Modulation of the Time Relation of Action Potential Impulses Propagating Along an Axon

Action potentials are successively evoked on a squid giant axon by a Gaussian impulse train which has a white spectral density for low frequencies. The time relations of the response impulses are different from those of the stimuli because of the refractory period of the axon which cuts off too short pulse intervals and modifies the traveling velocities of the action potentials. As a result, the action potential sequence acquires l/f component on the low frequency tail of the power spectral density. It is quite probable that the biological information which is carried by the time relations of the action potentials is disturbed by 1/f noise. The observed result is compared with the result of computer simulation.     

A novel process for the formation of poly(p-phenylene terephthalamide) film from liquid crystalline solutions

A novel process for the formation of biaxially balanced films of poly(p-phenylene terephthalamide) was developed. The liquid crystalline sulphuric acid solution is extruded through a slit die on a flat plate. The optically anisotropic to isotropic transition is generated by controlling the temperature and/or the water content in sulphuric acid before coagulation. The wet gel films are dried while holding their width and length constant. The films thus produced are transparent and biaxially oriented. Young's modulus of 12 GPa, tensile strength of 450 MPa, and elongation at break of 25% were obtained in the plane of the film. Such films which possess high dimensional and thermal stabilities are expected to be useful for new practical uses under severe conditions.     

Mass transfer process of hydrogen via ceramic proton conductor membrane of electrochemical hydrogen pump

The blanket tritium recovery system using the electrochemical hydrogen pump with proton conductor membrane has been proposed. The feature of the electrochemical hydrogen pump is that the driving force of hydrogen transportation is a potential difference. Therefore, it might be effective to apply the hydrogen pump to the blanket sweep gas (the low hydrogen and water vapor pressure). Perovskite-type ceramic such as SrCe_0.95Yb_0.05O_3−α, is one of the candidate proton conductor for hydrogen pump and its ionic hydrogen transportation properties have been investigated. In this work, the basic mass transfer equation for hydrogen, in which the apparent proton conductivity is used as the over-all mass transfer coefficient, is proposed. And then, the apparent proton conductivities were estimated from experimental data using these equations, and mass transfer of hydrogen via proton conductor membrane was discussed by using the apparent conductivity.     

Sputtering condition optimization of sputtered IrOx and TiN stimulus electrodes for retinal prosthesis

We have optimized the sputtering conditions for sputtered IrOx and TiN electrodes for retinal prosthesis. The basic electrochemical characteristics were evaluated by cyclic voltammetry, and the surface morphology was inspected by atomic force microscopy. To measure the charge delivery capacity (CDC), a 300‐µm diameter electrode was formed, a balanced biphasic current pulse was applied, and the voltage response was measured. From the experimental results, the CDCs of IrOx and TiN in the best sputtering conditions were improved by more than 8 and 4 times compared to that of Pt, respectively. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Infrared and near-infrared spectral evidence for water clustering in highly hydrated poly(methyl methacrylate)

First, we developed quantitative analytical methods of water in poly(methyl methacrylate) (PMMA) in various hydrated states by utilizing the first combination and OH stretching bands of water at about 5240 and 3630 cm-1, respectively. Next, we investigated how the state of water depended on its quantity or the mole ratio of water to the CO (denoted as the H2O/CO ratio), which only interacts with water in PMMA, mainly on the basis of the band feature of the OH stretching bands. Below the H2O/CO ratio of 0.032, the contained water, which shows two clear bands at about 3630 and 3550 cm-1, is hydrogen-bonded to two C=O groups as C=O::H-O-H::O=C to form "the hydration core". The spectrum of the water that exceeds the ratio in question shows one broader band only, the frequency of which shifts downward with the increasing hydration. From detailed analysis of the behavior of the OH stretching and combination bands in relation to the H2O/CO ratio, we have concluded that the water that exceeds the hydration ratio becomes mobile to aggregate or "cluster" around hydrated sites rather than nonhydrated ones in the PMMA matrix, although the latter is much larger in population.     

