466 research outputs found
Higher-Order Calculus of Variations on Time Scales
We prove a version of the Euler-Lagrange equations for certain problems of
the calculus of variations on time scales with higher-order delta derivatives.Comment: Corrected minor typo
Intermediate valence behavior in CeCo9Si4
The novel ternary compound CeCoSi has been studied by means of
specific heat, magnetisation, and transport measurements. Single crystal X-ray
Rietveld refinements reveal a fully ordered distribution of Ce, Co and Si atoms
with the tetragonal space group I4/mcm isostructural with other RCo9Si4. The
smaller lattice constants of CeCo9Si4 in comparison with the trend established
by other RCo9Si4 is indicative for intermediate valence of cerium. While
RCo9Si4 with R= Pr, .. Tb, and Y show ferromagnetism and LaCo9Si4 is nearly
ferromagnetic, CeCo9Si4 remains paramagnetic even in external fields as large
as 40 T, though its electronic specific heat coefficient (g~190 mJ/molK^2) is
of similar magnitude as that of metamagnetic LaCo9Si4 and weakly ferromagnetic
YCo9Si4.Comment: 2 pages, 3 figures, submitted to SCES 0
Superconductivity in novel Ge-based skutterudites: {Sr,Ba}Pt_4Ge_{12}
Combining experiments and ab initio models we report on
and as members of a novel class of superconducting
skutterudites, where Sr or Ba atoms stabilize a framework entirely formed by
Ge-atoms. Below K, and 5.10 K for and , respectively, electron-phonon coupled superconductivity
emerges, ascribed to intrinsic features of the Pt-Ge framework, where Ge-
states dominate the electronic structure at the Fermi energy.Comment: 4 pages, 4 figures, accepted for publication in PR
Sturm-Liouville operators on time scales
We establish the connection between Sturm-Liouville equations on time scales
and Sturm--Liouville equations with measure-valued coefficients. Based on this
connection we generalize several results for Sturm-Liouville equations on time
scales which have been obtained by various authors in the past.Comment: 12 page
Friction Coefficient for Deep-Inelastic Heavy-Ion Collisions
Based on the microscopic model, the friction coefficient for the relative
motion of nuclei in deep-inelastic heavy-ion collisions is calculated. The
radial dependence of the friction coefficient is studied and the results are
compared with those found by other methods. Based on this result, it was
demonstrated that the kinetic energy dissipation in deep-inelastic heavy-ion
collisions is a gradual process which takes up a significant part of a reaction
time. An advantage of the suggested method is that it allows one to consider
the relative motion of nuclei and the intrinsic motion self-consistently.Comment: 15 pages, RevTex, 7 Postscript figures, submitted to Phys. Rev.
Continuum corrections to the level density and its dependence on excitation energy, n-p asymmetry, and deformation
In the independent-particle model, the nuclear level density is determined
from the neutron and proton single-particle level densities. The
single-particle level density for the positive-energy continuum levels is
important at high excitation energies for stable nuclei and at all excitation
energies for nuclei near the drip lines. This single-particle level density is
subdivided into compound-nucleus and gas components. Two methods were
considered for this subdivision. First in the subtraction method, the
single-particle level density is determined from the scattering phase shifts.
In the Gamov method, only the narrow Gamov states or resonances are included.
The level densities calculated with these two methods are similar, both can be
approximated by the backshifted Fermi-gas expression with level-density
parameters that are dependent on A, but with very little dependence on the
neutron or proton richness of the nucleus. However, a small decrease in the
level-density parameter was predicted for some nuclei very close to the drip
lines. The largest difference between the calculations using the two methods
was the deformation dependence on the level density. The Gamov method predicts
a very strong peaking of the level density at sphericity for high excitation
energies. This leads to a suppression of deformed configurations and,
consequently, the fission rate predicted by the statistical model is reduced in
the Gamov method.Comment: 18 pages 24 figure
Phonon Dispersion Relations in PrBa2Cu3O6+x (x ~ 0.2)
We report measurements of the phonon dispersion relations in
non-superconducting, oxygen-deficient PrBa2Cu3O6+x (x ~ 0.2) by inelastic
neutron scattering. The data are compared with a model of the lattice dynamics
based on a common interaction potential. Good agreement is achieved for all but
two phonon branches, which are significantly softer than predicted. These modes
are found to arise predominantly from motion of the oxygen ions in the CuO2
planes. Analogous modes in YBa2Cu3O6 are well described by the common
interaction potential model.Comment: 4 pages, 3 figures. Minor changes following referees' comment
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