10,521 research outputs found
Partial regularity for manifold constrained p(x)-harmonic maps
We prove that manifold constrained -harmonic maps are
-regular outside a set of zero -dimensional Lebesgue's measure,
for some . We also provide an estimate from above of the
Hausdorff dimension of the singular set
Higher Integrability for Constrained Minimizers of Integral Functionals with (p,q)-Growth in low dimension
We prove higher summability for the gradient of minimizers of strongly convex
integral functionals of the Calculus of Variations with (p,q)-Growth conditions
in low dimension. Our procedure is set in the framework of Fractional Sobolev
Spaces and renders the desired regularity as the result of an approximation
technique relying on estimates obtained through a careful use of difference
quotients.Comment: 22 pages, 0 figure
Abell 370: A Cluster with a Pronounced Triaxial Morphology
We here combine Sunyaev-Zel'dovich effect, X-ray observations and
spectroscopic redshifts of member galaxies, to constrain the intrinsic
three-dimensional shape of the galaxy cluster: Abell 370. The cluster turns out
to be strongly elongated along the l.o.s., with two (or more) substructures in
the process of merging. Spectroscopy further suggests that the process must be
taking place at a small angle respect to the l.o.s.Comment: 7 pages, 2 figures. Contribution to the Proceedings of the COSPAR
Scientific Assembly, E1.2 "Clusters of Galaxies: New Insights from
XMM-Newton, Chandra and INTEGRAL", Paris (France), July 19-20, 2004. Accepted
for publication in Advances in Space Researc
Manifold constrained non-uniformly elliptic problems
We consider the problem of minimizing variational integrals defined on
\cc{nonlinear} Sobolev spaces of competitors taking values into the sphere. The
main novelty is that the underlying energy features a non-uniformly elliptic
integrand exhibiting different polynomial growth conditions and no homogeneity.
We develop a few intrinsic methods aimed at proving partial regularity of
minima and providing techniques for treating larger classes of similar
constrained non-uniformly elliptic variational problems. In order to give
estimates for the singular sets we use a general family of Hausdorff type
measures following the local geometry of the integrand. A suitable comparison
is provided with respect to the naturally associated capacities.Comment: 50 page
On the regularity of minima of non-autonomous functionals
We consider regularity issues for minima of non-autonomous functionals in the
Calculus of Variations exhibiting non-uniform ellipticity features. We provide
a few sharp regularity results for local minimizers that also cover the case of
functionals with nearly linear growth. The analysis is carried out provided
certain necessary approximation-in-energy conditions are satisfied. These are
related to the occurrence of the so-called Lavrentiev phenomenon that that
non-autonomous functionals might exhibit, and which is a natural obstruction to
regularity. In the case of vector valued problems we concentrate on higher
gradient integrability of minima. Instead, in the scalar case, we prove local
Lipschitz estimates. We also present an approach via a variant of Moser's
iteration technique that allows to reduce the analysis of several non-uniformly
elliptic problems to that for uniformly elliptic ones.Comment: 32 page
Normal state properties of an interacting large polaron gas
A simple approach to the many-polaron problem for both weak and intermediate
electron-phonon coupling and valid for densities much smaller than those
typical of metals is presented. Within the model the total energy, the
collective modes and the single-particle properties are studied and compared
with the available theories. It is shown the occurrence of a charge density
wave instability in the intermediate coupling regime.Comment: 26 pages, 12 figures. To appear on European Physical Journal
Modelling clusters of galaxies by f(R)-gravity
We consider the possibility that masses and gravitational potentials of
galaxy cluster, estimated at X-ray wavelengths, could be explained without
assuming huge amounts of dark matter, but in the context of -gravity.
Specifically, we take into account the weak field limit of such theories and
show that the corrected gravitational potential allows to estimate the total
mass of a sample of 12 clusters of galaxies. Results show that such a
gravitational potential provides a fair fit to the mass of visible matter (i.e.
gas + stars) estimated by X-ray observations, without the need of additional
dark matter while the size of the clusters, as already observed at different
scale for galaxies, strictly depends on the interaction lengths of the
corrections to the Newtonian potential.Comment: 18 pages, 34 figure
An Innovative Mission Management System for Fixed-Wing UAVs
This paper presents two innovative units linked together to build the main frame of a UAV Mis- sion Management System. The first unit is a Path Planner for small UAVs able to generate optimal paths in a tridimensional environment, generat- ing flyable and safe paths with the lowest com- putational effort. The second unit is the Flight Management System based on Nonlinear Model Predictive Control, that tracks the reference path and exploits a spherical camera model to avoid unpredicted obstacles along the path. The control system solves on-line (i.e. at each sampling time) a finite horizon (state horizon) open loop optimal control problem with a Genetic Algorithm. This algorithm finds the command sequence that min- imizes the tracking error with respect to the ref- erence path, driving the aircraft far from sensed obstacles and towards the desired trajectory
Optical properties of an interacting large polaron gas
The normal state conductivity of a system of interacting large polarons is
calculated within the Random Phase approximation and some numerical results are
presented. The behaviour of the optical absorption as a function of the charge
carrier density and of the temperature is analyzed for different values of the
electron-phonon coupling constant. It is shown that the conductivity exihibits
features similar to thos observed in the infrared spectra of the cuprates.Comment: 13 pages, 1 table, 3 figures (to be published ob Eur. Jour. Phys. B
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