Particle Mass Density Research Articles

Numerical study of an electrostatic plasma sheath containing two species of charged dust particles

A multi-fluid model is used to study the dynamics of a dusty plasma sheath consists of electrons, ions, and two species of charged dust particles, i.e., nano-size and micron-size particles. It is found that, when the sheath is dominated by the nano-size dust grains, spatially periodic fluctuations are developed in the profiles of the sheath potential, and the number density and velocity of the plasma and dust particles. Due to inertial effects, the fluctuations in the parameters of the micron-size grains are much lower than those of the other parameters. The competition between the electric and ion drag forces plays the primary role in development of the fluctuations. The spatial period of the fluctuations is approximately a few Debye lengths and their amplitude depends on the plasma and dust parameters. The fluctuations are reduced by the increase in the radius, mass density, and Mach number of the nano-size particles, as well as the density and Mach number of the ions. But, they are enhanced by the increase in the plasma number density and the electron temperature. The sheath thickness demonstrates a non-monotonic behavior against variation of the nanoparticle parameters, i.e., it first decreases quickly, shows a minimum, and then increases. However, the sheath width always decreases with the plasma number density and ion Mach number, while grows linearly with the electron temperature.

Metrology of laser-guided particles in air-filled hollow-core photonic crystal fiber

Micrometer-sized particles are trapped in front of an air-filled hollow-core photonic crystal fiber using a novel dual-beam trap. A backward guided mode produces a divergent beam that diffracts out of the core, and simultaneously a focused laser beam launches a forward-propagating mode into the core. By changing the backward/forward power balance, a trapped particle can be selectively launched into the hollow core. Once inside, particles can be optically propelled along several meters of fiber with mobilities as high as 19 cm·s(-1) W(-1) (precisely measured using in-fiber Doppler velocimetry). The results are in excellent agreement with theory. The system allows determination of fiber loss as well as the mass density and refractive index of single particles.

Cloud modeling of a network region in Hα

AbstractIn this paper, we analyze the physical properties of dark mottles in the chromospheric network using two‐dimensional spectroscopic observations in Hα obtained with the Göttingen Fabry‐Perot Spectrometer in the Vacuum Tower Telescope at the Observatory del Teide, Tenerife. Cloud modeling was applied to measure the mottles' optical thickness, source function, Doppler width, and line‐of‐sight velocity. Using these measurements, the number density of hydrogen atoms in levels 1 and 2, total particle density, electron density, temperature, gas pressure, and mass density parameters were determined with the method of Tsiropoula & Schmieder (1997). We also analyzed the temporal behaviour of a mottle using cloud parameters. Our result shows that it is dominated by 3 minute signals in source function, and 5 minutes or more in velocity (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Separation of Particles Employing Travelling-Wave Electrokinetic Phenomena and Inclined Gravity

In travelling-wave electric fields, particles are propelled along electrode arrays by a propulsion force. The propulsion force depends on an applied frequency, voltage and size of particles. In this paper, we present the separation method of micro particles using the propulsion force and inclined gravity. The suspensions of polystyrene beads were used as the method to demonstrate the general application for the selective retention or transportation of particles. The efficiency of the method depends on the size of particles and mass density of particles. Additionally the method can measure the propulsion force on particles by adjusting the inclined angle.

Fabrication and characterization of thermally actuated micromechanical resonators for airborne particle mass sensing: II. Device fabrication and characterization

This paper, the second of two parts, presents extensive measurement and characterization results on fabricated thermally actuated single-crystal silicon MEMS resonators analyzed in part I. The resonators have been fabricated using a single mask process on SOI substrates. Resonant frequencies in a few hundreds of kHz to a few MHz and equivalent motional conductances as high as 102 mA V−1 have been measured for the fabricated resonators. The measurement results have been compared to the resonator characteristics predicted by the model developed in part I showing a good agreement between the two. Despite the relatively low frequencies, high quality factors (Q) of the order of a few thousand have been measured for the resonators under atmospheric pressure. The mass sensitivities of some of the resonators were characterized by embedding them in a custom-made test setup and deposition of artificially generated aerosol particles with known size and composition. The resulting measured mass sensitivities are of the order of tens to hundreds of Hz ng−1 and are in agreement with the expected values based on the resonator's physical dimensions. Finally, measurement of mass density of arbitrary airborne particles in the surrounding lab environment has been demonstrated.

