Application Of High Voltage Pulses Research Articles

Enhancing Rare Earth Element Recovery from Coal Ash Using High-Voltage Electrical Pulses and Citric Acid Leaching

The study investigates the application of high-voltage electrical pulses (HVEP) as a pretreatment to enhance the leaching efficiency of rare earth elements (REE) from coal ash (CA) produced from the combustion of Ekibastuz Basin coal in Almaty, Kazakhstan. HVEP treatment was applied to the finest (<40 µm) non-magnetic fraction of CA under controlled conditions, optimizing discharge current, voltage, and treatment duration. Leaching experiments with 1 M citric acid at various solid-to-liquid ratios, temperatures, and durations were conducted on both treated and untreated samples. Results indicated that HVEP-treated CA significantly improved REE recovery rates compared to untreated samples, with optimal conditions achieving 74% cerium, 79% yttrium, and 77% lanthanum recovery. The leaching of untreated CA under the specified conditions allowed no more than 28% REE to be extracted into the solution. The leaching process was found to follow first-order kinetics, with the chemical reaction of metal dissolution being the rate-limiting step.

Importance of the electrophoresis and pulse energy for siRNA-mediated gene silencing by electroporation in differentiated primary human myotubes

BackgroundElectrotransfection is based on application of high-voltage pulses that transiently increase membrane permeability, which enables delivery of DNA and RNA in vitro and in vivo. Its advantage in applications such as gene therapy and vaccination is that it does not use viral vectors. Skeletal muscles are among the most commonly used target tissues. While siRNA delivery into undifferentiated myoblasts is very efficient, electrotransfection of siRNA into differentiated myotubes presents a challenge. Our aim was to develop efficient protocol for electroporation-based siRNA delivery in cultured primary human myotubes and to identify crucial mechanisms and parameters that would enable faster optimization of electrotransfection in various cell lines.ResultsWe established optimal electroporation parameters for efficient siRNA delivery in cultured myotubes and achieved efficient knock-down of HIF-1α while preserving cells viability. The results show that electropermeabilization is a crucial step for siRNA electrotransfection in myotubes. Decrease in viability was observed for higher electric energy of the pulses, conversely lower pulse energy enabled higher electrotransfection silencing yield. Experimental data together with the theoretical analysis demonstrate that siRNA electrotransfer is a complex process where electropermeabilization, electrophoresis, siRNA translocation, and viability are all functions of pulsing parameters. However, despite this complexity, we demonstrated that pulse parameters for efficient delivery of small molecule such as PI, can be used as a starting point for optimization of electroporation parameters for siRNA delivery into cells in vitro if viability is preserved.ConclusionsThe optimized experimental protocol provides the basis for application of electrotransfer for silencing of various target genes in cultured human myotubes and more broadly for electrotransfection of various primary cell and cell lines. Together with the theoretical analysis our data offer new insights into mechanisms that underlie electroporation-based delivery of short RNA molecules, which can aid to faster optimisation of the pulse parameters in vitro and in vivo.

Electrical pruning of Pinus radiata epicormic growths

A novel method for pruning epicormic growths with high voltage energy pulses is presented. This method could be utilized in autonomous forest management, for example by a drone carrying an electrical pulse generator and applicator pruning device. In a laboratory setting, short duration, high voltage pulses of electricity were generated using a capacitor network and a current source. These pulses were applied to Pinus radiata needles and the relative tissue injury to the needles was assessed by estimating electrolyte leakage from the needles in deionised water using electrical conductivity (EC) measurements. EC was positively correlated with the electrical energy applied. This validated the theory that electrical stimuli can cause increased cell death in plant matter. The cell damage, based on electrolyte leakage, caused by stimulating a Pinus radiata needle with a single 1.5 J pulse of energy was 21 % of the maximum, where the maximum was found to result in an EC of 333 µS/cm per gramme of needle in a 45 ml solution. These results from testing on needles removed from the tree confirm the potential of electrical pruning of epicormic growths. Future testing on live in-situ needles will be implemented to determine the level at which cell death induced by the application of high voltage pulses is sufficient to prune epicormic growths, given that mechanical and biotic factors of needles removed from the tree may enhance the rate of cell death in harvested samples.

