Kazunori Takashima

Single-molecule PCR using water-in-oil emulsion.

Polymerase chain reaction (PCR) using a single molecule of DNA is very useful for analysis, detection and cloning of the desired DNA fragment. We developed a simple PCR method utilizing a water-in-oil (W/O) emulsion that included numerous droplets of reaction mixture in bulk oil phase. These droplets, which were stable even at high temperatures, functioned as micro-reactors. This allows the effective concentration of template DNA to be increased, even for low concentrations of template DNA. The present method consists of a two-step thermal cycle. The first step was carried out using the W/O emulsion. During this step, the template DNA was amplified in the limited volume of the droplets in the W/O emulsion. The W/O emulsion was broken and the second PCR step was carried out. This method can be easily applied to amplify a single DNA molecule.

Performance evaluation of discharge plasma process for gaseous pollutant removal

Abstract Performance evaluation of non-thermal plasma (NTP) process has been carried out using NO as a model gas. The experimental results were evaluated using a simple model, which relates the change of NO concentration with specific input energy (SIE) (kJ/Nm 3 ). The results were also evaluated using the well-known parameters of energy cost, energy yield (EY) and G -value. As the SIE increased, the EY and the G -value decreased while the energy cost increased even under a given reaction condition. Based on these parameters best results were found in the smaller SIE region where the NO removal is poor. An approach has been developed to use the constant (hereafter referred to as energy constant k E (Nm 3 /kJ)) in a simple model to evaluate the system performance of non-thermal plasma reactor instead of conventional parameters. Unlike the three conventional parameters, the energy constant was not influenced by the SIE level under the range tested in the present work. The effects of various reaction conditions, such as initial concentration of NO, temperature, additive on the energy constant k E have been investigated. The comparison of k E values for different NO concentrations clearly showed that the NTP process is more efficient in treating gaseous pollutant in low concentration. The increase of NO concentration exponentially decreased the energy constant. Gas temperature showed a similar effect. The significance of the influence of the tested parameters on the energy constant k E has been found to be of the order of the gas composition, the initial concentration, and the gas temperature. Among the additives tested in this study, ethylene made the energy constant k E to a maximum value of 242×10 −3 .

Low-temperature NOx reduction processes using combined systems of pulsed corona discharge and catalysts

In this paper, we will report NOx removal via reduction processes using two types of combined system of pulse corona discharge and catalysts: the single-stage plasma-driven catalyst (PDC) system, and the two-stage plasma-enhanced selective catalytic reduction (PE-SCR) system. Several catalysts, such as γ-alumina catalysts, mechanically mixed catalysts of γ-alumina with BaTiO3 or TiO2, and Co-ZSM-5 were tested. In the PDC system, which is directly activated by the discharge plasma, it was found that the use of additives was necessary to achieve NOx removal by reduction. Removal rates of NO and NOx were linearly increased as the molar ratio of additive to NOx increased. The dependence of NO and NOx removal on the gas hourly space velocity (GHSV) at a fixed specific input energy (SIE) indicates that plasma-induced surface reaction on the catalyst plays an important role in the PDC system. It was found that the optimal GHSV of the PDC system with the γ-alumina catalyst was smaller than 6000 h-1. Mechanical mixing of γ-alumina with BaTiO3 or TiO2 did not enhance NO and NOx removal and γ-alumina alone was found to be the most suitable catalyst. The dielectric constant of the catalyst only influenced the plasma intensity, not the NOx removal. In the PE-SCR system, plasma-treated NOx (mostly NO2) was reduced effectively with NH3 over the Co-ZSM-5 catalyst at a relatively low temperature of 150 °C. Under optimal conditions the energy cost and energy yield were 25 eV/molecule and 21 g-N (kWh)-1, respectively.

OH radical generation by atmospheric pressure pulsed discharge plasma and its quantitative analysis by monitoring CO oxidation

OH radicals play a very important role in non-thermal plasma chemical reactions for decomposition of gaseous pollutants or synthesis of methanol from methane, etc. In this paper, the CO oxidation monitoring method, which has been used in atmospheric chemistry, was examined to measure the concentration of OH radicals produced by a pulsed discharge plasma. The concentration of OH radicals in the discharge plasma of H2O/Ar mixture gas was estimated by measuring the amount of CO2 produced through oxidation of CO by OH radicals. The experimental results and the calculated results showed that it is possible to measure OH radicals using this simple method. In this experimental work, the maximum concentration of OH radicals produced by the pulsed discharge plasma of H2O/Ar was measured to be 9.4×1014 molecules cm−3 pulse−1. Within the temperature range investigated in this study (50–150°C), the formation of OH radicals increased with increase in the specific input energy (discharge energy dissipated in unit volume of the gas; SIE) value and the content of H2O; in contrast, it decreased with increase in the gas temperature.

On the characteristics of the corona discharge in a wire-duct reactor

The aim of this paper is to study the effects of the magnitude and direction of air flow rate on the characteristics of the corona discharge generated in a wire-duct reactor. Two air flow directions were attempted: one parallel to, and the other normal to the discharge wire in the reactor. The corona current-voltage characteristics correlative with ozone generation were studied under different modes of applied voltage. The results have shown that dc and ac corona current-voltage characteristics depend significantly on the magnitude of the air flow rate in the reactor, whatever the direction of the air flow. The ozone concentration generated by either dc, ac or pulsed coronas with parallel flow is higher than that generated with normal flow with the same discharge conditions. The ozone concentration generated by pulsed coronas is higher than that generated by either dc or ac coronas with the same discharge conditions irrespective of the polarity of the pulsed corona.

