Effects Of Weak Electric Fields Research Articles

Spherical harmonics representation of the steady-state membrane potential shift induced by tDCS in realistic neuron models

Objective. We provide a systematic framework for quantifying the effect of externally applied weak electric fields on realistic neuron compartment models as captured by physiologically relevant quantities such as the membrane potential or transmembrane current as a function of the orientation of the field. Approach. We define a response function as the steady-state change of the membrane potential induced by a canonical external field of 1 V m−1 as a function of its orientation. We estimate the function values through simulations employing reconstructions of the rat somatosensory cortex from the Blue Brain Project. The response of different cell types is simulated using the NEURON simulation environment. We represent and analyze the angular response as an expansion in spherical harmonics. Main results. We report membrane perturbation values comparable to those in the literature, extend them to different cell types, and provide their profiles as spherical harmonic coefficients. We show that at rest, responses are dominated by their dipole terms (), in agreement with experimental findings and compartment theory. Indeed, we show analytically that for a passive cell, only the dipole term is nonzero. However, while minor, other terms are relevant for states different from resting. In particular, we show how and terms can modify the function to induce asymmetries in the response. Significance. This work provides a practical framework for the representation of the effects of weak electric fields on different neuron types and their main regions—an important milestone for developing micro- and mesoscale models and optimizing brain stimulation solutions.

Acute effects of weak electric fields on experimentally derived models of distinct cell types in the cortex

Acute effects of weak electric fields on experimentally derived models of distinct cell types in the cortex

Enhancement effects of weak electric field on uranium and manganese removal from leachate of uranium tailings impoundment by artificial wetland

Artificial wetlands (AWs) planted with Acorus Calamus L. and coupled with weak electric field (WEF) were constructed to investigate the effects of flow direction, hydraulic retention time (HRT), and WEF intensities on the removal of uranium and manganese from leachate of uranium tailings impoundment (LUTI), the distribution characteristics of the uranium and manganese in the AWs, and the growth and physiological responses of the plants in them. The results showed that the optimized removal rates of uranium and manganese from LUTI were observed to be 97.03% and 99.72%, respectively, in the upwelling AW planted with Acorus Calamus L. and coupled with WEF intensity of 0.3 V/cm when the HRT was 72 h. Compared with the group without WEF, the bioaccumulations of uranium and manganese by Acorus Calamus L were increased by 169.23% and 522.91%, respectively, the adsorption capacities of biofilms toward uranium and manganese were increased by 7.38% and 48.90%, respectively, the content of uranium in the substrates was decreased by 10.76%, while the manganese concentration had no significant difference, and the contents of uranium and manganese in the salt scale deposited on the cathode surface reached 51.20 and 653.11 mg/kg, respectively, when the WEF intensity was 0.3 V/cm in the AW. The applied WEF increased the activity of superoxide dismutase (SOD) and the content of glutathione (GSH), and reduced the content of malondialdehyde (MDA) in the leaves of Acorus Calamus L, so as to alleviate the stress of uranium and manganese on wetland plants in the AW. Therefore, the AW has potential application in the removal of uranium and manganese from LUTI.

Combined effect of weak electric field and ions on critical water cluster: Insight from molecular dynamics simulation

The effects of ion and electric field on the vapor–liquid transition of water, are studied by using the optimal point charge (OPC) water model in this paper. A canonical Molecular Dynamics (MD) simulation approach, which calculates equilibrium time and the number of water molecules in the clusters, is employed to study the factors affecting the nucleation of water molecules. In addition, Quantum Mechanics (QM) method is adopted to calculate the hydration free energy of ions as a supplement. The results demonstrate that the ion has a significant promoting effect on vapor–liquid nucleation below the critical nucleus size (1–3 nm). However, as the cluster grows, the ion will no longer promote cluster growth, due to electrostatic shielding effect from the aggregated water molecules. When a weak uniform electric field (less than 0.1 V/nm) is applied, the promotion of the ion reappears. According to the trajectory analysis of ion in the water droplet, we believe that the electric field changes the relative position of ions in the droplets, thus weakening the shielding of water molecules. It is further demonstrated by a proposed novel statistical method, which provides an alternative, visualized and effective approach to evaluate the promotion effect in similar analyses, compared to radial distribution function.

