An X-ray diffraction study of the amorphous structure of chemically vapor-deposited silicon nitride

X-ray diffraction measurements have been carried out for two kinds of samples of CVD-amorphous silicon nitride with different values of the density. From radial distribution analysis, it became clear that the short range structure in these samples resembles that of the crystalline β-phase. Coloring in CVD-amorphous Si₃N₄ was found to be induced by X-ray irradiation. Based on the deficient numbers of the first nearest neighbours in SiN bondings, it was proposed that CVD-amorphous Si₃N₄ consists of small clusters including vacancies in their matrix.     

Photoluminescence and photoluminescence excitation of AlGaAs/GaAs quantum wells with growth-interrupted heterointerfaces grown by molecular beam epitaxy

We have measured the photoluminescence (PL) and PL excitation (PLE) of AlGaAs/GaAs single quantum wells with growth-interrupted heterointerfaces. PLE shows the small Stokes shifts of less than 1 meV indicating the extremely flat heterointerfaces without microroughness. Photoluminescence spectra show four peaks originating from different monolayer terraces. These peaks exhibit a doublet splitting. We assigned this doublet to free excitons and excitons bound to neutral donors from the strong well width dependence of doublet splitting.     

Potassium hydrogen trans‐glutaconate monohydrate at 295, 245 and 40 K,and its rubidium analogue at 298 K

A centrosymmetric and short O—H?O hydrogen bond was found in isomorphic crystals of potassium hydrogen trans‐glutaconate monohydrate (potassium hydrogen trans‐pent‐2‐ene‐1,5‐dioate, K⁺·C₅H₅O₄^?·H₂O), (I), and rubidium hydrogen trans‐glutaconate monohydrate (rubidium hydrogen trans‐pent‐2‐ene‐1,5‐dioate, Rb⁺·C₅H₅O₄^?·H₂O), (II). The O?O distance at room temperature is 2.444 (3) Å in (I), and 2.417 (4) Å in (II). The O?O distance for (I) showed no significant decrease at low temperatures.     

Pressure-induced phase transformation in BaS

An X-ray diffraction study under pressure has shown that BaS, which has the NaCl type structure at ambient temperature and pressure, reversibly transforms to the CsCl type structure at 65 kbar with the volume decrease of 13.7%. This is the first pressure-induced phase transition from the NaCl to the CsCl type structure observed in alkaline-earth chalcogenides.     

Local structure of molten NaClO3 and KClO3 analyzed by pulsed neutron diffraction, Raman spectroscopy, and molecular orbital calculation

The short range structure of NaClO₃ and KClO₃ melts was investigated by time-of-flight neutron diffraction, Raman spectroscopy, and molecular orbital calculation. The structural parameters for each atomic pair were optimized in the Q-space, and the near neighbor Cl&&z.sbnd;O and O---O distances in the discrete ClO₃⁻ ion were evaluated at 0.147 nm and 0.235 nm for NaClO₃ melt, respectively, the corresponding values for KClO₃ melt being 0.149 nm and 0.239 nm. The coordination number of O around Cl was almost equal to 3. Four peaks were observed in Raman spectra of these melts, being identified as the vibrational modes typical of a ClO₃ trigonal pyramid. The arrangements of Na⁺ and K⁺ ions relative to the ClO₃⁻ ion were discussed and the optimized structure of NaClO₃ and KClO₃ melts was determined.     

Effect of three-body force on form factors

Conclusion The effect of increasing number of channels as well as the inclusion of the three-body force is very important in the charge form factor. We succeeded in getting a very good fit with the experimental result for³He. The experiment on³H is waited for. It will give important informations about the effect of the three-body force, as well as the neutron electro-magnetic form factor. A precise experiment about the first minimum of the magnetic form factor of³He is necessary.Presented at the symposium Mesons and light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

High-throughput solid-phase extraction of metal ions using an iminodiacetate chelating porous disk prepared by graft polymerization

A chelating porous sheet for use in solid-phase extraction was prepared by radiation-induced graft polymerization and subsequent chemical modifications. An epoxy-group-containing vinyl monomer was graft-polymerized onto a porous sheet made of polyethylene. The produced epoxy group of the graft chain was converted into an iminodiacetate group. The chelating porous sheet with a density of the iminodiacetate group of 2.1 mol/kg was cut into disks 13 mm in diameter to fit an empty cylindrical cartridge with a capacity of 6 mL. Breakthrough curves using the chelating-porous-disk-packed cartridge overlapped irrespective of the flow rate of the solution ranging up to 1500 mL/h because of negligible diffusional mass-transfer resistance of the copper ions to the iminodiacetate group of the graft chain.     

