Tetsuji Oda

The University of Tokyo, Tōkyō, Japan

Are you Tetsuji Oda?

Claim your profile

Publications (151)166.6 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Mouse melanoma cells in a culture medium are treated using a nanosecond pulsed streamer discharge plasma and the correlations between the rate of cell death and the densities of reactive species (OH, O, and NO) in the plasma are measured. The plasma is irradiated onto the culture medium surface with a vertical gas flow of an O2/N2 mixture from a glass tube at various gas flow rates and O2 concentrations. The densities of the reactive species are measured very close to the culture medium surface, where the reactive species interact with the culture medium, using laser-induced fluorescence. In the case of the N2 discharge (O2 = 0%), an increase in gas flow rate decreases OH density because it lowers the water vapor concentration by diluting the vapor, which is required for OH production. The increase in gas flow rate also leads to a decreased cell death rate. In the case of the O2/N2 discharge, on the other hand, an increase in O2 concentration at a fixed flow rate does not affect the rate of cell death, although it considerably changes the O and NO densities. These findings indicate that some reactive species derived from water vapor such as OH are responsible for the melanoma cell death, whereas those from O2, such as O and NO, are less likely responsible. They also indicate the importance of water evaporation from the culture medium surface in cell treatment.
    No preview · Article · Oct 2015 · Journal of Physics D Applied Physics
  • Source
    Ippei Yagi · Ryo Ono · Tetsuji Oda · Koichi Takaki
    [Show abstract] [Hide abstract]
    ABSTRACT: In plasma medicine, plasma is applied to a wet surface and is often accompanied by dry-gas flow. The dry-gas flow affects water evaporation from the wet surface and influences production of reactive species derived from water vapor, such as OH radicals. In this study, the effect of the dry-gas flow on two-dimensional distributions of humidity and OH radical density are examined by measuring them using laser-induced fluorescence (LIF). First, humidity is measured when nitrogen flows from a quartz tube of 4 mm inner diameter onto distilled water and agar media from 5 mm distance. NO gas is added to the nitrogen as a tracer and humidity is obtained from the quenching rate of NO molecules measured using LIF. This measurement has a spatial resolution of 0.2 mm3 and a temporal resolution of less than 220 ns. The two-dimensional humidity distribution shows that the dry-gas flow pushes away water vapor evaporating from the wet surface. As a result, a low-humidity region is formed near the quartz tube nozzle and a high-humidity region is formed near the wet surface. The thickness of the low-humidity region reduces with increasing gas flow rate. It is 0.1–0.5 mm for the flow rate of higher than 0.3 l min−1. Next, the OH density is measured when a nanosecond pulsed streamer discharge is applied to a distilled water surface with dry-air flow. The OH density decreases with increasing gas flow rate due to decreased humidity. When the flow rate is lower than 0.1 l min−1, the OH distribution is approximately uniform in the plasma region, while the humidity distribution shows a large gradient. The importance of the thin high-humidity region on the flux of reactive species onto the wet surface is discussed.
    Full-text · Article · Feb 2015 · Plasma Sources Science and Technology
  • Shungo Zen · Ryo Ono · Tetsuji Oda
    [Show abstract] [Hide abstract]
    ABSTRACT: Dye-sensitized solar cell (DSSCs) requires sintering of TiO2 photoelectrode at 450∼550 °C to be manufactured. However, the high-temperature sintering is disadvantageous because it limits the use of materials that cannot withstand high temperatures. In our previous work, we proposed plasma and low-pressure mercury (Hg) lamp ultraviolet (UV) treatments of the TiO2 electrode to reduce the sintering temperature by half. It was concluded that the effect of the surface treatment is due to reactive oxygen species (O3, O, OH) produced by the plasma and UV light. In this paper, we propose a new technique for TiO2 photoelectrode, which can reduce the sintering temperature from 450 °C to 150 °C. We were also succeded in manufacturing plastic DSSC at 150-°C sintered by using the new technique. The conversion efficiency of plastic DSSC was 2.9 %.
