4,136 research outputs found
Are primordial black holes produced by entropy perturbations in single field inflationary models?
We show that in single field inflationary models the super-horizon evolution
of curvature perturbations on comoving slices , which can cause
the production of primordial black holes (PBH), is not due to entropy
perturbations, but to the background evolution effect on the conversion between
entropy and curvature perturbations. We derive a general relation between the
time derivative of comoving curvature perturbations and entropy perturbations,
in terms of a conversion factor depending on the background evolution. Contrary
to previous results derived in the uniform density gauge assuming the gradient
term can be neglected on super-horizon scales, the relation is valid on any
scale for any minimally coupled single scalar field model, also on sub-horizon
scales where gradient terms are large.
We apply it to the case of quasi-inflection inflation, showing that while
entropy perturbations are decreasing, can grow on super-horizon
scales, due to a large increase of the conversion factor. This happens in the
time interval during which a sufficiently fast decrease of the equation of
state transforms into a growing mode that in slow-roll models would be a
decaying mode. The same mechanism also explains the super-horizon evolution of
in globally adiabatic systems, for which entropy perturbations
vanish on any scale, such as ultra slow-roll inflation and its generalizations
Decrease of the maximum speed in highway tunnels as a measure to foster energy savings and sustainability
The high energy consumption of the lighting installations in highway tunnels has become a hot topic in the last few years due to the high figures in terms of money, consumed energy, use of raw materials, emissions of greenhouse gases due to the remarkable number of manufactured elements, and maintenance, among others. In spite of the different strategies proposed up to date and their savings, the potential benefits of decreasing the maximum speed allowed in tunnels have not been considered in depth as a complementary measure yet. In this work, the impact of such a decrease in terms of energy consumption, number projectors, carbon dioxide (CO2) emissions, and yearly costs in energy is analyzed and discussed. The results strongly suggest the convenience of introducing maximum speed reduction in traffic regulations which, in addition, could create positive synergies with traffic safety
A Bayesian model for longitudinal circular data
The analysis of short longitudinal series of circular data may be problematic and to some extent has not been completely developed. In this paper we present a Bayesian analysis of a model for such data. The model is based on a radial projection onto the circle of a particular bivariate normal distribution. Inferences about the parameters of the model are based on samples from the corresponding joint posterior density which are obtained using a Metropolis-within-Gibbs scheme after the introduction of suitable latent variables. The procedure is illustrated both using a simulated data set and a realdata set previously analyzed in the literature.Circular data, Longitudinal data, Gibbs sampler, Latent variables, Mixed-effects linear models, Projected normal distribution
Recalibration of Pagel's method for HII regions considering the thermal structure, the ionization structure, and the depletion of O into dust grains
Using a sample of 28 HII regions from the literature with measured
temperature inhomogeneity parameter, t^2, we present a statistical correction
to the chemical abundances determined with the Te(4363/5007) method. We used
the t^2 values to correct the oxygen gaseous abundances and consider the oxygen
depletion into dust to calculate the total abundances for these objects. This
correction is used to obtain a new calibration of Pagel's strong-line method,
R_{23}, to determine oxygen abundances in HII regions. Our new calibration
simultaneously considers the temperature structure, the ionization structure,
and the fraction of oxygen depleted into dust grains. Previous calibrations in
the literature have included one or two of these factors; this is the first
time all three are taken into account. This recalibration conciliates the
systematic differences among the temperatures found from different methods. We
find that the total correction due to thermal inhomogeneities and dust
depletion amounts to an increase in the O/H ratio of HII regions by factors of
1.7 to 2.2 (or 0.22 to 0.35 dex). This result has important implications in
various areas of astrophysics such as the study of the higher end of the
initial mass function, the star formation rate, and the mass-metallicity
relation of galaxies, among others.Comment: 16 pages (preprint), 4 figures, 1 Table, accepted in ApJ
A multivariate generalized independent factor GARCH model with an application to financial stock returns
We propose a new multivariate factor GARCH model, the GICA-GARCH model ,
where the data are assumed to be generated by a set of independent components (ICs).
This model applies independent component analysis (ICA) to search the conditionally
heteroskedastic latent factors. We will use two ICA approaches to estimate the ICs. The
first one estimates the components maximizing their non-gaussianity, and the second
one exploits the temporal structure of the data. After estimating the ICs, we fit an
univariate GARCH model to the volatility of each IC. Thus, the GICA-GARCH reduces
the complexity to estimate a multivariate GARCH model by transforming it into a small
number of univariate volatility models. We report some simulation experiments to show
the ability of ICA to discover leading factors in a multivariate vector of financial data.
An empirical application to the Madrid stock market will be presented, where we
compare the forecasting accuracy of the GICA-GARCH model versus the orthogonal
GARCH one
Refrigeration Capacity and Effect of Ageing on the Operation of Cellulose Evaporative Cooling Pads, by Wind Tunnel Analysis
This study investigates the temperature reduction capacity and water consumption of a
fan-pad system installed in a greenhouse located in the coastal regions of Almería. The suitability
of this system for coastal zones with high environmental humidity during the summer is analyzed.
Historical temperature and relative humidity series are studied, obtaining the thermal difference and
maximum, medium, and minimum monthly water consumption of the pads based on the operation
data of the pads. Despite the high relative humidity of the air in the hottest hours of the day, a
decrease of 5.92 ºC in the mean temperature and a water consumption of 13.55 l/h per square meter
of an evaporative cooling pad are obtained in the month of August. Additionally, the operation of a
cellulose evaporative cooling pad installed for 3 years in a greenhouse is analyzed in a wind tunnel
and compared with that of a new pad of the same model. Over time and with low maintenance,
the porosity of the pad decreases due to salt incrustation. The salt incrustation makes airflow more
difficult in the pad, increasing the pressure drop by 170.04%; however, the air saturation efficiency of
the pad increases by 6.6% due to the greater contact time between the air and the waterMinisterio de Economía y Competitividad de España AGL2015-68050-RUnión Europea (FEDER) AGL2015-68050-
La teoría fuerte de los derechos sociales: reconstrucción y crítica | The Strong Theory of Social Rights: Reconstruction and Criticism
RESUMEN. En este artículo es objeto de análisis la teoría fuerte de los derechos sociales, que es presentada como una teoría unificadora del fundamento, la estructura normativa y los procedimientos de garantía de los diversos tipos de derechos y, en particular, de derechos sociales y de libertad. La teoría es objeto de una serie de consideraciones críticas que apuntan a algunos de sus presupuestos éticos, a sus consecuencias político-constitucionales, a sus problemáticos efectos económicos, al modo en que reconstruye la estructura normativa de los derechos que se considera deficiente y al modelo de garantía judicial propuesto para los derechos sociales que se reputa contraproducente. ABSTRACT. The topic of this article is the strong theory of social rights, which is described as an unifying theory on the grounds, the normative structure and the procedures for protecting different types of rights and, in particular, social rights and liberty rights. Some aspects of that theory are criticized, namely, some of its moral assumptions, its political and constitutional consequences, its troublesome economic effects, the way it presents the normative structure of rights which is considered flawed, and the model of judicial guarantee proposed for social rights which it is said to be counterproductive
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