Neste trabalho reportamos a produção da primeira armadilha magneto-ótica que confina simultaneamente duas espécies atômicas distintas: Sódio e Potássio. Para podermos realizar este aprisionamento, foi necessário vencer algumas dificuldades técnicas que justificam, inclusive, a escolha dos elementos utilizados. Nossa armadilha também foi utilizada para realizar o primeiro estudo de colisões frias entre átomos de espécies diferentes. Experimentalmente, as informações sobre essas colisões são obtidas através da medida da dinâmica de perdas da armadilha de S6dio em presença e ausência de átomos frios de Potássio. Observamos que o efeito de colisões heteronucleares e dez vezes menor do que as homonucleares. Esta diferença já era esperada devido ao menor alcance dos potenciais de interação entre átomos no caso de espécies distintas. Nossos resultados são comparados a uma teoria semi-clássica simples e se encontram em bom acordo com as previsões. Introduzimos uma nova técnica que consiste em mudar repentinamente a intensidade do laser aprisionador e observar a variação do número de átomos aprisionados. Medimos a taxa de perdas por colisão entre átomos de Potássio frios como função da intensidade do laser aprisionador. Essa técnica nos permite alcançar o regime de baixas intensidades, inclusive abaixo da intensidade de saturação, sem as limitações da técnica tradicional. Aplicamos essa técnica ao aprisionamento simultâneo e medimos a taxa de perdas por colisão do sódio na presença e ausência de potássio. Com essa medida somos capazes de estimar a seção e choque entre sódio e potássio ambos no estado fundamental / In this thesis we report the production of the first magneto-optical trap that confines simultaneously two atomic species, sodium and potassium. In order to realize this experiment we had to overcome some technical difficulties that justified our choice of these two elements. This trap was used to study cold collisions between two different species. The information about these collisions is obtained experimentally from the dynamics of the sodium trap loss process in the presence and absence of potassium atoms. We observed that the heteronuclear effect is ten times smaller than the homonuclear one. This difference is explained by the smaller range of the interaction potentials between different species. Our results are compared with the theoretical predictions of the semi-classical theory and show a good agreement with the predictions. We have introduced a new technique which consists of a sudden decrease of the laser intensity, after which we observe the temporal variation in the number of trapped atoms. We have measured the loss rate coefficient between cold potassium atoms as a function of light intensity of the trapping laser. This technique allowed us to reach the very low intensity regime, as low as 30% of the saturation intensity, without compromising the loading process. We applied this technique to the simultaneous trapping and measured the loss rate coefficient between cold sodium atoms in the presence and absence of cold potassium atoms. With this measurement we can estimate the value of the cross section between sodium and potassium in the ground state

Dentre os observáveis globais que permitem caracterizar a colisão entre íons pesados relativísticos, a multiplicidade de partículas é uma das variáveis mais fundamentais, diretamente ligada à densidade de energia da colisão. Serão apresentados resultados do estudo de multiplicidade de partículas carregadas para colisões centrais entre íons de chumbo a energias de 2.76 TeV (energia no centro de massa) utilizando o detector ATLAS no Large Hadron Collider (LHC). A multiplicidade na produção de partículas carregadas é medida utilizando dois métodos diferentes entre o intervalo de pseudorapidez || < 2.5 empregando o sistema de detectores semicondutores centrais de trajetórias do ATLAS. A seleção de eventos é crucial para esta análise e é aplicada a dados obtidos através de um trigger de minimum bias, impondo-se a coincidência entre o sinal do calorímetro de zero grau (ZDC) (|| > 8.3) e a coincidência entre o sinal do Minimum Bias Trigger Scintilator (MBTS) (2.1< || <3.8), de forma a remover da amostra de dados os eventos decorrentes da dissociação eletromagnética. Neste trabalho, eventos produzidos pelo gerador de eventos HIJING também foram analisados e os dados simulados reconstruídos utilizando-se os mesmos algoritmos empregados na análise dos dados reais. A multiplicidade e a densidade inclusiva de partículas foram medidas para as colisões mais centrais e estão em bom acordo com os resultados obtidos por outros experimentos. / From the global observables that allows the characterization of the heavy ion collisions at relativistic energies, the particle multiplicity is one of the most fundamental observables, directly related to the energy density of the collision. There will be presented results about the study of central collision charged particle multiplicity in Pb - Pb collisions at the 2.76 TeV center of mass energy using the ATLAS detector at the Large Hadron Collider (LHC). The particle multiplicity is measured using two different methods in the || < 2:5 rapidity interval, deploying the ATLAS inner tracker semiconductor system. The event selection plays a crucial role in this analysis and is applied on data acquired using a minimum bias trigger. Imposing the condition of coincidence between the two Zero Degree Calorimeters (ZDC) arms (|| > 8.3) and the coincidence of the Minimum Bias Trigger Scintillator (MBTS) detector (2.1 < || <3.8) the electromagnetic dissociation events are removed from the sample. For this work, events produced by the HIJING event generator were also analyzed and the simulated data was reconstructed using the same algorithms used on data. The multiplicities and inclusive particle density measured for most central collisions are in good agreement with the ones measured by other experiments.

