Electric Field Changes Research Articles

Consistent dust electrification from Arabian Gulf sea breezes

The Arabian Gulf region experiences regular thermally driven sea breeze circulations which occur all year round, penetrating hundreds of kilometres inland. As a sea breeze front moves inland, substantial electric fields are generated by separation of charged desert dust. In the first surface electric field measurements made in the United Arab Emirates (UAE), consistent and repeatable substantial electric field changes with magnitudes up to 7 kV m−1 have been detected at Al Ain (170 km from the western coast), during 80 separate sea breeze events in 2018. Every sea breeze frontal passage shows the same characteristic signature of a transient maximum peak in electric field lasting tens of minutes. Electric field changes during these events were always negative (i.e. enhancing the existing negative ‘fair weather’ electric field), in contrast to many other reported observations in dust storms in which conditions were less repeatable. The regular and substantial dust electrification found demonstrates that accurate representation of dust in climate and weather models requires electrical effects to be addressed, both in the generation process, and by considering aggregates in radiative transfer calculations as electrically aligned rather than randomly ordered. Furthermore, satellite aerosol retrievals are affected by the changed attenuation of electromagnetic radiation when dust particles are charged, for which corrections may be needed.

Efficiency droop in green InGaN/GaN light emitting diodes: Degradation mechanisms and initial characteristics

This paper describes a comprehensive analysis of the degradation mechanisms of green InGaN based high-power LEDs. The combination of electrical, optical and thermal measurement allows a separation of the degradation mechanisms and their influence on the performance of the devices. The results show that the LEDs have parasitic diodes in their initial state, which influence increases over the aging period. In addition, the recombination coefficients are calculated using the ABC model, which show an increase in the non-radiative recombination coefficients (ASRH and C) during stress time. The degradation causes a current-dependent decrease in the external quantum efficiency. Furthermore, a shift of the peak wavelength can be observed, which is due to a change of internal electric fields as well as to the increase of the Shockley-Read-Hall coefficient ASRH.

Electromechanical buckling analysis of boron nitride nanotube using molecular dynamic simulation

In this paper, the effect of electric field on axial buckling of boron nitride nanotubes is investigated. For this purpose, molecular dynamics simulation and continuum mechanics are used for the first time simultaneously. In molecular dynamics simulation, the potential between boron nitride atoms is considered as Tersoff and Timoshenko beam theory is used in continuum mechanics. In this paper, buckling of zigzag and armchair boron nitride nanotubes are investigated. Here, the effects of the electric field and the length of the boron nitride nanotube on the critical load are investigated and it is shown that the effect of the electric field is different with respect to the arrangement of atoms in the boron nitride nanotubes. In fact, the electric field creates axial and torsional loads on the zigzag and armchair nanotube, respectively. Axial buckling of the zigzag nanotube is dependent on the electric field, whereas in the armchair nanotubes, the electric field changes have no effect on the axial buckling. To better understand the impact of the electric field on axial buckling, these results are compared with the continuum mechanics.

Constraints on Recoil Leader Properties Estimated from X‐ray Emissions in Aircraft‐Triggered Discharges

AbstractDuring Airbus aircraft campaigns flying into thunderstorms in 2014–2016, X‐rays were observed during two stages of aircraft‐triggered lightning: nanosecond pulses of X‐rays associated with negative leader steps and bursts of X‐rays during recoil events. This work will focus on the observations of X‐ray bursts associated with recoils. Recoils are observed as microsecond‐fast changes in the local electric field, associated with large currents passing through the aircraft, and are found to sometimes be associated with bursts of X‐rays. From over 200 aircraft‐triggered lightning strikes, 54 recoil events were found to be associated with microsecond bursts of X‐rays. The majority of the bursts consist of 1–3 X‐ray pulses, with some bursts containing as many as 29 X‐ray pulses. We compare the observed superposed X‐ray spectrum with modeled spectra using a GEANT4 model of the detector and aircraft, to determine the source potential needed to accelerate the electrons that produce the observed X‐rays. A model of the recoil leader was made to determine the gap distance and gap potential between the recoil leader and the aircraft. From the modeling, we determine a solution space for the gap and leader lengths where the gap length is constrained by the observed minimum and maximum times between the onset of the X‐ray pulses and the onset of the current pulses detected at the aircraft (1 to 93 m). We also find two constraints from the fitting of the modeled spectra to the superposed spectrum, limiting the leader length to between 1 and ∼240 m.

