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The disintegration of a liquid jet emerging from a nozzle has been under investigation for several decades. A direct consequence of the liquid jet disintegration process is droplet formation. The breakup of a liquid jet into discrete droplets can be brought about by the use of a diverse forcing mechanism. Cavitation has been thought to assist the atomization process. Previous experimental studies, however, have dealt with cavitation as a secondary phenomenon assisting the primary atomization mechanism. In this dissertation, the role of the energy created by the collapse of cavitation bubbles, together with the liquid pressure perturbation is explicitly configured as a principal mechanism for the disintegration of the liquid jet. A prototype of an atomizer that uses this concept as a primary atomization mechanism was developed and experimentally tested using water as working fluid. The atomizer fabrication process and the experimental characterization results are presented. The parameters tested include liquid injection pressure, ultrasonic horn tip frequency, and the liquid flow rate. The experimental results obtained demonstrate improvement in the atomization of water. To fully characterize the new atomizer, a novel infrared thermography-based technique for the characterization and visualization of liquid sprays was developed. The technique was tested on the new atomizer and two automotive paint applicators. The technique uses an infrared thermography-based measurement in which a uniformly heated background acts as a thermal radiation source, and an infrared camera as the receiver. The infrared energy emitted by the source in traveling through the spray is attenuated by the presence of the droplets. The infrared intensity is captured by the receiver showing the attenuation in the image as a result of the presence of the spray. The captured thermal image is used to study detailed macroscopic features of the spray flow field and the evolution of the droplets as they are transferred from the applicator to the target surface. In addition, the thermal image is post-processed using theoretical and empirical equations to extract information from which the liquid volume fraction and number density within the spray are estimated.

Afin de mieux prévoir le type d’éruption (effusif ou explosif) des volcans d’arc, il est primordial d’étudier les vitesses d’ascension du magma dans le conduit volcanique. Un moyen d’appréhender ces modalités d’ascension est de déterminer les cinétiques des processus intervenant lors de la remontée magmatique. Ainsi, nous avons choisi d’étudier les cinétiques de cristallisation (vitesses de nucléation et de croissance) des microlites de plagioclase par une approche expérimentale, puis théorique, à partir de compositions synthétiques reproduisant le verre rhyolitique interstitiel du magma de la Montagne Pelée et son analogue simplifié (haplotonalite). Nos résultats révèlent que le magma décomprimé à partir de 200 MPa selon différentes vitesses de décompression (ΔP/Δt = 1200, 150 et 30 MPa/hr) jusqu'à une pression finale donnée entre 160 et 25 MPa, montre différentes modalités de cristallisation des plagioclases. En particulier, plus la vitesse de décompression est lente, plus la densité numérique de cristaux est élevée. Les vitesses de nucléation des plagioclases varient de 3.8E-03 à 1.5E-02 mm-2, tandis que celles de croissance variant peu, sont de l’ordre de 10-6 mm.s-1. La modélisation de la cristallisation nous a permis de i) mieux contraindre l’énergie d’interface plagioclase/haplotonalite, en déterminant des paramètres de forme et de rugosité du nucleus à appliquer à la théorie classique de la nucléation ii) démontrer que la vitesse de croissance des plagioclases est limitée soit par la diffusion, soit par les mécanismes à l’interface iii) et qu’une croissance des plagioclases par diffusion n’est pas systématiquement contrôlée par l’élément diffusant le plus lentement, et qu’elle dépend étroitement de la nucléation. Aussi, nous avons révélé l’importance de la composition du liquide silicaté sur les cinétiques de cristallisation, en particulier l’effet inhibiteur sur la nucléation de l’ajout de quelques ppm d’arsenic dans le liquide silicaté. / Magma ascension rate in volcanic conduit plays an important role in determining eruption dynamics of arc volcanoes (effusive or explosive). Investigating the kinetics of processes such as decompression induced crystallization may provide crucial information on the modality of magma ascent. We performed decompressioninduced isobaric crystallization-timed experiments starting with Mt Pelée rhyolitic glass composition and its simplified analogue (haplotonalite) to study plagioclase crystallization (nucleation and growth) kinetics. Our results reveal that a melt depressurized from 200 MPa to a given final pressure from 160 to 25 MPa according to different decompression rates (ΔP/Δt = 1200, 150 and 30 MPa/hr), shows various modalities of crystallization of plagioclases. In particular, the slower the decompression, the higher the numerical density. The crystallization modeling i) provides new constraints on the plagioclase/haplotonalite interfacial energy that controls the nucleation kinetics, by determining shape and roughness parameters ii) reveal that plagioclase crystallization is either controlled by diffusion or crystal/melt interfacial mechanisms, iii) demonstrates that plagioclase diffusion-controlled growth rate is not systematically controlled by the slowest diffusion element, and it closely depends on nucleation. Also, we revealed the importance of melt composition on crystallization kinetics, in particular the inhibitive effect on nucleation of trace arsenic addition in the melt.