Simulation of photoacoustic imaging of microcracks in silicon wafers using a structure-changeable multilayered thermal diffusion model

The detection characteristics for photoacoustic imaging of microcracks in silicon wafers were theoretically and quantitatively investigated using a numerical simulation. The simulation is based on a one-dimensional multilayered thermal diffusion model coupled with the thermal-wave impedance of each layer, the layer structures of which are constructed along the wafer surface and are variable according to the scanning position of the point heat source. As the modulation frequency was reduced, the spatial resolution of the temperature amplitude profile at the cracks decreased, showing good agreement with the experimentally obtained photoacoustic amplitude images. At a modulation frequency of 200 kHz, for cracks with narrow air gaps of up to 20 nm, which is much smaller than both the beam spot size of 1.5 microm and the thermal diffusion length of 12 microm, the temperature amplitude is twice that of regions without cracks, and the temperature contrast increased with an increase in the modulation frequency. These calculation results suggest the effectiveness of using a high modulation frequency, making it possible to detect microcracks of the order of 10 nm.     

Sensitive detection of chemical-induced genotoxicity by the Cypridina secretory luciferase reporter assay, using DNA repair-deficient strains of Saccharomyces cerevisiae

Yeast-based reporter assays are useful for detecting various genotoxic chemicals. We established a genotoxicity assay using recombinant strains of Saccharomyces cerevisiae, each containing a reporter plasmid with the secretory luciferase gene from Cypridina noctiluca, driven by a DNA damage-responsive promoter of the yeast RNR3 gene. This system detected the genotoxicity of methyl methanesulphonate (MMS) as sensitively as conventional yeast-based reporter assays, using the β-galactosidase gene in a concentration-dependent manner; it also detects four other genotoxic chemicals, allowing us to monitor DNA damage easily by skipping the cell extraction process for the assay. We examined Cypridina luciferase levels induced by MMS and three antitumour agents using a set of BY4741-derived deletion mutants, each defective in a DNA repair pathway or DNA damage checkpoint. Luciferase activities were particularly enhanced in mutant strains with mms2 Δ and mag1 Δ by exposure to MMS, rad59 Δ and mlh1 Δ to camptothecin and mms2 Δ and mlh1 Δ to mitomycin C, respectively, compared with their parent strains. Enhanced reporter activities were also found in some DNA repair mutants with cisplatin. These observations suggest that this Cypridina secretory luciferase reporter assay using yeast DNA repair mutants offers convenient and sensitive detection of the potential genotoxicity of numerous compounds, including antitumour drugs and studying the mechanisms of DNA damage response in yeast.     

Development of gate drive circuit for next‐generation ultrahigh‐speed switching devices

This paper describes a gate drive circuit which is capable of driving an ultrahigh‐speed switching device and of suppressing high‐frequency noise caused by its high dV/dt ratio of 104 V/μs order. SiC (silicon carbide)‐based power semiconductor devices are very promising as next‐generation ultrahigh‐speed switching devices. However, one of their application problems is how to drive them with less high‐frequency noise without sacrificing their ultrahigh‐speed operation capability. The paper proposes a new gate drive circuit specialized for such devices, which charges and discharges the input capacitance of the device by using an impulse voltage generated by inductors. This ultrahigh‐speed switching operation causes a high‐frequency common‐mode noise current in the gate drive circuit, which penetrates an isolated power‐supply transformer due to the parasitic capacitance between the primary and the secondary windings. In order to overcome this secondary problem, a toroidal multicore transformer is also proposed in the paper in order to reduce the parasitic capacitance drastically. By applying the former technique, the turn‐on time and turn‐off time of the power device were shortened by 50% and by 20%, compared with a conventional push‐pull gate drive circuit, respectively. In addition, the latter technique allows reduction of the peak common‐mode noise current to 25%, compared with the use of a conventional standard utility power‐supply transformer. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(4): 52–60, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21124