Stationary Ion Research Articles

Dissipative high-frequency envelope soliton modes in nonthermal plasmas

The linear and nonlinear properties of modulated high-frequency (electron-acoustic) electrostatic wave packets are investigated via a fluid-dynamical approach. A three-component plasma is considered, composed of two types of electrons at different temperatures (``cold'' and ``hot'' electrons) evolving against a cold stationary ion background. A weak dissipative effect is assumed, due to electron-neutral collisions. While the cold electrons are treated as an inertial fluid, the hot electrons are assumed to be in a non-Maxwellian state, described by a kappa ($\ensuremath{\kappa}$) type distribution. The linear characteristics of electron-acoustic waves are analyzed in detail, and a linear dispersion relation is obtained. Weakly damped electrostatic waves are shown to propagate above a wave number $k$ threshold, whose value is related to dissipation (and reduces to zero in its absence). Long-wavelength values (i.e., for $k$ below that threshold) are heavily damped and no propagation occurs. The nonlinear dynamics (modulational self-interaction) of wave packets in the propagating region is modeled via a dissipative nonlinear Schr\odinger type equation, derived via a multiscale perturbation technique for the wave envelope, which includes a dissipative term associated with the finite imaginary part of the nonlinearity term. The dynamical and structural characteristics (speed, amplitude, width) of dissipative localized modes representing the amplitude of modulated electron-acoustic wave packets in a collisional plasma are thus investigated for various values of relevant plasma (configuration) parameters, namely the superthermality index $\ensuremath{\kappa}$, the cold-to-hot electron density ratio, and collisionality (strength). Our analytical predictions are tested by computer simulations. A quasilinear perturbation method for near-integrable systems leads to a theoretical prediction for the wave amplitude decay, which is shown to match our numerical result. The results presented in this paper should be useful in understanding the dynamics of localized electrostatic disturbances in space plasmas, and also in laboratory plasmas, where the combined effect(s) of excess energetic (suprathermal) electrons and (weak) electron-neutral collisions may be relevant.

Analytical properties of linear electrostatic waves in two-component quantum and classical plasmas

We examine the properties of linear electrostatic waves in unmagnetised quantum and classical plasmas consisting of one or two populations of electrons with analytically tractable distribution functions in the presence of a stationary neutralising ion background. Beginning with the kinetic quantum plasma longitudinal susceptibility, we assess the effects due to increasing complexity of the background distribution function. Firstly, we analyse dispersion and Landau damping in one-component plasmas and consider distribution functions with a variety of analytical properties: the Dirac delta function, the Cauchy profile with two complex first-order poles, the squared Cauchy profile with two second-order poles and the inverse-quartic profile with four first-order poles; we also briefly discuss the non-meromorphic totally and arbitrarily degenerate Fermi–Dirac distribution. In order to study electrostatic instabilities, we then turn to plasmas with two populations of electrons streaming relative to each other in two cases: a symmetric case of two counter-streaming identical populations and a bump-on-tail case with a primary population and a delta-function beam. We obtain the corresponding linear kinetic dispersion relations and evaluate the properties of instabilities when the electron distribution functions are of the delta function, Cauchy, squared Cauchy or inverse-quartic types. In agreement with other studies, we find that in general quantum effects reduce the range of wavelengths for unstable modes at long wavelengths. We also find a second window of instability at shorter wavelengths and elucidate its nature as being due to quantum recoil. We note the possible implications for studies of laboratory and astrophysical quantum plasmas.

Ion-Acoustic Solitary Waves and Double Layers in a Magnetized Degenerate Quantum Plasma

The properties of ion-acoustic (IA) solitary waves (SWs) and double layers (DLs) in a four-component magnetized degenerate quantum plasma system (containing nondegenerate inertial light ion, both nonrelativistically and ultrarelativistically degenerate electrons and positrons, and immobile heavy ion) are theoretically investigated by the reductive perturbation method. The Korteweg-de Vries (K-dV), the modified K-dV, and the Gardner equations are derived to examine the basic features (viz. amplitude, speed, and width) of IA SWs and DLs. It is found that the effects of the ultrarelativistically degenerate electrons and positrons, stationary heavy ion, external magnetic field (obliqueness), and so on, significantly modify the basic features of the IA SWs and DLs. The basic features and the underlying physics of IA SWs and DLs, which are relevant to some astrophysical compact objects including white dwarfs and neutron stars, are pinpointed.

