Now showing items 19416-19435 of 20306

    • A two-dimensional, self-consistent model of galactic and anomalous cosmic rays in the solar wind

      Jokipii, J. R.; Florinski, Vladimir A. (The University of Arizona., 2001)
      We have developed a two-dimensional heliospheric model that includes galactic and anomalous cosmic rays as well as pickup ions. Cosmic rays are described via their number density in phase space, rather than pressure, as every preceding 2-D model has done. Cosmic-ray pressure is included in the total energy budget, allowing us to compute dynamical effects of the energetic particles on the solar wind. We include the magnetic field as well in order to consistently compute cosmic-ray diffusion coefficients. To accommodate' lower-energy cosmic rays with their short diffusion length, we implemented an adaptive mesh refinement code featuring improved spatial resolution near the termination shock. Our simulations show that galactic cosmic rays could substantially change the solar wind flow in the outer heliosphere. In particular, the solar wind is deflected towards the ecliptic plane during the positive solar cycle, resulting in faster wind near the current sheet. This is a result of large latitudinal gradients in the cosmic-ray pressure, caused by the difference in cosmic-ray drift patterns over latitude. We also found that anomalous cosmic rays have a minor effect on the solar wind. Their pressure is not sufficient to modify the termination shock significantly, a conclusion based on comparing model cosmic-ray spectra with observations. However, anomalous cosmic-ray acceleration occurs somewhat differently than thought before, and shock drift effects are not prominent. The spectra of these particles have an enhancement near the cutoff, that is not caused by shock drifts.
    • Two-person bargaining under incomplete information: An experimental study of new mechanisms

      Rapoport, Amnon; Parco, James Edward (The University of Arizona., 2002)
      New theoretical developments and recent experimental studies involving the sealed-bid k-double auction mechanism for bilateral bargaining under incomplete information have raised new questions about procedures that induce efficient bargaining behavior and about the applicability of extant adaptive learning models. It is now generally accepted that a theory of bargaining behavior for individuals who typically do not meet the stringent assumptions about common knowledge of rationality cannot be complete without systematic empirical investigations of the properties of the various mechanisms that structure bargaining. The aim of this dissertation is to critically explore the extent to which efficient bargaining outcomes can be achieved while dynamically accounting for individual behavior across repeated play of the game. In the first study, an endogenous bonus is introduced into the baseline single-stage game. Although theoretically doing so induces truth-telling behavior for both players, the experimental data provide very limited support. In the second study, the baseline game is extended by incorporating an additional, costless period of bargaining, thereby giving players an increased opportunity to reveal information about their respective reservation values. The data show that subjects quickly learn not to reveal information about their private valuation despite the increased opportunity to bilaterally improve efficiency. Finally, the third study investigates behavior sensitivity to variation in the trading parameter, k. Instead of following the historical precedent of setting k = ½, extreme values of k are invoked in an asymmetric information environment endowing a player with exclusive price-setting power. Although theoretical analysis suggests that expected profits for a seller (buyer) decreases (increases) in k, experimental results show that under conditions of dramatic information asymmetry, the observed share of the surplus is much smaller for the player with price setting power if countered with an information disadvantage resulting in poor support of the LES. Furthermore, the price setting power effectively counters the information disparity advantage demonstrated in previous studies. Results from a previously proposed reinforcement-based adaptive learning model not only demonstrate robust applicability across studies but also the model's ability to account remarkably well for the dynamics of play across iterations of the stage game.
    • Two-photon absorption and color centers: Effects on all-optical switching.

      Stegeman, George I.; DeLong, Kenneth Wayne.; Sargent, Murray, III; Wright, Ewan M.; Mizrahi, Victor (The University of Arizona., 1990)
      This dissertation explores the effects of two-photon absorption and color center induced absorption on all-optical switching devices. The amount of allowable two-photon absorption was quantified by the parameter T = 2βλ/n₂, where λ is the operating wavelength, β is the two-photon absorption coefficient, and n₂ is the nonlinear refractive index coefficient, the latter two being measured at λ. If the value of T exceeds unity, the operation of all-optical switching devices is in general degraded beyond usable regimes. This result was demonstrated by numerical experiments on systems of equations modelling a nonlinear directional coupler, a prototypical all-optical switching device. The value of T was measured in two fibers, one made of lead silicate glass, and one made of TiO₂-doped silica. We find the value of T to be greater than unity at a wavelength of 1.06 μm in both fibers. Significant color center formation was seen in the lead glass fiber. These color centers were created through two-photon absorption and destroyed through one-photon absorption. Color center induced absorption was seen to mimic two-photon absorption in certain regimes. The nonlinear optical response of semiconductor-doped glasses, an example of a one-photon resonant nonlinearity, was studied. A relaxation time which is dependent on the carrier density was found to be important when modelling the response of these glasses.
    • Two-photon Induced Photochemistry

