106 Matching Results

Results open in a new window/tab.

Studies on two classes of positive electrode materials for lithium-ion batteries (open access)

Studies on two classes of positive electrode materials for lithium-ion batteries

The development of advanced lithium-ion batteries is key to the success of many technologies, and in particular, hybrid electric vehicles. In addition to finding materials with higher energy and power densities, improvements in other factors such as cost, toxicity, lifetime, and safety are also required. Lithium transition metal oxide and LiFePO<sub>4</sub>/C composite materials offer several distinct advantages in achieving many of these goals and are the focus of this report. Two series of layered lithium transition metal oxides, namely LiNi<sub>1/3</sub>Co<sub>1/3-y</sub>M<sub>y</sub>Mn<sub>1/3</sub>O<sub>2</sub> (M=Al, Co, Fe, Ti) and LiNi<sub>0.4</sub>Co<sub>0.2-y</sub>M<sub>y</sub>Mn<sub>0.4</sub>O<sub>2</sub> (M = Al, Co, Fe), have been synthesized. The effect of substitution on the crystal structure is related to shifts in transport properties and ultimately to the electrochemical performance. Partial aluminum substitution creates a high-rate positive electrode material capable of delivering twice the discharge capacity of unsubstituted materials. Iron substituted materials suffer from limited electrochemical performance and poor cycling stability due to the degradation of the layered structure. Titanium substitution creates a very high rate positive electrode material due to a decrease in the anti-site defect concentration. LiFePO<sub>4</sub> is a very promising electrode material but suffers from poor electronic and ionic conductivity. To overcome this, two new techniques have been developed to synthesize high …
Date: December 1, 2008
Creator: Wilcox, James Douglas
System: The UNT Digital Library
A New Spin on Photoemission Spectroscopy (open access)

A New Spin on Photoemission Spectroscopy

The electronic spin degree of freedom is of general fundamental importance to all matter. Understanding its complex roles and behavior in the solid state, particularly in highly correlated and magnetic materials, has grown increasingly desirable as technology demands advanced devices and materials based on ever stricter comprehension and control of the electron spin. However, direct and efficient spin dependent probes of electronic structure are currently lacking. Angle Resolved Photoemission Spectroscopy (ARPES) has become one of the most successful experimental tools for elucidating solid state electronic structures, bolstered by-continual breakthroughs in efficient instrumentation. In contrast, spin-resolved photoemission spectroscopy has lagged behind due to a lack of similar instrumental advances. The power of photoemission spectroscopy and the pertinence of electronic spin in the current research climate combine to make breakthroughs in Spin and Angle Resolved Photoemission Spectroscopy (SARPES) a high priority . This thesis details the development of a unique instrument for efficient SARPES and represents a radical departure from conventional methods. A custom designed spin polarimeter based on low energy exchange scattering is developed, with projected efficiency gains of two orders of magnitude over current state-of-the-art polarimeters. For energy analysis, the popular hemispherical analyzer is eschewed for a custom Time-of-Flight (TOF) …
Date: December 1, 2008
Creator: Jozwiak, Chris
System: The UNT Digital Library
Measurement of the Λ<sup>0</sup><sub>b</sub> lifetime in Λ<sup>0</sup><sub>b</sub> → Λ<sup>+</sup><sub>c</sub>π<sup>-</sup> decays at the Collider Detector at Fermilab (open access)

Measurement of the Λ<sup>0</sup><sub>b</sub> lifetime in Λ<sup>0</sup><sub>b</sub> → Λ<sup>+</sup><sub>c</sub>π<sup>-</sup> decays at the Collider Detector at Fermilab