Radiative B meson decays into kpigamma and kpipigamma final states

We report observations of radiative B meson decays into the K+pi(-)gamma and K+pi(-)pi(+)gamma final states. In the B0-->K+pi(-)gamma channel, we present evidence for decays via an intermediate tensor meson state with a branching fraction of B(B0-->K(*)(2)(1430)(0)gamma)=[1.3+/-0.5(stat)+/-0.1(syst)]x10(-5). We measure the branching fraction B(B+-->K+pi(-)pi(+)gamma)=[2.4+/-0.5(stat) +0.4-0.2(syst)]x10(-5), in which the B+-->K(*0)pi(+)gamma and B+-->K+rho(0)gamma channels dominate. The analysis is based on a data set of 29.4 fb(-1) recorded by the Belle experiment at the KEKB collider.     

Structural Characteristic of Folding/Unfolding Intermediate of Pokeweed Anti-viral Protein Revealed by Time-resolved Fluorescence

The structural feature of unfolding intermediate of pokeweed anti-viral protein (PAP) was characterized using time-resolved fluorescence spectroscopic methods to elucidate protein folding/unfolding process. CD and fluorescence spectra consistently demonstrated that the unfolding of PAP completed at 4 M of guanidine hydrochloride (GuHCl). The fluorescence resonance energy transfer (FRET) and time-resolve fluorescence depolarization analysis of Trp208 and Trp237 located in the C-terminal domain of PAP suggested that peculiar unfolding intermediate populated before reaching to the unfolding state. The FRET distance of Trp237 to Tyr182 was extended to more than 28 Å with keeping the compact conformation in the unfolding intermediate state populated in the presence of 2 M GuHCl. On the other hand, Trp208 maintained the energy transfer pair with Tyr72 near the active site, although the rotational freedom was increased a little. There results suggest that the most distinguished structural feature of the unfolding intermediate of PAP is the separation of C-terminal domain from N-terminal domain. FRET and fluorescence depolarization studies also showed that C-terminal domain would be more separated to liberate the segmental motions of Trp208 and Trp237 distinctly at the unfolding state.     

Quantitative assessment of skeletal muscle activation using muscle functional MRI

The purpose of the present study is to determine whether muscle functional MRI (mfMRI) can be used to obtain three-dimensional (3-D) images useful for evaluating muscle activity, and if so, to measure the distribution of muscle activity within a medial gastrocnemius (MG) muscle. Seven men performed 5 sets of 10 repetitions of a calf-raise exercise with additional 15% of body-weight load. Magnetic resonance images were obtained before and immediately after the exercise. To threshold images, only those pixels showing transverse relaxation time (T2) greater than the mean+1 S.D. of the entire regions of interest (ROIs) in the preexercise image and T2 lower than the mean+1 S.D. of the entire ROIs in the postexercise image were identified. The survived pixels showing T2 are defined as active muscle. Those thresholded images were 3-D reconstructed, and this was used to determine area of active muscle along transverse, longitudinal and vertical axes. At the exercise level used in the present study, the percentage volume of activated muscle in the MG was 62.8+/-4.5%. There was a significant correlation between percentage volume of activated muscle and integrated electromyography (r=.78, P<.05). Percentage areas of activated muscle were significantly larger in the medial than in the lateral region, in the anterior than in the posterior region and in the distal than in the proximal region (P<.05). These results suggest that mfMRI can be used to evaluate the muscle activity and to determine intramuscular variations of activity within skeletal muscle.