High-density Particles Research Articles

Assembly along lines in boundary-driven dynamical system

We introduce a simple dynamical rule in which each particle locates a particle that is farthest from it and moves towards it. Repeated application of this algorithm results in the formation of unusual dynamical patterns: during the process of assembly the system self-organizes into slices of low particle density separated by lines of increasingly high particle density along which most particles move. As the process proceeds, pairs of lines meet and merge with each other until a single line remains and particles move along it towards the zone of assembly. We show that this pattern is governed by particles (attractors) situated on the instantaneous outer boundary of the system and that both in two and in three dimensions the lines are formed by zigzag motion of a particle towards a pair of nearly equidistant attractors. This novel line-dominated assembly is very different from the local assembly in which particles that move towards their nearest neighbors produce point-like clusters that coalesce into new point-like clusters, etc.

Advances in interferometric techniques for the analysis of the three-dimensional flow in a lid-driven cylindrical cavity

In this work, a qualitative and quantitative characterization of the three-dimensional flow in a lid-driven cylindrical cavity with different optical techniques is presented. Mach–Zehnder interferometry and photographic techniques have been used for a qualitative description of some flow features. However, the real challenge is to obtain quantitative measurements, as the cavity dimensions and geometry prevent the application of 3D digital techniques for measuring the flow velocity in the whole cavity with enough spatial resolution. Digital in-line holography was applied to the measure of the vortex-breakdown bubble that appears near the cavity bottom at Re = 2000. A 22 × 22 × 80 mm3 volume was recorded, its longest dimension parallel to the camera optical axis. This large volume in a liquid fluid combined with a high particle density forces us to develop new analysis strategies. Holograms have been analyzed using a new method, called Adaptive Cross Correlation with Tracking From Beginning, which includes the use of the reconstructed complex amplitude for particle localization. Particle tracking is based on the three-dimensional cross correlation of three-dimensional interrogation windows. The particle set defined in the first hologram is always used to find the particle position in subsequent holograms. This method provides an accurate 3D velocity map and the vortex-breakdown bubble spatial structure. Experimental and numerical data show a very good agreement. A new criterion for determining the accuracy in the particle position along the optical axis is introduced, achieving a spatial resolution of 0.1 mm. This tracking method can be applied not only to laminar flows but also to turbulent flows.

Design and numerical modeling of the thermoforming process of a WPC based formwork structure

In this study, we have explored the numerical modelling of the thermoforming of high-density polyethylene wood particle composites (WPC) into a formwork intended for construction applications. By using the parameters identified from oscillatory shear test, the Lodge model is used to describe the viscoelastic behavior of the WPC sheet. The forming stage of the WPC sheet is performed under the action of gas flow governed by the van der Waals equation of state. The thermoformability is firstly determined by simulating a free blowing of HDPE and highly charged WPC. Then, the numerical simulation of the formwork thermoforming is carried out on four types of WPC. The results have shown that the structure is subjected to increasing stress as the wood particle content increases, which consequently increases the risk of failure. Nevertheless, thermoforming is possible for WPC sheets with less than 40 % wood content. Simulations of the formwork under loadings have also shown good mechanical resistance at low thicknesses.

Microstructure and mechanical properties of oxide dispersion strengthened FeCoNi concentrated solid solution alloys

Microstructure and mechanical properties of two kinds of oxide dispersion strengthened concentrated solid solution alloys (CSAs), FeCoNi-1.5Y2O3 (FCNY) and FeCoNi-1.2Ti-1.5Y2O3 (FCNTY), are studied through a comparing investigation with FeCoNi (FCN) CSAs. All these alloys are fabricated by mechanical alloying, spark plasma sintering, hot rolling and annealing treatment. For three kinds of alloys, both the as-milled powders and bulk materials are of single face-centered cubic structure. Electron backscattered diffraction results reveal that the texture transformation is suppressed during the hot rolling process because the movement of grain boundaries is hindered by the oxide particles. Compared with FCN CSAs, grains are refined by 43% and 47% for FCNY and FCNTY CSAs, respectively. Nano-sized Y2O3 (monoclinic structure) and Y2Ti2O7 (pyrochlore structure) particles are uniformly distributed in FCNY and FCNTY CSAs, respectively. Both Y2O3 and Y2Ti2O7 particles show a semi-coherent relationship with the matrix. Yield strength of FCN, FCNY and FCNTY CSAs is 559, 981 and 1050 MPa, respectively. Theoretical calculations illustrate that high strength of FCNY and FCNTY CSAs comes from refined grains and high-density nano-sized oxide particles.

