847 research outputs found
Type Ia supernova counts at high z: signatures of cosmological models and progenitors
Determination of the rates at which supernovae of Type Ia (SNe Ia) occur in
the early Universe can give signatures of the time spent by the binary
progenitor systems to reach explosion and of the geometry of the Universe.
Observations made within the Supernova Cosmology Project are already providing
the first numbers. Here it is shown that, for any assumed SNe Ia progenitor,
SNe Ia counts up to are useful tests of the SNe Ia
progenitor systems and cosmological tracers of a possible non-zero value of the
cosmological constant, . The SNe Ia counts at high redshifts compare
differently with those at lower redshifts depending on the cosmological model.
Flat --dominated universes would show a more significant
increase of the SNe Ia counts at than a flat,
universe. Here we consider three sorts of universes: a flat universe with
, , ;
an open universe with , ,
; and a flat, --dominated universe with , , ). On the
other hand, the SNe Ia counts from one class of binary progenitors (double
degenerate systems) should not increase steeply in the to range,
contrary to what should be seen for other binary progenitors. A measurement of
the SNe Ia counts up to is within reach of ongoing SNe Ia searches
at high redshifts.Comment: 16 pages, incl. 2 figures. To appear in ApJ (Letters
Type Ia Supernova Scenarios and the Hubble Sequence
The dependence of the Type Ia supernova (SN Ia) rate on galaxy type is
examined for three currently proposed scenarios: merging of a
Chandrasekhar--mass CO white dwarf (WD) with a CO WD companion, explosion of a
sub--Chandrasekhar mass CO WD induced by accretion of material from a He star
companion, and explosion of a sub--Chandrasekhar CO WD in a symbiotic system.
The variation of the SNe Ia rate and explosion characteristics with time is
derived, and its correlation with parent population age and galaxy redshift is
discussed. Among current scenarios, CO + He star systems should be absent from
E galaxies. Explosion of CO WDs in symbiotic systems could account for the SNe
Ia rate in these galaxies. The same might be true for the CO + CO WD scenario,
depending on the value of the common envelope parameter. A testable prediction
of the sub--Chandrasekhar WD model is that the average brightness and kinetic
energy of the SN Ia events should increase with redshift for a given Hubble
type. Also for this scenario, going along the Hubble sequence from E to Sc
galaxies SNe Ia events should be brighter on average and should show larger
mean velocities of the ejecta. The observational correlations strongly suggest
that the characteristics of the SNe Ia explosion are linked to parent
population age. The scenario in which WDs with masses below the Chandrasekhar
mass explode appears the most promising one to explain the observed variation
of the SN Ia rate with galaxy type together with the luminosity--expansion
velocity trend.Comment: 16 pages uuencoded compressed Postscript, 2 figures included. ApJ
Letters, in pres
Blue carbon stocks in Baltic Sea eelgrass (Zostera marina) meadows
Although seagrasses cover only a minor fraction of the ocean seafloor, their
carbon sink capacity accounts for nearly one-fifth of the total oceanic
carbon burial and thus play a critical structural and functional role in
many coastal ecosystems. We sampled 10 eelgrass (<i>Zostera marina</i>) meadows in Finland and 10
in Denmark to explore seagrass carbon stocks (C<sub>org</sub> stock) and carbon
accumulation rates (C<sub>org</sub> accumulation) in the Baltic Sea area. The study
sites represent a gradient from sheltered to exposed locations in both
regions to reflect expected minimum and maximum stocks and accumulation. The
C<sub>org</sub> stock integrated over the top 25 cm of the sediment averaged 627 g C m<sup>−2</sup> in Finland, while in Denmark the average C<sub>org</sub> stock was over
6 times higher (4324 g C m<sup>−2</sup>). A conservative estimate of the total
organic carbon pool in the regions ranged between 6.98 and 44.9 t C ha<sup>−1</sup>.
Our results suggest that the Finnish eelgrass meadows are minor carbon sinks
compared to the Danish meadows, and that majority of the C<sub>org</sub> produced in
the Finnish meadows is exported. Our analysis further showed that
> 40 % of the variation in the C<sub>org</sub> stocks was explained by
sediment characteristics, i.e. dry density, porosity and silt content. In
addition, our analysis show that the root : shoot ratio of <i>Z. marina</i> explained
> 12 % and the contribution of <i>Z. marina</i> detritus to the sediment surface
C<sub>org</sub> pool explained > 10 % of the variation in the C<sub>org</sub> stocks.
