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The interactions of atomic and molecular hydrogen with bare interstellar dust grain surfaces are important for understanding H2 formation at relatively high temperatures (>20 K). We investigate the diffusion of physisorbed H atoms and the desorption energetics of H2 molecules on an amorphous diamond-like carbon (DLC) surface. From temperature-programmed desorption experiments with a resonance-enhanced multiphoton ionization (REMPI) method for H2 detection, the H2 coverage-dependent activation energies for H2 desorption are determined. The activation energies decrease with increasing H2 coverage and are centered at 30 meV with a narrow distribution. Using a combination of photostimulated desorption and REMPI methods, the time variations of the surface number density of H2 following atomic and molecular hydrogen depositions are studied. From these measurements, we show that H2 formation on a DLC surface is quite efficient, even at 20 K. A significant kinetic isotope effect for H2 and D2 recombination reactions suggests that H-atom diffusion on a DLC surface is mediated by quantum mechanical tunneling. In astrophysically relevant conditions, H2 recombination due to physisorbed H-atoms is unlikely to occur at 20 K, suggesting that chemisorbed H atoms might play a role in H2 formation at relatively high temperatures., 33 pages, 8 figures, Accepted for publication in ApJ

If their number density is high enough, clusters of axions can decay to photons via stimulated emission. We study both the special and general relativistic corrections to lasing in such dense axion clusters as they evolve in static spacetimes. Our main results are rate equations for the evolution of axion and photon number densities that include these corrections. We use Schwarzschild spacetime as a detailed example., 31 pages, 3 figures

In the arc-burning process of high-current vacuum arc(HCVA), the metal particles（MPs） splashed from the active anode will have a significant influence on the plasma characteristics of the arc column. In this paper, the influence of MPs with different characteristics on the characteristics of HCVA is studied by establishing a HCVA model containing single or multiple MPs. The simulation results show that when the MPs vaporized metal vapor (MV) enters the interelectrode region, once the arc column plasma cannot ionize all atoms immediately, the ionization layer and the neutral atom vapor area (NAVA) will be formed in the adjacent region of the MPs. When the metal particle (MP) diameter and temperature increase, the number of vaporized mental atoms increases, so that the influence range of metal vapor increases, and the area of ionization layer and the neutral atom vapor area increases. In addition, when the arc current increases or the MPs are closer to the cathode surface, the greater the ion number density and ion pressure around the MPs are, the stronger the compression on the metal vapor will be, resulting in the decrease of the area of nization layer and the neutral atom vapor, and the increase of the net ionization rate of the ion number density. When multiple MPs exist in the interelectrode region at the same time, the metal vapor vaporized by the MPs will affect each other. In the central region of multiple MPs, the density of metal vapor becomes the largest, while the net ionization rate of ion number density is distributed in the periphery region of the metal particle group.

One of the most straightforward approaches that widely used to solve the neutron transport equation is the diffusion equation approach. The diffusion equation describes the individual behavior of the average neutron trajectory when interacting with matter. Usually, the neutron diffusion equation is obtained under the assumption that scattering is isotropic in the laboratory system of coordinates, and neutrons have the same energy and region is homogeneous; this called a one-speed diffusion equation. It leads to the diffusion coefficient to be independent of the spatial position; the volume of the reactor is constant, and the number density of the fuel atoms is also relatively constant. In this study, multi-group neutron diffusion characteristics were introduced in two ways. First, they vary with energy in the finite slab reactor core using a one-dimensional multi-group diffusion equation with the Gauss-Seidel iteration method. Second, using Fick’s law directly. The study used macroscopic cross-sections in the U-PuN fuel cell level as initial input for 70 energy groups. The data library used is JFS-3-J33 for 70 energy groups, which is the library data of SLAROM computer codes from JAEA Japan. The first way indicates the diffusion coefficient characteristics of U-235 and Pu-239 fuel isotopes firmly have the same pattern in each group energy. They have fluctuations throughout the fast, intermediate, and thermal energy group regions because both isotopes are fertile material. On the other hand, the diffusion coefficient of U-238 fuels isotope tends to be stable in each energy group. This event occurs because the isotope of U-238 is natural uranium, which is included as a fertile material. The second way shows the diffusion coefficients characteristics of the nuclear fuel isotopes firmly have the same pattern in each energy group, especially in the fast and thermal energy group region. They have fluctuations only throughout the intermediate energy group regions because, in this area, there is a resonant region.

Although image measurement is essential in the analysis of acoustic cavitation bubbles, it is impossible to determine the position of the bubble along the optical axis of the imaging system from the images. Thus, the number density of the bubbles cannot be measured from the image. This paper proposed a method to determine bubbles’ positions along the optical axis using the bubble image brightness. The relationship among the bubble position along the optical axis, the bubble diameter, and the bubble image brightness is clarified using the bubble in the single bubble system. A measurement method of the bubble number density based on this relationship is established. Using this method, the time-averaged spatial distribution of bubble number density under ultrasonic horn is revealed.

Laser-induced plasma is often produced in the presence of background gas, which causes some new physical processes. In this work, a two-dimensional axisymmetric radiation fluid dynamics model is used to numerically simulate the expansion process of plasma under different pressures and gases, in which the multiple interaction processes of diffusion, viscosity and heat conduction between the laser ablated target vapor and the background gas are further considered, and the spatio-temporal evolutions of plasma parameters (species number density, expansion velocity, size and electron temperature) as well as the emission spectra are obtained. The consistency between the actual and simulated spectra of aluminum plasma in 1 atm argon verifies the correctness of the model and the numerical simulation, thus providing a refinement analysis method for the basic research of plasma expansion in gases and the application of laser-induced breakdown spectroscopy.

