Single Discharge Event Research Articles

A Novel Deep-Learning Framework to Identify and Locate Single and Multiple Partial Discharge Events

A Novel Deep-Learning Framework to Identify and Locate Single and Multiple Partial Discharge Events

High-speed imaging reveals the dynamics of the initiation and subsequent evolution of a nanosecond discharge propagating along the air–water interface

A nanosecond DBD-like discharge in a coplanar electrode configuration propagating along the water–air interface is an efficient source of reactive species to produce plasma-activated water. In this letter, we report on the mechanism of the discharge onset as well as on further developments over hundreds of nanoseconds. We combined ultrafast optical imaging with electrical characteristics to capture basic morphological imprints of individual discharge phases occurring during a single discharge event with high temporal resolution. We show that during the first nanoseconds, a diffuse bi-directional ionizing avalanche expands over the liquid surface at high speed (>5 105 m s−1). Later, discrete plasma filaments form from the diffuse plasma due to an ionization instability. The filaments, during their subsequent elongation (∼2 105 m s−1), retain the diffuse plasma at both ends. The filaments re-ignite in the same positions on the liquid surface over several successive (mainly capacitive) current pulses (∼1 μs apart), which result from discontinuities in the driving voltage.

Hydrogen Peroxide Production of Individual Nanosecond Pulsed Discharges Submerged in Water of Elevated Conductivity.

The production of hydrogen peroxide (H2 O2 ) is a key parameter for the performance of pulsed discharges submerged in water utilized as advanced oxidation process. So far, any related assessment of the underlying mechanism was conducted for the application of several hundred discharges, which did not allow for a correlation with physical processes. Moreover, the production was rarely investigated depending on water conductivity as one of the most important parameters for the development of submerged discharges. Accordingly, hydrogen peroxide generation was investigated here for individual single discharge events instigated with 100 ns high-voltage pulses in water with three different conductivities and was associated with the discharge development, i. e. spatial expansion and dissipated electrical energy. The approach necessitated the improvement of an electrochemical flow injection analysis based on the reaction of Prussian blue with H2 O2 . Hydrogen peroxide concentrations were quadratically increasing with propagation time and stable for different water conductivities. H2 O2 production per unit volume of a discharge was constant over time with an estimated rate constant of 3.2 mol ⋅ m-1 s-1 , averaged over the crosssectional area of all discharge filaments. However, the individually dissipated energy increased with conductivity, hence, the production efficiency decreased from 6.1 g ⋅ kWh-1 to 1.4 g ⋅ kWh-1 , which was explained by increased resistive losses within the bulk liquid.

Discharge communication study: a realist evaluation of discharge communication experiences of patients, general practitioners and hospital practitioners, alongside a corresponding discharge letter sample

ObjectivesTo develop a programme theory for the intervention of patients receiving discharge letters.DesignWe used a realist evaluation approach and captured multiple perspectives of hospital discharge to refine our previously developed...

The impact of run-of-river dams on sediment longitudinal connectivity and downstream channel equilibrium

Considerable research over the past several decades shows that dams, especially large, flow regulating structures, fragment watersheds and serve to disconnect the normative downstream flux of sediment and nutrients. Less attention has addressed smaller, channel-spanning Run-of-River (RoR) dams that are more commonly distributed throughout watersheds. Taking advantage of a suite of RoR dams in New England (USA), we quantify bedload flux into, through, and beyond the reservoir, and we calculate the residence time of gravel clasts.We used traditional channel surveys to evaluate (dis)equilibrium channel form and develop two equilibrium metrics based on bankfull shear stress and the bankfull Shields parameter. Additionally, we compartmentalize the bankfull channel Shields parameter as a linear combination of bedload and suspended load components to better quantify channel evolution in response to changes in sediment supply. To accomplish these goals, we embedded Radio Frequency Identification (RFID) PIT tags in 791 gravel clasts ranging in size from 15 mm to 81 mm, which were subsequently deployed within and upstream of the impounded reservoirs. Among the 503 tracers that were transported from their deployment location, the median cumulative distance traveled was 30 m and the maximum cumulative displacement during the study period was 758 m. Of the total tagged rocks placed at all five sites, 276 rocks were displaced over the dam, 204 of which spent time in the reservoir between high discharge events; the rest were transmitted through the reservoir and over the dam in a single high discharge event. Among those tracers that spent time in the reservoir prior to transmission over the dam, the average reservoir residence times at the different sites ranged from 19 to 203 days. The median grain sizes of tracers that were transported over the dam were identical to those that moved during the study period and similar to the median grain size of the channel bed. The distribution of virtual velocities of those tracers that moved was approximately log-normal and very broadly distributed over more than six orders of magnitude. An analysis of variance revealed that the distribution of velocities was partitioned into two statistically similar groups; with slower velocities in the two smaller watersheds (13 km2–21 km2) with higher average slopes compared to the larger watersheds (89 km2–438 km2) with lower average slopes. We conclude that RoR dams transmit and trap the upstream sediment supply within the same range of physical conditions that produce mobility and trapping in the river's natural reach-scale morphological units. Because RoR dams are likely not trapping more sediment than is typically sequestered in natural river reaches, these dams do not disconnect the normative downstream flux of sediment nor result in channel morphological disequilibrium downstream of the dam. Reaches below RoR dams have similar geomorphic properties to comparable equilibrium reaches unaffected by dams. However, the minimal effect that small, channel spanning RoR dams have on the morphological equilibrium state of a channel does not suggest that RoR dams have no ecological footprint.

