Now showing items 8046-8065 of 20306

    • Galois groups and Greenberg's conjecture

      McCallum, William G.; Marshall, David Clark (The University of Arizona., 2000)
      We consider the structure of a certain infinite Galois group over Q(ζp) the cyclotomic field of p-th roots of unity. Namely, we consider the Galois group of the maximal p-ramified pro- p-extension. Very little is known about this group. It has a free pro-p presentation in terms of g generators and s relations where g and s may be explicitly computed in terms of the p-rank of the class group of Q(ζp). The structure of the relations in the Galois group are shown to be very closely related to the relations in a certain Iwasawa module. The main result of this dissertation shows this Iwasawa module to be torsion free for a large class of cyclotomic fields. The result is equivalent to verifying Greenberg's pseudo-null conjecture for the given class of fields. As one consequence, we provide a large class of examples of cyclotomic fields which do not admit free pro-p-extensions of maximal rank.
    • Game-Enhanced Simulation as an Approach to Experiential Learning in Business English

      Warner, Chantelle; Punyalert, Sansanee; Warner, Chantelle; Dupuy, Beatrice; Reinhardt, Jonathon (The University of Arizona., 2017)
      This dissertation aims to integrate various learning approaches, i.e., multiple literacies, experiential learning, game-enhanced learning, and global simulation, into an extracurricular module, in which it remodels traditional ways of teaching input, specifically, the lexical- and grammatical-only approaches of business English at a private university in Bangkok, Thailand. Informed by those approaches, a game-enhanced simulation was specifically designed as an experiential space for L2 learners to experience the dynamic and real business contexts of language use. A strategy-simulation video game, RollerCoaster Tycoon 3 Platinum (RCT3), was selected and used in the implementation of the pilot course. The game was embedded in a global simulation of two amusement park companies – where students worked in groups of five to form characters and socially interact with others. The global simulation involved learners in a sequence of genre-based (e.g., memoranda and business presentations) and technology-based tasks (e.g., using Gmail, Google Docs, and LinkedIn). Ten second-year students from five disciplines – Accounting, Logistics Engineering, Technology and Creative Business, Logistics Management, and Airline Business Management, participated in the study. Within this game-enhanced simulation, it turned out that each student simulated the role of a department head that was relevant to her or his discipline, for example, department heads of Financial Management, Technical Service Management, Customer Relationship Management, Legal and Operations Management, and Human Capital Management. The findings show that the learners' interactivity within the gameplay depicted the pedagogical affordances of RCT3 for a business English simulation, that is, exploratory interactivity, goal-orientedness in gameplay, goal-orientedness for roleplaying, and emergent narratives. The data present how this videogame features an interplay between two game perspectives – ludology and narratology. That is, ludic affordances in RCT3 could be activated in a narrative system: meaningful personal or emergent narrative by well-designed global simulation tasks. The simulations were established through students’ interpretation and creativity in gameplay and roleplay as related to their disciplines. Moreover, the game-enhanced simulation appeared to provide learners with an effective social context for promoting global English development and professional identity formation, which moved them beyond the learning practices of traditional coursebooks and classroom settings. Students of the study had opportunities to use professional Discourses related to their disciplines as ways to establish their desired identities within the simulated global workplace.
    • Game-Theoretic Contract Models for Equipment Leasing and Maintenance Service Outsourcing