We consider the application of peaks theory to the calculation of the number density of peaks relevant for primordial black hole (PBH) formation. For PBHs, the final mass is related to the amplitude and scale of the perturbation from which it forms, where the scale is defined as the scale at which the compaction function peaks. We therefore extend peaks theory to calculate not only the abundance of peaks of a given amplitude, but peaks of a given amplitude and scale. A simple fitting formula is given in the high-peak limit relevant for PBH formation. We also adapt the calculation to use a Gaussian smoothing function, ensuring convergence regardless of the choice of power spectrum.

The number density and the arrangement of metal nanoparticles in composite materials have a significant effect on their performance and hence their suitability for use in sensors and devices. Forming one-dimensional arrays of metal nanoparticles is one way of controlling their number density and arrangement in the devices. In this study, we fabricated one-dimensional arrays of gold nanoparticles by adsorbing them on linearly distributed hard segments present on the surfaces of segmented polyurethane nanofibers, which were produced by electrospinning under a stretching force. The length of the one-dimensional array was approximately 500 nm. Futher-more, the interparticle distance was almost constant at approximately 14 nm. Thus, the proposed method is suitable for fabricationg one-dimensional arrays of metal nanoparticles with high precision.

Recently, pulsed lasers have demonstrated great potential in targeted synthesis in solution based nanomanufacturing, realizing high precision and accuracy in space, time and energy input. The unique temperature history induced by pulsed lasers is indispensable to understand the related fundamentals and to realize the precision control of deposition. In this study a heat transfer model was developed and applied to predict the temporal evolution and the spatial distribution of pulsed laser induced temperature change across the reaction sites. Chemically deposited ZnO crystals were studied as an example, showing the relationships among laser parameters and heating conditions, and deposited crystal characteristics. Peak temperature and heat accumulation induced by pulsed laser were found to affect deposited crystal number density and size. The nucleation number density distribution was found to be correlated with the spatial temperature distribution and inversely proportional to the crystal size. The presented heat transfer model is a crucial tool to understand crystallization fundamentals and it is essential for facilitating pulsed laser as a new tool for research, design, manufacturing and control.

The growth rate of bump on tail instability propagating in unmagnetized plasma has been derived. The dispersion relation has been characterized for (r,q) distribution function with spectral indices r and q which ultimately contributes towards tails and shoulder of distribution function. The growth rate of the bump on tail instability has been estimated numerically for different ratios of temperature and number density using solar wind data and also by varying values of indices r and q . The higher value of q play the role towards decreasing the growth rate where the instability has the higher value when the number density of the superthermal electrons in the bump is higher and the temperature is low. The maximum growth rate increases with the increase in number density of electrons and decreases with the increasing temperature in the bump.

Sprays are typically characterised by providing local drop size and velocity distributions and number density. The present work examines the possibility of obtaining such information using backlight photography, whereby two cameras are employed and the size and position of each imaged drop is obtained using a depth from defocus approach. A simple algorithm for estimating size and position from the two camera images is introduced and the sensitivity of this algorithm to various system parameters is investigated with simulations using synthetic images, measurements from a calibration facility, and measurements conducted in a sparse spray. Comparison measurements using the analysis of focused images are provided.

This paper describes the results of modeling of a dielectric barrier discharge (DBD). Filamentary structure of DBD is taken into account in the model by introducing the ratio of the cross section area of a microdischarge to the electrode area as a parameter of the model. Discharge and afterglow stages in the gas flow were studied using a zero-dimensional model for a DBD microdischarge channel. The results of modeling are compared with literature data for [O] number densities in a single pulse nanosecond discharge, and with our own measurements of ozone formation in the DBD. Measurements of ozone number density in oxygen and in mixtures of oxygen with methane served as means of validating the DBD model. The best agreement of the calculated and experimental dependences of [O3] number densities on the discharge energy load was observed, when processes involving vibrationally excited ozone were accounted for together with the discharge microstructure.

High power impulse magnetron sputtering (HiPIMS) discharge promises high ionization fraction and energetic ions in comparison with dc magnetron sputtering discharge. But acknowledge on the characteristics of HiPIMS plasma in the near-substrate region (substrate vicinity), which is of great importance for film deposition, is still limited. Here, optical emission spectroscopy combined with the collisional-radiative modelling are developed and used to determine the electron temperature and the number density of neutral sputtered atom for the chromium HiPIMS plasma in substrate vicinity. The optical emission spectroscopic analysis demonstrated the HiPIMS discharge of Cr sputtering process in low density mode was dominated by the electron impact ionization of argon atoms and excitation of chromium atoms. As the HiPIMS plasma in the substrate vicinity is far from the local thermal equilibrium state, the relative intensities of transition lines to ArI 4p states was used to calculate the electron temperature. Subsequently, the neutral chromium atoms density about 1017 m-3 was reported in the near-substrate region. Our findings have important implications for species generation in low density HiPIMS discharge, with applications in synthesis of dense chromium coatings.

