Microwave-assisted conversion of carbohydrates. State of the art and outlook

The valorisation of carbohydrates arising from the hydrolysis of renewable feedstocks (i.e., lignocellulosic biomass) is nowadays an area of utmost interest. In this context, the implementation of fast, expeditious and cost-effective methodologies for the modification of these naturally occurring compounds is becoming a prerequisite. With this aim, the application of microwaves has gained progressive attention in laboratories for making a range of high-added value sugars derivative scaffolds. The advantages of microwaves are numerous, and include enhancement of reaction rates and yields, combined with improved regio-, chemo- and anomeric selectivities.     

Critical duality

We look for a general framework in which the Ekeland duality can be formulated. We propose a scheme in which the parameter sets are provided with a coupling function which induces a conjugacy. The decision spaces are not supposed to have any special structure. We examine several examples. In particular, we consider some special classes of generalized convex functions.     

Investigating the relationship between cell cycle stage and diosgenin-induced megakaryocytic differentiation of HEL cells using sedimentation field-flow fractionation

Differentiation therapy could be one strategy for stopping cancer cell proliferation. A plant steroid, diosgenin, is known to induce megakaryocytic differentiation in human erythroleukemia (HEL) cells. In recent studies, the use of sedimentation field-flow fractionation (SdFFF) allowed the preparation of subpopulations that may differ in regard to sensitivity to differentiation induction. The specific goal of this study was to determine the relationship between cell cycle stage and sensitivity to megakaryocytic differentiation induction of HEL cells. After first confirming the capacity of diosgenin to specifically select targets, hyperlayer SdFFF cell sorting was used to prepare fractions according to cell cycle position from crude HEL cells. The sensitivities of these fractions to diosgenin-induced differentiation were then tested. The coupling of SdFFF cell separation to imaging flow cytometry showed that G1-phase cells were more sensitive to differentiation induction than S/G2M-phase cells, confirming the relationship between cell status at the start of induction, the extent of the biological event, and the potential of SdFFF in cancer research.     

Use of polymer-supported phenyltin for the creation of aryl-aryl or aryl-heteroaryl bonds via Stille cross-coupling reactions

An insoluble polymer-supported phenyltin reagent was successfully used in Stille cross-coupling reactions with aryl- and heteroaryl-halides. Cross-coupling products were isolated in good to high yields with very low contamination by tin and palladium residues after removal of the residual supported organotin halide. The regeneration and recyclability of the supported phenyltin reagent were also examined and proved to be possible, but required palladium cleaning of the grafted polymer to be efficient along 4 cycles when Pd(PPh₃)₄ was used as catalyst.     

Progressive hedging innovations for a class of stochastic mixed-integer resource allocation problems

Numerous planning problems can be formulated as multi-stage stochastic programs and many possess key discrete (integer) decision variables in one or more of the stages. Progressive hedging (PH) is a scenario-based decomposition technique that can be leveraged to solve such problems. Originally devised for problems possessing only continuous variables, PH has been successfully applied as a heuristic to solve multi-stage stochastic programs with integer variables. However, a variety of critical issues arise in practice when implementing PH for the discrete case, especially in the context of very difficult or large-scale mixed-integer problems. Failure to address these issues properly results in either non-convergence of the heuristic or unacceptably long run-times. We investigate these issues and describe algorithmic innovations in the context of a broad class of scenario-based resource allocation problem in which decision variables represent resources available at a cost and constraints enforce the need for sufficient combinations of resources. The necessity and efficacy of our techniques is empirically assessed on a two-stage stochastic network flow problem with integer variables in both stages.     

Necessary conditions for multistationarity in discrete dynamical systems

R. Thomas conjectured, 20 years ago, that the presence of a positive circuit in the interaction graph of a dynamical system is a necessary condition for the presence of several stable states. Recently, E. Remy et al. stated and proved the conjecture for Boolean dynamical systems. Using a similar approach, we generalize the result to discrete dynamical systems, and by focusing on the asynchronous dynamics that R. Thomas used in the course of his analysis of genetic networks, we obtain a more general variant of R. Thomas’ conjecture. In this way, we get a necessary condition for genetic networks to lead to differentiation.     

Metallation des halogenures d'aryle par le tributylstannyllithium dans le tetrahydrofuranne

The metallation of aryl halides with tributylstannyllithium in THF proceeds via at least three different mechanisms whose relative rates depend on the nature of the halogen, the substrate and the experimental conditions. In the case of aryl bromides, a halogenmetal exchange (major process) is competing with a radical mechanism. With aryl chlorides, an arynic process, a halogenmetal exchange and a radical mechanism are involved. Finally, with aryl fluorides, the arynic process is usual, but it may be strongly competed by a radical mechanism whenever suitable experimental conditions are arranged.     

Dynamical shape gradient for the Navier–Stokes system

This Note deals with the sensitivity analysis of a newtonian incompressible fluid driven by the Navier–Stokes equations with respect to the dynamic of the fluid domain boundary. The structure of the gradient with respect to the velocity of the domain for a given cost function is established. This result is obtained using new shape derivation tools for Eulerian functionals and the Min–Max derivation principle. To cite this article: R. Dziri et al., C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

Porous 3-D honeycomb architecture by self-assembly of helical H-bonded molecular tapes

Enantiopure dipeptide-derived 1,3,5-triazepan-2,6-diones and form H-bonded 3(1) helical molecular tapes with P chirality in the solid state; in the case of , these columnar tapes self-assemble through aromatic-aromatic interactions to give hollow tubular structures.