Bernard Claudet

Electronic band structure of AgCd2GaS4: theory and experiment

We report theoretical calculations of the band structure of AgCd2GaS4 using the full-potential linear augmented plane wave method and experimental measurements of the valence band x-ray photoelectron spectroscopy. We find that the valence band maximum and the conduction band minimum are located at the ? point of the Brillouin zone resulting in a direct energy gap of 1.0?eV compared to our measured experimental value of 2.15?eV. Our analysis of the partial density of states shows that there is a weak covalent interaction between Ag and Ga atoms and between Ag and Cd atoms, and a substantial covalent interaction between Ag and S atoms. Thus the Ga?Ag and Cd?Ag bonds are basically of ionic character, and Ag?S bonds are of covalent character. The theoretical results of the density of states are in agreement with the valence band x-ray photoelectron spectroscopy measurements with respect to spectral peak positions. We have analyzed the calculated density of states and find a strong/weak hybridization between the Ag, Cd, Ga and S states in the valence and conduction bands.

Fuzzy logic observers for a biological wastewater treatment process

In order to monitor and control biological processes, on-line measurements of the living part of the system are necessary but difficult or too expensive to obtain. This paper presents fuzzy estimators for the concentration of the substrate at the input, the total and partial alkalinity in the influent and in the effluent and the volatile fatty acid concentration at the output of the reactor. Those observers are built on available on-line measurements like pH, temperature, input flow rate and output gaseous flow rate. The observers are tested on a pilot-scale anaerobic digestion reactor for the treatment of raw industrial wine distillery vinasses.

Optically-induced linear electro-optics in Hg-1201 films

The photo-induced linear electro-optics effect (EOE) has been revealed in Hg0.89Pb0.17Ba0.11Ba2CuO4+δ (Hg-1201) single crystalline films coated on an MgO surface. Investigations have been performed using time-resolved measurements of the photovoltage, photocurrent, photoresistivity and linear EOE. A time delay shift between the non-linear optical response and photocurrent has been found. Applying external static magnetic fields (up to 1.7 T) we achieve a substantial decrease of the linear electro-optics coefficients. We discuss the possible origin of the observed phenomenon.

Nonlinear optical study of amorphous SiN:H films on the Si(111) substrate

A correlation between the resistivity-voltage dependences of the hydrogenated SiN/Si(111) films and the photo-induced third-harmonic generation (PITHG) at λ = 1064 nm in the reflected light regime was found. The contribution to the PITHG is both due to linear photo-induced surface changes as well as due to the hydrogen dopants. When the fundamental power density increases to higher than 1.2 GW/cm2, there occurs a drastic decrease of the PITHG. Maximal PITHG changes are observed at a pump-probe delay time about 18 ps and the value of the PITHG slightly increases with the enhanced applied dc-electric field during illumination by a third-harmonic laser beam as a photo-inducing one. The deviation from the tripled frequency wavelength to higher wavelengths substantially suppresses the output PITHG signal. The crucial role of the interface trapping levels and silicon-hydrogen charge transfer is shown.

Geometrical and Rayleigh number effects in the transient laminar free convection between two vertically eccentric spheres

Purpose – The purpose of this paper is to study the transient natural convection of a Newtonian fluid which develops in a closed spherical annulus delimited by two vertically eccentric spheres by using a bispherical coordinates system. The inner sphere is heated by a heat flux of constant density and the outer one is maintained isothermal.Design/methodology/approach – The transfer equations are written by using a bispherical coordinates system. The Navier‐Stokes equations are solved and coupled with the energy equation by using the alternating direction implicit (ADI) and the successive over relaxation (SOR) methods.Findings – The study of the stream function and the Nusselt number shows that the convection motion is reinforced for the geometries characterized by positive values of the eccentricity with heat exchange increasing. The Nusselt number increases with the modified Rayleigh number. The heat exchange increases with the radius ratio. The results show that the steady state is reached faster when th...