We present a series of recent experimental and numerical results which allow us to propose and explain the mechanisms for collisional cooling of a trapped ion by sequential binary collisions with atoms. Our experiments in hybrid atom-ion traps study the cooling of ions when the reservoir of the coolant atoms is spatially localized at the centre of the ion trap. Under these conditions the widely and long held expectation that for the ion to collisionally cool, the atom must be of lighter mass (i.e. mI > mA ) is overturned. Instead we show ion cooling for mI ⩽ mA in addition to mI > mA , and explain why earlier work establishing mass ratios does not apply to the experiments in hybrid traps. Further, for cooling of an ion A+ by the parent atom A, the mechanism of resonant charge exchange (RCE) allows for extremely efficient cooling of the ion A+. This mechanism is demonstrated by comparing the cooling rate of an ion with a localized ensemble of its parent atoms and with a lighter atomic species, where in the latter case the RCE mechanism does not exist. The difference in measured cooling rates for a given number density of the atoms and the theoretically calculated difference between elastic and RCE cross sections are used to show that the cooling efficiency per collision with RCE is much greater than the cooling by elastic collision. We conclude with some perspectives and prospects of future experiments.

We derive quantum Boltzmann equations for preheating by means of the density matrix formalism, which account for both the non-adiabatic particle production and the leading collisional processes between the produced particles. In so doing, we illustrate the pivotal role played by pair correlations in mediating the particle production. In addition, by numerically solving the relevant system of Boltzmann equations, we demonstrate that collisional processes lead to a suppression of the growth of the number density even at the very early stages of preheating., Comment: 31 pages, 9 figures, JCAP format. Text and equations changed to match published version

Using the three-component spectral model describing the FIRAS average continuum spectra, the exact analytical expressions for thermodynamic and radiative functions of Galactic far-infrared radiation are obtained. The COBE FIRAS instrument data in the 0.15 – 2.88 THz frequency interval at the mean temperatures of T 1 = 17.72 K, T 2 = 14 K and T 3 = 6.73 K are used for calculating the radiative and thermodynamic functions, such as the total radiation power per unit area, total energy density, total emissivity, number density of photons, Helmholtz free energy density, entropy density, heat capacity at constant volume and pressure for the warm, intermediate temperature and very cold components of the Galactic continuum spectra. The generalized Stefan-Boltzmann law for warm, intermediate-temperature and very cold components is constructed. The temperature dependence of each component is determined by the formula I S−B ( T ) = σ′ T 6 . This result is important when we construct the cosmological models of radiative transfer that can be applied inside the Galaxy. Within the framework of the three-component spectral model, the total number of photons in our Galaxy and the total radiation power (total luminosity) emitted from a surface of the Galaxy are calculated. Their values are N Gtotal = 1.3780 × 10 68 and I Gtotal ( T ) = 1.0482 × 10 36 W. Other radiative and thermodynamic properties of the Galactic far-infrared radiation (photon gas) of the Galaxy are calculated. The expressions for astrophysical parameters, such as the entropy density/Boltzmann constant and number density of the Galactic far-infrared photons are obtained. We assume that the obtained analytical expressions for thermodynamic and radiative functions may be useful for describing the continuum spectra of the far-infrared radiation for other galaxies.

The basic properties of the nonlinear propagation of the nonplanar (cylindrical and spherical) positron-acoustic (PA) shock waves (SHWs) in an unmagnetized electron-positron-ion (e-p-i) plasma containing immobile positive ions, mobile cold positrons, and superthermal (kappa distributed) hot positrons and electrons are investigated both analytically and numerically. The modified Burgers equation (mBE) is derived by using the reductive perturbation method. The basic features of PA SHWs are significantly modified by the cold positron kinematic viscosity (η), superthermal parameter of electrons (κe), superthermal parameter of hot positrons (κp), the ratio of the electron temperature to hot positron temperature (σ), the ratio of the electron number density to cold positron number density and the ratio of the hot positron number density to cold positron number density (μph). This study could be useful to identify the basic properties of nonlinear electrostatic disturbances in dissipative space and laboratory plasmas.

A theoretical study on the nonlinear propagation of nonplanar (cylindrical and spherical) electrostatic modifled ion-acoustic (mIA) shock structures has been carried out in an unmagnetized, collisionless four component degenerate plasma system (containing degenerate elec- tron ∞uids, inertial positively as well as negatively charged light ions, and positively charged static heavy ions). This investigation is valid for both non-relativistic and ultra-relativistic limits. The modifled Burgers (mB) equation has been derived by employing the reductive perturbation method, and used to numerically analyze the basic features of shock structures. It has been found that the efiects of degenerate pressure and number density of electron and inertial positively as well as negatively charged light ion ∞uids, and various charging state of positively charged static heavy ions signiflcantly modify the basic features of mIA shock structures. The implications of our results to dense plasmas in astrophysical compact objects (e.g., non-rotating white dwarfs, neutron stars, etc.) are brie∞y discussed.

Electron-acoustic shock waves (EASWs) in an unmagnetized four-component plasma (containing hot electrons and positrons following the q-nonextensive distribution, cold mobile viscous electron fluid, and immobile positive ions) are studied in nonplanar (cylindrical and spherical) geometry. With the help of the reductive perturbation method, the modified Burgers equation is derived. Analytically, the effects of nonplanar geometry, nonextensivity, relative number density and temperature ratios, and cold electron kinematic viscosity on the basic properties (viz. amplitude, width, speed, etc.) of EASWs are discussed. It is examined that the EASWs in nonplanar geometry significantly differ from those in planar geometry. The results of this investigation can be helpful in understanding the nonlinear features of EASWs in various astrophysical plasmas.