Reforming of heavy oil using nonthermal plasma

Reforming of heavy oils into light hydrocarbons has been experimentally studied using nonthermal plasma. The purpose of this study was to improve the understanding of the parameters for optimal design of the heavy oil reforming plasma reactor driven by AC high voltage. The low molecular weight hydrocarbons obtained constitute the NO/sub x/ removal system using light olefin hydrocarbons, such as ethylene and propylene as additives. In this paper, we examined the effect of the parameters such as gap distance of the electrodes and power applied. Results indicated that the reactions occurring in this heavy oil conversion process showed an important selective behavior. The major products obtained were hydrogen and hydrocarbon compounds with one, two, three, and four atoms of carbon, such as CH/sub 4/, C/sub 2/H/sub 4/, C/sub 2/H/sub 6/, C/sub 3/H/sub 6/, and C/sub 4/H/sub 10/, ethylene being the main compound. The optimum set of values for the parameters studied gave rise to efficiencies on the order of 2.3 /spl mu/mol/J.

Reactivity of methane in nonthermal plasma in the presence of oxygen and inert gases at atmospheric pressure

Partial oxidation of methane to methanol and formaldehyde as liquid fuels with oxygen diluted with inert gases was investigated experimentally using the pulsed discharge plasma method under conditions of room temperature and atmospheric pressure. The experimental results indicated that ethylene (C/sub 2/H/sub 4/), ethane (C/sub 2/H/sub 6/), methanol (CH/sub 3/OH), formaldehyde (HCHO), hydrogen (H/sub 2/), water (H/sub 2/O), carbon monoxide (CO), and carbon dioxide (CO/sub 2/) were detected as products and, especially, methanol, formaldehyde, and carbon monoxide were the major products of the plasma chemical reactions. Particularly, it was found that the methanol and formaldehyde production has an optimum specific input energy (SIE: defined as the electrical applied energy per unit volume). The highest methanol and formaldehyde production ability and selectivity were achieved with a relatively low SEE of 360 J/L and concentration of Argon of 50 vol.%. Under this optimum condition, the maximum liquid fuel (methanol and formaldehyde) production ability of about 0.7 /spl mu/mole/J, and selectivity of 64 mol%, were obtained.

Sterilization using dielectric barrier discharge at atmospheric pressure

The newly developed plasma method has advantages of low temperature operation, time-saving and non-toxicity over the conventional methods, such as dry heat, steam autoclave, /spl gamma/ -ray irradiation and ethylene oxide (EtO) gas. Sterilization effect of discharge plasma on Bacillus subtilis and Escherichia coli (E. coli) was investigated using dielectric barrier discharge (DBD) plasma under dry and wet conditions at atmospheric pressure. The wet plasma system showed much higher performance in terms of treatment time compared with the dry method as well as conventional ones. These results suggest that free radicals generated by discharge plasma played an important role in sterilization.

Development of an Optoelectrostatic Micropump Using a Focused Laser Beam in a High-Frequency Electric Field

In this paper, fluid flow generated by laser irradiation in a high-frequency electric field was investigated with a view to using it as the driving force for a micropump. We discovered an optoelectrostatic phenomenon known as optoelectrostatic microvortex (OEMV) ten years ago. The OEMV is generated around the focal point of a laser beam located in the center of an intense high-frequency electric field. The direction of the opposed flow is parallel to the ac electric field and perpendicular to the sides of the electrodes. In this paper, the laser focus was positioned near one of the electrodes. One-directional flow was generated toward the other electrode. This flow was generated in a microchannel by simultaneous application of an Nd:YAG laser (1064 nm) and an ac voltage. The flow velocity increased with both increasing laser power and increasing ac voltage. In addition, the flow velocity was affected by the ac frequency. The flow velocity around the focal point was several hundred micrometers per second. At a distance of 3 mm from the laser spot, a flow velocity of 25 mum/s (0.74 muL/s) was observed

Nonthermal plasma reactors for the production of light hydrocarbon olefins from heavy oil

During the last decade, nonthermal plasma technology was applied in many different fields, focusing attention on the destruction of harmful compounds in the air. This paper deals with nonthermal plasma reactors for the conversion of heavy oil into light hydrocarbon olefins, to be employed as gasoline components or to be added in small amounts for the catalytic reduction of nitrogen oxide compounds in the treatment of exhaust gas at power plants. For the process, the plate-plate nonthermal plasma reactor driven by AC high voltage was selected. The reactor was modeled as a function of parameter characteristics, using the methodology provided by the statistical experimental design. The parameters studied were gap distance between electrodes, carrier gas flow and applied power. Results indicate that the reactions occurring in the process of heavy oil conversion have an important selective behavior. The products obtained were C1-C4 hydrocarbons with ethylene as the main compound. Operating the parameters of the reactor within the established operative window of the system and close to the optimum conditions, efficiencies as high as 70 (ml/joule) were obtained. These values validate the process as an in-situ method to produce light olefins for the treatment of nitrogen oxides in the exhaust gas from diesel engines.