X-ray photoelectron diffraction (XPED) patterns from: III-V compound mixed crystals (Ga1-xAlxAs AND GaAs1-yPy). Comparison of experiment and single scattering calculations

X-ray photoelectron diffraction (XPED) measurements, together with single scattering calculations, were made for two III—V group compound semiconductor mixed crystals (Ga_1-xAl_xAs(110) and GaAs_1-yP_y(001)). Each pair of photoelectrons excited at equivalent atomic sites in the crystal (Ga 3d and Al 2p in Ga₁-xAl_xAs, and As 3d and P 2p in GaAs₁-yP_y) showed essentially the same XPED patterns. Single scattering calculations reproduced the observed XPED patterns fairly well. An obvious site dependence of XPED patterns was observed in both the experimental and calculated results. These results clearly show that, for a given kinetic energy, XPED patterns mainly depend on the site of emitter atoms in the crystal, not on the species of emitter atoms. Thus, XPED measurements can be used for crystal site determinations in a fingerprint manner.     

Precise control of dry etching for nanometer scale air-hole arrays in two-dimensional GaAs/AlGaAs photonic crystal slabs

Precise control of highly anisotropic reactive-ion-beam-etching (RIBE) for GaAs/AlGaAs-based two-dimensional photonic crystals (2DPCs) is investigated in terms of the substrate temperature, T_s, ion accelerating voltage, V_i, and Cl₂ gas pressure, p. T_s is shown to influence the shape of the sidewall, while the balance of the physical etching dominated by the value of V_i and the chemical etching dominated by the value of p is essential for keeping smooth and vertical sidewalls of 100-nm-scale air-holes. 2DPC air-hole patterns are defined by an electron beam (EB) lithography machine and air-holes are dry-etched with the EB resist as an etching mask. The optimized balance between the V_i and p for 0.5-1.0-μm-deep air-holes results in the high-rate-etching regime given at V_i = 500 V and p = 8 × 10⁻⁴ Torr using a 650-nm-thick resist mask, while the optimized balance for 50-nm-scale fine air-holes results in the low-rate-etching regime given at V_i = 330 V and p = 5 × 10⁻⁴ Torr using a 350-nm-thick resist mask. In particular, the latter condition is essential for fabricating topology-optimized 2DPC air-hole arrays with the minimum air-hole-size of 50 nm or less. These process conditions definitely contribute to excellent measured transmission spectra in good agreement with the calculated one in a near-infrared range.     

Ineffective OH Pinning of the Flipping Dynamics of a Spherical Guest within a Tight‐Fitting Tube

A supramolecular/synthetic method has been devised to affix a sterically hindered substituent onto a fullerene guest encapsulated in a tubular host. A two‐wheeled complex of (C₅₉N)‐(C₅₉N) with a tubular host was oxidatively bisected to afford a C₅₉N⁺ cation captured in the tube. The C₅₉N⁺ cation in the tube was then trapped by ethanol or water, which led to an oxy substituent pinned on the guest. The guest motions within the tube were modulated by the pinned substituent, and up‐and‐down flipping motions were halted by an ethoxy substituent. A hydroxy substituent, however, was ineffective in halting the flipping motions, despite the tight‐fitting relationship between the tubular host and the spherical guest. Theoretical calculations of the dynamics revealed that the flipping motions were assisted by OH‐π hydrogen bonds between the guest and the carbon‐rich wall and that sliding motions of the OH group were also facilitated by deformations of the tube.     

Synthetic Approach Toward Antibiotic Tunicamycins - VII Synthesis of Tunicamine and Tunicaminyl Uracil Derivative

A higher carbon carbohydrate moiety of antibiotic tunica-mycins named tunicamine has been synthesized in a protected form. The key reaction step of the synthesis is a potassium fluoride catalyzed Henry reaction of a 5-nitroribose derivative and a dial do-galactosamine derivative. The tunicamine derivative has been converted to a tunicaminyl uracil derivative by condenation with bis(trimethylsilyl) uracil.     

