Global ETD Search

221	A Radio Frequency Quadrupole Instrument for use with Accelerator Mass Spectrometry: Application to Low Kinetic Energy Reactive Isobar Suppression and Gas–phase Anion Reaction Studies Eliades, John Alexander 21 August 2012 (has links) A radio frequency (rf) quadrupole instrument, currently known as an Isobar Separator for Anions (ISA), has been integrated into an Accelerator Mass Spectrometry (AMS) system to facilitate anion–gas reactions before the tandem accelerator. An AMS Cs+ sputter source provided > 15 keV ions that were decelerated in the prototype ISA to < 20 eV for reaction in a single collision cell and re-accelerated for AMS analysis. Reaction based isobar suppression capabilities were assessed for smaller AMS systems and a new technique for gas–phase reaction studies was developed. Isobar suppression of 36S– and 12C3– for 36Cl analysis, and YF3– and ZrF3– for 90Sr analysis were studied in NO2 with deceleration to < 12 eV. Observed attenuation cross sections, σ [x 10^–15 cm^2], were σ(S– + NO2) = 6.6, σ(C3– + NO2) = 4.2, σ(YF3– + NO2) = 7.6, σ(ZrF3– + NO2) = 19. With 8 mTorr NO2, relative attenuations of S–/Cl– ~ 10^–6, C3–/Cl– ~ 10^–7, YF3–/SrF3– ~ 5 x 10^–5 and ZrF3–/SrF3– ~ 4 x 10^–6 were observed with Cl– ~ 30% and SrF3– > 90% transmission. Current isobar attenuation limits with < 1.75 MV accelerator terminal voltage and ppm impurity levels were calculated to be 36S–/Cl– ~ 4 x 10^–16, 12C3–/Cl– ~ 1.2 x 10^–16, 90YF3–/SrF3– ~ 10^–15 and 90ZrF3–/SrF3– ~ 10^–16. Using 1.75 MV, four 36Cl reference standards in the range 4 x 10^–13 < 36Cl/Cl < 4 x 10^–11 were analyzed with 8 mTorr NO2. The measured 36Cl/Cl ratios plotted very well against the accepted values. A sample impurity content S/Cl < 6 x 10^–5 was measured and a background level of 36S–/Cl < 9 x 10^–15 was determined. Useful currents of a wide variety of anions are produced in AMS sputter sources and molecules can be identified relatively unambiguously by stripping fragments from tandem accelerators. Reactions involving YF3–, ZrF3–, S– and SO– + NO2 in the ISA analyzed by AMS are described, and some interesting reactants are identified. radio frequency quadrupole rf quadrupole accelerator mass spectrometry AMS gas-phase reactions isobar suppression anion negative ion chlorine Cl 36Cl carbon trimer C3 sulphur sulfur sulphur oxide sulfur oxide SO methane CH4 nitrogen dioxide NO2 nitrous oxide N2O oxygen O2 argon Ar strontium Sr 90Sr SrF3 yttrium Y zirconium Zr ZrF3 trace isotope analysis superhalogen anion secondary ion mass spectrometry SIMS Cs sputter ion source rf quadrupole ion trajectory simulation anion gas reactions negative ion gas reactions gas-phase anion reactions S- + NO2 SO- + NO2 S- + N2O S- + O2 S- + Ar Cl- + NO2 Cl- + Ar Cl- + CH4 SrF3- + NO2 YF3- + NO2 ZrF3- + NO2 C3- + NO2 0768 0494 0605
222	A Radio Frequency Quadrupole Instrument for use with Accelerator Mass Spectrometry: Application to Low Kinetic Energy Reactive Isobar Suppression and Gas–phase Anion Reaction Studies Eliades, John Alexander 21 August 2012 (has links) A radio frequency (rf) quadrupole instrument, currently known as an Isobar Separator for Anions (ISA), has been integrated into an Accelerator Mass Spectrometry (AMS) system to facilitate anion–gas reactions before the tandem accelerator. An AMS Cs+ sputter source provided > 15 keV ions that were decelerated in the prototype ISA to < 20 eV for reaction in a single collision cell and re-accelerated for AMS analysis. Reaction based isobar suppression capabilities were assessed for smaller AMS systems and a new technique for gas–phase reaction studies was developed. Isobar suppression of 36S– and 12C3– for 36Cl analysis, and YF3– and ZrF3– for 90Sr analysis were studied in NO2 with deceleration to < 12 eV. Observed attenuation cross sections, σ [x 10^–15 cm^2], were σ(S– + NO2) = 6.6, σ(C3– + NO2) = 4.2, σ(YF3– + NO2) = 7.6, σ(ZrF3– + NO2) = 19. With 8 mTorr NO2, relative attenuations of S–/Cl– ~ 10^–6, C3–/Cl– ~ 10^–7, YF3–/SrF3– ~ 5 x 10^–5 and ZrF3–/SrF3– ~ 4 x 10^–6 were observed with Cl– ~ 30% and SrF3– > 90% transmission. Current isobar