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Dissertations and theses in the University Digital Conservancy comprise the official, approved version of these works. The dissertations and theses in the Digital Conservancy are submitted through the Graduate School in accordance with University standards. Works contributed to the Conservancy serve as a permanent University of Minnesota record of graduate student scholarship. Electronic submission of dissertations to the Digital Conservancy date from 2007. Master's Plan A theses date from 2009.

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0-Hecke algebra actions on flags, polynomials, and Stanley-Reisner rings
(2013-08) Huang, Jia
We study combinatorial aspects of the representation theory of the 0-Hecke algebra $H_n(0)$, a deformation of the group algebra of the symmetric group $\SS_n$. We study the action of $H_n(0)$ on the polynomial ring in $n$ variables. We show that the coinvariant algebra of this action naturally carries the regular representation of $H_n(0)$, giving an analogue of the well-known result for the symmetric group by Chevalley-Shephard-Todd. By investigating the action of $H_n(0)$ on coinvariants and %finite flag varieties, we interpret the generating functions counting the permutations with fixed inverse descent set by their inversion number and major index. We also study the $H_n(0)$-action on the cohomology rings of the Springer fibers, and similarly interpret the (noncommutative) Hall-Littlewood symmetric functions indexed by hook shapes.We generalize the last result from hooks to all compositions by defining an $H_n(0)$-action on the Stanley-Reisner ring of the Boolean algebra. By studying this action we obtain a family of multivariate noncommutative symmetric functions, which specialize to the noncommutative Hall-Littlewood symmetric functions and their $(q,t)$-analogues introduced by Bergeron and Zabrocki, and to a more general family of noncommutative symmetric functions having parameters associated with paths in binary trees introduced recently by Lascoux, Novelli, and Thibon. We also obtain multivariate quasisymmetric function identities from this $H_n(0)$-action, which specialize to results of Garsia and Gessel on generating functions of multivariate distributions of permutation statistics. More generally, for any finite Coxeter group $W$, we define an action of its Hecke algebra $H_W(q)$ on the Stanley-Reisner ring of its Coxeter complex. We find the invariant algebra of this action, and show that the coinvariant algebra of this action is isomorphic to the regular representation of $H_W(q)$ if $q$ is generic. When $q=0$ we find a decomposition for the coinvariant algebra as a multigraded $H_W(0)$-module.
A 0.45 V low power high PSRR subthreshold CMOS voltage reference
(2017-10) Palamedu Sundaram, Prakash
Voltage references are broadly used in analog and digital systems to generate a DC voltage independent of process, supply voltage and temperature (PVT) variations. Conventional band gap references (BGR) add the forward bias voltage across a PN junction with a voltage that is proportional to absolute temperature to produce an output that is insensitive to changes in temperature. BGRs generate a nearly temperature independent reference, of about 1.25 V, and therefore they require a higher supply voltage, which might not meet the low voltage constraints for low-power applications such as passive RFID’s, wearable and implantable medical devices. Also, BGRs use resistors that need more area on silicon. One possible solution to meet the low power requirement is to operate MOSFETs in subthreshold region. Most often, forward biased PN-junctions of BGRs are substituted with MOSFETs biased in the subthreshold region and achieves a supply voltage down to 0.6 V.\par This paper presents a sub-1V voltage reference circuit that has only MOS transistors, all working in subthreshold region with a supply voltage down to 0.45 V and a supply current of 1nA at room temperature for ultra-low power applications. The circuit is designed and simulated in 0.13um technology.
