Modelling farm vulnerability to flooding: towards the appraisal of vulnerability mitigation policies

International audienceIn France, two new kinds of flood management policies are promoted: floodplain restoration and vulnerability mitigation. Few experience feedback exist on these policies but they may have strong impacts on farms. Flood management on Rhône River is highly illustrative of these policies and local authorities would like to appraise the efficiency of these policies with an economic tool (Cost-Benefit Analysis) to help decision making. But the current methods of flood damage modelling do not make the appraisal of these policies possible; mainly because they do not take into account the organizational and temporal dimensions of damage formation and propagation at farm scale. After a presentation of the Rhône River context and policies, we review existing methods of flood damage modelling for agriculture and show the interest to focus on the farm scale instead of land plot scale. Based upon the theoretical frameworks for systemic approach, we detail the construction of our conceptual model of farm vulnerability before presenting a case study that shows how the model can be implemented to compute flood damage at farm scale. Finally, the outlooks concerning the use of the model to appraise vulnerability mitigation policies and its application at regional scale are developed

Caractérisation des stratégies de gestion pour la modélisation de la vulnérabilité des exploitations agricoles aux inondations : Lier les dimensions spatiale, organisationnelle et temporelle d'un système complexe

National audienceLes politiques publiques de gestion des inondations s'orientent vers la restauration des champs d'expansion de crue et de réduction de la vulnérabilité, qui auront un impact important sur les exploitations agricoles. L'évaluation des effets de ces politiques sur les exploitations agricoles n'est pas envisageable avec les méthodologies actuelles et le retour d'expérience quasiment inexistant. Il était donc nécessaire de développer un modèle de simulation des dommages directs et induits en prenant en compte la dimension systémique de l'exploitation agricole. Pour cela, nous proposons un modèle conceptuel de la vulnérabilité à l'échelle de l'exploitation agricole et montrons comment il nous a permis de mettre en évidence l'importance des stratégies de gestion post-inondation pour la modélisation des dommages. Nous présentons ensuite les résultats des enquêtes réalisées sur les exploitations arboricoles de la zone aval du Rhône pour la caractérisation de ces stratégies. Enfin, nous montrons comment nous avons intégré dans le modèle de simulation des dommages, les données recueillies par enquêtes. Les premiers résultats de simulation des dommages confirment l'importance de prendre en compte les effets induits de l'inondation sur le système " exploitation agricole ". En perspective, l'utilisation du modèle de simulation des dommages dans le cadre d'une évaluation économique des politiques de réduction de la vulnérabilité des exploitations agricoles sur la zone aval du Rhône est discutée

Temporal behavior of two-wave-mixing in photorefractive InP:Fe versus temperature

The temporal response of two-wave-mixing in photorefractive InP:Fe under a dc electric field at different temperatures has been studied. In particular, the temperature dependence of the characteristic time constant has been studied both theoretically and experimentally, showing a strongly decreasing time constant with increasing temperature

Surface effects on shape, self-organization and photoluminescence of InAs islands grown on InAlAs/InP(001)

International audienceInAs nanostructures were grown on In 0.52 Al 0.48 As alloy lattice matched on InP001 substrates by molecular beam epitaxy using specific growth parameters in order to improve island self-organization. We show how the change in InAs surface reconstruction via growth temperature from (24) to (21) and/or the use of InAlAs initial buffer surface treatments improve the island shape homogeneity either as quantum wires or as quantum dots. Differences in island shape and in carrier confinement are shown by atomic force microscopy and by photoluminescence measurements, respectively. We point out that such shape amendments induce drastic improvements to island size distribution and discernible changes in photoluminescence properties, in particular concerning polarization

Optical anisotropy and photoluminescence temperature dependence for self-assembled InAs quantum islands grown on vicinal (001) InP substrates

International audienceIn this paper, we report on a detailed investigation of the effect of misorientated InP(OOl) substrates on the optical properties of InAs quantum islands grown by molecular beam epitaxy in the Stranski-Krastanow regime. Temperature-dependent photoluminescence and polarization of photoluminescence (PPL) are studied. PPL shows a high degree of linear polarization, near 40%, for the sample grown on the substrate with 2°off miscut angle towards [110] direction (2°F) and only 16% for the sample grown on the substrate with 2°off miscut angle towards [010] direction (2°B). This result pointing out the growth ofInAs quantum wires (QWr) on 2°F substrate and of quasi-isotropic InAs quantum dots (QD) on 2°B substrate. The luminescence remains strong at 300 K as much as 36% of that at 8 K, indicating a strong spatial localization of the carriers in the InAs QIs grown on InP(OOl)

