Rozprawy doktorskie na temat „Gaseous”

Diffusivity of nonreactive gases in liquids provides a means of interpreting structure in the liquid state. Structural models of the liquid state include Hildebrand's condensed gas model and Eyring's pseudo-lattice model. The former model predicts a linear dependence of diffusivity with temperature while the latter model predicts linear dependence of log(D) versus 1/T. The limited temperature dependent diffusivity data to date with a typical precision of ± 5% do not permit distinguishing which temperature dependence is more linear. However, the present investigation shows that diffusivities of one gas solute in two nonpolar liquids indirectly supports a linear diffusivity temperature dependence by a Graham's law like relation. At a fixed temperature this relation equates relative diffusivities to the square root of the inverse molecular weights of the respective liquids. Diffusion of gases into nonpolar liquids have previously been measured by two techniques: (1) a pseudo-steady state technique developed by Hildebrand with diffusion through multiple capillaries and (2) a method by Walkley with diffusion through an open tube. Each of these methods requires prior knowledge of solubility of the gas in the liquid. An apparatus is constructed which combines these methods into a single experiment. Simultaneous solution of the two equations which describe the combined experiment yields both the solubility and diffusion coefficient. Diffusivities and solubilities of nitrogen, argon and oxygen into liquids of carbon tetrachloride and benzene as well as oxygen into water have been studied. The results compare favorably with the Literature. The diffusion cell for this technique consists of a capillary disk, which is flooded with liquid. Gas is admitted into the space over the open solvent. With temperature and pressure constant, volume uptake of the gas in the solvent is monitored. Time-volume uptake data is evaluated by the two diffusion equations. Although the experiment is conceptually easy, a small gas volume change over a prolonged period of time poses problems in data collection and experiment control. The data collection and control is simplified by dedicating a Microcomputer Interfaced Data Acquisition System (MIDAS) to the experiment.
Ph. D.

The experiment consisted of stopping negative pions in a high pressure gas target to measure the transfer rate π-p → π-d in mixtures of H2, D2 and HD gas. The gamma rays from the decay of the π ⁰ in π -p → n + π ⁰ were detected in coincidence using two large sodium iodide crystals. The probability that a pion be transferred to a deuteron from a pionic hydrogen complex was described in terms of a phenomenological model parameterized by B and ∧. Fits to the data yielded B = 0.77 ±0.14 and ∧ = 0.21 ±0.04. These values implied that the hydrogen capture ratio in an equal mix of H2 and D2 was F(H₂D₂) = 0.45 ±0.01. The capture ratio for HD was measured to be F(HD) = 0.355 ±0.021. The ratio F(H₂D₂)/F(HD) indicated that there was likely to be internal transfer in the breakup of π-HD favouring the π-d complex at about a 60% level.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

Un gaz à l'intérieur d’un microsystème ou d’un milieu poreux est dans un état hors équilibre, car le libre parcours moyen des molécules est comparable à la dimension caractéristique du milieu. Ce même état degaz, appelé raréfié, se retrouve en haute altitude ou dans un équipement de vide à basse pression. Ces gaz raréfiés suivent des types d’écoulements qui peuvent être décrits par des modèles cinétiques dérivés de l'équation de Boltzmann. Dans ce travail nous présentons les principaux modèles et leurs mises en oeuvre numériquepour la simulation des écoulements de gaz raréfiés. Parmi les modèles utilisés nous présentons les deux modèles complets de l'équation de Boltzmann, le modèle de Shakhov(S-model) pour un gaz monoatomique et le modèle de McCormack pour un mélange de gaz toujours monoatomiques. La méthode des vitesses discrètes est utilisée pour la discrétisation numérique dans l'espace des vitesses moléculaires et le schéma de type TVD est mis en œuvre dans l'espace physique. L’aspect original de ce travail se situe sur les régimes transitoires et, en particuliersur les comportements non-stationnaires des transferts de chaleur et de masse. Cependant, pour certaines configurations nous considérons uniquement les conditions stationnaires des écoulements et un schéma implicite est développé afin de réduire le coût de calcul. En utilisant ces approches numériques, nous présentons les résultats pour plusieurs types d’écoulements non-stationnaires, de gaz raréfiés monoatomiqueset de mélanges binaires de gaz monoatomiques
A gas inside the microsystems or the porous media is in its non-equilibrium state, due to the fact that the molecular mean free path is comparable to the characteristic dimension of the media. The same state of a gas, called rarefied, is found at high altitude or in the vacuum equipment working at low pressure. All these types of flow can be described by the kinetic models derived from the Boltzmann equation. This thesis presents the development of the numerical tools for the modeling and simulations of the rarefied gas flows. The two models of the full Boltzmann equation, the Shakhov model (S-model) for the single gas and the McCormack model for the gas mixture, are considered. The discrete velocity method is used to the numerical discretization in the molecular velocity space and the TVD-like scheme is implemented in the physical space. The main aspect of this work is centered around the transient properties of the gas flows and, especially, on the transient heat and mass transfer behaviors. However, for some configurations only steady-state solutions are considered and the implicit scheme is developed to reduce the computational cost. Using the proposed numerical approach several types of the transient rarefied single gas flows as well as the binary mixture of the monoatomic gases are studied

Longitudinal relaxation times T1 have been measured in 'He gas, using pulsed NMR, for number densities between 3x 1023 and 6x 102' spins/m' and temperatures between 0.6 and 15K. Relaxation takes place on or near the walls of the pyrex sample cells and measurements of Tl give information about the surface phases. A low temperature amplifier containing GaAs FET devices was developed to improve the spectrometer sensitivity. An amplifier noise temperature of 0.9 ± 0.5K was obtained at 1.16 MHz and an NMR signal was observed at 4.2K with the sensitivity being mainly limited by Johnson noise in the receiver coil. Baking the pyrex cells under vacuum and discharge cleaning the walls before sealing in the sample gas were found to increase the bulk gas Tl's by two or three orders of magnitude. A cryogenic wall coating of solid molecular hydrogen was found to delay the formation of a 'He monolayer on cooling and T, measurements were consistent with a binding energy of %, 13K for a 3He atom to a hydrogen surface. Once a 3He monolayer has formed the dipolar interaction between adsorbed spins is thought to be the dominant source of relaxation in the sealed cells. The presence of "He generally causes T, to rise on cooling below 2K due to preferential adsorption of "He at the surface. However, 'He atoms which dissolve in quasiparticle states in the superfluid helium film can be an extra source of relaxation. In the dirty cells relaxation probably takes place in quasiparticle states at the free surface of the saturated helium film, which are bound with an energy of 5.1 t 0.3K. In a cleaned, sealed cell a T, of ti 8 hours was measured at 7.7 MHz and 0.8K. In this case relaxation is probably occurring 2 or 3 helium layers away from the helium-hydrogen interface

The measurement of partial discharge (PD) activity is a commonly used tool to quantify the health of electrical insulation material in high voltage plant. Models of PD activity have been developed in order to provide insight into the physical conditions present in PD systems. Modern PD models typically use the approach taken in the work of Niemeyer in early 1990's, and so far have been primarily limited to investigating PD activity from simple controlled experiments. PD models have typically focused on PD activity in gaseous voids, which is also the case in this thesis. In this work a new PD activity model was developed. It addressed several of the shortcomings present in other PD activity models in order to provide a more physically accurate description of PD phenomena and to extend the scope of the model. The model was validated against experimental data in the literature, and was then used to simulate PD activity from a three-phase cable experiment, which is indicative of the more complex PD systems present in operational plant. However, despite this contribution it became evident that many of the assumptions and concepts used in the model, despite having a basis in the literature, have limited justification. A drift diffusion model was then used to test some of the physical concepts that are employed when modelling PD in voids. The results showed that many of these concepts may be erroneous, with discrepancies between the canonical reasoning and the simulation results. For example, the residual electric field, the electric field after a discharge, is significantly lower than the estimates used by PD activity models in the literature. It is concluded that in their current form PD activity models may not be t for purpose, and it is suggested that a new approach to modelling PD activity is required moving forward.