      Marder, Seth R.; McGrath, Dominic V.; Wang, Jing; Marder, Seth R.; McGrath, Dominic V.; Armstrong, Neal R.; Hruby, Victor J.; Saavedra, S. Scott (The University of Arizona., 2007)
      Two-photon absorption is the process in which a molecule absorbs two photons simultaneously. The two key advantages of two-photon processes over one-photon processes are the possibility of excitation of materials with high three-dimensional spatial resolution and deep light-penetration into absorbing materials. Based on bond-cleavage reactions activated by photon-induced intramolecular electron transfer, two-photon activatable acid and radical initiators and two-photon removable protecting groups have been successfully designed and synthesized for photopolymerization and three-dimensional microfabrication and for biomedical photo-triggers. The optical and chemical properties of synthesized molecules, such as quantum yield of acid generation, initiation efficiency of photopolymerization, and photolysis efficiency, have been studied by using a variety of physical and analytical techniques under one-photon conditions. The two-photon characteristics and applications of these molecules are being investigated in collaboration with other groups.

      Sargent, Murray; CAPRON, BARBARA ANNE.; Gibbs, Hyatt; Meystre, Pierre (The University of Arizona., 1986)
      This dissertation examines aspects of the interaction of multiple coherent light fields for the two-photon two-level model. In this model the interacting energy levels are not connected by an atomic dipole and a two-photon transition between them is necessary. We employ the density matrix formalism allowing easy comparison between the one- and two-photon two-level models. Significant differences are found due to dynamic Stark shifts and conjugate scattering off the pump-induced two-photon coherence. Averages over Doppler broadening are performed and the new upper-level relaxation mechanisms of decay to an intermediate nonresonant level and ionization from the upper state are included. The new relaxation mechanisms, introduced to the theory to better model experiments, are similar except that ionization is intensity dependent. They cause the resulting probe absorption spectra to become more complex and in general asymmetric. Doppler broadening is also important in experiments using gases. We analytically average over a Lorentzian velocity distribution for both co- and counterpropagating pump and probe beams. For copropagating fields the results are similar to those for the one-photon case averaged over inhomogeneous broadening, whereas counterpropagating pump and probe fields yield the so-called Doppler-free configuration that is normally only modelled to third order in the pump amplitude. We consider the pump field amplitude to all orders and find that as long as the width of the Doppler velocity distribution is significantly larger than the two-photon Rabi frequency the results are Doppler-free. The final part of the dissertation treats the question of two-photon squeezed states. This requires quantized sidemodes. Squeezed states are minimum uncertainty states with unequal variances in the two quadratures of the electromagnetic field amplitude. One way to generate these states is via multiwave mixing and we present here the first calculation for nondegenerate two-photon multiwave mixing as it applies to squeezed states. We find that in general two-photon squeezed states require lower intensities and detuning than those predicted by the one-photon model.
    • Two-photon spectroscopy of conjugated organic chromophores