DVC analysis of a polymer material subjected to tensile loading with synchrotron radiation tomography

Subsurface deformation behavior of a polymeric material is studied through the digital volume correlation (DVC) technique. Fundamental principles of the DVC technique are presented and the supplemental state-of-the-art algorithmic schemes to improve the efficiency and accuracy of the DVC analysis are also introduced. Tensile tests on an epoxy material are performed in conjunction with synchrotron radiation tomography. In order to create randomly distributed grayscale values in the tomograms for the following image analysis, microscale high-density particles are embedded when the epoxy specimens are fabricated. 3D tomographic images taken at multiple loading steps are utilized for the DVC analysis. The performance of the present DVC analysis is evaluated with the experimental data.

OH Production and Jet Length of an Atmospheric-Pressure Plasma Jet for Soft and Biomaterial Treatment

Atmospheric-pressure plasma jets (APPJs) are currently being studied and developed for the biomedical, chemistry, and physics communities because of their ability to produce desirable reactive species at low temperatures and at atmospheric pressures. Due to the high particle densities, small scales, and nonequilibrium nature of these plasmas, they can be difficult to predict and compare across devices. In this article, a plasma jet is operated over a range of conditions and characterized by using optical emission spectroscopy (OES) and synchronized imaging. The effect of the operating conditions on the gas temperature, jet length, plasma formation, and reactive species produced is reported. The jet is intended for the treatment of soft polymer and bio materials; thus, OH emissions were focused upon. It was found that OH production is dependent on gas flow and plasma density, while reactive nitrogen species are dependent on the plasma interaction with the surrounding air. In general, increasing voltage and frequency resulted in an increase of the reactive species produced. Higher flow rates increase the OH production, while lower flow rates improve the production of reactive nitrogen species. Higher flow rates and voltages also increase the jet length. The presence of each species is additionally dependent on the location relative to the plasma jet. The OH emissions decrease as the distance from the plasma source increases.

Vertical Distribution of Microplastics in the Water Column and Surficial Sediment from the Milwaukee River Basin to Lake Michigan.

Microplastic contamination was studied along a freshwater continuum from inland streams to the Milwaukee River estuary to Lake Michigan and vertically from the water surface, water subsurface, and sediment. Microplastics were detected in all 96 water samples and 9 sediment samples collected. Results indicated a gradient of polymer presence with depth: low-density particles decreased from the water surface to the subsurface to sediment, and high-density particles had the opposite result. Polymer identification results indicated that water surface and subsurface samples were dominated by low-density polypropylene particles, and sediment samples were dominated by more dense polyethylene terephthalate particles. Of the five particle-type categories (fragments, films, foams, pellets/beads, and fibers/lines), fibers/lines were the most common particle-type and were present in every water and sediment sample collected. Fibers represented 45% of all particles in water samples and were distributed vertically throughout the water column regardless of density. Sediment samples were dominated by black foams (66%, identified as styrene-butadiene rubber) and to a lesser extent fibers/lines (29%) with approximately 89% of all of the sediment particles coming from polymers with densities greater than 1.1 g cm-3. Results demonstrated that polymer density influenced partitioning between the water surface and subsurface and the underlying surficial sediment and the common practice of sampling only the water surface can result in substantial bias, especially in estuarine, harbor, and lake locations where water surface concentrations tend to overestimate mean water column concentrations.

Transplanting Fecal Virus-Like Particles Reduces High-Fat Diet-Induced Small Intestinal Bacterial Overgrowth in Mice.

Fecal microbiota transplantation (FMT) is an effective tool for treating Clostridium difficile infection in the setting of dysbiosis of the intestinal microbiome. FMT for other forms of human disorders linked to dysbiosis have been less effective. The fecal microbiota contains a high density of virus-like particles (VLP), up to 90% of which are bacteriophages, thought to have a role in regulating gut bacterial populations. We hypothesized that transplantation of the phage-containing fecal VLP fraction may reduce bacterial density in the dysbiotic setting of small intestinal bacterial overgrowth (SIBO). In an experiment using fecal transplantation, we compared the effect of the fecal VLP fraction (bacteria removed) against “Whole” FMT (bacteria intact) on the ileal microbiome. Recipients were either treated with a 30-day high-fat diet (HFD) as a model of dysbiosis to induce SIBO or were on a standard diet (SD). We observed that transplantation of fecal VLPs from donors on a HFD was sufficient to alter the ileal microbiota, but the effect was dependent on diet of the recipient. In recipients on a HFD, ileal bacterial density was reduced. In recipients on a SD, the ileal microbiome transitioned toward the composition associated with a HFD. In both recipient groups, transplantation of fecal VLP fraction alone produced the same outcome as whole FMT. Neither treatment altered expression of antimicrobial peptides. These findings demonstrated a potential role of VLPs, likely phages, for modifying the gut microbiome during dysbiosis.

