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In recent years, the interest in nonthermal plasma dynamics has grown significantly, within both industry and research. This has been driven by the development of several novel cold plasma technologies across a wide range of different fields, for example, for plasma medicine, chemical processing, pollution control, and surface treatment. The optimization of these technologies relies heavily upon the understanding of gas discharge plasmas: their generation, electrical characteristics, and interaction with their surroundings. Moreover, the manifestation of nonthermal plasmas in the form of streamers is of high relevance and critical importance to high voltage insulation technology, and has further significance to geophysical research concerning atmospheric discharges. The present work describes the development of the StrAFE (Streamers on Adaptive Finite Elements) package, a dedicated Python library built atop the popular open-source FEniCS finite element software, designed with the objective to simplify and to automate the solution of ionization front models. The library features support for mesh adaptivity, distributed memory parallelism, and an intuitive programming interface, while providing an exceptionally high level of user configurability. This article presents the software implementation, describes its features, and presents several code verification studies performed within simple and complex domains. It is concluded that the numerical results gained from this open-source framework are comparable to other well-established software in terms of accuracy. Therefore, it further demonstrates the great potential for open-source software to make significant contributions to technologies involving nonthermal plasmas, ionization fronts, and gas discharges.

The influence of pulse rise rate and pulse duration for ignition purposes in engines is investigated. A constant volume cell is used to characterize the breakdown voltage under nanosecond pulsed voltages with automotive sparkplugs having electrode gaps ranging from 0.2 mm to 1 mm. Two pulse generators are used to compare pulses with durations of 10 ns and 50 ns. Different pulse amplitudes are used, and air gaps with breakdown voltages ranging from 4 kV to 15 kV are investigated. The cell is filled with synthetic air with densities gap distances products that are relevant for internal combustion engines. This study shows that the pulse shape and rise rate influence the breakdown voltage. Under pulsed discharge, the breakdown voltage is always above the static breakdown voltage. The probability of pulsed discharge breakdown increases as both the pulse amplitude and duration increases. Furthermore, the breakdown voltage value increases with increasing pulse rise rate. The delay time between reaching the static breakdown voltage and the actual breakdown voltage decreases with increasing overvoltage. The delay time is constituted by statistical and formative times. Both the statistical and formative times decrease with increasing overvoltage. For ignition purposes, the pulse rise rate should be as high as possible to deliver a larger energy input in the breakdown phase. Furthermore, for reduced electrode erosion, the pulse duration should be short (10-20 ns) to reduce the probability for a transition to an arc.

The properties of obliquely propagating dissipative electron-acoustic solitary waves (OPdEASWs) have been investigated in a magnetized collisional superthermal plasma consisting of inertial cold electrons, inertialess hot electrons featuring $\kappa $ -distribution, and static ions via the fluid dynamical approach. Using the reductive perturbation technique, a nonlinear Schamel equation that governs the nonlinear features of OPdEASWs is obtained. The solitary wave solution of the Schamel equation is used to examine the basic features of small but finite amplitude OPdEASWs in such a magnetized collisional superthermal plasma. The basic features (width, amplitude, speed, and so on) of OPdEASWs are found to be modified by the different plasma configuration parameters, such as the superthermality index, obliquity angle, collisional parameter, trapping parameter, and external magnetic field. The nature of electrostatic disturbances, that may propagate in different realistic space and laboratory plasma systems (e.g., in Saturn ring), is briefly discussed. [ABSTRACT FROM AUTHOR]

Electrical discharge-based nonthermal plasma is being used for the past three decades at laboratory level to treat the oxides of nitrogen (NOX) present in diesel exhaust. To improve the NOX abatement, commercially available expensive catalysts and adsorbents are usually used in combination with plasma. In this article, a new line of experiments was initiated to explore plasma activation of the red mud, a cheap and abundant waste from aluminum industry. The dominance of plasma catalysis associated with plasma activation of red mud at room temperature has been discussed. At about 60 J/L, the plasma catalysis gave 91% NOX removal, when compared to 2% with plasma and 7% with plasma-cascaded red mud. The possible reaction mechanisms were identified in light of plasma activated red mud and the studies were carried out at different engine loads. The results have been discussed at length emphasizing the advantages of NOX removal through activation of red mud by electrical discharge plasma. [ABSTRACT FROM AUTHOR]

Two-stage pyrolysis/gasification and plasma conversion technology for the utilization of solid waste is an advanced and efficient technology of waste treatment and resource utilization, which is expected to overcome the shortcomings of a single pyrolysis/gasification process and produce high-quality syngas or other chemical products. This article summarizes this technology’s main process steps that then progress to the discussions of two categories of processes classified by thermal plasma and nonthermal plasma, focusing on the reactor combination and the influences of technical parameters. Besides, the mechanisms of two-stage pyrolysis/gasification and plasma conversion technology are discussed, as well as the engineering application and environmental impacts of this technology for the further comprehension of the overall performance. It is believed that two-stage pyrolysis/gasification and plasma conversion technology is considered to be a very potential, clean, efficient, and environment-friendly method for solid-waste treatment. [ABSTRACT FROM AUTHOR]

