Electric Field Model Research Articles

Nonnegative magnetoresistance in hydrodynamic regime of electron fluid transport in two-dimensional materials

Electron transport in ultraclean two-dimensional materials has received much attention. However, the sign of the magnetoresistance effect in various electron flow regimes remains controversial. In this work, the complete electron Boltzmann transport equation is numerically solved with the discrete ordinate method in the real space to clarify the condition of the negative magnetoresistance effect under a weak magnetic field. It turns out from the numerical results that this effect occurs only within the ballistic regime under a low electric field rather than the hydrodynamic regime. It is noteworthy that the existence of momentum-conserving scattering dramatically reverses the sign of magnetoresistance in the ballistic regime. When the electric field becomes strong enough compared to the magnetic field, its effect on the deflection of the electrons is not negligible and will lead to positive magnetoresistance in the whole parameter domain. The possible influence of boundary conditions and internal electric field models on the sign of magnetoresistance is also discussed. Our work provides insight into electron fluid transport under electromagnetic fields.

Energy Method for the Elliptic Boundary Value Problems with Asymmetric Operators in a Spherical Layer

Three-dimensional elliptic boundary value problems arising in the mathematical modeling of quasi-stationary electric fields and currents in conductors with gyrotropic conductivity tensor in domains homeomorphic to the spherical layer are considered. The same problems are mathematical models of thermal conductivity or diffusion in moving or gyrotropic media. The operators of the problems in the traditional formulation are non-symmetric. New statements of the problems with symmetric positive definite operators are proposed. For the four boundary value problems the quadratic energy functionals, to the minimization of which the solutions of these problems are reduced, are constructed. Estimates of the obtained quadratic forms are made in comparison with the form appearing in the Dirichlet principle for the Poisson equation

Time-domain dynamic electric field distribution of low-oscillation sculptured structure dispersive mirrors

The dispersion oscillation and damage threshold of a dispersive mirror (DM) are the key influencing factors for high-quality pulses and outputting high power density. Here, we studied the femtosecond damage behavior of low-oscillation DMs(LODM) with SiO2 sculptured layer. The monochromatic standing wave field(SWF) distribution widely used in ultrafast laser damage analysis is sufficient in Bragg mirror. In more complex systems, the actual electric field intensity(typically smaller) will dynamically change due to the broad bandwidth and the time difference of pulse propagation. Time-domain dynamic electric field intensity displays that the spatio-temporal evolution of the pulse within the stacks averages the electric field intensity, especially the electric field in the deeper layers. The dynamic effect of few-cycle pulses or attosecond pulses damage will be more meaningful. The time-domain dynamic electric field model can elucidate the ultrafast laser damage behavior. Introducing the time-domain dynamic electric model into the merit function can help us design optical coatings with high damage thresholds.

A Load-Dependent Model of Triboelectric Nanogenerators for Surface Roughness Sensing

The triboelectric nanogenerator (TENG) has the advantages of low cost, high efficiency, flexibility, lightness, and portability. Therefore, it has caused more and more attention as an electronic skin sensor. Generally, the research on intelligent components mainly focused on flexible pressure or temperature sensors. However, the surface roughness recognition of object material still remains a challenge. Meanwhile, most of the current surface roughness recognition methods need secondary processing of the sensor signal, and rarely use the signal generated by the sensor to directly identify the surface roughness. In this paper, the load-dependent electric field model is transplanted to the conductor-dielectric contact-separation TENG (CS-TENG), and the surface roughness of conductor can be differentiated theoretically based on the output of CS-TENG. To verify its effectiveness, the TENG devices were fabricated and the home-processed steels of different roughness act as the conductor layers. By contacting the conductor layer with the dielectric layer, the electric output signal based on contact induced electrification can be generated, which can be used to quantitatively estimate the surface roughness of steels. The test results demonstrate that the output of CS-TENG decreases with the increase of surface roughness, which coincides with the simulation prediction. This method is low cost and easy to implement, which provides a new design idea to extend the functions of TENGs as tactile electronic skins.

