888 research outputs found
Constraining f(R) gravity with PLANCK data on galaxy cluster profiles
Models of gravity that introduce corrections to the Newtonian
potential in the weak field limit are tested at the scale of galaxy clusters.
These models can explain the dynamics of spiral and elliptical galaxies without
resorting to dark matter. We compute the pressure profiles of 579 galaxy
clusters assuming that the gas is in hydrostatic equilibrium within the
potential well of the modified gravitational field. The predicted profiles are
compared with the average profile obtained by stacking the data of our cluster
sample in the Planck foreground clean map SMICA. We find that the resulting
profiles of these systems fit the data without requiring a dominant dark matter
component, with model parameters similar to those required to explain the
dynamics of galaxies. Our results do not rule out that clusters are dynamically
dominated by Dark Matter but support the idea that Extended Theories of Gravity
could provide an explanation to the dynamics of self-gravitating systems and to
the present period of accelerated expansion, alternative to the concordance
cosmological model.Comment: 10 pages, 5 figures, accepted for publication in MNRA
Probing gravity with PLANCK data on cluster pressure profiles
Analytical -gravity models introduce Yukawa-like corrections to the
Newtonian potential in the weak field limit. These models can explain the
dynamics of galaxies and cluster of galaxies without requiring dark matter. To
test the model, we have computed the pressure profile of 579 X-ray galaxy
clusters assuming the gas is in hydrostatic equilibrium within the potential
well of the modified gravitational potential. We have compared those profiles
with the ones measured in the foreground cleaned SMICA released by the Planck
Collaboration. Our results show that Extended Theories of Gravity explain the
dynamics of self-gravitating systems at cluster scales and represent an
alternative to dark matter haloes.Comment: 6 pages, 3 figures, 1 table. To be published in Journal of Physics:
Conference Series (JPCS) as the Proceedings of Spanish Relativity Meeting
201
Relativistic orbits and Gravitational Waves from gravitomagnetic corrections
Corrections to the relativistic theory of orbits are discussed considering
higher order approximations induced by gravitomagnetic effects. Beside the
standard periastron effect of General Relativity (GR), a new nutation effect
was found due to the orbital correction. According to
the presence of that new nutation effect we studied the gravitational waveforms
emitted through the capture in a gravitational field of a massive black hole
(MBH) of a compact object (neutron star (NS) or BH) via the quadrupole
approximation. We made a numerical study to obtain the emitted gravitational
wave (GW) amplitudes. We conclude that the effects we studied could be of
interest for the future space laser interferometric GW antenna LISA.Comment: 6 pages, 10 figures; Multifrequency Behaviour of High-Energy Cosmic
Sources, Vulcano Workshop 200
THE PAST AND THE FUTURE OF DIRECT SEARCH OF GW FROM PULSARS IN THE ERA OF GW ANTENNAS
In this paper we will give an overview of the past and present status of Gravitational Wave (GW) research associated with pulsars, taking into account the target sensitivity achieved from interferometric laser GW antennas such as Tama, Geo, Ligo and Virgo. We will see that the upper limits obtained with searches for periodic GW begin to be astrophysically interesting by imposing non-trivial constraints on the structure and evolution of the neutron stars. We will give prospects for the future detection of pulsar GW signals, with Advanced Ligo and Advanced Virgo and future enhanced detectors, e.g. the Einstein Telescope
THE PAST AND THE FUTURE OF DIRECT SEARCH OF GW FROM PULSARS IN THE ERA OF GW ANTENNAS
In this paper we will give an overview of the past and present status of Gravitational Wave (GW) research associated with pulsars, taking into account the target sensitivity achieved from interferometric laser GW antennas such as Tama, Geo, Ligo and Virgo. We will see that the upper limits obtained with searches for periodic GW begin to be astrophysically interesting by imposing non-trivial constraints on the structure and evolution of the neutron stars. We will give prospects for the future detection of pulsar GW signals, with Advanced Ligo and Advanced Virgo and future enhanced detectors, e.g. the Einstein Telescope
Jeans analysis of self-gravitating systems in f(R)-gravity
Dynamics and collapse of collisionless self-gravitating systems is described
by the coupled collisionless Boltzmann and Poisson equations derived from
-gravity in the weak field approximation. Specifically, we describe a
system at equilibrium by a time-independent distribution function
and two potentials and solutions of the modified
Poisson and collisionless Boltzmann equations. Considering a small perturbation
from the equilibrium and linearizing the field equations, it can be obtained a
dispersion relation. A dispersion equation is achieved for neutral
dust-particle systems where a generalized Jeans wave-number is obtained. This
analysis gives rise to unstable modes not present in the standard Jeans
analysis (derived assuming Newtonian gravity as weak filed limit of ).
In this perspective, we discuss several self-gravitating astrophysical systems
whose dynamics could be fully addressed in the framework of -gravity.Comment: 8 pages, 2 figures, Accepted for publication in PR
Stent-assisted detachable coil embolization of wide-necked renal artery aneurysms
Renal artery aneurysms (RAAs) are rare with an estimated incidence of 0.1% in the general population, and they represent approximately 25% of all visceral aneurysms. The gold standard of treatment is open surgery, but it is associated with a high risk of nephrectomy, mortality, and morbidity. Less invasive endovascular therapies are becoming increasingly common for the treatment of RAAs. Here, we aimed to report three cases of wide-necked complex renal artery aneurysms treated endovascularly using stent-assisted coil embolization with self-expandable stent nitinol Solitaire AB and Concerto Axium coils. In addition, we describe the use of the waffle-cone technique in a case of wide-necked saccular RAA involving the renal artery bifurcation. Technical success was achieved in all three cases with no early or late complications and no recurrences
Structural and optoelectronical characterization of Si-SiO_2/SiO_2 multilayers with applications in all Si tandem solar cells
SiO_2 multilayers with embedded Si nanocrystals (Si-ncs) were investigated as an approach for developing highly efficient all Si tandem solar cells. The nanostructured samples, fabricated by means of a reactive magnetron sputtering, were structurally and optoelectronically characterized using different techniques. High resolution transmission electron microscopy (TEM) and energy filtered images in TEM show a high density of Si-nc with uniform sizes below 4 nm, while electrical characterization indicates high resistance values (10^2 kΩ) of these samples. In order to develop a better understanding of the optoelectronical behavior, photocurrent I-V curves were measured, obtaining variations under "dark" or "illumination" conditions. Recombination lifetimes in the order of tenths of nanoseconds were estimated by applying the transverse pump/probe technique
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