Ce travail s'intéresse aux effets mécaniques créés par les décharges de surface et à leur efficacité comme actionneur. Une géométrie particulière d'électrodes permet de créer de manière pulsée un filament linéaire de plasma et de le chauffer très rapidement par effet Joule (à raison de plusieurs Joules en moins d'une microseconde). Ce chauffage rapide entraîne la formation d'ondes de choc qui peuvent interagir avec l'écoulement ambiant.Nous étudions le comportement électrique de la décharge de surface afin d'évaluer l'énergie déposée dans le filament de plasma par effet Joule. Pour ce faire, nous réalisons une étude paramétrique sur la configuration du circuit et nous déterminons les principaux paramètres qui pilotent la dynamique de la décharge. Différents modèles de résistance sont utilisés dans un code de simulation du circuit électrique, et leurs prédictions du courant et du dépôt d'énergie sont confrontées aux mesures expérimentales.Des mesures spectroscopiques dans différentes configurations de circuit donnent accès à certaines propriétés de la décharge comme la densité électronique, qui atteint des valeurs de 2x1018 cm-3. Le rayon du canal est également mesuré par imagerie rapide. Les ondes de chocs créées par la décharge de surface sont visualisées en imagerie Schlieren pour plusieurs configurations de circuit. Ces ondes de chocs créent une impulsion proportionnelle à l'énergie déposée dans la décharge. Nos développons un modèle de choc pour décrire la trajectoire du choc et pour calculer l'impulsion communiquée par la décharge de surface. Le modèle est en bon accord avec les mesures expérimentales et la décharge de surface a une efficacité mécanique de 0.12mNs/J pour notre configuration d'étude. Nous terminons cette étude en comparant cet actionneur potentiel avec d'autres actionneurs courants et proposons plusieurs pistes pour de futurs travaux. / In this study, we investigate the mechanical effects generated by pulsed surface discharges and their efficiency as an actuator. Using a specific electrode configuration, it is possible to create a short-lived, pulsed, rectilinear plasma channel and to heat it up rapidly (several Joules in less than a microsecond) through Joule heating. This fast energy deposition causes the formation of shock waves that can then interact with the surrounding flow.We study the electrical behavior of the pulsed surface discharge to assess the energy deposited in the plasma channel through Joule heating. To do so, we perform a parametric study on the circuit configuration and identify the main parameters driving the discharge dynamics. Several resistance models are implemented in a numerical description of the electrical circuit and their predictions of the current and deposited energy are compared with experimental measurements.Spectroscopic measurements in different circuit configurations give access to some of the plasma properties such as the electron number density that can reach values up to 2x1018 cm-3. Fast imaging also gives insight into the plasma channel radius. The shock waves generated by the pulsed surface discharge in different circuit configurations are visualized through Schlieren imaging. These shock waves generate an impulse that increases linearly with the energy deposited in the discharge. We develop a shock model to describe the shock trajectory and to compute the impulse imparted by the pulsed surface discharge. The model is in good agreement with our measurements and the pulsed surface discharge is found to have a mechanical efficiency of 0.12 mNs/J for our setup configuration. We conclude this study by comparing the proposed pulsed surface discharge actuator with other common designs and offer some directions for future studies.

