Theory of resonant forbidden Raman scattering in semiconductors

The Raman tensors for the electric field-induced and wavevector dependent scattering from LO phonons in semiconductors have been calculated near critical points using a perturbation treatment. The resulting expressions have analytic closed forms such that the dependence of the forbidden scattering intensity on the incident photon energy and the applied d.c. electric field can be evaluated from available energy band parameters. The forbidden LO scattering intensity of GaAs in the back scattering configuration has been numerically calculated near the e₁ and E₁ gaps as functions of the incident photon energy and the dc electric field. The result shows strong interference between the two scattering processes. The allowed TO and LO Raman scattering intensities of GaAs were also calculated at a wavelength of 1.06 μm from the SHG and Faust-Henry coefficients, and compared with the forbidden LO intensity.     

Structure and synthesis of nectrisine, a new immunomodulator isolated from a fungus.

The structure of a novel immunomodulator, nectrisine (1), has been elucidated on the basis of chemical and spectroscopic evidence. Its absolute stereochemistry was predicted on the basis of the dibenzoate chirality rule and finally confirmed by a synthesis from D-glucose.     

Drastic enhancement of TiO2-photocatalyzed reduction of nitrobenzene by loading Ag clusters

Ag clusters (mean diameter = 1.5 nm, standard deviation = 0.37 nm) were photodeposited on TiO(2) particles in a highly dispersed state. The loading of a small amount of the Ag clusters (0.24 wt %) dramatically enhanced both the activity for the TiO(2) photocatalytic reduction of nitrobenzene and the product selectivity of aniline. The essential action mechanism of the Ag clusters is discussed.     

Generation of a sub-20-fs single optical pulse by four-wave Raman mixing using two Raman cells filled with molecular hydrogen

To attempt to expand the spectral domain for pulse shortening, we generated several emission lines by stimulated Raman scattering and subsequent four-wave Raman mixing. The efficiency of generation of the Raman emission was improved by passing the beam through two Raman cells that were connected in series. The group-velocity dispersion induced by a Raman cell window and hydrogen was compensated for by means of a pair of chirped mirrors for pulse compression. By a phase lock of the emission lines in the process of four-wave Raman mixing, the pulse width was reduced from 114 to 17 fs in the second Raman cell.     

Chelating of titanium by lactic acid in the water-soluble diammonium tris(2-hydroxypropionato)titanate(IV)

Stable water-soluble diammonium tris(2-hydroxypropionato)titanate(IV) [ammonium trilactatotitanate(IV)], (NH4)2[Ti(C3H4O3)3], was prepared in the crystalline form. According to the X-ray single-crystal diffraction data, this compound crystallizes in the cubic cell with a = 11.649(4) angstroms, space group P2(1)3 (no. 198), and has Z = 4 molecules per unit cell. The 13C NMR data and Raman and IR spectra support the determined structure. The absence of nonbonded functional groups restricts the formation of oligomers in contrast to the reported speciation of citratoperoxotitanate(IV) complexes.     

Oxidation of 3-hydroxypiperidines with iodosylbenzene in water: tandem oxidative Grob fragmentation-cyclization reaction

Oxidation of 3-hydroxypiperidine with iodosylbenzene in water afforded 2-pyrrolidinone directly in good yields. The reaction probably involves oxidative Grob fragmentation yielding imino aldehyde, which upon hydrolysis produces 2-pyrrolidinone via a cyclization-oxidation sequence.     

Catalytic enantio- and diastereoselective aldol reactions of glycine-derived silicon enolate with aldehydes: an efficient approach to the asymmetric synthesis of anti-beta-hydroxy-alpha-amino acid derivatives

We have developed an efficient method for the asymmetric synthesis of anti-beta-hydroxy-alpha-amino acid derivatives based on highly enantio- and diastereoselective aldol reactions of the silicon enolate derived from N-trifluoroacetylglycinate with aldehydes using a chiral zirconium catalyst. The resulting N-trifluoroacetyl group is easily cleaved under either acidic or basic conditions and can be used directly as a protecting group for further transformations.     

Interpretations of Quantum Mechanics in Terms of Beable Algebras

In terms of beable algebras Halvorson and Clifton [International Journal of Theoretical Physics 38 (1999) 2441–2484] generalized the uniqueness theorem (Studies in History and Philosophy of Modern Physics 27 (1996) 181–219] which characterizes interpretations of quantum mechanics by preferred observables. We examine whether dispersion-free states on beable algebras in the generalized uniqueness theorem can be regarded as truth-value assignments in the case where a preferred observable is the set of all spectral projections of a density operator, and in the case where a preferred observable is the set of all spectral projections of the position operator as well.     

Mod Galois representations of solvable image

It is proved that, for a number field and a prime number , there exist only finitely many isomorphism classes of continuous semisimple Galois representations of into of fixed dimension and bounded Artin conductor outside which have solvable images. Some auxiliary results are also proved.