Number Density Distribution Research Articles

Numerical Analysis of Ar and Ar-H2 Atmospheric Plasma Spray With a Simplified Model

To study the difference of plasma spraying process between argon and argon-hydrogen working gas, a relative simplified fan-shaped numerical model of argon/argon-hydrogen atmospheric plasma spray process was set up to analyze the multi-physic field in the spraying gun. The model took electrodes especially cathode and anode boundary layers into consideration. In other words, a two-temperature plasma model was employed. With regard of both ionization and recombination of ions and electrons, their number density distributions, which are important to determine whether the injected particles are charged, were studied. The influence of secondary gas on plasma flow was investigated. According to the results, when adding hydrogen into the pure argon plasma, the temperature and velocity of the gas flow in spray gun chamber increased. The calculated results will provide theoretical guidance for the design and optimization of gun structure.

Estimating the number density and energy distribution of electrons in a cold atmospheric plasma using optical emission spectroscopy

Cold atmospheric plasmas are generous sources of chemically active species, the reaction rates which can be predicted only if the electron number density and the electron energy distribution function are known. Here, the authors present a procedure for estimating both these parameters from the optical emission spectrum of an argon plasma. The peaks in the spectrum were curve fitted with Voigt profiles, and their widths and areas were mapped to the number density and energy distribution of electrons in the plasma, using the mathematical models for Stark broadening and Corona population, respectively. These plasma parameters were optimized to establish a good match between the simulated and the experimental peak attributes. This analysis estimated the value of the electron number density to be approximately 1.5 × 1015 cm−3 and the mean electron temperature to be approximately 0.37 eV in their plasma. It also predicted that the energy distribution of electrons can be closely approximated using a Maxwellian distribution.

A Multi-Moment Sectional Method (MMSM) for tracking the soot Number Density Function

A new Multi-Moment Sectional Method (MMSM) is proposed for tracking the evolution of the soot Number Density Function (NDF). Unlike conventional sectional methods, in MMSM, multiple statistical moments are solved within each section, and the size distribution within each section is reconstructed from a polynomial profile or, for the last section, an exponential profile. MMSM can be reduced to a method of moments with a single section to minimize the computational cost and reduced to a sectional method when the number of moments per section is one. The MMSM approach is combined with a detailed univariate soot model and applied to the computation of the soot NDF in an ethylene laminar premixed flame. Compared to a pure sectional method, MMSM is shown to achieve a higher rate of convergence for the predicted total number density and particle size distribution.

Acoustic standing wave modulation of capacitively coupled plasmas

This work presents a concept of using acoustic standing waves to modulate plasmas. A 1D self-consistent fluid model combined with an acoustic standing wave model has been established to investigate the strong coupling effects between acoustic standing waves and capacitively coupled argon plasmas. The modulation effects are revealed by comparing the spatiotemporal distributions of electron density and excited species number density with and without the acoustic standing waves in one acoustic period, as well as the electric field, the electron temperature, the ionization and excitation rates, and the power density in one radio-frequency period. Under the nonlinear acoustic standing waves, the plasmas oscillate in between the electrodes, which indicates a strong modulation effect beyond conventional regimes. This modulation effect is primarily attributed to the neutral flux friction to the plasma species and secondarily to the variation of the neutral gas density. A pulsed excited species flux with a maximum value up to twice of the minimum can be achieved at the electrodes as a result of the acoustic standing wave modulation. The distributions of the ionization and excitation rates in one RF period are significantly influenced by the acoustic standing waves, due to the variation of the neutral gas density and electron temperature. This study initiates the effort to understand the mechanisms and characteristics of plasma discharges in a high-intensity acoustic standing wave field. Using acoustic waves to modulate plasmas has the potential to create many new applications and promote plasma-materials interactions.

Towards direct measurement of electrons in metastable states in K-feldspar: Do infrared-photoluminescence and radioluminescence probe the same trap?

