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Cold atmospheric plasmas are reportedly capable of enhancing the percutaneous absorption of drugs, which is a development direction of plasma medicine. This motivated us to study how the enhancement effect was realized. In this letter, gelatin gel films were used as surrogates of human tissues, NaNO2 was used as a representative of small-molecule drugs, and cross-field and linear-field plasma jets were used for the purpose of enhancing the penetration of NaNO2 through the gelatin gel films. The permeability of gelatin gel films was quantified by measuring the NO2– concentration in water which was covered by those films. It was found that the gas flow and electric field of cold plasmas played a crucial role in the permeability enhancement of the model tissues, but the effect of gas flow was mainly confined in the surface layer, while the effect of the electric field was holistic. Those effects might be attributed to the localized squeezing of particles by gas flow and the weakening of the ion-dipole interaction by the AC electric field. The enhancement effect decreases with the increasing mass fraction of gelatin because the macromolecules of gelatin could significantly hinder the penetration of small molecules in the model tissues. [ABSTRACT FROM AUTHOR]

A surface micro-discharge in atmospheric pressure He + N2 mixtures is studied in this paper with an emphasis on the discharge modes. With the N2 admixture increasing from 0.1% to 20%, the discharge evolves from a spatially diffuse mode to a filamentary mode during positive half-cycles of the applied voltage. However during the negative half-cycles, an additional patterned mode emerges between the diffuse and the filamentary modes, which has not been reported before to exist in surface micro-discharges. In the diffuse and patterned modes, the plasmas cover almost the entirety of the mesh area during one cycle after plasma ignition in all mesh elements, and the discharge power increases linearly with the applied voltage. In contrast, plasma coverage of the mesh area is only partial in the filamentary mode and the plasma is more unstable with the discharge power increasing exponentially with the applied voltage. As the surface micro-discharge evolves through the three modes, the density of excited species changes significantly, for instance, the density of N2+(B) drops by ∼20-fold from [N2] = 0.2% to 20%. The N2+(B) is predicted to be generated mainly through successive processes of Penning ionization by helium metastables and electron-impact excitation of N2+(X), the latter is most responsible for the density decrease of N2+(B) because much more N2+(X) is converted to N4+(X) as the increase of N2 fraction. Also, the electron density and electron temperature decrease with the discharge mode transition. [ABSTRACT FROM AUTHOR]

We present in this paper how oxygen additive impacts on the cold atmospheric-pressure helium plasmas by means of a one-dimensional fluid model. For the oxygen concentration [O2] > -0.1%, the influence of oxygen on the electron characteristics and the power dissipation becomes important, e.g., the electron density, the electron temperature in sheath, the electron-coupling power, and the sheath width decreasing by 1.6 to 16 folds with a two-log increase in [O2] from 0.1% to 10%. Also the discharge mode evolves from the y mode to the a mode. The reactive oxygen species are found to peak in the narrow range of [O2] = 0.4%-0.9% in the plasmas, similar to their power-coupling values. This applies to their wall fluxes except for those of O* and O2". These two species have very short lifetimes, thus only when generated in boundary layers within several micrometers next to the electrode can contribute to the fluxes. The dominant reactive oxygen species and the corresponding main reactions are schematically presented, and their relations are quantified for selected applications. [ABSTRACT FROM AUTHOR]

A new method for the interneedle-distance optimization of a multineedle-to-plane barrier discharge reactor is presented. As we know, there is gas breakdown when, in some regions between electrodes, the electric field is higher than the breakdown field; hence, the regionmay play a dominant role for the discharge, and the enhancement of its volume ratio in the reactor will allow an increase in discharge energy density. This can be achieved by structure optimization. With the finite-element method, the 3-D profiles of an electrostatic field in the reactor are acquired for a series of interneedle distances, thereby the one-to-one relationship between the volume ratio and interneedle distance is obtained. This allows the optimal interneedle distance for power input efficiency to be identified, as related to the maximal volume ratio. The optimal distance is between 7.2 and 8.4 mm in our simulation range, decreasing with the increase of operating voltages from 16 to 26 kV. The simulation results are experimentally validated by discharge energy measurement as well as the performance of SO2 removal from indoor air. This structure optimization method leads to a simple way to obtain the optimal interneedle distance for energy input efficiency and hence benefits commercial use. [ABSTRACT FROM AUTHOR]

