High-density Particles Research Articles

Influence of dust particles on the bulk electron density in radio frequency plasmas measured by microwave interferometry

The influence of dust particles, inserted in the rf plasma sheath of a capacitively coupled argon plasma, on the bulk electron density is investigated. The line integrated electron density has been measured using 160 GHz Gaussian beam microwave interferometry. A significant electron density increase compared to the dust free plasma was observed for high number densities of larger dust particles (d=12.3 μm). Furthermore, the rising electron density is combined with increasing optical plasma emission. For smaller dust particles (d=3.6 μm), no clear effect, but a tendency to a weak electron density reduction, was found. The results are compared to previous simulations of the impact ionization and excitation in dusty plasmas.

Coherent cyclotron motion beyond Kohn’s theorem

In solids, the high density of charged particles makes many-body interactions a pervasive principle governing optics and electronics[1-12]. However, Walter Kohn found in 1961 that the cyclotron resonance of Landau-quantized electrons is independent of the seemingly inescapable Coulomb interaction between electrons[2]. While this surprising theorem has been exploited in sophisticated quantum phenomena[13-15] such as ultrastrong light-matter coupling[16], superradiance[17], and coherent control[18], the complete absence of nonlinearities excludes many intriguing possibilities, such as quantum-logic protocols[19]. Here, we use intense terahertz pulses to drive the cyclotron response of a two-dimensional electron gas beyond the protective limits of Kohn's theorem. Anharmonic Landau ladder climbing and distinct terahertz four- and six-wave mixing signatures occur, which our theory links to dynamic Coulomb effects between electrons and the positively charged ion background. This new context for Kohn's theorem unveils previously inaccessible internal degrees of freedom of Landau electrons, opening up new realms of ultrafast quantum control for electrons.

An ultrastructural study of Trichophyton rubrum induced onychomycosis.

BackgroundTrichophyton rubrum (T.rubrum) caused onychomycosis is the most common nail fungal disease. The common diagnostic methods are direct microscopic examination and fungal culture. In this study we used scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to study the subungual ultrastructural changes in T. rubrum induced onychomycosis.MethodsSix outpatients with onychomycosis were recruited and T.rubrum infection was confirmed by fungal culture. Six toenail samples were collected and prepared for SEM characterization. The cultured fugal colonies were prepared for SEM and TEM characterization.Results1) SEM showed significant structural damages and the formation of a thin layer or a single layer of keratinocytes in all infected nail plates. Hyphae (piercing or penetrating keratinocytes layers), arthrospores and local bacterial aggregation were observed on the ventral surface of the nail plates. 2) SEM of the cultured fungal colony showed relatively straight, highly branched hyphae and microconidias; TEM showed branching hyphae that were composed of double-layer cell walls. Hyphae had nucleus, mitochondria, liposomes, lysosomes, scattered rough endoplasmic reticulum, myeloid bodies and aggregated ribosomes. There were high-density particles outside the hyphae.ConclusionSEM showed a large number of hyphae penetrated the keratinocytes layer, suggesting that T. rubrum can cause severe damage to the stratum corneum. TEM showed the ultrastructural features of T. rubrum-induced infection before treatment.

CFD simulation of viscosity modifier effect on cutting transport by oil based drilling fluid in wellbore

In this study particle transportation has been predicted in a wellbore for an oil based drilling fluid containing viscosity modifier using CFD simulation. The effects of fluid viscosity on particle transport capacity of fluid were studied by considering various particle parameters such as density, diameter, shape, and initial particle concentration and wellbore inclination through using the Algebraic Slip Mixture (ASM) model. Rheology of the drilling fluid was expressed by Herschel–Bulkley non-Newtonian fluid model. The influence of viscosifier concentration on fluid rheology show that it improves carrying capacity of particles but its effect attenuates in higher concentration. For 2 ppb of viscosifier in drilling fluid, the cutting transport capacity has been increased almost 12% whereas adding 4 ppb of viscosifier, only created about 14% escalation on the transportation of cuttings. Against this positive effect viscosity modifier make more pressure drop that was a costly effect for operation and this effect had constant rate (for each ppb viscosifier, pressure drop growth is equal to 200 kPa/m approximately). Also, the results indicate higher particle density or larger particle size results in less particles transportation in the wellbore. Increasing initial solid loading has an adverse impact on the transmission of solid particles in wellbore.

