Low temperature reflectivity study of ZnO/(Zn,Mg)O quantum wells grown on M-plane ZnO substrates

We report growth of high quality ZnO/Zn0.8Mg0.2O quantum well on M-plane oriented ZnO substrates. The optical properties of these quantum wells are studied by using reflectance spectroscopy. The optical spectra reveal strong in-plane optical anisotropies, as predicted by group theory, and marked reflectance structures, as an evidence of good interface morphologies. Signatures ofc onfined excitons built from the spin-orbit split-off valence band, the analog of exciton C in bulk ZnO are detected in normal incidence reflectivity experiments using a photon polarized along the c axis of the wurtzite lattice. Experiments performed in the context of an orthogonal photon polarization, at 90^{\circ}; of this axis, reveal confined states analogs of A and B bulk excitons. Envelope function calculations which include excitonic interaction nicely account for the experimental report

Plastic deformation of Na-aluminosilicate glasses under micro and nano-indentation

The transition « normal glass - anomalous glass » is followed on Na-aluminosilicate glass model system using micro- and nano-indentation investigatio

Are opinions expressed in land-use planning documents?

International audienceA great deal of research on information extraction from textual datasets has been performed in specific data contexts, such as movie reviews, commercial product evaluations, campaign speeches, etc. In this paper, we raise the question on how appropriate these methods are for documents related to land-use planning. The kind of information sought concerns the stakeholders, sentiments, geographic information, and everything else related to the territory. However, it is extremely challenging to link sentiments to the three dimensions that constitute geographic information (location, time, and theme). After highlighting the limitations of existing proposals and discussing issues related to textual data, we present a method called OPILAND (OPinion mIning from LAND-use planning documents) designed to semi-automatically mine opinions related to named-entities in specialized contexts. Experiments are conducted on a Thau lagoon dataset (France), and then applied on three datasets that are related to different areas in order to highlight the relevance and the broader applications of our proposal

OPILAND : identification de la perception des territoires par la fouille de texte

National audienceDe nombreux travaux ont été réalisés en extraction d'informations et plus particulièrement en fouille de données d'opinions dans des contextes spécifiques tels que les critiques de films, les évaluations de produits commerciaux, les discours électoraux... Dans le cadre du projet SENTERRITOIRE, nous nous posons la question de l'adéquation de ces méthodes pour des documents associés à l'aménagement des territoires. Ces documents renferment différents types d'informations se rapportant à des acteurs, des opinions, des informations géographiques, et tout autre aspect lié plus généralement à la notion de territoire. Cependant, il est extrêmement difficile d'identifier puis de lier les opinions à ces informations. Après avoir souligné les limites des propositions actuelles et les verrous soulevés par les données textuelles associées, nous proposons la mé- thode semi-automatique nommée OPILAND (OPinion mIning from LAND-use planning documents) combinant une chaîne de Traitement Automatique du Lan- gage Naturel et des techniques de Fouilles de Textes pour (1) détecter les entités nommées de type lieu et organisation, (2) construire un vocabulaire d'opinions relatif au domaine d'application, et (3) identifier les opinions relatives aux entités nommées traitées. Les expérimentations sont menées sur des données du bassin de Thau (France), puis appliquées sur trois corpus relatifs à d'autres domaines afin de mettre en avant la généricité de notre approche

Raman Mapping of the Indentation-Induced Densification of a Soda-Lime-Silicate Glass

International audienceMicro-Raman spectroscopy was used to map the Vickers indentation-induced densification on a window glass (soda-lime silicate glass), from the correlation between Raman spectrum and density. Both top surface and cross-section of the residual imprints were investigated. It is shown that the sample preparation needed for the investigation of the in-depth densification does not alter the results. The maximum densification ratio measured is about 3.8%, which is 60% of the maximum densification measured after a high-pressure hydrostatic loading. Within the experimental errors, densification maps are self-similar for the two indentation loads used 10 N and 20 N. A comparison with finite element results based on a constitutive model developed for silica is discussed

Phébus FPT3 - Overview of Main Results concerning the Behaviour of Fission Products and Structural Materials in the Containment