1,3-Butadiene-Induced DNA Damage: Ethnic Differences and Sources of Formation
(2022-07) Jokipii Krueger, Caitlin
In the United States, lung cancer is the leading cause of cancer-related deaths. Cigarette smoking is a major risk factor for lung cancer development, with approximately 80% of lung cancer cases directly related to smoking. Up to 1 in 4 smokers will develop lung cancer over the course of their lifetime. This risk varies by racial/ethnic group, with African Americans and Native Hawaiians at greater risk as compared to whites, and Japanese and Latinos at a relatively lower risk than whites. This racial/ethnic difference in risk is not explained by differences in smoking dose, diet, occupation, or socioeconomic status. Cigarette smoke is comprised of over 7000 chemical compounds, more than 70 of which are known human carcinogens. These carcinogens undergo metabolic activation to reactive species which can form adducts with DNA, leading to mutations and eventually lung cancer development. Polymorphisms in metabolic genes responsible for the bioactivation and detoxification of tobacco smoke carcinogens have been hypothesized to play a role in the racial/ethnic differences in lung cancer risk. Among tobacco smoke carcinogens, 1,3-butadiene (butadiene, BD) is one of the most abundant and has the highest cancer risk index. BD is metabolically activated to reactive epoxides 3,4-epoxy-1-butene (EB), 1,2-dihydroxy-3,4-epoxybutane (EBD), and 1,2,3,4-diepoxybutane (DEB) by CYP2E1 and 2A6. These epoxides can be detoxified through glutathione conjugation by GSTT1 to form 2-(N-acetyl-L-cystein-S-yl)-1-hydroxybut-3-ene and 1-(N-acetyl-L-cystein-S-yl)-2-hydroxybut-3-ene (MHBMA) from EB, N-acetyl-S-(3,4-dihydroxybutyl)-L-cysteine (DHBMA) from EB-derived hydroxymethylvinyl ketone (HMVK), 4-(N-acetyl-L-cystein-S-yl)-1,2,3-trihydroxybutane (THBMA) from EBD, and bis-butanediol mercapturic acid (bis-BDMA) from DEB. If not detoxified, these epoxide species can form covalent adducts with DNA such as N7-(1-hydroxy-3-buten-2-yl) guanine (EB-GII) from EB, N7-(2,3,4-trihydroxybut-1-yl) guanine (N7-THBG) from EBD, and 1,4-bis-(guan7-yl)-2,3-butanediol (bis-N7G-BD) from DEB. The first goal of this thesis work was to investigate urinary levels of EB-GII as a biomarker of lung cancer risk in smokers. In Chapter 2 of this thesis, we report the temporal stability and association with smoking of urinary EB-GII. Urinary EB-GII levels were stable over time in smokers, indicating that single adduct measurements provide reliable levels of EB-GII. Additionally, we observed a 34% decrease in the levels of urinary EB-GII upon smoking cessation, indicating that it is associated with smoking status but may also have other sources of formation. In Chapter 3 we quantified urinary EB-GII adducts in smokers and non-smokers belonging to three racial/ethnic groups with differing risks of lung cancer development: Native Hawaiian, white, and Japanese American. We observed higher levels of urinary EB-GII excretion in Japanese Americans as compared to whites and Native Hawaiians and these differences could not be explained by GSTT1 gene deletion or CYP2A6 activity. In Chapter 4 we directly examined the association between urinary EB-GII and lung cancer incidence, revealing that EB-GII levels are elevated in lung cancer cases as compared to smokers without lung cancer (OR = 1.91). In Chapters 2 and 3, we observed that there were low but detectable levels of urinary EB-GII in smokers following smoking cessation and in non-smokers, suggesting additional sources of EB-GII adduct formation. In Chapter 5, we utilized stable isotope tracing to investigate the formation of BD DNA adducts and metabolites from endogenous sources. Laboratory rats were treated with low ppm (0.3-3.0 ppm) concentrations of BD-d6 to approximate occupational exposure to BD (~1 ppm). Levels of exogenous (deuterated) EB-GII, MHBMA, and DHBMA increased in a dose-dependent manner following BD exposure, while endogenous (unlabeled) adducts and metabolites were unaffected by BD dose. While urinary EB-GII and MHBMA were formed primarily by exogenous exposure, significant amounts of endogenous DHBMA were observed. Additionally, urinary exogenous EB-GII was associated with butadiene-induced genomic EB-GII, suggesting that urinary EB-GII can be used as a non-invasive surrogate measurement for genomic BD-DNA damage. In Chapter 6, formation of a novel BD-DNA adduct, N6-[2-deoxy-D-erythro-pentofuranosyl]-2,6-diamino-3,4-dihydro-4-oxo-5-N-1-(oxiran-2-yl)propan-1-ol-formamidopyrimidine (DEB-FAPy-dG) was investigated. A sensitive isotope dilution nanoLC-ESI+-HRMS/MS methodology was developed and applied to quantitation of DEB-FAPy-dG formation in DEB treated calf thymus DNA. DEB-FAPy-dG formation was dependent on DEB concentration and pH, with higher adduct levels observed at higher pH. Detection of DEB-FAPy-dG in mouse embryonic fibroblast cells and nuclei treated with DEB was unsuccessful, likely due to the adduct forming in low quantities at physiological pH.
