Generation and amplification of pulsed Bessel beams by seeding an optical parametric amplifier

By using two very different seed pulses we demonstrate that the spatiotemporal gain properties of a chi(2) optical parametric amplifier can be exploited as an efficient conical reshaping mechanism leading to the generation and amplification of a pulsed Bessel beam.     

Weak stereospecific interactions in water. Excess enthalpies of aqueous solutions containing aldopyranosides at 25°C

The heats of dilution in water of methyl--D-galacto-, gluco-, and xylopyranosides and the heats of mixing with the respective -isomers were determined calorimetrically at 25°C. The excess enthalpies, expressed as virial expansions as a function of the molalities, lead to the evaluation of the self- and cross-interaction coefficients. As for other saccharide derivatives, the pairwise interaction coefficients are positive and larger than those for the parent monosacharides. The cross coefficients, in turn, are smaller than the homogeneous coefficients resulting in a favorable contribution to the free energy of mixing. This indicates the existence of a weak, water-mediated, but still stereospecific recognition between pairs of solute molecules.     

Spatial and vertical distributions of natural and anthropogenic radionuclides and cesium fractionation in sediments of the Var river and its tributaries (southeast France)

This paper reports results on the natural and anthropogenic radionuclides activity concentrations in sediments of the Var river and its tributaries. Natural (²³⁸U, ²³²Th and ⁴⁰K) and artificial (¹³⁷Cs) radionuclides activities were measured using high purity germanium detector. Measured activity concentrations differ widely; they depend on the pertinent environmental situation such as the presence of dams, and sediments type. Other factors controlling the distribution of the studied radioisotopes have been discussed. A sequential extraction method consisting of six operationally-defined fractions has been used for determining the geochemical partitioning of anthropogenic radionuclide ¹³⁷Cs in a 405–410 cm deep sediments collected in the lower valley of the Var river. This method corresponds to a modification of the three-stage sequential extraction procedure proposed by the Commission of the European Communities Bureau of Reference (BCR, now Standards, Measurements and Testing Program). Two steps with weak reagents, (fraction A: water; fraction B: nitric acid 0.001 M), were added before the first step of BCR (carbonate fraction) in order to better detect anthropogenic components. A total acid digestion of solid residues by microwave assisted was also added. The 6-steps extraction method was tested and validated by certified reference materials. ¹³⁷Cs was found mostly in the hydrosoluble fraction (20–24 %), oxide and hydroxide fraction (22–25 %) and in the residue (51–58 %), while ¹³³Cs was mostly found in the residual fraction (>97 %).     

A Robust,Eco‐Friendly Access to Secondary Thioamides through the Addition of Organolithium Reagents to Isothiocyanates in Cyclopentyl Methyl Ether (CPME)

The nucleophilic addition of widely available and variously functionalized organolithium reagents to isothiocyanates represents a straightforward, high‐yielding, one‐pot method to access secondary thioamides. The simple reaction conditions required and the broad scope (>50 cases examples) makes it a robust and reliable method to access both simple and complex thioamides, including enantiopure ones. Noxious and unpleasant‐smelling sulfurating agents, usually employed in the literature established methods, are avoided during the whole synthetic procedure thus, rendering the protocol highly attractive, also for sustainability aspects.     

All-optical AND gate based on Raman effect in silicon-on-insulator waveguide

An all-optical AND gate based on Raman effect in silicon-on-insulator technology is proposed. Stimulated Raman scattering, two photon absorption, free carrier dispersion, self and cross phase modulation induced by Kerr effect, walk-off and pump depletion are included in the complete mathematical model, avoiding any a priori-assumption. Finally, the design criteria to optimize the device performance are presented.     

Blue light and infrared continuum generation by soliton fission in a microstructured fiber

The nonlinear propagation of ultrashort pulses in a microstructured fiber is experimentally investigated. By working around 800 nm, in the anomalous dispersion region, clear evidence of pulse break-up and soliton propagation is obtained. This is consistent with the recently suggested mechanism of spectral broadening based upon the fission of higher order solitons into red-shifted fundamental solitons and blue-shifted dispersion waves. When 190-fs pulses at high input intensities are used, the output spectrum is made of a broad infrared supercontinuum coexisting with a sharp and very intense blue peak that takes up to 24% of the input power. We tentatively propose an explanation of this effect by invoking pulse-trapping phenomena controlled by the group-velocity matching of infrared and visible pulses. PACS 42.65.Tg; 42.81.Dp     

Characterization of the Palais–Smale sequences for the conformal Dirac–Einstein problem and applications

In this paper we study the Palais–Smale sequences of the conformal Dirac–Einstein problem. After we characterize the bubbling phenomena, we prove an Aubin type result leading to the existence of a positive solution. Then we show the existence of infinitely many solutions to the problem provided that the underlying manifold exhibits certain symmetries.     

Efficient access to 5-substituted thiazoles by a novel metallotropic rearrangement

A novel rearrangement process involving the migration of trimethylstannanyl or trimethylsilanyl groups around the thiazole ring provides access to either 2- or 5-metallated thiazoles by tuning the reaction conditions. The proposed mechanism, based on experimental evidence, is characterized by the catalytic role of thiazole bisadducts as metal-transfer agents.