by fluorescence microscopy, scanning electron microscopy, culturing, and sequence analyses of ribosomal DNA. A total of 703 bacteria and fungi were cultured from the accretion ice of subglacial Lake Vostok. Mean cell concentrations were from 2.3 to 12.3 cells per ml of ice meltwater, of which 5 to 84% were viable. These cell counts are substantially lower than previously reported values. A total of 54 unique ribosomal DNA sequences were determined and compared to recent taxa, of which 36 were fungi and 18 were bacteria. Fungi most closely related to Rhodotorula, Aureobasidium, Cryptococcus, Cladosporium and Penicillium, and bacteria related to Carnobacterium spp., Bacillus spp., Caulobacter and Micrococcus were identified based on sequence analysis from cultured isolates. These findings, plus tests for growth at low temperatures, indicate that Lake Vostok contains a mixture of heterotrophic psychrotolerant and psychrophilic species. The results revealed new genera of microorganisms not previously reported in Lake Vostok accretion ice, lower abundances of microorganisms, and demonstrated the necessity to use multiple methods to thoroughly characterize environmental ice.

Committee: Scott Rogers PhD (Advisor); George Bullerjahn PhD (Committee Member); R. Michael McKay PhD (Committee Member); Paul Morris PhD (Committee Member) Subjects: Biology; Ecology; Microbiology; Molecular Biology

Doctor of Philosophy, Case Western Reserve University, 2013, EMC - Mechanical Engineering

Numerous turbofan engine loss of thrust control events have led to a theory that ice is accreting on initially warmer than freezing internal engine hardware and affecting normal operation. The phenomenon is termed ice crystal icing. Previous ice crystal icing research on a simple airfoil empirically identified the effects of pressure, temperature and relative humidity on the equilibrium surface temperature and the characteristic ice that accretes. In these cases with freezing fraction and impinging particle temperature as experimental unknowns, the on-set of ice accretion on an initially warmer than freezing surface was found to correlate with a below freezing thermodynamic wet-bulb temperature. In the present work, a novel ice accretion model, based on a modified Tribus-Messinger (MTM) surface energy balance, is developed. Implementing the model, the effect on the equilibrium surface temperature and freezing fraction near the leading edge stagnation region of an airfoil operating in icing conditions is investigated by varying the parameters of ambient static pressure, ambient static temperature, relative humidity and impinging particle temperature. The previously identified effects of pressure, temperature and relative humidity are identified as well as a new impinging particle temperature effect. A below freezing adiabatic saturation temperature, analogous to the thermodynamic wet-bulb temperature is calculated and shown to correlate with the predicted onset of ice accretion. Implementing the MTM model to investigate the physics of the modified surface energy balance, the pressure, temperature, relative humidity and impinging particle temperature effects are shown to be coupled within the latent, convective and sensible energy terms of the modified balance. The model predicts the observed onset of accretion and characteristic ice that forms on the surface from two experimental test cases. Control of the onset of ice accretion for these cases is demonstr (open full item for complete abstract)

Committee: Joseph Prahl (Committee Chair) Subjects: Aerospace Engineering; Engineering; Mechanical Engineering; Physics