Self-Turbulent Flame Speeds

This paper reports an experimental investigation of premixed propane and methane-air flames propagating freely in tubes 1.5?m long and with diameters ranging from 26 to 141?mm. The thermo-acoustic instability was eliminated by means of a novel acoustic absorber placed at the closed end of the tube. We first remark that the flame can adopt different shapes either quasi-axisymmetric and normal to the mean direction of propagation, or inclined with a larger propagation speed because of the increase in flame surface area. The minima of the propagation speeds, corresponding to non-tilted flame propagation, are then analyzed using analytical models for the self-turbulent flame propagation. The concept of a cut-off wavelength appears to be relevant to explain the different behaviors observed on the rich side of methane-air and propane-air flames.     

1-Aryl- und 1-Alkyl-2-phthalimido-diazen-1-oxide,diacylierte Vertreter von trisubstituierten Triazen-1-oxiden: Bildung,Eigenschaften, Stereoisomerisierung und Fragmentierung

1-Aryl- and 1-Alkyl-2-phathalimido-diazene-1-oxides, Diacylated Examples of Trisubstituted Triazene-1-oxides: Formation, Properties, Stereoisomerization and Fragmentation¹) Oxidatively generated phthalimido-nitrene ( 1 ) reacts with nitrosobenzene ( 8a ), p-nitrosotoluene ( 8b ), o-nitrosotoluene ( 8c ), p-dimethylamino-nitrosobenzene ( 8d ), p-methoxycarbonyl-nitrosobenzene ( 8e ), 1, 1-dimethyl-1-nitrosoethane ( 8f ) and nitrosocyclohexane ( 8g ) to give the respective 1-substituted (Z)-2-phthalimidodiazene-1-oxides 14a-g . The constitution of 2-imidodiazene-1-oxides 14 is deduced from their spectroscopic properties. The UV. spectra of 14a-e are similar with those of the corresponding nitrobenzenes 18 , thus supporting the concept of comparibility of the phthalimido-N group with an O-atom and indicating that the phthalimido group is not in conjugation with the diazene-oxide function. This is in contrast to the situation in the non-acylated trisubstituted triazene-1-oxides 12 , where conjugation is extended over the chain of all three N-atoms as exhibited by the UV. spectra of (Z)-1, 3, 3-triphenyl-, (Z)-3, 3-dimethyl-1-phenyl-, (Z-3-methyl-1, 3-diphenyl-, (Z)-1-(1, 1-dimethylethyl)-3, 3-diphenyl-, and (Z)-1-(1, 1-dimethylethyl)-3, 3-dimethyltriazene-1-oxide ( 12a-e ). These triazene-1-oxides are formed by the reaction of 1, 1-disubstituted hydrazines 11 with three mol-equiv. of nitroso compounds 8 or from equimolar amounts of 11 and 8 in the presence of mercury oxide. Over 90% of 1, 2-diphenyldiazeneoxide ( 19 , R = C₆H₅) are isolated by the reaction 11 + 3 8a . Possible mechanisms of the reaction of 11 with 8 , and of the formation of 12 via triazanols D and of 19 (R = C₆H₅) via N-Phenylhydroxylamine ( 20 , R = C₆H₅) are given in Scheme 6 (in the latter case with experimental evidence). An independent synthesis of 12c confirms the constitutional assignment for 12 .     

Optimal stopping problems with discontinous reward: Regularity of the value function and viscosity solutions

In this paper we show that the solution of a stochastic boundary value problem with additive noise and with a completely nonlinear drift is a Markov field if only if the boundary condition is an initial or a final type condition     

Resonant coupling into hybrid 3D micro-resonator devices on organic/biomolecular film/glass photonic structures

We have designed and realized an integrated photonic family of micro-resonators (MR) on multilayer SU8/lipidic film/glass materials. Such a family involves hybrid 3D-MR structures composed of spherical glass-MR arranged upon organic pair-SU8-waveguides, an efficient coupling being ensured with a Langmuir-Blodgett Dipalmitoylphosphatidylcholine (DPPC-lipid from Avanti Polar^®) film whose thickness is ranging from 12 to 48 nm. We have characterized such add/drop filters, respectively, in intensity and spectral measurements, and experimentally achieved an evanescent resonant-photonic-coupling between the 3D-MR and the 4-ports structure through the DPPC-gap. Spectral resonances have been measured for 4-whispering gallery-modes (WGM) into such 3D-structures, respectively, characterized with a 0.97 nm free spectral range (FSR) and a high quality Q-factor up to 4.10⁴.     

Monitoring of calcium stearate formation by thermogravimetry

Naphthenates are produced when naphthenic acids present in crude oil are mixed with brine. They deposit at oil/water interface and are insoluble in either of the phases causing a large problem to the oil industry. Generally, naphthenates precipitate jointly with others compounds such as sulfates and carbonates. This fact makes difficult their characterization. In this study, calcium stearate formation from stearic acid was investigated, under different conditions, as a previous model to understanding of calcium naphthenate precipitation. Medium reactions distinct were studied and the results indicated that the ethanol medium was the most efficient for the formation of solids because in this only case, the stearic acid was completely converted into stearate. Monitoring of the conversion was performed by thermogravimetry in spite of this technique not be typical in salts characterization. Nevertheless, the thermogravimetric analysis showed that is possible to identify differences between an organic acid, a salt of this acid and an inorganic salt, in the same sample. Infrared spectra was used in order to confirm the results obtained by thermogravimetry. However, this technique showed less efficiency and sensibility.     

Basic expansions of solutions to the sixth Painlevé equation in the generic case

We consider the sixth Painlevé equation for generic values of its four complex parameters. By methods of power geometry, we obtain those asymptotic expansions of solutions to the equation near the singular point x = 0 for which the order of the first term is less than unity. We refer to these expansions as basic expansions. They form 10 families and include expansions of four types, namely, power, power-logarithmic, complicated, and exotic. All other asymptotic expansions of solutions to the equation near the three singular points x = 0, x = 1, and x = ∞ can be computed from the basic expansions with the use of symmetries of the equation. Most of these expansions are new.