Individual differences in neuroanatomy and neurophysiology predict effects of transcranial alternating current stimulation

BackgroundNoninvasive transcranial electrical stimulation (tES) research has been plagued with inconsistent effects. Recent work has suggested neuroanatomical and neurophysiological variability may alter tES efficacy. However, direct evidence is limited. ObjectiveWe have previously replicated effects of transcranial alternating current stimulation (tACS) on improving multitasking ability in young adults. Here, we attempt to assess whether these stimulation parameters have comparable effects in older adults (aged 60–80 years), which is a population known to have greater variability in neuroanatomy and neurophysiology. It is hypothesized that this variability in neuroanatomy and neurophysiology will be predictive of tACS efficacy. MethodsWe conducted a pre-registered study where tACS was applied above the prefrontal cortex (between electrodes F3-F4) while participants were engaged in multitasking. Participants were randomized to receive either 6-Hz (theta) tACS for 26.67 min daily for three days (80 min total; Long Exposure Theta group), 6-Hz tACS for 5.33 min daily (16-min total; Short Exposure Theta group), or 1-Hz tACS for 26.67 min (80 min total; Control group). To account for neuroanatomy, magnetic resonance imaging data was used to form individualized models of the tACS-induced electric field (EF) within the brain. To account for neurophysiology, electroencephalography data was used to identify individual peak theta frequency. ResultsResults indicated that only in the Long Theta group, performance change was correlated with modeled EF and peak theta frequency. Together, modeled EF and peak theta frequency accounted for 54%–65% of the variance in tACS-related performance improvements, which sustained for a month. ConclusionThese results demonstrate the importance of individual differences in neuroanatomy and neurophysiology in tACS research and help account for inconsistent effects across studies.

Thermospheric Neutral Winds as the Cause of Drift Shell Distortion in Earth’s Inner Radiation Belt

Recent analysis of energetic electron measurements from the Magnetic Electron Ion Spectrometer instruments onboard the Van Allen Probes showed a local time variation of the equatorial electron intensity in the Earth’s inner radiation belt. The local time asymmetry was interpreted as evidence of drift shell distortion by a large-scale electric field. It was also demonstrated that the inclusion of a simple dawn-to-dusk electric field model improved the agreement between observations and theoretical expectations. Yet, exactly what drives this electric field was left unexplained. We combine in-situ field and particle observations, together with a physics-based coupled model, the Rice Convection Model (RCM) Coupled Thermosphere-Ionosphere-Plasmasphere-electrodynamics (CTIPe), to revisit the local time asymmetry of the equatorial electron intensity observed in the innermost radiation belt. The study is based on the dawn-dusk difference in equatorial electron intensity measured at L = 1.30 during the first 60 days of the year 2014. Analysis of measured equatorial electron intensity in the 150–400 keV energy range, in-situ DC electric field measurements and wind dynamo modeling outputs provide consistent estimates of the order of 6–8 kV for the average dawn-to-dusk electric potential variation. This suggests that the dynamo electric fields produced by tidal motion of upper atmospheric winds flowing across Earth’s magnetic field lines - the quiet time ionospheric wind dynamo - are the main drivers of the drift shell distortion in the Earth’s inner radiation belt.

Modeling and Simulation of the Local Electric Fields at Stimulation Needles in Human Tissue for Regional Anesthesia

This work deals with the modeling and simulation of the electrical fields in human tissue, arising from the stimulation of nerves in regional anesthesia. Appropriate simplifications are made for chemical and electrical processes to generate a 3D model of a stimulation needle within the tissue. Electrical properties, such as conductivity and permittivity, of the tissues are defined and their influence regarding the local electric field around the needle tip is examined. Finally, the efficacy of a stimulation needle in stepwise more complex and realistic models of human tissue is described. The main purpose of this work is to establish a basic approach of working with such models and to use numerical field simulation to obtain a deeper understanding of the electric situation around the needles typically used in regional anesthesia.

