Absolute accuracy in membrane-based ac nanocalorimetry

To achieve accurate results in nanocalorimetry a detailed analysis and understanding of the behavior of the calorimetric system is required. There are especially two system-related aspects that should be taken in consideration: the properties of the empty cell and the effect of the thermal link between sample and cell. Here we study these two aspects for a membrane-based system where heater and thermometer are both in good contact with each other and the center of the membrane. Practical, analytical expressions for describing the frequency dependence of heat capacity, thermal conductance, and temperature oscillation of the system are formulated and compared with measurements and numerical simulations. We finally discuss the experimental conditions for an optimal working frequency, where high resolution and good absolute accuracy are combined

Coûts environnementaux du développement périurbain : impact des configurations urbaines et des choix résidentiels

[Departement_IRSTEA]Territoires [TR1_IRSTEA]DTAM [Axe_IRSTEA]DTAM1-REPRO [Axe_IRSTEA]DTAM-QT1-INEGALITESCe projet de recherche part du constat que la littérature existante sur la durabilité des espaces périurbains n'a pas apporté de réponse sur deux points particuliers. En premier lieu, la question du transport est généralement considérée du seul point de vue du transport de personnes, dans une optique d'équilibre partiel dans laquelle le transport des biens produits et consommés dans la ville n'est pas pris en compte. Or la théorie économique récente, dans le cadre des modèles d'économie géographique, montre que la localisation des ménages est étroitement liée à celle des entreprises, et que les configurations existant à l'équilibre dépendent fortement des interrelations entre ces deux catégories d'agents économiques. En d'autres termes, s'il est indispensable de considérer les choix résidentiels des ménages pour analyser les flux de transport engendrés par ces derniers, il est tout aussi indispensable de tenir compte des conséquences de ces localisations résidentielles sur la localisation des entreprises, et aussi des effets en retour des localisations des entreprises sur la distribution spatiale des ménages. Cette question fait l'objet du premier axe de notre recherche. En second lieu, les travaux existants négligent en général le fait que les espaces périurbains accueillent des ménages de catégories sociales variées qui ont des comportements différents en termes de déplacement. Or, il semble important de proposer une analyse du développement périurbain intégrant la question du choix résidentiel des ménages en fonction de leur catégorie sociale, ceci afin de dresser des pistes d'évolution possible des flux de transport engendrés par les espaces périurbains. C'est ce qui est développé dans le second axe de notre recherche. Enfin, ces analyses portant sur la localisation résidentielle des différentes catégories socio-professionnelles nous amènent aussi à analyser la ségrégation résidentielle dans les zones périurbaines, en lien avec les déterminants des choix de localisation résidentielle des ménages. / This research starts from the premise that the existing literature on the sustainability of suburban areas has not provided answers to two specific points. Firstly, the issue of transport is generally considered from the point of view of the transport of persons, in a partial equilibrium framework in which the transport of goods produced and consumed in the city is not taken into account. But the recent economic theory, with the new economic geography models, shows that the location of households is closely linked to the location of firms, and that the existing equilibrium configurations depend strongly on the interrelationships between these two categories of agent. In other words, it is essential to consider the residential choices of households to analyze the traffic flows they generate, but it is also necessary to take into account the consequences of these residential locations on the location of firms and the feedback effects of corporate locations on the spatial distribution of households. This question is the subject of the first axis of our research. Second, existing studies generally neglect the fact that the suburban areas host various social groups of households that have different behaviors in terms of mobility. However, it seems important to provide an analysis of suburban development incorporating the issue of residential choices of households according to their social class, in order to establish avenues for possible evolution of transport flows generated by the suburban areas. This is what is developed in the second focus of our research. Finally, the residential location of the different socio-professional categories is also analyzed in terms of urban segregation, in relation with the determinants of households’ choices

Depth-resolved particle associated microbial respiration in the northeast Atlantic

Atmospheric levels of carbon dioxide are tightly linked to the depth at which sinking particulate organic carbon (POC) is remineralised in the ocean. Rapid attenuation of downward POC flux typically occurs in the upper mesopelagic (top few hundred metres of the water column), with much slower loss rates deeper in the ocean. Currently, we lack understanding of the processes that drive POC attenuation, resulting in large uncertainties in the mesopelagic carbon budget. Attempts to balance the POC supply to the mesopelagic with respiration by zooplankton and microbes rarely succeed. Where a balance has been found, depth-resolved estimates reveal large compensating imbalances in the upper and lower mesopelagic. In particular, it has been suggested that respiration by free-living microbes and zooplankton in the upper mesopelagic are too low to explain the observed flux attenuation of POC within this layer. We test the hypothesis that particle-associated microbes contribute significantly to community respiration in the mesopelagic, measuring particle-associated microbial respiration of POC in the northeast Atlantic through shipboard measurements on individual marine snow aggregates collected at depth (36–500 m). We find very low rates of both absolute and carbon-specific particle-associated microbial respiration (< 3 % d−1), suggesting that this term cannot solve imbalances in the upper mesopelagic POC budget. The relative importance of particle-associated microbial respiration increases with depth, accounting for up to 33 % of POC loss in the mid-mesopelagic (128–500 m). We suggest that POC attenuation in the upper mesopelagic (36–128 m) is driven by the transformation of large, fast-sinking particles to smaller, slow-sinking and suspended particles via processes such as zooplankton fragmentation and solubilisation, and that this shift to non-sinking POC may help to explain imbalances in the mesopelagic carbon budget

Fourfold oscillations and anomalous magnetic irreversibility of magnetoresistance in the non-metallic regime of Pr1.85Ce0.15CuO4

Using magnetoresistance measurements as a function of applied magnetic field and its direction of application, we present sharp angular-dependent magnetoresistance oscillations for the electron-doped cuprates in their low-temperature non-metallic regime. The presence of irreversibility in the magnetoresistance measurements and the related strong anisotropy of the field dependence for different in-plane magnetic field orientations indicate that magnetic domains play an important role for the determination of electronic properties. These domains are likely related to the stripe phase reported previously in hole-doped cuprates.Comment: 11 pages, 5 figure