Positive Discharge Research Articles

Candida auris colonization or infection of the ear: A single-center study in South Korea from 2016 to 2018.

Candida auris was first identified in Japan from specimens obtained from the ear, but most reports since have reported invasive infections or non-ear based cases. We reviewed all the microbiology records from a single center in South Korea from February 2016 to July 2018. One hundred eleven isolates were positive for C. auris from 79 patients. All 79 patients positive for C. auris had positive ear discharge samples. All but one of the patients with C. auris had been to the otorhinolaryngology clinic. Symptom-driven ear culture was done for all but one patient, whose culture was performed for surveillance. Ear discharges were mostly purulent (60%) or serous (34%). We performed the environmental cultures at the otorhinolaryngology outpatient clinic to evaluate the environmental contamination of C. auris, but C. auris was not isolated from medical equipment and environmental surfaces.

Influence of front time on positive switching impulse discharge characteristics of UHVDC tower gaps

The front time of switching impulses has a significant influence on long air gap discharge performance, but most testing experiments have been conducted using standard impulses. Here, we carried out experiments investigating the discharge characteristics of a ±800 kV transmission line-tower gap (5–8 m) under positive switching impulses with different front times and obtained important physical parameters, such as the time and voltage of the leader inception, the leader propagation velocity, and the 50% breakdown voltage (U50). The results show that (1) the critical wave front time increases with the air gap distance; (2) for the tested gaps, the time and voltage of the leader inception show minimum dispersion when the front time is 250 μs; (3) an approximately U-shaped curve occurs between the front time and the average velocity of the continuous leader propagation, and the velocity is the slowest with a front time of 500 μs. The results illustrated that choosing standard switching impulses (250 μs/2500 μs) to conduct a discharge test in a ±800 kV transmission line-tower gap is both suitable and effective; however, when the operation voltage further increases, the front time should be increased appropriately when conducting switching impulse tests.

Two-dimensional electron density measurement of pulsed positive secondary streamer discharge in atmospheric-pressure air

Highly sensitive Talbot-type laser wavefront sensors with a temporal resolution of 5 ns were used for the single-shot visualisation of two-dimensional electron density distributions over pulsed positive secondary streamers generated in a 13 mm pin-to-plate gap installed in air under atmospheric pressure. The single-shot imaging demonstrated that the electron density in the primary streamer channel increased after passage of the secondary streamer front. The electron density inside the propagating secondary streamer showed almost uniform axial distribution and it kept approximately constant at 0.7– cm−3 for about 40 ns. This temporally stable electron density suggested that the reduced electric field inside the secondary streamer was approximately 110–120 Td during the propagation. In the end of the secondary streamer phase, the electron density decreased at a time constant of ∼10 ns.

A Study on the Primary Mode of Pulsed Positive Streamer Discharge in Water

The primary mode of the pulsed positive streamer discharge in water has been studied by the shadowgraph imaging techniques utilizing an ultrahigh speed frame camera system. The propagation speed and the flare angle of the fan-shaped primary streamer were measured and their dependence on the water conductivity and the applied voltage were investigated. The initial propagation speed of the primary streamer is about 4–6 km/s and rapidly decreases to about 1.5 km/s. The water conductivity and the applied voltage have no significant influence on the propagation speed of the primary streamer. The flare angle of fan-shaped structure of the primary streamer ranges from 150° to 210°, and increases with increasing the applied voltage. In the voltage range 15 to 17 kV, the water conductivity has no significant influence on the flare angle of the fan-shaped structure, but as the applied voltage increases beyond 18 kV, the flare angle of the fan-shaped structure decreases with increasing the water conductivity. Based on the plasma discharge in a bubble and the fact that the radius of primary streamer is about 200–400 $\mu \text{m}$ , the primary streamer in water seems to be incepted by the positive ions at the head of the discharge filament generated in the microbubble, which penetrates into the water through spattering process and forms a gaseous trajectory in the bulk water.