ALKOXYL AND METHYL RADICAL FORMATION DURING CLEAVAGE OF TERT-BUTVL HYDROPEROXIDE IN THE PRESENCE OF WLYSAGCHARIBES

Abstract

The cleavage of fed' -butyI hydrspersxlde by ferrous ions at pH 4 8 yrerdea two distinctive radlcals, alkoxyl and methyl radicals, detected by the electron spin resonance (ESW) technieue with the sF;n trap 5 5-dimethyl-? pyrrslsne-N-oxide (DMPOO) Free radicail formation was found to be dependent span the ferrous ran concentration Usrng drfferent BMPB concentrations, it was proved that aBkoxy l radtcais were formed intinally polysaccharzdes (PS), such a s giucomannan, lscust bean gum, xanthan, and carrageenan, retarded free radical formation, but no similar effect was obsermd far chztosan It is csnciuded that the suppressing effect is caused by the tron blndlng abrlnty of each PS.     

Oxidation of 4-Oxo-4H-1-Benzopyran-3-Carboxaldehydes with N-Bromosuccinimide

4-Oxo-4-H-1-benzopyran-3-carboxylic acids and their derivatives (esters and amides), 2, are known to possess interesting pharmacological activities.¹ As part of our synthetic studies of biologically active compounds, we needed to prepare a variety of 2 (carboxylic acids, esters, amides, etc.). An elegant method for the preparation of 4-oxo-4H-1-benzopyran-3-carboxaldehydes, 1, was reported independently by Nohara et al. ² and Harnish.³ However, despite a rather extensive effort by Nohara et al., the oxidation of 1 to 2 (Y=OH) has not been realized in good yield; thus the yields by Jones oxidation, the best reported method, ranged only from 9.5 to 39%.⁴     

Degradation of EPDM seal used for water supplying system

Degradation of ethylene-propylene-diene (EPDM) rubber seal used for supplying water system was investigated through spectroscopic techniques. The EPDM seal was utilized at 20-45 °C for about 3 years. It was characterized by solid state nuclear magnetic resonance spectroscopy equipped with field gradient fast magic angle spinning probe and Fourier transform-infrared spectroscopy. Morphology of the EPDM seal was observed by scanning electron microscopy, focused ion beam scanning electron microscopy and electron probe micro-analysis. The hardness and crosslink density of EPDM seal were reduced by a factor of one-half after using for supplying water system, even though it contains little amount of carbon-carbon double bond. Surface of the EPDM seal was significantly damaged by water. The degradation of EPDM seal was associated with chain scission and oxidation of EPDM.     

Synthesis and characterization of a cyclotriveratrylene-capped azaphosphatrane

A cyclotriveratrylene (CTV)-capped azaphosphatrane 4, which contains an endohedral proton within the cavity of the azaphosphatrane, was synthesized in high yield and then characterized. The endohedral proton of 4 was highly sheltered from strongly basic conditions by the CTV-capped structure.     

Geometrothermodynamics for black holes and de Sitter space

A general method to extract thermodynamic quantities from solutions of the Einstein equation is developed. In 1994, Wald established that the entropy of a black hole could be identified as a Noether charge associated with a Killing vector of a global space-time (pseudo-Riemann) manifold. We reconstruct Wald’s method using geometrical language, e.g., via differential forms defined on the local space-time (Minkowski) manifold. Concurrently, the abstract thermodynamics are also reconstructed using geometrical terminology, which is parallel to general relativity. The correspondence between the thermodynamics and general relativity can be seen clearly by comparing the two expressions. This comparison requires a modification of Wald’s method. The new method is applied to Schwarzschild, Kerr, and Kerr–Newman black holes and de Sitter space. The results are consistent with previous results obtained using various independent methods. This strongly supports the validity of the area theorem for black holes.