The transportation of drugs through model tissues that are being treated by an argon plasma jet was investigated in this paper. Gelatin gel films were used to construct the model tissues and lidocaine was used as a representative drug. The argon plasma jet enhanced the penetration of lidocaine and the enhancement rate increased with the discharge voltage and the frequency. When the discharge power of the plasma jet was low, it was deduced that the enhancement effect was mainly attributed to the electric field of the plasma jet. The enhancement effect was holistic and was hindered by the macromolecules of gelatin in the model tissues. When the discharge power of the plasma jet increased beyond a threshold level, the surface streamers of the plasma jet produced a deformation effect in the model tissue, thereby resulting in a star-shaped pattern on the surface of the model tissue. In that case, the penetration enhancement of lidocaine was dominated by the deformation effect; however, it was mainly confined to the surface layer. For comparison, a helium plasma jet was also used to enhance the penetration of lidocaine. When the discharge power was low, the enhancement effect of the helium plasma jet was higher than that of the argon plasma jet because the He gas flow and the electric field of He plasma jet enhanced the penetration of lidocaine jointly; however, the enhancement effect of the Ar plasma jet was only attributed to the electric field. When the discharge power increased beyond a threshold level, the enhancement effects of the two plasma jets were almost the same. [ABSTRACT FROM AUTHOR]

Surface dielectric barrier discharge is capable of generating large-scale, flexible-shape and chemically active plasmas in open air, and hence has attracted much attention with relevance to clinical applications. An important application requirement is that the plasma treatment should have good homogeneity, which can be reflected by the surface distributions of reactive species on the treated sample. In this letter, a surface air discharge was used to treat a model tissue made of gelatin gel, and the surface distributions of H+, and O3 were detected. When the air gap width between the plasma and the model tissue is 3 mm, it is found that the distributions have mesh patterns similar to that of the ground electrode, but O3 concentrates on the edges of each mesh element, while and H+ concentrate in the center part. A wider air gap width benefits the mixing of reactive species but their surface distributions are more inhomogeneous, which should ascribe to a weak gas flow caused by the ionic wind and/or the gas heating effect. Gas flow can also be generated by rotating the plasma source, which is found to achieve a good homogeneity of treatment with a slow rotating speed of 1.2–2.4 rpm. This approach is easy to implement in clinical applications. [ABSTRACT FROM AUTHOR]

The transportation of reactive oxygen species (ROS) in model tissues treated by an Ar  +  O2 plasma jet was investigated in this paper. Gelatin gel was used to make the model tissues, and KI-starch reagent was used as an indicator of ROS including O3, O and HO2. It was found that the transportation of ROS covered almost the whole surface of the model tissue with good uniformity, despite the small size of the plasma jet source. The center part of the model tissue was almost undyed, of which the area increased slightly with the gas flow rate. The surface pattern of ROS moved downwards with the inclination angle of plasma irradiation, because the molecular weight of argon is larger than that of air. This downward trend could be stopped by adding a certain amount of helium into the Ar  +  O2 plasma jet, which is beneficial to precisely control the effective treatment area in clinical applications. Moreover, the dependence of the penetration depth of O3 on the plasma treatment time or the water content of model tissues was formulated, with a similar trend but lower penetration speed than that of the He  +  O2 plasma jet as reported previously. [ABSTRACT FROM AUTHOR]

In this paper, helium plasma jets are used for water activation to explore the production mechanism of H2O2 in the water. Either positive or negative DC voltage is used for the plasma excitation. It is found that the concentration of aqueous H2O2 induced by the positive plasma jet is ~4 times larger than that by the negative plasma jet with similar average discharge current. Three production pathways of aqueous H2O2 are considered important in literature, including the electrolysis, the dissolution of gaseous H2O2, and the combination of aqueous OH. However, the first two pathways are found to have similar contributions on H2O2 production for the positive and negative plasma jets. It is deduced that the OH combination in the surface layer of the plasma-activated water is most responsible for the concentration difference of aqueous H2O2 between the two plasma jets. [ABSTRACT FROM AUTHOR]

Sebaceous gland tumour (SGT) is a rare tumour with a low incidence rate, which mainly occurs in the eyelid and periocular sebaceous gland. In 2019, our laboratory received a case involving a sebaceous gland tumour of the external auditory meatus for pathological diagnosis. It is a rare malignant tumour in the whole body. Data regarding a sebaceous gland tumour in the dog's external auditory meatus are few. This case is instructive for veterinary diagnosis and treatment. The dog recovered well after surgery at the outpatient department, and no recurrence was observed in the follow-up visit one year later. This study will help the identification of SGT in Spaniel dogs. [ABSTRACT FROM AUTHOR]

