Electric Field Oscillations Research Articles

Steady states stability features of the electron–positron plasma diode

Stationary states stability features of a planar geometry diode with electron and positron counter flows are studied. Such a diode may be considered as a model to elucidate the nature of the pulsar radio emission. The equation for the electric field perturbation amplitude is derived. The exact solution of this equation for the homogeneous stationary field is found. On the basis of the plasma dispersion relation, the stability threshold in terms of the electron current density is found above which the stationary solutions become unstable. This threshold turned out to be 2 times higher than the known Pierce threshold. It can be expected that the development of the detected instability will lead to the electric field oscillations that induce electromagnetic radiation.

Excitation of "forbidden" guided-wave plasmon polariton modes via direct reflectance using a low refractive index polymer coupling layer.

A surface plasmon polariton (SPP) is an excitation resulting from the coupling of light to a surface charge oscillation at a metal-dielectric interface. The excitation and detection of SPPs is foundational to the operating mechanism of a number of important technologies, most of which require SPP excitation via direct reflectance, commonly achieved via Attenuated Total Reflection (ATR) using the Kretschmann configuration. As a result, the accessible modes are fundamentally high-loss “leaky modes,” presenting a critical performance barrier. Recently, our group provided the first demonstration of “forbidden,” or guided-wave plasmon polariton modes (GW-PPMs), collective modes of a MIM structure with oscillatory electric field amplitude in the central insulator layer with up to an order of magnitude larger propagation lengths than those of traditional SPPs. However, in that work, GW-PPMs were accessed by indirect reflectance using Otto configuration ATR, making them of limited applied relevance. In this paper, we demonstrate a technique for direct reflectance excitation and detection of GW-PPMs. Specifically, we replace the air gap used in traditional Otto ATR with a low refractive index polymer coupling layer, mirroring a technique previously demonstrated to access Long-Range Surface Plasmon Polariton modes. We fit experimental ATR data using a robust theoretical model to confirm the character of the modes, as well as to explore the potential of this approach to enable advantageous propagation lengths. The ability to excite GW-PPMs using a device configuration that does not require an air gap could potentially enable transformative performance enhancements in a number of critical technologies.

Ion‐Ion Cross‐Field Instability of Lower Hybrid Waves in the Inner Coma of Comet 67P

AbstractWe show that an ion‐ion cross‐field streaming instability between cold newborn cometary ions and heated heavy ions that were picked up upstream is likely a contributing source of observed lower hybrid (LH) waves in the inner coma of comet 67P/Churyumov‐Gerasimenko. Electric field oscillations in the LH frequency range are common here, and have previously been attributed mainly to the lower‐hybrid drift instability, driven by gradients associated with observed local density fluctuations. However, the observed wave activity is not confined to such gradients, nor is it always strongest there. Thus, other instabilities are likely needed as well to explain the observed wave activity. Several previous works have shown the existence of multiple populations of cometary ions in the inner coma of 67P, distinguished by differences in mass, energy and/or flow direction. We here examine two selected time intervals in October and November 2015, with substantial wave activity in the LH frequency range, where we identify two distinct cometary ion populations: a bulk population of locally produced, predominantly radially outflowing ions, and a more tenuous population picked up further upstream and accelerated back toward the comet by the solar wind electric field. These two populations exhibit strong relative drifts (∼20 km/s, or about five times the pickup ion thermal velocity), and we perform an electrostatic dispersion analysis showing that conditions should be favorable for LH wave generation through the ion‐ion cross‐field instability.

Magnetic Field Alignment and Optical Anisotropy of MoS2 Nanosheets Dispersed in a Liquid Crystal Polymer.

Molybdenum disulfide (MoS2) nanosheets exhibit anisotropic optical and electronic properties, stemming from their shape and electronic structure. Unveiling this anisotropy for study and usage in materials and devices requires the ability to control the orientation of dispersed nanosheets, but to date this has proved a challenging proposition. Here, we demonstrate magnetic field driven alignment of MoS2 nanosheets in a liquid crystal (LC) polymer and unveil the optical properties of the resulting anisotropic assembly. Nanosheet optical anisotropy is observed spectroscopically by Raman and direction-dependent photoluminescence (PL) measurements. Resulting data indicate significantly lower PL emission due to optical excitation with electric field oscillation out of plane, parallel to the MoS2 c-axis, than that associated with perpendicular excitation, with the dichroic ratio Iperp/Ipar = 3. The approach developed here provides a useful route to elucidate anisotropic optical properties of MoS2 nanosheets and to utilize such properties in new materials and devices.

