Fraction Of Ions Research Articles

Structural and electrochemical properties of montmorillonite-poly(ethylene oxide) intercalated nanocomposites for lithium-ion batteries

Poly(ethylene oxide) has been intercalated inside the interlayer galleries of montmorillonite clay and the electrochemical properties of the nanocomposite have been investigated. Interlayer spacing and clay gallery width increase with increasing MMT concentration confirming intercalation of PEO into MMT as observed from XRD results. The fraction of free anions as calculated from FTIR, increases with increasing clay content and remains constant beyond 7.5 wt. % of clay content. Ionic conductivity of the order of 10−4 Scm−1 has been obtained in the case of MMT based electrolytes. The initial increase of conductivity with increasing MMT content can be attributed to the increase fraction of free ions which eventually increases ionic conductivity. After 7.5 wt. % of MMT loading ionic conductivity decreases due to the high viscosity of MMT. Interfacial stability results show that passivation takes place very slowly in MMT based electrolytes. Dielectric properties show that at high frequency relaxation takes place due to the segmental motion of polymer chains and it proves the hopping of ions.

Topology of reionisation times: Concepts, measurements, and comparisons to Gaussian random field predictions

Context. In the next decade, radio telescopes, such as the Square Kilometer Array (SKA), will explore the Universe at high redshift, and particularly during the epoch of reionisation (EoR). The first structures emerged during this epoch, and their radiation reionised the previously cold and neutral gas of the Universe, creating ionised bubbles that percolate at the end of the EoR (z ∼ 6). SKA will produce 2D images of the distribution of the neutral gas at many redshifts, pushing us to develop tools and simulations to understand its properties. Aims. With this paper, we aim to measure topological statistics of the EoR in the so-called reionisation time fields from both cosmological and semi-analytical simulations. This field informs us about the time of reionisation of the gas at each position; it is used to probe the inhomogeneities of reionisation histories and can be extracted from 21 cm maps. We also compare these measurements with analytical predictions obtained within Gaussian random field (GRF) theory. Methods. The GRF theory allows us to compute many statistics of a field, namely the probability distribution functions (PDFs) of the field or its gradient, isocontour length, critical point distributions, and skeleton length. We compare these theoretical predictions to measurements made on reionisation time fields extracted from an EMMA simulation and a 21cmFAST simulation at 1 cMpc/h resolution. We also compared our results to GRFs generated from the fitted power spectra of the simulation maps. Results. Both EMMA and 21cmFAST reionisation time fields (treion(r)) are close to being Gaussian fields, in contrast with the 21 cm, density, or ionisation fraction, which have all been shown to be non-Gaussian. Only accelerating ionisation fronts at the end of the EoR seem to be the cause of small non-gaussianities in treion(r). Overall, this topological description of reionisation times provides a new quantitative and reproducible way to characterise the EoR scenario. Under the assumption of GRFs, it enables the generation of reionisation models with their propagation, percolation, or seed statistics simply from the reionisation time power spectrum. Conversely, these topological statistics provide a means to constrain the properties of the power spectrum and by extension the physics that drive the propagation of radiation.

Wave Conversion, Decay, and Heating in a Partially Ionized Two-fluid Magneto-atmosphere

A ray-theoretic phase-space description of linear waves in a two-fluid (charges and neutrals) magnetized plasma is used to calculate analytic decay rates and mode transmission and conversion coefficients between fast and slow waves in two dimensions due to finite ion–neutral collision frequencies at an arbitrary ionization fraction. This is relevant to partially ionized astrophysical plasmas, in particular solar and stellar atmospheres. The most important parameter governing collisional effects is the ratio of the wave frequency to the neutral–charges collision frequency, ϵ = ω/ν nc, with secondary dependence on ionization fraction and wave attack angle. Comparison is made to the one-fluid magnetohydrodynamic case, and it is found that acoustic-to-acoustic and magnetic-to-magnetic transmission through the Alfvén-acoustic equipartition layer is decreased by a term of relative to one-fluid (infinite collision frequency), and correspondingly acoustic-to-magnetic and magnetic-to-acoustic conversion is increased. The neutral-acoustic mode is shown to dissipate rapidly as ν nc → ∞. Away from the mode conversion region, dissipative decay along the remaining magneto-acoustic rays scales as and is found to be much more effective on magnetically dominated rays compared to acoustically dominated rays. This produces a steep jump in dissipation in mode conversion regions, where the rays change character, and can produce localized heating there and beyond. Applications to the solar chromosphere are discussed.

