Analysis and Review of Chemical Reactions and Transport Processes in Pulsed Electrical Discharge Plasma Formed Directly in Liquid Water

Electrical discharges formed directly in liquid water include three general cases where (a) streamer-like plasma channels form in, but do not span, the electrode gap, (b) spark discharges produce transient plasma channels that span the electrode gap, and (c) arc discharges form plasma channels with relatively longer life times. Other factors including the input energy (from <1?J/pulse to >1?kJ/pulse) as well as solution properties and the rates of energy delivery affect the nature of the discharge channels. An understanding of the formation of chemical species, including the highly reactive hydroxyl radical and more stable molecular species such as hydrogen and hydrogen peroxide, in such plasma requires determination of temporal and spatial variations of temperature, pressure, plasma volume, and electrical characteristics including current, voltage (electric field), and plasma conductivity. In spark and arc discharges analysis of the physical processes has focused on hydrodynamic and thermal characterization, while only a limited amount of work has connected these physical processes to chemical reactions. On the other hand, the most successful model of the chemical reactions in streamer-like discharges relies on simple assumptions concerning the temperature and pressure in the plasma channels, while analysis of the physical processes is more limited. This paper reviews the literature on the mathematical modeling of electrical discharges in liquid water spanning the range from streamer-like to spark and arc discharges, and compares the properties and processes in these electrical discharges to those in electron beam radiolysis and ultrasound.     

The formation of ozone and UV radiation from high-power pulsed electric discharges

High-power electric discharges with pulse energies of from 0.15 J to 4 kJ were studied. The yields of UV photons and ozone were found to be approximately equal, which led us to conclude that discharge conditions under which UV radiation and ozone fully destroyed each other were possible. If ozone formation was suppressed, as when a negative volume charge was created in the spark gap region, the flux of UV photons reached 3 × 10²³ photons/(cm² s).     

Push–Pull archetype of reduced graphene oxide functionalized with polyfluorene for nonvolatile rewritable memory

A solution‐processable PFTPA‐convalently grafted reduced graphene oxide (RGO‐PFTPA) was synthesized by the 1,3‐dipolar cycloaddition of azomethine ylide. Bistable electrical switching and nonvolatile rewritable memory effects were demonstrated in a sandwich structure of indium tin oxide/RGO‐PFTPA/Al. The switch‐on voltage of the as‐fabricated device was around ?1.4 V, and the ON/OFF‐state current ratio was more than 10³. The ON–OFF transition process is reversible because the application of a high enough positive voltage can induce the reverse transfer of electrons, reducing the conductivity back to its initial OFF state. Both the OFF and ON states are accessible and very stable under a constant voltage stress of ?1 V for up to 3 h, or under a pulse voltage stress of ?1 V for up to 10⁸ continuous read cycles (pulse period = 2 μs, pulse width = 1 μs). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Pulsed Discharge Regeneration of Diesel Particulate Filters

A novel method for the removal of soot from a diesel particulate filter using pulsed electric discharges is presented. High voltage pulses of between 18 and 25 kV of nano to microsecond duration and with pulse energies of typically 100–200 mJ were applied to the filter via a series spark gap. Initial slow erosion of the soot layer proceeds via the formation of microdischarges. Subsequent spark discharges removed the accumulated soot more effectively from a larger filter volume. Average soot removal rates of ～0.1–0.2 g/min were achieved at 50 Hz breakdown frequency by optimizing both electrode geometry and breakdown voltage. On-engine long term testing of the technology showed soot removal by pulsed discharge to be reliable, efficient and uniform; a total of 100 g of soot was deposited and removed over 18 filter regeneration cycles.     

