Increasing Particle Density Research Articles

Mechanisms of grain refinement by intensive shearing of AZ91 alloy melt

It has been demonstrated recently that intensive melt shearing can be an effective approach to the grain refinement of both shape casting and continuous casting of Mg alloys. In the present study, the mechanisms of grain refinement by intensive melt shearing were investigated through a combination of both modelling and experimental approaches. The measurement of the cooling curves during solidification, quantification of grain size of the solidified samples, and image analysis of the MgO particle size and size distribution in the pressurized filtration samples were performed for the AZ91 alloy with and without intensive melt shearing. The experimental results were then used as input parameters for the free growth model to investigate the mechanisms of grain refinement by intensive melt shearing. The experimental results showed that, although intensive melt shearing does not change the nucleation starting temperature, it increases the nucleation finishing temperature, giving rise to a reduced nucleation undercooling. The theoretical modelling using the free growth model revealed quantitatively that intensive melt shearing can effectively disperse MgO particles densely populated in the oxide films into more individual particles in the alloy melt, resulting in an increase in the MgO particle density by three orders of magnitude and the density of active nucleating MgO particles by a factor of 20 compared with those of the non-sheared melt. Therefore, the grain refining effect of intensive melt shearing can be confidently attributed to the significantly increased refining efficiency of the naturally occurring MgO particles in the alloy melt as potent nucleation sites.

Particle collision frequency and particle density at equilibrium. Part 2

Using previously established relations based on particle collision frequency, a general equation for the change with time of particle density is presented. The equation is based on the supposition that the nano particle formation follows the mass interaction law, well known from the chemical kinetics. The solution of the equation in equilibrium conditions implies an exponential relation concerning the particle size distribution. Two possibilities exist: distribution with increasing particle density at increasing particle size and distribution with decreasing particle density at increasing particle size. At different values of atom density for the case of closed gas ambient, the size of the largest particle is determined. This allows determining the particle size distribution.

FUNDAMENTAL RESEARCH ON RADIOFREQUENCY ABLATION OF RAT BRAIN TISSUE BASED ON NEAR-INFRARED SPECTROSCOPY AND MIE THEORY

Near-infrared spectroscopy (NIRS) technology and Mie theory are utilized for fundamental research on radiofrequency ablation of biological tissue. Firstly, NIRS is utilized to monitor rats undergoing radiofrequency ablation surgery in real time so as to explore the relationship between reduced scattering coefficient ([Formula: see text]) and the degree of thermally induced tissue coagulation. Then, Mie theory is utilized to analyze the morphological structure change of biological tissue so as to explore the basic mechanism of the change of optical parameters caused by thermally induced tissue coagulation. Results show that there is a close relationship between [Formula: see text] and the degree of thermally induced tissue coagulation; the degree of thermal coagulation can be obtained by the value of [Formula: see text]; when biological tissue thermally coagulates, the average equivalent scattering particle decreases, the particle density increases, and the anisotropy factor decreases.

Influence of Temperature Evolution on Precipitation Behaviour of Second Phase Particles in Grain‐oriented Electrical Steels

AbstractA model concerning dynamic precipitation of second phase particles during hot deformation of conventional grain‐oriented electrical steels is proposed. The model involves the solid solubility of the elements forming MnS, the corresponding nucleation driving force, as well as the evolution of dislocation densities during hot deformation, which supplies sites for heterogeneous nucleation of MnS particles. The model describes the dynamic process in which temperature keeps decreasing and dislocation density keeps increasing. The influences of reheating temperature, initial rolling temperature, finishing temperature and deformation duration on the precipitation behaviour are involved. Calculations have been conducted based on the model, to simulate the precipitation behaviour of MnS particles during hot rolling of grain‐orientated electrical steels under different parameters. The results indicate that hot rolling is very important for dispersive precipitation of MnS particles. The increase of particle density is promoted by proper increase of reheating temperature or proper reduction of initial and finishing rolling temperature, in which the driving force and dislocation density are increased. The simulation results agree basically with the experimental observations in hot strip of a grain oriented electrical steel.

