1,383 research outputs found
Early star formation traced by the highest redshift quasars
The iron abundance relative to alpha-elements in the circumnuclear region of
quasars is regarded as a clock of the star formation history and, more
specifically, of the enrichment by SNIa. We investigate the iron abundance in a
sample of 22 quasars in the redshift range 3.0<z<6.4 by measuring their rest
frame UV FeII bump, which is shifted into the near-IR, and by comparing it with
the MgII 2798 flux. The observations were performed with a device that can
obtain near-IR spectra in the range 0.8-2.4 um in one shot, thereby enabling an
optimal removal of the continuum underlying the FeII bump. We detect iron in
all quasars including the highest redshift (z=6.4) quasar currently known. The
uniform observational technique and the wide redshift range allows a reliable
study of the trend of the FeII/MgII ratio with redshift. We find the FeII/MgII
ratio is nearly constant at all redshifts, although there is marginal evidence
for a higher FeII/MgII ratio in the quasars at z~6. If the FeII/MgII ratio
reflects the Fe/alpha abundance, this result suggests that the z~6 quasars have
already undergone a major episode of iron enrichment. We discuss the possible
implications of this finding for the star formation history at z>6. We also
detect a population of weak iron emitters at z~4.5, which are possibly hosted
in systems that evolved more slowly. Alternatively, the trend of the FeII/MgII
ratio at high redshift may reflect significantly different physical conditions
of the circumnuclear gas in such high redshift quasars.Comment: Replaced to match the accepted version (ApJL in press), 5 page
Motility of small nematodes in disordered wet granular media
The motility of the worm nematode \textit{Caenorhabditis elegans} is
investigated in shallow, wet granular media as a function of particle size
dispersity and area density (). Surprisingly, we find that the nematode's
propulsion speed is enhanced by the presence of particles in a fluid and is
nearly independent of area density. The undulation speed, often used to
differentiate locomotion gaits, is significantly affected by the bulk material
properties of wet mono- and polydisperse granular media for .
This difference is characterized by a change in the nematode's waveform from
swimming to crawling in dense polydisperse media \textit{only}. This change
highlights the organism's adaptability to subtle differences in local structure
and response between monodisperse and polydisperse media
Yttria and Ceria Doped Zirconia Thin Films Grown by Pulsed Laser Deposition
The Yttria stabilized Zirconia (YSZ) is a standard electrolyte for solid oxide fuel cells (SOFCs), which are potential candidates for next generation portable and mobile power sources. YSZ electrolyte thin films having a cubic single phase allow reducing the SOFC operating temperature without diminishing the electrochemical power density. Films of 8 mol % Yttria stabilized Zirconia (8YSZ) and films with addition of 4 weight % Ceria (8YSZ + 4CeO2) were grown by pulsed laser deposition (PLD) technique using 8YSZ and 8YSZ + 4CeO2 targets and a Nd-YAG laser (355 nm). Films have been deposited on Soda-Calcia-Silica glass and Si(100) substrates at room temperature. The morphology and structural characteristics of the samples have been studied by means of X-ray diffraction and scanning electron microscopy. Films of a cubic-YSZ single phase with thickness in the range of 1-3 µm were grown on different substrates.Fil: Saporiti, F.. Universidad de Buenos Aires. Facultad de IngenierÃa. Departamento de IngenierÃa Mecánica. Grupo de Materiales Avanzados; Argentina;Fil: Juarez, R. E.. Universidad de Buenos Aires. Facultad de IngenierÃa. Departamento de IngenierÃa Mecánica. Grupo de Materiales Avanzados; Argentina;Fil: Audebert, Fernando Enrique. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de TecnologÃas y Ciencias de la IngenierÃa; Argentina; Universidad de Buenos Aires. Facultad de IngenierÃa. Departamento de IngenierÃa Mecánica. Grupo de Materiales Avanzados; Argentina;Fil: Boudard, M.. Centre National de la Recherche Scientifique. Laboratoire des Matériaux et du Génie Physique; Francia
Psychometric properties of the Caregiver Preparedness Scale in caregivers of stroke survivors
Objective: To evaluate the psychometric characteristics of the Caregiver Preparedness Scale (CPS) in
caregivers of stroke survivors.
Background: Caregiver preparedness can have an important impact on both the caregiver and the stroke
survivor. The validity and reliability of the CPS has not been tested for the stroke-caregiver population.
Methods: We used a cross-sectional design to study a sample of 156 caregivers of stroke survivors.
Construct validity of the CPS was evaluated by confirmatory factor analysis (CFA). Internal consistency
and test-retest reliability were also evaluated.
Results: Caregivers were, on average, 54 year old (SD ¼ 13.2) and most were women (64.7%). CFA supported
the unidimensionality of the scale (comparative fit index ¼ 0.98). Reliability was also supported:
item-reliability index and itemetotal correlations above 0.30; composite reliability index ¼ 0.93;
Cronbach’s alpha ¼ 0.94; factor score determinacy ¼ 0.97; and test-retest reliability ¼ 0.92.
Conclusion: The CPS is valid and reliable in caregivers of stroke survivors. Scores on this scale may assist
health-care providers in identifying caregivers with less preparedness to provide specific interventions
Bribeproof mechanisms for two-values domains
Schummer (Journal of Economic Theory 2000) introduced the concept of
bribeproof mechanism which, in a context where monetary transfer between agents
is possible, requires that manipulations through bribes are ruled out.
