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FeRh-based alloys have attracted significant attention due to their magnetic phase transition and significant magnetocaloric effects. These properties position them as promising candidates for fundamental research and practical applications, including magnetic cooling and targeted drug delivery. The study of FeRh alloys, particularly those where Rhodium or Iron atoms are substituted with other transition metals, is crucial as certain substitutions preserve the alloy's magnetocaloric properties. However, even within a specific structural type and without considering competing phases, determining which atom (Fe or Rh) is replaced upon introducing a third element remains unclear. This paper addresses this ambiguity through ab initio calculations. We propose an approach to predict whether a dopant will replace Fe or Rh, offering insights into the electronic and structural factors influencing the substitution. Additionally, we present a dataset of ab initio calculations on doped FeRh alloys, which will support future data-driven modeling efforts. Our findings not only advance the understanding of FeRh-based alloys but also contribute to the design of novel materials for experimental and industrial applications. [ABSTRACT FROM AUTHOR]

In the previous studies of nonlinear saturation of the Buneman instability caused by high electron drift velocity relative to ions, the phase-space holes and the plateau on the electron velocity distribution function were identified as features of the saturation stage of instability [notably in the paper by Omura et al., J. Geophys. Res. 108, 1197 (2003)]. We have performed a much longer simulation of the Buneman instability and observed a secondary instability. This secondary instability generates fast electron-acoustic waves. By analyzing the phase-space plot of ions and electrons, we show that the fast electron heating and the formation of the plateau of electron velocity distribution function are not due to the quasi-linear diffusion but due to the nonlinear interaction of ion- and electron-acoustic solitary waves (phase-space holes) by exchange of trapped electrons in each wave. We also report the details on the intermittent and bursty nature of turbulence driven by this instability. [ABSTRACT FROM AUTHOR]

We study, by numerical and analytical means, the evolution of a collisionless plasma initiated between absorbing walls. The ensuing flow is described by rarefaction waves that travel inward from the boundaries, interact, and eventually vanish after crossing through, leading up to the asymptotic stage of the decay. Particle simulations indicate that the kinetic evolution strongly resembles one found in isentropic gas dynamics. Namely, a very gradual density profile forms in the expanding central region where the rarefaction waves interact, with an accompanying linear velocity profile. Asymptotically, the density falls off as 1 / t. The density and the flux at the boundary show little variation over the period when rarefaction waves still exist. Plasma potential, on the other hand, drops quite rapidly (on the underlying ion-acoustic timescale) to less than initial electron temperature Te when over 70% of the particles still remain in the system. This is due to electron kinetics being governed by conservation of adiabatic invariant in a slowly varying potential well. Analytical model of the velocity distribution is presented to explain the simulations. The results have implications for afterglow plasmas used in material processing and also for ion-extraction devices. One property of potential interest is good uniformity of the decaying plasma that occurs after approximately one ion-acoustic time. [ABSTRACT FROM AUTHOR]

Reliable prediction of aircraft poststalled dynamics is entirely dependent on the adequacy of the aerodynamic model. A mathematical model of aerodynamic characteristics of a light aircraft is developed for a wide range of angles of attack, sideslip, and angular rates. It is augmented by a model of uncertainties based on a set of repeated measurements of static aerodynamic characteristics. The effect of aerodynamic uncertainties on steady-state and oscillatory spin modes is directly calculated using a continuation on a parameter technique. The influence of aerodynamic uncertainties on spin entry/recovery is also analyzed. [ABSTRACT FROM AUTHOR]

In this paper, a novel method is proposed to enhance ion extraction flux from collision-free decaying plasma by injecting an energetic electron beam from the cathode surface. A numerical model accounting for initial plasma generation and relevant plasma-wall interactions is established and implemented into an electrostatic particle-in-cell code. The model and the numerical code are validated by comparing the results obtained without beam injection against known experimental scaling for the extraction process. Based on this validation, simulations with an externally injected electron beam are conducted. Our results show a significant enhancement of the ion extraction flux, as well as a corresponding reduction of the ion extraction time, e.g. by a factor of 3 when the beam current is set at 600 A m−2. The analysis of spatiotemporal evolution of the electric potential during the plasma expansion process shows the formation of a standing Langmuir wave, excited by the beam, in the bulk plasma. Interaction of this wave with the bulk electrons provides an efficient heating mechanism. Higher mean energy of plasma electrons leads to higher ion-acoustic speed, and thus, results in the enhancement of the ion extraction flux. [ABSTRACT FROM AUTHOR]

We study formation of the Vibrational Distribution Function (VDF) in a molecular gas at low pressure, when vibrational levels are excited by electron impact and deactivated in collisions with walls and show that this problem has a convenient analytical solution that can be used to obtain VDF and its dependence on external parameters. The VDF is determined by excitation of vibrational levels by an external source and deactivation in collisions with the wall. Deactivation in wall collisions is little known process. However, we found that the VDF is weakly dependent on the functional form of the actual form of probability for a vibrational number to transfer into a lower level at the wall. Because for a given excitation source of vibrational states, the problem is linear the solution for VDF involves solving linear matrix equation. The matrix equation can be easily solved if we approximate probability, in the form: In this case, the steady-state solution for VDF() simply involves a sum of source rates for levels above with a factor of As an example of application, we study the vibrational kinetics in a hydrogen gas and verify the analytical solution by comparing with a full model. [ABSTRACT FROM AUTHOR]