A 10,000-year lake-sediment based reconstruction of precipitation isotope values in the Canadian Rocky Mountains and implications for past changes in North American hydroclimate
(2019-01) Wagner, Zachary
Hydroclimate change in the Canadian Rocky Mountains is an important area of research, as demand for water resources in the Great Plains has been continuously increasing in recent years. The population of Alberta has one of the fastest growth rates in Canada, and cities like Calgary and Edmonton are dependent on surface and groundwater resources that originate from precipitation in the mountains. Recent increases in petroleum exploration have also amplified demands for water, along with the growing water requirements of industrial agriculture. The application of sound water resource management policies is essential, and historical records span only ~200 years, a time frame too short to capture the full range of climate variability. The development of paleoclimate proxy records from the Rocky Mountains is therefore necessary to attain a thorough perspective on potential changes in climate. Such data can, for example, inform water resource managers of possible shifts in precipitation seasonality and drought/pluvial events on timescales of decades to millennia. To this end, we present a 10,000-year oxygen isotope record as a proxy for precipitation seasonality linked to the Pacific North American pattern (PNA) which adds to a growing body of research in a region of high spatial complexity of hydroclimate. Shark Lake in Alberta, CA (50.8412°N, 115.3990°W; 1857 m above sea level) is a hydrologically open basin lake in the Canadian Rocky Mountains with one large outlet and numerous small inlets and groundwater springs. Winter precipitation is more depleted in the heavier 18O isotope relative to summer precipitation due to equilibrium fractionation from rain-out and phase changes. δ18O and δD values of Shark Lake water samples (collected during the summer) range from -18.9 to -20.0 ‰ and -141 to -150 ‰, respectively. The annual weighted average precipitation isotope ratios are -16.6 and -126 ‰ for oxygen and hydrogen, respectively. This indicates that Shark Lake principally receives water inputs from runoff or shallow groundwater that originated as precipitation during the cold season. We collected 1 m and 1.5 m long sediment cores using a modified Livingstone corer and used loss-on-ignition (LOI), x-ray diffraction (XRD), x-ray fluorescence (XRF) analyses to destermine sediment texture and composition. The sediment was dated using 14C from terrestrial plant fossils, as well as 210Pb and 137Cs for the surface sediment. We analyzed the isotopic composition (δ18O) of authigenic carbonate sediment from Shark Lake using mass spectrometry and applied these results as a proxy for precipitation seasonality. Lake water oxygen isotope ratios are captured by authigenic carbonates, which form during the spring and summer in response to pH changes associated with primary production. These carbonate minerals (calcite) precipitate in isotopic equilibrium and are deposited on the lakebed where they are preserved. The Shark Lake δ18O record demonstrates a transition from lower to higher average δ18O values from the middle to the late-Holocene at around 4500 yr BP. This is consistent with previous findings of changes in PNA-like atmospheric patterns during the middle Holocene, when a gradual shift from a more negative to a more positive mean state phase of the PNA occurred. This produced enhanced zonal atmospheric circulation in the Pacific Basin that led to a reduction in winter precipitation in northwestern North America and drier conditions in the southwestern part of the continent in the late Holocene relative to the middle Holocene. The Shark Lake δ18O record has a positive, significant correlation with other similar records from the Pacific Northwest, specifically those from Lime Lake (WA) and the OCNM (OR) speleothem, and has a negative, significant correlation with records from the southern Rocky Mountains and eastern North America, namely those from Bison Lake (CO), Cheeseman Lake (NL), Grinnell Lake (NJ), and the Buckeye Creek Cave speleothems (WV). Decadally resolved records are useful for tracking changes in PNA state and its interaction with other related climate oscillations such as the El Niño Southern Oscillation (ENSO) and the associated Pacific Decadal Oscillation (PDO). Open-basin lake records can also be combined with hydrologically closed-basin lake records to reconstruct pluvial and drought periods over the Holocene. The Shark Lake record increases the spatial resolution of mid- to late Holocene hydroclimate climate data in the Rocky Mountains and provides a baseline for natural variability in precipitation seasonality in a hydrologically important region.
The 13th-century “Constance” tales.
(2009-11) Leek, Thomas R.
Four texts from the 13th century make up the first attestations of the "Constance" plot, a version of ATU 706 "The Father who Wanted to Marry his Daughter." This dissertation harmonizes a comparative investigation of these tales with an analysis of the cultural milieu of the Middle Ages. The figure of the sexually persecuted and exiled daughter comes to the forefront of popular culture as discourse on repentance centers around the correction of monstrous sins. In the "Constance" tales, the daughter reconciles her repentant father and husband, between whom power is transferred on account of the heroine's suffering. A thematically similar anecdote in the Chronicle of Morea points toward an international motif of an errant daughter benefiting the man she marries against her father's initial wishes.
A 1D Fluid Model On The Circle, An Algorithm For Simulating Dense Crowds, And Stability For Programs With Seminorm Objective And Linear Constraints
(2020-04) Stewart, Samuel
In this thesis, we describe three contributions made to three different fields. First, we prove local stability of solutions to a 1D model equation of the 3D Euler equations. Second, we describe a model of human crowds where people are modeled by ellipses. Finally, we prove local stability of solutions for a family of convex programs.
