689 research outputs found
Resolving gravitational microlensing events with long-baseline optical interferometry. Prospects for the ESO Very Large Telescope Interferometer
Until now, the detailed interpretation of the observed microlensing events
has suffered from the fact that the physical parameters of the phenomenon
cannot be uniquely determined from the available astronomical measurements,
i.e. the photometric lightcurves. The situation will change in the near-future
with the availability of long-baseline, sensitive optical interferometers,
which should be able to resolve the images of the lensed objects into their
components. For this, it will be necessary to achieve a milliarcsecond
resolution on sources with typical magnitudes K \ga 12. Indeed, brighter
events have never been observed up to now by micro-lensing surveys. We discuss
the possibilities opened by the use of long baseline interferometry in general,
and in particular for one such facility, the ESO VLT Interferometer, which will
attain the required performance. We discuss the expected accuracy and limiting
magnitude of such measurements. On the basis of the database of the events
detected by the OGLE experiment, we estimate the number of microlenses that
could be available for measurements by the VLTI. We find that at least several
tens of events could be observed each year. In conjunction with the photometric
data, our ability to measure the angular separation between the microlensed
images will enable a direct and unambiguous determination of both their masses
and locations.Comment: Accepted for publication in Astronomy & Astrophysic
Un cas d’instabilité disciplinaire : des Sciences Naturelles aux Sciences de la Vie et de la Terre
L’enseignement de la biologie gĂ©ologie a connu en France d’importants changements dans les annĂ©es 80-90. Entre 1981 Ă 1992, la discipline scolaire des sciences naturelles change plusieurs fois d’appellation avant d’adopter sa dĂ©nomination contemporaine de Sciences de la Vie et de la Terre (SVT). Cet article s’intĂ©resse Ă ce cas d’instabilitĂ© disciplinaire en interrogeant les transformations diachroniques des contenus d’enseignement prescrits. La mĂ©thodologie articule un regard didactique sur l’évolution des programmes (analyses quantitative et qualitative des transformations curriculaire) Ă un regard socio-historique sur leurs coulisses d’écriture (travail d’archives).Â
Sonochemistry: Scope, Limitations… and Artifacts
Heterogeneous sonochemistry, generally described as the most useful aspect of sonochemistry, suffers from the difficulty of defining the experimental conditions for the reference (silent) reaction. Clearly the use of an efficient agitation system for the silent reaction strongly reduces
the value of the so-called sonochemical effect, which becomes in some cases, less than 1 (anti-sonochemical effect!).The 'cleaning' effect of ultrasound is extremely efficient to expel micro-crystals from the surface of an electrode which is simultaneously an immersion ultrasonic horn.
By sending out-of-phase electric pulses and acoustic pulses, new nano materials (metals, alloys, semiconductors, oxides) are easily prepared in high purity
Convergence Properties of a Randomized Primal-Dual Algorithm with Applications to Parallel MRI
The Stochastic Primal-Dual Hybrid Gradient (SPDHG) was proposed by Chambolle
et al. (2018) and is an efficient algorithm to solve some nonsmooth large-scale
optimization problems. In this paper we prove its almost sure convergence for
convex but not necessarily strongly convex functionals. We also look into its
application to parallel Magnetic Resonance Imaging reconstruction in order to
test performance of SPDHG. Our numerical results show that for a range of
settings SPDHG converges significantly faster than its deterministic
counterpart
On the convergence and sampling of randomized primal-dual algorithms and their application to parallel MRI reconstruction
Stochastic Primal-Dual Hybrid Gradient (SPDHG) is an algorithm to efficiently
solve a wide class of nonsmooth large-scale optimization problems. In this
paper we contribute to its theoretical foundations and prove its almost sure
convergence for convex but neither necessarily strongly convex nor smooth
functionals. We also prove its convergence for any sampling. In addition, we
study SPDHG for parallel Magnetic Resonance Imaging reconstruction, where data
from different coils are randomly selected at each iteration. We apply SPDHG
using a wide range of random sampling methods and compare its performance
across a range of settings, including mini-batch size and step size parameters.
We show that the sampling can significantly affect the convergence speed of
SPDHG and for many cases an optimal sampling can be identified
On the convergence and sampling of randomized primal-dual algorithms and their application to parallel MRI reconstruction
Stochastic Primal-Dual Hybrid Gradient (SPDHG) is an algorithm to efficiently
solve a wide class of nonsmooth large-scale optimization problems. In this
paper we contribute to its theoretical foundations and prove its almost sure
convergence for convex but neither necessarily strongly convex nor smooth
functionals. We also prove its convergence for any sampling. In addition, we
study SPDHG for parallel Magnetic Resonance Imaging reconstruction, where data
from different coils are randomly selected at each iteration. We apply SPDHG
using a wide range of random sampling methods and compare its performance
across a range of settings, including mini-batch size and step size parameters.
We show that the sampling can significantly affect the convergence speed of
SPDHG and for many cases an optimal sampling can be identified
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
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