Chapter one provides a brief history and current state of knowledge of the chemistry of organosilicon reactive intermediates relevant to this thesis. Chapter two outlines the experimental techniques used in the majority of work carried out in this thesis. Chapter three describes an experimental investigation of the pyrolysis of 4-dimethylsilylbut-l-ene and 5-dimethylsilylpent-l-ene, with and without excess methylchloride as a silyl radical trap. The results of computer modelling of the pyrolysis of 4-dimethylsilylbut-1-ene with excess methylchloride are described, in which information concerning the isomerisation of an alpha-silyl radical to a silyl radical via a hydrogen shift is obtained. Chapter four describes the results of an experimental investigation of the reactions of dimethylsilene and dimethylsilylene with anions. Chapters five and six contain the results of computer modelling of three related pyrolysis mechanisms composed of complex series of unimolecular rearrangements of silylenes, silenes, disilenes and disilacyclopropanes. Chapter seven describes an experimental determination of Arrhenius parameters for the trapping of dimethylsilene by butadiene, together with the results of pyrolysis of butadiene adducts of methylsilene, dimethylsilene and dimethylsilylene. Chapter eight is an experimental investigation of the pyrolysis of cis and trans dimethy1(1-propenyl)vinylsilane with excess 2,3-dimethylbutadiene as a silylene trap. Interpretation of the results as a cis-trans isomerisation and decomposition of the cis isomer via a silacyclopropane intermediate are reinforced by the results of computer modelling of both systems. Chapter nine describes an experimental investigation of the pyrolysis of 1, 2-dimethyldisilane with and without butadiene as a silylene trap. Computer modelling of the pyrolysis with the absence of butadiene is used to clarify the pyrolysis mechanism. Chapter ten is an experimental investigation of the pyrolysis of silacyclobutane and methylsilacyclobutane with excess butadiene to trap silylene intermediates and thus suppress secondary decomposition. Arrhenius parameters for the primary decomposition pathways are determined.

A model of the generation and release of fission gas, as well as the total swelling over time, was created. It uses an ideal spherical fuel grain with a time-dependent radius. UO2 and quasi-homogeneous SBR MOX fuels were simulated with this model, and the results were compared to a fixed grain radius model of gaseous swelling. Gaseous swelling and fission gas release were calculated for temperatures from 1600 K to 2200 K. The grain growth of UO2 was found to decrease the time needed to saturate the intergranular boundaries as compared to simple diffusion without grain growth. Small temperatures increased the time required for saturation, as did small rates of grain growth. Gaseous swelling was within the range of values found by experimental data.

Initiation and stabilization of detonation by hypersonic conical projectiles launched into combustible gas mixtures is investigated. This phenomenon must be understood for the design and optimization of specific hypersonic propulsion devices, such as the oblique detonation wave engine and the ram accelerator. The criteria for detonation initiation by a projectile is also related to fundamental aspects of detonation research, such as the requirement for direct initiation of a detonation by a blast wave. Experimental results of this problem also offer useful references for validation of numerical and theoretical modeling.Projectiles with cone half angles varying from 15° to 60° were launched into stoichiometric mixtures of hydrogen/oxygen with 70% argon dilution at initial pressures between 10 and 200 kPa. The projectiles were launched from a combustion-driven gas gun at velocities up to 2.2 km/s (corresponding to 133% of the Chapman Jouguet velocity). Pictures of the flowfields generated by the projectiles were taken via Schlieren photography.Five combustion regimes were observed about the projectile ranging from prompt and delayed oblique detonation wave formation, combustion instabilities, a wave splitting, and an inert shock wave. Two types of transition from the prompt oblique detonation wave regime to the inert shock regime were observed. The first (the delayed oblique detonation wave regime) showed an inert shock attached to the tip of the projectile followed by a sharp kink at the onset of an oblique detonation wave; this regime occurred by decreasing the cone angle at high mixture pressures. The second (the combustion instabilities regime) exhibited large density gradients due to combustion ignition and quenching phenomena; this regime occurred by decreasing the mixture pressure at large cone angles.A number of theoretical models were considered to predict critical conditions for the initiation of oblique detonations. The Lee-Vasiljev model agreed qualitatively well with the experimental results for relatively blunt projectiles (cone half-angle larger than 35°) and low mixture pressures (lower than 100 kPa). The trend of the critical Damköhler number calculated along the projectile cone surface was similar to that of the experimental results for slender cones (cone half-angles lower 35°) and high mixture pressures (higher than 100 kPa). Steady 2D simulations of reacting flows over finite wedges using the method of characteristics with a one-step Arrhenius chemical reaction model reproduced the three regimes observed for direct initiation of a detonation: the subcritical, critical and supercritical regimes. It is shown that in order for a 2D wedge to be equivalent to the problem of blast initiation of a detonation (which is the essence of the Lee-Vasiljev model), the Mach number normal to the oblique shock needs to be greater than 50 and the wedge angle has to be smaller than 30°. Simulations of reacting flows over semi-infinite wedges and cones were validated with CFD results. Excellent agreement was reached between the angle of overdriven oblique detonations obtained from the simulations and those from a polar analysis. For wedge or cone angles equal or lower than the minimum angle for which an oblique detonation is attached (according to the polar analysis), a Chapman-Jouguet oblique detonation was initiated. In the conical configuration, the curvature around the cone axis allowed an oblique detonation to be self-sustained at an angle less than without the curvature effect. At larger activation energies, the initiation process of an oblique detonation wave at the tip of a semi-infinite wedge or cone was identified. Unsteady 2D computational simulations were also conducted and showed the cellular structure of an oblique detonation wave. Instabilities in the form of transverse shock waves along the oblique detonation front arise for large activation energies.
Cette étude a pour objet l'initiation et la stabilisation d'une onde de détonation par un projectile conique hypersonique projeté dans un milieux combustible gazeux. On retrouve ce phénomène dans certains propulseurs hypersoniques, comme le moteur à onde de détonation oblique et le ram accelerator. Le critère pour l'initiation d'une détonation par un projectile est relié à des aspects fondamentaux de la recherche en détonique, tel que les conditions nécessaires pour l'initation directe d'une détonation par une forte onde de choc. Les résultats expérimentaux de ce problème offrent aussi d'utiles références pour la validation d'études numériques et théoriques. Des projectiles conique dont le demi-angle varie de 15° à 60° ont été lancés dans des mélanges stoechiométriques d'hydrogène et d'oxygène avec une dilution d'argon à 70% à des pressions initiales de 10 à 200 kPa. Les projectiles ont été accélérés par un canon qui produit la propulsion à partir de la combustion gazeuse de mélanges stoechiométriques composées d'hydrogène et d'oxygène à des pressions initiales élevées. Des vitesses de l'ordre de 2.2 km/s ont été atteintes, correspondant à 133% de la vitesse Chapman Jouguet. Des photographies de l'écoulement autour des projectiles ont été prises avec un système Schlieren. Cinq régimes de combustion ont été observés autour des projectiles: formation d'une onde de détonation oblique prompte et retardée, instabilités de combustion, séparation d'ondes, et onde de choc inerte. Deux types de transition entre les régimes de détonation oblique prompte et de choc inerte on été observés. La première (qui concerne le régime onde de détonation retardée) a produit une onde de choc inerte attachée au nez du projectile suivie d'une augmentation abrupte de l'angle de choc au passage à la détonation oblique. Cette transition a eu lieu en diminuant l'angle de cône à de hautes pression de mélange. La deuxième (qui concerne le régime instabilités de combustion) a révélé la présence de forts gradients de densité causés par des phénomènes d'allumage et d'extinction du mélange combustible. Cette transition a été observée en diminuant la pression de mélange à des angles de cône élevés. Quelques modèles théoriques ont été considérés afin de prédire les conditions critiques pour l'initiation de détonations obliques. Le modèle de Lee-Vasiljev s'est avéré en accord qualitatif avec les résultats expérimentaux pour des projectiles relativement émoussés (des demi-angles de cône plus grand que 35°) et de basses pressions de mélanges (plus petit que 100 kPa). La tendance du nombre de Damköhler critique calculé sur la surface du cône s'est avéré similaire à celle des résultats expérimentaux pour des projectiles élancés (des demi-anges de cône plus petit que 35°) et des pressions de mélanges élevées (plus grand que 100 kPa). Des simulations 2D en mode permanent d'écoulements réactifs autour de dièdres finis en utilisant la méthode des caractéristiques avec une réaction chimique de forme Arrhenius ont reproduis les trois régimes observés dans les études d'initiation directe de détonations: les régimes sous-critique, critique et sur-critique. Il est démontré qu'un dièdre est équivalent au problème d'initiation directe d'une détonation si le nombre de Mach normal au choc oblique est supérieur à 50 et si l'angle du dièdre est inférieur à 30°. Des simulations d'écoulements réactifs autour de dièdres et de cônes semi-infinis ont été validés avec des résultats numériques. Un excellent accord a été observé entre l'angle d'une détonation oblique forte obtenu des simulations et celui dérivé d'une analyse des polaires. Pour un angle de dièdre ou de cône égal ou inférieur à l'angle minimal pour lequel une détonation oblique est attachée, une détonation oblique Chapman-Jouguet a été initiée. Pour une configuration conique, la courbure autour de l'axe du cône a permis une détonation oblique d'être non supportée à un angle inférieur à celui sans l'effet de courbure.

