Segregation of Particles of Variable Size and Density in Falling Suspension Droplets

The problem of the falling under gravity suspension droplet was examined for cases where the droplet contains particles with different densities and different sizes. Cases examined include droplets composed of uniform-size particles with two different densities, of uniform-density particles of two different sizes, and of a distribution of particles of different densities. The study was conducted using both simulations based on Oseenlet particle interactions and laboratory experiments. It is observed that when the particles in the suspension droplet have different sizes and densities, an interesting segregation phenomenon occurs in which lighter/smaller particles are transported downward with the droplet and preferentially leave the droplet by entering into the droplet tail, whereas heavier/larger particles remain for longer periods of time in the droplet. When computations are performed with two particle densities or two particle sizes, a point is eventually reached where all of the lighter/smaller particles have been ejected from the droplet, and the droplet continues to fall with only the heavier/larger particles. A simple model explaining three stages of this segregation process is presented

The Interaction of Tungsten Dust with Human Skin Cells

In this chapter, we evaluate the tungsten (W) nanoparticle toxicity with respect to the normal human skin fibroblast cell. Tungsten dust formation is expected in the tokamak-type nuclear fusion installations, regarded as future devices for large-scale, sustainable, and carbon-free energy. This dust, composed of tungsten particles of variable size, from nanometers to micrometers, could be harmful to humans in the case of loss of vacuum accident (LOVA). In order to undertake the toxicity studies, tokamak-relevant dust has been deliberately produced in laboratory and afterward analyzed. Following that, cytotoxicity tests were performed using normal human skin fibroblast cell lines, BJ ATCC CRL 2522. Our study concludes that, at a low concentration (until 100 μg/mL), no cytotoxic effect of tungsten nanoparticles was observed. In contrast, at higher concentrations (up to 2 mg/mL), nanometric dust presents toxic effects on the cells

Density functional theory of phase coexistence in weakly polydisperse fluids

The recently proposed universal relations between the moments of the polydispersity distributions of a phase-separated weakly polydisperse system are analyzed in detail using the numerical results obtained by solving a simple density functional theory of a polydisperse fluid. It is shown that universal properties are the exception rather than the rule.Comment: 10 pages, 2 figures, to appear in PR

Analytic model for the ballistic adsorption of polydisperse mixtures

We study the ballistic adsorption of a polydisperse mixture of spheres onto a line. Within a mean-field approximation, the problem can be analytically solved by means of a kinetic equation for the gap distribution. In the mean-field approach, the adsorbed substrate as approximated as composed by {\em effective} particles with the {\em same} size, equal to the average diameter of the spheres in the original mixture. The analytic solution in the case of binary mixtures agrees quantitatively with direct Monte Carlo simulations of the model, and qualitatively with previous simulations of a related model in $d=2$.Comment: 6 pages, RevTex, includes 2 PS figures. Phys. Rev. E (in press

Highly porous photoluminescent diazaborole-linked polymers: synthesis, characterization, and application to selective gas adsorption

The formation of boron–nitrogen (B–N) bonds has been widely explored for the synthesis of small molecules, oligomers, or linear polymers; however, its use in constructing porous organic frameworks remains very scarce. In this study, three highly porous diazaborole-linked polymers (DBLPs) have been synthesized by condensation reactions using 2,3,6,7,14,15-hexaaminotriptycene and aryl boronic acids. DBLPs are microporous and exhibit high Brunauer–Emmett–Teller surface area (730–986 m2 g−1) which enable their use in small gas storage and separation. At ambient pressure, the amorphous polymers show high CO2 (DBLP-4: 4.5 mmol g−1 at 273 K) and H2 (DBLP-3: 2.13 wt% at 77 K) uptake while their physicochemical nature leads to high CO2/N2 (35–42) and moderate CO2/CH4 (4.9–6.2) selectivity. The electronic impact of integrating diazaborole moieties into the backbone of these polymers was investigated for DBLP-4 which exhibits green emission with a broad peak ranging from 350 to 680 nm upon excitation with 340 nm in DMF without photobleaching. This study demonstrates the effectiveness of B–N formation in targeting highly porous frameworks with promising optical properties

