Now showing items 1962-1981 of 19641

    • C-3 AND C-4 PHOTOSYNTHESIS, COMPETITION, AND THE LIMITS TO GRASS SPECIES DISTRIBUTIONS IN AN ARIZONA GRASSLAND.

      Schaffer, William M.; GUREVITCH, JESSICA. (The University of Arizona., 1982)
      In a warm, dry grassland in southeastern Arizona dominated by C₄ grasses the only C₃ grass found was restricted to dry, exposed ridge crests within the hottest and driest part of the region. This was precisely the opposite of what one would predict from physiological and biogeographic considerations, which would lead one to expect a C₃ grass in this environment to be growing on cooler or moister areas that would mitigate the effects of the inhospitable climate. Cover of C₄ grasses was very low on these ridge crests, and increased downslope with the greater volume of water available to high values on the lower slopes and in washes. It was suggested that this C₃ grass, Stipa neomexicana, had a very high tolerance of water stress, but a very poor tolerance of competition, and was limited to unfavorably dry sites by its competitively superior C₄ neighbors. Most species, regardless of photosynthetic type, could not survive in the harsh ridge crest environment, which therefore offered a refuge from competition. The hypothesis of competitive exclusion was tested by removal experiments conducted at ridge crest, midslope and lower slope positions along the topographic gradient of decreasing Stipa neomexicana and increasing C₄ grass cover. The predictions made under this hypothesis were confirmed. The presence of competitors limited the growth of mature plants, flower production, seedling establishment and seedling survival. The beneficial effects of the removal of competitors increased downslope. Competition depressed estimated finite rates of population increase for Stipa neomexicana. This depression was most severe on the lower slope. It was concluded that increasing competition from C₄ grasses along the topographic gradient was responsible for restricting Stipa neomexicana to the unfavorable ridge-crest sites.
    • The c-function for affine Kac-Moody algebras

      Pickrell, Doug; Dang, Son Xuan, 1964- (The University of Arizona., 1996)
      In this paper, we will first study the Harish-Chandra transform and the c-function for finite type Kac-Moody groups. The Harish-Chandra transform is essentially the Gelfand transform on L¹( K\G/K). From our point of view, the c-function arises as the Fourier transform of the diagonal distribution for Haar measures of K. A brief account of Kac-Moody algebras, especially affine Kac-Moody algebras, is also presented. Then we use a formula of Harish-Chandra for the c-function for finite type Kac-Moody groups to discuss the definition of the c-function for affine Kac-Moody algebras, especially the twisted affine Kac-Moody algebras. It turns out the c-function for an affine Kac-Moody algebra can be written as a product of trigonometric functions over the positive roots of the corresponding finite type Kac-Moody algebra. This finite type Kac-Moody algebra is the Lie algebra of a finite type Kac-Moody group G. Then the c-function can be thought as the Fourier transform of the diagonal distribution for a Haar type measure of G. For the affine Kac-Moody algebra of type A⁽¹⁾₁ , G is SL(2, C) and the measure is (trace(g* g))⁻³. This leads to the question of whether (trace( g* g))⁻ᵐ on SL(n, C) is that measure for the affine Kac-Moody algebra of type A⁽¹⁾(n-1). In the last part, for any positive integer l, the Harish-Chandra transform of (trace(g* g) ⁻⁽⁽ⁿ⁽ⁿ⁻¹⁾⁾/²⁾⁻¹ on SL(n, C) is calculated to check if the Fourier transform of the diagonal distribution for (trace(g* g) ⁻⁽⁽ⁿ⁽ⁿ⁻¹⁾⁾/²⁾⁻¹ is the c-function for the affine Kac-Moody algebra of type A⁽¹⁾(n-1).
    • The C-O-H-S gas system and its applications to terrestrial and extraterrestrial volcanism

      Gerlach, Terrance Melvin, 1941- (The University of Arizona., 1974)
    • The C.A.S.E. Approach (Corroboration, About Me, Science, Explain/Advise): Improving Communication with Vaccine-Hesitant Parents

