660 research outputs found
Delta-semidefinite and delta-convex quadratic forms in Banach spaces
A continuous quadratic form ("quadratic form", in short) on a Banach space
is: (a) delta-semidefinite (i.e., representable as a difference of two
nonnegative quadratic forms) if and only if the corresponding symmetric linear
operator factors through a Hilbert space; (b) delta-convex
(i.e., representable as a difference of two continuous convex functions) if and
only if is a UMD-operator. It follows, for instance, that each quadratic
form on an infinite-dimensional space () is: (a)
delta-semidefinite iff ; (b) delta-convex iff . Some other
related results concerning delta-convexity are proved and some open problems
are stated.Comment: 19 page
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
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
Determination of hydrogen permeability in uncoated and coated superalloys
Hydrogen permeability, diffusivity, and solubility data were obtained for eight wrought and cast high temperature alloys over the range 650 to 815 C. Data were obtained for both uncoated alloys and wrought alloys coated with four commercially available coatings. Activation energies for permeability, diffusivity and solubility were calculated
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