Effect of high-voltage electric pulses on yeast cells: factors influencing the killing efficiency

The decisive factors determining the killing efficiency of single rectangular electric pulses of 4–28 kV cm⁻¹ amplitude and 1–300 μs duration in Saccharomyces cerevisiae S6/1 are pulse amplitude and duration, cell size and growth phase, post-pulse temperature and medium conductivity. In S. cerevisiae, the minimum pulse duration ensuring substantial killing is about 10 μs, the minimum amplitude being about 2 kV cm⁻¹. The critical pulse-induced transmembrane breakthrough voltage is 0.75 V. A pulse-induced increase in membrane permeability for small species such as inorganic ions suffices to cause cell death. A preset killing rate can be achieved by varying pulse amplitude inversely to pulse duration. Comparison of killing data on S. cerevisiae S6/1 with those on the smaller-celled Kluyveramyces lactis showed the killing pulse amplitude to be roughly proportional to cell size except for low pulse amplitudes, at which smaller cells are much more killing-prone. In exponential S. cerevisiae cells increased pulse amplitude caused a sharp increase in killing while in stationary cells this effect was much lower and occurred only at pulse amplitude above 15–20 kV cm⁻¹. Elevated post-pulse temperature lowered the killing rate whereas lowered temperature promoted it, probably by affecting the pore resealing. Lowering medium conductivity from 66 to 46 μS m⁻¹ by suspension washing reduced the killing rate by 6–20%. Reproducible killing or electroporation therefore requires standardized cell concentration, and number of cell washings.     

Cytotoxicological aspects of organic arsenic compounds contained in marine products using the mammalian cell culture technique

Arsenobetaine, arsenocholine, trimethylarsine oxide and tetramethylarsonium iodide, which are contained in marine fishery products, were examined for their potencies on cell growth inhibition, chromosomal aberration and sister chromatid exchange (SCE). Arseno- betaine, the major water-soluble organic arsenic compound in marine animals, exhibited very low cytotoxicity towards mammalian cells. This compound showed no cell growth inhibition at a concentration of 10 mg cm⁻³ and the cytotoxicity was lower than 1/14 000th of that of sodium arsenite and 1/1600th of that of sodium arsenate towards BALB/c 3T3 cells. The chromosomal aberrations caused by arsenobetaine at a concentration of 10 mg cm⁻³ consisted mainly of chromatid gaps and chromatid breaks, but in this concentration chromosomal breakage owing to its osmotic pressure is likely to be considerable. No SCE was observed at a concentration of 1 mg cm⁻³. Arsenocholine and trimethylarsine oxide also showed no cell growth inhibited at a concentration of 10 mg cm⁻³. However, tetramethylarsonium iodide inhibition the growth of BALB/c 3T3 at a concentration of 8 mg cm⁻³. These compounds exhibited a low ability to induce chromosomal aberrations at a concentration range of 2–10 mg cm⁻³ and no SCE was observed at a concentration of 1.0 mg cm⁻³. These results suggested that the major and minor organic arsenic compounds contained in marine fishery products are much less cytotoxic inorganic arsenic, methylarsonic acid and dimethylarsinic acid. © 1998 John Wiley & Sons, Ltd.     

Chemical effects of self-sustained spark discharge: Simulation of processes in a liquid

A numerical model has been proposed for the formation of active species in water by the action of pulsed UV radiation generated in self-sustained spark discharge with an energy per pulse of 5.9 × 10^?2 J, a pulse duration of 100 μs, and a pulse repetition frequency of 10 Hz. The primary products formed in water are $HO_2^ \bullet$ radicals, O^· atoms, and N₂O molecules. The yield of nitric acid and low (experimentally undetectable) yields of ozone and hydrogen peroxide are described in terms of the model. The concentrations of the active species in water have been calculated. The results can be used in biophysical research.     

