647 research outputs found
Gravitational Waves Astronomy: a cornerstone for gravitational theories
Realizing a gravitational wave (GW) astronomy in next years is a great
challenge for the scientific community. By giving a significant amount of new
information, GWs will be a cornerstone for a better understanding of
gravitational physics. In this paper we re-discuss that the GW astronomy will
permit to solve a captivating issue of gravitation. In fact, it will be the
definitive test for Einstein's general relativity (GR), or, alternatively, a
strong endorsement for extended theories of gravity (ETG).Comment: To appear in Proceedings of the Workshop "Cosmology, the Quantum
Vacuum and Zeta Functions" for the celebration of Emilio Elizalde's sixtieth
birthday, Barcelona, March 8-10, 201
Abelian Magnetic Monopoles and Topologically Massive Vector Bosons in Scalar-Tensor Gravity with Torsion Potential
A Lagrangian formulation describing the electromagnetic interaction -
mediated by topologically massive vector bosons - between charged, spin-(1/2)
fermions with an abelian magnetic monopole in a curved spacetime with
non-minimal coupling and torsion potential is presented. The covariant field
equations are obtained. The issue of coexistence of massive photons and
magnetic monopoles is addressed in the present framework. It is found that
despite the topological nature of photon mass generation in curved spacetime
with isotropic dilaton field, the classical field theory describing the
nonrelativistic electromagnetic interaction between a point-like electric
charge and magnetic monopole is inconsistent.Comment: 18 pages, no figure
Use of 2-dimensional speckle-tracking echocardiography to assess left ventricular systolic function in dogs with systemic inflammatory response syndrome
Background: Early identification of systolic dysfunction in dogs with systemic inflammatory response syndrome (SIRS) potentially could improve the outcome and decrease mortality.
Objective: To compare 2-dimensional speckle tracking (2D-STE) with 2-dimensional (2D) and M-mode echocardiography in the evaluation of systolic function in SIRS dogs.
Animals: Seventeen SIRS and 17 healthy dogs.
Methods: Prospective observational case-control study. Each dog underwent physical examination, conventional echocardiography, 2D-STE, and C-reactive protein measurement.
Results: Dogs with SIRS had lower 2D-STE ejection fraction (X4D-EF; 44 ± 8 versus 53 ± 8; P =.003), endocardial global longitudinal strain (ENDO-G-Long-St; -14.6 ± 3.2 versus -18.5 ± 4.1; P =.003), and normalized left ventricular diameter in diastole (1.38 ± 0.25 versus 1.54 ± 0.17; P =.04) and systole (0.85 ± 0.18 versus 0.97 ± 0.11; P =.03) as compared to healthy dogs. Simpson method of disks (SMOD) right parasternal EF (55 ± 9 versus 60 ± 6; P =.07) and end systolic volume index (ESVI; 23 ± 10 versus 21 ± 6; P =.61), SMOD left apical EF (59 ± 9 versus 59 ± 6; P =.87) and ESVI (20 ± 8 versus 22 ± 6; P =.25), fractional shortening (FS; 34 ± 5 versus 33 ± 4; P =.39), M-mode EF (64 ± 7 versus 62 ± 5; P =.35), and ESVI (23 ± 11 versus 30 ± 9; P =.06) were not significantly different between SIRS and control group, respectively.
Conclusion and Clinical Importance: Speckle tracking X4D-EF and ENDO-G-Long-St are more sensitive than 2D and M-Mode FS, EF, and ESVI in detecting systolic impairment in dogs with SIRS
Effective temperature for black holes
The physical interpretation of black hole's quasinormal modes is fundamental
for realizing unitary quantum gravity theory as black holes are considered
theoretical laboratories for testing models of such an ultimate theory and
their quasinormal modes are natural candidates for an interpretation in terms
of quantum levels. The spectrum of black hole's quasinormal modes can be
re-analysed by introducing a black hole's effective temperature which takes
into account the fact that, as shown by Parikh and Wilczek, the radiation
spectrum cannot be strictly thermal. This issue changes in a fundamental way
the physical understanding of such a spectrum and enables a re-examination of
various results in the literature which realizes important modifies on quantum
physics of black holes. In particular, the formula of the horizon's area
quantization and the number of quanta of area result modified becoming
functions of the quantum "overtone" number n. Consequently, the famous formula
of Bekenstein-Hawking entropy, its sub-leading corrections and the number of
microstates are also modified. Black hole's entropy results a function of the
quantum overtone number too. We emphasize that this is the first time that
black hole's entropy is directly connected with a quantum number. Previous
results in the literature are re-obtained in the limit n \to \infty.Comment: 10 pages,accepted for publication in Journal of High Energy Physics.
