Electric Field Changes Research Articles

Theoretical study of a four-level EIT-type system in the presence of structured coupling light for microwave field detection.

In this work, we have theoretically studied the four-level atomic system for the measurement of a microwave (MW) field. We employed the electromagnetically induced transparency (EIT) technique for finding the MW field in the presence of a Laguerre-Gaussian (LG) beam as a coupling light. We have shown that, by the application of LG modes, narrower dips for the probe absorption spectrum can be generated, which can be easily identified and gives better resolution compared with the Gaussian mode. An exact location of dips in the probe absorption spectrum is found, and it is useful in the measurement of MW fields. We have estimated the FWHM of the probe absorption spectrum for Gaussian and LG coupling cases as 3.74×105 H z and 1.07×105 H z, respectively. Based on FWHM, we have found that minimum change in MW electric field in the order of 3.32µV c m -1 will be detectable in the case of the LG mode as a coupling beam.

Multiphysics Modeling of Volcanic Unrest at Mt. Ruapehu (New Zealand)

AbstractPre‐eruptive signals at the crater lake‐bearing Mt. Ruapehu (New Zealand) are either absent or hard to identify. Here, we report on geophysical anomalies arising from hydrothermal unrest (HTU) and magmatic unrest (MU) using multiphysics numerical modeling. Distinct spatio‐temporal anomalies are revealed when jointly solving for ground displacements and changes in gravitational and electrical potential fields for a set of subsurface disturbances including magma recharge and anomalous hydrothermal flow. Protracted hydrothermal injections induce measurable surface displacements (>0.5 cm) at Ruapehu's summit plateau, while magmatic pressurization (5–20 MPa) results in ground displacements below detection limits. Source density changes of 10 kg/m3 (MU simulations) and CO2 fluxes between 2,150 and 3,600 t/d (HTU simulations) induce resolvable residual gravity changes between +8 and −8 μGal at the plateau. Absolute self‐potential (SP) anomalies are predicted to vary between 0.3 and 2.5 mV for all unrest simulations and exceed the detection limit of conventional electric surveying. Parameter space exploration indicates that variations of up to 400% in the Biot‐Willis coefficient produce negligible differences in surface displacement in MU simulations, but strongly impact surface displacement in HTU simulations. Our interpretation of the findings is that monitoring of changes in SP and gravity should permit insights into MU at Ruapehu, while HTU is best characterized using ground displacements, residual gravity changes and SP anomalies. Our findings are useful to inform multiparameter monitoring strategies at Ruapehu and other volcanoes hosting crater lakes.

Characterization of the initial stage in upward lightning at the Gaisberg Tower: 2. Electric field signatures

• Near and far electric field signatures of IS current pulses were analyzed. • Electric field signatures of early-stage-IS bipolar current pulses were characterized. • Such bipolar pulses could be associated with upward leader inception. We examined the characteristics of electric field signatures occurring during the initial stage of 58 flashes measured simultaneously at near (170 m) and far (79 or 109 km) distances from the Gaisberg Tower located near Salzburg, Austria. Of the 340 field signatures measured at the near station, 68 (20%) were associated with current pulses occurring during the initiation and propagation phase (IPP) of the upward leader, and 272 (80%) were associated with pulses that occurred during the mature phase (MP) of the upward leader. Of the 68 field signatures of IPP pulses, 40 were associated with bipolar (IPP-B type) current pulses and 28 were associated with unipolar (IPP-U type) current pulses. Field signatures of IPP-B pulses were only detected at the near measurement station and appear to be associated with currents in relatively short (meter-scale) channel segments formed during the upward leader inception. At the far stations, field signatures of 84 IS pulses were recorded and analyzed. There was modest correlation between the background-to-peak current of IS pulses and near and far electric radiation field changes as well as between radiation field changes recorded at near and far distances.