attenuation limits with < 1.75 MV accelerator terminal voltage and ppm impurity levels were calculated to be 36S–/Cl– ~ 4 x 10^–16, 12C3–/Cl– ~ 1.2 x 10^–16, 90YF3–/SrF3– ~ 10^–15 and 90ZrF3–/SrF3– ~ 10^–16. Using 1.75 MV, four 36Cl reference standards in the range 4 x 10^–13 < 36Cl/Cl < 4 x 10^–11 were analyzed with 8 mTorr NO2. The measured 36Cl/Cl ratios plotted very well against the accepted values. A sample impurity content S/Cl < 6 x 10^–5 was measured and a background level of 36S–/Cl < 9 x 10^–15 was determined. Useful currents of a wide variety of anions are produced in AMS sputter sources and molecules can be identified relatively unambiguously by stripping fragments from tandem accelerators. Reactions involving YF3–, ZrF3–, S– and SO– + NO2 in the ISA analyzed by AMS are described, and some interesting reactants are identified. radio frequency quadrupole rf quadrupole accelerator mass spectrometry AMS gas-phase reactions isobar suppression anion negative ion chlorine Cl 36Cl carbon trimer C3 sulphur sulfur sulphur oxide sulfur oxide SO methane CH4 nitrogen dioxide NO2 nitrous oxide N2O oxygen O2 argon Ar strontium Sr 90Sr SrF3 yttrium Y zirconium Zr ZrF3 trace isotope analysis superhalogen anion secondary ion mass spectrometry SIMS Cs sputter ion source rf quadrupole ion trajectory simulation anion gas reactions negative ion gas reactions gas-phase anion reactions S- + NO2 SO- + NO2 S- + N2O S- + O2 S- + Ar Cl- + NO2 Cl- + Ar Cl- + CH4 SrF3- + NO2 YF3- + NO2 ZrF3- + NO2 C3- + NO2 0768 0494 0605
223	Quantum cascade laser spectroscopy : developments and applications Walker, Richard James January 2011 (has links) This thesis presents work examining the characteristics and applicability of quantum cascade lasers. An introduction is given explaining both the desire for a widely tunable, narrow bandwidth device working in the midinfrared, as well as detailing the ways in which quantum cascade lasers (QCLs) fulfill these requirements. The development and manufacture of QCLs are then discussed. The experimental section of this thesis is then split into three parts. Chapter 2 concerns the characterisation and application of several pulsed QCLs. The intrapulse mode of operation is employed and the effect of the resulting rapid frequency chirp upon molecular spectra is investigated in the form of rapid passage signals. The evolution of said rapid passage signals is then investigated as a function of chromophore pressure and identity, with different QCLs, chirp rates, and optical path lengths. The prospect of producing population transfer with chirped lasers is discussed. Chapters 3, 4, and 5 are then concerned with the application and characterisation of continuous wave QCLs. In these chapters a widely tunable commercially produced EC-QCL is utilised as well as two DFB QCLs, one of which is used in tandem with a home-made mount and temperature controller. In Chapter 3 a number of sensitive detection techniques are compared with the employment of wavelength modulation spectroscopy, long path cells and optical cavities, and the narrow bandwidth of QCLs utilised to determine a previously unknown spectral constant of DBr. Chapters 4 and 5 then utilise the high power of an external cavity quantum cascade laser in sub-Doppler Lamb-dip and polarisation spectroscopy measurements and then a pump-probe experiment. The laser linewidth is investigated on a millisecond timescale returning a current noise limited value of c.a. 2 MHz and the fundamental linewidth of the device investigated by altering the injection current. Chapter 5 is concerned with the pump-probe experiment, directly measuring the hot band absorption in a ladder like transition (R(6.5)$_\frac{1}{2}$ $v=1\leftarrow0$ and P(7.5)$_\frac{1}{2}$ $v=1\leftarrow0$). The Bennett peak in the hot band is observed with a DFB-QCL swept at $\sim 0.15$ MHz ns$^{-1}$ and is seen not just as a pump bandwidth limited lineshape, but as a highly velocity selected rapid passage signal. The effect of pressure, pump and probe scan rate and power upon this rapid passage signal is also studied. It is further noted that rapid thermalisation