Now showing items 15247-15266 of 20330

    • Quantifiable Changes in Nuclear Chromatin Structure of Oral Epithelium Based on Smoking Pack-Years in the Progression of Oral Squamous Cell Carcinoma (OSCC)

      Calhoun, Elizabeth; Navarrete, Jorge Ricardo; Alberts, David S.; Jacobs, Elizabeth; Julie, Bauman E. (The University of Arizona., 2021)
      The process of oncogenesis in the oral mucosa to oral squamous cell carcinoma (OSCC) initiation by tobacco smoke has been studied extensively worldwide. However, many questions remain. Across many fields, clinical and epidemiological data has shown that there is an association between tobacco and the development of OSCC and its oncogenic pathways1. Different studies have shown that tobacco can cause abnormal expression of key regulatory proteins, such as p53, MGMT, P13K, GLUT-1, p16, DAPK, along with other regulatory genes in the oral epithelium associated with the incidence of OSCC2. Despite the advancements in preventive and therapeutic treatment methods, there still remains a delay in OSCC diagnosis that contributes to predominantly elevated morbidity and mortality2,3. The majority of OSCC cases are identified in advanced clinical stages, such as stage III or IV. After primary treatment, recurrences of OSCC are found in more than half of patients, with 80% of cases found within the first 2 years following primary treatment3. Additionally, the 5-year survival rate is still lower than 50%, despite preventative and therapeutic strategies3. These factors indicate a serious public health issue. Currently, histological investigation is considered the “gold standard” of OSCC diagnosis. However, recent studies are now looking at the potential of using saliva, or a “liquid biopsy”, to detect biomarkers in the bodily fluids of OSCC patients. While promising, it is important to point out that these techniques are still dependent on the collection of saliva and our ability to detect cytokines, DNA molecules, RNA molecules, and circulating biomarkers. There is another promising method to detect biomarkers in the early diagnosis of OSCC patients: karyometry. Karyometry provides a process to identify a quantifiable integrating biomarker by looking at small nuclear changes that cannot be detected by the trained eye. A karyometric analysis may give us useful information regarding the early diagnosis of OSCC and disease progression. Our primary objective is to access the functionality of karyometric analysis in identifying and integrating biomarkers on the progression of OSCC. We will be running karyometric analysis on the oral epithelium to see the impact of smoking tobacco on the development of carcinogenesis to OSCC. It is our intent to show the several promising clinical uses karyometry and how it can be used in the detection and management of OSCC. Karyometry is painless, accessible, and low-cost source of helpful data for diagnostic and prognostic biomarker detection. It is worth exploring the potential benefits karyometry may have in cancer prevention.
    • Quantification and locality.

      Basilico, David Anthony.; Barss, Andy; Langendoen, Terry; Jelinek, Eloise (The University of Arizona., 1993)
      This dissertation develops a transformational theory of scope which is based not on the position to which an entire quantificational noun phrase (QNP) can move and adjoin but on the position and to which a quantificational determiner can move and adjoin. Following Heim (1982), a tripartite representation for sentences containing QNPs is adopted in which quantificational determiners move out of their containing noun phrases and adjoin to the sentence node at the level of Logical Form (LF). By utilizing this type of representation, asymmetries between the movement possibilities of a phrase and scope possibilities of a phrase can be captured. This dissertation argues that movement of an operator is free but constrained by the operator acquiring the selection index of the phrase which it binds. The selection index is percolated up the tree in a series of local relationships (government, specifier/head and X-Bar). This index percolation is dependent on the ability of a syntactic head to acquire an index. The necessity of this index percolation approach is demonstrated in the first chapter, which investigates the phenomenon of unselective binding between an adverbial operator and indefinite in restrictive 'if/when' clauses. It shows that this relationship is sensitive to some syntactic islands but not others. It demonstrates that the index percolation approach is the best way to capture the selective island sensitivities of this phenomenon. Additional motivation for this account is given in chapter two, which deals with internally headed relative clauses (IHRCs). Several parallels between IHRCs and restrictive 'if/when' clauses are noted. It shows that the binding of the internal head by the determiner associated with the IHRC is similar to the binding of an indefinite by an adverbial operator. The next two chapters treat the phenomenon of partial Wh-movement. These chapters further show the application of the index percolation account because they argue that the relationships noted above between an adverbial operator and indefinite and operator and internal head are analogous to the relationship between a partially moved WH-Phrase and the sentence initial scope marker. In chapter six, the scope of quantified possessive phrases in English is examined. This is a case where movement of a phrase and scope of a phrase sharply differ. The approach where the determiner of the possessive is moved alone, with index percolation from the phrase in the specifier position to the moved determiner, is shown to best handle these cases.
    • Quantification and Tracking of Transplanted Satellite Cells

