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3 from Perseus Tools and Information

1. Stade: Lower Saxony, Germany [Atlas site] (6.07)

2. Staden: Belgium [Atlas site] (5.74)

3. Staden: Hesse, Germany [Atlas site] (5.74)

1 from CCSD thèses-EN-ligne

1. browaeys, antoine; Piegeage magnetique d'un gaz d'helium metastable : vers la condensation de Bose-Einstein: Un gaz froid d'helium metastable ($2{^3S_1}$) polarise est un candidat possible pour l'observation de la condensation de Bose-Einstein. Des etudes theoriques predisent que le taux de collisions Penning, obstacles a l'obtention de hautes densites spatiales, est reduit de plusieurs ordres de grandeur du fait de la polarisation de l'echantillon. Cette reduction doit permettre d'observer la transition de phase a une temperature autour du $\mu$K. La polarisation est obtenue experimentalement en piegeant les atomes magnetiquement. La longueur de diffusion theorique elevee de l'helium dans l'etat $2{^3S_1}$ permet d'esperer un refroidissement evaporatif efficace dans le piege magnetique. Cette these resume les predictions theoriques sur les collisions inelastiques et elastiques entre atomes d'helium metastables et decrit le dispositif experimental conduisant au chargement du piege magnetique. La technique choisie est basee sur le pre-refroidissement laser des atomes par ralentissement d'un jet par laser assiste par effet Zeeman, suivi d'un piegeage magneto-optique et d'une phase de melasse optique. Une premiere limitation experimentale sur la densite spatiale que l'on peut atteindre appara\^{i}t au cours de cette etape. Elle est due aux collisions inelastiques assistees par la lumiere laser. Le nuage pre-refroidi est ensuite transfere dans le piege magnetique. Deux realisations experimentales de ce piegeage magnetique sont presentees. La premiere, demonstration de principe, est realisee dans un quadrup\^{o}le. La deuxieme est obtenue dans un piege de Ioffe-Pritchard. A ce stade de l'experience, on dispose d'un echantillon magnetique contenant $5\times 10^7$ atomes a une temperature de 200 $\mu$K, avec une duree de vie de 20 s. ---------- A cold gas sample of metastable helium atoms ($2^3S_1$) is a possible candidate for observing Bose-Einstein condensation. Theoretical studies predict that Penning collisions, a major obstacle for achieving high density, are suppressed by several orders of magnitude due to spin polarization of the sample. This suppression should allow the transition to happen in the $\mu$K range. This polarization is obtained by magnetostatic trapping of the atoms. The high predicted value of the scattering length for helium in the $2^3S_1$ state may allow an efficient evaporative cooling in the magnetic trap. This thesis summarizes the theoretical predictions about elastic and inelastic collisions between metastable helium atoms and describes the apparatus leading to the loading of the magnetic trap. The technique used is based on laser cooling of an atomic beam assisted by Zeeman effect, followed by magneto-optical trapping and optical molasses. A first experimental limitation in the spatial density is encoutered during this stage. It is due to inelastic collisions enhanced by laser light. The pre-cooled sample is then transferred to the magnetic trap. Two experimental realizations of magnetostatic trapping are presented. The first one in a quadrupole is only a proof of principle. The second one is achieved in a Ioffe-Pritchard trap. We now have a magnetically trapped sample of $5\times 10^7$ atoms at a temperature of 200 $\mu$K, with a lifetime of 20 s. [Text] [View with Perseus links] (0.31)

1 from Chemistry Preprint Server

1. Garnik Sargsyan; VISUALIZATION OF RELAXATION PROCESSES AT COOL-FLAME OXIDATION OF ACETALDEHYDE IN WELL-STIRRED REACTOR IN FLOW CONDITIONS: The cool-flame oxidation of hydrocarbons and others gas-phase reactions with the chain mechanism is interesting from the point of view of a finding of effective modes of reception of valuable intermediate products.The presence of the exited particles at reaction medium (observable luminescence which is growing out under relaxation of these particles) gives possibility to visualize process of research of modes of these reactions from the point of view of a finding of steady stades. The research of a role of internal energy of the participants of reaction is urgent also at an establishment the phenomena of oscillation under cool-flames oxidation.Ideal devices for reception both receiving cool-flames and the researches of mechanisms of their formation are vell-stirred flow reactors allowing to receive a reaction mix without thermal and concentration gradients. Averaging influence of a surface on homogeneous process from the point of view of stable products of superficial reactions, such reactors enable to observe the phenomena caused by interaction of superficial and volumetric processes. For example, the theoretical analysis shows, that if on a surface the exited molecules (because of heterogeneous recombination of radicals) are formed, the time of which life (because of his small value) does not allow them to penetrate in more deeps stratum of volume, their interaction with volumetric processes is located near to a surface, that results in appearance of volume oscillations structures [1]. The research of these structures enables to find more optimum modes of realization of oxidizing processes and opportunity of a choice of coverings of surfaces chemical reactors. [Text] [View with Perseus links] (0.28)

1 from OCLC Online Computer Library Center Theses and Dissertations Repository

1. Stade, Bernhard,--1848-1906.; De Isaiae vaticiniis aethiopicis /--Bernardus Stade.: Thesis - Leipzig., Bibliographical footnotes. [Text] (3.46)