Particle Density Distribution Research Articles

Electron dynamics and metastable species generation in atmospheric pressure non-equilibrium plasmas controlled by dual LF–RF frequency discharges

In this work, we report an approach to control electron dynamics and metastable species generation and enhance the density of atmospheric pressure non-equilibrium plasmas by using dual-frequency excitation sources. The atmospheric dielectric barrier discharge (DBD) of an α-mode radio frequency (RF = 5 MHz) discharge controlled by a low-frequency (LF = 50 kHz) bias is studied based on a one-dimensional (1D) fluid model. Results show that the variation in amplitude ratio of RF and LF modulates the electron dynamic process, resulting in different spatial distributions of electron and metastable particle densities. Moreover, it is further shown that the electron density is substantially increased when the LF component voltage amplitude is larger than 300 V for the initial setting. The discharge process is characterized by fast Fourier transform of the spatio-temporal evolution of the electron power absorption and discharge current. As the LF is applied, three-wave interactions induced by LF and RF coupling are clearly observed, where the sum and beat frequencies between LF and RF are increased, which results in a substantial increase in the electron density. On the other hand, the high RF harmonics, especially for the fundamental and the third harmonic components, are suppressed when increasing the LF component. This work demonstrates that dual-frequency excitation is efficacious to modulate the electron dynamic behaviors and metastable species generation of atmospheric pressure plasma, which can provide a possible approach of optimizing plasma parameters.

Nonlinear transport in the presence of a local dissipation

We characterize the particle transport, particle loss, and nonequilibrium steady states in a dissipative one-dimensional lattice connected to reservoirs at both ends. The free-fermion reservoirs are fixed at different chemical potentials, giving rise to particle transport. The dissipation is due to a local particle loss acting on the center site. We compute the conserved current and loss current as functions of voltage in the nonlinear regime using a Keldysh description. The currents show step-like features which are affected differently by the local loss: The steps are either smoothened, nearly unaffected, or even enhanced, depending on the spatial symmetry of the single-particle eigenstate giving rise to the step. Additionally, we compute the particle density and momentum distributions in the chain. At a finite voltage, two Fermi momenta can occur, connected to different wavelengths of Friedel oscillations on either side of the lossy site. We find that the wavelengths are determined by the chemical potentials in the reservoirs rather than the average density in the lattice.

Monte Carlo analysis of focused Gaussian beam in scattering media: Curvature correction and Mie scattering

We introduce curvature correction into the Monte Carlo (MC) technique to determine the suitable photon-step size and initial photon distribution in the focusing lens aperture, that can account for the effects of the radius of curvature on the axial intensity profile of a focused Gaussian beam that is propagated through a scattering medium. The scattering anisotropy of the medium is determined via the Mie scattering theory for given values of the scattering particle radius, density, and phase distribution values while optical ray tracing is used to determine the occurrence of scattering events. We evaluate the performance of the modified MC technique for random and periodic media by examining the axial intensity profiles of the propagating focused beam. Relative to the predictions of the scalar diffraction theory, curvature correction improves the accuracy of the MC results with decreasing step size s and increasing number of steps Ns. In the absence of scattering, the axial beam distribution approaches that of the scalar diffraction theory for a given numerical aperture (NA≤0.5), s, and Ns based on the Linfoot’s image quality criteria of fidelity, correlation quality and structural content.

Epoxidized graphene grid for highly efficient high-resolution cryoEM structural analysis

Functionalization of graphene is one of the most important fundamental technologies in a wide variety of fields including industry and biochemistry. We have successfully achieved a novel oxidative modification of graphene using photoactivated ClO2· as a mild oxidant and confirmed the oxidized graphene grid is storable with its functionality for at least three months under N2 atmosphere. Subsequent chemical functionalization enabled us to develop an epoxidized graphene grid (EG-grid™), which effectively adsorbs protein particles for electron cryomicroscopy (cryoEM) image analysis. The EG-grid dramatically improved the particle density and orientation distribution. The density maps of GroEL and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) were reconstructed at 1.99 and 2.16 Å resolution from only 504 and 241 micrographs, respectively. A sample solution of 0.1 mg ml−1 was sufficient to reconstruct a 3.10 Å resolution map of SARS-CoV-2 spike protein from 1163 micrographs. The map resolutions of β-galactosidase and apoferritin easily reached 1.81 Å and 1.29 Å resolution, respectively, indicating its atomic-resolution imaging capability. Thus, the EG-grid will be an extremely powerful tool for highly efficient high-resolution cryoEM structural analysis of biological macromolecules.