Propagation of Endogenous Electric Fields as a Possible Mechanism of Synchronization of Interictal Spikes in the Rat Neocortex

The effects of weak electric fields with parameters close to those of the electrical activity of brain structures on neural networks in the brain have been studied for several decades. Interest in these studies has increased recently in connection with the fact that the treatment of a number of diseases uses transcranial stimulation methods. The present study used linear regression and correlation analysis to establish a relationship between the magnitude of the interictal spike potential and the magnitude of the potential at the cortical point located a few millimeters from the point at which the spike is generated. A link was also found between the occurrence of interictal spikes at one point of the cortex and the synchronous appearance of electric potentials in neighboring areas. Blockade of sodium channels at the recording points was followed by increases in the linear regression coefficient and the correlation coefficient. This indicated that the actions of electric field potentials were more significant. To identify whether this relationship was random, the time sequence of a single channel was shifted in relation to another using the random numbers principle. The magnitudes of the linear regression and correlation coefficients decreased by an order of magnitude. Our results showed that the electric potential of a small interictal spike arising at one point on the cortex propagates to other areas with a short time delay.

Weak electric fields promote resonance in neuronal spiking activity: Analytical results from two-compartment cell and network models.

Transcranial brain stimulation and evidence of ephaptic coupling have sparked strong interests in understanding the effects of weak electric fields on the dynamics of neuronal populations. While their influence on the subthreshold membrane voltage can be biophysically well explained using spatially extended neuron models, mechanistic analyses of neuronal spiking and network activity have remained a methodological challenge. More generally, this challenge applies to phenomena for which single-compartment (point) neuron models are oversimplified. Here we employ a pyramidal neuron model that comprises two compartments, allowing to distinguish basal-somatic from apical dendritic inputs and accounting for an extracellular field in a biophysically minimalistic way. Using an analytical approach we fit its parameters to reproduce the response properties of a canonical, spatial model neuron and dissect the stochastic spiking dynamics of single cells and large networks. We show that oscillatory weak fields effectively mimic anti-correlated inputs at the soma and dendrite and strongly modulate neuronal spiking activity in a rather narrow frequency band. This effect carries over to coupled populations of pyramidal cells and inhibitory interneurons, boosting network-induced resonance in the beta and gamma frequency bands. Our work contributes a useful theoretical framework for mechanistic analyses of population dynamics going beyond point neuron models, and provides insights on modulation effects of extracellular fields due to the morphology of pyramidal cells.

Stability of the 5/2 fractional quantum Hall state in a Corbino disc sample with in-plane electric fields

Among the various geometries to study the fractional quantum Hall effect in two dimensional electron gas, the Corbino disc owns the advantage to probe the bulk properties directly. In this work we explore the influence of in-plane electric fields on the stability of the 5/2 fractional quantum Hall state realized in Corbino geometry. The effect of weak electric fields is investigated at ultra-low temperatures in order to compare with a theoretical proposal of enhanced Pfaffian state under weak electric fields.

Electrically tuned Förster resonances in collisions of NH3 with Rydberg He atoms

The effects of weak electric fields on resonant energy transfer between ${\mathrm{NH}}_{3}$ in the $X$ ${^{1}A}_{1}$ ground electronic state and Rydberg He atoms in triplet states with principal quantum numbers $n=36$--41 have been studied in a crossed-beam apparatus. For these values of $n$, electric dipole transitions between the Rydberg states that evolve adiabatically to the $|ns\ensuremath{\rangle}$ and $|np\ensuremath{\rangle}$ states in zero electric field can be tuned into resonance with the ground-state inversion transitions in ${\mathrm{NH}}_{3}$ using electric fields, with energy transfer occurring via F\"orster resonance. In the experiments the Rydberg He atoms, traveling in pulsed supersonic beams, were prepared by resonant two-photon excitation from the metastable $1s2s\phantom{\rule{0.16em}{0ex}}{^{3}S}_{1}$ level and crossed an effusive beam of ${\mathrm{NH}}_{3}$ before being detected by state-selective pulsed-electric-field ionization. The resonant-energy-transfer process was identified by monitoring changes in the ionization signal from the $|ns\ensuremath{\rangle}$ and $|np\ensuremath{\rangle}$ Rydberg states for each value of $n$. The electric-field dependence of the experimental data is in good agreement with the results of calculations in which the resonant dipole-dipole coupling between the collision partners was accounted for.

