Showing papers by "Université Paris-Saclay published in 1998"

Spin asymmetries A1 and structure functions g1 of the proton and the deuteron from polarized high energy muon scattering

Abstract: We present the final results of the spin asymmetries A1 and the spin structure functions g1 of the proton and the deuteron in the kinematic range 0.0008

Direct measurement of the top quark mass by the DO Collaboration

Abstract: We determine the top quark mass m{sub t} using t{bar t} pairs produced in the DO/ detector by {radical} (s) =1.8thinspTeV p{bar p} collisions in a 125thinsppb{sup {minus}1} exposure at the Fermilab Tevatron. We make a two constraint fit to m{sub t} in t{bar t}{r_arrow}bW{sup +}{bar b}W{sup {minus}} final states with one {ital W} boson decaying to q{bar q} and the other to e{nu} or {mu}{nu}. Likelihood fits to the data yield m{sub t}(l+jets)=173.3{plus_minus}5.6thinsp(stat)thinsp{plus_minus}thinsp5.5thinsp(s st) GeV/c{sup 2}. When this result is combined with an analysis of events in which both {ital W} bosons decay into leptons, we obtain m{sub t}=172.1{plus_minus}5.2thinsp(stat)thinsp{plus_minus}thinsp4.9thinsp(syst) GeV/c{sup 2}. An alternate analysis, using three constraint fits to fixed top quark masses, gives m{sub t}(l+jets)=176.0{plus_minus}7.9thinsp(stat){plus_minus}thinsp4.8thinsp(syst) GeV/c{sup 2}, consistent with the above result. Studies of kinematic distributions of the top quark candidates are also presented. {copyright} {ital 1998} {ital The American Physical Society}

Mossbauer-effect and x-ray-absorption spectral study of sonochemically prepared amorphous iron

Abstract: The Mossbauer spectra of amorphous iron, prepared by using sonochemical methods, exhibit a broad magnetic hyperfine sextet at both 78 and 295 K. The spectra do not change with time if the amorphous iron is not exposed to oxygen or moisture. An analysis of the spectra with the method of Lines and Eibschutz yields average magnetic hyperfine fields of 29.1 and 25.9 T at 78 and 295 K, respectively. The corresponding moments of 1.9 mu(B), and 1.7 mu(B), agree well with values obtained from earlier magnetization studies and, further, provide strong experimental support for earlier calculations of the magnetic moments in amorphous iron. The observed average isomer shifts of 0.27 and 0.14 mm/s obtained at 78 and 295 K, respectively, correspond to a decrease in the s-electron density at the iron-57 nucleus as compared to that of alpha-iron, a decrease which is consistent with the decreased coordination number of amorphous iron. The similarity of the 295 K iron K-edge x-ray-absorption spectrum of amorphous iron and alpha-iron, up to 7130 eV, indicates that the d-electron density of states just above the Fermi level is similar in both forms of iron. The absence of structural details above 7130 eV in the spectrum of amorphous iron indicates, in agreement with multiple-scattering calculations, that long-range order does not extend beyond the third shell of neighbors in amorphous iron. Greatly reduced extended x-ray-absorption-fine-structure scattering is observed at the iron K edge of amorphous iron as compared to alpha-iron. An analysis of the weak observed scattering reveals both a decrease in the average coordination number from 14 in alpha-iron to 10 in amorphous iron, and an asymmetric radial distribution function of the iron neighbors in the first shell. This asymmetric distribution yields for amorphous iron a minimum iron-iron distance of 2.40 Angstrom and an average iron-iron distance of 2.92 Angstrom. [S0163-1829(98)08817-1].

Conservation of nolR in the Sinorhizobium and Rhizobium Genera of the Rhizobiaceae Family

Abstract: In Sinorhizobium meliloti the NolR repressor displays differential negative regulation of nodulation genes and is required for optimal nodulation. Here, we demonstrate that the NolR function is not unique to S. meliloti but is also present in other species of the Rhizobiaceae family. DNA hybridization indicates the presence of nolR homologous sequences in species belonging to the Rhizobium and Sinorhizobium genera while no hybridization signal was detected in species from the Mesorhizobium, Bradyrhizo-bium, Azorhizobium, and Agrobacterium genera. We isolated the nolR gene from the Rhizobium leguminosarum bv. viciae strain TOM and showed that the TOM nolR gene acts similarly to S. meliloti nolR by repressing the expression of both the nodABCIJ and the nodD genes, resulting in decreased Nod factor production. The presence of a functional nolR gene in R. leguminosarum is correlated with an increased rate and extent of nodulation of pea. The conserved primary structure, the location of the DNA-binding domain,...

On the differences between high-energy proton and pion showers and their signals in a non-compensating calorimeter

Abstract: We present the results of experimental studies of hadron showers in a copper/quartz-fiber calorimeter, based on the detection of Cherenkov light. These studies show that there are very significant differences between the signals from protons and pions at the same energies. In the energy range between 200 and 375 GeV, where these studies were performed, the calorimeter’s response to protons was typically 10% smaller than the response to pions. On the other hand, the energy resolution was about 25% better for protons. In addition, the protons had a Gaussian line shape, whereas the pion response curve was asymmetric. These differences can be understood from the requirements of baryon number conservation in the shower development. They are expected to be present in any non-compensating calorimeter, to a degree determined by the e / h value.

