5,966 research outputs found
Effects of particle-number conservation on heat capacity of nuclei
By applying the particle-number projection to the finite-temperature BCS
theory, the -shaped heat capacity, which has recently been claimed to be a
fingerprint of the superfluid-to-normal phase transition in nuclei, is
reexamined. It is found that the particle-number (or number-parity) projection
gives -shapes in the heat capacity of nuclei which look qualitatively
similar to the observed ones. These -shapes are accounted for as effects of
the particle-number conservation on the quasiparticle excitations, and occur
even when we keep the superfluidity at all temperatures by assuming a constant
gap in the BCS theory. The present study illustrates significance of the
conservation laws in studying phase transitions of finite systems.Comment: RevTeX4, 12 pages including 5 figures (1 color figure), to be
published in PR
RPA calculations with Gaussian expansion method
The Gaussian expansion method (GEM) is extensively applied to the
calculations in the random-phase approximation (RPA). We adopt the
mass-independent basis-set that has been tested in the mean-field calculations.
By comparing the RPA results with those obtained by several other available
methods for Ca isotopes, using a density-dependent contact interaction and the
Woods-Saxon single-particle states, we confirm that energies, transition
strengths and widths of their distribution are described by the GEM bases to
good precision, for the , and collective states. The GEM is
then applied to the self-consistent RPA calculations with the finite-range
Gogny D1S interaction. The spurious center-of-mass motion is well separated
from the physical states in the response, and the energy-weighted sum
rules for the isoscalar transitions are fulfilled reasonably well. Properties
of low-energy transitions in Ca are argued in some detail.Comment: 30 pages including 12 figure
Can realistic interaction be useful for nuclear mean-field approaches?
Recent applications of the M3Y-type semi-realistic interaction to the nuclear
mean-field approaches are presented: (i) Prediction of magic numbers and (ii)
isotope shifts of nuclei with magic proton numbers. The results exemplify that
realistic interaction, which is derived from the base and
interaction, furnish a new theoretical instrument for advancing nuclear
mean-field approaches.Comment: 9 pages including 6 figures, published in EPJA 52, 185 (2016
New Bardeen-Cooper-Schrieffer-type theory at finite temperature with particle-number conservation
We formulate a new Bardeen-Cooper-Schrieffer (BCS)-type theory at finite
temperature, by deriving a set of variational equations of the free energy
after the particle-number projection. With its broad applicability, this theory
can be a useful tool for investigating the pairing phase transition in finite
systems with the particle-number conservation. This theory provides effects of
the symmetry-restoring fluctuation (SRF) for the pairing phenomena in finite
fermionic systems, distinctively from those of additional quantum fluctuations.
It is shown by numerical calculations that the phase transition is compatible
with the conservation in this theory, and that the SRF shifts up the critical
temperature (). This shift of occurs due to
reduction of degrees-of-freedom in canonical ensembles, and decreases only
slowly as the particle-number increases (or as the level spacing narrows), in
contrast to the conventional BCS theory.Comment: 10 pages including 3 figures, to be published in Phys. Rev.
Controlling edge states of zigzag carbon nanotubes by the Aharonov-Bohm flux
It has been known theoretically that localized states exist around zigzag
edges of a graphite ribbon and of a carbon nanotube, whose energy eigenvalues
are located between conduction and valence bands. We found that in metallic
single-walled zigzag carbon nanotubes two of the localized states become
critical, and that their localization length is sensitive to the mean curvature
of a tube and can be controlled by the Aharonov-Bohm flux. The curvature
induced mini-gap closes by the relatively weak magnetic field. Conductance
measurement in the presence of the Aharonov-Bohm flux can give information
about the curvature effect and the critical states.Comment: 5 pages, 4 figure
Binomial level densities
It is shown that nuclear level densities in a finite space are described by a
continuous binomial function, determined by the first three moments of the
Hamiltonian, and the dimensionality of the underlying vector space.
Experimental values for Mn, Fe, and Ni are very well
reproduced by the binomial form, which turns out to be almost perfectly
approximated by Bethe's formula with backshift. A proof is given that binomial
densities reproduce the low moments of Hamiltonians of any rank: A strong form
of the famous central limit result of Mon and French. Conditions under which
the proof may be extended to the full spectrum are examined.Comment: 4 pages 2 figures Second version (previous not totally superseeded
Interstellar extinction in the open clusters towards galactic longitude around 130 degrees
In this paper we present a detailed study of the intra-cluster reddening material in the young open clusters located around using colour-excess diagrams and two-colour diagrams. The study supports the universality of the extinction curves for , whereas for shorter wavelengths the curve depends upon the value of the (total-to-selective absorption in the cluster region). The value of in the case of NGC 654, NGC 869 and NGC 884 is found to be normal, whereas the value of in the cluster regions NGC 1502 and IC 1805 indicates an anomalous reddening law in these regions. It is also found that the extinction process in the band in the case of NGC 663 seems to be less efficient, whereas in the case of NGC 869 the process is more efficient
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