Sharp Particle Research Articles

Discrete and continuum modelling of rock-ice avalanches: vertical segregation and its feedback on flow mobility

Rock-ice avalanches are rapid, catastrophic mass flows consisting of massive rock and ice particles in alpine regions. Varying material properties of rock and ice particles cause them to spontaneously mix and segregate during the flow. However, the impacts of segregation on the mobility remain poorly understood and are overlooked in current rock-ice avalanche models. Here, we address modeling of segregation and its mobility feedback from both discrete and continuum points of view. Using the discrete element method, we simulate rock-ice avalanches, and the segregation that occur therein, as steady gravity-driven flows of particles different in size, density, and surface friction. Segregation results in sharp particle concentration gradients which, when coupled with the large surface friction difference between rocks and ice, lead to transitions in the flow kinematic profiles. We reveal that rocks and ice contact probabilities are key to modelling the effective friction and volume fraction of the mixture flows. Continuum equations are proposed to model the concentration dependence of the pressure, while segregation-induced flow velocity profiles are modelled using the non-local granular fluidity framework that accounts for microscopic frictional interactions. The findings are expected to promote more sophisticated modeling of rock-ice avalanches necessary for hazard risk reduction and mitigation.

Benchmarking Data Assimilation Algorithms For 3D Lagrangian Particle Tracking

This paper reports a comparison of three state-of-the-art data assimilation (DA) algorithms for 3D Lagrangian particle tracking (LPT): Vortex-In-Cell sharp (VIC#), FlowFit3, and neural-implicit particle advection (NIPA). Particle trajectories, termed “tracks,” are spatially sparse, and a reconstruction algorithm is commonly employed to estimate dense Eulerian fields using position, velocity, and/or acceleration data from the tracks. DA algorithms for LPT combine the tracks with a set of governing equations (or constraints) to enhance the accuracy of the velocity field, relative to interpolation methods, and infer additional quantities like pressure. We compare the performance of VIC#, FlowFit3, and NIPA with respect to their accuracy and computational cost. Accuracy is assessed in terms of the mean inter-particle distance, frame rate, and magnitude of tracking errors, and costs are reported in wall time. Synthetic and experimental data sets for homogeneous isotropic turbulence and turbulent boundary layer flows are evaluated; direct numerical simulations are used for the synthetic tests, and realistic localization errors are added to the simulated tracks. All three DA methods perform well in cases with the highest spatio-temporal sampling of the flow, and all three methods are relatively robust to the frame rate and magnitude of localization errors. NIPA is more resilient to sparse seeding than FlowFit or VIC#, which exhibit similar performance, but NIPA is also the most expensive technique by some margin. DA reconstructions are superior to interpolation across the board, with a reduction of error up to 80% in the experimental demonstration.

Preparation and properties of the fine ground strontium-based endodontic cements.

In this study, fine powders of tristrontium aluminate (S3A) and distrontium cerate (S2Ce) cement were prepared using a dry grinding process, and their mechanical and ion dissolution properties were estimated. Fine cements showed the particles about 10 μm in diameter or smaller with sharp particle size distribution curves. The setting reaction of the fine cements was rapid; therefore, a 0.1% w/v of citric acid solution was used as the retarder. The compressive strengths of the fine cements were improved compared to those of the coarse cements at both 1 and 28 days after mixing at a water/powder ratio (W/P) of 0.4. The dissolution of Sr and Al ions from fine S3A cement was enhanced. However, the relative flowability decreases with fine grinding. Further studies on flowability, handling property are required. Additionally, the biological effects of endodontic cement should be studied both in vitro and in vivo.