      Allen, Ronald E.; Elster, Jennifer Leith; Allen, Ronald E.; Lynch, Ronald M.; Riley, Mark R.; Rhoads, Robert P.; Williams, Stuart K. (The University of Arizona., 2009)
      Satellite cells are adult stem cells that contribute to hypertrophy and repair in muscles. It is hypothesized that in muscular dystrophy, the satellite cells population is depleted at a very early age, due to repeated muscle damage and repair. Satellite cell transplantation is a potentially useful therapy for muscle diseases, but the lack of an efficient delivery system has hindered its application. The presented work focuses on two specific aims that address the need for more effective cell delivery methods for cell-based therapy. In Specific Aim 1 enhanced tissue culture techniques, such as heat stress, are used to increase cell survival in satellite cell transplantation studies. Also addressed within this specific aim are methods to label and evaluate performance using real-time PCR techniques.Although much work remains to enhancing the viability of in vitro expanded myoblasts derived from satellite cells, a second important hurdle is the systemic delivery of satellite cells to multiple sites (all muscles, in the case of muscular dystrophies). In vitro and in vivo experiments are being undertaken to explore the physiological role of cell signaling systems involved in directed migration and to determine if these chemokine and growth factors can be manipulated to enhance efficacy of cell-based therapies involving skeletal muscle satellite cells. Specific Aim 2 addresses migration of satellite cells to sites of injury and methods to track transplanted cells within the host. Presented here is the use of FAST SPECT II imaging of 111-Indium oxine radiolabeled satellite cells. The long lifetime of 111-indium oxine and the ability to quantify label using FAST SPECT imaging techniques make this technique ideal for in-vivo tracking of transplanted satellite cells for week long studies. Without in-vivo imaging techniques cell fate studies require sequential animal sacrifice with histological sectioning. This not only increases the number of animals used but also adds a significant inter-animal variability to their assessment. The determination of cell fate after transplantation will have a major impact on cell therapy for treatment of muscle disease as well as other stem cell therapies.
    • Quantification of aquifer recharge distribution using environmental isotopes and regional hydrochemistry

      Adar, Eilon.; Neuman, Shlomo P.; Warrick, Arthur W.; Simpson, Eugene S.; Woolhiser, David A.; Matlock, William G.; Long, Austin (The University of Arizona., 1984)
      A mathematical model is proposed to estimate annual recharge rates from various sources into an aquifer, based on chemical and isotopic data. The aquifer is divided into mixing cells. For each mixing cell, annual mass balance equations are written which express the conservation of water, dissolved chemicals, and stable environmental isotopes. These equations are solved simultaneously for unknown recharge rates by quadratic programming. A similar approach was used earlier to estimate inflows into a river reach which acts as a single mixing cell. The sensitivity of the model to input errors is analyzed by applying it to synthetic data corrupted by artificial noise. The ability of the model to deal with real data is illustrated by applying it to the semiarid Aravaipa basin in southern Arizona.

      FLEENOR, WILLIAM ALFORD. (The University of Arizona., 1982)
      A quantitative competitive binding "triple sandwich" enzyme immunoassay was used to evaluate pathogen/class-specific antibody responses in Holstein-Friesian calves vaccinated against Clostridium perfringens B-toxin at various ages postpartum. Vaccination of dams at six weeks and again at two weeks prepartum increased pathogen-specific antibody levels in their colostrum and respective calf's serum. Calves initially vaccinated at three days produced both a primary and secondary pathogen-specific antibody response, whereas calves initially vaccinated at 12 and 21 days produced only secondary responses. Maternally-derived antibodies were found to suppress neonatal antibody production following primary immunization. They were also found to influence secondary humoral immune responses, although in a diminished capacity. Pathogen-specific IgG and IgM concentrations in dams' sera and colostra were found related to subsequent pathogen-specific IgG and IgM neonatal serum concentrations. Only pathogen-specific IgA in dams' colostra was correlated to neonatal levels, possibly owing to a different origin and role of this immunoglobulin class. All class-specific colostral immunoglobulin levels were related to subsequent neonatal concentrations. Based on results from this experiment, it is recommended that calves be vaccinated at three days postpartum with a booster administered at 63 days.

