18,676 research outputs found
Black hole formation in bidimensional dilaton gravity coupled to scalar matter systems
This work deals with the formation of black hole in bidimensional dilaton
gravity coupled to scalar matter fields. We investigate two scalar matter
systems, one described by a sixth power potential and the other defined with
two scalar fields containing up to the fourth power in the fields. The
topological solutions that appear in these cases allow the formation of black
holes in the corresponding dilaton gravity models.Comment: Latex, 9 pages. Published in Mod. Phys. Lett. A14 (1999) 268
Characterization of the stochastic time evolution of short-term average intercore crosstalk in multicore fibers with multiple interfering cores
A theoretical model for the stochastic time evolution of the intercore crosstalk (ICXT) in homogeneous weakly-coupled multicore fibers (MCF) with multiple interfering cores is proposed and validated experimentally. The model relies on the introduction of non-stationary time varying random phase shifts at every center point between the phase matching points of the MCF where the di erence of the e ective refractive indexes of the core of the originating signal and the core su ering from ICXT is zero. Closed form-expressions for the autocovariance of the short-term average ICXT (STAXT) with stationary and non-stationary phase shift models in MCFs with multiple excited cores are derived and validated by comparison with experimental results. These expressions enable estimating the decorrelation time of the STAXT generated by multiple interfering cores from the decorrelation times of the STAXT generated by each pair of cores. The proposed model and the ICXT measurements taken continuously over more than 150 hours show that the decorrelation time of the STAXT generated by multiple interfering cores exceeds the one obtained for the pair of cores with shorter decorrelation time. The proposed model is increasingly important to simulate and design MCF-based systems where the ICXT dynamics must be properly accounted for to develop e cient ICXT-tolerant techniques.info:eu-repo/semantics/publishedVersio
Magnetic field morphology in nearby molecular clouds as revealed by starlight and submillimetre polarization
Within four nearby (d < 160 pc) molecular clouds, we statistically evaluate
the structure of the interstellar magnetic field, projected on the plane of the
sky and integrated along the line of sight, as inferred from the polarized
thermal emission of Galactic dust observed by Planck at 353 GHz and from the
optical and NIR polarization of background starlight. We compare the dispersion
of the field orientation directly in vicinities with an area equivalent to that
subtended by the Planck effective beam at 353 GHz (10') and using the
second-order structure functions of the field orientation angles. We find that
the average dispersion of the starlight-inferred field orientations within
10'-diameter vicinities is less than 20 deg, and that at these scales the mean
field orientation is on average within 5 deg of that inferred from the
submillimetre polarization observations in the considered regions. We also find
that the dispersion of starlight polarization orientations and the polarization
fractions within these vicinities are well reproduced by a Gaussian model of
the turbulent structure of the magnetic field, in agreement with the findings
reported by the Planck collaboration at scales greater than 10' and for
comparable column densities. At scales greater than 10', we find differences of
up to 14.7 deg between the second-order structure functions obtained from
starlight and submillimetre polarization observations in the same positions in
the plane of the sky, but comparison with a Gaussian model of the turbulent
structure of the magnetic field indicates that these differences are small and
are consistent with the difference in angular resolution between both
techniques.Comment: 15 pages, 10 figures, submitted to A&
Growth and forage yield of tropical grasses in silvipastoril systems in Brazil.
Edição especial dos resumos do IUFRO World Congress, 25., 2019, Curitiba
Desempenho e variação genética de progênies de Pinus taeda procedentes de áreas de produção de sementes da África do Sul.
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