16 Matching Results

Search Results

Bulk gold catalyzed oxidation reactions of amines and isocyanides and iron porphyrin catalyzed N-H and O-H bond insertion/cyclization reactions of diamines and aminoalcohols

Description: This work involves two projects. The first project entails the study of bulk gold as a catalyst in oxidation reactions of isocyanides and amines. The main goal of this project was to study the activation and reactions of molecules at metal surfaces in order to assess how organometallic principles for homogeneous processes apply to heterogeneous catalysis. Since previous work had used oxygen as an oxidant in bulk gold catalyzed reactions, the generality of gold catalysis with other oxidants was examined. Amine N-oxides were chosen for study, due to their properties and use in the oxidation of carbonyl ligands in organometallic complexes. When amine N-oxides were used as an oxidant in the reaction of isocyanides with amines, the system was able to produce ureas from a variety of isocyanides, amines, and amine N-oxides. In addition, the rate was found to generally increase as the amine N-oxide concentration increased, and decrease with increased concentrations of the amine. Mechanistic studies revealed that the reaction likely involves transfer of an oxygen atom from the amine N-oxide to the adsorbed isocyanide to generate an isocyanate intermediate. Subsequent nucleophilic attack by the amine yields the urea. This is in contrast to the bulk gold-catalyzed reaction mechanism of isocyanides with amines and oxygen. Formation of urea in this case was proposed to proceed through a diaminocarbene intermediate. Moreover, formation of the proposed isocyanate intermediate is consistent with the reactions of metal carbonyl ligands, which are isoelectronic to isocyanides. Nucleophilic attack at coordinated CO by amine N-oxides produces CO{sub 2} and is analogous to the production of an isocyanate in this gold system. When the bulk gold-catalyzed oxidative dehydrogenation of amines was examined with amine N-oxides, the same products were afforded as when O{sub 2} was used as the oxidant. When the two types of oxidants were directly ...
Date: December 29, 2011
Creator: Klobukowski, Erik
Partner: UNT Libraries Government Documents Department

Adaptations in Electronic Structure Calculations in Heterogeneous Environments

Description: Modern quantum chemistry deals with electronic structure calculations of unprecedented complexity and accuracy. They demand full power of high-performance computing and must be in tune with the given architecture for superior e#14;ciency. To make such applications resourceaware, it is desirable to enable their static and dynamic adaptations using some external software (middleware), which may monitor both system availability and application needs, rather than mix science with system-related calls inside the application. The present work investigates scienti#12;c application interlinking with middleware based on the example of the computational chemistry package GAMESS and middleware NICAN. The existing synchronous model is limited by the possible delays due to the middleware processing time under the sustainable runtime system conditions. Proposed asynchronous and hybrid models aim at overcoming this limitation. When linked with NICAN, the fragment molecular orbital (FMO) method is capable of adapting statically and dynamically its fragment scheduling policy based on the computing platform conditions. Signi#12;cant execution time and throughput gains have been obtained due to such static adaptations when the compute nodes have very di#11;erent core counts. Dynamic adaptations are based on the main memory availability at run time. NICAN prompts FMO to postpone scheduling certain fragments, if there is not enough memory for their immediate execution. Hence, FMO may be able to complete the calculations whereas without such adaptations it aborts.
Date: November 29, 2011
Creator: Talamudupula, Sai
Partner: UNT Libraries Government Documents Department


Description: The salivary gland chromosomes of Chironomus tentans larvae collected from White Oak Creek, an area contaminated by radioactive waste from the Oak Ridge National Laboratory, and from six uncontaminated areas were examined for chromosomal aberrations. White Oak Creek populations were exposed to absorbed doses as high as 230 rads per year or about 1000 times background. Chromosomal maps were constructed to make a general comparison of the banding pattern of the salivary chromosomes of the C. tentans in the East Tennessee area with those of Canada and Europe. These maps were used as a reference in scoring aberrations. Fifteen different chromosomal aberrations were found in 365 larvae taken from the irradiated population as compared with five different aberrations observed in 356 larvae from six control populations, but the mean number of aberrations per larva did not differ in any of the populations. The quantitative amount of heterozygosity was essentially the same in the irradiated and the control population, but there were three times the variety of chromosomal aberrations found in the irradiated area. From this evidence it was concluded that chronic low-level irradiation from radioactive waste was increasing the variability of chromosomal aberrations without significantly increasing the frequency. It was also concluded that chromosomal polymorphism can be maintained in a natural population without superiority of the heterozygous individuals. (C.H.)
Date: January 29, 1964
Creator: Blaylock, B G; Auerbach, S I & Nelson, D J
Partner: UNT Libraries Government Documents Department

