Study of space-charge characteristics in polyethylene for power cable insulation by laser-induced pressure-pulse technique

By utilizing the laser induced pressure-pulse (LIPP) technique, the behavior of space charge in low-density polyethylene (LDPE) and crosslinked polyethylene (XLPE) films in contact with metal or carbon-loaded semiconducting layers was studied quantitatively to clarify the space-charge characteristics in power cables. Negative heterospace charge near the anode and positive space charge in the bulk were observed in unoxidized LDPE under the fields above 120 kV/mm. The amount of negative space charge increased with applied field, while positive space charge in the bulk disappeared with increasing applied field. This indicates that electron injection and ionization are enhanced by applied field. Prominent negative homospace charge was formed near the cathode in oxidized LDPE, which indicates that oxidation enhanced electron injection. The depth of charge centroid from the cathode became larger with increasing temperature. This indicates that the effective electron mobility increases with temperature. Negative space charge also was formed in the bulk in XLPE films with metal electrodes, which indicates that crosslinking enhanced electron injection. XLPE films with a carbon-loaded semiconducting layer showed both negative and positive homospace charges near the semiconducting layers, which indicates that both electrons and holes were injected from the semiconducting layer.     

Anion exchange membranes prepared from chloromethylstyrene and 2-methyl-5-vinylpyridine

Strongly basic anion exchange membranes were prepared by the radical copolymerization of chloromethylstyrene and 2-methyl-5-vinylpyridine. The formation of a three-dimensional structure and the presence of the quarternary pyridinium group were confirmed by infrared spectrum analysis and its strongly basic anion exchange properties. Their electrochemical properties and morphology were compared with those of the anion exchange membranes prepared from chloromethylstyrene-divinylbenzene and 2-methyl-5-vinylpyridine-divinylbenzene. The chloromethylstyrene-2-methyl-5-vinylpyridine membranes were proved to have larger anion exchange capacity, smaller electric resistance, larger water content, and higher permeability than the chloromethylstyrene-divinylbenzene and 2-methyl-5-vinylpyridine-divinylbenzene membranes. Also, the membranes have heterogeneity in the cross-linking structure.     

Role of reinforcing material in ion exchange membranes prepared by the paste method

Ion exchange membranes prepared by the paste method contain polyvinylchloide cloth as a reinforcing material, which is necessarily used to endow the membranes well-balanced properties: electrochemical and mechanical properties. The role of the reinforcing material was studied in terms of the membrane structure.     

Fabrication of two-dimensional photonic crystals with controlled defects by use of multiple exposures and direct write

We have developed an approach for relatively rapid and easy fabrication of large-area two-dimensional (2-D) photonic crystal structures with controlled defects in the lattice. The technique is based on the combination of two lithographic steps in UV-sensitive SU-8 photoresist. First, multiple exposures of interference fringes are used in combination with precise rotation of the sample to define a 2-D lattice of holes. Second, a strongly focused UV laser beam is used to define line-defect waveguides by localized exposure in the recorded but not yet developed lattice from the first step. After development, the mask is transferred into a GaAs substrate with dry etching in chemically assisted ion-beam etching.     

Blends of thermoplastic polyimide with epoxy resin: Part II Mechanical studies

Bifunctional epoxy resins have been modified with thermoplastic polyimide in order to improve their toughness. The effects of polyimide content, curing conditions, curing agents, and types of polyimide on the fracture properties have been examined. Relationships between the microstructure of the cured resins and their mechanical properties have also been investigated. This revised version was published online in November 2006 with corrections to the Cover Date.     

Two-dimensional potential profile measurement of GaAs HEMT's byKelvin probe force microscopy

Two-dimensional (2-D) potential profile of GaAs HEMT's under bias voltage has been successfully measured by combining Kelvin probe force microscopy with cleavage of the HEMT's. The spatial resolution evaluated by measuring GaAs-AlAs multiquantum-well structure was less than 70 nm. The measured depth profile of the potential shows a potential knee, which probably originates from the charge trapped at the interface between the epitaxial layer and the substrate. The high-field region is observed at the drain-side edge of the gate. The present KFM technique will yield a powerful tool for analysis of the electrical properties of the devices     

Safety assessment of genetically engineered yeast: elimination of mutagenicity of the yeast Saccharomyces cerevisiae by decreasing the activity of methylglyoxal synthase

Summary  Methylglyoxal synthase catalyses the transformation of dihydroxyacetonephosphate to methylglyoxal, a toxic 2-oxoaldehyde which is found to be present in the yeast Saccharomyces cerevisiae DKD-5D-H. Yeast cells in which genes for phosphoglucose isomerase, phosphofructokinase and triosephosphate isomerase had been extrachromosomally amplified by using a multi-copy plasmid showed an increased ability to induce mutagenesis in standard tests when compared to wild type yeast. This response is mainly due to the increased amount of methylglyoxal in the engineered cells. To decrease the mutagenic activity and make it possible to use genetically engineered yeasts for practical fermentation processes, a mutant having a decreased level of methylglyoxal synthase activity was isolated. When transformed with genes for the glycolytic enzymes, the mutant cells showed extremely low levels of methylglyoxal content and mutagenic activity, both levels being comparable with those of non-transformed DKD-5D-H cells.     

Structure analysis of Ni (1 1 0) surface using computer simulation of NICISS

The relaxation at a Ni (1 1 0) surface has been estimated using the computer simulation of the 180 neutral impact-collision ion scattering spectroscopy (NICISS). The computer simulations employing ACOCT program code based on the binary collision approximation (BCA) are performed for the case of 1.5 keV He⁺ ions incident along the direction of the Ni (1 1 0) surface. It is found that the experimental results are well reproduced by the ACOCT simulations including the inward relaxation of 7% of the first interlayer spacing and the outward relaxation of 5% of the second interlayer spacing at the Ni (1 1 0) surface.     

A piezoelectric-drive table and its application to micro-grinding of ceramic materials

A micro-positioning table with a 0.005 μm resolution has been developed to enhance the performance of a conventional grinding machine in the fine grinding of ceramics. A piezoelectric actuator with high stiffness and resolution has been applied to drive the table and to provide small depths of cut for the workpiece. The performance of the table is investigated with both open and closed-loop operation to drive the actuator. The accuracy and stiffness of the positioning are improved by means of the closed-loop control. Grinding experiments with ceramics, such as partially stabilized zirconia (PSZ) and hot-pressed silicon nitride (Si₃N₄), were carried out to demonstrate the performance of the table. The actual resolution of depth-of-cut control was determined by measuring ground groove depths on the ceramic surface. A mirror-like surface on the ceramic was easily obtained by grinding at the small depth of cut of 0.1 μm with the aid of the table.