Equatorial and low-latitude ionospheric TEC response to CIR-driven geomagnetic storms at different longitude sectors

In this study the response of ionospheric F-region to 18–21 September 2014, 19–24 January 2016, and 07–10 March 2016 CIR-driven storms in the equatorial and low-latitude region of America, Africa, Asia, and Pacific sectors are investigated. TEC data obtained from the Global Navigation Satellite System (GNSS) receivers, located in the four longitude sectors and electron density (Ne) measurements obtained from Swarm-A satellite were used. The storm time behavior of TEC was analyzed by computing its deviation from quiet monthly median TEC (ΔTEC). The rate of change of TEC index (ROTI) and the relative electron density perturbation (ΔNe/Ne) derived from GPS-TEC and Swarm-A, respectively, were used as ionospheric irregularity proxies. In this study, we have also analyzed the ionospheric current disturbances during the storm events using ground-based magnetic data. The result revealed that significant nighttime positive ionospheric storm reaching about 284% (Africa, nklg), 115% (Africa, dakr), and 191% (Pacific, naur) was observed during the storm main phase 19 September 2014, 20 January 2016, and 06 March 2016, respectively. This could be associated with oscillation in the IMF Bz and minimum value in ionospheric current disturbance (Diono). Nighttime negative ionospheric responses were also observed in the American sector during the storm main phase of 18–21 September 2014 and 19–24 January 2016 and in the Asian sector during 18–21 September 2014 events, possibly due to the combined effects of over-shielding/disturbance dynamo electric field and neutral composition change. During the storm recovery phases (21–23 January 2016, 07–10 March 2016), significant positive ionospheric storm were also noticed. The occurrence of ionospheric irregularities was observed over the equatorial and low-latitude region of America and Africa during the main phase of 18–21 September 2014, 19–24 January 2016, and 05–10 March 2016 storm events, possibly related with the enhancement in the zonal electric field observed during dusk period, when oscillation in IMF Bz exists. During main phase of the storms, while the occurrence of ionospheric irregularities over Asian and Pacific longitude sectors are suppressed, it frequently occurs over the American longitude sector. Postsunset behavior of plasma density irregularities observed by Swarm satellites is consistent with the ground-based observation of TEC fluctuations.

Effects of Waveguide Position on Electric Field and Temperature Profile in Natural Rubber Gloves during Vulcanization Process Using Microwave Energy

Natural rubber gloves (NRG) become a broader industry with fierce competition and demands. The vulcanization process is the most important and takes the longest time in the cycle period of the NRG manufacturing process, so it becomes of paramount importance to improve this process. The purpose of this research is to experimentally and computationally study the characteristics of the electric field as well as temperature profile in NRG during the microwave vulcanization process. The effects of position of waveguide placement are investigated for nine different positions. The experiment of NRG microwave vulcanization is performed for temperature distribution measurement. Three-dimensional models of NRG and microwave oven are considered. Finite element method (FEM) is utilized to solve a mathematic model of the transient Maxwell’s equation coupled with the transient heat transfer equation in order to determine the electric field and temperature profile via computer simulation. The computer simulation results are validated against the experimental results. The validation confirms that the computational model is able to represent the practical transport phenomena in NRG with high accuracy. The outcomes clearly reveal that the position of waveguide effects on the electric field as well as temperature profile in NRG during the microwave vulcanization process. The positioning of waveguides on both the front and backsides on the opposite side of the microwave oven provides higher intensity electric field and higher temperature profile than the positioning of waveguides in the middle of both the front and the backsides of the microwave oven. In addition, the middle backside is the appropriate position for waveguide in which NRG is uniformly dry and not burnt or overheated. However, it is found that there is no direct relationship between the electric field and temperature changes. This research guides to essential aspects of the design of NRG vulcanization to improve the efficiency of microwave and heat delivering along with other heating systems to heat any sorts of material.

