166 research outputs found
Dynamic vacuum variable and equilibrium approach in cosmology
A modified-gravity theory is considered with a four-form field strength F, a
variable gravitational coupling parameter G(F), and a standard matter action.
This theory provides a concrete realization of the general vacuum variable q as
the four-form amplitude F and allows for a study of its dynamics. The theory
gives a flat Friedmann-Robertson-Walker universe with rapid oscillations of the
effective vacuum energy density (cosmological "constant"), whose amplitude
drops to zero asymptotically. Extrapolating to the present age of the Universe,
the order of magnitude of the average vacuum energy density agrees with the
observed near-critical vacuum energy density of the present universe. It may
even be that this type of oscillating vacuum energy density constitutes a
significant part of the so-called cold dark matter in the standard
Friedmann-Robertson-Walker framework.Comment: 24 (not 25) pages, v7(=v6 with latex problem corrected): published
version in preprint styl
Monteggia fracture associated with ipsilateral intercondylar distal humeral fracture with posterior interosseous nerve palsy: case report, medico-legal implications, and methodological assessment analysis
BACKGROUND: The Monteggia fracture, defined as a fracture of the proximal third of the ulnar shaft associated with an anterior or posterior dislocation of the proximal radial epiphysis, is a serious injury accounting for 0.7% of all elbow fractures and dislocations in adults. For adult patients, good results can only be obtained through early diagnosis and adequate surgical treatment. Monteggia fracture-dislocations associated with distal humeral fracture are extremely rare injuries in adults and there are few cases described in the literature. Medico-legal implications arising from such conditions have a host of complexities that cannot be discounted.CASE REPORT: This case report revolves around a patient affected by a type I Monteggia fracture-dislocation, according to the Bado classification, associated with an ipsilateral intercondylar distal humeral fracture. To our knowledge, this combination of lesions has never been reported before in adult patients. A positive result was obtained due to early diagnosis, achievement of anatomical reduction, and optimal stabilization with internal fixation which made it possible to achieve early functional recovery.CONCLUSIONS: Monteggia fracture -dislocations associated with ipsilateral intercondylar distal humeral fracture are extremely rare in adults. In the case herein reported, a favorable outcome was obtained due to early diagnosis, achievement of anatomical reduction and management with internal fixation with plate and screws, as well as early functional training. Misdiagnosis makes such lesions risky in terms of potentially delayed treatment, increasing the need for surgical interventions and the possibility of high-risk complications and disabling sequelae, with possible medico -legal implications. In the case of unrecognized injuries under urgent circumstances, the injuries may become chronic, making the treatment more complex. The ultimate outcomes of a misdiagnosed Monteggia lesion can lead to very serious functional and aesthetic damage
Pharmacological characterization of a highly selective Rho kinase (ROCK) inhibitor and its therapeutic effects in experimental pulmonary hypertension
Galactic periodicity and the oscillating G model
We consider the model involving the oscillation of the effective
gravitational constant that has been put forward in an attempt to reconcile the
observed periodicity in the galaxy number distribution with the standard
cosmological models. This model involves a highly nonlinear dynamics which we
analyze numerically. We carry out a detailed study of the bound that
nucleosynthesis imposes on this model. The analysis shows that for any assumed
value for (the total energy density) one can fix the value of
(the baryonic energy density) in such a way as to
accommodate the observational constraints coming from the
primordial abundance. In particular, if we impose the inflationary value
the resulting baryonic energy density turns out to be . This result lies in the very narrow range allowed by the observed values of the primordial
abundances of the other light elements. The remaining fraction of
corresponds to dark matter represented by a scalar field.Comment: Latex file 29 pages with no figures. Please contact M.Salgado for
figures. A more careful study of the model appears in gr-qc/960603
Open Inflationary Universes in the Induced Gravity Theory
The induced gravity theory is a variant of Jordan--Brans--Dicke theory where
the `dilaton' field possesses a potential. It has the unusual feature that in
the presence of a false vacuum there is a {\em stable} static solution with the
dilaton field displaced from the minimum of its potential, giving perfect de
Sitter expansion. We demonstrate how this solution can be used to implement the
open inflationary universe scenario. The necessary second phase of inflation
after false vacuum decay by bubble nucleation is driven by the dilaton rolling
from the static point to the minimum of its potential. Because the static
solution is stable whilst the false vacuum persists, the required evolution
occurs for a wide range of initial conditions. As the exterior of the bubble is
perfect de Sitter space, there is no problem with fields rolling outside the
bubble, as in one of the related models considered by Linde and Mezhlumian, and
the expansion rates before and after tunnelling may be similar which prevents
problematic high-amplitude super-curvature modes from being generated. Once
normalized to the microwave background anisotropies seen by the COBE satellite,
the viable models form a one-parameter family for each possible .Comment: 7 pages RevTeX file with three figures incorporated (uses RevTeX and
epsf). Also available by e-mailing ARL, or by WWW at
http://star-www.maps.susx.ac.uk/papers/early_papers.htm
Symmetric vacuum scalar--tensor cosmology
The existence of point symmetries in the cosmological field equations of
generalized vacuum scalar--tensor theories is considered within the context of
the spatially homogeneous cosmologies. It is found that such symmetries only
occur in the Brans--Dicke theory when the dilaton field self--interacts.
Moreover, the interaction potential of the dilaton must take the form of a
cosmological constant. For the spatially flat, isotropic model, it is shown how
this point symmetry may be employed to generate a discrete scale factor duality
in the Brans--Dicke action.Comment: 10 pages, latex, To appear in Class. Quantum Gra
Classical Euclidean wormhole solutions in Palatini cosmology
We study the classical Euclidean wormholes in the context of extended
theories of gravity. With no loss of generality, we use the dynamical
equivalence between gravity and scalar-tensor theories to
construct a point-like Lagrangian in the flat FRW space time. We first show the
dynamical equivalence between Palatini gravity and the
Brans-Dicke theory with self-interacting potential, and then show the dynamical
equivalence between the Brans-Dicke theory with self-interacting potential and
the minimally coupled O'Hanlon theory. We show the existence of new Euclidean
wormhole solutions for this O'Hanlon theory and, for an special case, find out
the corresponding form of having wormhole solution. For small
values of the Ricci scalar, this is in agreement with the
wormhole solution obtained for higher order gravity theory .Comment: 11 page
Conformal Couplings in Induced Gravity
It is found that the induced gravity with conformal couplings requires the
conformal invariance in both classical and quantum levels for consistency. This
is also true for the induced gravity with an extended conformal coupling
interacting with torsion.Comment: 10 pages, Revtex3.0, to appear in General Relativity and Gravitatio
Phase Transition in Conformally Induced Gravity with Torsion
We have considered the quantum behavior of a conformally induced gravity in
the minimal Riemann-Cartan space. The regularized one-loop effective potential
considering the quantum fluctuations of the dilaton and the torsion fields in
the Coleman-Weinberg sector gives a sensible phase transition for an
inflationary phase in De Sitter space. For this effective potential, we have
analyzed the semi-classical equation of motion of the dilaton field in the
slow-rolling regime.Comment: 7pages, no figur
Open Inflation With Scalar-tensor Gravity
The open inflation model recently proposed by Hawking and Turok is
investigated in scalar-tensor gravity context. If the dilaton-like field has no
potential, the instanton of our model is singular but has a finite action. The
Gibbons-Hawking surface term vanishes and hence, can not be used to make
nonzero. To obtain a successful open inflation one should introduce
other matter fields or a potential for the dilaton-like fields.Comment: 10 pages.1 figure. Some comments and references are improved. to be
published in PR
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