Fuzzy Dark Matter as a Solution to Reconcile the Stellar Mass Density of High-z Massive Galaxies and Reionization History

The JWST early release data show unexpected high stellar mass densities of massive galaxies at 7 < z < 11. A high star formation efficiency is probably needed to explain this. However, such a high star formation efficiency would greatly increase the number of ionizing photons, which would be in serious conflict with current cosmic microwave background (CMB) and other measurements of cosmic reionization history. To solve this problem, we explore fuzzy dark matter (FDM), which is composed of ultra-light scalar particles, e.g., ultra-light axions, and calculate its halo mass function and stellar mass density for different axion masses. We find that a FDM model with m a ≃ 5 × 10−23 eV and a possible uncertainty range ∼3 × 10−23–10−22 eV can effectively suppress the formation of small halos and galaxies, so that with higher star formation efficiency both the JWST data at z ∼ 8 and the reionization history measurements from optical depth of CMB scattering and ionization fraction can be simultaneously matched. We also find that the JWST data at z ∼ 10 are still too high to fit in this scenario. We note that the estimated mean redshift of the sample may have large uncertainty, that it can be as low as z ∼ 9 depending on adopted spectral energy distribution templates and photometric-redshift code. In addition, warm dark matter with ∼keV mass can also be an alternative choice, since it should have similar effects on halo formation as FDM.

Heating and ionization by non-thermal electrons in the upper atmospheres of water-rich exoplanets

Context. The long-term evolution of an atmosphere and the remote detectability of its chemical constituents are susceptible to how the atmospheric gas responds to stellar irradiation. The response remains poorly characterized for water and its dissociation products, however, this knowledge is relevant to our understanding of hypothetical water-rich exoplanets. Aims. Our work investigates the effect of photoelectrons, namely, the non-thermal electrons produced by photoionizing stellar radiation on the heating and ionization of extended atmospheres dominated by the dissociation products of water. Methods. We used a Monte Carlo model and up-to-date collision cross sections to simulate the slowing down of photoelectrons in O-H mixtures for a range of fractional ionizations and photoelectron energies. Results. We find that that the fraction of energy of a photoelectron that goes into heating is similar in a pure H gas and in O–H mixtures, except for very low fractional ionizations, whereby the O atom remains an efficient sink of energy. The O–H mixtures will go on to produce more electrons because the O atom is particularly susceptible to ionization. We quantified all that information and present it in a way that can be easily incorporated into photochemical-hydrodynamical models. Conclusions. Neglecting the role of photoelectrons in models of water-rich atmospheres will result in overestimations of the atmospheric heating and, foreseeably, the mass-loss rates as well. It will also underestimate the rate at which the atmospheric gas becomes ionized, which may have implications for the detection of extended atmospheres with Lyman-α transmission spectroscopy. Our simulations for the small exoplanets π Men c and TRAPPIST-1 b reveal that they respond very differently to irradiation from their host stars, with water remaining in molecular form at lower pressures in the latter case.

Ion-driven destabilization of a toroidal electron plasma—A 3D3V PIC simulation

Ion-driven destabilization of a toroidal electron plasma in a small aspect ratio axisymmetric toroidal device is reported for A r + ions of different initial density values using a high fidelity 3D3V PIC solver. Stability of a recently discovered quiescent quasi-steady state (QQS) of a toroidal electron plasma obtained from “seed” solution as a result of entropy extremization at zero inertia is addressed in the presence of a small ion population. An initial value (f0) of the ion fraction (f = n i / n e) and the corresponding secondary electrons are “preloaded” into the system after the electron plasma attains a QQS state. This procedure is regarded as a proxy to the conventional production of ions in the experimental devices via impact ionization. The resulting electron plasma exhibits destabilized “center of charge motion” (m = 1) along with higher order harmonics with dominant power in the second harmonic. Gradual loss of ions (and also electrons) is observed resulting in time varying f values. Beyond a certain value of f0 ( ≥ 0.005), growth in wall probe current is observed, which saturates at later simulation time due to the loss of particles. Trajectories of ion particles indicate ion trapping in the potential well, which is qualitatively similar to the ion resonance instability in pure electron plasmas.