Mechanisms of plasma electrolytic oxidation of aluminum at the multi-hour timescales

AbstractWe present certain novel insights into the processes that occur during the prolonged (several hours) plasma electrolytic oxidation (PEO) of aluminum. Scanning electron microscopy (SEM) equipped with the energy-dispersive spectroscopy option (EDS) was used to study morphologies of the PEO-formed ceramic coating/substrate (C/S) surfaces on aluminum. The morphologies of the oxide layers' cross-sections have also been examined. The plasma electron temperature was calculated from the spectral lines measured by the optical emission spectroscopy (OES). The obtained results demonstrate that during the one single discharge event, a completely new inner oxide layer is being formed at the bottom of the discharge channel. This layer is positioned between the metal substrate and the previous Al2O3 layers. It appears that this new oxide layer, together with the gas trapped in the channel becomes a barrier for the dielectric breakdown that is higher than the original coating layer itself.

Discharge Behavior and Dielectric Breakdown of Oxide Films during Single Pulse Anodizing of Aluminum Micro-Electrodes.

Micro-arc discharge events and dielectric breakdown of oxide films play an important role in the formation process of plasma electrolytic oxidation coating. Single pulse anodization of micro-electrodes was employed to study the discharge behavior and dielectric breakdown of oxide films deposited on aluminum in an alkaline silicate electrolyte. Voltage and current waveforms of applied pulses were measured and surface morphology of micro-electrodes was characterized from images obtained using scanning electron microscope (SEM). A feasible identification method for the critical breakdown voltage of oxide film was introduced. Different current transients of voltage pulses were obtained, depending on applied pulse voltage and duration. In addition, the active capacitive effect and complex non-linear nature of plasma electrolytic oxidation process is confirmed using dynamic electrical characteristic curves. A good correlation between the pulse parameters and shape of discharge channels was observed. Circular opened pores were found to close with increasing potential and pulse width. Finally, the characteristic parameters of a single discharge event were estimated.

Modeling the Impact of Stream Discharge Events on Riparian Solute Dynamics.

The biogeochemical composition of stream water and the surrounding riparian water is mainly defined by the exchange of water and solutes between the stream and the riparian zone. Short-term fluctuations in near stream hydraulic head gradients (e.g., during stream flow events) can significantly influence the extent and rate of exchange processes. In this study, we simulate exchanges between streams and their riparian zone driven by stream stage fluctuations during single stream discharge events of varying peak height and duration. Simulated results show that strong stream flow events can trigger solute mobilization in riparian soils and subsequent export to the stream. The timing and amount of solute export is linked to the shape of the discharge event. Higher peaks and increased durations significantly enhance solute export, however, peak height is found to be the dominant control for overall mass export. Mobilized solutes are transported to the stream in two stages (1) by return flow of stream water that was stored in the riparian zone during the event and (2) by vertical movement to the groundwater under gravity drainage from the unsaturated parts of the riparian zone, which lasts for significantly longer time (> 400 days) resulting in long tailing of bank outflows and solute mass outfluxes. We conclude that strong stream discharge events can mobilize and transport solutes from near stream riparian soils into the stream. The impact of short-term stream discharge variations on solute exchange may last for long times after the flow event.

