21,025 research outputs found
Science with the World Space Observatory - Ultraviolet
The World Space Observatory-Ultraviolet (WSO-UV) will provide access to the
UV range during the next decade. The instrumentation on board will allow to
carry out high resolution imaging, high sensitivity imaging, high resolution
(R~55000) spectroscopy and low resolution (R~2500) long slit spectroscopy. In
this contribution, we briefly outline some of the key science issues that
WSO-UV will address during its lifetime. Among them, of special interest are:
the study of galaxy formation and the intergalactic medium; the astronomical
engines; the Milky Way formation and evol ution, and the formation of the Solar
System and the atmospheres of extrasolar p lanets.Comment: Just one text file (aigomezdecastro.tex). To be published in the
proceeding of the conference: "New Quest in Stellar Astrophysics II: UV
properties of evolved stellar populations" held in Puerto Vallarta - Mexico,
in april 200
Rationality and Brauer group of a moduli space of framed bundles
We prove that the moduli spaces of framed bundles over a smooth projective
curve are rational. We compute the Brauer group of these moduli spaces to be
zero under some assumption on the stability parameter.Comment: 7 pages, to appear in Tbilisi Math. J; v2. reference adde
The innermost regions of the jet in NRAO 150. Wobbling or internal rotation?
NRAO 150 is a very bright millimeter to radio quasar at redshift =1.52 for
which ultra-high-resolution VLBI monitoring has revealed a counter-clockwise
jet-position-angle wobbling at an angular speed /yr in the
innermost regions of the jet. In this paper we present new total and linearly
polarized VLBA images at 43 GHz extending previous studies to cover the
evolution of the jet in NRAO 150 between 2006 and early 2009. We propose a new
scenario to explain the counter-clockwise rotation of the jet position angle
based on a helical motion of the components in a jet viewed faced-on. This
alternative scenario is compatible with the interpretation suggested in
previous works once the indetermination of the absolute position of the
self-calibrated VLBI images is taken into account. Fitting of the jet
components motion to a simple internal rotation kinematical model shows that
this scenario is a likely alternative explanation for the behavior of the
innermost regions in the jet of NRAO 150.Comment: 5 pages, 4 figures, Presented in 'The Innermost Regions of
Relativistic Jets and Their Magnetic Fields' conference. Granada, Spain, 201
Changes in the trajectory of the radio jet in 0735+178?
We present multi-epoch 8.4 and 43 GHz Very Long Baseline Array images of the
BL Lac object 0735+178. The images confirm the presence of a twisted jet with
two sharp apparent bends of 90 within two milliarcseconds of the
core, resembling a helix in projection. The observed twisted geometry could be
the result of precession of the jet inlet, but is more likely produced by
pressure gradients in the external medium through which the jet propagates.
Quasi-stationary components are observed at the locations of the 90
bends, possibly produced by differential Doppler boosting. Identification of
components across epochs, since the earliest VLBI observations of this source
in 1979.2, proves difficult due to the sometimes large time gaps between
observations. One possible identification suggests the existence of
superluminal components following non--ballistic trajectories with velocities
up to . However, in images obtained after mid-1995,
components show a remarkable tendency to cluster near several jet positions,
suggesting a different scenario in which components have remained nearly
stationary in time at least since mid-1995. Comparison with the earlier
published data, covering more than 19 years of observations, suggests a
striking qualitative change in the jet trajectory sometime between mid-1992 and
mid-1995, with the twisted jet structure with stationary components becoming
apparent only at the later epochs. This would require a re-evaluation of the
physical parameters estimated for 0735+178, such as the observing viewing
angle, the plasma bulk Lorentz factor, and those deduced from these.Comment: 18 pages, 5 figures, accepted for publication in MNRA
The formation of planetary disks and winds: an ultraviolet view
Planetary systems are angular momentum reservoirs generated during star
formation. This accretion process produces very powerful engines able to drive
the optical jets and the molecular outflows. A fraction of the engine energy is
released into heating thus the temperature of the engine ranges from the 3000K
of the inner disk material to the 10MK in the areas where magnetic reconnection
occurs. There are important unsolved problems concerning the nature of the
engine, its evolution and the impact of the engine in the chemical evolution of
the inner disk. Of special relevance is the understanding of the shear layer
between the stellar photosphere and the disk; this layer controls a significant
fraction of the magnetic field building up and the subsequent dissipative
processes ougth to be studied in the UV.
This contribution focus on describing the connections between 1 Myr old suns
and the Sun and the requirements for new UV instrumentation to address their
evolution during this period. Two types of observations are shown to be needed:
monitoring programmes and high resolution imaging down to, at least,
milliarsecond scales.Comment: Accepted for publication in Astrophysics and Space Science 9 figure
Debats oberts en el camp de l'avaluació de serveis i programes socials
En aquest article identifiquem els debats principals que en l'actualitat, i segons la nostra opinió, tenen lloc dintre del camp de l'avaluació de serveis i programes socials. Aquests temes de debat són diversos i plurals, i hi ha diverses propostes i reflexions al seu voltant, ja que no tots els autors identifiquen els mateixos temes de debat, alhora que, com és lògic, la seva resolució (la posició adoptada davant de cada polèmica concreta) varia enormement d'un autor a un altre
La convergència lingüística: possible retardador del procés de gramaticalització?
En diferents zones d"Hispanoamèrica, la substitució del futur sintètic en -rá (cantaré, lloverá) per la construcció Ir a + Infinitiu (voy a cantar, va a llover) resulta cada vegada més evident (Bauhr, 1989; Troya, 1998; Almeida y Díaz, 1998; Blas Arroyo, 2005; Sedano, 2006). Si bé en les zones peninsulars monolingües aquesta substitució també es percep, sembla que en les zones bilingües on el castellà està en contacte amb el català la tendència és justament la contrària. En aquest article es pretén verificar aquesta tendència tot partint de la hipòtesi que la construcció Ir a + Infinitiu per expressar valors temporals prospectius es fa servir en menor grau, sobretot en els parlants amb el català como a L1. La justificació cal trobar-la en la influència del català sobre el castellà; concretament, en el paradigma verbal particular del català confusió amb el pretèrit perfet perifràstic (vaig cantar) i esforç articulatori i en el fet que Anar a + Infinitiu no ha gramaticalitzat els mateixos valors que el castellà a Ir a + Infinitiu manté els valors etimològics. Per comprovar-ho, ens valdrem del corpus RESOL; un corpus de dades orals constituït per 94 entrevistes semidirigides realitzades a nens de 6º de primària, i novament quan cursaven 1º de la ESO, a escoles de Mataró i de Manlleu. Un cop analitzat el corpus, les dades revelen que, efectivament, en les zones bilingües, els informants amb el català com a L1 tendeixen a utilitzar la forma sintètica en major grau que la forma analítica. En canvi, els parlants que tenen el castellà com a L1 fan servir majoritàriament la perífrasi Ir a + Infinitiu, tot i que aquest ús no es tan profús como en la resta de zones monolingües peninsulars. En definitiva, el fet de tenir el català como a L1 sembla ser un dels factor que condiciona o determina la proliferació de la construcció Ir a + Infinitiu en el castellà parlat a Catalunya, però, alhora, la convergència de diferents factors lingüístics és el que condiciona l"ús particular d"aquesta perífrasi verbal en la zona analitzada
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