118 research outputs found
ONE STEP ELECTRODEPOSITION OF CuInSe2 THIN FILMS
Formation of CuInSe2 (CIS) thin films from aqueous solution containing citrate as complexing agent is reported. The surface morphology and the composition of the deposited films are characterized by scanning electron microscopy (SEM). The texture of the deposits and their compositions are analyzed by X-ray diffraction and transmission electron microscopy (TEM). Annealing of the films at 350°C in flowing argon electrodeposited at potentials in the range [-0.24, -0.4 (V vs Ag/AgCl)] resulted in the formation of alpha-Cu 2 Se (JCPDS 24-1131) and CuSe (JCPDS 6-0427). On the contrary, annealing in the same conditions of the films electrodeposited between -0.4 and -0.6 V vs Ag/AgCl led to the formation of chalcopyrite CuInSe 2 (JCPDS 23-209) with alpha-Cu 2 Se (JCPDS 24-1131) as secondary phase. The formation of CuInSe 2 films with a chalcopyrite structure and good stoichiometry is observed.Formation of CuInSe2 (CIS) thin films from aqueous solution containing citrate as complexing agent is reported. The surface morphology and the composition of the deposited films are characterized by scanning electron microscopy (SEM). The texture of the deposits and their compositions are analyzed by X-ray diffraction and transmission electron microscopy (TEM). Annealing of the films at 350°C in flowing argon electrodeposited at potentials in the range [-0.24, -0.4 (V vs Ag/AgCl)] resulted in the formation of alpha-Cu 2 Se (JCPDS 24-1131) and CuSe (JCPDS 6-0427). On the contrary, annealing in the same conditions of the films electrodeposited between -0.4 and -0.6 V vs Ag/AgCl led to the formation of chalcopyrite CuInSe 2 (JCPDS 23-209) with alpha-Cu 2 Se (JCPDS 24-1131) as secondary phase. The formation of CuInSe 2 films with a chalcopyrite structure and good stoichiometry is observed
The ESPRI project: astrometric exoplanet search with PRIMA I. Instrument description and performance of first light observations
The ESPRI project relies on the astrometric capabilities offered by the PRIMA
facility of the Very Large Telescope Interferometer for the discovery and study
of planetary systems. Our survey consists of obtaining high-precision
astrometry for a large sample of stars over several years and to detect their
barycentric motions due to orbiting planets. We present the operation
principle, the instrument's implementation, and the results of a first series
of test observations. A comprehensive overview of the instrument infrastructure
is given and the observation strategy for dual-field relative astrometry is
presented. The differential delay lines, a key component of the PRIMA facility
which was delivered by the ESPRI consortium, are described and their
performance within the facility is discussed. Observations of bright visual
binaries are used to test the observation procedures and to establish the
instrument's astrometric precision and accuracy. The data reduction strategy
for astrometry and the necessary corrections to the raw data are presented.
Adaptive optics observations with NACO are used as an independent verification
of PRIMA astrometric observations. The PRIMA facility was used to carry out
tests of astrometric observations. The astrometric performance in terms of
precision is limited by the atmospheric turbulence at a level close to the
theoretical expectations and a precision of 30 micro-arcseconds was achieved.
In contrast, the astrometric accuracy is insufficient for the goals of the
ESPRI project and is currently limited by systematic errors that originate in
the part of the interferometer beamtrain which is not monitored by the internal
metrology system. Our observations led to the definition of corrective actions
required to make the facility ready for carrying out the ESPRI search for
extrasolar planets.Comment: 32 pages, 39 figures, Accepted for publication in Astronomy and
Astrophysic
A conscious rethink : Why is brain tissue commonly preserved in the archaeological record? Commentary on: Petrone P, Pucci P, Niola M, et al. Heat-induced brain vitrification from the Vesuvius eruption in C.E. 79. N Engl J Med 2020;382:383-4. DOI: 10.1056/NEJMc1909867
Brain tissue is ubiquitous in the archaeological record. Multiple, independent studies report the finding of black, resinous or shiny brain tissue, and Petrone et al. [2020 âHeat-induced Brain Vitrification from the Vesuvius Eruption in C.E. 79.â N Engl J Med. 382: 383â384; doi:10.1056/NEJMc1909867] raise the intriguing prospect of a role for vitrification in the preservation of ancient biomolecules. However, Petrone et al. (2020) have not made their raw data available, and no detailed laboratory or analytical methodology is offered. Issues of contamination and misinterpretation hampered a decade of research in biomolecular archaeology, such that addressing these sources of bias and facilitating validation of specious findings has become both routine and of paramount importance in the discipline. We argue that the evidence they present does not support their conclusion of heat-induced vitrification of human brain tissue, and that future studies should share palaeoproteomic data in an open access repository to facilitate comparative analysis of the recovery of ancient proteins and patterns of their degradation
Improving the astrometric performance of VLTI-PRIMA
In the summer of 2011, the first on-sky astrometric commissioning of
PRIMA-Astrometry delivered a performance of 3 m'' for a 10 '' separation on
bright objects, orders of magnitude away from its exoplanet requirement of 50
{\mu}'' ~ 20 {\mu}'' on objects as faint as 11 mag ~ 13 mag in K band. This
contribution focuses on upgrades and characterizations carried out since then.
The astrometric metrology was extended from the Coud\'e focus of the
Auxillary Telescopes to their secondary mirror, in order to reduce the baseline
instabilities and improve the astrometric performance. While carrying out this
extension, it was realized that the polarization retardance of the star
separator derotator had a major impact on both the astrometric metrology and
the fringe sensors. A local compensation of this retardance and the operation
on a symmetric baseline allowed a new astrometric commissioning. In October
2013, an improved astrometric performance of 160 {\mu}'' was demonstrated,
still short of the requirements. Instabilities in the astrometric baseline
still appear to be the dominating factor.