1H-NMR Metabolomics Characterizes Transition From Ebb To Flow In A Porcine Model Of Smoke Inhalation And Severe Burn Injury
(2018-06) Hendrickson, Cole
Burn injury initiates a metabolic response that, even when treated, causes muscle wasting and organ dysfunction in burn patients as long as two years following injury. This increased metabolic rate, termed “flow” phase in burn physiology, is initially masked by low blood pressure and inadequate oxygen supply in burn shock, known as “ebb” phase. Our study examined the metabolic transition between the “ebb” and “flow” phases of burn recovery using proton nuclear magnetic resonance (1H-NMR) spectroscopy in a porcine model of severe burn injury with additional smoke inhalation. We hypothesized the serum metabolomes of porcine subjects would be distinguishable by time point, and the changes in individual metabolite concentrations would characterize the shift from “ebb” to “flow” in burn physiology. Fifteen pigs received 40% total body surface area (TBSA) thermal burns with additional pine bark smoke inhalation treatment. Subjects were resuscitated and kept anesthetized until 72 hours post-burn or death. Arterial blood samples were drawn at baseline (pre-burn) and every 24 hours until 72 hours post-injury or death. The aqueous portion of each sample was analyzed in a 700MHz spectrometer and metabolite peaks were fit to spectra using Chenomx software. Thirty-eight metabolites were detected in 39 samples, and principal component analysis (PCA) was conducted to separate samples by time point. 51.6% of metabolite variability was captured in the first two principal components. We found post-burn metabolomes of porcine subjects to be distinguishable by time point using 1H-NMR and principal component analysis. We also constructed a framework for non-lactic acidosis in resuscitated burn subjects that emphasized oxidative stress and increased fatty acid catabolism as root causes of organic acid accumulation. Further studies will be required to confirm and elaborate on the post-burn metabolic pathways suggested by this analysis.
2,5-Cyclohexadienones as a Useful Launching Point for the Synthesis of the Briarane Diterpenoids and A Hypervalent Iodine-Mediated Synthesis of Oxazolines
(2015-05) Moon, Nicholas
The briarane diterpenoids are a large class of natural products derived from gorgonians and other corals from throughout the world. Despite the extremely large number of briaranes that have been isolated, along with the potent and diverse range of biological activities that have been observed, the total synthesis of the briaranes remains underexplored. A facile synthetic route to the briarane diterpenoids will aid in the further exploration of these molecules. Herein, we will describe a number of synthetic approaches that were evaluated to access a key fragment of the briarane diterpenoids. A key feature of all routes involves the use of 2,5-cyclohexadienone substrates as a diverse platform for the launching of the synthesis. Chapter 1 will provide background information on 2,5-cyclohexadienones. Methods for their synthesis, a survey of their diverse reactivity, and selected examples of their use in natural product synthesis will all be described. Emphasis will be given to reactivity patterns which aided us in our research. Chapter 2 will provide a brief survey of the briarane diterpenoids as well as some of the major biologically active families. Previous synthetic efforts used to access these molecules will also be described. Chapter 3 will describe our efforts to synthesize a key fragment of the briarane diterpenoids (referred to as the briarane stereotetrad) utilizing intermediates containing a bicyclic lactone. Chapter 4 will describe our successful efforts to access the briarane stereotetrad using monocyclic intermediates. The important influence of torsional strain in key steps, as well as a successful route to access the briarane stereotetrad will be described. Chapter 5 will report the results of a separate research project in which an iodine(III) promoted cyclization of N-allylamides to form oxazolines was studied. The development of optimum reaction conditions and the evaluation of the substrate scope will be described. Key results that suggest novel mechanistic details for this electrophilic oxidative cyclization will also be described.
2-Alkoxycarbonyl Allyl Ester Conjugates of NSAIDs as Potential Anticancer Agents
(2017-09) Lueth, Erica
Enzyme cyclooxygenase (COX) inhibition with non-steroidal anti-inflammatory drugs (NSAIDs) has long been utilized to treat inflammation and relieve pain. Several studies have shown that NSAIDs have also cancer preventative and tumor regressive effects. Prostaglandin E2 which acts as an inflammatory mediator influences many mechanisms that plays a significant role in tumorigenesis such as cell proliferation, angiogenesis, and metastasis. COX overexpression is a characteristic feature of most malignant tumors and contributes to poor outcomes in multiple malignancies. It has been reported that cancer incidence can be reduced by 25-40% in patients regularly taking low dose COX inhibitor aspirin on a daily basis, with the most compelling evidence acquired for colorectal cancer. We envisioned that NSAID conjugates derived from 2-alkoxycarbonyl allyl esters would have cytotoxicity enhancing prodrug properties with dual anti-inflammatory and intracellular alkylation. In the current work, 2-alkoxycarbonyl allyl ester conjugates of several common NSAIDs have been synthesized and tested for their cell proliferation inhibition properties in breast (MDA-MB-231, 4T1), pancreatic (MIA PaCa-2), and colorectal adenocarcinoma (WiDr) cell lines. Several of the synthesized derivatives exhibit good potency against all four cancer cell lines. The synthesized compounds have also been tested for their COX inhibition properties.