      Kania, Joanne Gail, 1937- (The University of Arizona., 1972)
    • Quantification of motor neuron adaptation to sustained and intermittent stimulation.

      Stuart, Douglas G.; Spielmann, John Michael.; Bloedel, James R.; Gruener, Raphael P.; Hamm, Thomas M.; Levine, Richard B. (The University of Arizona., 1991)
      In deeply anesthetized mammals, as typified by the adult cat, there is limited evidence that the firing-rate response of spinal motor neurons to sustained simulation usually features a progressive reduction in firing rate, termed late adaptation, that begins 1-2 s after the onset of sustained stimulation. The fullest description of late adaptation has been provided by Kernell & Monster (1982a,b) who evoked repetitive firing in spiral motor neurons of deeply anesthetized cats by the conventional procedure of an intracellular injection of a sustained depolarizing current. The main purpose of the present study was to extend on the results of their work. The first hypothesis tested was: Sustained depolarizing extracellular stimulation of motor neurons is more effective in maintaining repetitive discharge than sustained depolarizing intracellular stimulation. Investigations pioneered by Kernell & Monster (1982a,b) tested the association between late adaptation and other type (size)-related properties of motor neurons. Such analyses are within the rubric of Henneman's (1957, 1977) Size Principle, one component of which proposes that the properties of motor neurons and the muscle fibers they innervate are tightly coupled. The second hypothesis was proposed to continue this inquiry. It stated that: Late adaptation (during both sustained and intermittent stimulation), and other discharge-related properties of motor neurons are associated with other type (size)-related properties of these cells and their motor units. For both hypotheses, there was an emphasis on providing a quantitative description of late-adaptation. In the present study, the duration of repetitive firing in response to sustained stimulation significantly exceeded that in the Kernell & Monster (1982a,b) study, thereby providing evidence in support of the first hypothesis. For sustained stimulation, significant associations were found between the time constant of late adaptation and three neuromechanical properties of the cell's motor unit: axonal conduction velocity; twitch contraction time; and, peak tetanic force. Similarly, significant associations were found between the peak firing rate and these neuromechanical properties for both sustained and intermittent stimulation. Significant associations were also found between the extent of between-train adaptation during intermittent stimulation and two of the neuromechanical properties: axonal conduction velocity and peak tetanic force. These results provided evidence in support of the second hypothesis. In summary, the present work has provided a new opening in the study of the active (firing) properties of motor neurons, by quantitating late adaptation during sustained stimulation, and between-train adaptation during intermittent stimulation. This information provides new insights into the fundamental properties of motor neurons and adds important new firing-rate parameters to the continuing evaluation of Henneman's Size Principle.
    • A quantificational theory of aspect for Chinese and English

      Langendoen, D. Terence; Chen, Jianzhou (The University of Arizona., 2001)
      To systematically express the concepts of aspectual primitives such as "boundedness", "dynamicity", "punctuality", this dissertation presents a theory of aspect in the approach of quantificational predicate logic. The theory (called "Quantificational Representation of Aspect", or QRA) is originated from temporal predicate logic, with the aid of the Reichenbach temporal theory (1947). First of all, an analogy is drawn between the boundaries (viz. the telicity property) of a situation and quantification over temporal variables. Among the temporal variables, t and i together specify two boundaries of a situation, while r (reference time) and s (speech time) provide further temporal information necessary for aspectual interpretations. The theory thus presents a predicate fitted out with four temporal arguments--- s, r, t, i, in addition to its syntactic argument(s). Meanwhile, the (logical) relations among these arguments render the precise interpretation of each aspectual category. For example, John kissed Mary, a perfective sentence with an activity verb, is expressed under QRA as "∃s∃r∃t∀iKISS(s, r, t, i, john, mary), r = t + i ∧ r ≤ s". QRA offers a stronger expressive power than the traditional aspectual theories based on definitions or typology (e.g. Comrie 1976 and Bybee et al. 1994). Additionally, this theory has the advantage of explicating certain temporal characteristics of aspects, for instance, quantification over intervals (i.e. successive moments) that temporal predicate logic (relating two moments in time) is unable to achieve.
    • A Quantified Approach to Tomato Plant Growth Status for Greenhouse Production in a Semi Arid Climate

