Covariance-based approaches to aeroacoustic noise source analysis

In this paper, several covariance-based approaches are proposed for aeroacoustic noise source analysis under the assumptions of a single dominant source and all observers contaminated solely by uncorrelated noise. The Crame?r-Rao Bounds (CRB) of the unbiased source power estimates are also derived. The proposed methods are evaluated using both simulated data as well as data acquired from an airfoil trailing edge noise experiment in an open-jet aeroacoustic facility. The numerical examples show that the covariance-based algorithms significantly outperform an existing least-squares approach and provide accurate power estimates even under low signal-to-noise ratio (SNR) conditions. Furthermore, the mean-squared-errors (MSEs) of the so-obtained estimates are close to the corresponding CRB especially for a large number of data samples. The experimental results show that the power estimates of the proposed approaches are consistent with one another as long as the core analysis assumptions are obeyed.     

Mass transport controlled oxygen reduction at anthraquinone modified 3D-CNT electrodes with immobilized Trametes hirsuta laccase

Carbon nanotubes covalently modified with anthraquinone were used as an electrode for the immobilization of Trametes hirsuta laccase. The adsorbed laccase is capable of oxygen reduction at a mass transport controlled rate (up to 3.5 mA cm(-2)) in the absence of a soluble mediator. The storage and operational stability of the electrode are excellent.     

Loi limite et vitesse de convergence pour des séries géométriques aléatoires pondérées

We extend the Bovier–Picco–Zhang laws of the iterated logarithm for geometrically weighted random series, and give the rate of convergence towards the limit set. To cite this article: G. Stoica, C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

Effect of some parasite surface reactions on the variation of electrical conductance in the H2?Pt/Al2O3 system

The charge transfer at the interface H₂-0.5% Pt/Al₂O₃ was studied by using the transient response of the AC electrical conductance. The transient response for water and oxygen contaminated surface was of the overshoot-type.     

Spectrofluorimetric determination of phenyl-<Emphasis Type="Italic">β</Emphasis>-naphthylamine used as rubber antioxidant

Phenyl--naphthylamine (PBN) used as rubber antioxidant was found to have native fluorescence. A spectrofluorimetric method for determination of PBN in multicomponent mixtures of polymer additives is described. The apparent excitation and fluorescence wavelengths used are 348 and 413.5 nm, respectively. Maximum fluorescence intensity is obtained by irradiating PBN dissolved in ethanol, at room temperature. The fluorescence varies linearly with the concentration of PBN in the range of 0.04–4 g mL^–1. The accuracy and precision of the method are reported.     

Zero–Hopf bifurcation in a hyperchaotic Lorenz system

We characterize the zero–Hopf bifurcation at the singular points of a parameter codimension four hyperchaotic Lorenz system. Using averaging theory, we find sufficient conditions so that at the bifurcation points two periodic solutions emerge and describe the stability of these orbits.