Argon is a widely used working gas of plasmas, which is much cheaper than helium but on the other hand much more difficult to generate diffuse discharge at atmospheric pressure. In order to meet the application requirements, plenty of researches have been reported to facilitate the diffuse discharge happening for argon plasmas, and in this paper an approach of using ethanol gas (EtOH) impurity is investigated. The discharge characteristics of Ar + EtOH plasma jet are studied as a function of the applied voltage and the concentration of EtOH, from which the concentration of EtOH between ∼200 and ∼3300 parts per million (ppm) is determined necessary for the generation of diffuse discharge. Compared with the helium plasma jet in literature, it is deduced that the diffuse discharge is probably caused by the Penning ionization happening between the metastable argon and EtOH. The discharge products of Ar + EtOH (672 ppm) plasma jet are measured and the corresponding chemistry pathways are analyzed. About 20% of EtOH is decomposed via complex chemical reactions to form more than a dozen of neutral species, such as CH3CHO, CH3COOH, CO, H2O, and CnH2n+2 (n ≥ 3), and various kinds of ionic species, including C+, CH+, ArH+, CH3CH2O−, etc. [ABSTRACT FROM AUTHOR]

Flexible transparent materials are a hot spot in current research but also a key technical difficulty in industry. They are playing an increasingly important role in flexible transparent display applications such as organic light-emitting diodes, transparent electrodes, and so on. On the other hand, the present research on nanopatterned antennas is mainly concentrated on the optical frequency but rarely on the microwave (such as 3G, 4G, and 5G) and terahertz frequency band communications, where nanopatterned antennas can have many novel applications. To the authors’ knowledge, this is the first paper that presents a method for preparing a flexible transparent Au electromagnetic metamaterial nanopatterned antenna. We study its free-space performance at ultra-high frequency and its application in electronic products such as smartphones, tablets, personal computers, and wearable devices (such as smart watches) which have the function of mobile communication. The experimental results showed that the transparency of the antenna designed and fabricated in this work can be as high as 94%, and its efficiency can reach 74.5%–91.9% of antennas commonly seen at present in academia and industry. By adjusting the capacitive and inductive reactance of the nanopatterned antenna’s matching circuit, combined with its measured efficiency and 3D electromagnetic simulation results, we speculate on the mechanism of the Au electromagnetic metamaterial nanopatterned antenna with good performance. [ABSTRACT FROM AUTHOR]

In this paper, a novel large-scale plasma source is put forward, which can generate two modes of discharge, i.e. the surface dielectric barrier discharge and the plasma jet array, by just varying the helium gas flow rate. It is found that the discharge power changes a little with the increasing gas flow rate, but the densities of reactive species in the gas phase and in the treated water change a lot. In particular, the gaseous O3 has its density decreasing while the aqueous O3 has its concentration increasing with the increasing gas flow rate. In the plasma-treated water, the reactive nitrogen species such as nitrite and nitrate have their concentrations first increasing and then decreasing, while the reactive oxygen species such as H2O2, O3 and OH have their concentrations increasing monotonically, implying that the plasma source is well-adaptive for different application requirements. [ABSTRACT FROM AUTHOR]

In this paper, we report the observation of an interfacial pattern formation on the ITO surface by atmospheric pressure helium plasma jet-ITO interactions. By changing the voltage polarity of positive and negative pulses, the interfacial phenomenon displays two different pattern modes, i.e. a double ring pattern with a combination of homogeneous and filamentous modes as well as a single ring pattern with a homogeneous mode. The reasons may mainly be attributed to the spread of a radially outward traveling surface ionization wave that would cause electric field distributions and charge accumulations on the ITO surface. The spatial-temporal distribution of , He(3s3S), and O(3p5P) emissions are diagnosed to better understand the formation mechanism and the differences of plasma jet patterns under positive and negative polarities. Results show that the distribution of emission is the main contributor for generating the filament structure in a double ring pattern for positive polarity, the homogeneous mode pattern mainly depends on the distribution of O(3p5P) emission for positive and negative polarity. Additionally, in order to further systematically understand the behaviors of plasma jet patterns, some parametric results, such as behaviors versus pulse peak voltage, dielectric material, pulse repetition rate, and flow rate are investigated. Some interesting phenomena and additional insights for the plasma jet pattern are found with different parametric conditions. This study might help to better understand effects of plasma jets in interaction with surfaces, or its application in the medical sector. [ABSTRACT FROM AUTHOR]

