Cation distribution in manganese cobaltite spinels Co3−xMnxO4 (0 ≤ x ≤ 1) determined by thermal analysis

Thermogravimetric analysis was used in order to study the reduction in air of submicronic powders of Co3−x Mn x O4 spinels, with 0 ≤ x ≤ 1. For x = 0 (i.e. Co3O4), cation reduction occurred in a single step. It involved the CoIII ions at the octahedral sites, which were reduced to Co2+ on producing CoO. For 0 < x ≤ 1, the reduction occurred in two stages at increasing temperature with increasing amounts of manganese. The first step corresponded to the reduction of octahedral CoIII ions and the second was attributed to the reduction of octahedral Mn4+ ions to Mn3+. From the individual weight losses and the electrical neutrality of the lattice, the CoIII and Mn4+ ion concentrations were calculated. The distribution of cobalt and manganese ions present on each crystallographic site of the spinel was determined. In contrast to most previous studies that took into account either CoIII and Mn3+ or Co2+, CoIII and Mn4+ only, our thermal analysis study showed that Co2+/CoIII and Mn3+/Mn4+ pairs occupy the octahedral sites. These results were used to explain the resistivity measurements carried out on dense ceramics prepared from our powders sintered at low temperature (700–750 °C) in a Spark Plasma Sintering apparatus

Quality management and contractual incompleteness: grape procurement for high-end wines in Argentina

International audienceSourcing grapes from independent growers for use in top quality wines sold on the international market is a major organisational challenge for corporate wineries. Our paper adds to the small existing literature addressing these coordination issues in the New World wine sector, by going deeper into the specifics of the contracts, as well as the "transaction cost economising" argument. Based on a case-study carried out in the Argentine province of Mendoza, this article presents an in-depth analysis of the technical process, in order to identify the contractual hazards posed by asset specificity, measurement costs, and non-contractible actions. Drawing on contract completion and dual sourcing literature, it analyses the contractual and non contractual mechanisms (price incentives, grower monitoring, allocation of decision rights to the winery, role of backward integration into production) used to govern such grape transactions. Through our analysis, we were able to arrive at four main conclusions. Firstly, most agreements are still verbal, with the exception of occasional written contracts, limited to a few legal provisions. It became clear to us that this approach to forging agreements is not always adequate in managing the inherently complex interactions between grape varieties, soil, farming practices and wine-making processes in high-end wine production. Secondly, extensive decision rights are allocated to wineries, to deal with incompleteness. These are key decisions to be taken during the cropping and harvesting process. Thirdly, pricing is generally kept flexible, with grape prices negotiated ex-post. This means that trade imbalances tend to be resolved in the long term. Winegrowers also benefit from financial rewards to compensate for allocations. Finally, any potential opportunistic behaviour by wineries with regards to asset specificity (in particular yield limitation) and allocation of rights is kept at bay by mechanisms such as winery reputations and credit third-party guaranty. This type of behaviour by growers is similarly deterred through monitoring and vineyard ownership on the part of the wineries

Simultaneous Induction Heating and Electromagnetic Stirring of a Molten Glass Bath

International audienceThis paper studies solutions for an efficient induction heating and a strong electromagnetic stirring of the molten glass bath through the action of Lorentz forces in a direct induction furnace. Different spatial configurations of AC magnetic fields - travelling, rotating or helicoidal, and the generated molten glass electromagnetic stirring are studied with one-way coupled electromagnetic and hydrodynamic models. For imposed value of the active power induced in the molten glass, the numerical experiments offers the values of the total inductor current and of the supply frequency for which an efficient electromagnetic stirring of molten glass is achieved

An aperture masking mode for the MICADO instrument

MICADO is a near-IR camera for the Europea ELT, featuring an extended field (75" diameter) for imaging, and also spectrographic and high contrast imaging capabilities. It has been chosen by ESO as one of the two first-light instruments. Although it is ultimately aimed at being fed by the MCAO module called MAORY, MICADO will come with an internal SCAO system that will be complementary to it and will deliver a high performance on axis correction, suitable for coronagraphic and pupil masking applications. The basis of the pupil masking approach is to ensure the stability of the optical transfer function, even in the case of residual errors after AO correction (due to non common path errors and quasi-static aberrations). Preliminary designs of pupil masks are presented. Trade-offs and technical choices, especially regarding redundancy and pupil tracking, are explained.Comment: SPIE 2014 Proceeding -- Montrea

2-D constrained Navier-Stokes equation and intermediate asymptotics

We introduce a modified version of the two-dimensional Navier-Stokes equation, preserving energy and momentum of inertia, which is motivated by the occurrence of different dissipation time scales and related to the gradient flow structure of the 2-D Navier-Stokes equation. The hope is to understand intermediate asymptotics. The analysis we present here is purely formal. A rigorous study of this equation will be done in a forthcoming paper

Antireflective photonic structure for coherent nonlinear spectroscopy of single magnetic quantum dots

This work presents epitaxial growth and optical spectroscopy of CdTe quantum dots (QDs) in (Cd,Zn,Mg)Te barriers placed on the top of (Cd,Zn,Mg)Te distributed Bragg reflector. The formed photonic mode in our half-cavity structure permits to enhance the local excitation intensity and extraction efficiency of the QD photoluminescence, while suppressing the reflectance within the spectral range covering the QD transitions. This allows to perform coherent, nonlinear, resonant spectroscopy of individual QDs. The coherence dynamics of a charged exciton is measured via four-wave mixing, with the estimated dephasing time $T_2=(210\,\pm\,40)$ ps. The same structure contains QDs doped with single Mn$^{2+}$ ions, as detected in photoluminescence spectra. Our work therefore paves the way toward investigating and controlling an exciton coherence coupled, via $s$,$p$-$d$ exchange interaction, with an individual spin of a magnetic dopant.Comment: 6 pages, 5 figure

Environmental factors influence both abundance and genetic diversity in a widespread bird species.

Genetic diversity is one of the key evolutionary variables that correlate with population size, being of critical importance for population viability and the persistence of species. Genetic diversity can also have important ecological consequences within populations, and in turn, ecological factors may drive patterns of genetic diversity. However, the relationship between the genetic diversity of a population and how this interacts with ecological processes has so far only been investigated in a few studies. Here, we investigate the link between ecological factors, local population size, and allelic diversity, using a field study of a common bird species, the house sparrow (Passer domesticus). We studied sparrows outside the breeding season in a confined small valley dominated by dispersed farms and small-scale agriculture in southern France. Population surveys at 36 locations revealed that sparrows were more abundant in locations with high food availability. We then captured and genotyped 891 house sparrows at 10 microsatellite loci from a subset of these locations (N = 12). Population genetic analyses revealed weak genetic structure, where each locality represented a distinct substructure within the study area. We found that food availability was the main factor among others tested to influence the genetic structure between locations. These results suggest that ecological factors can have strong impacts on both population size per se and intrapopulation genetic variation even at a small scale. On a more general level, our data indicate that a patchy environment and low dispersal rate can result in fine-scale patterns of genetic diversity. Given the importance of genetic diversity for population viability, combining ecological and genetic data can help to identify factors limiting population size and determine the conservation potential of populations