In the last decade, sensitive observations have revealed that disc galaxies are surrounded by multiphase gaseous halos produced by the circulation of gas from the discs to the environment and vice-versa. This Thesis is a study of the gaseous halo of the Milky Way carried out via the modelling of the HI emission and the available absorption-line data. We fitted simple kinematical models to the HI LAB Survey and found that the Galaxy has a massive (~3x10^8 Mo) HI halo extending a few kiloparsecs above the plane. This layer rotates more slowly than the disc and shows a global inflow motion, a kinematics similar to that observed in the HI halos of nearby galaxies. We built a dynamical model of the galactic fountain to reproduce the properties of this layer. In this model, fountain clouds are ejected from the disc by SN feedback and - as suggested by hydrodynamical simulations - triggers the cooling of coronal gas, which is entrained by the cloud wakes and accretes onto the disc when the clouds fall back. For a proper choice of the parameters, the model reproduces well the HI data and predicts an accretion of coronal gas onto the disc at a rate of 2 Mo/yr. We extended this model to the warm-hot component of the halo, showing that most of the ion absorption features observed towards background sources are consistent with being produced in the turbulent wakes that lag behind the fountain clouds. Specifically, the column densities, positions, and velocities of the absorbers are well reproduced by our model. Finally, we studied the gas content of galaxies extracted from a cosmological N-body+SPH simulation, and found that an HI halo with the forementioned properties is not observed, probably due ti the relatively low resolution of the simulations.

Adsorption studies (xenon and iodine) in microporous materials have been carried out on various materials such as zeolites (FAU, MFI, SAV and CHA) and metal-organic frameworks (MOF-5, HKUST-1 and JUC-32). The as-synthesised and commercial zeolites containing Na⁺, Li⁺ or K⁺ cations and then subsequently ion-exchanged for other extra framework cations. The xenon adsorption in zeolites was interpreted using isosteric heats of adsorption (CHA) and also ¹²⁹Xe NMR (FAU). CHA type zeolites show a high affinity and capacity for xenon at low xenon pressures <10kPa. This affinity changes depending upon the extra framework cation present due to the positioning and size of the cation. The electric field gradient was a primary factor in the xenon adsorption since a neutral framework (ALPO-CHA) was found to have a lower affinity for xenon but having the same framework type. This was further highlighted by the introduction of Si into the framework and a comparison was made between the three structures CHA, ALPO-CHA and SAPO-34 with the latter being a silicon substituted aluminophosphate carrying a slightly negatively charged framework. Another framework studied was that of STA-7 (SAV) and it was found that varying the silicon within the framework had an effect upon the xenon adsorption. Xenon interaction with the MOFs was minimal when compared to the zeolites. MOF materials adsorbed more iodine per gram of material than any of the zeolites studied. In some materials, two different species of iodine exist. These species, I₂ (isolated) and (I₂)_n (wires) have different Raman frequencies and the (I₂)_n species have been observed in MOFs for the first time.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2003.
Includes bibliographical references (p. 147-156).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Hybrid atomistic-continuum formulations allow the simulation of complex hydrodynamic phenomena at the nano and micro scales without the prohibitive cost of a fully atomistic approach. This is achieved through a domain decomposition strategy whereby the atomistic model is limited to regions of the flow field where required and the continuum model is implemented side-by-side in the remainder of the domain within a single computational framework. The current work is focused on arguably the most critical elements of any hybrid formulation: the atomistic-continuum coupling method and the imposition of continuum boundary conditions on the atomistic subdomain. The relative merits of different approaches for both are delineated and demonstrated using sample test problems. For the case of incompressible steady gaseous flows a hybrid formulation is developed using a finite element method for the continuum subdomain and the direct simulation Monte Carlo (DSMC) method for the atomistic subdomain. The Schwarz alternating method is used to couple both subdomains using an overlap region across which the successive exchange of Dirichlet boundary conditions yields a steady state solution. This approach has the advantages of decoupling both length scales and time scales of the atomistic and continuum solvers leading to superior performance over conventional explicit schemes. Continuum boundary conditions are imposed on the atomistic subdomain using the Chapman-Enskog distribution function in conjunction with particle reservoirs. A driven cavity test problem shows convergence in 0(10) Schwarz iterations for flow Reynolds numbers 0(1).
(cont.) The Schwarz method is also, for the first time, extended to couple unsteady hybrid incompressible flows. Tests for an impulsively driven Couette flow highlight the versatility of this approach to advance solutions to arbitrary times through appropriate interpolation of Dirichlet boundary conditions. Techniques are also developed using limited ensemble averaging of the atomistic solution to realize significant computational savings over a standard ensemble averaging process while maintaining the same variance reduction. Finally an unsteady compressible hybrid formulation utilizing Adaptive Mesh and Algorithm Refinement (AMAR) technology is described. DSMC is used to model the atomistic regions on the finest grid of the adaptive hierarchy. The continuum flow is solved using a second order Godunov scheme. New gradient-based tolerance parameters are developed to provide robust detection and tracking of concentration diffusion fronts and stationary and moving shock waves. Extension of AMAR to binary gas mixtures is also completed and demonstrated using a binary gas shock wave test problem.
by Hettithanthrige Sanith Wijesinghe.
Ph.D.