      Perry, Joseph W.; Pond, Stephanie J. (The University of Arizona., 2003)
      The study of two-photon absorbing (TPA) chromophores has previously shown that intramolecular charge transfer (ICT) between electron donors (D) and acceptors (A) symmetrically substituted on a π-conjugated bridge can result in large values of the two photon cross section (δ). This work addresses the role of torsion in the π-backbone on δ, modulation of δ by solvent polarity, and development of two-photon excitable molecular sensors. Investigations of the one- and two-photon properties of di(styryl)benzene derivatives with terminal donor groups and cyano acceptors substituted either on the central phenyl ring or on the adjacent vinyl groups show that the position of the cyano group has a significant effect on the geometry and optical properties of the molecules. δ for vinyl substituted molecules is half that for phenylene substituted molecules and is similar to the values obtained for molecules with no acceptor groups. The one- and two-photon spectroscopic differences can be related to the donor-acceptor distance in these molecules and to the degree of torsion in conjugated backbone. Torsional effects on the electronic coupling of multi-chromophore molecules are also investigated. For quadrupolar TPA chromophores, solvent polarity weakly affects the linear absorption but strongly modifies the fluorescence spectral position and quantum yield (η). The TPA peak position does not shift with solvent polarity, however the magnitude of δ increases by up to a factor of two in acetonitrile relative to toluene. Analysis of the data in terms of the stabilization of intramolecular charge transfer by polar solvents is explored. Two-photon absorbing molecular sensors are investigated in which an ion binding group is incorporated as one of the donor groups (D-A-D' ) in a TPA molecule. When one monoaza-15-crown-5-ether macrocycle is bound to the chromophore, the two-photon induced fluorescence signal (ηδ) decreases seven-fold upon addition of magnesium ions, in part as delta is modulated, due to decreased ICT from the nitrogen lone pair involved in ion binding. In molecules incorporating 1,2-bis(o-aminophenoxy)-ethane- N,N,N',N'-tetraacetic acid, a 5-fold enhancement of ηδ is observed upon calcium ion binding in water at 720 nm. Changes in the TPA spectrum upon binding of Ca²⁺ in micellar systems are also observed.
    • Two-stage stochastic linear programming: Stochastic decomposition approaches.

      Higle, Julia L.; Yakowitz, Diana Schadl.; Sen, Suvrajeet; Szidarovszky, Ferenc; Suchanek, Ana; Shaked, Moshe (The University of Arizona., 1991)
      Stochastic linear programming problems are linear programming problems for which one or more data elements are described by random variables. Two-stage stochastic linear programming problems are problems in which a first stage decision is made before the random variables are observed. A second stage, or recourse decision, which varies with these observations compensates for any deficiencies which result from the earlier decision. Many applications areas including water resources, industrial management, economics and finance lead to two-stage stochastic linear programs with recourse. In this dissertation, two algorithms for solving stochastic linear programming problems with recourse are developed and tested. The first is referred to as Quadratic Stochastic Decomposition (QSD). This algorithm is an enhanced version of the Stochastic Decomposition (SD) algorithm of Higle and Sen (1988). The enhancements were designed to increase the computational efficiency of the SD algorithm by introducing a quadratic proximal term in the master program objective function and altering the manner in which the recourse function approximations are updated. We show that every accumulation point of an easily identifiable subsequence of points generated by the algorithm are optimal solutions to the stochastic program with probability 1. The various combinations of the enhancements are empirically investigated in a computational experiment using operations research problems from the literature. The second algorithm is an SD based algorithm for solving a stochastic linear program in which the recourse problem appears in the constraint set. This algorithm involves the use of an exact penalty function in the master program. We find that under certain conditions every accumulation point of a sequence of points generated by the algorithm is an optimal solution to the recourse constrained stochastic program, with probability 1. This algorithm is tested on several operations research problems.
    • A type I error investigation of modified Scheffe-based multiple-comparison procedures in factorial ANOVA, MANOVA, and multiple-regression situations

      Levin, Joel R.; Zhou, Dora Xinyue (The University of Arizona., 2004)
      The present study extends the previous one-way ANOVA multiple-comparison findings of Meyers and Beretvas (2003) to interaction comparisons in factorial ANOVA designs, one-factor MANOVA comparisons, and tests of partial regression coefficients in multiple regression, in specific regard to the practical utility of modified (sequential) Scheffe-based procedures. Researchers who are concerned with maintaining familywise Type I error rates while increasing statistical power are encouraged to consider these improved multiple-comparison methods.
    • Type Ia supernova explosions in binary systems: The impact on the secondary star and its consequences