Numerical and Experimental Investigation of the 4-Quadrant Behavior of Different Mixed Flow Diffuser Pumps

Besides operating a centrifugal pump under normal conditions there are additional operating conditions possible; for example, a pump operated as turbine. Another example would be a pump trip where there are several abnormal operating conditions possible when the direction of flow and/or the direction of rotation are changing. The machine behavior in every possible operation condition can be represented by the complete pump characteristics, often called the 4-quadrant (4Q) behavior of a centrifugal pump. To gather the 4Q behavior, a test rig allowing the flow direction as well as the rotation direction to be reverted is necessary, with time-consuming measurements at variable positive and negative discharge in both directions of rotation the complete pump characteristics are evaluated. In the present study, an approach to investigate the complete pump characteristics by means of computational fluid dynamics (CFD) calculations is presented. With steady-state calculations and additional transient CFD investigations in the normal operating conditions, the whole pump characteristics were calculated accurately. Two different types of mixed flow diffuser pumps were investigated—one equipped with adjustable impeller blades, the second one with comparable low specific speed. Experimental verifications have shown a remarkably good agreement. Furthermore, an exemplary numerical waterhammer analysis shows the successful application of the presented approach.

Mechanism of pH Variation and H2O2 Generation in Water Exposed to Pulsed Discharge Plasma

Positive and negative pulsed discharge plasma is generated above test liquid containing NaCl in Ar atmosphere, and the spatiotemporal variation of pH value in the liquid is visualized by a colorimetric method using bromothymol blue. Furthermore, polarity effects on H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> generation are examined by electrochemical calculation and a colorimetric method using titanium sulfate. When the positive pulsed discharge plasma is generated, the pH value of the liquid is decreased by H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> generation through the dissociation of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> , formed by the charge exchange reaction between Ar <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O, while the pH value of the vicinity of an earthed electrode is increased by OH <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> generation through the electrolysis of water. When the negative pulsed discharge plasma is generated, the pH value of the liquid is increased by OH <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> generation and H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> reduction, respectively, through the reaction of hydrated electrons with H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O and H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> , while the pH value in the vicinity of the earthed electrode is decreased by H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> generation through the electrolysis of water. The generation of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is found to be promoted when the positive pulsed discharge plasma is generated, and this increase rate of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is in approximate agreement with the calculated generation rate of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , which is produced from OH generated by electrolysis.

Velocity of initial propagation of positive nanosecond discharge in liquid water: dependence on high voltage amplitude and water conductivity

This study deals with the effect of water conductivity and high voltage pulse amplitude on the initial velocity of nanosecond discharge in liquid water. As variable parameters, we used water solutions with three different conductivities (2 μS cm−1, 100 μS cm−1, 500 μS cm−1), and positive high voltage pulses with four different amplitudes (80 kV, 91 kV, 100 kV, 113 kV). The discharge reactor consists of metallic electrodes in a point–to–plane geometry, both immersed in liquid water. The discharge was generated by a commercial nanosecond pulse power generator with positive HV pulses of ∼6 ns pulse duration (FWHM) and ∼2.5 ns rise time. ICCD time-resolved imaging microscopy with high temporal resolution (∼ns) was utilized as a suitable diagnostic tool for the discharge dynamic propagation. It can be concluded that the discharge visual characteristics and behaviour are not significantly influenced by water conductivity and the length of the filaments increases with the increasing voltage amplitude and reaches the maximum value of ∼1.8 mm for 90 kV. The initial propagation velocity also depends on the voltage amplitude and increases with the voltage. The effect of water conductivity on the propagation velocity is negligible. As far as we know, this paper is the first to bring insight into the topic of the effect of water conductivity on the nanosecond discharge propagation in liquid water.

On an estimate of turbulent transport in a magnetized plasma (on the 90th anniversary of the birth of B B Kadomtsev)

In 1964, B B Kadomtsev proposed that the results of a linear plasma instability analysis alone can be used to estimate the coefficients of turbulent transport across the magnetic field in a plasma. In this paper, we discuss examples of experimental support for this proposal that concern, specifically, the properties of a turbulent positive discharge column in a strong magnetic field, the ionization turbulence of a weakly ionized plasma in crossed electric and magnetic fields, and turbulence in a tokamak wall plasma.

On the Velocity‐Current Relation of Positive Leader Discharges

AbstractThe velocity‐current relation of positive leader discharges is of great importance in the research of lightning physics. However, the measured data in a wide range of current up to several hundred amperes are not available so far. To fill the gap, experiments on positive leader discharges in long air gaps under lightning impulses were carried out on the test site at an altitude of 2.1 km. The velocity and current of positive leaders were measured with the synchronized discharge current and high‐speed video frames. An empirical formula for the velocity‐current relation of positive leaders is given with the leader current up to 500 A. The measurements are also compared with the numerical simulations, and it is suggested that the initial tip radius of a propagating leader grows as the leader current increases.