Separation of mass spectra of hydrogen–deuterium exchanged ions obtained by electrospray of solutions of biopolymers with unknown primary structure

The work is dedicated to further development of our described method for analyzing mass spectra of biomolecules acquired as a result of hydrogen-deuterium exchange reactions (HDXs). The modified method consists of separating HDX distributions via their approximations by aminimum number of components corresponding to independent H/D substitutions and independent charge carrier retentions in different spatial isoforms or conformations of biomolecules with unknown primary structures. In this case, neither the natural isotopic distribution nor the exact number of active sites involved in HDXs and H+ or D+ attachments can be determined in advance. Original H/D electrospray mass spectra of an apamin solution were taken from our previous work. In that work, taking into account the natural isotopic distribution of apamin molecules, three main conformations of apamin ions were found as a result of separating the H/D mass spectra of the apamin solution for the gas flow with theaddition of about 10% ND3 molecules. Using the proposed modified method that does not require knowledge of the primary structure of the biomolecules gave similar results with slight deviations of calculated HDX distributions of the apamin ions from those obtained earlier. The maximum difference between mean values of the calculated HDX distributions for ions of the same charge in both cases does not exceed a few percent. In addition, HDX mass spectra of the apamin complex with an adduct of unknown structure were processed. Such analysis gave also three main fractions of ions with relatively large contributions when ND3 was injected into a radio-frequency quadrupole. In the absence of ND3 flow, the results of calculations for apamin and its complex were close to each other too. The formation of the apamin complex most probably in solution was confirmed by performed calculations.

Angle-dependent negative ion formation in H+ ions grazing scattering on Cu(100)

0.5–5 keV-energy H+ ions are scattered from Cu(100) in grazing incidences. The angle dependent positive and negative ion fractions have been measured in the non-specular scattering configuration. The positive-ion fractions for 0.5 and 1.0 keV incident energies are about 0% during the variation of the incident angle from 1° to 7°. Moreover, the non-monotonic trends of negative-ion fractions are observed for these two low energies, which may be ascribed to the sufficient Auger neutralization at the non-specular configuration.

Phase-field modeling of solid-state metathesis reactions with the charge neutrality constraint

In this work, we present a phase-field model that captures the evolution of ionic concentrations and phase fractions during solid-state metathesis (SSM) reactions where diffusion limits the rate of transformation. The evolution of the mole fraction of each ion is obtained via governing equations that describe the reduction of a free energy, which includes an energy landscape with local minima located at compositions corresponding to stable products. We utilized two Lagrange multipliers to impose constraints of electroneutrality as well as on the sum of mole fractions, which were then eliminated to derive set of two partial differential equations that describe the dynamics of the mole fraction evolution. From these governing equations, the expressions for effective mobilities for the cations and the anions were obtained. We first study the effect of mobilities of ions on the reaction kinetics, using a simple model considering the ions with an identical absolute value of charge numbers. The simulation results show that the overall characteristic mobility, defined as the sum of the two effective ionic mobilities, provides an excellent measure of the rate at which reaction progresses and that the ratio of the effective mobilities of the anions and the cations signifies the manner by which the reaction progresses. We then generalize the model to consider ions with different charge numbers and tuned the mobility of ions based on their diffusion coefficients reported in the literature and experimental data from a thin-film experiment for the synthesis of FeS2 to demonstrate the capability of the model to predict the phase evolution during SSM reactions. In particular, the simulation predicts nonplanar phase evolution, which is recently observed in thin-film reactions for the synthesis of FeS2 via transmission electron microscopy. The approach can serve as a basis for models for phase transformations in other multiphase ionic mixtures, such as in all-solid-state batteries and in ionic liquids.