The mean monetary value for the present carbon storage and carbon sink
capacity of eelgrass meadows in Finland and Denmark, were 281 and 1809 EUR ha<sup>−1</sup>, respectively. For a more comprehensive picture of
seagrass carbon storage capacity, we conclude that future blue carbon
studies should, in a more integrative way, investigate the interactions
between sediment biogeochemistry, seascape structure, plant species
architecture and the hydrodynamic regime
Developments in ROOT I/O and trees
For the last several months the main focus of development in the ROOT I/O
package has been code consolidation and performance improvements. Access to
remote files is affected both by bandwidth and latency. We introduced a
pre-fetch mechanism to minimize the number of transactions between client and
server and hence reducing the effect of latency. We will review the
implementation and how well it works in different conditions (gain of an order
of magnitude for remote file access). We will also review new utilities,
including a faster implementation of TTree cloning (gain of an order of
magnitude), a generic mechanism for object references, and a new entry list
mechanism tuned both for small and large number of selections. In addition to
reducing the coupling with the core module and becoming its owns library
(libRIO) (as part of the general restructuration of the ROOT libraries), the
I/O package has been enhanced in the area of XML and SQL support, thread
safety, schema evolution, TTreeFormula, and many other areas. We will also
discuss various ways, ROOT will be able to benefit from multi-core architecture
to improve I/O performances
Type Ia Supernovae: An Examination of Potential Progenitors and the Redshift Distribution
We examine the possibility that supernovae type Ia (SN Ia) are produced by
white dwarfs accreting from Roche-lobe filling evolved companions, under the
assumption that a strong optically thick stellar wind from accretor is able to
stabilize the mass transfer. We show that if a mass transfer phase on a thermal
timescale precedes a nuclear burning driven phase, then such systems (of which
the supersoft X-ray sources are a subgroup) can account for about 10% of the
inferred SN Ia rate.
In addition, we examine the cosmic history of the supernova rate, and we show
that the ratio of the rate of SN Ia to the rate of supernovae produced by
massive stars (supernovae of types II, Ib, Ic) should increase from about z = 1
towards lower redshifts.Comment: 29 pages, Latex, 6 figures, aasms4.sty, psfig.sty, to appear in The
Astrophysical Journa
Capacitación y supervisión a equipos técnicos: saldando una deuda pendiente en temas de discapacidad y vejez
El presente trabajo hace referencia a la experiencia que surge de la implementación del proyecto aprobado y financiado en 2010 por Extensión Universitaria de la UNLP, denominado “Capacitación y Supervisión a equipos interdisciplinarios: saldando una deuda pendiente en temas de vejez y discapacidad”. Fueron partícipes de esta experiencia estudiantes avanzados, graduados y profesores de las Facultades de Humanidades y Ciencias de la Educación, Psicología y Trabajo Social (en carácter de Unidad Ejecutora), y como co-participantes la Comisión Universitaria sobre Discapacidad (CUD), el INSSJyP – Pami, la Red Mayor Nodo La Plata y la Dirección de Servicios Sociales de la UNLP. La implementación del proyecto implicó las instancias de capacitación y supervisión institucional, destinado a equipos técnicos y profesionales que se desempeñaban en centros de salud, áreas de acción social municipal, organizaciones específicas de adultos mayores e instituciones de personas con discapacidad. La implementación del proyecto dio lugar a que se establecieran tres aspectos a analizar al momento de realizar la evaluación final del mismo: a) la realización de trabajos finales de los diversos destinatarios que con sus diferentes matrices disciplinarias problematizaron la temática de la vejez y la discapacidad, la apropiación de nuevos conocimientos que potenciaron el cuestionamiento de las prácticas vigentes, la incorporación de metodologías de análisis diagnóstico, el conocimiento, diseño e implementación de modelos de gestión y el fortalecimiento del trabajo interdisciplinario; b) la función de Extensión Universitaria de responder a las demandas de la sociedad ante las carencias en la formación académica de los graduados; y finalmente c) impulsar la formación de estudiantes avanzados que a través de la extensión acompañaron el proyecto y participaron activamente en el cumplimiento del mismo. Por otro lado, se debe destacar que esta experiencia de intervención aporta a la política pública a partir del trabajo multidimensional de los diversos actores implicados en la propuesta (Universidad; Estado Nacional; Organizaciones de la Sociedad Civil; Ciudadanos), así como la intención del proyecto en sí mismo de buscar constantemente el conocimiento y la reflexión que permita mejorar la calidad de trabajo de los profesionales, generar ambientes laborales saludables en las diversas instituciones, y consecuentemente contribuir a la mejora de la calidad de vida de quienes reciben los aportes profesionales, en este caso, la población adulta mayor y las personas con discapacidad
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