6,806 research outputs found
Pairing effect on the giant dipole resonance width at low temperature
The width of the giant dipole resonance (GDR) at finite temperature T in
Sn-120 is calculated within the Phonon Damping Model including the neutron
thermal pairing gap determined from the modified BCS theory. It is shown that
the effect of thermal pairing causes a smaller GDR width at T below 2 MeV as
compared to the one obtained neglecting pairing. This improves significantly
the agreement between theory and experiment including the most recent data
point at T = 1 MeV.Comment: 8 pages, 5 figures to be published in Physical Review
The hyperon mean free paths in the relativistic mean field
The - and -hyperon mean free paths in nuclei are firstly
calculated in the relativistic mean field (RMF) theory. The real parts of the
optical potential are derived from the RMF approach, while the imaginary parts
are obtained from those of nucleons with the relations:
and . With the
assumption, the depth of the imaginary potential for is
3.5 MeV, and for is 7 MeV at
low incident energy. We find that, the hyperon mean free path decreases with
the increase of the hyperon incident energies, from 200 MeV to 800 MeV; and in
the interior of the nuclei, the mean free path is about fm for
, and about fm for , depending on the hyperon
incident energy.Comment: 5 figures, 6 page
Model-based clustering and classification using mixtures of multivariate skewed power exponential distributions
Families of mixtures of multivariate power exponential (MPE) distributions
have been previously introduced and shown to be competitive for cluster
analysis in comparison to other elliptical mixtures including mixtures of
Gaussian distributions. Herein, we propose a family of mixtures of multivariate
skewed power exponential distributions to combine the flexibility of the MPE
distribution with the ability to model skewness. These mixtures are more robust
to variations from normality and can account for skewness, varying tail weight,
and peakedness of data. A generalized expectation-maximization approach
combining minorization-maximization and optimization based on accelerated line
search algorithms on the Stiefel manifold is used for parameter estimation.
These mixtures are implemented both in the model-based clustering and
classification frameworks. Both simulated and benchmark data are used for
illustration and comparison to other mixture families
A Unified Quantum NOT Gate
We study the feasibility of implementing a quantum NOT gate (approximate)
when the quantum state lies between two latitudes on the Bloch's sphere and
present an analytical formula for the optimized 1-to- quantum NOT gate. Our
result generalizes previous results concerning quantum NOT gate for a quantum
state distributed uniformly on the whole Bloch sphere as well as the phase
covariant quantum state. We have also shown that such 1-to- optimized NOT
gate can be implemented using a sequential generation scheme via matrix product
states (MPS)
Inelastic nucleon contributions in nuclear response functions
We estimate the contribution of inelastic nucleon excitations to the
inclusive cross section in the CEBAF kinematic range.
Calculations are based upon parameterizations of the nucleon structure
functions measured at SLAC. Nuclear binding effects are included in a
vector-scalar field theory, and are assumed have a minimal effect on the
nucleon excitation spectrum. We find that for q\lsim 1 GeV the elastic and
inelastic nucleon contributions to the nuclear response functions are
comparable, and can be separated, but with roughly a factor of two uncertainty
in the latter from the extrapolation from data. In contrast, for q\rsim 2 GeV
this uncertainty is greatly reduced but the elastic nucleon contribution is
heavily dominated by the inelastic nucleon background.Comment: 20 pages, 7 figures available from the authors at Department of
Physics and Astronomy, University of Rochester, Rochester NY 1462
Surfaces of Revolution with Constant Gaussian Curvature in Four-Space
In this paper, we show that the constant property of the Gaussian curvature
of surfaces of revolution in both and depend only
on the radius of rotation. We then give necessary and sufficient conditions for
the Gaussian curvature of the general rotational surfaces whose meridians lie
in two dimensional planes in to be constant, and define the
parametrization of the meridians when both the Gaussian curvature is constant
and the rates of rotation are equal.Comment: 8 paper
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