Prasad et al. (2017) recently developed a new method of measuring the dosimetric signal in feldspar, based on a Stokes-shifted photoluminescence emission (excitation energy ∼1.40eV (885 nm), emission energy∼1.30eV (955 nm)). The new signal, termed as infrared photoluminescence (IRPL), was shown to arise from radiative relaxation of the excited state of the principle trap (dosimetric trap), and allows non-destructive probing of the dosimetric information. Thus, IRPL provides a unique tool to study physical characteristics of these metastable states in feldspar, e.g., number density and spatial distribution, trap depth, photo-ionisation and capture cross-section, excited state lifetime, and tunneling probabilities. The IRPL emission is apparently related to the infrared radioluminescence (IR-RL) in K-feldspar (Trautmann et al., 1998); in the latter, however, the electrons relax after being trapped as a result of exposure to ionising radiation, rather than as a result of excitation within the trap.In this study, we report the discovery of a second IRPL emission centred at ∼1.41eV (880 nm) in a K-feldspar which arises in response to excitation with 1.49eV photons. Based on the temperature- and dose-dependent behaviour of IRPL and IR-RL, we conclude that the same defect(s) participates in these two emissions. However, IRPL emission is governed by the characteristics of the principle trap (defect) alone, whereas IR-RL depends additionally on thermally assisted transport within the band-tail states. Since IRPL is a site selective technique, it does not, unlike IR-RL, suffer from contamination from higher energy emissions (e.g. from Fe3+). This lack of contamination, and the possibility for thermal/optical pre-treatments and repeated measurements of the same trapped electrons, suggest that IRPL is a robust alternative to IR-RL.

Design concepts of small CANDLE reactor with melt-refining process

The innovative CANDLE (Constant Axial shape of Neutron flux, nuclide densities and power shape During Life of Energy production) burnup strategy has several advantages over conventional fast reactor designs: namely, the reactor characteristics do not change with burnup, it is possible to withdraw the burnup reactivity control mechanism, there is no need for orifice control along with burnup, and it is easy to extend reactor life by increasing the core height and using natural uranium as fresh fuel. Maintaining the fuel cladding integrity of a CANDLE reactor during operation is one of the key technological challenges that still need to be addressed. The introduction of the melt-refining process has shown great potential for solving this challenge in the high-burnup condition of large CANDLE reactors. The purpose of the present study was to design a small CANDLE reactor with the melt-refining process. With metallic fuel of natural uranium (90 wt% U, 10 wt% Zr), ODS cladding material, and lead-bismuth eutectic (44.5 wt% Pb, 55.5 wt% Bi) coolant, a 300-MWt reference core of 1.3-m radius and 2.2-m length can realize CANDLE burning. The results of our analysis demonstrate that it is possible to design a small CANDLE reactor with the melt-refining process. The analysis focused on the impacts of core homogenization, melt-refining, and the cooling and waiting times of the fuel. From the equilibrium analysis, the burning region velocity, neutron flux distribution, power density distribution, and core nuclide number density distribution were obtained. Applying the melt-refining process reduced the burning region velocity from 0.70 cm/year to 0.59 cm/year. Meanwhile, the minimum effective neutron multiplication factor and core averaged discharged fuel burnup were increased from 1.0047 to 1.0235, and from 435.2 GWd/t to 523.7 GWd/t, respectively.

A Globular Cluster Luminosity Function Distance to NGC 4993 Hosting a Binary Neutron Star Merger GW170817/GRB 170817A

Abstract NGC 4993 hosts a binary neutron star merger, GW170817/GRB 170817A, emitting gravitational waves and electromagnetic waves. The distance to this galaxy is not well established. We select the globular cluster candidates from the Hubble Space Telescope (HST)/ACS F606W images of NGC 4993 in the archive, using the structural parameters of the detected sources. The radial number density distribution of these candidates shows a significant central concentration around the galaxy center at the galactocentric distance r < 50″, showing that they are mostly the members of NGC 4993. Also, the luminosity function of these candidates is fit well by a Gaussian function. Therefore, the selected candidates at r < 50″ are mostly considered to be globular clusters in NGC 4993. We derive an extinction-corrected turnover Vega magnitude in the luminosity function of the globular clusters at 20″ < r < 50″, F606W (max)0 = 25.36 ± 0.08 (V 0 = 25.52 ± 0.11) mag. Adopting the calibration of the turnover magnitudes of the globular clusters, M V (max) = −7.58 ± 0.11, we derive a distance to NGC 4993, d = 41.65 ± 3.00 Mpc ( ). The systematic error of this method can be as large as ±0.3 mag. This value is consistent with the previous distance estimates based on the fundamental plane relation and the gravitational wave method in the literature. The distance in this study can be used to constrain the values of the parameters including the inclination angle of the binary system in the models of gravitational wave analysis.