Influence of electric field, blood velocity, and pharmacokinetics on electrochemotherapy efficiency

The convective delivery of chemotherapeutic drugs in cancerous tissues is directly proportional to the blood perfusion rate, which in turns can be transiently reduced by the application of high-voltage and short-duration electric pulses due to vessel vasoconstriction. However, electric pulses can also increase vessel wall and cell membrane permeabilities, boosting the extravasation and cell internalization of drug. These opposite effects, as well as possible adverse impacts on the viability of tissues and endothelial cells, suggest the importance of conducting in silico studies about the influence of physical parameters involved in electric-mediated drug transport. In the present work, the global method of approximate particular solutions for axisymmetric domains, together with two solution schemes (Gauss-Seidel iterative and linearization+successive over-relaxation), is applied for the simulation of drug transport in electroporated cancer tissues, using a continuum tumor cord approach and considering both the electropermeabilization and vasoconstriction phenomena. The developed global method of approximate particular solutions algorithm is validated with numerical and experimental results previously published, obtaining a satisfactory accuracy and convergence. Then, a parametric study about the influence of electric field magnitude and inlet blood velocity on the internalization efficacy, drug distribution uniformity, and cell-kill capacity of the treatment, as expressed by the number of internalized moles into viable cells, homogeneity of exposure to bound intracellular drug, and cell survival fraction, respectively, is analyzed for three pharmacokinetic profiles, namely one-short tri-exponential, mono-exponential, and uniform. According to numerical results, the trade-off between vasoconstriction and electropermeabilization effects and, consequently, the influence of electric field magnitude and inlet blood velocity on the assessment parameters considered here (efficacy, uniformity, and cell-kill capacity) is different for each pharmacokinetic profile deemed.

Polarity dependence of CO2 conversion in nanosecond pulsed large gap dielectric barrier discharges

The splitting of carbon dioxide was investigated for a coaxial dielectric barrier discharge, which was operated with nanosecond high-voltage pulses of 500 ns and amplitudes up to 20 kV at ambient temperature and atmospheric pressure. A non-thermal plasma could be established across a gap distance of 4 mm and a length of 90 mm for gas flows of 30–210 sccm of pure CO2 and with admixtures of Argon. The application of high-voltage pulses of either positive or negative polarity resulted in distinct differences in effective conversion and CO production. The highest observed conversion of 6.6%, corresponding to a CO production of 7%, was achieved for positive high-voltage pulses of 20 kV that were applied with a repetition rate of 3 kHz for a ratio of CO2:Ar of 1:2 at a flow rate of 30 sccm. Conversely, an operation with negative high-voltage pulses, for otherwise the same operating parameters, resulted in an effective conversion of only 5.3% and CO production of 5.4%. The corresponding conversion rates for specific energy input (SEI), concerning different operating parameters, could be related to reaction enthalpies that were calculated from thermodynamic functions. The differences in polarity were associated with discharge characteristics, i.e., plasmas appeared more filamentary for positive high-voltage pulses. In this case, a visible plasma could also be established for much lower pulse amplitudes.Graphical

Enhanced electrostatic energy storage achieved in BiFeO3-driven (Sr,Bi)TiO3 ceramics for high-voltage pulsed applications

The paradoxical relationship between ferroelectric polarization and dielectric breakdown to a great extent hinders the increase in energy storage properties of dielectric materials. A strategy of combining large polarization and high dielectric breakdown by composition optimization was designed in (Sr0.7Bi0.2)TiO3–BiFeO3 system. All ceramics show dense microstructures with fine grain sizes. A promising energy density of 3.67 J/cm3 with an efficiency of 89.1% can be obtained in 0.93(Sr0.7Bi0.2)TiO3-0.07BiFeO3 at 340 kV/cm. The energy density shows excellent temperature reliability in a wide temperature range till 160 °C and reliable fatigue endurance till 105 cycles. This research expands the strategy of combing large polarization and dielectric breakdown for developing novel dielectrics used in pulse power electronics.