We investigate the far-infrared properties of galaxies selected via deep, narrow-band imaging of the H$\alpha$ emission line in four redshift slices from $z=0.40$--$2.23$ over $\sim 1$deg$^2$ as part of the High-redshift Emission Line Survey (HiZELS). We use a stacking approach in the Herschel PACS/SPIRE bands, along with $850\,\mu$m imaging from SCUBA-2 to study the evolution of the dust properties of H$\alpha$-emitters selected above an evolving characteristic luminosity threshold, $0.2L^\star_{{\rm H}\alpha}(z)$. We investigate the relationship between the dust temperatures and the far-infrared luminosities of our stacked samples, finding that H$\alpha$-selection identifies cold, low-$L_{\rm IR}$ galaxies ($T_{\rm dust}\sim 14$k; $\log[L_{\rm IR}/{\rm L}_\odot]\sim 9.9$) at $z=0.40$, and more luminous, warmer systems ($T_{\rm dust}\sim 34$k; $\log[L_{\rm IR}/{\rm L}_\odot]\sim 11.5$) at $z=2.23$. Using a modified greybody model, we estimate "characteristic sizes" for the dust-emitting regions of HiZELS galaxies of $\sim 0.5$kpc, nearly an order of magnitude smaller than their stellar continuum sizes, which may provide indirect evidence of clumpy ISM structure. Lastly, we measure the dust masses from our far-IR SEDs along with metallicity-dependent gas-to-dust ratios ($\delta_{\rm GDR}$) to measure typical molecular gas masses of $\sim 10^{10}$M$_\odot$ for these bright H$\alpha$-emitters. The gas depletion timescales are shorter than the Hubble time at each redshift, suggesting probable replenishment of their gas reservoirs from the intergalactic medium. Based on the number density of H$\alpha$-selected galaxies, we find that typical star-forming galaxies brighter than $0.2L^{\star}_{{\rm H}\alpha}(z)$ host a significant fraction ($35\pm10$%) of the total gas content of the Universe, consistent with the predictions of the latest cosmological simulations., Comment: 17 pages, 4 figures, accepted for publication in The Astrophysical Journal

The key microstructural feature providing strength to age-hardenable Al alloys is nanoscale precipitates. Alloy development requires a reliable statistical assessment of these precipitates, in order to link the microstructure with material properties. Here, it is demonstrated that scanning precession electron diffraction combined with computational analysis enable the semi-automated extraction of precipitate statistics in an Al-Mg-Si-Cu alloy. Among the main findings is the precipitate number density, which agrees well with a conventional method based on manual counting and measurements. By virtue of its data analysis objectivity, our methodology is therefore seen as an advantageous alternative to existing routines, offering reproducibility and efficiency in alloy statistics. Additional results include improved qualitative information on phase distributions. The developed procedure is generic and applicable to any material containing nanoscale precipitates. Content from this work may be used under the terms of theCreative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd

A zero-dimensional model is used to study the processes of physical and chemical reactions in atmospheric plasma with different ionization degrees near the ground (0 km). The temporal evolutions of CO, CO2 and other main reactants (namely OH and O2), which affect the conversion of CO and CO2, are obtained for afterglow plasma with different initial values. The results show that the consumption rate of CO is largest when the initial electron number density ne0=1012 cm−3, i.e. the ionization degree is 0.000004%. The number density of CO2 is relatively small when ne0=1016 cm−3, i.e. the ionization degree is 0.04%, whereas they are very close under the condition of other ionization degrees. Considering the total number densities of CO and CO2 and the consumption rate of CO comprehensively, the best condition is ne0=1013 cm−3, i.e. the ionization degree is 0.00004% for reducing the densities of CO and CO2 in the atmospheric plasma. The temporal evolutions of N+, Ar+, CO+ and CO2+ are also shown, and the influences on the temporal evolutions of CO and CO2 are analyzed with increasing ionization degree.

A highly-sensitive in-situ diagnosis approach for nitrogen dioxide (NO2) has been developed in dielectric barrier discharge (DBD) based on pulsed cavity ring-down spectroscopy (CRDS). Absorption bands of NO2 in a spectral region from 508 nm to 509 nm were used, and a detection limit of 17.5 ppb was achieved. At this level of sensitivity, the quantitative and real-time monitoring of the production and removal of NO2 are accomplished for the first time in the discharge region. By measuring the removal amount and rate at different NO2 initial number densities from 1.54 × 1013 cm−3 to 2.79 × 1014 cm−3, we determined the relationship between them and NO2 initial number densities. The removal amount linearly increases with the initial number density, while the removal rate increases logarithmically. At a lower initial number density, the removal rate is limited. By considering the chemical kinetic mechanism in plasma, a qualitative explanation for the above phenomena is proposed: the additional NO2 produced by discharge limits the removal rate, since the NO2 concentration is dominated by the competition between the forward reactions (production) and the reverse reactions (removal).

Composition of species is one of the key parameters in calculating the plasma properties and assessing the plasma chemical processes. Unlike the calculation of LTE plasma composition, the calculation of 2T plasma composition still remains in dispute. Different researchers have chosen different methods which lead to different results. In this work, we compare two kinds of methods for calculating 2T plasma composition: the mass action law methods and extremum searching methods. The former methods include the two described by Potapov and van de Sanden et al mass action laws respectively. The latter methods include those of searching minimum Gibbs free energy and maximum entropy of a plasma system respectively. The entropy maximization method is first reported in this work and has the same power as the commonly used Gibbs free energy minimization method. We demonstrate both mathematically and numerically that the method of 2T Gibbs free minimization is completely the same as the 2T Potapov mass action law, and the method of 2T entropy maximization is exactly consistent with the 2T van de Sanden et al. mass action law if we assume that the term μi/Ti is independent of the number density ni. It is also found that the assumption of number density-independent μi/Ti mainly affects the density of charged particles. When the plasma reaches the LTE state, the composition obtained by the methods of entropy maximization with and without this assumption will be exactly the same.

