First enantioselective allylic etherification with phenols catalyzed by chiral ruthenium bisoxazoline complexes

Regio- and enantioselective substitution of cinnamyl chloride by phenols has been achieved with up to 82% enantiomeric excess, using a ruthenium catalyst prepared from [Cp*(CH(3)CN)(3)Ru][PF(6)] and a chiral bisoxazoline ligand.     

Fluorescence lifetimes and emission patterns probe the 3D orientation of the emitting chromophore in a multichromophoric system

In this Communication, we report on the fluorescence behavior of an individual first generation multichromophoric dendrimer. The fact that each of the chromophores in time acts as a fluorescent trap is demonstrated by directly probing the dipole orientation of the emitting chromophore by means of defocused wide-field imaging and comparing experimental and calculated emission patterns. It is shown that in such cases the electromagnetic boundary condition effect results in discrete changes in the fluorescence lifetime as a function of time for individual dendrimers.     

Segment dynamics in thin polystyrene films probed by single-molecule optics

Single fluorescent molecules (represented by spheres with a volume equal to the actual van der Waals volume of the molecule) has been embedded in a polystyrene matrix (left). Such molecules act as probes for the study of polymer nanoscale (segmental scale) dynamics in thin films deposited on a glass cover slide (right).     

Accurate determination of waveguide-fed p-i-n photodiode absorption

Experimental and theoretical determinations of the absorption of a waveguide fed GaInAs photodiode are presented. The absorption is determined as a function of the propagation length using μ-p-i-n diodes regularly spaced along the GaInAs absorbing layer. The detector absorption is as high as 2060 dB/cm. However, for propagation lengths longer than ~200 μm it falls to about 120 dB/cm. The results are analyzed using two different approaches. The first consists in determining the eigenmodes of both the passive waveguide and the detector/waveguide structure. The second is the beam propagation method (BPM). Both methods demonstrate that the absorption curve can be fully explained by the existence of two modes, of which the one with the lowest absorption is induced by the presence of an undoped InP buffer layer. Both eigenmode decomposition and BPM are in quantitative agreement with the experimental data     

Precise structure activity relationships in asymmetric catalysis using carbohydrate scaffolds to allow ready fine tuning: dialkylzinc-aldehyde additions

The ready construction of 24 stereochemically and functionally diverse carbohydrate ligand structures from a core D-glucosamine scaffold has allowed the evaluation of broad ranging structure activity relationships in ligand accelerated zincate additions to aldehydes, with variations in deltadeltaG+/+(R-S) of up to 5650 J mol(-1) that create opposing senses of asymmetric induction and that are consistent with models based on several ligand X-ray structures and molecular mechanics analysis. Factorial analysis of enantioselectivity using key dihedral angles and steric volume on N-2 also highlight the potential for the use of factorial design in ligand construction.     

GaInAs monolithic photoreceiver integrating p-i-n/JFET withdiffused junctions and a resistor

An integrated p-i-n/JFET/resistor has been developed using a GaInAs epitaxial structure grown on a planar substrate A four-layered structure allows separate optimization of both active devices. Owing to the good performances and high reliability of individual components, the sensitivity of these monolithic photoreceivers is evaluated as -29 dBm at 560 Mb/s (10^-9 bit error rate). Remarkable stability over time is exhibited     

The indecomposable representation of SO0(2, 2) on the one-particle space of the massless field in 1 + 1 dimension

In the continuum O(3) sigma model in two spatial dimensions, there are topological solitons whose size can be stabilized by adding Skyrme and potential terms. This Letter describes a lattice version, namely a natural way of modifying the 2D Heisenberg model to achieve topological stability on the lattice.     

High speed, high capacity ATM optical switches for futuretelecommunication transport networks

This paper describes the work carried out in the RACE Project R2039 ATMOS (asynchronous transfer mode optical switching). The project is briefly illustrated, together with its main goal: to develop and assess concepts and technology suitable for optical fast packet switching. The project's technical approach consisted in the exploitation of the space and wavelength domains for fast routing and buffering: The major achievements are then reported. Four different switch architecture concepts have been proposed, investigated and developed, all based on a high speed optical routing matrix electrically controlled at lower speed. The basic optical key components and subsystems (wavelength converters, space switches and optical buffers) are described in detail, with the outstanding results obtained and the corresponding projected performance. In particular, system demonstration of wavelength conversion at 10 and 20 Gb/s has been realized, to show the usefulness of the ATMOS technology both to implement optimized high performance optical packet-switching fabrics as well as transparent optical circuit-routing nodes. Four rack-mounted, reduced size demonstrators of basic switching matrices have been designed and implemented scalable to real system sizes. The obtained good results in terms of bit error rate and hardware integration are reported, showing that ATM switches are feasible with state of-the-art optical technology