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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
91

Thermal desorption, photodesorption, and photodissociation of water on amorphous ice and lunar surfaces

DeSimone, Alice Johnson 13 January 2014 (has links)
The temperature-programmed desorption profiles of water from three lunar analogs were measured. These experiments showed that glassy materials were hydrophobic, that water on multiphase materials occupied a continuum of adsorption sites, and that feldspar exhibited significant chemisorption of water. The competition between photodissociation and photodesorption of amorphous solid water (ASW) was investigated on three substrates: copper with a thin oxide coating, an impact melt breccia from Apollo 16, and a mare basalt from Apollo 17. The rotational temperature of desorbing H₂O did not vary significantly with substrate, but the H₂O time-of-flight spectra were broader on the lunar slabs than on copper. Additionally, the cross sections for water removal at low coverages were higher on the lunar slabs than on copper. O(³PJ) produced by 157-nm irradiation of ASW on the same three substrates was measured as a function of spin-orbit state, H₂O exposure, and irradiation time. The same Maxwell-Boltzmann components were present in each case, with translational temperatures of 10,000 K, 1800 K, 400 K, and the surface temperature, but the relative intensities of these components differed widely between substrates. Evidence for diffusion out of pores in the ASW and in the lunar slabs was observed for H2O exposures of at least 1 Langmuir. Cross sections for H2O and O(3PJ) depletion due to 157-nm irradiation of ASW were applied to icy grains in the rings of Saturn, and corresponding cross sections on the lunar substrates were used to estimate the flux of water desorbing from the Moon and the density of oxygen atoms in the lunar atmosphere.
92

Conditional betas, higher comoments and the cross-section of expected stock returns

Xu, Lei January 2010 (has links)
This thesis examines the performance of different models of conditional betas and higher comoments in the context of the cross-section of expected stock returns, both in-sample and out-of-sample. I first examine the performance of different conditional market beta models by using monthly returns of the Fama-French 25 portfolios formed by the quintiles of size and book-to-market ratio in Chapter 3. This is a cross-sectional test of the conditional CAPM. The models examined include simple OLS regressions, the macroeconomic variables model, the state-space model, the multivariate GARCH model and the realized beta model. The results show that the state-space model performs best in-sample with significant betas and insignificant intercepts. For the out-of-sample performance, however, none of the models examined can explain returns of the 25 portfolios. Next, I examine the recently proposed realized beta model, which is based on the realized volatility literature, by using individual stocks listed in the US market in Chapter 4. I extend the realized market beta model to betas of multi-factor asset pricing models. Models tested are the CAPM, the Fama-French three-factor model and a four-factor model including the three Fama-French factors and a momentum factor. Realized betas of different models are used in the cross-section regressions along with firm-level variables such as size, book-to-market ratio and past returns. The in-sample results show that market beta is significant and additional betas of multi-factor models can reduce although not eliminate the effects of firm-level variables. The out-of-sample results show that no betas are significant. The results are robust across different markets such as NYSE, AMEX and NASDAQ. In Chapter 5, I test if realized coskewness and cokurtosis can help explain the cross-section of stock returns. I add coskewness and cokurtosis to the factor pricing models tested in Chapter 4. The results show that the coefficients of coskewness and cokurtosis have the correct sign as predicted by the higher-moment CAPM theory but only cokurtosis is significant. Cokurtosis is significant not only in-sample but also out-of-sample, suggesting cokurtosis is an important risk. However, the effects of firm-level variables remain significant after higher moments are included, indicating a rejection of higher-moment asset pricing models. The results are also robust across different markets such as NYSE, AMEX and NASDAQ. The overall results of this thesis indicate a rejection of the conditional asset pricing models. Models of systematic risks, i.e. betas and higher comoments, cannot explain the cross-section of expected stock returns.
93

Assessment of Ephemeral Channel Cross-Section Morphology Following Pipeline Construction in Southern Arizona

Miller, Hennessy Felicia, Miller, Hennessy Felicia January 2017 (has links)
Morphologic change of ephemeral stream cross-sections is a natural component of fluvial geomorphology but disruptions to natural erosion and deposition by anthropogenic disturbances has the potential for cascading impacts down the channel corridor. The proximal impact of a natural gas pipeline construction on ephemeral stream cross-section geometry in southern Arizona was evaluated from July 2014 (pre-construction) to July 2016 (two years post construction). Cross-sections at three locations (upstream the pipeline Right-Of-Way (ROW)), through the middle of the ROW, and downstream of the ROW) were measured using Light Detection And Ranging (LIDAR) and field methods for 16 ephemeral streams. Results of both the LIDAR and field measurements indicated insignificant difference in cross-sectional area change between upstream, across, and downstream-ROW cross-sections [(F 2,64) = 0.341, p = 0.73; (F2,18)= 0.980, p = 0.395]. Sediment generated during pipeline construction appeared to have moved beyond the physical confines of the study site, which limited the assessment of larger-scale geomorphic impacts. Furthermore, the 2014-2016 study period experienced only small (high-recurrence frequency) precipitation events, indicating the absence of large flows capable of significant morphologic change. To further explain differences in cross-section area change between LIDAR datasets, a linear regression model was used to assess the predictive value of nine variables: year of measurement, drainage area, drainage density, basin slope, upstream-, across-, downstream-ROW cross-section locations, percent bare soil in basin, percent mesquite in basin, total precipitation, and number of storms with average precipitation above 25 mm/hour. Though the amount of bare soil in the basin and the second study period (February 2015-July 2016) at least partially explained the changes in cross-section area, the model was not a strong predictor of morphologic change during the 2014-2016 study period. The majority of the variability in cross-sectional area change in the study basins remained unexplained.
94