Development of oxide dispersion strengthened ferritic steel with enhanced strength–ductility combination through dispersion strengthening and back stress hardening

Oxide dispersion strengthened (ODS) ferritic steel is a potential structural material for fast neutron reactor and fusion reactor application. In this study, a new Fe–13Cr–2W-0.4Ti-0.6Zr/0.35Y2O3 ODS ferritic steel was designed and fabricated through hot isostatic pressing. Results show that the ODS ferritic steel consists of highly dispersive nano-oxide particles, identified as Y2(Ti0.4Zr0.6)2O7 and Y4Zr3O12, with average particle size of 5.34 nm and particle distribution density of 4.2 × 1023 m−3. In addition, heterogeneous coarse/ultrafine grains (CGs/UFGs) structure is also achieved in the matrix. The Fe–13Cr–2W-0.4Ti-0.6Zr/0.35Y2O3 ODS ferritic steel exhibits superior mechanical properties at both room temperature (σb = 1208 MPa, δ = 14%) and high temperature (σb, 700°C = 382 MPa, δ700°C = 32%). The high strength is mainly due to the synergistic effect of particle dispersion strengthening and back stress strengthening, while the good ductility can be attributed to the excellent deformation ability of the coarse grains and the back stress hardening effect induced by the heterogeneous CGs/UFGs structure.

Two-dimensional fluid simulation of spatial distribution of dust particles in a capacitively coupled silane plasma

In this work, we develop a two-dimensional fluid model to study the spatial density distributions of dust particles in a radio frequency capacitively coupled silane plasma. Unlike those scenarios based on the one-dimensional fluid model, in this work, the nonuniformity of the radial density distributions of dust particles is attributed mainly to the radial components of the electric field force and the ion drag force acting on the dust particles, leading to the two local density peaks near the electrode edges. It seems that dust particles tend to overcome the support of the electric field force and move much closer to the electrodes, as one of the density peaks indicates. Moreover, with the decrease of the radii of the discharge electrodes or the distance between them, the radial component of the ion drag force is enhanced, resulting in more dust particles gathering near the electrode edge region, and forming a ring-shaped particle density distribution. In the case of the discharge electrodes wrapped with dielectric materials, the uniformity of the radial density distributions of dust particles between the two electrodes is improved. Finally, the vortex motion of a single dust particle near the electrode edge region is also simulated in this work.

О некоторых задачах программного управления пучком траекторий. Часть I

This paper deals with problems of program control of a trajectory beam. We investigate formulations that arise when considering problems of charged particle beams control, as well as, for example, in image processing. In applied problems, it is often necessary to investigate the problem of the gravity center control of some set or changing the density distribution of particles according to some given one. The functionals proposed in the paper can be effectively used for the velocity field constructing in various image processing, in particular, medical diagnostic images. In this paper, the problem of constructing a velocity field is considered as a control and optimization problem, and, unlike the previous works of the authors, macroparameters characterizing the objects under study are used in optimization. In the article, variations of the studied functionals are obtained and the necessary optimality conditions are given.

Electron gases in toroidal shells: Mode coupling and state functions

Eigenvalues and wave functions describing free electron gases in toroidal shells are determined using a basis set expansion natural to the system geometry. Couplings between azimuthal and poloidal modes are found to be appreciable at lower values of ${m_\phi}$, modifying single particle density distributions within the shells. Thermodynamic state functions are calculated and contrasted with those of a solid toroidal volume.

Study of Physical and Mineral Properties of Soil Clay Landslide Location of IAIN Campus Ambon City

This study aims to determine physical and clay mineral properties of soils and how they affect the occurrence of erosion in the IAIN Campus Ambon. The results indicated that the two soil profiles shows a variety in soil properties. the largest distribution of soil particle density is 2.63 at soil layer P2L3 and the smallest is 2.26 at P1L1, the largest soil pore distribution is 60.12% at P2L1 and the smallest is 29.36% at P1L3, while the largest soil pores ratio distribution is 1.51% at P2L1 and the smallest is 0.42% at soil layer P1L3. The soil porosity reflects the level of the soil ability to pass water flow (permeability) or the speed of water flow to pass through the soil mass (percolation). By the decreasing of soil porosity and pore ratio in layers 3 and 4, the permeability is also slower. The major clay mineral found in both soil profiles is kaolinite, an unwell consolidated secondary clay mineral type 1:1 mixed with quartz, the most weathering resistant primary minerals. These two minerals have lower friction resistance due to the increasing of clay content in the lower soil profiles. The physical and hydrological soil properties as well as the presence of kaolinite and quartz in the lower soil layers are considered to be the cause of the erosion occurrence in the study area (IAIN campus).