Preclinical Study of Biphasic Asymmetric Pulsed Field Ablation.

Pulsed field ablation (PFA) is a novel method of pulmonary venous isolation in atrial fibrillation ablation and is featured by tissue-selective ablation. Isolation is achieved via the application of high-voltage microsecond pulses that create irreversible perforations in cell membranes (i.e., electroporation). We proposed a new biphasic asymmetric pulse mode and verified the lesion persistence and safety of this mode for pulmonary vein ostia ablation in preclinical studies. We found that biphasic asymmetric pulses can effectively reduce muscle contractions and drop ablation threshold. In the electroanatomic mapping, the ablation site showed a continuous low potential area, and the atrium was not captured after 30 days of pacing. Pathological staining showed that cardiomyocytes in the ablation area were replaced by fibroblasts and there was no damage outside the ablation zone. Our results show that pulmonary venous isolation using the biphasic asymmetric discharge mode is safe, durable, effective, and causes no damage to other tissues.

Periodic forced flow in a nanosecond pulsed cold atmospheric pressure argon plasma jet

This paper is devoted to the study of the argon flow modification in a cold atmospheric pressure plasma jet driven by nanosecond high voltage (HV) pulses, from single to multiple HV shots applications. A schlieren optical bench has been designed in order to visualize the argon flow downstream expansion in quiescent air, for moderate flow rates below 1 standard liter per minute. A coupled approach is used between charge coupled device (CCD) schlieren imaging and intensified CCD (ICCD) plasma plume imaging, both time-resolved. It is shown that the application of only one HV pulse (i.e. single HV shot) is enough to disturb the flow. The disturbed flow exhibits ripple propagation, on a timescale similar to the flow velocity. When operating in double HV shots, the second ionization wave can be used as a probe, to instantly visualize the flow structure any time after the first HV pulse application. For some flow rates, the ripple can increase in amplitude up to the point when it strongly deforms, or even stops, the plasma plume expansion, after which it is entrained by the flow and the plasma plume retrieves its full usual expansion. When a series of HV pulses are applied, the maximal disturbance of the flow is achieved for a certain pulse repetition frequency (PRF), specific of each flow rate. It is associated with ripples alternation in the plasma plume, in a 3D helical-like arrangement. For greater PRF, the ripples progressively vanish, and the flow is clearly less disturbed. Once the ripples have vanished, increasing further the PRF does not change the plasma plume and flow structures. We suggest that the repetitive plasma ignition mechanically forces the flow inside the capillary with consequences on the global flow structure, similarly to a forced backward-facing step flow with actuator.

Boosting up the capacitive energy storage performances of lead-free ceramics via grain engineering for pulse power applications

Exploring high-performance ceramics has been a great challenge for advanced electronic devices due to their limited capacitive energy storage densities in high-voltage pulse applications. The refinement of the microstructures can considerably optimize energy storage performances of dielectric ceramics by tailoring dielectric breakdown. Here, two-step sintering was employed to refine the microstructures of the lead-free 2.0 mol% Mn-doped 0.55 (0.94Na0.5Bi0.5TiO3-0.06BaTiO3)-0.45SrTiO3 bulk ceramics to offer the possibility of increasing energy storage performances. Compared with conventional sintering, fine grains by two-step sintering can be obtained, resulting in the obviously enhanced dielectric breakdown due to the increased fraction of grain boundary and the suppressed movement of domain walls. An ultrahigh charge energy storage density of 2.98 J/cm3 with a moderate efficiency (η) of 73.1% can be achieved at 28 kV/mm, accompanying with excellent temperature insensitivity in a wide range from 30 to 180 °C compared with the previous Na0.5Bi0.5TiO3-based derivatives. This work presented here strongly indicates that two-step sintering is a promising way to optimize the microstructural morphology and electrical performances of dielectric ceramics.

