177 research outputs found
On scission configuration in ternary fission
A static scission configuration in cold ternary fission has been considered
in the framework of two mean field approaches. The virial theorems has been
suggested to investigate correlations in the phase space, starting from a
kinetic equation. The inverse mean field method is applied to solve
single-particle Schredinger equation, instead of constrained selfconsistent
Hartree-Fock equations. It is shown, that it is possible to simulate
one-dimensional three-center system via inverse scattering method in the
approximation of reflectless single-particle potentialsComment: 11 pages, 1 figure, Fusion Dynamics at the Extremes, Int. Workshop,
Dubna, Russia, May 2000. To be published in World Scientifi
Accuracy of BCS-based approximations for pairing in small Fermi systems
We analyze the accuracy of BCS-based approximations for calculating
correlation energies and odd-even energy differences in 2-component fermionic
systems with a small number of pairs. The analysis is focused on comparing BCS
and projected BCS treatments with the exact solution of the pairing
Hamiltonian, considering parameter ranges appropriate for nuclear pairing
energies. We find that the projected BCS is quite accurate over the entire
range of coupling strengths in spaces of up to about 20 doubly degenerate
orbitals. It is also quite accurate for two cases we considered with a more
realistic Hamiltonian, representing the nuclei around 117Sn and 207Pb. However,
the projected BCS significantly underestimates the energies for much larger
spaces when the pairing is weak.Comment: 10 pages; 14 figure
Ternary configuration in the framework of inverse mean-field method
A static scission configuration in cold ternary fission has been considered
in the framework of mean field approach. The inverse scattering method is
applied to solve single-particle Schroedinger equation, instead of constrained
selfconsistent Hartree-Fock equations. It is shown, that it is possible to
simulate one-dimensional three-center system via inverse scattering method in
the approximation of reflectless single-particle potentials.Comment: 8 pages, 1 figure, iopart.cls, to be published in Int.J.Mod.Phys.
Collective excitations in the inner crust of neutron stars : supergiant resonances
We investigate the nuclear collective excitations of Wigner-Seitz cells
containing nuclear clusters immersed in a gas of neutrons. This baryonic
non-uniform system is specific to the structure of inner crust matter of
neutron stars. The collective excitations are studied in the framework of a
spherical Hartree-Fock-Bogoliubov + Quasiparticle Random Phase Approximation,
formulated in coordinate representation. The calculations are done for two
representative Wigner-Seitz cells with baryonic density equal to 0.02 fm
and 0.08 fm. It is shown that the excitations with low multipolarities
are concentrated almost entirely in one strongly collective mode which exhausts
a very large fraction of the energy-weighted sum rule. Since these collective
modes are located at very low energies compared to the giant resonances in
standard nuclei, they may affect significantly the specific heat of baryonic
inner crust matter of neutron stars.Comment: 6 pages, 4 figure
Generalized seniority scheme in light Sn isotopes
The yrast generalized seniority states are compared with the corresponding
shell model states for the case of the Sn isotopes Sn. For most of
the cases the energies agree within 100 keV and the overlaps of the wave
functions are greater than 0.7.Comment: 8 pages, revtex. Submitted to Phys. Rev.
Detecting Singleton Review Spammers Using Semantic Similarity
Online reviews have increasingly become a very important resource for
consumers when making purchases. Though it is becoming more and more difficult
for people to make well-informed buying decisions without being deceived by
fake reviews. Prior works on the opinion spam problem mostly considered
classifying fake reviews using behavioral user patterns. They focused on
prolific users who write more than a couple of reviews, discarding one-time
reviewers. The number of singleton reviewers however is expected to be high for
many review websites. While behavioral patterns are effective when dealing with
elite users, for one-time reviewers, the review text needs to be exploited. In
this paper we tackle the problem of detecting fake reviews written by the same
person using multiple names, posting each review under a different name. We
propose two methods to detect similar reviews and show the results generally
outperform the vectorial similarity measures used in prior works. The first
method extends the semantic similarity between words to the reviews level. The
second method is based on topic modeling and exploits the similarity of the
reviews topic distributions using two models: bag-of-words and
bag-of-opinion-phrases. The experiments were conducted on reviews from three
different datasets: Yelp (57K reviews), Trustpilot (9K reviews) and Ott dataset
(800 reviews).Comment: 6 pages, WWW 201
Nuclear Pairing: Surface or Bulk ?
We analyse how the spatial localisation properties of pairing correlations
are changing in a major neutron shell of heavy nuclei. It is shown that the
radial distribution of the pairing density depends strongly on whether the
chemical potential is close to a low or a high angular momentum level and has
very little sensitivity to whether the pairing force acts in the surface or in
the bulk. The averaged pairing density over one major shell is however rather
flat, practically independent of the pairing force. Hartree-Fock-Bogoliubov
calculations for the isotopic chain Sn are presented for
demonstration purposes.Comment: 12 pages, 5 figure
Temperature dependent BCS equations with continuum coupling
The temperature dependent BCS equations are modified in order to include the
contribution of the continuum single particle states. The influence of the
continuum upon the critical temperature corresponding to the phase transition
from a superfluid to a normal state and upon the behaviour of the excitation
energy and of the entropy is discussed.Comment: 9 pages, 3 figures, to appear in Phys. Rev.
A New Nonlinear Liquid Drop Model. Clusters as Solitons on The Nuclear Surface
By introducing in the hydrodynamic model, i.e. in the hydrodynamic equations
and the corresponding boundary conditions, the higher order terms in the
deviation of the shape, we obtain in the second order the Korteweg de Vries
equation (KdV). The same equation is obtained by introducing in the liquid drop
model (LDM), i.e. in the kinetic, surface and Coulomb terms, the higher terms
in the second order. The KdV equation has the cnoidal waves as steady-state
solutions. These waves could describe the small anharmonic vibrations of
spherical nuclei up to the solitary waves. The solitons could describe the
preformation of clusters on the nuclear surface. We apply this nonlinear liquid
drop model to the alpha formation in heavy nuclei. We find an additional
minimum in the total energy of such systems, corresponding to the solitons as
clusters on the nuclear surface. By introducing the shell effects we choose
this minimum to be degenerated with the ground state. The spectroscopic factor
is given by the ratio of the square amplitudes in the two minima.Comment: 27 pages, LateX, 8 figures, Submitted J. Phys. G: Nucl. Part. Phys.,
PACS: 23.60.+e, 21.60.Gx, 24.30.-v, 25.70.e
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