Masafumi Jinno

Analysis of a pulsed discharge within single bubbles in water under synchronized conditions

Synchronized generation of single bubbles and an underwater discharge in the bubbles was performed using pulsed injection of feed gas with a piezoelectric valve. The differences in the discharge appearance and the after-effect on the bubble were systematically studied with different kinds of gases. In molecular gases such as N2 and O2, surface discharge along the inner bubble surface predominated and the disturbance caused wrinkles on the bubble surface, while in rare gases, such as He, Ne and Ar, a large hump formed on the smooth surface due to a rather volumetric discharge. When the input power was increased, the discharge sometimes caused the collapse of a single bubble, producing smaller bubbles. It was observed by emission spectra that excited species of OH, H and O radicals were produced in the discharge plasma. The emission intensity ratio of the Hα line to the OH band was larger in He and Ne gases than in other gases, suggesting differences in the dissociation channels.

A dynamic collisional-radiative model of a low-pressure mercury-argon discharge lamp: a physical approach to modeling fluorescent lamps for circuit simulations

A dynamic collisional-radiative model of a low-pressure mercury (Hg)-argon (Ar) discharge lamp for application in circuit simulations is presented. The model is implemented in MATLAB as a set of coupled rate equations that are solved simultaneously to give the electron density, the density of the 6/sup 3/P/sub 0,1,2/ states and the electron temperature. These parameters are used to compute the electrical parameters of the discharge positive column and hence the time-dependent voltage-current characteristics of the lamp. The parameters predicted by the model are compared with published experimental data and show good agreement. Calculated lamp voltage-current characteristics based on the model are shown to be in good agreement with direct measurements on commercial fluorescent lamps.

Fundamental Research on Mercuryless Fluorescent Lamps II – External Electrode Operation with Pulsed Dielectric Barrier Discharge –

The characteristics of electrodeless xenon discharge fluorescent lamps using dielectric barrier discharge are described in this paper. All lamps were operated with pulsed discharge. The luminance of phosphor increases as the pressure of xenon increases. As the pressure of xenon increases, the second peak of phosphor emission increases. These increases seem to be caused by the VUV light of xenon excimers. Therefore, in order to obtain high luminance, xenon should be filled at high pressure. In the case of the lamp operated by inner electrodes, if only xenon is contained in the lamp, the cathode is bombarded and is damaged by the large mass of a xenon ion. On the other hand, the external electrode type is never damaged by the ions or electrons. Moreover, the efficacy of the external electrode type is as great as the inner electrode type, and it can be improved by increasing the distance between electrodes.

Fundamental Research on Mercuryless Fluorescent Lamps I – Inner Electrode Operation with Pulsed Discharge –

The characteristics of xenon-neon discharge fluorescent lamps with inner electrodes are described in this paper. All lamps were operated by pulsed discharge. When the partial pressure of neon is high, the ignition voltage and operation voltage are low because of the Penning effect. Thus, a higher mixing ratio of neon is desirable for lower ignition and operation voltages. However, the luminance of phosphor increases as the mixing ratio of xenon increases. As the pressure of xenon increases, the second peak of phosphor emission in afterglow increases. These increases seem to be caused by the VUV light of xenon excimers. Therefore, though there is the problem of ion bombardment of the cathode under a high operation voltage, the pulsed discharge of the xenon-neon mixture at a high xenon mixing ratio is desirable in mercuryless fluorescent lamps because a strong radiation of xenon excimer is obtained.

Nitrogen: a possible substitute for mercury as a UV-emitter for mercury-less low-pressure discharge fluorescent lamps using Penning-like energy transfer

Nitrogen is well known as a UV-emitter because of its 2nd positive band lying around 350 nm. However, it is a molecular gas and when energy is stored in rotational or vibrational levels, the gas temperature can become high enough to melt even the glass tube. To avoid such problems the authors tried to use the Penning-like effect between the argon metastables and nitrogen C 3Πu states with very low partial pressure of nitrogen compared with that of the argon. By adding a very small amount of nitrogen to argon, the discharge changes drastically. Though pure argon discharge and pure nitrogen discharge are both unstable and easy to constrict, a small amount of nitrogen improves the stability of the discharge and emits the nitrogen 2nd positive band UV light by energy transfer from the argon metastable to the nitrogen molecule C 3Πu state. Nitrogen-added argon fluorescent lamps operated at 30 kHz of alternative square voltage wave achieve about 4500 cd m−2 at 3.75 W and at 9.3 kPa of pressure with good dimming characteristics. The maximum luminance should be higher than this because the input power is limited by the power supply. At this condition the luminous efficacy achieves 7.1 lm W−1. These results show a possibility of argon–nitrogen fluorescent lamps as mercury-less fluorescent lamps.

