Synthèse et étude de modèles de NADH à noyaux accolés en série pyrrolo[2,3-b] et [3,2-b]pyridines

Pyrrolo[2,3-b] and [3,2-b]pyridines derivatives, precursors for annealated NADH models have been prepared. Several methods for building a pyridinic annealates ring have been used starting from 2- or 3-aminopyrrole. The corresponding dihydropyridine structure leads to highly reactive NADH models compounds and are very much more stable than common models.     

Some new aspects of the slow flow of a viscous fluid through an axisymmetric duct expansion or contraction. II — Experimental part

The flow of a newtonian viscous fluid through a cylindrical duct in the vicinity of a section discontinuity is studied using a visualization technique. The evolution with the Reynolds number of the features of the stationary vortex cell is given, in particular the reversibility of the flow is verified for the very small Reynolds numbers. In the creeping regime a detailed analysis of the velocity and strain-rate fields is performed.     

Low temperature deformation in iron studied with dislocation dynamics simulations

Tensile tests of iron single crystals reported in the literature were analyzed to deduce the effective stress associated to the double-kinks mechanism in order to establish a mobility law for screw dislocations. This mobility law is used to carry out the first dislocation dynamics simulations of low temperature deformation in iron. The sensitivity of the flow stress on temperature and strain rate is investigated and compared to experiment. First simulation results give an insight into the effect of temperature on the microstructure evolution and on the dislocation–dislocation interactions.     

Phase equilibria study of systems composed of refined babassu oil, lauric acid, ethanol, and water at 303.2 K

Deacidification of vegetable oils can be performed using liquid–liquid extraction as an alternative method to the classical chemical and physical refining processes. This paper reports experimental data for systems containing refined babassu oil, lauric acid, ethanol, and water at 303.2 K with different water mass fractions in the alcoholic solvent (0, 0.0557, 0.1045, 0.2029, and 0.2972). The dilution of solvent with water reduced the distribution coefficient values, which indicates a reduction in the loss of neutral oil. The experimental data were used to adjust the NRTL equation parameters. The global deviation between the observed and the estimated compositions was 0.0085, indicating that the model can accurately predict the behavior of the compounds at different levels of solvent hydration.     

Temperature behaviour of a liquid crystal comb polymer: Light scattering and noise of the scattered light

Measurements of the intensity of the monochromatic light transmitted through and scattered by a comb polymer with a polyacrylamide main chain were performed between room temperature and the isotropization temperature of the polymer. The stationary noise of the light scattered at low angle was measured in the same temperature interval. The transmitted intensity is observed to increase strongly above the smectic S_I2-S_c2 transition, where the intensity of the light scattered at low angles is maximized. The power dissipated by the molecular fluctuations dramatically increases above the transition between the two smectic phases. The spectral density curves display a Lorentzian character only below the S_I2-S_c2 transition. At higher temperatures, a more complex frequency behaviour of the stationary noise spectra is observed. Such a behaviour is interpreted in terms of a model explicitly invoking the effect of the Brownian movement of segments of the main chain (backbone) of the polymer on the side chain fluctuations. The parameters governing the Brownian movements of both main and side chains, and their evolution with temperature, are determined and discussed in the light of a simple structural model.     

Determination of the activation energy by stochastic analyses of molecular dynamics simulations of dislocation processes

An investigation is reported of the probability and the probability density of thermal activation of stress-driven dislocation processes, as simulated using molecular dynamics (MD). Stochastic analyses of the survival probability are found to lead to simple relationships between the loading history and the distribution of the interaction time and strength. It is shown that the determination of the activation energy associated to a thermally activated event can be achieved by a reduction of the stochastic process to a process obeying the Poisson's distribution, preserving the activation probability at the survival time. The method is applied to the kink-pair mechanism for screw dislocations in iron. Predictions are compared with experimental results and with other methods reported in the literature, which allows the difference in the approximations and in the assumptions considered in these models to be underlined.     

Gamma Knife® 3-D Dose Distribution Mapping by Magnetic Resonance Imaging

In medical processes where ionizing radiation is used, dose planning and dose delivery are the key elements to patient safety and treatment success, particularly, when the delivered dose in a single session of treatment can be an order of magnitude higher than the regular doses of radiotherapy. Therefore, the radiation dose should be well defined and precisely delivered to the target while minimizing radiation exposure to surrounding normal tissues [1]. Several methods have been proposed to obtain three-dimensional (3-D) dose distribution [2, 3]. In this paper, we propose an alternative method, which can be easily implemented in any stereotactic radiosurgery center with a magnetic resonance imaging (MRI) facility. A phantom with or without scattering centers filled with Fricke gel solution is irradiated with Gamma Knife^® system at a chosen spot. The phantom can be a replica of a human organ such as head, breast or any other organ. It can even be constructed from a real 3-D MR image of an organ of a patient using a computer-aided construction and irradiated at a specific region corresponding to the tumor position determined by MRI. The spin–lattice relaxation time T ₁ of different parts of the irradiated phantom is determined by localized spectroscopy. The T ₁-weighted phantom images are used to correlate the image pixels intensity to the absorbed dose and consequently a 3-D dose distribution with a high resolution is obtained.     

Investigation of precipitation hardening by dislocation dynamics simulations

Dislocation dynamics (DD) simulations are used to investigate precipitation-induced strengthening in a Zr–1% Nb alloy. A method is proposed to carry out simulations under dynamical conditions in connection with the microstructure of the investigated alloy. First, a sensitivity study of simulation parameters, suspected of altering simulation results, is presented. It allows setting up simulation conditions ensuring statistical representativeness. The effect of the strain rate is then investigated and analyzed in connection with the random distribution adopted to describe precipitation distribution. The strengthening induced by two different families of Nb precipitates is estimated from simulations whose simulation box is reduced to the volume of a single grain. It is shown that the obtained strengthening values are smaller than those predicted by most published models. Determination of total strengthening shows that usual superposition rules do not apply. A mixture law, fitting DD results well, is proposed in this paper.