Coalescing Cation Selectivity Approaches in Ionomers

Inconsistent selectivity measures used in the literature to quantify an ionomer’s preference for one ion over another make it challenging to compare uptake of different ions across studies. Preferential ion-partitioning, which leads to partially exchanged membranes, needs to be studied to gain a fundamental understanding of the nature of ion/membrane interactions as well as to begin to unravel how varying ion fractions, whether or not intentional, may affect the membrane’s properties and thus durability and performance. In this focus review, we use Nafion as a prototypical example to explore partial exchange studies and codify the various literature experiments and theory into a comprehensive whole, enabling formation of ionomer databases. A few representative approaches to selectivity are dissected to identify the points of divergence between them as well as to re-examine the embedded assumptions therein. Lastly, modeling strategies for ion selectivity of the membrane are reviewed to arrive at and correlate fundamental ion properties to ionomer selectivity.

Role of magnetic field and bias configuration on HiPIMS deposition of W films

In this work, the deposition of tungsten (W) films by High Power Impulse Magnetron Sputtering (HiPIMS) has been investigated. By adopting a combined modeling and experimental approach, the role of magnetic field strength and bias configuration on growth of W films has been studied since they are relevant parameters for the energetic and ionized HiPIMS environment. Modeling results showed that increasing the magnetic strength from 40 to 60 mT led to larger W ion fraction in the plasma and, contemporary, to higher ion back-attraction to the target. This, in turn, resulted in a similar W ion fraction in the flux towards the substrate for the two magnetic field strengths considered during the on-time of the voltage pulse. On the contrary, the W ion fraction became significantly different in the afterglow and the same happened to the ion flux composition. Exploiting the studied discharges, W films have been grown applying at substrate negative pulsed bias voltages, both synchronized and delayed to the voltage pulse onset. Films morphology, microstructure, residual stress, composition and density have been examined. In light of plasma differences retrieved from the numerical investigation, film growth and properties are discussed.

Planetary nurseries: vortices formed at smooth viscosity transition

ABSTRACT Excitation of Rossby wave instability and development of a large-scale vortex at the outer dead zone edge of protoplanetary discs is one of the leading theories that explains horseshoe-like brightness distribution in transition discs. Formation of such vortices requires a relatively sharp viscosity transition. Detailed modelling, however, indicates that viscosity transitions at the outer edge of the dead zone is relatively smooth. In this study, we present 2D global, non-isothermal, gas–dust coupled hydrodynamic simulations to investigate the possibility of vortex excitation at smooth viscosity transitions. Our models are based on a recently postulated scenario, wherein the recombination of charged particles on the surface of dust grains results in reduced ionization fraction and, in turn, the turbulence due to magnetorotational instability. Thus, the α-parameter for the disc viscosity depends on the local dust-to-gas mass ratio. We found that the smooth viscosity transitions at the outer edge of the dead zone can become Rossby unstable and form vortices. A single large-scale vortex develops if the dust content of the disc is well coupled to the gas; however, multiple small-scale vortices ensue for the case of less coupled dust. As both type of vortices are trapped at the dead zone outer edge, they provide sufficient time for dust growth. The solid content collected by the vortices can exceed several hundred Earth masses, while the dust-to-gas density ratio within often exceeds unity. Thus, such vortices function as planetary nurseries within the disc, providing ideal sites for formation of planetesimals and eventually planetary systems.

PHANGS–JWST First Results: Measuring Polycyclic Aromatic Hydrocarbon Properties across the Multiphase Interstellar Medium

Ratios of polycyclic aromatic hydrocarbon (PAH) vibrational bands are a promising tool for measuring the properties of the PAH population and their effect on star formation. The photometric bands of the MIRI and NIRCam instruments on JWST provide the opportunity to measure PAH emission features across entire galaxy disks at unprecedented resolution and sensitivity. Here we present the first results of this analysis in a sample of three nearby galaxies: NGC 628, NGC 1365, and NGC 7496. Based on the variations observed in the 3.3, 7.7, and 11.3 μm features, we infer changes to the average PAH size and ionization state across the different galaxy environments. High values of F335MPAH/F1130W and low values of F1130W/F770W are measured in H ii regions in all three galaxies. This suggests that these regions are populated by hotter PAHs, and/or that the PAH ionization fraction is larger. We see additional evidence of heating and/or changes in PAH size in regions with higher molecular gas content as well as increased ionization in regions with higher Hα intensity.

