J. André

Centre National de Recherches Météorologiques, Tolosa de Llenguadoc, Midi-Pyrénées, France

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Publications (19)41.77 Total impact

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    ABSTRACT: Polyelectrolyte membrane used in proton exchange membrane fuel cell (PEMFC) should act as a barrier to hydrogen and electrons. In the present work, fast and robust specific tools were developed both to characterize these properties and localize defects, such as pinholes or short-circuits, within the membrane electrode assembly (MEA). The identification of defective cells without disassembling the Axane's stack was performed in a single step through a passive electrical technique so-called “relaxometry” and by internal gas leak measurements. The flaws were further tracked inside MEA using Infrared Thermography in order to obtain their precise location. The latter, performed after stack disassembly, permitted to reveal the defects responsible for the Fuel Cell shutdown. A third step dealt with SEM examinations of the flaws in order to identify the origin and nature of the membrane failure.
    Fuel Cells 06/2012; 12(3-3):356-364. DOI:10.1002/fuce.201100161 · 2.08 Impact Factor
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    ABSTRACT: In this study, we investigated the long-term morphological and chemical changes of PEMFC cathode materials, with a special focus on the homogeneity of aging in different operating conditions (stationary or intermittent). The spatially-resolved physico-chemical analyses, performed at the cathode inlet/outlet region of the membrane electrode assembly, put in evidence that the cathode inlet ages much more rapidly than the cathode outlet in counter-flow mode, this effect being exacerbated at high cell current. The rationale for such observation is the existence of heterogeneities of local current density, essentially caused by the depletion in air partial pressure and the increase in water content along the gas-channel. We also evidenced heterogeneities of aging through the catalytic layer (CL). These heterogeneities are explained by the fact that Pt z+ ions produced by the corrosion of the Pt-Co/C nanoparticles are evacuated by the produced water exiting the CL [at the gas-diffusion layer (GDL)|CL interface] or consumed by H 2 crossing-over from the anode through the cathode [at the CL|proton-exchange membrane (PEM) interface], resulting in the formation of the so-called "platinum-band" in the PEM. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Fuel Cells 04/2012; 12(2-2):188-198. DOI:10.1002/fuce.201100073 · 2.08 Impact Factor
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    ABSTRACT: This paper provides further insights into the degradation mechanisms of nanometer-sized Pt 3Co/C particles under various proton-exchange membrane fuel cell (PEMFC) operating conditions. We confirm that Co atoms are continuously depleted from the mother Pt 3Co/C electrocatalyst because they can diffuse from the bulk to the surface of the material. The structure of the Pt-Co/C nanoparticles in the long-term is determined by a balance between Co surface segregation and formation of oxygenated species from water splitting. When the PEMFC is operated at high current density (low cathode potential, below the onset of surface oxide formation from water), a steady-state is reached between the rate of Co dissolution at the surface and Co surface segregation. Consequently, Co and Pt atoms remain homogeneously distributed within the Pt-Co/C particles and the thickness of the Pt-shell is maintained to a small value not detectable by atomic-resolution high-angle annular dark-field scanning transmission electron microscopy. When the PEMFC is operated at low current density (high cathode potential), the formation of surface oxides from water and the resulting "place-exchange" mechanism enhance the rate of diffusion of Co atoms to the surface. Consequently, the fresh Pt 3Co/C particles form core/shell particles with thick Pt-shells and Co content < 5 at% and, ultimately, "hollow" Pt nanoparticles (Kirkendall effect). To the best of our knowledge, this is the first report on the formation of "hollow" Pt particles in a PEMFC. © 2011 Elsevier Ltd. All rights reserved.
    Electrochimica Acta 12/2011; 56(28-28):10658-10667. DOI:10.1016/j.electacta.2011.03.073 · 4.50 Impact Factor
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    ABSTRACT: This study bridges the structure/composition of Pt-Co/C nanoparticles with their surface reactivity and their electrocatalytic activity. We show that Pt 3Co/C nanoparticles are not stable during PEMFC operation (H 2/air; j = 0.6 A cm -2, T = 70 °C) but suffer compositional changes at the nanoscale. In the first hours of operation, the dissolution of Co atoms at their surface yields to the formation of a Pt-enriched shell covering a Pt-Co alloy core ("Pt-skeleton") and increases the affinity of the surface to oxygenated and hydrogenated species. This structure does not ensure stability in PEMFC conditions but is rather a first step towards the formation of "Pt-shell/Pt-Co alloy core" structures with depleted Co content. In these operating conditions, the Pt-Co/C specific activity for the ORR varies linearly with the fraction of Co alloyed to Pt present in the core and is severely depreciated (ca. -50%) after 1124 h of operation. This is attributed to: (i) the decrease of both the strain and the ligand effect of Co atoms contained in the core (ii) the changes in the surface structure of the electrocatalyst (formation of a multilayer-thick Pt shell) and (iii) the relaxation of the Pt surface atoms. © 2010 Elsevier Ltd. All rights reserved.