Density modification of ice particles in ice slurry

One of the characteristic properties of ice slurry is the buoyancy of ice particles, which leads to ice separation in unmixed ice slurries and the necessity to agitate storage vessels if ice slurry is to be extracted. Based on this, an investigation into the density modification of ice particles has been undertaken. Additional particles with higher density than ice should act as ice forming nuclei during ice generation, for which suitable particles have been determined and tested. It was possible to show that not all added particles act as ice forming nuclei in the role of a cell nucleus. Furthermore, it can be assumed that various particles agglomerate on the surface of ice particles; hence the density of ice particles increased more than expected due to the incorporation of several particles in each ice particle. These modified ice particles may sediment to the bottom of the container due to the high density of the numerous heavy foreign particles.

Obtaining and characterization of spherical particles—new biogenic platforms

The technique of obtaining spherical particles from rod-like plant virus, tobacco mosaic virus, in a preparative scale was developed. The conditions of tobacco mosaic virus isolation for obtaining spherical particles were selected. Spherical particles were examined by methods of electron microscopy, nanoparticle tracking analysis, and dynamic light scattering. Information about inner structure of spherical particles was obtained. High electron density of spherical particles was demonstrated. The analysis of ultrathin sections showed that spherical particles are homogenous within and do not contain any cavities.

Favorable effect of in-situ generated platinum in the membrane on fuel cell membrane durability

The overall lifetime of polymer electrolyte fuel cells is often determined by the membrane durability. Platinum, which may dissolve from the catalyst layers during fuel cell operation and deposit in the membrane, has been shown to have both positive and negative effects on membrane stability. In the present work, we analyze what specific conditions are required in order to reach a favorable, membrane stabilizing effect with the controlled use of platinum in the membrane. Using accelerated membrane durability testing, field operated membrane samples, and electron microscopy, we demonstrate that a high platinum concentration with specific particle shapes and sizes is essential for enhanced membrane stability. Specifically, star shaped and dendritic particles with high particle density and high surface area are shown to be preferable. These particles contain high levels of Pt(111) and are expected to have high catalytic activity toward peroxide quenching and crossover gas consumption, thereby mitigating chemical membrane degradation. On the other hand, small, dispersed cubic particles are found to have no effect or the opposite, negative effect on membrane stability.

3D localization of high particle density images using sparse recovery.

If particles are too close in space, their images may be overlapped when they are observed with microscopes because of diffraction limitation, which makes them difficult to be distinguished or localized. This limitation also affects the efficiency of localization of those single-particle-localization microcopies, such as stochastic optical reconstruction microscopy (STORM) and (fluorescence) photoactivated localization microscopy [(F)PALM]. In this work, we developed a 3D sparse recovery (3D-SR) method, with the aim of localizing particles with high density in three dimensions, which cannot be resolved using original STROM or (F)PALM. A cylindrical lens was introduced to a traditional wide-field microscope in order to form the 3D point spread function for 3D-SR. The performance of the 3D-SR method was evaluated using simulation. Simulated results demonstrated that, even for particle densities as high as 4 μm-2 on a transversal projection, particles could still be localized with high accuracy. The standard deviations were found to be 25.59nm along the transverse direction and 50.42nm along the axial direction. Compared with the existing 3D localization methods used in high particle density cases, such as 3D-DAOSTORM, 3D-SR allows a higher activated fluorophore density per frame.

