641 research outputs found
Further Criteria for the Existence of Steady Line-Driven Winds
In Paper I, we showed that steady line-driven disk wind solutions can exist
by using "simple" models that mimic the disk environment. Here I extend the
concepts introduced in Paper I and discuss many details of the analysis of the
steady/unsteady nature of 1D line-driven winds. This work confirms the results
and conclusions of Paper I, and is thus consistent with the steady nature of
the 1D streamline line-driven disk wind models of Murray and collaborators and
the 2.5D line-driven disk wind models of Pereyra and collaborators. When
including gas pressures effects, as is routinely done in time-dependent
numerical models, I find that the spatial dependence of the nozzle function
continues to play a key role in determining the steady/unsteady nature of
supersonic line-driven wind solutions. I show here that the
existence/nonexistence of local wind solutions can be proved through the nozzle
function without integrating the equation of motion. This work sets a detailed
framework with which we will analyze, in a following paper, more realistic
models than the "simple" models of Paper I.Comment: 30 pages, 5 figures, accepted for publication by The Astrophysical
Journa
Characterizing a CCD detector for astronomical purposes: OAUNI Project
This work verifies the instrumental characteristics of the CCD detector which
is part of the UNI astronomical observatory. We measured the linearity of the
CCD detector of the SBIG STXL6303E camera, along with the associated gain and
readout noise. The linear response to the incident light of the detector is
extremely linear (R2 =99.99%), its effective gain is 1.65 +/- 0.01 e-/ADU and
its readout noise is 12.2 e-. These values are in agreement with the
manufacturer. We confirm that this detector is extremely precise to make
measurements for astronomical purposes.Comment: 6 pages, 8 figures, Published by TECNIA (UNI
La inclusión de la dimensión económica en la Evaluación de Impacto Ambiental
El objetivo de este trabajo es mostrar la importancia de incluir la dimensión económica en los Estudios deImpacto ambiental (EsIA). Dimensión económica que se incorpora a la evaluación “ex–ante” de inversiones a través del análisis beneficios costos (ABC) y la valoración económica de las externalidades (VEE). El trabajo muestra con ilustraciones y la presentación de dos casos las consecuencias no deseables de ignorar el ABC: a) Existencia de proyectos de eficiencia dudosa en términos de su resultado económico-social; y b) Escasez de proyectos ambientalmente eficientes, pero con escaso retorno económico privado
Proximal nested sampling with data-driven priors for physical scientists
Proximal nested sampling was introduced recently to open up Bayesian model
selection for high-dimensional problems such as computational imaging. The
framework is suitable for models with a log-convex likelihood, which are
ubiquitous in the imaging sciences. The purpose of this article is two-fold.
First, we review proximal nested sampling in a pedagogical manner in an attempt
to elucidate the framework for physical scientists. Second, we show how
proximal nested sampling can be extended in an empirical Bayes setting to
support data-driven priors, such as deep neural networks learned from training
data.Comment: 9 pages, 4 figure
Propósitos de una experiencia formativa con jóvenes : el sentido de las prácticas socioeducativas como vínculo entre educación y trabajo social
El objetivo de esta comunicación es reflexionar sobre nuestra propuesta de formación del curso Educación y Trabajo Social, analizando la integración de los saberes del campo de la pedagogía y del trabajo social, en torno a las prácticas socioeducativas como experiencia formativa.
Analizaremos la configuración de la propuesta pedagógica centrándonos en la relación entre enseñanza, aprendizaje y prácticas socioeducativas, como eje de la formación para la intervención profesional.