Uniaxial Deformation and Crazing in Glassy Polymer-Grafted Nanoparticle Ultrathin Films.

The deformation behavior of neat, glassy polymer-grafted nanoparticle (PGN) monolayer films is studied using coarse-grained molecular dynamics simulations and experiments on polystyrene-grafted silica. In both the simulations and experiments, apparent crazing behavior is observed during deformation. The PGN systems show a relatively more uniform, perforated sheet craze structure and significantly higher strain at break than reference homopolymers of the same length. Short chain, unentangled PGN monolayers are also simulated for comparison; these are brittle and break apart without crazing. The entangled PGN simulations are analyzed in detail for systems at both high and moderate graft density. Stress-strain curves show three distinct regions: yielding and strain localization, craze widening, and strain hardening preceding catastrophic failure. The PGN stress-strain behavior appears more similar to that of longer chain, highly entangled homopolymer films than to the reference homopolymer films of the same length as the graft chains, suggesting that the particles effectively add additional entanglement points. The moderate graft density particles have higher strain-to-failure and maximum stress than the high graft density particles. We suggest this increased robustness for lower graft density systems is due to their increased interpenetration of graft chains between neighboring particles, which leads to increased interparticle entanglements per chain.

Particle image velocimetry validation for quantifying bedload movement

A Particle Image Velocimetry (PIV) technique was validated for predicting movements of bedload particles. Synthetic images, similar to those from testing a physical model, were created with different image particle densities and particle displacements. A set of surface particles were digitally moved by rotating and translating them on top of a layer of stationary particles to replicate the mobile-bed layer in the physical model. The images were processed using PIV software and performance of the software to measure these movements was evaluated. The effect of image particle density, particle displacement, and interrogation window size on the PIV software performance was investigated. Study results showed that all investigated variables had a significant effect on the predicted velocities. Guidelines are provided for application of PIV to bedload transport based on study results. Optimum bedload velocity predictions were found with the combination of highest particle density and highest particle displacements.

Hollow Multihole Carbon Bowls: A Stress-Release Structure Design for High-Stability and High-Volumetric-Capacity Potassium-Ion Batteries.

Potassium-ion batteries are potential alternatives to lithium-ion batteries for large-scale energy storage considering the low cost and high abundance of potassium. However, it is challenging to obtain stable electrode materials capable of undergoing long-term potassiation/depotassiation due to the high accumulated stress associated with the huge volume variation of the electrode. Here, we simulate the von Mises stress distributions of four different carbon three-dimensional models under an isotropic initial stress by the finite element method and reveal the critical role of the structure of a hollow multihole bowl on the strain-relaxation behavior. In this regard, nitrogen/oxygen codoped carbon hollow multihole bowls (CHMBs) are synthesized via hydrothermal carbonization coupled with an emulsion-templating strategy using biomass as the carbon source. Consistent with our simulation results, the CHMB anode remains stable for over 1000 cycles and delivers a high reversible capacity of 304 mAh g-1 at 0.1 A g-1. In addition to the reduced stress accumulation, the good electrochemical performances are also attributed to the surface capacitive mechanism and the shortened electron/ion transport distance in CHMBs. In particular, the CHMB composite electrode has a volumetric specific capacity 56% higher than that of hollow spheres due to the high tapped density of the bowl-shaped particles.

Effect of Sc addition on the microstructure, mechanical properties, and damping capacity of Al–20Zn alloy

In this study, hot rolling (HR), solid solution treatment (ST), and friction stir processing (FSP) were applied to Al–20Zn and Al–20Zn–0.5Sc alloys to obtain their elongated, coarsened, and fine-equiaxed grain structures. Sc addition refined the grains of Al–20Zn alloys in any state. The dynamic precipitation during deformation, such as HR and FSP, was promoted by the Al3Sc phase in the alloy containing Sc. The strength of Al–20Zn alloy was improved by Sc addition. Furthermore, a reasonable ductility was obtained in the ST sample when added with Sc. The fine grains and high density of Al3Sc particles with grain boundary pinning effect resulted in increased high-temperature internal friction value and excellent damping stability of the HR and FSP Al–20Zn–0.5Sc samples.