      Liao, Haitao; Hamidi, Maryam; Son, Young-Jun; Fan, Neng; An, Lingling; Liao, Haitao (The University of Arizona., 2016)
      There is a major trend that manufacturers sell their services to customers instead of selling their products. These services can be provided through leasing, warranty, or maintenance outsourcing. In this dissertation, we have studied leasing and maintenance outsourcing services from different aspects of reliability-based maintenance, game-theoretic decision making, and inventory and supply chain management. We have studied how different interactions and relationships between the manufacturer and customer in service contracting affect the decisions they make and the profits they gain. The methods used to tackle the related decision-making processes are stochastic modeling, non-convex optimization, game-theoretical framework, and simulation. For equipment leasing, two non-cooperative game-theoretic models and a cooperative model have been developed to describe the relationships between the manufacturer (lessor) and customer (lessee). Through the lease contracts, the lessor decides on the maintenance policy of the leased equipment, and the lessee decides on the lease period and usage rate. In the non-cooperative simultaneous move scenario, the lessee and the lessor act simultaneously and independently to make their decisions. In the leader-follower non- cooperative contract, the lessor is the leader who specifies the maintenance policy first, and the lessee, as the follower, decides on the lease period and usage rate accordingly. We have next determined the total maximum profit and shown that the Nash and Stackelberg equilibria are different from the total maximum solution. As a result, the players can increase their total profit by cooperation. We have implemented the cooperative solution as an equilibrium through a nonlinear transfer-payment contract. Our results illustrate that cooperation can be regarded as a value-added strategy in establishing such lease contracts. Besides, our numerical results show that although cooperation always increases the total profit of the players, the magnitude of increase is case specific. When the lease price is low or the revenue is high, the profits in the non-cooperative contracts will be close to the cooperative alternative, while the cooperation may increase the total profit significantly in other cases. For maintenance outsourcing, we have studied different bargaining scenarios in determining the contract terms. First, we have considered the Nash bargaining solution to compute the bargaining profit of players. Next, we have considered the case where players pose threat against each other in order to increase their own bargaining position. We have determined the optimal threat strategy for each player. Our result shows that although such threatening decreases the efficiency of the contract, it can dramatically increase the profit of the player with a higher bargaining position. We have finally provided a solution to the problem of how the service agent and customer can cooperate and negotiate on the price. We have determined the discounted price as a result of negotiation. Indeed, the discounted price induces the customer to choose the total maximum maintenance policy. Our numerical examples illustrate the feasibility of using such a price-discount contract in maintenance service outsourcing. Moreover, one can see that both the customer and agent can benefit from this price-discount contract.
    • Games of Decentralized Inventory Management

      Dror, Moshe; Summerfield, Nichalin Suakkaphong; Dror, Moshe; Walker, Mark; Reynolds, Stanley S (The University of Arizona., 2010)
      Any decentralized retail or wholesale system of competing entities requires a benefit sharing arrangement when competing entities collaborate after their demands are realized. For instance, consider a distribution system similar to the observed behavior of independent car dealerships. If a dealership does not have in stock the car requested by a customer, it might consider acquiring it from a competing dealer. Such behavior raises questions about competitive procurement strategies that achieve system optimal outcomes. This dissertation consists of three main bodies of work contained respectively in chapters 2, 3, and 4. In the first work -- chapter 2, we examine a decentralized system that adopts an ex-post agreed transfer payment approach proposed by Anupindi et al. (Manuf. Serv. Oper.Manag. 4(3):349-368, 2001). In particular, we state a set of conditions on cost parameters and distributions that guarantee uniqueness of pure strategy Nash equilibrium. In the second work -- chapter 3, we introduce a multilevel graph framework that links decentralized inventory distribution models as a network of stochastic programming with recourse problems. This framework depicts independent retailers who maximize their individual expected profits, with each retailer independently procuring inventory in the ex-ante stage in response to forecasted demand and anticipated cooperative recourse action of all retailers in the system. The graph framework clarifies the modeling connection between problems in a taxonomy of decentralized inventory distribution models. This unifying perspective links the past work and shades light on future research directions. In the last work -- chapter 4, we examine and recast the biform games modeling framework as two-stage stochastic programming with recourse. Biform games modeling framework addresses two-stage games with competitive first stage and cooperative second stage without ex-ante agreement on profit sharing scheme. The two-stage stochastic programming view of biform games is demonstrated on examples from all the known examples regarding operational decision problems of competing firms from the literature. It allows an “old” mathematical methodology to showcase its versatility in modeling combined competitive and cooperative game options. In short, this dissertation provides important insights, clarifications, and strategic limitations regarding collaborations in decentralized distribution system.
    • Gamma-ray Imaging Diagnostic for Inertial Confinement Fusion

      Barber, Herbert B.; Furenlid, Lars R.; Lemieux, Daniel; Grim, Gary P.; Sasian, Jose (The University of Arizona., 2018)
      In Livermore California at the Lawrence Livermore National Laboratory exists the National Ignition Facility (NIF). The NIF’s goal is to study high-density high-temperature plasmas and try and reach thermalnuclear fusion by a method known as Inertial Confinement Fusion (ICF). This occurs when 192 UV lasers interact with the inner walls of a gold cylinder, known as a hohlraum, and produce X-rays. Inside the hohlraum consists a capsule filled with deuterium and tritium. The X-rays ablate the outer plastic shell causing an inward shockwave to compress the D-T fuel to high density and undergo nuclear fusion. The fusion reaction creates 14.1 MeV neutrons that can interact with the carbon 12 of the plastic outer shell producing 4.44 MeV gammas from 12C(n,n’γ)12C reactions. This dissertation examines and produces a prototype system to image these 4.44 MeV gammas. This is a valuable diagnostic system that can characterize the symmetry of the ablated surface, which gives information as to how symmetrically the capsule is imploding. A prototype Gamma-Ray Imaging system (GRI) was built and tested at two large facilities. The first is another ICF facility that implodes capsules but at a much lower yield. These capsules produced X-rays in the ~300-400 keV range that were successfully imaged using the GRI system. The second facility is the High Intensity Gamma Source (HIGS) at Duke University that uses a free electron laser Compton scattered off a relativistic electron packet to produce a 4.7 MeV gamma beam. A number of radiograph shadow targets were placed in the 32 mm wide gamma beam and imaged by the GRI system. The results of these two test are discussed in this dissertation. The GRI system along with the Neutron Imaging System, and other diagnostics systems, are intended to compliment each other and provide useful information that can be used to design future capsules or diagnose poor implosions. This will help NIF achieve its goal of thermonuclear fusion.
    • Gamma-ray imaging probes.