Thermohydrodynamic Analysis of High-Speed Water-Lubricated Spiral Groove Thrust Bearing Using Cavitating Flow Model

A thermohydrodynamic lubrication model of turbulent cavitating flow for high-speed spiral groove thrust bearing was developed considering the effects of cavitation, turbulence, inertia, breakage, and coalescence of bubbles. Comparing with the classical thermohydrodynamic model, this model can predict not only the distributions of pressure and temperature rise but also the distribution of bubble volume and bubble number density. Static characteristics of the water-lubricated spiral groove thrust bearing in the state of turbulent cavitating flow were analyzed, and the influences of multiple effects on the static characteristics of the bearing were researched. The numerical calculation result shows that the bubbles are mainly distributed in inlet and outlet of the spiral groove, the distribution of bubble volume is skewed under the equilibrium state, and small bubbles account for a large proportion of the cavitating flow under high-speed condition. Furthermore, the load carrying capacity and the leakage flow of the bearing decrease due to the effect of cavitation under high-speed. The maximum temperature rise of the bearing decreases due to the effect of cavitation effect.

Toward the accurate prediction of soot in engine applications

Soot emissions from internal combustion engines represent a major challenge to engine manufactures with ever most stringent emission regulations, not only in soot mass yielded but also in soot particle number. For example, a particulate number standard has been introduced in 2011 with Euro 5b for diesel engines and in 2014 with Euro 6 for petrol engines (a limit of 6 × 1011/km). Soot models provide a detailed insight into soot evolution processes and are thus an essential tool in today’s advanced engine designs. Therefore, continuous efforts are made to develop more physically based engine soot models and improve the prediction accuracy. The primary objective of this work is to identify and demonstrate the critical parameters for accurate soot predictions in internal combustion engine applications using the high-fidelity detailed soot model from an engineering point of view. A detailed soot model based on sectional method was used to solve the soot process in diesel and spark ignition direct injection gasoline engines. A series of sensitivity analyses were carried out to evaluate the importance and significance of wall boundary conditions, wall film formation and vaporization, multi-component fuel surrogate, and soot transport process in engine exhaust on soot predictions. The predicted results were compared in details to engine-out measurements in terms of soot mass, number density, and size distributions under various operating conditions. The model results demonstrate that the correct description of the spray–wall interaction and wall film vaporization, as well as the soot transport processes in full engine cycle, is critical for achieving reliable predictive capabilities in engine simulations, especially for spark ignition direct injection gasoline engines. The findings should help engineers in this field for more accurate soot predictions in engine simulations.

Spatial Distribution of Io's Neutral Oxygen Cloud Observed by Hisaki

AbstractWe report on the spatial distribution of a neutral oxygen cloud surrounding Jupiter's moon Io and along Io's orbit observed by the Hisaki satellite. Atomic oxygen and sulfur in Io's atmosphere escape from the exosphere mainly through atmospheric sputtering. Some of the neutral atoms escape from Io's gravitational sphere and form neutral clouds around Jupiter. The extreme ultraviolet spectrograph called EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics) installed on the Japan Aerospace Exploration Agency's Hisaki satellite observed the Io plasma torus continuously in 2014–2015, and we derived the spatial distribution of atomic oxygen emissions at 130.4 nm. The results show that Io's oxygen cloud is composed of two regions, namely, a dense region near Io and a diffuse region with a longitudinally homogeneous distribution along Io's orbit. The dense region mainly extends on the leading side of Io and inside of Io's orbit. The emissions spread out to 7.6 Jupiter radii (RJ). Based on Hisaki observations, we estimated the radial distribution of the atomic oxygen number density and oxygen ion source rate. The peak atomic oxygen number density is 80 cm−3, which is spread 1.2 RJ in the north‐south direction. We found more oxygen atoms inside Io's orbit than a previous study. We estimated the total oxygen ion source rate to be 410 kg/s, which is consistent with the value derived from a previous study that used a physical chemistry model based on Hisaki observations of ultraviolet emission ions in the Io plasma torus.