Parametric Model for Astrophysical Proton-Proton Interactions and Applications

Description: Observations of gamma-rays have been made from celestial sources such as active galaxies, gamma-ray bursts and supernova remnants as well as the Galactic ridge. The study of gamma rays can provide information about production mechanisms and cosmic-ray acceleration. In the high-energy regime, one of the dominant mechanisms for gamma-ray production is the decay of neutral pions produced in interactions of ultra-relativistic cosmic-ray nuclei and interstellar matter. Presented here is a parametric model for calculations of inclusive cross sections and transverse momentum distributions for secondary particles--gamma rays, e{sup {+-}}, {nu}{sub e}, {bar {nu}}{sub e}, {nu}{sub {mu}} and {bar {nu}}{sub {mu}}--produced in proton-proton interactions. This parametric model is derived on the proton-proton interaction model proposed by Kamae et al.; it includes the diffraction dissociation process, Feynman-scaling violation and the logarithmically rising inelastic proton-proton cross section. To improve fidelity to experimental data for lower energies, two baryon resonance excitation processes were added; one representing the {Delta}(1232) and the other multiple resonances with masses around 1600 MeV/c{sup 2}. The model predicts the power-law spectral index for all secondary particle to be about 0.05 lower in absolute value than that of the incident proton and their inclusive cross sections to be larger than those predicted by previous models based on the Feynman-scaling hypothesis. The applications of the presented model in astrophysics are plentiful. It has been implemented into the Galprop code to calculate the contribution due to pion decays in the Galactic plane. The model has also been used to estimate the cosmic-ray flux in the Large Magellanic Cloud based on HI, CO and gamma-ray observations. The transverse momentum distributions enable calculations when the proton distribution is anisotropic. It is shown that the gamma-ray spectrum and flux due to a pencil beam of protons varies drastically with viewing angle. A fanned proton jet with a ...
Date: January 29, 2008
Creator: Karlsson, Niklas & /Royal Inst. Tech., Stockholm
Partner: UNT Libraries Government Documents Department

Study of Charmed Baryon Sigma(C)(2800) Production at the BaBar Experiment

Description: This dissertation reports on a study of search for an orbitally excited state of charmed baryons {Sigma}{sub c}{sup 0}(2800) and {Sigma}{sub c}{sup ++}(2800). They measure the widths, momentum spectrum and production cross-section for these states decaying into a {Lambda}{sub c}{sup +} and a charged {pi}. The analysis uses 230 fb{sup -1} of data collected at BABAR detector operating at PEP-II collider at Stanford Linear Accelerator Center. The data is collected in the region of {Upsilon}(4S) an {approx} 40 MeV below the resonance. {Lambda}{sub c}{sup +} baryon is reconstructed in the decay mode pK{sup -}{pi}{sup +}. The {Sigma}{sub c}(2800) baryon production at continuum is observed to be quite significant for x{sub p} > 0.7, where x{sub p} = p/{radical}E{sup 2}+M{sup 2} is the scaled momentum and varies from 0.0 to 1.0. The momentum spectrum is measured by considering the corrected yield for momentum bins above x{sub p} > 0.5 and can be parameterized very well by a Peterson function, given by: dN/dx{sub p} {proportional_to} 1/x{sub p}(1 - 1/x{sub p} - {epsilon}/1-x{sub p}){sup 2}. The values for the peterson parameter {epsilon}, are found to be 0.050 {+-} 0.010 for {Sigma}{sub c}{sup 0}(2800) and 0.057 {+-} 0.012 for {Sigma}{sub c}{sup ++}(2800). They use the momentum spectrum to evaluate the production cross-sections to be: {sigma}(e{sup +}e{sup -} {yields} {Sigma}{sub c}{sup 0}(2800)X). {Beta}({Sigma}{sub c}{sup 0}(2800) {yields} {Lambda}{sub c}{sup +}{pi}{sup -}) = 1.36 {+-} 0.42 pb and {sigma}(e{sup +}e{sup -} {yields} {Sigma}{sub c}{sup ++}(2800)X).{Beta}({Sigma}{sub c}{sup ++}(2800){yields} {Lambda}{sub c}{sup +}{pi}{sup +}) = 1.68 {+-} 0.54 pb. The authors also measure the width to be 65.6 {+-} 14.9 MeV and 67.7 {+-} 16 MeV, for the neutral and charged modes, respectively, and the corresponding observed mass differences ({Lambda}{sub c}{sup +}{pi} - {Lambda}{sub c} + 2.285), are 2.8008 {+-} 0.0023GeV/c{sup 2} and 2.7980 {+-} 0.0028GeV/c{sup 2}. The uncertainty here ...
Date: February 29, 2008
Creator: Ahmded, Shamona & /SUNY, Stony Brook
Partner: UNT Libraries Government Documents Department