Lightning observations using broadband VHF interferometer and electric field measurements

A broadband radio interferometer for locating lightning emissions was built and deployed at the high-altitude research station on Mount Aragats (Armenia). The instrument operates in the frequency range from 24 to 78 MHz and employs three identical broadband flat-plate antennas which are located in the horizontal plane and form two orthogonal baselines of 13 m length. The time differences of arrival of the signals at pairs of antennas determined from the peak of the cross-correlation function are used to measure the azimuth and elevation angles of the radiation source as a function of time. This paper describes the operation of the interferometer and reports observations of lightning flashes complemented by synchronous measurements of fast wideband electric field waveforms and changes in the near-surface electrostatic field. Combined analysis of these data makes it possible to identify the type of lightning discharge. The capability of the system to classify lightning types is demonstrated by example observations of an intracloud and a cloud-to-ground lightning flashes.

Plasmonic nanostructures in photodetection, energy conversion and beyond

Abstract This review article aims to provide a comprehensive understanding of plasmonic nanostructures and their applications, especially on the integration of plasmonic nanostructures into devices. Over the past decades, plasmonic nanostructures and their applications have been intensively studied because of their outstanding features at the nanoscale. The fundamental characteristics of plasmonic nanostructures, in particular, the electric field enhancement, the generation of hot electrons, and thermoplasmonic effects, play essential roles in most of the practical applications. In general, these three main characteristics of plasmonic nanostructures occur concomitantly when electromagnetic waves interact with plasmonic nanostructures. However, comprehensive review investigating these three main effects of plasmonic nanostructures simultaneously remains elusive. In this article, the fundamental characteristics of plasmonic nanostructures are discussed, especially the interactions between electromagnetic waves and plasmonic nanostructures that lead to the change in near-field electric fields, the conversion of photon energy into hot electrons through plasmon decay, and the photothermal effects at the nanoscale. The applications, challenges faced in these three areas and the future trends are also discussed. This article will provide guidance towards integration of plasmonic nanostructures for functional devices for both academic researchers and engineers in the fields of silicon photonics, photodetection, sensing, and energy harvesting.

Contactless Strain Sensor Using Electret Technology for Highly Sensitive Stretch-Based Applications

The detection of mechanical stretching is usually based on piezoresistive effect made up of piezoelectric material. Here, we report a novel approach of autonomous contactless stretch sensor for detection of varying electric field based on electret technology. The present work proposes a novel approach that detects low-noise with high sensitivity for various stretch-based applications. Nanoparticle filled thin-film polymeric membrane are activated by corona injection to trap the charges and form a permanently charged electret and the contactless fixed electrode pair continuously monitors the change in electric field exerted by the tensile strain/deformation on the polymeric membrane. The sensor detects a peak output response of 4.7 V under 20% cyclic tensile strain with a sensitivity of 56 mV/%strain. By considering these merits of simple and scalable fabrication, outstanding performance and robust characteristic, we believe the autonomous contactless stretch sensor can open great opportunities not only for low-noise sensing/detection applications but can contribute to multitude large-scale applications such as intrusion detectors, microphones, pressure monitoring, sensing for security and safety applications.

Experimental study on the falling and coalescence characteristics of droplets under alternating electric fields

Droplet–interface collision coalescence is an important pattern of phase separation, especially for removing water from water-in-oil emulsions in electrostatic dehydrators. Deformation, migration to the interface, and coalescence of droplets driven by electric fields are fundamental processes but have not been completely understood. In this work, we studied the influences of three typical alternating current or pulsed electric fields on these dynamic processes of a single water droplet falling to the planar oil-water interface. The results depicted that the falling droplet oscillated in both shape and trajectory in an electric field. Specifically, the deformation of droplets should be able to follow the change of electric fields, while the migration may lag behind that. The pattern of droplet deformation matched the electric field waveform, and the frequency had different multiple relationship with the electrical frequency in the electric field of different waveforms. Moreover, the increment of electrical frequency could reduce the degree of droplet deformation and extend the falling time required for droplets to reach the interface. When the droplet coalesced with the interface, secondary droplets were observed if the applied electric field strength exceeded a critical value (Ecrit), detrimental to dehydration efficiency. Ecrit varied from different electric field waveforms and increased with elevated electrical frequencies. Compared to sinusoidal AC and square electric fields, the values of Ecrit in a pulsed DC electric field were highest in the experiments which could be more effective in suppressing the formation of secondary droplets. These findings will be useful for designing high efficient electro-dehydration plants.