Luminous phase of nanosecond discharge in deionized water: morphology, propagation velocity and optical emission

We employed the techniques of time-resolved intensified charge-coupled device (ICCD) microscopy and spectroscopy to register basic morphologic and emission fingerprints of micro-discharges produced in deionized water. Fast rise-time positive high-voltage pulses (full width at half maximum of ∼7 ns and amplitude of ∼100 kV) in a point-to-plane electrode geometry produced micro-discharges, either periodically or in a single-pulse regime with the energy of ∼0.1 J dissipated during a single discharge event. Time resolved ICCD images evidence typical streamer-like branched filamentary morphology. Luminous discharge filaments show very fast and approximately linear initial expansion of the length with propagation velocity of ∼2 × 105 m s−1. When the HV pulse reaches its maximum value, the length of the primary luminous filaments reaches ∼1.3 mm. After initial expansion, the length of luminous filaments collapses and can be characterised by velocity of ∼1.9 × 104 m s−1. The first collapse is followed by a second slightly slower expansion, which is driven by the arrival of a reflected HV pulse, and which can be roughly approximated by propagation velocity of ∼1.5 × 105 m s−1. The second collapse (occurring after second expansion) proceeds at a nearly identical velocity compared with the first one. By combining two ICCD based techniques, we have been able to associate, for the first time ever, characteristic emission spectra with the most important phases of the micro-discharge development. The UV–vis-NIR emission spectra show a broad-band continuum evolving during the first expansion and collapse, followed by the well-known HI/OI atomic lines occurring together with continuum emission during the second expansion and collapse. We conclude that bound–free and free–free radiative transitions are basic emission characteristics of the nanosecond discharge initiation mechanism in liquid water which does not involve the formation of vapour bubbles.

Evaluating Oil Spill Risks through Stochastic and Deterministic Trajectory Modeling

Oil spill risks associated with oil and gas exploration and production are changing as industry moves to deeper water. Computer-based modeling is typically used to quantify the fate and trajectory of sub sea releases (e.g., well blowouts). Stochastic modeling has become common as computational resources have grown, allowing for a large number of combinations of met ocean parameters to be evaluated. Simulating many potential realizations of a single discharge event allows for the calculation of spatially varying probabilities of oiling due to natural variability in the prevailing wind and current, but this needs to be treated separately from the likelihood of the sub sea release occurring to appropriately evaluate the oil spill risks of the offshore activity. Some industry guidance explicitly recognizes that the likelihood of a discharge event occurring is independent of the natural variability of the environmental setting and correctly treat these items as statistically independent; however, this distinction is sometimes lost in practice. In these instances, the resulting oil spill risk assessments may inadvertently be based on highly improbable combinations of release conditions and met ocean forcing. A transparent and robust risk-based oil spill risk assessment needs to explicitly communicate the differences between the likelihood of a release event occurring and the probabilities of the potential trajectories that could result under different combinations of met ocean parameters. This poster uses a hypothetical deepwater blowout to illustrate how stochastic and deterministic modeling can be combined to characterize the probability distribution associated with the (variable) potential consequence of a discharge event. The proposed modeling strategy allows for the set of trajectories generated by stochastic modeling to be ranked based on various metrics of interest (e.g., volume of water column swept, area of surface slick, or volume of oil ashore) so the distribution of potential consequence can be evaluated. Following recently industry guidance (IPECA-OGP), it is suggested that the most probably deterministic trajectory be paired with statistical analysis, although the strategy allows for an identifiable amount of conservatism to be incorporated into the analyses by selecting one or more other trajectories for detailed impacts assessment.

Single Defect Discharge Events in Vertical-Nanowire Tunnel-FETs

In this paper, we investigate the single defect discharge events in Ge-source n-type vertical nanowire tunnel field effect transistors, by monitoring the relaxation phase which follows bias temperature instability (BTI) stress. Threshold voltage shift induced by single discharge events follows a bimodal Weibull distribution, with the location parameter of the second mode being significantly higher than the first one. Both modes are temperature independent. Based on TCAD simulations, we propose that the second mode is associated with defects located at the source/channel junction close to the channel/oxide interface, while the first mode is ascribed to oxide traps far from the source/channel junction. Although present in smaller numbers, such traps with a larger average impact on the device characteristics are expected to dominate the BTI-induced variability in a large population of nanoscale devices for realistic applications.

