Electrically conducting suspensions formed by polyaniline

Polyaniline was synthesized with the chemical oxidation in the presence of poly(vinylpyrrolidone) as a surfactant for small-sizing polyaniline grains. It was dispersed in glycerin including sulfuric acid to yield electrically conducting solution. Voltammograms of the solution by the two-electrode measurement showed the proportionality of the Ohm's law in the cell voltage from −0.2 to 0.2 V. Voltammograms by the three-electrode measurement in the domain 0.0-1.5 V versus Ag|AgCl were different from the Ohmic law and Faradaic current of polyaniline, because of a mixture of both the contributions. The conductance did not vary with the volume fraction of polyaniline up to 20% and enhanced drastically until 35% with large fluctuation, and then increased proportionally with the volume fraction. This variation was explained in terms of the electric percolation with a threshold at the volume fraction of 20-35%. The mixture with over 45% fraction was actually solid. The suspension was applied to confirming the relation between the Ohmic current at a microelectrode and its diameter. The current showed a linear relation with the electrode diameter with a small intercept of the diameter, of which value corresponded to the size of polyaniline grains.     

Numerical analysis of slow current transients and power compression in GaAs FETs

Two-dimensional transient simulation of GaAs MESFETs is performed when the gate voltage and the drain voltage are both changed abruptly. Quasi-pulsed current-voltage (I-V) curves are derived from the transient characteristics. It is discussed how the slow current transients (lag phenomena) and the pulsed I-V curves are affected by the existence of substrate traps and surface states. It is shown that the so-called power compression could occur both due to substrate traps and due to surface states. Effects of impact ionization of carriers on these phenomena are also discussed. It is shown that the lag phenomena and the power compression are weakened when impact ionization of carriers becomes important, because generated holes may help the traps to change their ionized densities quickly.     

A switched-capacitor preprocessor for speech recognition

A switched-capacitor (SC) preprocessing system (preprocessor) which extracts and emphasizes the local peaks of the spectrum in real time is proposed for speech recognition systems. Main components of the system are a specially designed bandpass filter bank, a low-pass decimation filter bank, two-dimensional local peak extraction (LPE) filters, and a LPE filter selection circuit. Furthermore, a SC cascaded integrator-comb filter design technique is proposed to realize the decimation low-pass filter and the LPE filter. Finally, the system is tested by using two speech recognition systems.     

The induction of photocontact sensitivity in guinea pigs without UVB radiation

Allergic photocontact sensitization could be induced in guinea pigs with 3,3',4',5-tetrachlorosalicylanilide (TCSA), 3,4',5-tribromosalicylanilide (TBS), and bithionol using pretreatment with sodium lauryl sulfate (SLS) and long-wave ultraviolet (UVA) radiation. Mid-wave ultraviolet below 320 nm (UVB) was not necessary for the induction of sensitization. Combined use of SLS pretreatment with UVA radiation resulted in more effective sensitization than combined UVB and UVA radiation. Higher sensitization rates to TCSA and TBS were achieved by allowing rest periods between each of 5 2-hr exposures to UVA than by daily 1-hr exposures for 10 consecutive days. The opposite result was obtained with bithionol. Although UVB has been customarily used in the past for induction of photosensitivity, its role is only to irritate the site of induction.     

Thermodynamics of oxygen and nitrogen in liquid iron equilibrated with CaO- SiO2-Al2O3 slags

Nitrogen distribution ratios, L_N ( = (mass pct N)/[mass pct N]), between CaO-SiO₂-Al₂O₃ slags and liquid iron were measured at 1823 and 1873 K as a function of Si (or Al) content in metal, using lime and alumina crucibles. Based on these results and the reported values for activities of SiO₂ (or Al₂O₃), nitride capacities, C_(N), defined by (mass pct N) · PO₂/3/4/PN₂/1/2 were evaluated. Activities of SiO₂ (or Al₂O₃) obtained by using the values for L_N and C_(N) obtained in present and previous gas-slag experiments were compared with previous results. FUMIHIKO TAMURA formerly Graduate Student with the Department of Metallurgical Engineering, Tohoku University.     

Removal of estrogens from water using activated carbon and ozone

Estrogens (estron: E1; estradiol: E2; estriol: E3) are major water pollutants. For the removal of estrogens, activated carbon (AC) and ozone treatments were employed, and the chemical oxygen demand (COD) and pH of a single solution and multiple solution systems were investigated. The removal of estrogens increased with the amount of AC. The percentage of removed estrogens by AC in the single solution system was greater than that in the ternary solution system. The estrogens were completely removed using ozone, which also reduced COD and pH. The removal of estrogens increased the water quality and decreased the amount of organic carbon.     

Analysis of surface-state and impact-ionization effects on breakdown characteristics and gate-lag phenomena in narrowly recessed gate GaAs FETs

Effects of surface states and recess structures on breakdown characteristics of GaAs MESFETs are studied by two-dimensional (2-D) analysis. It is shown that the breakdown voltage could be raised when moderate densities of surface states are included. However, in a case with relatively high densities of surface states, the breakdown voltage could be drastically lowered when introducing a narrowly recessed gate structure. Effects of impact ionization on gate-lag phenomena in GaAs MESFETs are also studied. It is shown that the gate-lag becomes weaker when including the impact ionization. This is attributed to the fact that the potential profiles along the surface are drastically changed when the surface states capture generated carriers. It is suggested that there is a tradeoff relationship between raising the breakdown voltage and reducing the gate-lag.     

LCST phase separation and thermoreversible gelation in aqueous solutions of stereo-controlled poly(N-isopropylacrylamide)s

Stereoregular poly(N-isopropylacrylamide)s with controlled content of isotactic dyads have recently been synthesized, and interesting interference phenomena between LCST phase separation and high-temperature reversible gelation have been observed in their aqueous solutions. We develop a model solution in which dehydrated stereo-regular isotactic segments on polymers are driven into intermolecular cross-links leading to gelation. We theoretically calculate the phase diagrams for the varied content isotactic dyads and compare with the experimental data.     

Hydrothermal Wave Instability in a High-Aspect-Ratio Liquid Bridge of Pr > 200

The long-duration fluid physics experiments on a thermocapillary-driven flow have been carried out on the Japanese Experiment Module ‘Kibo’ aboard the International Space Station (ISS) since 2008. In these experiments, various aspects of thermocapillary convection in a half-zone (HZ) liquid bridge of high Prandtl number fluid have been examined under the advantages of the long-duration high-quality microgravity environment. In 2010, the authors succeeded to realize nonlinear convective fields in the HZ liquid bridge of rather high aspect ratio. Special attention was paid on to the complex convective fields, especially on the behaviors of the hydrothermal wave (HTW) over the free surface visualized by an infrared camera. In order to evaluate the characteristics of the nonlinear convective behaviors and their transition processes, the authors indicate the images taken by the infrared camera describing the time evolution of HTW, the spatio-temporal diagram, the Fourier analysis, and the pseudo-phase space, reconstructed from the time series of the scalar information of the liquid bridge, that is, surface temperature variation. In this paper, the authors introduce the signature of complex HTW behaviors observed at the long-duration on-orbit experiments, and make comparisons with some previous terrestrial and microgravity experiments.