Independent Tuning of Optical Transparency Window and Electrical Properties of Epitaxial SrVO3 Thin Films by Substrate Mismatch

Transparent metallic oxides are pivotal materials in information technology, photovoltaics, or even in architecture. They display the rare combination of metallicity and transparency in the visible range because of weak interband photon absorption and weak screening of free carriers to impinging light. However, the workhorse of current technology, indium tin oxide (ITO), is facing severe limitations and alternative approaches are needed. AMO₃ perovskites, M being a nd¹ transition metal, and A an alkaline earth, have a genuine metallic character and, in contrast to conventional metals, the electron–electron correlations within the nd¹ band enhance the carriers effective mass (m*) and bring the transparency window limit (marked by the plasma frequency, ω_p*) down to the infrared. Here, it is shown that epitaxial strain and carrier concentration allow fine tuning of optical properties (ω_p*) of SrVO₃ films by modulating m* due to strain‐induced selective symmetry breaking of 3d‐t_2g(xy, yz, xz) orbitals. Interestingly, the DC electrical properties can be varied by a large extent depending on growth conditions whereas the optical transparency window in the visible is basically preserved. These observations suggest that the harsh conditions required to grow optimal SrVO₃ films may not be a bottleneck for their future application.     

Biogas production from energy crops in northern Greece: economics of electricity generation associated with heat recovery in a greenhouse

Herein a techno-economic assessment was performed on an energy-crop-based biogas plant coupled with a greenhouse for utilizing thermal energy produced by cogeneration. Seven energy crops were evaluated: triticale, maize, alfalfa, sunflower, clover, barley and wheat. According to the evaluation, triticale was the most competitive energy crop under selected climate conditions for northern Greece. Although maize displays higher biomass yield and biogas potential than the drought-resistant crop triticale, it has high irrigation demand that contributes significantly to total production costs. For a triticale-based biogas production to become economically feasible, agricultural arable area larger than 500 ha, or biogas plant size larger than 1000 kW_el, is required. However, with public funding, biogas production becomes feasible at smaller area (>250 ha) or biogas plant size (>500 kW_el). The inclusion of a greenhouse into the design of the biogas plant contributes positively to the economic viability of the entire system. Under this scenario, greenhouse financial income accounts for about 17–18% of total income. Results of a sensitivity analysis suggest that the selection of an appropriate energy crop for biogas production should be based principally on both digestibility (specific methane yield) and biomass yield per hectare, these factors being more critical than biomass production costs.     

Thermodynamic and structural properties of LaNi5−yAly compounds and their related hydrides

Among the intermetallic compounds able to absorb reversibly large amounts of hydrogen in convenient conditions, LaNi₅ presents large possibility of substitution involving a change of the plateau pressure of the related hydrides in a wide range of pressure. The results presented concern the metallurgical, structural and thermodynamic properties of the compounds LaNi_5?yAl_y and their related hydrides:The limit of existence of pseudobinary intermetallic compounds with hexagonal structure P6/mmm is determined (Y_A1 = 1.25).The lattice parameters and cell volume of the intermetallic compounds are determined in terms of Y_A1. The enthalpy of formation of LaNi₅ and LaNi₄Al are measured by a calorimetric method.The lattice parameters and cell volume of the hydride are determined by X-ray diffraction.The study of the absorption and desorption hydrogen isotherms show a decrease of the plateau pressures with the increasing rate of aluminium and decrease of the capacity. The enthalpy and entropy of formation of hydrides are deduced from the study of the change of their equilibrium pressures as a function of temperature. Correlations are established between structural and thermodynamical properties of intermetallic compound of this series and their related hydrides.     

Comparison of sludge characteristics and performance of a submerged membrane bioreactor and an activated sludge process at high solids retention time

This work aims to compare biomass structure and performance of a submerged membrane bioreactor (SMBR) and an activated sludge process (ASP) treating the same domestic wastewater. The influence of the separation technique (membrane filtration or settling) and operation at high sludge-retention time (SRT) were investigated. Over the entire range of SRT (10-110 days), the SMBR achieved very good organic removal efficiencies, ranging from 90.8+/-0.2% to 94.2+/-1.6% based on total COD (TCOD), whereas those of ASP were between 87.4+/-1.8% and 90.3+/-0.8%. The contribution of the membrane in the increase in performance was due to total suspended solid retention and also partly due to retention of proteins and polysaccharides of the sludge supernatant. No significant difference in excess sludge production was observed between the two processes operated at the same SRT, but sludge production in SMBR decreased from 0.31 to 0.13 g(VSS)g(COD)(-1) as SRT increased from 9 to 110 days. The difference in sludge characteristics and performance was especially pronounced as SRT increased, resulting in deterioration of sludge settleability and effluent quality of the ASP (filamentous bacteria, increase of protein and polysaccharide release). Membrane filtration induced accumulation of soluble and colloidal proteins and polysaccharides which were progressively degraded in the supernatant as the SRT increased. At similar SRT, no significant difference was observed in the amount of extractable exocellular polymeric substances (bound EPS) from ASP and SMBR sludge. However as the SRT increased, the total specific amount of bound EPS in flocs decreased and the ratio proteins/polysaccharides also decreased. Concomitantly, laser diffraction analysis, microscopic observations, turbidity and DSVI measurement showed that the SRT increase induced significant modifications in sludge morphology in SMBR: decrease in floc size, densification of aggregates, and development of non-flocculating organisms.     

Reversible shift in the α-, β- and γ-proteobacteria populations of drinking water biofilms during discontinuous chlorination

As disinfection strategies could support a shift of some bacterial populations, the biodiversity of drinking water biofilms depending on the disinfectant concentrations was explored. The effect of different chlorine sequences applied for several weeks (0.1-0.4-0.1 mg Cl₂ L⁻¹ or vice versa) was tested on the abundance of the α-, β- and γ-proteobacteria populations, used as indicators of changes in bacterial populations within drinking water biofilms. Using dynamic (industrial pilot) and batch (bench scale) conditions, our work demonstrated the ability of the 3 proteobacteria subclasses to re-organize following discontinuous chlorinations. The β- and γ-proteobacteria subclasses were favoured by high free residual chlorine concentrations (0.4 mg Cl₂ L⁻¹) while α-proteobacteria population was sensitive to this oxidant level. The proteobacteria population shifts within the biofilm exposed to discontinuous chlorination were reversible. The resilience of the biofilm proteobacteria populations exposed to oxidant stress questioned the emergence of bacterial population less sensitive to chlorine.     

Généralisation de la méthode de l’ouverture pour l’étude du rayonnement paraxial des nouveaux concepts de réflecteurs

The computation and development of new types of antennas with reflectors have required the elaboration of a specific analytical method. The authors develop a software for processing reflectors of any profile, determined analytically or over a set of points, with surfaces of finite or perfect, isotropic or anisotropic reflectivity. In a first step, the choice of the equivalent aperture method combined with the fast Fourier transform is justified. An original implementation scheme of the method is then made conform to the above requirements and to the whole set of new concepts developped nowadays. The results obtained prove the precision of the new method and its suitability for radiation field simulation of antennas which are under construction for communication by satellites.