      Burrows, Adam; Marietta, Evonne Grace (The University of Arizona., 1999)
      One method of discriminating between the many Type Ia progenitor scenarios is searching for contaminating hydrogen stripped from the companion star. However, this requires understanding the effect of the impact on different companion stars to predict the amount of hydrogen stripped and its distribution in velocity and solid angle for the types of binary scenarios have been proposed as progenitor models. We present several 2-D numerical simulations of the impact of a Type Ia supernova explosion with low-mass main sequence, subgiant, and red giant companions. The binary parameters were chosen to represent several classes of single-degenerate, hydrogen-rich Type Ia progenitor models that have been suggested in the literature. We find that the main sequence and subgiant companions lose ∼15% of their mass as a result of the impact of the supernova shell. The red giant companions lose 96%-98% of their envelopes. The main sequence companion receives a kick of 86 km s⁻¹, the subgiant 49 km s⁻¹. In all cases, the kick received by the remnant is smaller than the original orbital velocity. Because it is too small to intercept more than a negligible amount of momentum, the red giant core will not receive a kick. The characteristic velocity of the stripped hydrogen is less than 10³ km s⁻¹ for all the scenarios: 420-590 km s⁻¹ for the red giant companions (depending on the scenario), 850 km s⁻¹ for the main sequence companion, and 900 km s⁻¹ for the subgiant companion. The stripped hydrogen contaminates a wide solid angle behind the companion: 115° from the downstream axis for the red giant, 66° for the main sequence star, and 72° for the subgiant. We find that the bulk of the stripped hydrogen is embedded within the low-velocity iron of the supernova ejecta and may be visible as narrow emission lines months after maximum light. However, to make any definitive predictions requires non-LTE radiative transfer calculations using the low-velocity distribution of the stripped hydrogen to determine the effect of hydrogen contamination on the late-time supernova spectrum.
    • Type II supernovae as distance indicators

      Pinto, Philip A.; Hamuy, Mario Andres (The University of Arizona., 2001)
      I report photometry and spectroscopy for 16 Type II supernovae (SNe) observed during the Calan/Tololo, SOIRS, and CTIO SN programs, a valuable resource for astrophysical studies. I perform a detailed assessment of the performance of the "expanding photosphere method" (EPM) in the determination of extragalactic distances. EPM proves very sensitive to the many steps involved in the analysis which can make it an art instead of an objective measurement tool. To minimize biases I implement objective procedures to compute synthetic magnitudes, measure true photospheric velocities, interpolate velocities, estimate dust extinction and realistic errors. While EPM performs well during the initial phases of SN evolution, I find distance residuals as large as 50% as the photosphere approaches the H recombination temperature. Despite the effort to lend credence to EPM, it proves necessary to exercise great care to avoid biasing the results. The main sources of uncertainties are observational errors (8%), dilution factors (11%), velocity interpolations (12%), and dust extinction (14%). The EPM Hubble diagram suggests the true error in an individual EPM distance is 20%. I find values of 63 ± 8 and 67 ± 7 km s⁻¹ Mpc⁻¹ for the Hubble constant, depending on the redshift sample chosen for the analysis. This result is independent of the extragalactic distance scale which yields 65 ± 5 from Cepheid/SNe la distances. From four objects the comparison of EPM and Tully-Fisher yields D(EPM)/D(TF) = 0.82 ± 0.12. I derive bolometric corrections for plateau SNe (SNe II-P) that permit me to obtain reliable bolometric luminosities from BVI photometry. Despite the great diversity displayed by SNe II-P, the duration of the plateau is approximately the same and the luminosities and expansion velocities measured in the middle of the plateau prove highly correlated. From the luminosity of the exponential tail I obtain ⁵⁶Co masses ranging between 0.02 and 0.28 M(⊙), and some evidence that SNe with brighter plateaus produce more Ni (and its daughter Co). The correlation between expansion velocity and luminosity permits me the use of SNe II-P as standard candles with a magnitude dispersion between 0.39-0.20 mag. Using SN 1987A to calibrate the Hubble diagram I get H₀ = 55 ± 12 and H₀ = 56 ± 9 from the V and I filters, respectively.
    • A typological investigation of dissimilation

      Archangeli, Diana; Suzuki, Keiichiro (The University of Arizona., 1998)
      This dissertation investigates the phenomenon of dissimilation from a theoretical perspective, with special attention to crosslinguistic patterns. After first arguing that the previous accounts based on the Obligatory Contour Principle (OCP) (Leben 1973, McCarthy 1979, 1986) are not satisfactory, I propose an alternative theory of identity avoidance, G sc ENERALIZED OCP (GOCP) which generalizes the applicability of the traditional OCP to a wider range of phenomena, not just autosegmental (i.e. featural) ones. My proposal asserts that identity avoidance between two elements in sequence is fundamental to linguistic theory, an idea that can be characterized by a universal constraint governing various types of dissimilatory phenomena. This concept is implemented within the framework of Optimality Theory (Prince and Smolensky 1993, McCarthy and Prince 1993a,b), which provides the flexibility for constraints to be both violable and rankable. Contrary to the traditional OCP based approach which is bound by various representational properties such as feature geometry and underspecification, the proposed approach abandons this representational dependency in favor of the richly articulated constraint-based system. Based on the data collected from 57 language cases, I then examine the various factors that play a role in dissimilation, including the elements involved, their adjacency relations, and the domain of dissimilation. I demonstrate that the GOCP constitutes a consistent formal apparatus on the one hand, and the versatility to accommodate the complexity of dissimilation patterns on the other. Moreover, it is shown that the present approach formally unifies the characterization of both the similarity effects and blocking effects by directly incorporating Local Conjunction as a uniform mechanism of accounting for the Similarity effect, OCP-subsidiary feature phenomena. As a result, these phenomena need not require novel theoretical devices for each case, but rather are construed as instances of the combination of multiple GOCP constraints.
    • Tyrosine kinase activity in the developing olfactory system of Manduca sexta