Dust in the interplanetary medium

The mass density of dust particles that form from asteroids and comets in the interplanetary medium of the solar system is, near 1 AU, comparable to the mass density of the solar wind. It is mainly contained in particles of micrometer size and larger. Dust and larger objects are destroyed by collisions and sublimation and hence feed heavy ions into the solar wind and the solar corona. Small dust particles are present in large number and as a result of their large charge to mass ratio deflected by electromagnetic forces in the solar wind. For nanodust particles of sizes ≃1–10 nm, recent calculations show trapping near the Sun and outside from about 0.15 AU ejection with velocities close to solar wind velocity. The fluxes of ejected nanodust are detected near 1 AU with the plasma wave instrument onboard the STEREO spacecraft. Although such electric signals have been observed during dust impacts before, the interpretation depends on several different parameters and data analysis is still in progress.

The longitudinal optic-like mode in molten alkali halides: A molecular dynamics approximation to inelastic x-ray scattering experiments

The contribution of the long-wavelength fluctuations in the particle number, mass, and charge densities to the inelastic x-ray scattering dynamical structure factor for molten NaI and other molten alkali halides is accurately analyzed in the high frequencies region of the longitudinal optic-like mode. Molecular dynamics simulation results at low wave numbers are reported for the time correlations between the density components in the reciprocal space, namely, the corresponding intermediate scattering functions, and their spectra, namely, the dynamical structure factors. The time correlations between the longitudinal currents and their spectra are also reported. The importance of cross correlations is discussed. Moreover, the role played by the collective behavior of the two ionic species is also investigated. It is concluded that the longitudinal optic-like mode in molten alkali halides is unlikely to be detected by inelastic x-ray scattering experiments.

Particle Optics in the Rayleigh Regime

Light scattering and absorption by particles suspended in the atmosphere modifies the transfer of solar energy in the atmosphere, thereby influencing global and regional climate change and atmospheric visibility. Of particular interest are the optical properties of particles in the Rayleigh regime, where particles are small compared with the wavelength of the scattered or absorbed light, because these particles experience little gravitational settlement and may have long atmospheric lifetimes. Optical properties of particles in the Rayleigh regime are commonly derived from electromagnetic theory using Maxwell’s equations and appropriate boundary conditions. The size dependence of particle scattering and absorption are derived here from the most basic principles for coherent processes such as Rayleigh scattering (i.e., add amplitudes if in phase) and incoherent processes such as absorption (i.e., add cross sections), at the same time yielding understanding of the upper particle size limit for the Rayleigh regime. The wavelength dependence of Rayleigh scattering and absorption are also obtained by adding a basic scale invariance for particle optics. Simple consequences for particle single-scattering albedo (“whiteness”) and the optical measurement of particle mass densities are explained. These alternative derivations complement the conventional understanding obtained from electromagnetic theory.

Effects of Coating of Dicarboxylic Acids on the Mass−Mobility Relationship of Soot Particles

Atandem differential mobility analyzer (TDMA) and a differential mobility analyzer-aerosol particle mass analyzer (DMA-APM) have been employed to study morphology and hygroscopicity of soot aerosol internally mixed with dicarboxylic acids. The effective densities, fractal dimensions, and dynamic shape factors of soot particles before and after coating with succinic and glutaric acids are determined. Coating of soot with succinic acid results in a significant increase in the particle mobility diameter, mass, and effective density, but these properties recover to their initial values once succinic acid is removed by heating, suggesting that no restructuring of the soot core occurs. This conclusion is also supported from the observation of similar fractal dimensions and dynamic shape factors for fresh and coated/heated soot aggregates. Also, no change is observed when succinic acid-coated aggregates are cycled through elevated relative humidity (5% to 90% to 5% RH) below the succinic acid deliquescence point. When soot is coated with glutaric acid, the particle mass increases, but the mobility diameter shrinks by 10-40%. Cycling the soot aerosol coated with glutaric acid through elevated relative humidity leads to an additional mass increase, indicating that condensed water remains within the coating even at low RH. The fractal dimension of soot particles increases after coating and remains high when glutaric acid is removed by heating. The dynamic shape factor of glutaric acid-coated and heated soot is significantly lower than that of fresh soot, suggesting a significant restructuring of the soot agglomerates by glutaric acid. The results imply that internal mixing of soot aerosol during atmospheric aging leads to changes in hygroscopicity, morphology, and effective density, which likely modify their effects on direct and indirect climate forcing and deposition in the human respiratory system.