In this work, a corona discharge system with array electrode was built for the rapid sterilization of a resistant pathogen (Acinetobacter baumannii). The electrical parameters, discharge pattern, ozone generation, and optic emission spectra were used to characterize the corona plasma. The discharge current and power of positive corona were larger than those of negative at the same applied voltage. The G-value of ozone generation of positive corona was about 7.31 times larger than that of negative corona, suggesting that the positive corona has higher energy efficiency. The ${A}$. baumannii sterilization efficiency of corona plasma was much higher than that of using ozone (at the same ozone concentration level). As for negative corona, 99.99% A. baumannii sterilization efficiency was achieved within 9-min treatment with 50-ppm ozone produced. Moreover, the A. baumannii sterilization efficiency of positive corona was higher than that of negative corona at the same applied voltage or discharge power, confirming that the energy efficiency of sterilization of positive corona was higher than that of negative corona. The optic emission spectra suggested that active species such as excited molecules, ions, and radicals were generated in the corona discharge. The as-produced active species played important roles in the sterilization process. [ABSTRACT FROM AUTHOR]

In this study, nitrogen oxides (NOx) and sulfur oxides (SOx) are removed using a wet-type plasma reactor without chemical agents. An NO and SO2 mixed gas is prepared and sent to the reactor. In the reactor, NO is oxidized to NO2 by air plasma first, and then NO2 and SO2 are absorbed into a water film on the inner wall of the reactor. The wastewater from the reactor contains nitrate ions (NO3−), nitrite ions (NO2−), sulfite ions (SO32−), and sulfate ions (SO42−). The nitrogen compounds such as NO3− and NO2− are harmful to human health and the environment; therefore, they must be treated before disposal. Accordingly, we treat the wastewater using argon (Ar) plasma to remove NO3− and NO2− after the NOx and SOx removal. The results show that more than 98% of the NOx and SO2 are removed, and the NO3− and NO2− ions in the wastewater are reduced by the Ar plasma; 25.6 mg of NO3− and 2.06 mg of NO2− are removed for 50 min. However, the pH does not increase with the reduction of these ions. In other words, NO3− and NO2− could not be reduced to N2 but be converted to other ions. From these results, it is confirmed that the wet-type discharge plasma reactor is useful for the simultaneous removal of NOxand SOx. Further investigations are required for the treatment of wastewater containing NO3− and NO2−. [ABSTRACT FROM AUTHOR]

This article presents a numerical model and simulation results for the flow stabilization problem behind a solid cylinder. Four dielectric barrier discharge actuators are attached to the cylinder surface, each consisting of two tape electrodes. The surface-exposed electrodes are supplied with a high sinusoidal voltage, whereas the embedded ones are electrically grounded. A surface low-temperature plasma is generated near the edge of the exposed electrode, where the electric field intensity is very high. Ions generated by the discharge drift along the cylinder surface and collide with neutral air molecules, generating airflow. This electrohydrodynamic flow suppresses, or completely eliminates, the flow separation in the downwind part of the cylindrical surface. It can also quench, or mitigate, the von Kármán vortices behind the cylinder. The simulation results reasonably agree with the experimental data published in the literature, validating the proposed numerical algorithm. [ABSTRACT FROM AUTHOR]

As NOx and SOx have significant environmental impacts, advanced treatments are required to remove them from the exhaust gas of a glass melting furnace. Here, we investigate a plasma-chemical hybrid process (PCHP) for this purpose. A pilot-scale experiment of the simultaneous removal of NOx and SOx using a PCHP combined with the existing semi-dry type desulfurization reactor is conducted on actual high-temperature exhaust gas from a glass melting furnace. NO (the majority of NOx exist as NO) in the exhaust gas is oxidized to NO2 using active oxygen (ozone: O3) generated by a plasma ozonizer. The exhaust gas must be cooled to less than 150 °C in order to suppress the thermal decomposition of O3, while the gas temperature at the outlet of the semi-dry reactor must be kept at 200–;250 °C to protect the dry-type electrostatic precipitator. Therefore, it is important to form a local cooling area for NO oxidation in the reactor. In this article, we use the three-fluid nozzles of O3, water, and air to form the local cooling area and effectively oxidize NO to NO2. In addition, we spray NaOH aqueous solution for SO2 absorption downstream of the NO oxidation area to allow sufficient time for NO oxidation. The SO2 reacts with NaOH to produce Na2SO3, a powerful reducing agent. Subsequently, NO2 reacts with Na2SO3 and is reduced to N2, and the Na2SO4 generated in this reaction is reused as a clarifier of the raw materials for glass manufacturing. As a result, the ratio of the amount of removed NO and NOx to the amount of injected O3 (de-NO/O3 and de-NOx/O3) is 64% and 78%, respectively; therefore, high efficiency is obtained. This article includes actual examples of the treatment of exhaust gas in a glass melting furnace, using PCHP de-SOx and de-NOx technologies along with results from pilot-scale experiments. [ABSTRACT FROM AUTHOR]