      Tolbert, Leslie P.; Dubuque, Suzanne Hope (The University of Arizona., 1998)
      To begin to determine the role tyrosine kinases play in the development of the antennal lobe in Manduca sexta, phosphotyrosine levels were examined immunocytochemically during critical periods of development. Tyrosine phosphorylation was found to be highest in the region of the antennal lobe known to contain the growing tips of antennal-lobe neurons and forming synapses. To explore the relationship between synapses and tyrosine kinase activity a marker for synapses was developed for light level microscopy. Manduca synaptotagmin was cloned and sequenced and a polyclonal antibody (SYNT76) was produced against the amino terminal of the predicted peptide sequence. SYNT76 labeled known synaptic neuropils in the brain of Manduca and recognized a single 61 kd protein on immunoblots. Immunocytochemical double labeling of antennal lobes for synaptotagmin and phosphotyrosine showed that although the patterns were very similar there was surprisingly little direct signal overlap. The similarity of immunolabeling suggests that tyrosine kinases may affect synapses in the developing antennal lobe but the lack of dramatic signal overlap shows that this association does not occur at the active zone. A trk-like protein was identified immunocytochemically, using an antibody against mammalian neurotrophin receptors, in the same regions of the developing lobe that contained high levels of phosphotyrosine. Trk-like proteins and phosphotyrosine were also found in the growing processes of cultured antennal lobe neurons. To examine the role of trk-like kinases in process outgrowth of antennal-lobe neurons, a tyrosine kinase inhibitor specific for trk-like kinases (Tyrphostin AG879) was applied to cultured neurons and was found to inhibit process outgrowth from antennal-lobe neurons significantly when compared to cells grown under control conditions. To determine the identity of the antennal-lobe trk-like proteins outside of their kinase domains the process of cloning trk-like messenger RNA was begun with reverse transcriptase polymerase chain reactions (RT-PCR). Northern blot analysis using RT-PCR fragments with significant sequence similarity to mammalian trk receptors identified a single 4.5 kb trk-like transcript in the brain and specifically in the antennal lobe during development. These data suggest that a trk-like kinase may mediate a developmental signal that causes antennal-lobe neurons to grow processes.
    • The U.S. foreign policy in the Persian Gulf, 1968-1988: From regional surrogate to direct military involvement.

      Bahramzadeh, Mohammad Ali.; Whiting, Allen S.; Wahlke, John C.; Muller, Edward N. (The University of Arizona., 1993)
      This study examines the U.S. foreign policy toward the Persian Gulf from 1968 to 1988 with an attempt to explain why and how particular U.S. foreign policy decisions were made. It further attempts to determine whether each president, within this time frame, pursued a different foreign policy toward the region. The indicators used to longitudinally measure foreign policy change were trade, both imports and exports between the U.S. and the Persian Gulf countries, bilateral treaties between them, and U.S. military sales to them. By examining the effect of presidential succession on selected patterns of American foreign policy behavior toward the area it is apparent that the pattern of interaction exhibits a clear continuity and in fact different administrations have not drastically altered the fundamental thrust of U.S. foreign policy. Furthermore, from a broad historical perspective, this study challenges the conventional notion that U.S. foreign policy has been "short-sighted" and often erratic. By examining two case studies, namely the Iran-Iraq war and U.S. decision to reflag Kuwaiti oil tankers, one can readily see that U.S. foreign policy is far from being reactive in its approach. In general, the evident suggests that the U.S. foreign policy in the Persian Gulf, in a broad conceptual framework, can be explained as a part of the rational decision making process where the U.S. foreign policy makers select the alternatives best suited to maximize the strategic goals and objectives.
    • U.S. Transnational Higher Education in Cambodia: Soft Power and Orientalism in Context

