3,672 research outputs found
Large-Eddy Simulation closures of passive scalar turbulence: a systematic approach
The issue of the parameterization of small scale (``subgrid'') turbulence is
addressed in the context of passive scalar transport. We focus on the Kraichnan
advection model which lends itself to the analytical investigation of the
closure problem. We derive systematically the dynamical equations which rule
the evolution of the coarse-grained scalar field. At the lowest-order
approximation in , being the characteristic scale of the filter
defining the coarse-grained scalar field and the inertial range separation,
we recover the classical eddy-diffusivity parameterization of small scales. At
the next-leading order a dynamical closure is obtained. The latter outperforms
the classical model and is therefore a natural candidate for subgrid modelling
of scalar transport in generic turbulent flows.Comment: 10 LaTex pages, 1 PS figure. Changes: comments added below previous
(3.10); Previous (3.16) has been corrected; Minor changes in the conclusion
The Phoenix Deep Survey: The 1.4 GHz microJansky catalogue
The initial Phoenix Deep Survey (PDS) observations with the Australia
Telescope Compact Array have been supplemented by additional 1.4 GHz
observations over the past few years. Here we present details of the
construction of a new mosaic image covering an area of 4.56 square degrees, an
investigation of the reliability of the source measurements, and the 1.4 GHz
source counts for the compiled radio catalogue. The mosaic achieves a 1-sigma
rms noise of 12 microJy at its most sensitive, and a homogeneous radio-selected
catalogue of over 2000 sources reaching flux densities as faint as 60 microJy
has been compiled. The source parameter measurements are found to be consistent
with the expected uncertainties from the image noise levels and the Gaussian
source fitting procedure. A radio-selected sample avoids the complications of
obscuration associated with optically-selected samples, and by utilising
complementary PDS observations including multicolour optical, near-infrared and
spectroscopic data, this radio catalogue will be used in a detailed
investigation of the evolution in star-formation spanning the redshift range 0
< z < 1. The homogeneity of the catalogue ensures a consistent picture of
galaxy evolution can be developed over the full cosmologically significant
redshift range of interest. The 1.4 GHz mosaic image and the source catalogue
are available on the web at http://www.atnf.csiro.au/~ahopkins/phoenix/ or from
the authors by request.Comment: 16 pages, 11 figures, 4 tables. Accepted for publication by A
CHARACTERIZATION OF EQUILIBRIUM CONDITIONS OF ADSORBED SILICAGEL/WATER BED ACCORDING TO DUBININASTAKHOV AND FREUNDLICH
Systems of adsorption have been studied as an alternative for the cooling systems for saving
electrical energy. The main advantage is the heat as the driving sources, for example, hot
water or waste heat, widely used in the industries, and solar energy. The pair adsorbent/
adsorbate determines the behavior of these systems. Therefore, the knowledge of the
equilibrium conditions between the adsorbent and the adsorbate is very important. The pair
silica gel/water has the advantage of exploiting low-temperature heat sources. In this paper,
the equilibrium conditions of the pair silica gel/water were investigated and the data were
used to identify the coefficients of Dubinin-Astakhov equation and Freundlich equation.
The experiments consisted of measuring temperature and pressure for different adsorbed
mass of water in the adsorbent (silica gel). The amount of adsorbed mass (kg) per adsorbent
mass (kg) used were: 0.007, 0.013, 0.024, 0.047, 0.092, 0.162 and 0.209. Both equations
showed good agreement with experimental data, the coefficients of regression (R2) were
0.991 on the Dubinin-Astakhov equation and 0.993 for the Freundlich equation
Economic efficiency of public secondary education expenditure: how different are developed and developing countries?