Evidence for genotoxic effects of resonant ELF magnetic fields

The possibility that extremely low frequency (ELF) magnetic fields affect the genomic integrity of the cell is the objective of this study. Human peripheral lymphocytes (HPLs) were exposed to different exposure conditions combining ac and static magnetic fields. We used the micronuclei (MN) cytogenetic technique, because MN formation is considered as a marker of chromosomal damage produced by genotoxic agents.The first set of experiments were performed at 50 Hz, 150 μT rms and 32 Hz, 75 μT and 150 μT rms magnetic fields with the static geomagnetic field components nulled. No effects were detected using the MN test on HPL as an indicator for cellular genomic damage when the static magnetic field was nulled. Moreover, such exposure to an ac magnetic field does not appear to interfere with the action of a powerful genotoxic agent mytomicin-C (MMC), i.e. there was no synergistic effect.The second set of experiments were conducted exposing cells to 32 Hz, 150 μT and 75 μT rms, parallel to a 42 μT dc magnetic field. The 75 μT rms, 32 Hz exposure condition was chosen to maximize the resonance effect on Ca²⁺ according to parametric resonance theory. We found a statistically significant increase of MN for both exposure conditions. This experiment provides evidence for the genotoxic effects of resonant ELF magnetic fields in human lymphocytes.     

Ignition of Quiescent Lean Propane–Air Mixtures at High Pressure by Nanosecond Repetitively Pulsed Discharges

We present an experimental study of lean mixture ignition by nanosecond repetitively pulsed (NRP) discharges. The plasma is created in a lean propane/air mixture at pressure up to 10 bar and equivalence ratio 0.7, premixed in a constant volume vessel. We characterize the initial spark radius, the ignition kernel development and the flame propagation as a function of pressure (up to 10 bar) and the pulse energy (1–6 mJ per pulse). Comparisons with a conventional igniter show that better results are obtained with NRP discharges in terms of flame propagation speed, in particular at high pressure, due to the increased wrinkling of the flame front that is induced by NRP discharges.     

A Miniature Electrolytic Conductivity Probe with a Wide Linear Range

A novel miniature electrolytic conductivity probe and its successful operation with modified bipolar pulse conductometry are presented. The probe based on a concentric ring‐disk electrode configuration of less than 1 mm in diameter featured extremely small detection volume, and conductivity was measured with a 1 μL solution. Rapid response, easy and quick washing, and virtually no consumption of samples by measurements were additional advantages of the suggested probe design. Poor linearity was observed with conventional AC conductometry due to a large cell constant and a small double layer capacitance of the probe. Measurement circuits for modified bipolar pulse conductometry were designed, and optimization of the various pulse parameters led to a wide linear dynamic range of 0.05–10 mS cm^?1, thus achieving high accuracy with a single‐point calibration. The suggested conductometric device could be conveniently applied to biological reagents and samples that are usually too little to be measured with conventional conductometers.     

Generation of Antimicrobial NO<Subscript>x</Subscript> by Atmospheric Air Transient Spark Discharge

Atmospheric pressure air plasma discharges generate potential antimicrobial agents, such as nitrogen oxides and ozone. Generation of nitrogen oxides was studied in a DC-driven self-pulsing (1–10 kHz) transient spark (TS) discharge. The precursors of NO_x production and the TS characteristics were studied by nanosecond time-resolved optical diagnostics: a photomultiplier module and a spectrometer coupled with fast intensified camera. Thanks to the short (~10–100 ns) high current (>1 A) spark current pulses, highly reactive non-equilibrium plasma is generated. Ozone was not detectable in the TS, probably due to higher gas temperature after the short spark current pulses, but the NO_x production rate of ~7 × 10¹⁶ molecules/J was achieved. The NO₂/NO ratio decreased with increasing TS repetition frequency, which is related to the complex frequency-dependent discharge properties and thus changing NO₂/NO generating mechanisms. Further optimization of NO₂ and NO production to improve the biomedical and antimicrobial effects is possible by modifying the electric circuit generating the TS discharge.     

Chromosomal aberrations resulting from UV exposures to G1 Xenopus cells

Abstract— The dose dependence of chromosomal aberration frequencies induced by UV light in G₁Xenopus cells has been examined. Total aberration frequencies did not exceed control levels until a dose of approximately 7.5 Jm^-2 was administered. Chromatid type aberrations were prevalent throughout the dose range 7.5–25.0 Jm^-2. Chromosome type aberration frequencies were comparatively low but exceeded control levels throughout the range 10.0–25.0 Jm^-2, Results of supporting experiments suggested that most of the chromosome type aberrations observed were in the second mitosis following exposures and were derived from aberrations which normally appear as chromatid types at the first mitosis following exposures.     