Optimizing mechanical properties and Ag ion release rate of silver coatings deposited on Ti-based high entropy alloys

This paper details the characterization of microstructure, texture, mechanical properties, and ion release behavior of antibacterial Ag thin films sputtered on two novel biomedical high entropy alloys (HEAs), namely the Ti23Ta10Hf27Nb12Zr28 (HEATi23) and Ti28Ta10Hf30Nb14Zr18 (HEATi28) alloys. Specifically, the influences of varying deposition time and Ar flow rate were investigated to reveal the mechanisms dictating the microstructure, texture, and mechanical properties of the coatings. In addition, static immersion experiments were carried out in simulated body fluid (SBF) for 28 days to establish the relationship between ion release from the coatings and the deposition parameters, microstructure, and surface texture. It was shown that texture evolution in Ag thin films depends on both film thickness and Ar flow rate, such that there exists a critical thickness at which the energy minimization mechanism is altered. A very good correlation was also observed between an increase in (111) peak intensity and a decrease in released Ag ion fraction. Overall, the findings of the work presented herein suggest that the alterations in Ag deposition parameters could be optimized to obtain the desired mechanical properties while enhancing the biocompatibility of the HEA substrates by coating them with antibacterial Ag films.

Charge transfer of keV-energy H+ ions in grazing scattering on Cu(100)

An experimental study of 0.5-5.0 keV-energy H+ ion scattering on Cu(100) has been presented at a grazing scattering angle of 7°. The velocity dependent ion fractions have been measured in this work. The positive-ion fraction increases with the increase of incident velocity, which can be described by the exponential scaling. In particular, the threshold velocity for the positive-ion fraction is observed at about 0.25 a.u., and explained by the Auger ionization process. The negative-ion fraction increases monotonically with the impact velocity, which can be explained by the first type of the parallel velocity effect. Considering the formation of positive ions and the contribution of the parallel velocity effect, the negative-ion fraction is calculated by the modified theoretical model and the general trend is consistent with the experimental data.

Evaluation of the quality of measurements of the testing laboratory during interlaboratory comparative tests

The article presents the statistical processing of the test results of the mass fraction of the chlorine ion (Cl) obtained from two accredited testing laboratories. The stages of statistical processing of the results of interlaboratory comparison tests are as follows: elimination of gross errors, determination of the uniformity of the sample, calculation of the assigned value, evaluation of the quality of the measurement results. The presence of gross errors in the sample was determined by the Grubbs test, and the uniformity of the sample was confirmed by the Fisher’s test and Student’s test. The assigned value was calculated by a robust method using algorithm A with an iterative scale. The quality of laboratory measurement results was evaluated using the z-score. The z-score value for each participant showed that the results of measuring the mass fraction of chlorine ion in cement samples were acceptable. The quality of the results of these laboratories is satisfactory and does not require corrective measures. These results of the test quality assessment can be used for the organizers of interlaboratory tests, as well as for accredited laboratories that check their qualifications.

Magnetically regulated collapse in the B335 protostar?