Coupling the Rice Convection Model‐Equilibrium to the Lyon‐Fedder‐Mobarry Global Magnetohydrodynamic Model

AbstractThe pursuit of realistic simulation of the physics of plasma transport, ring current formation and storm‐triggered Earth magnetic and electric field is an ongoing challenge in magnetospheric physics. To this end, we have implemented a coupling of the Lyon‐Fedder‐Mobarry (LFM) global magnetohydrodynamic model with the Rice convection model‐equilibrium (RCM‐E) of the inner‐magnetosphere and plasma sheet. This one‐way coupling scheme allows continuous update of the RCM‐E boundary conditions from the plasma moments calculated by the LFM while preserving entropy conservation. This results in a model that has the high‐resolution self‐consistent description of the inner magnetosphere and includes the effects of time‐dependent outer‐magnetospheric electromagnetic fields and plasma configurations. In addition, driving the RCM‐E in this way resolves the issue of having a plasma‐β‐constrained region in the coupled model of LFM‐RCM and expands the RCM‐E simulation region farther out into plasma sheet where the storm‐time plasma transportation takes place. In the ionosphere, the RCM‐E replaces the ionospheric electric field model of LFM with the one used by the RCM. The electric potential produced, along with the realistic ionospheric precipitation patterns shows strong consistency with the transportation patterns in the plasma sheet featured with well‐resolved bubbles and bursty bulk flows. Results from the simulations of an idealized event will be presented and discussed.

Proof of concept study to develop a novel connectivity-based electric-field modelling approach for individualized targeting of transcranial magnetic stimulation treatment

Resting state functional connectivity (rsFC) offers promise for individualizing stimulation targets for transcranial magnetic stimulation (TMS) treatments. However, current targeting approaches do not account for non-focal TMS effects or large-scale connectivity patterns. To overcome these limitations, we propose a novel targeting optimization approach that combines whole-brain rsFC and electric-field (e-field) modelling to identify single-subject, symptom-specific TMS targets. In this proof of concept study, we recruited 91 anxious misery (AM) patients and 25 controls. We measured depression symptoms (MADRS/HAMD) and recorded rsFC. We used a PCA regression to predict symptoms from rsFC and estimate the parameter vector, for input into our e-field augmented model. We modeled 17 left dlPFC and 7 M1 sites using 24 equally spaced coil orientations. We computed single-subject predicted ΔMADRS/HAMD scores for each site/orientation using the e-field augmented model, which comprises a linear combination of the following elementwise products (1) the estimated connectivity/symptom coefficients, (2) a vectorized e-field model for site/orientation, (3) rsFC matrix, scaled by a proportionality constant. In AM patients, our connectivity-based model predicted a significant decrease depression for sites near BA9, but not M1 for coil orientations perpendicular to the cortical gyrus. In control subjects, no site/orientation combination showed a significant predicted change. These results corroborate previous work suggesting the efficacy of left dlPFC stimulation for depression treatment, and predict better outcomes with individualized targeting. They also suggest that our novel connectivity-based e-field modelling approach may effectively identify potential TMS treatment responders and individualize TMS targeting to maximize the therapeutic impact.

Tree Canopies Influence Ground Level Atmospheric Electrical and Biogeochemical Variability

Static electric fields in the atmosphere are increasingly recognized as interacting with various organisms over several levels of biological organization. Recently, a link between atmospheric electrical variations and biogeochemical processes has been established in the context of open fields, yet biological structures like trees produce substantial alterations in atmospheric electric properties. Here, we assess whether these structural changes affect the dynamics of the electrical landscape and its relation to geochemical processes. To this end, we theoretically assess how trees alter their surrounding electric fields and empirically compare the temporal dynamics of atmospheric potential gradients, positive ions in the near-ground level atmosphere and soil electrochemical properties in an open field and under a tree. The developed model of electric fields around trees provides insight into the extent to which trees shield the underlying electric landscape, revealing that a substantial increase in atmospheric potential gradient only marginally affects the electric field under the canopy. We further show that soil electrochemical properties are tied to the temporal dynamics of positive ion in the near-ground level atmosphere, and that the presence of a tree reduces the temporal variability in both ground level positive ion concentrations and soil redox potential. This suggests that a tree can alter the temporal variability in atmospheric electricity and soil electro-chemistry, thereby likely indirectly influencing soil microorganisms and processes as well as electro-sensitive organisms that perceive and utilize atmospheric electric fields.

A reexamination of motor and prefrontal TMS in tobacco use disorder: Time for personalized dosing based on electric field modeling?