      Giacomelli, Gene A.; Renda da Costa, Paula MR; Giacomelli, Gene A.; Giacomelli, Gene A.; Kubota, Chieri; Riley, Mark; Silvertooth, Jeff (The University of Arizona., 2007)
      Balancing plant growth between vegetative and reproductive status is crucial for producing high quality greenhouse tomatoes while maintaining high productivity in long crop production seasons. In the tomato industry, certain plant morphological characteristics are used to classify plant growth status as vegetative, reproductive or balanced. Each growth status has been associated with distinct greenhouse environments which reduce or enhance transpiration.The effect of different transpiration on vegetative, reproductive or balanced plant growth status as defined by a set of plant morphological characteristics was investigated. To validate the practical significance of such classification, growth status was quantified as the relationship between variations in morphological characteristics and the fresh weight distributed between reproductive and vegetative organs.Two electrical conductivity (EC) levels of the nutrient solution, high and standard EC, were combined with two potential transpiration environments, low and high potential transpiration. All treatment combinations were contrasted with a reference greenhouse environment similar to the industry standard.Electrical conductivity had the greatest effect on morphological characteristics which were reduced in size with high EC. For each EC level, the response decreased for increasing potential transpiration. Stem diameter had the greatest sensitivity to the different treatment combinations. For the standard EC and for the range of potential transpirations achieved, stem diameter varied within a relatively narrow range, close to the industry standard 'threshold' used to classify a balanced tomato plant. A reproductive plant growth status, as evaluated by a smaller value than this threshold, was observed only with high EC. No vegetative plants were produced within any potential transpiration or EC treatment combination.High EC decreased the cumulative total fresh weight production by the same magnitude for all potential transpirations. Potential transpiration had a minimal effect on the total fresh weight production or on its components. As a result, the fresh weight ratio between reproductive and vegetative plant organs was similar for most potential transpiration environments, regardless of variations in stem diameter. Therefore, within the range of potential transpiration environments achieved, the distinction between vegetative and reproductive growth status as an indicator of fresh weight distribution and fruit yields could not be quantitatively validated.
    • Quantifying Ecosystem Trajectories: Tree Growth Response to Biophysical Gradients and Disturbance

      Falk, Donald A.; Marshall, Laura; Leavitt, Steven W.; McDowell, Nathan G.; Moore, David J.; Trouet, Valerie M. (The University of Arizona., 2019)
      Disturbance and climate are important drivers of tree physiological functioning, community assemblages and trends in recruitment and species presence across time and space. Fire exclusion-driven changes to the disturbance regime of frequent fire-adapted forests of the southern Rocky Mountains, North America, followed by modern megafires has strongly influenced stand structure and led to density increases in many forest types. Recent decadal drought has led to widespread mortality of some tree species, exacerbated fire extent and effects, and contributed to insect outbreaks. With climate change ongoing, hotter and drier conditions and droughts are expected, leading to increased risk of widespread tree mortality and vegetation type change. Forest ecosystem changes result from compounding effects on individual tree establishment, growth, and survival, which leads to changes in stand structure and composition, and drives patterns appreciable at the broadest scale. Here I focus on tree-environment interactions in the context of disturbance and climate across three scales, from tree-stand, to stand-watershed, to forest-ecosystem. By working across scales we can observe how fine-scale tree responses to interact with the environment to create broad patterns. At the tree scale, I considered the influence of increased forest density on tradeoffs of water and nutrient limitation affecting growth and physiological functioning in old-growth ponderosa pine (Pinus ponderosa Douglas ex C. Lawson) (Appendix A). I identified a novel interaction in which lower leaf nitrogen in dense stands was associated with lower tree-ring growth yet higher carbon isotope discrimination, rather than the expected negative relationship between discrimination and density-driven water stress. Reduced leaf nitrogen likely limited photosynthetic capacity, resulting in discrimination values more decoupled from water stress than is expected in the Southern Rockies. At the stand level to watershed scale, I investigated climate-growth relationships and species distributions across a biophysical gradient in southwestern mixed-conifer forest (Appendix B). I used model selection to find how climate drivers of tree-ring growth varied by species, elevation, and aspect, and found differences were in accordance with relative species drought tolerance. I combined this with stand-level regeneration patterns to predict shifts in species dominance across the watershed. In the absence of fire, I found increased regeneration in pinyon pine (Pinus edulis Engelm.) at low elevations and white fir (Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.) at high elevations, while regeneration of ponderosa pine and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) decreased everywhere across the study area. At the ecosystem scale I used Forest Inventory and Analysis (FIA) data to derive the novel Community Mean Tolerance Index, based on relating species shade and drought tolerance to ecosystem changes and applied it to investigate demographic trends within and across forest types (Appendix C). With the index I mapped responses within and across forest ecosystems in the southern Rocky Mountains, and found areas at risk for vegetation type conversion to oak woodland following severe fire. Substantial shifts in mean drought and shade tolerance in tree regeneration was found in forest types that had exceeded their historic fire interval. Across forest types, drought tolerance in seedling groups increased at lower elevation sites, while shade tolerance increased at higher elevation sites. The difference in drought tolerance across demographic groups was significantly associated with PRISM-derived recent temperature and precipitation means, indicating the potential for climate-driven community shifts. Investigating the effects of disturbance and climate on trees, watersheds, and ecosystems allows for a holistic view across scales of the current state of southwestern forests, and the potential for future changes.
    • Quantifying Geomorphic Features: Relative Albedos, Skeletonization, and Multifractality