Context. Whether or not magnetic fields play a key role in dynamically shaping the products of the star formation process is still largely debated. For example, in magnetized protostellar formation models, magnetic braking plays a major role in the regulation of the angular momentum transported from large envelope scales to the inner envelope, and is expected to be responsible for the resulting protostellar disk sizes. However, non-ideal magnetohydrodynamic effects that rule the coupling of the magnetic field to the gas also depend heavily on the local physical conditions, such as the ionization fraction of the gas. Aims. The purpose of this work is to observationally characterize the level of ionization of the gas at small envelope radii and to investigate its relation to the efficiency of the coupling between the star-forming gas and the magnetic field in the Class 0 protostar B335. Methods. We obtained molecular line emission maps of B335 with ALMA, which we use to measure the deuteration fraction of the gas, RD, its ionization fraction, χe, and the cosmic-ray ionization rate, ζCR, at envelope radii ≲1000 au. Results. We find large fractions of ionized gas, χe ≃ 1–8 × 10−6. Our observations also reveal an enhanced ionization that increases at small envelope radii, reaching values up to ζCR ≃ 10−14 s−1 at a few hundred astronomical units (au) from the central protostellar object. We show that this extreme ζCR can be attributed to the presence of cosmic rays accelerated close to the protostar. Conclusions. We report the first resolved map of ζCR at scales ≲1000 au in a solar-type Class 0 protostar, finding remarkably high values. Our observations suggest that local acceleration of cosmic rays, and not the penetration of interstellar Galactic cosmic rays, may be responsible for the gas ionization in the inner envelope, potentially down to disk-forming scales. If confirmed, our findings imply that protostellar disk properties may also be determined by local processes that set the coupling between the gas and the magnetic field, and not only by the amount of angular momentum available at large envelope scales and the magnetic field strength in protostellar cores. We stress that the gas ionization we find in B335 significantly stands out from the typical values routinely used in state-of-the-art models of protostellar formation and evolution. If the local processes of ionization uncovered in B335 are prototypical to low-mass protostars, our results call for a revision of the treatment of ionizing processes in magnetized models for star and disk formation.

Contribution of thermal dissociation during steel nitriding in electron beam plasma

We report the results of measurements of mass-to-charge ion composition of the beam plasma generated by a forevacuum plasma-cathode electron source in a nitrogen atmosphere during electron beam interaction with the surface of a steel sample. It has been found that as the sample surface temperature increases from 540 ℃ to 930 ℃, the fraction of atomic nitrogen ions in the spectrum increases by 4-10%. This increase in atomic nitrogen occurs at the backdrop of decreasing number of molecular nitrogen monoxide ions and is associated with thermal dissociation of its molecules.

Fe Ion Composition in Solar-Wind Streams in the Solar Corona and Heliosphere

Analysis of the distributions of Fe ions over the stages of ionization in solar-wind (SW) plasma provides valuable information on the formation of SW streams and plasma heating processes, as well as for identifying SW sources on the Sun. When passing SW plasma through the corona, its ion composition evolves and finally “freezes” at distances of the order of several solar radii from the solar surface, remaining further practically unchanged in the heliosphere. This makes it possible to obtain information about the physical conditions in its source and the solar corona from the SW charge state. Average charge QFe, which is usually used to characterize the distributions of Fe ions, does not take into account all the features of the evolution of the ion composition, which does not allow one to extract more detailed information about the state of SW plasma. In this study, to describe the charge state of Fe ions, three parameters q4, q8, and q12 are introduced, which characterize the relative fractions of ions with charges Z = 0–7, 8–11, and 12–20, respectively, and conditionally correspond to “cold,” “medium,” and “hot” SW plasma components. According to the measurements of the Fe ion composition in 2010 on the STEREO-A spacecraft, the characteristic values of these parameters for different types of SW streams are given. The problem of modeling ion distributions in SW plasma based on diagnostic data on the parameters of coronal sources is considered. Using the example of the event associated with coronal-mass ejection on August 18, 2010, it is shown that the parameters of the charge state of Fe ions calculated from the model distributions are in good agreement within errors with the measurement data.

THE INFLUENCE OF PLASMA ASSISTANCE MODES ON CHARACTERISTICS AND COMPOSITION OF PVD ZIRCONIUM NITRIDE COATINGS

Zirconium nitride coatings are deposited by a vacuum-arc method at a low (0.01-0.04 Pa) nitrogen partial pressure in the modes without and with plasma assistance. The plasma assistance is provided by the operation of a gas plasma source based on a non-self-sustained arc discharge with thermionic and hollow cathodes. This new low-inertia method has not been practically studied in terms of formation of nitride coatings with different architecture (single-layer, multi-layer, gradient coatings). We note that the effect of plasma assistance (an increase of the nitrogen concentration in the nitride coating with the increasing nitrogen ion fraction in the gas-metal plasma) is practically unobservable in the ZrN coatings formed under the selected conditions. Furthermore, their phase compositions do not noticeably change and their physical, mechanical and tribological properties are not significantly improved.