Aircraft spin susceptibility is a critical parameter for the flight safety. Recently developed quantitative methods for analysis of nonlinear systems are applied to analysis of aircraft spins. The parameters of aircraft spin modes are calculated using numerical continuation on a parameter. Polynomial approximations of the reduced fifth-order system with account of significant nonlinearities in the aircraft aerodynamic coefficients are derived near a number of stable spin equilibrium points and validated by simulation. For the calculated polynomial approximations, low bounds of ellipsoidal approximations of regions of attraction are estimated using the Lyapunov-based optimization technique. The estimated sizes of regions of attraction for different spin modes can be used as a measure of aircraft susceptibility to spin and relative danger of particular spins. [ABSTRACT FROM AUTHOR]

A neural network approach for modeling of unsteady aerodynamic characteristics in a wide angle-of-attack range is considered in the paper. Special tests have been carried out in TsAGI wind tunnel to investigate dynamic properties of unsteady aerodynamic characteristics of a generic transonic cruiser, which is a canard configuration. The aerodynamic derivatives have been studied with forced small-amplitude oscillations. In addition, forced large-amplitude oscillation tests have been carried out for the detailed investigation of dynamic effects on the unsteady aerodynamics in the extended flight envelope. To describe the nonlinear dependences of aerodynamic coefficients, observed in the dynamic experiments, two neural network models, which use the feed-forward and recurrent architectures, are developed and compared. A special regularization for the neural networks training taking into account that data are obtained in different experiments with different noise level is proposed to improve a model performance. The unsteady aerodynamics modeling results obtained with neural networks are compared with a state-space model results. [ABSTRACT FROM AUTHOR]

The effect of driving frequency in the range of 13.56–73 MHz on electron energy distribution and electron heating modes in a 50 mTorr capacitively coupled argon plasma discharge is studied using 1D-3V particle-in-cell simulations. Calculated electron energy probability functions exhibit three distinct "temperatures" for low-, mid-, and high-energy electrons at all the studied driving frequencies. When compared to published experimental data, the calculated probability functions show a reasonable agreement for the energy range resolved in the measurements (about 2–10 eV). Discrepancies due to limitations in experimental energy resolution outside this range lead to differences between computational and experimental values of the electron number density determined from the distribution functions, and the predicted effective electron temperature is within 25% of experimental values. The impedance of the discharge is interpreted in terms of a homogeneous equivalent circuit model, and the driving frequency dependence of the inferred combined sheath thickness is found to obey a known, theoretically derived, power law. The average power transferred from the field to the electrons (electron heating) is computed, and a region of negative heating near the sheath edge, particularly at higher driving frequencies, is identified. Analysis of the electron momentum equation shows that electron inertia, which on temporal averaging would be zero in a linear regime, is responsible for negative values of power deposition near the sheath edge at high driving frequencies due to the highly nonlinear behavior of the discharge. [ABSTRACT FROM AUTHOR]

The Debye sheath is shown to be unstable under general conditions. For surface materials with sufficient secondary electron emission (SEE) yields, the surface's current-voltage characteristic has an unstable branch when the bulk plasma temperature (Te) exceeds a critical value, or when there are fast electron populations present. The plasma-surface interaction becomes dynamic where the sheath may undergo spontaneous transitions or oscillations. Using particle-in-cell simulations, we analyze sheath instabilities occurring in a high Te plasma slab bounded by walls with SEE. As the plasma evolves, whenever the sheath enters an unstable state, its amplitude rapidly collapses, allowing a large flux of previously trapped electrons to hit the wall. These hot electrons induce more than one secondary on average, causing a net loss of electrons from the wall. The sheath collapse quenches when the surface charge becomes positive because the attractive field inhibits further electrons from escaping. Sheath instabilities influence the current balance, energy loss, cross-B-field transport and even the bulk plasma properties. Implications for discharges including Hall thrusters are discussed. More generally, the results show that common theories that treat emission as a fixed (time-independent) 'coefficient' do not capture the full extent of SEE effects. [ABSTRACT FROM AUTHOR]

A bounded plasma where the hot electrons impacting the walls produce more than one secondary on average is studied via particle-in-cell simulation. It is found that no classical Debye sheath or space-charge-limited sheath exists. Ions are not drawn to the walls and electrons are not repelled. Hence the unconfined plasma electrons travel unobstructed to the walls, causing extreme particle and energy fluxes. Each wall has a positive charge, forming a small potential barrier or "inverse sheath" that pulls some secondaries back to the wall to maintain the zero current condition. [ABSTRACT FROM AUTHOR]