      McEwen, Alfred S.; Schaefer, Ethan Immanuel; Hamilton, Christopher W.; Pelletier, Jon D.; Byrne, Shane; Baker, Victor R. (The University of Arizona., 2018)
      The qualitative and quantitative components of geomorphology are both essential, and complementary, modes of investigation. In the present work, I present three studies that each illustrate a different relationship between these two vital components. In a case study of transient, relatively dark linear features on the martian surface called recurring slope lineae (RSL), I provide an example in which (semi)qualitative geomorphic observations directly motivate quantitative analyses that in turn provide insights into the enigmatic nature of RSL. Specifically, these analyses suggest that RSL at the study site are more likely formed by dry granular flows than by groundwater. In a second investigation, I describe a new algorithm to derive the skeleton of a geomorphic polygon, such as the centerline for a river. This geomorphic study provides a persuasive illustration that geomorphology in general can benefit from the focused development of quantitative methods specifically tailored for geomorphic applications, especially in view of the continuing proliferation of remotely sensed data. As examples, I discuss the potential of the algorithm to provide broader analysis, and hence insights, into respective large databases of rivers on Earth and dust devil tracks on Mars. In the final study, we critically reevaluate the potential to interpret a lava flow’s type from the meter-scale geometry of its margin. We show that the previously unrecognized scale-dependence of these geometries and other complications (e.g., topographic confinement, transitional flow types) require a revised strategy for interpreting lava flow type remotely. This final study thus illustrates the need for the continual refinement of quantitative geomorphic models, which can underestimate the variability found in nature.

      Maddock III, Thomas; Ajami, Hoori; Troch, Peter A.; Meixner, Thomas; Hogan, James F.; Guertin, D. Phillip (The University of Arizona., 2009)
      Groundwater response to climate variability and land cover change is important for sustainable management of water resources in the Southwest US. Global Climate Models (GCM) project that the region will dry in the 21st century and the transition to a more arid climate may be under way. In semiarid Basin and Range systems, this impact is likely to be most pronounced in Mountain System Recharge (MSR), a process which constitutes a significant component of recharge in these basins. Despite the importance of MSR the physical processes that control MSR, and hence the climate change impacts, have not been fully investigated because of the complexity of recharge processes in mountainous catchments and limited observations. In this study, methodologies were developed to provide process-based understanding of MSR based on empirical and data-driven approaches. For the empirical approach, a hydrologically-based seasonal ratio the Normalized Seasonal Wetness Index (NSWI) was developed. It incorporates seasonal precipitation variability and temperature regimes to seasonal MSR estimation using existing empirical equations. Stable isotopic data was used to verify recharge partitioning. Using the NSWI and statistically downscaled monthly GCM precipitation and temperature data, climate change impacts on seasonal MSR are evaluated. Second, a novel data-based approach was developed to quantify mountain block recharge based on the catchment storage-discharge (S-Q) relationships and informed by isotopic data. Development of S-Q relationships across the Sabino Creek catchment, Arizona, allowed understanding of MBR dynamics across scale.Two ArcGIS desktop applications were developed for ArcGIS 9.2 to enhance recharge and evapotranspiration (ET) estimation: Arc-Recharge and RIPGIS-NET. Arc-Recharge was developed to quantify and distribute recharge along MODFLOW cells using spatially explicit precipitation data and a digital elevation model. RIPGIS-NET was developed to provide parameters for the RIP-ET package and to visualize MODFLOW results. RIP-ET is an improved MODFLOW ET module for simulating ET. RIPGIS-NET improves alluvial recharge estimation by providing spatially explicit riparian ET estimates. Using such tools and the above methods improves recharge and ET estimation in groundwater models by incorporating temporally and spatially explicit data and hence the assessment of climate variability and land cover change on groundwater resources can be improved.
    • Quantifying the Effects of Land Use Change on Forests and Fire Regimes in the Southern Canadian Rocky Mountains: 1610 CE-Present