    No preview · Article · Dec 2014
  • [Show abstract] [Hide abstract]
    ABSTRACT: The electrical and particle collection characteristics of a 1,200-m3/hr-dry electrostatic precipitator (ESP) and a 400-m3/hr-wet ESP for a 0.7 MW-Oxy-PC (oxygen-pulverized coal) combustion and carbon capture and storage (CCS) pilot plant were evaluated under varying air and oxygen combustion operational parameters of the ESPs. The corona current of a dry ESP reduced by oxy-firing was compared with that for the same applied voltage with air firing, which resulted in a decreased collection performance during oxy-firing at the same applied voltage. However, the decreased collection performance could be avoided by simply increasing the applied voltage to reach the same corona power consumption as with air firing because the collection performance of the ESP was an exponential function of the power consumption divided by the gas flow rate regardless of combustion conditions. The wet ESP used here had a thin water film on the collection plates due to the patented design of the collection plates, with water supplied by gravitational force from holes on the collection plates with TiO2nanoparticles coated on ball blasted surface. The system only consumed water at a rate of 1.7 L/min/m2. The collection efficiency of the wet ESP was higher than 90% even for fine particles and mists, which enabled an overall particle collection efficiency of 99.98% to be achieved with both the dry and wet ESPs, corresponding to total gravimetric emission of 1.8 mg/m3 at the inlet of the CCS facility. The wet ESP had the additional effect of removing SO2 and SO3 at 64.5% and 23.1% efficiency, respectively.
    No preview · Article · Nov 2014 · Journal of Aerosol Science
  • [Show abstract] [Hide abstract]
    ABSTRACT: An ultraviolet (UV) process using a low-pressure mercury lamp is affected by ambient humidity. It is due to strong influence of humidity on the production of ozone and other radicals by the UV light. In this paper, a photochemical reaction model under the irradiation of a low-pressure mercury lamp is developed, and the effect of humidity on the production of ozone and other radicals [O, O(D1), O2(a1Δg), O2(b1Σg+), OH, HO2, H, and H2O2] by a low-pressure mercury lamp is discussed using the reaction model. The validity of the reaction model is confirmed by comparing the ozone densities calculated using the model with experimentally measured ozone densities, and they showed good agreement. The reaction model shows that the ozone density decreases with increasing humidity for three reasons: (i) attenuation of 185 nm light due to absorption by H2O, leading to a decreased O atom production by O2 + hν(185 nm) ⟶ O + O which is required to produce ozone by O + O2 + M ⟶ O3 + M; (ii) ozone destruction by O3+hν(254nm)⟶O(D1)+O2(a1Δg), where the resulting O(D1) partly reacts with H2O before converting back to O3 after quenching to O; and (iii) an ozone destruction cycle OH + O3 ⟶ HO2 + O2 and HO2 + O3 ⟶ OH + 2O2. The effect of humidity on the densities of other radicals is also discussed using the reaction model.
    No preview · Article · Jan 2014 · Journal of Photochemistry and Photobiology A Chemistry
  • Yusuke Nakagawa · Ryo Ono · Tetsuji Oda
    [Show abstract] [Hide abstract]
    ABSTRACT: Plasma application for environment improvement is desirable. In order to improve the efficiency of toxic gas decomposition by plasma, it is worthwhile to clarify the behavior of radicals in nonthermal plasma. Although previous studies have revealed the behavior of radical densities and temperatures in atmospheric discharge, they are not yet connected to apprehension or simulation of practical toxic gas decomposition by atmospheric plasma. In this study, the coaxial dielectric barrier discharge cylinder reactor is prepared, where the radical behavior and the toxic gas decomposition efficiency can be measured altogether. The density of OH radical is directly measured by laser-induced fluorescence, and trichloroethylene (TCE) decomposition efficiency is also investigated in the same reactor. TCE decomposition efficiency is suppressed as background humidity increases. On another front, OH density measurement in ac barrier discharge indicates that OH density is about 2–4 $times 10^{11} hbox{cm}^{-3}$ in time and spatial average and saturated with increasing humidity. From the saturation pattern, the initial OH density is estimated to be about the order of $10^{14} hbox{cm}^{-3}$ in streamer site. In addition, TCE addition in background reduces OH density, which indicates that OH reacts with TCE. The reason for the suppression of decomposition efficiency with increasing humidity is estimated as a consequence of O radical reduction by water-originated particles.
