12,002 research outputs found
Superconducting Gap Nodal Surface and Fermi Surface: their partial overlap in cuprates
Electron correlation in cuprates leads to a global constraint on the gap function resulting in a gap
nodal surface. We give physical arguments supported by numerical results and
discuss some experimental results to argue that correlations also lead to a
local constraint on charge fluctuations in -space close to the Fermi
surface, which may result in a substantial overlap of the Fermi surface with
the gap nodal surface.Comment: RevTeX 3.0, 4 Pages, 6 PostScript Figures
Modified Bethe-Weizsacker mass formula with isotonic shift and new driplines
Nuclear masses are calculated using the modified Bethe-Weizsacker mass
formula in which the isotonic shifts have been incorporated. The results are
compared with the improved liquid drop model with isotonic shift. Mass excesses
predicted by this method compares well with the microscopic-macroscopic model
while being much more simple. The neutron and proton drip lines have been
predicted using this modified Bethe-Weizsacker mass formula with isotonic
shifts.Comment: 9 pages including 2 figure
Productivity Growth in the 1990s: Technology, Utilization, or Adjustment?
Measured productivity growth increased substantially during the second half of the 1990s. This paper examines whether this increase owes to an increase in the rate of technological change or whether it can be explained by non-technological factors relating to factor utilization, factor accumulation, or returns to scale. It finds that the recent increase in productivity growth does appear to arise from an increase in technological change. Cyclical utilization raised measured productivity growth relative to technology growth in the first part of the expansion, but lowered it subsequently. Factor adjustment leads to a steady-state understatement of technology growth by measured productivity growth. The understatement was greater in the second half of the expansion than the first. Changes in the distribution of inputs across industries with different returns to scale lead to a modest understatement in the growth in technology. Although the increase technological change is most pronounced in durable manufacturing, technological change also increased outside of manufacturing.
Productivity growth in the 1990s: technology, utilization, or adjustment
Measured productivity growth increased substantially during the second half of the 1990s. This paper examines whether this increase owes to an increase in the rate of technological change or whether it can be explained by non-technological factors relating to factor utilization, factor accumulation, or returns to scale. It finds that the recent increase in productivity growth does appear to arise from an increase in technological change. Cyclical utilization raised measured productivity growth relative to technology growth in the first part of the expansion, but lowered it subsequently. Factor adjustment leads to a steady-state understatement of technology growth by measured productivity growth. The understatement was greater in the second half of the expansion than the first. Changes in the distribution of inputs across industries with different returns to scale lead to a modest understatement in the growth in technology. Although the increase technological change is most pronounced in durable manufacturing, technological change also increased outside of manufacturing.Productivity ; Technology ; Manufactures
Folding model analysis of proton radioactivity of spherical proton emitters
Half lives of the decays of spherical nuclei away from proton drip line by
proton emissions are estimated theoretically. The quantum mechanical tunneling
probability is calculated within the WKB approximation. Microscopic
proton-nucleus interaction potentials are obtained by single folding the
densities of the daughter nuclei with M3Y effective interaction supplemented by
a zero-range pseudo-potential for exchange along with the density dependence.
Strengths of the M3Y interaction are extracted by fitting its matrix elements
in an oscillator basis to those elements of the G-matrix obtained with the
Reid-Elliott soft-core nucleon-nucleon interaction. Parameters of the density
dependence are obtained from the nuclear matter calculations. Spherical charge
distributions are used for calculating the Coulomb interaction potentials.
These calculations provide reasonable estimates for the observed proton
radioactivity lifetimes of proton rich nuclei for proton emissions from 26
ground and isomeric states of spherical proton emitters.Comment: 6 page
Equation of state for nuclear matter based on density dependent effective interaction
An interesting method of obtaining equation of state for nuclear matter, from
a density dependent M3Y interaction, by minimizing the energy per nucleon is
described. The density dependence parameters of the interaction are obtained by
reproducing the saturation energy per nucleon and the saturation density of
spin and isospin symmetric cold infinite nuclear matter. The nuclear matter
equation of state thus obtained is then used to calculate the pressure, the
energy density, the nuclear incompressibility and the velocity of sound in
nuclear medium. The results obtained are in good agreement with experimental
data and provide a unified description of radioactivity, scattering and nuclear
matter.Comment: 10 pages including 2 figure
Testing equality of variances in the analysis of repeated measurements
The problem of comparing the precisions of two instruments using repeated measurements can be cast as an extension of the Pitman-Morgan problem of testing equality of variances of a bivariate normal distribution. Hawkins (1981) decomposes the hypothesis of equal variances in this model into two subhypotheses for which simple tests exist. For the overall hypothesis he proposes to combine the tests of the subhypotheses using Fisher's method and empirically compares the component tests and their combination with the likelihood ratio test. In this paper an attempt is made to resolve some discrepancies and puzzling conclusions in Hawkins's study and to propose simple modifications.\ud
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The new tests are compared to the tests discussed by Hawkins and to each other both in terms of the finite sample power (estimated by Monte Carlo simulation) and theoretically in terms of asymptotic relative efficiencies
High Superconductivity, Skyrmions and the Berry Phase
It is here pointed out that the antiferromagnetic spin fluctuation may be
associated with a gauge field which gives rise to the antiferromagnetic ground
state chirality. This is associated with the chiral anomaly and Berry phase
when we consider the two dimensional spin system on the surface of a 3D sphere
with a monopole at the centre. This realizes the RVB state where spinons and
holons can be understood as chargeless spins and spinless holes attached with
magnetic flux. The attachment of the magnetic flux of the charge carrier
suggest, that this may be viewed as a skyrmion. The interaction of a massless
fermion representing a neutral spin with a gauge field along with the
interaction of a spinless hole with the gauge field enhances the
antiferromagnetic correlation along with the pseudogap at the underdoped
region. As the doping increases the antiferromagnetic long range order
disappears for the critical doping parameter . In this framework,
the superconducting pairing may be viewed as caused by skyrmion-skyrmion bound
states.Comment: 10 pages, accepted in Phys. Rev.
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