Achievement of a 920-MHz high resolution NMR

We have developed a 920-MHz NMR system and performed the proton NMR measurement of H(2)O and ethylbenzene using the superconducting magnet operating at 21.6 T (920 MHz for proton), which is the highest field produced by a superconducting NMR magnet in the persistent mode. From the NMR measurements, it is verified that both homogeneity and stability of the magnet have a specification sufficient for a high resolution NMR.     

LET distributions from CR-39 plates on Space Shuttle missions STS-84 and STS-91 and a comparison of the results of the CR-39 plates with those of RRMD-II and RRMD-III telescopes

The LET distributions during the Space Shuttle missions STS-84 (altitude 270-412 km, average 375 km; inclination angle, 51.6 degrees) and STS-91 (altitude 328-397 km, average 373 km; inclination angle, 51.6 degrees) were measured using CR-39 plastic nuclear track detectors. A correction for the dip-angle dependence of the track-formation sensitivity of the CR-39 plates was applied to the data analysis. The absorbed doses and the dose equivalents around RRMD Detector Units, estimated from the LET distributions in the LET region of 4-200 keV/micrometers, fluctuated with standard deviations of +/- 21% to +/- 35% in both flight experiments. The LET distributions obtained from the CR-39 plates agreed well with that obtained from RRMD-II in STS-91. However, the particle fluxes obtained from RRMD-III in STS-84 and STS-91 were two or three times higher than those obtained from RRMD-II and the CR-39 plates. It was concluded that the LET distributions obtained from RRMD-II and the CR-39 plates in the present flight experiments did not include the contribution of target-fragmented secondary heavy particles produced by low-LET particles, such as relativistic or semi-relativistic protons and helium ions, whereas RRMD-III was able to detect these secondary particles because of its low triggering level.     

Phosphane Sulfide/Octacarbonyldicobalt-Catalyzed Pauson - Khand Reaction Under an Atmospheric Pressure of Carbon Monoxide

Convenient access to cyclopentenones is provided by catalytic intra- and intermolecular Pauson - Khand reactions in the presence of octacarbonyldicobalt and tributylphosphane sulfide (see scheme). In contrast to other reactions of this type, they proceed under mild conditions (70 degrees C, 1 atm CO), and commercially available [Co(2)(CO)(8)] can be used without further purification.     

Excitation of Intra-4f Shell Luminescence of Rare Earth Ions (Er3+ and Yb3+) by the Energy Transfer from Si Nanocrystals

Photoluminescence (PL) properties of SiO₂ films containing Si nanocrystals (nc-Si) and Er³⁺ (Yb³⁺) were studied. PL peaks attributable to the recombination of electron–hole pairs in nc-Si (1.5eV) and the intra-4f shell transition of Er³⁺ (0.81eV) (Yb³⁺ (1.26eV)) were observed simultaneously at room temperature. Correlation of the two peaks was studied as a function of nanocrystalline size. It was found that the intensity of the Er³⁺-related (Yb³⁺-related) peak increases drastically as the size of nc-Si decreases. Temperature dependence of PL spectra was studied. In the case of Yb-doped samples, temperature quenching of the PL became small as the size decreased, while in the case of Er-doped samples, no remarkable temperature dependence was observed. Two major features of the quantum size effects of nc-Si, i.e., the band-gap widening and the increase in the PL efficiency with decreasing the size, are thought to contribute to the improvement of room temperature PL efficiency of Er³⁺ (Yb³⁺).     

Glow discharge cleaning of vacuum switch tubes

To clean the surfaces of parts inside a vacuum-switch tube (VST) the authors propose a technique which generates a glow discharge between the inner electrodes and the copper grid surrounding it. Photographic observation reveals that the glow discharge spreads out and cleans the whole surface inside the VST. A breakdown test between the inner electrodes shows the effect of the cleaning with this technique. Higher breakdown voltage between the inner electrodes is attained by performing this glow discharge cleaning in argon rather than hydrogen gas. The difference of the cleaning effect seems to be attributed to that of the energy transfer from ion species to the adsorbed molecules and microprotrusions on the surfaces     

Synthesis of novel liquid crystals having the perfluoropyrrolidino group

Novel liquid crystals which have the perfluoropyrrolidino group, a heterocyclic perfluoroalkyl group, and which show smectic phases have been synthesized with perfluoro-(2-pyrrolidinopropionyl fluoride) as one of the starting materials. Analogues with a polymerizable functional group also have been prepared and polymerized to give side chain liquid crystal polymers.     

Laser cooling of a single Ca+ ion: Observation of quantum jumps

This paper describes trapping and laser cooling of a Ca⁺ ion in an rf quadrupole ion trap. A single Ca⁺ ion is laser cooled to below 130 mK and quantum jumps are observed by exciting the ion into the metastable D _5/2 state via the P _3/2 state. The lifetime of the metastable D _5/2 state is estimated from the distribution of the dark periods of the quantum-jump signal. Collision-induced jumps between the metastable D _3/2 state and the D _5/2 state in a background gas are also directly observed.     

Carbon-13 NMR studies of the biologically active nor-diterpenoid dilactones from Podocarpus plants

Carbon-13 NMR signals of the biologically active norditerpenoid dilactones from Podocarpus plants were fully assigned by using selective ¹H decoupling, coupling constants (²J_CH), spin-lattice relaxation times (T₁) and correlation of the spectra of more than thirty dilactone congeners. The spectra of five nagilactones, B, C, D, E and F, which constitute representative members of three major structural types of the dilactones: (A) 8:14, 9:11-dienolide (α-pyrone) type, (B) 7α:8α-epoxy-9:11-enolide type, and (C) 7:8,9:11-dienolide type, were extensively analysed. Some characteristic steric interactions for the substituents on the ring system can be demonstrated from the spectral properties.