Recent advances in the synthesis, biological activities and various applications of ferrocene derivatives

Ferrocene derivatives constitute an important class of organometallic compounds with not only an extensive range of biological activities but also diverse industrial as well as material science applications. These stimulating features of ferrocene derivatives spurred us to review the recent advances in synthesis methods and biological and other applications reported in the latest literature. An effort has been made to summarize the recent developments in synthetic methods providing access to ferrocene scaffolds and the useful medicinal and material applications, including agricultural, catalytic, polymer, conducting, redox mediating, ferrocenyl stationary phase, rocket propellant and ion sensing applications. Ferrocene‐based bulky metallocenes are also discussed.

Some aspects of space-charge effect calculation in high-resolution mass spectrometry.

A variational 3D approach to the problem of simulating stationary distributions of ions in the radiofrequency low-vacuum ion traps with regard to Coulomb interaction and collisions of ions with buffer gas molecules is proposed. The software developed in the course of this work is employed to study the structure of stationary ion ensembles in the radiofrequency ion traps of various types. The effect of high-frequency and constant voltages, space-charge density, and buffer gas temperature on the formation of stationary distributions in the radiofrequency ion traps and their limiting capacitance is investigated. It is shown that the use of electrodes with a constant voltage in the presence of high enough ion density allows pre-filtering of ions directly in a high-frequency trap-accumulator.

Co-excitation of normal modes and burst ion signal in an ion-beam–plasma system

The co-excitation of plasma normal modes and a pseudo-mode (burst-ion signal) in a beam–plasma system containing a stationary ion beam is experimentally investigated in a double-plasma device. The ion waves are excited by applying a ramp voltage to an excitation grid (rather than separation grid) immersed in the beam–plasma system. By studying the dependence of the phase velocities of the excited signals on the characteristics of the ramp signal and on the ion-beam velocity, four kinds of coexisting waves can be identified, i.e., a fast and a slow ion-beam modes, an ion-acoustic mode, and the burst-ion signal, respectively.

Quantum Ion-Acoustic Oscillations in Single-Walled Carbon Nanotubes

Abstract Quantum ion-acoustic oscillations in single-walled carbon nanotubes are studied by employing a quantum hydrodynamics model. The dispersion equation is obtained by Fourier transformation, which exhibits the existence of quantum ion-acoustic wave affected by change of density balance due to presence of positive or negative heavy species as stationary ion clusters and wave potential at equilibrium. The numerical results are presented, and the role of quantum degeneracy, nanotube geometry, electron exchange-correlation effects, and concentration and polarity of heavy species on wave dispersion is pointed out for typical systems of interest.

Sudanese Thomsonite as Ion Exchanger to Removal Pb2+, Fe3+ and Ni2+ from Artificial Wastewater

Zeolite samples were collected from Wadkawly in Gadarif region. These samples were characterized with respect chemical properties by AAS, SEM and X-ray Diffraction Analysis (XRD) showed these samples to be composed of Thomsonite zeolite, exclusively. The sample was treated with strong brine solution to ensure that Na-zeolite was generated and used as the stationary ion exchanger phase. Solutions containing 100 ppm of heavy metal ions (Pb2+, Fe3+and Ni2+) were artificially prepared and then processed with Na-zeolite. Excellent extraction was achieved, with final residual concentration of 0.02 ppb, 3.0 ppb and 1.38 ppm for (Pb2+, Fe3+ and Ni2+) respectively and retention time 180 seconds for decreasing concentrations. This gives extraction efficiency of ~ 100%, 99.9%, and 98.6%, for Pb2+, Fe3+ and Ni2+, respectively. The relative efficiency is, therefore: Pb2+ > Fe3+ > Ni2+.

