191 research outputs found
Aeromagnetic anomaly images of Vulcano and Southern Lipari Islands (Aeolian Archipelago, Italy)
Newly acquired high-resolution, low-altitude aeromagnetic data over Vulcano Island and Southwestern Lipari in
the Southern Tyrrhenian Sea resolve the major volcanic features in the area associated with the past and present
activity. The magnetic character changes in amplitude and frequency from south-east to north-west. The Primordial
Vulcano, the Lentia Complex, the Piano Caldera units, the Fossa Caldera deposits, and the currently active
La Fossa cone and Vulcanello represent the main volcanic phases on Vulcano Island. They show a distinct
magnetic anomaly pattern, whereas prior to this survey, no magnetic signatures of these features were found
Coupling parameters and the form of the potential via Noether symmetry
We explore the conditions for the existence of Noether symmetries in the
dynamics of FRW metric, non minimally coupled with a scalar field, in the most
general situation, and with nonzero spatial curvature. When such symmetries are
present we find general exact solution for the Einstein equations. We also show
that non Noether symmetries can be found.
Finally,we present an extension of the procedure to the Kantowski- Sachs
metric which is particularly interesting in the case of degenerate Lagrangian.Comment: 13 pages, no figure
Is Noether Symmetric Approach Consistent With Dynamical Equation In Non-minimal Scalar-Tensor Theories?
The form of the coupling of the scalar field with gravity and the potential
have been found by applying Noether theorem to two dimensional minisuperspaces
in induced gravity model. It has been observed that though the forms thus
obtained are consistent with all the equations , yet they do
not satisfy the field equations for , in Robertson-Walker model. It
has been pointed out that this is not due to the degeneracy of the Lagrangian,
since this problem does not appear in case.It has also been shown that
though Noether theorem fails to extract any symmetry from the Lagrangian of
such model for , symmetry exists, which can easily be found by
studying the continuity equation.Comment: 7 pages, late
Identifying Patient Candidates for IL-1 Inhibition: Lessons From Real-World Cases
A subgroup of patients with gouty arthritis have a chronic recurring form that is particularly difficult to treat. Such patients experience repeated flares and often have abundant tophi. Many also have underlying comorbidities, such as renal impairment, cardiovascular disease, gastrointestinal disorders, obesity, and hypertension, which contraindicate the use of standard anti-inflammatory medications. Five patients with difficult to treat gouty arthritis who were either candidates and/or treated with anti-IL therapy are described.info:eu-repo/semantics/publishedVersio
Noether Symmetry of the Hyperextended Scalar Tensor theory for the FLRW models
We study in which conditions the Hyperextended Scalar Tensor theory in an
FLRW background admits a Noether symmetry and derive the vectors field
generating it.Comment: 11 page
On exact solutions for quintessential (inflationary) cosmological models with exponential potentials
We first study dark energy models with a minimally-coupled scalar field and
exponential potentials, admitting exact solutions for the cosmological
equations: actually, it turns out that for this class of potentials the
Einstein field equations exhibit alternative Lagrangians, and are completely
integrable and separable (i.e. it is possible to integrate the system
analytically, at least by quadratures). We analyze such solutions, especially
discussing when they are compatible with a late time quintessential expansion
of the universe. As a further issue, we discuss how such quintessential scalar
fields can be connected to the inflationary phase, building up, for this class
of potentials, a quintessential inflationary scenario: actually, it turns out
that the transition from inflation toward late-time exponential quintessential
tail admits a kination period, which is an indispensable ingredient of this
kind of theoretical models. All such considerations have also been done by
including radiation into the model.Comment: Revtex4, 10 figure
Exact Hypersurface-Homogeneous Solutions in Cosmology and Astrophysics
A framework is introduced which explains the existence and similarities of
most exact solutions of the Einstein equations with a wide range of sources for
the class of hypersurface-homogeneous spacetimes which admit a Hamiltonian
formulation. This class includes the spatially homogeneous cosmological models
and the astrophysically interesting static spherically symmetric models as well
as the stationary cylindrically symmetric models. The framework involves
methods for finding and exploiting hidden symmetries and invariant submanifolds
of the Hamiltonian formulation of the field equations. It unifies, simplifies
and extends most known work on hypersurface-homogeneous exact solutions. It is
shown that the same framework is also relevant to gravitational theories with a
similar structure, like Brans-Dicke or higher-dimensional theories.Comment: 41 pages, REVTEX/LaTeX 2.09 file (don't use LaTeX2e !!!) Accepted for
publication in Phys. Rev.
