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KIYAN Tsuyoshi

    Department of Electric and Electronic Engineering　Professor/Manager
Last Updated :2024/04/25

Researcher Information

Degree

  • Doctor of Science（Kumamoto University）
  • Doctor of Engineering（Kumamoto University）

J-Global ID

Research Interests

  • Plasma   Discharge   Pulsed Power   

Research Areas

  • Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Electrical power engineering
  • Energy / Basic plasma science
  • Energy / Applied plasma science

Published Papers

  • Tomohiro Furusato; Naokazu Ashizuka; Takeshi Kamagahara; Yoshinobu Matsuda; Takahiko Yamashita; Mitsuru Sasaki; Tsuyoshi Kiyan; Yuki Inada
    IEEE Transactions on Dielectrics and Electrical Insulation IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC 25 (5) 1807 - 1813 1070-9878 2018/10 [Refereed]
     
    The relation between breakdown characteristics and plasma temperature of a pulsed arc discharge in highly pressurized CO2 was investigated up to a supercritical phase. A transient arc discharge was generated by applying nanosecond pulsed voltage with a rising rate of 0.7 kV/ns to a point-to-plane gap of 1 mm. The breakdown voltage, arc current, and consumption energy increased with the CO(2 )density in the gas phase. However, they were constant at the CO2 densities in the supercritical phase. The plasma temperature determined from the blackbody radiation ranged from 8000 to 12000 K and its dependence with respect to the CO2 density was all similar to the breakdown voltage, arc current, and consumption energy characteristics except under the critical density of CO2 (469 kg/m(3)). Although the breakdown voltage, arc current, and consumption energy in supercritical phase were also constant against the CO2 density, the plasma temperature demonstrated a local decrease around the critical density. The anomaly of the plasma temperature is consistent with the calculated result of the isochoric specific heat of CO2 which has a local maximum around the critical density.
  • T. Furusato; N. Ashizuka; T. Kamagahara; T. Fujishima; T. Yamashita; M. Sasaki; T. Kiyan
    2017 IEEE 19th International Conference on Dielectric Liquids, ICDL 2017 Institute of Electrical and Electronics Engineers Inc. 2017- 1 - 4 2153-3733 2017/11 [Refereed]
     
    This study describes spectroscopic measurement of pulsed arc discharge in high pressure CO2 including supercritical (SC) phase (1.6-8.1 MPa). A positive nanosecond pulsed voltage was applied to a needle-to-plane electrode. Spectral broadening of OI at 777 nm increased from gas to sub-critical phase and decreased around the critical condition of CO2. The decrease was presumed to be caused by critical anomaly of thermal conductivity. In addition, spatial distribution of pulsed arc discharge emission intensity was processed from images taken. Basically, emission intensity was consistent with spectral broadening. Brightest emissions were observed in the SC phase (8.1 MPa).
  • T. Kamagahara; N. Ashizuka; T. Furusato; T. Fujishima; T. Yamashita; M. Sasaki; T. Kiyan
    2017 IEEE 19th International Conference on Dielectric Liquids, ICDL 2017 Institute of Electrical and Electronics Engineers Inc. 2017- 1 - 4 2153-3733 2017/11 [Refereed]
     
    In this paper, dependence of positive polarity nanosecond pulsed breakdown voltage on CO2 density was examined from gas to supercritical (SC) phases. The pulsed voltage with equivalent voltage rise rate (0.75 kV/ns) was applied to needle-to-plane electrode in all experimental conditions. In addition, the time lag of spark at high pressure gas and SC phases were investigated with Laue plots. The obtained results were as follows: 1) the breakdown voltage increased in gas phase and saturated in SC phase 2) the local reduction of breakdown voltage specifically appeared at medium density of 90.8 kg/m3 (gas phase) 3) in the high pressure gas phase (82.1 – 103.1 kg/m3), the statistical time lag was extremely small at 90.8 kg/m3 irrespective of constant formative time lag 4) it was difficult to quantify the formative and the statistical time lags in SC phase.
  • Takashi Ishikawa; Tomohiro Mori; Tsuyoshi Kiyan
    2016 IEEE International Power Modulator and High Voltage Conference, IPMHVC 2016 Institute of Electrical and Electronics Engineers Inc. 645 - 648 2017/08 [Refereed]
     
    Dielectric barrier discharge (DBD) reactor was investigated in order to improve the processing performance on nitric oxide (NO) removal. We investigated the influence of increasing the pulse repetition rate under the same specific energy density (SED) in simulated gas under the room temperature. Non-Thermal plasma was generated by applying a high voltage pulsed power supply to DBD reactor. The power supply having the magnetic pulse compression method is used to obtain a pulsed high voltage. The SED was adjusted by changing the applied voltage of the DBD reactor, and pulse repetition rate. The results indicate the following 1) the low applied voltage to DBD reactor is effective against NO removal performance 2) the high pulse repetition rate is effective against NO removal performance in same SED. The related results of detail will be reported.
  • Takashi Ishikawa; Tomohiro Mori; Tsuyoshi Kiyan
    IEEJ Transactions on Fundamentals and Materials Institute of Electrical Engineers of Japan 137 (9) 549 - 550 1347-5533 2017 [Refereed]
     
    We have developed a capacitor charger for 1 kV, 55 mJ/pulse, 5 kpps pulsed power application, which is attainable to 361.8 J/s in average charge power. The charger based on the forward type with two switches consists of topology having the advantage of lower voltage stress, and fast response due to control by a field programmable gate array. The charger is able to accomplish 1.6 μs of a short delay time that mean from the turn-off the inhibit signal to start charging time. Simulation results were applied to the selection of switch devices of laboratory prototype charger of 1 kV, 1 MHz.
  • Yuta Iwasaki; Takashi Ishikawa; Tomohiro Mori; Tsuyoshi Kiyan
    2015 IEEE PULSED POWER CONFERENCE (PPC) IEEE 438 - 441 2158-4915 2015 
    In this study, the experimental studies of the breakdown characteristics and post-breakdown phenomena of nanosecond pulse electric discharge in high pressure fluids including supercritical state of nitrogen have reported. A series of experiments of dielectric property, breakdown voltage were measured in the conditions of the pressure range of 0.1 to 13.0 MPa with the temperature of 298 K by applied to two type gap electrode configurations. For study of post-breakdown phenomena, the visualizations of pulse discharges were conducted using a Nd:YAG laser system as Schlieren diagnostics. The experimental results show as follow: 1) the measured breakdown voltage increase with increasing almost linearly pressure against at the experimental condition in which the phase variation changes from a gas to supercritical phases; 2) the dielectric recovery of SCN2 phase was recognized up to 1 kHz at nearly-complete except voltage dispersion; 3) shock wave velocity was estimated to about 400 m/s at the condition of P = 4 MPa, T = 298 K corresponding to SCN2 phase.
  • Z. B. Yang; S. H.R. Hosseini; T. Kiyan; S. Gnapowski; H. Akiyama
    IEEE Transactions on Dielectrics and Electrical Insulation Institute of Electrical and Electronics Engineers Inc. 21 (3) 1089 - 1094 1070-9878 2014 [Refereed]
     
