Effect Of Charge Fluctuations Research Articles

Effect of charged dust grains on the electrojet instabilities

The Farley-Buneman and Gradient Drift instabilities have been investigated using a fluid model, in a partially ionized dusty electrojet region in which dust and neutral particles constitute a uniform static background. The effects of dissociative electron-ion recombination and dust charge fluctuation on the instabilities also have been taken into account. The electron-ion dynamics are considered to derive the perturbed densities which further lead to the generalized dispersion relation. The dispersion relation describes the propagation of electrojet instabilities having frequency within dust ion acoustic range in a magnetized partially ionized dusty plasma. The dispersion relation is separately solved numerically and analytically for the two values of anisotropy parameters which correspond to the two different altitudes in the electrojet region. It is found that Gradient drift instability is unstable at a much longer wavelength as compared to Farley-Buneman instability both with or without dust. At lower altitudes(90 km) the increase of negative charge on dust decreases the threshold electron drift velocity for Farley-Buneman instability while it shows the opposite behavior at higher altitudes(100 km). A much lower electron drift velocity is required to excite the Gradient drift instability than the Farley-Buneman instability at both altitudes. The dissociative electron-ion recombination damps both modes much more than the dust charge fluctuation. A significant changes in threshold drift velocity is observed for the Farley-Buneman mode as compared to the Gradient Drift mode due to the two main damping mechanisms. The present analysis is applicable in the lower ionospheric electrojet region where meteoric ablation processes are dominant.

Predicting Experimental B22 Values and the Effects of Histidine Charge States for Monoclonal Antibodies Using Coarse-Grained Molecular Simulations.

Static light scattering (SLS) was used to characterize five monoclonal antibodies (MAbs) as a function of total ionic strength (TIS) at pH values between 5.5 and 7.0. Second osmotic virial coefficient (B22) values were determined experimentally for each MAb as a function of TIS using low protein concentration SLS data. Coarse-grained molecular simulations were performed to predict the B22 values for each MAb at a given pH and TIS. To include the effect of charge fluctuations of titratable residues in the B22 calculations, a statistical approach was introduced in the Monte Carlo algorithm based on the protonation probability based on a given pH value and the Henderson-Hasselbalch equation. The charged residues were allowed to fluctuate individually, based on the sampled microstates and the influence of electrostatic interactions on net protein-protein interactions during the simulations. Compared to static charge simulations, the new approach provided improved results compared to experimental B22 values at pH conditions near the pKa of titratable residues.

Effect of dust grains on the parametric coupling of a lower hybrid wave driven ion cyclotron wave in a tokamak plasma

In this article, the effect of dust charge fluctuations on the parametric upconversion of a lower hybrid wave into an ion cyclotron wave and a side band wave in a two-ion species tokamak plasma is studied. When the oscillatory velocity of plasma electrons is a few percent of the sound velocity, the lower hybrid wave becomes unstable and decays into two modes: an ion cyclotron wave mode and a low frequency lower hybrid side band wave. Furthermore, a ponderomotive force by a lower hybrid pump and a side band wave is exerted on the existing electrons, which drives the ion cyclotron decay mode. The presence of negatively charged dust grains and their shape, size, radius, and density influence the instability. The growth rate of instability is calculated by considering typical existing D–T (Deuterium–Tritium) dusty plasma parameters, and it is observed that the growth rate increases with the relative density of dust grains, number density of dust grains, oscillatory velocity of electrons, and amplitude of pump waves. However, the normalized growth rate increases with the unstable wave frequency, and it also increases as we increase the ratio of deuterium to tritium density. Here, the growth rate decreases with the increase in the size of dust grains and electron cyclotron frequency. The theoretical results summarized in the present study are able to efficiently elaborate the complexity produced in plasma properties in a tokamak due to the dust–plasma interactions, which are briefly discussed here.

