From dislocation junctions to forest hardening

The mechanisms of dislocation intersection and strain hardening in fcc crystals are examined with emphasis on the process of junction formation and destruction. Large-scale 3D simulations of dislocation dynamics were performed yielding access for the first time to statistically averaged quantities. These simulations provide a parameter-free estimate of the dislocation microstructure strength and of its scaling law. It is shown that forest hardening is dominated by short-range elastic processes and is insensitive to the detail of the dislocation core structure.     

Temperature mapping in a two-phase water-steam horizontal flow

This experimental study focuses on the investigation of a flow boiling that occurs during the cooling process of a high temperature heated horizontal channel. Unpressurized water is used as working fluid. An intrusive thermally instrumented cell enables the phase change to be detected at different positions inside the channel. Alongside, welded thermocouples on the external wall of the channel give information about the influence of the phase change. Several cooling flowrates are tested in order to study their influence on the phase change duration. Finally, experimental results are compared to numerical simulations to determine some characteristic parameters as bulk temperature and heat transfer coefficient.     

Cavitand supported tetraphosphine: cyclodextrin offers a useful platform for Suzuki-Miyaura cross-coupling

The cyclodextrin-tetraphosphine hybrid coined α-Cytep allows turnover numbers up to 340,000,000,000 and turnover frequencies up to 1,000,000,000 h(-1) to be reached in Suzuki-Miyaura reactions. These exceptional figures are clearly linked to the outstanding longevity of the reactive species induced by the ligand α-Cytep and illustrates the rising potential of cyclodextrins in catalytic applications.     

Synthesis and evaluation of new phosphonic,bisphosphonic and difluoromethylphosphonic acid monomers for dental application

Syntheses of novel 5-(methacryloyloxy)pentylphosphonic acid 1, 5-(methacryloyloxy)pentylidenebisphosphonic acid 2 and 1,1-difluoro-5-(methacryloyloxy)pentylphosphonic acid 3 are described. The ability of these monomers to adhere to hydroxyapatite was demonstrated using ³¹P CP-MAS NMR spectroscopy. Their copolymerization with N,N′-diethyl-1,3-bis(acrylamido)propane (DEBAAP) was investigated with photo differential scanning calorimetry. These mixtures exhibit a significantly higher reactivity than DEBAAP alone. Bisphosphonic acid 2 was shown to be significantly more reactive than monomers 1 and 3. Adhesive properties of these monomers were also studied. Adhesives based on bisphosphonic acid 2 and difluoromethylphosphonic acid 3 provide significantly higher dentin shear bond strength than the one based on phosphonic acid 1.     

Synthesis and polymerization kinetics of acrylamide phosphonic acids and esters as new dentine adhesives

In restorative dentistry, acrylamide monomers bearing phosphonic acid moieties have proved to be useful species for the formulation of dental self‐etch adhesives since they provide enhanced adhesion to hydroxyapatite and are not subject to hydrolysis, thus potentially improving their adhesive durability. Previous studies have demonstrated that phosphonic acid acrylamides increase the rate of photopolymerization of diacrylamide monomers. To understand whether this rate acceleration is specific to the acrylamide function of the monomer, or due to the phosphonic acid group per se, or is applicable only with a crosslinking reaction, we have synthesized several acrylamide and methacrylate monomers bearing phosphonic acid or phosphonate moieties and studied their photopolymerization kinetics. The acrylamide phosphonic acid was found to accelerate the polymerization rate but similar monomers bearing a phosphonate ester group had a much smaller effect. A similar accelerating effect was observed when the phosphonic acid‐based monomers were copolymerized with a monofunctional acrylamide monomer, excluding the possibility that the rate acceleration might be related to the crosslinking process. This rate effect is also observed when a nonpolymerizable organic phosphonic acid is present in the polymerizing medium. We suggest that the increase of the medium polarity is responsible for this rate enhancement effect. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Phosphine‐Free Palladium‐Catalyzed Allene Carbopalladation/Allylic Alkylation Domino Sequence: A New Route to 4‐(α‐Styryl) γ‐Lactams

Free to decide : Various 4‐(α‐styryl) γ‐lactams are synthesized in 61–88 % yield by a phosphine‐free palladium‐catalyzed carbopalladation/allylic alkylation domino sequence (see scheme). The cyclization is totally regio‐ and diastereoselective in favor of the 3,4‐trans‐disubstituted γ‐lactam. The process is successfully applied to the synthesis of a new aza analogue of the naturally occurring lignan (+)‐oxo‐parabenzlactone.