    The paper describes results of experimental studies to evaluate the effects of phasechange and/or density variation at the post-breakdown on the dielectric recovery characteristics of liquid and supercritical CO2. The study aims to explore the possibility of using supercritical CO2 to develop high-repetition-rate pulsed-power switches. The experimental setup consisted of a sphere-to-sphere 10 mm radius electrodes configuration with 50 μm gap distance. Three phases of pressurized CO2 subcritical liquid state (SLS), liquid with pressure higher than critical point (LHCP), and supercritical phase (SC), were used for the experiments. Experimental results revealed that SC CO2 has a very short recovery time making it an appropriate fluid for MHz range highly-repetitive switches. Post-breakdown stage in SLS consisted of gas phase and liquid phase at the plasma channel between the electrodes, with the alternative expansion-contraction motion behavior of gas bubble determining dielectric recovery characteristics. Post-breakdown stages in SC were similar to those in LHCP, generating a low density region at the post-breakdown, where the state of density variation determined dielectric recovery characteristic. The low density region could be compressed by the surrounding medium, resulting in a considerably shorter recovery time. © 1994-2012 IEEE.
  • Pyrrole conversion induced pulse discharge plasma over a water surface under high-pressure argon
    Wahyudiono; H. Watanabe; S. Machmudah; T. Kiyan; M. Sasaki; H. Akiyama; M. Goto
    Chemical Engineering and Processing: Process Intensification 61 51-57  2013 [Refereed]
  • Tomohiro Furusato; Takeshi Ihara; Tsuyoshi Kiyan; Sunao Katsuki; Masanori Hara; Hidenori Akiyama
    IEEE TRANSACTIONS ON PLASMA SCIENCE IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC 40 (11) 3105 - 3115 0093-3813 2012/11 [Refereed]
     
    This paper deals with the initiation mechanism of a negative nanosecond pulsed discharge in supercritical (SC) carbon dioxide that was examined in detail using Schlieren and photomultiplier techniques. A negative pulsed voltage with a rise time of about 90 ns and half-width of 410 ns was applied to the point electrode. The experimental results show that: 1) The negative primary streamer was of a form quite different than that of a positive one: a bushlike negative streamer and a filamentlike positive streamer; 2) a drastic change in the density dependence of streamer initiation voltage appeared around the subcritical phase in the characteristics for streamer initiation voltage versus medium density; and 3) a shock wave of speed 1-1.5 Mach began growth following a delay of around 50 ns from the streamer initiation. It was predicted from the analysis of the experimental results that the drastic change in the streamer initiation voltage versus medium density characteristics may be due to a transition between the two types of generation mechanisms of the initial electron: electron detachment from negative ions in the gas phase and field electron emission from the point electrode in the SC and liquid phases. The shock wave was presumed to be caused by thermal relaxation of the vibrational energy in carbon dioxide molecules in a decay process of the primary streamer.
  • Tomohiro Furusato; Takeshi Ihara; Suguru Kameda; Tsuyoshi Kiyan; Sunao Katsuki; Masanori Hara; Hidenori Akiyama
    IEEE TRANSACTIONS ON PLASMA SCIENCE IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC 40 (10) 2425 - 2430 0093-3813 2012/10 [Refereed]
     
    A positive pulsed prebreakdown in a needle-to-plane gap at CO2 phases up to supercritical (SC) condition was observed by means of Schlieren imaging method. Our observations confirmed that the pattern of positive prebreakdown discharge was a treelike streamer independent of medium phase and that the SC phase led to streamer branches of higher complexity than those in the gas and liquid phases. Both streamer branches' complexity and fractal dimension variation of the developing streamer were quantitatively assessed by means of fractal analysis. Experimental results are summarized as follows: 1) SC carbon dioxide (SCCO2) led to the greatest complexity of streamer branching in comparison with gas and liquid phases; 2) the fractal dimensions of gas, liquid, and SC phases of CO2 were estimated to around D = 1.47, 1.60, and 1.73 with a coefficient of determination R-2 > 0.99; and 3) the fractal dimension D in SCCO2 stayed constant at around D = 1.7 during the streamer growth phase.
  • Preparation of Diamond Like Carbon (DLC) and Its Functionalization with Supercritical Fluid Pulsed Discharge Treatment
    Mitsuru Sasaki; Koichi Nagafuchi; Wahyu Diono; Atsushi Nagira; Tsuyoshi Kiyan; Motonobu Goto; Hidenori Akiyama
    Proc. 10th International Symposium on Supercritical Fluids 1-6  2012/05 [Refereed]
  • T. Ihara; T. Furusato; S. Kameda; T. Kiyan; S. Katsuki; M. Hara; H. Akiyama
    JOURNAL OF PHYSICS D-APPLIED PHYSICS IOP PUBLISHING LTD 45 (7) 075204  0022-3727 2012/02 [Refereed]
     
    In this work, the initiation process of an electrical discharge in pressurized carbon dioxide up to the liquid and supercritical phases was investigated using Schlieren and photomultiplier techniques. A pulsed positive voltage with a rise time of about 40 ns and half-width of 150 ns was applied to a point-to-plane gap. The experimental results showed that the discharge started with a primary streamer consisting of a burst primary streamer and a successive primary streamer, and a back discharge followed them. It was predicted from an analysis of the experimental results that the initiation criterion of a burst primary streamer was electron multiplication on the order of 10(8) independent of the medium conditions. That is, a direct ionization process without bubble formation is supported as an initiation mechanism of nanosecond positive discharges in pressurized carbon dioxide. The medium state in the burst primary streamer channel was a gas or pseudo-gas of 50-200 kg m(-3) density.
  • Hidenori Akiyama; Tsuyoshi Kiyan; Seiichi Kamaga; Mariko Akiyama; Yasuhiro Ohshima; Kazutake Kozono
    2012 International Conference on Information Technology Based Higher Education and Training, ITHET 2012 2012 
    Credited lectures using the web-based e-learning in Japan began at higher education institutions in 2001. The lecture evaluation was done by using a questionnaire to students when the lecture began. The questionnaire survey is carried out again in 2012 after ten years' separation. The load to make e-learning contents is still high for professors. A rapid e-learning system including the production and distribution of e-learning streaming contents with animation and laser pointer has been developed. This system is in use. © 2012 IEEE.
  • Seiichi Kamaga; Kazutake Kozono; Mamoru Suemitsu; Yasuhiro Ohshima; Tsuyoshi Kiyan; Hidenori Akiyama
    IEEJ Transactions on Fundamentals and Materials 132 (12) 1118 - 1119 0385-4205 2012 
    A rapid e-Learning system including the production and distribution of e-learning streaming contents with animation and laser pointer has been developed. The KUMA (Kumamoto Universal and Multipurpose Authoring) system for the video conversion is improved as a core of the Rapid e-Learning system. About 100 students are able to access the contents at the same time by adjusting a transmission rate. The application server as Windows is improved by using the Java Servlet. © 2012 The Institute of Electrical Engineers of Japan.
  • Tomohiro Furusato; Takeshi Ihara; Tsuyoshi Kiyan; Sunao Katsuki; Masanori Hara; Hidenori Akiyama
    PROCEEDINGS OF THE 2012 IEEE INTERNATIONAL POWER MODULATOR AND HIGH VOLTAGE CONFERENCE IEEE 47 - 50 2380-808X 2012 [Refereed]
     
    The initiation mechanism of a negative pulsed discharge in pressurized carbon dioxide including supercritical (SC) phase was studied using pulsed Schlieren and photomultiplier techniques. The appearance of the negative streamer at its initial stage was quite different from the positive one: a bush of negative polarity and a filament of positive polarity. A clear discontinuity existed around the sub-critical phase, characterized by streamer initiation voltage versus medium condition: The streamer initiation voltage increased with the medium density in gas phase, but was mostly independent of the medium density in SC and liquid phases. Calculation of field emission current according to Fowler-Nordheim equation suggested that the streamer initiation in both SC and liquid phases was caused by field emission, while within gas phase, initial electrons might be supplied by electron detachment from CO2- ions.
  • Takeshi Ihara; Tsuyoshi Kiyan; Sunao Katsuki; Tomohiro Furusato; Masanori Hara; Hidenori Akiyama
    IEEE TRANSACTIONS ON PLASMA SCIENCE IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC 39 (11) 2650 - 2651 0093-3813 2011/11 [Refereed]
     