Controlling the structure of a glow discharge by supersonic gas flow

The effect of supersonic gas flow on glow discharge characteristics in interelectrode space is studied. First, gas outflow through a Laval nozzle with a central body was simulated: gas particle density distributions, gas flow velocity, Mach number, and temperature were obtained. Next, these profiles were used for numerical calculations of the parameters of a transverse glow discharge within the framework of an extended fluid description of the plasma. As a result, it was found that the cathode zones can both shrink and stretch depending on the parameters of the supersonic gas flow. The latter creates an inhomogeneous gas density in the interelectrode region and thereby affects the value of E/N, which determines the electrical characteristics of the discharge. Numerical simulation results are confirmed by experimental data.

Numerical study of microscopic particle arrangement of suspension flow in a narrow channel for the estimation of macroscopic rheological properties

In a narrow channel, the apparent relative viscosity of a suspension with finite-size particles is strongly dependent on its microscopic particle arrangement. Relative viscosity increases when suspended particles flow near the channel wall; thus, a suspension in a narrow channel does not always exhibit the same rheological properties even if the concentration is the same. In this study, we focus on the inertia and concentration of particles in a narrow channel and consider their effects on the microscopic particle arrangement and macroscopic suspension rheology. Two-dimensional pressure-driven suspension flow simulations were performed using a two-way coupling scheme, and normalized particle density distribution (PDD) were implemented to consider their particle arrangements. The results demonstrated that the velocity profiles for the particle suspension were changed by the Reynolds number and particle concentration because of the interactions between particles according to the power-law index. These changes affected the particle equilibrium positions in the channel, and the subsequent changes in solvent layer thickness caused changes in the macroscopic apparent viscosity. The behavior of microscopic particles played important roles in determining macroscopic rheology. Thus, we have confirmed that a normalized PDD can be used to estimate and assess the macroscopic rheology of a suspension.

Analysis of factors influencing infrared extinction area of explosive smokescreen

ObjectivesComparative studies of different smokescreen designs are essential to determine differences in extinction performance. This study aims to investigate the extinction performance of explosive smokescreen under different conditions, and to provide an evaluation method for the optimal design of its charge structure. MethodsThe process of formation of the smokescreen with a cylindrical charge structure is described based on the smoothed particle hydrodynamics method. The blast radius and particle density distribution of the smokescreen were calculated for different charge structures and charge ratios through simulations. Lambert–Beer's law was combined to obtain the infrared extinction area. An analysis was then conducted to determine the influence of the number of baffles in the charge structure and charge ratio on the extinction performance of the smokescreen. Field tests were conducted to verify the simulation results. ResultsIncreasing the number of baffles in the projectile structure made the particle distribution of the smokescreen more uniform and resulted in a larger infrared extinction area. An increase in the explosive quantity, made the smokescreen more dispersed. However, too much of the explosives caused the smokescreen to be sparse, reducing the infrared extinction area.

Study on microstructure and abrasive behaviors of inconel 718-WC composite coating fabricated by laser directed energy deposition

Additive manufacturing enables the development of high-performance materials by in-situ alloying of multiple components. In this study, Inconel 718-based composite, reinforced with tungsten carbide (WC), was synthesized on a 316L stainless steel substrate using laser directed energy deposition (DED). The microstructural evolution, distribution density of WC particles, and strengthening mechanisms of the DED-processed metal matrix composite (MMC) with different WC particle sizes and ratios are systematically investigated. It illustrated that increasing laser power enables the microstructure transforming from equiaxed to dendritic, which is attributed to the different cooling rates and temperature gradients. In addition, the morphology of the 60% WC ratio of the particle composite shows macrocracks. The incorporation of different sized WC affects retained WC distribution density and tailors a gradient layer around the edge of the WC particle. The in-situ WC-W2C phases precipitated in the deposited layer and the evenly distributed high level of ex-situ retained WC particles induce solid solution strengthening and dispersion strengthening, respectively. As a result, the optimal size of the 90 μm WC/Inconel 718 shows the highest wear resistance. The underlying strengthening mechanisms are elucidated. Consequently, the wear mechanism of Inconel 718-based composite reveals the typical abrasive wear characteristics in the presence of WC particles.