Surface trap characteristics of polyimide and effect of surface charge accumulation on surface flashover

Charge accumulation on the surface of insulation dielectric used in high voltage DC equipment is one of the important causes of surface flashover. Surface charge accumulation is closely related to surface trap characteristics. In this paper, the surface trap energy level distribution of polyimide (PI) was calculated and analyzed by the corona charging method and surface potential decay method. Besides, electron and hole trap characteristics were studied by changing the polarity and amplitude of the charging voltage. Furthermore, the influence of surface charge polarity and quantity on the flashover voltage was researched. Experimental results indicate that the energy level of traps corresponding to the maximum trapped charge density ranges around 0.94 eV. In addition, the energy level of the hole trap is slightly higher than that of the electron trap. The maximum charge density captured by the electron trap and hole trap is about 1.17 × 1021 and 1.03 × 1021 eV−1 m−3, respectively. The polarity of the surface charge can influence the conductivity characteristics of PI, the surface heterocharge reduces the volume conductivity by about 80% while the surface homocharge improves the volume conductivity of PI by about 6.4 times. Besides, both negative and positive surface charges can improve surface conductivity. The polarity of surface charge influences the flashover characteristics of PI, the flashover voltage increases by about 37.8% with the increase of homocharge density and decreases by about 23.8% with the increase of heterocharge density, which is related to the change of electric field near the cathode caused by surface charge accumulation.

On the Intensity of First Return Strokes in Positive Cloud‐To‐Ground Lightning in Winter

AbstractIntensities of about 700 first return strokes (RSs) in positive cloud‐to‐ground lightning flashes observed by a 14‐site Fast Antenna Lightning Mapping Array in one winter season are analyzed. Peak currents estimated from range‐normalized peak amplitudes of electric field change (E‐change) waveforms of RSs are used to represent their intensities. It is found that peak currents of positive RSs are positively correlated with their waveform parameters including pulse width, rise time, fall time and half‐peak width. Time differences between lightning initiation and first RSs are closely related with peak currents of positive RSs, with strong positive RSs usually associated with small time differences. Peak currents of positive RSs are also related with amplitudes of preceding leader pulses. Out of 674 positive RSs, 232 are preceded by positive leader pulses, and amplitudes of these pulses are positively correlated with peak currents of RSs. Strong positive RSs with peak currents larger than 150 kA are analyzed and compared with strong negative RSs. While strong negative RSs usually produce abnormal E‐change waveforms that are generally different from typical RS waveforms, strong positive RSs do not have such special features. Strongest positive RSs usually occur within a very short time (usually smaller than 10 ms) after lightning initiation and are more likely to be associated with positive preliminary breakdown pulses. It is inferred that these strongest RSs are usually preceded by a fast downward positive leader with a speed on the order of 106 m/s. Charge structures responsible for strong positive RSs are discussed.

Investigation on electronic properties modulation of vdW GaN/WSe2 heterostructure by electric field

In this paper, we designed two van der Waals (vdW) GaN/WSe2 heterostructures based on the GaN and WSe2 monolayers. And then we further investigated the effect of the external electric field on electronic properties of the more stable GaN/WSe2 vdW heterostructure by first-principle calculations. Results show that without external electric field, the GaN/WSe2 is a typical type-I band alignment heterostructure. But both the VBO and CBO are smaller than 1 eV, which limits their application in electric devices. So we further adopt an external electric field to adjust the electronic properties of the heterostructure. Results show that when applying an external electric field of [Formula: see text] V/Å, the band alignment of GaN/WSe2 heterostructure changes from type-I to type-II, and the electrons and holes are separated into different layers. Then the recombination of the holes and electrons is blocked and the lifetime of photo-induced carriers can be prolonged. To understand the inherent physical mechanism, the variation trends of the band gap and band offset as the change of external electric field were discussed. Results show that the location and contribution factors of conduction band minimum (CBM) and valence band maximum (VBM) caused by external electric field are the main factors causing this change in the heterostructure.

The change of electric field and relaxed elastic line via anholonomic coordinates with Darboux frame in [formula omitted

In this paper, intrinsic directional derivatives via anholonomic coordinates with respect to the Darboux frame in Minkowski 3-space R13 are obtained. Later, the evolution of electric field for three cases with respect to the Darboux frame in the q−lines direction in R13 is derived. Also, Darboux Lorentz equations in q−lines direction are found. Finally, an application relation to relaxed line via anholonomic coordinates in R13 is presented.

