47 research outputs found
Synthesis, optical band gap and thermoelectric properties of Sr1+xTiS3-y chalcogenide perovskites
Inorganic chalcogenide perovskites are semiconductors with attractive optoelectronic properties, which make
them of interest in different fields, such as energy harvesting. Some of these compounds have been poorly
investigated to date. For instance, very few works deal with the synthesis and characterization of Sr1+xTiS3. Here
we present a novel synthesis procedure to obtain Sr1+xTiS3-y powders. Moreover, we show for the first time an
experimental characterization of some fundamental properties of this compound that may be relevant for many
potential applications. First, we demonstrate that this perovskite shows very high thermal stability (up to 700â—¦C
in air and up to 1200â—¦C in Ar atmosphere). Next, we experimentally determine its optical band gap (about 0.97
eV) corresponding to a direct allowed transition, in agreement with previous predictions. Finally, we demonstrate a tuneable Seebeck coefficient (changing from n-type to p-type behaviour) by changing the amount of
sulfur vacanciesThis research has been funded by Spanish MICINN under
RTI2018-099794-B-I00 gran
Imaging the Kirkendall effect in pyrite (FeS2) thin films: cross-sectional microstructure and chemical features
This investigation provides novel data on the structure and chemical composition of pyrite thin films and new hints concerning their formation mechanism. From TEM-HAADF data, it has been found that the films are composed of two different layers: one is very compact and the other one is quite porous with many voids separating a few groups of grains. This porous layer is always in direct contact with the substrate, and its thickness is quite similar to that of the original Fe film. The average size of pyrite grains is equal in both layers, what suggests that the same process is responsible for their formation. Concentration profiles of sulfur, iron and some impurities (mainly sodium and oxygen from the glass substrate) through both layers are given in this work, and thus chemical inhomogeneities of the films are proved by the obtained stoichiometric ratios (S/Fe). Moreover, Na from sodalime glass substrates mainly accumulates at the pyrite grain boundaries and barely dopes them. The obtained results support the hypothesis that the iron sulfuration process essentially induces the diffusion of iron atoms, what leads to the porous layer formation as a manifestation of the Kirkendall Effect. Therefore, it seems that the same mechanisms that operate in the synthesis of surface hollow structures at the nanoscale are also active in the formation of pyrite thin films ranging from several tens to hundreds of nanometersMembers of MIRE Group acknowledge the financial support of the Spanish MICINN under project RTI2018-099794-B-I00. E. Flores acknowledges the intramural CSIC project 2D-MeSes funding and the service from the MiNa Laboratory at IMN, and funding from CM (project SpaceTec, S2013/ICE2822), MINECO (project CSIC13-4E1794) and EU (FEDER,FSE). Financial support through the project UMA18-FEDERJA-041 is gratefully acknowledge
Extensive antimicrobial resistance mobilization via Multicopy Plasmid Encapsidation mediated by temperate phages
Objectives: To investigate the relevance of multicopy plasmids in antimicrobial resistance and assess their mobilization mediated by phage particles Methods: Several databases with complete sequences of plasmids and annotated genes were analysed. The 16S methyltransferase gene armA conferring high-level aminoglycoside resistance was used as a marker in eight different plasmids, from different incompatibility groups, and with differing sizes and plasmid copy numbers. All plasmids were transformed into Escherichia coli bearing one of four different lysogenic phages. Upon induction, encapsidation of armA in phage particles was evaluated using qRT-PCR and Southern blotting. Results: Multicopy plasmids carry a vast set of emerging clinically important antimicrobial resistance genes. However, 60% of these plasmids do not bear mobility (MOB) genes. When carried on these multicopy plasmids, mobilization of a marker gene armA into phage capsids was up to 10000 times more frequent than when it was encoded by a large plasmid with a low copy number. Conclusions: Multicopy plasmids and phages, two major mobile genetic elements (MGE) in bacteria, represent a novel high-efficiency transmission route of antimicrobial resistance genes that deserves further investigation
TESS Duotransit Candidates from the Southern Ecliptic Hemisphere
Discovering transiting exoplanets with long orbital periods allows us to
study warm and cool planetary systems with temperatures similar to the planets
in our own Solar system. The TESS mission has photometrically surveyed the
entire Southern Ecliptic Hemisphere in Cycle 1 (August 2018 - July 2019), Cycle
3 (July 2020 - June 2021) and Cycle 5 (September 2022 - September 2023). We use
the observations from Cycle 1 and Cycle 3 to search for exoplanet systems that
show a single transit event in each year - which we call duotransits. The
periods of these planet candidates are typically in excess of 20 days, with the
lower limit determined by the duration of individual TESS observations. We find
85 duotransit candidates, which span a range of host star brightnesses between
8 < < 14, transit depths between 0.1 per cent and 1.8 per cent, and
transit durations between 2 and 10 hours with the upper limit determined by our
normalisation function. Of these candidates, 25 are already known, and 60 are
new. We present these candidates along with the status of photometric and
spectroscopic follow-up.Comment: 25 pages, 16 figures, submitted to Monthly Notices of the Royal
Astronomical Societ
NGTS-21b: An Inflated Super-Jupiter Orbiting a Metal-poor K dwarf
We report the discovery of NGTS-21b, a massive hot Jupiter orbiting a
low-mass star as part of the Next Generation Transit Survey (NGTS). The planet
has a mass and radius of M, and
R, and an orbital period of 1.543 days. The host is a K3V (, K) metal-poor (, dex) dwarf
star with a mass and radius of , M,and , R. Its age and rotation period of , Gyr
and , d respectively, are in accordance with the observed
moderately low stellar activity level. When comparing NGTS-21b with currently
known transiting hot Jupiters with similar equilibrium temperatures, it is
found to have one of the largest measured radii despite its large mass.
Inflation-free planetary structure models suggest the planet's atmosphere is
inflated by , while inflationary models predict a radius consistent
with observations, thus pointing to stellar irradiation as the probable origin
of NGTS-21b's radius inflation. Additionally, NGTS-21b's bulk density (, g/cm) is also amongst the largest within the population of
metal-poor giant hosts ([Fe/H] < 0.0), helping to reveal a falling upper
boundary in metallicity-planet density parameter space that is in concordance
with core accretion formation models. The discovery of rare planetary systems
such as NGTS-21 greatly contributes towards better constraints being placed on
the formation and evolution mechanisms of massive planets orbiting low-mass
stars.Comment: 12 pages, 13 figures, accepted for publication in MNRA