occurs within $v=1$ such that at pressures above c.a. 30 mTorr a broad NO doublet absorption is observed beneath the Bennett peak from which a total population transfer of c.a. $16 \%$ can be estimated. Finally an experiment is discussed in which this population transfer could be increased for use in secondary applications. Chapter 6 then presents initial measurements with two prototype pulsed 3.3 \si{\micro\metre} QCLs considering the prospects of such devices. A Fabry-P\'rot device is first studied using a Fourier transform spectrometer and temperature tuning used to produce a spectrum of the Q-branch of CH$_4$ around 3025 cm$^$. Experiments are then performed using a DFB QCL investigating the chirp rate of the system as an indicator of the rate of heat accumulation within the system. Heat management is of particular consideration when the sea-change is made from pulsed to continuous devices. For this device absorption spectra of two CH$_4$ transitions at 2971 cm$^$ are used to determine the chirp rate, which is found to be c.a. 1.8 GHz ns$^$, at least an order of magnitude higher than that of the longer wavelength pulsed devices considered in Chapter 2. 535
224	Vers des assemblages de complexes métalliques oligonucléaires, servant d’antenne solaire au niveau moléculaire Chartrand, Daniel 12 1900 (has links) Les fichiers additionnels sont les données cristallographiques en format CIF. Voir le site de la Cambridge Crystallographic Data Centre pour un visualiseur: http://www.ccdc.cam.ac.uk / Ce projet de recherche vise l’élaboration de systèmes métallosupramoléculaires artificiels imitant le processus naturel de la photosynthèse. Idéalement, ces systèmes seraient capables de fournir l’énergie et la séparation de charge nécessaire pour catalyser des réactions à transfert multiélectroniques, tel que l’hydrolyse de l’eau ou la réduction du gaz carbonique. La réalisation d’un tel système catalytique créerait une source d’énergie renouvelable, sous forme d’énergie chimique, crée directement à partir de l’énergie solaire. Le système envisagé, schématisé sous la forme d’une antenne, possède trois parties distinctes. Tout d’abord, des chromophores forment un état excité en captant l’énergie de la lumière visible du soleil. Vient ensuite un centre de liaison qui lie tous les chromophores et qui collecte l’énergie de cet état excité à travers un transfert d’électron. Cet électron est de nouveau transféré vers la dernière partie, un centre réactionnel catalytique. Cet assemblage permet de créer une séparation de charge entre le chromophore et le centre réactionnel qui sont séparés par le centre de liaison, évitant ainsi la recombinaison de charge. Le projet se focalise sur la synthèse, la caractérisation et l’application en photocatalyse d’assemblages chromophore–centre de liaison–catalyseur. Tout d’abord, une étude de chromophores à base de fluorène et de rhénium a été effectuée dans le but d’évaluer le transfert électronique entre ces deux composants. Ensuite, des centres de liaisons à base de dimère de rhodium tétraamidinate ont été créés et étudiés afin d’établir leurs caractéristiques photophysiques et électrochimiques. Puis un d’entre eux a été assemblé avec des chromophores de rhénium, créant ainsi des espèces moléculaires discrètes contenant d’un à quatre chromophores. Et pour finir, ces assemblages ont été combinés avec un catalyseur à base de cobalt, puis ont été testés dans des expériences de photoproduction d’hydrogène. Cette dernière partie a requis l’élaboration d’un photoréacteur qui est aussi décrite en détail dans cet ouvrage. / This research project involves synthetic metallosupramolecular systems developed to mimic the natural process of photosynthesis. Ideally, these systems would be able to provide the energy and the charge separation needed to catalyze multielectron-transfer reactions, such as water-splitting or carbon dioxide reduction. The realization of such a catalytic system would create a renewable energy source, in the form of chemical energy, created directly from solar energy. The system envisioned has three distinct parts in the form of an