Improvement in air–sea flux estimates derived from satellite observations

A new method is developed to estimate daily turbulent air–sea fluxes over the global ocean on a 0.25° grid. The required surface wind speed (w ₁₀) and specific air humidity (q ₁₀) at 10 m height are both estimated from remotely sensed measurements. w ₁₀ is obtained from the SeaWinds scatterometer on board the QuikSCAT satellite. A new empirical model relating brightness temperatures (T _b) from the Special Sensor Microwave Imager (SSM/I) and q ₁₀ is developed. It is an extension of the author's previous q ₁₀ model. In addition to T _b, the empirical model includes sea surface temperature (SST) and air–sea temperature difference data. The calibration of the new empirical q ₁₀ model utilizes q ₁₀ from the latest version of the National Oceanography Centre air–sea interaction gridded data set (NOCS2.0). Compared with mooring data, the new satellite q ₁₀ exhibits better statistical results than previous estimates. For instance, the bias, the root mean square (RMS), and the correlation coefficient values estimated from comparisons between satellite and moorings in the northeast Atlantic and the Mediterranean Sea are –0.04 g kg^?1, 0.87 g kg^?1, and 0.95, respectively. The new satellite q ₁₀ is used in combination with the newly reprocessed QuikSCAT V3, the latest version of SST analyses provided by the National Climatic Data Center (NCDC), and 10 m air temperature estimated from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalyses (ERA-Interim), to determine three daily gridded turbulent quantities at 0.25° spatial resolution: surface wind stress, latent heat flux (LHF), and sensible heat flux (SHF). Validation of the resulting fields is performed through a comprehensive comparison with daily, in situ values of LHF and SHF from buoys. In the northeast Atlantic basin, the satellite-derived daily LHF has bias, RMS, and correlation of 5 W m^?2, 27 W m^?2, and 0.89, respectively. For SHF, the statistical parameters are –2 W m^?2, 10 W m^?2, and 0.94, respectively. At global scale, the new satellite LHF and SHF are compared to NOCS2.0 daily estimates. Both daily fluxes exhibit similar spatial and seasonal variability. The main departures are found at latitudes south of 40° S, where satellite latent and sensible heat fluxes are generally larger.     

Hydrogen production from raw bioethanol steam reforming: Optimization of catalyst composition with improved stability against various impurities

The use of raw bioethanol is of major importance for a cost effective industrial application. Raw bioethanol contains higher alcohols as the main impurities and also aldehydes, amines, acids and esters. The effect of these impurities on the catalytic performances for ethanol steam reforming (ESR) has been studied, using a reference catalyst, Rh/MgAl₂O₄. It was shown that the aldehyde, the amine and methanol have no negative effect on the catalytic performances, contrary to the ester, acid and higher alcohols. The deactivation is mainly explained by coke formation favored by the presence of these impurities in the feed. In order to improve the stability of the catalyst and its performances in the presence of these deactivating impurities, the catalyst formulation, i.e. the composition of the support and of the metallic phase, was modified. The addition of rare earth elements instead of magnesium to the alumina support leads to a decrease of the strong and medium acid sites and to an increase of the basicity. On these modified supports, the dehydration reaction, leading to olefins, which are coke precursors, is disfavored, the ethanol conversion and the hydrogen yield are increased. The best catalytic performances were obtained with Rh/Y-Al₂O₃. Then, the metallic phase was also modified by adding a second metal (Ni, Pt or Pd). The Rh-Ni/Y-Al₂O₃ catalyst leads to the highest hydrogen yield. This catalyst, tested in the presence of raw bioethanol during 24 h was very stable compared to the reference catalyst Rh/MgAl₂O₄, which was strongly deactivated after 2 h of time-on –stream.     

Elaboration of a microstructured inkjet-printed carbon electrochemical capacitor

Carbon-based micro-supercapacitors dedicated to energy storage in self-powered modules were fabricated with inkjet printing technology on silicon substrate. An ink was first prepared by mixing an activated carbon powder with a PTFE polymer binder in ethylene glycol stabilized with a surfactant then deposited by inkjet on patterned gold current collectors with the substrate heated at 140 °C in order to assure a good homogeneity.Electrochemical micro-capacitors with electrodes in an interdigital configuration were fabricated, and characterized using electrochemical techniques in 1 M Et₄NBF₄ propylene carbonate electrolyte. These micro-devices show an excellent capacitive behavior over a wide potential range of 2.5 V for a cell capacitance of 2.1 mF cm⁻². The newly developed technology will allow the integration of the storage device as close as possible to the MEMS-based energy harvesting device, minimizing power losses through connections.     