Toward Planetesimals: Dense Chondrule Clumps in the Protoplanetary Nebula

We outline a scenario that traces a direct path from freely floating nebula particles to the first 10-100 km sized bodies in the terrestrial planet region, producing planetesimals that have properties matching those of primitive meteorite parent bodies. We call this primary accretion. The scenario draws on elements of previous work and introduces a new critical threshold for planetesimal formation. We presume the nebula to be weakly turbulent, which leads to dense concentrations of aerodynamically size-sorted particles that have properties similar to those observed in chondrites. The fractional volume of the nebula occupied by these dense zones or clumps obeys a probability distribution as a function of their density, and the densest concentrations have particle mass densities that are 100 times that of the gas. However, even these densest clumps are prevented by gas pressure from undergoing gravitational instability in the traditional sense (on a dynamical timescale). While in this state of arrested development, they are susceptible to disruption by the ram pressure of the differentially orbiting nebula gas. However, self-gravity can preserve sufficiently large and dense clumps from ram pressure disruption, allowing their entrained particles to sediment gently but inexorably toward their centers, producing 10-100 km sandpile planetesimals. Localized radial pressure fluctuations in the nebula, as well as interactions between differentially moving dense clumps, will also play a role that must be accounted for in future studies. The scenario is readily extended from meteorite parent bodies to primary accretion throughout the solar system.

SOFIE PMC observations during the northern summer of 2007

This work examines the first season of polar mesospheric cloud (PMC) observations from the Solar Occultation for Ice Experiment (SOFIE). SOFIE observations of temperature, water vapor, and PMC frequency, mass density, particle shape, and size distribution are used to characterize the seasonal evolution and altitude dependence of mesospheric ice and the surrounding environment. SOFIE indicates that ice is nearly always present during summer, and that the ice layer is continuous from about 81 km altitude to the mesopause and above. Ice particles are observed to be more aspherical above and below the extinction peak altitude, suggesting a relationship between particle shape and mass density. The smallest particles are observed near the top of the ice layer while the largest particles exist at low concentrations near cloud base. A strong correlation was found between water vapor and particle size with small particles existing when H 2O is low. This relationship holds when examining variability in altitude, and variability over time at one altitude.

Relationship of refractive index to mass density and self-consistency of mixing rules for multicomponent mixtures like ambient aerosols

This paper focuses on two important yet poorly addressed aspects of ambient aerosols: relationship of refractive index to mass density (index–density relationship) and consistency of the mixing rules used to calculate these two quantities of a multicomponent mixture like ambient aerosols with the index–density relationship. Combined empirical and theoretical analyses show that a denser material generally tends to have a larger refraction index because the applied electric field induces a greater number of electric dipoles, and that the index–density relationship can be described reasonably well by the Lorentz–Lorenz relation. It is shown that the commonly used volume–mean mixing rule for calculating the effective mass density, the Lorentz–Lorenz mixing rule and the molar refraction mixing rule for calculating effective refractive index form a set of mixing rules that are consistent with the Lorentz–Lorenz relation. The molar fraction mixing rule and the Lorentz–Lorenz mixing rule are shown to be equivalent for the Lorentz–Lorenz mixture while the linear volume-mixing rule is an approximation of the Lorentz–Lorenz mixing rule for quasi-homogeneous mixtures wherein the refractive indices of the constituents do not differ much. The results highlight the need for consistency of the mixing rules for calculating the effective refractive index and mass density with the index–density relationship, which not only provides a theoretical guide for judiciously choosing the mixing rules to calculate effective properties of ambient aerosols but also poses new challenges to develop an effective medium theory that applies to more than one quantity. An empirical power-law expression is obtained from the published data that relates the effective specific refractive index to the effective mass density of aerosol particles.

Cylindrical Hall – MHD Waves: A Nonlinear Solution

The exact nonlinear cylindrical solution for incompressible Hall – magnetohydrodynamic (HMHD) waves, including dissipation, essentially from electron – neutral collisions, is obtained in a uniformly rotating, weakly ionized plasma such as exists in photospheric flux tubes. The ω – k relation of the waves, called here Hall – MHD waves, demonstrates the dispersive nature of the waves, introduced by the Hall effect, at large axial and radial wavenumbers. The Hall – MHD waves are in general elliptically polarized. The partially ionized plasma supports lower frequency modes, lowered by the factor δ≡ratio of the ion mass density to the neutral particle mass density, as compared to the fully ionized plasma (δ=1). The relation between the velocity and the magnetic field fluctuations departs significantly from the equipartition found in Alfven waves. These short-wavelength and arbitrarily large amplitude waves could contribute toward the heating of the solar atmosphere.