T024 Modulation of gamma oscillations dynamics by weak electric fields

We are interested in the acute effects of weak electric fields on gamma oscillations, which is a critical neural substrate of information processing in the hippocampus. Stimulation with weak currents is known to have a relatively small effect on the firing of individual neurons. Yet, when applying stimulation during gamma activity in rodent slices, we find that the effects of fields are significantly amplified by the neuronal network. Using a computational model we demonstrate that this amplification is the result of the dynamic push and pull of the excitatory/inhibitory feedback loop, which is the hallmark of gamma oscillations. The recorded effects have a mixed spatial distribution in CA3, which is the hippocampal region with the strongest recursive feedback and the main generator of gamma activity. This recursive structure is sometimes thought to be the core processing unit for associative memories. Interestingly, when applying constant current stimulation, the enhancement of gamma activity and neuronal firing outlast the period of stimulation by several minutes, suggesting plastic effects of DC stimulation on this important associative neuronal network.

Extending Integrate-and-Fire Model Neurons to Account for the Effects of Weak Electric Fields and Input Filtering Mediated by the Dendrite

Transcranial brain stimulation and evidence of ephaptic coupling have recently sparked strong interests in understanding the effects of weak electric fields on the dynamics of brain networks and of coupled populations of neurons. The collective dynamics of large neuronal populations can be efficiently studied using single-compartment (point) model neurons of the integrate-and-fire (IF) type as their elements. These models, however, lack the dendritic morphology required to biophysically describe the effect of an extracellular electric field on the neuronal membrane voltage. Here, we extend the IF point neuron models to accurately reflect morphology dependent electric field effects extracted from a canonical spatial “ball-and-stick” (BS) neuron model. Even in the absence of an extracellular field, neuronal morphology by itself strongly affects the cellular response properties. We, therefore, derive additional components for leaky and nonlinear IF neuron models to reproduce the subthreshold voltage and spiking dynamics of the BS model exposed to both fluctuating somatic and dendritic inputs and an extracellular electric field. We show that an oscillatory electric field causes spike rate resonance, or equivalently, pronounced spike to field coherence. Its resonance frequency depends on the location of the synaptic background inputs. For somatic inputs the resonance appears in the beta and gamma frequency range, whereas for distal dendritic inputs it is shifted to even higher frequencies. Irrespective of an external electric field, the presence of a dendritic cable attenuates the subthreshold response at the soma to slowly-varying somatic inputs while implementing a low-pass filter for distal dendritic inputs. Our point neuron model extension is straightforward to implement and is computationally much more efficient compared to the original BS model. It is well suited for studying the dynamics of large populations of neurons with heterogeneous dendritic morphology with (and without) the influence of weak external electric fields.

Extending integrate-and fire model neurons to account for the effects of weak electric fields in the presence of dendrites

Transcranial brain stimulation techniques have recently sparked a strong interest in understanding the effects of weak electric fields on neuronal network dynamics (e.g. [1,2]). The collective dynamics of large populations of coupled neurons can be efficiently studied using single-compartment (point) model neurons of the integrate-and-fire (IF) type [3], which allow for a systematic model reduction at the population level [4,5], as opposed to multi-compartment Hodgkin-Huxley type models and complex morphologies. However, existing point neuron models cannot adequately reproduce the effects of an electric field on the somatic membrane potential, which are influenced by the presence of dendritic processes [2]. Here, we present an extension for IF type point neuron models to take into account the subthreshold effects of an oscillating weak uniform extracellular field, similar to those generated in the brain by transcranial electrical stimulation [6]. Based on a ball-and-stick neuron model (i.e., a passive finite dendritic cable with a lumped soma at its end) we analytically calculate the somatic membrane polarization induced by a weak extracellular electric field using the cable equation. From this polarization we derive an equivalent input current for leaky IF as well as adaptive nonlinear IF point neurons, which explicitly depends on the (soma+dendrite) neuron model and electric field parameters. The extended point neuron model can well reproduce the relationships between electric field properties (intensity, frequency) and neuronal responses (membrane polarization, sensitivity and phase), as observed by simulations of neuron models with complex morphologies and reported in the experimental literature [7]. Our point neuron model extension is simple to implement and well suited for application in IF based neural networks.

Dust gravitational drift wave in complex plasma under gravity

The dispersion relation of electrostatic waves in a complex plasma under gravity is presented. It is assumed that the waves propagate parallel to the external fields. The effects of weak electric field, neutral drag force, and ion drag force are also taken into account. The dispersion relation is numerically examined in an appropriate parameter space in which the gravity plays the dominant role in the dynamics of microparticles. The numerical results show that, in the low pressure complex plasma under gravity, a low frequency drift wave can be developed in the long wavelength limit. The stability state of this wave is switched at a certain critical wavenumber in such a way that the damped mode is transformed into a growing one. Furthermore, the influence of the external fields on the dispersion properties is analyzed. It is shown that the wave instability is essentially due to the electrostatic streaming of plasma particles. It is also found that by increasing the electric field strength, the stability switching occurs at smaller wavenumbers.