A quinhydrone biofuel cell based on an enzyme-induced pH gradient

We report on an alternative concept of biofuel cell functioning based on the unconventional use of enzymes to create a pH difference generating a potential difference between electrodes soaked in quinhydrone solutions. The electrode and quinhydrone solution were confined in a dialysis bag placed into a compartment containing either glucose oxidase and catalase for the biocathode or urease for the bioanode. In presence of 0.4 mol L⁻¹ glucose and urea, the enzyme reactions generate a pH difference of 3.55, both compartments being separated by an agar-agar wall. The resulting biofuel cell exhibits an open-circuit voltage and maximum power of 208 mV and 30.6 μW, respectively, without immobilization and electrical connection of the involved enzymes. In addition, this biofuel cell was able to provide continuously10 μA during 23 h, producing 0.133 J and 0.828 C. A similar biofuel cell configuration based only on dialysis bags was also developed. A graphite disk electrode elaborated by mechanical compression of graphite particles and quinhydrone, was placed in a dialysis bag itself confined into another dialysis bag containing enzyme solution. The resulting power and open-circuit voltage at saturating substrate conditions are 7.6 μW and 157 mV, respectively.     

Development of new test instruments and protocols for the diagnostic of fuel cell stacks

In the area of fuel cell research, most of the experimental techniques and equipments are still devoted to the analysis of single cells or very short stacks. However, the diagnosis of fuel cell stacks providing significant power levels is a critical aspect to be considered for the integration of fuel cell systems into real applications such as vehicles or stationary gensets. In this article, a new instrument developed in-lab is proposed in order to satisfy the requirements of electrochemical impedance studies to be led on large FC generators made of numerous individual cells. Moreover, new voltammetry protocols dedicated to PEMFC stack analysis are described. They enable for instance the study of membrane permeability and loss of platinum activity inside complete PEMFC assemblies.     

Monolithic integration of multiple-quantum-well lasers andmodulators for high-speed transmission

Monolithically integrated single frequency lasers and electroabsorption modulators are attracting considerable interest as optical sources for long-haul and high-bit-rate fiber-optic links. Their frequency chirpless nature has indeed allowed nonreturn-to-zero (NRZ) transmission beyond the chromatic dispersion limit. They also offer a great potential as soliton pulse generators. This paper discusses the many integration schemes devised for their realization with particular emphasis on the identical active layer (IAL) approach. Recent progress in their high-speed applications is reported     

SPME-GCMS study of the natural attenuation of aviation diesel spilled on the perennial ice cover of Lake Fryxell, Antarctica

In January 2003, a helicopter crashed on the 5 m thick perennial ice cover of Lake Fryxell (McMurdo Dry Valleys, East Antarctica), spilling approximately 730 l of aviation diesel fuel (JP5-AN8 mixture). The molecular composition of the initial fuel was analyzed by solid phase microextraction (SPME) gas chromatography-mass spectrometry (GC-MS), then compared to the composition of the contaminated ice, water, and sediments collected a year after the spill. Evaporation is the major agent of diesel weathering in meltpool waters and in the ice. This process is facilitated by the light non-aqueous phase liquid properties of the aviation diesel and by the net upward movement of the ice as a result of ablation. In contrast, in sediment-bearing ice, biodegradation by both alkane- and aromatic-degraders was the prominent attenuation mechanism. The composition of the diesel contaminant in the ice was also affected by the differential solubility of its constituents, some ice containing water-washed diesel and some ice containing exclusively relatively soluble low molecular weight aromatic hydrocarbons such as alkylbenzene and naphthalene homologues. The extent of evaporation, water washing and biodegradation between sites and at different depths in the ice are evaluated on the basis of molecular ratios and the results of JP5-AN8 diesel evaporation experiment at 4 degrees C. Immediate spread of the aviation diesel was enhanced where the presence of aeolian sediments induced formations of meltpools. However, in absence of melt pools, slow spreading of the diesel is possible through the porous ice and the ice cover aquifer.     

Generalized radiative transfer equation for porous medium upscaling: Application to the radiative Fourier law

Many porous media cannot be homogenized as Beerian semi-transparent media. Effective extinction, absorption and scattering coefficients can indeed have no physical meaning for small or intermediate optical thicknesses. A generalized radiative transfer equation (GRTE), directly based on the extinction cumulative distribution function, the absorption and scattering cumulative probabilities and the scattering phase function is established for this optical thickness range. It can be solved by a statistical Monte Carlo approach. For a phase of a porous medium that is optically thick at local scale, the GRTE degenerates into a classical Beerian RTE. In these conditions, a radiative conductivity tensor is directly obtained, by a perturbation method, and expressed with the radiative coefficients of this RTE and temperature. As illustrations, exhaustive radiative conductivity results are given for a set of overlapping transparent spheres within an opaque phase and for opaque rod bundles.