Comparison of positive and negative DC discharge under coal pyrolysis gas media at high temperatures

To study the characteristics of positive and negative DC discharge under coal pyrolysis gas media at 20 °C–600 °C, the IV characteristics and the current composition are analyzed under different conditions. Due to the difference of ionization mechanism, the corona onset voltage of negative corona is lower than that of positive corona under air gas medium. Under non-electronegative gas media, no corona occurs during negative discharge. However, during positive discharge, with the increase of output voltage, three types of discharge are successively observed, namely corona, glow and arc. Under N2 gas media and at 400 °C, the maximum collection efficiency of positive electrostatic precipitator is 98%, while that of negative electrostatic precipitator is 82%. When the collection efficiency is 70%, the energy consumption index of negative electrostatic precipitator is about 200 times higher than that of positive electrostatic precipitator. A linear relationship between I/V and V is observed and the ionic mobility can be calculated through the slope. At 350 °C, the ionic mobility under H2 gas medium is 5.25 cm2/(V*s) while the ionic mobility under N2 gas medium is 0.1 cm2/(V*s). The ionic mobility is proportional to the absolute temperature according to the discharge experimental data at 350 °C–600 °C. The factor βi, which is only related to gas media, is 0.0001653 cm2/(V*s*T) for N2 and 0.0087308 cm2/(V*s*T) for H2. These results assist in understanding the property of ESP at high temperatures.

New Design of Ion Blower Based on Needle-Dielectric-Needle Bipolar Corona Discharge

We present here a new design of ion blower based on bipolar corona discharge of needle-dielectric-needle configuration. With the help of the dielectric plate, the new ion blower can endure higher voltage before spark than the traditional bipolar corona discharge, with the similar discharge characteristics and current-voltage curve. The high operating voltage provides a much greater ionic wind velocity compared with the traditional needle-to-needle corona. The neutral ionic wind can reach as far as 0.45m with a velocity of 0.2m/s. This feature is very helpful for eliminating mechanical rotating components in the design of ion blowers, so that the size of ion blower can be greatly compressed and the noise significantly reduced, which is more suitable for electrostatic elimination in small areas and some specific scenarios. The design of self-balancing regulation unit can effectively monitor the charged characteristics of mixed ion wind and make corresponding adjustments to ensure the neutrality of positive and negative discharge. This new ion blower has an excellent performance, including an offset voltage of ±5V, a short discharge time of 5s or less at distance of 20cm.

A New Dual-Direction SCR With High Holding Voltage and Low Dynamic Resistance for 5 V Application

Dual-directional silicon-controlled rectifiers (DDSCRs), which provide both positive and negative electrostatic discharge (ESD) surge paths, are ESD protection devices with an excellent area efficiency. However, DDSCRs have a low holding voltage for use in 5 V-class applications, with a relatively high on-state resistance because of the elongated ESD surge path compared to unidirectional SCRs. In this paper, we propose a novel DDSCR with a higher holding voltage and a better ESD tolerance than conventional low-triggering DDSCRs (LTDDSCRs), realized by operating two additional parasitic bipolar transistors. The proposed ESD protection device was developed through a 0.18- $\mu \text{m}$ CMOS process, and a timeline pulse system was used to verify its properties. The measurement results show that the proposed ESD protection device exhibits an improved tolerance and a high holding voltage and is expected to be reliable in 5 V-class applications

A Contribution to the Investigation of Leader Tortuosity in Positive Long Rod-Plane Air Discharge

In recent years, the investigation of leader tortuosity in long air discharge is brought into focus, for it is the main factor that influents the 50% breakdown voltage and can be used to validate and test the discharge modes in the design of long air gap dimension. In order to find out whether the test data of the whole leader channels are accuracy to represent the leader propagation paths, a discharge test of a 4 m rod-plane air gap subjected to switching impulse voltage is carried out. And an observation platform is set up to synchronously record the voltage waveforms, the discharge currents, the leader propagation processes and the whole leader channels. A new method is proposed to subtract the final-jump part from the whole leader channel by identifying the leader tip height at the initiation of the final jump (LTH for short) from the CCD image. Then the test data of LTH and the leader propagation path are statistically obtained. And probability density functions (PDFs for short) of three different angles between consecutive segments of the leader propagation path are used to quantitatively describe the leader tortuosity. According to the analysis of the results, the mean value of LTH is nearly half the gap length in the gap axial direction. And an obvious difference can be discovered when comparing PDFs of the leader propagation paths with those of the whole leader channels. A conclusion to account for the difference is deduced that the leader paths during the final jump are much straighter than those during leader propagation. In the end, the present work recommends that the final-jump part should be subtracted from the whole leader channel when the test data of leader tortuosity are used in the numerical model for positive long air discharge.