The lifetime of the Λ<sup>0</sup><sub>b</sub> baryon (consisting of u, d and b quarks) is the theoretically most interesting of all b-hadron lifetimes. The lifetime of Λ<sup>0</sup><sub>b</sub> probes our understanding of how baryons with one heavy quark are put together and how they decay. Experimentally however, measurements of the Λ<sup>0</sup><sub>b</sub> lifetime have either lacked precision or have been inconsistent with one another. This thesis describes the measurement of Λ<sup>0</sup><sub>b</sub> lifetime in proton-antiproton collisions with center of mass energy of 1.96 TeV at Fermilab's Tevatron collider. Using 1070 ± 60pb<sup>-1</sup> of data collected by the Collider Detector at Fermilab (CDF), a clean sample of about 3,000 fully-reconstructed Λ<sup>0</sup><sub>b</sub> →Λ<sub>c</sub><sup>+</sup>π<sup>-</sup> decays (with Λ<sup>+</sup><sub>c</sub> subsequently decaying via Λ<sup>+</sup><sub>c</sub> → p<sup>+</sup> K<sup>-</sup> π<sup>+</sup>) is used to extract the lifetime of the Λ<sup>0</sup><sub>b</sub> baryon, which is found to be cτ(Λ<sup>0</sup><sub>b</sub>) = 422.8 ± 13.8(stat) ± 8.8(syst)μm. This is the most precise measurement of its kind, and is even better than the current world average. It also settles the recent controversy regarding the apparent inconsistency between CDF's other measurement and the rest of the world.
Date: September 1, 2008
Creator: Mumford, Jonathan Reid
System: The UNT Digital Library
Microwave power coupler for a superconducting multiple-cell cavity for accelerator application and its testing procedures (open access)

Microwave power coupler for a superconducting multiple-cell cavity for accelerator application and its testing procedures

Superconducting cavity resonators offer the advantage of high field intensity for a given input power, making them an attractive contender for particle accelerator applications. Power coupling into a superconducting cavity employed in a particle accelerator requires unique provisions to maintain high vacuum and cryogenic temperature on the cavity side, while operating with ambient conditions on the source side. Components introduced to fulfill mechanical requirements must show negligible obstruction of the propagation of the microwave with absence of critical locations that may give rise to electron multipaction, leading to a multiple section design, instead of an aperture, a probe, or a loop structure as found in conventional cavities. A coaxial power coupler for a superconducting multiple-cell cavity at 3.9 GHz has been developed. The cavity is intended to be employed as an accelerator to provide enhanced electron beam quality in a free-electron laser in Hamburg (FLASH) user facility. The design of the coupler called for two windows to sustain high vacuum in the cavity and two bellows to accommodate mechanical dimensional changes resulting from cryogenics. Suppression of multipacting was accomplished by the choice of conductor dimensions and materials with low second yield coefficients. Prior to integration with the cavity, the coupler …
Date: December 1, 2008
Creator: Li, Jianjian
System: The UNT Digital Library
A Direct Measurement of the $W$ Decay Width (open access)

A Direct Measurement of the $W$ Decay Width

A direct measurement of the W boson total decay width is presented in proton-antiproton collisions at √s = 1.96 TeV using data collected by the CDF II detector. The measurement is made by fitting a simulated signal to the tail of the transverse mass distribution in the electron and muon decay channels. An integrated luminosity of 350 pb<sup>-1</sup> is used, collected between February 2002 and August 2004. Combining the results from the separate decay channels gives the decay width as 2.038 ± 0.072 GeV in agreement with the theoretical prediction of 2.093 ± 0.002 GeV. A system is presented for the management of detector calibrations using a relational database schema. A description of the implementation and monitoring of a procedure to provide general users with a simple interface to the complete set of calibrations is also given.
Date: August 1, 2008
Creator: Vine, Troy
System: The UNT Digital Library
Beam Dynamics in a Muon Ionisation Cooling Channel (open access)

Beam Dynamics in a Muon Ionisation Cooling Channel

The Neutrino Factory has been proposed as a facility to provide an intense source of neutrinos suitable for the measurement of neutrino oscillation parameters and a possible CP violating phase to unprecedented precision. In the Neutrino Factory, neutrinos are produced by the decay of a muon beam with 20-50 GeV per muon. Initially, the muon beam occupies a large volume in phase space, which must be reduced before the beam can be accelerated. The proposed method to achieve this is to use a solenoidal ionisation colling channel.
Date: September 1, 2008
Creator: Rogers, Chris
System: The UNT Digital Library
Function and dynamics of aptamers: A case study on the malachite green aptamer (open access)

