Tunneling Conductance Dependence of the Tunneling Spectra in Bi2Sr2CaCu2O8

We have measured the tunneling spectra in Bi₂Sr₂CaCu₂O₈ with a scanning tunneling microscope(STM) at various tip-sample distances by changing the tunneling conductance in a controlled manner. When the tunneling conductance is increased from 1×10^–9 to 1×10^–5 S, the spectra do not show changes in particular. However, the gap value decreases steeply and the asymmetric back ground density of states turns inverted V-shaped one above 6×10^–4 S. The changes in the tunneling spectra at the high tunneling conductances are explained by the enhancement of the local carrier density induced by the pressure that the STM tip applied to the sample.     

Reaction of cytochrome P450 with cumene hydroperoxide: ESR spin-trapping evidence for the homolytic scission of the peroxide O-O bond by ferric cytochrome P450 1A2

ESR spin trapping was used to investigate the reaction of rabbit cytochrome P450 (P450) 1A2 with cumene hydroperoxide. Cumene hydroperoxide-derived peroxyl, alkoxyl, and carbon-centered radicals were formed and trapped during the reaction. The relative contributions of each radical adduct to the composite ESR spectrum were influenced by the concentration of the spin trap. Computer simulation of the experimental data obtained at various 5,5-dimethyl-1-pyrroline N-oxide (DMPO) concentrations was used to quantitate the contributions of each radical adduct to the composite ESR spectrum. The alkoxyl radical was the initial radical produced during the reaction. Experiments with 2-methyl-2-nitrosopropane identified the carbon-centered adducts as those of the methyl radical, hydroxymethyl radical, and a secondary carbon-centered radical. The reaction did not require NADPH-cytochrome P450 reductase or NADPH. It is concluded that the reaction involves the initial homolytic scission of the peroxide O-O bond to produce the cumoxyl radical. Methyl radicals were produced from the beta-scission of the cumoxyl radical. The peroxyl adduct was not observed in the absence of molecular oxygen. We conclude that the DMPO peroxyl radical adduct detected in the presence of oxygen was due to the methylperoxyl radical formed by the reaction of the methyl radical with oxygen. At a higher P450 concentration, a protein-derived radical adduct was also detected.     

A 300-MHz 25-/spl mu/A/Mb-leakage on-chip SRAM module featuring process-variation immunity and low-leakage-active mode for mobile-phone application processor

An on-chip 1-Mb SRAM suitable for embedding in the application processor used in mobile cellular phones was developed. This SRAM supports three operating modes - high-speed active mode, low-leakage low-speed active mode, and standby mode - and uses a subdivisional power-line control (SPC) scheme. The combination of three operating modes and the SPC scheme realizes low-power operation under actual usage conditions. It operates at 300 MHz, with leakage of 25 /spl mu/A/Mb in standby mode, and 50 /spl mu/A/Mb at the low-leakage active mode. This SRAM also uses a self-bias write scheme that decreases of minimum operating voltage by about 100 mV.     

Efficient third-harmonic generation of a picosecond laser pulsewith time delay

A new configuration based on the polarization-mismatching scheme with time delay for efficient frequency tripling conversion is proposed in this paper. The calculated results showed that the requirement for the efficient frequency tripling conversion of a 1-ps laser pulse is not only the optimization of peak intensity of the second-harmonic pulse, but also the optimization of the pulse duration ratio and temporal difference between the o-polarization second-harmonic pulse and the e-polarization first-harmonic pulse due to group-velocity mismatch among the interacting pulses. With the proposed scheme the group velocity mismatch can be compensated. Overall energy conversion efficiency increases from 55% to 75% under the optimized conditions at the intensity of 6 GW/cm². The temporal shape of the third-harmonic pulse with 1 ps pulse duration has no subpulses. The optimization of the efficient frequency tripling conversion for intensities of over 75 GW/cm² is also described. The results showed that the maximum tripling energy conversion efficiency is close to 80% with the optimized doubler and tripler     

Superconductivity in the tetragonal phase of La1.9Bi0.1CuO4+δ annealed under high oxygen pressure

We have investigated the relation between the crystal structure and superconductivity in La_1.9Bi_0.1CuO_4+δ , in which the phase separation observed in La₂CuO_4+δ is suppressed. A phase diagram in theT?δ plane is given for La_1.9Bi_0.1CuO_4+δ with excess oxygen. For very smallδ values, the crystal structure is orthorhombic, and an orthorhombic-tetragonal phase transition occurs markedly atδ ～ 0.03 in the measured temperature range between 13 and 293 K. Superconductivity is observed in the range of 0.04<δ<0.11. This is clear evidence thathigh-T _c superconductivity also appears in the tetragonal phase.     

Preparation of SiC particles coated with alumina hydrate: Effect of reaction condition on particle coalescence

Alumina-hydrate-coated SiC particles were prepared via a homogeneous precipitation method using urea, and the conditions for uniform coating and less coalescence of the particles were investigated. Coalescence of coated particles could be said to occur by collision and agglomeration followed by deposition of alumina hydrate on the agglomerated particles. Coalescence of coated particles was suppressed by use of low reaction temperature, low concentration of aluminium sulfate, high concentration of urea, intensive stirring, and a flow reactor.