Recently, plasma activated water (PAW) has drawn huge attention because it is considered to be useful for biomedical and agricultural applications. Because the PAW contains several nitrogen compounds such as nitrate, it can be used as a natural fertilizer. In this article, we report the comparative test results of PAW production by combining nonthermal plasma, thermal plasma, and hybrid methods. As a thermal plasma source, gas-jet assisted pulsed discharge (GAPD) under water was used, and the coaxial cylindrical dielectric barrier discharge (DBD) was adopted as the nonthermal plasma source. The difference in the radical generation rate between the two methods was identified. Some synergy effects in the formation of nitrate ion by the hybrid system were also confirmed. It is considered that the surface discharge through the air channel in GAPD formed by the gas jet stabilized more rapidly by increasing the conductivity of water by relatively high power DBD. This combination can greatly improve the energy efficiency of nitric acid production at relatively low input energies. [ABSTRACT FROM AUTHOR]

In this paper, a low-cost and portable plasma device is developed to generate atmospheric pressure nonthermal air plasma jet for safe and effective biomedical applications. The device mainly consists of a pen electrode, a high-frequency ac power supply, an ac/dc module, and a dc air pump, and it totally costs only U.S. $63 and has a small size of 280 mm $\times190$ mm $\times180$ mm. The appearance of two-mode discharge of half-wave and full-wave breakdown with the changing of applied voltage is identified, and the length of the plasma jet is optimized through studying on the influences of distance between two electrodes, gas flow rates, and hole diameters of the gas outflow in ground electrode. Stronger plasma with a longer jet length of 12 mm can be obtained in the full-wave breakdown discharge mode, while moderate plasma with a length of 8 mm can be obtained in the half-wave breakdown discharge mode. The discharge characteristics of the device such as the main generated active particle, voltage and current, discharge power, and operation temperature are obtained. It is shown that rich active species for biomedical application can be generated at low power of approximate 2 W and low operation temperature of approximate 40 °C. The developed device is tested for biomedical application, and the results of effective sterilization of C. albicans and blood coagulation are obtained. [ABSTRACT FROM AUTHOR]

Lean combustion in gasoline engine can reduce nitrogen oxide emission and fuel consumption greatly. However, as the fuel-air ratio approaches the lean-burn limit, the energy required to initiate the combustion increases dramatically, and the flame propagation speed decreases substantially. To enhance the lean combustion and expand the lean-burn limit of a sparkignition engine, a high-voltage nanosecond pulsed plasma is introduced to initiate the combustion of the engine. Discharge process and chemical reactions are calculated separately due to an essential difference in their timescales. The effect of discharge induced active particles on the ignition of the gasoline engine is studied, which shows that the ignition is primarily associated with the faster development of chain reaction due to O and O3 produced by the electron-impact dissociation in the discharge phase; these active particles can greatly shorten ignition delay time. The combustion enhancement for lean mixture is more pronounced than the stoichiometric gases, which indicates that the nonequilibrium plasma has a great potential to extend the lean-burn limit. [ABSTRACT FROM AUTHOR]

Multilayer dielectric barrier discharge (DBD) can efficiently enlarge the volume of homogeneous plasma and its interactional surface area with materials in vertical space, which seems attractive to the industry application. In this paper, a new plasma generator of DBD structure which has multilayers of dielectric barrier boards excited by repetitive submicrosecond pulsed power (0 to -100 kV, 130 Hz-1 kHz, pulsewidth 230 ns, and rise time 120 ns) is introduced, and homogeneous plasma has been obtained in atmospheric pressure air. Experiments on high-speed photography with an exposure time of 5 ns have been carried out to the discharge with three layers of dielectric barrier boards with each gap width of 2 mm. It demonstrates that luminance of the discharge distributes uniformly throughout the upper and the lower gaps. Also, the result of the time evolution image of a three-layer DBD is discussed in this paper, which shows that the two layers of luminous intensity keep good consistency with each other, and this indicates that breakdown of each gap layer happens at the same time in a multilayer DBD. A preliminary processing experiment for polytetrafluoroethylene film has been carried out by adopting homogeneous triplelayer DBD plasma. By testing the water contact angle of the polymer surface before and after the treatment, it was found that hydrophilism of the surface and efficiency of treatment could be effectively improved by the processing of each layer of discharge plasma. [ABSTRACT FROM AUTHOR]