      Lee, Jenny J.; Vance, Hillary; Rhoades, Gary; Koyama, Jill (The University of Arizona., 2021)
      In the expanding landscape of transnational higher education (TNHE), cases have begun to emerge that serve as possible bellwethers for future challenges. These challenges include geopolitical conflicts and concerns over foreign influence that threaten the viability of continued TNHE delivery. To explore this issue in depth, this study focused on a particular case, that of a U.S. TNHE program in Cambodia, at a time of increased tensions between home and host country.This study explored the perceptions, values, and attitudes of local students enrolled in a U.S. TNHE program in Cambodia and how their experiences and perceptions connected with the complex political relationship between the United States and Cambodia. 32 students, 4 staff members, and 5 faculty members involved in the program were interviewed to learn about their perceptions of the program and what values and attitudes they held related to both the program, its context, and their participation in it. Findings indicate that the soft power of the United States, in particular that of its higher education system, remains strong in spite of negative perceptions of U.S. politics and foreign policy, and despite the contentious nature of U.S./Cambodian relations. Additionally, the study found the presence of Orientalist tropes that were internalized by students when expressing their preference for U.S. higher education over Cambodian higher education, which have been reinforced by marketing and media, as well as by the opinions of family, friends, faculty, staff members, and acquaintances. By integrating these findings, this study illuminates how the soft power attraction of the United States helps TNHE programs exhibit resilience even in times of political crisis between sending and receiving countries. However, the long-term viability of such programs, and their reliance on U.S. soft power attraction, is questionable and subject to the changing nature of the political context. Additionally, with the increase in the number of TNHE providers and programs, practitioners should be cognizant of the messaging used to promote programs to students and their families. In this way, they can avoid reinforcement of negative perceptions of the host country to ensure that long term involvement in the local higher education landscape is rooted in respectful partnership and not by banking on the enduring attraction of U.S. soft power.
    • UA62784; a Putative Inhibitor of CENP-E Kinesin-like Protein and its Effects on Human Pancreatic Cancer Cells

      Dorr, Robert T.; Henderson, Meredith C.; Dorr, Robert T.; Bowden, G. Timothy; Gerner, Eugene W.; Cress, Anne E.; Martinez, Jesse D. (The University of Arizona., 2008)
      UA62784 is a novel fluorenone identified in a biologic screen of compounds that are selectively cytotoxic in DPC4 (deleted in pancreatic cancer)-deleted pancreatic cancer cells. We sought to determine the mechanism of action of UA62784, and discovered it to be a potent mitotic inhibitor. UA62784 affects the ATPase activity of the mitotic kinesin centromere protein E (CENP-E), but does not affect other known mitotic kinesins. This inhibition of ATPase activity is not caused by an inhibition of microtubule binding nor is it caused by a failure of the kinesin to translocate to the nucleus during mitosis. Despite the anti-cancer properties of this drug, UA62784 is relatively insoluble and is not suitable as a lead compound for further development.Once we determined the mechanism of action of UA62784, we sought to determine if analogs would demonstrate the same potent mitotic inhibition while also offering properties such as increased solubility. A small library of chemical analogs was generated wherein each compound was a slight variation of UA62784 (termed the DPC series). Several potential leads were identified which exhibited increased solubility and/or increased cytotoxic activity. When tested for CENP-E ATPase inhibition, some compounds were noted to inhibit other kinesins as well. We therefore created a screen where each of the DPC compounds was tested for activity in Eg5, CENP-E, MKLP-1, MCAK, and KIF3C kinesins. Within these data, there is a correlation between cellular IC50 and kinesin ATPase inhibition for CENP-E and MKLP-1. A few compounds emerged from these studies, including DPC046, which has a low cellular IC50 and inhibits all five kinesins to some degree. DPC046 was used in a mouse xenograft study to determine in vivo efficacy, but no significant tumor shrinkage was seen, likely due to solubility limitations affecting the amount of bioavailable compound.From these studies we conclude that the cytotoxic effects seen in UA62784 and its analogs are due, at least in part, to their inhibition of kinesin proteins. We demonstrate that compounds that inhibit CENP-E and other kinesin proteins hold promise in cytotoxically targeting pancreatic cancer cells. Further development is needed to optimize DPC046 compound solubility in order to increase in vivo efficacy.
    • Ultra narrow band fiber optic Bragg grating filters for atmospheric water vapor measurements