    A positive pulsed streamer in a needle-to-plane gap in supercritical carbon dioxide was observed by using a laser schlieren method. The treelike streamer is initiated at a needle electrode when the electric field reaches approximately 9 MV/cm and propagates spatially toward a plane electrode. The streamer is accompanied by the cylindrical and spherical shock waves. A low-density region along the streamer channel decays with time, and no bubble formation occurs finally.
  • Wahyudiono; Hiroshi Watanabe; Tsuyoshi Kiyan; Hidenori Akiyama; Mitsuru Sasaki; Motonobu Goto
    Transactions of the Materials Research Society of Japan The Materials Research Society of Japan 36 (3) 459 - 464 1382-3469 2011/09 [Refereed]
     
    Hydrothermality, as it is applicable at relatively low temperatures, is regarded as efficient for the selective decomposition of industrial wastewater disposal containing organic pollutants. Electrical discharge produced by high-voltage pulsed power has gained attention as a recently developed method used to generate hydrothermality required to degrade organic pollutants in waste water as this method not only generates a hydroxyl radical, it also generates atomic oxygen with a high oxidation potential. Here, we utilize these conditions to study the removal characteristics for aniline and its products. The experiments were conducted at 353 K and 5 MPa using a batch type reactor. Intermediate compounds from the conversion of aniline in the aqueous products were identified by gas chromatography mass spectrometry (GC-MS) and quantified using high performance liquid chromatography (HPLC). Aniline can be considered representative of the aromatic ring structures present in waste water. The maximum aniline conversion was 30.21 % with a 10000 times pulsed discharge plasma. The conversion of aniline increased with the existence of the electric filed which produced by pulsed discharge plasma. The results suggest the use of pulsed plasma is effective at the decomposition of aniline in hydrothermal conditions.
  • Tsuyoshi Kiyan; Takeshi Ihara; Suguru Kameda; Tomohiro Furusato; Masanori Hara; Hidenori Akiyama
    IEEE TRANSACTIONS ON PLASMA SCIENCE IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC 39 (8) 1729 - 1735 0093-3813 2011/08 [Refereed]
     
    Pulsed discharge plasma in supercritical fluids (SCFs) has attracted a great deal of attention in the field of plasma application for chemical processing. Characteristics of electrical breakdown are one of the important concerns for dielectric reliability of a plasma reactor with SCFs. In this paper, the pulsed breakdown voltages of quasi-uniform gaps were measured by changing the CO(2) medium from gas to supercritical phase at a given temperature, and Weibull statistical analysis was applied to the measured breakdown voltages. The area effect on breakdown voltage, which is known to give an equivalent effective constant to Weibull shape parameter m, was examined with three sphere-to-sphere gaps. The experimental results indicate that the dispersion in the pulsed breakdown voltage in pressurized carbon dioxide obeys Weibull distribution, and the Weibull shape parameter m depends on the state of the CO(2) medium. The dependence of m on the medium density that was obtained from direct analysis of breakdown voltages for a given electrode system indicated a similar tendency to that of the effective constant by area effect analysis.
  • T. Furusato; T. Ihara; S. Kameda; T. Kiyan; S. Katsuki; M. Hara; H. Akiyama
    Digest of Technical Papers-IEEE International Pulsed Power Conference 280 - 284 2011 
    This paper deals with visualization of positive pulsed streamers and arc discharge under a needle-to-plane gap in supercritical carbon dioxide (SCCO 2) by the Schlieren Method. In addition, differences in streamer branches in gas, liquid and supercritical phases of CO 2 are evaluated by means of fractal dimension. The experimental results are summarized as follows: 1) a tree-like streamer growing from the tip of needle was successfully visualized. The field strength for streamer initiation and the mean velocity of the streamer are estimated as approximately 9 MV/cm and 60 km/s, respectively. Pre-breakdown phenomena in SCCO 2 are divided into two processes: streamer growth and shockwave expansion. 2) Streamer branches in SC phase were found to be more complicated than in other phase of CO 2. 3) Bubble formation in the streamer initiation process was not recognized in SCCO 2. For dielectric breakdown, the cylindrical shockwave grows along the streamer channel. A trace of light emission is recognized near the center of the arc column with a residual image of the streamer. © 2011 IEEE.
  • T. Ihara; T. Furusato; S. Kameda; T. Kiyan; S. Katsuki; M. Hara; H. Akiyama
    Digest of Technical Papers-IEEE International Pulsed Power Conference 231 - 234 2011 
    Pulsed streamers in highly pressurized carbon dioxide up to and including the supercritical state were observed by means of Schlieren method. The fluid temperature was set to T = 305 K pressures, to P = 7.5 and 8.0 MPa. The gap was needle-to-plane the gap lengths in positive and negative were d = 7 and 1 mm, respectively. Pulse voltages of positive/negative polarity generated by a magnetic pulse compression generator were applied to the needle electrode. The main results obtained can be summarized as follows. 1) Positive streamers in supercritical state appeared as a branched tree associated with shock waves of spherical and cylindrical shapes. 2) The negative corona appearance in supercritical state differed greatly from the positive one, and was spherical without branches at the initial stage. The spherical shock wave started from the needle tip at the corona onset. Appearances of positive/negative discharge clearly differed. These results indicate a polarity effect on pulsed discharge phenomena. © 2011 IEEE.
  • Yasuhiro Ohshima; Kazutake Kozono; Seiichi Kamaga; Tsuyoshi Kiyan; Mamoru Suemitsu; Hidenori Akiyama
    2011 International Conference on Information Technology Based Higher Education and Training, ITHET 2011 2011 
    When an instructor creates an educational content with narration on Microsoft PowerPoint, it is the easiest method that he/she uses one's built-in feature of recording narration because there is no need to install any other software. We constructed the content authoring system for e-Learning, named Kumamoto Universal and Multipurpose Authoring (KUMA) system, which is based on cloud computing. Using the system, an instructor only has to upload the slide with narration created on PowerPoint to the system, and then he/she can publish a Windows Media streaming video and a PDF slide. The application of the system is the website of streaming video lectures contributed by researchers in the field of pulsed power, which we call "Streaming Book on Pulsed Power Engineering". Another application of it is the website of video lectures for graduate students as a part of blended learning. To deliver streaming videos to more than 100 students simultaneously, we need to configure quality of encoding streaming videos and estimate the amount of transferring data and the network traffic load. The purpose of this study is to examine the traffic load for streaming e-Learning content in applications of KUMA system. In this work, we use Windows Media Load Simulator to simulate the connections from more than 100 students. © 2011 IEEE.
  • Wahyudiono; Tsuyoshi Kiyan; Mitsuru Sasaki; Hidenori Akiyama; Motonobu Goto
    2011 IEEE REGION 10 CONFERENCE TENCON 2011 IEEE 986 - 990 2011 
    Electric field generated by pulsed high-voltage discharge plasma over water surface has been performed under high-pressure argon environments to convert pyrrole compound. In this work, oligomerization of pyrrole in water as a reaction media and the effects of various parameters with pulsed high-voltage arc discharge plasma are studied. Such as plasma applied under hydrothermal conditions generates high-energy electrons, ions, and radicals, which in turn may generate new reaction fields, leading to effective organic compounds oxidation for both homogeneous and heterogeneous reactions. Here, we utilize pulse discharge plasma over water surface to study the removal characteristics for pyrrole into more valuable higher amines group which has more fascinating for both the industry and the scientific community. In comparison, the reaction of pyrrole was also conducted in supercritical water at temperatures of 698-748 K and pressure of 30 MPa. The experiments were conducted at 313 K and 1 - 2 MPa using a batch type reactor. Intermediate compounds from the conversion of pyrrole in the aqueous products were identified by GC-MS (gas chromatography mass spectrometry) and quantified using high performance liquid chromatography (HPLC). The conversion of pyrrole could approach to 25 % and 80 % after treatment by pulsed discharge plasma and supercritical water, respectively.
  • Motonobu Goto; Mitsuru Sasaki; Wahyudiono; Koichi Nagafuchi; Hiroshi Watanabe; Tsuyoshi Kiyan; Takao Namihira; Hidenori Akiyama
    AIChE Annual Meeting, Conference Proceedings 2010/12 
    Micro-plasmas generated by pulsed discharge in sub- and supercritical fluids have possibilities as a novel reaction field. We have studied generation of pulsed discharge plasma in subcritical or supercritical fluids, such as carbon dioxide, water, or argon. Two-phase system, where liquid and supercritical fluid coexist, was also used as a media to generate discharge plasma. The discharge behavior was investigated in terms of breakdown phenomena. Plasma generated in supercritical carbon dioxide was used for the reaction of fatty acid. By treating in discharged plasma, reaction containing C-C bond cleavage and C-C bond formation proceeded. We applied plasma generated in subcritical water to chemical reactions of phenol and aniline. Phenol was decomposed in discharged plasma at 523 K and 25 MPa. The analysis of oily product found that phenol was converted into its oligomers and polymers, where hydroxyl radical of phenoxy radical was bonded at meta position in phenol. When aniline was used as a reactant, the polymerization of aniline was also observed. Discharge plasma was generated at the interface between supercritical fluid and water. The phenomena of plasma was observed and analyzed.
  • Development of Streaming Contents Generation System for Rapid e-Learning
    Seiichi Kamaga; Kazutake Kozono; Mamoru Suemitsu; Tsuyoshi Kiyan; Yasuhiro Ohshima; Hidenori Akiyama
    Proceedings of the 18th International Conference on Computers in Education 301 - 303 2010/11 [Refereed]
  • Masahiro Akiyama; Takashi Sakugawa; S. Hamid R. Hosseini; Eri Shiraishi; Tsuyoshi Kiyan; Hidenori Akiyama
    IEEE TRANSACTIONS ON PLASMA SCIENCE IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC 38 (10) 2588 - 2592 0093-3813 2010/10 [Refereed]
     
