Action d'oxydations et de réductions électrochimiques successives sur la structure superficielle d'électrodes d'or polycristallines: Étude optique et életrochimique

Flat, mechanically polished gold electrodes have been subjected to several hundred cycles of electrochemical oxidation and reduction (0.4 to 1.9 V NHE) in normal sulfuric acid. The evolution of these electrodes has been followed by electrochemical measurements (capacity and potentiokinetic curves) and optical (ellipsometry) measurements, and the surfaces have been examined by metallographic microscopy. After a number of cycles the electrochemical treatment transforms the originally disturbed surface into a structured surface, with appearance of grain boundaries and faceting analogous to thermal faceting. Considering the work of Vetter and Schultze, we interpret the restructuring of the electrode surface as being due to two facts: mobility of metal atoms, because of their delocalization during the oxygen desorption phase and the anisotropy of the surface energy, owing to the presence of adsorbed oxygen. The complex evolution of the optical properties of the metal cannot be accounted for simply by facetting, and thus we have been led to postulate an accumulation in the metal of traces of undesorbed oxygen.     

Numerical simulation of thermoconvective flows and more uniform depositions in a cold wall rectangular APCVD reactor

At atmospheric pressure, the usual flow conditions in the cold wall horizontal rectangular thermal CVD reactors correspond to steady longitudinal thermoconvective rolls that make non-uniform vapour depositions, in shape of longitudinal parallel ridges. In order to get more uniform depositions, the pressure is generally lowered under the atmospheric pressure to promote forced convection flows, instead of mixed convection ones. In the present paper, using three-dimensional direct numerical simulations, we propose and analyse a method to get uniform deposition without lowering the pressure in the reactor. It consists in adequately exciting the parallel thermoconvective rolls at channel inlet to make them unsteady, periodic and sinuous in order to get a uniform time average of the deposition. This method is shown to be adapted for the horizontal and rectangular APCVD reactors with large longitudinal and transversal aspect ratios, when the Reynolds number of the gas flow is O(100), whatever the value of the surface Damköhler number. This situation is encountered in the online or scrolling APCVD reactors used to deposit coatings on float glass in the flat glass industry for instance. The simulations are based on simplified models for the transport equations (Boussinesq model) and the kinetics of the heterogeneous reactions (deposition model of silicon from hydrogen and silane: SiH₄→Si+2H₂).     

(P,C) Cyclometalated Gold(III) Complexes: Highly Active Catalysts for the Hydroarylation of Alkynes

The first catalytic application of well‐defined (P,C) cyclometalated gold(III) complexes is reported. The bench‐stable bis(trifluoroacetyl) complexes 2 a , b perform very well in the intermolecular hydroarylation of alkynes. The reaction is broad in scope, it proceeds within few hours at 25 °C at catalytic loadings of 0.1–5 mol %. The electron‐rich arene adds across the C≡C bond with complete regio‐ and stereo‐selectivity. The significance of well‐defined gold(III) complexes and ligand design are highlighted in a powerful but challenging catalytic transformation.     

Chemical composition and antibacterial activity of the essential oil of Moroccan Juniperus phoenicea

The antibacterial activity of the essential oil from leaves of Juniperus phoenicea (Cupressaceae) and its chemical constituents were investigated in this study. The essential oil was obtained by hydro-distillation and analyzed by gas chromatography equipped with a flame ionisation detector (GC-FID), and gas chromatography coupled to a mass spectrometer (GC-MS). Sixty-three volatile compounds were identified representing 52 to 92% of the total oil compositions. The main monoterpenes were a-pinene (26.7-78.7%) and 6-3carene (7.6-15.4%). The antibacterial activity of J. phoenicea essential oil, when tested against both Gram-positive and Gram-negative bacteria, showed high activity against all bacteria tested, except Pseudomonas.     

Hindered Rotation in Some Organic Dithiocarbamates

Abstract

Hindered rotation in alkyldithiocarbamates of the type RR′NC(= S)SR″ [R, R′, R″ = Me, Me, Et (1); PhCH₂, Me, Et (2); PhCH₂, H, Et (3); PhCH₂, H, Me (4) and O(CH₂CH₂)₂, Et (5)′ has been investigated using variable-temperature ¹H NMR spectroscopy in CDCl₃, C₆D₆, and DMSO-d₆ solutions. Rotational parameters were calculated by the coalescence temperature method. Nitrogen substituent effects on the free energy of activation and on the equilibrium constant of unsymmetrical conformers at room temperature are discussed.     

A new attack on RSA with two or three decryption exponents

Let N=pq be an RSA modulus, i.e. the product of two large unknown primes of equal bit-size. In this paper, we describe an attack on RSA in the presence of two or three exponents e _i with the same modulus N and satisfying equations e _i x _i ??(N)y _i =z _i , where ?(N)=(p?1)(q?1) and x _i , y _i , z _i are unknown parameters. The new attack is an extension of Guo’s continued fraction attack as well as the Blömer and May lattice-reduction basis attack.     

Microcalorimetric Studies on the Promoter Function in E. Coli TG1 from P. Maltophilia AT18 Chromosome DNA

In this paper, a promoter-probe plasmid pKK232-8 was used as a vector, which functioned in Escherichia coli TG₁ host. The plasmid DNA fragments from Pseudomonas maltophilia AT18 chromosome DNA active as promoter inEscherichia coli TG₁, the promoter function was studied by means of microcalorimetry, the promoter is about 800 bp DNA, it can promote the chloramphenicol (Cm) gene in plasmid pKK232-8, the Cm resistance level is about 80 μg mL^–1, the promoter activity is high. It implicates that there are probably many promoters in Pseudomonas maltophilia AT18 chromosome. All these information is readily obtained by an LKB 2277-204 heat conduction microcalorimeter. Microcalorimetry is a quantitative, inexpensive, and versatile method for microbiological genetic research. This revised version was published online in August 2006 with corrections to the Cover Date.     

Approximation by Multipoles of the Multiple Acoustic Scattering by Small Obstacles in Three Dimensions and Application to the Foldy Theory of Isotropic Scattering

The asymptotic analysis carried out in this paper for the problem of a multiple scattering in three dimensions of a time-harmonic wave by obstacles whose size is small as compared with the wavelength establishes that the effect of the small bodies can be approximated at any order of accuracy by the field radiated by point sources. Among other issues, this asymptotic expansion of the wave furnishes a mathematical justification with optimal error estimates of Foldy’s method that consists in approximating each small obstacle by a point isotropic scatterer. Finally, it is shown how this theory can be further improved by adequately locating the center of phase of the point scatterers and the taking into account of self-interactions. In this way, it is established that the usual Foldy model may lead to an approximation whose asymptotic behavior is the same than that obtained when the multiple scattering effects are completely neglected.