Highly conductive alumina/NCN composites electrodes fabricated by gelcasting and reduction-sintering—An electrochemical behavior study in aggressive environments

A novel highly conductive alumina/nano-carbon network composites (alumina/NCN composites) was fabricated by gelcasting and reduction-sintering method under argon atmosphere. The electrochemical behaviors of the alumina/NCN composites were studied systematically in some aggressive solutions (HCl, H₂SO₄, HNO₃, NaOH, and KOH), using potentiodynamic polarization and chronoamperometry and X-ray diffraction and SEM observations. The results showed that the electrochemical stability and reproducibility of the composite electrodes in these diluted acids and alkalis were very good and had, in some extent, an electro-catalytic activity toward formation of hydrogen evolution and reduction of dissolved oxygen in aqueous solutions in comparison with a commercial graphite electrode. In addition, the pyrolyzed nano-carbon contents, size, and shape in the alumina matrix, have greatly effects on the electrochemical performances and electrode reactions in these solutions. It is found that the minimal residual carbon content of 0.62 wt.% in the matrix is enough to improve electrochemical performances and avoid to loss the ceramics physical properties at the same time. When the additional potential in all the tested electrolytes was at +1700 mV (vs. SCE), alumina particles at the electrode surface were not observed to dissolve into solution in this case, indicating the material being suitable for electrodes in aggressive solutions.     

Characteristics of porous polymer composite columns prepared by radiation cast-polymerization

Porous polymer composite columns having porous structure were prepared by radiation cast-polymerization of hydrophilic monomers at low temperature and their characteristics were studied. The porosity of the polymer increased with decreasing monomer concentration. The elution time of water in the polymer column increased with increasing monomer concentration and with decreasing irradiation temperature. The elution time was dependent on the degree of hydration of the polymer. The polymer with a degree of hydration of 0.2 to 0.4 gave the minimum elution time. The elution time decreased with the addition of porous inorganic substances.     

Growth of emerald crystals from PbO · V2O5 flux

The flux growth of emerald crystals by slow cooling in the PbO · V₂O₅ flux is reported. The crystals exhibited the typical emerald-green colour, were up to 1.8 mm in size and transparent. Their form was a regular hexagonal rod bounded by the well-developed {0001} and {10ˉ10} faces. The solubility of emerald in PbO · V₂O₅ was also investigated; about 9.0 g emerald was dissolved in 100 g PbO · V₂O₅ at 1200 °C. The solubility decreased gradually with decreasing temperature. Taking the solubility data into account, the presence of undissolved particles in the solution was found to be a necessary condition for the growth of large emerald crystals. Unsaturated solution at a soak temperature produced good and relatively small emerald crystals in a subsequent cooling experiment. Advantages of the PbO · V₂O₅ flux are also mentioned. Emerald crystals showing various kinds of imperfections, and even good crystals, were also present.     

2D Model-Following Servo System

This paper gives, in view of the feature of practical 2D (2-dimensional) systems, a formulation of the 2D model-following servo problem for the case where one of the independent variables of the considered 2D systems is unbounded and the other one is bounded. That is, to determine a control input such that the outputs of a given 2D plant asymptotically track, with tracking error as small as possible, the (step) response of a given 2D model system as the unbounded variable approaches infinite. It is shown that this problem under a specified quadratic performance index can be transformed into a 1D LQR problem, and thus can be solved by the well-known 1D approaches. The relation between the solvability condition obtained for the equivalent 1D LQR problem and the practical stabilizability and detectability of the original 2D plant is clarified. Its application to the design of non-unit memory linear multipass processes is also shown. Finally, a numerical example for metal rolling process is given to verify the effectiveness.     

A Microcomputer System for Spatiotemporal Visual Receptive Field Analysis

A microcomputer system was developed to measure visual spatiotemporal receptive fields. The system performs three functions: 1) generation of a binary spatiotemporal white-noise stimulus, 2) acquisition of spike discharges from retinal ganglion cells, and 3) extraction of the linear part of the spatiotemporal receptive flelds by cross correlating the input against the output. We have applied this system to the measurement of the spatiotemporal receptive fields of cat and catfish retinal ganglion cells.     

Microelectrode-based hydrogen peroxide detection during oxygen reduction at Pt disk electrode

We investigated the diffusion process of H₂O₂ generated during O₂ reduction at a Pt microdisk electrode used as a generator for scanning electrochemical microscopy (SECM). First, the amount of O₂ consumption and generated H₂O₂ at the Pt generator electrode are estimated using a detector electrode installed in the SECM. Based on the results, a large amount of O₂ consumption and generated H₂O₂ are detected at the center of each generator electrode. According to the measurement, the O₂ starvation and H₂O₂ detection currents can be defined. Subsequently, the O₂ starvation and H₂O₂ detection currents are measured by varying the generator size. As a result, these currents decrease with a decrease in the generator electrode size, however, the H₂O₂ diffusion process is changed for the generator diameter of less than 50 μm. Finally, the O₂ starvation and H₂O₂ detection measurements were conducted using a Nafion-coated Pt microdisk electrode. The amount of O₂ consumption is not suppressed, while the amount of generated H₂O₂ decreases with the Nafion layer prepared on the Pt electrode. This result indicates that the thickness of the H₂O₂ diffusion layer in the H₂SO₄ solution is dramatically diminished by coating the Nafion layer on the Pt generator.     

Antioxidant activity of Japanese pepper (Zanthoxylum piperitum DC.) fruit

Antioxidants were extracted from Japanese pepper (Zanthoxylum piperitum DC.) fruit and characterized. The antioxidant activity of the methanol extract from Japanese pepper fruit was found to be equal to that of α-tocopherol and stable under heat treatment. The main compounds that gave a significant antioxidant activity from the methanol extract were identified to be hyperoside (quercetin-3-O-galactoside) and quercitrin (quercetin-3-O-rhamnoside) as determined by HPLC, mass spectrometry, UV/Vis spectroscopy, and TLC. Radical-scavenging activities of hyperoside and quercitrin from Japanese pepper fruit were evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) method. As a result, hyperoside and quercitrin scavenged DPPH radical strongly with IC₅₀ values of 16 and 18 μM, respectively. These observations show the presence of strong antioxidants, namely hyperoside and quercitrin in Japanese pepper fruit.     

Design study of PbBi- and NaK-cooled small deep sea fast reactors

The liquid lead-bismuth eutectic (PbBi) has good compatibility with water, which is different from sodium. It is expected that the PbBi could be used as a coolant of the deep sea fast reactor (DSFR). Physics analysis of the PbBi-cooled small reactor cores with and without inner control rods performed using the computer program of a neutronics code system (SRAC95) shows that PbBi is suitable for the coolant of small reactors as well as NaK.     

Behavior of shock waves formed by unsteady supersonic jet injected into cell

The unsteady behavior of flow driven by a jet suddenly injected into a cell is numerically studied by solving the axisymmelric two-dimensional compressible Navier-Stokes equations. The system of the calculation is a model of the laser ablation of a certain duration followed by a discharging process through the exit hole at the down- stream end of the cell. In the calculations, the contour of the cell is changed while other parameters such as the Mach number of the jet, its duration, and the diameter of the cell exit are fixed. Monitoring the velocity at the exit hole is used to investigate the influence of the shape on the interaction between the shock wave and the jet. As the result, it was found that the velocity peak value and its arrival time at the downstream end of the cell exit are determined by the diameter of the cell.