Evolution of cylindrical/spherical shock formation in a dusty plasma with nonadiabatic dust charge variation

Cylindrical/spherical dust acoustic shock waves are studied in an unmagnetized plasma consisting of Maxwellian electrons, superthermal ions under the effect of nonadiabatic dust charge fluctuation. The dissipation is introduced in the system via nonadiabaticity, a new mechanism for the formation of shock waves. Using standard reductive perturbation method, nonplanar equation namely Korteweg–de Vries Burgers (KdVB) equation is derived and solution is obtained using the Weighted residual method. By use of weighted residual method, a progressive wave solution to nonplanar modified KdV Burgers equation is presented. It is shown that dust charge fluctuation produces dissipation which is responsible for shock formation. The solution shows that as one goes towards the axis of the cylinder or center of the sphere, the wave attenuates faster and the effects are shown in some 2D figures. We have studied various parametric influences on such shock structure and also showed how the gradual variations of these parameter affect the generation and structure of the shocks in their respective domain. Our results should be applicable to the formation of nonlinear DIA shock wave structures in regions in which dust grain is embedded in a Kappa distributed plasma, such as Saturn's magnetosphere.

Distribution of charge on floating dust particles over sunlit locations on Moon

Abstract The charging of fine particles within the photoelectron cloud is the key in characterizing the dusty plasma environment over sunlit locations. In this work, based on the statistical mechanics and charging kinetics of the floating dust particles within the photoelectron sheath over the sunlit lunar surface, the distribution of charge over floating particles has been investigated. The natural randomization of the dust charging currents, the anisotropy in sheath photoelectron population and electric field/ potential, and half Fermi Dirac velocity distribution of the emitted photoelectrons have been consistently accounted for in the formulation. In this framework, due to natural fluctuation, the charge on the floating dust particles is shown to be distributed over a wide range (∼100 e). This random fluctuation in charge might alter the static equilibrium of the floating dust particles and induce an altitudinal fluctuation (∼10%) about its mean position within the sheath. The concept and results suggest that the natural fluctuation of the dust charge could be a reason that the strict dust levitation under static force equilibrium is less likely to exhibit over the sunlit lunar surfaces. This effect of dust charge and subsequent altitudinal fluctuations have been found pronounced at larger latitudes (near the terminator region) and higher lunar altitudes.

Electron self-energy from quantum charge fluctuations in the layered t−J model with long-range Coulomb interaction

Employing a large-N scheme of the layered t-J model with the long-range Coulomb interaction, which captures fine details of the charge excitation spectra recently observed in cuprate superconductors, we explore the role of the charge fluctuations on the electron self-energy. We fix temperature at zero and focus on quantum charge fluctuations. We find a pronounced asymmetry of the imaginary part of the self-energy Im$\Sigma({\bf k}, \omega)$ with respect to $\omega = 0$, which is driven by strong electron correlation effects. The quasiparticle weight is reduced dramatically, which occurs almost isotropically along the Fermi surface. Concomitantly an incoherent band and a sharp side band are newly generated and acquire sizable spectral weight. All these features are driven by usual on-site charge fluctuations, which are realized in a rather high-energy region and yield plasmon excitations. On the other hand, the low-energy region with the scale of the superexchange interaction J is dominated by bond-charge fluctuations. Surprisingly, compared with the effect of the on-site charge fluctuations, their effect on the electron self-energy is much weaker even if the system approaches close to bond-charge instabilities. Furthermore, quantum charge dynamics does not produce a clear kink nor a pseudogap in the electron dispersion.

