Negative theta-pinch experiment

Plasma temperature obtained with a negative theta-pinch experiment is somewhat lower than that with an ordinary thete-pinch. This is consistent with a numerical calculation assuming Sagdeev resistivity.     

Observation of a donor-acceptor pair recombination in the edge emission of ZnSe crystal by electro-luminescence

An injection type electro-luminescence in ZnSe crystal has been studied by using ZnSe-SnO₂ hetero-junction at 20°K. In the emission peak observed around 2·70 eV, a clear energy shift toward the higher energy side with increasing injection current density has been found at low temperatures, which could be associated with the D-A pair (donor-acceptor pair) recombination process. The energy sum of the donor and acceptor activation is estimated to be larger than 137 meV. In the higher temperature region, this emission line turns out due to the ‘free-to-bound’ recombination, and the related acceptor ionization energy is considered to be ～120 meV. By taking into consideration the energies of bound exciton emission, the exciton localization energies and the related donor and acceptor ionization energies are evaluated.     

The activity of Escherichia coli cyclopropane fatty acid synthase depends on the presence of bicarbonate

Cyclopropane fatty acid (CFA) synthases catalyze the formation of cyclopropane rings on isolated and unactivated olefinic bonds within various fatty acids; the methylene carbon is derived from the activated methyl group of (S)-adenosylmethionine. The E. coli enzyme is the prototype for this class of enzymes, which include the cyclopropane mycolic acid (CMA) synthases, which are potential targets for the design of antituberculosis agents. Crystal structures of several CMA synthases have recently been solved, and electron density attributed to a bicarbonate ion was found in or near the active site. Because a functional assay for CMA synthases has not been developed, the relevance of the bicarbonate ion has not been established. CFA synthase is 30-35% identical to the CMA synthases that have been analyzed structurally, suggesting that the mechanisms of these enzymes are conserved. In this work, we show that indeed the activity of CFA synthase requires bicarbonate, and that it is inhibited by borate, a planar trigonal molecule that mimics the structure of bicarbonate. We also show that substitutions of the conserved amino acids that act as ligands to the bicarbonate ion based on the structure of CMA synthases result in drastic losses in the activity of the protein.     

A recyclable catalyst for asymmetric transfer hydrogenation with a formic acid-triethylamine mixture in ionic liquid

A novel task-specific ionic ligand with an imidazolium salt moiety was synthesized, and its catalytic ability and recyclability for asymmetric transfer hydrogenation of acetophenone derivatives with a formic acid-triethylamine azeotropic mixture in an ionic liquid [bmim][PF6] was examined.     

Behavior of semiconductive tin oxide electrodes in molten lithium chloride+potassium chloride eutectic

In molten LiCl+KCl eutectic at 450°C, current and differential capacity were measured with the potentiodynamic method at Sb-doped polycrystalline tin oxide films prepared on Pyrex glass substrates. SnO₂ electrodes usable in high temperature melts were constructed with special care to keep a definite working area. The melt-stable and semiconductive oxide shows a stable polarizable potential region with a span of about 1 V from chlorine evolution to cathodic decomposition of the oxide. Small residual current in the polarizable region indicates a possibility to use the oxide as an indicator electrode in the melt. The interfacial capacity is assigned to the space charge capacity of the electrode side and its potential dependence is explained using the Mott-Schottky equation. A linear Mott-Schottky plot was obtained after several potential scans and the flat band potential was estimated as ?1.29 V vs. 1 M Pt-(II)/Pt. The oxide surface in contact with the melt is subject to change during scanning in order to establish a stable melt-oxide interface where the specific adsorption of Cl^? ions plays an important role for the stabilization.     

Studies of lattice dynamics in 2HTaS2 by Raman scattering

Raman spectra are presented in the high and low temperature phases of 2H-TaS₂. In the normal phase at 380 K one A_1g- and two E_2g-modes have been observed at 400, 27 and 286 cm^-1, respectively. In the charge density wave state two extra peaks appear with strong scattering intensity in E_2g- symmetry and weak in A_1g-symmetry. The E_2g peak grows and hardens toward 50 cm^-1 with decreasing temperature. The temperature dependence is very similar to the E_2g-mode in 2H-TaSe₂ of similar 3a₀ × 3a₀ superstructure. Other peaks observed in 2H-TaSe₂ in the commensurate phase are not observed. This suggests the incommensurability of the charge density wave state in 2H-TaS₂.     

Migration of excimers in pyrene crystals

Emission decay times of the new excimer were measured for undoped and perylene doped pyrene crystals. From the decay times obtained, the temperature dependence of the diffusion coefficient of the excimers was deduced by assuming a model in which two electronic states of the new excimer are involved in the energy transfer process. Within this model, it was found that in the upper excimer state the excimers migrated by a hopping process, while in the lower excimer state they migrated as free excimer excitons while undergoing phonon scattering.     

Oxygen isotope effect in optimally doped Bi2Sr2CaCu2O8+δ studied by low-energy ARPES

Using angle-resolved photoemission spectroscopy (ARPES) with low-energy tunable photons, we studied the oxygen isotope effect in optimally doped Bi₂Sr₂CaCu₂O_8+δ (Bi2212). We found the oxygen isotope shift in the real part of the electron self-energies [ReΣ(ω)s] along the nodal direction derived not only from the momentum distribution curves (MDCs) but also from the energy distribution curves (EDCs). Present results indicate straightforwardly the coupling between the nodal electrons and the phonons.