Gas-Specific Characteristics of Argon Low-Frequency Atmospheric-Pressure Nonequilibrium Microplasma Jet

The authors have demonstrated an argon low-frequency microplasma jet and experimentally investigated the gas-specific difference compared with a helium jet, which has been used in many studies. Both argon and helium plasma jets show ambient neutral nitrogen molecule emissions as well as those of carrier gases; however, the emission of nitrogen molecule ions is observed only in the helium plasma jet. This is determined by whether the metastable level of the carrier gas is higher or lower than the ionization potential of the nitrogen molecule. Moreover, for a larger flow rate, the jet length decreased and green emission was observed, which is assigned to O (I) and ArO emissions.

Investigation of plasma induced electrical and chemical factors and their contribution processes to plasma gene transfection.

This study has been done to know what kind of factors in plasmas and processes on cells induce plasma gene transfection. We evaluated the contribution weight of three groups of the effects and processes, i.e. electrical, chemical and biochemical ones, inducing gene transfection. First, the laser produced plasma (LPP) was employed to estimate the contribution of the chemical factors. Second, liposomes were fabricated and employed to evaluate the effects of plasma irradiation on membrane under the condition without biochemical reaction. Third, the clathrin-dependent endocytosis, one of the biochemical processes was suppressed. It becomes clear that chemical factors (radicals and reactive oxygen/nitrogen species) do not work by itself alone and electrical factors (electrical current, charge and field) are essential to plasma gene transfection. It turned out the clathrin-dependent endocytosis is the process of the transfection against the 60% in all the transfected cells. The endocytosis and electrical poration are dominant in plasma gene transfection, and neither permeation through ion channels nor chemical poration is dominant processes. The simultaneous achievement of high transfection efficiency and high cell survivability is attributed to the optimization of the contribution weight among three groups of processes by controlling the weight of electrical and chemical factors.

Comparative Inactivation of Bacillus subtilis Spores Using a DBD-Driven Xenon Iodide Excilamp and a Conventional Mercury Lamp

In this paper, we compared the inactivation of Bacillus subtilis spores in water by means of a dielectric-barrier-discharge (DBD)-driven XeI* excilamp and a low-pressure mercury lamp. The main part ( ~ 76%) of the excilamp output was due to the B → X transition of XeI* exciplex at 253 nm. It is shown for the first time that a better sterilization action is achieved with the DBD-driven XeI* excilamp compared with the monochromatic mercury lamp at the same UV dose. The contribution of an atomic iodine emission in the range of 178-207 nm has been confirmed. Germ-reduction experiments with the XeI* excilamp have been carried out in a steady-state mode and in a water-flow reactor.

Relative enhancement of near-UV emission from a pulsed low-pressure mercury discharge lamp, using a rare gas mixture

In this paper, we explain the physical reasons for the enhancement of near-UV and visible emissions from a low-pressure mercury–argon discharge under pulse drive conditions. The conditions of operation that maximize the enhancement of near-UV and visible radiation, including the effect of the buffer gas, are investigated. We show that for a pulsed discharge, electron–ion recombination followed by cascade radiative transitions is the process responsible for most of the 365 nm emission and that argon with a small admixture of krypton is the buffer gas composition that leads to maximum radiative emission due to near-resonant energy transfers to mercury high-lying levels.

Luminance and efficacy improvement of low-pressure xenon pulsed fluorescent lamps by using an auxiliary external electrode

As the environmental awareness of people becomes stronger, the demand for mercury-free light sources also becomes stronger. The authors have been keeping their interest in developing mercury-free discharge lamps, especially in low-pressure xenon as the most promising UV sources to substitute mercury. In this paper the authors report the effect of auxiliary external electrode (AEE) on the pulsed xenon fluorescent lamps. In this research two types of structures are used. One is the standard type, which has one anode and one cathode inside the lamp. The other is the double anode type, which has two anodes and one cathode inside the lamp. By using the AEE the luminance and the efficacy are improved simultaneously. The luminance is improved by about 129% for the standard structure type and 20% for the double anode type. The efficacy is improved by 60% for the standard type and by 63% for the double anode type. We call this effect/method the Jinno?Motomura effect/method (JM-effect/method). Regarding the result of the xenon metastable atom distribution, measured by LIF, this effect is attributed to the plasma potential control and enlargement of the positive column by AEE.