Effects of Familial Alzheimer's Disease Mutations on the Folding Free Energy and Dipole-Dipole Interactions of the Amyloid β-Peptide.

Familial Alzheimer's disease (FAD) mutations of the amyloid β-peptide (Aβ) are known to lead to early onset and more aggressive Alzheimer's disease. FAD mutations such as "Iowa" (D23N), "Arctic" (E22G), "Italian" (E22K), and "Dutch" (E22Q) have been shown to accelerate Aβ aggregation relative to the wild-type (WT). The mechanism by which these mutations facilitate increased aggregation is unknown, but each mutation results in a change in the net charge of the peptide. Previous studies have used nonpolarizable force fields to study Aβ, providing some insight into how this protein unfolds. However, nonpolarizable force fields have fixed charges that lack the ability to redistribute in response to changes in local electric fields. Here, we performed polarizable molecular dynamics simulations on the full-length Aβ42 of WT and FAD mutations and calculated folding free energies of the Aβ15-27 fragment via umbrella sampling. By studying both the full-length Aβ42 and a fragment containing mutations and the central hydrophobic cluster (residues 17-21), we were able to systematically study how these FAD mutations impact secondary and tertiary structure and the thermodynamics of folding. Electrostatic interactions, including those between permanent and induced dipoles, affected side-chain properties, salt bridges, and solvent interactions. The FAD mutations resulted in shifts in the electronic structure and solvent accessibility at the central hydrophobic cluster and the hydrophobic C-terminal region. Using umbrella sampling, we found that the folding of the WT and E22 mutants is enthalpically driven, whereas the D23N mutant is entropically driven, arising from a different unfolding pathway and peptide-bond dipole response. Together, the unbiased, full-length, and umbrella sampling simulations of fragments reveal that the FAD mutations perturb nearby residues and others in hydrophobic regions to potentially alter solubility. These results highlight the role electronic polarizability plays in amyloid misfolding and the role of heterogeneous microenvironments that arise as conformational change takes place.

Effects of Bi substitution on electroresistance behaviours in La0.8-xBixNa0.2MnO3 manganites

The observation of the electroresistance (ER) effect related to the reduction of resistivity under increased applied current indicates the potential of manganite material for next-generation spintronic-based devices. The observed behaviour was attributed to the presence of magnetic inhomogeneity. However, such relation is still not well understood, hence the current-induced effect on the resistivity in monovalent-doped La0.8-xBixNa0.2MnO3 (x = 0–0.20) manganite prepared via solid-state method is reported. All samples exhibited low resistivity in the temperature ranges of 30 K–300 K under a higher applied current of 5 mA compared with 1 mA, leading to the observation of the ER effect. The reduction of resistivity in the metallic region was due to the enhancement of DE itinerant hopping and the decrease in the scattering effect of conduction electrons, whereas in the insulating region, resistivity reduction is suggested to be related to the weakening of the electron–lattice attraction, as indicated by the reduction in activation energy (Ea) of charge carriers. Both x = 0.15 and x = 0.20 samples respectively exhibited large ER effects of 158% and 171% at 300 K amongst the studied samples. The enhancement of ER with Bi substitution is suggested due to the presence of magnetic inhomogeneities induced by MnO6 distortion which favours the formation of filamentary conduction paths under the presence of high applied current. The findings indicate that Bi substitution in La0.8-xBixNa0.2MnO3 (x = 0–0.20) manganites enhanced the sensitivity to the changes in electric field which shows that the investigated samples could be potentially used for non-volatile memory devices.

