Natural resource management in the hillsides of Honduras: bioeconomic modeling at the micro-watershed level

The objective of this study is to simulate the effect of population pressure, market integration, technological improvement and policy decisions on natural resource management in the hillsides of Honduras. To do so, we developed a bioeconomic model that combines dynamic linear programming with a biophysical model, then applied this model to a typical microwatershed. Over recent years, farmers from the selected microwatershed have followed a "vegetables-intensive" pathway of development. We ran different scenarios with historical data over the period 1975 to 1995 and then projected 25 years into the future from 1995 to 2020. The results of the bioeconomic model presented in this paper help to test a number of induced innovation hypotheses. Many of our hypotheses are confirmed, but some of the model's results challenge conventional wisdom. The simulation results confirm that technology improvements such as irrigation and new varieties can help overcome diminishing returns to labor due to population pressure.Honduras., Natural resources., Water Management.,

Natural resource management in the hillsides of Honduras: bioeconomic modeling at the micro-watershed level

Barbier and Bergeron explore several hypotheses about the dynamics of natural resource management in the hillsides of La Lima and further explore the causes and consequences of the transition to vegetable production. To fully integrate agroecological factors, such as forest, water resources, and topography, the authors use a bioeconomic model that links farmers' resource management decisions to biophysical models. This captures production processes as well as the condition of natural resources. The model was used to run different scenarios over the period 1975 to 1995 and then to project into the future. The authors conclude that agroecological conditions are the most important factors de-termining incomes for villages with comparable agroecological conditions.Natural resources Honduras., Natural resources Management Mathematical models.,

Cathodoluminescence of stacking fault bound excitons for local probing of the exciton diffusion length in single GaN nanowires

We perform correlated studies of individual GaN nanowires in scanning electron microscopy combined to low temperature cathodoluminescence, microphotoluminescence, and scanning transmission electron microscopy. We show that some nanowires exhibit well localized regions emitting light at the energy of a stacking fault bound exciton (3.42 eV) and are able to observe the presence of a single stacking fault in these regions. Precise measurements of the cathodoluminescence signal in the vicinity of the stacking fault give access to the exciton diffusion length near this location

Shells of crystal field symmetries evidenced in oxide nano-crystals

By the use of a point charge model based on the Judd-Ofelt transition theory, the luminescence from Eu3+ ions embedded in Gd2O3 clusters is calculated and compared to the experimental data. The main result of the numerical study is that without invoking any other mechanisms such as crystal disorder, the pure geometrical argument of the symmetry breaking induced by the particle surface has influence on the energy level splitting. The modifications are also predicted to be observable in realistic conditions where unavoidable size dispersion has to be taken into account. The emission spectrum results from the contribution of three distinct regions, a cluster core, a cluster shell and a very surface, the latter being almost completely quenched in realistic conditions. Eventually, by detailing the spectra of the ions embedded at different positions in the cluster we get an estimate of about 0.5 nm for the extent of the crystal field induced Stark effect. Due to the similarity between Y2O3 and Gd2O3, these results apply also to Eu3+ doped Y2O3 nanoparticles

Photoinduced dynamics in protonated aromatic amino acid

UV photoinduced fragmentation of protonated aromatics amino acids have emerged the last few years, coming from a situation where nothing was known to what we think a good understanding of the optical properties. We will mainly focus this review on the tryptophan case. Three groups have mostly done spectroscopic studies and one has mainly been involved in dynamics studies of the excited states in the femtosecond/picosecond range and also in the fragmentation kinetics from nanosecond to millisecond. All these data, along with high level ab initio calculations, have shed light on the role of the different electronic states of the protonated molecules upon the fragmentation mechanisms

Quantification of water content and speciation in natural silicic glasses (phonolite, dacite, rhyolite) by confocal microRaman spectrometry

International audienceThe determination of total water content (H2OT: 0.1-10 wt%) and water speciation (H2Omolecular/OH) in volcanic products by confocal microRaman spectrometry are discussed for alkaline (phonolite) and calcalkaline (dacite and rhyolite) silicic glasses. Shape and spectral distribution of the total water band (H2OT) at not, vert, similar3550 cm−1 show systematic evolution with glass H2OT, water speciation and NBO/T. In the studied set of silicic samples, calibrations based on internal normalization of the H2OT band to a band related to vibration of aluminosilicate network (TOT) at not, vert, similar490 cm−1 vary with glass peraluminosity. An external calibration procedure using well-characterized glass standards is less composition-dependent and provides excellent linear correlation between total dissolved water content and height or area of the H2OT Raman band. Accuracy of deconvolution procedure of the H2OT band to quantify water speciation in water-rich and depolymerized glasses depends on the strength of OH hydrogen bonding. System confocal performance, scattering from embedding medium and glass microcrystallinity have a crucial influence on accuracy of Raman analyses of water content in glass-bearing rocks and melt inclusions in crystals

Caractéristique rhéologique de nanocomposites polypropylène/argile en régime transitoire

National audienceDans cette étude, nous nous intéressons au comportement rhéologique en régime transitoire de mélanges polypropylène/argile organophile. Les mélanges ont été préparés à l'état fondu, à l'aide d'un mélangeur interne et d'une extrudeuse bivis co-rotative. L'évolution du comportement rhéologique lors du démarrage a été étudiée en cisaillement simple aller-retour sur un rhéomètre à géométrie plan-plan. On observe un pic de contrainte au démarrage, ainsi qu'un effet de restructuration, qui se traduit par l'augmentation de l'amplitude du pic après un temps de repos. Le pic observé est différent suivant la morphologie des nanocomposites, notamment le niveau d'exfoliation. Deux modèles, basés sur deux phénomènes physiques différents, ont été étudiés. Le premier est un modèle thixotrope qui relie les propriétés rhéologiques aux mécanismes de création et de rupture des flocs. Le deuxième est un modèle généralement utilisé pour décrire le comportement rhéologique des polymère chargés de fibres courtes. Le modèle thixotrope prédit assez bien l'amplitude du pic de contrainte en fonction du temps de repos. Cependant, l'évolution de la contrainte au démarrage est moins bien modélisée. Le modèle de suspensions de fibres décrit mieux l'évolution de cette dernière, mais ne prend pas en compte l'effet de restructuration observé

A time splitting projection scheme for compressible two-phase flows. Application to the interaction of bubbles with ultrasound waves

This paper is focused on the numerical simulation of the interaction of an ultrasound wave with a bubble. Our interest is to develop a fully compressible solver in the two phases and to account for surface tension effects. As the volume oscillation of the bubble occurs in a low Mach number regime, a specific care must be paid to the effectiveness of the numerical method which is chosen to solve the compressible Euler equations. Three different numerical solvers, an explicit HLLC (Harten–Lax–van Leer-Contact) solver [48], a preconditioning explicit HLLC solver [14] and the compressible projection method , and , are described and assessed with a one dimensional spherical benchmark. From this preliminary test, we can conclude that the compressible projection method outclasses the other two, whether the spatial accuracy or the time step stability are considered. Multidimensional numerical simulations are next performed. As a basic implementation of the surface tension leads to strong spurious currents and numerical instabilities, a specific velocity/pressure time splitting is proposed to overcome this issue. Numerical evidences of the efficiency of this new numerical scheme are provided, since both the accuracy and the stability of the overall algorithm are enhanced if this new time splitting is used. Finally, the numerical simulation of the interaction of a moving and deformable bubble with a plane wave is presented in order to bring out the ability of the new method in a more complex situation