Function and dynamics of aptamers: A case study on the malachite green aptamer

Aptamers are short single-stranded nucleic acids that can bind to their targets with high specificity and high affinity. To study aptamer function and dynamics, the malachite green aptamer was chosen as a model. Malachite green (MG) bleaching, in which an OH- attacks the central carbon (C1) of MG, was inhibited in the presence of the malachite green aptamer (MGA). The inhibition of MG bleaching by MGA could be reversed by an antisense oligonucleotide (AS) complementary to the MGA binding pocket. Computational cavity analysis of the NMR structure of the MGA-MG complex predicted that the OH{sup -} is sterically excluded from the C1 of MG. The prediction was confirmed experimentally using variants of the MGA with changes in the MG binding pocket. This work shows that molecular reactivity can be reversibly regulated by an aptamer-AS pair based on steric hindrance. In addition to demonstrate that aptamers could control molecular reactivity, aptamer dynamics was studied with a strategy combining molecular dynamics (MD) simulation and experimental verification. MD simulation predicted that the MG binding pocket of the MGA is largely pre-organized and that binding of MG involves reorganization of the pocket and a simultaneous twisting of the MGA terminal stems around the pocket. …
Date: December 1, 2008
Creator: Wang, Tianjiao
System: The UNT Digital Library
Search for 1st Generation Leptoquarks in the eejj channel with the DZero experiment (open access)

Search for 1st Generation Leptoquarks in the eejj channel with the DZero experiment

An evidence of the existence of leptoquarks (LQ) would prove the validity of various extensions of the Standard Model of Particle Physics (SM). The search for first generation leptoquarks presented in this dissertation has been performed by analyzing a 1.02 fb{sup -1} sample of data collected by the D0 detector, events with a final state comprising two light jets and two electrons. The absence of an excess of events in comparison to SM expectations leads to exclude scalar LQ masses up to 292 GeV and vector LQ masses from 350 to 458 GeV, depending on the LQ-l-q coupling type. The great importance of a good jet energy measurement motivated the study of the instrumental backgrounds correlated to the calorimeter, as much as studies of the hadronic showers energy resolution in {gamma} + jets events.
Date: September 1, 2008
Creator: Barfuss, Anne-Fleur
System: The UNT Digital Library
Search for the neutral MSSM Higgs bosons in the ditau decay channels at CDF Run II (open access)

Search for the neutral MSSM Higgs bosons in the ditau decay channels at CDF Run II

This thesis presents the results on a search for the neutral MSSM Higgs bosons decaying to tau pairs, with least one of these taus decays leptonically. The search was performed with a sample of 1.8 fb{sup -1} of proton-antiproton collisions at {radical}s = 1.96 TeV provided by the Tevatron and collected by CDF Run II. No significant excess over the Standard Model prediction was found and a 95% confidence level exclusion limit have been set on the cross section times branching ratio as a function of the Higgs boson mass. This limit has been translated into the MSSM Higgs sector parameter plane, tan{beta} vs. M{sub A}, for the four different benchmark scenarios.
Date: April 1, 2008
Creator: Cuenca Almenar, Cristobal & /Valencia U., IFIC
System: The UNT Digital Library
Study of correlations between photoproduced pairs of charmed particles at Experiment E831/FOCUS (open access)

Study of correlations between photoproduced pairs of charmed particles at Experiment E831/FOCUS

The authors present the study of the charm-pair correlations produced in photon-nucleon interactions at &lt;E{sub {gamma}}&gt; = 175 GeV/c, by the Fermilab fixed target experiment E831/FOCUS. The E831/FOCUS experiment produced and reconstructed over one million charm particles. This high statistics allows the reconstruction of more than 7000 charm-pair mesons D{bar D}, 10 times the statistic of former experiments, and also allows to get, for the first time, about 600 totally reconstructed charm-pairs in the DD{sub s} and D{Lambda}{sub c} channels. They were able to study, with some detail, the kinematical correlations between the charm and anticharm particle forming a pair, in the square transverse momentum (p{sub T}{sup 2}), azimuthal angle difference ({Delta}{phi}), rapidity difference ({Delta}y) and the charm-pair mass variables. They observe some correlation for the longitudinal momenta, and a significant correlation for the transverse momenta of the charm and anticharm particles. They compare the experimental distributions with theoretical predictions based on the photon-gluon fusion model (PGF), for the production of c{bar c} quarks, and the standard Lund hadronization model. These models are implemented by the PYTHIA Monte Carlo event generator. The PYTHIA program allows the inclusion, in the simulation, of non-perturbative effects that have been shown to be important …
Date: August 1, 2008
Creator: Castromonte Flores, Cesar Manuel & /Rio de Janeiro, CBPF
System: The UNT Digital Library
Measuring Antineutrino Oscillations with the MINOS Experiment (open access)

