727 research outputs found
Comment on ``Theory of Spinodal Decomposition''
I comment on a paper by S. B. Goryachev [PRL vol 72, p.1850 (1994)] that
presents a theory of non-equilibrium dynamics for scalar systems quenched into
an ordered phase. Goryachev incorrectly applies only a global conservation
constraint to systems with local conservation laws.Comment: 2 pages LATeX (REVTeX macros), no figures. REVISIONS --- more to the
point. microscopic example added, presentation streamlined, long-range
interactions mentioned, to be published in Phys. Rev. Let
The s-process branching at 185W
The neutron capture cross section of the unstable nucleus 185W has been
derived from experimental photoactivation data of the inverse reaction
186W(gamma,n)185W. The new result of sigma = (687 +- 110) mbarn confirms the
theoretically predicted neutron capture cross section of 185W of sigma = 700
mbarn at kT = 30 keV. A neutron density in the classical s-process of n_n =
(3.8 +0.9 -0.8} * 1e8 cm-3 is derived from the new data for the 185W branching.
In a stellar s-process model one finds a significant overproduction of the
residual s-only nucleus 186Os.Comment: ApJ, in pres
Re(\gamm,n) cross section close to and above the neutron threshold
The neutron capture cross section of the unstable nucleus Re is
studied by investigating the inverse photodisintegration reaction
Re(,n). The special interest of the {\it s}-process branching
point Re is related to the question of possible {\it s}-process
contributions to the abundance of the {\it r}-process chronometer nucleus
^{187}^{186}\gamma^{186}$Os; the two predicted neutron-capture cross sections
differ by a factor of 2.4; this calls for future theoretical study.Comment: Phys. Rev. C, in pres
Non-equilibrium Phase-Ordering with a Global Conservation Law
In all dimensions, infinite-range Kawasaki spin exchange in a quenched Ising
model leads to an asymptotic length-scale
at because the kinetic coefficient is renormalized by the broken-bond
density, . For , activated kinetics recovers the
standard asymptotic growth-law, . However, at all temperatures,
infinite-range energy-transport is allowed by the spin-exchange dynamics. A
better implementation of global conservation, the microcanonical Creutz
algorithm, is well behaved and exhibits the standard non-conserved growth law,
, at all temperatures.Comment: 2 pages and 2 figures, uses epsf.st
On integrable system on with the second integral quartic in the momenta
We consider integrable system on the sphere with an additional integral
of fourth order in the momenta. At the special values of parameters this system
coincides with the Kowalevski-Goryachev-Chaplygin system.Comment: LaTeX, 6 page
Skyrme-Rpa Description of Dipole Giant Resonance in Heavy and Superheavy Nuclei
The E1(T=1) isovector dipole giant resonance (GDR) in heavy and super-heavy
deformed nuclei is analyzed over a sample of 18 rare-earth nuclei, 4 actinides
and three chains of super-heavy elements (Z=102, 114 and 120). Basis of the
description is self-consistent separable RPA (SRPA) using the Skyrme force
SLy6. The self-consistent model well reproduces the experimental data (energies
and widths) in the rare-earth and actinide region. The trend of the resonance
peak energies follows the estimates from collective models, showing a bias to
the volume mode for the rare-earths isotopes and a mix of volume and surface
modes for actinides and super-heavy elements. The widths of the GDR are mainly
determined by the Landau fragmentation which in turn is found to be strongly
influenced by deformation. A deformation splitting of the GDR can contribute
about one third to the width and about 1 MeV further broadening can be
associated to mechanism beyond the mean-field description (escape, coupling
with complex configurations).Comment: 9 pages, 12 figures, 2 table
Density-of-states picture and stability of ferromagnetism in the highly-correlated Hubbard model
The problem of stability of saturated and non-saturated ferromagnetism in the
Hubbard model is considered in terms of the one-particle Green's functions.
Approximations by Edwards and Hertz and some versions of the self-consistent
approximations based on the 1/z-expansion are considered. The account of
longitudinal fluctuations turns out to be essential for description of the
non-saturated state. The corresponding pictures of density of states are
obtained. "Kondo" density-of-states singularities owing to spin-flip processes
are analyzed. The critical electron concentrations for instabilities of
saturated ferromagnetism and paramagnetic state are calculated for various
lattices. Drawbacks of various approximations are discussed. A comparison with
the results of previous works is performed.Comment: 16 pages, 7 eps figure
Spherical model of the Stark effect in external scalar and vector fields
The Bohr-Sommerfeld quantization rule and the Gamow formula for the width of
quasistationary level are generalized by taking into account the relativistic
effects, spin and Lorentz structure of interaction potentials. The relativistic
quasi-classical theory of ionization of the Coulomb system (V_{Coul}=-\xi/r) by
radial-constant long-range scalar (S_{l.r.}=(1-\lambda)(\sigma r+V_0)) and
vector (V_{l.r.}=\lambda(\sigma r+V_0)) fields is constructed. In the limiting
cases the approximated analytical expressions for the position E_r and width
\Gamma of below-barrier resonances are obtained. The strong dependence of the
width \Gamma of below-barrier resonances on both the bound level energy and the
mixing constant \lambda is detected. The simple analytical formulae for
asymptotic coefficients of the Dirac radial wave functions at zero and infinity
are also obtained.Comment: 25 pages, 4 figures. Submitted to Int. J. Mod. Phys.
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