Caractérisation optique et géométrique des agrégats submicroniques multi-échelles de particules sphériques très diffusantes / Optical and geometrical characterization of submicron milti-scale aggregates of spherical particles quite scattering

Lagarrigue, Marthe 18 April 2011 (has links)
Les agrégats multi-échelles (sulfure de zinc: ZnS, ...) ont des propriétés physiques et physicochimiques présentant un grand intérêt industriel (industrie pharmaceutique, matériau, environnement...). L'objectif général de cette thèse est de caractériser ces agrégats multi-échelles par une méthode optique d'une part, et par une étude géométrique d'autre part. Le but est de trouver des relations simples entre propriétés optiques et géométriques. Les résultats présentés sont valables pour tout matériau à haut indice de réfraction.Ce travail comporte une première étape de modélisation en étudiant tout d'abord des modèles simples d'agrégats multi-échelles (agencement ordonné de particules élémentaires sphériques). Différents agrégats sont alors géométriquement modélisés suivant des paramètres de construction prédéfinis (volume global des agrégats, rayon des particules primaires...). Une analyse préliminaire optique puis une analyse géométrique sont alors effectuées afin de déterminer les paramètres respectifs à étudier: la section efficace moyenne de diffusion (...), calculée au moyen d'une extension de la théorie de Mie (GMM pour Generalized Multiparticle Mie) d'Y-L Xu, et des caractéristiques géométriques spécifiques (volume de matière, compacité...).Une seconde étape consiste à étudier les variations de la valeur de ... en fonction de celles des paramètres géométriques des agrégats. Des relations caractérisant ces variations sont établies. Enfin, une expression approchées pour la valeur de ... est recherchée sous la forme d'une loi de puissance, reposant sur des méthodes optiques approchées existantes et sur la sélection de caractéristiques géométriques pertinentes. Le modèle mis en place est robuste et présente un compromis entre précision et complexité. Le travail réalisé ouvre diverses perspectives comme la confrontation du modèle mathématique théorique obtenu, avec l'expérience. / Multiscale aggregates (zinc sulfide: ZnS, ...) havephysical and physicochemical properties of great industrial interest (e.g. pharmaceutical industriy, material, environment). The overall objective of this thesis is to characterize these multiscale aggregates by an optical method on the one hand, and a geometric study of the other. The goal is to find simple relations between optical and geometrical properties. The results presented are valid for any material with high refractive index.The first step of this work is to build in a simple way the multiscale aggregate (like ordered arrangement of spherical elementary particles). Different aggregates are then geometrically modeled thanks to predefined design parameters (e.g. particles radius, aggregates overall volume). A preleminary analysis of optical and geometrical analysis is then performed to determine the relevant parameters: the average scattering cross section (...), calculed using a generalization of the Mie theory (GMM for Generalized Multiparticle Mie) developped by Y.L. Xu, and specific geometric values features. An analysis of the behavior of the optical parameter and the geometrical characteristic (e.g. compactness, volume of matter...), with respect to the construction parameters of the aggregates, is then performed.A second step is to study variations of ... value versus the variation of the geometrical parameter of aggregates. Mathematical relations characterizing these variations are established. Finally, a study on the approximation of the ... value is carried out. A power law is proposed which is basedon previous optical approximate methods and on the selection of geometrical characteristics of the aggregates. The optical properties and geometrical characteristics of the clusters are fairly extensive and contrasted to give a general groundwork to this study. The work done opens various perspectives such as the confrontation of the theorical mathematical model obtained, with experiment.
95

Investigation of the Pressure Dependence of SO3 Formation

Naidoo, Jacinth 12 1900 (has links)
The kinetics of the pressure dependent O + SO2 + Ar reaction have been investigated using laser photolysis resonance fluorescence at temperatures of 289 K, 399 K, 581 K, 699 K, 842 K and 1040 K and at pressures from 30-665 torr. Falloff was observed for the first time in the pressure dependence. Application of Lindemann theory yielded an Arrhenius expression of k(T) = 3.3 x 10-32exp(-992/T) cm6 molecule-1 s-1 for the low pressure limit and k(T) = 8.47 x 10-14exp(-468/T) cm3 molecule-1 s-1 for the high pressure limit at temperatures between 289 and 842 K. The reaction is unusual as it possesses a positive activation energy at low temperature, yet at higher temperatures the activation energy is negative, illustrating a reaction barrier.
96

Measurement of the inclusive jet cross section with the ATLAS detector at the Large Hadron Collider