Direct treatment of water by dielectric barrier discharge plasma with pulse repetition rates in the range of 2.5-4 kHz and microsecond rise time scale was used to treat samples of water for up to 10 min. Very high concentration of nitrate ions was measured by ion chromatography, and explained by the plasma generator's operating parameters. It is shown that electrical conductivity increases and pH decreases with treatment time. These effects are enhanced at higher pulse repetition rates of the plasma discharge, provided that the power supply linearly scales power with output frequency. An increase in electrical conductivity of the treated water is in accordance with the concentration of produced nitrate ions and pH decrease. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) is commonly used as an anesthetic gas in hospitals. It is a greenhouse gas and should therefore be removed to limit pollution. As nonthermal plasma has low electron density, it has been considered effective for the treatment of low concentrations of gas. Moreover, N2O is extremely stable in the troposphere, and is therefore difficult to decompose. In this study, a system to remove high concentrations of N2 O using nonthermal plasma along with an adsorbent was investigated. A surface discharge plasma reactor was employed to decompose N2O gas. This gas simulated the waste gas from the anesthetic equipment used in operating theatres. Because of its high concentration, the decomposition of N2O afforded the mononitrogen oxides, nitric oxide, and nitrogen dioxide (NOx = NO + NO2), respectively. The generated NOx was adsorbed by the adsorbent. As a result, an N2O decomposition efficiency of 66% was achieved with air-based 12.8% N2O at a flow rate of 1.1 L/min and a plasma reactor input power of 375 W. Furthermore, 0.4% NO and 1.0% NO2 were generated during N 2O decomposition. Both gases were removed by the adsorbent. It was confirmed by the previous studies that the adsorbed NOx was decomposed by N2 plasma. It was demonstrated that the removal of high concentration of N2O could be accomplished by using a system that combines nonthermal plasma with an adsorbent. In practice, much higher volumes of N2O can be removed, without NOx formation, in a setup that involves a series of plasma reactors with recirculation, followed by an NOx reduction system with N2 plasma. [ABSTRACT FROM PUBLISHER]

In this paper, the regeneration of sooty surface by using nanosecond pulsed surface dielectric barrier discharge type reactor is investigated experimentally. The goal is to characterize the regeneration process as a function of the applied voltage magnitude and pulse polarity. The reactor is composed of two electrodes separated by a dielectric and are arranged asymmetrically. The power supply system provides high voltage pulses with the following characteristics: voltage up to ±10 kV; rise and decay time less than 50 ns; and a frequency of 2 kHz. The main results show that the regeneration performance increases with the applied voltage magnitude and the duration of treatment. Furthermore, depending on the polarity and the magnitude of the applied voltage pulse, the cleaned surface area can be either more uniform along the active electrode (negative pulses) or extended on the dielectric surface (positive pulses). The regeneration mechanism remains not very well understood, but it seems that the soot particle size is reduced mainly due to the interaction with ozone molecules and oxygen radicals generated by the discharge. [ABSTRACT FROM AUTHOR]

In this study, a micrometer-size plasma actuator, microplasma actuator, was developed and investigated for active flow control. The microplasma actuator could be driven by a relatively low voltage of less than 2 kVpp owing to its micrometer discharge gap. Such a low voltage is easily controllable with semiconductor switches. Discharge diagnostics included measurements of the discharge voltage, energy, and ozone generation. Emission spectra were also measured to determine the characteristics of the microplasma. The air flow induced by the microplasma actuator was measured by the particle tracking velocimetry method. Incense smoke of a submicron diameter was used as the tracer particles and a \textNd:YVO{4}\;{\text{532-nm}} laser was used for irradiation. Driving of the microplasma actuator generated an air flow in the order of 0.1 m/s and its direction was controlled with semiconductor switches. [ABSTRACT FROM PUBLISHER]

A pilot-scale simultaneous removal of \textNOx and \textSOx, as a nonthermal plasma and chemical hybrid process (PCHP), is carried out on combustion exhaust gas in a glass manufacturing system. The PCHP is implemented in an actual semi-dry-type exhaust gas treatment system. The exhaust gas (12 700 m3N/h) is produced by the combustion of fossil fuels and contains both \textNOx (160 ppm) and \textSOx (150 ppm). In PCHP, \textNO is oxidized to water-soluble \textNO{2} through a plasma process using ozone. \textNa{2}{\text{SO}}{3} is then produced as a byproduct in a desulfurizing process using a solution of NaOH. The generated \textNO{2} is then reduced to \textN{2} and \textNa{2}{\text{SO}}{4} using an \textNa{2}{\text{SO}}{3} solution, followed by the dried \textNa{2}{\text{SO}}{4} particles being removed in a semi-dry reactor by a dry-type electrostatic precipitator. Our findings show the molar ratio of \textNO to the injected ozone to be more than 0.75. \textNO and \textSOx removal efficiencies of 28% and 63% are obtained. Further, the paper discusses de- \textNOx by the use of a bag filter (BF) for the injection of the \textNaHCO{3} at the BF inlet. Due to the effect of ozone and \textNaHCO{3}, \textNOx removal efficiency is increased by up to 45%. Our results show that higher de- \textNOx and de-\textSOx efficiencies are obtained by maintaining a local exhaust gas temperature of less than 150 °C. Through this experiment, it is confirmed that this simultaneous treatment of \textNOx and \textSOx using semi-dry-type PCHP is highly effective and promising for exhaust gas treatment in glass manufacturing. [ABSTRACT FROM PUBLISHER]