Photoemission spectroscopy of planar and nanostructured surfaces

In this paper, I present some results for the process of excitation of bulk and surface plasmons during the emission of electrons in the proximity of surfaces of different shapes and dimensions. I describe in detail the effects due to the interaction between an electron and a stationary positive ion (or atomic hole) in the neighborhood of a metallic surface, paying special attention to the results obtained by my research group. We used the dielectric response of the metal and the specular reflection model for the case of planar surfaces, and the second quantization theory for nanostructured surfaces. In particular, we studied how the electron–hole pair interaction can influence the energy loss of the emerging electron. We investigated the importance of surface effects in the analysis of photoelectron spectroscopy. The method described here is useful for studying multiple plasmon excitations in nanostructures and for understanding the excited electron spectra of these nanostructures (different from those of the same bulk material).

Ion sound instability driven by the ion flows

Ion sound instabilities driven by the ion flow in a system of a finite length are considered by analytical and numerical methods. The ion sound waves are modified by the presence of stationary ion flow resulting in negative and positive energy modes. The instability develops due to coupling of negative and positive energy modes mediated by reflections from the boundary. It is shown that the wave dispersion due to deviation from quasineutrality is crucial for the stability. In finite length system, the dispersion is characterized by the length of the system measured in units of the Debye length. The instability is studied analytically and the results are compared with direct, initial value numerical simulations.

Effects of the electron–hole pair in Auger and X-ray photoemission spectroscopy from surfaces of Fe–Si

In this work, we investigate in detail the effects due to the interaction between an electron and a stationary positive ion (or atomic hole) in the neighborhood of a surface of Fe–Si, having a strong plasmon peak in their electron energy loss spectra, when it is excited with synchrotron radiation. We take into account the effects due to the sudden creation of an electron and the residual holes, one in the case of X-ray photoemission spectroscopy (XPS) and two in the case of Auger electron spectroscopy (AES).We use a semi classical dielectric formulation for the photoelectron trajectory, and we estimated the parameter rs, the radius of the sphere occupied by one electron in the solid, which is critical in order to define the electron density of the alloy. With the cited formulation, we have obtained a detailed behavior of the different contributions of the collective excitations in both processes.

Numerical thermalization in particle-in-cell simulations with Monte-Carlo collisions

Numerical thermalization in collisional one-dimensional (1D) electrostatic (ES) particle-in-cell (PIC) simulations was investigated. Two collision models, the pitch-angle scattering of electrons by the stationary ion background and large-angle collisions between the electrons and the neutral background, were included in the PIC simulation using Monte-Carlo methods. The numerical results show that the thermalization times in both models were considerably reduced by the additional Monte-Carlo collisions as demonstrated by comparisons with Turner's previous simulation results based on a head-on collision model [M. M. Turner, Phys. Plasmas 13, 033506 (2006)]. However, the breakdown of Dawson's scaling law in the collisional 1D ES PIC simulation is more complicated than that was observed by Turner, and the revised scaling law of the numerical thermalization time with numerical parameters are derived on the basis of the simulation results obtained in this study.

Characterising nanostructure functionality of a cellulose triacetate forward osmosis membrane using electrical impedance spectroscopy