Developing New Nanoprobes from Semiconductor Nanocrystals

Description: In recent years, semiconductor nanocrystal quantum dots havegarnered the spotlight as an important new class of biological labelingtool. Withoptical properties superior to conventional organicfluorophores from many aspects, such as high photostability andmultiplexing capability, quantum dots have been applied in a variety ofadvanced imaging applications. This dissertation research goes along withlarge amount of research efforts in this field, while focusing on thedesign and development of new nanoprobes from semiconductor nanocrystalsthat are aimed for useful imaging or sensing applications not possiblewith quantum dots alone. Specifically speaking, two strategies have beenapplied. In one, we have taken advantage of the increasing capability ofmanipulating the shape of semiconductor nanocrystals by developingsemiconductor quantum rods as fluorescent biological labels. In theother, we have assembled quantum dots and gold nanocrystals into discretenanostructures using DNA. The background information and synthesis,surface manipulation, property characterization and applications of thesenew nanoprobes in a few biological experiments are detailed in thedissertation.
Date: May 29, 2006
Creator: Fu, Aihua
Partner: UNT Libraries Government Documents Department

I: Low Frequency NMR and NQR Using a dc SQUID. II: Variable-temperature 13C CP/MAS of Organometallics

Description: NMR and NQR at low frequencies are difficult prospects due to small nuclear spin polarization. Furthermore, the sensitivity'of the inductive pickup circuitry of standard spectrometers is reduced as the frequency is lowered. I have used a cw-SQUID (Superconducting QUantum Interference Device) spectrometer, which has no such frequency dependence, to study the local atomic environment of {sup 14}N via the quadrupolar interaction. Because {sup 14}N has spin I = 1 and a 0-6 MHz frequency range, it is not possible to obtain well-resolved spectra in high magnetic fields. I have used a technique to observe {sup 14}N NQR resonances via their effect on neighboring protons mediated by the heteronuclear dipolar interaction to study peptides and narcotics. The sensitivity of the SQUID is not enough to measure low-frequency surface (or other low spin density) systems. The application of spin-polarized xenon has been previously used to enhance polarization in conventional NMR experiments. Because xenon only polarizes spins with which it is in contact, it is surface selective. While differences in chemical shifts between surface and bulk spins are not large, it is expected that the differences in quadrupole coupling constant should be very large due to the drastic change of the electric field gradient surrounding spins at the surface. With this in mind, I have taken preliminary steps to measure SQUID detected polarization transfer from Xe to another spin species at 4.2 K and in small magnetic fields (<50 G). In this regime, the spin-lattice relaxation of xenon is dependent on the applied magnetic field. The results of our efforts to characterize the relaxation of xenon are presented. The final section describes the solid-state variable-temperature (VT) one- and two-dimensional {sup 13}C cross polarization (CP)/magic angle spinning (MAS) NMR of Hf({eta}{sup 5}-C{sub 5}H{sub 5}){sub 2}({eta}{sup 1}-C{sub 5}H{sub 5}){sub 2}, Zr({eta}{sup 5}-C{sub 5}H{sub 5}){sub 3}({eta}{sup ...
Date: November 29, 1995
Creator: Ziegeweid, M.A.
Partner: UNT Libraries Government Documents Department


Description: We constrain the apex of the Cabibbo-Kobayashi-Maskawa unitarity triangle with measurements of B {yields} K*{pi} amplitudes from analyses of B{sup 0} {yields} K{sup +}{pi}{sup -}{pi}{sup 0} and B{sup 0} {yields} K{sub S}{pi}{sup +}{pi}{sup -} decays. This constraint is consistent with the world average. The B{sup 0} {yields} K{sup +}{pi}{sup -}{pi}{sup 0} decay mode is reconstructed from a sample of 454 million B{sup 0}{bar B}{sup 0} events collected by the BABAR detector at SLAC. We measure direct CP violation in B{sup 0} {yields} K*{sup +}{pi}{sup -} decays at the level of 3{sigma} when measurements from both B{sup 0} {yields} K{sup +}{pi}{sup -}{pi}{sup 0} and B{sup 0} {yields} K{sub S}{pi}{sup +}{pi}{sup -} decays are combined.
Date: April 29, 2010
Creator: Wagner, Andrew Phillips
Partner: UNT Libraries Government Documents Department

Searches for the Theta_s(1540)+ Strange-Pentaquark Candidate in e+e- Annihilation, Hadroproduction and Electroproduction with the BaBar Detector