antenna. First of all, chromophores go into an excited state, while capturing the visible light energy of the Sun. Then comes a hub which binds all the chromophores and collects this excited state energy through an electron transfer. This electron is then transferred again to the last part, a catalytic reaction center. This assembly creates a charge separation between the chromophore and the reaction center which are separated by the hub, thus avoiding the recombination of charge. The project focuses on the synthesis, characterization and application in photocatalysis of chromophore-hub-catalyst assemblies. First of all, a study of fluorene and rhenium based chromophores was made to assess the electronic transfer between these two components. Then, tetraamidinate rhodium dimer based hubs have been created and studied in order to establish their photophysical and electrochemical characteristics. Then one of these assemblies was formed with chromophores of rhenium, thus creating discrete molecular species containing one to four chromophores. And finally, these assemblies were combined with a cobalt-based catalyst and were tested for hydrogen photoproduction. The latter required the development of a photoreactor which is also described in detail in this thesis. rhénium chromophore fulvène transfert de charge isomérisation rhodium couplage Suzuki photophysique électrochimie paramètre d’Hammett paramètre de Taft solvatochromisme hydrogène photocatalyse cobalt chromatographie en phase gazeuse rhenium charge transfer isomerization Suzuki coupling photophysics electrochemistry density functional theory Hammett parameter Taft parameters solvatochromism hydrogen photocatalysis gas phase chromatography
225	Procédé d'élimination de la pollution de l'air par traitement photocatalytique : application aux COVs / Remediation process of air polllution using photocatalytic treatment : study of VOCs Vincent, Guillaume 04 September 2008 (has links) L’oxydation photocatalytique des Composés Organiques Volatils (COVs) apparaît comme un procédé très prometteur pour la réduction de la pollution atmosphérique. Ce travail avait pour objectif d’étudier l’oxydation photocatalytique de plusieurs COVs au sein d’un réacteur annulaire: méthyléthylcétone (MEK), acétone, 1-propanol ou encore triéthylamine (TEA). Dans une première partie, l’influence de plusieurs paramètres cinétiques tels que la concentration en polluant, l’intensité lumineuse, le temps de contact et le taux d’humidité a été étudiée. Un mécanisme de dégradation photocatalytique a été établi pour chaque polluant en fonction des sous-produits détectés par GC/MS. Dans une seconde partie, la diffusion de radicaux hydroxyles OH• dans la phase gazeuse, après activation photonique du TiO2, a été mise en évidence par Fluorescence Induite par Laser (LIF). Pour la première fois, ces radicaux OH• ont été détectés à des pressions proches des conditions atmosphériques. Dans ce cas, nous pouvons en conclure que la dégradation photocatalytique des COVs pourrait être partiellement due à une réaction en phase gazeuse entre les COVs et les radicaux OH• / Photocatalytic oxidation of airborne contaminants appears to be a promising process for remediation of air polluted by Volatile Organic Compounds (VOCs). The aim of our study is the photocatalytic oxidation of several VOCs using an annular reactor: methylethylketone (MEK), acetone, 1-propanol and triethylamine (TEA). First, the influence of different kinetic parameters such as pollutant concentration, incident light irradiance, contact time and humidity has been studied. A mechanistic pathway has been indeed proposed for each pollutant according to the produced intermediates species detected by GC/MS. Second, the diffusion of hydroxyls radicals OH• in gas phase, after photonic activation of TiO2, has been highlighted using Laser-Induced Fluorescence (LIF). For the first time, OH• radicals have been detected at atmospheric pressures, close to the major photocatalytic oxidation conditions, leading to the assumption that the photocatalytic degradation of VOCs might be at least partially occurs between pollutants and OH• radicals in gas-phase Dioxyde de titane (TiO2) Réactions en phase gazeuse Mécanismes réactionnels LIF Radicaux hydroxyles Sous-produits Modèles cinétiques Dégradation photocatalytique Composés Organiques Volatils (COVs) Titanium dioxide (TiO2) Gas phase reactions Degradation mechanisms LIF Volatile Organic Compounds (VOCs) Photocatalytic degradation Kinetic models By-products Hydroxyl radicals