Electromechanical coupling in the hyperpolarization-activated K+ channel KAT1.

Voltage-gated potassium (Kv) channels orchestrate electrical signaling and control cell volume by gating in response to either membrane depolarization or hyperpolarization. Yet, while all voltage-sensing domains transduce transmembrane electric field changes by a common mechanism involving the outward or inward translocation of gating charges1–3, the general determinants of channel gating polarity remain poorly understood4. Here, we suggest a molecular mechanism for electromechanical coupling and gating polarity in non-domain-swapped Kv channels based on the cryo-EM structure of KAT1, the hyperpolarization-activated Kv channel from Arabidopsis thaliana. KAT1 displays a depolarized voltage sensor, which interacts with a closed pore domain directly via two interfaces and indirectly via an intercalated phospholipid. Functional evaluation of KAT1 structure-guided mutants at the sensor-pore interfaces suggests a mechanism in which direct interaction between the sensor and C-linker hairpin in the adjacent pore subunit is the primary determinant of gating polarity. We suggest that a ~5–7 Å inward motion of the S4 sensor helix can underlie a direct-coupling mechanism, driving a conformational reorientation of the C-linker and ultimately opening the activation gate formed by the S6 intracellular bundle. This direct-coupling mechanism contrasts with allosteric mechanisms proposed for hyperpolarization-activated cyclic nucleotide-gated (HCN) channels5, and may represent an unexpected link between depolarization and hyperpolarization-activated channels.

Luminescence at low temperature in pure ZnO phosphors

In this paper, samples of pure ZnO were prepared through solid-state chemical reaction, and optical spectral properties were investigated at low temperature. It was found that the strong broad band emission was shifted to the blue side with increase of temperature. It is tentatively attributed to the change of local electric field from electric dipoles, orientation of which is sensitive to temperature. The ultraviolet sharp lines observed at low temperatures are assigned to bound excitons and their phonon replicas.

Electric field change and VHF waveforms of Positive Narrow Bipolar Events in Mississippi thunderstorms

Positive Narrow Bipolar Events (+NBEs) in Mississippi thunderstorms were studied using fast antennas (FA, bandwidth 16 Hz - 2.6 MHz) and VHF antennas (Log-RF, bandwidth 186–192 MHz). The waveform characteristics of 201 positive NBEs were determined using both sensors. The +NBEs were classified in two ways: by FA waveform into Types A-D and by +NBE occurrence relative to other lightning events into three groups called Isolated, Not-Isolated, and INBE. (An INBE initiates an intracloud flash.) The FA waveform properties of 188 positive NBEs were mainly in reasonable agreement with previous studies. The VHF waveform properties of +NBEs have not been studied previously. The VHF powers of 201 positive NBE ranged from 0.1–88.4 kW with an average value of 7.8 kW. Types C and D positive NBEs tended to be more energetic (average VHF powers of 9.2 and 13.2 kW) than Types A and B (average powers of 1.9 and 4.0 kW). The INBE group of +NBEs had a larger range of VHF powers (0.2–88.4 kW) than the combined power range of the Not-Isolated and Isolated groups (0.1–26.7 kW). The INBE group also had a larger average peak power (9.9 kW) than the Not-Isolated and Isolated Groups (4.0 and 8.7 kW, respectively). However, 53% of INBEs had peak VHF power < 5 kW, so an INBE does not require a large power to initiate an intracloud flash. For 90% of the 201 positive NBEs the magnitude of the time difference between the FA peak amplitude and the Log-RF peak power was ≤2 μs, but the FA peak amplitude showed almost no correlation with the Log-RF peak power.

Influence of Hot-Carriers on the On-State Resistance in Si and GaAs Photoconductive Semiconductor Switches Working at Long Pulse Width**Supported by the Rector’s Fund of China Academy of Engineering Physics (Grant No. YZJJLX2016002), and the National Natural Science Foundation of China (Grant Nos. 61504127 and U1530128).

We demonstrate that the transport of hot carriers may result in the phenomenon where an oscillated output current appears at the waveforms in a high-power photoconductive semiconductor switch (PCSS) working at long pulse width when the laser disappears or the electric field changes. The variational laser and electric field will affect the scattering rates of hot carriers and crystal lattice in high-power PCSS, and the drift velocity of hot carriers and also the on-state resistance will be changed. The present result is important for reducing the on-state resistance and improving the output characteristics of high-power Si/GaAs PCSS.