Finite size effect of harmonic measure estimation in a DLA model: Variable size of probe particles

A finite size effect in the probing of the harmonic measure in simulation of diffusion-limited aggregation (DLA) growth is investigated. We introduce a variable size of probe particles, to estimate harmonic measure and extract the fractal dimension of DLA clusters taking two limits, of vanishingly small probe particle size and of infinitely large size of a DLA cluster. We generate 1000 DLA clusters consisting of 50 million particles each, using an off-lattice killing-free algorithm developed in the early work. The introduced method leads to unprecedented accuracy in the estimation of the fractal dimension. We discuss the variation of the probability distribution function with the size of probing particles

Effect of turbulence on collisions of dust particles with planetesimals in protoplanetary disks

Planetesimals in gaseous protoplanetary disks may grow by collecting dust particles. Hydrodynamical studies show that small particles generally avoid collisions with the planetesimals because they are entrained by the flow around them. This occurs when $St$, the Stokes number, defined as the ratio of the dust stopping time to the planetesimal crossing time, becomes much smaller than unity. However, these studies have been limited to the laminar case, whereas these disks are believed to be turbulent. We want to estimate the influence of gas turbulence on the dust-planetesimal collision rate and on the impact speeds. We used three-dimensional direct numerical simulations of a fixed sphere (planetesimal) facing a laminar and turbulent flow seeded with small inertial particles (dust) subject to a Stokes drag. A no-slip boundary condition on the planetesimal surface is modeled via a penalty method. We find that turbulence can significantly increase the collision rate of dust particles with planetesimals. For a high turbulence case (when the amplitude of turbulent fluctuations is similar to the headwind velocity), we find that the collision probability remains equal to the geometrical rate or even higher for $St\geq 0.1$, i.e., for dust sizes an order of magnitude smaller than in the laminar case. We derive expressions to calculate impact probabilities as a function of dust and planetesimal size and turbulent intensity

Projectile compositions and modal frequencies on the chemistry of micrometeoroids LDEF experiment

The Chemistry of Micrometeoroids Experiment (LDEF instrument A0187-1) exposed witness plates of high-purity gold (greater than 99.99 percent Au) and commercial aluminum (greater than 99 percent Al) with the objective of analyzing the residues of cosmic-dust and orbital-debris particles associated with hypervelocity impact craters. The gold substrates were located approximately 8 deg off LDEF's trailing edge (Bay A03), while the aluminum surfaces resided in Bay A11, approximately 52 deg from LDEF's leading edge. SEM-EDX techniques were employed to analyze the residues associated with 199 impacts on the gold and 415 impacts on the aluminum surfaces. The residues that could be analyzed represent natural or man-made materials. The natural particles dominate at all particle sizes less than 5 micron. It is possible to subdivide both particle populations into subclasses. Chondritic compositions dominate the natural impactors (71 percent), followed by monomineralic, mafic-silicate compositions (26 percent), and by Fe-Ni rich sulfides (approximately 3 percent). Approximately 30 percent of all craters on the gold collectors were caused by man-made debris such as aluminum, paint flakes, and other disintegrated, structural and electronic components. Equations-of-state and associated calculations of shock stresses for typical LDEF impacts into the gold and aluminum substrates suggest that substantial vaporization may have occurred during many of the impacts and is the reason why approximately 50 percent of all craters did not contain sufficient residue to permit analysis by the SEM-EDX technique. After converting the crater diameters into projectile sizes using encounter speeds typical for the trailing-edge and forward-facing (Row 11) directions, and accounting for normalized exposure conditions of the CME collectors, we derived the absolute and relative fluxes of specific projectile classes. The natural impactors encounter all LDEF pointing directions with comparable, modal frequencies suggesting compositional (and dynamic) homogeneity of the interplanetary-dust environment in near-Earth orbit

A new method for the synthesis of hydrophobized, catalytically active Pt nanoparticles

This is the published version. Copyright © The Royal Society of Chemistry 2002A single step method for the synthesis of catalytically active, hydrophobic Pt nanoparticles by the spontaneous reduction of aqueous PtCl62− ions by hexadecylaniline molecules at a liquid–liquid interface is described