Cosmological Phase Transitions and Radius Stabilization in Higher Dimensions

Abstract: Recently there has been considerable interest in field theories and string theories with large extra spacetime dimensions. In this paper, we explore the role of such extra dimensions for cosmology, focusing on cosmological phase transitions in field theory and the Hagedorn transition and radius stabilization in string theory. In each case, we find that significant distinctions emerge from the usual case in which such large extra dimensions are absent. For example, for temperatures larger than the scale of the compactification radii, we show that the critical temperature above which symmetry restoration occurs is reduced relative to the usual four-dimensional case, and consequently cosmological phase transitions in extra dimensions are delayed. Furthermore, we argue that if phase transitions do occur at temperatures larger than the compactification scale, then they cannot be of first-order type. Extending our analysis to string theories with large internal dimensions, we focus on the Hagedorn transition and the new features that arise due to the presence of large internal dimensions. We also consider the role of thermal effects in establishing a potential for the radius of the compactified dimension, and we use this to propose a thermal mechanism for generating and stabilizing a large radius of compactification.

Phase Transformations under Ball Milling

Abstract: Under sustained ball milling, metallic alloys may achieve quasi-steady state structures which depend on the milling conditions (temperature, milling intensity) and on the composition of the alloy. This is established for the crystal to amorphous, the order-disorder and the dissolution transformations. While a simple mean field theory well accounts for the observed features of the order-disorder transition, atomic level computer simulations suggest new features which deserve experimental research: the microstructure would reach some dynamical steady state, the characteristic length of which depends on the milling conditions. For the order-disorder transition, it is anticipated that on top of the milling intensity, the details of the time and space structure of the intensity would affect the microstructure, an effect which is reminiscent of the cascade size effect for alloys under irradiation. Moreover, new results on phase separation under milling are presented, which suggest the possibility of a decreased solubility under milling.

Cesium ordering and electron localization-delocalization phenomena in the quasi-one-dimensional diphosphate tungsten bronzes: Cs1-xP8W8O40

Abstract: We present a structural investigation of the Cs1‒xP8W8O40 family of quasi-one-dimensional (quasi-1D) conductors, which exhibit intriguing charge transport properties where, for x small, the conductivity exhibits a crossover from a semiconducting to a metallic like regime when the temperature decreases. In these materials the W4O18 double zig-zag chains, together with the P2O7 diphosphate groups, delimit channels which are partially filled with the Cs+ ions. It is found, from an X-ray diffuse scattering investigation, that at room temperature the Cs+ ions are locally ordered on a lattice of well-defined sites in the channel direction and not ordered between neighboring channels. These Cs+ ions form 1D incommensurate concentration waves whose periodicity depends on the Cs+ stoichiometry. In CsP8W8O40 upon cooling, the intrachannel order increases significantly, and an interchannel order between the 1D Cs+ concentration waves develops. But, probably because of kinetic effects, no tridimensional (3D) long range order of the Cs+ ions is achieved at low temperature. The 3D low-temperature local order has been determined and it is found that the phase shift between the Cs+ concentration waves minimizes their Coulomb repulsions. This local order is increasingly reduced as the Cs concentration diminishes. We interpret the intriguing features of the electrical conductivity in relationship with the thermal evolution of the Cs ordering effects. We suggest that in Cs1‒xP8W8O40, for x small, a localization-delocalization transition of the Anderson type occurs due to the thermal variation of the Cs disorder. When x increases, the enhancement of the disorder leads to a localization of the electronic wave function in the whole temperature range measured. Finally, and probably because of the disorder, no charge density wave instability is revealed by our X-ray diffuse scattering investigation.

Epoxyethane-/ethynesulfonamides with antifilarial activities. Degradation kinetics and inhibitory effect on filarial malate dehydrogenase and lactate dehydrogenase.

Abstract: Some epoxyethane-/ethynesulfonamides had shown strong filaricidal activity with inconstant reproducibility as a result of a lack of stability in aqueous solution. The degradation in hydroxylic and aprotic solutions of two epoxyethanesulfonamides and one ethynesulfonamide was investigated using TLC, HPLC, GC and mass spectrometry. For both epoxydes, the degradation rate followed first-order kinetics and was more rapid in hydroxylic than in aprotic solutions. The degradation increased with the temperature whereas it was not modified with and without light exposure. Four kinds of degradation products were found: the first one involved the oxidation of the epoxyde bond, the second the breaking of the N-S bond, the third a desulfonation product and the fourth was not identified. In contrast, the stability of ethynesulfonamide was better than those of epoxyethanesulfonamide. These results suggest that epoxyethanesulfonamides should be kept at +4 degrees C before being injected to animals during the study of biological activity. Since epoxyde compounds are known to have inhibitory effects on parasite energy metabolism enzymes, the compunds were evaluated on two major filarial enzymes: lactate dehydrogenase (LDH) and cytoplasmic malate dehydrogenase (MDH). Both epoxyethanesulfonamides showed only a slight inhibitory effect on filarial LDH and MDH confirming the evidence that the main mode of action of these compounds remains to discover. Moreover, ethynesulfonamide and the degradation products of both epoxyethane-sulfonamides had no effect on LDH and MDH.