226	CFD Flame Spread Model Validation: Multi-Component Data Set Framework Wong, William Chiu-Kit 30 July 2012 (has links) "Review of the literature shows that the reported correlation between predictions and experimental data of flame spread vary greatly. The discrepancies displayed by the models are generally attributed to inaccurate input parameters, user effects, and inadequacy of the model. In most experiments, the metric to which the model is deemed accurate is based on the prediction of the heat release rate, but flame spread is a highly complex phenomenon that should not be simplified as such. Moreover, fire growth models are usually made up of distinctive groups of calculation on separate physical phenomena to predict processes that drive fire growth. Inaccuracies of any of these Â“sub-modelsÂ” will impact the overall flame spread prediction, hence identifying the sources of error and sensitivity of the subroutines may aid in the development of more accurate models. Combating this issue required that the phenomenon of flame spread be decomposed into four components to be studied separately: turbulent fluid dynamics, flame temperature, flame heat transfer, and condensed phase pyrolysis. Under this framework, aspects of a CFD model may be validated individually and cohesively. However, a lack of comprehensive datasets in the literature hampered this process. Hence, three progressively more complex sets of experiments, from free plume fires to fires against an inert wall to combustible wall fires, were conducted in order to obtain a variety of measurements related to the four inter-related components of flame spread. Multiple permutations of the tests using different source fuels, burner size, and source fire heat release rate allowed a large amount of comparable data to be collected for validation of different fire configurations. FDS simulations using mostly default parameters were executed and compared against the experimental data, but found to be inaccurate. Parametric study of the FDS software shows that there are little definitive trends in the correlation between changes in the predicted quantities and the modeling parameters. This highlights the intricate relationships shared between the subroutines utilized by FDS for calculations related to the four components of flame spread. This reveals a need to examine the underlying calculation methods and source code utilized in FDS." fiber reinforced plastic FRP pyrolysis heat flux plume velocity plume temperature 2-D flame spread flame spread rate Flame spread free plume inert wall combustible wall panel fire modeling CFD experimental data dataset turbulent buoyant fluid flow gas phase kinetics flame heat transfer condensed-phase pyrolysis
227	Numerical Methods in Reaction Rate Theory Frankcombe, Terry James Unknown Date (has links) Numerical methods are often required to solve chemical problems, either to verify theoretical models or to access information that is not readily available experimentally. This thesis deals with both situations, though in differing levels of detail. A major component of this thesis is devoted to developing new methods to determine a full eigendecomposition of the matrices derived from "low temperature" unimolecular master equations. When transient behaviour is of interest achieving relative accuracy for more than just the eigenvector corresponding to the smallest eigenvalue is of central importance. Three new methods are presented. The first is based on a weighted implementation of subspace projection methods, in this case explored for the well-known Arnoldi method. This weighted inner product subspace projection methodology is demonstrated to 780103 Chemical sciences master equation matrix methods EGME gas phase nonequilibrium kinetics spectral eigenvalues eigenvectors HONE ERS Nesbet WIPSP subspace projection relative accuracy precision MPFUN quadruple precision double precision Chebyshev Lanczos Arnoldi coal graphene carbon ab initio B3LYP gasification