Structural Evolution of Colloidal Gels During Constricted Microchannel Flow

We investigate the structure of colloidal gels flowing through constrictions in microchannels using confocal microscopy. As the gel traverses the constricted region, both the average velocity and particle density increase downstream. While the average flow profile is smoothly varying, stagnation zones develop at the constriction entry, leading to markedly nonuniform local flow profiles. Dense clusters undergo shear-induced yielding at intercluster boundaries, which enhances the structural heterogeneity of the suspension at the constriction outlet.

Time-dependent currents of one-dimensional bosons in an optical lattice

We analyse the time dependence of currents in a one-dimensional (1D) Bose gas in an optical lattice. For a 1D system, the stability of currents induced by accelerating the lattice exhibits a broad crossover as a function of the magnitude of the acceleration, and the strength of the inter-particle interactions. This differs markedly from mean-field results in higher dimensions. Using the infinite time evolving block decimation algorithm, we characterize this crossover by making quantitative predictions for the time-dependent behaviour of the currents and their decay rate. We also compute the time dependence of quasi-condensate fractions which can be measured directly in experiments. We compare our results to calculations based on phase-slip methods, finding agreement with the scaling as the particle density increases, but with significant deviations near unit filling.

A novel β-cyclodextrin polymer/tungsten carbide composite matrix for expanded bed adsorption: Preparation and characterization of physical properties

Abstract A series of matrices named CroCD–TuC are prepared by the reversed-phase suspension crosslinking technique for expanded bed adsorption. The matrices have regular spherical shape, and follow logarithmic normal size distribution with the range of 80–320 μm and mean diameter of 143–168 μm. The densifier of tungsten carbide embedded within the β -cyclodextrin polymer skeleton causes a significant increase of particle density. The maximum wet density of matrices is 2.09 g cm −3 , which shows a potential for the operation in an expanded bed at high flow rate. The matrices also have suitable water content and pore properties for the chromatographic separation use. Moreover, the addition of tungsten carbide improves the rigidity of the matrices, which can tolerate high pressure at high flow rate and show low compressibility in the column. The new matrices can also be ionized in NaOH solution, which may provide some beneficial information for peculiar usage.

Growth Mechanism of Polypyrrole through Electrochemical Polymerization

It is important to reveal the growth mechanism of the conductive polymer upon electrochemical polymerization in order to control the morphology of the film as a shape of the conductive polymer. In this paper, the relation between the structure of the polypyrrole as the conductive polymer and the quantity of electricity during galvanostatic polymerization was studied with the microscopic observation. With the quantity of electricity in the current density of 0.75 to 7.5 A·m−2, a particle of polypyrrole grew up to 15 µm in size at maximum while the thickness of the polypyrrole film was increased accompanying a stagnant behaviour around 25 µm to some extent, indicating increase in packing density of the polypyrrole particles.

Experimental Study of the Effect of Particle Density on Mixing Behavior in a Spout-Fluid Bed

The particle mixing behavior has been investigated experimentally in a spout-fluid bed. The bed material used is polypropylene particles, and the tracer employed is chosen from silica gel, mung beans, and glass beads. During all experiments, the completely segregated arrangement of particles is adopted as the initial packing condition. The gas velocity varies to cover internal jet, minimum spouting, and fully developed spouting conditions, in order to establish a full mixing map about the effect of particle density. The mixing behavior is analyzed in terms of flow patterns, concentration profile, and mixing index. The results show that the degree and rate of mixing are significantly affected by the particle density, and heavier particles achieve a higher mixing rate but a poorer mixing quality. The mixing map reveals that to reach the same mixing index, the spouting gas velocity needs to increase with the increase of particle density. Besides, provided that the jet gas velocity does not exceed the minimum...