Description: Since early in 2003, several experiments have presented evidence for the existence of a positive strangeness baryon state of mass around 1540 MeV/c{sup 2} and width <8 MeV, the {Theta}(1540), which decays to K{sup +}n and K{sup 0}p. Such a state has minimum quark content udud{bar s} and consequently has been interpreted as the S = +1 member of the anti-decuplet of pentaquark states proposed by Diakonov et al. Subsequently, the NA49 experiment presented evidence for the S = -2 member of the anti-decuplet, the {Xi}{sub 5}(1860){sup --}, but this has yet to be observed in any other experiment. Results from the search for the production of the {Theta}(1540) memember of the anti-decuplet of pentaquark states using data from e{sup +}e{sup -} collisions obtained with the BABAR detector at the PEP-II Collider are presented. No signal is observed, and cross section limits for the {Theta}(1540) are given; these prove to be well below the cross section values for ordinary baryons of similar mass. In addition, a search has been carried out for the electroproduction of the {Theta}(1540) in the material of the BABAR detector. Event selection procedures are discussed in detail, the results of this search are presented, and are discussed in the light of several other experiments.
Date: July 29, 2009
Creator: Coleman, Jonathan P.
Partner: UNT Libraries Government Documents Department

Towards the resolution of the solar neutrino problem

Description: A number of experiments have accumulated over the years a large amount of solar neutrino data. The data indicate that the observed solar neutrino flux is significantly smaller than expected and, furthermore, that the electron neutrino survival probability is energy dependent. This ''solar neutrino problem'' is best solved by assuming that the electron neutrino oscillates into another neutrino species. Even though one can classify the solar neutrino deficit as strong evidence for neutrino oscillations, it is not yet considered a definitive proof. Traditional objections are that the evidence for solar neutrino oscillations relies on a combination of hard, different experiments, and that the Standard Solar Model (SSM) might not be accurate enough to precisely predict the fluxes of different solar neutrino components. Even though it seems unlikely that modifications to the SSM alone can explain the current solar neutrino data, one still cannot completely discount the possibility that a combination of unknown systematic errors in some of the experiments and certain modifications to the SSM could conspire to yield the observed data. To conclusively demonstrate that there is indeed new physics in solar neutrinos, new experiments are aiming at detecting ''smoking gun'' signatures of neutrino oscillations, such as an anomalous seasonal variation in the observed neutrino flux or a day-night variation due to the regeneration of electron neutrinos in the Earth. In this dissertation we study the sensitivity reach of two upcoming neutrino experiments, Borexino and KamLAND, to both of these effects. Results of neutrino oscillation experiments for the case of two-flavor oscillations have always been presented on the (sin{sup 2} 2{theta}, {Delta}m{sup 2}) parameter space. We point out, however, that this parameterization misses the half of the parameter space {pi}/4 < {theta} {le} {pi}/2, which is physically inequivalent to the region 0 {le} {theta} {le} {pi}/4 in the presence ...
Date: August 29, 2000
Creator: Friedland, Alexander
Partner: UNT Libraries Government Documents Department

A simulation-based study of HighSpeed TCP and its deployment

Description: The current congestion control mechanism used in TCP has difficulty reaching full utilization on high speed links, particularly on wide-area connections. For example, the packet drop rate needed to fill a Gigabit pipe using the present TCP protocol is below the currently achievable fiber optic error rates. HighSpeed TCP was recently proposed as a modification of TCP's congestion control mechanism to allow it to achieve reasonable performance in high speed wide-area links. In this research, simulation results showing the performance of HighSpeed TCP and the impact of its use on the present implementation of TCP are presented. Network conditions including different degrees of congestion, different levels of loss rate, different degrees of bursty traffic and two distinct router queue management policies were simulated. The performance and fairness of HighSpeed TCP were compared to the existing TCP and solutions for bulk-data transfer using parallel streams.
Date: April 29, 2003
Creator: Souza, Evandro de
Partner: UNT Libraries Government Documents Department

Toward a New Generation of Student Outcome Measures: Connecticut's Common Core of Learning Assessment

Description: A report, "Toward a New Generation of Student Outcome Measures: Connecticut's Common Core of Learning Assessment" by Joan Boykoff Baron, Pascal D. Forgione, Jr. Douglas A. Rindone, Hanna Kruglanksi and Bruce Davey. Connecticut State, Department of Education, Division of Research, Evaluation and Assessment. 165 Capitol Avenue - Room 340. Hartford, Connecticut. Presented at American Education Association Annual Meeting, San Francisco, California. Part of Symposium 28.01 Beyond Effective Schools: Quality Indicators for Evaluation Schools and Districts. The Connecticut State Department of Education (CSDE) has begun a multi-year assessment of the extent to which students in Connecticut display the knowledge and traits described in the Common Core of Learning (CCL). Science and mathematics were the two chosen subjects to be assessed under CCL.
Date: March 29, 1989
Creator: Baron, Joan Boykoff; Forgione, Pascal D., Jr.; Rindone, Douglas A.; Kruglanksi, Hannah & Davey, Bruce
Partner: UNT Libraries Special Collections