Preparation and luminescence properties of SrTiO3:Pr,Al phosphor from the glycolate method

Spherical SrTiO₃:Pr³⁺,Al³⁺ phosphor with high crystallinity and uniform particle size distribution was formed from the glycolate precursor. The glycolate precursor was obtained by heating the mixed solution of metallic nitrates and titanium oxychloride in ethylene glycol up to 200 °C. The thermal decomposition of the glycolate precursor proceeded through three major stages, i.e., (i) evolution of glycols (∼200 °C), (ii) decomposition of glycolate precursor, and (iii) decomposition of strontium carbonate and crystallization of SrTiO₃:Pr³⁺,Al³⁺ phosphor.SrTiO₃:Pr³⁺,Al³⁺ phosphor exhibited a strong red emission, peaking at about 617 nm. SrTiO₃:Pr³⁺,Al³⁺ phosphor obtained from the glycolate complex has higher luminescent properties than the conventional solid state reaction and the Pechini method in terms of photoluminescence (PL) and cathodoluminescence (CL). High crystallinity, low residual carbon content and small grain size with uniform shape would enhance the luminescence intensity of phosphor by the glycolate method due to high surface area per unit volume and low organic content compared with the Pechini method. Also, Al³⁺ ion is more effective than Ga³⁺ ion to enhance PL intensity of SrTiO₃:Pr³⁺,Al³⁺ phosphor because of smaller Al³⁺ ion radius. Therefore, the glycolate method has been demonstrated to be a convenient and unique process for the production of muticomponent oxide with smaller grain size and higher crystallinity compared with the conventional mixed oxide reaction and the polymer precursor method.     

Anomalies of ultrasonic velocity in high-Tc ceramics YBa2Cu3Oy and BiSrCaCu2Oy

Ultrasonic longitudinal velocity and adsorption have been measured in ceramic superconductors YBa₂Cu₃O_y with various porosity and also in BiSrCaCu₂O_y. A velocity drop of about 400 ppm was found at T_c only in the measurements on cooling. The magnitude of the velocity drop is anomalously large compared with the value expected from the thermodynamics. A hysteresis of velocity with respect to temperature was observed in all the samples studied. It is suggested that some structural change at pore size level is responsible for this phenomenon.     

Cross sections and transverse single-spin asymmetries in forward neutral-pion production from proton collisions at sqrt[s]=200 GeV

Measurements of the production of forward high-energy pi(0) mesons from transversely polarized proton collisions at sqrt[s]=200 GeV are reported. The cross section is generally consistent with next-to-leading order perturbative QCD calculations. The analyzing power is small at x(F) below about 0.3, and becomes positive and large at higher x(F), similar to the trend in data at sqrt[s]< or =20 GeV. The analyzing power is in qualitative agreement with perturbative QCD model expectations. This is the first significant spin result seen for particles produced with p(T)>1 GeV/c at a polarized proton collider.     

Search for CP violation in the decay B0-->D*+/-D-/+

We report a search for CP-violating asymmetry in B0-->D(*+/-)D-/+ decays. The analysis employs two methods of B0 reconstruction: full and partial. In the full reconstruction method all daughter particles of the B0 are required to be detected; the partial reconstruction technique requires a fully reconstructed D- and only a slow pion from the D(*+)-->D0pi(+)(slow) decay. From a fit to the distribution of the time interval corresponding to the distance between two B meson decay points we calculate the CP-violating parameters and find the significance of nonzero CP asymmetry to be 2.7 standard deviations.     

Orientation-dependent C60 electronic structures revealed by photoemission spectroscopy

We observe, with angle-resolved photoemission, a dramatic change in the electronic structure of two C60 monolayers, deposited, respectively, on Ag (111) and (100) substrates, and similarly doped with potassium to half filling of the C60 lowest unoccupied molecular orbital. The Fermi surface symmetry, the bandwidth, and the curvature of the dispersion at Gamma point are different. Orientations of the C60 molecules on the two substrates are known to be the main structural difference between the two monolayers, and we present new band-structure calculations for some of these orientations. We conclude that orientations play a key role in the electronic structure of fullerides.     

Measurement of nonrandom event-by-event fluctuations of average transverse momentum in square root of (sNN)=200 GeV Au+Au and p+p collisions

Event-by-event fluctuations of the average transverse momentum of produced particles near midrapidity have been measured by the PHENIX Collaboration in square root of (sNN)=200 GeV Au+Au, and p+p collisions at the Relativistic Heavy Ion Collider. The fluctuations are observed to be in excess of the expectation for statistically independent particle emission for all centralities. The excess fluctuations exhibit a dependence on both the centrality of the collision and on the pT range over which the average is calculated. Both the centrality and pT dependence can be well reproduced by a simulation of random particle production with the addition of contributions from hard-scattering processes.     

A possibility of parallel and anti-parallel diffraction measurements on neutron diffractometer employing bent perfect crystal monochromator at the monochromatic focusing condition

In a conventional diffractometer having single monochromator, only one position, parallel position, is used for the diffraction experiment (i.e. detection) because the resolution property of the other one, anti-parallel position, is very poor. However, a bent perfect crystal (BPC) monochromator at monochromatic focusing condition can provide a quite flat and equal resolution property at both parallel and anti-parallel positions and thus one can have a chance to use both sides for the diffraction experiment. From the data of the FWHM and the Δd/d measured on three diffraction geometries (symmetric, asymmetric compression and asymmetric expansion), we can conclude that the simultaneous diffraction measurement in both parallel and anti-parallel positions can be achieved.