Soil genesis, mineralogy and chemical composition in a steatite outcrop under tropical humid climate in Brazil

Steatite is a metamorphic, ultramafic rock composed by talc, serpentine, magnetite and other unique minerals. Soils developed from this rock is typically unproductive due to high Mg and low P contents, high concentrations of heavy metals, and the extent of such limitations in the humid tropics is still poorly known. Here, we aimed to study pedogenesis, morphology and composition of eight soils formed from steatite in Minas Gerais, Brazil. These soils were a) Lithic Udorthents (3 pedons); b) Oxic Dystrudepts (2 pedons); and c) Acrudoxes (3 pedons). All soils presented high particle density but low bulk density due to high packing void porosity associated to granular structure. Soil pH and exchangeable Mg+2 were relatively high, whereas Mehlich-I P and exchangeable Al+3 were very low. X-ray fluorescence data showed that Entisols and Inceptisols have high (94 a 200 g kg−1) MgO contents, whereas Oxisols are highly enriched in Fe2O3, although still bearing MgO contents as high as 30 g kg−1. The Entisols and Inceptisols were mostly composed by talc, but also had Fe oxides and small amounts of kaolinite, whereas the dusky red Oxisols contained mostly hematite. Although present in the parent material, serpentine was not detected in soils. The considerable amounts of MgO in Oxisols can be explained by rock fragments preserved by a dark Fe oxide coating, visible in thin sections. Magnetic susceptibility was high and increased strongly with increasing weathering stage. Local topography strongly controlled soil formation and composition, which allowed for the existence of three climax vegetations: canyon cloud forest, semi-deciduous forest and savanna, suggesting that soil limitations to native plants are lower than expected.

Supported Catalyst Deactivation by Decomposition into Single Atoms Is Suppressed by Increasing Metal Loading.

In the high-temperature environments needed to perform catalytic processes, supported precious metal catalysts severely lose their activity over time. Even brief exposure to high temperatures can lead to significant losses in activity, which forces manufacturers to use large amounts of noble metals to ensure effective catalyst function for a required lifetime. Generally, loss of catalytic activity is attributed to nanoparticle sintering, or processes by which larger particles grow at the expense of smaller ones. Here, by independently controlling particle size and particle loading using colloidal nanocrystals, we reveal the opposite process as a novel deactivation mechanism: nanoparticles rapidly lose activity by high-temperature nanoparticle decomposition into inactive single atoms. This deactivation route is remarkably fast, leading to severe loss of activity in as little as ten minutes. Importantly, this deactivation pathway is strongly dependent on particle density and concentration of support defect sites. A quantitative statistical model explains how for certain reactions, higher particle densities can lead to more stable catalysts.

Fabrication and evaluation of electroplated Ni–diamond and Ni–B–diamond milling tools with a high density of diamond particles

Ni–diamond and Ni–B–diamond composite deposits were electroplated with a current density of 20 A/dm2 on a steel cylinder with a diameter of 6.0 mm in a Ni-Watt bath with different tetramethylammonium borohydride (TMAB) concentrations and 300-g/L synthetic diamond particles with sizes between 30 and 50 μm. Prior to Ni–diamond or Ni–B–diamond composite electroplating, a Ni undercoating with a thickness of 50 μm was electroplated on the steel cylinder. During composite electroplating, diamond particles were intermittently stirred with different stirring cycles in the plating bath. Experimental results show the distribution of diamond particles in the Ni or Ni–B deposit depends strongly on the stirring cycle. A composite deposit with a high diamond density can be achieved with intermittent stirring by using an on the period of 5 s and an off period of 80 s. From the results of milling test, an electroplated Ni–B–diamond milling tool with a high milling ability can be achieved after annealing at 300 °C or 500 °C for 30 min.

Improving the Flux Pinning With Artificial BCO Nanodots and Correlated Dislocations in YBCO Films Grown on IBAD-MgO Based Template

To improve the performance of high-temperature superconductors in electrical power systems, a modified IBAD-MgO based template is used as a substrate for the growth of YBa $_{2}$ Cu $_{3}$ O $_{6+x}$ (YBCO) doped with various concentrations of BaCeO $_{3}$ (BCO). The highest critical current density ( $J_\mathrm{c}$ ) in a wide applied field and angular range is realized in the films doped with 2 $\%$ and 4 $\%$ BCO content. This is explained to arise from the optimized BCO dopant concentration, which helps to immobilize more vortices both in low and high field ranges. Besides the vortex pinning by randomly distributed BCO nanoparticles, the edge-type dislocations, mainly occurring due to the underlying IBAD-MgO based template, are also a main source of pinning the vortices as seen by the appearance of $c$ -axis peak of $J_\mathrm{c} (\theta)$ in undoped and 2 $\%$ doped films. The disappearance of c-peak in films doped with higher concentration can be qualitatively explained by the vortex path model, where the paths of the vortices arising because of high density of BCO particles disguise the columnar type pinning effect coming from the threading dislocations within the films. Therefore, the BCO nanodots can be used for improving the flux pinning besides the threading dislocations in YBCO films on metal substrates.