Numerical Investigation on the Transient Evolution Mechanisms of Nonlinear Phenomena in a Helium Dielectric Barrier Discharge at Atmospheric Pressure

In this paper, the evolution and transition mechanisms of typical nonlinear phenomena in an atmospheric pressure helium dielectric barrier discharge (DBD) are investigated from the perspective of transient evolution properties through fluid modeling. By gradually up-regulating the interelectrode gap width, the discharge (steady state) evolves from symmetric single-period (SP1), through asymmetric single-period (AP1), into Period-2 (P2) state. Similar evolution trace can also be obtained when increasing the driving frequency. Right after the initial breakdown, the discharge goes through several transient periods featuring unstable asymmetric current pulses before the establishment of steady-state discharge. As the bifurcation parameter increases in excess of the critical value, the discrepancy between the seed electron level of positive and negative discharges accumulates over the transient periods, switching the discharge into AP1 state. After then, a further elevation in the gas gap width (or driving frequency) leads to the generation of a “moderate intensity” positive pulse. With the “moderate intensity” positive pulse and a stronger positive pulse emerging alternatively in the temporal waveform sequence, the discharge evolves into P2 state. Finally, based on the transient evolution mechanisms, a preliminary state-controlling method regarding the use of a first-peak-leveled applied voltage is proposed, which may shed light on the modification of nonlinear states in some practical DBD application scenarios.

Optical and Current Measurements of Lightning Attachment to the 356-m-High Shenzhen Meteorological Gradient Tower in Southern Coastal Area of China

This paper presents in detail the instrumentation for coordinated optical and current measurements of lightning discharges to a 356-m-high meteorological tower and the observation results. The tower, which is located at Shenzhen, a lower latitude coastal city in south China, was equipped with a non-inductive current shunt at its top and a high-speed camera and electromagnetic field sensors at 440 m away from the tower base. A total of 24 discharges to the tower were well documented in the period of April to June of 2019. Three of them were analyzed in detail with the focus being given to the feature of upward leaders initiated from the tower: Case 1 - a connecting upward positive leader (connecting UPL) induced by a downward negative in a downward negative discharge, Case 2 - an upward positive leader (UPL) in the initial stage of an upward negative discharge, and Case 3 - an upward negative leader (UNL) in the initial stage of an upward positive discharge. All the three leaders had a stepping feature during their initial stages, each step producing an isolated but oscillated current pulse with a time scale of 1 μs. The connecting UPL had 5 steps during its initial 2.6 ms, with a step interval ranging in 0.1~1.5 ms and a current pulse peak in 1~5 kA. The UPL had also 5 steps but during its initial 200 μs, with a step interval ranging in 20~50 μs, a step length in 0.8~2.2 m, a current pulse peak in 0.5~2.2 kA, and a leader average speed in 0.4~1.1 × 10 5 m/s. The UNL had 8 steps during its initial 104 μs, with a step interval ranging in 13.6~22 μs, a step length in 3.9~7.1 m, a current pulse peak in 2.3~12.5 kA, and a leader average speed in 1.9~6.6 × 10 5 m/s.

Modeling of Positive Switching Impulse Discharge of UHV Transmission Line Air Gaps

Positive switching impulse discharge characteristics are an important basis for the external insulation design of transmission line towers. At present, the characteristics are obtained mainly by real tower discharge tests. Since the existing research on the discharge model is not perfect, test designs are not reasonable, which results in high costs. The influence of line height and tower width on the discharge characteristics of Ultra High Voltage (UHV) transmission lines air gaps is studied in this paper. The results show that the line height had little influence on the breakdown voltage of air gaps in UHV transmission lines. A tower-width discharge model was obtained by fitting the breakdown voltage of air gaps with different gap lengths and tower widths. By analyzing the gap characteristic factors of different transmission lines, a discharge model of different tower air gaps in UHV transmission lines was presented. The breakdown voltage calculated by the models was in good agreement with the test results, and the errors were not more than 5%.

