Calculated and experimental NMR chemical shifts of p-menthane-3,9-diols. A combination of molecular dynamics and quantum mechanics to determine the structure and the solvent effects

NMR chemical shifts have been experimentally measured and theoretically estimated for all the carbon atoms of (1R,3S,4S,8S)-p-menthane-3,9-diol in chloroform solution. Theoretical estimations were performed using a combination of molecular dynamics simulations and quantum mechanical calculations. Molecular dynamics simulations were used to obtain the most populated conformations of the (1R,3S:4S,8S)-p-menthane-3,9-diol as well as the distribution of the solvent molecules around it. Quantum mechanical calculations of NMR chemical shifts were performed on the most relevant conformations employing the GIAO-DFT formalism. A special emphasis was put in evaluating the effects of the surrounding solvent molecules. For this purpose, supermolecule calculations were performed on complexes constituted by the solute and n chloroform molecules, where n ranges from 3 to 16. An excellent agreement with experimental data has been obtained following this computational strategy.     

Remarkable effect of pore size on the catalytic activity of mesoporous silica for the acetalization of cyclohexanone with methanol

The catalytic activity of mesoporous silica (MCM-41) for the acetalization of cyclohexanone shows a volcano-shaped dependence on the pore diameter. The diameter of the cyclohexanone molecule is ca. 0.75 nm, while its acetalization with methanol was well accelerated on MCM-41 with a pore diameter of approximately 1.9 nm, and smaller or larger pores were not suitable for the catalysis. The catalytic activity was independent of the Al concentration.     

Selective introducing of aryl and amino groups: reaction of benzanthrone and organometallic reagents

The reaction of benzanthrone and aryl magnesium bromides produced 6-aryl-substituted benzanthrones in moderate to good yields. Similarly, 6-alkylaminobenzanthrones were selectively prepared by the reaction of benzanthrone and lithium alkylamides. In contrast, for the lithium arylamides, the arylamino groups were selectively introduced at the 4-position of the benzanthrone.     

Current transport property in GdBCO coated conductor with artificial pinning centers in a wide range of temperature,magnetic field up to 27 T,and field angle

We have investigated current transport property in Gd₁Ba₂Cu₃O_7−δ coated conductor with artificial pinning centers in a wide range of temperature, magnetic field, B up to 27 T, and field angle. Due to the additional c-axis correlated pins, critical current density, J_c in B//c was enhanced and the improvement was observed in wide range of B. On the other hand, around B⊥c below 65 K, the angular dependence of n-value showed a valley-like behavior, although the J_c was increasing. In addition, the temperature dependence of the pinning force density defined as J_c × B was not scaled on an expected master curve. These results indicate the pinning in B⊥c is governed by different mechanism below 65 K and high magnetic field.     

First observation of o-Ps to p-Ps transition and first direct measurement of positronium hyperfine splitting with sub-THz light

Positronium is an ideal system for the research of the bound state QED. The hyperfine splitting of positronium (Ps-HFS, about 203 GHz) is an important observable but all previous measurements of Ps-HFS had been measured indirectly using Zeeman splitting. There might be the unknown systematic errors on the uniformity of magnetic field. We are trying to measure Ps-HFS directly using sub-THz radiation. We developed an optical system to accumulate high power (about 10 kW) radiation in a Fabry-Pérot resonant cavity and observed the positronium hyperfine transition for the first time.     

Highly selective pumping of an excited state by Doppler-free multiphoton absorption

It is shown that the Doppler-free three or higher order multiphoton absorption be used for the efficient and highly selective pumping, if the light intensity and frequency are adequately chosen.     

Raman and luminescence processes under the resonant two-photon excitation of an excitonic molecule in CuCl

Emission spectra and its decay time under the resonant two-photon excitation of an excitonic molecule in CuCl were observed using a tunable dye laser. The Raman and luminescence processes were separated from their different decay times. The ratios of these two processes were estimated for the transverse and longitudinal excitons, respectively, at various band widths of the exciting laser.     

Microfabrication techniques used in Japan for VLSI and other devices

Lead films of thickness 100 Å, 250 Å. and 350 Å were vacuum deposited on AI and laser treated in air using single pulses (7 ns FWHM) from a Nd: glass laser operating in TEM₀₀ mode, at peak energy densities of 1.5-5.0 J/cm². Rutherford back-scattering of 1.8 MeV He⁺ ions was employed to determine the depth profiles of Pb in Al. Up to about 1.4 J/cm², we observe only evaporation loss of Pb and formation of Pb-rich cells on the surface. At higher energies, liquid phase diffusion of Pb is observed up to 4 J/cm², beyond which convection effects are seen. A quantitative analysis of data for 350 Å film at 3.0 J/cm² shows evidence of nonequilibrium segregation effects.