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Large-scale linear transformer drivers (LTDs) are composed of numerous high-power gas switches, and switch prefire is a frequent operational fault. To detect and locate the faulty switch accurately and efficiently, a two-terminal location method is proposed. A B-dot sensor is integrated on the gas switch's shell to collect the discharging signal. All the B-dot sensors are connected in parallel through cables of equal length. The fault position can be determined by the time delay of the signals at the two terminals. A diode is inserted between the B-dot sensor's coil and the cable core to ensure low-loss transmission of the signal. Two methods are applied in fault location, including time-of-arrival (TOA) and time reversal (TR). For the TOA method, an energy criterion and a phase criterion are applied and compared. The accuracy of the energy criterion is greatly influenced by the signal-to-noise ratio, while the phase criterion requires a reasonable estimate of the actual delay to account for the impact of phase periodicity. The TR method based on a precise simulation model is established, which demonstrates high precision in location. The TR method has been tested and validated on a single stage LTD module. Moreover, the location method for double switches prefire is discussed theoretically. The method proposed in this paper will be helpful to improve the efficiency of the commissioning, operation, and maintenance of the large-scale LTD devices. [ABSTRACT FROM AUTHOR]

The use of linear transformer drivers (LTDs) is widely considered the most promising technological approach for the development of future pulsed-power accelerators. In large-scale pulsed-power accelerators, abnormal conditions like switch prefire can occur frequently during tests and normal operations due to the presence of a large number of switches. The diagnosis of such faults based on signature waveforms requires further investigation. According to previous research, the characteristics of the magnetic cores greatly influence the fault waveforms. In this paper, a full-cycle mathematical model of the magnetic core is established utilizing a classical Preisach model based on experimental results. This model is coupled with the LTD circuit model in simulations, and simulation results are obtained under the condition of switch prefire. The simulation results are in good agreement with the experimental results from a four-stage LTD module with a sharing shell and de-ionized water insulated transmission line. The magnetization process of the cores is also determined under prefire conditions. Analyses of the magnetization process indicate that the completely demagnetized core shows high permeability under positive excitation and that the permeability abruptly decreases as the excitation is reversed. The hysteresis characteristics result in a phenomenon in which the output voltage in the prefired stage is almost unipolar. Finally, the features of the fault voltages captured in the experiments are also explained. [ABSTRACT FROM AUTHOR]

Environmental hypoxia is becoming more prevalent in aquatic environments of mandarin fish (Siniperca chuatsi) aquaculture because of eutrophication and climate change. Little information is available on the molecular mechanisms of the detrimental effects of hypoxia in this species. In this study, the authors assembled a transcriptome for mandarin fish exposed to lower oxygen conditions at different times (24 and 96 h). The antioxidant enzymatic activities of catalase, glutathione, superoxide dismutase, glutamic pyruvic transaminase and malondialdehyde significantly increased at 6 or 12 h but decreased after reaching a climax during 96 h hypoxia stress. The gene ontology study revealed 27,616 transcripts, whereas the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed 25 linked pathways. Significant changes in the expression of certain genes involved in protein processing in the endoplasmic reticulum, the calcium signalling system and inositol phosphate metabolism were discovered using the KEGG pathway analysis. In the liver, 97 genes were differentially expressed between the control and experimental groups. The expression level of 28 differentially expressed genes (DEGs) under different hypoxic stress conditions was detected using real‐time PCR and compared to transcriptome sequencing results. The result showed that some genes in the experimental group associated with hypoxic stress, such as hif, ho‐1a, ho‐1b, igfbp1, hsp90α and hsp90 β, were significantly upregulated compared with those in the control group. The large amount of transcriptome data from this research has enlarged the mandarin fish gene and genome bioinformation. The identified DEGs and pathways are useful in further studies of biological responses to hypoxia. [ABSTRACT FROM AUTHOR]

To calibrate non-contact sensors with fast response and high scale factor, it is critical to develop step pulse generators capable of generating standard high voltage step pulses and accurately measuring the generated waveform. In this paper, two types of step pulse generators are designed with output voltages of 2 kV and 100 kV. The 2 kV step pulse generator can generate a step pulse with a rise time of ∼300 ps and an adjustable pulse width. A step pulse with a rise time less than 5 ns and a pulse width over 1 μs can be generated with the 100 kV step pulse generator. The uncertainty of 2 kV step pulse generator is then analyzed by simulations and experiments. Finally, a performance comparison with step pulse generators in previous studies is carried out. Bandwidth, linearity and repeatability of the sensors can be verified with the designed two step pulse generators. [ABSTRACT FROM AUTHOR]

C4F7N/CO2 mixture has been widely studied as an environmental-friendly insulating gas expected to replace sulfur hexafluoride (SF6) in high-voltage equipment. In high-voltage power systems, the medium dielectric characteristics under switching impulse (SI) voltage are an important factor in insulation coordination. Nevertheless, few studies on this aspect of C4F7N/CO2 mixture have been reported. This article investigates the surface flashover of a cylindrical insulator in a C4F7N/CO2 mixture under switching voltage. The effects of molar fraction, gas pressure, creepage distance, and insulator materials on surface flashover voltage are studied in a uniform field. The result shows that the increase of flashover voltage indicates a saturation trend with the increase of C4F7N molar fraction and pressure, respectively. The dielectric strength of 13% C4F7N/87% CO2 relative to SF6 can reach at least 84%. The limiting factors of the flashover voltage increase under high pressure are preliminarily discussed. Additionally, the empirical formula on the critical flashover electrical field has been obtained, which can provide a reference for insulation design for environment-friendly gas insulation equipment. [ABSTRACT FROM AUTHOR]

A pulsed power supply with a short rise time and high repetition frequency is favorable to driving diffusive plasma for strongly oxidizing radical (O3, OH) generation and increasing the system's energy efficiency. In this paper, a 10-stage solid-state linear transformer driver (LTD) with a nanosecond rise time is developed to drive plasma for wastewater treatment. To decrease the rise time, a control system with low jitter is developed to improve the synchronization of pulses using an optocoupler isolation chip. A 10-stage LTD with a rise time of 6.2 ns is realized in the case that the rise time of the single-stage LTD is 5.4 ns. The results show that the LTD can generate pulses on a 300 Ω resistive load with a repetition frequency of 10 kHz, an amplitude of 8.80 kV, an overshoot less than 3.97%, and a reverse overshoot less than 4.82%. The rise time (6.2–33.0 ns), the pulse width (35.9–200.0 ns), and the fall time (10.5–27.6 ns) can be adjusted flexibly and independently by controlling the drive signals of metal oxide semiconductor field effect transistors. The pulsed generator is utilized to drive plasma in the needle-water electrode system. The preliminary experimental results show that the plasma includes abundant oxygen atoms and hydroxyl radicals with high activity, and it is suitable for wastewater treatment. [ABSTRACT FROM AUTHOR]