Measuring Antineutrino Oscillations with the MINOS Experiment

MINOS is a long baseline neutrino oscillation experiment. A manmade beam of predominantly muon neutrinos is detected both 1 km and 735 km from the production point by two functionally identical detectors. A comparison of the energy spectra measured by the two detectors shows the energy-dependent disappearance of muon neutrinos characteristic of oscillations and allows a measurement of the parameters governing the oscillations. This thesis presents work leading to measurements of disappearance in the 6% {bar {nu}}{sub {mu}} background in that beam. A calibration is developed to correct for time-dependent changes in the responses of both detectors, reducing the corresponding uncertainty on hadronic energy measurements from 1.8% to 0.4% in the near detector and from 0.8% to 0.4% in the far detector. A method of selecting charged current {bar {nu}}{sub {mu}} events is developed, with purities (efficiencies) of 96.5% (74.4%) at the near detector, and 98.8% (70.9%) at the far detector in the region below 10 GeV reconstructed antineutrino energy. A method of using the measured near detector neutrino energy spectrum to predict that expected at the far detector is discussed, and developed for use in the {bar {nu}}{sub {mu}} analysis. Sources of systematic uncertainty contributing to the oscillation measurements …
Date: September 1, 2008
Creator: Evans, Justin John
System: The UNT Digital Library
A search for resonant Z pair production (open access)

A search for resonant Z pair production

I describe a search for anomalous production of Z pairs through a new massive resonance X in 2.5-2.9 fb{sup -1} of p{bar p} collisions at {radical}s = 1.96 TeV using the CDFII Detector at the Fermilab Tevatron. I reconstruct Z pairs through their decays to electrons, muons, and quarks. To achieve perhaps the most efficient lepton reconstruction ever used at CDF, I apply a thorough understanding of the detector and new reconstruction software heavily revised for this purpose. In particular, I have designed and employ new general-purpose algorithms for tracking at large {eta} in order to increase muon acceptance. Upon analyzing the unblinded signal samples, I observe no X {yields} ZZ candidates and set upper limits on the production cross section using a Kaluza-Klein graviton-like acceptance.
Date: December 1, 2008
Creator: Boveia, Antonio
System: The UNT Digital Library
Scanning tuneeling microscopy studies of fivefold surfaces of icosahedral Al-Pd-Mn quasicrystals and of thin silver films on those surfaces (open access)

Scanning tuneeling microscopy studies of fivefold surfaces of icosahedral Al-Pd-Mn quasicrystals and of thin silver films on those surfaces

The present work in this dissertation mainly focuses on the clean fivefold surfaces of i-Al-Pd-Mn quasicrystals as well as the nucleation and growth of Ag films on these surfaces. In addition, Ag film growth on NiAl(110) has been explored in the frame of this dissertation. First, we have investigated the equilibration of a fivefold surface of icosahedral Al-Pd-Mn quasicrystal at 900-915 K and 925-950 K, using Omicron variable temperature scanning tunneling microscope (STM). Annealing at low temperatures resulted in many voids on some terraces while the others were almost void-free. After annealing at 925-950K, void-rich terraces became much rarer. Our STM images suggest that through growth and coalescence of the voids, a different termination becomes exposed on host terraces. All of these observations in our study indicate that even after the quasicrystalline terrace-step structure appears, it evolves with time and temperature. More specifically, based on the STM observations, we conclude that during the annealing a wide range of energetically similar layers nucleate as surface terminations, however, with increasing temperature (and time) this distribution gets narrower via elimination of the metastable void-rich terraces. Next, we have examined the bulk structural models of icosahedral Al-Pd-Mn quasicrystal in terms of the densities, compositions …
Date: December 1, 2008
Creator: Unal, Baris
System: The UNT Digital Library
Search for standard model Higgs bosons decaying to w-boson pairs in proton-anti-proton collisions at s**(1/2) = 1.96 TeV (open access)

Search for standard model Higgs bosons decaying to w-boson pairs in proton-anti-proton collisions at s**(1/2) = 1.96 TeV

