743 research outputs found
Boundary conditions at spatial infinity for fields in Casimir calculations
The importance of imposing proper boundary conditions for fields at spatial
infinity in the Casimir calculations is elucidated.Comment: 8 pages, 1 figure, submitted to the Proceedings of The Seventh
Workshop QFEXT'05 (Barcelona, September 5-9, 2005
Skyrme-Random-Phase-Approximation description of E1 strength in 92-100Mo
The isovector dipole E1 strength in Mo isotopes with A=92,94,96,98,100 is
analyzed within the self-consistent separable random-phase approximation (SRPA)
model with Skyrme forces SkT6, SkM*, SLy6, and SkI3. The special attention is
paid to the low-energy region near the particle thresholds (4-12 MeV), which is
important for understanding of astrophysical processes. We show that, due to a
compensation effect, the influence of nuclear deformation on E1 strength below
10-12 MeV is quite modest. At the same time, in agreement with previous
predictions, the deformation increases the strength at higher energy. At 4-8
MeV the strength is mainly determined by the tail of E1 giant resonance. The
four Skyrme forces differ in description of the whole giant resonance but give
rather similar results below 12 MeV.Comment: 12 pages, 7 figures, to be published in Int. J. Mod. Phys. (E) as
contribution to Proceedings of 15th Nuclear Physics Workshop (Kazimierz,
Poland, 2008
New analytic running coupling in QCD: higher loop levels
The properties of the new analytic running coupling are investigated at the
higher loop levels. The expression for this invariant charge, independent of
the normalization point, is obtained by invoking the asymptotic freedom
condition. It is shown that at any loop level the relevant function has
the universal behaviors at small and large values of the invariant charge. Due
to this feature the new analytic running coupling possesses the universal
asymptotics both in the ultraviolet and infrared regions irrespective of the
loop level. The consistency of the model considered with the general definition
of the QCD invariant charge is shown.Comment: LaTeX 2.09, 12 pages with 5 EPS figures, uses mpla1.sty; enlarged
version is accepted for publication in Mod. Phys. Lett.
TDDFT with Skyrme Forces: Effect of Time-Odd Densities on Electric Giant Resonances
Time-odd densities and their effect on electric giant resonances are
investigated within the self-consistent separable random-phase-approximation
(SRPA) model for various Skyrme forces (SkT6, SkO, SkM*, SIII, SGII, SLy4,
SLy6, SkI3). Time-odd densities restore Galilean invariance of the Skyrme
functional, violated by the effective-mass and spin-orbital terms. In even-even
nuclei these densities do not contribute to the ground state but can affect the
dynamics. As a particular case, we explore the role of the current density in
description of isovector E1 and isoscalar E2 giant resonances in a chain of Nd
spherical and deformed isotopes with A=134-158. Relation of the current to the
effective masses and relevant parameters of the Skyrme functional is analyzed.
It is shown that current contribution to E1 and E2 resonances is generally
essential and fully determined by the values and signs of the isovector and
isoscalar effective-mass parameters of the force. The contribution is the same
for all the isotope chain, i.e. for both standard and exotic nuclei.Comment: 14 pages, 7 figures, will be published in Proceed. of 14th Nuclear
Physics Workshop (Kazimierez, Poland, September, 2007) Comment: latex error
in openning Fig. 2 was correcte
Self-Consistent Separable RPA For Density- and Current-Dependent Forces
Self-consistent factorization of two-body residual interaction is proposed
for arbitrary density- and current-dependent energy functionals. Following this
procedure, a separable RPA (SRPA) method is constructed. SRPA dramatically
simplifies the calculations and demonstrates quick convergence to exact
results. The method is tested for SkM* forces.Comment: 10 pages, 1 figure, contribution to Proceedings of 7th International
Spring Seminar on Nuclear Physics, Maiori, Italy, May 27-31, 200
Shock Wave Structure in a Strongly Nonlinear Granular Lattice with Viscous Dissipation
The shock wave structure in a one-dimensional lattice (e.g. granular chain)
with a power law dependence of force on displacement between particles with
viscous dissipation is considered and compared to the corresponding long wave
approximation. A dissipative term depending on the relative velocity between
neighboring particles is included in the discrete model to investigate its
influence on the shape of steady shock profiles. The critical viscosity
coefficient is obtained from the long-wave approximation for arbitrary values
of the exponent n and denotes the transition from an oscillatory to a monotonic
shock profile in stronly nonlinear systems. The expression for the critical
viscosity coefficient converges to the known equation for the critical