    No preview · Article · Jan 2014 · IEEE Transactions on Industry Applications
  • Atsushi Komuro · Ryo Ono · Tetsuji Oda
    [Show abstract] [Hide abstract]
    ABSTRACT: The effect of pulse rise rate on a streamer discharge is investigated through both experiments and simulations. Pulsed voltages with a pulse rise rate of 0.11–0.52 kV ns−1 are applied to point-to-plane electrode configurations, and the effects are observed from ICCD photographs. The streamer emission of light is simulated by a previously developed two-dimensional streamer simulation model, and the simulation results are compared with experimental results. The results show that as the pulse rise rate is decreased, there is a decrease in the discharge current, velocity of the primary streamer, diameter of the streamer channel and emission length of the secondary streamer. The simulated reduced electric field of the primary streamer head remains constant and does not depend on the pulse rise rate. The simulated temporal variations of O and OH radical production show that almost the same number of the radicals are produced in the primary streamer, regardless of the pulse rise rate. However, the radical production in the secondary streamer decreases as the pulse rise rate decreases. Therefore, the pulse rise rate affects the ratio of radical production in the primary streamer to that in the secondary streamer.
    No preview · Article · Jun 2013 · Plasma Sources Science and Technology
  • Shungo Zen · Daiki Saito · Ryo Ono · Tetsuji Oda
    [Show abstract] [Hide abstract]
    ABSTRACT: Dye-sensitized solar cells (DSSCs) require the sintering of TiO2 paste at 450–550 °C in their manufacture. However, high-temperature sintering is disadvantageous because it limits the use of materials that cannot withstand high temperatures. We have developed a new technique for reducing the sintering temperature through ultraviolet (UV) treatment of the TiO2 photoelectrode. The UV treatment enables the sintering temperature to be reduced 250 °C while maintaining the energy conversion efficiency.
    No preview · Article · Jun 2013 · Chemistry Letters
  • H. J. Kim · B. Han · G. B. Cho · Y. J. Kim · J. S. Yoo · T. Oda
    [Show abstract] [Hide abstract]
    ABSTRACT: An electrostatic diesel particulate matter filtration system (EDPS) has been tested using 3000 cc diesel engines operating at steady state and standard (European Stationary Cycle (ESC) 13 mode) conditions. The system consisted of a flowthrough filter (FTF) and a charging device with a round perforated plate imposing an electrostatic field onto the FTF. An insulating device for the high-voltage electrode was protected from pollutant deposition by using an air slit at velocity of 7 m/s to maintain a stable corona discharge under an exhaust temperature exceeding 300°C. Under steady-state engine conditions, the performance test of the EDPS showed high collection performance (based on the particulate matter (PM) number) of nearly 80–99%, while the efficiency of the FTF remained at 15–50%. Comparing the performance of the EDPS with a commercialised diesel particulate filter (DPF) and an FTF under the ESC 13 mode, the EDPS was almost 40% more efficient than the FTF and 10% less efficient than the DPF, while achieving 73% lower pressure drop than the DPF. Thus, the novel filtration system can achieve collection performance similar to the DPF with significantly less pressure drop.