Piezostrain control of anomalous Hall resistivity of [Co/Pt]3–Pb(Mg1/3Nb2/3)O3–PbTiO3 heterostructure

The anomalous Hall effect (AHE) in [Co/Pt]3 thin films with perpendicular magnetic anisotropy grown on Pb(Mg1/3Nb2/3)O3–Pb0.7Ti0.3O3 substrates is investigated under application of different electric fields at various temperatures. As the sweeping mode of application of the electric field changes from symmetric bipolar to asymmetric bipolar, the butterfly-like behavior of the resistivity vs electric field curves is converted into loop-like behavior, which is attributed to the piezostrain effect. The anomalous Hall conductivity σAH vs longitudinal conductivity σxx characteristics at the corresponding temperatures indicate two AHE mechanisms, which include the side jump and/or intrinsic mechanisms. In addition, the σAH–σxx curve shows obvious changes under different electric fields, which means that the AHE can be mediated. These results are highly important for further understanding of the mechanism by which the electric field can control the AHE.

Observation of the Whole Discharge Process During a Multi-stroke Triggered Lightning by Continuous Interferometer

The discharge process is often discussed in the lightning physics. VHF (very high frequency) observations play an important role in studying lightning discharge processes, because they show where air breakdown occurs. Triggered lightning flashes are ideal research objects, because they are generated in a fixed time and place. Regular experiments of triggering lightning have been conducted by Chinese Academy of Meteorological Sciences since 2006, and 189 lightning flashes are triggered successfully. Besides regular observations, such as fast/slow antenna, channel-based current and high-speed video, the continuous interferometer (CINTF) is developed and deployed at the site for triggered lightning after 2016 in order to observe detailed discharge processes. The CINTF can provide high-precision location with time resolution of around 1 μs.A multi-stroke triggered lightning with 8 return strokes is observed by a self-developed lightning continuous interferometer during Guangdong Comprehensive Observation Experiment on Lightning Discharge on 11 June 2019. The whole discharge processes, including precursor current pulse, initial precursor current pulse, initial continuous current and return strokes, last for about 1600 ms. The channel-based current, electric field change and radiation source positions are obtained. CINTF results show that the radiation signal generated from discrete precursor current pulse with a minimum value of about 8 A can be detected. The average transfer charge of initial precursor current pulse is twice as much as that of the precursor current pulse. During the initial continuous current stage after continuously developing of the upward positive leader, the obviously forward channel extension is the main discharge form at the beginning, and then the extension can be accompanied by discontinuously backward propagation, and recoil leader often occurs in the following stage. M-component in the ICC stage is caused by two discharge processes:Forward positive streamer (or leader) or recoil leader generated in the existing channel. Multi recoil leaders occur during the whole M process, which maintain M discharge. The main discharge form in return stroke stage is recoiling discharge. There are multi recoil leaders before return strokes, however, most of them cannot develop to ground, keep as an attempted leader until the last leader-stroke occurs. Adjacent two strokes with a short duration time of 4.5 ms have the same optical channel in optical images, but they are obviously different in development paths, which lead to a very short RS interval.

Ionospheric TEC disturbances over China during the strong geomagnetic storm in September 2017

From September 7 to 8, 2017, a G4-level strong geomagnetic storm occurred, which seriously impacted on the Earth’s ionosphere. In this work, the global ionospheric maps released by Chinese Academy of Sciences are used to investigate the ionospheric responses over China and its adjacent regions during the strong storm. The prominent TEC enhancements, which mainly associated with the neutral wind and eastward prompt penetration electric field, are observed at equatorial ionization anomaly crests during the main phase of the storm on 8 September 2017. Compared with those on 8 September, the TEC enhancements move to lower-latitude regions during the recovery phase on 9 September. A moderate storm occurred well before the start of the strong storm causes similar middle-latitude TEC enhancements on 7 September. However, the weak TEC depletion is observed at middle and low latitude on 9–10 September, which could be associated with the prevailing westward disturbance electric field or storm-time neural composition changes. In addition, the storm-time RMS and STD values of the ionospheric TEC grids over China increase significantly due to the major geomagnetic storm. The maximum of the RMS reaches 12.0 TECU, while the maximum of the STD reaches 8.3 TECU at ~04UT on 8 September.

