2,621 research outputs found
Discovery of a Candidate Inner Oort Cloud Planetoid
We report the discovery of the minor planet (90377) Sedna, the most distant object ever seen in the solar system. Prediscovery images from 2001, 2002, and 2003 have allowed us to refine the orbit sufficiently to conclude that Sedna is on a highly eccentric orbit that permanently resides well beyond the Kuiper Belt with a semimajor axis of 480 ± 40 AU and a perihelion of 76 ± 4 AU. Such an orbit is unexpected in our current understanding of the solar system but could be the result of scattering by a yet-to-be-discovered planet, perturbation by an anomalously close stellar encounter, or formation of the solar system within a cluster of stars. In all of these cases a significant additional population is likely present, and in the two most likely cases Sedna is best considered a member of the inner Oort Cloud, which then extends to much smaller semimajor axes than previously expected. Continued discovery and orbital characterization of objects in this inner Oort Cloud will verify the genesis of this unexpected population
Finite element formulation of general boundary conditions for incompressible flows
We study the finite element formulation of general boundary conditions for
incompressible flow problems. Distinguishing between the contributions from the
inviscid and viscid parts of the equations, we use Nitsche's method to develop
a discrete weighted weak formulation valid for all values of the viscosity
parameter, including the limit case of the Euler equations. In order to control
the discrete kinetic energy, additional consistent terms are introduced. We
treat the limit case as a (degenerate) system of hyperbolic equations, using a
balanced spectral decomposition of the flux Jacobian matrix, in analogy with
compressible flows. Then, following the theory of Friedrich's systems, the
natural characteristic boundary condition is generalized to the considered
physical boundary conditions. Several numerical experiments, including standard
benchmarks for viscous flows as well as inviscid flows are presented
Primera cita de Myotis daubentonii (Kuhl, 1817), per a les Illes Balears
Abstract not availabl
The magnetic field configuration of a solar prominence inferred from spectropolarimetric observations in the He I 10830 A triplet
Context: The determination of the magnetic field vector in quiescent solar
prominences is possible by interpreting the Hanle and Zeeman effects in
spectral lines. However, observational measurements are scarce and lack high
spatial resolution. Aims: To determine the magnetic field vector configuration
along a quiescent solar prominence by interpreting spectropolarimetric
measurements in the He I 1083.0 nm triplet obtained with the Tenerife Infrared
Polarimeter installed at the German Vacuum Tower Telescope of the Observatorio
del Teide. Methods. The He I 1083.0 nm triplet Stokes profiles are analyzed
with an inversion code that takes into account the physics responsible of the
polarization signals in this triplet. The results are put into a solar context
with the help of extreme ultraviolet observations taken with the Solar Dynamic
Observatory and the Solar Terrestrial Relations Observatory satellites.
Results: For the most probable magnetic field vector configuration, the
analysis depicts a mean field strength of 7 gauss. We do not find local
variations in the field strength except that the field is, in average, lower in
the prominence body than in the prominence feet, where the field strength
reaches 25 gauss. The averaged magnetic field inclination with respect to the
local vertical is 77 degrees. The acute angle of the magnetic field vector with
the prominence main axis is 24 degrees for the sinistral chirality case and 58
degrees for the dextral chirality. These inferences are in rough agreement with
previous results obtained from the analysis of data acquired with lower spatial
resolutions.Comment: Accepted in A&
Análisis de un protocolo para la ciclofotocoagulación láser diodo según la estratificación del riesgo
Los procedimientos ciclodestructivos son una alternativa en el manejo quirúrgico del
glaucoma avanzado y con pobre pronóstico visual. Como en la mayoría de cirugías para
glaucoma, existe, para la ciclofotocoagulación un protocolo estándar (técnica clásica); el
cual puede ser modificado según el efecto deseado y el riesgo de complicaciones, a un
protocolo menos agresivo (técnica de fotocoagulación lenta). Se propone describir una serie de casos de la aplicación, según el riesgo presumible de
fracaso o complicaciones, de dos protocolos de tratamiento (clásico y coagulación lenta)
de la ciclofotocoagulación láser diodo transescleral, sus resultados y complicaciones.Máster en Subespecialidades Oftalmológica
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