Cold atmospheric-pressure plasmas in Ar + H2O gas mixtures are a promising alternative to He + H2O plasmas as both can produce reactive oxygen species of relevance for many applications and argon is cheaper than helium. Although He + H2O plasmas have been the subject of multiple experimental and computational studies, Ar + H2O plasmas have received less attention. In this work we investigate the composition and chemical pathways in Ar + H2O plasmas by means of a global model that incorporates 57 species and 1228 chemical reactions. Water vapor concentrations from 1 ppm to saturation (32 000 ppm) are considered in the study and abrupt transitions in power dissipation channels, species densities and chemical pathways are found when the water concentration increases from 100 to 1000 ppm. In this region the plasma transitions from an electropositive discharge in which most power is coupled to electrons into an electronegative one in which most power is coupled to ions. While increasing electronegativity is also observed in He + H2O plasmas, in Ar + H2O plasmas the transition is more abrupt because Penning processes do not contribute to gas ionization and the changes in the electron energy distribution function and mean electron energy caused by the increasing water concentration result in electron-neutral excitation and ionization rates changing by many orders of magnitude in a relatively small range of water concentrations. Insights into the main chemical species and pathways governing the production and loss of electrons, O, OH, OH(A) and H2O2 are provided as part of the study. [ABSTRACT FROM AUTHOR]

In this letter, a 1D fluid model has been used to study the electron heating and particle transport in dual frequency atmospheric-pressure helium capacitive discharge with a high-frequency (HF) voltage of 10 MHz and a low-frequency (LF) voltage of 1 MHz. The electric field is decoupled to three components: the HF, the LF and the direct current (DC) ones, and they have much different effects on the plasmas. The eletrons in plasma bulk are mainly heated by the HF electric field, while in plasma sheath they are heated and cooled by the LF and DC electric fields, respectively. With a fixed total input power, the increase of LF power leads to great enhancement of the electrode fluxes of electrons and ions, especially for the energetic electrons of Te  >  2 eV, because more power is dissipated in the vicinity of electrodes and the inelastic collision is more pronounced. Therefore, the particle transport on the treated sample can be greatly enhanced without additional gas heating in dual frequency plasmas, which meets the application requirements more compared to the single frequency plasmas. [ABSTRACT FROM AUTHOR]

We present in this study how DC bias voltage impacts on the fluxes of reactive species on the skin tissue by means of a plasma–tissue interaction model. The DC bias voltage inputs less than 2% of the total discharge power, and hence it has little influence on the whole plasma characteritics including the volume-averaged densities of reactive species and the heating effect. However, it pushes the plasma bulk towards the skin surface, which significantly changes the local plasma characteristics in the vicinity of the skin surface, and in consequence remarkably enhances the flux densities of reactive species on the skin tissue. With the consideration of plasma dosage and heat damage on the skin tissue, DC bias voltage is a better approach compared with the common approach of increasing the plasma power. Since the DC voltage is easy to apply on the human body, it is a promising approach for use in clincial applications. [ABSTRACT FROM AUTHOR]

Gelatin gels are used as surrogates of human tissues to study their barrier effects on incoming reactive oxygen and nitrogen species (RONS) generated by surface air discharge. The penetration depth of nitrite into gelatin gel is measured in real time during plasma treatment, and the permeabilities of nitrite, nitrate, O3 and H2O2 through gelatin gel films are quantified by measuring their concentrations in the water underneath such films after plasma treatment. It is found that the penetration speed of nitrite increases linearly with the mass fraction of water in the gelatin gels, and the permeabilities of nitrite and O3 are comparably smaller than that for H2O2 and nitrate due to differences in their chemistry in gelatin gels. These results provide a quantitative basis to estimate the penetration processes of RONS in human tissues, and they also confirm that the composition of RONS is strongly dependent on the tissue depth and the plasma treatment time. A small electric field of up to 20 V cm−1 can greatly reduce the barrier effects of the tissue model regardless of their directions, for which the underlying mechanism is unclear. However, the electric field force on the objective RONS should not be the dominant mechanism. [ABSTRACT FROM AUTHOR]