This thesis describes a search for standard model Higgs bosons decaying to W boson pairs in proton-anti-proton collisions at a center of mass energy of 1.96 TeV using the CDF II detector. The decay to W bosons is dominant for Higgs masses greater than about 135 GeV. The final state examined consists of two leptons and missing transverse energy from the leptonic decay of one or more W bosons. The signal production mechanisms included are gluon fusion, associated production with a W or Z boson, and vector boson fusion. Matrix element calculations and artificial neural networks are used to discriminate signal from background for Higgs masses in the range 110 {le} M{sub H} {le} 200 GeV. No significant excess of events is observed at any of the Higgs masses investigated. Upper limits on the standard model Higgs cross section are set at 95% confidence for each Higgs mass investigated, the most stringent limit being 1.63 times the predicted standard model cross section for a Higgs mass of 160 GeV.
Date: December 1, 2008
Creator: Hidas, Dean Andrew & U., /Duke
System: The UNT Digital Library
Trigger Detectors of the Forward Muon System for the D0 Experiment (open access)

Trigger Detectors of the Forward Muon System for the D0 Experiment

None
Date: December 1, 2008
Creator: Vasilyev, I.
System: The UNT Digital Library
Nonperturbative Dynamics of Strong Interactions from Gauge/Gravity Duality (open access)

Nonperturbative Dynamics of Strong Interactions from Gauge/Gravity Duality

This thesis studies important dynamical observables of strong interactions such as form factors. It is known that Quantum Chromodynamics (QCD) is a theory which describes strong interactions. For large energies, one can apply perturbative techniques to solve some of the QCD problems. However, for low energies QCD enters into the nonperturbative regime, where different analytical or numerical tools have to be applied to solve problems of strong interactions. The holographic dual model of QCD is such an analytical tool that allows one to solve some nonperturbative QCD problems by translating them into a dual five-dimensional theory defined on some warped Anti de Sitter (AdS) background. Working within the framework of the holographic dual model of QCD, we develop a formalism to calculate form factors and wave functions of vector mesons and pions. As a result, we provide predictions of the electric radius, the magnetic and quadrupole moments which can be directly verified in lattice ca
Date: August 1, 2008
Creator: Grigoryan, Hovhannes
System: The UNT Digital Library
t anti-t production cross section measurement using soft electron tagging in p anti-p collisions at s**(1/2) = 1.96-TeV (open access)

t anti-t production cross section measurement using soft electron tagging in p anti-p collisions at s**(1/2) = 1.96-TeV

We measure the production cross section of t{bar t} events in p{bar p} collisions at {radical}s = 1.96 TeV. The data was collected by the CDF experiment in Run 2 of the Tevatron accelerator at the Fermi National Accelerator Laboratory between 2002 and 2007. 1.7 fb{sup -1} of data was recorded during this time period. We reconstruct t{bar t} events in the lepton+jets channel, whereby one W boson - resulting from the decay of the top quark pairs - decays leptonically and the other hadronically. The dominant background to this process is the production of W bosons in association with multiple jets. To distinguish t{bar t} from background, we identify soft electrons from the semileptonic decay of heavy flavor jets produced in t{bar t} events. We measure a cross section of {sigma}{sub p{bar p}} = 7.8 {+-} 2.4(stat) {+-} 1.6(syst) {+-} 0.5(lumi).
Date: September 1, 2008
Creator: Chou, John Paul & U., /Harvard
System: The UNT Digital Library
Development of high performance scientific components for interoperability of computing packages (open access)

Development of high performance scientific components for interoperability of computing packages

Three major high performance quantum chemistry computational packages, NWChem, GAMESS and MPQC have been developed by different research efforts following different design patterns. The goal is to achieve interoperability among these packages by overcoming the challenges caused by the different communication patterns and software design of each of these packages. A chemistry algorithm is hard to develop as well as being a time consuming process; integration of large quantum chemistry packages will allow resource sharing and thus avoid reinvention of the wheel. Creating connections between these incompatible packages is the major motivation of the proposed work. This interoperability is achieved by bringing the benefits of Component Based Software Engineering through a plug-and-play component framework called Common Component Architecture (CCA). In this thesis, I present a strategy and process used for interfacing two widely used and important computational chemistry methodologies: Quantum Mechanics and Molecular Mechanics. To show the feasibility of the proposed approach the Tuning and Analysis Utility (TAU) has been coupled with NWChem code and its CCA components. Results show that the overhead is negligible when compared to the ease and potential of organizing and coping with large-scale software applications.
Date: December 1, 2008
Creator: Gulabani, Teena Pratap
System: The UNT Digital Library
Observations and Measurements of Orbitally Excited L=1 B Mesons at the D0 Experiment (open access)