Results of experimental and computational study of the dynamics and structure of atmospheric-pressure air plasma jets formed by barrier discharge in a thin dielectric tube are presented. Formation of plasma bullet-guided streamers, moving along the jet with velocity varying in the range (1–3) $\times 10^{{\mathrm {7}}}$ cm \text{s}^{{\mathrm {-1}}} , is observed. Simulation, for conditions of the experiment, gives the streamer radius, velocity, and propagation length in reasonable agreement with the experimental data. [ABSTRACT FROM AUTHOR]

In this paper, an atmospheric touchable surface dielectric barrier discharge nonthermal plasma system was introduced. The typical plasma area, pulsed voltage, pulsed current, pulse frequency, and plasma power are 459 cm2, 6 kV, 5.5 A, 10 kHz and 140 W, respectively. Its disinfection performance was evaluated on agar plate, glass, and silicone hand by four bacteria including Escherichia coli, Staphylococcus aureus, Staphylococcus albus, and Pseudomonas aeruginosa. The efficiency of plasma disinfection was enhanced with increasing voltage and frequency, but had no significant difference with bacteria type. For a 10-s treatment of agar and silicone hand, the log reductions of bacteria were 2.35–2.6 and 2.85–3.26, respectively. After a 5-s treatment of glass, 3.3–3.68 log reduction of bacteria could be obtained. [ABSTRACT FROM AUTHOR]

In this paper, the relationship between reduced electric field and ozone efficiency was determined between $\sim 120$ and 280 Td, with an optimized efficiency of $\sim 207$ g/kWh at $\sim 123$ Td. An equivalent circuit with stray capacitance was used to analyze the filament current in the barrier discharge. The statistical distribution of the filament currents was found to change with different conditions, observing decreased mean amplitude and a narrower distribution with increased pressure and barrier thickness. Under the same reduced electric field, higher ozone efficiency was achieved at a lower current and narrower distribution. [ABSTRACT FROM AUTHOR]

This paper investigated hydroxyl radicals and hydrogen peroxide formation under a needle-plate electrode configuration using positive-polarity dc discharges generated in air, nitrogen, and helium. The discharge mode in air and nitrogen was found to change above ultrapure water; initially, a nanosecond pulse discharge was observed, transitioning to a diffuse discharge due to the increasing conductivity of the water. The discharge in helium was a nanosecond pulse discharge and the repetition rate increased with increasing water conductivity. It was found that hydroxyl radicals contribute to 7%, 78%, and 70% of hydrogen peroxide formation when using the ultrapure water in air, nitrogen, and helium, respectively. It is suggested that hydroxyl radicals are formed by water reactions with energetic positive ions and the neutral particles, such as N2+, He+, O, H, and HO2. Part of hydrogen peroxide is directly formed from atoms and radical reactions with water in nitrogen and helium, while oxygen reactions are heavily involved for hydrogen peroxide formation in air. A fluorophotometry method, using terephthalic acid, was used to directly quantify the formation of hydroxyl radicals and compared with the tert-butanol method. [ABSTRACT FROM AUTHOR]

Surface dielectric barrier discharges (SDBDs) have prospects for a wide variety of applications in the field of flow control. In order to study the characteristics of SDBDs excited using microsecond pulses, a compact microsecond-pulse generator with square pulses is developed and tested. The output voltage has amplitudes of 0\sim 10 kV, pulse repetition rates of 1\sim 5 kHz, and pulsewidths of 5\sim 30~\mu \texts . The square voltage has a rise time of 120 ns and a fall time of 12 \mu \texts . Moreover, the working principle of the main circuit and drive circuit is introduced. The microsecond-pulse generator is tested without a load. The results show that the pulsed generator has a stable output and the drive circuit can effectively synchronously trigger IGBT switches. Furthermore, the effects of the output parameters of the generator on SDBDs characteristics are investigated. The experimental results show discharge currents occur both on the rise time and on the fall time of the voltage. The discharge mainly occurs at the rise time, and the discharge current increases with the voltage amplitude. The pulsewidth and repetition rate have little influence on discharge current. [ABSTRACT FROM AUTHOR]

Gliding arc discharge (GAD) has the properties of both thermal and nonthermal plasma conditions. GAD plasma in the atmospheric pressure with argon/nitrogen and its characteristics are described. Some experimental results about alternating current gliding arc plasma generator have been obtained. It seems that the current density strongly depends on the gas type, and increased with increasing discharge current and gas flow rate. In addition, the discharge current of GAD in nitrogen gas (N2) is greater than one in argon gas (Ar) because of N2 needs more breakdown voltage than Ar. The intensity of GAD increased with increasing the gas flow rate. The oscillograms of discharge current in each case of Ar and N2 were obtained. The electron temperatures of Ar and N2 plasma were calculated to be 22 800 and 8400 K, respectively. The characteristics of both Ar and N2 gases in atmospheric pressure, such as current density, electron density with flow rates (5, 10, 20, and 40) standard cubic foot per hour, were investigated and all experimental results were classified. An experimental study was carried out through using of GAD device for medical treatment by exposing three human blood samples of leukemia to the nonthermal GAD plasma for different periods. [ABSTRACT FROM AUTHOR]

