Experimental study of ultrasonic beam sectors for energy conversion into Lamb waves and Rayleigh waves

When a bounded beam is incident on an immersed plate Lamb waves or Rayleigh waves can be generated. Because the amplitude of a bounded beam is not constant along its wave front, a specific beam profile is formed that influences the local efficiency of energy conversion of incident sound into Lamb waves or Rayleigh waves. Understanding this phenomenon is important for ultrasonic immersion experiments of objects because the quality of such experiments highly depends on the amount of energy transmitted into the object. This paper shows by means of experiments based on monochromatic Schlieren photography that the area within the bounded beam responsible for Lamb wave generation differs from that responsible for Rayleigh wave generation. Furthermore it provides experimental verification of an earlier numerical study concerning Rayleigh wave generation.     

Deplacements homolytiques intramoleculaires : V - epoxy-2,3 propanation des acides et derives par thermolyse du peroxyde d'allyle et de t-butyle

The thermolysis of the allyl t-hutylperoxide has been performed in esters, acids, anhydrides, nitriles and amides. Only esters and acetonitrile have been 2,3-epoxy-propanated. With acids, the reaction product is the alkanoate of the hydroxymethyl-γ-butyrolactone corresponding to the cyclization of the expected epoxyacid and it is isolated with a good yield ; the same compound is obtained putting the anhydride in place of the acid.     

Intramolecular homolytic displacements 7 — Free radical additions to unsaturated peroxy compounds : Synthesis of oxygenated heterocycles

Free radical additions of hydrogen donor solvents to tert-butyl perpent-4-enoate have given 4-substituted γ-butyrolactones, with yields of 50 % or greater. Such reactions applied to allyl-tert-butyl peroxide have produced 2,3-epoxypropanation of these solvents. Similar addition-elimination processes occurred with tert-butyl 4-methyl-perpent-4-enoate, tert-butyl 2,2-dimethyl-perpent-4-enoate and tert-butyl-methallyl peroxide, but they failed with tert-butyl 5-methyl-perhex-4-enoate and tert-butyl-3-methyl-but-2-enyl peroxide.     

Influence of a finite strain on vibration of a bounded Timoshenko beam

The goal of this work is to study the eigenmodes of shearable beams with initial finite strain. A three dimensional model is developed on the base of Cosserat continuum mechanics. The characteristics of waves propagation superimposed upon finite pre-stress are obtained using the (rigorous) calculation of the Hamiltonian action. The results are applied on vibration of beam supporting a finite longitudinal strain. Nonlinear effect according to the pre-stress is obtained for various boundary conditions and through a nondimensional formalism.     

Deplacements homolytiques intramoleculaires : III-decomposition du peroxyde d'allyle et de t-butyle dans les ethers et les cyclanes: expoxy-2,3 propanation de ces solvants

Product analysis of the thermolysis of allyl t-butyl peroxide in cyclohexane and tetrahydrofuran shows that an important induced decomposition of the peroxide occurs by the addition of radicals derived from the solvent, to the peroxide double bond, followed by an intramolecular homolytic displacement of the t-butoxyl group. Such a reaction is a 2,3-epoxypropanation of the solvent in which the initiator is decomposed. The reaction is shown to be general, by using other ethers and cycloalkanes as solvents.     

Contribution à la modélisation géométrique et thermodynamique d'une classe de milieux faiblement continus

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(Manuscrit accepté le 18 juin, 1996)     

Photo-Fenton degradation of resorcinol mediated by catalysts based on iron species supported on polymers

Novel Fe supported catalysts were prepared by immobilizing iron species on commercial polyethylene via three different methods: (1) acidic pre-treatment of the polyethylene followed by impregnation in aqueous Fe(NO₃)₃, (2) TiO₂ photo-catalytic pre-treatment of the polyethylene followed by forced hydrolysis of Fe(NO₃)₃, and (3) direct photo-Fenton attack with concomitant iron deposition on the polyethylene surface. The last method required soft conditions and led to the most photo-active Fe–polyethylene film. With this material, at a non-adjusted initial pH of 5.6 in the presence of H₂O₂, total degradation and 50% of resorcinol mineralization were observed in 40 and 60 min, respectively. Photo-Fenton functionalization/Fe-deposition process was also applied to polypropylene, high-impact polystyrene, and polymethylmethacrylate films. The efficiencies of all the prepared heterogeneous photo-catalysts were similar to that of an homogeneous photo-Fenton system containing the same amount of Fe^3+/2+ that leached during “heterogeneous” processes. That demonstrated than in our systems mainly homogeneous photo-Fenton reactions were responsible for the resorcinol degradation. The photo-catalytic activity observed for the Fe/polymer was a function of the specific polymer capacity to release the initially deposited iron into the solution.