Ces dernières années, les agrégats d'hélium superfluides ont fait l'objet de nombreuses études aussi bien expérimentales que théoriques. Le fruit de ces études a permis le développement de méthodes spectroscopiques innovantes (HENDI) utilisant les nanogouttes d'hélium comme l'ultime matrice, exploitant ainsi la très faible température de ce milieu particulier et sa faible interaction avec les dopants pour une meilleure résolution spectrale. Cependant, un nombre important de questions subsiste quant aux agrégats d'hélium dopés, particulièrement, ceux dopés par les alcalino-terreux. En effet, la position d'une impureté au sein de la gouttelette d'hélium est loin d'être un problème trivial pour certaines espèces telles les alcalino-terreux. Ceci est particulièrement vrai dans le cas où l'impureté est l'atome de magnésium. Des preuves expérimentales d'un état solvaté du magnésium sont annoncées dans la littérature tandis que de récentes expériences laissent penser à une position plutôt surfacique du magnésium dans les agrégats d'hélium. Du point de vue théorique, la même ambiguïté persiste quant à la position de Mg dans la nanogoutte d'hélium. Dans le but de contribuer à une meilleure compréhension des clusters d'hélium dopés par les métaux alcalino-terreux (Mg et Ca), nous avons, au cours de ce travail, dû déterminer avec précision les énergies d'interactions des états fondamentaux des systèmes van der Waals CaHe et MgHe. Pour ce faire, des méthodes ab initio telles les approches des clusters couplés (CC) mais aussi perturbationnelles (MP2 et MP4) ont été appliquées à ces deux systèmes avec succès. Les meilleurs potentiels d'interaction ont été utilisés par la suite comme potentiels d'interactions de paire dans l'approche Monte Carlo à diffusion (DMC) en combinaison de deux types de potentiel d'interaction pour l'hélium. Aussi bien pour CaHen que pour MgHen, des simulations DMC ont été produites depuis n = 1 jusqu'à n = 220, le résultat principal en est une position surfacique de l'impureté quelque soit l'alcalino-terreux considéré. Dans le cas particulièrement délicat des clusters d'hélium dopés par le magnésium, des calculs de DMC avec des contraintes géométriques montrent que le potentiel radial effectif de Mg dans He20 et He50 est plutôt plat. Enfin, sont présentés également les résultats concernant la recombinaison dynamique de deux atomes de magnésium à l'intérieur d'un agrégat d'environ 2000 atomes d'hélium utilisant une méthode basée sur un potentiel effectif pour l'interaction He-He

Cette thèse est consacrée aux propriétés des exciton-polaritons, les particules mixtes formées à partir de la lumière et la matière dans les microcavités de semi-conducteurs dans le régime de couplage fort. D'abord, j'analyse la possibilité de condensation de Bose des exciton- polaritons à température ambiante dans les microcavités de GaN avec les équations de Boltzmann semi-classiques. Puis les effets de polarisation dans le régime d'oscillateur paramétrique sont étudiés avec les équations de Boltzmann semi-classiques avec pseudospin. La deuxième partie de la thèse est consacrée aux propriétés des condensats et modes macrooccupés des exciton-polaritons. Leur polarisation, dispersion des excitations, propagation, localisation et superfluidité sont décrits avec l'équation de Gross-Pitaevskii

The dynamical mass determination of galaxies and systems of galaxies shows a large excess of mass above what one observes directly. This excess of mass indicates the presence of dark matter. The nature of this dark matter is still unknown and dark matter in the outer regions of large stellar structures such as clusters of galaxies might provide enough matter to close the universe. In this dissertation we investigate in detail the mass distribution of the Coma cluster. We show that optical data alone are unable to distinguish between a wide range of possible mass distribution for the Coma cluster. Low-mass models must have larger central density than high-mass models and require that the galaxies move on near-circular orbits, whereas high-mass models require the galaxy orbits to be predominantly radial. The optical data constrain the amount of dark matter very poorly. The X-ray data can also be used for a mass determination of the Coma cluster. These data may require the mass of the cluster to be more concentrated to the core than a light-traces-mass model if the central temperature of the gas is high. However, they do not put any constraint on the mass distribution beyond a Mpc or two. The above analysis, and most other approaches, assume the existence of dark matter. An alternative approach has been proposed by Milgrom (1983a,b,c): in his theory, the Newtonian law of motion breaks down in a weak field, and must be modified. The present analysis shows that this model is also consistent with optical and X-ray data on the Coma cluster, although a good fit required values for Milgrom's "universal" parameter aₒ to be 2h¹·⁵ (Hₒ = 50 h km/s/Mpc) higher than those inferred from the rotation curves of spiral galaxies. Finally, we investigate whether the model of an expanding cluster dominated by a massive binary galaxy, first suggested by Valtonen and Byrd (1979), is consistent with optical data on the surface density and velocity dispersion of the Coma cluster. We simulate the evolution of this model for a wide variety of initial conditions. We find that galaxy counts in the model can be made to agree with observation, but that the observed velocity dispersion profile cannot be reproduced. A number of other arguments suggest that the central galaxies in Coma cannot be as massive as required by the model. This model is not a viable representation of the Coma cluster.