A condition for sheath instability due to secondary electron emission (SEE) is derived for low collisionality plasmas. When the SEE coefficient of the electrons bordering the depleted loss cone in energy space exceeds unity, the sheath potential is unstable to a negative perturbation. This result explains three different instability phenomena observed in Hall thruster simulations including a newly found state with spontaneous ∼20 MHz oscillations. When instabilities occur, the SEE propagating between the walls becomes the dominant contribution to the particle flux, energy loss and axial transport [ABSTRACT FROM AUTHOR]

Abstract: The dynamic derivatives are widely used in linear aerodynamic models in order to determine the flying qualities of an aircraft: the ability to predict them reliably, quickly and sufficiently early in the design process is vital in order to avoid late and costly component redesigns. This paper describes experimental and computational research dealing with the determination of dynamic derivatives carried out within the FP6 European project SimSAC. Numerical and experimental results are compared for two aircraft configurations: a generic civil transport aircraft, wing-fuselage-tail configuration called the DLR-F12 and a generic Transonic CRuiser, which is a canard configuration. Static and dynamic wind tunnel tests have been carried out for both configurations and are briefly described within this paper. The data generated for both the DLR-F12 and TCR configurations include force and pressure coefficients obtained during small amplitude pitch, roll and yaw oscillations while the data for the TCR configuration also include large amplitude oscillations, in order to investigate the dynamic effects on nonlinear aerodynamic characteristics. In addition, dynamic derivatives have been determined for both configurations with a large panel of tools, from linear aerodynamic (Vortex Lattice Methods) to CFD. This work confirms that an increase in fidelity level enables the dynamic derivatives to be calculated more accurately. Linear aerodynamics tools are shown to give satisfactory results but are very sensitive to the geometry/mesh input data. Although all the quasi-steady CFD approaches give comparable results (robustness) for steady dynamic derivatives, they do not allow the prediction of unsteady components for the dynamic derivatives (angular derivatives with respect to time): this can be done with either a fully unsteady approach i.e. with a time-marching scheme or with frequency domain solvers, both of which provide comparable results for the DLR-F12 test case. As far as the canard configuration is concerned, strong limitations for the linear aerodynamic tools are observed. A key aspect of this work are the acceleration techniques developed for CFD methods, which allow the computational time to be dramatically reduced while providing comparable results. [Copyright &y& Elsevier]

The linear problem of inviscid incompressible flow around a high-aspect-ratio wing at an angle of attack and in the presence of steady pitching and rolling rotation is considered. The main integral equation of the problem is reduced to a sequence of one-dimensional integral equations without use of the matched asymptotic expansions method. The first few terms of the series for the circulation distribution over the wing surface are calculated. For an elliptic high-aspect-ratio wing the corresponding aerodynamic forces are calculated. The derivatives of the aerodynamic coefficients of the wing with respect to the angle of attack and the angular velocities are determined. The asymptotic expressions obtained are compared with the results of numerical calculations of the corresponding derivatives using the discrete vortex method. [ABSTRACT FROM AUTHOR]

The article discusses a study which examined the influence of steady pitch rate on 2-dimensional airfoil aerodynamic characteristics of an airplane. The effects of steady pitch rate was stimulated using curved models approximation. The formulas for the numerical computation of aerodynamic loads estimation are presented.

We study classical, modified, and weak Banach-Mazur distances between sums of the spaces ℓ. We calculate explicitly the classical and weak Banach-Mazur distances between sums of the spaces ℓ and obtain bounds for ratios of distances between sums of the spaces ℓ. Bibliography: 14 titles. [ABSTRACT FROM AUTHOR]

The linear problem of the time-dependent inviscid flow past a thin symmetric airfoil with a control on its trailing edge deflected in accordance with an arbitrary law is considered. The aerodynamic loads on the airfoil are calculated. The intensity of the vortex wake shed from the airfoil is determined by numerically solving a Volterra integral equation of the first kind. Questions of the mathematical modeling of the time-dependent aerodynamic loads in a form convenient for the joint solution of the problems of aerodynamics and flight dynamics are also considered. The results of the modeling are compared with the numerical solutions obtained. [ABSTRACT FROM AUTHOR]

Presents a study on the importance of knowing the explicit dependence of the loads on the airfoil upper-surface separation point location of an aircraft. Linear thin airfoil theory with flow separation; Comparison of analytic and computational results for airfoil in separated flow; Conclusions