    The high reliability, high repetition rate, high performance, and compactness of pulsed-power generators are required for industrial applications. Also, the control of a pulsed-power generator becomes more complicated with increasing functions. An all-solid-state pulsed-power generator can be controlled by using a field-programmable gate array (FPGA). The pulsed-power generator consists of a charger, a magnetic pulse compression circuit, and a controller using the FPGA. The performance characteristics of the pulsed-power generator, such as the variable firing interval from shot to shot and the diagnosis of incorrect operation, are easily achieved by rewriting the programming of the Verilog hardware description language on the FPGA.
  • Tsuyoshi Kiyan; Takeshi Ihara; Suguru Kameda; Sunao Katsuki; Masanori Hara; Hidenori Akiyama
    Proceedings of 4th Japan/US Symposium On Pulsed Power And Plasma Applications 2010 (36) 69 - 73 2010/08
  • KIYAN Tsuyoshi; IHARA Takeshi; AKIYAMA Hidenori; HARA Masanori
    Journal of plasma and fusion research 社団法人プラズマ・核融合学会 86 (6) 317 - 323 0918-7928 2010/06 [Refereed]
     
    工業応用と放電物理の面で興味があり,かつ,熱力学ならびに電気的特性の著しく異なる水,二酸化炭素,ヘリウムの超臨界状態における誘電,放電,プラズマ特性を概観した.また,亜臨界水中のパルスプラズマ放電によるフェノールの転化に関する最近の実験にも触れた.
  • M. Mitsugi; A. Yoshida; H. Watanabe; T. Kiyan; M. Takade; K. Miyaji; T. Namihira; Y. Kuwahara; H. Akiyama; M. Hara; M. Sasaki; M. Goto
    INTERNATIONAL CONFERENCE ON HIGH PRESSURE SCIENCE AND TECHNOLOGY, JOINT AIRAPT-22 AND HPCJ-50 IOP PUBLISHING LTD 215 (1) 012088  1742-6588 2010 [Refereed]
     
    Supercritical fluid with plasma is a type of green processing media because this technique does not use catalyst and toxic solvents. In this study, we carried out experiments of organic materials in the presence of discharged plasma in sub-and supercritical water to evaluate the possibility for new reactions. For this purpose, we used SUS316 reactor that generates plasma at temperature and pressure up to 573K and 30MPa, respectively. 100 mmol/L aqueous phenol solution was used as starting material. The reactions were carried out at temperature of 523K and under pressure of 25MPa. After a series of reactions, water-soluble, water-insoluble (oily products), solid residue and gaseous product were obtained. For the analysis of these products, HPLC, GC-MS, TOC, GC-TCD and TOF-MS were used. The highest phenol conversion was 16.96% obtained at 523K, 25MPa and with 4000 times discharged plasma. Polymerized phenol was obtained as a product.
  • Kazutake Kozono; Seiichi Kamaga; Tsuyoshi Kiyan; Yasuhiro Ohshima; Yuuki Akitomi; Hidenori Akiyama
    IEEJ Transactions on Fundamentals and Materials 130 (1) 103 - 109 0385-4205 2010 [Refereed]
     
    An e-Learning authoring system for advanced graduate education has been developed. The general goal is developing not only the e-Learning authoring system but also the universal and multipurpose system using a streaming technology. Here is the development of the web-based authoring system using the streaming technology. The important information technology of this system is to convert from PowerPoint file with sound into Windows Media file. The developed system gives professors or instructors who are not familiar with the information technology, especially the streaming technology an easy making of the e-Learning contents using the streaming technology. © 2010 The Institute of Electrical Engineers of Japan.
  • 超臨界二酸化炭素におけるナノ秒パルスストリーマの観測
    猪原武士; 喜屋武毅; 勝木淳; 原雅則; 秋山秀典
    放電学会誌 53 (3) 2010
  • Takeshi Ihara; Tsuyoshi Kiyan; Sunao Katsuki; Takashi Sakugawa; Masanori Hara; Hidenori Akiyama
    Proceedings of the 2010 IEEE International Power Modulator and High Voltage Conference, IPMHVC 2010 670 - 673 2010 
    This paper describes the temporal development of pulsed discharges in supercritical carbon dioxide (SCCO2). A magnetic pulsed compression generator with a step-up transformer was used to deliver high voltage pulses to a 5 mm-gap needle-to-plate electrode in SCCO2 (9.4 MPa and 313 K). A time-resolved shadowgraph method was employed to observe pre- and post-breakdown phenomena. A continuous wave Ar laser (488 nm) was used as light source and a gated ICCD camera was synchronized with the pulsed discharge. The observation shows that the sequence of pulsed discharge phenomena in SCCO2 including branched streamer in the pre-breakdown phase, shock wave propagation and density fluctuation in the post-breakdown phase. Rayleigh-Taylor instability was observed in the boundary between gaseous and SC regions. © 2010 IEEE.
  • Mamoru Suemitsu; Yuuki Akitomi; Tsuyoshi Kiyan; Yasuhiro Ohshima; Kazutake Kozono; Seiichi Kamaga; Hidenori Akiyama
    2010 9th International Conference on Information Technology Based Higher Education and Training, ITHET 2010 136 - 139 2010 
    A web-based authoring system for rapid e-Learning has been developed. This system not only converts PowerPoint with voice into an e-Learning content using multimedia technology, but also publishes an e-Learning content. Using this system, even a researcher who is not familiar with the Information Technology can easily create an e-Learning content. This system named as Kumamoto Universal and Multipurpose Authoring system is helpful to spread rapid e-Learning. ©2010 IEEE.
  • Conversion of Organic Compounds by Pulsed Discharge Plasma in Sub- and Supercritical Fluids
    Motonobu Goto; Mitsuru Sasaki; Wahyudiono; Koichi Nagafuchi; Hiroshi Watanabe; Tsuyoshi Kiyan; Takao Namihira; Hidenori Akiyama
    Bulletin of the American Physical Society 55 (7) 2008  2010 [Refereed]
  • Mitsuru Sasaki; Wahyu Diono; Tsuyoshi Kiyan; Hidenori Akiyama; Motonobu Goto; Yousuke Suga; Toshiyuki Watanabe
    TENCON 2010: 2010 IEEE REGION 10 CONFERENCE IEEE 2108 - 2112 2159-3442 2010 [Refereed]
     