FPT3 was the last of the five in-pile integral experiments in the Phébus FP programme, whose overall purpose was to investigate fuel rod degradation and behaviour of Fission Products (FPs) released via the primary coolant circuit into the containment building. The results contribute to validation of models and computer codes used to calculate the source term for a severe accident with core meltdown in light water reactors. Unlike the previous tests, FPT3 used B4C as absorber material in the pre-irradiated (24.5 GWd/tU) fuel bundle, while featuring a steam-poor period as in FPT2, that used Ag/In/Cd absorber. The main FPT3 containment results are summarised: the source term of FPs, fuel and structural materials from the experimental circuit into the containment; the composition, morphology and deposition processes of aerosols in the containment atmosphere; the specific behaviour of the radiologically-significant FP iodine; and finally the performance of Passive Autocatalytic Recombiners (PARs) exposed to the containment atmosphere just after the transient. The major elements contributing to the aerosol mass in the containment are the volatile FPs Cs and Mo, the control rod material B, the cladding material Sn, and the instrumentation materials Re and W (specific to Phébus tests). The fractional compositions, leaving aside the control rod materials, were very similar in FPT2 and FPT3. After reactor shutdown, homogenisation of the aerosol size in the containment led to only one aerosol population, similar to the previous tests. Long-term aerosol deposition in the containment is dominated by gravitational settling and diffusiophoresis, but also significant deposits were measured on the vertical wall, consisting of multi-component aerosols, again comparable with FPT2. A significant result of FPT3 is that iodine is mainly in gaseous form in the atmosphere up to containment isolation; the rest in aerosol form. Another important result is the fast decrease of the iodine concentration in the atmosphere, for total iodine (gas and aerosol), mainly due to deposition on the painted condensers; the depletion of the airborne aerosols Cs and Te was about a factor of 3 slower. As in FPT2, gaseous iodine is mainly in molecular form. Iodine collected in the sump is essentially in soluble form throughout, probably due to the replacement of Ag/In/Cd by B4C as the absorber material. Concerning the PARs, which were introduced in the vessel when the overall aerosol, FP and hydrogen releases in the containment atmosphere had ended, analysis of their surface temperature evolution indicated that, despite the very low oxygen concentration in the FPT3 containment, they worked quite well and were not poisoned by FPs during their 30 minute exposure time.JRC.F.5-Safety of present nuclear reactor

Sol-Gel Derived Hybrid Thin Films: The Chemistry behind Processing

International audienceDespite their apparent simple preparation by sol-gel process, silsesquioxanes based materials are quite complex and rich systems. Accordingly, a clear understanding of their elaboration chemistry and its relations to process and properties are important matter. In the particular case of thin film preparation, vitrification must be controlled to ensure high throughput and reliability. Using methylsilsesquioxane based films as a relevant model and a combination of IR spectroscopy, mass spectrometry, and solution 29Si NMR, a meaningful description of the film structure was obtained. Furthermore, vitrification, observed by dynamic mechanical analysis, was shown to depend strongly on the amounts of cages and extended structures present in the films. More interestingly, the proportion of these species can be tuned through a careful control of the elaboration chemistry. On one hand, long aging and high dilution yield a larger amount of cages, which results in a delay of the vitrification. On the other hand, pH appears as the convenient parameter to finely adjust the time span during which high quality films can be prepared from the sols, while preserving the film composition and final properties

Exciton radiative properties in nonpolar homoepitaxial ZnO/(Zn,Mg)O quantum wells

International audiencePhotoluminescence spectra of nonpolar M-plane ZnO/Zn0.8Mg0.2O quantum wells exhibit strong excitonic peaks from low (10 K) to high (325 K) temperatures. We find that the total integrated intensity remains quasiconstant and that the exciton lifetime increases linearly with the temperature from a value of 750 ps at 100 K until about 2.4 ns at 325 K. This behavior is well described by an original model accounting for the exciton phase space filling. This indicates that radiative recombination of free excitons is dominating the quantum well photoluminescence even at room temperature

Internal electric field in wurtzite ZnO/Zn0.78Mg0.22O quantum wells.

International audienceContinuous-wave, time-integrated, and time-resolved photoluminescence experiments are used to study the excitonic optical recombinations in wurtzite ZnO/Zn0.78Mg0.22O quantum wells of varying widths. By comparing experimental results with a variational calculation of excitonic energies and oscillator strengths, we determine the magnitude (0.9MV∕cm) of the longitudinal electric field that is induced by both spontaneous and piezoelectric polarizations. The quantum-confined Stark effect counteracts quantum confinement effects for well widths larger than 3nm, leading to emission energies that can lie 0.5eV below the ZnO excitonic gap and to radiative lifetimes that can be larger than milliseconds