Cette thèse décrit plusieurs résultats expérimentaux impliquant le phénomène de la filamentation laser qui se produit lorsque des impulsions laser ultrabrèves se progagent dans l'air avec une intensité de l'ordre de ~ 10¹³ W/cm2. Un laser titane-saphir est utilisé pour gé- nérer des impulsions femtosecondes dans l'infrarouge (800 nm). En raison de ses propriétés particulières, cette forme de propagation est étudiée pour de nombreuses applications. Nous nous concentrons dans cette thèse sur la télédétection et l'identification de polluants atmosph ériques. Notre objectif est d'améliorer les résultats et de résoudre certains problèmes dans la détection de polluants, en particulier de ceux qui ont le même spectre de fluorescence induit par filamentation. Tous les résultats présentés ici ont été obtenus en laboratoire. La télédétection de polluants dans l'atmosphère implique la propagation de filaments à haute altitude où la pression atmosphérique est basse. Il est donc important de bien comprendre le phénomène de la filamentation dans ces conditions. Nous avons expérimentalement et numériquement étudié l'effet d'une basse pression sur un filament unique dans l'air. Les expériences furent réalisées en variant la pression à l'intérieur d'une cellule entre 0,3 et 1 fois la pression atmosphérique normale (1 atm ~ 1:01 X 10⁵ Pa). Une approche pour détecter à distance la présence de polluants atmosphériques est de capter la fluorescence émise par les fragments moléculaires créés lors du passage de l'impulsion laser. Ce signal est toutefois lourdement atténué avant d'atteindre le détecteur en raison de la grande distance de propagation dans ces applications et il est important de trouver des moyens pour augmenter le signal de fluorescence. Nous avons donc étudié la possibilité d'utiliser le filament lui-même comme milieu de gain dans la direction de propagation pour amplifier les émissions des impuretés de l'air. Il avait déjà été démontré qu'un filament peut amplifier le signal rétrodiffusé dans l'air pur alors nous avons débuté nos expériences dans l'air pour ensuite étudier des mélanges air-hydrocarbones ( 2% de CH₄, C₂H₂ et C₂H₄ dans l'air). Nous avons détecté la fluorescence émise par l'azote neutre à ~ 337 nm dans l'air pur et par les fragments CH à ~ 431 nm dans des mélanges air-hydrocarbones. Dans les deux cas, le signal de fluorescence émis dans la direction opposée à celle du laser a augmenté de manière nonlin éaire en fonction de la longueur du filament, tandis que celui émis sur les côtés montrait une tendance linéaire. Le dernier chapitre de cette thèse traite d'une nouvelle approche pour identifier les molé- cules basée sur leur alignement. Nous montrons en effet que des polluants dans l'air peuvent être détectés et identifiés en mesurant les constantes de rotation de diférentes molécules. Il est important de noter que cette technique permet de distinguer des polluants dont les fragments émettent le même spectre de fluorescence (les mêmes raies atomiques et bandes moléculaires). Les résultats présentés dans cette thèse ont été obtenus par des études de type pompe-sonde utilisant le signal diffusé de l'impulsion de sonde, contrairement à d'autres expériences qui détectent la lumière transmise. Le fait d'observer le signal diffusé plutôt que celui transmis rend cette technique pertinente pour des applications de télédétection. Même si les molécules dans un gaz sont orientées de façon aléatoire, une impulsion ultrabrève et intense peut forcer les molécules à s'aligner non seulement pendant le passage de l'impulsion mais aussi après. Plus spécifiquement, un paquet d'onde rotationnel peut être créé par une impulsion femtoseconde, ce qui génère un alignement moléculaire en l'absence de champ après le passage de l'impulsion qui peut se reformer à intervalles réguliers. En plus de permettre la détermination des constantes de rotation et l'identication des molécules, cette technique donne également accès à des informations sur la dissipation dans le milieu en étudiant l'évolution du paquet d'onde sur une longue période (plusieurs retours périodiques de l'alignement moléculaire) après le passage de l'impulsion.
Cette thèse décrit plusieurs résultats expérimentaux impliquant le phénomène de la filamentation laser qui se produit lorsque des impulsions laser ultrabrèves se progagent dans l'air avec une intensité de l'ordre de ~ 10¹³ W/cm2. Un laser titane-saphir est utilisé pour gé- nérer des impulsions femtosecondes dans l'infrarouge (800 nm). En raison de ses propriétés particulières, cette forme de propagation est étudiée pour de nombreuses applications. Nous nous concentrons dans cette thèse sur la télédétection et l'identification de polluants atmosph ériques. Notre objectif est d'améliorer les résultats et de résoudre certains problèmes dans la détection de polluants, en particulier de ceux qui ont le même spectre de fluorescence induit par filamentation. Tous les résultats présentés ici ont été obtenus en laboratoire. La télédétection de polluants dans l'atmosphère implique la propagation de filaments à haute altitude où la pression atmosphérique est basse. Il est donc important de bien comprendre le phénomène de la filamentation dans ces conditions. Nous avons expérimentalement et numériquement étudié l'effet d'une basse pression sur un filament unique dans l'air. Les expériences furent réalisées en variant la pression à l'intérieur d'une cellule entre 0,3 et 1 fois la pression atmosphérique normale (1 atm ~ 1:01 X 10⁵ Pa). Une approche pour détecter à distance la présence de polluants atmosphériques est de capter la fluorescence émise par les fragments moléculaires créés lors du passage de l'impulsion laser. Ce signal est toutefois lourdement atténué avant d'atteindre le détecteur en raison de la grande distance de propagation dans ces applications et il est important de trouver des moyens pour augmenter le signal de fluorescence. Nous avons donc étudié la possibilité d'utiliser le filament lui-même comme milieu de gain dans la direction de propagation pour amplifier les émissions des impuretés de l'air. Il avait déjà été démontré qu'un filament peut amplifier le signal rétrodiffusé dans l'air pur alors nous avons débuté nos expériences dans l'air pour ensuite étudier des mélanges air-hydrocarbones ( 2% de CH₄, C₂H₂ et C₂H₄ dans l'air). Nous avons détecté la fluorescence émise par l'azote neutre à ~ 337 nm dans l'air pur et par les fragments CH à ~ 431 nm dans des mélanges air-hydrocarbones. Dans les deux cas, le signal de fluorescence émis dans la direction opposée à celle du laser a augmenté de manière nonlin éaire en fonction de la longueur du filament, tandis que celui émis sur les côtés montrait une tendance linéaire. Le dernier chapitre de cette thèse traite d'une nouvelle approche pour identifier les molé- cules basée sur leur alignement. Nous montrons en effet que des polluants dans l'air peuvent être détectés et identifiés en mesurant les constantes de rotation de diférentes molécules. Il est important de noter que cette technique permet de distinguer des polluants dont les fragments émettent le même spectre de fluorescence (les mêmes raies atomiques et bandes moléculaires). Les résultats présentés dans cette thèse ont été obtenus par des études de type pompe-sonde utilisant le signal diffusé de l'impulsion de sonde, contrairement à d'autres expériences qui détectent la lumière transmise. Le fait d'observer le signal diffusé plutôt que celui transmis rend cette technique pertinente pour des applications de télédétection. Même si les molécules dans un gaz sont orientées de façon aléatoire, une impulsion ultrabrève et intense peut forcer les molécules à s'aligner non seulement pendant le passage de l'impulsion mais aussi après. Plus spécifiquement, un paquet d'onde rotationnel peut être créé par une impulsion femtoseconde, ce qui génère un alignement moléculaire en l'absence de champ après le passage de l'impulsion qui peut se reformer à intervalles réguliers. En plus de permettre la détermination des constantes de rotation et l'identication des molécules, cette technique donne également accès à des informations sur la dissipation dans le milieu en étudiant l'évolution du paquet d'onde sur une longue période (plusieurs retours périodiques de l'alignement moléculaire) après le passage de l'impulsion.
This thesis presents experimental results obtained during filamentation of ultrashort and intense laser pulses, with an intensity of ~ 10¹³ W/cm2 in air. A femtosecond Ti:Sapphire laser was used to generate pulses in the infrared at 800 nm. Because of some unique features of the filaments, this particular form of propagation has been considered for many applications. In this work, we focus our attention on remote sensing and the detection and identification of atmospheric pollutants. The goal is to improve the results and resolve some problems in the detection of air pollutants, especially those with the same filament-induced fluorescence spectrum. The presented experiments were performed inside a laboratory. The remote sensing of pollutants in the atmosphere mainly relies on the propagation of filaments at high altitude where the pressure is low. For this application, it is therefore important to have a good understanding of filamentation in these real conditions. We experimentally and numerically studied the effect of lowering the pressure on a single filament in air. The experiment was done by varying air pressure inside a cell between 0.3 and 1 standard atmospheric pressure (1 atm ~ 1:01 X 10⁵ Pa). One way to remotely detect atmospheric pollutants is to record the returning fluorescence signal from the molecular fragments that are created during filamentation. Because the propagation distance is large in these spectroscopic experiments, the signal is heavily attenuated before reaching the detector and it is important to look for a solution to enhance the fluorescence signal. We therefore investigated the possibility of using the filament itself as a gain medium along the propagation direction to amplify the emission of some impurities in air. It is known that the femtosecond laser filament can amplify backward-directed signal in pure air, so we started our experiments in air, and then extended them to air-hydrocarbons mixtures (2% de CH₄, C₂H₂ et C₂H₄ dans l'air). The fluorescence emission from neutral nitrogen at ~ 337 nm in pure air and from CH fragments at ~ 431 nm in air-hydrocarbons mixtures was detected. In both cases, the fluorescence signal emitted in the direction opposed to the laser propagation increased nonlinearly with the filament length, unlike the emission directed on the sides which showed a linear trend. The last chapter of the thesis introduces a new way to identify molecules that relies on their alignment. Indeed by measuring the rotational constants of different molecules using iv eld-free molecular alignment, we show that pollutants can be detected and identied in air. It is important to mention that this approach can distinguish pollutants for which the excited fragments have the same fluorescence spectra (same atomic lines and molecular bands). The results reported in this thesis were obtained by a pump-probe experiment where the scattered signal of the probe pulse was detected, as opposed to other experiments which collected the transmitted light. Observing the scattered signal instead of the transmitted one makes this technique appropriate for remote sensing applications. Even though molecules are randomly oriented in the gas phase, it is shown that ultrafast intense laser pulses can force molecules to align both in the presence of the laser feld as well as after the passage of the pulse. More specifically, a rotational wavepacket can be created by an ultrashort laser pulse, leading to a feld-free alignment of the molecules after the laser pulse has passed which can revive at regular intervals. Therefore, in addition to finding rotational constants and identifying molecules, it is possible to extract information about the dissipative medium by studying the changes in the wavepacket a long time (several periodic revivals of molecular alignment) after the passage of the pulse.
This thesis presents experimental results obtained during filamentation of ultrashort and intense laser pulses, with an intensity of ~ 10¹³ W/cm2 in air. A femtosecond Ti:Sapphire laser was used to generate pulses in the infrared at 800 nm. Because of some unique features of the filaments, this particular form of propagation has been considered for many applications. In this work, we focus our attention on remote sensing and the detection and identification of atmospheric pollutants. The goal is to improve the results and resolve some problems in the detection of air pollutants, especially those with the same filament-induced fluorescence spectrum. The presented experiments were performed inside a laboratory. The remote sensing of pollutants in the atmosphere mainly relies on the propagation of filaments at high altitude where the pressure is low. For this application, it is therefore important to have a good understanding of filamentation in these real conditions. We experimentally and numerically studied the effect of lowering the pressure on a single filament in air. The experiment was done by varying air pressure inside a cell between 0.3 and 1 standard atmospheric pressure (1 atm ~ 1:01 X 10⁵ Pa). One way to remotely detect atmospheric pollutants is to record the returning fluorescence signal from the molecular fragments that are created during filamentation. Because the propagation distance is large in these spectroscopic experiments, the signal is heavily attenuated before reaching the detector and it is important to look for a solution to enhance the fluorescence signal. We therefore investigated the possibility of using the filament itself as a gain medium along the propagation direction to amplify the emission of some impurities in air. It is known that the femtosecond laser filament can amplify backward-directed signal in pure air, so we started our experiments in air, and then extended them to air-hydrocarbons mixtures (2% de CH₄, C₂H₂ et C₂H₄ dans l'air). The fluorescence emission from neutral nitrogen at ~ 337 nm in pure air and from CH fragments at ~ 431 nm in air-hydrocarbons mixtures was detected. In both cases, the fluorescence signal emitted in the direction opposed to the laser propagation increased nonlinearly with the filament length, unlike the emission directed on the sides which showed a linear trend. The last chapter of the thesis introduces a new way to identify molecules that relies on their alignment. Indeed by measuring the rotational constants of different molecules using iv eld-free molecular alignment, we show that pollutants can be detected and identied in air. It is important to mention that this approach can distinguish pollutants for which the excited fragments have the same fluorescence spectra (same atomic lines and molecular bands). The results reported in this thesis were obtained by a pump-probe experiment where the scattered signal of the probe pulse was detected, as opposed to other experiments which collected the transmitted light. Observing the scattered signal instead of the transmitted one makes this technique appropriate for remote sensing applications. Even though molecules are randomly oriented in the gas phase, it is shown that ultrafast intense laser pulses can force molecules to align both in the presence of the laser feld as well as after the passage of the pulse. More specifically, a rotational wavepacket can be created by an ultrashort laser pulse, leading to a feld-free alignment of the molecules after the laser pulse has passed which can revive at regular intervals. Therefore, in addition to finding rotational constants and identifying molecules, it is possible to extract information about the dissipative medium by studying the changes in the wavepacket a long time (several periodic revivals of molecular alignment) after the passage of the pulse.
Filamentation laser
Filamentation laser

