Organocatalyzed Conjugate Addition of Carbonyl Compounds to Nitrodienes/Nitroenynes and Synthetic Applications

The purpose of this study is to point out the synthetic utility of a new class of Michael acceptors (nitrodienes and nitroenynes). The highly enantioselective organocatalytic Michael addition of carbonyl compounds to these functionalized nitroolefins has been carried out in the presence of (S)‐diphenylprolinol silyl ether to achieve some interesting building blocks in high selectivities. The adducts thus obtained can be easily converted by taking advantage of the corresponding unsaturated carbon‐carbon bond. In presence of the double bond, metathesis or electrophilic activation could be carried out whereas in the presence of the triple bond electrophilic activation could be conducted. We thus focused on a gold‐catalyzed cyclization of the bis‐homopropargylic alcohol to afford the corresponding substituted tetrahydrofuran. Then, we also demonstrated that organic and gold catalysts were compatible in a one‐pot process. Indeed, we developed a one‐pot enantioselective organocatalytic Michael addition to a nitroenyne followed by a gold‐catalyzed acetalization/cyclization to achieve tetrahydrofuranyl ethers in high diastereo‐ and enantioselectivities with excellent yields.     

Damage quantification in aluminium alloys using in situ tensile tests in X-ray tomography

This paper presents results obtained using in situ tensile experiments allowing the observation of damage nucleation, growth and coalescence. Three different aluminium alloys (2024, 7449 and 5754) exhibiting various mechanical properties were chosen to produce a wide data base. Smooth and notched axisymetric samples were cut out of the raw materials to introduce different levels of initial stress triaxiality using the geometry of the samples. In the different cases, the damage steps (initiation, growth and coalescence) were clearly visualised during interrupted and continuous in situ tensile tests in synchrotron X-ray tomography. The imaging was performed with a voxel size of 1.6 μm. The X-ray tomography method also gives a precise image of the outer shape of the sample and its change during deformation can then be analysed. This allows to calculate precisely the true strain vs true stress curve and also an approximation of the stress triaxiality using the Bridgman formula. The results show that damage can be visualised but also quantified precisely in the different cases in terms of nucleation and growth, coalescence being also evident in the results but still hard to quantify so far. Finally, a previously developed model for damage growth during ductile straining based on the Rice and Tracey approach can be fitted to the results.     

Reducing CO2 emissions from oil shale semicoke smoldering combustion by varying the carbonate and fixed carbon contents

One technique used to recover oil from ground oil shale, or to burn oil shale semicoke, consists of propagating a smoldering front through a packed bed. One drawback of this technique is that the mineral structure of the shale is decarbonated due to the high temperature of the front. This phenomenon causes 70% of the CO₂ emissions released during such processes. The remaining 30% result from the fixed carbon oxidation. With the aim of decreasing the front temperature and thus avoiding decarbonation at the front passage, the impact of two parameters was experimentally tested in this work: first, increasing the amount of carbonates, as they may play the role of a heat sink, and second, decreasing the amount of fixed carbon in the medium. It is shown that increasing the amount of carbonates can only decrease the front temperature to 800 °C but not lower, which is still too high to avoid decarbonation. On the other hand, the front temperature can be decreased enough for decarbonation to be almost completely avoided by reducing the amount of fixed carbon. At the low temperatures reached, almost all the fixed carbon is oxidized, but not all the oxygen transported in the air is consumed by the chemical front. The velocity of the front is consequently decreased.     

Geometric characterization, hydraulic behavior and upscaling of 3D fissured geologic media

In this article, we present numerical modeling and upscaling procedures for highly fissured and discontinuous geologic media, such as ‘karsts’. In particular, we propose a geomorphological generation model, and we address the ‘upscaling’ problem for flow in a highly fissured porous medium (‘what is the macroscale hydraulic behavior of the fissured porous medium?’). The morphological model is partly Boolean, based on statistical distributions of discrete objects (voids), combined with a (random) continuum representation for the underlying porous matrix. Various methods for constraining these two types of media are discussed (self-consistent thresholding; genetic dissolution). Hydraulic simulations are then conducted with the 3D finite volume code BIGFLOW, for the case of 3D composite media with constant matrix and high ‘fissure/matrix’ permeability contrast. The hydrodynamic equations are based on either Darcy’s linear head loss law, or on a linear/quadratic combination of Darcy and Ward–Forchheimer quadratic law (inertial effects). The numerical experiments are conducted for saturated steady flow under permeametric boundary conditions. They are used to analyze the equivalent macroscale behavior of fissured media, as well as quasi-percolation effects, in comparison with analytical results and bounds (Darcian case, low Reynolds). In addition, at moderate to large Reynolds numbers, the macroscale effects of non-Darcian (inertial) head losses are also analyzed.     