The effect of a uniform magnetic field on particle transport in low-pressure radio frequency (RF) capacitively coupled plasma (CCP) has been studied using a particle-in-cell model. Three distinct regimes of plasma behavior can be identified as a function of the magnetic field. In the first regime at low magnetic fields, asymmetric plasma profiles are observed within the CCP chamber due to the effect of E → × B → drift. As the magnetic field increases, instabilities develop and form self-organized spoke-shaped structures that are distinctly seen within the bulk plasma closer to the sheath. In this second regime, the spoke-shaped coherent structures rotate inside the plasma chamber in the − E → × B → direction, where E → and B → are the DC electric and magnetic field vectors, respectively, and the DC electric field exists in the sheath and pre-sheath regions. The spoke rotation frequency is in the megahertz range. As the magnetic field strength increases further, the rotating coherent spokes continue to exist near the sheath. The coherent structures are, however, accompanied by new small-scale incoherent structures originating and moving within the bulk plasma region away from the sheath. This is the third regime of plasma behavior. The threshold values of the magnetic field between these regimes were found not to vary with changing plasma reactor geometry (e.g., area ratio between ground and powered electrodes) or the use of an external capacitor between the RF-powered electrode and the RF source. The threshold values of the magnetic field between these regimes shift toward higher values with increasing gas pressure. Analysis of the results indicates that the rotating structures are due to the lower hybrid instability driven by density gradients and electron-neutral collisions. This paper provides guidance on the upper limit of the magnetic field for instability-free operation in low-pressure CCP-based semiconductor deposition and etch systems that use the external magnetic field for plasma uniformity control. [ABSTRACT FROM AUTHOR]

Hollow cathodes for plasma switch applications are investigated via 2D3V particle-in-cell simulations of the channel and plume region. The kinetic nature of the plasma within the channel is dependent on the thermalization rate of electrons, emitted from the insert. When Coulomb collisions occur at a much greater rate than ionization or excitation collisions, the electron energy distribution function rapidly relaxes to a Maxwellian and the plasma within the channel can be described accurately via a fluid model. In contrast, if inelastic processes are much faster than Coulomb collisions, then the electron energy distribution function in the channel exhibits a notable high-energy tail, and a kinetic treatment is required. This criterion is applied to hollow cathodes from the literature, revealing that a fluid approach is suitable for most electric propulsion applications, whereas a kinetic treatment can be more critical to accurate modeling of plasma switches. [ABSTRACT FROM AUTHOR]

Airframe icing causes significant degradation of aerodynamic characteristics and influences the flight safety. Wind tunnel study of longitudinal steady and unsteady aerodynamic characteristics of a transport aircraft in icing conditions is carried out in order to develop mathematical model of aerodynamics in the extended flight envelope. The wind tunnel results are validated through flight tests conducted for the real aircraft. Large, glaze-horn ice shapes, corresponding to holding flight phase, are considered. Influence of an ice protection system as well as its failure is examined. Effect of icing on the unsteady aerodynamics characteristics is studied not only through wind tunnel tests but also via analysis of subsequent influence on the flight dynamics of the aircraft. The conducted study shows that the ice shapes of the holding phase lead to reduced stall angle of attack (AoA), maximum lift, and longitudinal damping. Flight dynamics analysis demonstrates that dangerous aircraft behaviour in the form of high AoA departure and limit cycle oscillations (LCO) can be observed at smaller elevator deflections for the iced aircraft. The account for icing influence on the unsteady aerodynamics in the flight dynamics simulations revealed degradation of the dynamic response and deterioration of phase portraits of the system. Even for small AoA and elevator deflection, the aircraft might be trapped into the basin of attraction of high-AoA LCO. In addition, incorporating icing effects in unsteady aerodynamics manifest larger amplitude of LCO. [ABSTRACT FROM AUTHOR]

A quasi-analytical model was developed to map out the low-pressure (left-hand) branch of the Paschen curve at very high voltage when electrons are in the runaway regime and charge exchange/ionization avalanche sustained by ions and fast neutral atoms becomes important. The model was applied to helium gas between parallel-plate electrodes, at potentials ranging in magnitude between 10 and 1000 kV. The respective value of reduced electric field E/n varied in the range of 50−6000 kTd (1 kTd = 10−18 Vm2), with reduced density nd (where n is the gas density and d is the inter-electrode distance) on the order of 1020 m−2. Three regimes of the breakdown have been identified according to the relative share of impact ionization by electrons, by ions, and by fast neutrals. The analytically derived Paschen curve is compared to those obtained with a detailed particle-in-cell/Monte Carlo simulation, and also through experimental measurements (L Xu, A V Khrabrov, I D Kaganovich and T J Sommerer 2017 Phys. Plasmas 24 093511). The model provides accurate predictions for E/n up to ∼103 kTd, constrained by availability and quality of required input data. [ABSTRACT FROM AUTHOR]

The possible application of the results of numerical modeling in developing an approximate phenomenological mathematical aerodynamic model applicable in solving the problems of dynamics is studied with reference to the example of the unsteady flow past the NACA 0015 airfoil oscillating in the angle of attack at different frequencies, amplitudes, and mean angles of attack. For this purpose, the Reynolds equations are solved in both steady and unsteady formulations, together with the k–ω SST turbulence model. The results of the calculations are validated by means of comparing them with the experimental data. The model of the normal force and the longitudinal moment formulated within the framework of an approach introducing an internal dynamic variable is identified according to the data of calculations. The results of the modeling are compared with the numerical and experimental data. The comparison with the conventional approach to the modeling based on the linear unsteady model with the use of dynamic derivatives is also carried out. [ABSTRACT FROM AUTHOR]