    No preview · Article · Jun 2013 · International Journal of Automotive Technology
  • Atsushi Komuro · Ryo Ono · Tetsuji Oda
    [Show abstract] [Hide abstract]
    ABSTRACT: The production process of OH radicals in an atmospheric-pressure streamer discharge is studied. A streamer discharge model is developed to analyse the characteristics of a pulsed positive streamer discharge in point-to-plane electrodes filled with humid air at atmospheric pressure. The results indicate that the behaviour of OH radicals in and after the discharge pulse is characterized by three reaction processes: 'OH-production', 'OH-cycle' and 'OH-recombination'. The first process of OH-production includes dissociation reactions of H2O with O(1D) and N2, which are the main production processes of OH in the discharge. Immediately after the OH-production process, the OH radicals are destroyed by a reaction with O(3P) to form O2 and H. Then the subsequent reactions produce OH again through the reaction of H + HO2, which is the OH-cycle process. Finally, the OH radicals are consumed by the OH-recombination process.
    No preview · Article · Apr 2013 · Journal of Physics D Applied Physics
  • T. Oda · Y. Nakagawa · R. Ono
    [Show abstract] [Hide abstract]
    ABSTRACT: Optical diagnosis of high pressure plasma is one of the most powerful tools for investigating chemical reaction mechanisms in the high pressure plasma region. The authors developed various optical measurement systems by using tunable lasers, such as (two-photon-)laser-induced-fluorescence, coherent-anti-Stokes Raman scattering, time evolution of optical emission imaging and others for detecting O3, O, OH, N, NO* and other radicals in atmospheric pressure plasma. Outline of basic measuring techniques developed by the authors for high pressure plasma diagnosis are explained and real examples of plasma diagnosis are demonstrated in this paper. For example, density distributions of single nitrogen (N) and excited nitrogen molecule (N2(A)) below the discharge needle generated by the pulse plasma suggest that single N might be generated in the secondary streamer, while N2(A) might be generated in the primary streamer, and single N decomposes NO more than N2(A).
    No preview · Article · Mar 2013 · Journal of Physics Conference Series
  • [Show abstract] [Hide abstract]
    ABSTRACT: A novel positive-polarity electrostatic precipitator (ESP) was developed using an ionization stage (0.4 x 0.4 x 0.14 m(3) ) with 16 carbon fiber ionizers in each channel and a collection stage (0.4 x 0.4 x 0.21 m(3) ) with parallel metallic plates. The single-pass collection efficiency and clean air delivery rate (CADR) were measured by standard tests using KCl particles in 0.25-0.35 μm. Performance was determined using the Deutsch equation and established diffusion and field-charging theories, and also compared with the commercialized HEPA filter type air cleaner. Experimental results showed that the single-pass collection efficiency of the ESP ranged from 50 to 95% and decreased with the flow rate (10 to 20 m(3) /min) but increased with the voltage applied to the ionizers (6 to 8 kV) and collection plates (-5 to -7 kV). The ESP with 18 m(3) /min achieved a CADR of 12.1 m(3) /min with a voltage of 8 kV applied to the ionization stage, and with a voltage of -6 kV applied to the collection stage. The concentration of ozone in the test chamber (30.4 m(3) ), a maximum value of 5.4 ppb over 12 hours of continuous operation, was much lower than the current indoor regulation (50 ppb). © 2013 John Wiley & Sons A/S. Published by Blackwell Publishing Ltd.
    No preview · Article · Feb 2013 · Indoor Air
  • Y. Nakagawa · R. Ono · T. Oda
    [Show abstract] [Hide abstract]
    ABSTRACT: In order to solve air pollution problem, atmospheric plasma application is desirable. In this study, we realized the real-time OH density measurement in trichloroethylene (TCE) decomposition by coaxial cylinder pulsed barrier discharge. Laser-induced fluorescence measurement indicated that OH density is about 30 ppm at 3 μs after discharge when +28 kV is applied. As for the negative discharge, OH measurement revealed that OH production is almost the same but OH density is about a half compared to those in positive discharge, due to the difference in streamer radius. The TeE addition in background accelerated OH decay, and by chemical reaction simulation, OH-TeE reaction coefficient was estimated to be about 2.3 × 10-12 [cm3/s]. Humidity effect on TeE decomposition efficiency in N2 pulsed barrier discharge is also investigated using the same reactor. The increasing humidity resulted in enhancement of TeE decomposition efficiency, indicating that OH plays important role in TeE decomposition.