Microstructures and grain refinement performance of Al–Ti–B–C grain refiner via powder metallurgy

The Al-5Ti-0.5B-0.5C grain refiner was prepared by powder metallurgy (PM). Microstructures of the grain refiner and its grain refinement performance in commercially pure aluminum (Al) were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). It is found that the average grain size of commercially pure Al can be reduced from ~15,000 to ~180 μm by the addition of Al-5Ti-0.5B-0.5C grain refiner prepared by PM, based on 0.01 wt% Ti addition. The grain refinement efficiency begins to decrease slightly when the grain refiner is kept in the melt for 60 min. The grain refinement is attributed to high stability, proper size, and high density of Al3Ti, TiB2, and TiC particles.

Characterization of particles suspended in a volume of optical medium at high concentrations by coherent image processing

We give a broad discussion of existing typical works devoted to particle image processing. We propose the approach based on the postprocessing of coherent images of the particles at various planes of the volume. These images can be obtained both by reconstruction of inline digital hologram and by means of defocussing of the lens with high numerical aperture. Processing of the reconstructed holograms or recorded images is carried out using the proposed image analysis approach based on the edge-point linking and thresholding technique, which is considered to be simple to implement and reliable. After the review of existing methods and approaches, we noted that, in general, only cases of low concentrations are considered and, therefore, we investigated the performance of our proposed approach for characterization of particles of high density in a volume of optical medium. In this study of the method, we increase the concentration of particles until we ensure that every volume element comprises many particle images, yet these images do not create a speckle pattern, and look for the concentrations at which normalized density distributions of the particles can be constructed with an acceptable error for us. It is shown that the proposed approach exhibits good results of recognition and allows investigation of high concentrations.

Advanced Performances of Full Concentration Gradient Li[Ni0.65Co0.08Mn0.27]O2 Cathode Materials for Lithium Ion Batteries

Full concentration gradient (FCG) cathode material which consists of Ni-rich core Li[Ni0.89Co0.01Mn0.10]O2 and Ni-less outer layer Li[Ni0.61Co0.09Mn0.30]O2 was synthesized by co-precipitation method.1,2 A gradually changing concentration gradients for Ni, Co, and Mn extended from the core to the surface within a single cathode particle with an average composition of Li[Ni0.65Co0.08Mn0.27]O2. We have evaluated electrochemical and thermal properties of the FCG cathode material and compared it with the conventional cathode (CC) material, Li[Ni0.65Co0.08Mn0.27]O2 without the concentration gradient. The BET surface area measurement demonstrated the presence of high-density primary particles in the FCG cathode material. The FCG cathode exhibited higher discharge capacity, excellent cycle retention and superior thermal stability compared to the CC Li[Ni0.65Co0.08Mn0.27]O2 cathode material.1

Trapping of interacting propelled colloidal particles in inhomogeneous media.

A trapping mechanism for propelled colloidal particles based on an inhomogeneous drive is presented and studied by means of computer simulations. In experiments this method can be realized using photophoretic Janus particles driven by a light source, which is partially blocked by a shading mask. This leads to an accumulation of particles in the passive part. An equation for an accumulation parameter is derived using the effective inhomogeneous diffusion constant generated by the inhomogeneous drive. The impact of particle interaction on the trapping mechanism is studied, as well as the interplay between passivity-induced trapping and the emergent self-clustering of systems containing a high density of active particles. The combination of both effects makes the clusters more controllable for applications.

Synthesis, Photoluminescence and Infrared Emissivity of SnO<sub>2</sub> Nanocrystalline Thin Films

SnO2 nanocrystalline thin films (NCTFs) with high quality and low infrared emissivity were synthesized through a simple hydrothermal process designed by orthogonal design theory. The microstructure, morphology, photoluminescence (PL) property and the infrared emissivity (IRE) property of as-prepared products were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), fluorescence spectrophotometer, and infrared spectroradio meter (ISM) respectively. The results show that two emission peaks are observed in PL spectra, which can be deconvoluted by Gaussian profile fitting into four emission peaks centered at about 380, 420, 460 and 520 nm respectively. The influences of crystallinity, concentration of particles and resistivity on IRE were systematically investigated, revealing that the better crystallinity, higher particle density and better conductivity are favorable for lowering IRE.