Poleward Moving Auroral Arcs and Pc5 Oscillations

AbstractWe present an example of one‐to‐one correspondence between poleward moving auroral arcs (PMAAs) and Pc5 oscillations observed at the Time History of Events and Macroscale Interactions during Substorms (THEMIS) Ground Based Observatory station Gillam. The PMAAs consisted of four successive intensifications (named PMAA1, PMAA2, PMAA3 and PMAA4) with a period of 3∼4 min over the magnetic latitudes from 68° to 70° in the auroral oval and varied coherently with the H‐component of magnetic field Pc5 oscillations. PMAA1 and PMAA2 appeared clearly at the magnetic latitude ∼69°, and the following two PMAAs, which were dimmer, appeared at the magnetic latitude ∼68°. PMAA1 and PMAA2 exhibited features of field‐line resonances with the maximum luminosity at the magnetic latitude ∼69.5° and ∼69.4°, respectively. The ground Pc5 oscillations were concurrent with toroidal mode Pc5 oscillation observed at the THEMIS‐D, ‐E, and ‐A satellites at ∼4 MLT in the outer magnetosphere. The magnetic and electric field oscillations at THEMIS were synchronized with the PMAAs. The magnetic energy of the THEMIS Pc5 oscillations is estimated using a numerical model of damped toroidal oscillations and compared with the kinetic energy of precipitating electrons associated with the field aligned current carried by the toroidal oscillations. The result reveals that the Pc5 magnetic energy is much larger than the kinetic energy, implying the magnetic energy is important for producing auroral emissions in the ionosphere. We also perform a simulation of the relationship between PMAAs and toroidal mode Pc5 oscillations. The simulation explains the observed spatial and temporal structures of the PMAAs.

Electrically stimulated bioactivity in hydroxyapatite/β-tricalcium phosphate/polyvinylidene fluoride biocomposites

The search for new advanced biomaterials with special characteristics that allow the development of novel techniques to accelerate the healing process of economically active individuals has been widely encouraged. In recent years, electrical stimuli have emerged as potential tools for accelerating bone cell regeneration. In this study, hydroxyapatite/β-tricalcium phosphate/polyvinylidene fluoride biocomposites were synthesized, and electrical stimuli were used to improve and accelerate bone regeneration in vitro. Scanning electron microscopy, fast Fourier transform infrared, and energy-dispersive X-ray spectroscopy analyses revealed the strong influence of oscillating electric fields on the kinetics of apatite (synthetic bone) growth on the studied biocomposites. Biocomposite samples immersed in simulated body fluid exhibit higher apatite growth rates under the application of an oscillating (3 Hz) electric field of 235 kV/m for 36 h in comparison with samples not subjected to the electric stimulus.

Multi-Component Electroacoustic Waves (Mceaw) In Piezo Crystalline Textures: Applied Opportunities

In this paper is shown, that in each sagittal plane of the piezoelectric texture, both the one-component elastic shear wave and the two-component elastic plane deformation wave can be accompanied by either oscillations of the transverse component of the electric field or oscillations of the plane electric field. Four such packets of multicomponent electroelastic waves are formed.Necessary and sufficient conditions are obtained that allow the formulation of a two-dimensional problem of electroelasticity in a vibrated sagittal plane of a piezocrystal, where separate excitation and propagation of a multicomponent quasistatic electroelastic wave is possible.

Spectroscopy of Electric-Field Oscillations in the Solar Wind During the Passage of a Type III Radio Burst Using Observations Compared with Self-Similar Theory

Spectroscopy of Electric-Field Oscillations in the Solar Wind During the Passage of a Type III Radio Burst Using Observations Compared with Self-Similar Theory

Bistability of Dielectrically Anisotropic Nematic Crystals and the Adaptation of Endothelial Collectives to Stress Fields.

Endothelial monolayers physiologically adapt to flow and flow‐induced wall shear stress, attaining ordered configurations in which elongation, orientation, and polarization are coherently organized over many cells. Here, with the flow direction unchanged, a peculiar bi‐stable (along the flow direction or perpendicular to it) cell alignment is observed, emerging as a function of the flow intensity alone, while cell polarization is purely instructed by flow directionality. Driven by the experimental findings, the parallelism between endothelia is delineated under a flow field and the transition of dual‐frequency nematic liquid crystals under an external oscillatory electric field. The resulting physical model reproduces the two stable configurations and the energy landscape of the corresponding system transitions. In addition, it reveals the existence of a disordered, metastable state emerging upon system perturbation. This intermediate state, experimentally demonstrated in endothelial monolayers, is shown to expose the cellular system to a weakening of cell‐to‐cell junctions to the detriment of the monolayer integrity. The flow‐adaptation of monolayers composed of healthy and senescent endothelia is successfully predicted by the model with adjustable nematic parameters. These results may help to understand the maladaptive response of in vivo endothelial tissues to disturbed hemodynamics and the progressive functional decay of senescent endothelia.