Limiting behaviour of particles in Taylor–Couette flow

Negatively buoyant inertial particles are tracked in a steady Taylor vortex background flow with gravity acting along the axis of the cylinders. Particles are found to either fall through the apparatus due to gravity or to be within retention zones. The particles within these retention zones tend towards a limit orbit in the meridional plane. It is found that for particles with density close to that of the background fluid, the size of the retention zone is relatively large with the centre of the limit orbit being close to that of the Taylor vortex. As the particle density increases, the size of the retention zone decreases and the centre of the limit orbit moves away from the centre of the Taylor vortex. The effect of varying the fluid and particle parameters on the retention zone and orbit size is investigated.

Traffic of indistinguishable particles in complex networks

In this paper, we apply a simple walk mechanism to the study of the traffic of many indistinguishable particles in complex networks. The network with particles stands for a particle system, and every vertex in the network stands for a quantum state with the corresponding energy determined by the vertex degree. Although the particles are indistinguishable, the quantum states can be distinguished. When the many indistinguishable particles walk randomly in the system for a long enough time and the system reaches dynamic equilibrium, we find that under different restrictive conditions the particle distributions satisfy different forms, including the Bose–Einstein distribution, the Fermi–Dirac distribution and the non-Fermi distribution (as we temporarily call it). As for the Bose–Einstein distribution, we find that only if the particle density is larger than zero, with increasing particle density, do more and more particles condense in the lowest energy level. While the particle density is very low, the particle distribution transforms from the quantum statistical form to the classically statistical form, i.e., transforms from the Bose distribution or the Fermi distribution to the Boltzmann distribution. The numerical results fit well with the analytical predictions.

Sequential density fractionation across soils of contrasting mineralogy: evidence for both microbial- and mineral-controlled soil organic matter stabilization

Sequential density fractionation separated soil particles into “light” predominantly mineral-free organic matter vs. increasingly “heavy” organo-mineral particles in four soils of widely differing mineralogy. With increasing particle density C concentration decreased, implying that the soil organic matter (OM) accumulations were thinner. With thinner accumulations we saw evidence for both an increase in 14C-based mean residence time (MRT) of the OM and a shift from plant to microbial origin.Evidence for the latter included: (1) a decrease in C/N, (2) a decrease in lignin phenols and an increase in their oxidation state, and (3) an increase in δ13C and δ15N. Although bulk-soil OM levels varied substantially across the four soils, trends in OM composition and MRT across the density fractions were similar. In the intermediate density fractions (~1.8–2.6 g cm−3), most of the reactive sites available for interaction with organic molecules were provided by aluminosilicate clays, and OM characteristics were consistent with a layered mode of OM accumulation. With increasing density (lower OM loading) within this range, OM showed evidence of an increasingly microbial origin. We hypothesize that this microbially derived OM was young at the time of attachment to the mineral surfaces but that it persisted due to both binding with mineral surfaces and protection beneath layers of younger, less microbially processed C. As a result of these processes, the OM increased in MRT, oxidation state, and degree of microbial processing in the sequentially denser intermediate fractions. Thus mineral surface chemistry is assumed to play little role in determining OM composition in these intermediate fractions. As the separation density was increased beyond ~2.6 g cm−3, mineralogy shifted markedly: aluminosilicate clays gave way first to light primary minerals including quartz, then at even higher densities to various Fe-bearing primary minerals. Correspondingly, we observed a marked drop in δ15N, a weaker decrease in extent of microbial processing of lignin phenols, and some evidence of a rise in C/N ratio. At the same time, however, 14C-based MRT time continued its increase. The increase in MRT, despite decreases in degree of microbial alteration, suggests that mineral surface composition (especially Fe concentration) plays a strong role in determining OM composition across these two densest fractions.