A combination of optical emission and absorption spectroscopy of argon 2p-1s transitions (Paschen notation) combined with collisional-radiative (CR) modelling of argon 2p states was used to characterize microwave argon plasmas at atmospheric pressure in presence of N2, O2, and H2 admixtures. In particular, the neutral gas temperature (obtained from the broadening of argon 2p2-1s2 and 2p3-1s2 emission lines), the number density of argon 1s5 atoms (obtained from absorption spectroscopy of the argon 2p9-1s5 transition using a tunable laser diode), the electron temperature (obtained from the comparison between measured and simulated argon 2p-to-1s relative line emission intensities), and the electron density (obtained from the Stark broadening of the Hβ line and argon relative line emission intensities) were recorded as a function of the axial distance along the microwave plasma column. The results show that, for a given position in the plasma and a higher amount of admixture in the nominally pure argon plasma, the neutral gas temperature increases and the electron number density decreases, while the electron temperature and the population of argon metastable atoms first decreases and then increases at higher concentrations. With such information, a detailed analysis of the electron power balance was performed. It is found that less than 1% of the admixture in the argon plasma already absorbed more than 80% of the microwave power. Part of this energy is used for neutral gas heating, mostly through electron-impact excitation of rotational levels.

What causes scattering of ultrasound from normal soft tissues such as the liver, thyroid, and prostate? Commonly, the answer is formulated around the properties of spherical scatterers, related to cellular shapes and sizes. However, an alternative view is that the closely packed cells forming the tissue parenchyma create the reference media, and the long cylindrical-shaped fluid vessels serve as the scattering sites. Under a weak scattering or Born approximation for the extracellular fluid in the vessels, and assuming an isotropic distribution of cylindrical channels across a wide range of diameters, consistent with a fractal branching pattern, some simple predictions can be made about the nature of backscatter as a function of frequency in soft tissues. Specifically, a number of plausible shapes would predict that backscatter increases as a power law of frequency, where the power law is determined by the function governing the number density of the vessels versus diameter. These results are compared with some historical models developed over the last 100 years in scattering theory and point to the need for higher spatial resolution and higher bandwidths to obtain more precise measures of the key parameters in normal tissues, and to better identify the dominant structures responsible for backscatter in everyday clinical imaging.

Solid polymer electrolytes based on poly(vinyl alcohol) (PVA) with different wt% ionic liquid (IL), 1-Butyl-2, 3-dimethylimidazolium tetraflouroborate [BDMITFB] were prepared using solution cast technique. Prepared samples were characterized using AC impedance spectroscopic technique. AC conductivity spectra of PVA-IL based system at different concentrations/temperatures have been discussed. The fitted AC conductivity spectra using Jonscher's power law (JPL) exhibits the correlated barrier hopping (CBH) type conduction mechanism. The scaled AC conductivity spectra of PVA-IL based films with temperature/concentrations collapsed into a single master curve indicating the ion conduction mechanism have the same origin. For higher IL loaded samples (20 and 25wt%) mobility, μ dc conductivity, σlsubgdcl/subg as well as total number density of charge carriers, N increases with increasing IL content in PVA. Dielectric permittivity (e' and e'') and electric modulus (M' and M'') study of prepared samples has been done. Temperature dependent dc conductivity for prepared polymeric films follows the Arrhenius type thermally activated process.

The spatial distribution of N2 plasma in the reactor chamber of an ion-filtered inductively-coupled-plasma metal-organic-chemical-vapor-deposition (IF-ICP-MOCVD) was studied. The selective absorption of the ion filter with a showerhead structure was simulated based on the simplification of the reaction model of N2 plasma and demonstrated by the optical emission spectroscopy and the growth of GaN film. The simulation shows that the number density of nitrogen ions on the pedestal was reduced by one order of magnitude with the showerhead ion filter compared to the counterpart without any ion filter, and that matches the measured spectra of OES. Meanwhile, N2(A3 )—a nitrogen metastable particle crucial to the growth of III-nitrides—keeps a moderate number density and the ratio of the number density of N2(A3 ) to the number density of nitrogen ions was increased up to 4–5 times as the showerhead ion filter has a relatively high transmission to nitrogen metastable particles. GaN films were successfully grown with our home-made IF-ICP-MOCVD at 480 °C, which shows great potential in the epitaxy of III-nitrides at low temperature.

Magnetomotive ultrasound (MMUS) contrasts superparamagnetic iron-oxide nanoparticles (SPIOs) that undergo submicrometer-scale displacements in response to a magnetic gradient force applied to an imaging sample. Typically, MMUS signals are defined in a way that is proportional to the medium displacement, rendering an indirect measure of the density distribution of SPIOs embedded within. Displacement-based MMUS, however, suffers from 'halo effects' that extend into regions without SPIOs due to their inherent mechanical coupling with the medium. To reduce such effects and to provide a more accurate representation of the SPIO density distribution, we propose a model-based inversion of MMUS displacement fields by reconstructing the body force distribution. Displacement fields are modelled using the static Navier-Cauchy equation for linear, homogeneous, and isotropic media, and the body force fields are, in turn, reconstructed by minimizing a regularized least-squares error functional between the modelled and the measured displacement fields. This reconstruction, when performed on displacement fields of two tissue-mimicking phantoms with cuboidal SPIO-laden inclusions, improved the range of errors in measured heights and widths of the inclusions from 54%-282% pre-inversion to-15%-20%. Likewise, the post-inversion contrast to noise ratios (CNRs) of the images were significantly larger than displacement-derived CNRs alone (p = 0.0078, Wilcoxon signed rank test). Qualitatively, it was found that inversion ameliorates halo effects and increases overall detectability of the inclusion. These findings highlight the utility of model-based inversion as a tool for both signal processing and accurate characterization of the number density distribution of SPIOs in magnetomotive imaging.