Comparison of in vitro corrosion products on CoCrMo generated via oscillatory electric fields before and after removal of proteinaceous layer

Although surgical success and patient mobility have greatly benefited from the increased modularity found in modern hip prosthetics, significant corrosion complications remain. Whereas the majority of biometallic corrosion research focuses on fretting and/or crevice corrosion, this manuscript investigates a largely unexplored biometallic corrosion phenomenon, induced via low magnitude, high frequency electric potential oscillations without mechanical wear.A detailed comparative study is provided for each test condition before and after the removal of the organic deposition film. Samples shielded from electrical oscillation showed no corrosion activity, whereas samples subjected to electrical activity showed significant corrosion activity. Consistent with in vivo corrosion analysis, the protruding growths contained: Cr2O3, CoO, CoOH, and compounds containing Ca, P, and Cr (VI). In addition to protruding growths, select electrical activity is identified as initiating significant pitting between the organic layer and the metallic surface.This manuscript highlights the following key findings: 1. The presence of low magnitude, high frequency electrical oscillation is sufficient to generate corrosion products, chemically consistent with those recovered in vivo. 2. Variation in electrical signal form significantly alters the initial organic deposition and predominate corrosion mode. 3. The formation of surface pitting, under electrical excitation, was preceded by substantial accumulation of P and Ca in the organic deposition layer.

Ohmic vs. conventional heating: Influence of moderate electric fields on properties of egg white protein gels

The present study investigates properties of heat-induced, self-standing gels of globular proteins. Native egg white protein (EWP) with 9,8 wt% protein and 0,395 wt% NaCl content was adjusted to pH = 7,0 and heated from 25 to 85 °C via Ohmic heating (OH) and conventional heating (COV) with respective come-up times (CUT, 240 and 1200 s) and holding times (HOLD, 30 and 900 s). Gels heated under OH showed lower denaturation levels and less water holding capacity. When HOLD was short, the firmness of OH gels exceeded COV gel firmness but deceeded at long HOLD. Similarly, at short HOLD OH samples presented higher hydrophobic interactions whereas at long HOLD COV gels showed more hydrophobic interactions. This correlated with changes of intermolecular beta-sheet structures which increased with HOLD at COV but decreased or remained unchanged during OH. Furthermore, as an SDS-PAGE revealed the main EWP, ovalbumin, did not fully denature when heated via OH, this lead to the assumption that the oscillatory electric field partially interferes the complete denaturation and development of intermolecular beta-sheet structures and hydrophobic interactions during thermal gelation of this protein. Scanning electron microscopy also showed deviances in network structures between OH and COV as COV gels exhibited a denser and OH gels a more open and porous network structure.

Single-shot measurement of few-cycle optical waveforms on a chip

The measurement of transient optical fields has proven critical to understanding the dynamical mechanisms underlying ultrafast physical and chemical phenomena, and is key to realizing higher speeds in electronics and telecommunications. Complete characterization of optical waveforms, however, requires an optical oscilloscope capable of resolving the electric field oscillations with sub-femtosecond resolution and with single-shot operation. Here, we show that strong-field nonlinear excitation of photocurrents in a silicon-based image sensor chip can provide the sub-cycle optical gate necessary to characterize carrier-envelope phase-stable optical waveforms in the mid-infrared. By mapping the temporal delay between an intense excitation and weak perturbing pulse onto a transverse spatial coordinate of the image sensor, we show that the technique allows single-shot measurement of few-cycle waveforms.

Effect of ionization waves on dust chain formation in a DC discharge

An interesting aspect of complex plasma is its ability to self-organize into a variety of structural configurations and undergo transitions between these states. A striking phenomenon is the isotropic-to-string transition observed in electrorheological complex plasma under the influence of a symmetric ion wake field. Such transitions have been investigated using the Plasma Kristall-4 (PK-4) microgravity laboratory on the International Space Station. Recent experiments and numerical simulations have shown that, under PK-4-relevant discharge conditions, the seemingly homogeneous direct current discharge column is highly inhomogeneous, with large axial electric field oscillations associated with ionization waves occurring on microsecond time scales. A multi-scale numerical model of the dust–plasma interactions is employed to investigate the role of the electric field in the charge of individual dust grains, the ion wake field and the order of string-like structures. Results are compared with those for dust strings formed in similar conditions in the PK-4 experiment.