This dissertation explores the use of anion photoelectron imaging to interrogate electronic dynamics in small chemical systems with an emphasis on photoelectron angular distributions. Experimental ion generation, mass selection, laser photodetachment and photoelectron imaging were performed in a negative-ion photoelectron imaging spectrometer described in detail. Results for photodetachment from the simplest anion, H⁻, are used to illustrate fundamental principles of quantum mechanics and provide basic insight into the physics behind photoelectron imaging from a pedagogical perspective. This perspective is expanded by introducing imaging results for additional, representative atomic and small molecular anions (O⁻, NH₂⁻ and N₃⁻) obtained at multiple photon energies to address the energy-dependence of photoelectron angular distributions both conceptually and semi-quantitatively in terms of interfering partial photoelectron waves. The effect of solvation on several of these species (H⁻, O⁻, and NH₂⁻) is addressed in photoelectron imaging of several series of cluster anions. The 532 and 355 nm energy spectra for H⁻(NH₃)n and NH₂⁻(NH₃)n (n = 0-5) reveal that these species are accurately described as the core anion solute stabilized electrostatically by n loosely coordinated NH3 molecules. The photoelectron angular distributions for solvated H⁻ deviate strongly from those predicted for unsolvated H⁻ as the electron kinetic energy approaches zero, indicating a shift in the partial-wave balance consistent with both solvation-induced perturbation (and symmetry-breaking) of the H⁻ parent orbital and photoelectron-solvent scattering. The photoelectron energy spectra obtained for the cluster series [O(N₂O)n]⁻ and [NO(N₂O)n]⁻ indicate the presence of multiple structural isomers of the anion cores, the former displaying sharp core-switching at n = 4, the latter isomer coexistence over the entire range studied. The photoelectron angular distributions for detachment from the O⁻(N₂O)n and NO⁻(N₂O)n isomers deviate strongly from those expected for bare O⁻ and NO⁻, respectively, in the region of an anionic shape resonance of N₂O, suggesting resonant photoelectron-solvent scattering. Partial-wave models for two-centered photoelectron interference in photodetachment from dissociating I₂⁻ is presented and discussed in the context of previous results. New time-resolved photoelectron imaging results for I₂⁻, for both parallel and perpendicular pump and probe beam polarizations, are presented and briefly discussed. Finally, new ideas and directions are proposed.

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No description available.

By virtue of its proximity, the Virgo Cluster is an ideal laboratory for us to test our understanding of the formation of structure in our Universe. In this spirit, we present a dynamical study of 33 gas-poor and 34 gas-rich Virgo galaxies as part of the Spectroscopic and H-band Imaging of Virgo survey. Our final spectroscopic data set was acquired at the 3.5-m telescope at the Apache Point Observatory. Hα rotation curves for the gas-rich galaxies were modelled with a multi-parameter fit function from which various velocity measurements were inferred. Analog values were measured off of the observed rotation curves, but yielded noisier scaling relations, such as the luminosity-velocity relation (also known as the Tully-Fisher relation). Our best i-band Tully-Fisher relation has slope α=-7.2 ± 0.5 and intercept M_i(2.3)=-21.5 ± 1.1 mag, matching similar previous studies. Our study takes advantage of our own, as well as literature, data; we plan to continue expanding our compilation in order to build the largest Tully-Fisher relation for a cluster to date. Following extensive testing of the IDL routine pPXF, extended velocity dispersion profiles were extracted for our gas-poor galaxies. Considering the lack of a common standard for the measurement of a fiducial galaxy velocity dispersion in the literature, we have endeavoured to rectify this situation by determining the radius at which the measured velocity dispersion, coupled with the galaxy luminosity, yields the tightest Faber-Jackson relation. We found that radius to be 1.5 R_e, which exceeds the extent of most dispersion profiles in other works. The slope of our Faber-Jackson relation is α=-4.3 ± 0.2, which closely matches the virial value of 4. This analysis will soon be applied to a study of the Virgo Cluster Fundamental Plane. Rotation correction of our dispersion profiles will also permit the study of galaxies' velocity dispersion profile shapes in an attempt to refine our understanding of the overall manifold of galaxy structural parameters. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2012-12-22 19:09:06.192