    In this work, reactions of phenol were carried out in supercritical argon (critical temperature, Tc: 150.7 K, critical pressure, Pc: 4.8 MPa) with pulsed discharge plasma to understand reaction characteristics and to evaluate possibility that this technique will be applicable for a new "green" polymerization technique of functional polymeric materials. Experiments in subcritical water or in supercritical argon were conducted through the operation of a specially-designed SUS316 batch-type reactor (inner volume: 900 mL) at 373-523 K and 1-25 MPa, or at 303-373 K and 5 - 15 MPa, respectively. The electrode configuration consisted of a point (negative electrode) and a planar surface (positive electrode), which were made of tungsten and stainless steel, respectively. The distance between the two electrodes was fixed at 1 mm. Two kinds of power supply devices (BPFN and MPC) were employed. As results using a BPFN, it was found that reaction behavior in subcritical water at 373-523 K, 1-25 MPa with less than 4000 times pulsed discharges basically similar to that in supercritical argon, but polymerized products of phenol could be obtained under larger pulsed discharge times like 5000 times at identical conditions. In contrast, phenol could be converted into hydroquinone but no polymerized product could be confirmed in supercritical argon. On the surface of the electrode used, it was found that phenol could be converted into amorphous graphite oxide with pulsed discharge plasma treatment in supercritical argon. This finding will be expected as a new method for the carbon-based functional materials in supercritical argon.
  • Tsuyoshi Kiyan; Mitsuru Sasaki; Takeshi Ihara; Takao Namihira; Masanori Hara; Motonobu Goto; Hidenori Akiyama
    PLASMA PROCESSES AND POLYMERS WILEY-V C H VERLAG GMBH 6 (11) 778 - 785 1612-8850 2009/11 [Refereed]
     
    This paper deals with two fundamental experimental studies with respect to plasma processes in highly pressurized carbon dioxide (CO(2)) and water: pulsed discharge phenomena in CO(2) up to supercritical condition as a basic study of plasma production and polymerization of phenol with a pulsed discharge plasma in sub-critical water as an application of a discharge plasma for chemical reactions. The experiments showed that: 1) the measured electrical breakdown voltage in supercritical CO(2) had a relatively large dispersion compared with that in the gas and liquid phases, and was almost independent of the CO(2) density, 2) the delay time for breakdown increased gradually with increasing density, and there was a large fluctuation around the sub-critical phase or high-pressure gas phase, 3) the highest conversion of phenol into products in the water experiments under temperatures of 301 to 525 K and pressures of 0.1 to 20 MPa was about 17% under the experimental condition of 52 3 K, 20 MPa and 4 000 pulsed discharge shots and 4) phenol synthesis could only be obtained at higher temperatures in pulsed discharge plasma.
  • Maya Takade; Tsuyoshi Kiyan; Kazusa Miyaji; Takao Namihira; Masanori Hara; Hidenori Akiyama
    Journal of Plasma and Fusion Research SERIES (JPFR-S) 8 1326 - 1329 2009/09 [Refereed]
  • T. Kiyan; K. Miyaji; T. Ihara; M. Hara; H. Akiyama
    2009 IEEE PULSED POWER CONFERENCE, VOLS 1 AND 2 IEEE 431 - 434 2009 [Refereed]
     
    Statistical characteristics of pulsed breakdown voltage of pressurized carbon dioxide up to supercritical condition were investigated experimentally. The tested gap is a sphere-to-sphere and the gap length and sphere diameter are around 140 mu m and 20 mm, respectively. The experimental results show the followings: 1) in the supercritical phase, the scattering in measured breakdown voltage increases with increasing the medium density, 2) the shape parameters in Weibull distribution of breakdown voltage at gas, liquid and supercritical phase are the range of 4 similar to 25, 5.5 similar to 9 and 4 similar to 29, respectively, 3) the maximum shape parameter appears in the density range of 200 to 300 kg m(-3) in supercritical phase, and 4) two values of shape parameter were observed at the measurement conditions of 580 kg m(-3) and 787 kg m(-3) in supercritical phase.
  • Reaction of Organic compound Induced by Pulse Discharge Plasma in Subcritical Water
    M. Goto; M. Mitsugi; A. Yoshida; M. Sasaki; T. Kiyan; T. Namihira; H. Akiyama
    Proceedings of 19th International Symposium on Plasma Chemistry (10.04) 1-4  2009 [Refereed]
  • Tsuyoshi Kiyan; Maya Takade; Takao Namihira; Masanori Hara; Mitsuru Sasaki; Motonobu Goto; Hidenori Akiyama
    IEEE TRANSACTIONS ON PLASMA SCIENCE IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC 36 (3) 821 - 827 0093-3813 2008/06 [Refereed]
     
    This paper deals with the effect of the polarity and gap geometry on dc breakdown voltage characteristics of a point-to-plane gap in supercritical carbon dioxide (SC CO2) that is required to design a plasma reactor. In the experiments, the gap width d and the curvature radius of the point tip r were changed in the range of 80 to 300 pm and 50 to 170 pin respectively, and the CO2 state was controlled within the gas, liquid, and SC phases. The experimental results showed that a remarkable polarity effect appeared under certain gap conditions. As a result, it was found that negative polarity and a higher stressed electrode are desired conditions for the dc plasma reactor since an active corona supplying rich chemical radicals appears in SC CO2 under such conditions.
  • S. Xiao; T. Kiyan; P. F. Blackmore; K. H. Schoenbach
    PROCEEDINGS OF THE 2008 IEEE INTERNATIONAL POWER MODULATORS AND HIGH VOLTAGE CONFERENCE IEEE 69 - 72 2380-808X 2008 [Refereed]
     
    A new method for stimulating platelet aggregation that does not rely on thrombin is based on the effect of ultrashort (nanosecond) pulsed electric fields. Nanosecond pulsed electric fields stimulate a variety of physiological responses, among them, Ca2+ fluxes, which in turn lead to platelet activation. We have shown that when platelet rich plasma was pulsed with one 300 ns pulse at 30 kV/cm, platelets aggregated and a platelet gel was produced. In addition, platelet derived growth factor (PDGF) release from platelets was observed. Since platelet aggregation occurs just minutes after pulsing, the pulse generator, the platelet gel reactor and the gel delivery system need to be integrated into one, easy-to-use system. Another consideration is the volume of activated platelet gel required for a treatment This requires a batch mode platelet exposure system where relatively large quantities of platelet gel can be treated in less than three minutes. We have built a compact, easy to use, pulsed power generator with a Blumlein line pulse-forming network that generates pulses of 300 ns duration. The impedance of the Blumlein fine is 10 Omega, matching the resistance of the exposure cell, a custom-made 6-mm chamber, which contains 5.4 ml of the platelet rich plasma. The output voltage can be varied, up to 20 kV, allowing the generation of electric fields of up to 30 kV/cm in the chamber. In order to minimize the time required for activation of the 70 ml of platelet gel, we operate the system in a batch mode. The activated platelet gel will then be sprayed onto the wound using a spray gun. Further testing of the platelet gel activation system will be conducted on diabetic wounds.
  • M. Goto; M. Sasaki; T. Kiyan; T. Fang; B. C. Roy; T. Namihira; H. Akiyama; M. Hara
    JOINT 21ST AIRAPT AND 45TH EHPRG INTERNATIONAL CONFERENCE ON HIGH PRESSURE SCIENCE AND TECHNOLOGY IOP PUBLISHING LTD 121 (8) 082009  1742-6588 2008 [Refereed]
     