      Peek, Gloanna; Stevens, Jessica Celeste; Peek, Gloanna; McArthur, Donna B.; Badger, Terry A. (The University of Arizona., 2016)
      OBJECTIVES: The anti-vaccination movement is prevalent in today's media with claims which continue to create feelings of fear and trepidation in the minds of many parents. The C.A.S.E. Approach (Corroboration, About Me, Science, Explain/Advise) is a method ofcommunication to be used in formulating meaningful, rapid responses to parents hesitant to vaccinating their children. This DNP project assessed the effects of a C.A.S.E. Approach learning module on family nurse practitioner (FNP) students' perceived levels of knowledge and self-efficacy regarding vaccination discussion with vaccine hesitant parents (VHPs). METHODS: This DNP project used a pretest-posttest design to measure the effects of the C.A.S.E. Approach training intervention on both knowledge and self-efficacy levels of FNP students. Fourteen students participated in this study. Each took the 20-question pretest C.A.S.E. Approach Questionnaire, then participated in the C.A.S.E. Approach learning module,and finished by repeating the questionnaire as a posttest following the intervention. The questionnaire was designed using four-item Likert questions scored 1 (strongly disagree) to 4(strongly agree), wherein higher scores reflected better understanding and self-efficacy in the C.A.S.E. Approach. Students were recruited via an online classroom format within a nursing course offered at the University of Arizona: Nursing 612, Introduction to Pediatrics. All testing and module information was accessed online and questionnaire responses were stored at Qualtrics.com, also online. RESULTS: Students' posttest scores following the intervention of the C.A.S.E. Approach learning module were significantly higher than pretest scores. Perceived knowledge (p< 0.001)of the C.A.S.E. Approach increased more significantly than did perceived self-efficacy (p =0.001) of the C.A.S.E. Approach following the module. Mean test scores increased on average 14.29 points in perceived knowledge of the C.A.S.E. Approach following the module, and 7.93 points for perceived self-efficacy following the module. CONCLUSION: Key findings included an observed increase in participating students' perceived knowledge regarding the C.A.S.E. Approach as well as an observed increase inparticipating students' perceived self-efficacy in using the C.A.S.E. Approach. There was strong statistical evidence (p≤0.05) to suggest the learning module increased student knowledge andself-efficacy regarding vaccine discussion.
    • C.P.E. Bach's "Rondos for Connoisseurs and Amateurs"

      Webb, Robin Timothy (The University of Arizona., 1984)
    • Cable-drawn farming system analysis and control development

      Coates, Wayne E.; Siemens, Mark Cornelius, 1965- (The University of Arizona., 1996)
      Four types of cable drawn farming systems, a single engine system, a double engine system, a perimeter system, and a double implement system, were analyzed to determine which was best suited for Arizona. The systems were compared in terms of relative cost, reliability/simplicity and field capacity. Field capacity computation variables were implement width, implement speed, tower travel speed, implement carrier travel speed, and implement rotation time. The analysis showed the single engine system was the least expensive, simplest system with a field capacity identical to that of the double engine system, eight percent lower than the double implement system, and approximately thirteen percent higher than the perimeter system. Based on these results, the single implement system was judged superior to the others. The parameters affecting single implement system performance were then examined to optimize performance. The evaluation yielded a recommendation that the system be designed to have a tower speed of 48 ft/min, and a rotation time of 7.5 seconds. A positioning system for the mobile truss of a cable drawn farming system was also developed and tested. The system used a linear move irrigation system's above ground cable guidance system for steering, a wicket positioning system for stopping the machine at the indexing locations, and a wire-alignment system to control inner tower alignment. The system was tested over a length of 280 ft using a five tower, 575 ft long, linear move irrigation system. It was found that the above ground cable guidance system provided ±0.5 ft steering accuracy, the wicket positioning system controlled the power unit and end tower position within ±0.2 ft of the target destination, and that the wire alignment system controlled inner tower position within ±0.3 ft of the target destination. Statistical analysis of the test results showed the probability of position error being controlled to within ±0.4 ft and ±0.8 ft to be at the 99.7% and 99.99% confidence levels, respectively.
    • The cadaver experience: The effects of self-esteem and denial on existential terror in medical students.

