9,446 research outputs found
Plasma Jets and Eruptions in Solar Coronal Holes: a 3D flux emergence experiment
A three-dimensional numerical experiment of the launching of a hot and fast
coronal jet followed by several violent eruptions is analyzed in detail. These
events are initiated through the emergence of a magnetic flux rope from the
solar interior into a coronal hole. We explore the evolution of the emerging
magnetically-dominated plasma dome surmounted by a current sheet and the
ensuing pattern of reconnection. A hot and fast coronal jet with inverted-Y
shape is produced that shows properties comparable to those frequently observed
with EUV and X-Ray detectors. We analyze its 3D shape, its inhomogeneous
internal structure, and its rise and decay phases, lasting for some 15-20 min
each. Particular attention is devoted to the field-line connectivities and the
reconnection pattern. We also study the cool and high-density volume that
appears encircling the emerged dome. The decay of the jet is followed by a
violent phase with a total of five eruptions. The first of them seems to follow
the general pattern of tether-cutting reconnection in a sheared arcade,
although modified by the field topology created by the preceding reconnection
evolution. The two following eruptions take place near and above the strong
field-concentrations at the surface. They show a twisted, \Omega-loop like rope
expanding in height, with twist being turned into writhe, thus hinting at a
kink instability (perhaps combined with a torus-instability) as the cause of
the eruption. The succession of a main jet ejection and a number of violent
eruptions that resemble mini-CME's and their physical properties suggest that
this experiment may provide a model for the blowout jets recently proposed in
the literature.Comment: Accepted for publication in The Astrophysical Journal (vol 770, June
2013
Are tornado-like magnetic structures able to support solar prominence plasma?
Recent high-resolution and high-cadence observations have surprisingly
suggested that prominence barbs exhibit apparent rotating motions suggestive of
a tornado-like structure. Additional evidence has been provided by Doppler
measurements. The observations reveal opposite velocities for both hot and cool
plasma on the two sides of a prominence barb. This motion is persistent for
several hours and has been interpreted in terms of rotational motion of
prominence feet. Several authors suggest that such barb motions are rotating
helical structures around a vertical axis similar to tornadoes on Earth. One of
the difficulties of such a proposal is how to support cool prominence plasma in
almost-vertical structures against gravity. In this work we model analytically
a tornado-like structure and try to determine possible mechanisms to support
the prominence plasma. We have found that the Lorentz force can indeed support
the barb plasma provided the magnetic structure is sufficiently twisted and/or
significant poloidal flows are present.Comment: Accepted for publication in ApJ
Para una poética del imaginario espacial en la narrativa de Roberto Bolaño
El artÃculo intenta poner de relieve dos configuraciones espaciales especÃficas vinculadas con el quehacer narrativo de Roberto Bolaño. La primera se vincula con un determinado espacio personal, construido por los signos y su acción significante, que configuran una suerte de espacio literario abismal. La segunda, que se expresa en los tramos de la textualidad, se caracteriza por una escritura derivativa y expansiva, y por una sintaxis que procede por la abundancia, la repetición sostenida y la acumulación rizomática.The article tries to emphasize in two specific spatial configurations of Roberto Bolaño's narrative. The first one relates to a particular personal space, built by the signs and his significant action, that form a sort of abysmal literary space. The second one, which is expressed in the sections of textuality, is characterized by a derivative and expansive writing and for a syntax that by abundance proceeds the sustained repetition and the rhizomatic accumulation
Análisis crÃtico de los informes de evaluación de la amenaza del crimen organizado en la Unión Europea (Oganised Crime Threat Assessment, OCTA)
Tradicionalmente, la orientación reactiva de los cuerpos de seguridad ha hecho que prevalezca un modelo de orientación estratégica basado en la capacidad de respuesta ante hechos consumados o que se encuentran en proceso de ejecución. En la actualidad, diversos factores están condicionando los esfuerzos policiales hacia un modelo de estrategia prospectiva
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