    Electrochimica Acta 12/2010; 56(2-2):776-783. DOI:10.1016/j.electacta.2010.09.038 · 4.50 Impact Factor
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    ABSTRACT: Pt 3Co/C electrocatalysts are not stable when operated in real PEMFC conditions but face variations of their chemical composition. The latter signs that Co atoms can segregate from the bulk to the surface of the nanoparticles, which we believe is activated by the formation of surface oxides and the leaching of Co at the surface. Consequently, the alloyed Pt 3Co/C nanoparticles slowly evolve towards Pt shell/Pt-Co alloy core structures with depleted Co content and a Pt-enriched shell. © 2010 Elsevier B.V. All rights reserved.
    Electrochemistry Communications 09/2010; 12(9-9):1161-1164. DOI:10.1016/j.elecom.2010.06.007 · 4.85 Impact Factor
  • 60th Annual Meeting of the ISE60th Annual Meeting of the ISE; 01/2010
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    ABSTRACT: The Belgian Society for Medical Informatics (MIM) organized a survey in 1986 in order to assess the present state of development of medical informatics in Belgium. Questionnaires were sent to hospitals, laboratories, private practitioners and pharmacists, as well as to social security organizations and software industries. The response rate was higher in hospitals (93%) than in any other category. Results showed a large number of computerized hospitals (93% of general acute care hospitals and 91% of psychiatric hospitals). There has been a sharp increase (+ 15%) in computerization of the admission, accounting and billing procedures since 1985, most likely in relation with administrative rules issued by the Belgian Government. The same trend (+ 20%) has been observed for computer applications in clinical laboratories, between 1984 and 1985. There is almost one computer terminal for ten beds in the hospitals with more than 200 beds in 1986. This figure exemplifies the present trend to on-line access to data. Computerized instrumental aids to medicine such as text processing, imaging or computerized interpretation of signals have known a rapid extension during recent years, although less comprehensive than administrative applications in hospitals and in social security organizations. The present state of other applications in medicine (general practice, pharmacy, etc.) was more difficult to assess as those information systems remain more pinpointed. In all medical fields, there appears to be a new rise in computer programs offered by software companies.
    Medical informatics = Médecine et informatique 07/2009; 12(4):249-62. DOI:10.3109/14639238709010063
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    ABSTRACT: The main thrust of the HAPEX-MOBILHY experiment was towards investigating techniques involved in integrating the turbulent surface fluxes measured at local sites to a larger scale approaching that used in general circulation models.Some aspects of the field data collected at various times and spatial scales are presented. Annual cycle of the soil moisture at many sites is discussed in relation with outputs of a large scale hydrological model. At shorter time scales, the spatial variability of surface energy partition is examined with regard to spatial contrasts in albedo, surface roughness and plant properties related to the two main vegetation classes found in the HAPEX square: A pine forest and the nearby agricultural area.Finally, examples of daily spatial integration with an atmospheric mesoscale model including a comprehensive treatment of land surface processes are presented.
    Surveys in Geophysics 01/1991; 12(1):31-61. DOI:10.1007/BF01903411 · 5.11 Impact Factor
  • J.C. Andre · P. Bougeault · J.P. Goutorbe
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    Philosophical Transactions of The Royal Society B Biological Sciences 08/1989; 324(1223). DOI:10.1098/rstb.1989.0055 · 6.31 Impact Factor
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    ABSTRACT: The possibility of forecasting seeing quality from routine meteorological data used as input to a numerical model of the boundary layer is discussed after demonstrating examples of reasonably good agreement between observed and calculated seeing on three nights when observed image diameter did not exceed 2 arc sec. Under poor seeing conditions (5 arc sec) agreement was not achieved. The comparisons were made between optical measurements by the Anglo-Australian Observatory and calculations based on temperature soundings from an aircraft and an empirical relationship for estimating dome seeing effects. It is argued that even limited seeing forecasts would assist in optimizing the observing schedules of highly utilized telescopes. A numerical model appears useful to predict C2(N) profiles of the atmosphere but cannot handle dome seeing effects, which often constitute a significant contribution to overall image quality.