En esta reflexión consideramos a la Enseñanza como una práctica social, que se conforma a través de un proceso de interacción socio-histórica, cultural y política que promueve la formación. Por ello, proponemos la formación del/de la futuro/a profesional en trabajo social, incentivando la construcción de saberes en torno a la cuestión social vinculados con el ámbito socioeducativo, mediante el análisis de problemáticas comunitarias situadas, desde una perspectiva socio-pedagógica en función de la cual, orienta su práctica de intervención en la comunidad en el marco de programas institucionales de nuestra unidad académica.Fil: Pereyra, Sonia N.. Universidad Nacional de San Luis.Fil: Calderón, Marcela I.. Universidad Nacional de San Luis
Mental models for the negation of conjunctions and disjunctions
This study investigates why reasoning that involves negation is extremely difficult. We presented participants with reasoning problems containing sentences with negation of conjunctions and disjunctions in order to test predictions derived from the Mental Models Theory of human thought. According to this theory, reasoning consists of representing and comparing possibilities. Different sentential forms would require different cognitive demands. In particular, responses to a sentential negation task would be modulated by working memory load. This prediction would hold for correct responses but also for the general pattern of responses that includes incorrect responses when the task offers different response options. A within-subjects experimental design with selection paradigm was applied to test these predictions. Experimental comparisons and a complementary descriptive study yielded evidence consistent with the theory-driven predictions derived from the Mental Models Theory. The working memory load was critical for the modulation of correct responses and overall responses. We discussed alternative accounts, and suggested additional predictions for further evaluation of these phenomena
On the Steady Nature of Line-Driven Disk Winds
We perform an analytic investigation of the stability of line-driven disk
winds, independent of hydrodynamic simulations. Our motive is to determine
whether or not line-driven disk winds can account for the wide/broad UV
resonance absorption lines seen in cataclysmic variables (CVs) and
quasi-stellar objects (QSOs). In both CVs and QSOs observations generally
indicate that the absorption arising in the outflowing winds has a steady
velocity structure on time scales exceeding years (for CVs) and decades (for
QSOs). However, published results from hydrodynamic simulations of line-driven
disk winds are mixed, with some researchers claiming that the models are
inherently unsteady, while other models produce steady winds. The analytic
investigation presented here shows that if the accretion disk is steady, then
the line-driven disk wind emanating from it can also be steady. In particular,
we show that a gravitational force initially increasing along the wind
streamline, which is characteristic of disk winds, does not imply an unsteady
wind. The steady nature of line-driven disk winds is consistent with the 1D
streamline disk-wind models of Murray and collaborators and the 2.5D
time-dependent models of Pereyra and collaborators. This paper emphasizes the
underlying physics behind the steady nature of line-driven disk winds using
mathematically simple models that mimic the disk environmen
Characteristic QSO Accretion Disk Temperatures from Spectroscopic Continuum Variability
Using Sloan Digital Sky Survey (SDSS) quasar spectra taken at multiple
epochs, we find that the composite flux density differences in the rest frame
wavelength range 1300-6000 AA can be fit by a standard thermal accretion disk
model where the accretion rate has changed from one epoch to the next (without
considering additional continuum emission components). The fit to the composite
residual has two free parameters: a normalizing constant and the average
characteristic temperature . In turn the characteristic temperature
is dependent on the ratio of the mass accretion rate to the square of the black
hole mass. We therefore conclude that most of the UV/optical variability may be
due to processes involving the disk, and thus that a significant fraction of
the UV/optical spectrum may come directly from the disk.Comment: 31 pages, 8 figure
Control de especies de plata alojadas en zeolita A para la optimización de la adsorción por interacción Π
En las zeolitas intercambiadas con Ag+, la activación térmica o reducción química son metodologías para lograr la formación de nano-especies en la estructura del sólido. El proceso involucra la transferencia de carga desde el oxígeno, perteneciente a la red del sólido o al agente reductor químico, hacia el orbital 5s de los cationes Ag+. En este trabajo se estudiaron, mediante HRTEM y UV-vis, diferentes estrategias para el control de las propiedades de las especies de Ag estabilizadas en una zeolita A sintetizada en nuestro laboratorio
On the Steady Nature of Line-Driven Disk Winds: Application to Cataclysmic Variables
We apply the semi-analytical analysis of the steady nature of line-driven
winds presented in two earlier papers to disk winds driven by the flux
distribution of a standard Shakura & Sunyaev (1973) disk for typical
cataclysmic variable (CV) parameters. We find that the wind critical point
tends to be closer to the disk surface towards the inner disk regions. Our main
conclusion, however, is that a line-driven wind, arising from a steady disk
flux distribution of a standard Shakura-Sunyaev disk capable of locally
supplying the corresponding mass flow, is steady. These results confirm the
findings of an earlier paper that studied "simple" flux distributions that are
more readily analyzable than those presented here. These results are consistent
with the steady velocity nature of outflows observationally inferred for both
CVs and quasi-stellar objects (QSOs). We find good agreement with the 2.5D CV
disk wind models of Pereyra and collaborators. These results suggest that the
likely scenario to account for the wind outflows commonly observed in CVs is
the line-driven accretion disk wind scenario, as suggested early-on by Cordova
& Mason (1982). For QSOs, these results show that the line-driven accretion
disk wind continues to be a promising scenario to account for the outflows
detected in broad absorption line (BAL) QSOs, as suggested early-on by Turnshek
(1984), and analyzed in detail by Murray et al. (1995).Comment: 35 pages, 20 figure
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