ObjectiveIn this study, we reexamined the use of 120% resting motor threshold (rMT) dosing for transcranial magnetic stimulation (TMS) over the left dorsolateral prefrontal cortex (DLPFC) using electric field modeling. MethodsWe computed electric field models in 38 tobacco use disorder (TUD) participants to compare figure-8 coil induced electric fields at 100% rMT over the primary motor cortex (M1), and 100% and 120% rMT over the DLPFC. We then calculated the percentage of rMT needed for motor-equivalent induced electric fields at the DLPFC and modeled this intensity for each person. ResultsElectric fields from 100% rMT stimulation over M1 were significantly larger than what was modeled in the DLPFC using 100% rMT (p < 0.001) and 120% rMT stimulation (p = 0.013). On average, TMS would need to be delivered at 133.5% rMT (range = 79.9 to 247.5%) to produce motor-equivalent induced electric fields at the DLPFC of 158.2 V/m. ConclusionsTMS would have to be applied at an average of 133.5% rMT over the left DLPFC to produce equivalent electric fields to 100% rMT stimulation over M1 in these 38 TUD patients. The high interindividual variability between motor and prefrontal electric fields for each participant supports using personalized electric field modeling for TMS dosing to ensure that each participant is not under- or over-stimulated. SignificanceThese electric field modeling in TUD data suggest that 120% rMT stimulation over the DLPFC delivers sub-motor equivalent electric fields in many individuals (73.7%). With further validation, electric field modeling may be an impactful method of individually dosing TMS.

Low‐Latitude Plasma Drifts From the Horizontal Neutral Wind Model and a Coupled Ionosphere‐Electric Field Model

AbstractResults from a dynamo electric field model are presented to examine the consistency of the widely used empirical models of low‐latitude plasma drifts and thermospheric neutral winds. The sector defined by the Jicamarca Radar measured plasma drifts is used due to the greater certainty of the empirical vertical plasma drifts. The plasma drifts produced by the Horizontal Wind Model (HWM) in a coupled ionosphere‐electric field model for geomagnetically quiet and moderate solar conditions are compared against empirical models of equatorial plasma drifts for the Peruvian sector. The HWM generates reasonable sunset prereversal enhancement of the vertical drift in all but May, June, July, and August when no prereversal enhancement exists in the empirical results. The daytime vertical drifts are deficient during all seasons. A solar diurnal and semi‐diurnal tidal forcing are required in the E region (100–150 km) to bring the HWM into better agreement as a dynamo driver for the daytime electric fields associated with the broad Solar Quiet current system.

The novel positive colossal electroresistance in PbPdO2 thin film with (002) preferred orientation

Doped PbPdO2 materials have attracted much attention as a spin gapless semiconductor (SGS) with the important properties of colossal electroresistance (CER) and giant magnetoresistance (GMR). In this study, the PbPdO2 thin films with (002) preferred orientation were prepared by pulsed laser deposition (PLD), and the temperature dependences of resistance and resistivity, R (T) and ρI (T), were measured under different applied DC currents. Remarkably, a positive CER effect induced by the current was firstly observed in the PbPdO2 films. In particular, it is novelty found that the positive CER value of PbPdO2 with I = 10 μA and T = 10 K reached about 300%. Moreover, the cyclic ρI (T) curves were also measured for I = 0.01 and 10 μA going back and forth between 10 K and 400 K. The time dependences of ρt/ρ0 ratio with T = 100 K, 300 K, 400 K and I = 0.01 and 0.1 μA were also obtained. A critical temperature Tc with about T = 260 K for all applied currents was found. As T > Tc，the band gap of the film is enhanced by the combined effect of the temperature and current. At the same time, Pb and O vacancies, and the evolution of oxygen valence states in the PbPdO2 film were observed by energy dispersive spectrometer (EDS), electron paramagnetic resonance (EPR) and in-situ x-ray photoelectron spectroscopy (XPS). Especially, the charge transport between O1− and O2− was confirmed by in-situ XPS. Finally, based on first-principles calculation, an internal electric field model and its induced potential barrier were established, which well explains the positive CER effect and the critical temperature Tc.