(Invited) Review of Identification Methods of 1/f Noise Mechanisms in Polymer-Based OTFTs

We study the low frequency noise, also known as flicker noise (1/f), in polymer-based Organic Thin Film Transistors, and we review techniques to identify the mechanisms of the 1/f noise based on a specific model of the device. We found that the quality of the gate dielectric and its interface may determine the dominant noise mechamism.Three theories have been formulated to explain the origin of 1/f noise in FET devices: the carrier number fluctuation (∆N) theory[1], the mobility fluctuation (∆µ) theory [2], and the ∆N - ∆µ theory [3], which assumes that effects of insulator charge fluctuations affect the carrier mobility at the interface. The ∆N - ∆µ theory reduces to the ∆N model when the surface mobility is not affected by carrier number fluctuation.According to the ∆N - ∆µ theory [3]the plot of SID(f)/ID 2 and [gm/ID]2 against ID (gm being the transconductance and ID the drain current) allows us to identify the noise mechanism. When both curves are parallel, 1/f noise must be due to carrier number fluctuation. If there is a slight deviation from this parallel behavior, it must be due to the correlated surface mobility fludtuation (∆N - ∆µ model).A number of analysis of the noise in OTFTs have been published. In most of them, it is found to be a bulk phenomenon[4,5], and as a result the main mechanism is assumed to be mobility fluctuation. However, very often these analysis are not very complete and are based on crystalline MOSFET models instead of specific OTFT models. On the other hand, it was demonstrated that the analysis must be made over a range wide of bias in order to accurately determine the origin of noise [6,7].We studied the origin of 1/f noise two polymeric p-type OTFT technologies developed by CEA´Liten (France).We found that in the older technology the slopes, in log-log scale, of SID(f)/ID 2 and [gm/ID]2, versus ID had quite different values. This means that the main mechanism of noise in OTFTs is not the fluctuation of the number of carriers. Plotting SID(f)/I2 Dvs (VGS-Vth) in log-log scale (Vth being the threshold voltage) for devices with different channel lengths, channel width W=2000 µm and at VDS = 1 V, we observed that the extracted slope is close to -1 (Table 1). This indicates that noise is due to the fluctuation of carrier mobility, due to the lower quality of the materials and fabrication defects. The threshold voltage was extracted assuming a physically-based OTFT model with a power-law based model of the field effect mobility [8].In the second technology, mobility values are higher, 2-3 cm2/(V s). The normalized current noise PSD follows the squared-transconductance ratio variation (Fig. 1), not the inverse of the drain current. We concluded that the low frequency in the targeted devices of the second technology is originated from the carrier number fluctuation due to trapping/release of charge carriers by trap states uniformly distributed within the gate oxide. The extracted values of gate dielectric trap-states density are comparable to values obtained in conventional Si-based MOSFETs [7], indicating the higher quality of the gate dielectric and its interface with the polymeric material compared to the first studied technology and other previously reported OTFT devices.[1] McWhorter A. L.. "1/f noise and germanium surface prosperities," Semiconductor Surface Physics. R. H. Kingdton (Ed), University of Pennsylvania Press, Philadelphia, PA, 1957, pp. 207-228.[2] Hooge F. N., "1/f noise is no surface effect", Physics Letters, 29A (3), 1969, 139–140[3] Ghibaudo, G., et al..,‘Improved analysis of low frequency noise in field-effect MOS transistors’, Phys. Status Solidi. A , 1991, 124, pp. 571-581[4] L. Ke, S., et al., “Low frequency noise analysis on organic thin film transistors,” Journal of Applied Physics 104, 124502 (2008).[5] H. Kang and V. Subramanian, “Measurement and analysis of 1/f noise under switched bias in organic thin film transistors,” Applied Physics Letters 104, 023301 (2014).[6] Y. Xu, et al., “Origin of low-frequency noise in pentacene field-effect transistors,” Solid-State Electronics 61, 106–110 (2011).[7] W. E. Muhea, et al.. “1/f noise analysis in high mobility polymer-based OTFTs with non-fluorinated dielectric,” Appl. Phys. Lett. 114, 243301 (2019).[8] C.H. Kim; et al., “A Compact Model for Organic Field-Effect Transistors With Improved Output Asymptotic Behaviors,” IEEE Trans. on Electron Devices, vol. 60, no. 3, pp. 1136-1141, March 2013. Figure 1