Stratification of Colloidal Particles on a Surface: Study by a Colloidal Probe Atomic Force Microscopy Combined with a Transform Theory.

Colloidal probe atomic force microscopy (CP-AFM) can be used for measuring force curves between the colloidal probe and the substrate in a colloidal suspension. In the experiment, an oscillatory force curve reflecting the layer structure of the colloidal particles on the substrate is usually obtained. However, the force curve is not equivalent to the interfacial structure of the colloidal particles. In this paper, the force curve is transformed into the number density distribution of the colloidal particles as a function of the distance from the substrate surface using our newly developed transform theory. It is found by the transform theory that the interfacial stratification is enhanced by an increase in an absolute value of the surface potential of the colloidal particle, despite a simultaneous increase in a repulsive electrostatic interaction between the substrate and the colloidal particle. To elucidate the mechanism of the stratification, an integral equation theory is employed. It is found that crowding of the colloidal particles in the bulk due to the increase in the absolute value of the surface potential of the colloidal particle leads to pushing out some colloidal particles to the wall. The combined method of CP-AFM and the transform theory (the experimental-theoretical study of the interfacial stratification) is related to colloidal crystallization, glass transition, and aggregation on a surface. Thus, the combined method is important for developments of colloidal nanotechnologies.

Binary black hole mergers within the LIGO horizon: statistical properties and prospects for detecting electromagnetic counterparts

Binary black holes (BBHs) are one of the endpoints of isolated binary evolution, and their mergers a leading channel for gravitational wave events. Here, using the evolutionary code \textsc{StarTrack}, we study the statistical properties of the BBH population from isolated binary evolution for a range of progenitor star metallicities and BH natal kicks. We compute the mass function and the distribution of the primary BH spin $a$ as a result of mass accretion during the binary evolution, and find that this is not an efficient process to spin up BHs, producing an increase by at most $a\sim$~0.2--0.3 for very low natal BH spins. We further compute the distribution of merger sites within the host galaxy, after tracking the motion of the binaries in the potentials of a massive spiral, a massive elliptical, and a dwarf galaxy. We find that a fraction of 70-90\% of mergers in massive galaxies and of 40-60\% in dwarfs (range mostly sensitive to the natal kicks) is expected to occur inside of their hosts. The number density distribution at the merger sites further allows us to estimate the broadband luminosity distribution that BBH mergers would produce, \textit{if} associated with a kinetic energy release in an outflow, {which, as a reference, we assume at the level inferred for the \textit{Fermi} GBM counterpart to GW150914, with the understanding that current limits from the O1 and O2 runs would require such emission to be produced within a jet of angular size within $\lesssim 50^\circ$.}

Numerical calculation of the reflection, absorption and transmission of a nonuniform plasma slab based on FDTD

In this paper, reflection, absorption and transmission characteristics of nonuniform plasma layer with varying electron number density are analyzed. The plasma number density profile is parabolic. Finite-difference time-domain (FDTD) and subslabs approximation methods are utilized and the results are validated. In FDTD, we use auxiliary differential equation (ADE) to simulate the plasma dispersive characteristics. In subslabs method, the plasma layer is divided into several thin subslabs with constant electron number density in each subslab. Partial reflection coefficients at each subslab boundary with different electromagnetic parameters are calculated. The total reflected and transmitted coefficients are then deduced using transmission line method. The reflected, transmitted and absorption power ratio with respect to the incident power is acquired. Their functional dependence on the number density, collision frequency and the distribution of number density, collision frequency is studied.