Measurement of the properties of a CO2 laser induced air-plasma by double floating probe and spectroscopic techniques

The laser-induced breakdown spark has recently been advanced as a method for real-time, in-situ spectrochemical analysis of gases. Many of these analyses take place in ambient air. To better characterize this source, we have measured the temporal variation of temperature and electron density in an air plasma induced by a CO₂ laser operating at 0.5 and 0.8 J/pulse. The electron temperature was measured by the double floating-probe technique (DFP). An excitation temperature for oxygen atoms was determined spectroscopically by Boltzmann plots. Electron density in the plasma was measured from the Stark broadening of the 715.6-nm line of 01. At 0.5 J/pulse, the DFP temperature ranged from 175000 K at 5 μs to less than 10000 K at 25 μs, while the 01 excitation temperature ranged from 19000 K at 1 μs to above 11 000 K at 25 μs. The excitation temperature and electron density agree with values calculated by others from local thermodynamic equilibrium models of an air plasma. While the electron temperature from the DFP method is much higher than the excitation temperature at 5 μs, at times greater than 25 μs the two have converged, implying thermodynamic equilibration between the species.     

Cucurbit[6]uril Hyperpolarized Chemical Exchange Saturation Transfer Pulse Sequence Parameter Optimization and Detectability Limit Assessment at 3.0T

Molecular imaging is the future of personalized medicine; however, it requires effective contrast agents. Hyperpolarized chemical exchange saturation transfer (HyperCEST) can boost the signal of Hyperpolarized ¹²⁹Xe MRI and render it a molecular imaging modality of high efficiency. Cucurbit[6]uril (CB6) has been successfully employed in vivo as a contrast agent for HyperCEST MRI, however its performance in a clinical MRI scanner has yet to be optimized. In this study, MRI pulse sequence parameter optimization was first performed in CB6 solutions in phosphate-buffered saline (PBS), and subsequently in whole sterile citrated bovine blood. The performance of four different depolarization pulse shapes (sinusoidal, 3-lobe sinc (3LS), rectangular (block), and hyperbolic secant (hypsec) was optimized. The detectability limits of CB6 in a clinical 3.0T MRI scanner was assessed using the optimized pulse sequences. The 3LS depolarization pulses performed best, and demonstrated 24 % depletion in a 25 μM solution of CB6 in PBS. It performed similarly in blood. The CB6 detectability limit was found to be 100 μM in citrated bovine blood with a correspondent HyperCEST depletion of 30 % ±9 %. For the first time, the HP ¹²⁹Xe HyperCEST effect was observed in red blood cells (RBC) and had a similar strength as HyperCEST in plasma.     

Oxidative conversion of cyclohexane in discharge plasma maintained with different high-voltage power sources

The influence of the pulse parameters of supply voltage in a barrier discharge reactor on the yield of incomplete oxidation of cyclohexane was studied. It was shown that the voltage pulse parameters have an insignificant effect on both the product composition of cyclohexane oxidation and on selectivity for the products cyclohexanone (40.8%), cyclohexanol (49.5%), and water (9.7%). The lowest power consumption for the conversion of cyclohexane was achieved with the use of a sine wave generator operating at a frequency of 50 Hz (3.0 kWh kg^?1) and a harmonic generator with a pulse duration of 15.3 μs and a pulse repetition frequency of 980 Hz (3.5 kWh kg^?1). The space mode of barrier discharge was realized with the use of a generator of microsecond (53 μs) alternating voltage pulses.     

