17,646 research outputs found
Circular Orbits in Einstein-Gauss-Bonnet Gravity
The stability under radial and vertical perturbations of circular orbits
associated to particles orbiting a spherically symmetric center of attraction
is study in the context of the n-dimensional: Newtonian theory of gravitation,
Einstein's general relativity, and Einstein-Gauss-Bonnet theory of gravitation.
The presence of a cosmological constant is also considered. We find that this
constant as well as the Gauss-Bonnet coupling constant are crucial to have
stability for .Comment: 11 pages, 4 figs, RevTex, Phys. Rev. D, in pres
Cyclic cycle systems of the complete multipartite graph
In this paper, we study the existence problem for cyclic -cycle
decompositions of the graph , the complete multipartite graph with
parts of size , and give necessary and sufficient conditions for their
existence in the case that
Aneurisma na artéria aorta em caprinos.
Resumo: De 726 caprinos necropsiados, dois (0,28%) apresentaram aneurisma na arteria aorta, sendo um macho com idade de 48 meses e uma femea com cerca de 30 meses. Os animais eram oriundos de um rebanho mantido em regime semi-extensivo com pastejo em caatinga nativa e pernoite em aprisco. Macroscopicamente observou-se palidez das mucosas externas e das visceras. Nas cavidades toracica e abdominal estavam presentes grandes coagulos resultantes da ruptura das partes afetadas das arterias. As lesoes das arterias aorta toracica e abdominal foram carcterizadas pela dilatacao das paredes formando estruturas saculares com presenca de inumeros coagulos e tecidos necroticos de aproximadamente 10cm a 20cm de comprimento. Histologicamente, observou-se a destruicao do tecido endotelial, necrose e infiltracao de leucocitos das camadas intima, media e muscular da arteria. Acredita-se que a causa primaria dos aneurismas detectados esteja relacionado com os processos inflamatorios presentes em outros orgaos. [Aneurism in the aorta artery in goats]. Abstract: Two (0.28%) of 726 necropsyed goats presented aneurism In the aorta artery, one being a male with 48 months and the other, a female about 30 months of age. The animais carne from a herd in semi-extensive regime, grazing in caatinga vegetation and spending the nights in appropriate pan. Paleness in external mucosa and viscera was observed macroscopically. Large coagula were presented in the thoracic and abdominal cavities, dueto ruptura ol the aneurismatic parts of the blood vessels. The lesions of thoracic and abdominal aortas were characterized by wali dilations forming saccular struc-tures, with presenco of many coagula and necrotic tissues of about 10cm to 20cm of length. Histo-logically, a destruetion In the endotelial tissues, nacrosis and infiltration of leucocytes in the intimate, median, and muscular Iayers were observed. It is believed that the primary cause of the aneurisms detected in this study would be related to teh inflamatory processes of other organs
The Structure and Star-Formation History of NGC 5461
We compute photoionization models for the giant extragalactic H II region NGC
5461, and compare their predictions to several observational constraints. Since
we aim at reproducing not only the global properties of the region, but its
local structure also, the models are constrained to reproduce the observed
density profile, and our analysis takes into consideration the bias introduced
by the shapes and sizes of the slits used by different observers. We find that
an asymmetric nebula with a gaussian density distribution, powered by a young
burst of 3.1 Myr, satisfactorily reproduces most of the constraints, and that
the star-formation efficiency inferred from the model agrees with current
estimates. Our results strongly depend on the assumed density law, since
constant density models overestimate the hardness of the ionizing field,
affecting the deduced properties of the central stellar cluster. We illustrate
the features of our best model, and discuss the possible sources of errors and
uncertainties affecting the outcome of this type of studies.Comment: 33 pages (LaTeX), 3 .eps figures. to be published in ApJ, May 200
Effective action in DSR1 quantum field theory
We present the one-loop effective action of a quantum scalar field with DSR1
space-time symmetry as a sum over field modes. The effective action has real
and imaginary parts and manifest charge conjugation asymmetry, which provides
an alternative theoretical setting to the study of the particle-antiparticle
asymmetry in nature.Comment: 8 page