Effect of the Tundish Gunning Materials on the Steel Cleanliness

AbstractTo clarify the interaction mechanism between distinct tundish gunning materials (GM) and liquid steel, two kinds of gunning materials, namely MgO, Al2O3 GM, were tested. SEM, EDS, XRD and chemical analysis were carried out for steel and GM to investigate the change of chemical composition of steel in contact with GM and the interface microstructure between steel and GM after high temperature holding experiments. The steel cleanliness in terms of inclusion number density, size and size distribution was evaluated. It was found that the reducible component, low-melting-point phases and the pores in GM were passageway for steel penetration. The Al2O3 GM was less prone to steel penetration due to its poor wetting and the dense transition layer. MgO GM provided more oxygen and showed a stronger oxidizing capacity due to its higher content of reducible oxides (10.5 wt.% SiO2+2 wt.% Fe2O3). The use of Al2O3 GM resulted in an improved steel cleanliness and consequently could be a promising refractory in the tundish lining.

Number Density Distribution of Bubbles Forming Near a Wall in a Beverage

To clarify the spatial structure of number density distribution of bubbles in stout beer poured into a container, we investigated local time development of the void fraction and velocity of bubbles. The propagation velocity of the texture, i.e. the number density distribution, appearing near the inclined wall of the container is measured by the images analysis. We measured the local void fraction using brightness of images while the velocity of bubbles by means of Particle Tracking Velocimetry. As the result of measurements, we found the local void fraction and the bubbles advection velocity increase and decrease repeatedly with a time delay. We conclude the pattern of the number density distribution of bubbles is composed of fluid blobs which contain less bubbles; extruding and suction flows respectively toward and from the interior of the container form respectively in front and back of the blobs.

Effect of settling particles on the stability of a particle-laden flow in a vertical plane channel

The stability of a viscous particle-laden flow in a vertical plane channel in the presence of the gravity force is studied. The flow is described using a two-fluid “dusty-gas” model with negligibly small volume fraction of fines and two-way coupling of the phases. Two different profiles of the particle number density in the main flow are considered: homogeneous and non-homogeneous in the form of two layers symmetric about the channel axis. The novel element of the linear-stability problem formulation is a particle velocity slip in the main flow caused by the gravity-induced settling of the dispersed phase. The eigenvalue problem for a linearized system of governing equations is solved using the orthonormalization and QZ algorithms. For a uniform particle number density distribution, it is found that there exists a domain in the plane of Froude and Stokes numbers, in which the two-phase flow in a vertical channel is stable for an arbitrary Reynolds number. This stability domain corresponds to relatively sm...

Jovian Auroral Ion Precipitation: Field‐Aligned Currents and Ultraviolet Emissions

AbstractA model is described for the transport of magnetospheric oxygen ions with low charge state and energies up to several MeV/nucleon (MeV/u) as they precipitate into Jupiter's polar atmosphere. A revised and updated hybrid Monte Carlo model originally developed by Ozak et al. (2010, https://doi.org/10.1029/2010JA015635) is used to model the Jovian X‐ray aurora. The current model uses a wide range of incident oxygen ion energies (10 keV/u to 5 MeV/u) and the most up‐to‐date collision cross sections. In addition, the effects of the secondary electrons generated from the heavy ion precipitation are included using a two‐stream transport model that computes the secondary electron fluxes and their escape from the atmosphere. The model also determines H2 Lyman‐Werner band emission intensities, including a predicted spectrum and the associated color ratio. Implications of the new model results for interpretation of data from National Aeronautics and Space Administration's Juno mission are discussed. In particular, the model predicts that for a 2 MeV/u oxygen ion energy input of 10 mW/m2: (1) escaping electrons are produced with an energy range from 1 eV to 4 keV, which is a smaller range than previous models by Ozak et al. (2013, https://doi.org/10.1002/2013GL50812) predicted, (2) H2 band emission rates of 75 kR are generated, similar to previous estimates, and (3) a newly calculated Lyman and Werner band color ratio of 10 is expected. The color ratios are put into a context of various methane number density distributions.

