10,279 research outputs found
Gravitomagnetic time delay and the Lense-Thirring effect in Brans-Dicke theory of gravity
We discuss the gravitomagnetic time delay and the Lense-Thirring effect in
the context of Brans-Dicke theory of gravity. We compare the theoretical
results obtained with those predicted by general relativity. We show that
within the accuracy of experiments designed to measure these effects both
theories predict essentially the same result.Comment: 10 pages Typeset using REVTE
Experience with the Open Source based implementation for ATLAS Conditions Data Management System
Conditions Data in high energy physics experiments is frequently seen as
every data needed for reconstruction besides the event data itself. This
includes all sorts of slowly evolving data like detector alignment, calibration
and robustness, and data from detector control system. Also, every Conditions
Data Object is associated with a time interval of validity and a version.
Besides that, quite often is useful to tag collections of Conditions Data
Objects altogether. These issues have already been investigated and a data
model has been proposed and used for different implementations based in
commercial DBMSs, both at CERN and for the BaBar experiment. The special case
of the ATLAS complex trigger that requires online access to calibration and
alignment data poses new challenges that have to be met using a flexible and
customizable solution more in the line of Open Source components. Motivated by
the ATLAS challenges we have developed an alternative implementation, based in
an Open Source RDBMS. Several issues were investigated land will be described
in this paper:
-The best way to map the conditions data model into the relational database
concept considering what are foreseen as the most frequent queries.
-The clustering model best suited to address the scalability problem.
-Extensive tests were performed and will be described.
The very promising results from these tests are attracting the attention from
the HEP community and driving further developments.Comment: 8 pages, 4 figures, 3 tables, conferenc
A new model for gravitational potential perturbations in disks of spiral galaxies. An application to our Galaxy
We propose a new, more realistic, description of the perturbed gravitational
potential of spiral galaxies, with spiral arms having Gaussian-shaped groove
profiles. We investigate the stable stellar orbits in galactic disks, using the
new perturbed potential. The influence of the bulge mass on the stellar orbits
in the inner regions of a disk is also investigated. The new description offers
the advantage of easy control of the parameters of the Gaussian profile of its
potential. We find a range of values for the perturbation amplitude from 400 to
800 km^2 s^{-2} kpc^{-1} which implies a maximum ratio of the tangential force
to the axisymmetric force between 3% and 6%, approximately. Good
self-consistency of arm shapes is obtained between the Inner Lindblad resonance
(ILR) and the 4:1 resonance. Near the 4:1 resonance the response density starts
to deviate from the imposed logarithmic spiral form. This creates bifurcations
that appear as short arms. Therefore the deviation from a perfect logarithmic
spiral in galaxies can be understood as a natural effect of the 4:1 resonance.
Beyond the 4:1 resonance we find closed orbits which have similarities with the
arms observed in our Galaxy. In regions near the center, in the presence of a
massive bulge, elongated stellar orbits appear naturally, without imposing any
bar-shaped potential, but only extending the spiral perturbation a little
inward of the ILR. This suggests that a bar is formed with a half-size around 3
kpc by a mechanism similar to that of the spiral arms. The potential energy
perturbation that we adopted represents an important step in the direction of
self-consistency, compared to previous sine function descriptions of the
potential. Our model produces a realistic description of the spiral structure,
able to explain several details that were not yet understood.Comment: 12 pag., 11 fig. Accepted for publication in A&A, 2012 December 1
Global aspects of gravitomagnetism
We consider global properties of gravitomagnetism by investigating the
gravitomagnetic field of a rotating cosmic string. We show that although the
gravitomagnetic field produced by such a configuration of matter vanishes
locally, it can be detected globally. In this context we discuss the
gravitational analogue of the Aharonov-Bohm effect.Comment: 10 pages - Typeset using REVTE
Gaussian superpositions in scalar-tensor quantum cosmological models
A free scalar field minimally coupled to gravity model is quantized and the
Wheeler-DeWitt equation in minisuperspace is solved analytically, exhibiting
positive and negative frequency modes. The analysis is performed for positive,
negative and zero values of the curvature of the spatial section. Gaussian
superpositions of the modes are constructed, and the quantum bohmian
trajectories are determined in the framework of the Bohm-de Broglie
interpretation of quantum cosmology. Oscillating universes appear in all cases,
but with a characteristic scale of the order of the Planck scale. Bouncing
regular solutions emerge for the flat curvature case. They contract classically
from infinity until a minimum size, where quantum effects become important
acting as repulsive forces avoiding the singularity and creating an
inflationary phase, expanding afterwards to an infinite size, approaching the
classical expansion as long as the scale factor increases. These are
non-singular solutions which are viable models to describe the early Universe.Comment: 14 pages, LaTeX, 3 Postscript figures, uses graficx.st
SOPHIE velocimetry of Kepler transit candidates VI. An additional companion in the KOI-13 system
We report the discovery of a new stellar companion in the KOI-13 system.