In order to realize the optimal design of the cable supporting system for the purpose of material saving and energy saving and green manufacturing, the strength-stiffness ratio is proposed in the paper in nondimensional form, which defines quantitatively the relation between the static load strength and stiffness of the cable tray. On the premise of ensuring service safety, the correlation between the strength and stiffness of the cable tray under static load is discussed extensively through the theoretical analysis of the mechanical model. The weakest link in the carrying capacity of the cable tray as well as the issue that needs to pay attention is proposed in the process of design and the test of the cable tray. A reasonable strength-stiffness ratio will help to make full use of the potential of material strengths. The value of the strength-stiffness ratio is obtainable by means of the finite element method or by the loading test of the cable tray. It is shown through the analysis that the value of the strength-stiffness ratio being setting in the range close to but less than 1 will make comparatively reasonable material utilization and will help the deflection test going smoothly to obtain a relatively safer allowable working load for the cable tray. [ABSTRACT FROM AUTHOR]

The fast linear transformer driver (FLTD) utilizes a water-insulated transmission line as its secondary. To monitor the fast pulsed current and locate the fault, a compact self-integrating current sensor is developed. Print circuit board (PCB) coils and PCB integrating resistors are used to form the current sensor. By soldering a large number of chip resistors, PCB integrating resistors with various resistance and low inductance can be obtained. The current sensor is designed in a coaxial structure to reduce its inductance and size and can be installed on the inner conductor of the FLTD's secondary water-insulated transmission line with a small opening. The principle and matching schemes for the current sensor are theoretically analyzed with the circuit principle. Both simple matching and two-stage division can be used to obtain signals without oscillation. The time constant of the two schemes is the same. However, the sensitivity of the current sensor with two-stage division is lower than that with simple matching. A 100 kV step pulse generator is used as the pulsed high current generator to verify the properties of the current sensor. The designed current sensor could respond to the step current pulse with the rise time of 4 ns. The matching scheme is verified to be effective with step response experiments. Finally, the influence of the parameters, which are the coil type, the angle between the PCB coil and the magnetic flux, the resistance of the integrating resistor, and the length of the measuring cable, on the output signal of the current sensor is studied. [ABSTRACT FROM AUTHOR]

In recent years, atmospheric pressure glow discharge has become an active research area for many scholars because of its broad industrial application prospects. However, much of the research is focused more on how to acquire this type of discharge or how to use it in some fields; there is a lack of clear and universally accepted theories. In this paper, we described the polarity effect in the process of atmospheric pressure glow discharge driven by a resonant power supply, from the standpoint of the differences in electric field direction in the pin-to-plate gap. We also discussed the characteristics of the discharge waveform, the characteristics of discharge images and the light-intensity distribution on the centerline of the discharge channel. Also studied were the polarity effect of unipolar discharge and the influence of different output-voltage amplitudes on the polarity effect. We found that both positive and negative discharges looked like a typical glow discharge. The voltage and current waveforms of unipolar discharge have a rapidly rising slope, and there is strong ionization near the anode. In the process of a unipolar discharge, there is an obvious γ discharge stage, and the α mode discharge has an obvious high-slope stage, whereas the slope of this process of a negative discharge is more gradual, and the polarity effects of positive and negative unipolar discharges become less and less obvious with the increase in the output-voltage amplitude of power supply. [ABSTRACT FROM AUTHOR]

High power pseudospark switches (PSSs) can control pulsed high voltage, high peak current discharges. In this paper, a PSS in series with a saturable inductor at the anode is investigated. The commutation process is analyzed with a time-resolved method. And the effects of the number of magnetic cores and anode voltages on discharge characteristics are studied experimentally. At the beginning of commutation process, when the anode voltage is 10.4 kV with four magnetic cores, the inductor is unsaturated, and there is a flat plateau of the forward voltage drop after the anode voltage drops rapidly to about 200 V, at the same time the current rise rate is 2.8 kA/ $\mu \text{s}$. When the inductor is saturated, there is a voltage spike that occurs at the end of the flat plateau, and the current simultaneously rises rapidly at the rate of 6.4 kA/ $\mu \text{s}$. The current sharp rise lags behind the voltage drop of the pseudospark gap, and the electrode erosion and energy dissipation reduce significantly. When the anode voltage is 15.6 kV, the commutation losses reduce by about 30% with seven cores in series at the anode. As a result, it is evident that the discharge process will speed up if the anode voltage is higher. And the trigger delay decreases by up to 8% when the anode voltage varies from 5.2 to 15.6 kV. Finally, in order to obtain a reproducible pseudospark discharge by the use of a saturable inductor, the number of magnetic cores has to be optimized for different anode voltages. [ABSTRACT FROM AUTHOR]

Owing to the strong penetration ability of X-rays and the imaging visibility, X-ray inspection has been gradually applied to power grids. However, various problems occur in the promotion and application of X-ray inspection in ultra high voltage gas-insulated switchgear (UHV GIS) owing to its large size. These problems relate to parameter selection, photography, protection area, random defect recognition, and risk assessment based on the X-ray image. In this paper, an X-ray digital imaging system is set up for UHV GIS inspection. Parameter selection for UHV GIS is discussed, and we demonstrate that UHV GIS can be photographed under a source-to-detector distance (SDD) of 2.8 m, a tube voltage of 300 kV, and an exposure of >240 mA·s. A photographic method for UHV GIS, entailing adjustment of the position of the imaging plate with a fixed position of the X-ray generator, is proposed to reduce the difficulty in image stitching. The influence of the parameters on imaging quality is discussed, and we show that the brightness and contrast increase with increasing exposure or decreasing SDD. The interactions between parameters are qualitatively introduced. Moreover, the sensitivity of X-ray inspection in UHV GIS is studied under selected parameters, and the sensitivity of X-ray inspection to copper particles and aluminum particles in UHV GIS are shown to be <0.7 mm and <1.1 mm, respectively. Radiation protection for operators is also discussed. In addition, a pseudo-color scheme for identifying random tiny defects is proposed to reduce human error. Finally, the risk level of defects with X-ray inspection is defined by size feature. [ABSTRACT FROM AUTHOR]

This paper reports on an investigation into the surface flashover of an insulator in a C4F7N/CO2 mixture which is used as an alternative to SF6. To date, no studies on this aspect have been reported in the literature. This study was done for a uniform field using a 220 kV AC experimental platform. The influence of molar fraction, gas pressure and creepage distance is reported and compared to that in SF6. The results show that small quantities of C4F7N mixed in CO2 can increase the surface flashover voltage but, as the fraction of C4F7N increases, saturation of the surface flashover occurs. The relative surface flashover voltage of 13.0% C4F7N/87.0% CO2 is approximately 80% that of SF6. The empirical formulae on the critical flashover electrical field has been obtained, which may be referenced in the design of environment friendly high voltage equipment. [ABSTRACT FROM AUTHOR]