      Herman, Benjamin M.; Vann, Lelia Belle (The University of Arizona., 2003)
      Optical fibers have revolutionized telecommunications. Much of the success of optical fiber lies in its near-ideal properties: low transmission loss, high optical damage threshold, and low optical nonlinearity. The photosensitivity of an optical fiber was accidentally discovered by Hill, et al. in 1978. However, the technological advances made in the field of photosensitive optical fibers are relatively recent. This fascinating technology of photosensitive fiber is based on the principle of a simple in-line all-fiber optical filter. It has been shown that the transmission spectrum of a fiber Bragg grating can be tailored by incorporating multiple phase-shift regions during the fabrication process. Phase shifts open up ultra narrowband transmission windows inside the stop band of the Bragg grating. As a specific application, this research is focused on applying this technology in future space-based water vapor DIfferential Absorption LIDAR (DIAL) systems to improve the performance of space-based LIDAR systems by rejecting the reflected solar background. The primary goal of this research effort was to demonstrate the feasibility of using ultra narrow band fiber optic Bragg grating filters for atmospheric water vapor measurements. Fiber Bragg gratings were fabricated such that two transmission filter peaks occurred and were tunable, one peak at a 946 nm water vapor absorption line and another peak at a region of no absorption. Both transmission peaks were in the middle of a 2.66-nm stop band. Experimental demonstration of both pressure and temperature tuning was achieved and characterization of the performance of several custom-made optical fiber Bragg grating filters was made. To our knowledge these are the first optical fiber gratings made in this frequency range and for this application. The bandwidth and efficiency of these filters were measured and then these measurements were compared with theoretical calculations using a piecewise matrix form of the coupled-mode equation. Finally, an ultra narrow band water vapor DIAL filter was characterized having two pass bands less than 8 pm and peak transmissions greater than 80 percent. Such fiber optic filters are now ready for integrating into space-based water vapor LIDAR systems. More broadly, these filters have the characteristics that will revolutionized satellite remote-sensing.
    • Ultra-Precision Non-Contact Metrology for Optical Shop and Alignment Applications

      Liang, Rongguang; Khreishi, Manal A.; Schwiegerling, James; Kupinski, Matthew (The University of Arizona., 2019)
      New, unconventional designs for modern optical systems strive for superior performance at lower cost and volume. These compact optical instruments, with larger fields of view and faster f-numbers, call for more challenging prescriptions to meet their ambitious requirements. Freeform optical surfaces have the potential to enable these compact, high-performance systems, but are more challenging to characterize and hence to fabricate. This work enables the use of precision coordinate measuring machine (CMM) for a wide range of optical testing and alignment applications, including the testing and integration of freeform and aspheric optics. In this dissertation, the capabilities of this non-contact, precision metrology instrument have been stretched beyond its everyday applications. Advanced data collection and reduction techniques have been developed to determine the as-built prescription of optical surfaces, as well as the alignment with respect to the part and global coordinate systems. For measurement of low-order surface error and prescription parameters, when compared to interferometry and other optical shop techniques that rely on optical path difference or slope error, these techniques have greater dynamic range and, in some cases, precision that approaches the sensitivity of traditional methods. For example, the CMM, when equipped with a non-contact probe that utilizes a chromatic confocal principle, has a dynamic range measured in mm, a sensitivity measured in nm, yet does not require a null corrector or other custom-made components. In one case, the CMM was used to measure the surface error and as-built prescriptions of two freeform mirrors for a reflective telescope. The CMM was then utilized to align the telescope, as confirmed by an end-to-end interferometric test used to evaluate the system performance. In another example, the CMM was paired with a laser radar (LR) to align a different telescope that uses off-axis, polynomial aspheres in a three mirror anastigmat (TMA) configuration. The CMM enables fast determination of as-built prescription parameters and surface error without the types of systematic errors that are inherent in some traditional optical test setups, like the removal of power or other aberration from alignment of the test setup. The applicability of this work was further studied for large, convex aspheres using the spare secondary mirror for the Hubble Space Telescope (HST) and, via simulation, for large meter-class optics such as the Giant Magellan Telescope (GMT) secondary mirror segments. This measurement technique was further extended to other types of optical surfaces, like gratings and spatial filters. In the case of gratings, it is shown that one can derive as-built period, amplitude, and grating vector quickly and accurately from a few, fast scans.
    • Ultra-Sensitive and Selective Whispering Gallery Mode Microtoroid Chemical Sensor