      Towner, Ronald H.; Falk, Donald A.; Taylor, Erana Jae; Kuhn, Steven L.; Zedeño, María Nieves (The University of Arizona., 2021)
      This work examines the effects of land use change in the Southern Canadian Rocky Mountains (SCRM) on forests and fire regimes from the 1600s to present. It begins by examining how the topographic environment has influenced the geographic distribution of human use of the SCRM. It then examines how fire regimes and fire synchrony varied across the region with respect to the nature and intensity of human land use. The third section of the dissertation assesses the viability of a method combining unmanned aerial systems (UAS) with dendrochronology for understanding forest volume dynamics. In summary, the first two parts examine how changes in human use of the landscape have influenced forests and fire regimes, while the third part tests a new method of acquiring and assessing forest data that may help direct future land use policy.
    • Quantifying Uncertainties in Imaging-Based Precision Medicine

      Barrett, Harrison H.; Henscheid, Nicholas; Watkins, Joseph C.; Kunyansky, Leonid (The University of Arizona., 2018)
      In this work, we present a rigorous mathematical framework for the usage of multiple patient-specific molecular images to enable model-based precision medicine, a paradigm of medical decision making defined by the employment of mathematical models of treatment efficacy to direct optimized treatment decisions for individual patients. We address the question of how to define and compute patient-specific probability of treatment success, using random field theory to define the notion of in silico virtual patient ensembles and patient-specific virtual clinical trials. We then provide a novel and rigorous deterministic and statistical analysis of photon-processing Emission Computed Tomography (ECT) data, highlighting the importance of functions and Poisson statistics in defining the virtual patient ensemble and probability of treatment success. We discuss novel high-performance parallel numerical methods to simulate virtual patient ensembles and photon processing ECT systems; these simulations will advance our understanding of the uncertainties inherent in imaging-based precision medicine. Finally, we present a spatially resolved model for chemotherapy efficacy that employs ECT data, and demonstrate how our framework can be used to define, compute and optimize patient-specific probability of treatment success in this setting.

      BRIKOWSKI, TOM HARRY. (The University of Arizona., 1987)
      Hydrothermal activity is one of the dominant processes affecting the chemical and thermal evolution of oceanic crust at the mid-ocean ridge (MOR), but little is known about the sub-surface portions of ridge hydrothermal systems. These systems can be investigated using numerical modeling techniques, and models of two-dimensional cross-sections are utilized in this study to investigate the behavior of MOR hydrothermal systems. The influence of magma chamber geometry is explored by modeling two extremes of proposed geometry. Seismological evidence supports a dike-like 2 km half-width chamber, and models of this chamber indicate that: (1) complete crystallization of the magma requires 30,000 years, (2) hydrothermal upflow and hot springs are concentrated in a narrow band within 1.5 km of the ridge axis for the lifetime of the system, (3) a large hydrothermal cell forms and remains centered above the distal tip of the intrusion for the lifetime of the system, (4) effective hydrothermal activity ends by 70,000 yrs. Petrological evidence supports a wide sill-like chamber 15 km in half-width, and models of this chamber indicate that: (1) complete crystallization of the magma requires 100,000 yrs, (2) hydrothermal vents are present at the ridge axis, but most of the vents are located 5-10 km away from the axis, (3) a large hydrothermal cell develops at the distal tip of the magma chamber, while a series of small but vigorous cells develops directly above the intrusion, both features migrate toward the ridge axis as the magma solidifies, (4) effective hydrothermal activity ends by 170,000 yrs. Substantially different hydrothermal systems develop around these two chamber geometries and comparison of the models shows this is because different patterns of near-critical P-T conditions developed around them. The fundamental influence on the nature and pattern of hydrothermal circulation at MOR is the distribution of near-critical conditions.
    • Quantitative analysis of soil microbial diversity in the hyperarid Atacama Desert, Chile