      Chatel, Daniel Mark.; Greenberg, Jeff; Fahey, Shirley; McCloskey, Laura (The University of Arizona., 1992)
      Eighty-four medical students at the University of Arizona were administered measures of self-esteem, medical attitudes, social desirability, purpose in life, satisfaction with life, state and trait anxiety one week before their first cadaver dissecting experience. On the day of the experience, half of the subjects completed these measures again in addition to a death anxiety scale just prior to their first cadaver exposure. The other half completed these measures immediately after their first cadaver exposure. Results found main effects of self-esteem with high self-esteem subjects endorsing higher purpose in life and medical attitudes and lower state anxiety and death anxiety. Time by condition interactions were found for state anxiety and purpose in life, with both significantly higher in subjects assessed following exposure to the cadaver. Finally, a main effect for condition was also seen with regard to fear of death, with those exposed to the cadaver scoring significantly higher. Implications with regard to terror management theory and medical education were discussed. In particular, the results tend to support the notion of self-esteem as a psychological buffer against the existential anxiety resulting from an awareness of mortality. Further, results also suggest that cadaver dissection is a powerful emotional experience for physicians in training, significantly affecting their attitudes and requiring sensitivity of medical educators to the psychological impact of cadaver dissection.
    • THE CADAVEROUS CITY: THE EVERYDAY LIFE OF THE DEAD IN MEXICO CITY, 1875-1930

      López, Amanda M.; Beezley, William H.; Barickman, Bert J.; Few, Martha; Gosner, Kevin (The University of Arizona., 2010)
      This dissertation explores burial practices and funeral rituals in Mexico City during the late-nineteenth and early-twentieth centuries. I argue that international shifts in ideas about public health, class, and nationalism were reflected in new spaces and practices for dead bodies. Furthermore, I examine how mass death challenged traditional burial practices. The daily practices involved in managing the disposal and veneration of dead bodies illuminate the social and cultural challenges in building modern cities and the ways in which these projects are adopted or rejected by the citizenry. The first three chapters focus on the modernization of burial practices in the nineteenth century. Burial reform laws in the 1850s led to the foundation of the capital's first large, modern cemetery, the Panteón de Dolores, by the Liberal government in 1879. The cemetery became a microcosm for the clean, modern city, mapping the new social class configuration through the distribution of its graves. Quickly the administrators of the Dolores Cemetery failed to meet ideal due to the realities of daily operation. The cemetery had been imagined as a space that reflected elite ideas of modernity, but it served a capital that was mostly indigent. In response to overcrowding, the technology of cremation, which targeted the poor, created a class division between those who could be buried and those who had to be cremated. Government officials successfully constructed a modern, sterile approach to death and began to wrest away control of the symbolic power of death from the Catholic Church. The last two chapters focus on the temporary breakdown of these practices and the reinterpretation of funeral rituals in the early twentieth century. Instability and high mortality rates during the Revolution of 1910-1920 led to overcrowding in cemeteries and spread the dead beyond the cemetery, including impromptu battlefield cremations. A comparison of three funerals in 1928-1929 shows new ways in which the funeral was used to perform ideas about the nation, family, and masculinity. The Revolution's unmanageable casualty levels and the advent modern, secular funerary practices in the period before the Revolution influenced how the government, military, and civilians handled and memorialized death.
    • CAGE-SIZE, GENDER AND MEASUREMENT ISSUES IN THE STUDY OF MUSCLE FATIGABILITY (HISTOCHEMISTRY).

      Stuart, Douglas G.; Rankin, Lucinda Lee; Angevine, Jay B., Jr.; Allen, Ronald E.; Burt, Janis M.; Enoka, Roger M.; Hasan, Ziaul (The University of Arizona., 1987)
      To study the detrimental effects of hypokinesia, many models of reduced muscular activity (i.e., reduced-use), including alterations in the size of the living environment, have been developed. Although significant structural and functional changes have been documented, the effect of reduced-use on muscle fatigability remains unclear. This project was designed to study the effects of cage-size on selected properties of rat hindlimb muscle, with particular emphasis on fatigue. Further, in view of the lack of information on the potential effect of gender, both males and females were studied. The rats were raised in either a small, conventional cage or one approximately 133 times larger. Subsequently, terminal experiments were performed to characterize the contractile properties, fiber-type composition and oxidative potential of two hindlimb muscles of the small- and large-cage-reared rats. The test muscles, soleus and extensor digitorum longus, were selected on the basis of their pronounced differences in function, usage and fiber-type composition. The results suggest that reductions in cage-size can influence the properties of skeletal muscle (specifically, muscle mass, force and fatigability) and that this effect is a function of both gender and interanimal differences. However, due to the large variability exhibited by all three factors, their overall effect will be minimal. An analysis of the response of the test muscles to a 6 min fatigue test revealed three findings. First, both muscles exhibited a wide range of fatigability, an unexpected finding particularly for soleus but in keeping with the multiplicity of factors discussed above. Second, the association observed between whole-muscle force and the electromyogram (e.m.g.) was found to be dependent upon the measure used to quantify the e.m.g., the fiber-type composition of the muscle and its degree of fatigability. And third, a coexistence of twitch potentiation and muscle fatigue was observed which also was dependent upon the fiber-type composition and the extent of fatigue. Finally, a comparison of qualitative and quantitative histochemical analyses revealed broad, overlapping ranges for oxidative enzyme activity for each of the three muscle-fiber types. This suggests that differences in fatigability usually attributed to different fiber types are not due solely to differences in oxidative potential.
    • Calcium Modulation of PARP-mediated Cell Death