2-hydrazinoquinoline as a novel derivatization agent for LC-MS-based metabolomic investigation of ketoacidosis in streptozotocin-elicited diabetes
(2013-07) Lu, Yuwei
Short-chain carboxylic acids, aldehydes, and ketones are important intermediates and end products of many metabolic processes. Their levels in biofluids and tissues can reflect the status of specific metabolic reactions, the homeostasis of whole metabolic system, and the well-being of a biological entity. Traditionally, GC-MS has been widely used for analyzing carboxylic acids, aldehydes, and ketones in biological samples after chemical derivatization. However, due to poor compatibility of common GC columns with water, the derivatization process in GC-MS is often complicated and time consuming, especially for the metabolites in biofluids and tissues. Recently, new chemical derivatization techniques have been developed to enhance the sensitivity and performance of LC-MS for analyzing these metabolites. In this study, the use of 2-hydrazinoquinoline (HQ) as a novel derivatization agent for LC-MS analysis of carboxylic acids, aldehydes, and ketones in biological samples was explored, and the conditions for the derivatization reaction were optimized. The metabolites in urine, serum, and tissue extracts can be conveniently derivatized in a 60-min process. The formation of carboxylic acid derivatives is attributed to the esterification reaction between HQ and carboxyl group, while the production of aldehyde and ketone derivatives is through the formation of Schiff bases between HQ and carbonyl group. Compared to other known hydrazine derivatization agents, including 2-hydrazinopyridine, 2-picolylamine and dansyl hydrazine, HQ can react with a broader spectrum of intermediary metabolites in biological samples, and can achieve better chromatographic performance in reversed phase LC system and higher ionization efficiency in electrospray source. Using this HQ-based approach, the metabolic disorder induced by streptozotocin-elicited diabetes was examined by the LC-MS-based metabolomics. The results showed the time-dependent separation of mouse urine samples from STZ treatment in a multivariate model of urinary metabolites. Both known and novel small-molecule biomarkers associated with STZ-induced ketoacidosis were conveniently identified and subsequently elucidated, reflecting the dramatic changes in nutrient (glucose, amino acid, and lipid) and energy metabolism after STZ treatment. Overall, HQ derivatization of carboxylic acids, aldehydes, and ketones can be an effective platform for the LC-MS-based metabolomic investigation of endogenous metabolism.
2-Swappability and the Edge-Reconstruction Number of Regular Graphs
(2018-05) Ross, Michael
The edge-reconstruction number of a graph $G$, denoted $\ERN(G)$, is the size of the smallest multiset of unlabeled, edge-deleted subgraphs of $G$, from which the structure of $G$ can be uniquely determined. That there was some connection between the areas of edge reconstruction and swapping numbers has been known since the swapping number of a graph was first introduced by Froncek, Hlavacek, and Rosenberg in 2014\cite{edgeswap}. The present paper illustrates the depth of that connection by proving several bridging results between those areas; in particular, when the graphs in question are both regular and 2-swappable. Formerly, it had been conjectured that for $r\geq 3$ regular graphs, $\ERN(G) \leq 2.$ However, results of the present paper led to the discovery of four infinite families of $r\geq 3$ regular graphs with $\ERN(G) \geq 3$, while giving some promising leads for further discoveries in edge reconstruction.
21st Century media effects: choice, predispositions, and their impact on agenda setting and priming.
(2009-12) Holmes, Justin Whitely
In the past 25 years, we have seen a massive shift to communication technologies that allow increased choice of content for citizens. Using an experiment, this study explores the relationship between individual differences, increased choice, and media effects such as agenda setting and priming. It finds that increased choice greatly attenuates both attention to political news and subsequent priming and framing effects.
A 24-channel radio frequency receive array for magnetic resonance imaging of primates at 10.5 T
(2023-08) Jungst, Steve
Magnetic resonance imaging (MRI) is a unique modality which offers many advantages and challenges compared to other imaging technologies. The radio frequency (RF) coil is one of the key hardware sub-systems, which drives overall MRI system performance to enable higher resolution imaging and the collection of high fidelity information about organism structure and function. To optimize RF coil performance, notably the signal-to-noise ratio (SNR) of the received signal, it is imperative that each coil be custom made to the specific static field strength of the MRI system, the anatomical region of interest, and the desired experimental constraints. This thesis explores some of the technical underpinnings of MRI with a focus on RF coil construction for non-human primate (NHP) imaging. A 24-channel RF receive array coil with integrated transmitter is presented, followed by a discussion of its performance, imaging results, and future directions.