Microwave Radiation Associated with Lightning Initiation Events of Negative Cloud-to-Ground Flashes

In this paper, we examined the initiation events of ten negative cloud-to-ground (CG) flashes detected close to measurement stations on 12 November (CG-1 to CG-5) and 24 November (CG-6 to CG-10), 2019. All CG flashes were accompanied by microwave and very-high frequency (VHF) radiation pulses. We recorded all the CG flashes from two measurement stations (ST1 and ST2), which are separated by 13.3 km and consist of fast and slow antenna (FA and SA) sensors, a magnetic field (B-field) sensor, a VHF sensor (60 MHz), and a microwave sensor (~1 GHz). The key finding is that all of the microwave radiation pulses detected before the onset of initial electric field changes (IECs) preceded all VHF radiation pulses with an average lead time of 1.53 µs, ranging between 0.3 and 3.0 µs (for all CG flashes within reversal distance). A total of 50%, 17%, and 33% CG flashes were initiated by a single radiation pulse, two radiation pulses, and three radiation pulses, respectively, and were followed by IECs. Some VHF pulses are classified as short VHF radiation pulses (pulse duration less than 0.5 µs). The average duration from the first microwave and VHF pulses to the onset of IECs were 53.4 µs and 32.78 µs, respectively. The VHF radiation pulses detected before the IECs are suggested to be emitted by short-length positive streamers. Because the microwave radiation pulses were detected earlier (average lead time of 1.53 µs) than VHF radiation pulses, it is most likely that the microwave pulses were emitted by an electron avalanche process.

The effect of dissolution by periodic reverse current on the microstructure of bamboo-shaped porous anodic alumina

• Periodic reverse current with small amplitude can promote the growth of the porous layer. • Periodic reverse current has the effect of pore expansion. • The water reduction speed increases during the reverse voltage stage. • The ions driven by the electric field change with the direction of current. • H+ (H2O) and OH− are the main ions that move in the reverse voltage stage. In this paper, the effects of a cyclic anodizing method with the introduction of periodic reverse current are reported. The effects of the periodic reverse current on the microstructure of bamboo-shaped porous anodic alumina (PAA) film are investigated using positive and negative current triangular waveforms. The results of the experiment showed that when the reverse current in each current cycle was I D ' = -5 mA, the growth velocity was the fastest. The analysis found that the introduction of the periodic reverse current was beneficial to increasing the growth velocity of the porous anodic alumina film and had the additional effect of pore expansion. However, with any further increase of the periodic reverse current, the growth velocity of the porous anodic alumina film gradually decreased, and the period length showed a decreasing trend. The main reason for this phenomenon is that in a larger reverse voltage phase, the ions driven by the electric field are mainly H + (H 2 O) and OH − . Then the reaction that occurs is mainly dissolution. With large pore size and adjustable period length, this porous anodic alumina film can be used as a template for the synthesis of nanomaterials, which have practical significance for the synthesis of nanodevices.

The influence of leader charge on current intensity and spectral characteristics of return strokes

The characteristic parameters reflecting the current intensity in lightning return stroke discharge channel are the primary concern in the field of lightning physics research and protection. Based on the spectrum and the corresponding fast electric field change waveforms for 9 natural cloud-to-ground lightnings including multiple return strokes, part of the total charge quantity in the corresponding leader channel was estimated by different methods, and its influence on current intensity and spectral characteristics of return strokes were further investigated. The results show, that for the same lightning, part of the leader charge quantity estimated by using the two methods according to the electric field change waveforms is in good agreement with the electron number per channel length calculated by basing on leader spectrum, it is also found that part of the neutralized leader charges is positively correlated with the peak current, the radius of the core current-carrying channel and the total intensity of ionic lines in the spectrum. These results mean that the current intensity of the lightning return stroke discharge mainly depends on the charge quantity being stored in the previous leader process. The radius of the core current-carrying channel is closely related to the current intensity. Moreover, the intensity of the ionic line in the spectrum can directly reflect the current intensity, which is an ideal observable parameter for studying the current characteristics.