      Bartels, Peter; Wild, Walter James. (The University of Arizona., 1988)
      External nuclear medicine diagnostic imaging of early primary and metastatic lung cancer tumors is difficult due to the poor sensitivity and resolution of existing gamma cameras. Nonimaging counting detectors used for internal tumor detection give ambiguous results because distant background variations are difficult to discriminate from neighboring tumor sites. This suggests that an internal imaging nuclear medicine probe, particularly an esophageal probe, may be advantageously used to detect small tumors because of the ability to discriminate against background variations and the capability to get close to sites neighboring the esophagus. The design, theory of operation, preliminary bench tests, characterization of noise behavior and optimization of such an imaging probe is the central theme of this work. The central concept lies in the representation of the aperture shell by a sequence of binary digits. This, coupled with the mode of operation which is data encoding within an axial slice of space, leads to the fundamental imaging equation in which the coding operation is conveniently described by a circulant matrix operator. The coding/decoding process is a classic coded-aperture problem, and various estimators to achieve decoding are discussed. Some estimators require a priori information about the object (or object class) being imaged; the only unbiased estimator that does not impose this requirement is the simple inverse-matrix operator. The effects of noise on the estimate (or reconstruction) is discussed for general noise models and various codes/decoding operators. The choice of an optimal aperture for detector count times of clinical relevance is examined using a statistical class-separability formalism.
    • Gamma-ray lines from asymmetric supernovae

      Pinto, Philip A.; Hungerford, Aimee L. (The University of Arizona., 2004)
      High energy emission from supernovae provide a direct window into the quantity and distribution of radioactive elements produced in these explosions. Combining supernova explosion calculations with 3D Monte Carlo gamma-ray transport, I have studied the effect mixing and asymmetries have on the hard X-ray and gamma-ray spectra. Two types of asymmetries (bipolar and unipolar) are investigated, the parameters of which are motivated by the most recent findings from multi-dimensional core-collapse supernova simulations. These bipolar and unipolar asymmetries are imposed artificially on 1-dimensional stellar progenitor structures and their evolution is followed using a 3-dimensional smoothed particle hydrodynamics (SPH) code. Global asymmetries in the explosion enhance the outward mixing of heavy elements such as 56Ni, reducing the observable emergence time for the hard X-ray continuum and gamma-ray line emission over that of symmetrically mixed models. The details of the velocity asymmetry lead to very different nickel distributions in the outer envelope. The high energy spectra resulting from these models predict an angular variation for the correspondence between the emergence time of the hard X-ray continuum and the broadening of the gamma-line profiles. The unipolar explosion models, in particular, demonstrate that redshifted gamma-ray line profiles are attainable at epochs where gamma-ray emission arises predominantly from the outer extent of the nickel distribution. The departure from a symmetric explosion scenario manifests itself most clearly in the extended nickel, making gamma-ray line observations an ideal probe of the initial explosion asymmetry.
    • Garcilaso en Italia: arte y política en la lírica del "Príncipe de la poesía española"