No description available.

Mes recherches au Commissariat à l'Énergie Atomique concernent principalement la modélisa- <br />tion mathématique et la simulation numérique pour la physique des plasmas. Ce mémoire présente <br />mes contributions dans ce domaine.

Une famille d'astéroïdes véritable (génétique) est un ensemble de fragments issus de la fragmentation d'un corps parent, et qui ont des orbites similaires autour du soleil. La famille de Eos est un regroupement dynamique de plus de 450 astéroïdes à environ 3 UA du soleil. J'ai observé et fait l'analyse spectroscopique minutieuse de 45 astéroïdes de la famille de Eos. J'ai ainsi trouvé des caractéristiques communes et uniques, propres à la famille de Eos, me permettant d'établir un lien génétique unissant tous les membres. Cela m'a permis aussi d'identifier deux intrus c'est à dire des astéroïdes étrangers à la famille. Grâce à l'analyse des paramètres spectroscopiques, j'en ai déduit que le corps parent de Eos était partiellement différentié et que les processus de l'altération de l'espace avaient joué un rôle, quoique mineur dans la diversité spectrale des membres de la famille de Eos. J'ai simulé une famille synthétique de fragments grâce à un modèle semi empirique de collision catastrophique. J'ai ainsi obtenu un modèle synthétique de la famille de Koronis, famille au sein de laquelle la sonde Galileo a découvert l'unique preuve directe d'un système binaire. Dans ce contexte, j'ai développé un code pour suivre, aussitôt après l'impact, l'évolution dynamique des fragments, en tenant compte de leurs interactions, collisions et réaccumulation. J'ai trouvé que la formation de systèmes binaires formés de couples de fragments de masse comparable, à la suite d'une collision catastrophique est possible (environ un pour cent des fragments). Enfin, j'ai étudié des astéroïdes candidats à des missions spatiales. J'ai analysé les spectres de 253 Mathilde (mission NEAR), des spectres infrarouges du satellite ISO et des spectres des astéroïdes candidats à la mission ROSETTA. Sur ces derniers, j'en ai conclu que le choix idéal de la sélection finale devrait inclure 140 Siwa qui de par sa taille et son type spectral (C) constitue un objet plus primitif.

Predictions of mechanical collisions between two bodies frequently cannot be completed by the impulse-momentum equation together with a complete description of the motion of the system at the initial contact. Additional account must be taken of the deformations and frictional interaction induced by the impulsive reaction force, where the bodies contact one another, as these play an important role in the outcome of the collision. During the time the bodies are in contact, elastic, friction and inertia properties combine to produce a complex variation of sliding and sticking through out the contact surface. For accurately predicting the impulse and velocity changes during contact, a considerably simplified, coupled, conservative model, which captures the essential characteristics of the elastic-friction interaction during contact loading, is investigated in this thesis. In this simplified model, the interface between two colliding bodies resembles the behavior of a pair of mutually perpendicular, non-linear springs which react independently with the exception that the stiffness of the tangential "spring" is influenced by the normal displacement. These elastic properties, in combination with inertial properties derived from generalized impulse-momentum laws, form a "spring-mass" system for which numerical integration yields the prediction of rebound velocities. For comparison, an explicit non-linear finite element code, DYNA3D, developed at Lawrence Livermore National Laboratory for analyzing the transient dynamic response of three-dimensional solids, is used to predict the responses of an elastic sphere and elastic rod, each colliding with a rigid plane with varying initial velocities and configurations. Results are also compared with results of a complex analysis of collisions of spheres by Maw, Barber, and Fawcett (1976). / Graduation date: 1999

Arthur V. Phelps, O.T. Fundingsland [and] Sanborn C. Brown. / "July 23, 1951." / Bibliography: p. 9. / Army Signal Corps Contract No. DA36-039 sc-100 Project No. 3-99-10-022. Dept. of the Army Project No. 3-99-10-022.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2005. / Bibliography: leaves 81-83.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Thesis--Rijksuniversiteit te Leiden. / Summary also in Dutch. eContent provider-neutral record in process. Description based on print version record. Includes bibliographies.