39,602 research outputs found
Resolvent Estimates in L^p for the Stokes Operator in Lipschitz Domains
We establish the resolvent estimates for the Stokes operator in
Lipschitz domains in , for . The result, in particular, implies that the Stokes operator in a
three-dimensional Lipschitz domain generates a bounded analytic semigroup in
for (3/2)-\varep < p< 3+\epsilon. This gives an affirmative answer to a
conjecture of M. Taylor.Comment: 28 page. Minor revision was made regarding the definition of the
Stokes operator in Lipschitz domain
Application of density dependent parametrization models to asymmetric nuclear matter
Density dependent parametrization models of the nucleon-meson effective
couplings, including the isovector scalar \delta-field, are applied to
asymmetric nuclear matter. The nuclear equation of state and the neutron star
properties are studied in an effective Lagrangian density approach, using the
relativistic mean field hadron theory. It is known that the introduction of a
\delta-meson in the constant coupling scheme leads to an increase of the
symmetry energy at high density and so to larger neutron star masses, in a pure
nucleon-lepton scheme. We use here a more microscopic density dependent model
of the nucleon-meson couplings to study the properties of neutron star matter
and to re-examine the \delta-field effects in asymmetric nuclear matter. Our
calculations show that, due to the increase of the effective \delta coupling at
high density, with density dependent couplings the neutron star masses in fact
can be even reduced.Comment: 5 pages, 4 figure
Nonexistence theorems for traversable wormholes
Gauss-Bonnet formula is used to derive a new and simple theorem of
nonexistence of vacuum static nonsingular lorentzian wormholes. We also derive
simple proofs for the nonexistence of lorentzian wormhole solutions for some
classes of static matter such as, for instance, real scalar fields with a
generic potential obeying and massless fermions fields
Small-q electron-phonon scattering and linear dc resistivity in high-T_c oxides
We examine the effect on the DC resistivity of small-q electron-phonon
scattering, in a system with the electronic topology of the high-T_c oxides.
Despite the fact that the scattering is dominantly forward, its contribution to
the transport can be significant due to ``ondulations'' of the bands in the
flat region and to the umpklapp process. When the extended van-Hove
singularities are sufficiently close to the acoustic branch of the
phonons contribute significantly to the transport. In that case one can obtain
linear dependent resistivity down to temperatures as low as 10 K, even if
electrons are scattered also by optical phonons of about 500 K as reported by
Raman measurements.Comment: LATEX file and 4 Postscript figure
Material and doping dependence of the nodal and anti-nodal dispersion renormalizations in single- and multi-layer cuprates
In this paper we present a review of bosonic renormalization effects on
electronic carriers observed from angle-resolved photoemission spectra in the
cuprates. We specifically discuss the viewpoint that these renormalizations
represent coupling of the electrons to the lattice, and review how the wide
range of materials dependence, such as the number of CuO layers, and the
doping dependence can be straightforwardly understood as arising due to novel
electron-phonon coupling.Comment: 9 pages and 6 figures. Submitted as a review article for Advances in
Condensed Matter Physic
Aging of the Nonlinear Optical Susceptibility of colloidal solutions
Using Z-scan and dynamic light scattering measurements we investigate the
nonlinear optics response of a colloidal solution undergoing dynamics slowing
down with age. We study the high optical nonlinearity of an organic dye
(Rhodamine B) dispersed in a water-clay (Laponite) solution, at different clay
concentrations (2.0 wt% - 2.6 wt%), experiencing the gelation process. We
determine the clay platelets self diffusion coefficient and, by its comparison
with the structural relaxation time, we conclude that the gelation process
proceeds through the structuring of interconnecting clay platelets network
rather than through clusters growth and aggregation.Comment: 4 figures, 4 page
Collective behaviour without collective order in wild swarms of midges
Collective behaviour is a widespread phenomenon in biology, cutting through a
huge span of scales, from cell colonies up to bird flocks and fish schools. The
most prominent trait of collective behaviour is the emergence of global order:
individuals synchronize their states, giving the stunning impression that the
group behaves as one. In many biological systems, though, it is unclear whether
global order is present. A paradigmatic case is that of insect swarms, whose
erratic movements seem to suggest that group formation is a mere epiphenomenon
of the independent interaction of each individual with an external landmark. In
these cases, whether or not the group behaves truly collectively is debated.
Here, we experimentally study swarms of midges in the field and measure how
much the change of direction of one midge affects that of other individuals. We
discover that, despite the lack of collective order, swarms display very strong
correlations, totally incompatible with models of noninteracting particles. We
find that correlation increases sharply with the swarm's density, indicating
that the interaction between midges is based on a metric perception mechanism.
By means of numerical simulations we demonstrate that such growing correlation
is typical of a system close to an ordering transition. Our findings suggest
that correlation, rather than order, is the true hallmark of collective
behaviour in biological systems.Comment: The original version has been split into two parts. This first part
focuses on order vs. correlation. The second part, about finite-size scaling,
will be included in a separate paper. 15 pages, 6 figures, 1 table, 5 video
- …