The process of numerical thermalization in particle-in-cell (PIC) simulations has been studied extensively. It is analogous to Coulomb collisions in real plasmas, causing particle velocity distributions (VDFs) to evolve toward a Maxwellian as macroparticles experience polarization drag and resonantly interact with the fluctuation spectrum. This paper presents a practical tutorial on the effects of numerical thermalization in 2D PIC applications. Scenarios of interest include simulations, which must be run for many thousands of plasma periods and contain a population of cold electrons that leave the simulation space very slowly. This is particularly relevant to many low-temperature plasma discharges and materials processing applications. We present numerical drag and diffusion coefficients and their associated timescales for a variety of grid resolutions, discussing the circumstances under which the electron VDF is modified by numerical thermalization. Though the effects described here have been known for many decades, direct comparison of analytically derived, velocity-dependent numerical relaxation timescales to those of other relevant processes has not often been applied in practice due to complications that arise in calculating thermalization rates in 1D simulations. Using these comparisons, we estimate the impact of numerical thermalization in several examples of low-temperature plasma applications including capacitively coupled plasma discharges, inductively coupled plasma discharges, beam plasmas, and hollow cathode discharges. Finally, we discuss possible strategies for mitigating numerical relaxation effects in 2D PIC simulations. [ABSTRACT FROM AUTHOR]

Occurrence of unintended gas breakdown in the narrow gaps of plasma processing chambers is one of the critical challenges in developing advanced plasma sources. We present a combined experimental and theoretical study of unintended discharges in the narrow gaps of plasma processing chambers and report significant drop of the gas breakdown voltage in the presence of a background plasma facing the gap. Experimentally measured breakdown voltages decrease in subsequent breakdown events due to wall erosion caused by the discharge. Therefore, preventing and mitigating the first discharge is of paramount importance. An analysis of kinetic simulation results indicates that the charged particle influx from the background plasma in the processing chamber into the gap is responsible for the onset of early breakdown: higher charged particle density within the gap modifies the electric field profile, allowing unintended breakdowns to occur at a significantly reduced threshold voltage. [ABSTRACT FROM AUTHOR]

The two particle-in-cell codes EDIPIC and LSP are benchmarked and validated for a parallel-plate glow discharge in helium, in which the axial electric field had been carefully measured, primarily to investigate and improve the fidelity of their collision models. The scattering anisotropy of electron-impact ionization, as well as the value of the secondary-electron emission yield, are not well known in this case. The experimental uncertainty for the emission yield corresponds to a factor of two variation in the cathode current. If the emission yield is tuned to make the cathode current computed by each code match the experiment, the computed electric fields are in excellent agreement with each other, and within about 10% of the experimental value. The non-monotonic variation of the width of the cathode fall with the applied voltage seen in the experiment is reproduced by both codes. The electron temperature in the negative glow is within experimental error bars for both codes, but the density of slow trapped electrons is underestimated. A more detailed code comparison done for several synthetic cases of electron-beam injection into helium gas shows that the codes are in excellent agreement for ionization rate, as well as for elastic and excitation collisions with isotropic scattering pattern. The remaining significant discrepancies between the two codes are due to differences in their electron binary-collision models, and for anisotropic scattering due to elastic and excitation collisions. [ABSTRACT FROM AUTHOR]

The principles of aerodynamic modeling in the extended flight envelope, which is characterized by the development of separated flow, are outlined and illustrated for a generic transport airplane. The importance of different test techniques for generating wind-tunnel data and the procedure for blending the obtained experimental data for aerodynamic modeling are discussed. Complementary use of computational fluid dynamics simulations reveals a substantial effect of the Reynolds number on the intensity of aerodynamic autorotation, which is later reflected in the aerodynamic model. Validation criteria for an extended envelope aerodynamic model are discussed, and the important role of professional test pilots with poststall flying experience in tuning aerodynamic model parameters is emphasized. The paper presents an approach to aerodynamic modeling that was implemented in the project titled "Simulation of Upset Recovery in Aviation" (2009-2012), funded by the European Union under the Seventh Framework Programme. The developed poststall aerodynamic model of a generic airliner configuration for a wide range of angles of attack, sideslip, and angular rate was successfully validated by a number of professional test pilots on hexapod- and centrifuge-based flight simulator platforms. [ABSTRACT FROM AUTHOR]

