722 research outputs found
Far infrared properties of the rare-earth scandate DyScO3
We present reflectance measurements in the infrared region on a single
crystal the rare earth scandate DyScO3. Measurements performed between room
temperature and 10 K allow to determine the frequency of the infrared-active
phonons, never investigated experimentally, and to get information on their
temperature dependence. A comparison with the phonon peak frequency resulting
from ab-initio computations is also provided. We finally report detailed data
on the frequency dependence of the complex refractive index of DyScO3 in the
terahertz region, which is important in the analysis of terahertz measurements
on thin films deposited on DyScO3
Temperature-dependent Raman scattering of DyScO3 and GdScO3 single crystals
We report a temperature-dependent Raman scattering investigation of DyScO3
and GdScO3 single crystals from room temperature up to 1200 {\deg}C. With
increasing temperature, all modes decrease monotonously in wavenumber without
anomaly, which attests the absence of a structural phase transition. The high
temperature spectral signature and extrapolation of band positions to higher
temperatures suggest a decreasing orthorhombic distortion towards the ideal
cubic structure. Our study indicates that this orthorhombic-to-cubic phase
transition is close to or higher than the melting point of both rare-earth
scandates (\approx 2100 {\deg}C), which might exclude the possibility of the
experimental observation of such a phase transition before melting. The
temperature-dependent shift of Raman phonons is also discussed in the context
of thermal expansion
Analytical theory of short-pulse free-electron laser oscillators
A simple model for the nonlinear evolution of a short-pulse free-electron laser oscillator in the small gain regime is derived. An analysis of the linearized system allows the definition and calculation of the eigenmodes characterizing the small signal regime. An arbitrary solution of the nonlinear system can then be expanded in terms of these supermodes. In the single-supermode approximation, the system reduces to a Landau-Ginzburg equation, which allows the efficiency and saturated power to be obtained as functions of cavity detuning and cavity losses. In the limit of small cavity detuning, electrons emit superradiantly, with an efficiency inversely proportional to the number of radiation wavelengths within the optical pulse, and power proportional to the square of the bunch charge. In the multisupermode regime, limit cycles and period doubling behavior are observed and interpreted as a competition between supermodes. Finally, the analytical and numerical results are compared with the experimental observations from the Free-Electron Laser for Infrared eXperiments experiment
Magnetic properties of the honeycomb oxide NaCoTeO
We have studied the magnetic properties of NaCoTeO, which
features a honeycomb lattice of magnetic Co ions, through macroscopic
characterization and neutron diffraction on a powder sample. We have shown that
this material orders in a zig-zag antiferromagnetic structure. In addition to
allowing a linear magnetoelectric coupling, this magnetic arrangement displays
very peculiar spatial magnetic correlations, larger in the honeycomb planes
than between the planes, which do not evolve with the temperature. We have
investigated this behavior by Monte Carlo calculations using the
-- model on a honeycomb lattice with a small interplane
interaction. Our model reproduces the experimental neutron structure factor,
although its absence of temperature evolution must be due to additional
ingredients, such as chemical disorder or quantum fluctuations enhanced by the
proximity to a phase boundary.Comment: 9 pages, 13 figure
Gene flow estimation with microsatellites in a Malagasy seed orchard of Eucalyptus grandis
International audienceEucalyptus grandis has a mixed-mating repro- ductive system. Malagasy Eucalyptus seed orchards were established 15 years ago with two aims both based on panmixia: open-pollinated seed production and genetic improvement. The panmixia hypothesis has never been confirmed in the seed orchard. From a seedling seed- orchard stand comprising 349 trees and using data obtained with six selected microsatellite markers, pater- nity analysis was performed for 724 offspring collected on 30 adult trees. Paternity assignment, based on exclu- sion procedures and likelihood-ratio method, was achieved with high accuracy; the exclusion probability value was 0.997. The outcrossing rate was very high (96.7%). More than 50% of potential male trees (199 out of 349) in the seed orchard contributed to pollination for 440 offspring of 30 progenies (8.6% of the basic population). The pollination rate from outside the seed orchard was high (39.2%), but might be due to the small size of this seed orchard. This study showed that "panmixia-like pollination" can be assume
Directly characterizing the relative strength and momentum dependence of electron-phonon coupling using resonant inelastic x-ray scattering
The coupling between lattice and charge degrees of freedom in condensed
matter materials is ubiquitous and can often result in interesting properties
and ordered phases, including conventional superconductivity, charge density
wave order, and metal-insulator transitions. Angle-resolved photoemission
spectroscopy and both neutron and non-resonant x-ray scattering serve as
effective probes for determining the behavior of appropriate, individual
degrees of freedom -- the electronic structure and lattice excitation, or
phonon dispersion, respectively. However, each provides less direct information
about the mutual coupling between the degrees of freedom, usual through