The discharge mode characteristics of cathodes may strongly influence the discharge stability and performance of electrostatic thrusters. In this article, discharge characteristics and mode transition phenomenon of the ring-cusp magnetically confined plasma bridge neutralizer (RCM-PBN) were experimentally studied using argon as the working gas. The dependences of anode current and oscillation amplitude on anode voltage, argon flow rate, heater power, and cathode-to-anode distance were investigated. Plasma properties were measured and plasma plume images were taken under different discharge modes. Two distinct discharge modes were observed during the experiments: high oscillation mode and low oscillation mode. In the high oscillation mode, the plasma plume appears dim, the anode current is low, and the oscillation level is more than 2%. While in the low oscillation mode, a spot-like structure close to the orifice is observed. The plume becomes brighter, the anode current increases, and the oscillation level decreases below 2%. The RCM-PBN was found to transition into the low oscillation mode by increasing anode voltage, flow rate, heater power and by decreasing the cathode-to-anode distance. [ABSTRACT FROM AUTHOR]

To monitor fast pulsed voltage in the transmission line of the fast linear transformer driver, a compact and self-integrating capacitive sensor is developed. A printed circuit board (PCB) with multi-layer ceramic capacitors (MLCCs) serves as a low-voltage arm. Given the reflow structure of the PCB and a parallel arrangement of MLCCs, the residual inductance of the PCB low-voltage arm can be effectively reduced. Moreover, its capacitance can be easily adjusted. The capacitive sensor is designed using a coaxial structure, suitable for installation on the inner high voltage electrode of the secondary water-insulated transmission line. Three matching schemes for the measuring cable are discussed, showing that two-stage division with matching at the end of the cable is more suitable for fast pulsed voltage measurement due to its high dividing ratio and flat frequency response. A square wave with a rise time of ∼1.5 ns and a pulse width of ∼200 ns is used to verify the properties of the capacitive sensor. The results show that the rise time of the designed capacitive sensor can reach 1.5 ns when a short cable is used. Increasing capacitance of the low-voltage arm or resistance at the cable entrance will increase the time constant of the capacitive sensor, which improves its low-frequency properties. A long cable will significantly reduce the high-frequency response and the magnitude of the signal from the capacitive sensor. [ABSTRACT FROM AUTHOR]

An electrostatic calibration technique is highly flexible in producing a wide range of force and it is widely applied for nano-newton to micro-newton thrust stand calibration. This paper proposes a novel method for electrostatic comb implementation and related experiments have been carried out. Based on the printed circuit board and commercial fins, the comb can be realized flexibly with the output force conveniently extended. The force generated by this kind of comb is theoretically analyzed. Different from the traditional comb structure, the conductive area of the comb fixed plate is minimized to improve the force consistency over engagement. The influence of fin length, fin number, applied voltage, and engagement on the output force has been studied experimentally. The final comb system is capable of producing steady force in the range 13-5040 μN with the relative error within 5%. With a high voltage pulse generator, this system could produce calibration impulse bit in the range 1-1000 μN s for which the lowest level can be far more extended to the nanonewton range with a shorter pulse width, a lower voltage, and a reduced number of fins. Moreover, the calibrator has a rather flat force-engagement characteristic when the engagement is in the range of 6 mm–16 mm, while the variation of electrostatic force is within 5%. This calibrator has a wide output range and great consistency, and it is beneficial for the thrust stand calibration. [ABSTRACT FROM AUTHOR]

Overheating is one of the severe defects in gas-insulated switchgear (GIS). However, researches on decomposition characteristics of SF6 under overheating conditions are relatively limited. In this paper, SF6 decomposition products are studied under three overheating conditions which are overheating of solid insulation, overheating of metal, and overheating of metal adjacent to insulating material. Influence of overheating temperature, gas pressure, initial moisture content and adsorbent on the decomposition characteristics of SF6 is discussed. The results show that typical decomposition products of SF6 under overheating of solid insulation are H2, CO, CO2, CH4, SOF2, SO2, H2S, COS and CF4, and typical decomposition products of SF6 under overheating of metal are SOF2, SO2, CO and CO2. Besides, typical decomposition products of SF6 under overheating of metal adjacent to insulating material are CO, CO2, SOF2, SO2, CF4, CS2 and COS. Types of overheating can be recognized by characteristic ratio of (SOF2+SO2)/(CO+CO2): for overheating of solid insulation, the ratio is 0 to 0.25, and for overheating involving metal, it is greater than 1. Two types of overheating involving metal can be distinguished by their characteristic products such as CS2, COS and CF4. [ABSTRACT FROM AUTHOR]

The capillary-based pulsed plasma thruster (PPT) has high-energy transfer efficiency, which provides potential to improve traditional PPT performance. In this paper, the discharge characteristics of a capillary-based PPT have been investigated. First, the typical process of voltage and current waveform is recognized. It is featured with a fast voltage drop (~25 ns) and a consequent damped sine wave oscillation discharge. Then based on the circuit analysis, the equivalent plasma resistance has been calculated. The current waveform is well fit with a linearly increasing resistance model. The influence of charging voltage has also been studied. The deposited energy increases while the transfer efficiency decreases with the increasing applied voltage. The cavity dimension has effects on the equivalent circuit parameters. The results show that longer cavity and smaller diameter lead to more deposited energy and higher transfer efficiency. The influence of voltage and capillary dimension on the mass shot characteristic has been discussed. Finally, the estimated impulse bit has been calculated and the impulse bit characteristics have been discussed. These results can contribute to the further optimization of PPT. [ABSTRACT FROM PUBLISHER]

The lifetime tests for High Voltage Ceramic Capacitors (HVCC) were investigated under repetitive frequency operation at 25 Hz and three kinds of failure modes were summarized. The significant innovation of this paper is testing HVCC, made in the laboratory, under repetitive pulses and proposing several effective improvement methods. The results show that the lifetime of HVCC meets inverse power-law with the applied voltage and the voltage acceleration factor is about 5.8. Failure modes of HVCC are inner breakdown of ceramic dielectric, interface breakdown of ceramic-epoxy and abscission of brass terminals. The inner breakdown is in connection with abrupt destructive discharge under much higher stress while the interface breakdown is related to interface delamination and development of electrical trees in relatively low strength. The third failure mode is always caused by high current density. Based on the failure modes, several methods were taken to improve the performance of HVCC, which included coating semiconductor at the edge of silver layers, adding coupling agent to ceramic-epoxy interface and improving the structure of brass terminals. The lifetime of HVCC under repetitive frequency operation has been extended greatly from 103 shots to more than 105 shots after the investigation and improvement. [ABSTRACT FROM AUTHOR]