      Kinkade, Richard P.; Celaya Bustamante, Gaston A.; Fiore, Robert L.; Chuffe, Eliud; Kinkade, Richard P. (The University of Arizona., 2011)
      Este estudio analiza el contenido político en la poesía lírico-amorosa del poeta Garcilaso de la Vega y las repercusiones que ha tenido en el desarrollo y evolución de la literatura y la cultura del Siglo de oro español. En esta investigación se demuestra que existen motivaciones políticas específicas en el discurso lírico de Garcilaso, poeta considerado como el más amoroso, emotivo y sincero del Renacimiento español.La aproximación analítica aquí propuesta obedece al hecho de que la crítica tradicional ha dejado de lado el reconocimiento de las implicaciones que la poesía de Garcilaso ha tenido, en términos de lo político, en este período histórico-literario. Los criterios tradicionales generales en torno a los poemas de Garcilaso han señalado que sus poemas mejores logrados han sido aquellos en donde el poeta expresa sus más profundos, emotivos y sinceros sentimientos por su dama.Uno de los cometidos de este estudio consiste en demostrar que el valor de la poesía de Garcilaso no ha sido apreciado a cabalidad debido a la utilización del criterio de sinceridad para aproximarse a ella. Asimismo, el objetivo principal de este trabajo es establecer que mediante el reconocimiento del factor político en su poesía, así como la descripción y las formas en que es presentado, es posible revalorar la trascendencia que Garcilaso tuvo dentro del contexto de la evolución de la poesía española de los siglos XVI y XVII.
    • GARNET-ORTHOPYROXENE EQUILIBRIA IN THE FMAS SYSTEM: EXPERIMENTAL AND THEORETICAL STUDIES, AND GEOLOGICAL APPLICATIONS (GEOTHERMOMETRY, GEOBAROMETRY).

      Ganguly, J.; LEE, HAN YEANG.; Damon, P.; Drake, M.; Eastoe, C.; Ruiz, J. (The University of Arizona., 1986)
      Equilibrium relations between garnet and orthopyroxene have been investigated by reversal experiments in the range of 20-45Kb and 975-1400°C in the FeO-MgO-Al₂O₃-SiO₂(FMAS) system. The Fe-Mg exchange reaction seems to have little or no compositional dependence at these conditions. The experimental results can be fitted adequately by the linear relation: ln K(D) = 2243/T°K - 0.9522 at 25Kb where K(D) = (X(Fe)/X(Mg))ᴳᵗ/(X(Fe)/X(Mg))ᴼᵖˣ. Combination of the available data for the mixing properties of garnet and V° for the Fe-Mg exchange reaction with the above experimental results yields the following geothermometric expression for the common natural assemblages that can be represented essentially within the system CaO-MnO-FeO-MgO-Al₂O₃-SiO₂. T°K = (1968 + 11P(Kb) + 1510(X(Ca)+X(Mn))ᴳᵗ)/(ln K(D) + 0.9522). The stability field of pyrope+quartz, defined by the reaction pryope+quartz=opx+sill, has been calculated as a function of P,T,X(Fe)ᴳᵗ in the FMAS system using the reversal experimental data of Perkins (1983) in the MAS system, and the present data on K(D)(Fe-Mg) between garnet and orthopyroxene. This reaction is very sensitive to pressure and compositional effects. Combination of P,T conditions for the garnet stability and that defined by (K(D)(Fe-Mg))ᴳᵗ⁻ᴼᵖˣ yields a simultaneous solution for both P and T of equilibration of garnet and orthopyroxene in the presence of Al₂SiO₅ and SiO₂. The effect of FeO on Al₂O₃ solubility in orthopyroxene in equilibrium with garnet has been determined experimentally at several pressures at 975 and 1200°C. These data have been modeled to develop a thermodynamic method for the calculation of Al₂O₃ in orthopyroxene as a function of P,T and composition. The Al₂O₃ isopleths have moderate P-T slopes, and provide virtually the only means of determining the pressure of mantle derived rocks.
    • Garnet: A graph-based octilinear mixed-signal Steiner tree routing system

      Carothers, Jo Dale; Newbould, Rexford D. (The University of Arizona., 2004)
      A compatibility graph-based, general area router for integrated circuit (IC) designs is presented. The highly flexible constraint system allows a number of modern and mixed-signal routing requirements to be handled, even for a large number of nets. The IC router can efficiently construct near-minimal Steiner trees for multi-terminal nets in both classical rectilinear, or Manhattan, geometry as well as octilinear geometries. These Steiner trees can be constructed around blockages, and in the presence of obstacles such as other nets. A method for routing trees through weighted areas is also introduced. The routing system can predict congested routing areas before routing is performed, and appropriately weight congested areas in order to reduce net congestion. Finally, a fast crosstalk violation checker can run alongside the routing engine. Each portion of the router is bounded by O(n log(n)) runtime, or less, making the entire routing process bounded by the same runtime. The system thus scales well to handle a very large number of exact routes in a fully mixed-signal aware engine, in either rectilinear or newly-introduced octilinear geometries.
    • THE GAS COMPOSITION AND VERTICAL CLOUD STRUCTURE OF JUPITER'S TROPOSPHERE DERIVED FROM FIVE MICRON SPECTROSCOPIC OBSERVATIONS.