The atmospheric pressure dielectric barrier discharge in helium is a pulsed discharge in nature and the moment of maximum species densities is almost consistent with peak discharge current density. In this paper, a one-dimensional fluid model is used to investigate the temporal structure of plasma species in an atmospheric He-N2 dielectric barrier discharge (DBD). It is demonstrated that there exist microsecond delays of the moments of the maximum electron and ion densities from the peak of discharge current density. These time delays are caused by a competition between the electron impact and Penning ionizations, modulated by the N2 level in the plasma-forming gas. Besides, significant electron wall losses lead to the DBD being more positively charged and, with a distinct temporal separation in the peak electron and cation densities, the plasma is characterized with repetitive bursts of net positive charges. The temporal details of ionic and reactive plasma species may provide a new idea for some biological processes. [ABSTRACT FROM AUTHOR]

The paper presents the results of a numerical simulation of the effects of N2 on the characteristics of Trichel pulses in SF6 at 0.4 MPa. The simulation was performed in a 2D axisymmetric geometry assuming a three species discharge model for the applied voltage on the discharge electrode to be −25 kV. Three drift-diffusion equations coupled with Poisson's equation are considered to determine the dynamic behavior of Trichel pulses and the temporal and spatial distributions of charged species. The reduced ionization coefficient, the reduced attachment coefficient, the electron mobility, and the electron diffusion coefficient of SF6/N2 mixtures are obtained by solving the two-term Boltzmann equations. The content of N2 varies from 20% to 80%. The distribution of three charged species and the reduced electric field at the discharge tip are presented at different instants of time to explain the formation mechanism of the Trichel pulses in SF6/N2 mixtures. The time-dependent current, the total number of electrons, the positive ions, and the negative ions as well as the reduced electric field at the discharge tip under different SF6/N2 mixtures are analyzed to investigate the sensitivities of these properties to the N2 content. [ABSTRACT FROM AUTHOR]

The application of cold atmospheric plasma jet in cancer treatment has received extensive attention. Research on the spatial distribution of the anticancer effects induced by plasma jet is of great significance for further promoting its clinical application. Here, based on two-dimensional monolayer cells and three-dimensional (3D) multicellular tumor spheroids, the distributions of anticancer effects induced by He plasma jet irradiation on tumor tissue were studied in detail. It was found that the effective anticancer area of the plasma jet was affected by the gas flow rate. Further studies showed that the plasma jet caused physical damage in the central region of the anticancer area and induced apoptosis in the peripheral region due to the reactive oxygen species (ROS) generated by the plasma jet. In addition, the anticancer results on 3D multicellular tumor spheroids indicated that the apoptosis rate and the anticancer depth of the plasma jet were different at different distances from the plasma-irradiated spot. This study could help us better understand the actual anticancer effects of a plasma jet on living tumor tissues, and it may provide beneficial information for optimizing the plasma jet treatment method in future clinical applications. [ABSTRACT FROM AUTHOR]

Microbial cells in chronic wounds seriously delay wound healing and thus the inactivation of microbial cells is a critical step in the therapeutic process. Cold atmospheric-pressure plasma (CAP) can efficiently inactivate microbial cells and could be developed into an effective strategy for topical antimicrobial treatment. However, the details of microbial inactivation in tissues by CAP, including the effective depth of the plasma and the variation of the microbial species, are still unclear. Therefore, in this study, agarose gels containing microbial cells were used as a model of infected tissues and were treated with surface discharge plasma with the working gas of argon and 1% synthetic air. It was found that the depths of microbial inactivation were proportional to the plasma treatment time and were also related to the microbial species. The ROS penetration was dependent on the plasma treatment time, the diffusion process, and the existence of microbial cells. The plasma-generated ROS caused microbial cells to release ROS, which slightly increased the ROS penetration depths. This study of microbial inactivation by plasma in model tissues could increase the mechanism of plasma inactivation and as a treatment in the biomedical field. [ABSTRACT FROM AUTHOR]

