49 research outputs found
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 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
A measurement of the proton structure function is reported
for momentum transfer squared between 4.5 and 1600 and
for Bjorken between and 0.13 using data collected by the
HERA experiment H1 in 1993. It is observed that increases
significantly with decreasing , confirming our previous measurement made
with one tenth of the data available in this analysis. The 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 .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 lâEXAFS Ă lâĂ©tude de lâeffet alcalin mixte dans les verres silicates
Nous avons enregistrĂ© des spectres de photoabsorption sur des verres appartenant au systĂšme ternaire SIO2 - Cs2O - Rb2O au voisinage des seuils de la raie LIII du cĂ©sium (5012 eV) et de la rale K du rubidium (15200 eV). La comparaison des spectres EXAFS dĂ©crit la variation de lâenvironnement de lâion alcalin lorsquâon 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 â 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 systĂšme pseudo-ternaire Y2O3-CuO-BaO sur le frittage de composĂ©s proches de la composition supraconductrice YBa 2Cu3O7-p. Dans ce travail prĂ©liminaire, on s'est intĂ©ressĂ© Ă mettre en Ă©vidence les transformations solide â liquide de ce systĂšme, au voisinage de la composition (123). Deux transformations apparaissent Ă 915 et 935 °C, selon la composition du produit, elles jouent un rĂŽle important sur le frittage et l'homogĂ©nĂ©itĂ© chimique du produit frittĂ©. Il ne semble pas y avoir de transformations liquides dans le domaine (123)-(211)-BaCuO2, il en rĂ©sulte une homogĂ©nĂ©itĂ© chimique plus grande des Ă©chantillons frittĂ©s
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'oxygÚne obtenus aprÚs 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'oxygÚne appartenant aux plans