Visible fluorescence spectroscopy of single proteins at liquid-helium temperature

Fluorescence spectroscopy of single proteins at liquid-helium temperatures reveals a relation between structural dynamics and biological functions of the proteins. The technical difficulties in detecting visible fluorescence are chromatic aberration and optical background. They were overcome by a new optical design using reflective optics and employing two-photon excitation. The fluorescence spectrum of single green-fluorescent proteins taken at a temperature of 1.5 K makes a distinction between different metastable conformations that last for tens of seconds.     

Bifurcation phenomena of a magnetic island at a rational surface in a magnetic-shear control experiment

Three states of a magnetic island are observed when the magnetic shear at the rational surface is modified using inductive current associated with the neutral beam current drive in the Large Helical Device. One state is the healed magnetic island with a zero island width. The second state is the saturated magnetic island with partial flattening of the T(e) profile. The third state is characterized by the global flattening of the T(e) profile in the core region. As the plasma assumes each of the three states consecutively through a bifurcation process a clear hysteresis in the relation between the size of the magnetic island and the magnetic shear is observed.     

Microcrystalline silicon–germanium thin films prepared by the chemical transport process using hydrogen radicals

We propose microcrystalline silicon–germanium (μc-SiGe) as a bottom cell material of triple-junction solar cells in order to improve the conversion efficiency of thin film solar cells. The μc-SiGe thin films were prepared by the chemical transport process using Si and Ge targets exposed to hydrogen radicals. We successfully produced highly photosensitive μc-SiGe films with relatively low Ge composition by increasing the gas pressure, and observed the photovoltaic effect in pin solar cell structures. However, it was difficult to produce μc-SiGe films with higher Ge composition. We found that a small amount of argon introduction into the chemical transport process enables us to increase Ge composition at the high pressure. Moreover, the argon introduction seems effective to maintain the electrical properties in relatively high Ge composition. The results suggest that the μc-SiGe thin films prepared by the chemical transport process are one of the candidates for new photovoltaic materials.     

2+2] Cycloaddition reactions of ethylene derivatives with the Si(100)-2 x 1 surface: a theoretical study

Possible mechanisms of the [2+2] cycloaddition reactions of ethylene (1), propylene (2), vinyl chloride (3), and styrene (4) with the Si(100)-2 x 1 surface have been investigated by theoretical calculations with the unrestricted density functional theory (DFT) and the second-order M?ller-Plesset perturbation theory (MP2). Facile occurrence of the studied reactions is supported by the low activation energies (2.45-5.76 kcal/mol) in the rate-determining steps. The buckled Si(100) surface facilitates the reactions via the low-symmetric pathways. The reactions follow the diradical mechanism of thermal [2+2] cycloaddition reactions between pi-electron donors (the ethylene derivatives) and acceptors (the Si surface) through a pi-complex precursor and a singlet diradical intermediate. The influence of substituents on the relative reactivity takes a qualitative sequence of 1 < 2 < 3 < 4. The natural bond orbital (NBO) analysis and the released heat of some model reactions suggest that the relative reactivity might be partially understood by the pi-electron-donating abilities of the substituent to stabilize the radical centers at the transition states of the rate-determining steps.     

Constituents of holothuroidea, 14. Isolation and structure of new glucocerebroside molecular species from the sea cucumber Stichopus japonicus

Five glucocerebroside molecular species, SJC-1-SJC-5, have been isolated from the less polar lipid fraction of a chloroform/methanol extract of the sea cucumber Stichopus japonicus. The structures of these glucocerebroside molecular species were determined on the basis of chemical and spectroscopic evidence. SJC-1, SJC-2, and SJC-3 are typical sphingosine- and phytosphingosine-type glucocerebroside molecular species with nonhydroxylated and hydroxylated fatty acyl moieties. SJC-4 and SJC-5 are also sphingosine-type glucocerebroside molecular species with hydroxylated fatty acyl moieties, although they are new glucocerebroside molecular species with unique sphingosine bases.     

Self-assembly of biphenylene-bridged hybrid mesoporous solid with molecular-scale periodicity in the pore walls

A synthesis of ordered biphenylene-bridged mesoporous material with a crystal-like periodic pore wall structure is reported.     

Double Commuting Compressed Shifts and Generalized Interpolation in the Hardy Space over the Bidisk

This paper deals with an operator theory of compressed shifts on the Hardy space over the bidisk. We give commutant lifting type theorems and some interpolation theorems in two variables.     

Pseudo-capacitance on exfoliated carbon fiber in sulfuric acid electrolyte

The specific capacitance of exfoliated carbon fibers (ExCF) which were synthesized from pitch-based carbon fibers showed a strong dependence with the concentration of sulfuric acid electrolyte and reached 1.4 F/m² in 18 M H₂SO₄ solution. Since the capacitance value is quite large compared with the case of conventional activated carbons, faradic reactions (charge transfer reactions) are the cause of pseudo-capacitance. ExCF, however, gave a featureless cyclic voltammogram in 18 M H₂SO₄ solution. In the case of exfoliated natural graphite, the intercalation of H₂SO₄ molecules is evidenced by redox peaks observed in the voltammograms in the same conditions. Therefore, a strong interaction between the H₂SO₄ molecules and the ExCF surface might be the reason for the origin of pseudo-capacitance with ExCF in H₂SO₄ electrolyte. PACS 81.05.Uw; 82.45.Fk; 82.47.Uv     

Heat capacity and phase transition of a five-coordinated antiferromagnet,IODOBIS (N,N-diethyldithiocarbamato) iron (III), in the temperature range from 0.4 TO 300 K

The heat capacity of iodobis (N,N-diethyldithiocarbamato) iron (III) has been measured between 0.4 and 300 K. A phase transition from an antiferromagnetic to a paramagnetic state was found at T_N = (1.937 ± 0.010) K, and a Schottky-type anomaly arising from a zero-field single ion splitting was observed around 12 K. The total magnetic entropy and enthalpy, including the phase transition and the Schottky-type anomaly, are 11.36JK^?1mol^?1 and 134.5 J mol^?1, respectively. The entropy is approximately equal to Rln 4 ( = 11.53 JK^?1mol^?1), confirming that the spin manifold is really a quartet. The entropy and enthalpy due to the phase transition are estimated to be (5.57±0.01)JK^?1mol^?1 and (13.2±0.05)Jmol^?1, respectively. The entropy and enthalpy above t_n are quite large, as in the case of the related compound chlorobis (N,N-diethyldithiocarbamato) iron (III). This fact suggests that the present complex may be considered to have a two-dimensional type of magnetic structure from a thermodynamic point of view. A correlation diagram between the transition entropy and energy is proposed, this being a diagnostic for the determination of the magnetic dimensionality.