A 250-year assessment of human impacts on Lake Superior: an updated paleolimnological perspective
(2013-05) Chraibi, Victoria Lindsay Shaw
To understand environmental conditions in Lake Superior over the last two centuries, we conducted a paleolimnological study on two sediment cores collected in the eastern and western regions of the lake. We examined the diatom community assemblages, trace metals, sediment characteristics, and GIS-reconstructed human land use to evaluate the historical impacts of human activities. During European settlement and agricultural development, there is clear indication the diatom community reorganized due to nutrient enrichment. Trace metal profiles tracked a period of mining and ore processing which temporarily increased metal loads to the lake in the mid- to late-20th century. In recent decades, more oligotrophic diatom species were favored, suggesting nutrient decreases associated with remedial activities. The diatom community has reorganized to be dominated by Cyclotella species, providing evidence that water quality changes are being influenced by atmospheric nitrogen deposition and changes in the lake's physical and chemical processes associated with climate change.
2D Mott Hopping of Vortices in an Amorphous Indium Oxide Film
(2018-07) Percher, Ilana
The electron transport behavior of a thin film of amorphous indium oxide was studied as it was driven across the superconductor-insulator transition by a perpendicular magnetic field. For the range of field values between zero and the critical field of the transition, a positive slope in temperature dependence of the resistance was observed in the data. These data are best described by the form of two dimensional Mott variable range hopping as applied to vortices. The quality of this fit is demonstrated over several orders of magnitude in resistance and over a broad range of fields using several methods of analysis. The observation of variable range hopping of vortices is the main result of this work. Data from a second sample were also found to be consistent with vortex variable range hopping, as were data extracted from a paper within the literature. These examples suggest that this behavior has probably been overlooked in the past. The field-dependence of the characteristic hopping temperature T_0 at very low fields was predicted using a granular model for the thin film. This is consistent with the picture of effective granularity induced in a highly disordered superconductor, which also explains various properties of the film, including the magnetoresistance peak observed at high fields. What was not observed, however, was a crossover from Mott to some other hopping behavior at high fields, where corrections to the hopping exponent due to vortex-vortex interactions were expected. The reason for this is an open question.
2D Peskin Problems of an Immersed Elastic Filament in Stokes Flow
(2018-05) Rodenberg, Analise
In the work that follows we investigate a class of problems where a one dimensional closed elastic structure is immersed in a plane of steady Stokes flow. The dynamics are governed by a boundary integral equation describing the configuration of the immersed structure. Depending on the choice of elasticity law, we break our class into either a semilinear or fully nonlinear system of equations. In the nonlinear setting, we prove that the linearization of the system generates an analytic semigroup and use it to prove local existence and uniqueness in low regularity H\"{o}lder spaces. In the semilinear setting, we remove the principle operator via small scale decomposition and use it to build similar local existence results. Further, we establish spatial smoothness of solutions by careful estimates on a class of commutators. Using these regularity results, we are able to establish that the only equilibria of the system are uniformly parameterized circles which we then prove nonlinear stability about. Finally, we identify a quantity which classifies global-in-time behavior.
2D Plasmonics for Gas Sensing and Polarization Optics
(2021-12) khaliji, kaveh
Two-dimensional (2D) materials emerged in 2004 with the isolation of graphene, a one-atom-thick honeycomb lattice of carbon atoms. The first reports on light interaction with polarizable 2D matter, i.e. 2D polaritons, came out in 2011 wereexperiments confirmed graphene's ability to sustain plasmon polaritons. Today, the 2D family is extended far beyond graphene which can host a full suite of different polaritonic modes with record-high light confinement and optical responses that can be tuned via lattice strain, optical pumping, or electrostatic gating. In this thesis we aim to exploit the optical and plasmonic responses of 2D materials to explore new system designs for selective gas sensing and ubiquitous polarization transformation. Truly robust and selective sensing of gases via remote standard optical spectroscopy, if achieved, has widespread use in key industries, including environmental, semiconductor, healthcare, and security. To date, the impeding challenge hasbeen the weak optical absorption of the gas molecules, which prevents optical read-out of gas traces at minute concentration. To overcome the weak sensitivity of optical techniques, we propose novel strategies, by utilizing plasmons in graphene to enhance light-gas interaction via promoting multiple trapping mechanisms, including surface adsorption, optical tweezing, and electrostatic bias. We discuss the relative strengths of these trapping forces and found gas adsorption in a typical nanoribbon array plasmonic setup produces measurable dips in optical extinction of magnitude 0.1 % for gas concentration of about parts per thousand level. We discuss the dynamic and nonlocal polarizability of two-dimensional electron gas with finite energy bandwidth (FBW-2DEG). This was motivated by recent developments in twisted 2D materials which exhibit isolated electronic bands and finite bandwidths. We show that a FBW allows for plasmon modes of quasi- at dispersion and large momenta to emerge. The FBW-2DEG can also potentially support low-loss plasmon modes immune