Far-ultraviolet (FUV) spectral images of Jupiter's moon Europa were obtained by the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) on 20 occasions between the years 1999 and 2015. In this thesis these data are analyzed to look for Lyman-alpha emissions from a hydrogen corona. This hydrogen corona was recently discovered in absorption, also from HST Lyman-alpha images but with Europa in transit of Jupiter, and the aim of this study is to confirm the existence of the corona also in emission. Europa's thin atmosphere is dominated by molecular oxygen, mainly produced by radiolysis and sputtering of the icy surface. Atomic hydrogen, the main target for this study, is produced by sputtering from the surface and the dissociation of H2 and H2O. It quickly escapes the gravity of Europa. To study the hydrogen corona in the spectral STIS images the data need to be processed to remove the other Lyman-alpha contributions to the image. These other contributions include emissions from the geocorona, emissions from the interplanetary medium (IPM), dark current in the detector and sunlight reflected from the surface of Europa. To estimate the contribution to the image from the hydrogen corona, a basic model of the expected emissions from the corona is developed. By fitting this model to the processed STIS data values of the hydrogen density and the surface Lyman-alpha albedo of the moon are obtained. The results confirm the presence of a hydrogen corona, with varying densities between the different observations but generally about twice as large as the results from the previous study. The uncertainty for the results is however large and there is a clear correlation between hydrogen density and background level in the image, for which the reason is poorly understood. No hemispheric variability or connections to the true anomaly of the moon are found, but the hydrogen density seems to be increasing during the time of the observations. The results for the albedo is consistent with previous results, indicating a lower albedo on the leading than on the trailing hemisphere.

>Magister Scientiae - MSc / Measuring the evolution of the abundance of galaxy clusters puts constraints on cosmological parameters like the cosmological density parameter m, σ8 and the dark energy equation of state parameter, w. Current observations that promise to give large cluster counts and their properties are those that rely on the Sunyaev-Zeldovich effect (SZE) from clusters. We study the contamination of the SZ signals from galaxy clusters by cluster infrared (IR) galaxies and particularly faint IR galaxies. We use the Millennium simulation database to extract galaxy clusters and deduce contaminant IR fluxes using the star formation rate - IR luminosity relations. We use the IR spectral energy distribution(SED) to obtain the monochromatic fluxes at 145 GHz, 217 GHz and 265 GHz, which are the observation frequencies of the Atacama Cosmology Telescope (ACT). Taking ACT as a case study, we selected all clusters with Mvir ≥ 2 × 1014 M⊙, and consider all galaxies in a cluster with star formation rate sfr ≥ 0.2 M⊙yr−1 as IR galaxies. From the fluxes of these selected sources, we compute their contribution to the SZE temperature fluctuations.We find that the galaxies in clusters have a non-neglible contribution to the SZ signals.In massive and rich clusters the contribution can be as high as 100 μK at z = 0.36,which is substantial when compared to the thermal SZE of & 270μK for such clusters.This effect can be reduced significantly if proper modelling of IR sources is done to pick out the point sources within clusters. We also find that irrespective of the mass range,the average contaminant temperature fluctuation T can be modelled as a power-law: T = Czm, where z is the redshift, m = 1.8 ± 0.07 and C takes on a range of values(0.008 to 0.9) depending on the cluster mass and the observation frequency respectively.We also study some properties of simulated galaxy clusters like substructures in clusters,2D projected distributions and number density profiles, which are all discussed in the results.

<p>A specific class of small-scale plasmas (column diameters in a sub-mm to mm range) at rarefied pressures (under 10 Torr) enclosed in glass tubes hold significant interest currently in the scope  of  tunable  plasma  devices.  Specifically,  applications  of  these  plasmas  include  plasma antennas and plasma photonic crystals. Reliable diagnostics are necessary for the development and implementation of these technologies as conventional tools are inadequate in such small-scale plasmas.</p> <p>Coherent microwave scattering in the Thomson regime (TMS) was recently demonstrated for diagnostics of electron number density in miniature free-standing laser-induced plasmas in air under  10  Torr  with  plasma  column  diameters  <  0.5  mm.  However,  measurements  by  TMS diagnostics have never been applied for small-scale plasma objects enclosed within glass tubes. Additionally, TMS measurements were never independently confirmed with a previously verified experimental technique. This work aims to validate results of TMS measurements for small-scale plasma  objects  enclosed  within  glass  tubes  using  the  previously  established  and  well-known hairpin resonator probe. A DC discharge plasma column of fairly large diameter (about 1.5 cm) is used in the experiments to ensure reliable non-intrusive measurements by the hairpin resonator probe.</p> <p>The experiments were conducted in a DC discharge tube with a diameter of 1.5 cm and a length of 7 cm. TMS diagnostics yielded electron number densities of about 5.9×10¹⁰cm^-3, 2.8 ×10¹⁰cm^-3and  1.8 ×10¹⁰cm^-3at  pressures  of  0.2,  0.5  and  2.5  Torr,  respectively.  The corresponding  densities  measured  with  the  hairpin  resonator  probe  were  4.8×10¹⁰cm^-3,  3.8 ×10¹⁰cm^-3 and 2.6 ×10¹⁰cm^-3. Discrepancies between the two techniques were within 30% and can be attributed mainly to inaccuracies in the sheath thickness estimation required the hairpin resonator probe results.</p>

