New insights on the mechanisms of the pH-independent reactions of benzo[a]pyrenes 7,8-diol 9,10-epoxides.

The rates and products of the reactions of (+/-)-7beta,8alpha-dihydroxy-9beta,10beta-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (1) and (+/-)-7beta,8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (2) in water and dioxane-water mixtures have been determined over a pH range wider than that of earlier studies. This study provides additional insight on the mechanisms of the pH-independent reactions of 1 and 2. The rate profile for reaction of 1 shows acid-catalyzed hydrolysis at pH <5, a rate plateau at pH 5-9.5, a negative inflection at pH 10-11.5, and a rate increase at pH >11.5. The rate decrease between pH 10 and pH 11.5 is accompanied by a decrease in the yield of tetrols from 60% (pH 8) to 29% (pH 11.2) and is interpreted to be the result of a partial change in mechanism brought about by attack of hydroxide ion acting as a base to deprotonate a carbocation intermediate and regenerate 1 at pH >10, thus reducing the contribution of the pathway for tetrol formation in which water attacks the carbocation. The rate profile for the reaction of 2 exhibits only a single rate plateau at intermediate pH, along with increases in rate at low and high pH because of second-order reactions of 2 with H+ and HO-, respectively. The lack of a rate depression at pH >10 and the product studies for the reaction of 2 in dilute sodium azide solutions suggest that the tetrol-forming reactions of the pH-independent reaction of 2 are concerted or near-concerted.     

Effect of BaTiO3 on the aging process of PLA fibers obtained by centrifugal spinning

This study focused on the fabrication of a composite of polylactic acid fibers reinforced with barium titanate (BT) and obtained by centrifugal spinning. Different concentrations of inorganic powder (5, 10, and 15 wt%) have been added to the polymeric solution and the samples have been studied to monitor any modification in chemical, morphological, thermal, and mechanical properties. Subsequently, samples have been subjected to UV/O₃ irradiation at two different times (5 and 10 min) with the aim to verify the resistance to aging, which is considered a key factor for medical applications and outdoor. The presence of BT influenced strongly the structure of the fibers in many aspects. Samples with the lowest amount of BT showed a clear decrease of chemical and consequently of mechanical properties manifested with the breakage of the fibers subjected to treatment. The other composites apparently showed similar chemical properties comparing with the one without fillers but the mechanical properties clearly decreased. However, what emerged from the study is a clear stability during the aging tests promoted by the presence of BT. The samples with 10 and 15 wt% of BT presented chemical, thermal, and mechanical stabilities differently from the other samples. These results suggested that the fillers clearly modified the degree of crystallinity acting as nucleation agents and promoting the development of a stable crystalline phase during the treatment.     

Space correlation measurements in a forced shear layer with wall injection

Comprehension of wall-injection flow in a channel in the presence of different geometric discontinuities is necessary as part of the general investigations concerning combustion instabilities of solid propellant rocket motors. In order to characterise the aerodynamic flow field and to evaluate the influence of an obstacle inside a porous channel in such a case, experimental studies were conducted on a 1/40 scale model of the new ARIANE V motor. In fact, the flow is only induced by wall-injection and the presence of an obstacle creates a particular shear layer development in the obstacle wake. Particular attention was given to the unstable dynamic conditions of the shear layer. A thermal seeding of the shear layer was made in order to qualify the heat transfer therein, and especially to emphasise the turbulent structure development. Transverse and longitudinal spatial correlations were measured to characterise turbulence scales in the shear layer. At the origin of the shear layer, the decay of turbulence memory is found to be similar to that observed in a forced flow boundary layer, but the injecting wall modifies the change in structures. The wall flow is found to preserve the turbulent structures in such a way that the turbulence memory predominates in a longitudinal direction.List of Symbols f frequency (Hz) - h channel height (m) - h _v obstacle height (m) - L mean dimension of large structures (m) - P pressure (Pa) - m mass flow rate (kg/s) - r distance between probes in X direction (m) - r ^+(–) distance between probes in Y direction (m) - u longitudinal velocity in X direction (m/s) - v transversal velocity in Y direction (m/s) - T temperature (K) - x,y,z axis system (m) - t = T-T _amb (K) - v kinematic viscosity (mVs) - density (kg/m³) - characteristic porous size (urn) - _u longitudinal rms (m/s) - I _u dynamic turbulence intensity _u /u _max - I _T thermal turbulence intensity - M Mach number u/a - Re _w wall Reynolds number v _w h/v - Re _c longitudinal Reynolds number u _c h/v - R _uT thermal dynamic correlation coefficient - St Strouhal number fh/u - X,Y,Z axis system normalised by the channel height h - X _S longitudinal position of the obstacle - X X-X _S - amb ambient reference - c flowing cavity - fav head end - l lateral direction - g longitudinal direction max maximum at a longitudinal position - w wall The authors thank the CNES for its financial support, and in particular E. Robert and R. Bee.     

Optimality conditions and duality in nonsmooth multiobjective optimization problems

Exploiting some tools of modern variational analysis involving the approximate extremal principle, the fuzzy sum rule for the Fréchet subdifferential, the sum rule for the limiting subdifferential and the scalarization formulae of the coderivatives, we establish necessary conditions for (weakly) efficient solutions of a multiobjective optimization problem with inequality and equality constraints. Sufficient conditions for (weakly) efficient solutions of an aforesaid problem are also provided by means of employing L-(strictly) invex-infine functions defined in terms of the limiting subdifferential. In addition, we introduce types of Wolfe and Mond–Weir dual problems and investigate weak/strong duality relations.     

A numerical evaluation of very oscillatory infinite integrals by asymptotics

Recently, Levin and Sidi have given some nonlinear methods for the accurate evaluation of slowly converging infinite integrals. But, one needs to solve some very instable linear systems, when, for example, the integrand have an increasingly rapid oscillatory behavior at infinity. In this work, we present a direct method, which avoids the instable linear systems.     

Radiation-resistant polypropylene improved by a compatibilizer

A compatibilizer is normally added to enhance the compatibility during blending of two polymers. Polypropylene (PP) has two degradations, during irradiation and also during storage after irradiation in radiation sterilization. A compatibilizer was added to PP to reduce these degradations. Compatibilizers, such as hydrogenated styrene (10 mol%)/butadiene rubber (CPB-2) and ethylene/propylene rubber grafted with maleic anhydride, were found to retard remarkably the above-mentioned degradations of PP. The compatibilizer concentration required for enhancing the radiation resistance of PP depends on the radiation resistance before addition of the compatibilizer. Poor radiation-resistant PP of a lower molecular weight (Melt flow index, 10) required a higher concentration, above 10% of CPB-2 to impart radiation resistance, but high-molecular-weight PP (Melt flow index, 1.0) and copolypropylene (CPP) with an ethylene content of 2.5% required CPB-2 of 5% and 10% to induce sufficient radiation resistance. Furthermore, CPB-2 was effective for improvement of transparency besides its contribution to radiation resistance of PP. The CPB-2 lead to lower crystallinity to retard the crystallization of PP and CPP and also may result in a mixed monoclinic and smectic structure giving radiation resistance.