Electrical Impedance spectra generated in situ, in real time for cellulose triacetate forward osmosis (CTA-ES) FO membranes was resolved with the Maxwell–Wagner theory to reveal distinct structures including the active separation layer and porous support. Two distinct structural elements with capacitance of 7.7×10−6 (F/m2) and 7.8×10−4 (F/m2) and a corresponding thickness of 43(±13) μm and 80(±11) nm representing the porous support and active separation layer respectively were determined from spectra acquired on membranes operating in Active Layer Draw Side (ALDS) mode on 0.5M potassium chloride draw solutions. Overall membrane thickness of 33–61 μm determined using Electrical Impedance Spectroscopy (EIS) compared favourably to a thickness range of 50–90μm measured by Scanning Electron Microscopy. A stationary ion layer with a capacitance of 7.7×10−6 (F/m2) was visible on the porous support at draw solutions of 0.5M KCl in the ALDS mode. However, as the concentration of the draw solution increased, thereby increasing the conductivity of the region, EIS was unable to interpret the interactions between stationary ion layer and the porous support. Reversing the membrane orientation to Active Layer Feed Side (ALFS) increased the amount of internal concentration polarisation (ICP) in the porous support compared with ALDS mode resulting in a decrease in FO flux from 3.9(±0.2) L/m2h to 2.5(±0.2) L/m2h. The presence of ICP and its subsequent impact on flux decline may be revealed from EIS spectra by observing an overall increase in conductance. While EIS remains a viable technique to characterise membrane structure and thickness, identification of coupled effects of internal and external concentration polarisation in situ remains elusive and requires further improvement of signal to noise ratio at higher concentrations and improvement in Maxwell–Wagner fitting algorithms.

Comment on ‘Propagation of solitary waves and shock wavelength in the pair plasma (J. Plasma Phys. 78, 525–529, 2012)’

In a recent paper ‘Propagation of solitary waves and shock wavelength in the pair plasma (J. Plasma Phys. 78, 525–529, 2012)’, Malekolkalami and Mohammadi investigate nonlinear electrostatic solitary waves in a plasma comprising adiabatic electrons and positrons, and a stationary ion background. The paper contains two parts: First, the solitary wave properties are discussed through a pseudopotential approach, and then the influence of a small dissipation is intuitively sketched without theoretical underpinning. Small dissipation is claimed to lead to a shock wave whose wavelength is determined by linear oscillator analysis. Unfortunately, there are errors and inconsistencies in both the parts, and their combination is incoherent.

Steric effects on ion dynamics near charged electrodes

We present a modified Poisson–Nernst–Planck (mPNP) model to include steric effects on ion dynamics near charged electrodes. This contribution appears directly on chemical potential of each ion in solution as a non-electrostatic term. The model consists in a partial-differential-algebraic equation (PDAE) system, which after spatial discretization was solved by the well-established DASSLC code, implemented in EMSO simulator. A careful dimensional analysis was carried out to turn the PDAE system dimensionless with normalized spatial domain. Size correlation (SC) effects for equally sized ions avoid unphysical charge densities near the electrodes (especially at high voltages), and also give some insights on double layer formation. Time evolution of free charge density profiles show a diffusion controlled dynamics with a very fast response (t∼10−8s). The methodology proposed here allows the inclusion of new contributions on PNP model framework for ion dynamics, as well as to solve both stationary and dynamical ion distributions, taking advantage of the EMSO software simulator features.

Multi-scale modeling of ion transport in high-strain ionomers with conducting powder electrodes

Ionomeric polymer transducers exhibit electromechanical coupling capabilities. The ion transport due to electric stimulus is the primary mechanism of actuation for a class of polymeric active materials known as ionomeric polymer transducers. In this article, a two-dimensional Monte Carlo simulation of ion hopping has been developed to describe ion transport in materials that have fixed and mobile charge similar to the structure of the ionic polymer transducer. Such Monte Carlo simulations were performed to study the influence of conducting powder electrodes on stationary ion distribution in actuation. Ion accumulation around the powder sphere at the cathode is clearly observed in simulation results. Moreover, based on the unique property of stationary charge density of ionomeric polymer transducers in actuation, this article proposed a novel multi-scale model connecting Monte Carlo simulation for the material boundaries and a continuum model for the central part. To validate this multi-scale model, the simulation results are compared with experimental measurements. Both transient and steady-state responses from the experiments show reasonable agreement with those from the multi-scale model.