Phreatic volcanic eruption preceded by observable shallow groundwater flow at Iwo-Yama, Kirishima Volcanic Complex, Japan

It is difficult to forecast phreatic eruptions because they are often characterised by an abrupt onset at shallow depths beneath volcanoes. Here we show that temporal changes in the tilt, tremor, and horizontal electric field have occurred repeatedly near the vent of a small phreatic eruption at Iwo-Yama, Kirishima Volcanic Complex, Japan. Such geophysical changes were observed 13 times, with one of these events occurring immediately before the onset of the 2018 phreatic eruption. These observations suggest that shallow hydrothermal intrusions, which are observed as tilt changes with tremors, commonly induce near-surface cold groundwater flow, which is observed as electric-field changes. Near-surface groundwater flows towards the active vent, potentially inhibiting a phreatic eruption. However, explosive phreatic eruptions occur when the intrusion is shallow and cold groundwater flow is depleted. The near-surface groundwater is key in controlling the occurrence of phreatic eruptions and can be monitored using electric-field measurements.

Annealing effects on epitaxial (K,Na)NbO3 thin films grown on Si substrates

Epitaxial (K,Na)NbO3 (KNN) thin films were deposited on (001)SrRuO3/Pt/ZrO2/Si substrates by RF magnetron sputtering, and post-annealing effects on the as-deposited epitaxial KNN thin films were investigated. According to the findings, by annealing, the crystal system of these thin films changes from a tetragonal to an orthorhombic system because of the release of internal stress. The asymmetry of polarization–electric field hysteresis loops along the electric field changes from a positive to a negative side by annealing. This means that stable spontaneous polarization P s changes from the upward to downward direction with an increase in the number of A-site vacancies. In addition, the displacement–electric field curves of epitaxial KNN/Si unimorph cantilevers exhibit asymmetric behaviors. A relatively high converse piezoelectric coefficient ∣e 31,f ∣ = 6.4 C m−2 is obtained for 5 h annealed epitaxial KNN thin films.

Characteristics of Fast Electric Field Generated by Negative Lightning in Northern Peninsular Malaysia.

The development and advancement of lightning locating system (LLS) reaches until 2021 and the characteristics of lightning can be studied by observing the electric field produced by lightning. There are several studies proven that preliminary breakdown pulses (PBPs) are always preceded the return stroke, the duration of the PBPs and the time for the PBPs preceded the return stroke tend to be different depends on the types of lightning, regions, and location. This paper observed and recorded the fast electric field changes of negative cloud to ground lightning (CG). Total of ten sample data was captured on 13 May 2021 and selected to be analyzed in detail. Information such as rise time to peak, duration of preliminary breakdown pulses has been recorded. The captured result is compared with the results from other papers. The results show that the PBPs duration are very similar when compared with local results which shows an average of 2.347 ms. While the average time for PBPs to precede the first return stroke is around 9.44 ms and the rise time from 10% to 90% peak of first return stroke shows an average time of 4.86 μs

Dependence of lightning current on resistance and radius of discharge plasma channel

The current transmission characteristics of lightning discharge are closely related to lightning hazard mechanisms. The conductive properties of a lightning plasma channel were analyzed based on the spectra of nine negative cloud-to-ground lightning events recorded by a high-speed slit-less spectrograph and the theory of plasma conductivity. Combined with the information of synchronous electric field change caused by lightning, we estimated the peak current and corresponding current-carrying channel radius and further investigated the dependence of the discharge current on the resistance and radius of the discharge plasma channel. The results showed that there was a nonlinear relationship between the peak current and the resistance per unit length of the discharge channel. The radius of the current-carrying channel was positively correlated with the current intensity. Radius was an important parameter that affects the magnitude of the current. The electrical conductivity and the radius of the current-carrying channel have a coupling effect on the current transmission, which is the main factor determining the current transmission feature in the discharge plasma channel.

Spectroscopic features and electronic properties on tetrazole-based energetic cocrystals under external electric field

The optimized geometry, molecular orbitals, electronic properties and spectra wtheere calculated by DFT-B3LYP and PBE0 methods with 6–311 + g(d, p) and def2-TZVP basis sets. The results show that the change of electric field intensity has a great influence on the NH bond in the tetrazole ring skeleton, and it is more easily-broken under negative electric field. When the electric field changes, the NH bond is always the trigger bond. With the increase of external electric field, the energy gaps of 5-(nitrimino)-1H-tetrazole (A) and 1-methyl-5-(nitrimino)-1H-tetrazole (B) gradually become smaller, and chemical reactions are more likely to occur. Infrared and UV–Vis spectra show obvious vibration effects under external electric field, and both structures A and B show different degrees of red-shift or blue-shift. A and B exhibit basically similar properties under electric field, indicating that the hydrogen atoms and methyl groups on the tetrazole ring in the structure have little effect on the cocrystal.