to elastic or inelastic scattering-assistedLandau damping (dissipation via electron-hole pair excitation). This is of prime significance, since it allows for plasmon modes with concurrent tight spatial confinement and long propagation lengths, the two metrics critical to most branches of plasmonic science, e.g. communication, sensing, lasing, and more. The polarization of scattered light contains vital clues to nature of its light-matter interactions. The ability to control light polarization plays a key role in metrology applications such as stress analysis in glass or plastic, pharmaceutical or food ingredient analysis, biological imaging among others. The recent reports on rich near-field polaritonic-optics of twisted 2D materials with in-plane optical anisotropy, such as twisted Black Phosphorus and -MoO3, motivated us to explore the far-field polarization properties of such setups. We show that a stack of twisted anisotropic 2D materials with electrostatic control can function as arbitrary-birefringent wave-plate or arbitrary polarizer with tunable degree of non-normality. The twisted stack, thus gives access to a plethora of polarization transformers including rotators, pseudo-rotators, symmetric and ambidextrous polarizers. We explore the far-field scattering properties of anisotropic 2D materials in ribbon array configuration. Our study reveals the plasmon-enhanced linear birefringence/dichroism in these ultrathin metasurfaces, where linearly polarized incidentlight can be scattered into its orthogonal polarization or be converted into circular polarized light. We found wide modulation in both amplitude and phase of the scattered light via tuning the operating frequency or material's anisotropy.
A 3-dimensional analysis of the Cassiopeia a supernova remnant.
(2011-10) Isensee, Karl Andrew
We present a multi-wavelength study of the nearby supernova remnant Cassiopeia A (Cas A). Easily resolvable supernova remnants such as Cas A provide a unique opportunity to test supernova explosion models. Additionally, we can observe key processes in the interstellar medium as the ejecta from the initial explosion encounter Cas A’s powerful shocks. In order to accomplish these science goals, we used the Spitzer Space Telescope’s Infrared Spectrograph to create a high resolution spectral map of select regions of Cas A, allowing us to make a Doppler reconstruction of its 3-dimensional structure structure. In the center of the remnant, we find relatively pristine ejecta that have not yet reached Cas A’s reverse shock or interacted with the circumstellar environment. We observe O, Si, and S emission. These ejecta can form both sheet-like structures as well as filaments. Si and O, which come from different nucleosynthetic layers of the star, are observed to be coincident in some regions, and separated by >500 km s−1 in others. Observed ejecta traveling toward us are, on average, #24;800 km s−1 slower than the material traveling away from us. We compare our observations to recent supernova explosion models and find that no single model can simultaneously reproduce all the observed features. However, models of different supernova explosions can collectively produce the observed geometries and structures of the emission interior to Cas A’s reverse shock. We use the results from the models to address the conditions during the supernova explosion, concentrating on asymmetries in the shock structure. We also predict that the back surface of Cassiopeia A will begin brightening in #24;30 years, and the front surface in #24;100 years. We then used similar observations from 3 regions on Cas A’s reverse shock in order to create more 3-dimensional maps. In these regions, we observe supernova ejecta both immediately before and during the shock-ejecta interaction. We determine that the reverse shock of the remnant is spherical to within 7%, although the center of this sphere is offset from the geometric center of the remnant by 810 km s−1. We determine that the velocity width of the nucleosynthetic layers is #24;1000 km s−1 in a given region, although the velocity width of a layer along any given line of sight is <250 km s−1. Si and O are observed to be coincident in some directions, but segregated by up to #24;500 km s−1 in other directions. We again compare these observations of the nucleosynthetic layers to predictions from supernova explosion models in an attempt to constrain such models. Finally, we observe small-scale velocity structures in the recently shocked ejecta. We determine that this corrugation is likely caused during the supernova explosion itself, rather than hundreds of years later at the remnant’s reverse shock. Finally, we present a detailed multi-epoch X-ray analysis of Cas A using Chandra X-ray Observatory exposures from 2000, 2002, and 2004. We identify the most recently shocked X-ray ejecta with ionization timescales of #24;1010 cm−3 s, nearly an order of magnitude smaller than previously identified shocked ejecta. These ejecta are then used to determine if the original nucleosynthetic layers of the star are arriving at Cas A’s reverse shock at different times. We use recent collisional ionization models that allow us to correlate observed changes in spectrum with a rough estimate of when the Mg and Fe layers reached the reverse shock. We find several regions that have a signature consistent with a separation of #24;200 km s−1 between layers, although we find that most regions show no sign of separation greater than 65 km s−1. This method is able to detect substantially smaller separations between layers than earlier X-ray techniques. We test various supernova explosion models against our observations by comparing our observed velocity separation between layers to predictions from the models. We conclude that any mixing between nucleosynthetic layers is most likely caused by Rayleigh-Taylor filamentation and not partial explosive nucleosynthesis in the layers. Our observations of spectral changes provide feedback for future models which will address important physical issues such as the role of cosmic ray production at a supernova remnant’s reverse shock.
