AGAPE: a microlensing search in the direction of M31

A status report of the microlensing search by the pixel method in the direction of M31, on the 2 meter telescope at Pic du Midi is given. Pixels are stable to a level better than 0.5%. Pixel variations as small as 0.02 magnitude can clearly be detected

Energy Flow in the Hadronic Final State of Diffractive and Non-Diffractive Deep-Inelastic Scattering at HERA

An investigation of the hadronic final state in diffractive and non--diffractive deep--inelastic electron--proton scattering at HERA is presented, where diffractive data are selected experimentally by demanding a large gap in pseudo --rapidity around the proton remnant direction. The transverse energy flow in the hadronic final state is evaluated using a set of estimators which quantify topological properties. Using available Monte Carlo QCD calculations, it is demonstrated that the final state in diffractive DIS exhibits the features expected if the interaction is interpreted as the scattering of an electron off a current quark with associated effects of perturbative QCD. A model in which deep--inelastic diffraction is taken to be the exchange of a pomeron with partonic structure is found to reproduce the measurements well. Models for deep--inelastic $ep$ scattering, in which a sizeable diffractive contribution is present because of non--perturbative effects in the production of the hadronic final state, reproduce the general tendencies of the data but in all give a worse description.Comment: 22 pages, latex, 6 Figures appended as uuencoded fil

A Measurement of the Proton Structure Function F ⁣2(x,Q2)F_{\!2}(x,Q^2)

A measurement of the proton structure function $F_{\!2}(x,Q^2)$ is reported for momentum transfer squared $Q^2$ between 4.5 $GeV^2$ and 1600 $GeV^2$ and for Bjorken $x$ between $1.8\cdot10^{-4}$ and 0.13 using data collected by the HERA experiment H1 in 1993. It is observed that $F_{\!2}$ increases significantly with decreasing $x$, confirming our previous measurement made with one tenth of the data available in this analysis. The $Q^2$ dependence is approximately logarithmic over the full kinematic range covered. The subsample of deep inelastic events with a large pseudo-rapidity gap in the hadronic energy flow close to the proton remnant is used to measure the "diffractive" contribution to $F_{\!2}$.Comment: 32 pages, ps, appended as compressed, uuencoded fil

STRUCTURAL DIAGNOSTIC OF HIGH TEMPERATURE LIQUID PHASES BY 27Al NMR

L'amélioration des procédés de soudage par plasma ou laser suppose une bonne connaissance des propriétés microscopiques du liquide constituant la zone fondue. Le développement de nouvelles sondes de résonance magnétique nucléaire permet d'atteindre cet objectif. L'analyse de la raie de résonance de 27Al dans des oxydes liquides alumineux montre un régime d'échange rapide entre des coordinences quatre, cinq et six et une dépendance de la position de cette raie en fonction de la composition du liquide.Improvements of welding processes by plasma or laser require a good knowledge of the microscopic properties of the liquid associated to the melted area. The development of new high temperature NMR probes allows to reach such a goal. In the case of alumina bearing liquids, the analysis of the 27Al resonance line shows a rapid exchange regime of Al in four, five or six fold coordination together with a dependence of the resonance line versus the liquid composition

Apport de l’EXAFS à l’étude de l’effet alcalin mixte dans les verres silicates

Nous avons enregistré des spectres de photoabsorption sur des verres appartenant au système ternaire SIO2 - Cs2O - Rb2O au voisinage des seuils de la raie LIII du césium (5012 eV) et de la rale K du rubidium (15200 eV). La comparaison des spectres EXAFS décrit la variation de l’environnement de l’ion alcalin lorsqu’on remplace progressivement un Ion alcalin par un autre

Study of Crystallisation of Yttrium Garnets Y3R5O12 (R = Al, Ga) by High Temperature EXAFS

In this paper, we present a new high temperature EXAFS device using a laser heating system and aerodynamic levitation for experiments up to 2300°C. We report here the first spectra of Y K-edge for YAG at room temperature and in the liquid

Frittage de YBaCuO, implications du diagramme de phases

The motivations of this experimental work are to underline the implications between the phases diagram constitution and the sintering of YBaCuO superconductors. This preliminary work is focussed on the solid → liquid transformations of this system, in the vicinity of the (123) phase. Two transformations are observed at 915 and 935 °C depending of the composition of the compound. They both have an important role on the sintering process and the chemical homogeneity of the ceramic. No such transformations seems to occur in the domain (123)-(211)-BaCuO2, the sintered sample has therefore a better chemical homogeneity.Les motivations de ce travail sont d'examiner les implications du diagramme de phases du système pseudo-ternaire Y2O3-CuO-BaO sur le frittage de composés proches de la composition supraconductrice YBa 2Cu3O7-p. Dans ce travail préliminaire, on s'est intéressé à mettre en évidence les transformations solide → liquide de ce système, au voisinage de la composition (123). Deux transformations apparaissent à 915 et 935 °C, selon la composition du produit, elles jouent un rôle important sur le frittage et l'homogénéité chimique du produit fritté. Il ne semble pas y avoir de transformations liquides dans le domaine (123)-(211)-BaCuO2, il en résulte une homogénéité chimique plus grande des échantillons frittés

Caractérisation structurale et thermique d'amorphes à base d'alumine et d'oxydes de lanthanides (Ln = La, Ce, Pr, Nd, Sm, Gd, Tb)

Spat cooling under air of binary Al2O3-Ln2O 3 mixtures allowed us to obtained amorphous phases. Thermal behaviour of these materials and the coordination of the rare-earth ion are studied.L'hypertrempe à l'air des binaires Al2O3-Ln 2O3 permet d'obtenir des matériaux amorphes. Leur comportement thermique, ainsi que l'environnement local de l'ion lanthanidique sont précisés

17O NMR in planes and chains of YBa2Cu3O7

We report the first observation of 17O NMR spectra in YBa 2Cu3O7 obtained after selective gas exchanges performed at 300 and 850°C. We are able to assign the narrow (weakly shifted) signal to the (1/2, - 1/2) transition of oxygen atoms in CuO chains and the broad (strongly shifted) signal to the 0-sites in CuO2 planes.Nous prisentons les premiers résultats de spectres RMN de l'isotope 17Ode l'oxygène obtenus après échange gazeux à 300 et 850° C. Nous sommes en mesure d'attribuer le signal étroit (et faiblement déplacé) à la transition 1/2, - 1/2 des atomes des chaines Cu O et le signal large (fortement déplacé) aux sites d'oxygène appartenant aux plans