Este estudio mide la eficiencia del gasto público en educación secundaria en 35 países desarrollados y en desarrollo mediante el uso de una metodología semiparamétrica DEA (análisis envolvente de datos) en dos pasos. En primer lugar, implementamos dos modelos de frontera transfronteriza para el período 2009-2012: uno que utiliza un aporte físico (es decir, relación maestro-alumno) y otro que utiliza un aporte monetario (es decir, gasto gubernamental por estudiante secundario). Estos resultados se corrigen por los efectos del PIB per cápita y el logro educativo de los adultos como insumos no discrecionales. Obtenemos cuatro resultados importantes: (i) los países desarrollados y en desarrollo tienen los mismos procesos de producción educativa cuando se comparan utilizando insumos físicos, pero no cuando se los compara con insumos monetarios; (ii) los países en desarrollo podrían aumentar sus tasas de matrícula y puntajes PISA en aproximadamente un 9% y un 5%, respectivamente, al mantener las mismas proporciones maestro-alumno y los niveles de gasto público que los países desarrollados; (iii) Irlanda, Japón y Corea son países eficientes en los dos modelos de frontera (Colombia también se incluye en esta categoría cuando se utiliza la relación maestro-alumno como insumo); y (iv) la sólida evidencia empírica indica que tanto el ingreso como el logro educativo de los padres afectan positivamente la eficiencia de la educación pública en ambos modelos.This study measures the efficiency of public secondary education expenditure in 35 developing and developed countries using a two-step semi-parametric DEA (data envelopment analysis) methodology. First, we implement two cross-country frontier models for the 2009-2012 period: one using a physical input (i.e., teacher-pupil ratio) and one using a monetary input (i.e., government expenditure per secondary student). These results are corrected by the effects of GDP per capita and adult educational attainment as non-discretionary inputs. We obtain four important results: (i) developed and developing countries have the same education production processes when they are compared using physical inputs but not when compared using monetary inputs; (ii) developing countries could increase their enrollment rates and PISA scores by approximately 9% and 5%, respectively, by maintaining the same teacher-pupil ratios and public spending levels as developed countries; (iii) Ireland, Japan and Korea are efficient countries in the two frontier models (Colombia is also included in this category when the teacher-pupil ratio is used as input); and (iv) robust empirical evidence indicates that both income and parental educational attainment positively affect the efficiency of public education in both models
Competition controls the rate of transition between the peripheral pools of CD4+CD25− and CD4+CD25+ T cells
Recent reports have hinted that it is possible to regenerate CD4+CD25+ regulatory T cells (Treg) from CD4+CD25− cells, a phenomenon termed conversion. We evaluated the relative contribution of this process to the Treg pool by transferring purified populations of CD4+ T cells into T cell-deficient mice. We report that conversion of CD25− cells into the CD4+CD25+Treg pool is minor if other bona fide CD25+ Tregs are present. Moreover, in the same hosts, the loss of CD25 expression by a population of Tregs also decreases in the presence of co-injected CD4+CD25− cells. Thus, the rate of exchange between CD25− and CD25+ T-cell populations is determined by the presence or absence of T-cell competitors. Our results attest for the role of competition in the contribution of different T-cell subsets for the regeneration of the peripheral CD4+ T-cell pool during lymphopeni
Coarse-grained description of a passive scalar
The issue of the parameterization of small-scale dynamics is addressed in the
context of passive-scalar turbulence. The basic idea of our strategy is to
identify dynamical equations for the coarse-grained scalar dynamics starting
from closed equations for two-point statistical indicators. With the aim of
performing a fully-analytical study, the Kraichnan advection model is
considered. The white-in-time character of the latter model indeed leads to
closed equations for the equal-time scalar correlation functions. The classical
closure problem however still arises if a standard filtering procedure is
applied to those equations in the spirit of the large-eddy-simulation strategy.
