Improvement of linewidth enhancement factor in 1.55-μmmultiple-quantum-well laser diodes

The improvement of the linewidth enhancement factor in complex-coupled laser diode (CC-LD), or loss-coupled, was confirmed by measuring the spontaneous emission spectra below threshold from the sidewall of laser diodes. In addition, the serial resistance of the device was measured. The linewidth enhancement factor is improved by the presence of a light absorbing InGaAs grating for loss coupled distributed-feedback (DFB) laser diode (LD). We report the comparison of the linewidth enhancement factors of Fabry-Perot (FP) LD, conventional DFB-LD, and loss coupled DFB-LDs     

Calretinin and calbindin D28K immunoreactivity in the superficial layers of the rabbit superior colliculus

Calretinin and calbindin D28K were localized in the superficial layers of rabbit superior colliculus (SC). Calretinin and calbindin D28K-immunoreactive (-IR) neurons were concentrated in the upper superficial gray layer. Calretinin-IR fibers were found in the optic layer. The majority of calretinin-IR cells were small- to medium-sized vertical fusiform neurons and neurons with round or stellate-shaped somas with small varicose dendrites. The morphology of calbindin D28 K-IR neurons was different from that of calretinin neurons. Anti-calbindin D28K-IR neurons usually had fusiform cell bodies and a thick primary dendrite with small branches forming a dendritic bouquet. Two-color immunofluorescence revealed that no cells expressed both proteins. Following unilateral enucleation a marked reduction of calretinin-IR fibers in the contralateral side to the enucleation was found. Enucleation appeared to have no effect on the cell bodies labeled with either protein. The results suggest the anti-calretinin immunoreactivity in the superficial layer of rabbit SC contrasts starkly with that of other animals.     

Vacuum ultraviolet optical properties of (La,Gd)PO4:RE (RE=Eu, Tb)

Vacuum ultraviolet excitation spectra of phosphors (La,Gd)PO₄:RE³⁺ (RE=Eu or Tb) and X-ray photoelectron spectra of LaPO₄ and GdPO₄ are investigated. The vacuum ultraviolet excitation intensity of (La,Gd)PO₄:RE³⁺ is enhanced with the increasing of Gd³⁺ content, which implies that Gd³⁺ plays an intermediate role in energy transfer from host absorption band to RE³⁺. When Gd³⁺ is doped into LaPO₄:Eu³⁺, charge transfer band (CT band) begins to shift to higher energy region and the overlap degree of CT band and the host absorption band gets greater with more Gd³⁺ doped into LaPO₄. These results suggest that the dopant (Gd³⁺) gives an important influence on energy transfer efficiency. The top of LaPO₄ valance band is formed by the 2p level of O²⁻, whereas that of GdPO₄ valance band is formed by the 2p level of O²⁻ and the 4f level of Gd³⁺, showing the differences in band structures between LaPO₄ and GdPO₄.     

Stress corrosion cracking of Al-Zn-Mg alloy AA-7039 by slow strain-rate method

The stress corrosion behaviour of Al-Zn-Mg alloy AA-7039 in an aqueous 3.5 wt % Nad solution (pH=1) was studied with the specimens under constant strain rate as function of ageing state and cold working. The tests were carried out at temperatures of 30 and 45°C and strain rates between 7.6×10^–7 and 7.6×10^–6 sec^–1 and the apparent activation energy for mechanical deformation in oil and stress corrosion cracking (SCC) process in NaCl solution were determined. The fracture energy in NaCl solution under constant strain rate, as compared with experiments in oil, was lowered in the overaged specimens and markedly lowered in sequence of the peak-aged and the underaged specimens. The values of fracture energy for peak-aged and overaged specimens were nearly similar to those in oil at the higher strain rate of 7.6×10^–6 sec^–1. The relative fracture energy was comparatively lowered in the fine-grained specimens, as compared to coarsegrained specimens. The apparent activation energy for mechanical processes in oil was found to be 103 kJ mol^–1 in the peak-aged and 96.5 kJ mol^–1 in the overaged specimens. Those for SCC processes in NaCl solution were 47.5 kJ mol^–1 in the peak-aged and 51.5 kJ mol^–1 in the overaged specimens. The results suggest that stress corrosion (SC) cracks are initiated by electrochemical dissolution of grain boundaries (gbs) and propagated by mechanical processes such as creep.     