Surface discharge plasmas have advantages in various applications, such as the treatment of wound infections. However, the effects of surface discharge plasmas on biofilms have not been studied. In this study, the inactivation of methicillin-resistant Staphylococcus aureus biofilms by surface discharge plasmas with four working gases, namely, He  +  1% air, Ar  +  1% air, synthetic air, and natural air, was investigated to elucidate the correlation between the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) and the biofilm eradication performance. The experimental results demonstrated that the surface plasma with Ar  +  1% air produced the highest concentrations of excited reactive species in gas phase and of and /.NO2/ONOO− in the liquid phase, while the surface plasma with synthetic air produced largest amount of and 1O2 in the liquid phase. For methicillin-resistant S. aureus biofilms, the inactivation effects of the surface plasmas with Ar  +  1% air and natural air were similar and more pronounced compared with the other gases, while the inactivation effect of surface plasma with He  +  1% air was the least pronounced. The biofilm inactivation and ROS penetration by He  +  1% air plasma could be enhanced by a low concentration of nitrite and nitrate. Based on the results, it was proposed that plasma-generated long-lived species promoted the penetration of reactive species in biofilms, and the penetrated ROS and RNS jointly contributed to the inactivation of methicillin-resistant S. aureus biofilms. [ABSTRACT FROM AUTHOR]

Viruses are serious pathogenic contamination that severely affect the environment and human health. Cold atmospheric-pressure plasma efficiently inactivates pathogenic bacteria, however, the mechanism of virus inactivation by plasma is not fully understood. In this study, surface plasma in argon mixed with 1% air and plasma-activated water were used to treat water containing bacteriophages. Both agents efficiently inactivated bacteriophages T4, Φ174, and MS2 in a time-dependent manner. Prolonged storage had marginal effects on the anti-viral activity of plasma-activated water. DNA and protein analysis revealed that the reactive species generated by plasma damaged both nucleic acid and proteins, in consistent with the morphological examination showing that plasma treatment caused the aggregation of bacteriophages. The inactivation of bacteriophages was alleviated by the singlet oxygen scavengers, demonstrating that singlet oxygen played a primary role in this process. Our findings provide a potentially effective disinfecting strategy to combat the environmental viruses using cold atmospheric-pressure plasma and plasma-activated water. [ABSTRACT FROM AUTHOR]

Although the formation and propagation of plasma plume for atmospheric pressure plasmas have been intensively studied, how does the plasma plume terminate is still little known. In this letter, helium plasma plumes are generated in a long quartz tube by pulsed voltages and a constant gas flow. The voltages have a variable pulse width (PW) from 0.5μs to 200μs. It is found that the plasma plume terminates right after the falling edge of each voltage pulse when PW<20μs, whereas it terminates before the falling edge. When PW is larger than 30 μs, the duration of plasma plume starts to decrease, and the termination is found to occur at the current zero moment of the discharge current through the high-voltage electrode, which is much different from that through the ground electrode. This indicates that part of the discharge current is shunted by the plasma plume to its downstream gas region. An equivalent circuit model is developed, from which the surface charge deposited on the quartz tube is found crucial for accelerating the termination of a plasma plume when PW>30μs. [ABSTRACT FROM AUTHOR]

A comparative study on aqueous reactive species in deionized water treated by two types of plasma jets is presented. Classified by the direction of the electric field in the jet device, a linear-field jet and cross-field jet have been set up. Concentrations of several aqueous reactive species are measured quantitatively by chemical fluorescent assays and electron spin resonance spectrometer. Results show that these two-type plasma jets would generate approximately the same gaseous reactive species under the same discharge power, but the linear-field plasma jet is much more efficient at delivering those species to the remote deionized water. This leads to a much more aqueous short-lived species including OH and produced in water, which are mainly correlated to the solvation of gaseous short-lived species such as ions and electrons. Regarding the long-lived species of aqueous H2O2, the concentration grows faster when treated by the linear-field plasma jet in the initial stage, but after 10 min it is similar to that treated by the cross-field counterpart due to the vapor–liquid equilibrium. The aqueous peroxynitrite is also predicted to be produced as a result of the air inclusion in the feeding gas. [ABSTRACT FROM AUTHOR]

In this paper, atmospheric pressure N2/O2 plasma jets with homogeneous shielding gas excited by nanosecond pulse are obtained to generate simplex reactive nitrogen species (RNS) and reactive oxygen species (ROS), respectively, for the purpose of studying the simplex RNS and ROS to induce the myeloma cell apoptosis with the same discharge power. The results reveal that the cell death rate by the N2 plasma jet with N2 shielding gas is about two times that of the O2 plasma jet with O2 shielding gas for the equivalent treatment time. By diagnosing the reactive species of ONOO−, H2O2, OH and in medium, our findings suggest the cell death rate after plasma jets treatment has a positive correlation with the concentration of ONOO−. Therefore, the ONOO− in medium is thought to play an important role in the process of inducing myeloma cell apoptosis. [ABSTRACT FROM AUTHOR]