In mature forests, gains and losses of nitrogen may be dominated by the gaseous transformations, asymbiotic nitrogen fixation and biological denitrification. Both are reduction reactions and are affected by moisture conditions, temperature, pH, supply of organic carbon and the availability of mineral nitrogen. Gaseous nitrogen inputs, due to asymbiotic nitrogen fixation, and outputs, due to biological denitrification were quantified for a mature coniferous forest in southwestern British Columbia. Forest floor material, mineral soil, decaying wood, foliage and bark were incubated in an atmosphere of 0.1 atm acetylene to allow the simultaneous measurement of N₂0 production by denitrifying bacteria and acetylene reduction by free-living bacteria and blue-green algae. Forest floor material accounted for 80% of a total annual input of 0.8 kg N ha⁻1 a⁻1. Relatively small amounts of nitrogen were fixed in mineral soil, decaying wood and foliage and no indication of nitrogen fixation activity in bark was detected. Traces of denitrification were found, but gaseous output of nitrogen was effectively 0.0 kg N ha⁻1 a⁻1. It is hypothesized that this forest may prevent nitrogen Joss by outcompeting other sinks for mineral nitrogen, thereby allowing a slow accretion of nitrogen by asymbiotic nitrogen fixation and bulk precipitation input.
Forestry, Faculty of
Graduate