      Maier, Raina M.; Drees, Kevin Paul (The University of Arizona., 2004)
      The Atacama Desert of northern Chile is one of the most arid regions on Earth. The central plateau, between the coastal escarpment and the Andes, is devoid of vegetation and receives only millimeters of rain every few years. Though plants are absent in the soils of this desert, perhaps bacteria can survive, and even thrive, in these hyperarid conditions. This dissertation represents the first comprehensive study of bacterial diversity in the driest central latitudes (approximately 24°S) of the Atacama Desert. Study 1 covers the development of a soil DNA extraction method for the study of soil bacterial populations. This method was field tested in an ecology study in the Santa Catalina Mountains of southern Arizona. In Study 2, Atacama soils were sampled in two transects at approximately 24°S and 25°S. The first transect runs across the absolute (plantless) desert and through several narrow bands of sparse vegetation at high altitudes in the Andes. The second transect is within the well-developed fog zone near Paposo on the Pacific coastal escarpment, where an endemic plant community called lomas is established. Analysis of DGGE profiles of bacterial !6S rRNA genes extracted from these soils with Kruskal's Isotonic Multidimensional Scaling indicates that the bacterial populations cluster into several groups, including the low diversity populations of the core absolute desert, and the higher diversity high elevation Andean populations influenced by the vegetation of Andean biomes. Only one group clustered in the lomas; the rest of the profiles were unique, demonstrating the high diversity of bacterial populations within this diverse vegetation community. Soil 3107, which is within the absolute desert, clustered with the Andean bacterial populations. This soil lies within the transition zone between the low precipitation of the absolute desert (approximately 2.4 mm per year) and the higher precipitation of the high elevation Andes (approximately 47.1 mm per year). This Andean bacterial population may extend further into the absolute desert than the Andean vascular plants due to superior aridity tolerance. Alternatively, this bacterial population may be a relic from when the Andean vegetation advanced through this elevation in a wet period 3000 years ago.
    • A quantitative analysis of the dust devil

      Sinclair, Peter Charles, 1929- (The University of Arizona., 1966)

      CHIGWE, CHARLES FRANCISCO BRADLEY.; Briggs, Robert E.; Ray, Dennis T.; Stith, Lee S.; Nutting, William L.; Watson, Theo F. (The University of Arizona., 1984)
      This study sought to determine the effects of reselection on the adaptation of a grain sorghum (Sorghum bicolor (L.) Moench) population to heat and drought. A random-mating population, NP9BR, was subjected to selection under heat and moisture stress for nine generations to improve its resistance to drought. One hundred single plants selected from the original (C₀) and the reselected (C₉) population were grouped by maturity and evaluated for drought resistance by measuring morphological and agronomic characters under wet (normal irrigation) and dry (restricted irrigation) conditions at the University of Arizona, Marana Agricultural Center, Arizona. Eighty of the selections were grown under a sprinkler irrigation gradient system at Yuma Mesa Agricultural Center, Arizona. Selection under drought conditions reduced plant height, head exsertion, leaf width and length, and seed weight of the population. Blooming was evened out from predominantly early in C₀ to early, medium and late maturing in C₉. Moisture stress reduced grain yield by an overall 16%. The medium maturing selections suffered less yield reduction than the early and late. Although C₉ progenies showed a greater reduction in grain yield, several of them produced equal yields in wet and dry treatments. Leaf width and length were significantly correlated (p = .1%) with yield under dry conditions in all maturity groups. Most selections with very short narrow leaves had small heads and low yields. Some with medium leaf width and length out-yielded broad-leaved ones especially under dry conditions. Forty percent of the selections from C₉ had good head production characteristics under the irrigation gradient system, compared to only 20% from C₀. There were four times as many selections in C₀ unable to produce heads under the system as there were in C₉. The majority of genotypes with good head production in both populations came from the early maturing group. The highest grain yields came from C₀ selections but some C₉ selections with comparable yields were observed. This study indicates that phenotypic selection may still have potential for isolating high-yield genotypes from random-mating populations but may be inadequate for separating differences in drought tolerance among genotypes.