In order to evaluate the antioxidant and anti-inflammatory effects of glycyrrhetinic acid (GA) on carbon tetrachloride (CCl 4 )-induced damage in precision-cut liver slices (PCLS) from Jian carp ( Cyprinus carpio . Jian), an acute liver damage model was established in this study. The viability of PCLS, levels of anti-oxidases in liver homogenates, expression of inflammation-related genes including nuclear factor-κB ( nf-κB )/ c-rel , inducible nitric oxide synthase ( inos ), interleukin-1β ( il-1β ), interleukin-6 ( il-6 ) and interleukin-8 ( il-8 ), and protein levels of ( nf-κB )/ c-rel in liver tissues were measured. The results showed that pretreatment of PCLS with GA at 5 and 10 μg/mL for 6 h significantly inhibited the cytotoxicity of CCl 4 . GA attenuated CCl 4 -induced oxidative stress in PCLS through promoting the recovery of superoxide dismutase (SOD) and glutathione (GSH) levels, and inhibiting malondialdehyde (MDA) synthesis. In inflammatory response, GA at both 5 and 10 μg/mL significantly inhibited the increase in mRNA levels of inflammatory cytokines including nf-kƁ / c-rel , inos , il-1β , il-6 and il-8 , and the protein level of Nf-kƁ/C-rel induced by CCl 4 . Furthermore, treatment with pyrrolyl dithiocarbamate (PDTC, 4 μg/mL), an inhibitor of nuclear transcription factor nf-kB , significantly inhibited nf-kB levels, and transcription of downstream cytokines inos , il-1β , il-6 and il-8 , also the viability of PCLS was significantly increased. These results indicated that GA suppressed inflammation and reduced cytotoxicity by inhibiting the nf-kƁ signaling pathway, and plays a role in liver protection. [ABSTRACT FROM AUTHOR]

Electrohydraulic shock waves (ESWs) are widely applied to many fields such as sterilization, lithotripsy, food processing, and so on. Based on high-pulsed power technology, electrical explosion is increasingly utilized to generate shock waves with steep fronts and short duration. In order to further magnify the shock waves, we have proposed a new technique by using energetic materials (EMs) loads. This paper investigated the fracturing effect of the ESWs generated by plasma-ignited EMs explosion. During the ESWs fracturing process, a large-scale triaxial stress pressurizing equipment and a dynamic strain measurement system were applied to the shale samples. The most evident experimental results showed that a large number of cell-shaped multiple cracks developed after the ESWs fracturing process. In addition, interior crack morphology and fluorescent tracing proved the evidence of penetration cracks. These cracks contributed to a great reduction of fracture pressure in fracturing test, which laid a scientific foundation for ESWs technique to be a promising method of well stimulation in those low permeability reservoir and further optimized into a new plugging relief and injection gain technology. [ABSTRACT FROM PUBLISHER]

Sun-photometer measurements at Hefei, an urban site located in central East China, were examined to investigate the variations of aerosol loading and optical properties. It is found that aerosol optical thickness (AOT) keeps higher in winter/spring and gets relatively lower in summer/autumn. The large AOT in winter is caused by anthropogenic sulfate/nitrate aerosols, while in spring dust particles elevate the background aerosol loading and the excessive fine-mode particles eventually lead to severe pollution. There is a dramatic decline of AOT during summer, with monthly averaged AOT reaching the maximum in June and soon the minimum in August. Meanwhile, aerosol size decreases consistently and single scattering albedo (SSA) reaches its minimum in July. During summertime large-sized particles play a key role to change the air from clean to mild-pollution situation, while the presence of massive small-sized particles makes the air being even more polluted. These complicated summer patterns are possibly related to the three key processes that are active in the high temperature/humidity environment concentrating on sulfate/nitrate aerosols, i.e., gas-to-particle transformation, hygroscopic growth, and wet scavenging. Regardless of season, the increase of SSA with increasing AOT occurs across the visible and near-infrared bands, suggesting the dominant negative/cooling effect with the elevated aerosol loading. The SSA spectra under varying AOT monotonically decrease with wavelength. The relatively large slope arises in summer, reinforcing the dominance of sulfate/nitrate aerosols that induce severe pollution in summer season around this city. [ABSTRACT FROM AUTHOR]

The low-impedance impulse voltage calibrator of high accuracy and stability can be used as a primary reference of impulse voltage. It is recommended to be utilized in the calibration of the reference measuring system composed of impulse resistor divider and digital recorder in IEC 61083. The impulse voltage calibrator is made up of resistors and capacitors of given values. The parameters of its output waveform, Up , T1 , and T2 , can be calculated based on the parameters of the circuit elements and circuit principle of the calibrator. The uncertainties of the waveform parameters are always evaluated by Guide to the Expression of Uncertainty in Measurement (GUM) in previous publications. However, GUM exhibits some limitations when it is applied. In this paper, a 1-kV low-impedance impulse voltage calibrator ( 1.56~\mu \texts/60~\mu \texts ) is developed. The values and uncertainties of Up , T1 , and T2 are evaluated with another two new approaches, Monte Carlo method and random fuzzy variable (RFV). Particularly, the combination of several RFVs with both random and nonrandom effects is also discussed when RFV method is applied. The detailed process of each approach is presented and the results are compared. [ABSTRACT FROM PUBLISHER]

Corona and spark are two typical discharge types in gas-insulated switchgear (GIS). Studies on the SF6 decomposition characteristics under corona and spark are significant for the safe operation of the GIS. In this paper, the discharge energy/charge and SF6 decomposition products under ac corona with point-to-plane electrode defect and spark with floating potential defect were investigated under different electrode dimensions, applied voltages, SF6 gas pressures, adsorbents and moisture contents. The upper limit of the formation rates, feature extraction, and the amount of wear of the GIS were also discussed. The results show that the influences of gas pressure and moisture content on the discharge energy and SF6 decomposition products under two different defects are distinguishable. In addition, the concentration ratios of (SOF2+SO2)/(SO2F2) under corona and spark lie in the ranges, 0-1, and 1?5, respectively. The formation rates of SF6 decomposition products calculated from experimental results under corona discharge lie in the range, 0.1-5 μmoles/J. However, the formation rates under spark are usually in the range, 0.02-0.04 μmoles/J, which are far lower than that under corona. Theoretically the upper limit of the formation rates under corona and spark are estimated to be in the ranges, 67-540 μmoles/J, and 188- 376 nmoles/J respectively. Besides, the concentration ratios and formation rates can be used to distinguish the discharge types and the amount of wear of the GIS can be estimated. [ABSTRACT FROM AUTHOR]