Design and optimization of a medium flow differential mobility analyzer (MF-DMA) for classification of high-density particles

AbstractA new design of a Differential Mobility Analyzer (DMA) was tested with medium aerosol flow rates ranging from 1.5 to 10 slm and high-density particles. The vacuum-tight construction makes i...

Milling parameters of Al-Cu and Al-Si cast alloys

The work presented here was carried out on an Al-6%Cu-0.7%Si alloy (used in as cast, T5 and T7 aged conditions), in comparison with B319.0 (T7 by treated at the two places where treatment appears) and A356.0 (T6 treatment) alloys. Wet milling was carried out on 15 blocks of each alloy using new inserts for 120-m machining distance. A total of 75 blocks were employed. The results show that the cutting forces for the Al-Cu based alloys are not affected by the applied heat treatment. The presence of Cu in the B319.0 neutralized, to some extent, the harmful effect of the hard Si particles. Maximum cutting forces were obtained from machining the A356.0 alloy treated in the T6 condition, due to the presence of a high density of hard eutectic Si particles (~ 41500 particles/mm2), in addition to the dense precipitation of ultra-fine Mg2Si particles. Thus, the presence of 6%Cu in the Al-Cu-based alloy may act as a self-lubricant leading to much smoother finishing surfaces compared with those exhibited by B319.0 and A356.0 alloys. Similar observations were reported on the wearing of the drilling tools. Moreover, after 120-m machining distance, tiny burrs were found adhered to the outer edges of the workpiece, whereas burrs in the case of the A356.0 alloy were separated from the block.

Geometric frustration induces the transition between rotation and counterrotation in swirled granular media.

Granular material in a swirled container exhibits a curious transition as the number of particles is increased: At low densities, the particle cluster rotates in the same direction as the swirling motion of the container, while at high densities it rotates in the opposite direction. We investigate this phenomenon experimentally and numerically using a corotating reference frame in which the system reaches a statistical steady state. In this steady state, the particles form a cluster whose translational degrees of freedom are stationary, while the individual particles constantly circulate around the cluster's center of mass, similar to a ball rolling along the wall within a rotating drum. We show that the transition to counterrotation is friction dependent. At high particle densities, frictional effects result in geometric frustration, which prevents particles from cooperatively rolling and spinning. Consequently, the particle cluster rolls like a rigid body with no-slip conditions on the container wall, which necessarily counterrotates around its own axis. Numerical simulations verify that both wall-disk friction and disk-disk friction are critical for inducing counterrotation.

Two-Dimensional Nonclose-Packed Colloidal Crystals by the Electrostatic Adsorption of Three-Dimensional Charged Colloidal Crystals.

We demonstrate that nonclose-packed two-dimensional (2D) colloidal crystals fixed on flat solid surfaces can be obtained by the electrostatic adsorption of three-dimensional (3D) charged colloidal crystals onto oppositely charged substrates. 3D colloidal crystals of negatively charged polystyrene (diameter d = 500 nm) and silica (d = 510 and 550 nm) particles were formed in their aqueous dispersions. Then, a single layer of the 3D crystals (the particle volume fraction = ∼0.07-0.3) was adsorbed onto a glass surface, which was earlier modified with 3-aminopropyltriethoxysilane (APTES), a cationic silane coupling reagent. Under salt-free conditions, the lowermost layer of the 3D crystals, which was oriented parallel to the substrate, was adsorbed onto the substrate surface, forming 2D crystals. Centimeter-sized, large 2D silica crystals were produced by combining a unidirectional 3D crystallization of the silica colloid under a base concentration gradient and a unidirectional adsorption under an acidic concentration gradient, which allowed tuning of the charge number on the APTES-modified substrate. The interparticle separations of the resulted 2D crystals did not vary greatly (within 5%) over a large area (length: 2 cm); however, the separations were smaller than the initial value because of gravitational sedimentation. We also produced 2D crystals of gold particles (d = 250 nm), which we expect to be applicable as plasmonic materials. The present study will provide a facile strategy to produce nonclose-packed 2D colloidal crystals of various types of particles, including large and high-density particles.