Positive Discharge Research Articles

Positive column dynamics of a low-current atmospheric pressure discharge in flowing argon

We present the results of studies of a cold-plasma atmospheric pressure discharge in argon flow, in both DC and pulse-periodic modes. The burning voltage and the discharge current were 200 V and 15 mA in continuous mode; in pulse-periodic mode the voltage was 220 V and the current 15 mA for a pulse repetition rate of 100 kHz. Special attention was given to the positive column dynamics during the discharge stages of initiation, burning, and extinction. The main method of investigation employed optical diagnostics of the plasma in the visible range with high time resolution. The positive discharge column is shown to be a constricted current channel in the form of an elongated loop. In continuous mode, the length of the positive column, from anode attachment to inflection point outside the discharge system, is several millimeters. In pulsed mode, the positive column is an unsteady plasma formation, the length of which increases at about 4 m s−1, and reaches the same dimension over a time of order 1 ms. We find that the positive column plasma includes hydroxyl molecules OH, nitrogen N2, and atomic oxygen O I, along with atoms of the working gas argon. Observation of the time evolution of the optical emission from the plasma-forming gas shows that the plasma glow of the positive column is mainly determined by argon Ar I radiation, with maximum intensity at the trailing edge of the current pulse.

Study on High Frequency Surface Discharge Characteristics of SiO2 Modified Polyimide Film.

Polyimide (PI) can be used as a cladding insulation for high frequency power transformers, and along-side discharge can lead to insulation failure, so material modification techniques are used. In this paper, different doped nano-SiO2 are introduced into polyimide for nanocomposite modification. The results of testing the life time of high-frequency electrical stress along-side discharge show that the 10% SiO2 doping has the longest life time. The results show that: for composites prone to corona, their flashover causes more damage, and both positive half-cycle and polarity reversal discharges are more violent; compared to pure PI, the positive half-cycle and overall discharge amplitude and number of modified films are smaller, but the negative half-cycle is larger; at creeping development stages, the number of discharges is smaller, and the discharge amplitude of both films fluctuates in the mid-term, with the modified films having fewer discharges and the PI films discharging more violently in the later stages. The increase in the intensity of the discharge was greater in the later stages, and the amplitude and number of discharges were much higher than those of the modified film, which led to a rapid breakdown of the pure polyimide film. Further research found that resistivity plays an important role in the structural properties of the material in the middle and late stages, light energy absorption in the modified film plays an important role, the distribution of traps also affects the discharge process, and in the late stages of the discharge, the heating of the material itself has a greater impact on the breakdown, so the pure polyimide film as a whole discharges more severely and has the shortest life.

Influence of Magnetic Field on Characteristics of Corona Discharge in Wire-Cylinder Electrodes Configuration

The behavior of corona discharge was investigated in wire–cylinder electrodes under the effect of a crossed magnetic field. Townsend’s formula was used commonly with a modified empirical formula to evaluate the different parameters of corona discharge in positive and negative discharge. By using a least-squares fitting, the dimensional constants A, K, and the exponent n displayed a significant dependence on the applied magnetic field. An improvement of pre-breakdown has been achieved by using a crossed magnetic field. For both polarities, while the magnetic field is present, breakdown voltage VB and corona inception voltage V0 increased, whereas the corona current decreases. In addition, the corona inception voltage was greater in positive corona in the absence of a magnetic field, while the opposite occurred regarding the crossed magnetic field. Furthermore, the breakdown streamer demonstrated significant triggering in the negative corona by applying the magnetic field.

