Frequency dependent Shubnikov-De Haas oscillations in Si-MOS-FET under high magnetic fields

The quantum oscillations in the AC magnetoconductance was studied for inversion layers in Si-MOS-FETs under high magnetic fields at 1.5 K. Each peak in the Shubnikov-de Haas oscillation was found to be remarkably sharpened with increasing frequency up to 50 MHz. It was also found that the width of the gate voltage for non-conductive region (σ_xx=0) increases with increasing frequency.     

Hydrogen bond directed self-assembly of core-substituted naphthalene bisimides with melamines in solution and at the graphite interface

A series of red and blue highly fluorescent core-substituted naphthalene bisimide dyes has been synthesized and they have been investigated as supramolecular building blocks. NMR and UV-Vis titration experiments of these dyes with complementary melamines revealed the formation of triple hydrogen bonds (DAD-ADA arrays) in solution. At stoichiometric ratios, ditopic melamine receptors could dissolve otherwise insoluble bisimides by means of hydrogen bonding, even in aliphatic solvents. At the solution/graphite interface, one-dimensional chains of hydrogen bonded naphthalene bisimides and two-dimensional adlayers of ditopic melamines are formed for the pure compounds but little evidence for heterocomplexes between the two complementary building blocks could be obtained.     

Enantioselective acylation of secondary alcohols catalyzed by chiral N-heterocyclic carbenes

[reaction: see text] The synthetic utility of chiral N-heterocyclic carbenes, which have been used mainly in transition metal-catalyzed reactions as a ligand, was demonstrated by the enantioselective acylation of secondary alcohols.     

Control of bacteria adhesion by cell-wall engineering

UDP-MurNAc-pentapeptide derivative bacterial cell-wall precursors were synthesized as effective tools for surface display on living bacteria. Lactobacilli were incubated in the ketone-modified precursor-containing medium, and the ketone moiety was displayed on the bacterial surface through cell-wall biosynthesis. Oligomannose was coupled with the ketone moiety on the bacterial surface via a aminooxyl linker, thereby displaying this oligosaccharide on the surface of the bacteria. The increase in the adhesion of the sugar-displaying bacteria onto a concanavalin A-attached film compared to that of native bacteria was confirmed by microscopic observation and surface plasmon resonance measurement. The incorporation of the artificial cell-wall precursors was enhanced when incubated with fosfomycin, an inhibitor of cell-wall precursor biosynthesis.     

Reduction of propagation and bending losses of heterostructured photonic crystal waveguides by use of a high-delta structure

We describe the fabrication and evaluation of a low-loss, high-delta optical waveguide consisting of heterostructured photonic crystals. The waveguide is composed of a multilayer stack of Ta2O5/SiO2 and is prepared by use of the autocloning technique. Light is guided in the waveguide by the difference in the effective refractive indices of the constituent photonic crystals. By improving the design of the core region so that is has a flat multilayer structure, we achieve delta = 3.09% for the in-plane direction and net propagation loss of 0.56 dB/mm at lambda = 1.6 microm. Experiments also suggest that the bending loss of the waveguide can be reduced to less than 0.1 dB if the curvature radius is larger than 700 microm.     

Pseudogap formation in the intermetallic compounds (Fe1-xVx)3Al

Optical conductivity data of the intermetallic compounds (Fe1-xVx)3Al ( 0相似文献