2,659 research outputs found
Different faces of the phantom
The SNe type Ia data admit that the Universe today may be dominated by some
exotic matter with negative pressure violating all energy conditions. Such
exotic matter is called {\it phantom matter} due to the anomalies connected
with violation of the energy conditions. If a phantom matter dominates the
matter content of the universe, it can develop a singularity in a finite future
proper time. Here we show that, under certain conditions, the evolution of
perturbations of this matter may lead to avoidance of this future singularity
(the Big Rip). At the same time, we show that local concentrations of a phantom
field may form, among other regular configurations, black holes with
asymptotically flat static regions, separated by an event horizon from an
expanding, singularity-free, asymptotically de Sitter universe.Comment: 6 pages, presented at IRGAC 2006, Barcelona, 11-15 July 200
Exact Foldy-Wouthuysen transformation for gravitational waves and magnetic field background
We consider an exact Foldy-Wouthuysen transformation for the Dirac spinor
field on the combined background of a gravitational wave and constant uniform
magnetic field. By taking the classical limit of the spinor field Hamiltonian
we arrive at the equations of motion for the non-relativistic spinning
particle. Two different kinds of the gravitational fields are considered and in
both cases the effect of the gravitational wave on the spinor field and on the
corresponding spinning particle may be enforced by the sufficiently strong
magnetic field. This result can be relevant for the astrophysical applications
and, in principle, useful for creating the gravitational wave detectors based
on atomic physics and precise interferometry
Strong curvature singularities in quasispherical asymptotically de Sitter dust collapse
We study the occurrence, visibility, and curvature strength of singularities
in dust-containing Szekeres spacetimes (which possess no Killing vectors) with
a positive cosmological constant. We find that such singularities can be
locally naked, Tipler strong, and develop from a non-zero-measure set of
regular initial data. When examined along timelike geodesics, the singularity's
curvature strength is found to be independent of the initial data.Comment: 16 pages, LaTeX, uses IOP package, 2 eps figures; accepted for
publication in Class. Quantum Gra
Strategies for decolorization of textile industry effluents by white-rot-fungi with peach palm residue
The aim of this interdisciplinary approach is to provide innovative solutions to
environmental problems, in particular, improving the treatment of textile industrial effluents and finding a
use for the residual biomass generated from palm tree (Bactris gasipaes) extraction. Three types of white-rot
fungi were cultivated applying different strategies for the decolorization the textile effluents: i) solid-state
fermentation (SSF), ii) submerged fermentation (SF), and iii) adsorption. In all cases, it was used the
peach-palm residue. In the SSF strategy, the decolorization process and laccase production were enhanced
by increasing the concentration of final effluent. Even though the highest decolorization percentage (80%)
was attained after 10 days of fermentation with G. lucidum EF 31 applied in the treatment of a final effluent,
no significant differences were found in relation to the other two fungi. The decolorization efficiency
obtained in the SF was lower compared with SSF, however, the presence of final effluent in the SF process
improved the laccase activity. It was noted that the addition of peach-palm residue in this system provides a
habitat for the fungus as well as a suitable source material for laccase production with the consequent
decolorization of the effluent.This research was supported by the Brazilian
Ministry of Science, Technology and Innovation
(MCTI) (Grant 402593/2013-8). The authors are
grateful to the Coordenação de Aperfeiçoamento de
Pessoal de NĂvel Superior (Capes) and Conselho
Nacional de Desenvolvimento CientĂfico e TecnolĂłgico
(CNPq) for scholarships. The author L. B. B.
Tavares is the holder of a CNPq fellowship
Dynamics of spin correlations in the spin-1/2 isotropic XY chain in a transverse field
Dynamic xx spin pair correlation functions for the isotropic spin-1/2 XY
chain are calculated numerically for long open chains in the presence of a
transverse magnetic field at finite temperature. As an application we discuss
the temperature dependence of the spin-spin relaxation time in PrCl_3.Comment: 2 pages, latex, 2 figures, abstract of the paper presented at Ampere
Summer School ``Applications of Magnetic Resonance in Novel Materials''
Nafplion, Greece, 3-9 September, 2000, partially published in J. Phys. A:
Math. Gen. 33, 3063 (2000
Quantum spinor field in the FRW universe with a constant electromagnetic background
The article is a natural continuation of our paper {\em Quantum scalar field
in FRW Universe with constant electromagnetic background}, Int. J. Mod. Phys.
{\bf A12}, 4837 (1997). We generalize the latter consideration to the case of
massive spinor field, which is placed in FRW Universe of special type with a
constant electromagnetic field. To this end special sets of exact solutions of
Dirac equation in the background under consideration are constructed and
classified. Using these solutions representations for out-in, in-in, and
out-out spinor Green functions are explicitly constructed as proper-time
integrals over the corresponding contours in complex proper-time plane. The
vacuum-to-vacuum transition amplitude and number of created particles are found
and vacuum instability is discussed. The mean values of the current and
energy-momentum tensor are evaluated, and different approximations for them are
presented. The back reaction related to particle creation and to the
polarization of the unstable vacuum is estimated in different regimes.Comment: 36 pages, LaTex fil
Caracterização molecular inicial da mancha de curvularia (Curvularia inaequalis) em plantas de cana-de-açúcar.
Peripheral heavy ion collisions as a probe of the nuclear gluon distribution
At high energies a quark-gluon plasma is expected to be formed in heavy ion
collisions at RHIC and LHC. The theoretical description of these processes is
directly associated to a complete knowledge of the details of medium effects in
the nuclear gluon distribution. In this paper we analyze the possibility to
constraint the behavior of this distribution considering peripheral heavy ion
collisions. We reanalyze the photoproduction of heavy quarks for the deduction
of the in-medium gluon distribution using three current parameterizations for
this parton distribution. Moreover, we show that the elastic photoproduction of
vector mesons is a potential process to probe the nuclear gluon distribution.Comment: 8 figures, accepted for publication in Physicsl review
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