Distribution of carbon contamination in MgAl2O4 spinel occurring during spark-plasma-sintering (SPS) processing: I – Effect of heating rate and post-annealing

Carbon contamination from the carbon paper/dies during spark-plasma-sintering (SPS) processing was examined in the MgAl₂O₄ spinel. The carbon contamination sensitively changes with the heating rate during the SPS processing. At the high heating rate of 100 °C/min, the carbon contamination having organized structures occurred over almost the entire area from the surface to deep inside the SPSed spinel disk. In contrast, at the slow heating rate of 10 °C/min, the carbon contamination having disordered structures occurred only around the surface area. The carbon phases transform into high pressure CO/CO₂ gases by post-annealing in air and lead to pore formation along the grain junctions. The pore formation significantly occurs at the high heating rate due to the large amount of the contaminant carbon phases. This suggests that if once the carbon contamination was formed in the materials, it is very difficult to remove the carbon phases from the materials.     

Electron transport in InGaO3(ZnO)m (m=integer) studied using single-crystalline thin films and transparent MISFETs

We have investigated the characteristics of transparent metal-insulator-semiconductor field-effect transistors (MISFETs) fabricated using InGaO₃(ZnO)_m (m=integer) single-crystalline thin films as n-channel layers and amorphous alumina as gate insulator films. The MISFETs exhibit good characteristics such as insensitivity to visible light illumination, off-current as low as ∼1 nA with a positive threshold voltage of ∼3 V and on/off current ratio of 10⁵. The field-effect mobility increased from ∼1 to ∼10 cm² (V s)⁻¹ as the m-value increased. Room temperature Hall mobility also increased. However, unexpectedly these values were lower than the field-effect mobility. It is explained by existence of shallow localized state in the homologous compounds.     

A scheme of picosecond pulse shaping using gain saturationcharacteristics of semiconductor laser amplifiers

To obtain high power, well shaped picosecond pulses from gain-switched semiconductor lasers, the use of dynamic gain saturation characteristics of semiconductor laser amplifiers was investigated theoretically and experimentally. A configuration of a reflected-wave amplifier (RWA) with single-side external coupling is introduced for pulse shaping, which is found to be suitable for enhancing dynamic gain saturation. By a combination of a distributed feedback laser oscillator at 1.3 μm in wavelength and a reflected-wave amplifier of 400 μm cavity length with asymmetric facet reflectivities of 0.01% and 30%, single-mode optical pulses with almost no tailing, full width at half maximum of 15 ps, and peak power exceeding 50 mW were obtained without pulse broadening, despite the considerable tail structure of the incident pulse     

Responses of plasma norepinephrine and heart rate during exercise in patients after Fontan operation and patients with residual right ventricular outflow tract obstruction after definitive reconstruction

In a fetal autopsy series, we have explored the occurrence of renal tubular dysgenesis in twins. Renal tubular dysgenesis was found exclusively among those monozygotic twins with evidence of twin transfusion syndrome, particularly in those donor twins with oligohydramnios and growth restriction. We infer that hypotension in the donor twin of the twin transfusion syndrome pair is responsible for the failure of proximal convoluted tubule differentiation, and the disturbance of renal function is manifested as oligohydramnios prenatally, and either oliguria or tubular dysfunction postnatally.     

Regulation of Kv4.2 and Kv1.4 K+ channel expression by myocardial hypertrophic factors in cultured newborn rat ventricular cells

Postnatal development and myocardial hypertrophy are associated with alterations in cardiac voltage-gated K+ channels. To investigate mechanisms underlying this K+ channel remodeling, expression of Kv4.2 and Kv1.4 K+ channel alpha-subunits was examined in cultured newborn rat ventricular myocytes by Western blot analysis using polyclonal antibodies against each of the subunits. At day 5 of cell culture, Kv1.4 protein was expressed at higher level than Kv4.2; as the age of culture progressed, Kv1.4 was significantly diminished while Kv4.2 increased with time in culture and became the predominant K+ channel protein. Such K+ channel isoform switch from Kv1.4 to Kv4.2 resembles that of the development in vivo. A 72-h treatment with exogenous triiodothyronine (T3, 0.1 microM) to cultured neonatal myocytes enhanced the expression of Kv4.2 by 73% and decreased the Kv1.4 expression by 22%. The effects of T3 were associated with an increase in the protein-to-DNA ratio indicating myocyte hypertrophy. On the other hand, a 72-h treatment with cardiac non-myocyte cell (NMC)-conditioned growth medium (NCGM) or phenylephrine (20 microM) induced similar cell hypertrophy, but in sharp contrast to T3, both markedly suppressed the Kv4.2 channel protein level. In addition, the trophic and the Kv4.2-downregulating effects of NCGM could be mimicked by exogenous endothelin-1 (0.1 microM), a paracrine factor secreted from cardiac NMCs. Our observations for the first time suggest that cardiac Kv4.2 and Kv1.4 K+ channel alpha-subunits are differentially regulated by a variety of myocardial hypertrophic factors. That T3 accelerated the developmental K+ channel isoform switch from Kv1.4 to Kv4.2 in vitro indicates the critical importance of thyroid hormone in postnatal K+ channel remodeling. Cardiac NMCs and alpha-adrenoceptor activation may contribute to the reduced outward K+ channel density in hypertrophied cardiomyocytes.     

Protein modelling using a chimera reference protein derived from exons

Bovine pancreatic /S-trypsin (PDB ID-code: 1TPO) which is registeredin the Brookhaven Protein Data Bank (PDB) consists of four exons.The results of homology searches for each exon in the PDB showedthat homologous proteins were tonin (PDB ID-code: 1TON), ratmast cell protease (PDB ID-code: 3RP2_A), kaffikrein A (PDBID-code: 2PKA_B) and kallikrein A (2PKA_B) respectively. Thus,for the three-dimensional structure prediction of 1TPO, a chimeraprotein was constructed from the three proteins mentioned aboveand the 3-D structure prediction was performed using this chimerareference protein. The modelled structure of 1TPO was energeticallyoptimized by molecular mechanics and molecular dynamics simulationand was compared with its X-ray crystal structure registeredin the PDB. The root mean square deviations (r.m.s.d.) of mainchain atoms and the neighbouring active site (5 sphere fromHis57, AsplO2 and Serl95) between the modelled structure andthe X-ray structure were 1.66 and 0.94 respectively. Porcinepancreatic elastase (PDB ID-code: 3EST) which is registeredin the PDB was used as the reference protein and the modelledstructure from 3EST was also compared with the X-ray data. Ther.m.s.d. of main chain atoms and that of the active site were2.14 and 1.18 respectively. These results dearly support thepropriety of this method using the chimera reference protein.