Dynamics of surface charge and electric field distributions on basin‐type insulator in GIS/GIL due to voltage polarity reversal

In this study, a simulation model of surface charge accumulation has been established. The model considers three accumulation ways, i.e. electrical conduction within the gas, through insulator volume and along the insulator surface. The generation, diffusion, drift and recombination of charge carriers are also taken into account. Based on it, the influence of polarity reversal, reversal time on surface charge and electric field distribution on a basin-type insulator are studied. The polarity of the surface charges and the direction of the electric field change after the voltage polarity reversal. When the preload voltage is equal to reversal voltage, the surface charge and the electric field distributions at steady state before and after voltage polarity reversal are all the same with opposite sign, and not affected by the reversal time. However, the time to reach the steady state varies with different reversal time. The steady-state surface charge and electric field increased with the rise of reversal voltage. The transient normal and tangential electric field would not exceed the value of the steady state, which means voltage polarity reversal has no additional influence on insulation performance. This research can provide guidance to the design and manufacture of DC GIS/GIL.

On the Transition From Initial Leader to Stepped Leader in Negative Cloud‐to‐Ground Lightning

AbstractHigh‐speed video and electric field change data are used to describe the first 5 ms of a negative cloud‐to‐ground flash. These observations reveal an evolution in character of the luminosity and electric field change pulses as two branches of the leader separately transition from initial leader to propagating as a negative stepped leader (SL). For the first time reported, there is evidence of weak luminosity coincident with the initiating event, a weak bipolar pulse 60 μs prior to the first initial breakdown (IB) pulse. During the IB stage, the initial leader advances intermittently at intervals of 100–280 μs, in separate light bursts that are bright for a few 20‐μs frames and are time coincident with IB pulses. In the intervals between IB pulses, the initial leader is dim or invisible during the earliest 1.8 ms. Within 2 ms, the leader propagation begins transitioning to an early SL phase, in which the leader tip advances at more regular intervals of 40–80 μs during relatively dim and brief steps which are coincident with SL pulses having short duration, small amplitude, and typically unipolar waveform. These data indicate that when the entire initial leader length behind the lower end begins to remain illuminated between bursts, the propagation mode changes from IB bursts to SL steps, and the IB stage ends. The results support a hypothesis that the early initial leader development occurs in the absence of a continuously hot channel, thus the initial leader propagation is physically unlike the self‐propagating SL advance.

The Energy Landscape of Voltage Sensing in Ci-VSP

The Ciona intestinalis voltage-sensing phosphatase (Ci-VSP) is a membrane associated phosphatidylinositol lipid phosphatase. The enzymatic activity of the cytoplasmic phosphatase domain is directly regulated by changes in the transmembrane electric field through conformational rearrangements at the voltage-sensing domain (VSD). Ci-VSD shares high sequence and structural similarity with the VSD of voltage-gated cation and proton channels, and is the only membrane-spanning domain of Ci-VSP. Previously, we have determined the structure of Ci-VSD in its resting (Down) and activated (Up) conformations. Thus, this system provides us with a great opportunity to study the energetics of the gating mechanism of this isolated VSD. Using mutagenesis, electrophysiology, modeling and molecular dynamics simulations, we systematically investigated residue-residue interactions between the segments of the VSD and the interactions between the VSD and lipids during a complete functional gating cycle. We found that Ci-VSD can adopt mainly four conformational states: the Up and Down states determined by crystallography, in addition to a further down (‘Down-minus’) and a further up (‘Up-plus’) states. One helix turn translation of the S4 segment drives the transition between two adjacent states. Upon depolarization, the VSD rearranges from the ‘Down-minus’ state to the ‘Up-plus’ state in a sequential stepwise way, translating one positively charged residue across the membrane electric field at each transition, resulting in a gating charge of ∼3 e0. Furthermore, cysteine mutations on the extracellular side of S4 can form metal-ion bridges with lipid phosphate group and decrease the total gating charge displacement with intensity depending on the external Cd2+ concentration, while cysteine mutations on the S1−S3 segments have little effect, representing minor conformational changes of them during gating and do not contribute to the gating charge.