      Larson, Harold P.; BJORAKER, GORDON LEE. (The University of Arizona., 1985)
      Spectroscopic observations of Jupiter at 5 microns were analyzed in order to derive the gas composition and vertical cloud structure for the 2 to 6 bar portion of the Jovian troposphere. Two infrared data sets were used. The first one consisted of high spectral resolution observations of Jupiter between -40 and +40 latitude acquired from the Kuiper Airborne Observatory. The second data set consisted of high spatial resolution measurements of Jupiter's belts and zones using the Voyager 1 Infrared Interferometer Spectrometer and Radiometer (IRIS). A spectrum synthesis program was used to calculate the emergent radiance from Jupiter's atmosphere between 1800 and 2250 cm⁻¹. The temperature-pressure profile and spectroscopic line parameters for seven molecules were specified. Gas mole fractions were adjusted until the calculated spectrum agreed with the observations within error limits. Molecular hydrogen is an important absorber at 5 microns. Absorption coefficients were generated as functions of frequency and temperature. Unit optical depth at 5 microns due to H₂ takes place between 5 and 7 bars in Jupiter's atmosphere. The airborne spectrum was used to infer the mole fractions of NH₃, PH₃, CH₄, CH₃D, CO, GeH₄, and H₂O for the 2 to 6 bar portion of Jupiter's troposphere. Elemental ratios were calculated and compared with model predictions. The N/H ratio is 1.5 ± 0.2 times the Lambert (1978) values for the Sun. The P/H ratio is 1.0 ± 0.1 times the Anders and Ebihara (1982) meteoritic value. The C/H ratio is 3.6 ± 0.7 times solar. The D/H ratio is 1.2 x 10⁻⁵. The mole fractions of CO and GeH₄ are (1.0 ± 0.3) x 10⁻⁹ and (7.0 ± 4) x 10⁻¹⁰, respectively. The mole fraction of H₂O was found to be the same in Jupiter's belts and zones, except for a factor of 2 depletion in the North Equatorial Belt Hot Spots. The H₂O mole fraction for the 2 to 4 bar region is (4.0 ± 1.0) x 10⁻⁶. This value increases with depth to (3.0 ± 2.0) x 10⁻⁵ at 6 bars. The H₂O ice cloud would be located near 2 bars. The O/H ratio at P = 6 bars is depleted by a factor of 40 with respect to the Sun. The thermal emission signature at 5 microns of optically thick clouds was used to develop a one-dimensional cloud model for Jupiter. The belt-to-zone variation in 5 micron flux is attributed to a massive cloud layer at 2 bars, T = 200 K, composed of NH₄SH and H₂O ice. A lower cloud at 5 bars is inconsistent with the IRIS data. Continuum absorption by H₂ determines the penetration depth at 5 microns, not a lower cloud layer.
    • Gas permeability changes in rock salt during deformation.

      Daemen, J.; Stormont, John Charles.; Farmer, I.; Harpalani, S.; Desai, C.; Kiousis, P. (The University of Arizona., 1990)
      A laboratory, field and numerical study of the changes in gas permeability which rock salt experiences during deformation is given. The laboratory tests involves gas permeability and porosity measurements coincident with hydrostatic and triaxial quasi-static, stress-rate controlled compression tests. The permeability and porosity of the as-received samples decrease significantly as a result of hydrostatic loading. These changes are largely irreversible, and are believed to "heal" or return the rock to a condition comparable to its undisturbed state. Deviatoric loading induces a dramatic change in pore structure. The permeability can increase more than 5 orders of magnitude over the initial (healed) state as the samples are loaded. The gas permeability changes are consistent with flow paths initially developing along the grain boundaries and then along axial secondary tensile cracks. The results from two sets of in situ gas permeability measurements from the underground workings of the WIPP Facility are given. The results consistently indicate that there is no measurable gas permeability prior to disturbing the rock by excavation. In the immediate vicinity of an excavation, the gas permeability can be 5 orders of magnitude greater than the undisturbed permeability. A numerical procedure to predict the in situ permeability is developed based on the results of the laboratory tests. The stress and strain fields surrounding excavations in rock salt, predicted with an elastoplastic model, are used in a model of gas permeability based on the equivalent channel model. The zone of the gas permeable rock is predicted well, but the magnitude of the gas permeability is underpredicted very near excavations. The gas permeability which develops in situ is principally a result of flow along dilated grain boundaries.
    • Gas Phase Etching of Silicon Dioxide Films