Comments are welcom
Thermodynamic analysis of black hole solutions in gravitating nonlinear electrodynamics
We perform a general study of the thermodynamic properties of static
electrically charged black hole solutions of nonlinear electrodynamics
minimally coupled to gravitation in three space dimensions. The Lagrangian
densities governing the dynamics of these models in flat space are defined as
arbitrary functions of the gauge field invariants, constrained by some
requirements for physical admissibility. The exhaustive classification of these
theories in flat space, in terms of the behaviour of the Lagrangian densities
in vacuum and on the boundary of their domain of definition, defines twelve
families of admissible models. When these models are coupled to gravity, the
flat space classification leads to a complete characterization of the
associated sets of gravitating electrostatic spherically symmetric solutions by
their central and asymptotic behaviours. We focus on nine of these families,
which support asymptotically Schwarzschild-like black hole configurations, for
which the thermodynamic analysis is possible and pertinent. In this way, the
thermodynamic laws are extended to the sets of black hole solutions of these
families, for which the generic behaviours of the relevant state variables are
classified and thoroughly analyzed in terms of the aforementioned boundary
properties of the Lagrangians. Moreover, we find universal scaling laws (which
hold and are the same for all the black hole solutions of models belonging to
any of the nine families) running the thermodynamic variables with the electric
charge and the horizon radius. These scale transformations form a one-parameter
multiplicative group, leading to universal "renormalization group"-like
first-order differential equations. The beams of characteristics of these
equations generate the full set of black hole states associated to any of these
gravitating nonlinear electrodynamics...Comment: 51 single column pages, 19 postscript figures, 2 tables, GRG tex
style; minor corrections added; final version appearing in General Relativity
and Gravitatio
Reconstruction of the equation of state for the cyclic universes in homogeneous and isotropic cosmology
We study the cosmological evolutions of the equation of state (EoS) for the
universe in the homogeneous and isotropic
Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) space-time. In particular, we
reconstruct the cyclic universes by using the Weierstrass and Jacobian elliptic
functions. It is explicitly illustrated that in several models the universe
always stays in the non-phantom (quintessence) phase, whereas there also exist
models in which the crossing of the phantom divide can be realized in the
reconstructed cyclic universes.Comment: 29 pages, 8 figures, version accepted for publication in Central
European Journal of Physic
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Integrated pest management strategies for cabbage stem flea beetle (Psylliodes chrysocephala) in oilseed rape
Oilseed rape (OSR) is the second largest source of vegetable oil globally and the most important biofuel feedstock in the European Union (EU) but production of this important crop is threatened by a small insect; Psylliodes chrysocepaha â the cabbage stem flea beetle (CSFB). The EU ban on use of neonicotinoid seed treatments and resistance of CSFB to pyrethroid insecticides have left farmers with limited control options resulting in drastic reductions in production. Integrated pest management (IPM) may offer a solution. We review the lifecycle of CSFB and the current
options available, or in the research pipeline, for the eight IPM principles of the EU Sustainable Use of Pesticides Directive (Directive-2009/128/EC). A full IPM strategy for CSFB barely exists. Although there are a range of preventative measures these require scientific validation; critically, resistant/tolerant OSR cultivars are not yet available. Existing monitoring methods are time
consuming and there are no commercial models to enable decision support based on predictions migration timing or population size. Available thresholds are not based on physiological tolerances of the plant making it hard to adapt them to changing market prices for the crop and
costs of control. Non-synthetic alternatives tested and registered for use against CSFB are lacking, making resistance management impossible. CSFB control is therefore dependent upon conservation biocontrol. Natural enemies of CSFB are present, but quantification of their effects is
needed and habitat management strategies to exploit their potential. Although some EU countries have local initiatives to reduce insecticide use and encourage use of âgreenerâ alternatives, there is no formal process for ranking these and little information available to help farmers make choices. We summarise the main knowledge gaps and future research needed to improve measures for CSFB control and to facilitate development of a full IPM strategy for this pest -and sustainable oilseeds production
Orbital effects of a monochromatic plane gravitational wave with ultra-low frequency incident on a gravitationally bound two-body system
We analytically compute the long-term orbital variations of a test particle
orbiting a central body acted upon by an incident monochromatic plane
gravitational wave. We assume that the characteristic size of the perturbed
two-body system is much smaller than the wavelength of the wave. Moreover, we
also suppose that the wave's frequency is much smaller than the particle's
orbital one. We make neither a priori assumptions about the direction of the
wavevector nor on the orbital geometry of the planet. We find that, while the
semi-major axis is left unaffected, the eccentricity, the inclination, the
longitude of the ascending node, the longitude of pericenter and the mean
anomaly undergo non-vanishing long-term changes. They are not secular trends
because of the slow modulation introduced by the tidal matrix coefficients and
by the orbital elements themselves. They could be useful to indepenedently
constrain the ultra-low frequency waves which may have been indirectly detected
in the BICEP2 experiment. Our calculation holds, in general, for any
gravitationally bound two-body system whose characteristic frequency is much
larger than the frequency of the external wave. It is also valid for a generic
perturbation of tidal type with constant coefficients over timescales of the
order of the orbital period of the perturbed particle.Comment: LaTex2e, 24 pages, no figures, no tables. Changes suggested by the
referees include
Phenomenology of the Lense-Thirring effect in the Solar System
Recent years have seen increasing efforts to directly measure some aspects of
the general relativistic gravitomagnetic interaction in several astronomical
scenarios in the solar system. After briefly overviewing the concept of
gravitomagnetism from a theoretical point of view, we review the performed or
proposed attempts to detect the Lense-Thirring effect affecting the orbital
motions of natural and artificial bodies in the gravitational fields of the
Sun, Earth, Mars and Jupiter. In particular, we will focus on the evaluation of
the impact of several sources of systematic uncertainties of dynamical origin
to realistically elucidate the present and future perspectives in directly
measuring such an elusive relativistic effect.Comment: LaTex, 51 pages, 14 figures, 22 tables. Invited review, to appear in
Astrophysics and Space Science (ApSS). Some uncited references in the text
now correctly quoted. One reference added. A footnote adde
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