In this paper, a new multiple-needle-cylinder reactor is designed to study the Escherichia coli inactivation with an unstable pulsed arc discharge in water and investigate the influence of several parameters for promoting its industrial application. The results show that the inactivation rate is mainly determined by energy density. About three orders reduction can be obtained with an initial cell count of 3\times 10^5 CFU/mL and energy density around 2 J/mL. The inactivation rate can almost reach 100% when the energy density is around 8 J/mL. For reaching the maximum inactivation rate of this system, the parameters including initial water conductivity below 50~\mu \textS /cm, initial cell count over 10^4 CFU/mL, and bubbling flow rate around 3.5 L/min are recommended. The water conductivity, pH value, and concentrations of hydrogen peroxide and ozone are also measured during the treatment to evaluate their influence. The transmission electron microscopy images of E. coli indicate that the intracellular morphology changes after plasma treatment. [ABSTRACT FROM AUTHOR]

Space- and time-resolved discharge-images from a nonthermal atmospheric-pressure indirect-plasma jet have been observed using a high-speed single-frame camera to investigate the electron temperature. The propagation velocity of the indirect Ar-plasma along the plasma column has been shown to be on the order of 10^\mathrm \mathbf 4 m/s, and that corresponds to an ion acoustic velocity on the order of 10^\mathrm \mathbf 2 m/s. Plasma has been generated by varying input discharge voltages from 2.0 to 4.0 kV at a driving frequency of 40 kHz. Particularly, the average electron temperature in slow electron energy nonthermal atmospheric-pressure indirect-plasma jet has been found to be about 0.3 eV. [ABSTRACT FROM PUBLISHER]

In this paper, organic electroluminescence fluoropolymer film devices, i.e., organic light-emitting diodes (OLEDs) comprising polychlorotrifluoroethylene (PCTFE) films treated by an atmospheric-pressure nonthermal plasma (NTP) graft-polymerization process, are investigated. PCTFE films can provide a long lifetime for OLEDs because of their excellent gas barrier properties; however, they are difficult to laminate, owing to low adhesiveness. The surfaces of PCTFE films are treated by an atmospheric-pressure NTP-graft-polymerization process to improve their adhesiveness, and then, indium tin oxide and a luminous layer are deposited on the treated PCTFE films. As a result, OLEDs comprising PCTFE films are successfully demonstrated. [ABSTRACT FROM AUTHOR]

An atmospheric-pressure plasma jet array source driven by a pulsed bipolar wave of several tens of kilohertz was designed and characterized. This source was assembled with each individual module. Thus, it is possible to adjust the area of treatment by arranging the number of jets. It has the potential to greatly enhance the scale of surface treatment over that of a single plasma jet. Multiple plasma plumes were generated and propagated to grounded-surface relatively uniformly without an auxiliary circuit. Due to the large separation between each jet, plasma bullets propagate through their individual gas channels. The transition from the bullet to the continuous modes occurred at an applied voltage of 5.5 \mathrmkV\mathrm {pp} . The interaction between adjacent plasma plumes and behaviors of primary bullet and subbullet are investigated with intensified charge coupled device camera images. [ABSTRACT FROM PUBLISHER]

The hybrid plasma catalysis system was investigated for dry reforming of methane (DRM) with CO2 to form syngas. First, dielectric barrier discharge (DBD) alone was evaluated for the effectiveness in conversion of CO2 and CH4, and with the applied voltage of 15.0–19.5 kV, and frequency of 200 Hz. The ratio of feeding gas (CH4/CO2) and total gas flow rate were controlled at 1 and 40 mL/min, respectively. The results indicate that conversions of CO2 and CH4 significantly increase with increasing applied voltage. The conversion of both greenhouse gases (CO2 and CH4) achieved the maximum value of 18.9% and 24.0%, respectively, at applied voltage of 19.5 kV. Selectivity of CO decreases from 53.6% to 42.4% as applied voltage is increased from 15.0 to 19.5 kV, while selectivity of H2 increases from 30.1% to 35.8%. In addition, the influences of gas flow rate and ratio of feeding gas were also explored for DBD-alone system, and the results indicate that energy efficiency of syngas generation can be significantly increased as the flow rate is increased. As a catalyst with a high dielectric constant is placed into the discharge zone, the conversions of two gases (CO2 and CH4) reach 27.3% and 31.2%, respectively, at applied voltage of 19.5 kV. Selectivity of CO decreases from 59.4% to 49.6% as applied voltage is increased from 15 to 19.5 kV, while selectivity of H2 increases from 32.0% to 38.3%. In the meantime, energy efficiency of syngas generation is increased by 0.3%. Overall, this paper indicates that combining DBD with a catalyst of high dielectric constant is a viable process for DRM. [ABSTRACT FROM PUBLISHER]