Single discharge events increase reactive efficiency of the hyporheic zone

AbstractIn this study, we investigate the impact of single stream discharge events on water exchange, solute transport, and reactions in the hyporheic zone below a natural in‐stream gravel bar. We set up a reactive transport groundwater model with streamflow scenarios that vary by event duration and peak discharge. A steady ambient groundwater flow field is assumed that results in losing, neutral, or gaining stream conditions depending on the stream stage. Across the streambed dissolved oxygen, organic carbon, and nitrate are transported into the subsurface. Additional nitrate is received from upwelling groundwater. Aerobic respiration and denitrification are simulated for scenarios with different stream solute concentrations. Results show that hyporheic exchange flux, solute transport, and consumption increase during events. However, their intensities depend highly on the interplay between event characteristics and ambient groundwater conditions. During events where reversals in the hydraulic gradient occur stream water and solutes infiltrate deeper into the aquifer where they have more time to react. For those events, the reactive efficiency of the hyporheic zone (solute consumption as fraction of influx) for aerobic respiration and denitrification is up to 2.7 and 10 times higher compared to base flow conditions. The fraction of stream nitrate load consumed in the hyporheic zone increases with stream discharge (up to 150 mg/m2/h), but remains below the value under base flow conditions for weak events. Events also increase denitrification of groundwater borne nitrate, but groundwater nitrate flux to the stream decreases by up to 33% due to temporary gradient reversals.

The mechanism of evolution of microdischarges at the beginning of the PEO process on aluminum

Abstract In this study, we present the results of investigation of plasma electrolytic anodization of aluminum by means of different experimental techniques, in few first minutes of the process. Scanning electron microscopy equipped with X-ray energy dispersive spectroscopy was used to study the aluminum oxide coating morphology, microstructure and composition as well as cross-sections of the obtained coating. The mechanism of evolution of microdischarges at the beginning of the plasma electrolytic anodization process is proposed. Our results indicate that during a single discharge event, new inner oxide layer is formed at the bottom of discharge channel, between the metal substrate and the Al 2 O 3 layer. That new oxide layer and the gas that remains in the channel seem to present a higher barrier for dielectric breakdown then the original coating layer.

Numerical Modeling of Electrical Discharges in Long Air Gaps Tested With Positive Switching Impulses

The numerical modeling of electrical discharges occurring in atmospheric air has been in continuous development during the past decades in different fields, such as high-voltage techniques and lightning protection. Different methodologies have been proposed to represent the physical phenomena taking place at a single full discharge event, departing both from experimental and theoretical approaches. The implementation of these methodologies in numerical routines combined with the use of numerical methods to determine the electric potential distribution permits the creation of models whose predictions closely agree with the real case situations, where electrode arrangements might have nonsymmetric geometries. In this paper, we present an improved version of a simulation methodology for representing electrical discharges in long air gaps. This simulation methodology includes new elements like: 1) the 3-D leader channel tortuosity based on laboratory experimental measurements and 2) two new methods for the estimation of the electric charge contained in the so-called leader-corona region based on the electrostatic potential of fictitious potential rings representing the active region in front of the leader tip. Results from the simulation were compared with experimental records and a reasonably good agreement is found between them.

Ignition modes of nanosecond discharge with bubbles in distilled water

Here, we present the microscopic physical characteristics of nanosecond discharges with an array of bubbles in distilled water. In particular, applying a single high-voltage pulse, four delayed intensified charge-coupled device cameras successfully visualized four successive images during a single discharge event. We identified three distinctive modes of ignition inside a bubble, depending on the relative location of the bubble with respect to pin-to-hollow needle electrodes when a single bubble was located in an inter-electrode gap of 1 mm: anode-driven ignition, cathode-driven ignition, and co-ignition near both electrodes. Anode- and cathode-driven ignitions evolved into either a complete propagation of the streamer or an incomplete propagation, which were limited in location by proximity to an ignition location, while co-ignitions consistently showed complete propagation. When we increased the gap to 2 mm to accommodate multiple bubbles in the gap, an ignited bubble near the cathode was able to cause the ignition of an upper adjacent bubble. Bubble–bubble interface zones can also be spots of ignition, such that we observed simultaneous co-ignitions in the zones of bubble–bubble interfaces and near electrodes with triple bubbles. We compared the experimental results of discharge propagation with different ignition modes between Ar, He, and N2 bubbles. In addition, numerical simulations for static electric fields reasonably supported observed ignition behavior such that field intensity was locally enhanced.

Features of the Energy Parameters and the Composition of the Ion Flow From the Plasma at the Spark Stage of Vacuum Discharge

The mass-energy spectra of the ion flow from the plasma of a 300 kV, 200-ns vacuum discharge are analyzed. The composition of the anomalous accelerated ion flow is compared for the different values of the discharge gap spacing. The energy distributions for the ion species are obtained in single discharge events together with the relevant current and voltage waveforms synchronized with each other. It is revealed that the peak energy values in the energy distributions closely correspond, with significant probability, to the voltage values associated with the points in time at which bursts appear in the current waveform. Estimates of the coefficient of correlation between these quantities are obtained.