This thesis describes a series of experiments undertaken to collect Angle Resolved Mass Spectra (ARMS) in order to investigate the scattering of ions during collisional activation. In particular, data were obtained to see if the angle resolved mass spectra of the scattered ions could be explained by assuming that the scattering angle θ was directly related to the energy gained by the ions during collisional activation. Initially data were obtained on a slightly modified commercially available mass spectrometer using the z-deflection method. The inherently poor angular resolution of this method limited the scope of these experiments to an investigation of the effect of experimental variables on ARMS data. To overcome the problems of the z-deflection method a swinging source was designed and fitted to the mass spectrometer. The major advantages of this source were that θ was selected mechanically and that the pre- and post-collision angular resolutions of the experiments could be varied, but were independent of the masses of the ions. Using the source, data similar to those published by other groups were obtained. Interpreting these data, however, was difficult because fragment ion abundances contained contributions from decompositions occurring outside the collision chamber. A modification was made to the source which enabled these ions to be excluded from the data and the effect of this modification on the ARMS spectra obtained is discussed.

Mercury is an atmospheric global pollutant with complex cycling behavior. Two-thirds of the mercury present in our atmosphere is anthropogenic in origin. Chemical oxidation of gaseous elemental mercury governs the deposition rate of mercury over most lakes, land, and oceans. A major uncertainty comes from the effect of atmospheric surfaces such as aerosols. Much research is devoted to mercury capture technologies to be used in coal fire power plants, which are the major source of anthropogenic emissions.This thesis is a report on oxidation kinetics and mechanistic studies relevant to mercury-scavenging reactions. It provides an overview of the mechanisms of mercury oxidation by ozone, nitrogen dioxide, and titanium dioxide (exposed to ultra-violet light). The role of surfaces was quantified, as appropriate for each system. Crossover effects between gaseous co-pollutants (e.g. CO, SO2) and surfaces (SiO2, TiO2) are discussed. Rate constants were measured for each process and product studies were performed and compared with the available literature. The effects of different surfaces and gases on the oxidation of mercury by ozone were measured. This reaction was confirmed to be a surface-enhanced gas phase initiated reaction with a second-order rate constant for pure gas-phase (kgas = (5.40 +/- 0.56) x 10-19 cm3 molec-1 s-1) and an enhanced surface component (ksur = (2.91 +/- 0.12) x 10-15 cm7 molec-1 s-1), or knet = (6.1 +/- 1.1) x 10-19 cm3 molec-1 s-1. Water vapor had no effect on the rate but liquid water and gaseous carbon monoxide both rapidly accelerated the reaction. Mechanisms were placed in context with atmospheric oxidative scavenging processes. Future work may combine aerosols (soot, acid, silica) in ozone oxidation reactions and/or addition of SO2 gas. The feasibility of removing mercury from a coal flue gas via titanium dioxide and ultra violet light was investigated. Discussed are some of the possible surface chemistry models of oxidation. The uptake rates of mercury over photosensitized titanium dioxide films was described by the Langmuir-Hinshelwood rate equation, where KHg = (5.1 +/- 2.4) x 10-14 cm3 molec-1 and k = (7.4 +/- 2.5) x 1014 molec cm-2 min-1. Effects of sulfur dioxide and water were evaluated but neither was found to impede the reaction. By contrast low oxygen level strongly impeded oxidation rates. Deposits of HgO on titania surfaces were widely dispersed in concentrated clusters. Currently there is no explanation to this pattern. Future experiments may use light emitting diodes to capture Hg0(g) over TiO2The oxidation of mercury by nitrogen dioxide was found to be a pure gas phase reaction, second order with respect to NO2, where k = (3.5 +/- 0.5) x 10-35 cm6 molec-2 s-1. The mechanism was conjectured to be a two-step addition of NO2 to Hg0; at higher NO2 concentrations the reaction may be first order with respect to NO2 but further experiments would be required for validation. The rate constant was also found in agreement with a previous study. Rates were unaffected by changes in pressure, available surfaces, presence of SO2, and water. It was discovered that TiO2 surfaces saturated in HgO deposits, when exposed to NO2 were 'revived' in Hg uptake activity. It is suspected the reaction between HgO and NO2 re-disperses the deposits.
Le mercure est un polluant atmosphérique globale avec le comportement les cyclismes complexes. Deux tiers du mercure présent dans notre atmosphère est d'origine anthropique. L'oxydation chimique de mercure élémentaire gazeux régit la vitesse des dépôts de mercure sur la plupart des lacs, des terres et des océans. Une incertitude majeure provient de l'effet des surfaces atmosphériques tels que les aérosols. Beaucoup de recherches sont consacrées aux technologies de captage du mercure pour être utilisés dans les centrales au charbon de puissance de feu, qui sont la principale source d'émissions anthropiques.Cette thèse est un rapport sur la cinétique d'oxydation et d'études mécanistiques relatives au mercure-balayage réactions. Il donne un aperçu des mécanismes d'oxydation du mercure par l'ozone, le dioxyde d'azote et dioxyde de titane (exposé à la lumière ultraviolette). Le rôle des surfaces ont été quantifiés, comme il convient pour chaque système. Effets de coupure entre gazeux co-polluants (par exemple CO, SO2) et les surfaces (SiO2, TiO2) sont discutées. Les constantes de vitesse ont été mesurées pour chaque processus et études de produits ont été effectués et comparés avec la littérature disponible.Les effets de différentes surfaces et de gaz sur l'oxydation du mercure par l'ozone ont été mesurés. Cette réaction a été confirmé à une phase gazeuse augmenter a la surface réaction initiée avec un taux de second ordre constant de pures en phase gazeuse (kgaz = (5,40 +/- 0,56) x 10-19 cm3 moléc-1 s-1) et une surface améliorée composant (ksur = (2,91 +/- 0,12) x 10-15 cm7 moléc-1 s-1), ou knet = (6,1 +/- 1,1) x 10-19 cm3 molec-1 s-1. La vapeur d'eau n'a eu aucun effet sur la vitesse, mais l'eau liquide et de monoxyde de carbone gazeux, à la fois rapidement accéléré la réaction. Des mécanismes ont été mis en contexte avec l'atmosphère oxydant processus de balayage. Les travaux futurs peuvent combiner les aérosols (suie, de l'acide, de la silice) dans les réactions d'oxydation de l'ozone et / ou ajout de SO2.La faisabilité de l'élimination du mercure des gaz de combustion de charbon par du dioxyde de titane et de lumière ultra-violette a été étudiée. Discuté sont quelques-uns des modèles possibles chimie de surface de l'oxydation. La vitesse d'absorption de mercure au cours photosensibilisées films de dioxyde de titane a été décrit par l'équation du taux de Langmuir-Hinshelwood, où KHg = (5,1 +/- 2,4) x 10-14 cm3 moléc-1 et k = (7,4 +/- 2,5) x 1014 cm-2 moléc-1 min-1. Effets du dioxyde de soufre et de l'eau ont été évalués, mais ni a été trouvée pour empêcher la réaction. Par niveau d'oxygène à faible contraste fortement entravé les taux d'oxydation. Dépôts sur des surfaces de HgO oxyde de titane ont été largement dispersés dans les amas concentré. Actuellement, il n'existe pas d'explication à ce modèle. Les expériences futures peuvent utiliser des diodes électroluminescentes à saisir Hg0 (g) sur TiO2. L'oxydation du mercure par le dioxyde d'azote a été trouvé à une réaction gaz pur phase du second ordre par rapport au NO2, où k = (3,5 +/- 0,5) x 10-35 cm6 molec-2 s-1. Le mécanisme a été conjecturé être un ajout en deux étapes de NO2 à Hg0(g); à des concentrations élevées de NO2 la réaction peut être de premier ordre à l'égard de NO2, mais d'autres expériences seraient nécessaires pour la validation. La constante de vitesse a également été trouvé en accord avec une étude précédente. Les vitesses ont été affectées par les changements de pression, les surfaces disponibles, la présence de SO2, et l'eau. On a découvert que le TiO2 surfaces saturées dans les dépôts HgO(s), lorsqu'ils sont exposés à de NO2 ont été 'relancé' dans l'activité d'absorption de mercure. Il est soupçonné de la réaction entre HgO(s) et NO2 disperse les dépôts.