    Publications of the Astronomical Society of the Pacific 02/1986; 98:376-387. DOI:10.1086/131769 · 3.23 Impact Factor
  • J.-C. Andre · P. Lacarrere · K. Traore
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    ABSTRACT: The parameterization of pressure effects on triple correlations is shown to be an important part of the closure problem. Based on arguments relevant to homogeneous and isotropic turbulence, it is argued that pressure effects are not only of a relaxative nature. In the case of turbulent thermal convection, a parameterization scheme including nonlinear and rapid effects is proposed and used within the framework of a third-order model. Comparison with experimental results by Ferreira (1978) indicates that the rapid part of pressure effects represents an important contribution to the budget of triple correlations and that it prevents the development of spurious stable stratification in the interior of the convective layer.
  • J. C. André · G. de Moor · P. Lacarrère · R. Du Vachat
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    ABSTRACT: A high-order model is proposed for the study of the 24 h evolution of clear planetary boundary layers. The model includes the rate equations of correlations up to the third order, as required for an accurate description of daytime convective phenomena, but it also takes into account interactions between radiative transfer and turbulence in order to achieve a physically reasonable description of the nocturnal structure of the boundary layer. This numerical model is tested against the Wangara boundary layer data of Day 33 and Night 33-34 (Clarke et al., 197l). The computed daytime mean structure of the boundary layer compares favorably with the Wangara data, while the daytime turbulent structure, expressed in the framework of the convective similarity theory, is in particularly good quantitative agreement with a number of experimental and numerical data concerning convection in the boundary layer, with particular concern to the production of turbulence at the top of the mixed layer. The computed nocturnal mean structure is shown to be driven principally by radiative transfer and the mesoscale pressure gradient. It agrees with the observed nocturnal structure with the exception that the height of the turbulent surface layer is underestimated in the model, but it is shown that this height is very sensitive to the imposed boundary conditions. The computed nocturnal turbulent structure is explained on a qualitative basis by the interactions between shear generation of turbulence, thermal stratification and radiative phenomena. It is also shown that generation and vertical propagation of nocturnal turbulence, which are of primary interest for environmental purposes, are strongly influenced by turbulence and radiative transfer interactions.
    Journal of the Atmospheric Sciences 10/1978; 35(10):1861-1883. DOI:10.1175/1520-0469(1978)035<1861:MTHEOT>2.0.CO;2 · 3.04 Impact Factor
  • J. C. Andre · G. de Moor · P. Lacarrere · G. Therry · R. Du Vachat
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    ABSTRACT: A new treatment of third order moments is proposed for the study of inhomogeneous turbulence: the equations for the rate of change of third order correlations should be used in conjunction with the quasi-normal approximation and with the enforcement of some generalized Schwarz inequalities ('clipping' mechanism) relating third and second order moments, the clipping mechanism being intended to preserve realizability. Together with rather classical formulations for pressure and dissipative terms, this approximation is used for numerical modeling of a penetrative convection experiment and of an asymmetric channel flow experiment.
  • J. C. André · G. de Moor · P. Lacarrère · R. Du Vachat
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    ABSTRACT: The quasi-normal theory modified by the clipping approximation is used to construct a numerical model of vertically inhomogeneous turbulence in a Boussinesq fluid. The pressure-correlation terms are expressed according to recently proposed formulations. With the aid of the horizontal homogeneity assumption the model is applied to the description of a laboratory experiment on penetrative convection and the numerical results are compared to the experimental data. It is found that the model does reproduce the measured vertical variations of mean temperature, turbulent beat flux, eddy kinetic energy and temperature variance, as well as a third-order correlation such as the vertical flux of eddy kinetic energy. The stationarity of the vertical profiles of various turbulent quantities, when scaled by the convective velocity and temperature, is also verified.
    Journal of the Atmospheric Sciences 02/1976; 33(3):482-491. DOI:10.1175/1520-0469(1976)033<0482:TAFIFP>2.0.CO;2 · 3.04 Impact Factor
  • J. C. André · G. de Moor · P. Lacarrère · R. Du Vachat
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    ABSTRACT: A modification of the quasi-normal theory is proposed for the study of inhomogeneous turbulent flows. In this approximation realizability conditions for third-order correlations are enforced. These conditions are based on generalized Schwarz' inequalities which limit the growth of triple correlations and the approximation consists in `clipping' these last quantities when they violate their respective inequalities. By requiring that the inequalities be satisfied, we take into account the damping effect of fourth-order correlations. The equations corresponding to this approximation are derived for the case of inhomogeneous turbulence in a Boussinesq fluid with the aid of a recently proposed hypothesis for pressure correlation terms.
    Journal of the Atmospheric Sciences 02/1976; 33(3):476-481. DOI:10.1175/1520-0469(1976)033<0476:TAFIFP>2.0.CO;2 · 3.04 Impact Factor
  • J. C. ANDRE · G. De Moor · P. Lacarrere · R. du Vachat
    Lecture Notes in Physics 01/1976; DOI:10.1007/BFb0120597