190 research outputs found
Recommended from our members
Paris: The slightly altered, slightly metamorphosed CM that bridges the gap between CMs and Cos
A fresh, 1.3 kilo stone was found in Paris. It is a CM chondrite with metal, Fe-sulfide, FeS-rich PCPs and relict mesostasis and is ~3.0 ± 0.1. Petrographic and oxygen isotope evidence indicates that it has affinities with the CO chondrites
Texture investigation of the superelastic Ti-24Nb-4Zr-8Sn alloy
International audienceIn this work, the influence of crystallographic texture on mechanical properties was investigated by X-ray diffraction in the superelastic Ti-24Nb-4Zr-8Sn alloy. Different textures were obtained by changing the cold rolling reduction rate and the following thermal treatment (solution treatment or flash thermal treatment). The tensile tests performed show that Young's modulus, elongation at rupture and ultimate tensile strength are not influenced by texture. However, the superelastic property of the Ti-24Nb-4Zr-8Sn alloy after solution treatment clearly increases with the textural change into the γ-fiber texture with a (1 1 1)View the MathML source main component due to the increase of cold rolling rate. Contrarily, the texture change induced by the increase of cold rolling rate has no influence on superelasticity after flash thermal treatment. Flash thermal treatment gives also higher recovery strain than solution treatment due to a smaller grain size
Gravitational lens modelling in a citizen science context
We develop a method to enable collaborative modelling of gravitational lenses
and lens candidates, that could be used by non-professional lens enthusiasts.
It uses an existing free-form modelling program (glass), but enables the input
to this code to be provided in a novel way, via a user-generated diagram that
is essentially a sketch of an arrival-time surface. We report on an
implementation of this method, SpaghettiLens, which has been tested in a
modelling challenge using 29 simulated lenses drawn from a larger set created
for the Space Warps citizen science strong lens search. We find that volunteers
from this online community asserted the image parities and time ordering
consistently in some lenses, but made errors in other lenses depending on the
image morphology. While errors in image parity and time ordering lead to large
errors in the mass distribution, the enclosed mass was found to be more robust:
the model-derived Einstein radii found by the volunteers were consistent with
those produced by one of the professional team, suggesting that given the
appropriate tools, gravitational lens modelling is a data analysis activity
that can be crowd-sourced to good effect. Ideas for improvement are discussed,
these include (a) overcoming the tendency of the models to be shallower than
the correct answer in test cases, leading to systematic overestimation of the
Einstein radius by 10 per cent at present, and (b) detailed modelling of arcs.Comment: 10 pages, 12 figure
Models of gravitational lens candidates from Space Warps CFHTLS
We report modelling follow-up of recently-discovered gravitational-lens
candidates in the Canada France Hawaii Telescope Legacy Survey. Lens modelling
was done by a small group of specially-interested volunteers from the
SpaceWarps citizen-science community who originally found the candidate lenses.
Models are categorised according to seven diagnostics indicating (a) the image
morphology and how clear or indistinct it is, (b) whether the mass map and
synthetic lensed image appear to be plausible, and (c) how the lens-model mass
compares with the stellar mass and the abundance-matched halo mass. The lensing
masses range from ~10^11 Msun to >10^13 Msun. Preliminary estimates of the
stellar masses show a smaller spread in stellar mass (except for two lenses): a
factor of a few below or above ~10^11 Msun. Therefore, we expect the
stellar-to-total mass fraction to decline sharply as lensing mass increases.
The most massive system with a convincing model is J1434+522 (SW05). The two
low-mass outliers are J0206-095 (SW19) and J2217+015 (SW42); if these two are
indeed lenses, they probe an interesting regime of very low star-formation
efficiency. Some improvements to the modelling software (SpaghettiLens), and
discussion of strategies regarding scaling to future surveys with more and
frequent discoveries, are included.Comment: 16 pages, 10 figures, 1 table, online supplement table_1.csv contains
additional detailed numbers shown in table 1 and figure
Hubble Asteroid Hunter: II. Identifying strong gravitational lenses in HST images with crowdsourcing
The Hubble Space Telescope (HST) archives constitute a rich dataset of high
resolution images to mine for strong gravitational lenses. While many HST
programs specifically target strong lenses, they can also be present by
coincidence in other HST observations. We aim to identify non-targeted strong
gravitational lenses in almost two decades of images from the ESA it Hubble
Space Telescope archive (eHST), without any prior selection on the lens
properties. We used crowdsourcing on the Hubble Asteroid Hunter (HAH) citizen
science project to identify strong lenses, alongside asteroid trails, in
publicly available large field-of-view HST images. We visually inspected 2354
objects tagged by citizen scientists as strong lenses to clean the sample and
identify the genuine lenses. We report the detection of 252 strong
gravitational lens candidates, which were not the primary targets of the HST
observations. 198 of them are new, not previously reported by other studies,
consisting of 45 A grades, 74 B grades and 79 C grades. The majority are
galaxy-galaxy configurations. The newly detected lenses are, on average, 1.3
magnitudes fainter than previous HST searches. This sample of strong lenses
with high resolution HST imaging is ideal to follow-up with spectroscopy, for
lens modelling and scientific analyses. This paper presents an unbiased search
of lenses, which enabled us to find a high variety of lens configurations,