Cascade model for particle concentration and enstrophy in fully developed turbulence with mass-loading feedback

A cascade model is described based on multiplier distributions determined from three-dimensional (3D) direct numerical simulations (DNS) of turbulent particle laden flows, which include two-way coupling between the phases at global mass loadings equal to unity. The governing Eulerian equations are solved using psuedospectral methods on up to 512(3) computional grid points. DNS results for particle concentration and enstrophy at Taylor microscale Reynolds numbers in the range 34-170 were used to directly determine multiplier distributions on spatial scales three times the Kolmogorov length scale. The multiplier probability distribution functions (PDFs) are well characterized by the beta distribution function. The width of the PDFs, which is a measure of intermittency, decreases with increasing mass loading within the local region where the multipliers are measured. The functional form of this dependence is not sensitive to Reynolds numbers in the range considered. A partition correlation probability is included in the cascade model to account for the observed spatial anticorrelation between particle concentration and enstrophy. Joint probability distribution functions of concentration and enstrophy generated using the cascade model are shown to be in excellent agreement with those derived directly from our 3D simulations. Probabilities predicted by the cascade model are presented at Reynolds numbers well beyond what is achievable by direct simulation. These results clearly indicate that particle mass loading significantly reduces the probabilities of high particle concentration and enstrophy relative to those resulting from unloaded runs. Particle mass density appears to reach a limit at around 100 times the gas density. This approach has promise for significant computational savings in certain applications.

Effect of ion streaming on particle–particle interactions in a dusty plasma

Dust particles in low-temperature, low-pressure plasmas form Coulomb crystals and display collective behavior under select conditions. The trajectories of ions can be perturbed as they pass by negatively charged dust particles and, in some cases, will converge beyond the particle. This process, called ion streaming, produces a positive potential in the wakefield of the particle that can be large enough to perturb interparticle dynamics. In this paper, we discuss results from a three-dimensional model for dust particle transport in plasma processing reactors with which we investigated the effects of ion streaming on particle–particle interactions. When including the wakefield potential produced by ion streaming, dust particles can form vertically correlated pairs when trapped in electrical potential wells. The ion-streaming force was found to be significant only over a select range of pressures and for given combinations of particle sizes and mass densities. The formation of vertically correlated pairs critically depends on the shape of the potential well. Wakefield forces can also affect the order of multilayer lattices by producing vertical correlations between particles in adjacent layers.

Response of Polyelectrolyte Complexes to Subsequent Addition of Sodium Chloride: Time-Dependent Static Light Scattering Studies

Summary: The applications of polyelectrolyte complexes range from large-scale industrial products to special uses in biotechnology and medicine, yet one significant problem is their instability against changes in their environmental conditions, particularly the addition of salts. This concerns the colloidal stability as well as the stability of ionic bindings. Previous work on the effect of sodium chloride revealed that not only additional aggregation, but also complete dissolution may occur, depending on the nature of the polyelectrolyte components used. In these studies, the systems required up to one hour to become stable. Multi-angle static light scattering was used to investigate the processes taking place after the addition of NaCl to polyelectrolyte complexes (PEC) formed in pure water. PECs were prepared with polymethacrylate as polyanion and poly(diallyldimethylammonium chloride) and a copolymer of this polycation with 53 mol-% of acrylamide. These systems were chosen because of their interesting behavior: secondary aggregation, swelling, and dissolution at a critical salt concentration. The time-dependence of these effects was studied in detail by static light scattering. Aggregation and swelling demonstrated by changes in particle mass, radius, and structure density of the PEC.

Dilute granular flow around an immersed cylinder

In this paper we investigate a two-dimensional dilute granular flow around an immersed cylinder using discrete element computer simulations. Simulation measurements of the drag force acting on the cylinder, Fd, are expressed in terms of a dimensionless drag coefficient, Cd=Fd/[12ρν∞U∞2(D+d)], where ρ is the upstream particle mass density, ν∞ is the upstream solid fraction, U∞ is the upstream velocity, and (D+d) is the sum of the cylinder diameter, D, and surrounding particle diameter, d. The drag coefficient increases rapidly with decreasing Mach number for subsonic Mach numbers, but remains insensitive to Mach number for supersonic values. The drag coefficient is also a strong function of the flow Knudsen number, with the drag coefficient increasing with increasing Knudsen number and approaching an asymptotic value for very large Knudsen numbers. The drag coefficient decreases with decreasing normal coefficient of restitution and is relatively insensitive to the friction coefficient. Bow shock structures and expansion fans are also observed in the simulations and are compared to similar structures observed in compressible gas flows.