Over the recent years, technological changes in the music industry have altered the geography of music production and non-creative music work. Progress in information and communication technology has lead to decreasing revenues from record sales, which in turn has affected traditional income models for musicians, in particular income from record sales. Therefore, contemporary musicians need to spend longer periods on tour, thus being spatially fragmented in a multitude of geographies while performing artistic work practices. In light of such changes, new music geographies have started to gain the attention for performing artistic work, in particular temporary geographies at popular music festivals as well as digital online communities.This dissertation explores these spaces of music work and creativity, and the roles played by such spaces for Swedish musicians’ working lives. By using a triangulation of methods, this dissertation addresses three important features of the contemporary music profession. First, I explore the geographies of networks and network relations, and the role of networks for coping with contemporary working conditions. Second, I pay attention to the spaces of non-creative work, particularly in festival backstage areas. Third, I focus on how, when and where musicians perform creative work, and the relation between traditional studio locations and new opportunities for creative work while being on tour. Based on interviews, observations and netnographies, I argue that contemporary musicians perform much non-creative work in temporary festival backstage areas and in online communities while creative work preferably is located to traditional studio environments. I also argue that while female musicians and new-established musicians at large, due to increasing competition, have started to explore online communities, established musicians benefit from networking in face-to-face gatherings in order to gain job opportunities. Thus, there is a distinction between different groups of musicians based on career stage and gender.

Approved for public release; distribution is unlimited / S tasks. Discrete Event Simulation (DES) often involves repeated, independent runs of the same models with different input parameters. A system which is able to run many replications quickly is more useful than one in which a single monolithic application runs quickly. A loosely coupled parallel system is indicated. Inexpensive commodity hardware, high speed local area networking, and open source software have created the potential to create just such loosely coupled parallel systems. These systems are constructed from Linux-based computers and are called Beowulf clusters. This thesis presents an analysis of clusters in high-performance computing and establishes a testbed implementation at the MOVES Institute. It describes the steps necessary to create a cluster, factors to consider in selecting hardware and software, and describes the process of creating applications that can run on the cluster. Monitoring the running cluster and system administration are also addressed. / Major, Hellenic Army

We present a stacked weak-lensing analysis of 27 richness selected galaxy clusters at 0.40 <= z <= 0.62 in the COnstrain Dark Energy with X-ray galaxy clusters (CODEX) survey. The fields were observed in five bands with the Canada-France-Hawaii Telescope (CFHT). We measure the stacked surface mass density profile with a 14 sigma significance in the radial range 0.1 < R Mpc h(-1) < 2.5. The profile is well described by the halo model, with the main halo term following a Navarro-Frenk-White profile (NFW) profile and including the off-centring effect. We select the background sample using a conservative colour-magnitude method to reduce the potential systematic errors and contamination by cluster member galaxies. We perform a Bayesian analysis for the stacked profile and constrain the best-fitting NFW parameters M-200c = 6.6(- 0.8)(+1.0) x 10(14) h(-1)M(circle dot) and c(200c) = 3.7(+0.7) (-0.6). The off-centring effect was modelled based on previous observational results found for redMaPPer Sloan Digital Sky Survey clusters. Our constraints on M(200)c and c(200)c allow us to investigate the consistency with numerical predictions and select a concentration-mass relation to describe the high richness CODEX sample. Comparing our best-fitting values forM(200c) and c(200c) with other observational surveys at different redshifts, we find no evidence for evolution in the concentration-mass relation, though it could be mitigated by particular selection functions. Similar to previous studies investigating the X-ray luminosity-mass relation, our data suggest a lower evolution than expected from self-similarity.