Numerical Modelling of Positive Surface Discharges in C-C4F8/CF3I/N2 Gas Mixture under Non-Uniform Field

As an environmentally friendly gas with good insulation and stable chemical properties, CF3I gas mixture is considered as a potential alternative to SF6 gas to compensate for the shortcomings of SF6 gas as a greenhouse gas. This article attempts to study the CF3I ternary gas mixtures with c-C4F8 and N2 by considering the process of streamer development in surface discharge. The model of surface discharge in CF3I gas mixture under DC voltage was established by COMSOL, and the drift-diffusion equations of particles was solved to show the discharge process, and the changes of electric field and particle concentration, etc. during the development of streamer were obtained, which provides the theoretical basis for the reliable diagnosis of partial discharge. On this basis, the model is compared with models for two other different gases (SF6/N2, artificial air) in terms of particle characteristics, streamer characteristics and streamer branches characteristics. Finally, it is concluded that under this model, although the insulation characteristics in CF3I gas mixture are weaker than those in SF6, the difference is not large and both are much better than those in artificial air, so c-C4F8/CF3I can be considered as a potential substitute for SF6.

The Spontaneous Nature of Lightning Initiation Revealed

AbstractHere, we present new radio interferometer beamforming observations of lightning initiation using data from the Low‐Frequency Array (LOFAR). We show that the first lightning source in the flash increases exponentially in intensity by two orders of magnitude in 15 μs, while propagating 88 m away from the initiation location at a constant speed of 4.8 ± 0.1 × 106 m/s. A second source replaces the first source at the initiation location, and subsequent propagation of the lightning leader follows. We interpret the first source to be a rapidly propagating and intensifying positive streamer discharge that subsequently produces a hot leader channel near the initiation point. How lightning initiates is one of the greatest unsolved problems in the atmospheric sciences, and these results shed light on this longstanding mystery.

470. Relapsing COVID-19 Pneumonia in Patients Receiving Rituximab Therapy

BackgroundRituximab is a monoclonal antibody against the CD20 antigen on B-lymphocytes leading to B-cell death and depletion. Patients who receive rituximab and are infected with the novel severe acute respiratory syndrome coronavirus-2 (SARS-CoV2) causing coronavirus disease (COVID-19) may have increased difficultly clearing the virus and be at risk for persistent disease. While the limited literature available is mixed regarding the severity of COVID-19 in patients receiving rituximab, there is minimal literature regarding persistent and relapsing COVID-19 in this patient population. This is a case series of patients with persistent COVID-19 who previously received rituximab. MethodsThis is a retrospective review of 5 patients admitted between 1/1/2021 and 5/1/2021 to our institution with confirmed COVID-19 and receipt of rituximab for any indication within the previous 12 months. Information regarding hospital readmissions, time course of positive infection, medical management, disease severity, and discharge disposition were collected.ResultsFive patients, median age of 46, currently or recently on rituximab therapy were admitted a median of 2 times due to persistent, severe COVID-19 (Table 1). Patients received their initial COVID-19 diagnosis a median of 34 days (8-102 days) since their last rituximab administration and had documented SARS-CoV-2 infection a median of 66 days (19-195 days; Figure 1). All 5 patients received remdesivir and corticosteroids over the course of their COVID-19 disease and 2 patients received convalescent plasma therapy 1 and 5 days prior to a positive SARS-CoV-2 antibody IgG.Figure 1. Patient SARS-CoV-2 Infection Course Table 1. Patient Clinical and Therapeutic Data ConclusionRituximab therapy may be associated with persistent or relapsing COVID-19 disease. Controlled investigations are necessary to evaluate the exact impact anti-CD20 agents have on the course of COVID-19 and whether convalescent plasma or other therapies can prevent relapsing disease.Disclosures All Authors: No reported disclosures

Experimental study of heat transfer enhancement with point-to-ring corona discharge

In this study, we experimentally inquire into the mechanism of the electric field for heat transfer enhancement by a point-to-ring corona gas discharge with either positive or negative applied voltage. We use a self-assembly 2D2C particle imaging velocimetry system to visualize and record the flow field. Results show that in our configuration the onset voltage of positive corona discharge is only slightly higher than that of the negative corona as a relatively large ring electrode is used. The current-voltage relationship follows Townsend's quadratic equation. The electrode distance has a slight effect on the current-voltage relationship. The time-averaged velocity demonstrates that the positive corona produces a faster and thinner jet compared to the negative one, and the region of the ionic wind is limited at low corona voltage. In addition, it is observed that the ionic wind can dramatically enhance heat transfer by ∼ 200%, and the enhancement effect of the positive discharge is more significant than that of the negative one. Furthermore, the proposed ionic wind generator has low power consumption, and therefore it is energy efficient.