Driving electrochemical corrosion of implanted CoCrMo metal via oscillatory electric fields without mechanical wear

Decades of research have been dedicated to understanding the corrosion mechanisms of metal based implanted prosthetics utilized in modern surgical procedures. Focused primarily on mechanically driven wear, current fretting and crevice corrosion investigations have yet to precisely replicate the complex chemical composition of corrosion products recovered from patients’ periprosthetic tissue. This work specifically targets the creation of corrosion products at the metal on metal junction utilized in modular hip prosthetics. Moreover, this manuscript serves as an initial investigation into the potential interaction between implanted CoCrMo metal alloy and low amplitude electrical oscillation, similar in magnitude to those which may develop from ambient electromagnetic radiation. It is believed that introduction of such an electrical oscillation may be able to initiate electrochemical reactions between the metal and surrounding fluid, forming the precursor to secondary wear particles, without mechanically eroding the metal’s natural passivation layer. Here, we show that a low magnitude electrical oscillation (≤ 200 mV) in the megahertz frequency (106 Hz) range is capable of initiating corrosion on implanted CoCrMo without the addition of mechanical wear. Specifically, a 50 MHz, 200 mVpp sine wave generates corrosion products comprising of Cr, P, Ca, O, and C, which is consistent with previous literature on the analysis of failed hip prosthetics. These findings demonstrate that mechanical wear may not be required to initiate the production of chemically complex corrosion products.

Lane dynamics in pair-ion plasmas: effect of obstacle and geometric aspect ratio

Lane formation dynamics of driven two-dimensional pair-ion plasmas is investigated in under-damped cases where the effect of particle inertia cannot be neglected. Extensive Langevin dynamics simulations using an OpenMP parallel program are carried out to analyse the effect of obstacle and geometric aspect ratio on lane formation dynamics previously reported in Sarma et al. (Phys. Plasmas, vol. 27, 2020, 012106) and Baruah et al. (J. Plasma Phys., vol. 87, 2021, 905870202). Lanes are found to form when like particles move along or opposite to the applied field direction. Lane order parameter, cumulative order parameter and distribution of the order parameter have been implemented to detect phase transition. The effect of geometric aspect ratio on the stability of lanes is systematically determined in both the presence and absence of an obstacle. Here, a specular reflective boundary condition is implemented to mimic an obstacle. We demonstrate that an obstacle promotes the merging of lanes, and the system gradually transitions to a partially mixed phase with higher value of aspect ratio. The occurrence of lane mixing phenomena at the separation boundary of two oppositely flowing lanes at higher value of aspect ratio is observed. In the presence of an oscillatory electric field, the lane merging tendency is reduced to a large extent as compared to the system where a constant electric field is applied. Furthermore, in the presence of both space- and time-varying electric fields, an appearance of a void is observed on either side of the obstacle. The study finds that the presence of an external magnetic field promotes acceleration of the phase transition process towards the lane mixing phase; it also reveals the existence of electric field drift in the system. Our findings may prove to be useful in understanding the nature of lane dynamics in naturally occurring pair-ion plasma systems as well as their relevance to technological applications that exploit or mitigate self-organization.

Harmonic Extraction in Graphene: Monte Carlo Analysis of the Substrate Influence.

Graphene on different substrates, such as SiO, h-BN and AlO, has been subjected to oscillatory electric fields to analyse the response of the carriers in order to explore the generation of terahertz radiation by means of high-order harmonic extraction. The properties of the ensemble Monte Carlo simulator employed for such study have allowed us to evaluate the high-order harmonic intensity and the spectral density of velocity fluctuations under different amplitudes of the periodic electric field, proving that strong field conditions are preferable for the established goal. Furthermore, by comparison of both harmonic intensity and noise level, the threshold bandwidth for harmonic extraction has been determined. The results have shown that graphene on h-BN presents the best featuring of the cases under analysis and that in comparison to III–V semiconductors, it is a very good option for high-order harmonic extraction under AC electric fields with large amplitudes.