Modelling of the evolution of a droplet cloud in a turbulent flow

The effects of droplet inertia and turbulent mixing on the droplet number density distribution in a turbulent flow field are studied. A formulation of the turbulent convective diffusion equation for the droplet number density, based on the modified Fully Lagrangian Approach, is proposed. The Fully Lagrangian Approach for the dispersed phase is extended to account for the Hessian of transformation from Eulerian to Lagrangian variables. Droplets with moderate inertia are assumed to be transported and dispersed by large scale structures of a filtered field in the Large Eddy Simulation (LES) framework. Turbulent fluctuations, not visible in the filtered solution for the droplet velocity field, induce an additional diffusion mass flux and hence additional dispersion of the droplets. The Lagrangian formulation of the transport equation for the droplet number density and the modified Fully Lagrangian Approach (FLA) make it possible to resolve the flow regions with intersecting droplet trajectories in the filtered flow field. Thus, we can cope successfully with the problems of multivalued filtered droplet velocity regions and caustic formation. The spatial derivatives for the droplet number density are calculated by projecting the FLA solution on the Eulerian mesh, resulting in a hybrid Lagrangian–Eulerian approach to the problem. The main approximations for the method are supported by the calculation of droplet mixing in an unsteady one-dimensional flow field formed by large-scale oscillations with an imposed small-scale modulation. The results of the calculations for droplet mixing in decaying homogeneous and isotropic turbulence are validated by the results of Direct Numerical Simulations (DNS) for several values of the Stokes number.

Computational and experimental investigation of plasma deflagration jets and detonation shocks in coaxial plasma accelerators

We present a magnetohydrodynamic (MHD) numerical simulation to study the physical mechanisms underlying plasma acceleration in a coaxial plasma gun. Coaxial plasma accelerators are known to exhibit two distinct modes of operation depending on the delay between gas loading and capacitor discharging. Shorter delays lead to a high velocity plasma deflagration jet and longer delays produce detonation shocks. During a single operational cycle that typically consists of two discharge events, the plasma acceleration exhibits a behavior characterized by a mode transition from deflagration to detonation. The first of the discharge events, a deflagration that occurs when the discharge expands into an initially evacuated domain, requires a modification of the standard MHD algorithm to account for rarefied regions of the simulation domain. The conventional approach of using a low background density gas to mimic the vacuum background results in the formation of an artificial shock, inconsistent with the physics of free expansion. To this end, we present a plasma-vacuum interface tracking framework with the objective of predicting a physically consistent free expansion, devoid of the spurious shock obtained with the low background density approach. The interface tracking formulation is integrated within the MHD framework to simulate the plasma deflagration and the second discharge event, a plasma detonation, formed due to its initiation in a background prefilled with gas remnant from the deflagration. The mode transition behavior obtained in the simulations is qualitatively compared to that observed in the experiments using high framing rate Schlieren videography. The deflagration mode is further investigated to understand the jet formation process and the axial velocities obtained are compared against experimentally obtained deflagration plasma front velocities. The simulations are also used to provide insight into the conditions responsible for the generation and sustenance of the magnetic pinch. The pinch width and number density distribution are compared to experimentally obtained data to calibrate the inlet boundary conditions used to set up the plasma acceleration problem.

Stellar Stream and Halo Structure in the Andromeda Galaxy from a Subaru/Hyper Suprime-Cam Survey*

Abstract We present wide and deep photometry of the northwestern part of the halo of the Andromeda galaxy (M31) using Hyper Suprime-Cam on the Subaru Telescope. The survey covers a 9.2 deg2 field in the g, i, and NB515 bands and shows a clear red giant branch (RGB) of M31's halo stars and a pronounced red clump (RC) feature. The spatial distribution of RC stars shows a prominent stream feature, the Northwestern (NW) Stream, and a diffuse substructure in the southern part of our survey field. We estimate the distances based on the RC method and obtain = 24.63 ± 0.191 (random) ± 0.057 (systematic) and 24.29 ± 0.211 (random) ± 0.057 (systematic) mag for the NW Stream and diffuse substructure, respectively, implying that the NW Stream is located behind M31, whereas the diffuse substructure is located in front of it. We also estimate line-of-sight distances along the NW Stream and find that the southern part of the stream is ∼20 kpc closer to us relative to the northern part. The distance to the NW Stream inferred from the isochrone fitting to the color–magnitude diagram favors the RC-based distance, but the tip of the RGB (TRGB)-based distance estimated for NB515-selected RGB stars does not agree with it. The surface number density distribution of RC stars across the NW Stream is found to be approximately Gaussian with an FWHM of ∼25 arcmin (5.7 kpc), with a slight skew to the southwest side. That along the NW Stream shows a complicated structure, including variations in number density and a significant gap in the stream.