      Muscat, Anthony J.; Montano, Gerardo; Muscat, Anthony J.; Shadman, Farhang; Ogden, Kimberly (The University of Arizona., 2006)
      The gas phase etching of thermal silicon dioxide films was investigated with in situ Fourier Transformed Infrared Spectroscopy (FTIR) and ex situ X-ray Photoelectron Spectroscopy (XPS). The initiation process, the bulk etching of the oxide, and the termination mechanism were characterized as a function of reactant concentration, temperature, and pressure. The experiments were carried out in a custom made vessel with a gas panel and a data acquisition and control system (DA&C) capable of lowering flow and pressure disturbances originated by reactant introduction. The FTIR technique used to monitor the reaction in real time allowed distinguishing reactions that initiated in a gas/solid regime from reactions that started in a gas/liquid/solid regime. This study was focused on the gas/solid initiation process in order to expand the general assumption in published works that a condensed layer is previously required to initiate and sustain the reaction. It was found in this investigation that, depending on the experimental parameters, the water layer is not always a requisite for the initiation of the reaction but a consequence of the etching process. The FTIR data also showed the role in the initiation process of gas phase heterogeneous associated species, specifically (HF)H₂O and (HF)₂H₂O. After the initiation period, the experimental conditions determined the amount of water present on the surface of the sample, which in turn determined the local environment of the reaction and by extension the etching species. Reactions developing in a gas/solid regime were found to be slow, with etching rates of less than 1 °A/sec. Contrarily, reactions taking place in a gas/liquid/solid regime reached etching rates of 100 °A/sec, a maximum value determined by transport limitations. The condensed layer was found to be especially sensitive to temperature since a variation of 15 ° C changed the local environment from gas/liquid/solid to gas/solid. Finally, it was corroborated through the XPS analysis that the removal process in the gas phase leaves the silicon surfaces with high fluorine and oxygen concentrations in the form of SiFₓ and SiOH.
    • Gas Phase Structural Studies of Peptide Fragment Ions: Structural Insights into Mass Spectrometry Fragmentation Mechanisms

      Wysocki, Vicki H.; Gucinski, Ashley Christine; Aspinwall, Craig A.; Pemberton, Jeanne; Wysocki, Vicki H. (The University of Arizona., 2011)
      This dissertation presents extensive structural studies of gas-phase peptide fragment ions, with a specific focus on b₂⁺ ions. Fragment ion structures can provide important insights into peptide fragmentation mechanisms. Based on the structures formed, information about the preference of competing b ion formation pathways can be obtained. b₂⁺ ion structures are of interest because of their large relative abundances in MS/MS spectra, which are difficult to predict. Prior to this work, only a few b₂⁺ ion structures were determined; these systems featured only aliphatic residues and all formed oxazolones. The work presented herein examines the influence of basic, acidic, and backbone-attached sidechains on peptide fragmentation mechanisms, as revealed by the resulting b₂⁺ fragment ion structure(s) formed. Specifically, the structures of several histidine, aspartic acid, and proline-containing b₂⁺ ions are determined by using action IRMPD spectroscopy, fragment ion HDX, and DFT calculations. The structures of a series of histidine analogue-containing b₂⁺ ions reveal that the location and availability of the pi-nitrogen is essential for diketopiperazine formation. The histidine sidechain bulk or strain interferes with the complete trans-cis isomerization required for diketopiperazine formation, so the oxazolone structure is also present. Xxx- Pro b₂⁺ ions favor oxazolone formation with aliphatic N-terminal residues. HP favors the diketopiperazine, combining the histidine effect and the proline cis conformation propensity. For Xxx-Asp b₂⁺ ions, aspartic acid significantly influences b₂⁺ ion structure only with an N-terminal histidine or lysine; both HD and KD form a mixture of oxazolone, anhydride, and diketopiperazine structures, presenting the first spectroscopic evidence for the anhydride b₂⁺ion structure. The HA and AH b₂⁺ ions feature the same structures, but HP and PH do not, showing that residue position matters. Additionally, while relative intensities and HDX rates featured some fluctuation, peptide precursor composition differences did not alter the mixture of b₂⁺ ion structures formed for a given b₂⁺ ion. To complement existing gas-phase structural methods, the utility of a new technique, QCID-HDX-IRMPD, was applied to m/z 552.28 from YAGFL-OH. Both the standard b₅⁺ fragment ion and an isobaric non-C-terminal water loss ion are present. Without separation of these isomers, MS/MS spectral interpretation would be complicated.
    • Gas Phase Structures and Molecular Constants of Dimers and Molecules Determined using Microwave Spectroscopy