As a new approach to shale gas exploitation, electrical explosion shock wave has become a research hotspot in recent years. Strain measurement plays an essential part in electrical explosion research. However, in conventional strain measurement, the spatial electromagnetic interference produced by the discharge could affect the measurement accuracy, or even damage experimental instruments. For strain measurement in a strong electromagnetic field, a novel strain measurement system, based on resistance strain gauges and a designed conditioning circuit, was tested and evaluated. The compensation method was used to eliminate the intense interference, and a five-order Butterworth low-pass filter was designed and implemented to remove high-frequency noise. Simulation and experimental results showed that the strain could be expediently figured out by measuring the output voltage of the conditioning circuit. And in the strong electromagnetic field, dynamic strains varied from 860 $\mu \varepsilon $ to 1400 $\mu \varepsilon $ were measured by the novel system in both axial and circular directions. [ABSTRACT FROM PUBLISHER]

High-performance trigger generators with high amplitude, fast rise time, low jitter are essential for large-scaled pulsed-power systems. Most of the trigger generators are also tiny multistage pulsed-power systems with complicated structures. In this paper, a high-performance trigger generator was proposed by combining the advantages of low-jitter semiconductor switch and high-power gas switch. An avalanche transistor Marx circuit was developed. It was used to trigger a two-stage Marx generator based on trigatron switch. The output characteristics of the Marx circuit based on avalanche transistors and the two-stage Marx generator were studied. The experimental results show that a subnanosecond jitter, nanosecond rise time, high-voltage trigger generator can be achieved by triggering trigatron switch with an avalanche transistor circuit. [ABSTRACT FROM PUBLISHER]

We investigated the protective effects of curcumin on liver-damaged Cyprinus carpio var . Jian (Jian carp). The carp were fed 0.1%, 0.5%, or 1.0% curcumin for 60 days, then injected intraperitoneally with 30% carbon tetrachloride solution. Liver and blood samples were collected to measure the liver index, serum- and liver-associated enzymes, liver histology, nuclear factor-κB (NF-κB)/c-Rel, interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and IL-12 mRNA expression, and the level of NF-κB/c-Rel protein in the liver, and for a comet assay. We found that 0.5% and 1.0% curcumin significantly reduced the CCl 4 -induced increase in the liver index. The comet assay showed that the tail moment, olive tail moment, tail length, and tail DNA% improved in fish pretreated with 0.5 or 1.0% curcumin. CCl 4 -induced histological changes, including extensive hepatocyte degeneration, indistinct cell borders, nuclear condensation, and karyolysis were clearly reduced after treatment with 0.5% and 1.0% curcumin. Moreover, 0.5% and 1.0% curcumin significantly inhibited the CCl 4 -induced increase in serum glutamic oxaloacetic transaminase and promoted the restoration of superoxide dismutase in the liver; 1.0% curcumin significantly reduced serum glutamic pyruvic transaminase and lactate dehydrogenase and hepatic malondialdehyde, but significantly increased the total antioxidant capacity and glutathione levels in the liver. The CCl 4 -induced upregulation of NF-κB/c-Rel, IL-1β, and TNF-α mRNAs and NF-κB/c-Rel protein levels was inhibited by 0.5% and 1.0% curcumin, and IL-12 mRNA was reduced by all three doses of curcumin. The effects of curcumin on the liver index, enzymes, histological changes, and cytokines were dose-dependent. Our results indicate that curcumin reduces CCl 4 -induced liver damage in Jian carp by upregulating antioxidative activities and inhibiting NF-κB, IL-1β, TNF-α, and IL-12 expression. [ABSTRACT FROM AUTHOR]

In this paper, a novel repetitive frequency square-wave generator named pulse forming line-based repetitive square-wave generator (PFLRSG)-based coaxial pulse forming lines (PFLs) and coupled magnetic switches (MSs) is proposed. The generator is capable of amplitude multiplication, high-frequency operation, and rise-time compression. The operation principle is to charge PFLs in parallel via coupled inductors when MSs are unsaturated and discharge in series when MSs saturate to form square-wave voltage pulses across the matched load, with the common diode arrays as the last stage to sharpen the rise-time. The amplitude of the output pulse is dependent on the charging voltage and impedance matching between the PFLs and the load. The pulsewidth is determined by the transmission time of the PFLs. With the principle, circuit topology of a two-stage PFLRSG is presented. Test stand yields an output square-wave pulse with frequency of 1–10 kHz, amplitude of 8.6 kV, rise-time of 60 ns, and half width of 500 ns into a 150- \(\Omega \) matched load. Furthermore, design rules are proposed so that topologies of PFLRSGs with stages other than two can be conveniently derived. As an example, a 4-stage PFLRSG is proposed. [ABSTRACT FROM AUTHOR]

SF6 insulated current transformers (CTs) are widely used in high-voltage power systems due to their favorable insulating properties. Field experience shows that the high moisture content in an SF6-insulated CT is an important factor responsible for its insulation faults. Furthermore, the moisture content in an SF6-insulated system is generally dependent on the ambient temperature. Thus, in this paper, the temperature distribution and moisture content of an SF6-insulated CT are studied by considering current flowing through it and a sharp change in the ambient temperature. It is found that the temperature distribution of an SF6-insulated CT in operation is extremely uneven, and the measured moisture content becomes higher than the initial moisture content. The relative humidity in the lower part of the CT might reach a dangerous level when the ambient temperature changes rapidly. The mechanism of moisture condensation is proposed to explain the experimental results. Besides, the possible preventive measures for insulation failure are also discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] The Chinese version of Freiburg Mindfulness Inventory was firstly validated. [•] The mindfulness-performance link was further investigated with 136NPP operators. [•] The presence facet was found to influence operators’ performance. [•] Task complexity was found to be an important moderator of this relationship. [•] The cost-benefit of being mindful was different on task/safety performance. [Copyright &y& Elsevier]

In this paper, a novel repetitive frequency Fitch booster (named coupled magnetic switch (MS)-based Fitch booster or CMSFB) that is capable of both rise-time compression and amplitude multiplication is proposed. The operation principle is to charge capacitors in parallel via coupled MSs and reverse voltage polarity of every other capacitor to form voltage pulses across the load, with diodes blocking discharges from even stages to odd ones. Test stand shows that the four-stage CMSFB effectively boosts the input voltage from 8.5 kV in peak and 8.6 \mu\s in rise time to 33.6 kV in peak and 1.6 \mu\s in rise time. A following two-stage magnetic pulse compression network further compresses the voltage rise time to obtain the output voltage with a rise time of 84 ns, an amplitude of 31.2 kV, and a frequency of 1 kHz. Meanwhile, calculations show that the total core volume of a pulser with a CMSFB is much lower than one without it, and saved core volume increases with an increase in the number of the CMSFB stages. For the four-stage test stand, in particular, the total core volume is reduced to almost half, from 1540 to 775 \cm^3. [ABSTRACT FROM PUBLISHER]