      Monks, Terrence J.; Muñoz, Frances M.; Monks, Terrence J.; Lau, Serrine S.; Regan, John W.; Wondrak, Georg; Boitano, Scott (The University of Arizona., 2015)
      Many pathological conditions, including renal disease, are associated with oxidative stress. 2,3,5-tris(Glutathion-S-yl)hydroquinone (TGHQ), a potent nephrotoxic and nephrocarcinogenic metabolite of benzene and hydroquinone, generates reactive oxygen species (ROS), can cause DNA strand breaks, and the subsequent activation of DNA repair proteins, including poly(ADP-ribose) polymerase (PARP)-1. Under robust oxidative damage, PARP-1 is hyper-activated, which causes elevations in intracellular calcium concentrations (iCa²⁺), NAD⁺ and ATP depletion, and ultimately necrotic cell death. The role of Ca²⁺ in PARP-dependent necrotic cell death remains unclear. We therefore sought to determine the relationship between Ca²⁺ and PARP-1 during TGHQ-induced necrotic cell death in human renal proximal tubule epithelial cells (HK-2). Extracellular Ca²⁺ is responsible for coupling PARP-1 activation to increases in iCa²⁺ during TGHQ-induced cell death. Moreover, organelles such as the endoplasmic reticulum and the mitochondria, which contain intracellular Ca²⁺ stores play no role in increases of iCa²⁺. PARP-1 inhibition attenuates increases in iCa²⁺ induced by TGHQ, and treatment with 2-aminoethoxydiphenyl borate (2-APB), a store-operated Ca²⁺ channel (SOC) inhibitor, restored cell viability, levels of NAD⁺, and attenuated PAR protein-ribosylation (PARylation). Concurrent with SOC activation having a direct effect on PARP-1 activity, and PARP-1 inhibition attenuating increases in iCa²⁺, the results suggest that PARP-1 and SOCs are coupled during TGHQ-induced cell death. We also explored the relationship between SOC activation and PARP-1 downstream of PARP-1 activity. Poly(ADP-ribose)glycohydrolase (PARG), which catalyzes the degradation of PARs to yield free ADP-ribose (ADPR), is known to activate SOCs. Interestingly, siRNA knockdown of PARG modestly increased PAR ribosylation, but did not restore cell viability in the presence of TGHQ, indicating that free ADPR is not responsible for SOC activation in HK-2 cells. Overall, our results suggest that PARP-1 and Ca²⁺ are coupled through SOC entry, and that this relationship may involve alternative PAR-mediated signaling that leads to necrotic cell death. To further elucidate the role of PAR polymers in response to TGHQ, we determined the cellular co-localization of PAR by immunofluorescent staining. PAR polymers originally co-localized in the nucleus, and in the cytosol at later time points. Immunoprecipitation with a pADPr antibody and further analysis via mass spectrometry revealed PARylation of many stress-related proteins and Ca²⁺-related proteins upon TGHQ treatment. We therefore speculate that cytosolic PAR may cause downstream signaling, PARylating proteins that activate store-operated Ca²⁺ entry either directly through Ca²⁺-related proteins or PARylation of stress-related proteins. Thus, PARylation of proteins may contribute to increases in iCa²⁺ concentrations, leading to PARP-1-dependent necrotic cell death. Our studies provide new insight into PARP-mediated necrotic cell death. Ca²⁺ is coupled to PARP-1 hyperactivation through SOCs, where iCa²⁺ increases are independent of PARG activity, demonstrating a novel signaling pathway for PARP-dependent necrotic cell death.
    • CALCULATED AND OBSERVED LINE STRENGTH RATIOS IN CESIUM II

      Jones, Douglas Wayne (The University of Arizona., 1979)
    • THE CALCULATION OF LOWER BOUNDS TO ATOMIC ENERGIES.