    No preview · Conference Paper · Jan 2013
  • I. Yagi · R. Ono · T. Oda · K. Takaki

    No preview · Article · Jan 2013
  • A. Komuro · R. Ono · T. Oda

    No preview · Article · Jan 2013
  • Source
    Yusuke Nakagawa · Yuta Tomimura · Ryo Ono · Tetsuji Oda
    [Show abstract] [Hide abstract]
    ABSTRACT: Dilute trichloroethylene (about 250 ppm TCE) in air was decomposed by the non-thermal plasma processing. Two factors were focused. One is the amount effect of the ozone decomposition catalyst. The authors reported already that the energy efficiency of dilute TCE decomposition was much improved if the catalyst is enough but the maximum efficiency was not yet realized. Moreover, the residual ozone concentration was still pretty high at high specific energy density of 100 J/L. Especially that concentration should be less than 0.1 ppm if the processed gas was exhausted in the living space. If the catalyst amount is enlarged for the same volume gas flow rate, higher decomposition efficiency is observed still more. Most TCE (more than 90%) is decomposed at SED of 10 J/L, if the 3g catalyst was used in this case but carbon balance was not so high. Moreover, the leakage of the ozone was pretty high if SED is more than 20J/L. The decomposition byproducts will be discussed at the meeting because the carbon balance is not so good at SED of more than 40J/L. As the second target, humidity effect for the decomposition efficiency was examined again and some new results are obtained. The former experiment was done at dry condition (no artificial humidifying) but the decomposition efficiency was improved at the humidity of 20 % (still pretty dry). That fact will be explained by the generation and behavior of OH radicals. OH radical is observed by using OPO laser fluorescence method now. That discussion will be done at the meeting.
    Preview · Article · Jan 2013 · International Journal of Plasma Environmental Science and Technology
  • Atsushi Komuro · Ryo Ono · Tetsuji Oda
    [Show abstract] [Hide abstract]
    ABSTRACT: A streamer discharge has been considered to be an effective production source of chemically active radicals. However, theoretical understanding of the discharge phenomenon and the chemical kinetics is still poor. This study is devoted to reveal the radical behaviors in an atmospheric pressure streamer discharge in H2O/O2/N2 gas mixtures. The present model includes a discharge model, a gas dynamics model and chemical kinetics model with vibrationally excited molecules. It is shown that the numerically obtained axial distributions of O, N and OH radical are consistent with our experimental results. Direct dissociation processes, two-step dissociation with vibrationally excited molecules and a quenching of excited O atoms are predominant for O, N and OH radical productions, respectively. In addition, a gas temperature and decay rates of radicals in post-discharge periods are also compared with our experimental results. Numerically simulated gas temperatures in post-discharge phase increase as humidity increase. This tendency has already shown in our previous experimental results and it is successfully reproduced in our model. It is also shown that the rise in gas temperature affects subsequent radical decay processes.
    No preview · Article · Oct 2012
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Dye-sensitized solar cell (DSSC) is receiving increasing attention as low-cost photovoltaic device. The DSSC has a nanoporous TiO 2 electrode made by sintering a TiO 2 paste applied on a conductive glass plate at 450-550 °C. To improve the performance of the TiO 2 electrode, we have developed surface treatment of the TiO 2 electrode using dielectric barrier discharge (DBD). The DBD treatment improves the energy conversion efficiency, η, of DSSC by a factor of 1.1. In addition, the DBD treatment has an effect of lowering the sintering temperature, T s , of TiO 2 paste. Without the DBD treatment, η decreases with T s and becomes 0% for T s ≤ 300 °C. On the other hand, with the DBD treatment, η = 0.8η 0 for T s = 300 °C and η = 0.3η 0 for T s = 150 °C, where η 0 is the energy conversion efficiency for DSSC sintered at 450 °C without the DBD treatment. The DBD treatment is also applied to plastic substrate DSSC in addition to the glass substrate DSSC. However, the DBD treatment causes damage to the TiO 2 electrode and cannot be applied to the plastic substrate DSSC. More moderate DBD treatment is required for the plastic substrate DSSC to avoid the damage on the TiO 2 elec-trode.