Galactic cosmic ray distribution in the simplest model of termination shock near the heliospheric boundaries

The termination shock at the heliospheric boundary is simulated in terms of a two-layer turbulent medium for which the average radial component of solar wind velocity is nonzero inside the heliosphere and zero for external magnetic inhomogeneities. Galactic cosmic rays (GCRs) are scattered more strongly in the solar wind than in the interstellar medium. A boundary value problem for density is defined to describe GCR propagation in the given two-layer medium. The exact analytical solution of it is derived. The phase density and GCR fluxes in the whole range of the particle energies, as well as the degree of anisotropy of high-energy GCRs, are determined. The qualitative agreement of theoretical calculations and observed GCR distributions is obtained. In particular, in the region near the termination shock, an increase in the high-energy particle density and a decrease in the low-energy particle density are observed.

Partitioning of organic matter in continental margin sediments among density fractions

Hydrodynamic processes sort and redistribute organic matter (OM) and minerals on continental margins. Density fractionations were conducted on sediments from diverse margins (Mexico margin, Gulf of Mexico, Mississippi River delta, Eel River margin) to investigate the nature, provenance and age of OM among density fractions. Mass, elemental (C and N), lignin, and surface area distributions, as well as stable carbon and radiocarbon isotopic compositions were measured. The lowest density fractions (< 1.6 g cm − 3 ) contained the highest organic carbon (OC) (up to 45%) and lignin concentrations (up to 8 mg g − 1 ) due to abundant woody debris, whereas high density fractions (> 2.5 g cm − 3 ) were OC-poor (%OC < 0.5) mineral material. Most sediment mass was found in the mesodensity fractions (1.6 to 2.5 g cm − 3 ) that contained the highest proportion of OC (up to ~ 75%) for each sediment. Stable carbon isotope compositions (δ 13C − 25.5‰ to − 22.9‰) show terrigenous OC as a significant component of density isolates from the river-dominated sediments (Gulf of Mexico, Mississippi River, and Eel margin), whereas the Mexico margin, least influenced by riverine input, was dominated by autochthonous marine OC (δ 13C ~ − 21.5‰). Radiocarbon compositions of density fractions indicate significant pre-aged OC (Δ 14C as low as − 900‰) in river-influenced sediments but not on the Mexico margin (Δ 14C > − 200‰). Ratios of vanillic acid to vanillin (Ad/Al)v among lignin oxidation products increase with increasing particle density suggesting variable lignin sources or selective degradation of lignin among the different density fractions.

Changes in soil physical properties of forest floor horizons due to long-term deposition of lignite fly ash

From the beginning of the twentieth century until the 1990s, energy in Upper Lusatia, Saxony in Eastern Germany was produced at power plants that burnt lignite coals. As a result, alkaline fly ash and aerosols from the combustion of brown coal have accumulated in adjacent areas that are partly under forestry. We ask the question, “how have these atmospheric depositions of fly ash influenced the soil physical properties (bulk density, particle density, saturated hydraulic conductivity, pore size distribution, and water repellency) of forest floor horizons?” The experimental sites represented typical soil types and stands of the sylviculturally used areas in the region of Upper Lusatia. Three forest sites were located close to the emission sources, where high amounts of fly ashes accumulated, and three control sites were without fly ash enrichment. Pore size distribution, saturated hydraulic conductivity, and bulk density were examined with undisturbed samples (metal cylinder 100 cm³). Disturbed samples were used for the characterization of particle density, texture, and water repellency (Wilhelmy plate method). Additionally, the carbon content was determined. Scanning electron microscopy was used to show fly ash enrichment. The enrichment of mineral fly ash particles could be proven for sites close to the emission source. Using scanning electron microscopy, spherical fly ash particles could be identified. Total quantities of persistent fly ash enrichment amounted to approximately 150-280 Mg ha–1. The enrichment of fly ash affected the soil-physical characteristics. Close to the emission source (sandy fly ashes), particle density, air capacity, and saturated hydraulic conductivity were significantly increased, whereas the plant available water was significantly reduced. With increasing distance from the emission source (silty fly ashes or no ash enrichment), air capacity and saturated hydraulic conductivity were reduced, while an increase of plant available water was observed. Furthermore, the forest floor horizons close to the emission source were characterized by significantly reduced water repellency due to the dominance of hydrophilic mineral fly ash particles. Fly ash deposition in Upper Lusatia must be considered as relevant for properties of forest soils. Mean particle density was significantly higher at sites with fly ash accumulation. This indicates the admixture of mineral particles. While bulk densities were not noticeably influenced, the increase of particle density and the dominance of sandy to coarse silty particles close to the emission sources cause an increase in total porosity, air capacity, and a relative reduction of plant available water. Hollows in spherical fly ash particles might contribute to the meso- and macropores. Due to the admixture of hydrophilic fly ash, the enriched forest floor horizons feature a distinct increase in potential wettability, which coincides with a higher pore and, hence, nutrient and contaminant accessibility. In combination with a higher saturated hydraulic conductivity, an increase in translocation of dissolved substances can be expected especially in the course of acidification, which causes an additional mobilization of nutrients and contaminants. With this study, we could prove the impact of fly ash enrichment on physical soil properties of forest floor horizons. Via SEM, we detected fly ash particles. The amounts of persistent fly ash accumulation could modify particle density, thickness, bulk density, and carbon content. To characterize hydraulic properties, we investigated the pore size distribution, the saturated hydraulic conductivity, and a water repellency parameter. Thereby, we detected a distinct increase of coarse pores and an accompanying extremely high saturated hydraulic conductivity. The water repellency parameter indicated a significant decrease of hydrophobicity of fly-ash-enriched forest floor horizons. Fly ash enrichment in forest floor horizons not only causes distinct chemical modifications but also alters soil physical properties, which must be considered in further hydrological investigations, as they may influence seepage of water and contaminant translocation within the soil and into groundwater.

