Aging time dependence of catastrophic optical damage (COD) failureof a 0.98-μm GaInAs-GaInP strained quantum-well laser

In this paper, we studied the aging time dependence of the catastrophic optical damage (COD) failure of an Al-free uncoated 0.98-μm GaInAs-GaInP strained quantum-well laser with an injection current as a parameter. Based on the stress-strength model, we first investigated experimentally the dependence of the critical power level (CPL) at which COD would take place upon the aging time. Then applying a statistical treatment to this result, we found for the first time that CPL data at each aging time could be considered to distribute according to the Weibull statistics, and the decrease rate of the CPL with the aging time depended very strongly on the injection current. Finally, using the relationship between the decrease rate of the CPL with the aging time and the current, we predicted roughly the time of a COD failure occurrence for both large and small current cases. As a result, we clarified that for our Al-free uncoated 0.98-μm laser, a COD failure became a fatal problem in the case of a large-current (high-power) operation     

Intestinal metaplasia with adherent Helicobacter pylori: a hybrid epithelium with both gastric and intestinal features

Helicobacter pylori seem to avoid areas of intestinal metaplasia in the gastric mucosa, but attachment of these bacteria to epithelium with the appearance of incomplete intestinal metaplasia has been documented. To characterize the nature of the epithelium to which H pylori was attached, we carried out an immunohistochemical study using monoclonal antibodies against gastric surface mucous cell mucins (M1), blood group-related carbohydrates antigens (Le(a), sialyl Le(a), Le(b), type 1H, and type 2H) and sialyl Tn antigen. The results of this study suggest that these areas of H pylori attachment represent a hybrid epithelium whose cells share characteristics of both gastric surface mucous cells and intestinal metaplastic cells. Whether all areas of incomplete intestinal metaplasia represent an intermediate stage between the normal gastric epithelium and the fully developed complete type of metaplasia remains to be determined.     

Structures and electronic properties of surface/edges of nanodiamond and nanographite

The structure, electronic and magnetic properties of nanodiamond and nanographite/nanographene are investigated. Detonation nanodiamond particles that are covered with amorphous graphitic composites are hydrothermally treated to remove the graphitic surface composites and to terminate the surface carbon atoms with hydrogen. The number of localized spins of dangling bonds and the hydrogen concentration increase upon the increase in the hydrothermal treatment time up to 40 h. Above 40 h, both drop discontinuously, a surface structural reconstruction was suggested. The creation of dangling bonds and an incomplete hydrogenation of the surface carbon atoms destabilize the surface, resulting in the structural reconstruction. Nanodiamond particles are thermally converted to nanographite/nanographene. A single nanographene sheet is successfully prepared by heat-treating nanodiamond particles. The edge of graphene sheet with its edge carbon atoms being hydrogen-terminated is investigated by UHV-STM/STS. Zigzag edges are found to have non-bonding π-state of edge origin, in good agreement with theoretical prediction.     

Fabrication and operation limit of lead-free PTCR ceramics using BaTiO3–(Bi1/2Na1/2)TiO3 system

The electric properties of BaTiO₃–(Bi_1/2Na_1/2)TiO₃ (BT–BNT) solid solution ceramics were studied as a lead-free PTCR (positive temperature coefficient of resistivity) thermistor material usable over 130°C. For determining the maximum switching temperature T _s, the phase diagram of BT–BNT binary system was clarified. Two semiconductorization processes and their electric properties are described. The lanthanum(La)-doped BBNT ceramics sintered in air still showed dielectric behaviors, but the niobium(Nb)-doped ones had a low resistivity at room temperature, ρ _RT, on the order of 10³ Ωcm and showed a PTC behavior. Sintering under a low O₂ atmosphere produces BT–BNT ceramics with less than 10² Ωcm compared to those prepared in air. Our current research produced the BBNT ceramics with T _s values around 210°C by increasing the (Bi_1/2Na_1/2) content in the ceramics.     

Thermoelectric properties of β-FeSi2 with B4C and BN dispersion by mechanical alloying

The B₄C- and BN-dispersed -FeSi₂ thermoelectric materials were synthesized by mechanical alloying and subsequent hot pressing. The effects of the B₄C and BN dispersion on the thermoelectric properties, such as Seebeck coefficient, electrical resistivity and thermal conductivity etc., of the -FeSi₂ were investigated. For the sample with B₄C and BN addition, a larger amount of the residual phase was detected in the X-ray diffraction patterns than the sample without addition. In the case of the BN addition, the Seebeck coefficient was enhanced by BN addition above 700 K, and the electrical resistivity also increased with increasing amount of BN. This is considered to result from doping of a small amount of B into the phase due to partial decomposition of the BN phase. The fine dispersion of BN particles in the phase matrix was quite effective for reducing the thermal conductivity as compared to the B₄C addition over the entire temperature range. The figure of merit, Z, of the -FeSi₂ was significantly enhanced by BN addition.