Optical modes in semiconductor microtube ring resonators

We demonstrate optical modes in InGaAs/GaAs microtubes acting as optical ring resonators. Self-supporting microtubes were fabricated by optical lithography and wet-etching processes utilizing the self-rolling mechanism of strained bilayers. The optical modes were probed by the photoluminescence of InAs quantum dots embedded in the tube's wall. In this novel microtube ring resonator we find a spectrum of sharp modes. They are in very good agreement with the theoretical results for a closed thin dielectric waveguide.     

Precipitation of metal-cupferron complexes from homogeneous solution-II: determination of titanium

The cupferron complex of titanium has been precipitated by the addition of phenylhydroxylamine and sodium nitrite to a cold acidic solution of the metal. Details of the method are given. Separation of titanium from aluminium, borate, phosphate and vanadate is described.     

Precipitation of metal-cupferron complexes from homogeneous solution-I: determination of copper

The cupferron complex of copper has been precipitated from homogeneous solution by the addition of phenylhydroxylamine and sodium nitrite to a cold, acidic solution containing copper(II) ions. The precipitate can be dried at 90 +/- 5 degrees and weighed without ignition to the oxide. Less than 3 mg of copper can be determined. A fairly high concentration of acetic acid is tolerable. Separation from large quantities of zinc, nickel and silver has been achieved.     

On the mechanism of the reductive cleavage of anti-9-phenyl-cis-bicyclo[6.1.0]nona-2,4,6-triene

Treatment of the title compound (1a) with potassium in liquid ammonia at ca ?33° immediately afforded the benzylcyclooctatetraene dianion (4a) which, upon quenching with iodine-pentane, gave benzylcyclooctatetraene (5) as the only isolable product. In contrast, treatment of1a with potassium amide in liquid ammonia at ?69° initially afforded the 9-phenylmethylenecyclooctatrienyl anion (6a) as a short-lived intermediate which was then converted to the α-aminobenzylcyclooctatetraene dianion (7a). These results, coupled with the observation that cis-bicyclo[6.1.0]nona-2,4-diene (12) in potassium amide-liquid ammonia affords the cis-bicyclo[6.1.0]nonadienyl anion (8b) which then slowly opens to the methylcyclooctatetraene dianion (4b) at ?12°, lead to the conclusion that4a is produced by a reductive cleavage of1avia a radical anion or dianion.     

PHOTOSELECTION AND TRANSIENT LINEAR DICHROISM WITH ORIENTED IMMOBILIZED PURPLE MEMBRANES: EVIDENCE FOR MOTION OF THE C(20)-METHYL GROUP OF THE CHROMOPHORE TOWARDS THE CYTOPLASMIC SIDE OF THE MEMBRANE*

Abstract— We have determined the transition dipole moment orientation of the chromophore during the photocycle of bacteriorhodopsin by photoselection and time-resolved linear dichroism experiments with samples of oriented immobilized purple membranes. This technique offers two important advantages over experiments with isotropic aqueous suspensions: (1) the depolarization due to the rotational diffusion of the membranes is eliminated, (2) the sensitivity for detecting the orientation of the transition dipole moment of intermediates is greatly increased. The appropriate equations for the analysis of time-resolved linear dichroism experiments with samples of oriented immobilized membranes will be presented. In the transition from the ground state of bacteriorhodopsin to the M-intermediate, the transition dipole moment tilts out of the plane of the membrane by about 3°. On the basis of current structural information on the plane of the chromophore and the orientation of its C(19) and C(20) methyl groups, a tilt of the transition dipole moment into the plane of the membrane would have been expected if it is assumed that the orientation of the conjugated polyene chain from C(5) to C(13) is the same in both states. The experimental result may be explained by an 11° tilt of the C(5) to C(13) part of the chain out of the plane of the membrane with the C(20) methyl group moving towards the cytoplasmic side of the membrane by about 1.7 Å and the cyclohexene ring staying fixed. This interpretation is supported by recent neutron diffraction experiments on the chromophore position in the M-intermediate.     

Probleme der Signifikanzberechnung in der Marktforschung

Ohne Zusammenfassung     

A Highly Asymmetric Gold(III) η3-Allyl Complex

A highly asymmetric Au^III η³-allyl complex has been generated by treating Au(η¹-allyl)Br(tpy) (tpy=2-(p-tolyl)pyridine) with AgNTf₂. The resulting η³-allyl complex has been characterized by NMR spectroscopy and X-ray crystallography. DFT calculations and variable temperature ¹H NMR suggest that the allyl ligand is highly fluxional.