Temperature dependence of aluminum nitride reflectance spectra in vacuum ultraviolet region

Temperature dependence of optical reflectance spectra in vacuum ultraviolet region for aluminum nitride has been measured on high-quality single crystal with synchrotron radiation. The dominant structure due to the interband transition is observed at photon energy around 7.7 eV. With decreasing temperature, the energy position of the dominant structure in the reflectance spectra shifts towards higher energy. The experimental data has been fitted to the Bose-Einstein expression and the obtained parameter related to the strength of the electron-phonon interactions is much smaller than that for the peak at 6.2 eV, suggesting that the higher-lying interband transition energy decreases more slowly with increasing temperature in aluminum nitride (AlN).     

A Relationship Among Gentzen's Proof-Reduction,Kirby-Paris' Hydra Game and Buchholz's Hydra Game

We first note that Gentzen's proof-reduction for his consistency proof of PA can be directly interpreted as moves of Kirby-Paris' Hydra Game, which implies a direct independence proof of the game (Section 1 and Appendix). Buchholz's Hydra Game for labeled hydras is known to be much stronger than PA. However, we show that the one-dimensional version of Buchholz's Game can be exactly identified to Kirby-Paris' Game (which is two-dimensional but without labels), by a simple and natural interpretation (Section 2). Jervell proposed another type of a combinatorial game, by abstracting Gentzen's proof-reductions and showed that his game is independent of PA. We show (Section 3) that this Jervell's game is actually much stronger than PA, by showing that the critical ordinal of Jervell's game is φ_ω (0) (while that of PA or of Kirby-Paris' Game is φ₁ (0) = ?₀) in the Veblen hierarchy of ordinals.     

Total synthesis of tylosin

Tylosin has been synthesized byregio- and stereoselective introduction of the amino disaccharide moiety and D-mycinose onto the previously synthesized 16-membered-ring aglycone.     

Surface Modification of Fine Particles with a SnO<Subscript>2</Subscript> Film by Using a Polyhedral-Barrel Sputtering System

Fine particles were modified with a thin film of SnO₂ by using a barrel sputtering system that is a dry process. The conditions for the preparation of SnO₂ were studied by reactive sputtering onto a glass plate substrate. The optimal conditions for the preparation of tetragonal SnO₂ were identified as 60% partial oxygen pressure and 1.0 Pa total gas pressure with the substrate at room temperature. Under the optimized conditions, the surfaces of Al flake particles were modified with a thin film of SnO₂. XRD and SEM/EDS analysis of the prepared samples showed that the Al particle surfaces were uniformly modified by a thin film of SnO₂ in all cases. The film thicknesses were 80, 130, and 180 nm at RF outputs of 195, 350, and 490 W. These measured thicknesses coincided with the values estimated from the interference colors of the samples.     

Conformation of drawn poly(trimethylene terephthalate) studied by solid-state 13C NMR

The change in the conformation of the flexible O-CH2-CH2-CH2-O segment of poly(trimethylene terephthalate) (PTT) monofilament caused by drawing was investigated by means of the gamma-gauche effect on the 13C solid-state NMR chemical shift of the internal methylene carbon, combined with the NMR relaxations. The conformation around the O-CH2 and CH2-O bonds for as-spun fiber was trans/trans. On drawing, followed by heat treatment, the conformation changed to gauche/gauche. The ratio of gauche/gauche to trans/trans for the drawn PTT fiber was determined quantitatively.     

Dielectric relaxation in the paracrystalline phase in polyacrylonitrile

Thermal expansion and dielectric relaxation of polyacrylonitrile were measured in the temperature range from ?75 to 152°C. at frequencies from 30 cps to 3 Mc./sec. The thermal expansion curve and the temperature dependence of logarithmic relaxation time both show an inflection at 85°C. An x-ray study by Bohn reveals that this inflection comes from the thermal expansion of the paracrystalline phase of this polymer, and consequently the transition at 85°C. and the associated relaxation are ascribed to molecular motion in the paracrystalline phase. The relaxation strength increases with increasing temperature above this point. The transition is caused by freezing of the bending vibration of chains whereas the relaxation results from rotational vibration. The length of segments in this phase is roughly estimated to be ca. 100 A. by comparing the observed relaxation strength with the theory developed on the basis of the above considerations.     