Thermal Emission from HII Galaxies: Discovering the Youngest Systems
We studied the radio properties of very young massive regions of star
formation in HII galaxies, with the aim of detecting episodes of recent star
formation in an early phase of evolution where the first supernovae start to
appear. Our sample consists of 31 HII galaxies, characterized by strong
Hydrogen emission lines, for which low resolution VLA 3.5cm and 6cm
observations were obtained. The radio spectral energy distribution has a range
of behaviours; 1) there are galaxies where the SED is characterized by a
synchrotron-type slope, 2) galaxies with a thermal slope, and, 3) galaxies with
possible free-free absorption at long wavelengths. The latter SEDs were found
in a few galaxies and represent a signature of heavily embedded massive star
clusters closely related to the early stages of massive star formation. Based
on the comparison of the star formation rates determined from the recombination
lines and those determined from the radio emission we find that SFR(Ha) is on
average five times higher than SFR(1.4GHz). We confirm this tendency by
comparing the ratio between the observed flux at 20 cm and the expected one,
calculated based on the Ha star formation rates, both for the galaxies in our
sample and for normal ones. This analysis shows that this ratio is a factor of
2 smaller in our galaxies than in normal ones, indicating that they fall below
the FIR/radio correlation. These results suggest that the emission of these
galaxies is dominated by a recent and massive star formation event in which the
first supernovae (SN) just started to explode. We conclude that the systematic
lack of synchrotron emission in those systems with the largest equivalent width
of Hb can only be explained if those are young starbursts of less than 3.5Myr
of age.Comment: Accepted for publication in Ap
An Optical Study of Stellar and Interstellar Environments of Seven Luminous and Ultraluminous X-Ray Sources
We have studied the stellar and interstellar environments of two luminous
X-ray sources and five ultraluminous X-ray sources (ULXs) in order to gain
insight into their nature. Archival Hubble Space Telescope images were used to
identify the optical counterparts of the ULXs Ho IX X-1 and NGC 1313 X-2, and
to make photometric measurements of the local stellar populations of these and
the luminous source IC 10 X-1. We obtained high-dispersion spectroscopic
observations of the nebulae around these seven sources to search for He II
lambda-4686 emission and to estimate the expansion velocities and kinetic
energies of these nebulae. Our observations did not detect nebular He II
emission from any source, with the exception of LMC X-1; this is either because
we missed the He III regions or because the nebulae are too diffuse to produce
He II surface brightnesses that lie within our detection limit. We compare the
observed ionization and kinematics of the supershells around the ULXs Ho IX X-1
and NGC 1313 X-2 with the energy feedback expected from the underlying stellar
population to assess whether additional energy contributions from the ULXs are
needed. In both cases, we find insufficient UV fluxes or mechanical energies
from the stellar population; thus these ULXs may be partially responsible for
the ionization and energetics of their supershells. All seven sources we
studied are in young stellar environments and six of them have optical
counterparts with masses >~7 M_sun; thus, these sources are most likely
high-mass X-ray binaries.Comment: 30 pages, 9 figures. Numerous minor revisions, primarily to more
accurately cite earlier work by Pakull and Mirioni, and to correct
typographical errors. Removed a misleading sentence in the Introduction (re:
X-ray photoionization by ULXs). Accepted for publication in The Astrophysical
Journal. Figures have been reduced in resolution for space requirements;
full-resolution figures may be requested by email to [email protected]
Ampliação do banco in vitro do gênero Ananas.
A conservação in vitro é uma estratégia que deve ser considerada para a criação de cópias de segurança de importantes coleções de germoplasma. Além de apresentar vantagens sobre a conservação em campo, permite a disponibilização de acessos para uso e intercâmbio de forma rápida e segura. A Embrapa possui uma coleção de germoplasma de abacaxi com 624 acessos do gênero Ananas e espécies afins, em condições de campo. Uma duplicata de segurança in vitro vem sendo introduzida desde 2003, com aproximadamente 200 acessos já estabelecidos.PDF. 097_11
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