      Greenlee, W. M.; RUSSELL, DAVID MARTIN. (The University of Arizona., 1983)
      The goal of this dissertation has been to develop a method that enables one to calculate accurate, rigorous lower bounds to the eigenvalues of the standard nonrelativistic spin-free Hamiltonian for an atom with N electrons. Lower bounds are necessary in order to complement upper bounds obtained from the Hartree-Fock and Rayleigh-Ritz techniques. Without accurate lower bounds, it is impossible to estimate the error of the approximate values of the energies. By combining two heretofore distinct methods and using the symmetry properties of the Hamiltonian, this goal has been achieved. The first of the two methods is the method of intermediate problems. By beginning with an appropriately chosen "base operator" H⁰, one forms a sequence of intermediate Hamiltonians Hᵏ, k = 1,2,..., whose corresponding eigenvalues form a sequence of lower bounds to the eigenvalues of the original Hamiltonian H. Complications which occurred in this method due to the stability of essential spectra under compact perturbations were later surmounted with the use of abstract separation of variables by D. W. Fox. The second technique, the effective field method, provides a lower bound operator to the interelectron repulsion term in H that is of the form of a sum of separable potentials. This latter technique reduces the eigenvalue problem for H⁰ to a sum of single particle operators. With the use of a special potential, the Hulthen potential, one may construct an explicitly solvable base problem from the effective field method, if one uses the method of intermediate problems to calculate lower bounds to non-S states. This base problem is then suitable as a starting point for the method of intermediate problems with the Fox modifications. The eigenvalues of the new base problem are already comparable to the celebrated Thomas-Fermi energies. The final part of the dissertation provides a practical procedure for determining the physically realizable spectra of the intermediate operators. This is accomplished by restricting the Hamiltonian to subspaces of proper physical symmetry so that the resulting lower bounds will be to eigenvalues of physical significance.
    • Calculation of the Resummed Radiation Reaction to Order 1/M Using Heavy Fermion Effective Theory

      Fleming, Sean P.; Hill, Andrew; Rutherfoord, John; Su, Shufang; Gralla, Samuel E.; Meinel, Stefan (The University of Arizona., 2020)
      The Abraham-Lorentz-Dirac equation, which is the widely-accepted expression for the recoil force experienced by a radiating charge (known as the \textit{radiation reaction}), displays strange, unphysical behavior. As such, it has been rife with controversy and confusion for over a century. For most of that time, these issues were treated mostly as curiosities and left to the musings of theoreticians. But the advent of high-intensity pulsed tabletop lasers in recent decades has made the radiation reaction relevant to modern experimental physics, which has led to a resurgence of research into the topic. In this dissertation, we calculate the radiation reaction to order $m^{-1}$ experienced by a charge of mass $m$ in an external electromagnetic field resulting from emission of a single photon. To accomplish this, we use heavy fermion effective theory (HFET), which is an effective field theory of QED, and model the total electromagnetic field as the superposition of a quantized self-field associated with the charge and a classical external field. HFET is a novel approach that greatly simplifies the calculation compared to full QED. The simplified calculations allow us to resum our force expression to all orders in $e A_{\text{cl}}$, where $A_{\text{cl}}$ is the background field; this is a novel result. Wilson lines arise in our expressions as a result of resummation.
    • Calculation of transport properties of liquid metals and their alloys via molecular dynamics

