Measurements of acoustic waves generated by electrical breakdown in a polypropylene film

Electrical breakdown of a polymer film generates a pressure wave that is believed to include information about the breakdown initiation point. We measured the breakdown pressure wave and the space charge distribution up to the electrical breakdown field by using the pulsed electro‐acoustic method in a 30 µm thick polypropylene film. We discuss electrical breakdown phenomena based on the breakdown pressure wave and the dependence of the space charge distribution on the applied field and temperature. At room temperature, the observed breakdown pressure wave had a pulse‐like shape with a width that depended on the polarity of the applied field. Positive space charge accumulation was observed near the cathode as a hetero space charge near the electrical breakdown field. At 60 °C, the width of the breakdown pressure wave showed no dependence on the applied field polarity and positive space charge accumulation was observed inside the film near the electrical breakdown field. These experimental results suggest that electrical breakdown phenomena are affected by hetero space charge accumulation and that the initiation point of electrical breakdown corresponds to the position of hetero space charge accumulation in 30 µm thick polypropylene film. ©1999 Scripta Technica, Electr Eng Jpn, 126(3): 1–8, 1999     

deNOx Performance and Reaction Mechanism of the Di-Air System

The detailed reaction mechanism of Di-Air, which showed the unprecedented high deNO_x performance at high temperature conditions, was studied in this work. Since the Di-Air phenomenon occurs with continuous short pulse injections of hydrocarbons over NSR (NO_x storage and reduction) catalyst, this study focused on the specific function of HC as an effective reductant for NO_x reduction reaction. As a first step, the deNO_x performance was compared with three different reductant gases including CO, H₂ and C₃H₆ in a modified synthetic gas bench equipped with a gas injector which enables continuous small amount of injections. At inlet gas temperature of 450 °C C₃H₆ showed the best deNO_x performance whereas H₂ was the best at 150 °C. Moreover the result of temperature programmed desorption showed that intermediate species represented by –NCO (isocyanates) produced from C₃H₆ was thermally more stable than that produced from CO. These results confirmed that the injected HC reacts with adsorbed NO_x on NSR catalyst generating thermally stable intermediates, which could contribute the high deNO_x performance at high temperature conditions.     

Bounds in the Lyapunov matrix differential equation

Upper and lower bounds for the trace of the solution of the Lyapunov matrix differential equation are derived. It is shown that they are obtained as solutions to simple scalar differential equations. As a special case, the bounds for the stationary solution give ones for the solution to the Lyapunov algebraic equation.     

Wideband phase-locked loop circuit with real-time phase correction for frequency modulation atomic force microscopy

We have developed a wideband phase-locked loop (PLL) circuit with real-time phase correction for high-speed and accurate force measurements by frequency modulation atomic force microscopy (FM-AFM) in liquid. A high-speed operation of FM-AFM requires the use of a high frequency cantilever which, however, increases frequency-dependent phase delay caused by the signal delay within the cantilever excitation loop. Such phase delay leads to an error in the force measurements by FM-AFM especially with a low Q factor. Here, we present a method to compensate this phase delay in real time. Combined with a wideband PLL using a subtraction-based phase comparator, the method allows to perform an accurate and high-speed force measurement by FM-AFM. We demonstrate the improved performance by applying the developed PLL to three-dimensional force measurements at a mica/water interface.     

Thermal Decomposition of RDX Composite Propellants

The thermal decomposition characteristics of RDX, binders, and RDX composite propellants were studied using thermal analytical techniques. Three kinds of binders were tested to elucidate the role of binder on the burning rate of the propellants. There were no apparent correlations between the thermal decomposition rates of binders and the burning rates of propellants, whereas there was a correlation between the decomposition temperature and the burning rate of the propellants. It is found that the major factor which controls the burning rate is the initial thermal-decomposition stage of the binders. Thus, the burning rate of nitramine composite propellants appeared to be largely dependent on the physical and chemical properties of binder.     

Water distribution at solid/liquid interfaces visualized by frequency modulation atomic force microscopy

Interfacial phenomena at solid/water interfaces play an important role in a wide range of industrial technologies and biological processes. However, it has been a great challenge to directly probe the molecular-scale behavior of water at solid/water interfaces. Recently, there have been tremendous advancements in frequency modulation atomic force microscopy (FM-AFM), enabling its operation in liquids with atomic resolution. The high spatial and force resolutions of FM-AFM have enabled the visualization of one-dimensional (1D) profiles of the hydration force, two-dimensional (2D) images of hydration layers and three-dimensional (3D) images of the water distribution at solid/water interfaces. Here I present an overview of the recent advances in FM-AFM instrumentation and its applications to the study of solid/water interfaces.     