Performance of expanded polystyrene particles in deep bed filtration

The efficiency of filtration through a bed of expanded polystyrene (EPS) of different characteristics was investigated on the example of separation of iron hydroxide flocks from water. The effects studied included the EPS density, bed equivalent diameter, and bed uniformity coefficient. Studies by scanning electron microscopy showed that surface roughness of EPS particles is primarily determined by particle density. Low-density EPS particles have higher roughness than the high-density ones, and this fact has a great effect on the filtration cycle. Low-density particles yield a low head loss and long filtration cycle, which decrease with increasing particle density. As far as the bed equivalent diameter is concerned, only a small increase in particle size of the existing particle formulation decreases significantly the filtration cycle. It is very important to notice that similar bed equivalent diameter can be achieved by mixing different particle fractions, changing at the same time the uniformity coefficient. That is the reason why we investigated the effect of uniformity coefficient and showed that there exists its optimum value, yielding a maximum filtration cycle. Our investigation showed that the uniformity coefficient is of crucial importance in the optimization of EPS bed filtration.

The catalytic effect of Pt nanoparticles supported on silicon oxide nanowire

3.5 nm sized Pt nanocatalysts supported on silicon oxide nanowires (SiOXNWs) were fabricatedby decorating the SiOXNWs with Pt nanoparticles using a simple physical deposition system without anysurface pretreatment. High curvature of the nanowire surface together withthe weak metal–substrate interaction helped to maintain discrete particlemorphology with spherical shapes during deposition. Catalytic efficiency of theSiOXNWs coated with Pt nanoparticles was demonstrated through reduction of methylene blue in thepresence of sodium borohydride. It was demonstrated that the highly curved nanowiresurface allowed the Pt nanoparticles to be loaded with increased particle density, providinga larger surface area for the catalytic reaction. It was also shown that a simple heattreatment in vacuum improves the effectiveness of the Pt nanoparticles as a catalystwithout loss of catalytic activity when used repeatedly. We expect that this metalnanoparticle-decorated nanowire can be easily extended to other heterogeneous reactionsand can also be used as a template for building three-dimensional hierarchicalnanostructures.