Correct prediction of composition heterogeneities and grain structure across a steel ingot is critical in optimizing the industrial processing parameters for enhanced performance. The columnar to equiaxed transtion (CET) is a microstructural transition which is strictly controlled as it affects the mechanical properties of the final product along with the macrosegregation patterns. Larger equiaxed regions are preferred for most industrial applications. CET is significantly affected by the number density of equiaxed grains and by the nucleation undercooling. 8 kg 42CrMo4 alloy steel ingots (240 mm x 60 mm x 60 mm) were cast. The cast structure was characterized by ASCOMETAL. The experiments were simulated with a process-scale model of solidification that incorporates a multiscale description of the microstructure formation. The goal of the present study is to show the capabilities of such a process-scale solidification model to explain the observed structure distributions (extent of the columnar and equiaxed zones, equiaxed-to-columnar transition).

Study of bubble distribution characteristics is the basis to understand the mechanism of gas-liquid two-phase flow in multiphase pumps. In the present work, a method based on Eulerian-Eulerian approach was used for the simulation of the flow in a multiphase rotodynamic pump. The bubble size was calculated through a bubble number density equation. The distribution characteristics of bubbles were analysed in conditions of different inlet gas volume fraction (IGVF). The results show that bubbles move to the hub and a homogeneous bubble size distribution can be observed due to the rotational effect and stirring action of the impeller blades. The bubble size increases in the vicinity of interaction region because of the rotor-stator interaction. Collision rate of bubbles increase and a large bubble size is shown in the diffuser, which is resulted from the decrease of bubble velocity. It is found that high IGVF cause small distance between bubbles so that collision rate of bubbles increase. Largest bubble size and gas volume fraction are obtained when IGVF is 15%.

By employing the reductive perturbation technique, the propagation of cylindrical and spherical ion acoustic solitary waves is studied in an unmagnetized dense relativistic plasma, consisting of relativistically degenerate electrons and cold fluid ions. A modified Korteweg-de-Vries equation is derived and its numerical solutions have been analyzed to identify the basic features of electrostatic solitary structures that may form in such a degenerate Fermi plasma. Different degrees of relativistic electron degeneracy are discussed and compared. It is found that increasing number density leads to decrease the amplitude the width of the ion acoustic solitary wave in both the cylindrical and spherical geometries. The relevance of the work to the compact astrophysical objects, particularly white dwarfs is pointed out.

Electron-positron pair production in a strong laser field enhanced by an assisted high frequency weak field is investigated by solving the quantum Vlasov equation. The average and residual pair number densities are obtained for sinusoid electric field and it is found that the high frequency assisted weak field will enhance pair production significantly. There exists an optimal frequency of assisted field that makes the pair production number density get a maximum one, which is a few orders of higher than that without assisted field. We also discuss the other possible assisted fields.

In this paper, based on the quasi-stationary magneto-hydrodynamic (MHD) model, vacuum arc characteristics are simulated and analyzed at different moments under power-frequency current. For a vacuum arc with sinusoidal current under a uniform axial magnetic field (AMF), simulation results show that at the moment of peak value current, maximal values appear in the ion number density, axial current density, heat flux density, electron temperature, plasma pressure and azimuthal magnetic field. At the same time, the distributions of these parameters along the radial position are mostly nonuniform as compared with those at other moments. In the first 1/4 cycle, the ion number density, axial current density and plasma pressure increase with time, but the growth rate decreases with time. Simulation results are partially compared with experimental results published in other papers. Simulations and experimental results both show that the arc light intensity near the cathode side is stronger than that near the anode side for diffusing vacuum arcs.

An improved two-dimensional axisymmetric swirl model based on former work has been developed to describe the detailed physical process in the formation and development of vacuum arc cathode spot. In the current model, the influence of plasma cloud, evaporation, backing ion, thermo-field (T-F) emission, back-diffused electron, self-generated magnetic field and Lorentz force are all considered. External parameters include electron temperature, near cathode voltage drop, average charge number, ion number density, space function and time function. The compositions of current density, energy flux density and external pressure are discussed and the influence of external parameters are studied. Simulation results show that electron current density from T-F emission is the most important component for current density; as for energy flux density and pressure, ion flux from plasma cloud is dominant. Ablation on a refractory metal is much less than that on a fusible metal under the same external conditions. The simulation results are in good agreement with other researchers' results.

Mega and medium-sized cities in China are facing the increasingly serious aerosol pollution, among them Xi'an is one of the typical cities. During the early stage of ash haze, aerosol concentration is rising so fast that the simulation of the process is difficult. This article uses the population balance equation (PBE) describing the distribution of fine particles, and solves the changing process of particle size distribution by the moment method. Population balance equation, a non-linear hyperbolic equation about number density function, is employed to describe micro-behaviors (aggregation, breakage, growth) of disperse phase and resulting variation of particle size distribution. By expressing PBEs for both batch and continuous operations in a general form, and using weighted residual method to derive the moment equations, different moments can be tracked directly. Three examples of simulation results show that compared with the analytical solution, relative error of this method is within 10−5 and has the characteristics of high precision and low computation amount. In early 2016, the early stage of PM2.5 pollution in Xi'an is simulated and the simulation results and experimental results are highly consistent.