Achieving large-scale kinetic modeling is a crucial task for the development and optimization of modern plasma devices. With the trend of decreasing pressure in applications, such as plasma etching, kinetic simulations are necessary to self-consistently capture the particle dynamics. The standard, explicit, electrostatic, momentum-conserving particle-in-cell method suffers from restrictive stability constraints on spatial cell size and temporal time step, requiring resolution of the electron Debye length and electron plasma period, respectively. This results in a very high computational cost, making the technique prohibitive for large volume device modeling. We investigate the direct implicit algorithm and the explicit energy conserving algorithm as alternatives to the standard approach, both of which can reduce computational cost with a minimal (or controllable) impact on results. These algorithms are implemented into the well-tested EDIPIC-2D and LTP-PIC codes, and their performance is evaluated via 2D capacitively coupled plasma discharge simulations. The investigation reveals that both approaches enable the utilization of cell sizes larger than the Debye length, resulting in a reduced runtime, while incurring only minor inaccuracies in plasma parameters. The direct implicit method also allows for time steps larger than the electron plasma period; however, care must be taken to avoid numerical heating or cooling. It is demonstrated that by appropriately adjusting the ratio of cell size to time step, it is possible to mitigate this effect to an acceptable level. [ABSTRACT FROM AUTHOR]

Low-pressure capacitively-coupled discharges with additional dc bias applied to a separate electrode are utilized in plasma-assisted etching for semiconductor device manufacturing. Measurements of the electron velocity distribution function (EVDF) of the flux impinging on the wafer, as well as in the plasma bulk, show a thermal population and additional peaks within a broad range of energies. That range extends from the thermal level up to the value for the ‘ballistic’ peak, corresponding to the bias potential. The non-thermal electron flux has been correlated to alleviating the electron shading effect and providing etch-resistance properties to masking photoresist layers. ‘Middle-energy peak electrons’ at energies of several hundred eV may provide an additional sustaining mechanism for the discharge. These features in the electron velocity (or energy) distribution functions are possibly caused by secondary electrons emitted from the electrodes and interacting with two high-voltage sheaths: a stationary sheath at the dc electrode and an oscillating self-biased sheath at the powered electrode. Since at those energies the mean free path for large-angle scattering (momentum relaxation length) is comparable to, or exceeds the size of the discharge gap, these ‘ballistic’ electrons will not be fully scattered by the background gas as they traverse the inter-electrode space. We have performed test-particle simulations in which the features in the EVDF of electrons impacting the RF electrode are fully resolved at all energies. An analytical model has been developed to predict existence of peaked and step-like structures in the EVDF. Those features can be explained by analyzing the kinematics of electron trajectories in the discharge gap. Step-like structures in the EVDF near the powered electrode appear due to accumulation of electrons emitted from the dc electrode within a portion of the RF cycle, and their subsequent release. Trapping occurs when the RF sheath voltage exceeds the applied bias, and is decreasing. The secondary electrons originating from the dc-biased surface also form a peak near the energy equal to the bias potential. Additional peaks, at lower energies, are formed by the electrons emitted from the RF electrode and eventually escaping to it. The latter can be grouped according to the number of bounces between the sheaths during their residence time in the discharge. Each of such groups may give rise to an individual peak in the distribution. The trap-and-release theory developed in this paper provides a convincing explanation for the observations of the ballistic and ‘middle energy peak’ electrons detected in experiments. [ABSTRACT FROM AUTHOR]

Benchmarking and validation are prerequisites for using simulation codes as predictive tools. In this work, we have developed a Global Model for Negative Hydrogen Ion Source (GMNHIS) and performed benchmarking of the GMNHIS against another independently developed code, Global Enhanced Vibrational Kinetic Model (GEVKM). This is the first study to present a quite comprehensive benchmarking test of this kind for models of negative hydrogen ion sources (NHIS), and excellent agreements have been achieved for collisional energy loss per electron-ion pair created, electron number density, electron temperature, densities of H 3 + and H 2 + ions, and densities of H(n = 1–3) atoms. Very small discrepancies in number densities of H − ions and H + ions, as well as the vibrational distribution function of hydrogen molecules, can be attributed to the differences in the chemical reactions datasets. The GEVKM includes additional chemical reactions that are more important at high pressures. In addition, we validated the GMNHIS against experimental data obtained in an electron cyclotron resonance discharge used for H − production. The model qualitatively (and even quantitatively for certain conditions) reproduces the experimental H − number density. The H − number density as a function of pressure first increases at pressures below 1.6 Pa and then saturates for higher pressures. This dependence was analyzed by evaluating contributions from different reaction pathways to the creation and loss of the H − ions. The developed codes can be used for predicting the H − production, improving the performance of NHIS, and ultimately optimizing the parameters of negative ion beams for fusion reactors. [ABSTRACT FROM AUTHOR]

An independent control of the flux and energy of ions impacting on an object immersed in a plasma is often desirable for many industrial processes such as microelectronics manufacturing. We demonstrate that a simultaneous control of these quantities is possible by a suitable choice of a static magnetic field applied parallel to the plane electrodes in a standard single frequency capacitively coupled plasma device. Our particle-in-cell simulations show a 60% reduction in the sheath width (that improves control of ion energy) and a fourfold increase in the ion flux at the electrode as a consequence of the altered ion and electron dynamics due to the ambient magnetic field. A detailed analysis of the particle dynamics is presented, and the optimized operating parameters of the device are discussed. The present technique offers a simple and attractive alternative to conventional dual frequency based devices that often suffer from undesirable limitations arising from frequency coupling and electromagnetic effects. [ABSTRACT FROM AUTHOR]