This paper investigated the bacterial inactivation/sterilization effects of a gas-liquid gliding arc discharge reactor, which created plasma at atmospheric pressure and ambient temperature. Bacteria Escherichia coli were subjected to plasma treatment and the survivability was examined. With the bacteria suspension circulated at defined flow rate, the E. coli cells were almost killed in <3 min. The inactivation efficiency with circulation was much higher than that with no circulation, and it could even reach a reduction of 7 logarithm units in the number of viable bacteria within 30 s after 1-min treatment. Flow rates of the suspension caused slightly impact on the bacteria inactivation to a certain extent. Observations of scanning electron microscopy images helped to draw a conclusion that gas-liquid gliding arc discharge plasma acts under various mechanisms driven essentially by oxidation and electric effect. The results demonstrate that gas-liquid gliding arc discharge allows a rapid and complete inactivation of E. coli bacteria in the water, which shows the great industrial interest of gliding arc discharge technique for decontamination. [ABSTRACT FROM PUBLISHER]

Atmosphere pressure weakly ionized plasma has been utilized to polymerize gas phase acetylene in a needle-to-plane electrode configuration. The approach used in this research is novel as it did not rely on complicated power supplies or expensive materials and it results in a needle-to-ground geometry. The activated acetylene molecules in an argon environment were deposited onto a substrate to grow thin plasma-polymerized acetylene films. Using independent methods, a deposition rate between 2.2 and 23 nm/s was measured when an average free electron power of 94 mW was used. [ABSTRACT FROM AUTHOR]

Atmospheric pressure low-temperature plasmas produced by dielectric barrier discharge (DBD) provide a promising approach for civilian application of pulsed power technology. In this paper, repetitive nanosecond pulses were generated using a magnetic compression solid-state pulsed power generator, and the rise time and pulse duration of the nanosecond pulse are \sim30 and 70 ns, respectively. The DBD in open air is created using two kinds of electrodes, i.e., water and metal electrodes. The electrical, luminous, and optical characteristics of the DBDs under these two electrodes are studied and compared. The experimental results show that no filaments are observed and the discharge is homogeneous when water electrodes are used. The DBD still behaves in a filamentary mode when the discharge gap is extended to 4 cm in the case of metal electrodes. The results are validated by fast images taken by an intensified charge-coupled device camera. In addition, some discussion about the experimental results is presented. Improvement of discharge uniformity is due to the effect of resistive stabilization using water electrodes. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the effects of various background gases on the formation and sustenance of a plasma jet. A helium plasma is ignited inside a dielectric tube and introduced into a vacuum chamber where the gas composition and pressure can be controlled. The gas composition inside the chamber is altered by separately injecting various background gases, such as air, nitrogen, and argon. Here, we report that, in order to sustain a plasma jet, there needs to be a physical boundary layer around the helium flow. This boundary can be in the form of a solid surface that encapsulates the flow, or a background gas other than helium. If only helium is present inside the chamber, no propagating jet is created; rather a diffuse plasma fills the chamber. If another gas is introduced, then the diffuse plasma reverts into a jet. Additionally, we discovered what can be considered as the signature emission line from a plasma jet operating with helium. This emission line is at 587.4 nm (He). This line appears in the emission profile only in the presence of a plasma jet, and disappears as the plasma transitions to a diffuse state at the same applied power parameters and pressure. [ABSTRACT FROM PUBLISHER]

To investigate the tooth bleaching effect of a low concentration hydrogen peroxide (\H2\O2) assisted by a nonthermal plasma, extracted human teeth were treated by a nonthermal plasma in the presence of varying concentrations of hydrogen peroxide gel. The results showed that combining plasma treatment with a low concentration hydrogen peroxide (6%) achieved a superior bleaching effect compared with a high concentration of hydrogen peroxide (35%) in the absence of a plasma. Furthermore, the bleaching efficacy did not significantly increase with increasing \H2\O2 concentration above 6% in the presence of the plasma. Compared with the control group (hydrogen peroxide without plasma), the plasma generated two to three times as many \cdot\OH radicals, which are believed to be one of the key reactive species that contribute to the bleaching effect. [ABSTRACT FROM PUBLISHER]

It has been observed that current pulses in corona-based atmospheric-pressure weakly ionized plasma can be synchronized between needles, dependent on the gap between the needles. This observation was made via a series of experiments utilizing a statistically significant number of current pulses at varying spacing between needles. [ABSTRACT FROM PUBLISHER]