      Kukolich, Stephen G.; Daly, Adam Michael; Kukolich, Stephen G.; Sanov, Andre; Enemark, John H.; Lichtenberger, Dennis L.; Ziurys, Lucy M. (The University of Arizona., 2010)
      Gas phase structures and other molecular parameters have been investigated for several molecules and dimers using pulsed beam Fourier Transform Microwave Spectroscopy. An automated control system has been designed and implemented for the microwave spectrometer that has allowed a systematic observation of the microwave spectrum for many molecules. The theoretical models that are available to the gas phase structural chemist, density functional theory and ab-initio methods, are described with detailed comparisons to experimental results. Experimental data was generated for systems involving hydrogen bonded dimers, organic molecules, inorganic molecules and organometallic molecules. Rotational constants and quadrupole coupling constants were determined using the microwave spectra. This data and isotopic investigations have been used to determine key structural parameters and molecular properties.
    • Gas phase surface preparation and activation of silicon using ultraviolet activated chemistries

      Muscat, Anthony J.; Finstad, Casey Charles (The University of Arizona., 2004)
      Microelectronic devices have been scaled down to the point where lateral dimensions are on the order of a hundred atoms and a film thicknesses might be less than ten atoms. This makes surface preparation an increasingly important part of the fabrication process. The atoms and molecules terminating surfaces between processing steps are now a relatively large fraction of the overall film thickness. These terminating monolayers have to function as passivation layers, diffusion barriers, and seed layers for subsequent thin film depositions. This work demonstrates that precise control of the atoms and molecules on a silicon surface can be achieved using gas phase processes. The Research Cluster Apparatus (RCA) was built with a reactor for oxide removal using hydrofluoric acid and water vapor (HF/vapor), and a reactor for the removal of metallic and organic contaminates using ultraviolet activated chlorine gas (UV-Cl₂). Both reactors were integrated via high vacuum with a surface analysis chamber so samples could be characterized without atmospheric exposure. The capabilities of the system were demonstrated by using an HF/vapor (100 Torr, 27°C, 200 s) and UV-Cl₂ (10 Torr Cl₂, 90°C, 15 min) sequence to remove a mixed oxide/fluorocarbon residue, characteristic of contamination generated by reactive ion etching (RIE). To demonstrate the metals removal capability, oxidized copper was cleaned from silicon. The UV-Cl₂ chemistry leaves the surface terminated with chlorine atoms, rather than hydrogen, promoting a deposition reaction with ammonia (1-1000 Torr, 75°C, 5-60 min) to produce a surface terminated with up to 0.3 monolayers of surface amine groups, as measured by XPS. The highly polar N-H bonds of surface amines can be used as a seed layer to promote nucleation of high-k dielectric films deposited on silicon using atomic layer deposition (ALD). To enhance the deposition of the amines, photolysis (λ < 217 nm) of gas phase ammonia (UV-NH₃) generated NH₂ photofragments that reacted with hydrogen terminated Si(100), saturating at up to 1.7 ML (10 Torr NH₃, 75°C, 35 mW/cm²). These processes help enable further miniaturization by adding another mechanism for atomic-level manipulation of surface properties to the nanotechnology toolbox.
    • Gas slippage and matrix shrinkage effects on permeability of coal.

      Chen, Guoliang.; Harpalani, S.; Kemeny, John; Kim, Y. C.; Lever, Paul; Poulton, Mary (The University of Arizona., 1994)
      The permeability of coal is one of the most important basic parameters in the simulation of gas transport in coalbeds and in the evaluation of the commercial feasibility of coalbed gas reservoirs. However, the permeability of coal and its variation as gas is produced are still not well understood. Unlike that in conventional gas reservoirs, the gas permeability of a coalbed is influenced during gas production, not only by the simultaneous changes in effective stress and gas slippage, but also by the matrix shrinkage associated with gas desorption. The objective of this work was to investigate experimentally the matrix shrinkage and gas slippage effects on the permeability of coal. Since these effects occur simultaneously during gas production, a theory to separate these effects was first developed. This dissertation presents a technique to conduct laboratory experiments to estimate their individual contribution, along with the results obtained for quantitative relationships of the gas slippage and matrix shrinkage effects with gas pressure. The results show that the total permeability of the coal sample increased dramatically due to gas slippage and matrix shrinkage effects with decrease in pressure. When the gas pressure is above 250 psi, the effect of matrix shrinkage dominates. As gas pressure falls below 250 psi, both the gas slippage and matrix shrinkage effects play important role in influencing the permeability. Finally, the change in permeability of coal sample resulting from gas slippage was found to be proportional to the reciprocal of the gas pressure. The change in permeability due to matrix shrinkage was found to be linearly proportional to the volumetric strain associated with desorption. Since the latter is linearly proportional to the amount of gas desorbed, the change in permeability is a linear function of the amount of desorbing gas.
    • Gas trapping in amorphous water ice: A theoretical and experimental approach

