46,404 research outputs found
Stability of branched pull-back projective foliations
We prove that, if , a singular foliation on which can be written as pull-back, where is a foliation in of degree with one or three invariant lines in general
position and , is an
appropriated rational map, is stable under holomorphic deformations. As a
consequence we conclude that the closure of the sets are new irreducible components of the space of
holomorphic foliations of certain degrees.Comment: arXiv admin note: substantial text overlap with arXiv:1503.07827,
arXiv:1503.0071
Branched pull-back components of the space of codimension 1 foliations on
Let be written as , where is a
foliation in with three invariant lines in general position,
say , and ,
is a nonlinear rational map. Using
local stability results of singular holomorphic foliations, we prove that: if
, the foliation is globally stable under holomorphic
deformations. As a consequence we obtain new irreducible componentes for the
space of codimension one foliations on . We present also a result
which characterizes holomorphic foliations on which
can be obtained as a pull back of foliations on of degree
with three invariant lines in general position.Comment: arXiv admin note: text overlap with arXiv:1503.0071
Irreducible components of the space of foliations by surfaces
Let be written as , where is
a -dimensional foliation on and a non-linear generic rational map. We use local
stability results of singular holomorphic foliations, to prove that: if , a foliation by complex surfaces on is globally
stable under holomorphic deformations. As a consequence, we obtain irreducible
components for the space of two-dimensional foliations in . We
present also a result which characterizes holomorphic foliations on which can be obtained as a pull back of 1- foliations in
of degree
Achieving Super-Resolution in Multi-Rate Sampling Systems via Efficient Semidefinite Programming
Super-resolution theory aims to estimate the discrete components lying in a
continuous space that constitute a sparse signal with optimal precision. This
work investigates the potential of recent super-resolution techniques for
spectral estimation in multi-rate sampling systems. It shows that, under the
existence of a common supporting grid, and under a minimal separation
constraint, the frequencies of a spectrally sparse signal can be exactly
jointly recovered from the output of a semidefinite program (SDP). The
algorithmic complexity of this approach is discussed, and an equivalent SDP of
minimal dimension is derived by extending the Gram parametrization properties
of sparse trigonometric polynomials
Persistence in the Zero-Temperature Dynamics of the Random Ising Ferromagnet on a Voronoi-Delaunay lattice
The zero-temperature Glauber dynamic is used to investigate the persistence
probability in the randomic two-dimensional ferromagnetic Ising model on
a Voronoi-Delaunay tessellation. We consider the coupling factor varying
with the distance between the first neighbors to be , with . The persistence probability of spins flip,
that does not depends on time , is found to decay to a non-zero value
depending on the parameter . Nevertheless, the quantity
decays exponentially to zero over long times.
Furthermore, the fraction of spins that do not change at a time is a
monotonically increasing function of the parameter . Our results are
consistent with the ones obtained for the diluted ferromagnetic Ising model on
a square lattice.Comment: 3 pages, 3 Figure
Critical behavior of the 3D-Ising model on a poissonian random lattice
The single-cluster Monte Carlo algorithm and the reweighting technique are
used to simulate the 3D-ferromagnetic Ising model on three dimensional
Voronoi-Delaunay lattices. It is assumed that the coupling factor varies
with the distance between the first neighbors as ,
with . The critical exponents , , and are
calculated, and according to the present estimates for the critical exponents,
we argue that this random system belongs to the same universality class of the
pure three-dimensional ferromegnetic Ising model.Comment: 4 pages, 5 figure
System-environment correlations for dephasing two-qubit states coupled to thermal baths
Based on the exact dynamics of a two-qubit system and environment, we
investigate system-environment (SE) quantum and classical correlations. The
coupling is chosen to represent a dephasing channel for one of the qubits and
the environment is a proper thermal bath. First we discuss the general issue of
dilation for qubit phase damping. Based on the usual thermal bath of harmonic
oscillators, we derive criteria of separability and entanglement between an
initial state and the environment. Applying these criteria to initial
Werner states, we find that entanglement between the system and environment is
built up in time for temperatures below a certain critical temperature
. On the other hand, the total state remains separable
during those short times that are relevant for decoherence and loss of
entanglement in the two-qubit state. Close to the SE
correlations oscillate between separable and entangled. Even though these
oscillations are also observed in the entanglement between the two qubits, no
simple relation between the loss of entanglement in the two-qubit system and
the build-up of entanglement between the system and environment is found.Comment: 10 pages, published versio
PN and galactic chemical evolution
Recent applications of PN to the study of galactic chemical evolution are
reviewed, such as PN and stellar populations, abundance gradients, including
their space and time variations, determination of the He/H radial gradient and
of the helium-to-metals enrichment ratio, and the [O/Fe] x [Fe/H] relation in
the solar neighbourhood and in the galactic bulge.Comment: 8 pages, 3 postscript figures, TeX, uses psfig.sty, to be published
in: Planetary Nebulae and their Role in the Universe, IAU Symposium 209,
edited by R. Sutherland, S. Kwok, M. Dopita, ASP (2002) also available at
http://www.iagusp.usp.br/~maciel/index.htm
Pull-back components of the space of foliations of codimension
We present a new list of irreducible components for the space of
k-dimensional holomorphic foliations on , , .
They are associated to pull-back of dimension one foliations on by non-linear rational maps
Metallicity gradients in the Milky Way
Radial metallicity gradients are observed in the disks of the Milky Way and
in several other spiral galaxies. In the case of the Milky Way, many objects
can be used to determine the gradients, such as HII regions, B stars, Cepheids,
open clusters and planetary nebulae. Several elements can be studied, such as
oxygen, sulphur, neon, and argon in photoionized nebulae, and iron and other
elements in cepheids, open clusters and stars. As a consequence, the number of
observational characteristics inferred from the study of abundance gradients is
very large, so that in the past few years they have become one of the main
observational constraints of chemical evolution models. In this paper, we
present some recent observational evidences of abundance gradients based on
several classes of objects. We will focus on (i) the magnitude of the
gradients, (ii) the space variations, and (iii) the evidences of a time
variation of the abundance gradients. Some comments on recent theoretical
models are also given, in an effort to highlight their predictions concerning
abundance gradients and their variations.Comment: 8 pages, 3 figures, uses iaus.cls, in press, IAU Symp. 265, Chemical
abundances in the Universe: Connecting the first Stars to Planets, Ed. K.
Cunha, M. Spite, B. Barbu
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