Fabrication of a Nano-Si3N4/Nano-C Composite by High-Energy Ball Milling and Spark Plasma Sintering

A nano-Si₃N₄/5 wt% nano-C composite was successfully fabricated for the first time via high-energy ball milling, followed by spark plasma sintering. The milling promoted the amorphization of the starting powders; most of the carbon particles were transformed into nano-size and embedded in the amorphous phase. This, combined with a low sintering temperature and a rapid densification rate, prevented the reactions between carbon and the other starting powders, leading to a uniform nano/nano-composite microstructure. Nano-sized carbon grains with an average diameter of about 10 nm were homogeneously dispersed in nano-sized (about 70 nm) Si₃N₄ grain boundaries. The hardness of the obtained nano-ceramics is comparable with that of conventional Si₃N₄, whereas Young's modulus is significantly decreased.     

A criterion for reverse control action of TCUL controls and their deactivation timings

The dynamic behaviors of the TCUL controls are investigated from the viewpoint of the effect of control actions on voltage stability as well as on voltage regulations, taking into account the interference among the multiple control actions of TCULS. The Liapunov stability theorem is applied to a system having nonlinear voltage-dependent loads to derive conditions for stability. We define the term “reverse control action for multiple TCULS” to indicate undesirable tap operations, where multiple controls as a whole cause the decrease in voltages of specific nodes, leading to voltage collapse, in spite of normal individual operations. A criterion to detect the phenomena is derived and then a new control strategy based on this criterion is demonstrated. In this demonstration, unsuitably acting TCULs are individually deactivated at their most effective timings to improve voltage stability. The effectiveness of the proposed criterion and its application to the deactivation control have successfully been confirmed through numerical simulations in a radial network with three cascaded TCUL transformers, where a specific area of a real system is reduced to form the example system.     

Development and performance evaluation of a GC-FPD method for quantification of ethephon in feeds

An analytical method of ethephon in feeds by GC-FPD was developed. Ethephon was extracted with ethyl acetate-hydrochloric acid (100 : 1) from feed samples. The extract was treated with added trimethylsilyldiazomethane in acetone-acetic acid (99 : 1) and this methylation procedure was repeated three times. Methylated ethephon was cleaned up on a graphitized carbon mini-column and a silicagel mini-column, and determined by GC-FPD. A method performance study in 7 laboratories was conducted with three kinds of samples spiked with ethephon at 10 mg/kg, 1 mg/kg and 0.5 mg/kg. The recovery of ethephon ranged from 81.8% to 90.8% (the reproducibility standard deviation (RSDr) were within 11%) and HorRat values were 0.58 to 0.94. The limit of detection (S/N≧3) and the limit of quantitation (S/N≧10) of ethephon in samples except hay were 0.02 mg/kg and 0.05 mg/kg, respectively. In the case of hay, the corresponding values were 0.2 mg/kg and 0.5 mg/kg, respectively.     

Electrical Properties of a Bismuth Layer-Structured Ba2Bi4Ti5O18 Single Crystal

Ba₂Bi₄Ti₅O₁₈ single crystals were grown, and their dielectric permittivity, conductivity, and ferroelectricity were investigated along the a -(or b -)axis and the c -axis separately. The dielectric permittivity at 1 MHz along the a -(or b -)axis was 2000 at the Curie temperature (360°C); this value was 8 times greater than that along the c -axis. The dc conductivity was greater along the a -(or b -)axis than that along the c -axis, by one order of magnitude. In regard to the ferroelectricity, the saturated remanent polarization was 120 mC/m² and the saturated coercive field was 3 MV/m along the a -(or b -)axis; values of 8.5 mC/m² and 0.81 MV/m, respectively, were observed along the c -axis. The Ba₂Bi₄Ti₅O₁₈ single crystals had large electrical anisotropies, which were due to the layered structure.     

An efficient construction and application usefulness of rectangle greedy covers

We develop efficient construction methods of a rectangle greedy cover (RGC), and evaluate its usefulness in applications. An RGC is a greedy cover of the set of given positive instances by exclusive axis-parallel hyperrectangles, namely, axis-parallel hyperrectangles that exclude all the given negative instances. An RGC is expected to be a compact classification rule with high readability because the number of its component rectangles is expected to be small and it can be seen as a disjunctive normal form, which is one of the most readable representations for us.     

Orientational control of pentacene crystals on SiO2 by graphoepitaxy to improve lateral carrier transport

We controlled the in-plane orientation of pentacene grains by graphoepitaxy using patterned amorphous-SiO₂/Si substrates on which periodic grooves with slope edges had been formed. Pentacene crystals exhibited a clear tendency to align their b-axes perpendicular to the groove edges. Organic thin-film transistors were fabricated on the patterned and flat substrates and their transistor characteristics were compared. Although the patterned substrates increased the apparent mobility by only 10–20%, the number of grain boundaries with high potential barriers to carrier transport was reduced to half of that on flat substrates. This improvement is expected to enhance the response speed of pentacene organic thin-film transistors and suppress the sensitivity of their characteristics to the operating temperature.     

Properties of mixed-oxide MoO3/V2O5 electrochromic films coated from peroxo-polymolybdovanadate solutions

Peroxo-polymolybdovanadates with various mole ratios of Mo/V are formed by direct reaction of a mixture of metallic Mo and V with hydrogen peroxide solution. Homogeneous amorphous thin films about 0.4 μm are fabricated on an ITO glass substrate by a spin-coating technique using the peroxo-polymolybdovanadate solutions. After heat-treatment at a desired temperature (80–120°C) in air for 1 h, they show reversible electrochromism in an organic Li-electrolyte solution, and change color between greenish yellow and violet. The potential (E) versus composition (x, Li content per mole of Mo_yV_1−yO_z) diagrams for these mixed films could be approximated by two straight lines with different slopes, which suggests that in these films there are two kinds of sites with different site energies. The changes in electrochromism with heat-treatment are also discussed in relation to the micro-structure of the films.     

Carrier transport and structural properties of polysilicon films prepared by layer-by-layer technique

Polycrystalline silicon (poly-Si) films have been deposited on glass substrates by a layer-by-layer technique at very low temperature, 300°C, using fluorinated precursors. The electronic transport was characterized by Hall effect and conductivity measurements over a wide temperature range, 100 K to 400 K. The structure of the materials is a function of the film thickness. The measured Hall mobility increases as the thickness increases. The Hall mobility Arrhenius plot shows linear dependence with a negative slope over the temperature range examined, suggesting that carrier conduction is limited by grain boundary barriers.