High-Throughput Contact Flow Lithography.

High-throughput fabrication of graphically encoded hydrogel microparticles is achieved by combining flow contact lithography in a multichannel microfluidic device and a high capacity 25 mm LED UV source. Production rates of chemically homogeneous particles are improved by two orders of magnitude. Additionally, the custom-built contact lithography instrument provides an affordable solution for patterning complex microstructures on surfaces.

THE DISTRIBUTION AND ANNIHILATION OF DARK MATTER AROUND BLACK HOLES

We use a Monte Carlo code to calculate the geodesic orbits of test particles around Kerr black holes, generating a distribution function of both bound and unbound populations of dark matter (DM) particles. From this distribution function, we calculate annihilation rates and observable gamma-ray spectra for a few simple DM models. The features of these spectra are sensitive to the black hole spin, observer inclination, and detailed properties of the DM annihilation cross-section and density profile. Confirming earlier analytic work, we find that for rapidly spinning black holes, the collisional Penrose process can reach efficiencies exceeding 600%, leading to a high-energy tail in the annihilation spectrum. The high particle density and large proper volume of the region immediately surrounding the horizon ensures that the observed flux from these extreme events is non-negligible.

Correlation Equation for Predicting the Single-Collector Contact Efficiency of Colloids in a Horizontal Flow.

The single-collector contact efficiency (η0) for physicochemical colloid filtration under horizontal flow in saturated porous media was calculated using trajectory analysis in three dimensions. Past studies have developed correlation equations for colloids with densities close to that of water, such as bacteria and latex particles. A new correlation equation was developed for predicting η0 based on a large number of trajectory simulations to account for higher-density particles representative of metal colloids. The correlation equation was developed by assuming Brownian diffusion, interception, and gravitational sedimentation contributed to η0 in an additive manner. Numerical simulations for colloid trajectory analysis used for calculating η0 were based on horizontal flow around a collector under the action of van der Waals attractive forces, gravity, and hydrodynamic forces as well as Brownian motion. The derived correlation equation shows excellent agreement with existing correlation equations for particles with density close to that of water. However, the correlation equation presented in this study shows that η0 of high-density colloids, such as metal particles, transported under horizontal flow deviates from that predicted by existing correlations for colloids larger than 4 μm and under low approach velocities. Simulations of trajectory paths show that a significantly reduced contact of high-density colloids larger than 4 μm in size with a collector is due to gravity forces causing trajectory paths to deviate away from the underside of collectors. The new correlation equation is suitable for predicting the single collector efficiency of large particles (several hundred nanometers to several micrometers) and with a large amount of density transport in the horizontal flow mode but is unsuitable for particles with a quite small size (several to tens of nanometers) and for the particle with a large amount of density flow in the vertical flow mode. The trajectory analysis was conducted for particles under favorable deposition conditions.

A microarray MEMS device for biolistic delivery of vaccine and drug powders

We report a biolistic technology platform for physical delivery of particle formulations of drugs or vaccines using parallel arrays of microchannels, which generate highly collimated jets of particles with high spatial resolution. Our approach allows for effective delivery of therapeutics sequentially or concurrently (in mixture) at a specified target location or treatment area. We show this new platform enables the delivery of a broad range of particles with various densities and sizes into both in vitro and ex vivo skin models. Penetration depths of ∼1 mm have been achieved following a single ejection of 200 µg high-density gold particles, as well as 13.6 µg low-density polystyrene-based particles into gelatin-based skin simulants at 70 psi inlet gas pressure. Ejection of multiple shots at one treatment site enabled deeper penetration of ∼3 mm in vitro, and delivery of a higher dose of 1 mg gold particles at similar inlet gas pressure. We demonstrate that particle penetration depths can be optimized in vitro by adjusting the inlet pressure of the carrier gas, and dosing is controlled by drug reservoirs that hold precise quantities of the payload, which can be ejected continuously or in pulses. Future investigations include comparison between continuous versus pulsatile payload deliveries. We have successfully delivered plasmid DNA (pDNA)-coated gold particles (1.15 µm diameter) into ex vivo murine and porcine skin at low inlet pressures of ∼30 psi. Integrity analysis of these pDNA-coated gold particles confirmed the preservation of full-length pDNA after each particle preparation and jetting procedures. This technology platform provides distinct capabilities to effectively deliver a broad range of particle formulations into skin with specially designed high-speed microarray ejector nozzles.