The propagation of a gaseous detonation wave into a porous medium has been studied experimentally and theoretically. The porous medium is composed of inert spheres of equal diameter contained within a detonation tube. The propagation mechanisms were elucidated by means of high-speed Schlieren and open shutter photography of the wave-particle interactions in 2-D obstacle arrays, to simulate the phenomenon in actual porous media. It is found that a Chapman-Jouguet (CJ) detonation can transmit into a porous medium filled with detonable gas and continue to propagate as a quasi-steady combustion wave. There exists a continuous spectrum of averaged combustion wave velocities ($ rm0.3 le V/V sb{CJ} le 1)$ spanning the lean and rich propagation limits and exhibiting a maximum value at the most sensitive composition. A decrease in the particle size of the medium has the effect of narrowing the detonability range and reducing the velocity for a given mixture. It is clearly demonstrated that the propagation phenomenon, and thus the velocity, is governed by the relative length scales of the detonable mixture (critical tube diameter $ rm d sb{c})$ and of the porous medium (average pore size $ rm d sb{p}).$ An empirical correlation was established between the wave velocity (V/V$ sb{CJ})$ and the properties of the system, via the ratio $ rm d sb{c}/d sb{p}.$ The global wave propagation mechanism, for the major part of the possible range of velocities, i.e., $ rm V/V sb{CJ} ge 0.5,$ consists of periodic phases of detonation failure by diffraction around obstacles (i.e., the particles), followed by local reinitiation at detonative Mach stems formed by shock wave-particle interactions. This is essentially identical to the propagation of "quasidetonations" studied by Teodorczyk et al. (1988, 1991), in linear arrangements of obstacles. When local reinitiation of detonation is not possible, ignition transfer in the pores is controlled by the turbulent jetting of hot combustion produc

Gas electron diffraction (GED) is a technique that has been developed to study the molecular structure of species in the gas phase. This thesis focuses on the reconstruction of the Canterbury GED apparatus (moved from Edinburgh, UK) and the requirements for modifying the apparatus to incorporate a mass spectrometer (MS) so diffraction and MS data can be obtained within a single experiment. The combined GED-MS system has been identified in previous work in the Masters group as a necessary development for studying the structure of short-lived species generated in situ. This is particularly true for the study of ketene, which as shown in this thesis, can be generated from several precursors as part of a multiple product pyrolysis system. While GED data for ketene generated from acetic anhydride has been refined, the species formed from the pyrolysis of Meldrum’s acid were determined to be too difficult to deconvolute without additional experimental data from MS. A computational study of possible ketene derivatives that could be studied with a GED-MS apparatus is also presented. Lastly, this thesis details a structural study of the gas-phase structures of tris(chloromethyl)amine and a family of substituted disilane systems which have been determined in the gas phase for the first time. A comprehensive GED, Raman spectroscopy and ab initio study have been undertaken for tris(chloromethyl)amine [N(CH2Cl)3] which is shown to have a different structure in the solid and gas phase. Further work in the form of a molecular dynamics investigation has been identified as necessary to describe the low amplitude motion of one of the CH2Cl groups in the gas phase to allow for the GED refinement to be completed. The work on the substituted disilane systems X3SiSiXMe2 (X = F, Cl, Br, I) and X3SiSiMe3 (X = H, F, Cl, Br) demonstrates the effect of increased halogen substitution on the electronic effects of the disilanes, and the effect that the methyl groups have as larger halogens increase the steric bulk of the system.

This thesis presents the results of a series of experiential investigations into the formation, dissociation and reactivity of gaseous ions. Firstly, using a time-of-flight mass spectrometer coupled with a 2D ion coincidence technique, studies of the electron ionization of a number of small gas-phase molecules are presented. Relative partial ionization cross-sections (PICS) are derived for the formation of positively charged fragment ions, following electron ionization of H2S, CH3OH and CF3I. The 2D ion coincidence technique enables fragment ions formed by dissociative single, double, triple and quadruple ionization to be distinguished and quantified. This information also allows precursor specific relative PICS to be determined. While the relative PICS quantify the overall yield of each fragment ion, the precursor specific relative PICS quantify the contribution from single, double, triple and quadruple ionization to the relative yields of each fragment ion. Such information is essential for the accurate modelling, and the understanding, of the chemical processes occurring in energetic environments, such as industrial plasmas and planetary atmospheres. Comparison of the relative PICS data to existing measurements of the PICS for these molecules generally shows good agreement for experiments in which the efficient collection of translationally energetic ions is demonstrated. In addition, information on the energetics and dissociation dynamics involved in the fragmentation of H2S2+, CH3OH2+, CF3I2+ and CF3I3+ are provided by interpretation of ion pair peaks recorded in the 2D ion coincidence spectra. Secondly, this thesis also presents the results of an investigation into the photoionization of CF3I, using the threshold photoelectron-photoion-photoion coincidence (iPEPICO) endstation on the vacuum-ultraviolet beamline at the Swiss Light Source. These experiments were part of a scoping study to see if this existing apparatus could be used to study multiple ionization. The photoionization spectra are interpreted and discussed, and issues with the current experimental arrangement, which may be improved for future visits, are addressed. Finally, studies of I2+ collisions with OCS, carried out using a crossed ion beam experiment with a time-of-flight mass spectrometer, are presented. Two bond-forming reactions producing IO+ and IS+ are observed, together with the more ubiquitous electron transfer reactions. These electron transfer reactions are rationalised using the Reaction Window model.

The separation of submicron particles suspended in gaseous flows is a problem of great importance and is the subject of sustained research efforts. This is motivated by several challenges presented by modern science and technology requiring high separation efficiencies for submicron particles.Continuous acoustic particles separation is a novel technique based on the acoustophoresis phenomenon, in which a particle within an acoustic field is manipulated using acoustic forces on its surface. This technique has the potential to overcome some of the limitations of common techniques for the separation of submicron particles, as well as performing advanced tasks such as sorting particles according to their size or density.In this thesis, the separation of submicron solid particles suspended in air is investigated experimentally, with a focus on the effect of key design parameters (acoustic, flow, geometry) on the efficiency of the process. A simple method based on laser light scattering was also used to provide qualitative information on the particle number density as a function of position in the channel. This technique allowed to quickly investigate the effect of a wide range of parameters on the acoustic separation efficiency including the pressure amplitude, the frequency of the standing wave, the average flow velocity and the parallelism of the channel walls.   The results demonstrate conclusively that acoustic manipulation is possible for submicron particles and that the acoustic force scales following the trends expected from theoretical models developed in the continuum regime. From the size of the particles used it however follows that the observed separation is the result of transition regime acoustophoresis, with a Knudsen number on the order of 0.2.