      Deymier, Pierre A.; Cherne, Frank Joseph (The University of Arizona., 2000)
      The advanced casting modeler requires accurate viscosity and diffusivity data of liquid metals and their alloys. The present work discusses the use of equilibrium and non-equilibrium molecular dynamics techniques to obtain such data without having to rely on oversimplified phenomenological expressions or difficult and expensive experiments. Utilizing the embedded atom method (EAM), the viscosities and diffusivities for a series of equilibrium and non-equilibrium molecular dynamics simulations of nickel, aluminum, and nickel-aluminum alloys are presented. A critical comparison between the equilibrium and non-equilibrium methods is presented. Besides the transport properties, structural data for the liquids are also evaluated. EAM does a poor job of describing the transport properties of nickel-aluminum alloys, particularly near the equiatomic concentration. It has been suggested that charge transfer between nickel and aluminum atoms is responsible for the discrepancy between numerical calculations and available experimental data. A modified electronic distribution function has been developed to simulate the charge transfer associated with compound formation. The effects of such a "charge transfer" modification to the embedded atom method are evaluated. The results of these simulations indicate that the embedded atom method combined with molecular dynamics may be used as a method to predict reasonably the transport properties.
    • Calculator Use In Developmental Mathematics in a Community College

      Johnson, Bruce; Turner, Erin; Aguilar, Darla Jean; Johnson, Bruce; Turner, Erin; Griego-Jones, Toni (The University of Arizona., 2008)
      The purpose of this study was to examine instructor and student usage of calculators in basic mathematics and prealgebra courses at a community college. Researcher-created surveys were given to 54 instructors and 198 students. The results showed instructors were fairly evenly divided about policies regarding the use of calculators. The major reason for not allowing calculators was that students needed to develop basic skills, and the major reason for allowing calculators was to concentrate on learning concepts. Students used calculators mainly for computation and seldom reported instructors using calculators in class for any other reason. Students were more likely to see calculators as learning tools than were teachers, who saw calculators mainly as computation machines. The results also indicated that instructors were confused about department calculator policies, and students were confused about classroom calculator use policies.
    • Calibrated, Multiband Radiometric Measurements of the Optical Radiation from Lightning

      Krider, E. Philip; Betterton, Eric A.; Quick, Mason G.; Krider, E. Philip; Betterton, Eric A.; Cummins, Kenneth L.; Dereniak, Eustace L.; Ritchie, Elizabeth A.; Weidman, Charles D. (The University of Arizona., 2014)
      Calibrated, multiband radiometric measurements of the optical radiation emitted by rocket-triggered lightning (RTL) have been made in the ultraviolet (UV, 200-360 nm), the visible and near infrared (VNIR, 400-1000 nm), and the long wave infrared (LWIR, 8-12 µm) spectral bands. Measurements were recorded from a distance of 198 m at the University of Florida International Center for Lightning Research and Testing (ICLRT) during the summers of 2011 and 2012. The ICLRT provided time-correlated measurements of the current at the base of the RTL channels. Following the onset of a return stroke, the dominant mechanism for the initial rise of the UV and VNIR waveforms was the geometrical growth of the channel in the field-of-view of the sensors. The UV emissions peaked about 0.7 µs after the current peak, with a peak spectral power emitted by the source per unit length of channel of 10 ± 7 kW/(nm-m) in the UV. The VNIR emissions peaked 0.9 µs after the current peak, with a spectral power of at 7 ± 4 kW/(nm-m). The LWIR emissions peaked 30-50 µs after the current peak, and the mean peak spectral power was 940 ± 380 mW/(nm-m), a value that is about 4 orders of magnitude lower than the other spectral band emissions. In some returns strokes the LWIR peak coincides with a secondary maximum in the VNIR band that occurs during a steady decrease in channel current. Examples of the optical waveforms in each spectral band are shown as a function of time and are discussed in the context of the current measured at the channel base. Source power estimates in the VNIR band have a mean and standard deviation of 2.5 ± 2.2 MW/m and are in excellent agreement with similar estimates of the emission from natural subsequent strokes that remain in a pre-existing channel which have a mean and standard deviation of 2.3 ± 3.4 MW/m. The peak optical power emitted by RTL in the UV and VNIR bands are observed to be proportional to the square of the peak current at the channel base. The same trend was found for natural lightning using peak currents estimates provided by the National Lightning Detection Network. Ratios of the optical power to the electromagnetic power emitted at the time of peak current suggest the radiative efficiency in the VNIR band is a few percent during the early onset of a return stroke. The majority of return strokes in RTL are found to emit most of their optical energy during the initial impulse phase.
    • Calibration and Interpretation of Holocene Paleoecological Records of Diversity from Lake Tanganyika, East Africa