Risk factors for surgical site infection after cesarean delivery in a rural area in China: A case–controlled study

BackgroundWe aimed to determine the prevalence and risk factors of surgical site infection (SSI) after cesarean delivery (CD) in a rural area in China. MethodsWe identified 155 patients with incisional and organ/space SSIs by International Classification of Disease codes and matched them with 465 patients (controls) in a time-matched retrospective quality assurance analysis. Multiple logistic regression analyses were performed to examine the risk factors for SSI: the work-years of providers, the number of antenatal care (ANC) visits, CD after labor, positive discharge culture, postoperative C-reactive protein (CRP) levels and fever. Resultsand discussion: During the study, 155 women with SSI were identified among the 8640 patients who delivered by CD. The incidence of SSIs was 179 per 10 000patients (95%CI: 151–207 per 10 000 patients). The total duration of hospitalization in patients with SSI was 14.49 ± 8.68 days compared with 7.96 ± 2.35 days in patients with no SSI (P < 0.01). Multiple logistic regression analysis showed that the work-years of providers (odds ratio [OR] = 3.729, 95% confidence interval [CI]: 1.463–9.501, p = 0.006), irregular ANC visits (OR = 3.245, 95% CI: 1.264–8.329, p = 0.028), CD after labor (OR = 2.545, 95% CI: 0.935–6.926, p = 0.020), postoperative CRP level (OR = 2.545, 95% CI: 0.935–6.926, p = 0.016) and a positive discharge culture (OR = 2.954, 95% CI: 0.305–28.643, p = 0.019) were positively associated with SSI. However, the rates of maternal request (OR = 0.186, 95% CI: 0.065–0.535, p = 0.002) and postoperative fever (OR = 0.208, 95% CI: 0.087–0.494, p = 0.001) were negatively related to SSI. ConclusionsSpecial attentions should be paid to CD patients who had irregular ANC visits, attempted labor, a positive discharge culture, higher CRP levels and fever after surgery, who had a greater risk of SSI.

An experimental study of impulse-current-induced mechanical effects on laminated carbon fibre-reinforced polymer composites

Lightning strike damage has become a primary issue limiting the extensive application of carbon fibre-reinforced polymer (CFRP) composites in the aerospace field. A detailed understanding of the physical interactions involved in the lightning strike process is still lacking, especially regarding the lightning-induced mechanical effects that potentially contribute to fracture and ply delamination in CFRP structures. This paper presents research on shock wave pressure induced by impulse currents on CFRP laminates. A novel method that exploits a polyvinylidene fluoride (PVDF) piezoelectric sensor was developed to directly measure the pressure induced by arc channel expansion. The influences of discharge polarity, strike distance and surface condition on the shock wave pressure were investigated. The results showed that the shock wave pressure produced by negative discharge was greater than that produced by positive discharge, the difference between which was reasonably explained based on the polarity effect concept. Increases in current amplitude and strike distance both contributed to larger measured pressures. A woven copper mesh protection could diminish the shock wave pressure to some extent, while an additional insulating epoxy resin layer enhanced it. Analysis results demonstrated that the pressure imposed on the laminated samples was related to the energy injected into the arc channel. In addition, the energy consumed by vaporized materials at the interface between the arc root and sample was defined as another source of shock wave pressure. The presence of an insulating layer confined the diffusion of the plasma channel at the arc root, as confirmed by high-speed imaging observations.