Field-Time Breakdown Characteristics of Air, N2, CO2, and SF6

The dielectric performance of gases in insulation systems used in high voltage power and pulsed power applications is a subject of intensive theoretical and experimental investigations. Transient breakdown processes in gases stressed with short, high-field impulses, have been studied for many decades. However, there are still significant gaps in the understanding of the main breakdown processes and mechanisms associated with fast transient breakdown processes in gases. This knowledge is important for the optimization of gaseous insulating systems and for the coordination of gaseous insulation in power and pulsed power apparatuses. This information is also required for the development of gas-filled components such as circuit breakers and plasma closing switches. This article is aimed at the analysis of the field-time breakdown characteristics of air, N2, CO2, and SF6, using kinetic and drift-diffusion approaches. The kinetic approach is based upon the avalanche-to-streamer transition criterion, while the fluid drift-diffusion model requires self-consistent numerical solution of the continuity equations for charged species, and the Poisson equation for the electric field. The time to breakdown as a function of the applied field was obtained for all investigated gases. The obtained analytical results agree well with the experimental data reported in the literature, which suggests that both approaches can be used for insulation coordination, and for the development of gas-insulated power and pulsed power systems and components.

Application of high voltage pulse for reduction of membrane fouling in membrane bio-reactor and kinetic approach to fouling rate reduction

Application of high voltage pulse for reduction of membrane fouling in membrane bio-reactor and kinetic approach to fouling rate reduction

Covalent Biofunctionalization of the Inner Surfaces of a Hollow-Fiber Capillary Bundle Using Packed-Bed Plasma Ion Implantation.

Hollow-fiber capillary bundles are widely used in the production of medical devices for blood oxygenation and purification purposes such as in cardiopulmonary bypass, hemodialysis, and hemofiltration, but the blood interfacing inner surfaces of these capillaries provide poor hemocompatibility. Here, we present a novel method of packed-bed plasma ion implantation (PBPII) for the modification of the inner surfaces of polymeric hollow-fiber bundles enclosed in a cassette. The method is simple and can be performed on an intact hollow-fiber bundle cassette by the placement of a hollow cylindrical electrode, connected to a negative high-voltage pulse generator, around the cassette. The method does not require the insertion of electrodes inside the capillaries or the cassette. Nitrogen gas is fed into the capillaries inside the cassette by connecting the inlet of the cassette to a gas source. Upon the application of negative high-voltage bias pulses to the electrode, plasma is ignited inside the cassette, achieving the surface modification of both the internal and external surfaces of the capillaries. Fourier transform infrared-attenuated total reflectance spectroscopy of the PBPII-treated capillaries revealed the formation of aromatic C═C bonds, indicating the progressive carbonization of the capillary surfaces. The PBPII treatment was found to be uniform along the capillaries and independent of the radial position in the cassette. Atomic force microscopy of cross sections through the capillaries revealed that the increased stiffness associated with the carbonized layer on the inner surface of the PBPII-treated capillary has a depth (∼40 nm) consistent with that expected for ions accelerated by the applied bias voltage. The modified internal surfaces of the capillary bundle showed a greatly increased wettability and could be biofunctionalized by covalently immobilizing protein directly from the buffer solution. The direct, reagent-free protein immobilization was demonstrated using tropoelastin as an example protein. Covalent binding of the protein was confirmed by its resistance to removal by hot sodium dodecyl sulfate detergent washing, which is known to disrupt physical binding.

A numerical investigation into key factors controlling hard rock excavation via electropulse stimulation

Electropulse stimulation provides an energy-efficient means of excavating hard rocks through repeated application of high voltage pulses to the rock surface. As such, it has the potential to confer significant advantages to mining and drilling operations for mineral and energy resources. Nevertheless, before these benefits can be realized, a better understanding of these processes is required to improve their deployment in the field. In this paper, we employ a recently developed model of the grain-scale processes involved in electropulse stimulation to examine excavation of hard rock under realistic operating conditions. To that end, we investigate the maximum applied voltage within ranges of 120–600 kV, to observe the onset of rock fragmentation. We further study the effect of grain size on rock breakage, by comparing fine (granodiorite) and coarse grained (granite) rocks. Lastly, the pore fluid salinity is investigated, since the electric conductivity of the pore fluid is shown to be a governing factor for the electrical conductivity of the modeled system. This study demonstrates that all investigated factors are crucial to the efficiency of rock fragmentation by electropulsing.