A scrutiny of the existing time differencing carrier phase (TDCP) velocity estimation algorithms has revealed several shortcomings that could be further improved. One of these is that the velocity estimation at epoch t would require the receiver positions at epoch t+Δt or more are available. Another is the usage of satellite velocities in the calculations which would increase the receiver computational load and degrade the accuracy. In this paper, an improved TDCP velocity estimation approach has been proposed and tested. The new approach depends only on receiver position at epoch t and satellite positions at epoch t and t+Δt. Satellite velocities are not required in this calculation. This proposed algorithm has been validated using static and kinematic field test data, showing that equivalent velocity accuracy achievable by using differential GPS techniques can be made possible with the proposed standalone GPS method. [ABSTRACT FROM AUTHOR]

Abstract: Many bacterial surface proteins containing an LPXTG motif are anchored to the cell wall peptidoglycan by catalysis with the thiol transpeptidase sortase. The transpeptidation and hydrolysis reactions of sortase have been proposed to proceed through a common acyl enzyme intermediate. The reactions of Staphylococcus aureus sortase with fluorogenic substrate Abz-LPETG-Dnp in the presence or absence of triglycine were characterized in this study to gain additional insight into the kinetic mechanism of sortase. We report here the development of a reverse-phase HPLC assay to identify and characterize sortase reaction intermediates. The HPLC results provide for the first time clear evidence for the formation of a kinetically competent acyl enzyme intermediate during the overall transpeptidation reaction. The results also suggest that sortase undergoes an unexpected intramolecular acyl transfer reaction in the absence of a nucleophile. The significance of this type of HPLC assay as a tool to study enzyme mechanism is discussed. [Copyright &y& Elsevier]

Chemical byproducts analysis has been recognized as a powerful diagnosis method for SF6 gas-insulated switchgear (GIS). The authors have previously demonstrated that a carbon nanotube (CNT) gas sensor could detect partial discharge (PD) generated in SF6 gas. However, PD-generated decomposition gas species, which were responsible for the CNT gas sensor response, have not been identified yet. In this paper, two kinds of experiments were conducted in order to identify the responsible decomposition gas species. At first, the decomposition gas molecules adsorbed on CNTs were analyzed by Fourier transformation infrared (FTIR) spectroscopy. FTIR absorbance was observed around 735 cm-1 after CNTs were exposed to PD generated in SF6. In the second experiment, the CNT gas sensor responses to typical SF6 decomposition products (HF and SF4) were examined. The CNT gas sensor responded to these gases in the same way as to PD generated in SF6+ SF4 response was larger than HF response. Based on these results, SF4 and SOF2 emerged as candidates for the responsible decomposition gases. Electrochemical interactions between adsorbed gas molecules and CNT were discussed based on theoretical predictions of molecular orbital calculations. The calculation results suggested that both of SOF2 and SF4 could increase the CNT gas sensor conductance. [ABSTRACT FROM AUTHOR]

A fluorescence polarization competition assay has been developed to screen for inhibitors of the Escherichia coli FtsZ/ZipA protein–protein interaction. A previously published X-ray costructure demonstrated that a 17-amino-acid peptide, corresponding to FtsZ C-terminal residues 367–383 (FtsZ367-383), interacts with the C-terminal FtsZ binding domain of ZipA (ZipA185-328). Phage display was employed to identify a unique but related peptide which when further modified and labeled was shown to have a higher affinity to ZipA185-328 than the FtsZ367-383 peptide and binds to the same site. This peptide had a six fold increase in fluorescence polarization upon binding to ZipA185-328 compared to a two fold increase for the FtsZ367-383 fluorophore. As a result, assay parameters using the phage display peptide were further optimized and adapted for the high-throughput screen. A high-throughput screen of 250,000 compounds identified 29 hits with inhibition equal to or greater than 30% at 50 μg/ml. An X-ray costructure of a promising small molecule in this library complexed with ZipA185-328 (KI=12 μM) revealed that the compound binds to the same hydrophobic pocket as the FtsZ367-383 peptide. [Copyright &y& Elsevier]

In recent years, several novel avalanche transistor-based power synthesis topologies have been proposed to improve the output performance of pulse generators based on avalanche transistors. The most promising is the topology based on avalanche transistors Marx Bank Circuits (MBCs) and linear transformer driver (LTD). However, it suffers from the same problems as other semiconductor switch-based LTD generators. The greater the number of LTD modules, the higher the requirements for synchronization and drive capability of the trigger system. This paper proposes a new self-triggering topology for pulse generators based on avalanche transistors MBCs and LTD, which significantly simplifies the entire generator's requirement for trigger system synchronization and driving capability. First, the circuit topology and its operation principle are introduced. Then, three prototypes with one trigger LTD module and three self-triggering LTD modules are developed. The output characteristics are experimentally investigated. The results verify the feasibility of the proposed topology. Finally, the output amplitude and the rise time are 3.35 kV/3.7 ns, 4.12 kV/3.7 ns, and 4.88 kV/4.0 ns on a 25 Ω resistive load, respectively. All generators can operate at 1 kHz. The topology proposed in the article maximally simplifies the requirements for synchronization and drive capability of the trigger system for generators based on avalanche transistor MBCs and LTD. [ABSTRACT FROM AUTHOR]

Pulsed power technology is gradually forming a development trend of civil-military integration, which puts forward more requirements for pulsed power generators. This paper takes magnetic switches (MSs) as the starting point and reviews recent advancements in pulse generators based on MSs. First, the working mechanism of the MS "rapid inductance drop after magnetic core saturation" is analyzed. Second, the basic uses of MSs are introduced with specific examples, namely, magnetic compression unit, saturated pulse transformer, and magnetic delay switches. Then, the typical topologies of pulse generators based on MSs are discussed, including transmission line, Marx, Fitch, linear transformer driver, and semiconductor opening switch pumping circuits. These circuits' technical characteristics and parameter levels are highlighted. Finally, the existing problems and future development trends of MS-based solid-state pulse generators are discussed. [ABSTRACT FROM AUTHOR]