      Lunine, Jonathan I.; Dai, Wei (The University of Arizona., 2000)
      The solar system began with the collapse of a dense molecular cloud, which is rich in atoms, dust grains and diverse molecules. The complexity of different physical and chemical processes which happened during the formation of the early solar system constitute a major topic within our scientific community, even though a complete model of the solar nebula including all such processes has not been constructed. This thesis deals with some of these chemical and physical processes and consists of two phases. In the first phase of my work, I have studied the heating of water-ice grains during infall into the solar nebula from the surrounding collapsing cloud. The investigations in this phase extend previous studies (Lunine et al., 1991) in two aspects. Firstly, we revise the previous grain heating model. The calculations for large fluffy grains (up to 10μm) are conducted. Secondly, we explicitly incorporate terms associated with various exothermic and endothermic reactions which contribute to the thermal evolution of the grains in our computation. By tracking the threshold temperatures reached as a function of grain size, density and infall velocity, we are able to quantify the evolution of infalling interstellar grains. Once the volatiles were brought in by the ice grains, codeposition of diversed volatiles on the surface of refractory grains happened in the cold solar nebula region. Disk dynamical evolution leads to a background temperature below 50K at distance beyond 20AU. Studies have shown that amorphous water ice forms at this temperature range. Amorphous ice can volumetrically absorbs a large amount of volatiles. My work in the second phase consists of investigations of amorphous water ice, especially its property of trapping various volatiles under conditions well outside the stability field of the condensed phases of the volatiles. A statistical thermodynamical model has been established. It is used to predict fractional abundances of trapped volatiles in different temperature and pressure conditions. Our investigations involve both theoretical and experimental studies.
    • Gas, Dust, and Quenching of Dusty Galaxies in the Early Universe

      Marrone, Daniel; Spilker, Justin Scott; Marrone, Daniel; Besla, Gurtina; Fan, Xiaohui; Marrone, Daniel; Shirley, Yancy; Weiner, Benjamin (The University of Arizona., 2017)
      In this dissertation, I study various aspects related to the gas and star formation in dusty star-forming galaxies in the distant universe. My dissertation is heavily based on observations made by the Atacama Large Millimeter/submillimeter Array (ALMA), observing a sample of gravitationally lensed high-redshift dusty galaxies originally discovered by the South Pole Telescope (SPT). In addition to the introductions to the individual chapters, Chapter 1 provides a broader background to the study of these objects and places them in the overall context of galaxy evolution. In Chapter 2 I describe a technique designed to search for faint molecular lines in the spectrum of high-redshift dusty galaxies. The brightest molecular lines in the spectra of these objects are due to carbon monoxide, but a host of other species are present in the interstellar media. These other molecules trace gas of a wide range of temperatures and densities, but are generally ten times fainter than the brighter CO lines. I detected several other molecular lines, and used them to characterize the conditions of the interstellar gas. This work was published in Spilker et al. (2014). In Chapter 3, I describe a technique for modeling the effects of gravitational lensing which is optimized for data from interferometers such as ALMA. Using these models and data for a large sample of objects from ALMA, I studied the intrinsic properties of the sample such as the source sizes and luminosities. I used these intrinsic properties to revisit topics from the literature which benefit from the additional size information I determined. This work was published in Spilker et al. (2016). In Chapter 4, I use the modeling technique I developed to investigate the relationship between the star formation and the cold molecular gas from which stars form in two objects selected from the SPT sample. Using the models of the source, I was able to determine the mass of molecular gas in these objects using several independent methods. I found that the molecular gas reservoirs are more extended than the star formation, which has implications for the "law'" used as a prescription for star formation in many simulations. This work was published in Spilker et al. (2015). Chapter 5 describes ongoing work to determine what will happen to the dusty galaxies after their active phase of star formation ends, and what processes dominate that change. Since their discovery, these dusty galaxies have been thought to be progenitors of early quiescent galaxies. In this chapter, I show observations of a massive molecular outflow from a single object, which may be responsible for removing the raw material for star formation. Finally, in Chapter 6, I end with a summary of this dissertation.