      Su, Judith; Li, Cheng; McLeod, Euan; Kolesik, Miro (The University of Arizona., 2022)
      Optical Whispering gallery mode (WGM) microresonators, which benefit from an ultra-high quality (Q) factor and small mode volume to significantly enhance light-matter interaction, stand out from other sensors, and are utilized in a variety of biochemical sensing or physical parameter detection applications. Physical or chemical reactions occurring in the evanescent field of the polymer-treated microtoroid equatorial plane will be translated into variations of the WGM spectra, which will, in turn, be recorded and analyzed through techniques such as frequency locking, balanced detection, and post data processing. The overall platform is known as the Frequency-locked optical whispering evanescent resonator (FLOWER) system. The performance and characteristics of ultra-sensitive and selective WGM gas sensors are evaluated and demonstrated in this dissertation. Two approaches to further improve the system are proposed, one based on plasmonic near-field enhancement to improve the sensitivity and the other on a fiber metrology method using Rayleigh backscattering to eliminate the thermal noise of the sensing system. Finally, another sensing application using the dual-FLOWER system for particle shape analysis is introduced.
    • Ultrafast carrier and gain dynamics in strongly confined semiconductor quantum dots.

      Giessen, Harald Willi.; Peyghambarian, Nasser; Kippelen, Bernard; Binder, Rudolf (The University of Arizona., 1995)
      This thesis investigates the carrier and gain dynamics of semiconductor quantum dots in the strong quantum confinement regime (i.e. the dot radius is smaller than the bulk excitonic Bohr radius). The materials under investigation are InP and CdSe. We can summarize our findings as follows: For the first time, the quantum confined ground state in InP quantum dots has been observed at room temperature by femtosecond spectral holeburning. This is the first confirmation of the observation of a strongly confined quantum dot made of III-V semiconductor materials. In CdSe quantum dots with a radius of half the bulk exciton Bohr radius, the carrier and gain dynamics have been investigated. The predicted phonon bottleneck, which should slow down carrier relaxation up to nanoseconds, has not been found. The carrier relaxation rates are rather on the order of 1 eV/ps. Gain has been found for the first time in strongly confined quantum dots. The existence of gain was proven by spectral holeburning in the gain region. The gain buildup and decay dynamics have been studied on a femtosecond and picosecond timescale. A multi-level model including biexcitons accounts for the gain formation. The model has been confirmed by three-beam spectral holeburning experiments and femtosecond pump-probe experiments with circularly polarized light. Some quantum dots did not show gain under high optical excitation but instead exhibited photodarkening. The carrier separation and localization dynamics of this photodarkening process has been studied on a femtosecond timescale. For the first time, the shift of the bleaching towards lower energy during the localization process could be observed on a femtosecond timescale. Finally, pulse propagation in bulk CdSe at multiple Pi-pulses has been studied. For the first time, strong evidence for the observation of self induced transparency in semiconductors has been found. Also, optical precursors, probably of nonlinear nature, have been found.
    • Ultrafast carrier dynamics and enhanced electroabsorption in (gallium,indium)arsenide/(aluminum,indium)arsenide asymmetric double quantum well structures.

      Krol, Mark Francis.; Peyghambarian, Nasser; Binder, Rudolf; Kippelen, Bernard (The University of Arizona., 1995)
      An experimental study, utilizing a novel nondegenerate transmission pump/probe technique, of ultrafast electron and hole tunneling in (Ga,In)As/Al,In)As asymmetric double quantum wells (ADQWs) is presented. A single time constant is observed at low carrier densities indicating the holes tunnel from the narrow well (NW) to the wide well (WW) at least as fast as electrons. At high carrier densities a two component decay is observed, consistent with phase-space filling and space-charge effects blocking tunneling carriers. The fast transfer of electrons was confirmed to be a LO-phonon assisted process. A detailed theoretical study of ultrafast hole tunneling at low carrier densities indicates that in ternary materials alloy disorder is responsible for fast hole transfer between the wells. Enhanced electroabsorption in selectively doped (Ga,In)As/(Al,In)As ADQWs by the use of real space electron transfer is demonstrated. The electron concentration in both the WW and NW is investigated by field-dependent absorption and photoluminescence spectroscopy. The results are compared to absorption changes in an undoped ADQW structure which utilizes the quantum confined Stark effect. The doped modulator exhibits a significantly larger red-shift with applied field than the undoped structure.