viscosity in the weakly nonlinear case. Values of viscosity based on this
expression are comparable to the values obtained in the numerical analysis of a
discrete particle lattice with a Herzian contact interaction corresponding to n
= 3/2. An initial disturbance in a discrete system approaches a stationary
shock profile after traveling a short distance that is comparable to the width
of the leading pulse of a stationary shock front. The shock front width is
minimized when the viscosity is equal to its critical value.Comment: 20 pages, 6 figure
How Hertzian solitary waves interact with boundaries in a 1-D granular medium
We perform measurements, numerical simulations, and quantitative comparisons
with available theory on solitary wave propagation in a linear chain of beads
without static preconstrain. By designing a nonintrusive force sensor to
measure the impulse as it propagates along the chain, we study the solitary
wave reflection at a wall. We show that the main features of solitary wave
reflection depend on wall mechanical properties. Since previous studies on
solitary waves have been performed at walls without these considerations, our
experiment provides a more reliable tool to characterize solitary wave
propagation. We find, for the first time, precise quantitative agreements.Comment: Proof corrections, ReVTeX, 11 pages, 3 eps (Focus and related papers
on http://www.supmeca.fr/perso/jobs/
Solitary and shock waves in discrete double power-law materials
A novel strongly nonlinear laminar metamaterial supporting new types of
solitary and shock waves with impact energy mitigating capabilities is
presented. It consists of steel plates with intermittent polymer toroidal rings
acting as strongly nonlinear springs with large allowable strain. Their
force-displacement relationship is described by the addition of two power-law
relationships resulting in a solitary wave speed and width depending on the
amplitude. This double nonlinearity allows splitting of an initial impulse into
two separate strongly nonlinear solitary wave trains. Solitary and shock waves
are observed experimentally and analyzed numerically in an assembly with Teflon
o-rings.Comment: 14 pages, 6 figure
Pairing and deformation effects in nuclear excitation spectra
We investigate effects of pairing and of quadrupole deformation on two sorts
of nuclear excitations,-vibrational states and dipole
resonances (isovector dipole, pygmy, compression, toroidal). The analysis is
performed within the quasiparticle random-phase approximation (QRPA) based on
the Skyrme energy functional using the Skyrme parametrization SLy6. Particular
attention is paid to i) the role of the particle-particle (pp) channel in the
residual interaction of QRPA, ii) comparison of volume pairing (VP) and surface
pairing (SP), iii) peculiarities of deformation splitting in the various
resonances. We find that the impact of the pp-channel on the considered
excitations is negligible. This conclusion applies also to any other excitation
except for the states. Furthermore, the difference between VP and
SP is found small (with exception of peak height in the toroidal mode). In the
low-energy isovector dipole (pygmy) and isoscalar toroidal modes, the branch
is shown to dominate over one in the range of
excitation energy 8--10 MeV. The effect becomes impressive for the
toroidal resonance whose low-energy part is concentrated in a high peak of
almost pure nature. This peculiarity may be used as a fingerprint
of the toroidal mode in future experiments. The interplay between pygmy,
toroidal and compression resonances is discussed, the interpretation of the
observed isoscalar giant dipole resonance is partly revised.Comment: 12 pages, 12 figure
Momentum distribution in heavy deformed nuclei: role of effective mass
The impact of nuclear deformation on the momentum distributions (MD) of
occupied proton states in U is studied with a phenomenological
Woods-Saxon (WS) shell model and the self-consistent Skyrme-Hartree-Fock (SHF)
scheme. Four Skyrme parameterizations (SkT6, SkM*, SLy6, SkI3) with different
effective masses are used. The calculations reveal significant deformation
effects in the low-momentum domain of states, mainly of
those lying near the Fermi surface. For other states, the deformation effect on
MD is rather small and may be neglected. The most remarkable result is that the
very different Skyrme parameterizations and the WS potential give about
identical MD. This means that the value of effective mass, being crucial for
the description of the spectra, is not important for the spatial shape of the
wave functions and thus for the MD. In general, it seems that, for the
description of MD at MeV/c, one may use any single-particle
scheme (phenomenological or self-consistent) fitted properly to the global
ground state properties.Comment: 14 pages, 6 figure
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