34 research outputs found
Anisotropy of Vortex-Liquid and Vortex-Solid Phases in Single Crystals of BiSrCaCuO: Violation of the Scaling Law
The vortex-liquid and vortex-solid phases in single crystals of
BiSrCaCuO placed in tilted magnetic fields are studied
by in-plane resistivity measurements using the Corbino geometry to avoid
spurious surface barrier effects. It was found that the anisotropy of the
vortex-solid phase increases with temperature and exhibits a maximum at
. In contrast, the anisotropy of the vortex-liquid rises
monotonically across the whole measured temperature range. The observed
behavior is discussed in the context of dimensional crossover and thermal
fluctuations of vortices in the strongly layered system.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
An attempt to understand exclusive pi+ electroproduction
Hard exclusive pi+ electroproduction is investigated within the handbag
approach. The prominent role of the pion-pole contribution is demonstrated. It
is also shown that the experimental data require a twist-3 effect which ensues
from the helicity-flip generalized parton distribution H_T and the twist-3 pion
wave function. The results calculated from this handbag approach are compared
in detail with the experimental data on cross sections and spin asymmetries
measured with a polarized target. It is also commented on consequences of this
approach for exclusive \pi^0 and vector-meson electroproduction.Comment: 35 pages, 12 figures, using Latex, a number of additional comments
have been included in the text, e.g. in paragraph above (3) or at end of
sect.
Physical property characterization of single step synthesized NdFeAsO0.80F0.20 bulk 50K superconductor
We report an easy single step synthesis route of title compound
NdFeAsO0.80F0.20 superconductor having bulk superconductivity below 50 K. The
title compound is synthesized via solid-state reaction route by encapsulation
in an evacuated (10-3 Torr) quartz tube. Rietveld analysis of powder X-ray
diffraction data shows that compound crystallized in tetragonal structure with
space group P4/nmm. R(T)H measurements showed superconductivity with Tc (R=0)
at 48 K and a very high upper critical field (Hc2) of up to 345 Tesla. Magnetic
measurements exhibited bulk superconductivity in terms of diamagnetic onset
below 50 K. The lower critical field (Hc1) is around 1000 Oe at 5 K. In normal
state i.e., above 60 K, the compound exhibited purely paramagnetic behavior and
thus ruling out the presence of any ordered FeOx impurity in the matrix. In
specific heat measurements a jump is observed in the vicinity of
superconducting transition (Tc) along with an upturn at below T=4 K due to the
AFM ordering of Nd+3 ions in the system. The Thermo-electric power (TEP) is
negative down to Tc, thus indicating dominant carriers to be of n-type in
NdFeAsO0.80F0.20 superconductor. The granularity of the bulk superconducting
NdFeAsO0.8F0.2 sample is investigated and the intra and inter grain
contributions have been individuated by looking at various amplitude and
frequencies of the applied AC drive magnetic field.Comment: 26pages text + Figures: comments/suggestions welcome
([email protected] & http://www.freewebs.com/vpsawana
High-dimensional maximum marginal likelihood item factor analysis by adaptive quadrature
Although the Bock–Aitkin likelihood-based estimation method for factor analysis of dichotomous item response data has important advantages over classical analysis of item tetrachoric correlations, a serious limitation of the method is its reliance on fixed-point Gauss-Hermite (G-H) quadrature in the solution of the likelihood equations and likelihood-ratio tests. When the number of latent dimensions is large, computational considerations require that the number of quadrature points per dimension be few. But with large numbers of items, the dispersion of the likelihood, given the response pattern, becomes so small that the likelihood cannot be accurately evaluated with the sparse fixed points in the latent space. In this paper, we demonstrate that substantial improvement in accuracy can be obtained by adapting the quadrature points to the location and dispersion of the likelihood surfaces corresponding to each distinct pattern in the data. In particular, we show that adaptive G-H quadrature, combined with mean and covariance adjustments at each iteration of an EM algorithm, produces an accurate fast-converging solution with as few as two points per dimension. Evaluations of this method with simulated data are shown to yield accurate recovery of the generating factor loadings for models of upto eight dimensions. Unlike an earlier application of adaptive Gibbs sampling to this problem by Meng and Schilling, the simulations also confirm the validity of the present method in calculating likelihood-ratio chi-square statistics for determining the number of factors required in the model. Finally, we apply the method to a sample of real data from a test of teacher qualifications.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43596/1/11336_2003_Article_1141.pd
Measurements of the t(t)Overbar charge asymmetry using the dilepton decay channel in pp collisions at root s=7 TeV
The tt¯ charge asymmetry in proton-proton collisions at s√ = 7 TeV is measured using the dilepton decay channel (ee, e μ , or μμ ). The data correspond to a total integrated luminosity of 5.0 fb −1 , collected by the CMS experiment at the LHC. The tt and lepton charge asymmetries, defined as the differences in absolute values of the rapidities between the reconstructed top quarks and antiquarks and of the pseudorapidities between the positive and negative leptons, respectively, are measured to be A C = −0 . 010 ± 0 . 017 (stat . ) ± 0 . 008 (syst . ) and AlepC = 0 . 009 ± 0 . 010 (stat . ) ± 0 . 006 (syst . ). The lepton charge asymmetry is also measured as a function of the invariant mass, rapidity, and transverse momentum of the tt¯ system. All measurements are consistent with the expectations of the standard model
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Survey and preliminary evaluation of potential geothermal energy applications for Riverside, California
A preliminary assessment of the potential applications for geothermal energy in Riverside, California, was made. This assessment includes both potential electrical and non-electrical applications, and focuses on the following factors: the location of nearby geothermal resources; characteristics of these resources; types of applications suited to each resource; technical and economic feasibility of these applications; the potential impact on the energy demand of each application, and potential deterrents to the utilization of geothermal energy for the most promising application. It is concluded that geothermal energy has a promising potential to supply electricity, space heating and cooling, and process heat to Riverside. There are sufficient geothermal resources within 200 miles to supply the electrical requirements of Riverside for thousands of years. Depending on the particular reservoir involved, this electricity can probably be generated at costs ranging from 1 to 3 times the cost of conventional electric power generation. Over this distance, the additional unit cost for energy transmission should be comparatively small. The geothermal resource at nearby Arrowhead Hot Springs has the potential to supply space heating and cooling and process heat to Riverside for a hundred years. The technology for these non-electric uses is available. The cost of using geothermal energy for these applications is estimated at 1 to 2 times the cost of conventional fuels, depending on the population density of the service area. The most difficult problems in the possible use of geothermal energy in Riverside appear to be institutional difficulties in electric applications