Harmonic blue light generation in periodically poled bulk near-stoichiometric MgO:LiNbO/sub 3/

A periodically poled structure with 6.95 /spl mu/m period and 10 mm interaction length was fabricated in a 1 mm-thick 1.8 mol% MgO doped near-stoichiometric LiNbO/sub 3/ (MgSLN) by using a multi-pulse poling technique. Blue SHG characteristics of this periodically poled MgSLN were investigated, in comparison with a periodically poled 5 mol% MgO doped congruent LiNbO/sub 3/.     

The fabrication and thermomechanical behavior of Al and Ti SMA composites

Two kinds of composites—Ti-Ni shape-memory alloy (SMA) fiber-reinforced 6061 aluminum matrix composite and Ti-Pd(Ni) SMA-reinforced titanium-matrix composite—were fabricated by various processing methods and their microstructure and thermomechanical behavior were investigated. In both sets of composites, an increase in yield stress at high temperature was mainly caused by residual compressive stress created in the matrix in association with shape-memory effects of the embedded SMAs. For more information, contact Kiyoshi Mizuuchi, Osaka Municipal Technical Research Institute, Osaka 536-8553, Japan; e-mail: mizuuchi@omtri.city.osaka.jp.     

Blue-light generation by frequency doubling of a laser diode in aperiodically domain-inverted LiTaO3 waveguide

The authors report quasi-phase matched second-harmonic generation by frequency doubling of a laser diode in LiTaO₃ having a first-order periodically domain-inverted region and proton-exchanged channel waveguide. A deep domain-inverted region and a low-loss channel waveguide with strong confinement are formed by using proton-exchange and quick heat treatment techniques. Utilizing this structure, a high normalized conversion efficiency of 157%/W is obtained with a Ti:Al₂O₃ laser. Using a temperature-controlled laser diode and AR coating on the input and output facet of the waveguide, the laser diode maintains single-mode oscillation without any mode hopping. Consequently, 1.1 mW of blue light is obtained at a wavelength of 436.5 nm     

Division of labor among monomers within the Mu transposase tetramer

A single tetramer of Mu transposase (MuA) pairs the recombination sites, cleaves the donor DNA, and joins these ends to a target DNA by strand transfer. Analysis of C-terminal deletion derivatives of MuA reveals that a 30 amino acid region between residues 575 and 605 is critical for these three steps. Although inactive on its own, a deletion protein lacking this region assembles with the wild-type protein. These mixed tetramers carry out donor cleavage but do not promote strand transfer, even when the donor cleavage stage is bypassed. These data suggest that the active center of the transposase is composed of the C-terminus of four MuA monomers; one dimer carries out donor cleavage while all four monomers contribute to strand transfer.     

Thermal expansion and mechanical properties of pure magnesium containing zirconium tungsten phosphate particles with negative thermal expansion

The magnesium composites containing Zr₂(WO₄)(PO₄)₂ (ZWP) particles with negative thermal expansion (NTE) were synthesized. Dense, unreacted Mg/ZWP composites were fabricated by extruding the two component powders. The coefficient of thermal expansion (CTE) and the mechanical properties of the composites were examined. The CTE of Mg/ZWP composites decreased with an increase in the amount of ZWP in the composites, though the effect was not significant probably because of the low bulk modulus of ZWP. Although there was a tension–compression asymmetry in the room temperature yield strength of Mg without ZWP, the difference reduced in the composites. The decreased asymmetry of yield behavior was suggested to be resulting from the tensile residual stress in the matrix produced during fabrication process because of the NTE of ZWP.     

Plasma Confinement Characteristics in Heliotron J--Spontaneous Change of Plasma Confinement State

Spontaneous transition of the plasma confinement mode was observed in the helicalaxis heliotron device “Heliotron J“ for three different plasma heating schemes, i.e. ECHonly, NBI-only and the combination of ECH and NBI. The transition seems to occur above a certain critical density. In addition to the confinement transition, a spontaneous shift of the hitting position of the divertor plasma flux on the wall was observed. This shift could be related with the change of the edge field topology caused by non-inductive toroidal currents.     