Theoretical approach to faradaic admittance of hydrogen absorption reaction on metal membrane electrode

Faradaic admittance of hydrogen absorption reaction (har) on metal membrane electrode has been derived on the basic of “two models” of the har under the permeable boundary condition by using an extension of Armstrong's kinetic approach. In the case of the har through adsorbed phase (model A), two limiting cases of the Faradaic admittance are considered depending upon the magnitude of rate of hydrogen transfer from bulk to metal surface. One involves the diffusion-controlled har for fast rate of hydrogen transfer and the other is the interface-controlled har for slow rate of hydrogen transfer from bulk to metal surface. Depressing and/or tailing of the second semicircle, often found in the complex-plane impedance spectra for hydrogen evolution reaction (her), is fairly explained by the diffusion-controlled har. In the case of the direct har without passing through the adsorbed phase (model B), the Faradaic admittance is differentiated by the absence of adsorption capacitance from that based upon the model A.     

Effect of aluminium content on the anodic behaviour of copper-aluminium alloys in 3.5 wt% NaCl solution

Anodic behaviour of heterogeneous Cu-Al alloys in 3.5 wt% NaCl solution has been investigated as a function of aluminium content by potentiodynamic polarization, cyclic voltammetry and potentiostatic current transient experiments and compared to pure Cu and homogeneous Cu-Al alloys. The specimens were subjected to various anodic potentials and subsequent analyses by scanning electron microscopy (SEM) supplemented with energy dispersion spectroscopy (EDS). The pure Cu and single -phase Cu-Al alloys showed that a relatively thick protective CuCl film forms at active-passive transition potentials and transforms into CuO or Cu(OH)₂ at the passivation potential, resulting in high limiting current densities. However, the Cu-10 wt% Al alloy is passivated to Al(OH)₃, impeding the transformation of the thick CuCl layer which contains AlCl or Al(OH)₂Cl salt into CuO or Cu(OH)₂. At high applied anodic potential, the Cu₂(OH)₃Cl phase forms on the deteriorated passive film Al(OH)₃.     

PASSIVATION EFFECTS ON CRACK CLOSURE IN THE FATIGUE CRACK PROPAGATION OF A PEAK-AGED Al-Li-Zr ALLOY IN NaCl AND Na2SO4 SOLUTIONS

Abstract Fatigue cracking of a peak-aged Al-Li-Zr alloy was investigated by measuring crack closure as a function of applied anodic potential in 0.6 M NaCl and 0.5 M Na₂SO₄ solutions with an unloading elastic compliance technique, and by comparison with crack closure in dry air. The present work involves complementary anodic behaviour of the Al-Li-Zr alloy in both solutions by potentiodynamic polarization and potentiostatic current transient experiments. From the repassivation rates in the passivation potential range in both solutions, it is indicated that a more stable passive film is formed at lower applied anodic potential than at higher applied anodic potential. The intrinsic fatigue crack propagation (FCP) rates under unstable passivation potential in both solutions were significantly larger than those obtained in dry air. Under stable passivation potential in both solutions, however, the intrinsic FCP rates in the low ΔK_eff range were slightly lower than those obtained in dry air. The crack closure in the low ΔK_eff range increased under stable passivation potential, in dry air and under unstable passivation potential. The high crack closures appearing in the low ΔK_eff range were characterized by a tortuous fracture surface in dry air, and the occurrence of various crack paths such as rolling plane delamination under unstable passivation potential. The difference between environmental crack closures under stable and unstable passivation conditions is discussed in terms of environment-assisted crack-tip damage processes.     

Antimicrobial activity of torilin isolated from Torilis japonica fruit against Bacillus subtilis

ABSTRACT:  Torilis japonica fruit has been used in therapeutic antimicrobial treatments in Korea and China since ancient times, but there is still little information on the mechanism underlying this activity. We found that the ethanol extract of T. japonica fruit showed excellent antimicrobial activity against Bacillus subtilis ATCC 6633 spores and vegetative cells. The crude ethanol extract (75%) reduced the spore concentration by 3 log cycles and the vegetative cell concentration to lower than the detection level (reduction in spore concentration by more than 6 orders of magnitude) at a concentration of 1% (w/v). The ethanol extract of T. japonica fruit was fractionated into n -hexane (H) and a water layer. The active antimicrobial compound was isolated and purified from the hexane layer, and identified as torilin (5-[1-(acetyloxy)-1-methylethyl]-3,8-dimethyl-2-oxo-1,2,4,5,6,7,8,8a-octa-hydroazulen-6-yl(2 E )-2-methylbut-2-enoate; C₂₂H₃₂O₅). Torilin immediately reduced vegetative cells counts by 5 to 6 orders of magnitude, and reduced spores counts by 1 order of magnitude. The integrity of structures such as the inner, middle, and outer layers of the coat and the cortex, protoplast membrane, and core are vital to spores. Torilin functions as a surfactant with hydrophilic and hydrophobic properties related to denaturalization of various proteins. The distortion of coat proteins due to direct binding polar groups of spore coats with hydrophilic groups of torilin may be responsible for the observed rapid inactivation of bacterial spores.