A novel technique based on sub-wavelength plasma structure effects on enhancement of RF communication signals on a receiving antenna is carried out in this paper in laboratory experiments and analyzed by corresponding numerical simulations. Considerable intensification on receiving signal gain up to ~10 dB in comparison with that without the plasma modulation is observed experimentally in ~1 GHz RF band, with an effective enhancement bandwidth of ~340 MHz and the fractional bandwidth of ~34%. Then, the optimal modulation parameters of plasma are further studied by a numerical simulation. It is shown that the number density, the layer thickness, and the collision frequency of the plasma, as well as the relative distance between the plasma layer and antenna synergistically affect the modulation. Compared to the metallic antenna with the same overall dimension, the modulated antenna covered by the sub-wavelength plasma structure features higher receiving efficiency and lower radar cross section in the studied RF band. The mechanism of the reception enhancement is further revealed by analyzing characteristics of electromagnetic scattering and electric field distribution in the sub-wavelength plasma layer. The results then exhibit scientific significance and application potential of sub-wavelength plasma modulation on compact receiving antennas with higher performance and better feature of radar stealth.

A one-pot synthesis of palladium nanoparticles (Pd NPs) supported on polycarbosilane (PCS) nanowires, which also served as reducing agents, was conducted using wet and dry processing methods. Relatively small Pd NPs with diameters of approximately 2 nm and narrow size distributions were directly formed along the nanowires without aggregation owing to the on-site reduction of Pd ions. In particular, the supported Pd NPs prepared from Pd(II) acetylacetonate vapor through dry processing at a temperature of 180 °C exhibited a higher number density as compared with that of the Pd NPs fabricated through wet processing. In addition, the catalytic activity of the obtained Pd/PCS nanowires for the oxidation of CO was evaluated up to 200 °C. The CO molecules were completely converted to CO2 in the presence of Pd/PCS nanowires even at temperatures below 120 °C.

We aim to develop an ultrasonic tissue characterization method for the follow-up of healing ulcers by diagnosing collagen fibers properties. In this paper, we demonstrated a computer simulation with simulation phantoms reflecting irregularly distributed collagen fibers to evaluate the relationship between physical properties, such as number density and periodicity, and the estimated characteristics of the echo amplitude envelope using the homodyned-K distribution. Moreover, the consistency between echo signal characteristics and the structures of ex vivo human tissues was verified from the measured data of normal skin and nonhealed ulcers. In the simulation study, speckle or coherent signal characteristics are identified as periodically or uniformly distributed collagen fibers with high number density and high periodicity. This result shows the effectiveness of the analysis using the homodyned-K distribution for tissues with complicated structures. Normal skin analysis results are characterized as including speckle or low-coherence signal components, and a nonhealed ulcer is different from normal skin with respect to the physical properties of collagen fibers.

We investigate the corrections which relativistic light-cone computations induce on the correlation of the tangential shear with galaxy number counts, also known as galaxy-galaxy lensing. The standard-approach to galaxy-galaxy lensing treats the number density of sources in a foreground bin as observable, whereas it is in reality unobservable due to the presence of relativistic corrections. We find that already in the redshift range covered by the DES first year data, these currently neglected relativistic terms lead to a systematic correction of up to 50% in the density-shear correlation function for the highest redshift bins. This correction is dominated by the the fact that a redshift bin of number counts does not only lens sources in a background bin, but is itself again lensed by all masses between the observer and the counted source population. Relativistic corrections are currently ignored in the standard galaxy-galaxy analyses, and the additional lensing of a counted source populations is only included in the error budget (via the covariance matrix). At increasingly higher redshifts and larger scales, these relativistic and lensing corrections become however increasingly more important, and we here argue that it is then more efficient, and also cleaner, to account for these corrections in the density-shear correlations., version published in JCAP

Active Brownian Particles (ABPs) transmit a swim pressure $\Pi^{swim}=n\zeta D^{swim}$ to the container boundaries, where $\zeta$ is the drag coefficient, $D^{swim}$ is the swim diffusivity and $n$ is the uniform bulk number density far from the container walls. In this work we extend the notion of the isotropic swim pressure to the anisotropic tensorial swim stress $\mathbf{\sigma}^{swim} = - n \zeta \mathbf{D}^{swim}$, which is related to the anisotropic swim diffusivity $\mathbf{D}^{swim}$. We demonstrate this relationship with ABPs that achieve nematic orientational order via a bulk external field. The anisotropic swim stress is obtained analytically for dilute ABPs in both 2D and 3D systems, and the anisotropy is shown to grow exponentially with the strength of the external field. We verify that the normal component of the anisotropic swim stress applies a pressure $\Pi^{swim}=-(\mathbf{\sigma}^{swim}\cdot\mathbf{n})\cdot\mathbf{n}$ on a wall with normal vector $\mathbf{n}$, and, through Brownian dynamics simulations, this pressure is shown to be the force per unit area transmitted by the active particles. Since ABPs have no friction with a wall, the difference between the normal and tangential stress components -- the normal stress difference -- generates a net flow of ABPs along the wall, which is a generic property of active matter systems.

Determination of the negative ion number density of and in a DC discharge of oxygen plasma was made employing Langmuir probe in conjunction with eclipse laser photo-detachment technique. The temporal evolution of the extra electrons resulting from the photo-detachment of and were used to evaluate the negative ion number density. The ratio of number density to varied from 0.03 to 0.22. Number density of both and increased with increasing power and decreased as the pressure was increased. Electron number density was evaluated from the electron energy distribution function (EEDF) using the I–V recorded characteristic curves. Electron temperature between 2 and 2.7 eV were obtained. Influence of the metastable state is discussed.