Comprehensive Analysis of Electric Field Characteristics for Multi-Winding Medium Frequency Transformer

The multi-winding medium frequency transformer (MMFT) has attracted widespread attention, since its application in power electronic transformers can simplify the system structure and reduce the volume and weight. However, the special working conditions of MMFT due to high voltage and high power density increase the difficulty of insulation design for MMFT. For this issue, this paper presents a comprehensive analysis of electric filed characteristics for MMFT. First, the electric field model of MMFT is established using the 2-D finite element method. Based on it, the influences of connection mode, core structure, and hollow winding on the electric field characteristics of MMFT are studied, including the overall electric field distribution, maximum electric field intensity, and the electric field intensity along a fixed path. The results show that there are differences in the maximum electric field intensity for different connection modes and different core structures, which provides references for MMFT insulation design. The proposed modeling method and analysis results in this paper are important for insulation improvement of MMFT.

On the unusual properties dielectric constant of the electric field of the free atmosphere

On the basis of experimental data vertical distribution electric field strength of the atmosphere, the applied problem of fitting constants in the model of the average self-consistent electric field is solved.The model is based on the nonlinear Poisson equation. Such an approach is not trivial because generally known in meteorology interpolation exponential function describing the empirical distribution of the electric field, space charge density and conductivity with a height not quite correctly reproduce a stable stratification of the electric field. Since aircraft measurements are carried out in a natural environment, the dielectric constant is lost, which leads to underestimated values of the electron-ion concentration.This is due to the fact that the potential in situ is screened and the Gauss theorem does not hold for it, and if it does, then for the radius of the Gaussian sphere it is less than the Debye screening radius. For a large Gaussian sphere, only the near-wall part of the electrometer is experimentally determined, and the shielded (inner) part does not contribute to the field flux through the surface by the dynamic screening of the electron. The magnitude of the screening of electrons in air is very large due to the dynamic polarizability of the medium and consists of two parts — the Debye and ion-plasma screening spheres. This, in turn, requires a redefinition of the dielectric constant for correct reproduction of field measurements. Thus, the verification of the dielectric constant was carried out on different experimental data, and its values lie within the same limits as the values obtained from the classical relations of Penn, Debye, and Landau.

Analysis of electrostatic levitation control system and oscillation method for material properties measurement.

Electrostatic levitation is an important method of studying material properties. Without using a container, a physical object is levitated between electrostatic plates and melted to the liquid state using a laser. Then, measurements are made via fast cooling or oscillation. Control technology is critical to the electrostatic levitation system. Uncertainty regarding the sample charge during the start-up and laser-melting periods often causes disturbances or causes levitation to fail. In this paper, we design a two-step adaptive control strategy with charge estimation and feed-forward control. This method can better adapt to charge uncertainty during the initial stage. In addition, we propose an innovative new method of superimposing oscillation signals via software to measure the material surface tension and viscosity. Unlike the traditional method, this approach does not require extra hardware resources and is flexible with regard to regulating the frequency and amplitude. A control system model with an accurate electric field model is established and used to simulate control progress in order to illustrate the advantage of our control method. Experiments based on a high-speed vision-servo system also validate the effectiveness of the adaptive and oscillation control strategies.

Comparison of electric field modeling pipelines for transcranial direct current stimulation

ObjectivesElectric field modeling utilizes structural brain magnetic resonance images (MRI) to model the electric field induced by non-invasive transcranial direct current stimulation (tDCS) in a given individual. Electric field modeling is being integrated with clinical outcomes to improve understanding of inter-individual variability in tDCS effects and to optimize tDCS parameters, thereby enhancing the predictability of clinical effects. The successful integration of modeling in clinical use will primarily be driven by choice of tools and procedures implemented in computational modeling. Thus, the electric field predictions from different modeling pipelines need to be investigated to ensure the validity and reproducibility of tDCS modeling results across clinical or translational studies. MethodsWe used T1w structural MRI from 32 healthy volunteer subjects and modeled the electric field distribution for a fronto-temporal tDCS montage. For five different computational modeling pipelines, we quantitatively compared brain tissue segmentation and electric field predicted in whole-brain, brain tissues and target brain regions between the modeling pipelines. ResultsOur comparisons at various levels did not reveal any systematic trend with regards to similarity or dissimilarity of electric field predicted in brain tissues and target brain regions. The inconsistent trends in the predicted electric field indicate variation in the procedures, routines and algorithms used within and across the modeling pipelines. ConclusionOur results suggest that studies integrating electric field modeling and clinical outcomes of tDCS will highly depend upon the choice of the modeling pipelines and procedures. We propose that using these pipelines for further research and clinical applications should be subject to careful consideration, and indicate general recommendations.