including exotic lenses. We demonstrate the power of crowdsourcing in visually
identifying strong lenses and the benefits of exploring large archival
datasets. This study shows the potential of using crowdsourcing in combination
with artificial intelligence for the detection and validation of strong lenses
in future large-scale surveys such as ESA's future mission Euclid or in JWST
archival images.Comment: 24 page, 14 figures, 5 tables, accepted for publication in A&A June
28 202
The geochemistry of gem opals as evidence of their origin
International audienceSeventy-seven gem opals from ten countries were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) through a dilution process, in order to establish the nature of the impurities. The results are correlated to the mode of formation and physical properties and are instrumental in establishing the geographical origin of a gem opal. The geochemistry of an opal is shown to be dependant mostly on the host rock, at least for examples from Mexico and Brazil, even if modified by weathering processes. In order of decreasing concentration, the main impurities present are Al, Ca, Fe, K, Na, and Mg (more than 500 ppm). Other noticeable elements in lesser amounts are Ba, followed by Zr, Sr, Rb, U, and Pb. For the first time, geochemistry helps to discriminate some varieties of opals. The Ba content, as well as the chondritenormalized REE pattern, are the keys to separating sedimentary opals (BaN110 ppm, Eu and Ce anomalies) from volcanic opals (Bab110 ppm, no Eu or Ce anomaly). The Ca content, and to a lesser extent that of Mg, Al, K and Nb, helps to distinguish gem opals from different volcanic environments. The limited range of concentrations for all elements in precious (play-of-color) compared to common opals, indicates that this variety must have very specific, or more restricted, conditions of formation. We tentatively interpreted the presence of impurities in terms of crystallochemistry, even if opal is a poorly crystallized or amorphous material. The main replacement is the substitution of Si4+ by Al3+ and Fe3+. The induced charge imbalance is compensated chiefly by Ca2+, Mg2+, Mn2+, Ba2+, K+, and Na+. In terms of origin of color, greater concentrations of iron induce darker colors (from yellow to "chocolate brown"). This element inhibits luminescence for concentrations above 1000 ppm, whereas already a low content in U (=1 ppm) induces a green luminescence
Design of a nitrogen-implanted titanium-based superelastic alloy with optimized properties for biomedical applications
International audienceIn this study, a superelastic Ni-free Ti-based biomedical alloy was treated in surface by the implantation of nitrogen ions for the first time. The N-implanted surface was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and secondary ion mass spectroscopy, and the superficial mechanical properties were evaluated by nano-indentation and by ball-on-disk tribological tests. To investigate the biocompatibility, the corrosion resistance of the N-implanted Ti alloy was evaluated in simulated body fluids (SBF) complemented by in-vitro cytocompatibility tests on human fetal osteoblasts. After implantation, surface analysis methods revealed the formation of a titanium-based nitride on the substrate surface. Consequently, an increase in superficial hardness and a significant reduction of friction coefficient were observed compared to the non-implanted sample. Also, a better corrosion resistance and a significant decrease in ion release rates have been obtained. Cell culture experiments indicated that the cytocompatibility of the N-implanted Ti alloy was superior to that of the corresponding non-treated sample. Thus, this new functional N-implanted titanium-based superelastic alloy presents the optimized properties that are required for various medical devices: superelasticity, high superficial mechanical properties, high corrosion resistance and excellent cytocompatibility
First results of the 14.5 GHz GANIL ECR source with the C.W. and the pulsed operation mode
International audienceA 14.5 GHz ECR source has been designed and built at GANIL in order to improve the currents, mainly the heaviest ion beam intensities (Pb, U). We give the first results obtained with the C.W operation used on the cyclotron machines, and those we can get with the pulsed operalion mode which concerns Linacs and other machines
Space Warps II. New Gravitational Lens Candidates from the CFHTLS Discovered through Citizen Science
We report the discovery of 29 promising (and 59 total) new lens candidates
from the CFHT Legacy Survey (CFHTLS) based on about 11 million classifications
performed by citizen scientists as part of the first Space Warps lens search.
The goal of the blind lens search was to identify lens candidates missed by
robots (the RingFinder on galaxy scales and ArcFinder on group/cluster scales)
which had been previously used to mine the CFHTLS for lenses. We compare some
properties of the samples detected by these algorithms to the Space Warps
sample and find them to be broadly similar. The image separation distribution
calculated from the Space Warps sample shows that previous constraints on the
average density profile of lens galaxies are robust. SpaceWarps recovers about
65% of known lenses, while the new candidates show a richer variety compared to
those found by the two robots. This detection rate could be increased to 80% by
only using classifications performed by expert volunteers (albeit at the cost
of a lower purity), indicating that the training and performance calibration of
the citizen scientists is very important for the success of Space Warps. In
this work we present the SIMCT pipeline, used for generating in situ a sample
of realistic simulated lensed images. This training sample, along with the
false positives identified during the search, has a legacy value for testing
future lens finding algorithms. We make the pipeline and the training set
publicly available.Comment: 23 pages, 12 figures, MNRAS accepted, minor to moderate changes in
this versio
- …