High-Q whispering gallery modes in a spherical shell dielectric resonator: Characterization at microwave frequencies

We present a numerical and experimental characterization of high-Q whispering gallery resonant modes excited in a fused quartz spherical shell operated in the 18-26.5 GHz band; easy coupling and selection of modes is a most advantageous feature of the proposed structure with respect to ordinary bulk resonators. The numerical results, based on a finite element algorithm, well match experimental data, which also show the capability of our device to perform gaseous spectroscopy measurements. Received 25 October 2002 Published online 4 February 2003     

Les reactions de redistribution dans la chimie du bore. Etude des reactions de competition des groupements NMe2, Cl,SMe, OMe,F sur des centres bore mono et difonctionnels R2B- ET RB<

A quantitative ¹H and ¹¹B NMR study of the redistribution equilibria between the NMe₂ group and the Cl, SMe,OMe and F substituents on the mono and difunctional boron centers (R₂B- and RB<) is reported. The preferential affinity of the amino group towards dialkylated boron centers is shown by the examination of the “intersystem” constant sets. A relative affinity scale is proposed.     

Hétérocycles à fonction quinone. 7. Benzo[f]quinazolinediones-7,10 à action antitumorale potentielle

Few benzo[f]quinazoline-7,10-diones 4a-c are prepared by oxidation, with potassium nitrosodisulfonate, of the corresponding benzo[f]quinazolinamines, made by reduction of the nitro analogues which were obtained from 8-methoxybenzo[f]quinazolin-1(2H)-one. The compound 4a shows an interesting cytotoxicity.     

Hybrid Xerogel Structure and Molecular Guest Dynamics

A new experimental approach to study the porosity of hybrid organic-inorganic glasses is reported. It relies upon nuclear magnetic resonance observation of molecular guest dynamics. It is shown that in MTEOS xerogels, there exists an interconnected organic-rich network in which organic guests are trapped and can eventually diffuse. The interpore translational diffusion is strongly activated and its spatial extension gives information on the pore connectivity, whose decay is characterized by the interpore jump probability given by the theoretical model.     

Reaction de redistribution entre le tripropylbore et ses produits d'oxydation: Etude par résonance du Noyau 11B

A study by B¹¹ NMR of the system tripropylborane–boron trioxide shows that scrambling reactions occur between the alkylborane and its oxidation products; this involves a redistribution of the mono-(? C₃H₇) and difunctional (? O? ) substituents attached to boron, leading to molecules of varying size and structure.     

Motion of electron-hole drops in low magnetic fields

The effect of magnetic fields on the motion of electron-hole drops in germanium is studied. A non-uniform strain is used to provide a known and controllable driving force for drop motion in the sample plane. Contrary to the results of earlier experiments in which drop motion was normal to the sample plane, the results are consistent with conventional models of drop-phenomenon interaction and weak magnetic fields have no observable effects on this motion.     

Étude des Phénomènes de Redistribution dans les Systèmes BR3/BT3 avec T = –OCH3, –SCH3, –N(CH3)2

Proton and ¹¹B magnetic resonance studies of the redistribution in the system BR₃/BT₃ (R = C₃H₇, T = OCH₃, SCH₃ and N(CH₃)₂) show that equilibria between different species BR_nT_3–n (n = 0, 1, 2, 3) occur. In general it appears that the mixed species (n = 1 and 2) are more favoured than would be the case for completely random scrambling; however, consideration of steric and electronic factors may explain this phenomenon.