Selective weakening of mineralised synthetic particles by high voltage pulses

The phenomena of high voltage pulse (HVP) selective breakage and HVP weakening have been reported separately in the literature, but the relation between the two HVP applications has previously not been investigated. Synthetic particles made of Epirez high strength grout were cast with and without embedded metalliferous minerals of chalcopyrite and pyrite and used in a study of HVP selective breakage and weakening. When metalliferous grains were embedded in the grout, there were added either as a single grain occurrence or as a fine disseminated texture. The HVP products were assessed using the JKRBT breakage characterisation method for the mineralised particles and the barren particles (with no metalliferous minerals contained), respectively. It has been found that the HVP weakening effect mainly occurs in the mineralised particles, with a reduction in particle competence (indicated by the relative change in A × b value) between 172% and 200% for the pyrite fines dispersed synthetic particles, and 70% relative reduction for the single chalcopyrite grain embedded synthetic particles. The barren synthetic particles do not exhibit a statistically significant weakening effect and appear much more competent than the mineralised particles after HVP treatment. This finding suggests that in mineral processing circuit design utilising the HVP technology, benefits associated with HVP weakening on the downstream comminution process would be maximised by combining the HVP pre-concentration and weakening applications, in doing so removing the barren unweakened rocks from the process.

Optical characterization of plasmas produced by concurrent application of laser and high voltage pulses

Laser Induced Breakdown Spectroscopy (LIBS) is a simple, powerful analytic technique that is limited by a relatively low sensibility to detect traces. To improve LIBS sensitivity an option often used consists in applying a second source of excitation such as an electric discharge. This work’s goal is to investigate the interaction of a laser-produced plasma on an aluminum target with a self-triggered electric discharge. The plasma dynamics has been investigated using shadowgraphy, fast photography and the application of narrow band-pass filters to follow the evolution of the ionic and neutral species. Results show that within the initial microseconds, the spatial extent of the laser-produced plasma increases due to the presence of a low density region induced by the spark channel. Furthermore, it was found that the electric arc mainly re-excite the ionic species while the neutral ones remains unaffected.

Collision of ionization waves in long discharge tubes

This research focuses on interaction of ionization waves (IW) generated in long discharge tubes (1 m length and 1.5 cm in diameter) filled with neon or argon under pressure about 1 Torr and, in particular, on simplest case of such interference which is collision of the opposite directed IW of positive polarity. The waves were triggered from two electrodes of the tube by simultaneous application of the same high voltage pulse and propagated toward the tube center until their collision. Space and time stability of the collisions was achieved via decreasing time delay of the initial breakdowns which trigger IW by employment of both memory effect and photo-desorption of wall surface electrons. Significant memory effect occurred for the pulse repetition rate over 100 Hz. Multiple IW transition from the electrode forms specific one-electrode discharge; as a result the problem of IW collision was transformed into the observation of two opposite one-electrode discharges interaction. Patterns of IW interfering were registered via deviation of their kinematic characteristics (x-t diagrams) from ones for non-collided wave. This method shows that two ionization waves travel toward each other with decreasing speeds and subsequent degradation of the emission. An area near the tube center where IWs emission was not detected was considered as the IW suppression zone. The zone width depends on voltage amplitude, gas type and pressure.

Petrophysical variation of coal treated by cyclic high-voltage electrical pulse for coalbed methane recovery