SF 6 positive DC partial discharge decomposition components under four typical insulation defects

The condition monitoring and fault diagnosis method based on decomposed component analysis (DCA) for SF6 gas-insulated equipment, which mainly aiming at AC SF6 gas-insulated equipment, has become a research hotspot. Therefore, SF6 positive DC partial discharge (PD) decomposition experiments under four typical insulation defects were conducted in this work. The result showed that there is a significant correlation between the generation rules of the five SF6 decomposition components (CF4, CO2, SO2F2, SOF2 and SO2) and the types of defects. The phenomenon was attributed to the variations in the properties of the four insulation defects. In addition, comparing with AC PD experiment, for the protrusion, contamination and gap defect models, the amounts and generation rates of the five characteristic decomposition components under positive DC are less than those under AC by the same defect; however, for the particles defect, it is by contrary. This could be attributed to the essential difference between AC PD and positive DC PD. Therefore, the theory of AC DCA could provide reference to construct DCA diagnostic model for DC SF6 gas-insulated equipment, but cannot be applied mechanically.

Positive streamer corona, single filament, transient glow, dc glow, spark, and their transitions in atmospheric air

By using a ballast resistor having resistance of 10 MΩ, varying the gap distance from 23 mm to 0 mm and using a fixed dc voltage at 14 kV, the streamer corona, single filament, transient glow, dc glow, and spark modes and their transitions are demonstrated in positive needle-to-plate air discharge at atmospheric pressure. The electrical characteristics, the rotational temperature, and vibrational temperature of N2, as well as the temporal behavior of streamer propagation in these discharge modes, are investigated. First, to the best of our knowledge, the transient glow mode between the single filament mode and the dc glow mode, operated in a stable repetitive fashion, is reported for the first time in positive dc air discharges. The pulse repetition frequency ranges from 7.5 to 15 kHz. The current density and the rotational temperature are in the range of 27–105 A/mm2 and 600–850 K, respectively. Its temporal behavior reveals that after the primary streamer arrives at the cathode, the secondary streamer initiates within several nanoseconds near the anode and then propagates at a high speed of 105–106 m/s. There is no transition to spark even after the secondary streamer arrives at the cathode. Second, the transition from single filament to transient glow is characterized by the sudden decrease in the pulse repetition frequency and the abrupt increase in the current amplitude, the pulse width, and the gas temperature. Third, the transition from transient glow to dc glow is identified visibly by the formation of typical glow structure (positive column, Faraday dark space, and negative glow), which is accompanied by the transition of the discharge current from nanosecond pulse to dc. In addition, both the ballast resistor and the stray capacitor exert significant influence on the transition of discharge modes.

An Inverted Magnetron Operating in HiPIMS Mode

An ionized physical vapor deposition technique for thin ferromagnetic films is proposed. The technique is based on high power impulse magnetron sputtering (HiPIMS) with positive discharge polarity. A gapped-target was employed as the cathode of the magnetron. By applying positive HiPIMS pulses to the anode, sputtered particles inside the magnetron source were ionized and extracted through the gap. Using a discharge current with a peak of about 13 A, an ion flux in the order of 1021 m−2s−1 was obtained at a distance of 45 mm from the magnetron. In addition, deposition rates of up to 1.1 Å/s for nickel films were achieved using a 30 Hz repetition rate and 300 µs pulse width.

Experimental Study on Lightning Attachment Manner to Wind Turbine Blades With Lightning Protection System

Different types of lightning protection systems (LPSs) have been developed for wind turbines to protect the blades from lightning strikes. However, severe damages caused by lightning strikes still happen frequently, which creates huge costs. Experiments using a 5-m blade specimen with tip receptors from 1.5-MW wind turbine blades under 3-m air gap were conducted to investigate the lightning attachment manner to the wind turbine blade with LPS in different situations. Factors including the polarity of the lightning strikes, the orientation of the blade, and the lateral distances (LDs) between the wind turbine blade and the lightning downward leader were taken into account. It was found that the types of discharge paths under positive and negative lightning strikes are quite different, and the positive discharges are much more dangerous to wind turbine blade than the negative ones. The LD between the downward leader and the wind turbine blade is a key factor that influences the interception efficiency. Three types of receptor interception failures were discovered. Multiple upward leaders may incept from the blade body as to intercept the downward leader. However, the protection range of the tip receptor is quite limited, and the connection of the tip receptor and the blade body is the most vulnerable position hit by the lightning strikes. The results present the useful reference to the optimal design of the wind turbine blade LPS.