The plasma bridge neutralizer (PBN) based on a tungsten filament is a promising technique of a thermionic DC electron source where a hot filament is immersed in an inert gas flow and electrons are "bridged" from a small orifice to the ion beam. PBNs have been widely used in space propulsion and industrial applications due to their relatively simple structure and low power consumption. However, they have well-known disadvantages, namely, low emission current density and short lifetime. In this article, we propose a novel ring-cusp magnetically confined PBN (RCM-PBN) to address these issues. In the RCM-PBN, electrons are confined by a ring-cusp magnetic field, which improves the ionization efficiency and reduces the discharge chamber wall losses. Electrical insulation of the orifice plate from the chamber wall prevents a large number of electrons from being collected by the orifice plate, which greatly improves the extracted electron current. The effects of different operating parameters on the extracted electron current were studied through experiments. It was found that the increase in the extracted electron current with the extraction voltage was related to the anode spot formation. Analysis of the gas utilization factor and electron extraction cost shows that the optimal operating condition was obtained at an argon mass flow rate of 1.2 SCCM and a heater power of 45 W. At its optimum, a stable electron current of 1.1 A was extracted from the RCM-PBN with a gas utilization factor of 12.8 and an electron extraction cost of 143 W/A. [ABSTRACT FROM AUTHOR]

This paper studied the plasma plume evolution process of a capillary discharge based pulsed plasma thruster. Time-resolved imaging and optical emission spectroscopy were applied to investigate the plume morphology and plasma species characteristics. It showed that ionized particles (mainly C II and F II) were accelerated early in the pulse and neutral particles (mainly C I and F I) later. An optical time-of-flight (OTOF) method was developed using a photodiode array combined with narrow bandpass filters. The equivalent streaming velocity of the plasma plume was evaluated with the OTOF technique. Measurements of individual species showed that both the ionized and the neutral species could be effectively accelerated by gasdynamic forces, and the ionized particles could reach a higher velocity. A Doppler shift measurement of the plasma plume was also performed to compare it with the findings from the OTOF method. The plasma plume streaming velocity of a thruster with a discharge energy of 5 J was measured and found to be (25.34 ± 0.17) km/s (OTOF) and (22.36 ± 4.02) km/s (Doppler shift). In addition, differences between the operation processes of the capillary discharge based pulsed plasma thruster and the electromagnetic pulsed plasma thruster were analyzed. [ABSTRACT FROM AUTHOR]

Emerging tumor immunotherapy methods encompass bispecific antibodies (BSABs), immune checkpoint inhibitors (ICIs), and adoptive cell immunotherapy. BSABs belong to the antibody family that can specifically recognize two different antigens or epitopes on the same antigen. These antibodies demonstrate superior clinical efficacy than monoclonal antibodies, indicating their role as a promising tumor immunotherapy option. Immune checkpoints are also important in tumor immunotherapy. Programmed cell death protein-1 (PD-1) is a widely acknowledged immune checkpoint target with effective anti-tumor activity. PD-1 inhibitors have demonstrated notable therapeutic efficacy in treating hematological and solid tumors; however, more than 50% of patients undergoing this treatment exhibit a poor response. However, ICI-based combination therapies (ICI combination therapies) have been demonstrated to synergistically increase anti-tumor effects and immune response rates. In this review, we compare the clinical efficacy and side effects of BSABs and ICI combination therapies in real-world tumor immunotherapy, aiming to provide evidence-based approaches for clinical research and personalized tumor diagnosis and treatment. [ABSTRACT FROM AUTHOR]

There are many advantages in obtaining low-temperature plasmas that are rich in active particles by atmospheric pressure glow discharge, so there has been a lot of research on the acquisition method and application of it. However, there is a lack of knowledge about the mechanism of atmospheric pressure glow discharge driven by an AC resonant power supply. In this paper, we describe our study of the characteristic differences between half-cycle positive and negative atmospheric pressure glow discharges driven in open air by an AC resonant power supply, and we describe our analysis of the associated physical mechanism. The comparison and analysis of experimental results indicate that both positive-cycle and negative-cycle discharges led to typical glow discharge and no streamer discharge appeared in the discharge process. There were still charged particles in the discharge channel when the discharge current was zero. With increasing amplitude of the output voltage of the power supply, the glow area near the electrode surface and the plasma distribution area in the discharge channel increased. When the output voltage of the power supply was low, the negative polarity discharge was more likely to form in the gap of the pin-to-plate electrode. In the AC discharge process, the α-mode discharge was dominant, and the developing speed of the positive-cycle discharge was faster than that of the negative-cycle discharge. The polarity effect became less obvious with the increase in the output voltage amplitude of the power supply. [ABSTRACT FROM AUTHOR]

The Blumlein pulse forming network (PFN) has widely been used in pulsed power technology to generate square waves with short pulse widths. In this paper, we developed a repetitive frequency square wave generator based on Blumlein PFN and pseudospark switch (PSS). A Blumlein PFN with unequal capacitances has been proposed, and the PFN parameters have been optimized for better output waveforms. A single-gap PSS with a withstand voltage of 40 kV and a repetitive frequency of 100 Hz has been designed to switch the Blumlein PFN. The experiment results show that the square wave generator can output pulses with a voltage of 26 kV, a rise time of 25 ns, and a pulse width of 90 ns on a matched load of 11 Ω. It has operated steadily for 10 h with a repetitive frequency of 100 Hz, and the jitter remains at around 1 ns after 1.05 × 106 shots. [ABSTRACT FROM AUTHOR]

The studies of intracloud discharges may shed light on the microphysical structure of thunderclouds, as both the magnitude and the sign of charge separation due to graupel collides with ice crystals within the strong updrafts are influenced by the surrounding environment. Here, a compact all-fiber coherent Doppler wind lidar (CDWL) working at the 1.5 µm wavelength is applied for probing the dynamics and microphysics structure of thunderstorms. Thanks to the precise spectrum measurement, multi-component spectra signals of thunderstorms can be analyzed by the CDWL. The spectrum width, skewness, and Doppler velocity of CDWL is used to separate and identify the particle composition and polarity. In the experiment, the thundercloud properties are detected by the CDWL, 10.6 cm Doppler weather radar (DWR), and Advanced Geosynchronous Radiation Imager (AGRI) onboard Fengyun-4 satellites. In particular, the spectrum width and skewness of the thundercloud below the 0 ∘C isotherm are increased, and when a cloud-ground lightning occurs, there is additional graupel with a velocity greater than 5 ms-1. It indicates that this region is a melting layer, and lightning activity changes the motion characteristics of graupel, affecting the charge structure of the whole thundercloud. In general, our findings provide details on the velocity, phase, and composition of particles in the outside updraft region of the thunderstorm. The identification and analysis of graupel is particularly important. It is proved that the precise spectrum of CDWL is a promising indicator for studying the charge structure of thunderstorms. [ABSTRACT FROM AUTHOR]

