Isotopic shift in angle-resolved photoemission spectra of Bi2Sr2CaCu2O8 due to quadratic electron-phonon coupling

In connection with the experiment on oxygen isotope effect of Bi₂Sr₂CaCu₂O₈ with the angle-resolved photoemission spectroscopy (ARPES), we theoretically study the isotope-induced band shift in ARPES by the Hartree-Fork and quantum Monte Carlo methods. We find that this band shift can be clarified based on a quadratically coupled electron-phonon (e-ph) model. The large ratio of band shift versus phonon energy change is connected with the softening effect of phonon, and the positive-negative sign change is due to the momentum dependence of the e-ph coupling.     

Acyclic diene metathesis (ADMET) of vinylsilanes over Re2O7–Al2O3 catalyst

Tetravinylsilane and divinylsilanes have been successfully metathesized for the first time over Re₂O₇/Al₂O₃ catalyst promoted with tetrabutyltin under mild reaction conditions. All of the products were acyclic oligomers via intermolecular metathesis; the cyclic products via intramolecular metathesis were not formed.     

Diluent effects on molecular motions and glass transition in polymers. I. Polystyrene–toluene

The effects of diluent on molecular motions and glass transition in the polystyrene–toluene system was studied by means of dielectric, thermal, and NMR measurements. Three dielectric relaxations were observed between 80 and 400°K. On the basis of NMR measurements on solutions in toluene and in deuterated toluene, relaxation processes were assigned to segmental motions of polystyrene, rotations of toluene, and the local motions of polystyrene and toluene in order of appearance from the high-temperature side. The concentration dependence of the relaxation strength and of the activation energy for the primary relaxation (that at the highest temperature) show a step increment at about 50% by weight. The activation plots for the primary process were expressed by the Vogel–Tamman equation. With this equation, the temperatures at which the mean dielectric relaxation time becomes 100 sec is determined. This agrees well with the glass-transition temperature T_g and hence T_g in concentrated solution is expressed by in terms of the parameters A, B, and T₀ of the Vogel–Tamman equation. The values of A and B are, respectively, about 12 and 0.65 and independent of the concentration. The physical meaning of these parameters is discussed.     

Fabrication of Optical Components and Modules Using Photo-fabrication Technique

We describe optical components and optical modules using a photofabrication technique to demonstrate applicability of the technique for optical purposes. A thick plate and a prism were fabricated to study fabric characteristics. Examples of optical modules implemented by the photofabrication technique are a beam expander and an interferometer baseplate.     

Luminescence spectrum from hexagonal YMnO3

Luminescence spectrum and its temperature dependence have been investigated for hexagonal YMnO₃ crystal which is ferroelectric below T_C=914 K and becomes simultaneously antiferromagnetic below T_N=74 K. The luminescence spectrum is as broad as two-magnon Raman scattering spectrum. The luminescence intensity is comparable to the latter at room temperature and it increases rapidly as the temperature decreases. These characteristics are discussed based upon other optical responses and theoretical results.     

Effects of diluent on molecular motion and glass transitions in polymers. II. The system polyvinylchloride–tetrahydrofuran

Dielectric measurements, differential thermal analyses, and density measurements are reported on concentrated solutions of polyvinylchloride in tetrahydrofuran. The relaxation processes observed between 80 and 400°K have been classified into four types. From the analysis of experimental data, the primary process at the highest temperature and the process at the lowest temperature are assigned, respectively, to segmental motion of the polymer and motion of the solvent. Activation plots for the primary process conform to the Vogel–Tamman equation. The dielectric glass-transition temperature T'_g (defined as the temperature at which the dielectric relaxation time is 100 sec) determined with this equation agrees well with the glass-transition temperature T_g from thermal analysis. Therefore, T_g can be represented by an expression of the form The parameters of the Vogel–Tamman equation A and B are nearly independent of concentration, whereas T_o depends strongly on concentration. The dipole moment per monomeric unit calculated from the experimental data changes with concentration and exhibits steep increments around 30% and 90% by weight. The width of the distribution of the relaxation time also increases with the concentration. The results were compared with those for the system polystyrene–toluene studies in the same way.     

Studies on the syntheses of heterocyclic and natural compounds. Part 939: An efficient and stereoselective synthesis of des-a-ring steroids—potential intermediates to estradiol,cortisone and progesterone

A stereoselective synthesis of des-A-ring steroids $\text{9}$ and $\text{17}$ has been achieved by an intramolecular cycloaddition of 3-isopropenyl-5-(4-methoxybenzocyclobutenyl) pentan-2-one-2-ethylene ketal $\text{7}$ and 1-(4-methoxy-benzocyclobutenyl)-4-methylpent-4-en-3-ol $\text{16}$, respectively.     

Simultaneous determination of 14 lanthanides and yttrium in rare earth ores by inductively-coupled plasma atomic emission spectrometry

A method is described for simultaneous determination of 14 lanthanides and yttrium in monazites and xenotimes by inductively-coupled plasma atomic emission spectrometry. The ore samples were decomposed by heating with nitric acid/perchloric acid or hydrofluoric/nitric/perchloric acids, or sulfuric acid, or by fusion with sodium carbonate. Among these methods, treatment of the samples with sulfuric acid, by evaporation to dryness followed by dissolution of the residue with hydrochloric acid is recommended; it provided complete decomposition for the five monazites and xenotimes examined. The accuracy and precision of the results were significantly influenced by spectral interferences of the rare earth elements themselves; correction methods and factors are given. The chondrite-normalized rare-earth patterns were examined to characterize the monazite and xenotime samples.     

Synthesis and thermal properties of poly(cycloalkyl methacrylate)s bearing bridged- and fused-ring structures

Radical polymerizations of some cycloalkyl methacrylates bearing bridged- and fused-ring structures, i.e., bornyl methacrylate (BoMA), isobornyl methacrylate (IBoMA), 2-decahydronaphthyl methacrylate (DNMA), and 3-tetracyclo [4.4.0^2,5.1^7,10] dodecyl methacrylate (TCDMA), were carried out. The radical polymerization reactivities of these monomers depended on the structure of the cycloalkyl ester groups in the following order: TCDMA > BoMA > DNMA > CHMA > IBoMA > MMA, where CHMA and MMA are cyclohexyl and methyl methacrylates, respectively. The propagation and termination rate constants of these monomers were evaluated from the polymer radical concentration determined by electron spin resonance spectroscopy. The solubilities and microstructures of the resulting polymers were examined. Thermal properties, i.e., glass transition temperatures and decomposition behaviors, of the polymers were also investigated and related to the structures of the polymer side chain. © 1993 John Wiley & Sons, Inc.