MRI study of bread baking: experimental device and MRI signal analysis

An oven dedicated to a magnetic resonance imager (MRI) was designed and constructed for continuous monitoring of the entire baking process. The general aim was to test whether response variables conventionally measured on bread loaves, such as temperature, density, and water loss, were consistent with those reported for similar products baked in classical convection ovens. MRI images acquired during baking are presented and discussed, emphasising the need to develop quantitative MRI methods allowing conversion of the MRI signal into one variable of interest, such as local density or local water content.     

Averaged solute transport during solidification of a binary mixture: Active dispersion in dendritic structures

The macroscopic conservation equations governing solute transport during solidification of binary alloys are derived using an averaging procedure in the context of macroscale nonequilibrium. Special attention is focused on the derivation of the associated closure problems, leading to the determination of the effective dispersion tensor and macroscopic interphase coefficients that characterize active dispersion phenomena. These closure problems are solved numerically using schematic structures and digitized images of real columnar dendritic structures observed experimentally during solidification of succinonitrile-4 wt pct acetone. The influence of the geometry and dispersion on the effective solute-properties transport is analyzed, and comparison with passive dispersion is provided. The theoretical and numerical results indicate, first, that tortuosity effects are small, and this is related to the impact of the boundary condition at the interface between the two phases, and, second, that dispersion becomes very important only at very large Péclet numbers.     

Le développement de la notion de vitesse relative.

Administered a modified version of a Piagetian test on the concept of relative velocity (including questions on the duration of relative displacements) to 96 children placed in age groups of 7, 9, 11, and 13 yr. It was found that (a) the developmental stages of the concept were comparable to those observed by Piaget except for formal operations which seem to evolve later; (b) the combination of 2 movements of same direction but unequal velocity is more difficult to synthesize than any other; (c) success on the problem of durations is not a prerequisite of at least partial success on the problem of velocities; and (d) complete success on the problem of velocities is not necessarily verbalized in spatio-temporal terms. To explain the difficulty observed in synthesizing velocities, the importance of the instructions (e.g., specifying the speed of each mobile) and of changes in the spatial order of the mobiles was emphasized. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparative Lattice-Dynamical Study of the Raman Spectra of Monoclinic and Tetragonal Phases of Zirconia and Hafnia

An interpretation of the Raman spectra of monoclinic ZrO₂ and monoclinic HfO₂ is made by analyzing the results of the zirconia–hafnia substitution jointly with a lattice dynamical treatment of both structures. The Raman spectra of tetragonal ZrO₂ and tetragonal HfO₂ are also interpreted. Emphasis is put on their relations to the spectrum of the parent cubic structure and on the position of the soft mode. The band assignment proposed earlier by other researchers is critically reconsidered.     

Le r?le du surplombement dans l'estimation perceptive des longueurs de deux horizontales a extrémités decalées.

Asked a total of 84 children and adults in 4 age groups (means = 5.11, 7.8, 9.8, 11.5, and 24.4 yrs) to match, by the method of adjustment, the lengths of 2 horizontal lines staggered so as to form 2 sides of a parallelogram under 2 main conditions (variable over the standard or standard over the variable) and a control condition (variable and standard in prolongation). Results show that the variable was generally overestimated, this overestimation did not differ significantly from 1 condition to another, and this overestimation decreased significantly with age. Results suggest that this systematic error would not be attributed to the top positioning but rather to the movement of the variable, which would be a source of overestimation by drawing the relative frequency of S's perceptive centrations. The decrement of the error with age could be explained by the development of perceptual activity, allowing a more balanced centration on the standard and the variable. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)