Observations and Measurements of Orbitally Excited L=1 B Mesons at the D0 Experiment

This thesis describes investigations of the first set of orbitally excited (L = 1) states for both the B{sub d}{sup 0} and B{sub s}{sup 0} meson systems (B**{sub d} and B**{sub s}). The data sample corresponds to 1.35 fb{sup -1} of integrated luminosity, collected in 2002-2006 by the D0 detector, during the Run IIa operation of the Tevatron p{bar p} colliding beam accelerator. The B**{sub d} states are fully reconstructed in decays to B{sup (*)+} {pi}{sup -}, with B{sup (*)+} {yields} {gamma} J/{psi}K{sup +}, J/{psi} {yields} {mu}{sup +}{mu}{sup -}, yielding 662 {+-} 91 events, and providing the first strong evidence for the resolution of two narrow resonances, B{sub 1} and B*{sub 2}. The masses are extracted from a binned {chi}{sup 2} fit to the invariant mass distribution, giving M(B{sub 1}) = 5720.7 {+-} 2.4(stat.) {+-} 1.3(syst.) {+-} 0.5 (PDG) MeV/c{sup 2} and M(B*{sub 2}) = 5746.9 {+-} 2.4(stat.) {+-} 1.0(syst.) {+-} 0.5(PDG) MeV/c{sup 2}. The production rate of narrow B**{sub d} {yields} B{pi} resonances relative to the B{sup +} meson is determined to be [13.9 {+-} 1.9(stat.) {+-} 3.2(syst.)]%. The same B{sup +} sample is also used to reconstruct the analogous states in the B{sub s}{sup 0} system, in decays …
Date: September 1, 2008
Creator: Williams, Mark Richard James
System: The UNT Digital Library
Measurement of the top quark mass in the dilepton final state using the matrix element method (open access)

Measurement of the top quark mass in the dilepton final state using the matrix element method

The top quark, discovered in 1995 by the CDF and D0 experiments at the Fermilab Tevatron Collider, is the heaviest known fundamental particle. The precise knowledge of its mass yields important constraints on the mass of the yet-unobserved Higgs boson and allows to probe for physics beyond the Standard Model. The first measurement of the top quark mass in the dilepton channel with the Matrix Element method at the D0 experiment is presented. After a short description of the experimental environment and the reconstruction chain from hits in the detector to physical objects, a detailed review of the Matrix Element method is given. The Matrix Element method is based on the likelihood to observe a given event under the assumption of the quantity to be measured, e.g. the mass of the top quark. The method has undergone significant modifications and improvements compared to previous measurements in the lepton+jets channel: the two undetected neutrinos require a new reconstruction scheme for the four-momenta of the final state particles, the small event sample demands the modeling of additional jets in the signal likelihood, and a new likelihood is designed to account for the main source of background containing tauonic Z decay. The Matrix …
Date: December 1, 2008
Creator: Grohsjean, Alexander
System: The UNT Digital Library
Measurement of the charged kaon mass with the MIPP RICH (open access)

Measurement of the charged kaon mass with the MIPP RICH

The currently accepted value of the charged kaon mass is 493.677 {+-} 0.013 MeV (26 ppm). It is a weighted average of six measurements, most of which use kaonic atom X-ray energy techniques. The two most recent and precise results dominate the average but differ by 122 ppm. Inconsistency in the data set needs to be resolved, preferably using independent techniques. One possibility uses the Cherenkov effect. A measurement of the charged kaon mass using this technique is presented. The data was taken with the Main Injector Particle Production experiment at Fermi National Accelerator Laboratory using a tagged beam of protons, kaons, and pions ranging in momentum from 37 GeV/c to 63 GeV/c. The measured value is 491.3 {+-} 1.7 MeV. This is within 1.4{sigma} of the current value. An improvement in precision by a factor of 35 would make this technique competitive for resolving the ambiguity in the X-ray data.
Date: August 1, 2008
Creator: Graf, Nicholas J.
System: The UNT Digital Library
An Adaptive Landscape Classification Procedure using Geoinformatics and Artificial Neural Networks (open access)

An Adaptive Landscape Classification Procedure using Geoinformatics and Artificial Neural Networks