Parametric studies of emission from a plasma gun source for atomic spectroscopy

A detailed parametric study of the effects of electrical discharge parameters on the spatially and temporally resolved emission from the expelled plume of a plasma gun atomic emission source was performed. Expulsion properties were found to depend on the dI/dt of the discharge current. Low-inductance discharges produced plasmas with propagation velocities (about 1.2 km s⁻¹) which were independent of discharge energy and probably controlled by the properties of the support gas in the discharge chamber. Added-inductance discharges produced plumes with significantly lower propagation velocities and less efficient atomization and expulsion of analyte. Continuum background emission was attributable to two processes, depending upon the spatial location in the plasma: decaying background from the rapidly cooling expelled plasma (lower regions) and collision of the initially-expelled plasma with some of the continuously-expelled plasma gun vapor (upper regions). The line-to-background ratio is optimized when using the highest-energy, low-inductance discharges coupled with integration of emission only from the upper regions of the plume (>10 mm) after the first emission pulse (> 75 μs).     

Carbon‐nanotube Modified Screen‐printed Electrode for the Simultaneous Determination of Nitrite and Uric Acid in Biological Fluids Using Batch‐injection Amperometric Detection

A portable electroanalytical system applied for rapid and simultaneous determination of uric acid (UA) and nitrite (NIT) in human biological fluids (urine, saliva and blood) is reported. The system is based on batch‐injection analysis with multiple‐pulse amperometric (BIA‐MPA) detection using screen‐printed electrodes (SPEs) modified with multi‐walled carbon nanotubes. Sample dilution in optimized electrolyte (0.1 mol L⁻¹ Britton‐Robinson buffer pH 2) followed by injection of 100 μL on the electrode surface using an electronic micropipette is performed. UA is detected at +0.45 V and both UA+NIT at +0.70 V. Linear calibration plots for UA and NIT were obtained over the range of 1–500 μmol L⁻¹ with detection limits of 0.05 and 0.06 μmol L⁻¹, respectively. For comparison, a differential‐pulse voltammetric (DPV) method was optimized, and linear calibration plots for UA and NIT were obtained over range of 1–30 μmol L⁻¹ and 1–40 μmol L⁻¹ with detection limits of 0.1 and 0.3 μmol L⁻¹, respectively. BIA‐MPA is highly precise (RSD<1.3 %), fast (160 h⁻¹) and free from sample‐matrix interferences as recovery values ranged from 77 to 121 % for spiked samples (short contact time of sample aliquot with SPE). Contrarily, recovery tests conducted using DPV did not provide adequate recovery values (>150 %), probably due to the longer contact time of the SPE with the biological samples during analysis leading to a severe interference of sample matrices.     

Isolation and evaluation of cytogenetic effect of Brahmi saponins on cultured human lymphocytes exposed in vitro

Major saponins of Brahmi (Bacopa monniera, Fam: Scrophulariaceae) – bacosides A and B – were isolated from the total methanol extract and characterised based on melting point, TLC, IR, ¹H NMR and ¹³C NMR. They were evaluated for their in vitro cytogenetic effects on human peripheral blood lymphocytes by chromosomal aberration (CA) assay and sister chromatid exchange (SCE) assay. The frequency of chromatid type aberrations and reciprocal interchanges between sister chromatids in the treated cells was scored in comparison to the untreated control. At 30 μg/mL dose, bacoside A showed a statistically significant increase in the frequency of both CA and SCE and bacoside B showed an increase only in SCE. Our report of the genotoxicity of the saponins is significant in view of the reports of anticancer activity of Brahmi extracts.     

Dünnschicht-chromatographische Trennung der 2,4-Dinitrophenylhydrazone von Formaldehyd,Acetaldehyd, Acrolein,Crotonaldehyd und Furfurol

The only useful nuclide for neutron activation of lead is the 0.8 s ^207mPb. Therefore, using a fast pneumatic transfer system, the sensitivities obtainable in steady state and pulse irradiation in a nuclear reactor were investigated. It turned out that under ideal conditions 1 μg lead is still easily measurable, whereas for steady state irradiation a sensitivity of 50 μg lead was found. However, for the samples to be investigated the dead-time caused by the matrix effected a shift of this relation in such a way that the sensitivity for steady state and pulse irradiation was about 100 μg lead.