Effect of non adiabatic dust charge fluctuation on nonplanar dust acoustic waves in superthermal polarized plasma

Some properties of cylindrical/spherical dust acoustic solitary waves have been studied in collisionless dusty plasma with variable charges under the influence of polarization force by reductive perturbation method. It is shown that the collisionless damping due to dust charge fluctuation causes the dust acoustic wave propagation to be described by the nonplanar damped Korteweg de Vries equation. By use of weighted residual method, a progressive wave solution to nonplanar damped KdV equation is presented for the first time. It is shown that dust charge fluctuation produce damping which is responsible for wave attenuation. The solution shows that as one goes towards the axis of the cylinder or centre of the sphere, the wave attenuates faster and the effects are shown in some 2D figures. Within a small amplitude limit, the influence of dust charge fluctuation, polarisation power, superthermality and ion temperature on the time evolution of dust acoustic solitons is also demonstrated. In laboratory experiments and space regions, findings obtained here may shed light on the salient characteristics of DA waves.

Kinetic theory of effect of dust charge fluctuations on the parametric decay of lower hybrid wave instability by relativistic runaway electrons in tokamak

Dust charge fluctuation effect on the parametric decay of lower hybrid wave instability by relativistic runaway electrons is studied in a tokamak using kinetic treatment. Parametric upconversion of lower hybrid pump waves into relativistic runaway electron mode and upper sideband mode is described. A ponderomotive force is exerted on the runaway electrons by lower hybrid pump wave possessing large amplitude and upper sideband wave, which drives the runaway electron mode. The coupling of the oscillatory velocity of electrons with density perturbations produces nonlinear density perturbations on the upper sideband frequency. As a result, runaway generation is enhanced by a lower hybrid wave and the growth rate of the instability is measured as the square of the amplitude of the pump wave. Moreover, the presence of dust charge fluctuations and their number density in the tokamak have an appreciable effect on the growth rate of lower hybrid wave instabilities, which in turn affects the actual performance of the ITER due to the potential safety and operational issues.

Particle-in-cell simulation of the effect of dust charge fluctuation on ion acoustic waves in a dusty plasma

A new hybrid-particle-in-cell (PIC)-Monte Carlo Collision (h-PIC-MCC) algorithm is presented here. The code correctly simulates the damping of ion acoustic wave due to dust charge fluctuation in a dusty plasma along with other kinetic effects such as Landau damping. In the model, on event of a collision between a charged particle and a dust particle, a randomised probability determines whether the charged particle is absorbed by the dust with the collision cross section being determined dynamically by the overall interaction scenario. We find that this method is versatile enough as it can also include the size and mass distribution for the dust particles, in addition to the charged species dynamics. As such, it can be adopted to study numerous phenomena that occur in diverse dusty plasma environments. We believe that the damping of the ion acoustic wave through dust charge fluctuation is being demonstrated, for the first time, with a PIC code, in this work.

New method for rekindling the explosive waves in Maxwellian space plasmas

Our interest is to study the nonlinear wave phenomena in complex plasma constituents with Maxwellian electrons and ions. The main aim is to use a new method known as the (G′/G) method to exhibit the effects of dust charge fluctuations on the evolution of nonlinear waves. The coherent features of the shock and solitary waves along with the generation of high-energy waves have been amplified through the solution of the Korteweg–de Vries–Burgers equation, and the different natures of the waves were found successfully. Results are discussed graphically with the thoughtful choice of typical plasma parameters from different space plasma environments, exactly those found in cosmic dusty plasmas laden in ionospheric auroral region, radial spokes of Saturn’s rings, planetary nebulae and solar F-corona region. All conclusions are in good accordance with the actual occurrences and could be of interest to further investigations of space. Moreover, the applicability of the present method is hoped to be a great enhancement by its use as ingenious mechanism used to evaluate the soliton dynamics and Burgers shock waves.