The Adaptive Landscape Classification Procedure (ALCP), which links the advanced geospatial analysis capabilities of Geographic Information Systems (GISs) and Artificial Neural Networks (ANNs) and particularly Self-Organizing Maps (SOMs), is proposed as a method for establishing and reducing complex data relationships. Its adaptive and evolutionary capability is evaluated for situations where varying types of data can be combined to address different prediction and/or management needs such as hydrologic response, water quality, aquatic habitat, groundwater recharge, land use, instrumentation placement, and forecast scenarios. The research presented here documents and presents favorable results of a procedure that aims to be a powerful and flexible spatial data classifier that fuses the strengths of geoinformatics and the intelligence of SOMs to provide data patterns and spatial information for environmental managers and researchers. This research shows how evaluation and analysis of spatial and/or temporal patterns in the landscape can provide insight into complex ecological, hydrological, climatic, and other natural and anthropogenic-influenced processes. Certainly, environmental management and research within heterogeneous watersheds provide challenges for consistent evaluation and understanding of system functions. For instance, watersheds over a range of scales are likely to exhibit varying levels of diversity in their characteristics of climate, hydrology, physiography, ecology, and anthropogenic …
Date: August 1, 2008
Creator: Coleman, Andre M.
System: The UNT Digital Library
Polymer nanocomposites for high-temperature composite repair (open access)

Polymer nanocomposites for high-temperature composite repair

A novel repair agent for resin-injection repair of advanced high temperature composites was developed and characterized. The repair agent was based on bisphenol E cyanate ester (BECy) and reinforced with alumina nanoparticles. To ensure good dispersion and compatibility with the BECy matrix in nanocomposites, the alumina nanoparticles were functionalized with silanes. The BECy nanocomposites, containing bare and functionalized alumina nanoparticles, were prepared and evaluated for their thermal, mechanical, rheological, and viscoelastic properties. The monomer of BECy has an extremely low viscosity at ambient temperature, which is good for processability. The cured BECy polymer is a highly cross-linked network with excellent thermal mechanical properties, with a high glass transition temperature (T{sub g}) of 270 C and decomposition temperature above 350 C. The incorporation of alumina nanoparticles enhances the mechanical and rheological properties of the BECy nanocomposites. Additionally, the alumina nanoparticles are shown to catalyze the cure of BECy. Characterization of the nanocomposites included dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis, rheological and rheokinetic evaluation, and transmission electron microscopy. The experimental results show that the BECy nanocomposite is a good candidate as repair agent for resin-injection repair applications.
Date: December 1, 2008
Creator: Sheng, Xia
System: The UNT Digital Library
Measurement of direct CP violation in b -> scc and b -> dcc quark transitions using B+ -> J/psiK+ and B+ -> J/psi pi+ decays (open access)

Measurement of direct CP violation in b -> scc and b -> dcc quark transitions using B+ -> J/psiK+ and B+ -> J/psi pi+ decays

This thesis describes the measurement of the direct CP violation in the b {yields} sc{bar c} transition using the decay B{sup +} {yields} J/{psi}K{sup +}, and in the b {yields} dc{bar c} transition using the decay B{sup +} {yields} J/{psi}{pi}{sup +}. The decays of B{sup +} mesons are reconstructed in approximately 2.8 fb{sup -1} of data recorded by D0 detector in 2002-2007 during Run II of Fermilab Tevatron collider. Using the unbinned likelihood fit, a signal of 40,222 {+-} 242 of B{sup +} {yields} J/{psi}K{sup +} and 1,578 {+-} 119 of B{sup +} {yields} J/{psi}{pi}{sup +} events is obtained. The corresponding direct CP violation asymmetries are measured to be A{sub CP}(B{sup +} {yields} J/{psi}(1S)K{sup +}) = +0.0077 {+-} 0.0061(stat.) {+-} 0.0027(syst.), and A{sub CP}(B{sup +} {yields} J/{psi}(1S){pi}{sup +}) = - 0.089 {+-} 0.081(stat.) {+-} 0.028(syst.). The result on A{sub CP} (B{sup +} {yields} J/{psi}(1S)K{sup +}) is consistent with the 2007 world average and is the most precise measurement of this asymmetry, with uncertainty approaching the level of the Standard Model prediction. The result on A{sub CP} (B{sup +} {yields} J/{psi}(1S){pi}{sup +}) constitutes the first measurement of this asymmetry at the hadron collider, with uncertainty at the level of the 2007 …
Date: December 1, 2008
Creator: Holubyev, K.
System: The UNT Digital Library