self-energy effects, which tend to renormalize and broaden spectral features
precisely where the coupling is strong, impacting ones ability to quantitively
characterize the coupling. Here we demonstrate that resonant inelastic x-ray
scattering, or RIXS, can be an effective tool to directly determine the
relative strength and momentum dependence of the electron-phonon coupling in
condensed matter systems. Using a diagrammatic approach for an 8-band model of
copper oxides, we study the contributions from the lowest order diagrams to the
full RIXS intensity for a realistic scattering geometry, accounting for matrix
element effects in the scattering cross-section as well as the momentum
dependence of the electron-phonon coupling vertex. A detailed examination of
these maps offers a unique perspective into the characteristics of
electron-phonon coupling, which complements both neutron and non-resonant x-ray
scattering, as well as Raman and infrared conductivity.Comment: 10 pages, 10 figure
Correction of moisture effects on near infrared calibration for the analysis of phenol content in eucalyptus wood extracts
Les méthodes basées sur la spectroscopie proche infrarouge pour estimer les propriétés du bois sont sensibles aux variations des paramètres physiques (température, granulométrie. . . ). Le bois étant un matériau hygroscopique sensible, l'influence de l'humidité sur l'absorbance et l'étalonnage proche infrarouge a été étudiée afin de mieux considérer les possibilités d'applications dans des conditions réelles.Un étalonnage de référence de la quantité de polyphénols présents dans les extraits a été établi à partir de spectres d'une collection de bois d'hybrides d'Eucalyptus urophylla × E. grandis à humidité constante fixée. D'autres spectres ont été obtenus sur des échantillons de même provenance mais à 8 teneurs en eau couvrant une large plage de variation. L'influence de l'humidité sur l'absorbance proche infrarouge puis sur l'estimation par le modèle de référence a été analysée. / Methods based on near infrared spectroscopy used to assess wood properties are susceptible to variations in physical parameters (temperature, grain size, etc). As wood is a hygroscopically sensitive material, we studied the effects of moisure on near infrared absorbance and calibration to accurately determine the application potential of this technique under routine. A collection of Eucalyptus urophylla x E. grandis hybrid wood pieces were analysed to obtain reference calibration of polyphenol contents in wood extracts via NIR spectra acquired under constant moisture conditions.Others specimens from the same source were assessed to obtain spectra for eight moisture contents spanning a broad variation range. The effects of moisture on absorption and on estimates based on a reference model were analysed. An increase in moisture content prompteda rise in near infrared absorption over the entire spectrum and the water O-H absorption bands. The polyphenol content estimates obtained by assessing specimens against the reference calibration at variable moisture contents revealed prediction bias. Five correction methods were then tested on enhance the robustness relative to moisture. In-depth calibration and external parameter orthogonalization were found to be the most efficient methods for offsetting this factor
Oakscan: procédé de mesure rapide et non destructif des polyphénols du bois de chêne de tonnellerie
Les polyphénols extractibles contenus dans le bois de chêne des barriques de tonnellerie sont des composés très importants car ils ont une influence sur la couleur et sur les propriétés organoleptiques des vins qu'ils enrichissent. Les analyses chimiques de laboratoire qui permettent de les mesurer sont réalisées sur des extractions, nécessitent un délai de réalisation très long et ne permettent d'analyser que des lots de matière par échantillonnage. Le procédé de mesure rapide et non destructif Oakscan® a été développé par la tonnellerie Radoux. Il se fonde sur la spectrométrie proche infrarouge et permet de mesurer la teneur en polyphénols en quelques secondes, directement sur le bois massif. Le contenu polyphénolique de chaque douelle est alors mesuré, permettant une meilleure maitrise de la matière première entrant dans la composition des fûts
Vibrational properties of SrCu2O2 studied via Density Functional Theory calculations and compared to Raman and infrared spectroscopy measurements
International audienceThe SrCu2O2 material is a p-type transparent conductive oxide. A theoretical study of the SrCu2O2 crystal is performed with a state of the art implementation of the Density Functional Theory. The simulated crystal structure is compared with available X-ray diffraction data and previous theoretical modeling. Density Functional Perturbation Theory is used to study the vibrational properties of the SrCu2O2 crystal. A symmetry analysis of the optical phonon eigenvectors at the Brillouin zone center is proposed. The Raman spectra simulated using the derivatives of the dielectric susceptibility, show a good agreement with Raman scattering experimental results
Phase transition close to room temperature in BiFeO3 thin films
BiFeO3 (BFO) multiferroic oxide has a complex phase diagram that can be
mapped by appropriately substrate-induced strain in epitaxial films. By using
Raman spectroscopy, we conclusively show that films of the so-called
supertetragonal T-BFO phase, stabilized under compressive strain, displays a
reversible temperature-induced phase transition at about 100\circ, thus close
to room temperature.Comment: accepted in J. Phys.: Condens. Matter (Fast Track Communication
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