A modified cross-correlation algorithm for PIV image processing of particle-fluid two-phase flow

PIV (Particle Image Velocimetry) technique for flow field measurement has achieved popular self-identify through over ten years development, and its application range is becoming wider and wider. PIV post-processing techniques have a great influence on the success of particle-fluid two-phase flow field measurement and thus become a hot and difficult topic. In the present study, a Phase Respective Identification Algorithm (PRIA) is introduced to separate low-density solid particles or bubbles and high-density tracer particles from the PIV image of particle-fluid two-phase flow. PTV (Particle Tracking Velocimetry) technique is employed to calculate the velocity fields of low-density solid particles or bubbles. For the velocity fields of high-density solid particles or bubble phase and continuous phase traced by high-density smaller particles, based on the thought of wavelet transform and multi-resolution analysis and the theory of cross-correlation of image, a delaminated processing algorithm (MCCWM) is presented to conquer the limitation of conventional Fourier transform. The algorithm is firstly testified on synthetic two-phase flows, such as uniform steady flow, shearing flow and rotating flow, and the computational results from the simulated particle images are in reasonable agreement with the given simulated data. The algorithm is then applied to images of actual bubble-liquid two-phase flow and jet flow, and the results also confirmed that the algorithm proposed in the present study has good performance and reliability for post-processing PIV images of particle-fluid two-phase flow.

Advantages of a conservative velocity interpolation (CVI) scheme for particle-in-cell methods with application in geodynamic modeling.

The particle‐in‐cell method is generally considered a flexible and robust method to model the geodynamic problems with chemical heterogeneity. However, velocity interpolation from grid points to particle locations is often performed without considering the divergence of the velocity field, which can lead to significant particle dispersion or clustering if those particles move through regions of strong velocity gradients. This may ultimately result in cells void of particles, which, if left untreated, may, in turn, lead to numerical inaccuracies. Here we apply a two‐dimensional conservative velocity interpolation (CVI) scheme to steady state and time‐dependent flow fields with strong velocity gradients (e.g., due to large local viscosity variation) and derive and apply the three‐dimensional equivalent. We show that the introduction of CVI significantly reduces the dispersion and clustering of particles in both steady state and time‐dependent flow problems and maintains a locally steady number of particles, without the need for ad hoc remedies such as very high initial particle densities or reseeding during the calculation. We illustrate that this method provides a significant improvement to particle distributions in common geodynamic modeling problems such as subduction zones or lithosphere‐asthenosphere boundary dynamics.

A permanent, asymmetric dust cloud around the Moon.

Interplanetary dust particles hit the surfaces of airless bodies in the Solar System, generating charged and neutral gas clouds, as well as secondary ejecta dust particles. Gravitationally bound ejecta clouds that form dust exospheres were recognized by in situ dust instruments around the icy moons of Jupiter and Saturn, but have hitherto not been observed near bodies with refractory regolith surfaces. High-altitude Apollo 15 and 17 observations of a 'horizon glow' indicated a putative population of high-density small dust particles near the lunar terminators, although later orbital observations yielded upper limits on the abundance of such particles that were a factor of about 10(4) lower than that necessary to produce the Apollo results. Here we report observations of a permanent, asymmetric dust cloud around the Moon, caused by impacts of high-speed cometary dust particles on eccentric orbits, as opposed to particles of asteroidal origin following near-circular paths striking the Moon at lower speeds. The density of the lunar ejecta cloud increases during the annual meteor showers, especially the Geminids, because the lunar surface is exposed to the same stream of interplanetary dust particles. We expect all airless planetary objects to be immersed in similar tenuous clouds of dust.