Preparation and properties of a fullerene/polysiloxane hybrid from chemically modified fullerene and polymethoxysiloxane

An organic–inorganic hybrid was prepared by simply mixing a fullerene derivative with polymethoxysiloxane. First, C₆₀ was subjected to a radical addition reaction with 4,4′-azobis(4-cyanovaleric acid) to provide a C₆₀ derivative. Polymethoxysiloxane was prepared by a controlled hydrolytic condensation of tetramethoxysilane. These two compounds were mixed and heated to provide hybrid bulk body. The hybrid bulk body showed high mechanical strength and elastic modulus compared with polymethoxysiloxane or the C₆₀/polymethoxysiloxane hybrid. The formation of a dense siloxane network was established by a homogeneous mixing of the C₆₀ derivative with polymethoxysiloxane.     

Stereoselective Syntheses of all the Possible Stereoisomers of Coronafacic Acid

An efficient and stereoselective syntheses of all the possible stereoisomers of coronafacic acid (CFA) has been developed. The stereochemistries of C3a and C7a were controlled in a diastereoselective Diels-Alder type cycloaddition using a chiral auxiliary. CFA and 6-epi-CFA were synthesized by hydrogenation of a common intermediate. During the synthesis of 6-epi-CFA, we established that its cis-fused configuration is important for the introduction of C4-C5 double bond by dehydration. This report is the first practical synthesis of both 6-epi-CFA, and its enantiomer.     

High-speed recovery of germanium in a convection-aided mode using functional porous hollow-fiber membranes

A porous hollow-fiber membrane capable of recovery of germanium from a liquid stream was prepared by radiation-induced graft polymerization of an epoxy-group-containing vinyl monomer, glycidyl methacrylate, and subsequent functionalization with 2,2'-iminodiethanol, di-2-propanolamine, N-methylglucamine, and 3-amino-1,2-propanediol. The functional group density was as high as 1.4 mol per kg of the resultant hollow fiber. The polymer chains containing functional groups surrounding the pores enabled a high-speed recovery of germanium during permeation of a germanium oxide (GeO2) solution through the pores of the hollow fiber. Because of a negligible diffusional mass-transfer resistance, germanium concentration changes with the effluent volume, i.e., breakthrough curves, overlapped irrespective of the residence time of the solution, which ranged from 0.37 to 3.7 s across the hollow fiber. After repeated use of adsorption and elution, the adsorption capacity did not deteriorate.     

syn-selective direct catalytic asymmetric Mannich-type reactions of hydroxyketones using Y{N(SiMe3)2}3/linked-BINOL complexes

[reaction, structure: see text] Chiral Y{N(SiMe3)2}3/linked-BINOL catalyst generated Y-enolate in situ from various hydroxyketones (R2 = aryl, heteroaryl). Beta-amino-alpha-hydroxy ketones (R1 = aryl, heteroaryl, alkenyl) were obtained syn-selectively (up to 96/4) in high ee (up to 98%) and good yield (up to 98% yield).     

Generic cosmic-censorship violation in anti-de Sitter space

We consider (four-dimensional) gravity coupled to a scalar field with potential V(phi). The potential satisfies the positive energy theorem for solutions that asymptotically tend to a negative local minimum. We show that for a large class of such potentials, there is an open set of smooth initial data that evolve to naked singularities. Hence cosmic censorship does not hold for certain reasonable matter theories in asymptotically anti-de Sitter spacetimes. The asymptotically flat case is more subtle. We suspect that potentials with a local Minkowski minimum may similarly lead to violations of cosmic censorship in asymptotically flat spacetimes, but we do not have definite results.     

Conformally invariant powers of the Laplacian -- A complete nonexistence theorem

We show that on conformal manifolds of even dimension there is no conformally invariant natural differential operator between density bundles with leading part a power of the Laplacian for n/2$">. This shows that a large class of invariant operators on conformally flat manifolds do not generalise to arbitrarily curved manifolds and that the theorem of Graham, Jenne, Mason and Sparling, asserting the existence of curved version of for , is sharp.

     

Generation of 360-nm ultraviolet light in first-order periodically poled bulk MgO:LiNbO3

Ultraviolet second-harmonic generation in first-order periodically poled MgO:LiNbO3 is presented. Using a high-voltage multipulse application method, we fabricated a first-order nonlinear grating with a period of 1.8 microm and depth of approximately 150 microm over 10-mm interaction length in a 1-mm-thick MgO:LiNbO3 substrate. In a single-pass configuration, continuous-wave 30-mW UV light at 362.5 nm was generated for a fundamental power of 522 mW, corresponding to a normalized conversion efficiency of 11%/W.     

Wave packet dynamics in a quasi-one-dimensional metal-halogen complex studied by ultrafast time-resolved spectroscopy

An ultrafast optical response is studied in a quasi-one-dimensional halogen-bridged mixed-valence metal complex [Pt(en)(2)] [Pt(en)2I2] (ClO4)(4) with ultrafast time resolution. Wave packet motions both in the ground and self-trapped exciton (STE) states are observed as oscillatory modulations in the time-resolved reflectivity. The wave packet motion on the STE potential surface begins after about 50 fs with respect to the photoexcitation. This delay is attributed to the lattice relaxation from the free exciton state to the STE state.