      Alin, Simone Rebecca; Cohen, Andrew; Flessa, Karl; Overpeck, Jonathan; Reinthal, Peter; Robichaux, Robert (The University of Arizona., 2001)
      Lake Tanganyika is a complex, tropical ecosystem in East Africa, harboring an estimated 2,100 species. Extensive watershed deforestation threatens the biodiversity and ecological integrity of the lake. In this dissertation, ecological and paleoecological methods were employed to study the distribution of invertebrate biodiversity through space and time, with particular emphasis on linkages between biodiversity and land –use patterns. Ecological surveys of fish, mollusc, and ostracod crustacean diversity at sites in northern Lake Tanganyika representing different levels of watershed disturbance revealed a negative correlation between biodiversity and intensity of watershed disturbance. To elucidate the long -term relationship between disturbance and biodiversity, paleoecological records of invertebrates offshore from watersheds experiencing different degrees of anthropogenic disturbance were examined. Life, death, and fossil assemblages of ostracod valves were compared to assess the reliability and natural variability inherent to the paleoecological record. These comparisons indicated that paleoecological (i.e. death and fossil) assemblages reliably preserve information on species richness, abundance, and occurrence frequency at comparable -to- annual resolution. Unlike life assemblages, species composition of paleoecological assemblages reflects input of species from multiple habitat types. Ostracod paleoecological assemblages are characterized by spatiotemporal averaging that renders them representative of larger areas and longer time spans than life assemblages. Thus, paleoecological assemblages provide an efficient means of characterizing longer -term, site -average conditions. Natural variability in ostracod fossil assemblages from a sediment core representing the Late Glacial to the present indicates that abundance of individual ostracod species is highly variable. Ostracod assemblages were preserved in only the most recent 2,500 years of sediment. Species composition of ostracod assemblages reflects lake water depth. Core geochemical data indicate that the coring site may have been below the oxycline for ~2,000 years, inhibiting ostracod survival and preservation. Paleoecological, sedimentological, and stable isotope data revealed differences in biodiversity and watershed disturbance through time offshore from a pair of sites. The protected site is offshore from Gombe Stream National Park (Tanzania), the other offshore from a deforested watershed outside the park. Offshore from the deforested watershed, sedimentation rates increased, and turnover in ostracod species composition occurred during the past 50 years. Comparable changes were not observed offshore from the park.
    • Calibration and testing of the 6.5 m MMT adaptive optics system

      Angel, Roger P.; Johnson, Robert L. (The University of Arizona., 2001)
      This dissertation describes the development, calibration, and testing of the adaptive optics system for the 6.5 m Multiple Mirror Telescope. By employing a deformable secondary mirror, the MMT adaptive optics system uniquely solves several problems typical of astronomical adaptive optics systems. Extra components are eliminated, improving throughput and reducing emissivity. Since the adaptive secondary is integral to the telescope, a corrected beam is presented to any instrument mounted at Cassegrain focus. The testing of an adaptive mirror, which is large and convex, poses a new and difficult problem. I present a test apparatus that allows complete calibration and operation, in closed-loop, of the entire adaptive optics system in the laboratory. The test apparatus replicates the optical path of the telescope with a wavefront error of less than 500 nm RMS. To simulate atmospheric turbulence, machined acrylic plates are included. A phase-shifting interferometer allows calibration of the Shack-Hartmann wavefront sensor and reconstruction algorithms; comparisons agree to one-third of the root-mean-square wavefront. First, techniques were developed to align the apparatus and measure residual aberration. Then, the wavefront sensor was calibrated by measuring its response to introduced tilt. Lastly, a Fourier wave-optics approach was used to produce a modal wavefront reconstructor. The adaptive secondary mirror uses electro-magnetic force actuators. Capacitive position sensors are placed at each actuator to permit control of the mirror shape without measuring the reflected wavefront. These sensors have nanometer resolution, but require calibration. To calibrate the sensors, I developed a small optical instrument which measures the thickness of transparent films to an absolute accuracy of 5 nm with a precision of 2 nm. The device has applications far beyond the scope of this research. Twenty-four of these optical gap sensors have been built to calibrate the 336 capacitive sensors on the adaptive secondary mirror. Mirror displacements measured using gap sensors and a phase-shifting interferometer agree to 2 percent of the displacement. The gap sensors allow for quick and accurate calibration of the capacitive sensors without the difficulty of installing an interferometer on the telescope.