Linear and nonlinear pulse propagation in coupled resonator slow-wave optical structures

The linear and nonlinear characteristics of optical slow-wave structures made of direct coupled Fabry–Pérot and Ring Resonators are discussed. The main properties of an infinitely long slow-wave structure are derived analytically with an approach based on the Bloch theory. The spectral behaviour is periodical and closed form expressions for the bandwidth, the group velocity, the dispersion and the linear and nonlinear induced phase shift are derived. For structures of finite length the results still hold providing that proper input/output matching sections are added. In slow-wave structures most of the propagation parameters are enhanced by a factor S called the slowing ratio. In particular nonlinearities result strongly enhanced by the resonant propagation, so that slow-wave structures are likely to become a key point for all-optical processing devices. A numerical simulator has been implemented and several numerical examples of propagation are discussed. It is also shown as soliton propagation is supported by slow-wave structures, demonstrating the flexibility and potentiality of these structures in the field of the all-optical processing.     

A laser Doppler velocimeter for pulsatile water flow measurements in resonant hydraulic circuits

Described is a laser Doppler velocimeter designed to measure a small oscillatory velocity component superposed to the steady water flow of a resonant hydraulic circuit in fully developed turbulent conditions. A frequency tracker with lock-in analysis of the velocity output is used. The rms amplitude of the oscillatory velocity component is measured with an accuracy of 1.5 mm s^-1, and the mean velocity is about 3 ms^-1. The resonance behaviour of the velocity amplitude measured at a fixed point of the circuit is reported for the exciting frequency range 2–5 Hz.     

Beniamino Segre

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Beniamino Segre

     

Relaxation of Disordered Magnets in the Griffiths' Regime

We study the relaxation to equilibrium of discrete spin systems with random finite range (not necessarily ferromagnetic) interactions in the Griffiths' regime. We prove that the speed of convergence to the unique reversible Gibbs measure is almost surely faster than any stretched exponential, at least if the probability distribution of the interaction decays faster than exponential (e.g. Gaussian). Furthermore, if the interaction is uniformly bounded, the average over the disorder of the time–autocorrelation function, goes to equilibrium as (in d > 1), in agreement with previous results obtained for the dilute Ising model. Received: 12 June 1996 / Accepted: 23 January 1997     

Excitons in rare gas atoms and solids

Excitons in rare gas are described using the integral equation approach and an appropriate semi-empirical simplification of the short-range terms. In the solids, polarization effects are taken into account using a semi-continuum model in analogy with F-centre problem. Reasonable agreement with experiments is obtained for exciton binding energy shifts passing from atoms to crystals.     

Formation and decomposition of the rutile-type compound FeSbO4

The reaction between Fe₂O₃ (hematite) and Sb₂O₃ leading to the formation of the rutile-type compound FeSbO₄ was analysed by means of DTA and TG, performed under various O₂ partial pressures up to 1673 K. The reaction products were identified by means of XRD analysis. Three transformations occur in the analysed temperature range: 1. oxidation of Sb₂O₃ to Sb₂O₄ between 745 and 768 K; 2. formation of FeSbO₄ between 1226 and 1246 K; 3. decomposition of FeSbO₄ without melting above 1543-1591 K. The TG-DTA and XRD analysis results indicate that deviations from perfect stoichiometry are likely to exist inside FeSbO₄. This revised version was published online in July 2006 with corrections to the Cover Date.     

The synthesis of (+)- and (−)-1-benzoyl-1,2,2a,3,4,5-hexahydrobenz[cd]indol-4-amine, and preparation of LY228729.

Racemic epoxide5 was reacted with S-Phenylethylamine to afford diastereomers6 and7, from which amino alcohol6 could be isolated directly. Aziridine formation and tandem-hydrogenolysis provided optically pure primary amine2 (31% from racemic4), which was further elaborated to LY228729 (15), an interesting 5HT_1a receptor agonist.     

Oxidative decarboxylation of arylacetic acids by means of tetrabutylammonium periodate

Tetrabutylammonium periodate (TBAPI) in refluxing dioxane is able to convert arylacetic acids into the corresponding nor-aldehydes in good yields.     

Electron states in Ge and Si under uniaxial stress

The electron states in Ge and Si under uniaxial stress in the (100) direction are computed with the pseudopotential method. The theoretical results are compared with optical measurements of the indirect absorption edge in Si and Ge under uniaxial stress and with the polarization dependence and the splittings of donor levels.