228	Numerical Methods in Reaction Rate Theory Frankcombe, Terry James Unknown Date (has links) Numerical methods are often required to solve chemical problems, either to verify theoretical models or to access information that is not readily available experimentally. This thesis deals with both situations, though in differing levels of detail. A major component of this thesis is devoted to developing new methods to determine a full eigendecomposition of the matrices derived from "low temperature" unimolecular master equations. When transient behaviour is of interest achieving relative accuracy for more than just the eigenvector corresponding to the smallest eigenvalue is of central importance. Three new methods are presented. The first is based on a weighted implementation of subspace projection methods, in this case explored for the well-known Arnoldi method. This weighted inner product subspace projection methodology is demonstrated to 780103 Chemical sciences master equation matrix methods EGME gas phase nonequilibrium kinetics spectral eigenvalues eigenvectors HONE ERS Nesbet WIPSP subspace projection relative accuracy precision MPFUN quadruple precision double precision Chebyshev Lanczos Arnoldi coal graphene carbon ab initio B3LYP gasification
229	Numerical Methods in Reaction Rate Theory Frankcombe, Terry James Unknown Date (has links) Numerical methods are often required to solve chemical problems, either to verify theoretical models or to access information that is not readily available experimentally. This thesis deals with both situations, though in differing levels of detail. A major component of this thesis is devoted to developing new methods to determine a full eigendecomposition of the matrices derived from "low temperature" unimolecular master equations. When transient behaviour is of interest achieving relative accuracy for more than just the eigenvector corresponding to the smallest eigenvalue is of central importance. Three new methods are presented. The first is based on a weighted implementation of subspace projection methods, in this case explored for the well-known Arnoldi method. This weighted inner product subspace projection methodology is demonstrated to 780103 Chemical sciences master equation matrix methods EGME gas phase nonequilibrium kinetics spectral eigenvalues eigenvectors HONE ERS Nesbet WIPSP subspace projection relative accuracy precision MPFUN quadruple precision double precision Chebyshev Lanczos Arnoldi coal graphene carbon ab initio B3LYP gasification
230	Numerical Methods in Reaction Rate Theory Frankcombe, Terry James Unknown Date (has links) Numerical methods are often required to solve chemical problems, either to verify theoretical models or to access information that is not readily available experimentally. This thesis deals with both situations, though in differing levels of detail. A major component of this thesis is devoted to developing new methods to determine a full eigendecomposition of the matrices derived from "low temperature" unimolecular master equations. When transient behaviour is of interest achieving relative accuracy for more than just the eigenvector corresponding to the smallest eigenvalue is of central importance. Three new methods are presented. The first is based on a weighted implementation of subspace projection methods, in this case explored for the well-known Arnoldi method. This weighted inner product subspace projection methodology is demonstrated to 780103 Chemical sciences master equation matrix methods EGME gas phase nonequilibrium kinetics spectral eigenvalues eigenvectors HONE ERS Nesbet WIPSP subspace projection relative accuracy precision MPFUN quadruple precision double precision Chebyshev Lanczos Arnoldi coal graphene carbon ab initio B3LYP gasification

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