Using infrared thermography in order to compare laser and hybrid (laser+MIG) welding processes

In order to deepen the understanding of the differences between laser and laser-arc hybrid welding, comparisons were undertaken using thermography. The experiments were carried out for a T assembly of aluminium alloy plates. Modelling, based on the finite element method approach, was realized using IR temperature measurements and seam geometry. For a value of the power supply, depicted as a surface source in the hybrid case, agreement was found between simulated and measured temperatures. The arc power supply efficiency value is similar to the usually used value.     

Synthesis of adaptative and amphiphilic polymer model conetworks by versatile combination of ATRP,ROP, and “Click chemistry”

Well‐defined adaptative and amphiphilic polymer conetworks based on hydrophilic poly(N,N‐dimethylamino‐2‐ethyl methacrylate) (PDMAEMA) and hydrophobic poly(ε‐caprolactone) (PCL) have been prepared by combination of ATRP, ROP, and “Click chemistry.” Telechelic α,ω‐alkyne terminated PCL crosslinker was obtained by ring‐opening polymerization (ROP) of CL in THF at 80 °C initiated by 1,4‐butanediol and catalyzed by tin(II) bis 2‐ethyl hexanoate (Sn(Oct)₂), followed by the quantitative esterification of hydroxyl end‐groups by activated 4‐pentynoic acid. In parallel, an azido‐containing PDMAEMA‐based copolymer was obtained in a three‐step strategy involving primarily the copolymerization of DMAEMA with newly synthesized 2‐(2‐azidoethoxy)ethyl methacrylate (AEEMA) monomer. The latter was obtained by nucleophilic substitution of chloride atom from 2‐(2‐chloroethoxy)ethanol by an azide group followed by the esterification reaction of the hydroxyl group with methacrylic anhydride. The copolymerization was carried out in an equivolumic mixture of H₂O and isopropanol at r.t. and initiated by a ω‐bromoisobutyryl oligo PEO macroinitiator in the presence of various ligated copper(I)‐based catalysts. In a last step, both polymer precursors were chemically linked by the Huisgen‐1,3‐dipolar cycloaddition in anhydrous THF at r.t. using CuBr complexed by 2,2′‐bipyridine ligand as catalyst. Final material was characterized by the means of DSC and SEM, both attesting of a homogeneous distribution of the PCL crosslinkers and a highly porous structure in this new amphiphilic model conetworks. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4997–5013, 2008     

Diffusion and segregation of niobium in fcc-nickel

Niobium is one of the major alloying elements, among the refractory elements, contributing to the strengthening of superalloys. Consequently, data about its behavior and its migration mechanism in fcc-Ni are essential knowledge to understand and control the strengthening in such alloys. We present in this work Nb interactions, solubility and diffusion in Ni performed by using the GGA approximation of the density functional theory. The substituted site is found to be the most favorable configuration in comparison to the tetrahedral and octahedral sites. The effect of temperature on solubility is discussed taking into account the thermal expansion of the lattice parameter and the vibrational contribution. Its diffusion mechanism is also discussed and compared to the literature. We finally discuss the segregation of Nb atoms on a Σ(5)-(012) symmetric tilt grain boundary.     

Evaluation of photolyase (Photosome) repair activity in human keratinocytes after a single dose of ultraviolet B irradiation using the comet assay

Photosome is constituted of photolyases included in liposomes. Photolyase is a bacterial enzyme that can repair ultraviolet B (UVB)-induced cyclobutane pyrimidine dimers (CPD) in eukaryotic cells. A modified version of the alkaline comet assay has been set up to evaluate the repair activity of this enzyme after a single dose of UVB (312 nm, 0.06 J/cm2) in human keratinocytes. The formation of single strand breaks (SSB) induced by the UVA photoactivation of the enzyme (1.2 J/cm2) was inhibited by the pretreatment of the cells with 4 mM L-ergothioneine (ERT) during 30 min at 37 degrees C. To increase the sensitivity of the comet assay, an additional lysis was used with a buffer containing sodium dodecyl sulfate (0.5%) and proteinase K (0.1 mg/ml) for 60 min at 37 degrees C. Unrepaired CPD by photolyase were revealed by a second enzymatic treatment with T4 endonuclease V, a CPD specific glycosylase. UVB irradiation increased the SSB level in keratinocytes and additional T4NV treatment enhanced this SSB level by 1.5-2.0-fold confirming that CPD were the major base modifications generated by UVB irradiation. UVA-photoactivated Photosome repaired CPD lesions and decreased the SSB levels by 2.6-3.3-fold. Photosome could be an additional component of sunscreens to reduce the development of skin cancer.     