Doglioni, Caterina January 2012 (has links)
This thesis presents the measurement of the inclusive jet cross section using data collected in 2010 by the ATLAS detector, with a particular focus on the reconstruction and calibration techniques used for jets in this measurement and on the estimate of the systematic uncertainty on their energy scale. The inclusive jet cross section measurement is used as input to fits of parton distribution functions. Although the PDF analysis in this thesis is preliminary and its main purpose is to serve as a proof of principle for future studies, improvements in the knowledge of the gluon density are observed thanks to the inclusion of ATLAS data.
97

Využití aktivačních detektorů při měření neutronového pole v modelových sestavách ADTS / Use of activation detectors for neutron field measurement in models of ADTS

Chudoba, Petr January 2013 (has links)
Accelerator driven transmutation systems could be a solution to the problem with long-lived nuclear waste and opening the way to thorium fuel cycle. Due to intensive neutron source based on spallation reaction are these systems very litle dependent on the arrangement of the core and fuel quality. These systems can transmute the spent fuel, eventually 232Th or 238U without affecting maintenance of fission reaction. Additionally subcritical blanket ensures high safety. For these systems it is necessary to know the cross sections of reactions of fast neutrons produced in the spallation reaction with different materials. This data is necessary not only for the selection of appropriate construction materials, but also for creation of programs simulating accelerator driven transmutation systems. This thesis is focused on the experimental determination of cross sections of reactions 89Y(n,2n)88Y and 89Y(n,3n)87Y with neutron energies from 17,6 to 33,6 MeV. Yttrium is analyzed for its (n,xn) threshold reactions, which makes it appropriet activation detector for study of the neutron fields in model configurations of accelerator driven transmutation systems. The obtained cross sections are unique, in that so far there are no experimental data for used neutron energies.
98

Diboson physics with CMS detector

Svintradze, Irakli January 1900 (has links)
Doctor of Philosophy / Department of Physics / Yurii Maravin / In this dissertation, you will find a study of di-boson production in pp collision with the Compact Muon Solenoid (CMS) detector at Large Hadron Collider (LHC). A study of Z+gamma process is performed on the data collected by the CMS during 2011 and corresponding to integrated luminosity L= 5 fb[superscript]-1. The study consists of two parts: cross section measurement and setting the limits on anomalous trilinear gauge couplings (aTGC) between a Z boson and a photon. The measured cross-section of Z+gamma agrees within the uncertainties with the standard model predicted cross section at next to leading order. Having found no excess in cross section measurement, we set the 95% con fidence level (C.L.) limit on aTGC. Another study discussed is a study of a low-scale walking Technicolor model with rho[subscript]T and a[subscript]T production in the fully leptonic fi nal state at 95% C.L. in proton-proton collisions at center of mass energy 10 TeV scenario using Monte Carlo simulation. We conclude that such processes can be excluded with 366 pb[superscript]-1 of data for rho[superscript]T masses up to 400 GeV and the observation would require 2.8 fb[superscript]-1 of data with 5 sigma precision.
99

Measurement of the Zγγ production cross section at proton-proton collisions with the CMS experiment / Measurement of the Zgammagamma production cross section at proton-proton collisions with the CMS experiment

McBride, Sachiko Toda January 1900 (has links)
Doctor of Philosophy / Department of Physics / Yurii Y. Maravin / This thesis presents the first study of a rare production of Z boson in association with two photons (Zγγ), where the Z boson decays into a pair of muons or electrons, by proton-proton collisions at the Large Hadron Collider (LHC). This study uses full data samples that have been collected with the Compact Muon Solenoid (CMS) detector in 2012 with a center of mass energy of 8TeV, corresponding to an integrated luminosity of 19.7 fb⁻¹. The Zγγ production cross section is measured within a fiducial region defined by two leptons with two photons where transverse momentum over 15 GeV and distance between gamma and lepton above 0.4. Using the obtained samples, the Zγγ cross section is measured to be: 12.6 ±1.6 (stat.) ± 1.7 (syst.) ± 0.3 (lumi.) fb. where stat., syst., and lumi. denote the statistical uncertainty, systematic uncertainty, and the uncertainty in integrated luminosity, respectively. This result is in an excellent agreement with the theoretical prediction of 13.0 ± 1.5 fb.
100

Probing top quark and Higgs boson production in multijet events at the LHC with the ATLAS detector / Sonder la production du quark top et du boson de Higgs dans les évènements multi-jet avec expérience Atlas auprès du LHC

Bertella, Claudia 30 September 2013 (has links)
Sonder la production du quark top et du boson de Higgs dans les évènements multi-jet avec expérience Atlas auprès du LHC.Le détecteur Atlas est une expérience généraliste placé auprès du collisionneur proton-proton circulaire de 27 km de circonférence, LHC. Le LHC est conçu pour produire des collisions avec une énergie nominale au centre de masse de l'ordre de racine carré8 = 14 Tev et une luminosité instantané de 10-34cm-2s-1. / Probing top quark and Higgs boson production in multi-jet avents at the LHC with the Atlas detector.The Atlas detector is a general purpose detector located at the Large Hadron Collider (LHC). It aims at the discovery af new physics phenomena and improving our knowledge of the standart Model (SM).

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