Laboratory experiments and field application of high-voltage electrical pulse (HVEP) technology, a good method for coalbed methane (CBM) enhancement, have achieved great progress. However, previous studies mainly concentrated on the crushing effect of a single pulse on coal, ignoring the influence of multiple cyclic electrical pulses on the pore structure. Besides, the current in electrical breakdown was rarely studied. In this study, the effect of cyclic number on pore variation was investigated, and the mechanism of electrical breakdown was discussed by measuring the current waveform. Moreover, the micro fissure and pore variations of coal before and after electrical breakdown were measured by adopting scanning electron microscopy (SEM) and low temperature liquid nitrogen adsorption (LT-N2A). Under the action of cyclic HVEP, both Linhua (LH) anthracite coal and Hongliu (HL) bituminous coal can be crushed into small pieces. SEM results indicate that the number of cracks increase with the number of cycle. LT-N2A analyses show that the cumulative pore volumes and surface areas of LH and HL coals both increase after electrical breakdown, so does the pore structure fractal dimension, which provides a smoother channel for CBM desorption. Additionally, the great energy instantly injected into the coal could produce huge expansion stress and immediately break the coal from inside. Current waveforms during the breakdown demonstrate that the peak current increase with the number of cycle, whereas the breakdown time decrease with it. This indicates the alteration of electrical properties of coal during the breakdown, which affects the next discharge.

New flatness‐based control of a high‐voltage generator for medical X‐ray applications

This study presents a new flatness-based control scheme for the quantum series–parallel LCC-type resonant converter with output voltage doubler for high-voltage pulse applications, like medical X-ray imaging. Based on a previously derived continuous time model of the system, a flat output of the system model is shown. Moreover, an optimised trajectory planning algorithm with limited resonant current and the controller design are addressed. Details on the experimental set-up and the real-time controller implementation on an FPGA are given. Measurement results show the accuracy of the presented control method.

Optimizing lateral homogeneity of ion-induced surface modifications of non-planar dielectric polyethylene components employing ion fluence simulations and optical measurements of the sp2-dependent reflectivity

Abstract An approach to enhance the durability of artificial joint replacements is to modify the surface of their polymeric bearing material to diamond-like carbon (DLC) by ion-induced polymer-to-DLC-transformation in a plasma-immersion ion implantation process. Due to the dielectric character of the polymer and thus the impossibility of direct application of high voltage pulses to the component, this process requires an additional accelerator electrode above the surface. We here present two useful tools to optimize the geometry of such electrodes. First, we simulate the ions’ trajectories for various electrode geometries and receive the resulting fluence distribution across the surface of the treated part. Second, we introduce a novel optical method to determine non-destructively the local ratio of sp2 hybridized carbon atoms and thus the locally implanted fluence utilizing changes in reflectivity. Combining both tools, we here optimize, by way of example, the geometry of a grid electrode to obtain a homogeneous DLC-modification of a typical hip replacement inlay.

Overcoming sheaths overlapping in a small diameter metallic tube with one end closed and using a high density plasma from a high power pulsed hollow cathode discharge

High voltage sheaths are formed when plasmas are produced by application of high negative voltage pulses to conductive supports or components, as in Plasma Immersion Ion Implantation (PIII) treatments of materials surfaces. For parts with concave shape, as inside metal tubes, these sheaths behave quite differently according to the tube configuration and size, as well as, PIII treatment pressure of operation and pulsing parameters. In this work, an SS304 tube of 1.1 cm internal diameter and 20 cm length was pulsed typically at -0.5 to -2.6 kV, 20 μs pulse length, 500 Hz repetition rate, nitrogen pressure of 5x10-2 mbar and with one side closed configuration. Different currents (between 10 and 30 A) were used to produce plasmas with sheaths that overlapped or not, depending on the currents used. To study these sheath behaviors, a simple plasma diagnostic technique based on a bi-dimensional mapping of the deposition of sputtered materials and by etching via the plasma on a Si wafer target surface, both coming out from the tube, was used. This mapping showed clearly the border line situation between overlapping and non-overlapping sheaths in that small tube which allowed to estimate the plasma density to be around 1011 cm-3 at such a sheath condition, as previously anticipated by Sheridan. Above that border condition, nitrogen PIII was successfully obtained in such a small tube of SS304, producing TiN and Ti2N in samples of Ti6Al4V placed inside the tube, when temperatures higher than 800°C were reached there. Below the border, no significant uptake of nitrogen was possible. Using this type of experimental set-up, it is now possible to explore different hollow cathode behaviors, efficient or high temperature (above 800°C) PIII conditions and also new utilizations of the plasma ejected from the tube.