Dust magneto-gravitational drift wave in g×B configuration

The dispersion relation of electrostatic waves in a magnetized complex plasma under gravity is presented. It is assumed that the waves propagate perpendicular to the external fields. The effects of weak electric field, neutral drag force, and ion drag force are also taken into account. The dispersion relation is numerically examined in an appropriate parameter space in which the gravity plays the dominant role in the dynamics of magnetized microparticles. The numerical results show that an unstable low frequency drift wave can be developed in the long wavelength limit. This unstable mode is transformed into an aperiodic stationary structure at a cut-off wavenumber. Furthermore, the influence of the external fields on the dispersion properties is analyzed. It is shown that the instability is essentially due to the E×B drift motion of plasma particles. However, in the absence of weak electric field, the g×B drift motion of microparticles can cause the instability in a wide range of wavenumbers. It is also found that by increasing the magnetic field strength, the wave frequency is first increased and then decreased. This behaviour is explained by the existence of an extremum point in the dust magneto-gravitational drift velocity.

Transient electric field response of laminar premixed flames

In this study the effects of weak electric fields on laminar premixed Bunsen flames were studied using planar laser-induced fluorescence (PLIF) of the formaldehyde molecules and the OH-radicals for flame structure characterization. Simultaneously particle image velocimetry (PIV) is applied to determine the changed flow field of the flame when a positively charged electrode is placed over a laminar Bunsen type flame while the burner is grounded. By application of static fields the flame front is pushed towards the burner and is constrained, which can be attributed to the momentum transfer by the ionic wind. For rich flames the ionic wind effect is intensified due to the increase of the charge carriers and larger momentum transfer of positively charged ions to the neutral species. Consequently, a stronger flow deceleration results in the order of 0.8–1.6m/s in the post-oxidation zone at supply voltages of 6kV. The ionic wind was maximized for increased flow velocity which is attributed to the increased flame surface and number of charged species. An excitation of the flame with voltage step functions was conducted to study its transient behavior. First flame response was detected at the flame root point with a response time of 2–4ms, which is an order of magnitude faster than values provided in the literature for the integral flame. This first flame response occurred after the space charge zones were built-up and the main flame response was detected 6ms after the voltage rising edge in the whole flame.

Tunability of absorption threshold frequencies and Stark shift in the InSb narrow gap spherical quantum layer

In this work the interband optical absorption and Stark shift in the ensemble of InSb spherical quantum layers are investigated. Calculations are carried out both for the cases of parabolic and Kane's dispersion laws. The distribution of layers by their inner radii is taken into account. The effect of weak electric field on the energy levels coupling is investigated as well. It is found out that the energy spectrum 1s1p1d2s1f2p… for spherical quantum dot turns to the spectrum 1s1p1d1f2s2p… for spherical quantum layer with enough large value of inner radius. It is also shown that in the spherical quantum layer, where the coupling between neighboring states is not negligible, there is no square low dependence of Stark shift on electric field strength in contrast to the rotator model.

Multifractal analysis of the electronic states in the Fibonacci superlattice under weak electric fields

Influence of the weak electric field on the electronic structure of the Fibonacci superlattice is considered. The electric field produces a nonlinear dynamics of the energy spectrum of the aperiodic superlattice. Mechanism of the nonlinearity is explained in terms of energy levels anticrossings. The multifractal formalism is applied to investigate the effect of weak electric field on the statistical properties of electronic eigenfunctions. It is shown that the applied electric field does not remove the multifractal character of the electronic eigenfunctions, and that the singularity spectrum remains non-parabolic, however with a modified shape. Changes of the distances between energy levels of neighbouring eigenstates lead to the changes of the inverse participation ratio of the corresponding eigenfunctions in the weak electric field. It is demonstrated, that the local minima of the inverse participation ratio in the vicinity of the anticrossings correspond to discontinuity of the first derivative of the difference between marginal values of the singularity strength. Analysis of the generalized dimension as a function of the electric field shows that the electric field correlates spatial fluctuations of the neighbouring electronic eigenfunction amplitudes in the vicinity of anticrossings, and the nonlinear character of the scaling exponent confirms multifractality of the corresponding electronic eigenfunctions.