An analytical approximation for differential cross-section of electron scattering on helium atoms is introduced. It is intended for Monte Carlo simulations, which, instead of angular distributions based on experimental data (or on first-principle calculations), usually rely on approximations that are accurate yet numerically efficient. The approximation is based on the screened-Coulomb differential cross-section with energy-dependent screening. For helium, a two-pole approximation of the screening parameter is found to be highly accurate over a wide range of energies. [ABSTRACT FROM AUTHOR]

The coupled development of aerodynamic asymmetry and hysteresis of the aerodynamic characteristics of an aircraft model with the straight wing (zero sweepback wing) of high aspect ratio λ = 10.6 is experimentally studied when the angle of attack varies from 0 to 20° and vice versa. The appearance of hysteresis is accompanied by the asymmetric flow separation from the wing panels. An increase in the Reynolds number Re from 0.24 × 106 to 0.32 × 106 leads to strengthening of the hysteresis effects. It is shown that the asymmetric deflection of ailerons by 40° and/or spoilers by –60° can lead to disappearance of asymmetry or change in its sign. [ABSTRACT FROM AUTHOR]

Recently, Patil et al. [Phys. Rev. Res. 4, 013059 (2022)] have reported the existence of an enhanced operating regime when a low-pressure (5 mTorr) capacitively coupled discharge (CCP) is driven by a very high radio frequency (60 MHz) source in the presence of a weak external magnetic field applied parallel to its electrodes. Their particle-in-cell simulations show that a significantly higher bulk plasma density and ion flux can be achieved at the electrode when the electron cyclotron frequency equals half of the applied radio frequency for a given fixed voltage. In the present work, we take a detailed look at this phenomenon and further delineate the effect of this "electron bounce-cyclotron resonance (EBCR)" on the electron and ion dynamics of the system. We find that the ionization collision rate and stochastic heating are maximum under resonance condition. The electron energy distribution function also indicates that the population of tail-end electrons is highest for the case where EBCR is maximum. Formation of electric field transients in the bulk plasma region is also seen at lower values of applied magnetic field. Finally, we demonstrate that the EBCR-induced effect is a low-pressure phenomenon and weakens as the neutral gas pressure increases. The potential utility of this effect to advance the operational performance of CCP devices for industrial purposes is discussed. [ABSTRACT FROM AUTHOR]

A new comparatively simple quasi-one-dimensional physicomathematical model of plasma acceleration in an ablative pulsed plasma thruster with a capacitive energy storage is proposed. In spite of its simplicity, the model adequately reflects the main physical processes occurring in the thruster channel in the course of plasma blob acceleration: the blob dynamics, plasma radiation, absorption of radiation by the Teflon channel walls, ablation of the wall material, and plasma ionization. The results of computer simulations agree well with the experimental results. [ABSTRACT FROM AUTHOR]

Domain-specific knowledge is often recorded by experts in the form of unstructured text. For example, in the medical domain, clinical notes from electronic health records contain a wealth of information. Similar practices are found in other domains. The challenge we discuss in this paper is how to identify and extract part names from technicians repair notes, a noisy unstructured text data source from General Motors' archives of solved vehicle repair problems, with the goal to develop a robust and dynamic reasoning system to be used as a repair adviser by service technicians. In the present work, we discuss two approaches to this problem. We present an algorithm for ontology-guided entity disambiguation that uses existing knowledge sources, such as domain-specific taxonomies and other structured data. We illustrate its use in the automotive domain, using GM parts ontology and the unit structure of repair manuals text to build context models, which are then used to disambiguate mentions of part-related entities in the text. We also describe extraction of part names with a small amount of annotated data using hidden Markov models (HMM) with shrinkage, achieving an f-score of approximately 80%. Next, we used linear-chain conditional random fields (CRF) in order to model observation dependencies present in the repair notes. Using CRF did not lead to improved performance, but a slight improvement over the HMM results was obtained by using a weighted combination of the HMM and CRF models. [ABSTRACT FROM AUTHOR]

This paper reviews and discusses recent experimental, theoretical, and numerical studies of plasma-wall interaction in a weakly collisional magnetized plasma bounded with channel walls made from different materials. A low-pressure E \times B plasma discharge of the Hall thruster was used to characterize the electron current across the magnetic field and its dependence on the applied voltage and the electron-induced secondary electron emission (SEE) from the channel wall. The presence of a depleted anisotropic electron energy distribution function with beams of secondary electrons was predicted to explain the enhancement of the electron cross-field current observed in experiments. Without the SEE, the electron cross-field transport can be reduced from anomalously high to nearly classical collisional level. The suppression of the SEE was achieved using an engineered carbon-velvet material for the channel walls. Both theoretically and experimentally, it is shown that the electron emission from the walls can limit the maximum achievable electric field in the magnetized plasma. With nonemitting walls, the maximum electric field in the thruster can approach a fundamental limit for a quasi-neutral plasma. [ABSTRACT FROM AUTHOR]

