1,022 research outputs found
Study of the Al-grading effect in the crystallisation of chalcopyrite Cu(In,Al)Se2 thin films selenised at different temperatures
Chalcopyrite CuIn1âxAlxSe2 (CIAS) thin films with an atomic ratio of Al/(In + Al) = 0.4 were grown by a two-stage process onto soda-lime glass substrates. The selenisation was carried out at different temperatures, ranging from 400 °C to 550 °C, for metallic precursors layers evaporated with two different sequences. The first sequence, C1, was evaporated with the Al as the last layer, while in the second one, C2, the In was the last evaporated element. The optical, structural and morphological characterisations led to the conclusion that the precursors sequence determines the crystallisation pathway, resulting in C1 the best option due to the homogeneity of the depth distribution of the elements. The influence of the selenisation temperature was also studied, finding 540 °C as the optimum one, since it allows to achieve the highest band gap value for the C1 sequence and for the given composition
Apodized pupil Lyot coronagraphs for arbitrary apertures. V. Hybrid Shaped Pupil designs for imaging Earth-like planets with future space observatories
We introduce a new class of solutions for Apodized Pupil Lyot Coronagraphs
(APLC) with segmented aperture telescopes to remove broadband diffracted light
from a star with a contrast level of . These new coronagraphs provide
a key advance to enabling direct imaging and spectroscopy of Earth twins with
future large space missions. Building on shaped pupil (SP) apodization
optimizations, our approach enables two-dimensional optimizations of the system
to address any aperture features such as central obstruction, support
structures or segment gaps. We illustrate the technique with a design that
could reach contrast level at 34\,mas for a 12\,m segmented telescope
over a 10\% bandpass centered at a wavelength 500\,nm. These
designs can be optimized specifically for the presence of a resolved star, and
in our example, for stellar angular size up to 1.1\,mas. This would allow
probing the vicinity of Sun-like stars located beyond 4.4\,pc, therefore fully
retiring this concern. If the fraction of stars with Earth-like planets is
\eta_{\Earth}=0.1, with 18\% throughput, assuming a perfect, stable wavefront
and considering photon noise only, 12.5 exo-Earth candidates could be detected
around nearby stars with this design and a 12\,m space telescope during a
five-year mission with two years dedicated to exo-Earth detection (one total
year of exposure time and another year of overheads). Our new hybrid APLC/SP
solutions represent the first numerical solution of a coronagraph based on
existing mask technologies and compatible with segmented apertures, and that
can provide contrast compatible with detecting and studying Earth-like planets
around nearby stars. They represent an important step forward towards enabling
these science goals with future large space missions.Comment: 9 pages, 6 figures, ApJ accepted on 01/04/201
The paleoneurology of Ichthyopterygia and Sauropterygia:Diverse Endocranial Anatomies of Secondarily Aquatic Diapsids
Most meso- and megapredatory niches across Mesozoic marine ecosystems were gradually occupied by the secondarily aquatic Ichthyopterygia and Sauropterygia. Although their presumed Early Triassic origins remain obscured, the subsequent radiation and diversification of these diapsid superorders is reasonably well documented in the fossil record. In the first quarter of the twentieth century, the Triassic sauropterygian genera Nothosaurus and Placodus were among the first taxa for which the cranial endocast was extracted and described. The advent of computed tomography, circa 50 years after these pivotal paleoneurological investigations, has led to its adoption as the tool of choice for the non-destructive assessment of neurosensory adaptations in extinct vertebrates. Despite the increasing availability of paleoneurological data on extinct diapsids, Ichthyopterygia and Sauropterygia have received relatively modest, albeit growing, attention since. Here we review paleoneurological insights gleaned from these fossils to date and identify endocranial and neurosensory modifications associated with increasingly pelagic lifestyles and ecological specializations. Nevertheless, a broader ichthyopterygian and sauropterygian sample will be required to facilitate high-resolution taxon-wide comparisons and discern between endocranial changes accompanying progressive adaptation to aquatic niches and conservative features informing on phylogenetic identity. Systematic evaluation will reveal the neurosensory developments that facilitated these Mesozoic ecological success stories in aquatic environments
Homodyne estimation of Gaussian quantum discord
We address the experimental estimation of Gaussian quantum discord for
two-mode squeezed thermal state, and demonstrate a measurement scheme based on
a pair of homodyne detectors assisted by Bayesian analysis which provides
nearly optimal estimation for small value of discord. Besides, though homodyne
detection is not optimal for Gaussian discord, the noise ratio to the ultimate
quantum limit, as dictacted by the quantum Cramer-Rao bound, is limited to
about 10 dB.Comment: 5+3 pages, 3 figures, published versio
Heralded processes on continuous-variable spaces as quantum maps
Conditional evolution is crucial for generating non-Gaussian resources for
quantum information tasks in the continuous variable scenario. However, tools
are lacking for a convenient representation of heralded process in terms of
quantum maps for continuous variable states, in the same way as Wigner
functions are able to give a compact description of the quantum state. Here we
propose and study such a representation, based on the introduction of a
suitable transfer function to describe the action of a quantum operation on the
Wigner function. We also reconstruct the maps of two relevant examples of
conditional process, that is, noiseless amplification and photon addition, by
combining experimental data and a detailed physical model. This analysis allows
to fully characterize the effect of experimental imperfections in their
implementations.Comment: 9 pages, 8 figures. Minor change
Optimal interactions of light with magnetic and electric resonant particles
This work studies the limits of far and near-field electromagnetic response
of sub-wavelength scatterers, like the unitary limit and of lossless
scatterers, and the ideal absorption limit of lossy particles. These limit
behaviors are described in terms of analytic formulas that approximate finite
size effects while rigorously including radiative corrections. This analysis
predicts the electric and/or magnetic limit responses of both metallic and
dielectric nanoparticles while quantitatively describing near-field
enhancements.Comment: 9 pages, 8 figures, 2 table
Anisotropic eddy-viscosity concept for strongly detached unsteady flows
The accurate prediction of the flow physics around bodies at high Reynolds number is a challenge in aerodynamics nowadays. In the context of turbulent flow modeling, recent advances like large eddy simulation (LES) and hybrid methods [detached eddy simulation (DES)] have considerably improved the physical relevance of the numerical simulation. However, the LES approach is still limited to the low-Reynolds-number range concerning wall flows. The unsteady Reynolds-averaged NavierâStokes (URANS) approach remains a widespread and robust methodology for complex flow computation, especially in the near-wall region. Complex statistical models like second-order closure schemes [differential Reynolds stress modeling (DRSM)] improve the prediction of these properties and can provide an efficient simulationofturbulent stresses. Fromacomputational pointofview, the main drawbacks of such approaches are a higher cost, especially in unsteady 3-D flows and above all, numerical instabilities
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