Two-dimensional colloidal particle assembly in ionic surfactant solutions under an oscillatory electric field

Assembling colloidal particles under oscillatory electric field (OEF) has become an emerging bottom-up technique to synthesize advanced materials and fabricate micro/nano devices. Surfactants have often been used in colloidal dispersions to improve their stability. However, the precise role of surfactants in particle assembly processes under OEF is unknown. Here, we systematically study the effects of ionic surfactants on the colloidal particle assembly process subject to a fixed OEF, by using an anionic surfactant (sodium dodecyl sulfate) and a cationic surfactant (cetyltrimethylammonium bromide). In the concentration range below the critical micelle concentration (CMC), the particles tend to form three different aggregate structures, including randomly close-packed, hexagonally close-packed crystals, and randomly non close-packed structures. In the concentration range at CMC and above, the particles cannot assemble into any aggregate structures under the given OEF. With increasing surfactant concentration, the average interparticle separation distance within the aggregate can be regulated in a wide range. We qualitatively interpret the observed variation of particle assembly behaviors in different surfactant solutions based on the particle/particle interaction energy, implying that the repulsive electric double-layer interaction is significantly enhanced with increasing ionic surfactant concentration and hinders the particles approaching close to the high-energy barrier. These results suggest that the particle aggregate structure and interparticle separation distance of the two-dimensional colloidal assembly can be manipulated by controlling the ionic surfactant concentration according to the requirements of practical applications.

Spin-boson model of quantum dissipation in graphene: Nonlinear electrical response

Dissipation in the quantum solid of graphene is couched in the methodology of nonequilibrium statistical mechanics of an open quantum system. Of specific interest is the absorption accompanied by relaxation of energy because of an external frequency-dependent oscillatory electric field. At optical frequencies and for sizable amplitude of the electric field, the response is nonlinear, the treatment of which is simplified by means of a ``rotating wave approximation'' in which rapidly changing, off-resonance terms are omitted. The characteristic resonant frequency is what quantifies the tunneling between the valence and the conduction bands across the so-called Dirac point in graphene. The valence and the conduction states are mapped into the eigenstates of pseudo Pauli spin operators and the corresponding Hamiltonian, when embedded in a dissipative heat bath comprising the surrounding phonons and other electrons, makes possible a comprehensive analysis in terms of the much-studied spin-boson model of dissipative quantum statistical mechanics. A master equation for the density operator associated with this Hamiltonian yields rate equations for the mean population of the valence and the conduction states as well as the transition (matrix elements) between them. Further approximation of these rate equations allows contact with phenomenological treatments of the nonlinear optical conductivity. The present paper then provides a microscopic framework for investigating the response characteristics of a material of great topical interest using contemporary methods of quantum dissipation.

Quantifying the origin of membrane polarization

SUMMARY There has been substantial interest in applying induced polarization phenomena, which broadly include electrode and membrane polarization, to characterize organic contamination and biogeochemical environments. Several phenomenological models, semi-quantitative models and models for particular pore shapes have been proposed for understanding membrane polarization. Here, we present a theoretical framework that directly relates membrane polarization to intrinsic statistical properties of porous materials through a two-point correlation function of fixed charges in the pore space. Our framework provides a new way of modelling complex pore structures with a few statistical parameters and quantifies how two distinct physical processes drive complex conductivity response in the absence of conducting grains. One process is a coupling of the static inhomogeneous conductivity to the induced oscillatory electric field, whereas the second process is a coupling of the static electric field to the induced conductivity modulation. Including both effects, we quantitatively predict the frequency-dependent membrane polarization and show excellent agreement between our predictions and experiments in model porous materials.

PH-Mediated Aggregation-to-Separation Transition for Colloids Near Electrodes in Oscillatory Electric Fields.

Colloids in low-frequency (<1 kHz) oscillatory electric fields near planar electrodes aggregate in neutral pH electrolytes due to electrohydrodynamic (EHD) flow but separate in alkaline pH electrolytes. Colloid ζ-potential and electrolyte ion mobilities are thought to play roles in the underlying mechanism for this phenomenon, but a unifying theory for why particles aggregate in some electrolytes and separate in others remains to be established. Here, we show that increasing local pH near the electrode with an electrochemical reaction causes a colloidal aggregation-to-separation transition in oscillatory electric fields that induce strong attractive EHD flows. An electroactive molecule, para-benzoquinone, was electrochemically reduced at the electrode to locally increase the solution pH near the colloids. Superimposing a sufficiently large steady electrochemical potential onto an oscillatory potential caused a reversible aggregation-to-separation transition. Counterintuitively, decreasing frequency, which increases attractive EHD drag forces, caused a similar aggregation-to-separation transition. Even more interesting, multiple transitions were observed while varying the oscillatory potential. Taken together, these results suggested that the oscillatory potential induced a repulsive hydrodynamic drag force. Scaling arguments for the recently discovered asymmetric rectified electric field (AREF) showed that a repulsive AREF-induced electroosmotic (EO) flow competed with attractive EHD flow. A pairwise colloidal force balance including these competing flows exhibited flow inversions qualitatively consistent with experimentally observed aggregation-to-separation transitions. Broadly, these results emphasize the importance of AREF-induced EO flows in colloid aggregation and separation in low-frequency oscillatory electric fields.