Dielectric barrier discharge is attractive for air pollution control, except for its low energy efficiency and high operating voltage. For the sake of commercial use, multineedle to plane electrodes is investigated in this paper, and its optimization is achieved both by simulation and experiments. [ABSTRACT FROM AUTHOR]

Nitric oxide NO is one of the major targets for environmental monitoring, but the existing NO sensors are limited by their low sensitivity and narrow test range. Here, a NO gas sensor employing multiwalled carbon nanotubes (MWCNTs) was fabricated, and its properties in NO-N2 mixture were investigated from both emission and ionization. The current I e passing through the nanotubes cathode was found to decrease with increasing NO concentration and increase linearly in different slopes with the extracting voltage U e. It is shown that the Schottky barrier of the MWCNTs calculated by I e increased with NO concentration due to the adsorption of NO gas, which restrained the electron emission and consequently weakened the ionization. The positive ion currents I c passing through the collecting electrode at different voltages of U e were found to monotonically decrease with increasing NO concentration, which was induced by both of the reduced electron emission and the consumption of the two excited metastable states N2(A³u +) and N2(a'¹u -) by NO. The sensor exhibited high sensitivity at the low temperature of 30 °C. The calculated conductivity was found to be able to take place of Ic for NO detection in a wide voltage range of 80-150 V U e. [ABSTRACT FROM AUTHOR]

Recently, much attention has been paid to SF6-CO2 mixtures as one of substitutes for pure SF6 gas. In this paper, the dielectric breakdown properties of hot SF6-CO2 mixtures are investigated at temperatures of 300-3500K and pressures of 0.01-1.0 MPa. Under the assumptions of local thermodynamic equilibrium and local chemical equilibrium, the equilibrium compositions of hot SF6-CO2 mixtures with different CO2 proportions are obtained based on Gibbs free energy minimization. The cross sections for interactions between electrons and neutral species are presented. Some unknown ionization cross sections are determined theoretically using Deutsch-Märk (DM) formalism based on quantum chemistry. Two-term Boltzmann equation is adopted to calculate the electron energy distribution function, reduced ionization coefficient, reduced attachment coefficient, and reduced effective ionization coefficient. Then the reduced critical electric field strength of mixtures, corresponding to dielectric breakdown performances, is determined when the generation and loss of electrons are balanced. Finally, the influences of temperature, pressure, and CO2 proportion on the reduced critical electric field strength are studied. It is found that a large percentage of CO2 can obviously reduce concentrations of high-energy electrons. At temperatures above 1750 K, an addition of CO2 to SF6 gas can enhance dielectric breakdown performances. However, at low temperatures, too much CO2 added into mixtures can reduce dielectric breakdown abilities. In addition, increasing gas pressure can improve dielectric breakdown performances. But the influence will be no more significant if pressure is over 0.8 MPa. [ABSTRACT FROM AUTHOR]

Cold atmospheric plasma (CAP) is a novel modality for cancer therapy with high selectivity, and few side effects without the chance of drug resistance. However, fully determining the cellular targets of CAP and improving the clinical applicability of CAP remain challenging. Here, we assessed the sensitivity of cancer cells in different phases of the cell cycle to plasma to find the ‘sensitive period’ in cancer cells to plasma. Plasma was shown to exert significant anticancer effects on HeLa and MCF-7 cells at different phases during the cell cycle. The anticancer effects of plasma are irradiation time- and incubation time-dependent. However, although plasma-induced extracellular and intracellular oxidative pressure are identical, throughout the cell cycle, S- and M-phase cancer cells are more susceptible to plasma irradiation than G1- and G2-phase cells. Our results suggest that plasma induces the apoptosis of S-phase cancer cells by interfering with DNA replication and M-phase cells by impeding sister chromosome segregation. Therefore, the anti-cancer efficiency of CAP techniques might be further improved by their combination with an anticarcinogen that blocks the cell cycle in the ‘sensitive period’. [ABSTRACT FROM AUTHOR]