A seismometer that can be used to study pre-quake signals.

The sensitive, broadband seismometer described in this paper is based on frequency modulation and a two-dimensional (2D) Fourier transform method to obtain time vs frequency (and seismic amplitude) recordings. The intent was to develop an instrument that could compare seismic recordings with variables (as signals) that, for rational reasons, might be active before a seismic rupture and, thus, possibly serve as quake warning indicators. Five such variables were eventually incorporated into the instrument and tested as amplitudes: electric field changes, the electromagnetic spectrum between 3 and 30Hz (extremely low frequency as Schumann-like emissions), the electromagnetic spectrum between 0.3 and 3Hz (possibly ionospheric Alfvén waves acting through the geomagnetic field), and short period seismic resonances at 10.1 and 15.9Hz. All five of the sensors actually detected possible precursors of the seismic events that followed them. However, the 3-30Hz electromagnetic signals showed up in less than 10% of the recorded earthquakes. The signals of the 0.3-3Hz band were also not in all quake recordings. Broadband strobing was recorded before several earthquakes and was especially prominent for hours before a quake near Wyatt MO and Bardwell KY on 2017-03-19. The strobe issue appears to be worthy of further scrutiny. The lack of a good electric conduction mechanism between earthquake hypocenters and the earth-ionosphere cavity may be the reason why the Schumann-like emissions of the 3-30Hz band were not observed for most earthquakes. A magnetometer is a preferred next step because it could increase the percentage of quakes with observable effects. In addition, a short period seismic resonator for 20Hz is another desirable addition.

Observation of light-driven band structure via multiband high-harmonic spectroscopy

Intense light–matter interactions have revolutionized our ability to probe and manipulate quantum systems at sub-femtosecond timescales1, opening routes to the all-optical control of electronic currents in solids at petahertz rates2–7. Such control typically requires electric-field amplitudes in the range of almost volts per angstrom, when the voltage drop across a lattice site becomes comparable to the characteristic bandgap energies. In this regime, intense light–matter interaction induces notable modifications to the electronic and optical properties8–10, dramatically modifying the crystal band structure. Yet, identifying and characterizing such modifications remain an outstanding problem. As the oscillating electric field changes within the driving field’s cycle, does the band structure follow and how can it be defined? Here we address this fundamental question, proposing all-optical spectroscopy to probe the laser-induced closing of the bandgap between adjacent conduction bands. Our work reveals the link between nonlinear light–matter interactions in strongly driven crystals and the sub-cycle modifications in their effective band structure.

Stability-Guided Strategies to Mitigate Dendritic Growth in Lithium-Metal Batteries

Dendritic growth is a leading cause of degradation and catastrophic failure of lithium-metal batteries. Deep understanding of this phenomenon would facilitate the design of strategies to reduce, or completely suppress, the instabilities characterizing electrodeposition on the lithium anode. We present a linear-stability analysis, which utilizes the Poisson-Nernst-Planck equations to describe Li-ion transport and, crucially, accounts for the lack of electroneutrality. This allows us to investigate the impact of electric-field gradients near the electrode surface on both ion diffusion and its anisotropy. Our analysis indicates that the use of anisotropic electrolytes (i.e., electrolytes with anisotropic diffusion coefficients of the Li ions) and the control of the local electric field can suppress dendritic growth of lithium metal. Specifically, changes in the local electric field can be used to enhance the longitudinal (perpendicular to the electrode) component of the cation diffusion coefficient tensor, which decreases the maximum growth rate of the dendrites. Electrolytes with electric field-dependent diffusion coefficients would reduce dendritic growth in small batteries, while anisotropic electrolytes (or separators with anisotropic pore structures or columnized membranes) are appropriate for batteries of any size.