Non-thermal plasma by positive corona glow discharge using nano-structured Cu/CuO coated electrodes for benzene removal from air flow; removal enhancement and energy efficiency improvement

• Benzene removal was about 67% with retention time of 5 s by Cu coating. • Cu coating showed uniform glow discharge along the discharge electrode. • The energy efficiency is increased by Cu-coating. • Glow column discharge was seen in CuO nanoparticle coating. • Benzene mineralization reached over 96% by Cu-coating. Benzene removal was investigated in the positive discharge non-thermal plasma. The wire-tube configuration was used for comparison of the discharge specifications and removal of benzene in three treatment conditions including not-coated stainless steel electrodes (D = 1 mm), Nano-hill Cu-coated stainless steel electrodes, and CuO nanoparticles coated stainless steel electrodes. A thermo-chemical electroless plating process was used for preparation of the electrodes. Comprehensive structural differences were seen between the electrodes and consequently different electrical discharge and pollution removal were observed. The results showed that the Cu was made much uniform coating and caused an obvious uniform discharge along the discharge electrode and the most removal efficiency of benzene was resulted with Cu-coated one up to 66.8 ± 2.8%, wherein the SCO 2 and the energy efficiency ( EE ) were 96.9 ± 0.1% and 1.85 ± 0.06 g/kWh, respectively. Given the results, 27.6% of energy efficiency improvement was obtained by Cu-coated reactor comparing the stainless steel. Also, it showed higher ozone destruction rate as the reaction constant [ k (L/J)] was obtained 2.9 × 10 −3 , 1.2 × 10 −3 and 1.6 × 10 −3 , respectively for Cu, CuO, and not-coated reactor.

High rate of positive vaginal discharge cytology at the time of colpotomy in gynecologic cancer patients

High rate of positive vaginal discharge cytology at the time of colpotomy in gynecologic cancer patients

Spatial distribution and time evolution of metal-containing plasma of a low-current atmospheric pressure discharge with magnesium cathode

The spatial intensity distribution and temporal dynamics of the plasma generated by an atmospheric pressure discharge with magnesium cathode in an argon flow are investigated in a coaxial geometry discharge system. The repetition rate of unipolar pulses was 56 kHz and the pulse duration was 12 μs. The steady-state amplitude of the discharge current was 100 mA at a voltage of about 130 V. Under this operating mode, a local melting of the active cathode surface took place. The evaporated magnesium atoms were captured by the working gas flow and formed a green glow plume around the positive discharge column outside the anode nozzle. The image of the plasma formation was projected onto the entrance slit of the monochromator. The spatial distribution of the radiation intensity and evolution in time of its selected monochromatic components were measured. The radiation spectrum contained groups of ion and magnesium atom lines with wavelengths of 285.21 nm (singlet resonant Mg I); 383.08, 383.36, 383.9 nm (triplet Mg I); 517.3, 517.5, 518.1 nm (triplet Mg I). The results of this work are promising with regard to studying open-type spontaneous radiation sources, as well as the generation of combined gas-metal plasma flows at atmospheric pressure.

Study on Dominant Parameters Determining Streamer Initiation From Hydrometeors in Thundercloud Fields

AbstractThis study reports a study trying to find the dominant factor on streamer initiation from an isolated hydrometeor in thundercloud fields at 7 km altitude corresponding to an atmosphere pressure of about 0.453 atm. Three parameters are considered including hydrometeor size, shape, and electric quantity. The simulation results indicate that a larger hydrometeor is more likely to initiate a streamer discharge at a lower ambient field for noncharged hydrometeors. The charge on hydrometeor plays a prominent role when a charged hydrometeor has a smaller size, and it is easier to initiate a streamer in this case. At 0.25 Ek, a positive streamer discharge has been presented for a charged hydrometeor with a radius of 0.5 mm. The critical field to form streamer discharge for a column shape hydrometeor without charge is much smaller than that for a spherical hydrometeor. If smaller hydrometeors are charged, the critical field for a spherical hydrometeor becomes lower than that for a column one. The electric quantity charged on hydrometeor has little effect on the critical field for both spherical and column hydrometeors, when the hydrometeor size is larger enough. The charge on hydrometeor plays a dominant role in streamer initiation when hydrometeor is smaller, but hydrometeor shape becomes more important for larger hydrometeor. Streamer discharge can be predicted by Meek number, but stable streamer cannot be ensured. Streamer branch will be met when ambient field is lower than 0.25 Ek.

Optimized Nanopores Opened on N-Doped Carbon Nanohorns Filled with Fe/Fe2O3 Nanoparticles as Advanced Electrocatalysts for the Oxygen Evolution Reaction.