In this paper, The Monte Carlo simulation program has been used to calculation the electron energy distribution function (EEDF) and electric transport parameters for the gas mixtures of The trif leoroiodo methane (CF3I) 'environment friendly' with a noble gases (Argon, Helium, kryptos, Neon and Xenon). The electron transport parameters are assessed in the range of E/N (E is the electric field and N is the gas number density of background gas molecules) between 100 to 2000Td (1 Townsend = 10-17 V cm2) at room temperature. These parameters, namely are electron mean energy (e), the density –normalized longitudinal diffusion coefficient (NDL) and the density –normalized mobility (μN). In contrast, the impact of CF3I in the noble gases mixture is strongly apparent in the values for the electron mean energy, the density –normalized longitudinal diffusion coefficient and the density –normalized mobility. Note in the results of the calculation agreed well with the experimental results.

We cross-correlate the positions of damped Lyman-$\alpha$ systems (DLAs) and their parent quasar catalog with a convergence map derived from the Planck cosmic microwave background (CMB) temperature data. We make consistent measurements of the lensing signal of both samples in both Fourier and configuration space. By interpreting the excess signal present in the DLA catalog with respect to the parent quasar catalog as caused by the large scale structure traced by DLAs, we are able to infer the bias of these objects: $b_{\rm DLA}=2.6\pm0.9$. These results are consistent with previous measurements made in cross-correlation with the Lyman-$\alpha$ forest, although the current noise in the lensing data and the low number density of DLAs limits the constraining power of this measurement. We discuss the robustness of the analysis with respect to a number different systematic effects and forecast prospects of carrying out this measurement with data from future experiments., Comment: 20 pages, 7 figures. Pipeline available at https://github.com/damonge/QxK

Near-infrared continuous wave cavity ring-down spectroscopy was applied to measure the OH radicals in dielectric barrier discharge plasmas, which play an important role in combustion systems, atmospheric chemistry and the removal of air pollutants by non-thermal plasmas. The P-branches of OH X2∏i ν″ = 2 ← ν″ = 0) bands were used for number density measurements. The OH number density and plasma temperature were determined for different applied voltages, gas pressures and concentrations of both oxygen and water. The temporal evolution of the OH number density was obtained by using the “time window method, which was used to extract individual ring-down times at different times in a half period of the sine wave applied voltage in dielectric barrier discharge plasmas.

Catalysis by supported single metal atoms has demonstrated tremendous potential for practical applications due to their unique catalytic properties. Unless they are strongly anchored to the support surfaces, supported single atoms, however, are thermodynamically unstable, which poses a major obstacle for broad applications of single-atom catalysts (SACs). In order to develop strategies to improve the stability of SACs, we need to understand the intrinsic nature of the sintering processes of supported single metal atoms, especially under various gas environments that are relevant to important catalytic reactions. We report on the synthesis of high number density Pt1/Fe2O3 SACs using a facial strong adsorption method and the study of the mobility of these supported Pt single atoms at 250 °C under various gas environments that are relevant to CO oxidation, water-gas shift, and hydrogenation reactions. Under the oxidative gas environment, Fe2O3 supported Pt single atoms are stable even at high temperatures. The presence of either CO or H2 molecules in the gas environment, however, facilitates the movement of the Pt atoms. The strong interaction between CO and Pt weakens the binding between the Pt atoms and the support, facilitating the movement of the Pt single atoms. The dissociation of H2 molecules on the Pt atoms and their subsequent interaction with the oxygen species of the support surfaces dislodge the surface oxygen anchored Pt atoms, resulting in the formation of Pt clusters. The addition of H2O molecules to the CO or H2 significantly accelerates the sintering of the Fe2O3 supported Pt single atoms. An anchoring-site determined sintering mechanism is further proposed, which is related to the metal-support interaction.

We delineate the conditions under which the consistency relation for the non-Gaussian bias and the universality of the halo mass function hold in the context of microscopic Lagrangian descriptions of halos. The former is valid provided that the collapse barrier depends only on the physical fields (instead of fields normalized by their variance for example) and explicitly includes the effect of {\it all} physical fields such as the tidal shear. The latter holds provided that the response of the halo number density to a long-wavelength density fluctuation is equivalent to the response induced by shifting the spherical collapse threshold. Our results apply to any Lagrangian halo bias prescription. Effective "moving" barriers, which are ubiquitous in the literature, do not generally satisfy the consistency relation. Microscopic barriers including the tidal shear lead to two additional, second-order Lagrangian bias parameters which ensure that the consistency relation is satisfied. We provide analytic expressions for them., 20 pages, no figure. JCAP format

Vertically aligned carbon nanotubes (VA-CNTs) are suggested for utilization as a new catalyst support of polymer electrolyte fuel cells (PEFCs). The independent control of the diameter and number density of VA-CNTs is essential for application in PEFCs. As the catalyst for VA-CNT growth, we fabricated CoFe2O4 nanoparticle (NP) films using the Langmuir–Blodgett (LB) technique. Using the LB technique, we were able to separately control the diameter and number density of VA-CNTs. The number density of VA-CNTs was changed by mixing with the filler moleculer, palmitic acid (C16). The VA-CNT diameter was changed by the adjusting the CoFe2O4 NP diameter. However, the heat-induced aggregation of CoFe2O4 NPs occurred in thermal chemical vapor deposition to synthesize VA-CNTs. Therefore, we examined how to minimize the effect of heat-induced aggregation of CoFe2O4 NPs. As a result, selection of the appropriate number density and diameter of CoFe2O4 NPs was found to be important for the control of VA-CNT diameter.