Theoretical analysis of ion-enhanced thermionic emission for low-temperature, non-equilibrium gas discharges

When thermionic emission is used in a gas discharge, the ions exiting the discharge will influence the local electric field at the cathode. This effect is similar to the Schottky effect, as the potential field due to the ion can effectively reduce the potential barrier (work function) at the cathode and increase emission. In this work, this enhancement phenomenon is treated theoretically to understand how Schottky emission is enhanced due to the presence of an ion—so-called ion-enhanced Schottky emission. The effect of a stationary ion is determined through the analytical and numerical solution of the potential energy fields involved in the problem, including the applied field, electron image charge, and the ion potential field. The time-averaged enhancement due to an ion drifting towards the cathode is calculated, and an effective emission coefficient is predicted. These analyses show that a single stationary ion can significantly enhance thermionic emission, more than doubling the emission current depending on its location, but the enhancement is less significant (∼5–10%) when the motion of the ion is considered. However, the enhancement effect is more pronounced at moderate electric fields (∼105 V m−1) due to the residence time of the ion near the cathode. These results reveal the impact ions in the discharge may have on emission and how this needs to be considered when designing devices that integrate thermionic emission and discharges.

Nonlinear, stationary electrostatic ion cyclotron waves: Exact solutions for solitons, periodic waves, and wedge shaped waveforms

The theory of fully nonlinear stationary electrostatic ion cyclotron waves is further developed. The existence of two fundamental constants of motion; namely, momentum flux density parallel to the background magnetic field and energy density, facilitates the reduction of the wave structure equation to a first order differential equation. For subsonic waves propagating sufficiently obliquely to the magnetic field, soliton solutions can be constructed. Importantly, analytic expressions for the amplitude of the soliton show that it increases with decreasing wave Mach number and with increasing obliquity to the magnetic field. In the subsonic, quasi-parallel case, periodic waves exist whose compressive and rarefactive amplitudes are asymmetric about the “initial” point. A critical “driver” field exists that gives rise to a soliton-like structure which corresponds to infinite wavelength. If the wave speed is supersonic, periodic waves may also be constructed. The aforementioned asymmetry in the waveform arises from the flow being driven towards the local sonic point in the compressive phase and away from it in the rarefactive phase. As the initial driver field approaches the critical value, the end point of the compressive phase becomes sonic and the waveform develops a wedge shape. This feature and the amplitudes of the compressive and rarefactive portions of the periodic waves are illustrated through new analytic expressions that follow from the equilibrium points of a wave structure equation which includes a driver field. These expressions are illustrated with figures that illuminate the nature of the solitons. The presently described wedge-shaped waveforms also occur in water waves, for similar “transonic” reasons, when a Coriolis force is included.

Solid phase extraction of petroleum carboxylic acids using a functionalized alumina as stationary phase

Petroleum essentially consists of a mixture of organic compounds, mainly containing carbon and hydrogen, and, in minor quantities, compounds with nitrogen, sulphur, and oxygen. Some of these compounds, such as naphthenic acids, can cause corrosion in pipes and equipment used in processing plants. Considering that the methods of separation or clean up the target compounds in low concentrations and in complex matrix use large amounts of solvents or stationary phases, is necessary to study new methodologies that consume smaller amounts of solvent and stationary phases to identify the acid components present in complex matrix, such as crude oil samples. The proposed study aimed to recover acid compounds using the solid phase extraction method, employing different types of commercial stationary ion exchange phases (SAX and NH(2)) and new phase alumina functionalized with 1,4-bis(n-propyl)diazoniabicyclo[2.2.2]octane chloride silsesquioxane (Dab-Al(2)O(3)), synthesized in this work. Carboxylic acids were used as standard mixture in the solid phase extraction for further calculation of recovery yield. Then, the real sample (petroleum) was fractionated into saturates, aromatics, resins, and asphaltenes, and the resin fraction of petroleum (B1) was eluted through stationary ion exchange phases. The stationary phase synthesized in this work showed an efficiency of ion exchange comparable to that of the commercial stationary phases.

Polyanion Type Cathodes for Stationary Lithium Ion Batteries

not Available.