We give a brief introduction to atomic physics and the motivation behind our experiments in the first chapter. The electron’s electric dipole moment is an interesting quantity which is yet to be measured. In the 3rd Chapter, we use the technique of chopped non-linear magneto-optic rotation (NMOR) in a room temperature Cs vapor cell to measure the permanent electric dipole moment (EDM) in the atom. The cell has paraffin coating on the walls to increase the relaxation time. The signature of the EDM is a shift in the Larmor precession frequency correlated with the application of an E field. We analyze errors in the technique, and show that the main source of systematic error is the appearance of a longitudinal magnetic field when an electric field is applied. This error can be eliminated by doing measurements on the two ground hyperfine levels. Using an E field of 2.6 kV/cm, we place an upper limit on the electron EDM of 2.9 × 10−22 e-cm with 95% confidence. This limit can be increased by 7 orders-of-magnitude—and brought below the current best experimental value. We give future directions for how this may be achieved. In chapter 4, we examine the Hanle effect for linear and circularly polarized light for different ground states and we find opposite behavior in the transmission signal. In one case, it shifts from enhanced transmission to enhanced absorption and vice-versa in the other case. In Chapter 5, we study the transmission spectrum at different temperatures and device a way to find the number density. We then verify the Clausius-Clapeyron equation and also find the latent heat of vaporization of Cs. Finally, we wrap up with conclusions and future directions.

No description available.

An inconsistency exists in bubble force models used in the standard Euler-Euler simulations. The bubble force models are typically developed by assuming that the forces act on the bubbles' centers of mass. However, in the standard Euler-Euler model, each bubble force is a function of the local gas volume fraction because the phase-averaging method is used. This inconsistency can lead to gas over-concentration in the center or near the wall of a channel when the bubble diameter is larger than the computational cell size. Besides, a mesh-independent solution may not exist in such cases. In addition, the bubble deformation is not fully considered in the standard Euler-Euler model. In this thesis, a particle-center-averaging method is used to represent the bubble forces as forces that act on the bubbles' centers of mass. A particle-center-averaged Euler-Euler approach for bubbly flow simulations is developed by combining the particle-center-averaged Euler-Euler framework with a Gaussian convolution method. The convolution method is used to convert the phase-averaged and the particle-center-averaged quantities. The remediation of the inconsistency in the standard Euler-Euler model by the particle-center-averaging method is demonstrated using a simplified two-dimensional test case. Bubbly flows in different vertical pipes are used to validate the particle-center-averaged Euler-Euler approach. The bubbly flow simulation results for the particle-center-averaged Euler-Euler model and the standard Euler-Euler model are compared with experimental data. For monodisperse simulations, the particle-center-averaging method alleviates the over-predictions of the gas volume fraction peaks for wall-peaking cases and for finely dispersed flow case. Whereas, no improvement is found in the simulated gas volume fraction for center-peaking cases because the over-prediction caused by the inconsistency has been smoothed by the turbulent dispersion. Moreover, the axial gas and liquid velocities simulated with both Euler-Euler models are similar, which proves that the closure models for bubble forces and turbulence are correctly applied in the particle-center-averaged Euler-Euler model. For fixed polydisperse simulations, the particle-center-averaging method can also alleviate the over-prediction of the gas volume fraction peak in the center or near the wall of a pipe. The axial gas velocities simulated with both Euler-Euler models are about the same. Comparisons are also made for the simulation results of bubbly flows in a cylindrical bubble column and the experimental data. The gas volume fractions and the axial gas velocities simulated with both Euler-Euler models almost coincide with each other, which indicates that the sink and source terms for the continuity equations and the degassing boundary are set correctly in the particle-center-averaged Euler-Euler model. An oblate ellipsoidal bubble shape is considered in the particle-center-averaged Euler-Euler simulations by an anisotropic diffusion. The influence of bubble shape on the simulation results of bubbly pipe flows is investigated. The results show that considering the oblate ellipsoidal bubble shape in simulations can further alleviate the over-predictions of the gas volume fraction peaks for wall peaking cases, but it has little influence on the gas volume fractions of center-peaking cases and the axial gas velocities.