Size effect on magnetism of Fe thin films in Fe/Ir superlattices

In ferromagnetic thin films, the Curie temperature variation with the thickness is always considered as continuous when the thickness is varied from n to n+1 atomic planes. We show that it is not the case for Fe in Fe/Ir superlattices. For an integer number of atomic planes, a unique magnetic transition is observed by susceptibility measurements, whereas two magnetic transitions are observed for fractional numbers of planes. This behavior is attributed to successive transitions of areas with n and n+1 atomic planes, for which the T(c)'s are not the same. Indeed, the magnetic correlation length is presumably shorter than the average size of the terraces. Monte Carlo simulations are performed to support this explanation.     

No adaptation in the amplitude modulation domain in trained listeners

The present study shows that on average, exposure to a 15 min, 5 kHz tone modulated sinusoidally in amplitude at 16 Hz with a 100% depth does not affect significantly amplitude modulation (AM) detection thresholds measured between 4 and 64 Hz when listeners are extensively trained to the AM detection task, with and without adaptor before data collection. These results are compatible with previous work given that a clear 6-dB adaptation effect was observed during the first pilot trials. However, the results reveal that adaptation effects are not robust, and suggest that the mechanisms underlying adaptation to AM must be reevaluated.     

Metalloenzyme-Mediated Thiol-Yne Addition Towards Photoisomerizable Fluorescent Dyes

Proteins are able to irreversibly assemble biologically active ligands from building blocks bearing complementary reactive functions due their spatial proximity, through a kinetic target-guided synthetic process (also named in situ click chemistry). Although linkages thus formed are mostly passive, some of them have shown to significantly contribute to the protein binding through for instance hydrogen bonding and stacking interactions. Biocompatible reactions and click chemistry are a formidable source of inspiration for developing such new protein-directed ligations. This study reports a proximity-induced thiol-yne synthesis of carbonic anhydrase inhibitors. Not only this example widens the arsenal of kinetic target-guided synthesis (KTGS) eligible reactions, but the obtained product displayed unsuspected photophysical properties. The corresponding vinyl sulfide linkage conjugated to a coumarin core proved to be engaged in a monodirectional Z to E photoisomerization process. Further investigations guided by theoretical calculations showed that fine-tuning of the nature of the substituents on the coumarin moiety allows to obtain a bidirectional photochemical process, thus discovering a new photoswitching moiety, displaying moreover fluorescence properties. Due to the spectral tunability of coumarin derivatives, this work should open new opportunities for the design of vinyl sulfide-based photoswitch systems with modular photophysical properties.     

Highly Enantioselective Rhodium(I)‐Catalyzed Carbonyl Carboacylations Initiated by CC Bond Activation

The lactone motif is ubiquitous in natural products and pharmaceuticals. The Tishchenko disproportionation of two aldehydes, a carbonyl hydroacylation, is an efficient and atom‐economic access to lactones. However, these reaction types are limited to the transfer of a hydride to the accepting carbonyl group. The transfer of alkyl groups enabling the formation of C? C bonds during the ester formation would be of significant interest. Reported herein is such asymmetric carbonyl carboacylation of aldehydes and ketones, thus affording complex bicyclic lactones in excellent enantioselectivities. The rhodium(I)‐catalyzed transformation is induced by an enantiotopic C? C bond activation of a cyclobutanone and the formed rhodacyclic intermediate reacts with aldehyde or ketone groups to give highly functionalized lactones.