Combinatorial problems related to the enumeration of lambda terms in the untyped lambda calculus and in the Church-style simply typed lambda calculus with a single atom are considered. For the case of untyped lambda calculus, a system of equations for generating functions that enumerate lambda terms is derived. For the typed lambda calculus, the inhabited types are enumerated, as well as their primitive inhabitants. Bibliography: 11 titles. [ABSTRACT FROM AUTHOR]

This article, titled "Direct implicit and explicit energy-conserving particle-in-cell methods for modeling of capacitively coupled plasma devices," was published in the journal Physics of Plasmas on October 26, 2023. It contains a scatter plot (Fig. 16) that shows the relationship between averaged electron temperature and the ratio of time step to spatial step for different cases. However, there was an error in the figure when it was originally published online, but it has since been corrected in all online versions of the article as of October 30, 2023. The authors of the article are Haomin Sun, Soham Banerjee, Sarveshwar Sharma, Andrew Tasman Powis, Alexander V. Khrabrov, Dmytro Sydorenko, Jian Chen, and Igor D. Kaganovich. [Extracted from the article]

The dynamics of a modern aircraft at high angles of attack is complicated, with hazardous phenomena such as wing rock, stall, and spin. The paper presents a technique for cost-effective and safe studying of conventional and critical flight regimes and control validation using an autonomous scaled aircraft model mounted in a three-degree-of-freedom gimbal in a wind tunnel. The similarity of the dynamics at high angles of attack of the wind-tunnel model and the free-flying model is demonstrated. To suppress the wing rock and to prevent the stall, two control laws are designed using linear matrix inequalities and model reference adaptive control techniques. The controllers are tested in a semifree flight of the autonomous scaled model in the wind tunnel. Wing rock suppression and stall and spin prevention are demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: The compounds Lu2Fe17−x Mn x , in which , with the Th2Ni17-type crystal structure were synthesized. Their structural and magnetic properties are presented. The Lu2Fe17−x Mn x compounds with are ferromagnets at low temperatures and antiferromagnets at high temperatures. Their temperature of “ferromagnet–antiferromagnet” phase transition surprisingly increases very fast from 135 to 253 K with a growing content of Mn, whereas Néel temperature stays practically unchanged (∼278 K) and is close to Curie temperature for the compound with . The compounds from the range are ferromagnets only with a near constant value. [Copyright &y& Elsevier]

Abstract: Magnetic properties of the Ce2Fe17− x Mn x , x=0–2, alloys in magnetic fields up to 40T are reported. The compounds with x=0.5–1 are helical antiferromagnets and those with 1

Abstract: The magnetic properties have been studied for the series of RNi5− x Cu x intermetallics with R=Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu; x⩽2.5. Compositional dependences of magnetic susceptibility for the Pauli paramagnets (R=Y, La, Ce, Lu) and the Curie temperature for ferromagnets (R=Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm) have maximum at and 1, respectively. The substitution of Cu for Ni is accompanied by decreasing spontaneous magnetic moment and increasing coercive force of all ferromagnetic RNi5− x Cu x but GdNi5− x Cu x . These results are explained in the frame of band magnetism, random local crystal field, and domain wall pinning theories. [Copyright &y& Elsevier]

The magnetic properties of Tb1−xYxMn6Sn6 compounds (0≤x≤1) have been studied in high magnetic fields up to 40 T. The compounds for x≤0.6 are found to be ferrimagnets, while for x≥0.9 they are antiferromagnets. The Curie and spin-reorientation temperatures of the ferrimagnets gradually decrease with increasing x. First-order magnetization processes are observed for the compounds with x≤0.2. For the antiferromagnetic YMn6Sn6 and Tb0.1Y0.9Mn6Sn6 compounds, metamagnetic transitions are observed. Using susceptibility measurements we plotted the concentration magnetic phase diagram of the system. The effect of pressure on the magnetization curve of Tb0.1Y0.9Mn6Sn6 was studied at 4.2 K. The critical field of the metamagnetic transition decreases from 1.6 down to 1.0 T with increasing pressure up to 1.2 GPa. [Copyright &y& Elsevier]

Emission from surfaces is known to cause enhanced wall heating and enhanced energy loss from plasma electrons. When E × B fields are present, emitted electrons are heated by the drift motion and cause enhanced transport along E. All emission effects are normally predicted to reach a maximum when the sheath becomes space-charge limited because any ‘additional’ emitted electrons return to the wall. But the returning electrons are also heated in the E × B drift, further enhancing transport, and return to the wall with extra energy, further enhancing the energy flux. Returning electrons can gain enough energy to induce secondaries, thereby self-amplifying to higher intensities. This newly analyzed mechanism could affect the wall heating, transport and global energy balance under certain conditions. Theory and simulations are presented. [ABSTRACT FROM AUTHOR]