Effects of charged dust particles on nonlinear ion acoustic solitary waves in a relativistic plasma

Effects of dust charges on the nonlinear ion acoustic solitary waves in a fully relativistic dusty plasma for both cases of negative and positive dusts are numerically studied based on the pseudopotential method. In the presence of dusty particles, it is found that various types of nonlinear acoustic waves exist in forms which can be viewed as sequential combinations of three kinds of elementary solitary waves: bump, dip, and kink-type solitary waves. The number and the sequence of the constituent elementary solitary waves in a given nonlinear waves depend more sensitively on dust particle density than any other parameters. For negatively charged dust particles of low density, the nonlinear wave is in the shape of bumpy solitary wave. For a somewhat higher density, the wave changes into a form which can be viewed as a combination of bump and dip-type solitary waves. As the density is increased further, a more complex nonlinear wave composed of bump, kink, and dip-type solitary waves emerges. For a much higher density of dust particle, the nonlinear wave can have a shape that can be considered as a combination of bump and kink-type solitary waves. For the case of positively charged dust particles, two kinds of nonlinear waves can exist: bump-type solitary wave and a combination of bump and kink solitary waves. For both cases of negative and positive dust particles, it is found that single dip-type solitary wave does not exist. It is also found that as dust particle density increases, the signature of the elementary waves becomes less prominent.

Infectious bursal disease virus is an icosahedral polyploid dsRNA virus

Viruses are a paradigm of the economy of genome resources, reflected in their multiplication strategy and for their own structure. Although there is enormous structural diversity, the viral genome is always enclosed within a proteinaceous coat, and most virus species are haploid; the only exception to this rule are the highly pleomorphic enveloped viruses. We performed an in-depth characterization of infectious bursal disease virus (IBDV), a non-enveloped icosahedral dsRNA virus with a bisegmented genome. Up to 6 natural populations can be purified, which share a similar protein composition but show higher sedimentation coefficients as particle density increases. Stoichiometry analysis of their genome indicated that these biophysical differences correlate with the copy number of dsRNA segments inside the viral capsid. This is a demonstration of a functional polyploid icosahedral dsRNA virus. We show that IBDV particles with greater genome copy number have higher infectivity rates. Our results show an unprecedented replicative strategy for dsRNA viruses and suggest that birnaviruses are living viral entities encompassing numerous functional and structural characteristics of positive and negative ssRNA viruses.

A coupled DEM/CFD analysis of the effect of air on powder flow during die filling

AbstractDie filling from a stationary shoe in a vacuum and in the presence of air was numerically analyzed using an Eulerian‐Lagrangian model, which employs a discrete element method (DEM) for the particles and computational fluid dynamics (CFD) for the air with a two‐way air‐particle interaction coupling term. Monodisperse and polydisperse powder systems have been simulated to explore the effect of the presence of air on the die filling process. For die filling with monodisperse powders, the influences of particle size and density on the flow behavior were explored. The numerical simulations revealed that the presence of air has a significant impact on the powder flow behavior, especially for systems with smaller and/or lighter particles. Flow has been characterized in terms of a dimensionless mass flow rate, and it has been shown that for die filling in a vacuum this is constant. The flow characteristics for die filling in air can be classified into two regimes. There is an air‐inert regime in which the particle size and density are sufficiently large that the effect of air flow becomes negligible, and the dimensionless mass flow rate is essentially identical to that obtained for die filling in a vacuum. There is also an air‐sensitive regime, for smaller particle sizes and lower particle densities, in which the dimensionless mass flow rate increases as the particle size and density increase. The effects of particle‐size distribution and adhesion on the flow behavior have also been investigated. It was found that, in a vacuum, the dimensionless mass flow rate for polydisperse systems is nearly identical to that for monodisperse systems. In the presence of air, a lower dimensionless mass flow rate is obtained for polydisperse systems compared to monodisperse systems, demonstrating that air effects become more significant. Furthermore, it has been shown that, as expected, the dimensionless mass flow rate decreases as the surface energy increases (i.e., for more cohesive powders). © 2008 American Institute of Chemical Engineers AIChE J, 2009