Attenuation of plasmaspheric hiss associated with the enhanced magnetospheric electric field

Abstract. We report an attenuation of hiss wave intensity in the duskside of the outer plasmasphere in response to enhanced convection and a substorm based on Van Allen Probe observations. Using test particle codes, we simulate the dynamics of energetic electron fluxes based on a realistic magnetospheric electric field model driven by solar wind and subauroral polarization stream. We suggest that the enhanced magnetospheric electric field causes the outward and sunward motion of energetic electrons, corresponding to the decrease of energetic electron fluxes on the duskside, leading to the subsequent attenuation of hiss wave intensity. The results indicate that the enhanced electric field can significantly change the energetic electron distributions, which provide free energy for hiss wave amplification. This new finding is critical for understanding the generation of plasmaspheric hiss and its response to solar wind and substorm activity.

Unravelling Ipsilateral Interactions Between Left Dorsal Premotor and Primary Motor Cortex: A Proof of Concept Study

Few studies have identified the intrahemispheric functional connectivity between the ipsilateral dorsal premotor cortex (PMd) and the primary motor hand area (M1hand) due to technical limitations. In this proof-of-concept study, a novel neuronavigated dsTMS set-up was employed, combining stimulation over left PMd and left M1hand using the edge of a butterfly coil and a small cooled-coil. This arrangement was warranted because coil (over)heating and inter coil distance are limiting factors when investigating connectivity between stimulation targets in close proximity and over a longer duration. The proposed set-up was designed to deal with these limitations. Specifically, the effect of four dual-site transcranial magnetic stimulation (dsTMS) protocols on twenty-eight right-handed participants (12 males) was evaluated. These protocols differed in stimulus order, interstimulus interval and current direction induced in PMd. A structural scan with electric (E-)field modeling was obtained from seven participants prior to dsTMS, demonstrating that PMd and M1hand were effectively stimulated. Results indicate that one protocol, in which a latero-medial current was induced in PMd 2.8 ms prior to stimulation over M1hand, induced a sex-mediated effect. In males, significant inhibition of motor-evoked potentials was identified, whereas females demonstrated a facilitatory effect that did not survive correction for multiple comparisons. E-field simulations revealed that the E-field induced by the coil targeting PMd was maximal in PMd, with weaker E-field strengths extending to regions beyond PMd. Summarizing, the current dsTMS set-up enabled stimulating at an inter-target distance of 35 mm without any indications of coil-overheating.

ASHLEY: A New Empirical Model for the High‐Latitude Electron Precipitation and Electric Field

AbstractIn this study, a new high‐latitude empirical model is introduced, named for Auroral energy Spectrum and High‐Latitude Electric field variabilitY (ASHLEY). This model improves specifications of soft electron precipitations and electric field variability that are not well represented in existing high‐latitude empirical models. ASHLEY consists of three components, ASHLEY‐A, ASHLEY‐E, and ASHLEY‐Evar, which are developed based on the electron precipitation and bulk ion drift measurements from the Defense Meteorological Satellite Program (DMSP) satellites during the most recent solar cycle. On the one hand, unlike most existing high‐latitude electron precipitation models, which have assumptions about the energy spectrum of incident electrons, the electron precipitation component of ASHLEY, ASHLEY‐A, provides the differential energy fluxes in the 19 DMSP energy channels under different geophysical conditions without making any assumptions about the energy spectrum. It has been found that the relaxation of spectral assumptions significantly improves soft electron precipitation specifications with respect to a Maxwellian spectrum (up to several orders of magnitude). On the other hand, ASHLEY provides consistent mean electric field and electric field variability under different geophysical conditions by ASHLEY‐E and ASHLEY‐Evar components, respectively. This is different from most existing electric field models which only focus on the large‐scale mean electric field and ignore the electric field variability. Furthermore, the consistency between the electric field and electron precipitation is better taken into account in ASHLEY.