    The generation of non-thermal plasmas was studied under supercritical conditions. This is interesting in view of both the basic phenomena involved and of potential industrial applications. When supercritical fluids are combined with discharge plasma they develop unique characteristics, including an enhanced chemical reactivity. This is the motivation for investigating the generation of discharge plasma in supercritical CO2. In this study, breakdown voltages were measured in CO2 in order to generate electric discharges in supercritical CO2. The experimental data show that the breakdown voltage increased smoothly up to the intersection points, but beyond these points the rates of increase of the breakdown voltage are different. This phenomenon can be explained with the help of pressure-density curves of carbon dioxide at a constant temperature. In addition, the generated plasma in supercritical CO2 was applied to several chemical reactions. The alpha conversion of tocopherols and transesterification of soybean oil with methanol were investigated. In addition, we explored the possibility of replacing catalysts with plasma in supercritical CO2.
  • T. Namihira; S. Sakai; M. Matsuda; D. Wang; T. Kiyan; H. Akiyama; K. Okamoto; K. Toda
    Plasma Science and Technology 9 (6) 747 - 751 1009-0630 2007/12 [Refereed]
     
    Nitric oxide (NO) is increasingly being used in medical treatments of high blood pressure, acute respiratory distress syndrome and other illnesses related to the lungs. Currently a NO inhalation system consists of a gas cylinder of N2 mixed with a high concentration of NO. This arrangement is potentially risky due to the possibility of an accidental leak of NO from the cylinder. The presence of NO in the air leads to the formation of nitric dioxide (NO2), which is toxic to the lungs. Therefore, an on-site generator of NO would be highly desirable for medical doctors to use with patients with lung disease. To develop the NO inhalation system without a gas cylinder, which would include a high concentration of NO, NAMIHIRA et al have recently reported on the production of NO from room air using a pulsed arc discharge. In the present work, the temperature of the pulsed arc discharge plasma used to generate NO was measured to optimize the discharge condition. The results of the temperature measurements showed the temperature of the pulsed arc discharge plasma reached about 10,000 K immediately after discharge initiation and gradually decreased over tens of microseconds. In addition, it was found that NO was formed in a discharge plasma having temperatures higher than 9,000 K and a smaller input energy into the discharge plasma generates NO more efficiently than a larger one.
  • Application of Pulsed Arc and Streamer Discharge Plasmas in Sub- and Supercritical Fluids toChemical Reactions
    Mitsuru Sasaki; Tao Fang; Tsuyoshi Kiyan; Takashi Saito; Takaomi Morishima; A. Uemura; Maya Takade; Bhupesh C. Roy; Takao Namihira; Motonobu Goto; Hidenori Akiyama; M. Hara
    Proceedings of International Symposium on EcoTopia Science 251105  2007/12 [Refereed]
  • Tsuyoshi Kiyan; Akihiro Uemura; Bhupesh C. Roy; Takao Namihira; Masanori Hara; Mitsuru Sasaki; Motonobu Goto; Hidenori Akiyama
    IEEE TRANSACTIONS ON PLASMA SCIENCE IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC 35 (3) 656 - 662 0093-3813 2007/06 [Refereed]
     
    This paper deals with the experimental results on prebreakdown phenomena and breakdown voltage characteristics of a negative dc point-to-plane gap in-compressed carbon dioxide up to the supercritical pressure as the first step to develop a plasma reactor with supercritical carbon dioxide. The gap length and the curvature radius of the point tip were 200 and around 35 pin, respectively. The experimental results show the following: 1) corona discharge preceding complete breakdown is observed more clearly in liquid and supercritical fluid than in gas; 2) the estimated discharge onset voltage according to the streamer theory is in fairly good agreement with the measured breakdown voltage in the gas density region of 0.1-30 kg. m(-3); 3) the breakdown mechanism in liquid can be classified into two categories: bubble-triggered breakdown at lower pressure and non bubble-triggered breakdown at higher pressure; 4) the breakdown mechanism in supercritical fluid is similar to that in higher pressured liquid; and 5) the density and temperature dependences of breakdown voltage in liquid and supercritical fluid are related closely with the breakdown mechanism.
  • Takao Namihira; Shunsuke Sakai; Takahiro Yamaguchi; Kunihiro Yamamoto; Chiemi Yamada; Tsuyoshi Kiyan; Takaishi Sakugawa; Sunac Katsuki; Hidenori Akiyama
    IEEE TRANSACTIONS ON PLASMA SCIENCE IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC 35 (3) 614 - 618 0093-3813 2007/06 [Refereed]
     
    A pulsed discharge produced underwater has been an attractive method to treat waste water. For the optimization and realization of the water treatment system utilizing underwater pulsed discharge, modeling analysis could be one of the essential works. However, there is still no simulation work about the underwater pulsed discharge due to the lack of knowledge about its characteristic parameters such as electron temperature, electron density, and so on. In this paper, the temperature and the electron density in a pulsed discharge plasma produced underwater are measured and presented. A magnetic pulse compressor (NIPC) was developed and used to create the electrical discharge in water. The developed MPC is all-solid state and is, therefore, a maintenance-free generator. To define the temperature and the electron density in an underwater pulsed discharge plasma, two kinds of spectroscopic measurements, called the line-pair method and Stark broadening, were carried out. According to the experimental results, the temperature and the electron density in the pulsed discharge plasma between point-plane electrodes immersed in water are determined to be 15000 K and 10(18)/cm(3), respectively.
  • Chaohai Zhang; Chunguang Ji; Zhen Liu; Tsuyoshi Kiyan; Hidenori Akiyama
    DYNAMICS OF CONTINUOUS DISCRETE AND IMPULSIVE SYSTEMS-SERIES B-APPLICATIONS & ALGORITHMS WATAM PRESS 14 73 - 80 1492-8760 2007/06 [Refereed]
     
    The measurements for breakdown voltages have been made with point-plane electrodes for high-pressure carbon dioxide up to supercritical conditions at different temperatures. The breakdown voltages depend on electrode gap, temperature and pressure of gas while preserving the intrinsic nonlinear combination of these characteristics. Artificial neural network was used to model the complex nonlinear relationship. The predicted breakdown voltages using neural network have been compared with the measured ones.
  • M. Takade; K. Tanaka; A. Uemura; B. C. Roy; T. Kiyan; T. Namihira; M. Sasaki; H. Akiyama; M. Goto; M. Hara
    2007 IEEE PULSED POWER CONFERENCE, VOLS 1-4 IEEE 1644 - 1647 2007 [Refereed]
     
    This paper reports the experimental results on the corona onset voltage and breakdown voltage by positive and negative dc discharges in carbon dioxide medium within the pressure range of 0.1 to 15MPa under the needle to plane electrode. From the experimental results of dc discharge, negative corona discharges are observed more clearly in liquid and supercritical phase than in gas phase of carbon dioxide. However, in our experimental condition, positive corona discharge was not found for dc discharges. The breakdown mechanism in liquid can be classified into two categories on account of the bubble-triggered formation.
  • T. Kiyan; K. Tanaka; A. Uemura; M. Takade; B. C. Roy; T. Namihira; M. Sasaki; H. Akiyama; M. Goto; M. Hara
    2007 IEEE PULSED POWER CONFERENCE, VOLS 1-4 IEEE 1528 - 1531 2007 [Refereed]
     