In preparation to a review held in January 2014, a plan was developed to
further improve the astrometric and faint target performance of PRIMA
Astrometry. On the astrometric aspect, it involved the extension of the
internal longitudinal metrology to primary space, the design and implementation
of an external baseline metrology, and the development of an astrometric
internal fringes mode. On the faint target aspect, investigations of the
performance of the fringe sensor units and the development of an AO system
(NAOMI) were in the plan. Following this review, ESO decided to take a proposal
to the April 2014 STC that PRIMA be cancelled, and that ESO resources be
concentrated on ensuring that Gravity and Matisse are a success. This proposal
was recommended by the STC in May 2014, and endorsed by ESO.Comment: 12 pages, 9 figures, 2 tables, Proceeding of SPIE conference in
Montrea
Opening a new window to other worlds with spectropolarimetry
A high level of diversity has already been observed among the planets of our
own Solar System. As such, one expects extrasolar planets to present a wide
range of distinctive features, therefore the characterisation of Earth- and
super Earth-like planets is becoming of key importance in scientific research.
The SEARCH (Spectropolarimetric Exoplanet AtmospheRe CHaracerisation) mission
proposal of this paper represents one possible approach to realising these
objectives. The mission goals of SEARCH include the detailed characterisation
of a wide variety of exoplanets, ranging from terrestrial planets to gas
giants. More specifically, SEARCH will determine atmospheric properties such as
cloud coverage, surface pressure and atmospheric composition, and may also be
capable of identifying basic surface features. To resolve a planet with a semi
major axis of down to 1.4AU and 30pc distant SEARCH will have a mirror system
consisting of two segments, with elliptical rim, cut out of a parabolic mirror.
This will yield an effective diameter of 9 meters along one axis. A phase mask
coronagraph along with an integral spectrograph will be used to overcome the
contrast ratio of star to planet light. Such a mission would provide invaluable
data on the diversity present in extrasolar planetary systems and much more
could be learned from the similarities and differences compared to our own
Solar System. This would allow our theories of planetary formation, atmospheric
accretion and evolution to be tested, and our understanding of regions such as
the outer limit of the Habitable Zone to be further improved.Comment: 23 pages, accepted for publication in Experimental Astronom
First principles study of point defects in titanium oxycarbide
We have performed first principles density functional theory calculations to study the formation energy of point defects
in TiC, TiO and TiCO compounds. The formation energy of isolated vacancies were obtained for different equilibrium
conditions. For binary compounds, we have also calculated the formation energy of antisite defects. It was found that
the defect formation energies strongly depend on the chemical environment. Our results show that C vacancies are
easily formed in TiC and TiCO. For the TiO compound, Ti vacancies are highly probable to occur and O vacancies
are also easily formed under titanium rich atmosphere.Fundação para a CiĂȘncia e a Tecnologia (FCT) â Programa Operacional âCiĂȘncia , Tecnologia, Inovaçãoâ â CONC-REEQ/443/EEI/2005, POCTI/CTM/69362/200
The Genomic Signature of Crop-Wild Introgression in Maize
The evolutionary significance of hybridization and subsequent introgression
has long been appreciated, but evaluation of the genome-wide effects of these
phenomena has only recently become possible. Crop-wild study systems represent
ideal opportunities to examine evolution through hybridization. For example,
maize and the conspecific wild teosinte Zea mays ssp. mexicana, (hereafter,
mexicana) are known to hybridize in the fields of highland Mexico. Despite
widespread evidence of gene flow, maize and mexicana maintain distinct
morphologies and have done so in sympatry for thousands of years. Neither the
genomic extent nor the evolutionary importance of introgression between these
taxa is understood. In this study we assessed patterns of genome-wide
introgression based on 39,029 single nucleotide polymorphisms genotyped in 189
individuals from nine sympatric maize-mexicana populations and reference
allopatric populations. While portions of the maize and mexicana genomes were
particularly resistant to introgression (notably near known
cross-incompatibility and domestication loci), we detected widespread evidence
for introgression in both directions of gene flow. Through further
characterization of these regions and preliminary growth chamber experiments,
we found evidence suggestive of the incorporation of adaptive mexicana alleles
into maize during its expansion to the highlands of central Mexico. In
contrast, very little evidence was found for adaptive introgression from maize
to mexicana. The methods we have applied here can be replicated widely, and
such analyses have the potential to greatly informing our understanding of
evolution through introgressive hybridization. Crop species, due to their
exceptional genomic resources and frequent histories of spread into sympatry
with relatives, should be particularly influential in these studies
Spitzer + VLTI-GRAVITY Measure the Lens Mass of a Nearby Microlensing Event
We report the lens mass and distance measurements of the nearby microlensing
event TCP J05074264+2447555. We measure the microlens parallax vector
using Spitzer and ground-based light curves with constraints on
the direction of lens-source relative proper motion derived from Very Large
Telescope Interferometer (VLTI) GRAVITY observations. Combining this
determination with the angular Einstein radius
measured by VLTI GRAVITY observations, we find that the lens is a star with
mass at a distance . We find that the blended light basically all comes from the lens.
The lens-source proper motion is , so with currently available adaptive-optics (AO) instruments,
the lens and source can be resolved in 2021. This is the first microlensing
event whose lens mass is unambiguously measured by interferometry + satellite
parallax observations, which opens a new window for mass measurements of
isolated objects such as stellar-mass black holes.Comment: 3 Figures and 6 Tables Submitted to AAS Journa
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