The decomposition of bromomethane (\CH3\Br) , which is an ozone-depleting substance, is carried out using a pulsed dielectric barrier discharge. To accomplish this, a plasma reactor comprising a stainless discharge wire electrode and a quartz cylinder wrapped with a copper mesh as the ground electrode is employed. This reactor is energized by a pulsed high-voltage power supply using an insulated-gate bipolar transistor. The effects of humidity, flow rate, and initial \CH3\Br concentration on \CH3 \Br decomposition are investigated. The relative humidity is found to slightly affect the \CH3\Br decomposition. Additionally, the \CH3\Br decomposition efficiency is found to decrease with increasing gas flow rate; however, the amount of decomposed \CH3\Br increases with gas flow rate. More than 95% \CH3\Br decomposition efficiency is achieved at a gas flow rate of 1 L/min and initial \CH3\Br concentrations of 1000, 5000, and 10 000 ppm. Gas chromatography/mass spectroscopy analysis shows that approximately 95% of the decomposed \CH3\Br is converted to HBr, which can be easily removed using an alkaline scrubber. The energy efficiency of the \CH3 \Br decomposition increases with the initial concentration at the same specific energy. In addition, the specific energy decreases when the energy efficiency is maintained by increasing the gas flow rate. [ABSTRACT FROM AUTHOR]

We evaluated a nonthermal plasma jet for a respective use to prevent infections from bacteria and yeasts. The plasma jet is generated from the flow of ambient air with 8 slm through a microhollow cathode discharge assembly that is operated with a direct current of 30 mA. With these parameters, the temperature in the jet reaches 43 ^\circ\C at 10 mm from the discharge. Agar plates that were inoculated with Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii, and Candida kefyr were treated at this distance, moving the plates through the jet in a meander that covered a 2 cm by 2 cm area. Different exposure times were realized by changing the speed of the movement and adjusting the distance between consecutive passes. S. aureus was most responsive to the exposure with a reduction in the number of colony forming units of 5.5 log steps in 40 s. All other microorganisms show a more gradual inactivation with exposure times. For all bacteria, a clearing of the treated area is achieved in about 2.5–3.5 min, corresponding to log-reduction factors of 5.5–6.5. Complete inactivation of the yeast requires about 7 min. Both S. aureus and C. kefyr show considerable inactivation also outside the immediate treatment area, while P. aeruginosa and A. baumannii do not. We conclude that differences in the morphologies of the membrane structures are responsible for the diverging results, together with a targeted response to different agents provided with the plasma jet. For the gram negative bacteria, we hold short-lived agents, acting across a short range, responsible, while for the other microorganisms, longer lived species seem more important. Our measurements show that neither heat, ultraviolet radiation, nor the generation of ozone can be responsible for the observed results. The most prominent long lived reaction product found is nitric oxide, which, by itself or through induced chemical reactions, might affect cell viability. [ABSTRACT FROM PUBLISHER]

Gliding discharges can generate nonthermal plasma at atmospheric pressure. Therefore, they are widely used in plasma-assisted ignition and combustion. In this paper, the gliding discharge sustained by a resonant ac power supply was obtained with a pin-to-pin electrode geometry, and the characteristics of such discharge were investigated through its voltage–current and discharge images. Inceptive, nonstable, and stable stages involved in this gliding discharge were studied. Experimental results showed that the discharge was first ignited by a spark with a current peak of tens of amperes and soon turned into a stable stage, where the discharge respectively behaved in repetitive spark mode with a current peak of several amperes in a small gap and glowlike mode with a current peak of several microamperes in a relatively large gap spacing. Under a certain situation, a nonstable discharge was observed, which changed from a spark discharge to a glowlike discharge after some time. In addition, both the discharge stability and the breakdown voltage were influenced by the air flow. The discharge became unstable when the air flow exceeded 3 L/min. [ABSTRACT FROM PUBLISHER]

The purpose of this study is to evaluate the changes in dental enamel (morphology, elemental composition, microhardness, and roughness) after applying hydrogen peroxide in conjunction with a nonthermal plasma to bleach the teeth. Extracted human teeth were randomly placed in six groups. Two control groups (one group with no bleaching agent and no plasma treatment of the teeth and another one with only hydrogen peroxide as the bleaching agent) and four plasma groups (receiving hydrogen peroxide of varying concentrations 6%, 15%, 25%, and 35%, in conjunction with a plasma treatment) were prepared. The surface morphology before and after treatment was assessed using a scanning electron microscope (SEM), and the change in the elemental composition was analyzed by an energy-dispersive X-ray spectroscopy system. A total of 36 extracted teeth were used to evaluate the change in enamel microhardness and surface roughness. The use of hydrogen peroxide as a bleaching agent, even in the absence of plasma exposure, causes various etching patterns that are attributable to demineralization during the treatment process. These patterns are more pronounced as the hydrogen peroxide concentration increases. The surface roughness tests confirmed the findings from the SEM analysis. We only found minor essentially insignificant changes in the elemental composition of the enamel and in the surface microhardness as a result of the treatment using hydrogen peroxide and a cold plasma. The use of a cold plasma in conjunction with hydrogen peroxide of varying concentrations in tooth bleaching causes minor changes in the tooth enamel changes that are comparable to those resulting from the standard treatment using 35 % hydrogen peroxide gel without a plasma. [ABSTRACT FROM PUBLISHER]