In the presence of H2O and O2, the dissociation products of SF6 will decompose to form several main stable byproducts (i.e. SOF2, SOF4 and SO2F2) in an electrical discharge. These byproducts are chemically active and have been shown experimentally to be associated with discharge faults. However, the relationships between the discharges and types of decomposition components are still not clear, mainly due to the fact that the complex chemical processes during SF6 discharges are not fully understood. In order to comprehensively investigate the decomposition of SF6, an approach combining density functional theory (DFT) and transition state theory (TST) was used to study the pathways of SF6 decomposition in mixtures with H2O and O2 that involve electrically-neutral species. The complex chemical reactions were analyzed, and the corresponding rate constants were predicted. The structural optimizations, vibrational frequency calculations and zero-point energy calculations of the species involved in each chemical reaction considered were carried out using the DFT-B3LYP method. Single-point energies were calculated using the CCSD(T) method. Based on the energy information obtained, the rate constants were predicted by TST, over a large temperature range, from 300 to 12 000 K. [ABSTRACT FROM AUTHOR]

SF6 is widely used in electrical equipment as an insulating gas. In the presence of an electric arc, partial discharge (PD) or spark, SF6 dissociation products (such as SF2, SF3 and SF4) react with the unavoidable gas impurities (such as water vapor and oxygen), electrodes and surrounding solid insulation materials, forming several toxic and corrosive byproducts. The main stable decomposition products are SO2F, SO2F2 and SOF2, which have been confirmed experimentally to have a direct relationship with discharge faults, and are thus expected to be useful in the fault diagnosis of power equipment. Various studies have been performed of the main SF6 decomposition species and their concentrations under different types of faults. However, most of the experiments focused on the qualitative analysis of the relationship between the stable products and discharge faults. Although some theoretical research on the formation of main SF6 derivatives have been carried out using chemical kinetics models, the basic data (chemical reactions and their rate constants) adopted in the model are inaccurate and incomplete. The complex chemical reactions of SF6 with the impurities are ignored in most cases. The rate constants of some reactions obtained at ambient temperature or in a narrow temperature range are adopted in the models over a far greater range, for example up to 12 000 K, due to the difficulty in the experimental measurement and theoretical estimation of rate coefficients, particularly at high temperatures. Therefore, improved theoretical models require not only the consideration of additional SF6 decomposition reactions in the presence of impurities but also on improved values of rate constants. This paper is devoted to determining the rate constants of the chemical reactions relating to the main byproducts of SF6 decomposition in SF6 gas-insulated power equipment: SO2F, SOF2 and SO2F2. Quantum chemistry calculations with density functional theory, conventional transition state theory and Wigner’s tunneling effect correction are employed to estimate the rate constants of four important chemical reactions: F  +  SO2F  →  SO2F2, F2  +  SO2  →  SO2F2, SO2F  +  SF5  →  SF6  +  SO2 and SOF3  +  SF3  →  SF4  +  SOF2. The results are derived for a large temperature range, from 300 to 12 000 K, and finally fitted by a three-parameter Arrhenius equation. This work lays a basis for the further study of the SF6 decomposition mechanism by means of chemical kinetics modelling. [ABSTRACT FROM AUTHOR]

The dielectric breakdown properties of hot SF6 gas during the dielectric recovery phase play an important role in understanding gas breakdown occurring in high-voltage circuit breakers. This paper is devoted to the theoretical investigation of dielectric breakdown properties of hot SF6 gas contaminated by copper at temperatures of 300–3500 K and pressures of 0.01–1.6 MPa. The equilibrium compositions of SF6–Cu mixtures are obtained with the consideration of condensed species. The unknown ionization cross sections for CuS, CuF and CuF2 are calculated using a Deutsch–Märk (DM) formalism based on quantum chemistry. The two-term Boltzmann equation is adopted to numerically calculate the electron energy distribution function, collision ionization coefficient and electron attachment coefficient. Then the reduced critical electric field strength is determined when the effective ionization coefficient equals to zero. The influences of the Cu proportion and gas pressure on the dielectric breakdown properties are investigated. It is shown that the existence of copper compounds increases the concentration of high-energy electrons significantly, even for the case with a very low percentage (e.g. 1% Cu). With the increase of copper content, the value of (E/N)cr is reduced remarkably at temperatures below 3000 K, but enhanced slightly above 3000 K. It is also found that the increase of pressure can improve the dielectric breakdown performance of hot SF6–Cu mixtures. [ABSTRACT FROM AUTHOR]