Effects of charge fluctuation and charge regulation on the phase transitions in stoichiometric VO2

Detailed electrical and photoemission studies were carried out to probe the chemical nature of the insulating ground state of VO2, whose properties have been an issue for accurate prediction by common theoretical probes. The effects of a systematic modulation of oxygen over-stoichiometry of VO2 from 1.86 to 2.44 on the band structure and insulator–metal transitions are presented for the first time. Results offer a different perspective on the temperature- and doping-induced IMT process. They suggest that charge fluctuation in the metallic phase of intrinsic VO2 results in the formation of e− and h+ pairs that lead to delocalized polaronic V3+ and V5+ cation states. The metal-to-insulator transition is linked to the cooperative effects of changes in the V–O bond length, localization of V3+ electrons at V5+ sites, which results in the formation of V4+–V4+ dimers, and removal of pi^{*} screening electrons. It is shown that the nature of phase transitions is linked to the lattice V3+/V5+ concentrations of stoichiometric VO2 and that electronic transitions are regulated by the interplay between charge fluctuation, charge redistribution, and structural transition.

Charge fluctuations at the Si–SiO2 interface and its effect on surface recombination in solar cells

The Si–SiO2 interface has and will continue to play a major role in the development of silicon photovoltaic devices. This work presents a detailed examination of how charge at or near this interface influences device performance. New understanding is identified on the effect of charge-induced potential fluctuations at the silicon surface. Such fluctuations have been considered in Si–SiO2 recombination models previously, where a universal value of electrical potential deviation was used to represent the effect. However, the approach disregards that the variation occurs in the charge concentration rather than the potential. We modify the models to accurately reflect fluctuations in external charge, allowing a precise representation of surface recombination velocity, with self-consistent Dit, σp, and σn parameters. Correctly accounting for these parameters can provide insights into the passivation mechanisms which can aid the development of future devices. Using the corrected model, we find that the effect of charge fluctuation at the Si–SiO2 interface is significant for the depletion regime to the weak inversion regime. This indicates that surface passivation dielectrics must operate with charge concentrations in excess of 2x1012 q/cm2 to avoid these effects. TCAD device simulations show that the efficiency of future PERC cells can improve up to 1% absolute when optimally charged dielectric coatings are applied both at the front and rear surfaces.

Connecting the SYK Dots

We study a putative (strange) metal-to-insulator transition in a granular array of the Sachdev–Ye–Kitaev (SYK) quantum dots, each occupied by a large number N ≫ 1 of charge-carrying fermions. Extending the previous studies, we complement the SYK couplings by the physically relevant Coulomb interactions and focus on the effects of charge fluctuations, evaluating the conductivity and density of states. The latter were found to demonstrate marked changes of behavior when the effective inter-site tunneling became comparable to the renormalized Coulomb energy, thereby signifying the transition in question.

Near-Critical Phase Behavior in Polyelectrolyte Solutions: Effect of Charge Fluctuations.

The critical behaviors in polyelectrolyte (PE) solutions are studied by a renormalized Gaussian fluctuation theory. PEs are fully charged linear wormlike chains. The electrostatic interactions are considered in a continuum solvent while ignoring other interactions. The effects of temperature on the criticality are explored in a salt-free polyanion solution, and the effects of salt are explored in a symmetric mixed solution of polycation and polyanion. An unphysical phase coexistence (UPPC), in which a metastable dense phase coexists with an unstable dilute phase, always exists in the phase diagram. In the near-critical region, the UPPC could interfere with the real phase coexistence. The classical critical point is replaced by a "critical line", giving a flat top for the phase diagram. These behaviors are due to the effect of charge fluctuation in the near-critical region. Our results explain why the mean field approach overestimates the critical salt density by about 10% to experimental data in the study of coacervation between oppositely charged PEs.