QC 20150522

Detonations in gases usually propagate with lateral strain rates, in either weakly confined or varying-cross-section or curved or even small-sized geometries. Lateral strain rates have been generally known to significantly impact the detonation dynamics, i.e., decreasing the propagation speeds lower than the theoretical Chapman-Jouguet (CJ) velocities, increasing the propagation limit pressures as well as cell sizes. Since the detonation-based engines require the reliable control of the accurate ignition and stable propagation of a detonation wave, it is desirable to have the predictive capability of the response of detonation dynamics to lateral strain rates, for achieving the practical purposes of detonation applications. Therefore, the present thesis aims to provide such predictability, by quantifying the effect of lateral strain rates on detonation dynamics from both the experimental and numerical modelling perspectives. Experimentally, this study extended the exponential horn technique of Radulescu and Borzou (2018) to a range of characteristic mixtures with varied detonation instability levels, i.e., from the weakly unstable system of 2H₂/O₂/7Ar to the highly unstable one of CH₄/2O₂. Steady detonation waves were obtained at the macro-scale, with the very regular H₂/O₂/Ar detonation cellular structures characterized by reactive transverse waves while the unstable hydrocarbon-oxygen detonation reaction zone structures in the presence of significant unreacted gas pockets. The meaningful D-K curves characterizing the relationships between the detonation mean propagation speeds and lateral strain rates were directly obtained from experiments. Comprehensive comparisons were then made between experiments and predictions from the generalized ZND model with lateral strain rates. Excellent agreement was found for the stable H₂/O₂/Ar detonations due to the much longer thermally insensitive reaction zone lengths compared to the characteristic induction zone lengths, while substantial departures exist for the highly unstable CH₄/2O₂ detonations. The degree of departure was found to correlate well with the detonation instability. As compared to the laminar ZND wave, the more unstable hydrocarbon-oxygen detonations manifested themselves in the significantly enhanced global rates of energy release with the notably suppressed thermal character of ignition. Implications of such a globally enhanced burning mechanism highlight the important role of diffusive processes involved in turbulent burning of the unreacted gas pockets. Finally, empirical global reaction rate laws were developed for effectively capturing the dynamics of unstable detonations. Numerically, this work proposed a novel model for evaluating the effect of boundary layer losses on cellular structures of 2D detonations in narrow channels. The boundary-layer-induced lateral strain rate was evaluated using the negative boundary layer displacement of Mirels' theory. With the theoretical Mirels' constant KM reduced by a factor of 2, the experimentally obtained 2H₂/O₂/7Ar detonations can be very well reproduced by simulations using the resulting quasi-2D formulation. It was further found out that detonation cellular cycle dynamics can be modified by the presence of boundary layer losses, yielding larger velocity fluctuations and more rapid decay rates of the lead shock. The exponential sensitivity of detonation cell sizes to velocity deficits, controlled by the global activation energy, highlights the importance of providing the detonation speed when reporting experimentally measured cell sizes.

Mestrado em Engenharia Física
A new position sensitive gas photomultiplier for the Vacuum Ultraviolet (VUV) region is presented in this work. The detector is composed by two THGEMs, followed by a 2D-THCOBRA being operated in Ne/CH4(5%), at 1 bar pressure in single photon mode. The 2D-THCOBRA is an hybrid microstructure which combines the robustness and the resistance to discharges of a THGEM with the two independent charge multiplication stages and the position discrimination of the 2D-MHSP. In this work the 2D-THCOBRA influence in the charge gain and IBF values was studied. The position resolution of the entire system was also studied. The achieved results shown a charge gain of 106 and, for this gain values, an IBF value of about 20%. Position resolutions below 300 μm were also obtained.
O presente trabalho baseia-se no desenvolvimento e estudo de um fotomultiplicador gasoso na região do Utra-Violeta de Vazio (UVV) e com capacidade de discriminação de posição. O detector é constituído por duas THGEM seguidas de uma 2D-THCOBRA, a operar em Ne/CH4(5%) à pressão de 1 bar e em modo de fotão único. A 2D-THCOBRA é uma estrutura híbrida, que resulta da combinação entre uma THGEM e uma 2D-MHSP, beneficiando da robustez e resistência às descargas da primeira e dos dois estágios de multiplicação e da capacidade de discriminação da posição da 2D-MHSP. Neste trabalho foi estudada a influência dos potenciais aplicados aos eléctrodos da 2D-THCOBRA no ganho e no refluxo de iões (IBF) do detector. Foi ainda avaliada a resolução em posição deste detector. Foram medidos ganhos da ordem de 106 e, para estes valores de ganho, IBF na ordem dos 20%. Obteve-se ainda resoluções em posição inferiores a 300 μm.

In order to combat the climate change caused by increasing emissions of CO2 from industrial processes, Carbon Capture and Storage (CCS) technologies have been accepted worldwide to address these pressing global warming concerns. So as to efficiently manage material and financial losses across the entire stream, accurate accounting and monitoring through fiscal metering of CO2 in CCS transportation pipelines are core and required features for the deployment of CCS technologies. Moreover, these technical requirements are part of the legal compliance schemes and guidelines from various regulatory bodies. This thesis reports experimental studies of two different metering technologies, an Averaging Pitot Tube (APT) and a Coriolis mass flowmeter (CMF), for CO2 flow measurement, together with the design and implementation of a CO2 flow calibration facility. A prototype system for the leak detection of the gas phase of CO2 is also developed. A review of the methodologies and technologies for the flow measurement and leak detection of CO2 gas is firstly given, followed by the discussion of the main challenges and technical requirements in their applications. Based on this review, two flow metering technologies, APT and CMF, are selected for experimental studies and a calibration platform using both volumetric and direct mass measurement methods for the gas phase of CO2 is also developed. The APT and CMF were calibrated and evaluated in the test facility. Experimental results obtained in this test facility demonstrate that the instruments are capable of accurately metering gaseous CO2 within a measurement uncertainty of ±1.5%. Flow characterization of the fluid under wet and mixed components conditions were further assessed with both meters. Under wet CO2 flow, results obtained show that both flow instruments are subject to significant measurement errors. The APT gave an error of up to ±25%, for a liquid fraction of 20%, while the error of the CMF was up ±6%, for a liquid fraction of 10%. Further investigations show that these errors can, however, be corrected through simple and straightforward algorithms that can be easily incorporated into computing processes in the flowmeters. In binary gaseous mixture tests, the CMF proved to be very reliable in the gas combination processes and likewise in the metering of the CO2 mixture (≤ ±1%), while a higher degree of uncertainty was registered for the APT (≤ ±4%). Overall analyses from investigations confirmed the APT and CMF instruments as promising technologies for CO2 flow measurement and can be further improved for application in actual CCS conditions. In addition, this thesis describes experimental investigations of the leak detection of CO2 gas from a pipeline, with emphasis on full controllability and flexibility of the operational process. An imaging system using passive temperature change detection techniques is designed, implemented and evaluated. The effectiveness of the developed technique is examined on a laboratory-scale flow rig system. Results obtained from tests confirmed the operability of the system configuration and validation of the thermal imaging approach. Suggestions for future development and enhancement of the proposed techniques are finally given.