    Full-text · Article · Oct 2012
  • Seiya Yonemori · Ryo Ono · Tetsuji Oda
    [Show abstract] [Hide abstract]
    ABSTRACT: An atmospheric-pressure helium plasma jet is getting much attention because of its low heat load. It is known that active species such as OH radical play important role in many plasma processes, for example, in plasma medical care or in plasma sterilization. When using the plasma jet for surface treatment, it is important that the amount of OH radical provided into objectives. We measured OH density in the vicinity of the surface of objectives using laser induced fluorescence (LIF). The plasma jet was generated when AC 8 kHz, 10 kV was applied. When the plasma jet extended onto the dry glass surface, the maximum OH density was 0.2 ppm. On the other hand, the maximum OH density was 1 ppm when the plasma jet extended onto the wet surface. In addition, time-evolution of OH density between two successive voltage pulses was measured. On the edge of the plasma jet, OH density was at maximum and rapidly decreased between two pulses. Those results suggest that there are three ways of OH production; first, the dissociation of H2O included in discharge gas; secondly, the dissociation of H2O included in the ambient air; finally, the dissociation of H2O evaporates from the wet surface.
    No preview · Article · Oct 2012
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To remove particles in corrosive gases generated by semiconductor industries, we have developed a novel non-metallic, two-stage electrostatic precipitator (ESP). Carbon brush electrodes and grounded carbon fiber-reinforced polymer (CFRP) form the ionization stage, and polyvinyl chloride collection plates are used in the collection stage of the ESP The collection performance of the ESP downstream of a wet scrubber was evaluated with KC1, silica, and mist particles (0.01-10 pm), changing design and operation parameters such as the ESP length, voltage, and flow rate. A long-term and regeneration performance (12-hr) test was conducted at the maximum operation conditions of the scrubber and ESP and the performance was then demonstrated for 1 month with exhaust gases from wet scrubbers at the rooftop of a semiconductor manufacturing plant in Korea. The results showed that the electrical and collection performance of the ESP (16 channels, 400x400 mm2) was maintained with different grounded plate materials (stainless steel and CFRP) and different lengths of the ionization stage. The collection efficiency of the ESP at high air velocity was enhanced with increases in applied voltages and collection plate lengths. The ESP (16 channels with 100 mm length, 400x400 mm2x540 mm with a 10-mm gap) removed more than 90% of silica and mistparticles with 10 and 12 kV applied to the ESPat the air velocity of 2 m/s and liquid-to-gas ratio of 3.6 L/m3. Decreased performance after 13 hours ofcontinuous operation was recovered to the initial performance level by 5 min of water washing. Moreover during the 1-month operation at the demonstration site, the ESP showed average collection efficiencies of 97% based on particle number and 92% based on total particle mass, which were achieved with a much smaller specific corona power of 0.28 W/m3/hr compared with conventional ESPs.
    Preview · Article · Aug 2012 · Journal of the Air & Waste Management Association (1995)

Publication Stats

2k Citations
166.60 Total Impact Points

Institutions

  • 1990-2015
    • The University of Tokyo
      • • Department of Electrical and Electronics Engineering
      • • Department of Electrical Engineering and Information Systems
      • • Department of Medical Engineering
      Tōkyō, Japan
  • 2004
    • Tokyo Electron
      Edo, Tōkyō, Japan
  • 1989-1998
    • Kumamoto University
      Kumamoto, Kumamoto Prefecture, Japan