Study of Residual Particle Concentrations Generated by the Ultrasonic Nebulization of Deionized Water Stored in Different Container Types

A scanning mobility particle sizer has been used to quantify residual particle number and mass concentrations generated by ultrasonic nebulization of deionized (DI) water stored in a variety of bottles. High variability of residual particles was found not only between different bottle types but also between different bottles of the same type. Degradation of the water quality, quantified as increased residual mass and number concentrations as a function of time, occurred to varying degrees for water stored in different bottle types. Overall, glass bottles showed the highest residual particle concentrations and exhibited the poorest stability over time. After a storage period of 3 weeks, DI water stored in Pyrex bottles showed average increases in particle mass and number densities in the aerosol of over 250% and 60%, respectively. Total dissolved impurity levels in the water increased from 110 to 290 ng mL(-1) over the 3-week period. It is hypothesized that leaching from the bottle walls increases impurity levels in the water over time. Leaching was observed for both glass and polymer bottles. Contrary to this trend, residual particle concentrations from deionized water stored in Teflon bottles showed a net decrease during the measurement period. With respect to absolute residual particle concentrations and storage stability, a Teflon bottle yielded the best performance. Total residual particle mass and number densities for Teflon were less than a factor of 15% and 1%, respectively, as compared to residual particle levels observed for the Pyrex bottle. Absolute dissolved impurity levels in the water for the Teflon bottle decreased from 7.8 to 3.7 ng mL(-1) over the 4-week period.

Interaction of a moving shock wave with a two-phase reacting medium

The flow field, that develops when a moving shock wave hits a two-phase medium of gas and particles, has a practical application to industrial accidents such as explosions at coal mine and in grain elevator and furthermore to solid propellant combustion in rocket engine. Therefore, a successful prediction of the thermo-fluid mechanical characteristics development of gas and particles is very crucial and imperative for the successful design and operation of rocket nozzles and energy conversion systems. This paper describes an interaction phenomenon when a moving shock wave hits a two-phase medium of gas and particles with/without chemical reaction. A particle-laden gas is considered to be located along a ramp so that numerical integration is accomplished from the tip of ramp for a finite period. For the numerical solution, a fully conservative unsteady implicit second order time-accurate sub-iteration method and the second order Total Variation Diminishing scheme are used with the finite volume method for gas phase. For particle phase, the Monotonic Upstream Schemes for Conservation Laws as well as the solution of the Riemann problem for the particle motion equations is also used together with the schemes above. Transient development of thermo-fluid mechanical characteristics is calculated and discussed by changing the particle mass density and particle specific heat. For the case of the reacting particle-laden gas flow, a carbon particle-laden oxygen gas is considered to be located along a ramp. The results are discussed by comparison with the cases of the pure gas and the inert particle-laden gas. Major results reveal that when the particle mass density is smaller, there is a stronger interaction between two phases so that the velocity and temperature differences between two phases more rapidly decrease. When the particle specific heat is varied, only a thermal effect is observed while the other effects are minor. The case with reacting particles yields significantly different results due to chemical reaction such that the gas density does not monotonously but rapidly decrease due to the slip line in the relaxation zone, while the pressure and temperature become higher in comparison with the non-reacting case. But the dynamic variation would be only secondary to the thermal one.

Phase separation dynamics in binary fluids containing quenched or mobile filler particles

The dynamics of phase separation of binary fluids in the presence of quenched or mobile filler particles, with preferential attraction for one of the two fluid components, is investigated by means of extensive molecular dynamics simulations in two dimensions. When the filler particles are quenched, we found that they lead to a slowing-down of the kinetics that is enhanced as the density of the filler particles is increased. The domain growth in this case is found to follow a crossover scaling form which links domain growth in pure binary mixtures to that in the presence of quenched filler particles. On the other hand, when the filler particles are annealed, systematic simulations for various values of single filler particle mass, μc, and filler particle density, ρc, show that the filler particles only affect the nonuniversal prefactor of the power law. The power law itself remains given by t2/3, characteristic of inertial growth that is typically observed in pure binary fluid mixtures. The prefactor is found to depend on μc as μc−1/3 as expected in phase separating fluid in the inertial regime.