The Structure of Nanosecond Repetitively Pulsed Spark Discharges in Air

Nanosecond repetitively pulsed (NRP) spark discharges have been generated in room-temperature air at atmospheric pressure. Single-shot image sequences of NRP spark discharges show that the path of the spark discharge channel can change with each pulse as well as during a single pulse, suggesting that several filaments can be generated within a single discharge event.

Nanosecond Pulsed Discharge Phenomenology in Micrometer-Sized Radially Confined Air Gap

Geometry effects on nanosecond-scale pulsed corona discharges propagating in rectangular glass tubes are reported in this paper. Both the section and thickness of the tubes are the parameters which are used to investigate the discharge phenomenology. Three picosecond high-speed ICCD cameras are used to derive the propagation velocities from a single discharge event. Propagation is significantly speeded up in radially highly confined gaps and promoted close to edges. Inception of weak discharges along the tubes can be observed.

An Investigation of Magnetic-Field-Assisted Material Removal in Micro-EDM for Nonmagnetic Materials

Previous magnetic-field-assisted microelectrical discharge machining (μ-EDM) techniques have been limited to use with magnetic materials. Therefore, a novel process has been developed and tested to improve material removal rate in magnetic-field-assisted μ-EDM for nonmagnetic materials. The workpiece electrodes were oriented to promote directionality in the current flowing through the workpiece, while an external magnetic field was applied in such a way as to produce a Lorentz force in the melt pool. Single-discharge events were carried out on nonmagnetic Grade 5 titanium workpieces to investigate the mechanical effects of the Lorentz force on material removal. Erosion efficiency, melt pool volume analysis, plasma temperature, electron density, and debris field characterization were used as the response metrics to quantify and explain the change in material removal with the applied Lorentz force. By orienting the Lorentz force to act in a direction pointing into the workpiece surface, volume of material removed was shown to increase by up to nearly 50%. Furthermore, erosion efficiency is observed to increase by over 54%. Plasma temperature is unaffected and electron density shows a slight decrease with the addition of the Lorentz force. The distribution of debris around the crater is shifted to greater distances from the discharge center with the Lorentz force. Taken together, these facts strongly suggest that the Lorentz force process developed produces a mechanical effect on the melt pool to aid in increasing material removal. The application of the Lorentz force is not found to negatively impact tool wear.

Hydrodynamics and sediment-transport in the nearshore of Poverty Bay, New Zealand: Observations of nearshore sediment segregation and oceanic storms

Nearshore regions act as an interface between the terrestrial environment and deeper waters. As such, they play important roles in the dispersal of fluvial sediment and the transport of sand to and from the shoreline. This study focused on the nearshore of Poverty Bay, New Zealand, and the processes controlling the dispersal of sediment from the main source, the Waipaoa River. Hydrodynamics and sediment-transport in water shallower than 15 m were observed from April through mid-September 2006. This deployment afforded observations during 3–4 periods of elevated river discharge and 5 dry storms. Similar wind, river discharge, wave, current, and turbidity patterns were characterized during three of the wet storms. At the beginning of each event, winds blew shoreward, increasing wave heights to 2–3 m within Poverty Bay. As the cyclonic storms moved through the system the winds reversed direction and became seaward, reducing the local wave height and orbital velocity while river discharge remained elevated. At these times, high river discharge and relatively small waves enabled fluvially derived suspended sediment to deposit in shallow water. Altimetry measurements indicated that at least 7 cm was deposited at a 15 m deep site during a single discharge event. Turbidity and seabed observations showed this deposition to be removed, however, as large swell waves from the Southern Ocean triggered resuspension of the material within three weeks of deposition. Consequently, two periods of dispersal were associated with each discharge pulse, one coinciding with fluvial delivery, and a second driven by wave resuspension a few weeks later. These observations of nearfield sediment deposition contradict current hypotheses of very limited sediment deposition in shallow water offshore of small mountainous rivers when floods and high-energy, large wave and fast current, oceanic conditions coincide. Consistently shoreward near-bed currents, observed along the 10 m isobath of Poverty Bay, were attributed to a combination of estuarine circulation, Stokes drift, and wind driven upwelling. Velocities measured at the 15 m isobath, however, were directed more alongshore and diverged from those at the 10 m isobath. The divergence in the currents observed at the 10 and 15 m locations seemed to facilitate segregation of coarse and fine sediment, with sand transported near-bed toward the beach, while suspended silts and clays were exported to deeper water.