Unfortunately, in many domains, the only bribeproof mechanisms are the trivial
ones which return a fixed outcome.
This work presents one of the few constructions of non-trivial bribeproof
mechanisms for these quasi-linear environments. Though the suggested
construction applies to rather restricted domains, the results obtained are
tight: For several natural problems, the method yields the only possible
bribeproof mechanism and no such mechanism is possible on more general domains.Comment: Extended abstract accepted to SAGT 2016. This ArXiv version corrects
typos in the proofs of Theorem 7 and Claims 28-29 of prior ArXiv versio
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Comparison of forest regeneration in two sites with different primate abundances in Northwestern Ecuador
There is increasing evidence that large-bodied primates play important roles as seed dispersers and in the maintenance of tree diversity in forest ecosystems. In this study we compared forest regeneration at two sites with differing primate abundances in the Ecuadorian Chocoan rainforest. We predicted: (1) significant differences in primate abundance between the two sites; (2) higher understory tree species richness and density at the site with greater primate abundance; (3) the site with lower primate abundance characterized by tree species dispersed by non-primate biotic agents and/or abiotic factors. We compared two sites, Tesoro Escondido (TE) a campesino cooperative, and the El Pambilar (EP) wildlife refuge that both maintain populations of mantled howler monkey (Alouatta palliata), the brown-headed spider monkey (Ateles fusciceps fusciceps) and the capuchin monkey (Cebus capucinus). We characterized canopy structure by point-quadrant sampling, determined primate abundance and sampled seedlings/saplings in 1 m2 plots, classifying tree species based on three dispersal syndromes: adapted for primate dispersal, dispersed by other biological agents, and abiotic dispersal. We compared sites in terms of primate abundance (groups and individuals observed per day) and regeneration characteristics (overall density, species richness, and dispersal syndrome). We carried out within site comparisons and constructed understory tree species accumulation curves. Overall the forests were structurally similar - with significantly higher densities of A. f. fusciceps at TE. Encounter rates for the other two primate species were similar at both sites. Understory tree density and species richness was significantly higher in TE with no stabilization of tree species accumulation curves. The species accumulation curve for understory trees at EP stabilized. Higher densities and species richness of primate dispersed tree species were observed at TE, with non-primate biotically dispersed tree species the dominant dispersal syndrome at both sites. Our observations are consistent with those from other studies investigating the role of large-bodied frugivorous primates in forest regeneration, and point to a general pattern: future lowland tropical forest tree diversity depends on maintaining robust populations of large primate species in these systems. It is highly probable that the maintenance of high levels of tree diversity in Chocoan rainforests is dependent on the conservation of its largest resident primate, the critically endangered brown-headed spider monkey (A. f. fusciceps)
The Indoor Radon Concentration within the Tunnels of the Cholula Pyramid Through a Nuclear Tracks Methodology
Global organizations, including the World Health Organization (WHO), the Environmental Protection Agency of the United States (US-EPA) and the European Atomic Energy Community (EURATOM) recognize that radon gas as one of the main contributors to environmental radiation exposure for humans. Accordingly, a study and analysis of the indoors radon concentrate in the Cholula Pyramid contributes to understand the Radon dynamic inside of the Pyramid tunnels and to evaluate the radiological health risk to visitors, archaeologists, anthropologists and persons who spend extended periods inside the Pyramid. In this paper, the radon measurements along the Pyramid tunnels are presented. The Nuclear Track Methodology (NTM) was chosen for the measurements, using a close end-cup device developed at the Dosimetry Application Project (DAP) of the Physics Institute UNAM, following very well established protocols for the chemical etching and reading with the Counting Analysis Digital Imaging System (CADIS). The Cholula Pyramid consists of eight stages of constructions, each built in different periods of time. Cholula Pyramid is recognized as the pyramid with the largest base in the World, with 400 meters per side and 65 meters high. The tunnels of the pyramid were built in 1931 by architect Ignacio Marquina, with the aim of exploring and studying the structure. The results show an important indoor radon concentration in the measured tunnels, several times higher than levels recommended by United States Environmental Protection Agency (US-EPA). The recommendation will be to mitigate the radon concentration levels, in order to avoid unnecessary exposition to the people
Confirmation of the Luminous Blue Variable status of MWC 930
We present spectroscopic and photometric observations of the emission-line
star MWC 930 (V446 Sct) during its long-term optical brightening in 2006--2013.
Based on our earlier data we suggested that the object has features found in
Luminous Blue Variables (LBV), such as a high luminosity (~3 10^5 Lsun, a low
wind terminal velocity (~ 140 km/s), and a tendency to show strong brightness
variations (~1 mag over 20 years). For the last ~7 years it has been exhibiting
a continuous optical and near-IR brightening along with a change of the
emission-line spectrum appearance and cooling of the star's photosphere. We
present the object's --band light curve, analyze the spectral variations,
and compare the observed properties with those of other recognized Galactic
LBVs, such as AG Car and HR Car. Overall we conclude the MWC 930 is a bona fide
Galactic LBV that is currently in the middle of an S Dor cycle.Comment: 12 pages, 7 figure
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