N-doped carbon nanohorns filled with Fe nanoparticles (Fe-N-CNHs) were produced by one-step positive pressure-assisted arc discharge in the Ar and N2 mixture. After oxidation treatments in air, Fe was converted into Fe2O3, and nanopores were opened on CNHs from 1 to 5 nm controlled by oxidation temperature. Fe-N-CNHs oxidized in O2 at 550 °C (Fe2O3-N-CNH550ox) show 245 mV at 20 mA cm-1, which is much smaller than that of the ones oxidized at 500 °C (Fe2O3-N-CNH500ox), contributing to the larger pore size on CNHs (3-5 nm vs 2-3 nm) and a larger number of nanopores caused by the enhanced sidewall nanopores. However, the stability of Fe2O3-N-CNH550ox becomes much poorer than that of Fe2O3-N-CNH500ox after 2000 cycles. The unique relationship between the overpotential and long-term stability can be explained by the consideration of the size of Fe2O3 nanoparticles and nanopores on CNHs. Furthermore, the stability for Fe2O3-N-CNH550ox can be rapidly increased after heat treatment in Ar for 1 h caused by shrinking the size of tip nanopores. Herein, we first reveal that the performance of OER is related to the nanopore size of carbon carriers and the catalyst of nanometal particles. The optimization of pore-opening conditions in carbon carriers can be achieved a superior electrocatalytic OER performance, including a low overpotential at high current density and long-term stability.

A diffuse argon plume generated downstream of an atmospheric pressure plasma jet equipped with a positively biased electrode

Compared with the diffuse mode of helium plasma jets, a filamentary mode is normally produced in the plasma plume with less expensive inert gas, such as argon, which is undesirable because intense discharge in the filamentary mode may cause damage to fragile samples. Many efforts have been attempted to realize the diffuse mode of an argon plasma jet. In this paper, the diffuse mode is realized in an atmospheric pressure argon plasma jet with increasing biased voltage (V b) applied to a downstream plate electrode. Results show that the diffuse mode transits from the filamentary mode with the increase of V b. Waveforms of voltage, current and integrated light emission reveal that the filament originates from a positive discharge with a needle anode, while the diffuse mode results from negative discharges with a needle cathode, which consist of a Trichel-pulse phase and a slower-varying phase. By fast photography, the positive discharge is attributed to a streamer regime, whereas the negative discharges belong to a Townsend-discharge regime. From optical emission spectroscopy, electron density, electron excitation temperature, vibrational temperature, and rotational temperature are studied as functions of V b.

A compound plume with solid and hollow parts formed downstream of an argon plasma jet at atmospheric pressure

Plasma jet is able to produce abundant active species in plasma plume, whose morphology is a key issue for its various application fields. In this paper, we report the first observation of a compound plume with a solid part and a hollow one in an argon plasma jet. Results indicate that the compound plume can only be formed under proper conditions. Integrated emission waveform reveals that the compound plume initiates with periodicity. By fast photography, it is found that after a passage of straight-line propagation, some positive discharges behave as a curved propagation due to the influence of residual ions. Moreover, the solid part comes from negative discharges and the straight-line propagation of positive discharges. In contrast, the hollow part originates from the curved propagation of positive discharges. Optical emission spectroscopy verifies the existence of residual ions. These results can enrich the morphology of plasma plume.

Morphology of positive ionization waves in atmospheric pressure air: influence of electrode set-up geometry

