All-optical sampling and magnification based on XPM-induced focusing

International audienceWe theoretically and experimentally investigate the design of an all-optical noiseless magnification and sampling function free from any active gain medium and associated high-power continuous wave pump source. The proposed technique is based on the co-propagation of an arbitrary shaped signal together with an orthogonally polarized intense fast sinusoidal beating within a normally dispersive optical fiber. Basically, the strong nonlinear phase shift induced by the sinusoidal pump beam on the orthogonal weak signal through cross-phase modulation turns the defocusing regime into localized temporal focusing effects. This periodic focusing is then responsible for the generation of a high-repetition-rate temporal comb upon the incident signal whose amplitude is directly proportional to its initial shape. This internal redistribution of energy leads to a simultaneous sampling and magnification of the signal intensity profile. This process allows us to experimentally demonstrate a 40-GHz sampling operation as well as an 8-dB magnification of an arbitrary shaped nanosecond signal around 1550 nm in a 5-km long normally dispersive fiber. The experimental observations are in quantitative agreement with numerical and theoretical analysis

Membrane-based TBADT recovery as a strategy to increase the sustainability of continuous-flow photocatalytic HAT transformations

Photocatalytic hydrogen atom transfer (HAT) processes have been the object of numerous studies showcasing the potential of the homogeneous photocatalyst tetrabutylammonium decatungstate (TBADT) for the functionalization of C(sp(3))–H bonds. However, to translate these studies into large-scale industrial processes, careful considerations of catalyst loading, cost, and removal are required. This work presents organic solvent nanofiltration (OSN) as an answer to reduce TBADT consumption, increase its turnover number and lower its concentration in the product solution, thus enabling large-scale photocatalytic HAT-based transformations. The operating parameters for a suitable membrane for TBADT recovery in acetonitrile were optimized. Continuous photocatalytic C(sp(3))-H alkylation and amination reactions were carried out with in-line TBADT recovery via two OSN steps. Promisingly, the observed product yields for the reactions with in-line catalyst recycling are comparable to those of reactions performed with pristine TBADT, therefore highlighting that not only catalyst recovery (>99%, TON > 8400) is a possibility, but also that it does not happen at the expense of reaction performance

Tele-revista: representaciones, imágenes y libertad política en un informativo de la televisión pública suiza para la emigración española

Desde 1973 hasta 2003 la televisión pública suiza emitió el programa Telerevista una vez cada dos semanas, los fines de semana, y con una duración de quince minutos. Tele-revista era un programa en español dirigido a los emigrantes españoles en el país helvético que contenía reportajes de temas relacionados con la realidad de la comunidad española. En una primera parte abordaremos la imagen y la puesta en escena del poder institucional de la administración española en Suiza en el programa y de su evolución a lo largo del tiempo. En una segunda parte trataremos los esfuerzos del programa por formar a los espectadores en cuestiones de democracia y libertades en Suiza. Finalmente nos ocuparemos de la presencia cada vez mayor en la información cultural del programa de las particularidades y de las relaciones entre cultura popular y alta cultura.Between 1973 and 2003 Swiss television used to broadcast at the weekend the biweekly news magazine Tele-revista, which lasted 15 minutes. Tele-revista was sent in Spanish and addressed to Spanish migrants living in Switzerland. It contained reportages about the Spanish community’s reality. This paper focuses first on the image and the staging of the Spanish administration’s institutional power in Switzerland and its evolution in the course of time. Then it will consider the efforts to educate the audience in matters of democracy and liberties in Switzerland. Finally it will treat the increasing presence in the magazine’s cultural section of the characteristics and the relation between popular and high culture

Modular allylation of C(sp³)-H bonds by combining decatungstate photocatalysis and HWE olefination in flow

The late-stage introduction of allyl groups provides an opportunity to synthetic organic chemists for subsequent diversification, furnishing a rapid access to new chemical space. Here, we report the development of a modular synthetic sequence for the allylation of strong aliphatic C(sp(3))–H bonds. Our sequence features the merger of two distinct steps to accomplish this goal, including a photocatalytic Hydrogen Atom Transfer and an ensuing Horner–Wadsworth–Emmons (HWE) reaction. This practical protocol enables the modular and scalable allylation of valuable building blocks and has been applied to structurally complex molecules

Conical defects in growing sheets

A growing or shrinking disc will adopt a conical shape, its intrinsic geometry characterized by a surplus angle $se$ at the apex. If growth is slow, the cone will find its equilibrium. Whereas this is trivial if $se <= 0$, the disc can fold into one of a discrete infinite number of states if $se$ is positive. We construct these states in the regime where bending dominates, determine their energies and how stress is distributed in them. For each state a critical value of $se$ is identified beyond which the cone touches itself. Before this occurs, all states are stable; the ground state has two-fold symmetry.Comment: 4 pages, 4 figures, LaTeX, RevTeX style. New version corresponds to the one published in PR