    This paper reports the experimental results on the breakdown voltage and phenomena in carbon dioxide medium at 298, 304 and 373 K and within the pressure range of 0.1 to 12.0/20.0 MPa under the point-to-plane electrode using negative dc and pulsed discharge. From the experimental results of negative de discharge, corona discharges with preceding as well as complete breakdown are observed more clearly in liquid and in supercritical phase than in gas phase of carbon dioxide. The calculated electric field intensity on the tip of point electrode at the corona onset voltage is about 450 MV/m; it suggests that corona is triggered by the field emission of electron. The breakdown mechanism of liquid phase can be classified into two categories in comparison with critical pressure of medium. On the other hand, in the experimental result of pulse electric discharge, the time delay of pulse forming and the relevance of the medium density were found.
  • T. Kiyan; A. Uemura; K. Tanaka; C. H. Zhang; T. Namihira; T. Sakugawa; S. Katsuki; H. Akiyama; B. C. Roy; M. Sasaki; M. Goto
    Digest of Technical Papers-IEEE International Pulsed Power Conference 942 - 945 2007 [Refereed]
     
    In recent years, several studies about electrical discharge plasma in supercritical carbon dioxide (CO2) have been carried out. One of the unique characteristics of supercritical fluid is a large density fluctuation near the critical point that can result in marked dramatic changes of thermal conductivity. Therefore, the electrical discharge plasma produced in supercritical fluid has unique features and reactions unlike those of normal plasma produced in gas phase. In our experiments, two types of large volume plasma, namely the pulsed streamer discharge and the pulsed arc discharge have been generated in a supercritical CO2. It was found that the characteristic of the pulsed discharge plasma in supercritical CO2 depends on the change of the CO2 density near the critical region. © 2005 IEEE.
  • S. Sakai; M. Matsuda; D. Wang; T. Kiyan; T. Namihira; H. Akiyama; K. Okamoto; K. Toda
    2007 IEEE PULSED POWER CONFERENCE, VOLS 1-4 IEEE 752 - + 2007 [Refereed]
     
    In 1987, Nitric oxide (NO) was identified as an effective treatment involving endothelium-derived relaxing factor (EDRF)(1). NO has attracted lots of attention from the discovery. And now, NO is increasingly being used in medical treatments for some illness related lung. Currently a system of NO inhalation has a gas cylinder of N-2 mixed with a high concentration of NO. However, this method is potentially risky due to the possibility of accidental leak of NO from the cylinder. In addition, gas cylinder is too heavy to carry around and too expensive to be used for all patients. Therefore, an on-site generation of NO would be highly desirable for patient, who is suffering lung disease, and medical doctors. Previous researches reported that NO is produced by pulsed arc discharge in the mixture of N-2 and O-2, and NO concentration increases with the increasing of pulse repetition rate and energy storage capacitance(2,4). In this paper, the detail about a prototype of NO generator by pulsed arc discharge based on the optimal discharge condition has been reported. As the results, it is observed that NO concentration in the outlet gas is about almost 1000ppm and rise time is about 20 to 30 sec. These conditions are enough for NO inhalation therapy. Additionally, NO concentration is adjustable by changing pulse repetition rate. [GRAPHICS]
  • C. H. Zhang; T. Namihira; T. Kiyan; K. Nakashima; S. Katsuki; H. Akiyama; H. Ito; Y. Imaizumi
    Digest of Technical Papers-IEEE International Pulsed Power Conference 1377 - 1380 2007 
    In this paper, the measurement and analysis of shockwaves generated by pulsed discharge in water are made with FUJI pressure measuring film. When pressure is applied, the reaction takes place between the color-forming material and color-developing material coated on the bases of the film, and color corresponding to the level of pressure is generated. Based on these results the energy transferred to the water and the average pressure of a shockwave are estimated. In addition, the electrical parameters and electrode configuration are optimized for maximum energy transformation efficiency into shock waves. © 2005 IEEE.
  • T. Namihira; T. Yamaguchi; K. Yamamoto; J. Choi; T. Kiyan; T. Sakugawa; S. Katsuki; H. Akiyama
    Digest of Technical Papers-IEEE International Pulsed Power Conference 1013 - 1016 2007 
    Recently, pulsed discharge plasma produced underwater has been an attractive method to treat wasted water. It is well known that pulsed discharge in water has some physical effects, such as an intense electric field at a tip of discharge plasma, an ultra violet radiation, a chemically radical formation and shockwave generation, for cleaning water. However, the physical characteristics of the pulsed discharge plasma induced underwater are still unclear. For the optimization of the water treatment system utilizing pulsed discharge in water, it is essential to have knowledge about the plasma feature generated by electrical discharge underwater. In this paper, the temperature of and the electron density in the discharge plasma underwater are described. The magnetic pulse compressor (MPC) was developed and was used to cause the electrical breakdown in water. The developed MPC is all-solid state and is, therefore, maintenance-free generator. Two kind of spectroscopic measurements called as the line-pair method and the Stark broadening carried out for define the temperature of and the electron density in plasma produced underwater. According to experimental results, the temperature of and electron density in the discharge plasma between point-plane electrodes immersed in water are determined 15,000 K and 1018/cm3, respectively. © 2005 IEEE.
  • T. Sakugawa; T. Yamaguchi; K. Yamamoto; T. Kiyan; T. Namihira; S. Katsuki; H. Akiyama
    Digest of Technical Papers-IEEE International Pulsed Power Conference 1057 - 1060 2007 
    Pulsed power has been used to produce non-thermal plasmas in gases that generate a high electric field at the tip of streamer discharges, where high energy electrons, free radicals, and ozone are produced. Recently, all solid state pulsed power generators, which are operated with high repetition rate, long lifetime and high reliability, have been developed for industrial applications, such as high repetition rate pulsed gas lasers, high energy density plasma (EUV sources) and water discharges. We have studied and developed repetitive all solid state pulsed power system for applications to water discharge. The developed system consists of a photo-voltaic generator, a Pb battery, an inverter, a controller, a command charger, a high-speed thyristor, a magnetic pulse compression circuit and a pulse transformer, and has mobility. This system can generate an output peak voltage of over 100 kV with voltage rise time of 200 ns. In this work, large volume streamer like discharges in water were produced by the developed system and this discharge plasma used to treat water with point-to-plane simple electrodes. © 2005 IEEE.
  • Characteristics of Direct Current Electric Discharges in Supercritical Carbon Dioxide
    Tsuyoshi Kiyan; Akihiro Uemura; Bhupesh Chandra Roy; Takao Namihira; Hidenori Akiyama; Mitsuru Sasaki; Motonobu Goto; Masanori Hara
    Proceedings of 8th International Symposium on Supercritical Fluids OB-2-13  2006/11
  • Temperature measurement of pulsed arc discharge
    T. Namihira; S. Sakai; K. Matsunaga; D. Wang; T. Kiyan; H. Akiyama; K. Okamoto; S. Ohira; K. Toda
    Proceedings of the16th International Conference on Gas Discharges and their Applications 2 657 - 660 2006/09
  • 佐久川貴志; 喜屋武毅; 浪平隆男; 勝木淳; 秋山秀典
    材料試験技術 日本材料試験技術協会 51 (3) 124-128 - 128 0285-2470 2006/07
  • Hidenori Akiyama; Akemi Teramoto; Kazutake Kozono; Tsuyoshi Kiyan
    7th International Conference on Information Technology Based Higher Education and Training, ITHET 677 - 681 2006 [Refereed]
     
    Innovative Ph.D. program has been conducted to produce young scientists of a top level in the world. This program has been supported by the Ministry of Education, Japan, as one of 21st century COE (Center of Excellence) programs. Ten professors with different specialty educate Ph.D. students through a weekly COE seminar, a training camp, an international workshop and others. The web-based e-learning and web-based meeting systems are used extensively in this program. New authoring software, which can build high quality e-learning contents efficiently, has been developed and used here. This program has been producing about 10 Ph.D. scientists every year since 2003. © 2006 IEEE.
  • Takao Namihira; Mitsuhiro Shigeishi; Kazuyuki Nakashima; Akira Murakami; Kaori Kuroki; Tsuyoshi Kiyan; Yuichi Tomoda; Takashi Sakugawa; Sunao Katsuki; Hidenori Akiyama; Masayasu Ohtsu
    IEEJ Transactions on Fundamentals and Materials Institute of Electrical Engineers of Japan 126 (3) 197 - 198 1347-5533 2006 [Refereed]
     