Boron Nitride Thin Films with Anisotropic Optical Properties from Microscale Particle Density Distributions

Unusual optical anisotropy was experimentally observed in hexagonal boron nitride thin films produced from bulk boron nitride via ultrasonication. Both the linear and circular polarisation demonstrated a well-defined single axis of anisotropy over a large sample area. To understand this phenomenon, we employed statistical analysis of optical microscopy images and atomic force microscopy to reveal an ordered particle density distribution at the microscopic level corresponding to the optical axis observed in the polarisation data. The direction of the observed ordering matched the axis of anisotropy. Hence, we attribute the measured optical anisotropy of the thin films to microscopic variations in the particle density distribution.

High-energy-density ferroelectric polymer nanocomposites utilizing the Coulomb-blockade effect

Ferroelectric polymers have been regarded as promising dielectric materials for high volumetric energy density dielectric capacitors due to their high dielectric constant and facile processability. However, ferroelectric dielectric polymers suffer from high intrinsic loss, resulting in low charge-discharge efficiency and insufficient breakdown strength. Here, a sandwich-structured ferroelectric polymer nanocomposite with high energy density is fabricated by sandwiching an array of ultra-small metal particles grown in-situ between two layers of ferroelectric polymers. Due to the unique Coulomb-blockade effect of the ultra-small metal particles, the nanocomposites with suitable distribution density of metal particles exhibit significantly suppressed leakage current density and superior breakdown strength. Compared with Au and Ag, the Pt particle with the highest work function is more effective in improving the capacitive performance of the polymer. In addition, it is revealed that within the theoretical particle size range where the Coulomb-blockade takes effect, the nanocomposite with larger metal particles exhibits better capacitive performance. The optimal composition with an extremely low fraction (0.07 vol%) of 10-nm-size Pt nanoparticles shows a remarkable discharge energy density of 28.6 J/cm3 and a charge-discharge efficiency of 76%. This method effectively suppresses the energy loss of ferroelectric polymers, and bypasses the dispersion issues in the traditional polymer nanocomposites, providing a new paradigm for fabricating high-energy-density and high-efficiency polymer dielectrics.

Settling of Iron and Aluminum Particles in Acid Solutions for Acid Drainage Remediation

Mineral processing is intensive in water usage. Unfortunately, a large portion of this valuable asset is contaminated by toxic species that leach from tailings or mineral ore, leading to the formation of acid drainage. Water from acid drainages can still be recovered by passive environmentally friendly treatments. An underestimated passive treatment is the settling of harmful metals, such as iron and aluminum. In this sense, floc settling from acid drainage has not been well studied. The objective of this work is to research the phenomena governing iron and aluminum floc settling in acid drainage, particularly, the chemical conditions that promote settling. The settling velocity of iron and aluminum flocs was studied in a column at different pH and iron/aluminum concentrations. Stability was studied through zeta potential. According to the results, iron flocs settle faster than aluminum and aluminum+iron (mixed) flocs, and a lower pH promotes a higher settling velocity and greater floc stability, which a lower zeta potential (which favors aggregation) allows for. The results improve the understanding of the interactions between the chemical and physical processes involved in floc settling, which, in turn, can improve the optimization of water treatment design. Future experiments must include particle size distribution, floc porosity, and effective particle density of iron and/or aluminum particles in acid waters.