The Suprathermal Particles and Charge Fluctuation Effects on Waves in Complex Plasma

In the frame of kinetic theory we investigated the effects of suprathermal particles and dust charge fluctuations due to the inelastic collision between the dust grains and plasma particles by calculating the longitudinal dielectric permittivity in an unmagnetized dusty plasma on the wave modes propagating in a complex plasma. The ion and electron distribution were assumed to be Maxwell and Kapa distribution in the systems. It was shown that the wave frequency can be analyzed for various values of the spectral index K and the dust charge fluctuations. The landau damping rate and Propagation rate in dust charge fluctuation presence increase

The effect of dust grains on the Weibel instability in presence of large amplitude electrostatic waves

Theoretical investigations on the effect of dust charge fluctuations on Weibel instability in a plasma, with an electron beam in the presence of large amplitude electrostatic Langmuir waves, have been performed. It is observed that the dust charge fluctuations enhance the growth rate of electromagnetic (EM) perturbations. An increase in the electron to ion temperature ratio amplifies the EM perturbations, leading to an enhanced magnetic field due to Weibel instability. It has been found that the growth rate of Weibel instability strongly depends on the dust grain size for different values of ion to electron density ratio δm. Moreover, the electron to ion temperature ratio also destabilizes the Weibel instability.

Understanding attenuated solvent reorganization energies near electrode interfaces.

In this manuscript, we examine the role of image charge effects on the electrostatic potential fluctuations experienced by ionic species in the vicinity of an electrode surface. We combine simulation and theory to quantify these fluctuations and how they vary with distance from the electrode surface. We observe that the potential distribution narrows significantly for species within a few electrolyte screening lengths of the electrode. We attribute this narrowing to the effects of image charge fluctuations originating from the polarization response of the electrode. We show that the physical consequences of these image charge effects can be captured in the context of a simple analytical field theory with anti-symmetric boundary conditions. We contextualize these results by discussing their implications for rates of Marcus-like outer-sphere interfacial electron transfer.

Radiative and gravitating modes in the partially ionized magnetized dusty plasma

In the present study, fluid theory is used to investigate the gravitational and radiative condensation instabilities of a partially ionized magnetized dusty plasma system. The effects of ion and electron capture by dust grains, the charge variation of dust grains, and the radiative effects of electron species are also taken into account. The dynamics of all four species are considered to derive modified densities that further lead to a general dispersion relation. The general dispersion relation describes the propagation of low frequency electrostatic dust acoustic waves in magnetized self-gravitating partially ionized dusty plasma with ionization-recombination, dust charge variations, and radiative effects. Gravitational modes of propagation and radiative modes of propagation are illustrated separately for both parallel and perpendicular cases. Conditions for instabilities are also derived to explain the gravitational collapse and radiative condensation of the system. The numerical results are presented to signify the role of dust neutral collision frequency, dust charge fluctuation, magnetic field, and recombination ionization effects on both the radiative condensation and gravitational instabilities. The relevance of the present study to interstellar molecular clouds is also discussed and the effect of considered parameters on the critical wavelength, critical wave number, luminosity, etc., has been investigated.

Effects of nuclear charge fluctuations on dilepton photoproduction

Fluctuations of dilepton production from two photon interactions are studied in semi-central and peripheral nuclear collisions. Based on the Weizsäcker–Williams approach, electromagnetic (EM) fields generated by moving nuclear charges are approximated as quasi-real photons. As fluctuating EM fields in each collision event are hard to be measured directly in experiments due to its short lifetime, we study the dilepton photoproduction with fluctuating EM fields, which are crucial for the EM fields induced chiral and charged particle evolutions, and calculate the relative standard deviation of the dilepton mass spectrum with the event-by-event fluctuating nuclear charge distributions. This fluctuation effect becomes smaller in more peripheral collisions where the shift of proton positions is implicit for EM fields outside the nucleus. The uncertainty of effective impact parameter Δb on the standard deviation is also studied, and its effect is around one-third of the effect of nuclear charge fluctuations when Δ b is taken as ∼1 fm.