We show both how to perform exact closures and how to identify the
corresponding coarse-grained scalar evolution.Comment: 22 pages; submitted to Journal of Turbulenc
Análise da qualidade das águas superficiais de Ponte de Lima
No âmbito do tema recursos hídricos e o conceito de sustentabilidade, foi desenvolvido um estudo de caracterização do estado das águas superficiais, de uma área geográfica específica do Alto Minho. O desenvolvimento do estudo assentou numa base temporal e espacial de análise de parâmetros organolépticos, físico-químicos e microbiológicos. Fez-se uma previsão espacial e temporal de parâmetros de qualidade ao longo do rio, de montante para jusante, exclusivamente até aos pontos de amostragem (estações) referentes à área em estudo. Caracterizou-se alguns aspectos hidrográficos da bacia hidrográfica onde está inserida a região em estudo e também deu-se alguma relevância a aspectos sanitários da Estação de Tratamento de Águas Residuais da região. Foram também definidas algumas tendências em termos de indicadores fulcrais de sustentabilidade
A hot Jupiter transiting a mid-K dwarf found in the pre-OmegaCam Transit Survey
We describe the pre-OmegaTranS project, a deep survey for transiting
extra-solar planets in the Carina region of the Galactic Disk. In 2006-2008 we
observed a single dense stellar field with a very high cadence of ~2min using
the ESO Wide Field Imager at the La Silla Observatory. Using the Astronomical
Wide-field System for Europe and the Munich Difference Imaging Analysis
pipeline, a module that has been developed for this project, we created the
light curves of 16000 stars with more than 4000 data points which we searched
for periodic transit signals using a box-fitting least-squares detection
algorithm. All light curves are publicly available. In the course of the
pre-OmegaTranS project we identified two planet candidates - POTS-1b and
POTS-C2b - which we present in this work. With extensive follow-up observations
we were able to confirm one of them, POTS-1b, a hot Jupiter transiting a mid-K
dwarf. The planet has a mass of 2.31+-0.77M_Jup and a radius of 0.94+-0.04R_Jup
and a period of P=3.16d. The host star POTS-1 has a radius of 0.59+-0.02R_Sun
and a mass of 0.70+-0.05M_Sun. Due to its low apparent brightness of I=16.1mag
the follow-up and confirmation of POTS-1b was particularly challenging and
costly.Comment: 18 pages, 23 figures, accepted for publication in MNRA
An intra-vehicular wireless sensor network based on Android mobile devices and bluetooth low energy
This chapter presents the development and test of an intra-vehicular wireless sensor network (IVWSN), based on Bluetooth Low Energy (BLE), designed to present to the driver, in real-time, information collected from multiple sensors distributed inside of the car, using a human-machine interface (HMI) implemented on an Android smartphone. The architecture of the implemented BLE network is composed by the smartphone, which has the role of central station, and two BLE modules (peripheral stations) based on the CC2540 system-on-chip (SoC), which collect relevant sensor information from the battery system and the traction system of a plug-in electric car. Results based on an experimental performance evaluation of the wireless network show that the network is able to satisfy the application requirements, as long as the network parameters are properly configured taking into account the peculiarities of the BLE data transfer modes and the observed limitations of the BLE platform used in the implementation of the IVWSN.This work is supported by FCT with the reference project UID/EEA/04436/2013, COMPETE 2020 with the code POCI-01-0145-FEDER-006941
Microjansky radio sources in DC0107-46 (Abell 2877)
The cluster DC0107-46 (Abell 2877) lies within the Phoenix Deep Survey, made
at 1.4 GHz with the Australia Telescope Compact Array. Of 89 known optical
cluster members, 70 lie within the radio survey area. Of these 70 galaxies, 15
(21%) are detected, with luminosities as faint as 10^20 W/Hz. Spectroscopic
observations are available for 14/15 of the radio-detected cluster galaxies.
Six galaxies show only absorption features and are typical low-luminosity AGN
radio sources. One galaxy hosts a Seyfert 2 nucleus, two are star-forming
galaxies, and the remaining five may be star-forming galaxies, AGNs, or both.Comment: 14 pages, 3 figures, Accepted by ApJS (v128n2p JUN 2000 issue
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