A numerical parametric study on positive diffuse discharges in point-to-plane geometry in air at atmospheric pressure is presented. Different discharge characteristics are studied: ignition time, connection time to the grounded cathode plane, shape of the discharge and its maximum radius at the connection time, evolution of the maximum electric field in the discharge front and velocity of the ionization front during its propagation. First, a case at a DC voltage of 50 kV applied on a rod anode ended by a semi-sphere with a radius of 100 μm set at 1.6 cm from a grounded cathode plane is considered. The influence of the rod radius, the position of a disc holder, the shape of the anode electrode and the radial extension of the computational domain are studied. The radius of curvature of the anode tip (varied between 100 and 1000 μm) and the shape of the anode electrode (rod or hyperbola) are shown to have a negligible influence on discharge characteristics. Conversely, the presence of a disc holder or a small radial computational domain lead to a decrease of the maximum discharge radius at the connection time and a change in the discharge shape from a conical to an ellipsoidal shape. These changes on the discharge morphology have only a limited impact on the propagation velocity of the discharge front and maximum electric field on the discharge axis. Then, a point-to-plane geometry with a rod electrode of 50 μm radius, in a 1.6 cm gap, with a 100 kV voltage applied with a rise time of 1 ns is studied. The influence of a disc holder on the discharge characteristics is the same as for lower DC voltages. Finally, the time evolution of the absolute value of the electric field at different test points on the discharge axis is studied. Close to the anode tip, rapidly after the peak of electric field due to the passage of the ionization front, the electric field in the discharge channel is shown to increase to values higher than the breakdown field.

Comparing simulations and experiments of positive streamers in air: steps toward model validation

We compare simulations and experiments of single positive streamer discharges in air at 100 mbar, aiming toward model validation. Experimentally, streamers are generated in a plate–plate geometry with a protruding needle. We are able to capture the complete time evolution of reproducible single-filament streamers with a ns gate-time camera. A 2D axisymmetric drift-diffusion-reaction fluid model is used to simulate streamers under conditions closely matching those of the experiments. Streamer velocities, radii and light emission profiles are compared between model and experiment. Good qualitative agreement is observed between the experimental and simulated optical emission profiles, and for the streamer velocity and radius during the entire evolution. Quantitatively, the simulated streamer velocity is about 20% to 30% lower at the same streamer length, and the simulated radius is about 1 mm (20% to 30%) smaller. The effect of various parameters on the agreement between model and experiment is studied, such as the used transport data, the background ionization level, the photoionization rate, the gas temperature, the voltage rise time and the voltage boundary conditions. An increase in gas temperature due to the 50 Hz experimental repetition frequency could probably account for some of the observed discrepancies.

Buck and Boost Inverter

Abstract: A versatile operation of any electronic circuitry depends on the power source supplying the power for its operation. The buck converter is implemented using an integrated circuit(IC), LM317. The constructed buck converter was tested for load and line regulation cited in the datasheets for stability. The test and analysis for the linear buck converter was done using setup. The output measurements indicate that the power supply is functional. The measured output values results of the test circuit. The developed output power supply unit is important in measurements, laboratories and test setup. It is implemented for all general applications that require power supply unit. XL6009 module is a DC to DC BUCK-BOOST converter module that operates at a switching frequency of 400kHz. In such high frequency, it provides smaller sized filter components compared with low frequency switching regulators. An improved SingleStage Buck-Boost inverter is provided, using only three or four power semiconductor switches. The inverter can handle a wide range of dc input voltages and produce a fixed ac output voltage. The inverter is well suited to distributed power generation systems such as photovoltaic and wind power and fuel cells, for standalone or grid connected applications. The inverter has a single charge loop, a positive discharge loop and a negative discharge loop. In this complete design of the converter is carried out. This application report gives details regarding this conversion with examples

A DESCRIPTIVE STUDY OF BACTERIOLOGICAL SPECTRUM OF ORTHOPEDIC IMPLANT INFECTION IN CLOSED FRACTURES

Background- Surgical Site Infection (SSI) is defined as pain associated with erythema, induration, local tenderness, pus discharge or any culture positive or negative discharge from a surgically created wound.&#x0D; Methods- Descriptive type of Observational study conducted on Patients in the department of Orthopaedics.&#x0D; Results- 6.00% patients have wound infection. Gram positive 83.33% patients have found with Staph. Aureus and Gram- negative 16.67% patients have found with Pseudomonas.&#x0D; Conclusion- Infection in closed fractures with implants was quite high. The adverse outcome of SSIs related to a clean orthopedic surgical procedure can be associated with significant morbidity, cost, and even mortality.&#x0D; Keywords- SSI, Closed, Implants