Soot Size Determination In A Swirl Stratified Premixed Ethylene-Air Flame By A Sampling Probe And Elastic Light Scattering

An experimental study was performed to measure the size and number density distributions of soot particles produced in turbulent, stratified (high spatial equivalence ratio gradient), swirled (rotating flow) premixed ethylene-air flames at atmospheric pressure. Soot particle size and number density measurements are initially performed using a Scanning Mobility Particle Sizer (SMPS). For this purpose, two-stage sampling and dilution device designed for hot gas analysis was used. The dilution rate of the sampling apparatus was evaluated to ensure a most representative probing. In a second step, the ex-situ measurements were replaced by single-shot measurements recorded with a high cadency planar multi-angle light scattering (2D-MALS) laser diagnostic technique, based on the relationship between aggregate size and light scattering angle. In a third step, results obtained by the SMPS as well as by the optical diagnostic were compared. Because a direct confrontation of the obtained results obtained is not feasible due to difference in nature of both techniques, a two-step post-processing methodology as developed. For this purpose, the median electric mobility diameters measured by SMPS were converted into diameters of gyration by means of a semi-empirical conversion tool. Moreover, a time average data processing was applied to the soot size distributions recorded by 2D-MALS, considering that SMPS measurements performed over a relatively large acquisition time converge to a single value. Results obtained in stratified swirled premixed flames by SMPS exhibit an overall good agreement with the optical measurements. This good similarity between the results provides a remarkably high degree of confidence in the quality of the measurements for both measurement systems investigated. Furthermore, the results suggest that a comparison of soot aggregate size and number density measurements between a sampling probe and a light scattering technique is still possible in turbulent flames at atmospheric pressure. While the current work has focused on the performances of SMPS and the 2D-MALS approach on a one-to-one basis, future work will also address the application of these diagnostics to high-pressure two-phase flames for which measurements are made in confined environments.

Characterization of an aerosolized nanoparticle beam beyond the diffraction limit through strong field ionization

The study of nanomaterials is an active area of research for technological applications as well as fundamental science. A common method for studying properties of isolated nanoparticles is by an in-vacuum particle beam produced via an aerodynamic lens. Despite being common practice, characterization of such beams has proven difficult as light scattering detection techniques fail for particles with sizes beyond the diffraction limit. Here we present a new technique for characterizing such nanoparticle beams using strong field ionization. By focusing an ultrafast, mJ-level laser into the particle beam, a nanoparticle within the laser focus is ionized and easily detected by its ejected electrons. This method grants direct access to the nanoparticle density at the location of the focus, and by scanning the focus through the transverse and longitudinal profiles of the particle beam we attain the 3-dimensional particle density distribution for a cylindrically symmetric beam. Further, we show that strong field ionization is effective in detecting spherical nanoparticles as small as 10 nm in diameter. Additionally, this technique is an effective tool in optimizing the particle beam for specific applications. As an example we show that the particle beam density and width can be manipulated by restricting the gas flow into the aerodynamic lens.

Production of strange hadrons in jets and underlying events in pp and p–Pb collisions with ALICE

The production of strange (, Λ) and multi-strange (Ξ± and Ω±) hadrons in jets and underlying events in pp and p–Pb collisions is studied with ALICE at the LHC. Transverse momentum (p T) differential density distribution of particles produced in a jet is compared to that of inclusive particle production and that in underlying events. The particle yield ratios of and as a function of p T are also investigated in jets and underlying events. The production of the multi-strange hadrons, Ξ± and Ω±, and the corresponding ratio in jets and underlying events are measured for the first time. The p T-differential density distribution of hadrons associated with hard scattering decreases slower than that for inclusive production. The baryon-to-meson and baryon-to-baryon ratios measured in jets exhibit clear differences from values obtained from the inclusive spectra in the intermediate p T range. The p T distribution of strange hadrons produced in jets is also studied in pp collisions at and and in p–Pb collisions at . The p T spectra of particle produced in jets are independent of collision systems and collision energies. No apparent collision energy and collision system dependence is observed for the particle yield ratios of and associated with energetic jets. These new results are compared to PYTHIA 8 event generator. The ratio are generally reproduced by the model, but large discrepancies between data and PYTHIA simulations are observed for .

Investigation of sheath properties in a warm plasma with two kappa-distributed electrons and monoenergetic electron beam

Sheath formation criterion of an electropositive plasma consisting of singly charged positive ions, two kappa-distributed electron species with different effective temperatures and a monoenergetic electron beam is investigated by the Sagdeev potential approach. Using this criterion, effects of electron beam, superthermality of electron species as well as temperature and concentration of positive ions on the sheath properties are studied numerically. It is shown that the temperature of positive ions, concentration and superthermality of electron species and presence of electron beam affect Bohm velocity of positive ions. Also, it is observed that density distribution of the charged particles and sheath thickness increase in the presence of electron beam. In addition, it is found that with increasing the ion temperature, the sheath width and density distribution of the charged particles in the sheath area decrease.