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Millet P.,University Paris - Sud | Ngameni R.,University Paris - Sud | Decaux C.,ADEME | Grigoriev S.A.,RAS Research Center Kurchatov Institute
International Journal of Hydrogen Energy | Year: 2011

Permeation across metallic membranes is a process used in the industry for purifying hydrogen. In conventional technology, a few tens of micrometers thick metallic membranes made of palladium alloys are used in the 400-600 °C temperature range, using a driving force of several bars for enhanced kinetics. In stationary conditions of flow, the diffusion-controlled transport of atomic hydrogen across the membrane is usually rate-determining. When thin (sub-micron thick) membranes are used, surface rate contributions become more significant. To optimize permeation performances, there is therefore a need for separately measuring surface and bulk rate contributions. In this communication, we report on the kinetics of hydrogen permeation across Pd77Ag23 metallic membranes using pneumato-chemical impedance spectroscopy. The role of different operating parameters (temperature, surface state, membrane microstructure) on the kinetics of permeation is analyzed and discussed. © 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Source


Dequiedt S.,University of Burgundy | Saby N.P.A.,Unite Us | Lelievre M.,University of Burgundy | Jolivet C.,Unite Us | And 6 more authors.
Global Ecology and Biogeography | Year: 2011

Aim The spatial organization of soil microbial communities on large scales and the identification of environmental factors structuring their distribution have been little investigated. The overall objective of this study was to determine the spatial patterning of microbial biomass in soils over a wide extent and to rank the environmental filters most influencing this distribution. Location French territory using the French Soil Quality Monitoring Network. This network covers the entire French territory and soils were sampled at 2150 sites along a systematic grid. Methods The soil DNA extracted from all these soils was expressed in terms of soil molecular microbial biomass and related to other soil and land-use data over French territory. Results This study provides the first extensive map of microbial biomass and reveals the heterogeneous and spatially structured distribution of this biomass on the scale of France. The main factors driving biomass distribution are the physico-chemical properties of the soil (texture, pH and total organic carbon) as well as land use. Soils from land used for intensive agriculture, especially monoculture and vineyards, exhibited the smallest biomass pools. Interestingly, factors known to influence the large-scale distribution of macroorganisms, such as climatic factors, were not identified as important drivers for microbial communities. Main conclusions Microbial abundance is spatially structured and dependent on local filters such as soil characteristics and land use but is relatively independent of global filters such as climatic factors or the presence of natural barriers. Our study confirms that the biogeography of microorganisms differs fundamentally from the biogeography of 'macroorganisms' and that soil management can have significant large-scale effects. © 2011 Blackwell Publishing Ltd. Source


Saadi Z.,University of Maine, France | Rasmont A.,Materia Nova | Cesar G.,SERPBIO | Bewa H.,ADEME | Benguigui L.,University of Maine, France
Journal of Polymers and the Environment | Year: 2012

The biodegradability of polymers by microorganisms is generally studied in a real environment that contains a natural mixture of fungi and bacteria. The present research mainly focused on the purely fungal degradation of poly(l-lactide), PLLA, to enclose the part of fungi in a real process of biodegradation and to understand the kinetics of biodegradation. Respirometric tests were realized in soil at 30 °C, and in compost at 30 and 58 °C. Results indicated that temperature is the predominant parameter governing the fungal degradation of PLLA. Moreover, in real compost, the biodegradation kinetics of the PLLA revealed a synergy between bacteria and fungi. The curves of PLLA and cellulose biodegradation were modeled by Hill sigmoïd. Fungal degradation was completed by investigating the physical and the chemical properties of the polymer during the process of degradation using several analytical methods such as matrix assisted laser desorption ionization-time of fly spectroscopy, infrared spectroscopy, size exclusion chromatography, and differential scanning calorimetry. These experiments led to a better understanding of the various stages of fungal degradation of PLLA: hydrolysis as well as mineralization. Furthermore, metabolizing products (by-products) of PLLA was investigated also. © 2011 Springer Science+Business Media, LLC. Source


Leconte F.,ADEME | Leconte F.,British Petroleum | Bouyer J.,CEREMA Direction Territoriale Est | Claverie R.,CEREMA Direction Territoriale Est | Petrissans M.,British Petroleum
Building and Environment | Year: 2015

In the context of expansion of cities and raise of climate change awareness, urban planers are looking for methods and tools in order to take into account the urban heat island phenomenon. This study analyzes the way urban fabric modifies urban climate through the utilization of a climate scheme called Local Climate Zone (LCZ). This classification has been applied in Nancy (France). Urban indicators have been calculated so as to build 13 LCZ in the Great Nancy Area. The screen-height air temperature distribution has been investigated inside these LCZ via mobile measurements. Air temperature amplitude has mainly demonstrated lower values at nighttime than in daytime in urbanized LCZ types. Recurrent microscale hotspots and coldspots have been located in LCZ presenting heterogeneous urban fabric. Two Control Sites (CS) have been built in each LCZ. The CS average temperature has revealed good likeness with the spatially averaged air temperature. Average nocturnal air temperature differences between pairs of LCZ types have been obtained. These differences vary from less than 1°°C for close LCZ types to more than 4°°C for dissimilar LCZ types. © 2014 Elsevier Ltd. Source


Vaudelet P.,Bordeaux Montaigne University | Revil A.,Colorado School of Mines | Revil A.,University of Savoy | Schmutz M.,Bordeaux Montaigne University | And 2 more authors.
Water Resources Research | Year: 2011

Two sets of experiments were designed to understand the change in induced polarization associated with the sorption of copper and sodium, exhibiting distinct sorption behavior on a silica sand. A sand column experiment was first performed to see the change in the complex conductivity during the advective transport of a copper sulfate solution. A second set of experiments was done with the sand at equilibrium with various solutions of NaCl and CuSO 4. In the first experiment, the copper sulfate solution replaced a sodium chloride solution, keeping the electrical conductivity of the solution nearly constant. During the passage of the copper sulfate solution, the apparent phase angle decreased from 3 ± 0.2 to 0.5 ± 0.2 mrad, while the magnitude of the conductivity of the sand remained nearly constant. A quantitative model is proposed to explain the change in the complex conductivity as a function of the chemistry assuming a polarization mechanism associated with the Stern layer (the inner part of the electrical double layer coating the water-mineral interface). The Stern layer polarization is combined with a complexation model describing the competitive sorption of copper and sodium at the pore water interface. The change of the phase lag is directly associated with the ion exchange between sodium and copper at the surface of the silica grains. The explanation of the observed phase differences between Na and Cu relies on their different complexation behaviors, with Na being loosely absorbed, while Cu forms relatively strong complexation with both inner (monodentate) and outer sphere (bidentate) complexes. The replacement of Cu 2+ by Na+ is less favorable; therefore, the kinetics of such a replacement is much slower than for the opposite replacement (Na + by Cu2+). We were able to reproduce the changes in the phase lags at thermodynamic equilibrium near the relaxation frequency and in the frequency domain. These measurements and modeling results open the door to the quantitative interpretation of spectral induced polarization data in the field in terms of quantification of the sorption processes. Copyright 2011 by the American Geophysical Union. Source

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