3-Dimensional Changes in Position and Inclination of Ectopically Erupting Maxillary Canines in Response to Slow Maxillary Expansion: A Retrospective Study
(2024-04) Ng, Casey
At an incidence of 0.8-2.8%, the impacted maxillary canine constitutes one of the more challenging orthodontic problems to manage, often involving interdisciplinary coordination of surgical exposure of the impacted tooth followed by orthodontic traction to align the canine within the dental arch. In addition to the increased orthodontic treatment time, cost, and complexity, other sequelae of impacted canines include root resorption of adjacent teeth, cyst formation, and malocclusion. Interceptive treatment with maxillary expansion has been shown to reduce the risk of ectopically erupting canines (EECs) developing into impacted canines. Although effects of maxillary expansion on ectopic canine eruption have been studied, most have focused on rapid, rather than slow, maxillary expansion protocols and either clinical outcomes or canine localization on 2-dimensional imaging. Therefore, little is known about positional effects in the buccopalatal direction. The novel approach of investigating changes in eruption path in response to slow maxillary expansion based on cone beam computed tomography (CBCT) measurements was used in this study to facilitate precise localization of erupting maxillary canines in all 3 dimensions. In this retrospective study, CBCT records of 24 EECs treated with quad helix slow maxillary expansion (EEC 2x4 + QH group) were compared against those of 15 EECs treated with 2x4 fixed appliance (EEC 2x4 group, control treatment), 39 normally erupting canines (NECs) treated with quad helix appliance (NEC 2x4 + QH group, control diagnosis), and 24 NECs treated with 2x4 appliance (NEC 2x4 group). Linear and angular measurements pertaining to canine position and angulation were made in all 3 dimensions to determine differences at pre-treatment and post-treatment timepoints, as well as change across timepoints. Results showed that 67% of EECs corrected to a normal position, as defined by sector location, in both 2x4 appliance and quad helix appliance treatment groups. Significantly greater uprighting of the erupting canine angulation from a coronal view was found in EECs treated with 2x4 appliance, compared to EECs undergoing the same treatment. On the other hand, the quad helix appliance was found to significantly normalize medial displacement of EECs at cusp tip and apical levels, cause greater uprighting of the EEC inclination from a sagittal view compared to NEC controls, and maintain a normal vertical eruption rate in EECs. Therefore, the improvement in canine eruption path effected by the 2x4 appliance and quad helix appliance are brought about by mechanisms in differing planes of space.
3-year survival estimates of short (less than or equal to 6 mm) length implants and the relationship to crown-to-implant ratios.
(2011-12) Saldarriaga, Augusto V.
INTRODUCTION: The literature regarding survival of short implants is conflicting. Furthermore, excessive crown-to-implant ratios have been cited in the literature as being detrimental to implant survival. Hence, the purpose of this study was to determine the 3- year survival estimates, and the relationship between crown-to-implant ratios and survival of short, roughened, plateau-design implants. Additionally, risk factors for failure were evaluated. MATERIAL AND METHOD: This retrospective cohort study involved 341 patients who possessed at least 1 single ≤6mm length plateau-design implant supported restoration that had been surgically placed between August 2000 and June 2007. An electronic chart review was conducted to acquire data on patient demographics, implant location, bone density, length of time in function and/or implant failure, as well as the most recent digital periapical radiographs in which the entire crown and implant were visible. Data analysis was conducted utilizing appropriate univariate and multivariate regression statistics, as well as non-parametric Kaplan-Meier survival analysis in order to determine the overall 3-year survival rate. RESULTS: Data from 573 single implant-supported fixed restorations were tabulated and included in the study. 13 implants failed overall. The 3-year Kaplan-Meier survival analysis adjusted for clustered observations was found to be 93.9%. The average (SD) crown-to-implant ratio of implants that were in function was 2.06 (0.4), and the average (SD) crown-to-implant ratio of those that failed was 2.02 (0.3). This difference was not statistically significant. Results from the multivariate model found quality of bone, and history of adjacent endodontically treated teeth to be statistically associated with implant failure, with hazard ratios of 13.2 and 2.7 respectively (P ≤ 0.05). CONCLUSIONS:The results of this study suggest that the survival of short, roughened, plateau-design dental implants is comparable to implants of traditional lengths, which suggests that these implants are a clinically acceptable option where alveolar bone height is limited or anatomic limitations exist.

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