KOI-13 is composed by two fast-rotating A-type stars of similar magnitude. One
of these two stars hosts a transiting planet discovered by Kepler. We obtained
new radial velocity measurements using the SOPHIE spectrograph at the
Observatoire de Haute-Provence that revealed an additional companion in this
system. This companion has a mass between 0.4 and 1 Msun and orbits one of the
two main stars with a period of 65.831 \pm 0.029 days and an eccentricity of
0.52 \pm 0.02. The radial velocities of the two stars were derived using a
model of two fast-rotating line profiles. From the residuals, we found a hint
of the stellar variations seen in the Kepler light curve with an amplitude of
about 1.41 km/s and a period close to the rotational period. This signal
appears to be about three order of magnitude larger than expected for stellar
activity. From the analysis of the residuals, we also put a 3-sigma upper-limit
on the mass of the transiting planet KOI-13.01 of 14.8 Mjup and 9.4 Mjup,
depending on which star hosts the transit. We found that this new companion has
no significant impact on the photometric determination of the mass of KOI-13.01
but is expected to affect precise infrared photometry. Finally, using dynamical
simulations, we infer that the new companion is orbiting around KOI-13B while
the transiting planet candidate is expected to orbit KOI-13A. Thus, the
transiting planet candidate KOI-13.01 is orbiting the main component of a
hierarchical triple system.Comment: Accepted in A&A Letters. 4 pages including 4 figures and the RV tabl
Spontaneous spinal epidural haematoma due to arteriovenous malformation in a child
Spontaneous spinal epidural haematoma (SSEH) is a rare clinical entity, especially in infants, in whom only a few cases have been reported. In a paediatric emergency setting, SSEH should be considered as part of the differential diagnosis for acute extremity weakness and paraesthesia. Epidural vascular malformations are often suspected in these cases but have rarely been demonstrated. The authors report herein a case of SSEH in a 9-year-old boy arising from an epidural vascular malformation. He initially presented with sudden intense cervicodorsal pain followed by hypotonic lower extremities and progressive motor weakness, with no sensory change. The MRI showed an acute extradural haematoma extending from C7 to T4 with compression of the spinal cord. After submission to decompression surgery, he presented full recovery in 1 month. The histopathological analysis revealed a vascular malformation.info:eu-repo/semantics/publishedVersio
Utilização do modelo ZAE/FAO para a estimativa da produtividade do sorgo em Alagoas.
O manejo adequado, como a escolha da época de plantio ou o uso da irrigação, permite o maior aproveitamento dos recursos hídricos disponíveis no ambiente. Pode-se estimar a produtividade agrícola da cultura do sorgo através de modelos, desde que calibrados, permitindo variar os manejos. Dessa forma é possível conhecer a resposta da cultura à disponibilidade hídrica de cada local e sua variação ao longo do ano. Assim o objetivo do trabalho foi calibrar o modelo ZAE, estimar a produtividade e avaliar quais as épocas de plantio com menor risco para a cultura do sorgo no Estado de Alagoas. Para calibração do modelo ZAE/FAO foram utilizados dados provenientes do Programa de Melhoramento Genético de Sorgo do Nordeste na região de Araripina ? PE, após a calibração foram simulados os cenários para as cidades de Água Branca, Arapiraca, Palmeira dos Índios e Porto de Pedras, em Alagoas, baseados na época de plantio (a cada 10 dias) x CAD do solo (30, 40 e 65 mm) X sistema de plantio (sequeiro). O modelo apresentou ótimo ajuste, com R2 = 0,87; índice de Wilmont (d) = 0,94; índice de confiabilidade (IC) de 0,87. As produtividades variaram de 1,8 a 1,9 Mg ha-¹, em Água Branca, de 3,7 a 4,1 Mg ha-¹ em Arapiraca, 1,9 a 2,0 Mg ha-¹ em Palmeira dos Índios, 2,2 a 2,3 Mg ha-¹ em Porto de Pedras, no mês de plantio mais produtivo
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