Evidence for an entropy bound from fundamentally discrete gravity
The various entropy bounds that exist in the literature suggest that
spacetime is fundamentally discrete, and hint at an underlying relationship
between geometry and "information". The foundation of this relationship is yet
to be uncovered, but should manifest itself in a theory of quantum gravity. We
present a measure for the maximal entropy of spherically symmetric spacelike
regions within the causal set approach to quantum gravity. In terms of the
proposal, a bound for the entropy contained in this region can be derived from
a counting of potential "degrees of freedom" associated to the Cauchy horizon
of its future domain of dependence. For different spherically symmetric
spacelike regions in Minkowski spacetime of arbitrary dimension, we show that
this proposal leads, in the continuum approximation, to Susskind's well-known
spherical entropy bound.Comment: 25 pages, 9 figures. Comment on Bekenstein bound added and smaller
corrections. To be published in Class.Quant.Gra
Viability of Noether symmetry of F(R) theory of gravity
Canonization of F(R) theory of gravity to explore Noether symmetry is
performed treating R - 6(\frac{\ddot a}{a} + \frac{\dot a^2}{a^2} +
\frac{k}{a^2}) = 0 as a constraint of the theory in Robertson-Walker
space-time, which implies that R is taken as an auxiliary variable. Although it
yields correct field equations, Noether symmetry does not allow linear term in
the action, and as such does not produce a viable cosmological model. Here, we
show that this technique of exploring Noether symmetry does not allow even a
non-linear form of F(R), if the configuration space is enlarged by including a
scalar field in addition, or taking anisotropic models into account.
Surprisingly enough, it does not reproduce the symmetry that already exists in
the literature (A. K. Sanyal, B. Modak, C. Rubano and E. Piedipalumbo,
Gen.Relativ.Grav.37, 407 (2005), arXiv:astro-ph/0310610) for scalar tensor
theory of gravity in the presence of R^2 term. Thus, R can not be treated as an
auxiliary variable and hence Noether symmetry of arbitrary form of F(R) theory
of gravity remains obscure. However, there exists in general, a conserved
current for F(R) theory of gravity in the presence of a non-minimally coupled
scalar-tensor theory (A. K. Sanyal, Phys.Lett.B624, 81 (2005),
arXiv:hep-th/0504021 and Mod.Phys.Lett.A25, 2667 (2010), arXiv:0910.2385
[astro-ph.CO]). Here, we briefly expatiate the non-Noether conserved current
and cite an example to reveal its importance in finding cosmological solution
for such an action, taking F(R) \propto R^{3/2}.Comment: 16 pages, 1 figure. appears in Int J Theoretical Phys (2012
Dark energy and dark matter from an inhomogeneous dilaton
A cosmological scenario is proposed where the dark matter (DM) and dark
energy (DE) of the universe are two simultaneous manifestations of an
inhomogenous dilaton. The equation of state of the field is scale-dependent and
pressureless at galactic and larger scales and it has negative pressure as a DE
at very large scales. The dilaton drives an inflationary phase followed by a
kinetic energy-dominated one, as in the "quintessential inflation" model
introduced by Peebles & Vilenkin, and soon after the end of inflation particle
production seeds the first inhomogeneities that lead to galaxy formation. The
dilaton is trapped near the minimum of the potential where it oscillates like a
massive field, and the excess of kinetic energy is dissipated via the mechanism
of "gravitational cooling" first introduced by Seidel & Suen. The
inhomogeneities therefore behave like solitonic oscillations around the minimum
of the potential, known as "oscillatons", that we propose account for most DM
in galaxies. Those regions where the dilaton does not transform enough kinetic
energy into reheating or carry an excess of it from regions that have cooled,
evolve to the tail of the potential as DE, driving the acceleration of the
universe.Comment: 9 pages, 8 figures, uses revtex, submitted PR
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