Electric Field-induced dynamical evolution of spiral wave in the regular networks of Hodgkin–Huxley neurons

An additional gradient force is often used to simulate the polarization effect induced by the external field in the reaction–diffusion systems. The polarization effect of weak electric field on the regular networks of Hodgkin–Huxley neurons is measured by imposing an additive term V E on physiological membrane potential at the cellular level, and the dynamical evolution of spiral wave subjected to the external electric field is investigated. A statistical variable is defined to study the dynamical evolution of spiral wave due to polarization effect. In the numerical simulation, 40000 neurons placed in the 200 × 200 square array with nearest neighbor connection type. It is found that spiral wave encounters death and the networks become homogeneous when the intensity of electric field exceeds the critical value, otherwise, spiral wave keeps alive completely. On the other hand, breakup of spiral wave occurs as the intensity of electric field exceeds the critical value in the presence of weak channel noise, otherwise, spiral wave keeps robustness to the external field completely. The critical value can be detected from the abrupt changes in the curve for factors of synchronization vs. control parameter, a smaller factor of synchronization is detected when the spiral wave keeps alive.

Chemical effects of weak electric fields in the trailing columns of sprite streamers

The chemical effects of undervoltage electric fields in the trailing columns of sprite streamers are investigated. The existence of such fields is suggested by observations of ELF radiation associated with optical emissions of bright sprites that has been interpreted as evidence for intense electrical currents flowing in the body of the sprite. In this paper an earlier nonlinear coupled chemical kinetics modelling study involving 80+ species and 800+ reactions of the chemical response to the passage of a sprite streamer at 70 km altitude is extended to include undervoltage fields in the trailing region behind the compact streamer head that would be responsible for driving such currents. Recent high speed imaging observations combined with chemical modelling results suggest that the trailing field is less than ∼0.5Ek, where Ek is the threshold electric field for the ionization avalanche. Electron densities are slightly decreased on account of enhanced dissociative attachment in the undervoltage environment. The effects on the densities of O(3P) and the metastable species O(1D) and are enhancements by a modest factor of 2 or less compared with a field-free tail. O2(a 1Δg) shows slightly greater enhancements, by up to a factor of 3, and O− shows enhancements by up to a factor of 5.

Effect of laser radiation and electric field on combustion of hydrocarbon-air mixtures

Publications on combustion of hydrocarbon-air mixtures under the action of a weak electric field and laser radiation are analyzed. A specific feature of the authors’ experimental study is a pulsed-periodic action of an electric field and focused laser radiation, which does not lead to electric discharge or optical breakdown. Numerous experiments reveal a noticeable effect of weak electric fields on combustion processes. Application of an electric field may result in expansion of the limits of flammability and combustion of fuel-air mixtures, changes (decrease or increase) in the burning rate, shifting of flame stabilization toward lean mixtures, reduction of the concentration of hazardous substances (for instance, NOx and CO) in combustion products, etc.

Effect of electrokinetic transport on the vulnerability of PAH-degrading bacteria in a model aquifer

There has been increasing interest in employing electro-bioremediation, a hybrid technology of bioremediation and electrokinetics, to overcome the low bioavailability of hydrophobic organic contaminants (HOC) by homogenizing sorption-retarded HOC and immobilised microorganisms. Present electro-remediation approaches mainly aim at macroscale pollutant extraction and tend to neglect possible impacts of direct current (DC) on the physiology of microorganisms. The effect of weak electric fields (X = 1 V cm(-1)) on the fitness of electrokinetically dispersed fluorene-degrading Sphingomonas sp. LB126 in bench-scale model aquifers was investigated by flow cytometry using propidium iodide (PI) as an indicator that distinguishes between PI-permeable (cells with porous membranes, i.e. dead or vulnerable) and PI-impermeable bacteria. After 15.5 h of DC treatment 56% of all cells recovered were dispersed at the centimetre scale relative to 29% in the absence of DC. There was no overall negative effect of the 15.5-h DC treatment on cell vulnerability, as 7.0% of the DC-treated bacteria exhibited PI-staining compared to 6.5% of the control population. Minor differences were observed in the subpopulation that had been mobilised by electroosmosis with an approximately twofold increase in the percentage of PI-stained cells relative to the control. Enhanced PI staining did not correlate with reduced culturability of the cells on rich-medium agar plates. Relative to the control, DC-treated cells mobilised by electroosmosis were threefold more culturable, confirming earlier data that that PI-cell membrane permeability does not always indicate reduced viability of oligotrophic environmental bacteria. Our findings suggest that electrokinetics is a valuable mechanism to transport viable and culturable polycyclic aromatic hydrocarbon (PAH)-degrading bacteria in soil or sediments.