1,224 research outputs found
A refined analysis of the low-mass eclipsing binary system T-Cyg1-12664
The observational mass-radius relation of main sequence stars with masses
between ~0.3 and 1.0 Msun reveals deviations between the stellar radii
predicted by models and the observed radii of stars in detached binaries. We
generate an accurate physical model of the low-mass eclipsing binary
T-Cyg1-12664 in the Kepler mission field to measure the physical parameters of
its components and to compare them with the prediction of theoretical stellar
evolution models. We analyze the Kepler mission light curve of T-Cyg1-12664 to
accurately measure the times and phases of the primary and secondary eclipse.
In addition, we measure the rotational period of the primary component by
analyzing the out-of-eclipse oscillations that are due to spots. We accurately
constrain the effective temperature of the system using ground-based absolute
photometry in B, V, Rc, and Ic. We also obtain and analyze V, Rc, Ic
differential light curves to measure the eccentricity and the orbital
inclination of the system, and a precise Teff ratio. From the joint analysis of
new radial velocities and those in the literature we measure the individual
masses of the stars. Finally, we use the PHOEBE code to generate a physical
model of the system. T-Cyg1-12664 is a low eccentricity system, located
d=360+/-22 pc away from us, with an orbital period of P=4.1287955(4) days, and
an orbital inclination i=86.969+/-0.056 degrees. It is composed of two very
different stars with an active G6 primary with Teff1=5560+/-160 K,
M1=0.680+/-0.045 Msun, R1=0.799+/-0.017 Rsun, and a M3V secondary star with
Teff2=3460+/-210 K, M2=0.376+/-0.017 Msun, and R2=0.3475+/-0.0081 Rsun. The
primary star is an oversized and spotted active star, hotter than the stars in
its mass range. The secondary is a cool star near the mass boundary for fully
convective stars (M~0.35 Msun), whose parameters appear to be in agreement with
low-mass stellar model.Comment: 18 pages, 15 figures, 15 table
Dielectric Function of Diluted Magnetic Semiconductors in the Infrared Regime
We present a study of the dielectric function of metallic (III,Mn)V diluted
magnetic semiconductors in the infrared regime. Our theoretical approach is
based on the kinetic exchange model for carrier induced (III,Mn)V
ferromagnetism. The dielectric function is calculated within the random phase
approximation and, within this metallic regime, we treat disorder effects
perturbatively and thermal effects within the mean field approximation. We also
discuss the implications of this calculations on carrier concentration
measurements from the optical f-sum rule and the analysis of plasmon-phonon
coupled modes in Raman spectra.Comment: 6 pages, 6 figures include
Desarrollo de actividades de evaluación para un sistema on-line de aprendizaje de idiomas
Actas de: VII Jornada de Innovación Pedagógica. Proyecto ADA-Madrid: Experiencias de evaluación en e-learning. Madrid, 13 abril 2012.En este artículo describimos la aplicación LEGA (Learning English? Go Ahead!), desarrollada con la finalidad de integrar las diferentes actividades de evaluación definidas en los exámenes de la Universidad de Cambridge para el programa ESOL (English for Speakers of Other Languages). Entre los objetivos de la aplicación destacan la integración de diferentes tecnologías para facilitar la interacción natural persona-máquina y la adaptación de la misma teniendo en cuenta las preferencias y evolución específica de cada uno de sus usuarios durante el proceso de aprendizaje.In this paper we describe the LEGA system (Learning English? Go Ahead!), developed with the aim of integrating the set of assessment exercises defined by the University of Cambridge in the ESOL program (English for Speakers of Other Languages). The objectives of the application include integrating different technologies to facilitate human-machine natural interaction and its adaptation to consider users’ specific preferences and evolution during the learning process.Publicad
Spatio-temporal patterns and morphological characterisation of multispecies pelagic fish schools in the North-Western Mediterranean Sea
Echosounder data from four surveys (1992, 1993, 1995 and 1996) is used to investigate the spatio-temporal variability of school behaviour in North-Western Mediterranean waters. The schools are described using morphological, energetic, spatial and temporal descriptors. The variability in the morphological, positional and energetic parameters of the schools is attributable more to the size of the school's individuals (juveniles or adults) than to the relative composition (percentage) of pelagic species in the area. This fact made difficult the identification of species in the studied area. The concentration of schools in certain geographic zones is determined by local oceanographic characteristics that favour the trophic or reproductive activity of these species. The diurnal aggregative behaviour of pelagic species is typical of the zone and no schools were detected at night. The biomass of the pelagic species in the area under consideration has diminished during the 4-year study period and no relationship was found between the number of schools and the biomass evaluated. This is the first time that the schools of small pelagic fishes from the Spanish Mediterranean Sea have been described and the information could be useful to the management and exploitation of the fisheries in the areaPublicado
Recovery of Pseudomonas savastanoi pv. savastanoi from symptomless shoots of naturally infected olive trees
Seasonal dynamics of Pseudomonas savastanoi pv. savastanoi (Psv) on stems and leaves from symptomless
shoots of naturally infected olive trees was monitored in Spanish olive orchards. Data inferred from the comparison between washing of leaves and dilution-plating versus leaf printing of individual leaves suggested that Psv population sizes varied by over several orders of magnitude, among leaves sampled concurrently from the same shoot. We did not find significant differences between leaves and stems, in respect to the number of samples where Psv was isolated or detected by PCR, showing that Psv colonizes both leaves and stems. The frequencies of Psv isolation and average populations were highly variable among field plots. No correlation between Psv populations and those of non-Psv bacteria in any plant material or field plot was observed. However, where both Psv and yellow Pantoea agglomerans colonies were isolated a positive correlation was found. In a selected field plot, dynamics of Psv over three years showed significant differences between summer and the rest of seasons. The highest Psv population occurred in warm, rainy months, while low numbers were generally found in hot and dry months. [Int Microbiol 2007; 10(2):77-84
A tunable floating-gate CMOS transconductor based on current multiplication
In this paper a novel transconductor based on floating
gate techniques that performs current multiplication for tuning is
presented. The multiplication is achieved using transistors
operating in weak and moderate inversion together with floating
voltage sources implemented conveniently by floating capacitors.
Besides, a tuning scheme is proposed to set the transconductance
parameter accurately. The resulting circuit features compactness,
low voltage operation, and rail-to-rail input range. Measurement
and simulation results using a 0.5um CMOS technology are
presented to confirm all the circuits and strategies proposed
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