Processing of Al/SiC composites in continuous solid–liquid co-existent state by SPS and their thermal properties

Silicon carbide (SiC)-particle-dispersed-aluminum (Al) matrix composites were fabricated in a unique fabrication method, where the powder mixture of SiC, pure Al and Al–5mass% Si alloy was uniquely designed to form continuous solid–liquid co-existent state during spark plasma sintering (SPS) process. Composites fabricated in such a way can be well consolidated by heating during SPS processing in a temperature range between 798 K and 876 K for a heating duration of 1.56 ks. Microstructures of the composites thus fabricated were examined by scanning electron microscopy and no reaction was detected at the interface between the SiC particle and the Al matrix. The relative packing density of the Al–matrix composite containing SiC was higher than 99% in a volume fraction range of SiC between 40% and 55%. Thermal conductivity of the composite increased with increasing the SiC content in the composite at a SiC fraction range between 40 vol.% and 50 vol.%. The highest thermal conductivity was obtained for Al–50 vol.% SiC composite and reached 252 W/mK. The coefficient of thermal expansion of the composites falls in the upper line of Kerner’s model, indicating strong bonding between the SiC particle and the Al matrix in the composite.     

A large nucleoprotein assembly at the ends of the viral DNA mediates retroviral DNA integration

We have probed the nucleoprotein organization of Moloney murine leukemia virus (MLV) pre-integration complexes using a novel footprinting technique that utilizes a simplified in vitro phage Mu transposition system. We find that several hundred base pairs at each end of the viral DNA are organized in a large nucleoprotein complex, which we call the intasome. This structure is not formed when pre-integration complexes are made by infecting cells with integrase-minus virus, demonstrating a requirement for integrase. In contrast, footprinting of internal regions of the viral DNA did not reveal significant differences between pre-integration complexes with and without integrase. Treatment with high salt disrupts the intasome in parallel with loss of intermolecular integration activity. We show that a cellular factor is required for reconstitution of the intasome. Finally, we demonstrate that DNA-protein interactions involving extensive regions at the ends of the viral DNA are functionally important for retroviral DNA integration activity. Current in vitro integration systems utilizing purified integrase lack the full fidelity of the in vivo reaction. Our results indicate that both host factors and long viral DNA substrates may be required to reconstitute an in vitro system with all the hallmarks of DNA integration in vivo.     

The new mode of urban renewal for the former outcaste minority people and areas in Japan

Urban renewal in Japan has mainly consisted of redevelopment by private capital redevelopment of commercial areas and, in some case, by the public sector. Redevelopment of residential districts has lagged behind due to the predominance of private ownership and complicated development rights relationships. In the midst of this, the redevelopment of low-standard housing environments in the Buraku districts, where the formerly discriminated-against minority, the Burakumin, live is an extremely rare example of housing renewal. The Buraku liberation movement was able to exercise great political power, and large amounts of national funds were invested over a 27-year period in the Buraku as Dowa assimilation projects. Their living environments were remarkably improved, but unfortunately at present apartment building slums, carrying social overtones of ghetto, are reappearing and these are becoming areas where a new class of the poor are gathering to live. Because of splits within the Buraku liberation movement and political opposition, assessment of the value of Dowa assimilation projects is divided, and society tends to evade the issue. Against that background, in recent years creative and self-reliant means of community development that do not depend on national government funds have emerged from within the Dowa districts. In this article we draw attention to these undertakings as indispensable for the evolution of a high-level advanced capitalistic society into a sustainable society, and introduce them as progressive examples of Japanese Machizukuri (urban rejuvenation).     

Quasi-phase-matched second harmonic generation device in Mg-doped LiNbO3 and its application to high-density optical disk system

The resistance to photorefractive damage is investigated for several nonlinear crystals. A quasi-phase-matched (QPM) second harmonic generation (SHG) waveguide device is fabricated in 5 mol% Mg-doped LiNbO₃ which has high resistance to optical damage. The SHG blue laser of the QPM-SHG waveguide device and a tunable distributed Bragg reflector (DBR) laser diode is demonstrated, wherein output stability of continuous blue light is measured. The SHG blue laser, using the QPM-SHG waveguide device with broadened flat matching response, shows good modulation characteristics. The pulsed peak power of 23 mW with rectangular modulated waveform is generated. The SHG blue laser is installed to an optical head, and good recording and readout characteristics are demonstrated. Moreover, butt-coupled SHG blue laser is examined to gain a miniature module with volume of 0·8 cc.