Correlation between the structure of water in the vicinity of carboxybetaine polymers and their blood-compatibility

The structure and hydrogen bonding of water in the vicinity of carboxybetaine homopolymer (poly[1-carboxy-N,N-dimethyl-N-(2'-methacryloyloxyethyl)methanaminium inner salt] (PolyCMB), and a random copolymer of CMB and n-butyl methacrylate, Poly(CMB-r-BMA), with various molecular weights were analyzed in their aqueous solutions and thin film with contours of O-H stretching of Raman and attenuated total reflection infrared (ATR-IR) spectra, respectively. The relative intensity of the collective band (C value) corresponding to a long-range coupling of O-H stretchings of the Raman spectra for aqueous solution of Poly(CMB-r-BMA) was very close to that for pure water, which is in contrast with the smaller C value in aqueous solution of ordinary polyelectrolytes. The number of hydrogen bonds collapsed by the presence of one monomer residue (N(corr) value) of PolyCMB and Poly(CMB-r-BMA) (CMB, 45 mol %) (M(w), 1.14 x 10(4) and 1.78 x 10(4), respectively) could be calculated from the C value. The N(corr) values were much smaller than those for ordinary polyelectrolytes and close to those for nonionic water-soluble polymers such as poly(ethylene glycol) and poly(N-vinylpyrrolidone). Furthermore, a water-insoluble Poly(CMB-r-BMA) with a large BMA content (M(w) = 347 kD, CMB 27 mol %) could be cast as a thin film (thickness, ca. 10 microm) on a ZnSe crystal for the ATR-IR analyses. At an early stage of sorption of water into the Poly(CMB-r-BMA) film, the O-H stretching band of IR spectra for the water incorporated in the film was similar to that for free water, which is in contrast with the drastic change in the O-H stretching band of water incorporated in polymer films such as poly(methyl methacrylate) (PMMA) and poly(n-butyl methacrylate) (PBMA). The theoretical vibrational frequency for water molecules hydrating a betaine molecule calculated by using a density functional method supported the experimental results. The adhesion of human platelets to Poly(CMB-r-BMA) films was much less than that to PMMA and PBMA. With an increase in the content of CMB residue, the number of platelets adhered to the Poly(CMB-r-BMA) film drastically decreased and then gradually increased, probably due to the increase in the roughness of the film surface. These results suggest that the carboxybetaine monomer residues with a zwitterionic structure do not significantly disturb the hydrogen bonding between water molecules in both aqueous solution and thin film systems, resulting in the excellent blood-compatibility of the carboxybetaine polymers.     

GaCl(3)-catalyzed ortho-ethynylation of phenols

Phenols are ethynylated at the ortho position with silylated chloroethyne in the presence of a catalytic amount of GaCl3 and lithium phenoxide. The lithium salt is essential for the catalysis, and addition of 2,6-di(tert-butyl)-4-methylpyridine inhibits desilylation and hydration of the products. The reaction can be applied to various substituted phenols giving the ortho-ethynylated products in high yields, and the turnover numbers based on GaCl3 are between 8 and 10. The reaction mechanism involves addition of in situ formed phenoxygallium to the haloethyne followed by the elimination of GaCl3.     

Effect of encaged aromatic guests on the shape and connectivity of molecular cavity in crystalline polystyrene evaluated by molecular simulations

The delta form of crystalline syndiotactic polystyrene is a clathrate molecular compound in which various aromatic molecules are encaged. We have investigated the size, shape, and connectivity of the molecular cavity in the crystal using a molecular dynamics simulation. The effects of the guest species on the cavity structure were investigated in detail. In order to systematically vary the guest structure, various aromatic guests, e.g., benzene, toluene, p-xylene, m-xylene, o and mesitylene were examined. The interstitial spaces between the guests and the polymer chains were analyzed by cluster analysis of the free volumes. The individual cavity volumes into which the guests are clathrated were also evaluated. It was found that the guest molecules can greatly affect not only the cavity size and shape but also the connectivity of the cavities. The transport of small molecules in the crystal is discussed in connection with the cavity structure.