Core-level X-ray photoemission spectral shift through the successive phase transitions in layered TlInS2

Temperature-dependent change in core-level electronic structures of the layered semiconductor-ferroelectric TlInS₂ with incommensurate phase has been investigated by means of X-ray photoemission spectroscopy. The temperature dependence of the relative peak position for each core level (Tl 4f, In 3d and S 2p) is found to differ very much in the regions bordering each other at the normal-incommensurate phase transition point of 218 K. The obtained data suggest that the charge distribution in TlInS₂ dramatically changes upon passing from the normal phase (T > 218 K) to the spatially modulated incommensurate phase (T < 218 K).     

Architecture of nanostructured polymers by segregated domain crosslinking of block‐graft copolymer micelles

Polystyrene‐block‐polyisoprene (PS‐block‐PI; high 3,4‐structure) diblock copolymer was prepared by living anionic polymerization. For transfer into a reactive intermediate, the hydroxylation of the double bonds of PI block was achieved by hydroboration, followed by oxidation. Esterification of the hydroxy‐derivative with stearoyl chloride or decanoyl chloride resulted in block‐graft copolymers composed of PS (flexible chain)‐grafted long alkane (stretched chains). After partial chloromethylation of PS block copolymer, photofunctional N,N‐diethyldithiocarbamate (DC) groups were introduced into such pendant sites by reaction with the corresponding sodium salt. We studied the self‐assemblies of photofunctional block‐graft copolymers in a selective solvent, such as heptane, and constructed nanostructured polymers by crosslinking PS cores under UV irradiation. © 2001 Society of Chemical Industry     

Cortical speech processing mechanisms while vocalizing visually presented languages

To elucidate cortical processing during vocalization, we used positron emission tomography to measure regional cerebral blood flow during vocalization in six Japanese subjects. During reading Japanese sentences used daily or short syllables aloud, the visual cortices, the left Heschl's gyrus, Broca's area, the primary motor area of the articulatory organs, the supplementary motor area and the cerebellum were significantly activated, compared with resting conditions. The superior temporal gyri were rarely activated. Significant activation of the cerebellum was observed by comparing cortical activity during reading sentences used daily with that during reading meaningless short syllables. These results suggest that vocalization of familiar materials is taken over by the cerebellum, rather than cortical speech areas, and without engagement of the superior temporal gyri.     

Damping enhancement of multimachine power system using adaptive generator control system with neural networks

The authors proposed a nonlinear adaptive generator control system with neutral networks for improving damping of power systems, and showed its effectiveness in a one-machine infinite bus test power system in a previous paper. The proposed neurocontrol system adaptively generates appropriate supplementary control signals to the conventional controllers such as the automatic voltage regulator and speed governor so as to enhance transient stability and damping of the power system. In this paper, the applicability of the proposed neurocontrol system to multimachine power systems is discussed. Digital time simulations are carried out for a 4-machine test power system, where one or several synchronous generators is equipped with the neurocontrol system. As a result, also in the multimachine power system, the proposed adaptive neurocontrol systems improve the system damping effectively and they work adaptively against the wide changes of the operating conditions and the network configuration.     

Diffusion of nonstoichiometric defects in n-GaP crystals

Diffusion of nonstoichiometry-related point defects from a LEC-grown GaP substrate to a Te-doped GaP n-type epitaxial layer was investigated by means of photocapacitance. It was revealed that deep donor level at E_C−2.1 eV was introduced into GaP substrate with annealing under phosphorus vapor pressure. Thus, the 2.1 eV deep level is thought to be involved with excess P atoms such as interstitial phosphorus atoms. In Te-doped crystal, 2.1 eV level was detected and the density increased as the time of substrate annealing increased. By measuring PHCAP spectra of samples with different thickness of epitaxial layer, diffusion profile of the defects from the substrate interface was obtained. From this, the diffusion coefficient at 850°C is estimated to be 8×10^–11 cm²/s.     

1. Factors Influencing the Reaction Selectivity between Carbohydrate and Lignin Model Compounds

A cellulose model compound, methyl β-D-glucopyranoside (MGP), was subjected to oxygen-alkali treatment in the presence of various kinds of lignin model compounds. Only in the presence of a lignin model compound reactive with oxygen, a significant degradation of MGP was observed and the rate and the extent of its degradation were strongly dependent on the structure and the amount of a lignin model compound. Depression of MGP degradation was found to be achieved by two clearly distinguished mechanisms. One is an enhancement of the degradation of a lignin model compound without the acceleration of MGP degradation and the other is a depression of MGP degradation without significantly deteriorating the degradation of a lignin model compound. An increase in oxygen pressure and a 10% methanol addition belonged to the former case and a change in the ratio of metal ions and a 1% methanol addition belonged to the latter case. The addition of magnesium sometimes resulted in the acceleration of MGP degradation, depending on its ratio to iron.     

Thermal neutron detection with Ce doped LiCaAlF6 single crystals

Cerium-doped LiCaAlF₆ (Ce:LiCAF) crystals have been studied as scintillators in application to thermal neutron detection. Three crystals: high-doping Ce:LiCAF, low-doping Ce:LiCAF with 50% enrichment of ⁶Li (both 10 mm×10 mm×2 mm, rectangular) and high-doping Ce:LiCAF with 95% enrichment of ⁶Li (Ø50.8 mm×2 mm, discus) coupled to Photonis XP5300B PMT, were tested. The response of these crystals to neutrons emitted from a paraffin moderated ²³⁸PuBe source has been investigated. Thermal neutron peaks have been found at a Gamma Equivalent Energy (GEE) of ∼2.5 MeV for high-doping Ce:LiCAF (50% ⁶Li), ∼2 MeV for low-doping Ce:LiCAF (50% ⁶Li) and ∼1.9 MeV for high-doping Ce:LiCAF (95% ⁶Li). The light output of Ce:LiCAF was also measured (175-250 phe/MeV from sample to sample). Lithium-6 glass GS20 from Saint Gobain was used as a reference scintillator (Ø50 mm×2 mm, circle). Relative neutron efficiency, normalized to that of GS20 lithium glass, as well as gamma-neutron intrinsic efficiency for all tested samples was calculated. Intrinsic efficiency on thermal neutron detection for small Ce:LiCAF samples was estimated at about 32-35% of that of GS20 and for large Ce:LiCAF sample as about 82% of that of GS20.