Results 1 - 10 of 1486
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[en] Results are presented on preliminary measurements of the branching fractions for B+ → JψφK+, B0 → J/ψφKS0, B0 → J/ψη and B0 → ψη(prime) using 56 million B(bar B) events collected at the Υ(4S) resonance with the BABAR detector at PEP-II. We measure branching fractions of Β(B+ → J/ψφK+) = (4.4 ± 1.4(stat) ± 0.5(syst)) x 10-5 and Β(B0 → J/ψφKS0) = (5.1 ± 1.9(stat) ± 0.5(syst)) x 10-5, and set upper limits at 90% C.L. for branching fractions Β(B0 → J/ψφ) < 9.2 x 10-6, Β(B0 → J/ψη) < 2.7 x 10-5, and Β(B0 → J/ψη(prime)) < 6.3 x 10-5
[en] The authors report preliminary measurements of the branching fractions for B+ → J/ψφK+, B0 → J/ψφKS0, B0 → J/ψφ, B0 → J/ψη and B0 → J/ψη(prime) using 56 million B(bar B) events collected at the Υ(4S) resonance with the BABAR detector at PEP-II. They measure branching fractions of Β(B+ → J/ψφK+) = (4.4 ± 1.4(stat) ± 0.7(syst)) x 10-5 and Β(B0 → J/ψφKS0) = (5.1 ± 1.9(stat) ± 0.9(syst)) x 10-5, and set upper limits at 90% C.L. for branching fractions Β(B0 → J/ψφ) < 0.95 x 10-5, Β(B0 → J/ψη) < 2.7 x 10-5, and Β(B0 → J/ψη(prime)) < 6.4 x 10-5
[en] The isotope shifts and hyperfine structure splittings of nine stable xenon isotopes in the mass range from 124 to 136 were measured using the electronic transition 5d4D72-6p4P520 in the Xe II spectrum. The method of collinear fast-ion--beam laser spectroscopy was utilized to achieve Doppler-free resolution and a high sensitivity. An ion-beam apparatus consisting of an Einzel lens, a switch magnet, and two electrostatic quadrupole triplets was designed to transport the ions from an on-line ion source through the TRISTAN isotope separator to the interaction region where, at resonance, the fluorescence signal was observed. A line-shape analysis, based on an asymmetrical exponential function, was developed to interpret the recorded data. Changes in the mean square charge radii δ(r2)/sup AA'/ for the chain of stable xenon isotopes were extracted from the measured isotope shifts. The hyperfine-structure constants A and B, the nuclear magnetic dipole moment μ/sub l/, and the electric quadrupole moment Q were evaluated from the splittings. The effect of the nuclear deformation below the magic number 82 is discussed in the two-parameter liquid drop model and the three-parameter droplet model. A comparison of the δ(r2)/sup AA'/ of Xe with those of the neighboring elements of Cs and Ba is made
[en] An analytical method is presented for deriving the thermomechanical properties of polycrystalline materials under high-pressure (P) and high-temperature (T) conditions. This method deals with non-uniform stress among heterogeneous crystal grains and surface strain in nanocrystalline materials by examining peak-width variation under different P-T conditions. Because the method deals directly with lattice d spacing and local deformation caused by stress, it can be applied to process any diffraction profile, independent of detection mode. In addition, a correction routine is developed using diffraction elastic ratios to deal with severe surface strain and/or strain anisotropy effects related to nano-scale grain sizes, so that significant data scatter can be reduced in a physically meaningful way. Graphical illustration of the resultant microstrain analysis can identify micro/local yields at the grain-to-grain interactions resulting from high stress concentration, and macro/bulk yield of the plastic deformation over the entire sample. This simple and straightforward approach is capable of revealing the corresponding micro and/or macro yield stresses, grain crushing or growth, work hardening or softening, and thermal relaxation under high-P-T conditions, as well as the intrinsic residual strain and/or surface strain in the polycrystalline bulk. In addition, this approach allows the instrumental contribution to be illustrated and subtracted in a straightforward manner, thus avoiding the potential complexities and errors resulting from instrument correction. Applications of the method are demonstrated by studies of (alpha)-SiC (6H, moissanite) and of micro- and nanocrystalline nickel by synchrotron X-ray and time-of-flight neutron diffraction.
[en] The cyclic hardening of fiber-reinforced metal matrix composites has been explored using tungsten monofilament-reinforced monocrystalline copper composite specimens. This composite showed the same overall hardening tendencies as monolithic copper single crystals, i.e., rapid hardening, momentary softening and saturation, but at much higher stress levels as compared to the behavior in the copper single crystals. The back stress of the composites was found both very high and much larger than the friction stress so that there was a pronounced Bauschinger effect. The high cyclic stress in the composite was predominantly due to the back stress which resulted from the interaction between the fiber and dislocations. The fiber did not have a significant effect on the friction stress
[en] The crystal structure and defects in a commercial TWS-100 β-SiC whisker were observed and analyzed by means of high-resolution transmission electron microscopy. It was found that the SiC whiskers with triangular or hexagonal cross-sections both have a face-centered cubic structure, while their crystal defects are different. The defects in the triangular whisker are mainly stacking faults on the (1 1 1) planes which are not perpendicular to the whisker axis, however, in the hexagonal whisker there are a great amount of micro-twins and stacking faults on the (1 1 1) planes perpendicular to the whisker axis. The high-density defects account for the hexagonal close-packed (HCP) diffraction patter obtained in the HCP β-SiC whiskers, which is first pointed out by analyzing the crystal structure of the β-SiC whisker
[en] Three separate papers are included which report research progress during this period: (1) A new railgun configuration with perforated sidewalls, (2) development of a fuseless small-bore railgun for injection of high-speed hydrogen pellets into magnetically confined plasmas, and (3) controls and diagnostics on a fuseless railgun for solid hydrogen pellet injection
[en] Pressure-volume-temperature measurements have been carried out using synchrotron X-ray diffraction for wuestite at static pressures of 1.9, 2.6, and 5.4 GPa. Our results revealed that the composition change of wuestite and, hence, rearrangements of defect structures are primarily caused by the magnetite (Fe3O4) exsolution at temperatures of 523-723 K. Based on the isobaric volume-temperature data collected during cooling, the contribution of compositional variations to the unit-cell volumes of wuestite in the ranges of 300-673 K and 723-1073 K is negligibly small, within the experimental uncertainties. These observations suggest that the measured volume changes in the range of 300-673 K and 723-1,073 K can be attributed to the metal-oxygen bond expansion. Owing to the magnetite exsolution, thermal expansion data are obtained in each experiment at 1.9, 2.6, and 5.4 GPa for wuestite of two different compositions, Fe0.987O and Fe0.942O. At all three pressures, Fe0.942O shows a thermal expansion that is about 30% larger than Fe0.987O. Such findings represent the first experimental evidence of a substantial effect of nonstoichiometry on thermal expansivity, and based on previous thermodynamic calculations of the defect formation and interaction, this effect is likely associated with the distinct defects arrangements in iron-rich and more iron-deficient wuestite. This study also presents thermal equations of state for wuestite of two different compositions. Such volume-related properties at high temperatures are experimentally difficult to obtain in wuestite but important for thermodynamic studies in the binary Fe-O system.