Effect of total pressure on the formation and size evolution of silicon quantum dots in silicon nitride films

The size of silicon quantum dots (Si QDs) embedded in silicon nitride (SiN(x)) has been controlled by varying the total pressure in the plasma-enhanced chemical vapor deposition (PECVD) reactor. This is evidenced by transmission electron microscopy and results in a shift in the light emission peak of the quantum dots. We show that the luminescence in our structures is attributed to the quantum confinement effect. These findings give a strong indication that the quality (density and size distribution) of Si QDs can be improved by optimizing the deposition parameters which opens a route to the fabrication of an all-Si tandem solar cell

Feasibility of nanofluid-based optical filters

In this article we report recent modeling and design work indicating that mixtures of nanoparticles in liquids can be used as an alternative to conventional optical filters. The major motivation for creating liquid optical filters is that they can be pumped in and out of a system to meet transient needs in an application. To demonstrate the versatility of this new class of filters, we present the design of nanofluids for use as long-pass, short-pass, and bandpass optical filters using a simple Monte Carlo optimization procedure. With relatively simple mixtures, we achieve filters with <15% mean-squared deviation in transmittance from conventional filters. We also discuss the current commercial feasibility of nanofluid-based optical filters by including an estimation of today's off-the-shelf cost of the materials. While the limited availability of quality commercial nanoparticles makes it hard to compete with conventional filters, new synthesis methods and economies of scale could enable nanofluid-based optical filters in the near future. As such, this study lays the groundwork for creating a new class of selective optical filters for a wide range of applications, namely communications, electronics, optical sensors, lighting, photography, medicine, and many more

Dynamic saturation of an intersublevel transition in self-organized InAs/In(x)A(1-x)lAs quantum dots

International audienceWe have observed a dynamic saturation of an intersublevel transition in InAs/InxAl1-xAs quantum dots related to the discrete nature of electron states using midinfrared femtosecond spectroscopy. This dynamic saturation is a consequence of the gradual filling of the discrete quantum-dot electron states due to the capture of electrons injected in the barrier. Our interpretation of the differential transmission experiments is confirmed by a comparison with a rate-equation model with the capture and intersublevel relaxation time as fit parameters yielding 10 ps and 1 ps, respectively. We discuss the mechanism responsible for these relaxation times

Growth of GaInTlAs layers on InP by molecular beam epitaxy

International audienceGrowth of GaInTlAs alloys on InP001 has been attempted by solid source molecular beam epitaxy. Thallium incorporation into Ga 1x In x As matrices was studied as a function of substrate temperature, arsenic overpressure, matrix composition, and growth rate. At high temperatures 350 °C thallium evaporates, whereas at intermediary temperatures 270-350 °C thallium segregates into droplets on the surface. Only in the low temperature range 180-260 °C can thallium be incorporated in some conditions, leading to mirror-like surfaces. Up to 18% Tl content was incorporated into a Ga 0.70 In 0.30 As matrix and up to 40% Tl into a GaAs matrix. For these high Tl concentrations, Tl droplets are avoided and Tl incorporation is achieved only when using high arsenic pressures. However, this limits surface adatom diffusion and leads to amorphous, polycrystalline, or twinned materials. Finally, a narrow window for single-crystal growth has been found for low Tl contents 4% using optimized growth conditions with low V/III pressure ratios and high growth rates

Five thousand years of tropical lake sediment DNA records from Benin

Until now, sedimentary DNA (sedDNA) studies have only focused on cold and temperate regions were DNA is relatively well preserved. Consequently, the tropics, where vegetation is hyperdiverse and natural archives are rare, have been neglected and deserve attention. In this study, we used next-generation sequencing to barcode sedDNA from Lake Sele, localized in the tropical lowlands of Benin (Africa), and compared the taxonomic diversity detected by DNA analyses with pollen assemblages. Plant sedDNA was successfully amplified from 33 of the 34 successfully extracted samples. In total, 43 taxa were identified along the 5,000 years spanned by the sediment: 22 taxa were identified at the family level and 21 at the genus level. The plant diversity recovered through sedDNA from Lake Sele showed a specific local signal and limited overlapping with pollen. Introduced plants, grown and cultivated close to the water, such as sweet potato, were also well recorded by sedDNA. It appears, therefore, to be a promising approach to studying past diversity in tropical regions, and could help in tracking the introduction and history of agriculture. This is the first time this method has been used in the field of domestication and dissemination of several specific crops, and the results are very encouraging