    In Japan, the recycling ratio of concrete scraps has been kept over 98 % after the Law for the Recycling of Construction Materials was enforced in 2000. In the present, most of concrete scraps were recycled as the Lower Subbase Course Material. On the other hand, it is predicted to be difficult to keep this higher recycling ratio in the near future because concrete scraps increase rapidly and would reach to over 3 times of present situation in 2010. In addition, the demand of concrete scraps as the Lower Subbase Course Material has been decreased. Therefore, new way to reuse concrete scraps must be developed. Concrete scraps normally consist of 70 % of coarse aggregate, 19 % of water and 11 % of cement. To obtain the higher recycling ratio, the higher recycling ratio of coarse aggregate is desired. In this paper, a new method for recycling coarse aggregate from concrete scraps has been developed and demonstrated. The system includes a Marx generator and a point to hemisphere mesh electrode immersed in water. In the demonstration, the test piece of concrete scrap was located between the electrodes and was treated by the pulsed discharge. After discharge treatment of test piece, the recycling coarse aggregates were evaluated under JIS and TS and had enough quality for utilization as the coarse aggregate.
  • Takashi Sakugawa; Takahiro Yamaguchi; Kunihiro Yamamoto; Jaegu Choi; Tsuyoshi Kiyan; Takao Namihira; Sunao Katsuki; Hidenori Akiyama
    IEEJ Transactions on Fundamentals and Materials 社団法人 電気学会 126 (7) 703 - 708 0385-4205 2006 [Refereed]
     
    Pulsed power has been used to produce non-thermal plasmas in gases that generate a high electric field at the tip of streamer discharges, where high energy electrons, free radicals, and ozone are produced. Recently, all solid-state pulsed power generators, which are operated with high repetition rate, long lifetime and high reliability, have been developed for industrial applications, such as high repetition rate pulsed gas lasers, high energy density plasma (EUV sources) and water discharges. We have studied and developed repetitive all solid-state pulsed power system for discharge in water. The developed system consists of a photo-voltaic generator, a Pb battery, an inverter, a controller, a command charger, a high-speed thyristor, a magnetic pulse compression circuit and a pulse transformer, and has mobility. This system can generate an output peak voltage of over 100 kV with voltage rise time of 200 ns. In this work, large volume streamer like discharges in water were produced by the developed system and this discharge plasma used to treat algae (Microcystis) with point-to-plane simple electrodes.
  • 熊本大学e-Learning station の試行と展望
    中野 裕司; 鈴木 和久; 太田 泰史; 喜屋武 毅; 清水 百合子; 野口 千里; 喜多 敏博; 秋山 秀典
    メディア教育研究 1 (2) 23 - 33 2005 [Refereed]
  • CH Zhang; T Kiyan; T Namihira; A Uemura; S Katsuki; H Akiyama; T Fang; M Sasaki; M Goto
    Conference Record of the 2005 IEEE Industry Applications Conference, Vols 1-4 IEEE 3 1845 - 1848 0197-2618 2005 
    The generation of dc corona discharges in supercritical CO2 using a point-plane electrode is studied experimentally. The results reveal a bizarre situation for CO2 breakdown voltages, which is much lower in near the supercritical point than the measured in the normal high pressure gas. An explanation is probably because of the extensive cluster formation under the supercritical fluid condition. Therefore, it can be concluded that corona discharge in supercritical fluid condition may be generated with very low voltage.
  • Mitsuru Sasaki; Takao Namihira; Bhupesh C. Roy; Motonobu Goto; Hidenori Akiyama; Tsuyoshi Kiyan; Takashi Sakugawa; Sunao Katsuki
    Joint 20th AIRAPT and 43rd EHPRG International Conference on High Pressure Science and Technology 2005/01 
    Large-capacity discharge plasmas have great capability of many applications such as sterilization, deodorization, dioxin treatment, and water treatment. We have tried to generate large-capacity discharge plasmas in high-prebure and high-Temperature fluids including their supercritical states and recently found that the discharge plasmas could be generated in supercritical carbon dioxide. For this purpose, we designed and manufactured an experimental apparatus, and tried to explore the operating conditions where the plasmas could be generated through the experiments at various conditions (305-333 K and 0.1-20.0 MPa) in supercritical CO2. As a result, it was found that discharge plasmas could be produced in supercritical CO2 as well as in gaseous CO2 and the brightneb of the plasmas became higher as the prebure increased at a constant temperature. It was also found that the breakdown voltage depended upon the density of CO2 at near-And supercritical prebures at above the critical temperature of CO2. Next, this phenomenon in supercritical CO2 was applied to reactions of organic compounds for developing a super-rapid molecular conversion method.
  • Tsuyoshi Kiyan; Yasushi Ohta; Hiroshi Nakano; Toshihiro Kita; Ryuichi Matsuba; Kenichi Sugitani; Yasuo Musashi; Masahiro Migita; Kazutaka Tsuji; Masaru Hashimoto; Takeshi Kida; Norio Iriguchi; Hidenori Akiyama
    Journal for Academic Computing and Networking National university corporation of Information Processing Center Council 7 (7) 33 - 42 1343-2915 2003/09 [Refereed]
     
    As a part of the LINK (Local Initiative Network Kumamoto (Knowledge)) project, the network connection system was constructed between the Kumamoto Prefecture and the Kumamoto University with several network servers; Web, e-Learning, TV conference and streaming distribution servers. We have designed the the regional cooperation activities support system by the combination of the TV conference server and the streaming distribution server. The system can distribute the contents of TV conference as the live stream over the Internet by combining one of the TV conference client and the encoder client of the streaming server. We will present the system configuration for "The Regional contribution symposium in Kumamoto University" as an example, and discuss the problem of the degradation of the video quality and the audio delay, and indicate their solutions.
  • T. Kiyan; T. Maekawa; S. Yokoi
    Modern Physics Letters A 17 (27) 1813 - 1823 0217-7323 2002/09 [Refereed]
     
    It is pointed out that in the 331-like model which uses both fundamental and complex conjugate representations for an assignment of the representations to the left-handed quarks and the scalar representation to their corresponding right-handed counterparts, the nature of the scalar should be taken into account in order to make the fermion triangle anomalies in the theory anomaly-free, i.e. renormalizable in a sense with no anomalies, even after the spontaneous symmetry breaking.
  • Positive Definite Scalar Product in Functional Space on U(n)(SO(n)) and Representation Matrix Elements of U(n, 1)(SO(n, 1)) with their Continuation and Contraction to those of U(n+1)(SO(n+1)) and IU(n)(ISO(n))
    K. Kawano; T. Kiyan; T. Maekawa; A. Tangoda
    Physical Science PINSA 65A (4) 439 - 480 1999 [Refereed]

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  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2013/04 -2016/03 
    Author : KIYAN Tsuyoshi
     
    In this study, our aim is the evaluation of the functionality of the supercritical switches using nitrogen in pulsed power system. In a series of experiments, we carried out the visualization of a pulsed discharge with shock wave and the estimate of propagation speed, the dielectric breakdown characteristics of pressurization nitrogen, the recovery characteristics of a system, in high pressure nitrogen including the supercritical state. From the experimental results, the propagation speed of the shock wave was estimated to be about 400 m / s (1.25 times the speed of sound in the experimental conditions). In order to verify the operation of the fluid switch, supercritical switch was designed and manufactured that can be controlled by frequency. Dielectric recovery ratio represents roughly 1.0 which responds to the state of a system being recovered. It was found that the possibility to operation of the trigatron of supercritical nitrogen can run up to about 1kHz.

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