Marx bank circuits (MBCs) based on avalanche transistors are widely used to generate nanosecond pulses with high power, high repetition rate, and low jitter. However, it was observed that avalanche transistors in the first and second stages of traditional M×N-stage MBCs have high failure rates. This paper proposes an auxiliary triggering topology (ATT) for improving the reliability of high-power MBCs based on avalanche transistors. The operation principles of ATT and failure mechanisms of traditional MBCs are analyzed. By adopting ATT, the auxiliary triggering pulse is generated between the base and emitter of the transistor, and the switching mode is changed from “overvoltage switching-on” to “triggering switching-on.” The combined effect of overvoltage ramp and auxiliary triggering pulse significantly reduces the failure rate and prolongs the lifetime of easily damaged transistors. Two high-power nanosecond pulse generators, 3 × 12-stage and 6 × 10-stage MBCs adopting ATT, are developed to verify the feasibility of the proposed configuration. The output amplitude and the rising time are 8.5 kV/6 ns and 17 kV/6 ns at the open end of coaxial cable with 75-Ω impedance, respectively. Both generators are tested continuously at the repetition rate of 2 kHz for 60 min and no failure occurs, which shows much better performance in repetition rate and reliability than traditional M×N-stage MBCs. [ABSTRACT FROM AUTHOR]

Low power capillary discharge based pulsed plasma thrusters (CDPPTs) are electrothermally dominated thrusters and they have aroused renewed interest in the investigation and enhancement of the basic performance for the application of micro/nano satellites recently. Research on the ignition mechanism of a CDPPT has been conducted to provide insight into the optimization of the structure design and promotion of the lifetime performance. It has been found that the electrical parameters, the geometry parameters, and the cumulative effect of discharge jointly determine the discharge ignition characteristics. A single ignition process is divided into the breakdown of igniter and the development of the main discharge, while the results show that the jitter of the ignition delay time is mainly introduced from the former. Shorter ignition delay time and lower jitter can be obtained with a higher ignition energy and main charging voltage or a shorter and narrower cavity, which is positively correlated to the electric field distribution along the propellant surface. Moreover, with long duration experiments, it reveals that the surface deposits and morphology of propellant and igniter are the dominant factors that cause the dispersity of the ignition effect and main discharge characteristics. [ABSTRACT FROM AUTHOR]

Aberrant miRNA expression has been detected in various tumor tissues, which may be considered as a marker for early cancer diagnosis. One miRNA has multiple downstream target genes, which can be regulated by multiple upstream other miRNAs. Hence, this dynamic regulation is likely characterized by volatility, and thus, finding the appropriate time point for tests becomes essential for the use of miRNAs as an early marker of tumor diagnosis. In this study, we established a chronic liver cancer progression model in mice by using low doses of the harmful substance microcystin-LR (MC-LR). On the basis of miRNAs microarray assay, we further tested seven miRNAs that showed characteristic expression changes in pre-hepatocarcinogenesis. Our results showed that the levels of four miRNAs (miR-122-5p, miR-125-5p, miR-199a-5p, and miR-503-5p) decreased dramatically, whereas those of two miRNAs (miR-222-5p and miR-590-5p) increased significantly in the early stages, which were all accompanied by an increase in atypia of hepatocytes. MiR-490-5p was a sensitive molecular, suitable only for evaluation of pathological changes in young mice. Therefore the combination the seven of miRNAs for a set may prove to be an effective method in healthy assessment of environmental toxicants for detection of hepatocarcinogenesis caused by hazardous materials. [ABSTRACT FROM AUTHOR]

In this paper, a study concerning self-breakdown voltage characteristics, electrode erosion, and degradation of the insulator, of a two-electrode spark-gap switch has been presented based on experiments. A 6 ?F pulse capacitor and a DC high voltage source (set at ?40 kV) were utilized to achieve ?0.1 pulses per second repetitive arc discharge between two fixed Cu-W (Cu30/W70) alloy electrodes in the 1.2 L airtight chamber of the switch. With average transfer charge of 2.2 C per shot, this switch was tested for 5800 shots altogether. The results demonstrated the electrode erosion rate of the cathode was 6.3434?10?6 cm3/C whereas that of anode was 5.4691?10?6 cm3/C. Besides, by analyzing electrode surfaces' morphology and PTFE insulator surfaces' compositions after 5800 shots with the help of a scanning electron microscope, a dynamic 3D aspheric metrology instrument, an X-ray photoelectron spectrometer, a metallographic microscope, and a Mettler-Toledo analytical balance, some evidence of physical processes and chemical reactions between plasma channel, electrode materials, and insulation materials could be observed. Moreover, the chamber was opened and inspected for 10 times during the whole procedure, thus providing an overall description of the variation of the switch. It should also be pointed out that owing to complex mechanisms during the aging process, the self-breakdown voltage followed a mixed Normal distribution other than any other simple distributions. [ABSTRACT FROM AUTHOR]

Experiments concerning the self-breakdown voltage characteristics have been done and a simplified model has been proposed to describe the phenomena in this study. A test platform has been established to investigate the Cu-W (90 wt%) two-electrode switch working in a small airtight cavity (1.2 L). The switch was tested under the conditions of frequency of ?0.1 Hz, self-breakdown voltage of ?30 kV, and peak current of ?60 kA for more than 20000 shots. Inevitably, the process is accompanied with the insulation and electrode's aging in the switch, including the variation of gas components and electrode surface states, which eventually alters the self-breakdown voltage. The results of the experiment demonstrated that the lifetime of the switch could be divided into three stages. In the third stage, this switch showed a satisfactory reliability and stability of the self-breakdown voltage: mean of 32.4 kV and standard deviation of 2.0 %. Besides, from the view of statistics, calculation results proved that the 20000 shots' self-breakdown voltage obeyed mixed Normal distribution, whereas a continuous small sample of that simply followed Normal distribution or Weibull distribution. Moreover, it could be anticipated from the results that the Cu-W spark gap switch could have a lifetime more than 20000 shots (total charge transferred was 13259 C). However, in fact, the lifetime was terminated in advance by insulation degradation in the switch. [ABSTRACT FROM AUTHOR]

Underwater discharge is the typical method used to generate plasma in a liquid phase environment and is employed in many engineering applications. This study analyzes the formation and development process of the positive streamer in water under microsecond voltage. The effects of voltage amplitude, liquid conductivity, and the presence of bubbles on the underwater discharge characteristics are analyzed by establishing a two-dimensional finite element simulation model of a needle-plate gap. The simulation results show that the electron density of the streamer in water can reach 1023 m−3, and as the applied voltage amplitude increases, the development speed of the streamer increases and the head of the stream bifurcates. Moreover, when the conductivity of the water is high, the development speed of the streamer and the density of charged particles increase. Furthermore, the presence of bubbles significantly impacts the development of the discharge morphology, causing the channel to have multiple bifurcations. [ABSTRACT FROM AUTHOR]