Atomic-resolution imaging in liquid by frequency modulation atomic force microscopy using small cantilevers with megahertz-order resonance frequencies

In this study, we have investigated the performance of liquid-environment FM-AFM with various cantilevers having different dimensions from theoretical and experimental aspects. The results show that reduction of the cantilever dimensions provides improvement in the minimum detectable force as long as the tip height is sufficiently long compared with the width of the cantilever. However, we also found two important issues to be overcome to achieve this theoretically expected performance. The stable photothermal excitation of a small cantilever requires much higher pointing stability of the exciting laser beam than that for a long cantilever. We present a way to satisfy this stringent requirement using a temperature controlled laser diode module and a polarization-maintaining optical fiber. Another issue is associated with the tip. While a small carbon tip formed by electron beam deposition (EBD) is desirable for small cantilevers, we found that an EBD tip is not suitable for atomic-scale applications due to the weak tip-sample interaction. Here we show that the tip-sample interaction can be greatly enhanced by coating the tip with Si. With these improvements, we demonstrate atomic-resolution imaging of mica in liquid using a small cantilever with a megahertz-order resonance frequency. In addition, we experimentally demonstrate the improvement in the minimum detectable force obtained by the small cantilever in measurements of oscillatory hydration forces.     

Coronary hyperreactivity to adrenergic stimulation and increased nocturnal vagal tone trigger coronary vasospasm

The present study was undertaken to analyse the effect of fluoxetine upon murine T-lymphocyte proliferation. We found that fluoxetine exerted a dual effect, which depended on the degree of lymphocyte activation: at mitogenic concentration (2 microg/mL) of concavalin A (Con A), we observed an inhibitory effect on cellular proliferation, whereas, on submitogenic Con A concentration (1 microg/mL), fluoxetine stimulated the cellular response. Given these facts, we studied PKC activation and calcium mobilisation in both stimulatory and inhibitory effects of fluoxetine on T-cell proliferation. We observed that fluoxetine increased PKC translocation obtained with 1 microg/mL Con A concentration, whereas PKC was degraded when 2 microg/mL was used. This mechanism is thought to be mediated by calcium mobilisation. According to our results, fluoxetine seemed to modulate calcium influx, which, in turn, would influence PKC translocation, modulating the immune response.     

Ion implantation model considering crystal structure effects

An ion implantation model for crystalline targets is proposed. The model is based on the Monte Carlo method. Ion behavior is determined by directly referring to three-dimensional crystal structure data. Both channeling and dechanneling can be well simulated by modeling many-body scattering with lattice atoms and introducing atom thermal vibration effects. This model is used to simulate low-energy boron implantation in crystal silicon. Significant boron distribution tail spreading is predicted due to subchanneling effects, even if the ion beam is tilted and/or the crystal surface is covered with amorphous layers. These predictions agree with experimental data. Amorphization effects on two-dimensional boron distribution were also investigated. It was predicted that locally insufficient preamorphization causes marked lateral spreading of boron     

Space charge formation and breakdown in polyethylene influenced by the interface with semiconducting electrodes

This paper deals with the influence of interface between polyethylene and semiconducting electrode on the space charge formation and electrical breakdown. Low‐density polyethylene (LDPE) films attached with different semiconducting electrodes were subjected to the DC breakdown test, and corresponding space charge distribution was measured. A heat treatment to LDPE itself did not bring about a significant change in space charge profile; however, when a semiconducting electrode was hot‐pressed, the impurities would migrate into LDPE at high temperature, leading to the change in space charge profile. Furthermore, it was suggested from the comparison between the results with degassed and as‐received semiconducting electrodes that some carriers relating to impurities in the electrode would move into LDPE under the voltage. In addition, it was shown that the breakdown is not determined by the field at the cathode which can supply sufficient electrons, but by the maximum field across the specimen, suggesting that an increase in conduction current due to the generation and/or injection, rather than the electronic avalanche process, leads to the breakdown. © 2001 Scripta Technica, Electr Eng Jpn, 138(3): 19–25, 2002