Review of the basic methods for characterizing integrated-optic waveguides

This article presents a short review of the various methods of characterizing integrated-optic waveguides. It is intended to acquaint researchers, particularly beginners in this field, with the principles of some of the widely used techniques of characterizing one-dimensional (planar) and two-dimensional (such as channel or rib) waueguides.     

Addition en catalyse redox d'halogenures benzyliques sur les doubles liaisons

Benzyl chloride is shown to add to olefins in DMF in the presence of CuCl/bipyridyl, CuCl/phenanthroline or FeCl₂. Addition of p-nitrobenzyl chloride takes place under milder conditions.     

Synthetic models related to dna-intercalating molecules a study of the ring-ring stacking interactions between 8-alkoxypsoralen and thymine.

As a contribution to the problem of the intercalation and photobinding of psoralens to DNA, model compounds were prepared in which the psoralen ring is linked to thymine by a polymethylene bridge. The ring-ring intramolecular interaction in the models was assessed by hypochromism measurement in the UV.     

Heterodyne spectroscopy at very low frequencies

We have studied the spectrum of light scattered by capillary waves, thermally excited at the free surface of highly viscous liquids, by heterodyne spectroscopy techniques. We were able to measure spectral widths down to 0.2 Hz.     

Self phase-modulation in the breakdown of gases by ultra-short pulses

In a gas breakdown experiment with ultra-short optical pulses, the transmitted laser light shows spectral alterations attributed to a self phase-modulation. This effect is due to the refractive index change accompanying the ionization growth. A numerical treatment indicates that the predominant mechanism is cascade collisionnal ionization.     

New flavin and deazaflavin oligonucleotide conjugates for the amperometric detection of DNA hybridization

The functionalization of an oligonucleotide by flavin and deazaflavin derivatives allowed an amperometric determination of the hybridization process through the disappearance of the electroactivity of the free oligonucleotide and the appearance of a new electrochemical signal characteristic of the resulting duplex.     

11-Aminoundecanoic acid: a versatile unit for the generation of low molecular weight gelators for water and organic solvents

The use of 11-aminoundecanoic acid as a synthetic building-block allows the systematic preparation of (oligo)amide organogelators-including chiral ones-which display remarkable gelation properties in organic solvents and water.     

Catalytic efficiency of a new tridentate ferrocenyl phosphine auxiliary: Sonogashira cross-coupling reactions of alkynes with aryl bromides and chlorides at low catalyst loadings of 10(-1) to 10(-4) mol %

[structure: see text] The catalytic activity in Sonogashira cross-coupling reactions of alkynes with a variety of aryl halides (including chlorides) using a multidentate ferrocenyl phosphine is presented. The novel mixed ferrocenyl aryl/alkyl triphosphine is thermally stable and insensitive to air or moisture, and its robustness allows aryl alkynylation at 10(-1) to 10(-4) mol % catalyst loadings with TONs up to 250,000. Copper-free coupling using phenylacetylene is also accessible in good yield.     

Regioselective formation of alkylidenecyclopropanes from 2-substituted cyclobutylidenes generated from geminal dibromocyclobutanes and methyllithium

Four different 2-substituted geminal dibromocyclobutanes were reacted with methyllithium at -78 degrees C. In contrast to previous studies using diazocyclobutanes as carbene precursors at temperatures above 200 degrees C via reaction of the corresponding tosylhydrazone sodium salts, the organometallic route in each case produces only an alkylidenecyclopropane that could be isolated in good yields. B3LYP calculations were employed to rationalize the observed regioselective ring contraction of the generated cyclobutyliden(oid)s. [reaction: see text]     

The strange eigenmode in Lagrangian coordinates

For a distribution advected by a simple chaotic map with diffusion, the "strange eigenmode" is investigated from the Lagrangian (material) viewpoint and compared to its Eulerian (spatial) counterpart. The eigenmode embodies the balance between diffusion and exponential stretching by a chaotic flow. It is not strictly an eigenmode in Lagrangian coordinates, because its spectrum is rescaled exponentially rapidly.