Confocal microscopy 3D imaging and bioreactivity of La Palma volcanic ash particles

In September 2021 an eruption began of Cumbre Vieja, La Palma (Spain) that lasted 3 months. Previous studies have shown that volcanic ash particles can be associated with adverse effects on human health however, the reasons for this are unclear. Particle shape has been shown to contribute to cellular uptake in prostate cancer cells. Hence we aimed to study 3D structure, elemental composition and effects on cultured lung cells of particles collected from the La Palma volcanic eruption. 3D imaging of PM10 sized and below particles was performed using a LEXT OLS4100 confocal microscope (Olympus Corporation, Japan). A Zeiss EVO 50 (Carl Zeiss AG, Germany) Scanning Electron Microscope (SEM) was used to assess elemental composition. In addition, volcanic particle concentration dose response for pneumococcal adhesion to A549 human alveolar epithelial cells was investigated. Confocal microscopy showed that some PM10 and below sized particles had sharp or angular 3D appearance. SEM x-ray analysis indicated silicate particles with calcium, aluminium and iron. We observed increased colony forming units indicating increased Pneumococcal adhesion due to exposure of cells to volcanic particles. Thus in addition to the toxic nature of some volcanic particles, we suggest that the observed sharp surface particle features may help to explain adverse health effects associated with volcanic eruptions.

Holographic Lieb lattice and gapping its Dirac band

We first point out that the Laia-Tong model realizes the Lieb lattice in the holographic setup. It generates a flat band of sharp particle spectrum together with a Dirac band of unparticle spectrum. We provided an understanding why the Laia-Tong model’s boundary condition generate a flat band and compared it with the mechanism of “compact localized orbits” in the lattice models to provide a physical reason why Lieb and Laia-Tong model should be identified based on the similarity in the flat band generation mechanism. We then construct a model which opens a gap to the Dirac band so that one can realize a well-separated flat band. We then study the phase transition between the gapped and gapless phases analytically. We also made methodological progress to find a few other possible quantizations and we express the Green functions in any quantization in terms of that in the standard quantization. Finally we carried out the problem of back reaction to show that the qualitative feature remains the same.

Efficacy of Nanosilica Coatings in Calcium Looping Reactors.

Nanosilica coatings are considered a simple physical treatment to alleviate the effect of cohesion on powder flowability. In limestone powders, these coatings buffer the rise in cohesion at high temperatures. Here, we investigate the role of particle size in the efficiency (and resilience) of these layers. To this end, this work examines a series of four limestone powders with very sharp particle size distributions: average particle size ranged from 15 to 60 μm. All the samples were treated with nanosilica at different concentrations from 0 to 0.82 wt %. Powders were subjected to short- and long-term storage conditions in calcium looping based systems: temperatures that vary from 25 to 500 °C and moderate consolidations (up to 2 kPa). Experiments monitored powder cohesion and its ability to flow by tracking the tensile strength of different samples while fluidized freely. Fluidization profiles were also used to infer variation in packings and the internal friction of the powder bed. Interestingly, for particle sizes below 50 μm, the nanosilica treatment mitigated cohesion significantly-the more nanosilica content, the better the flowability performance. However, at high temperatures, the efficiency of nanosilica coatings declined in 60 μm samples. Scanning electron microscopy images confirmed that only 60 μm samples presented surfaces barely coated after the experiments. In conclusion, nanosilica coatings on limestone are not stable beyond the 50 μm threshold. This is a critical finding for thermochemical systems based on the calcium looping process, since larger particles can still exhibit a significant degree of cohesion at high temperatures.

Description of global EGAM in the maximum of local frequency during current ramp-up discharges in DIII-D

Energetic-particle-induced geodesic acoustic modes, EGAMs (Fu, Phys. Rev. Let., vol. 101, 2008, pp. 185002), driven by neutral beam injection (NBI), have been observed in many DIII-D tokamak experiments (Nazikian et al., Phys. Rev. Lett., vol. 101, 2008, pp. 185001). This mechanism has been theoretically investigated in (Qiu et al., Plasma Phys. Control. Fusion, vol. 52, 2010, pp. 095003), using a sharp energetic particle distribution function, and in (Qu et al., Plasma Phys. Control. Fusion, vol. 59, 2017, pp. 055018), where the dispersion relation and eigenmode behaviour were obtained for the situation of early beam scenario, that is, for times smaller than the beam slowing down time. In this work, we extend these studies determining the eigenmode for beyond the slowing down time, in a scenario with reverse safety factor $q$ profile, where a small concentration of energetic ions can produce an off-axis maximum in the GAM dispersion relation. The characteristics of EGAM are analytically studied with the drift kinetic equation together with the MHD code NOVA. The toroidal energetic ion transit frequency, coupled with the GAM frequency, produces the maximum in the dispersion relation where the eigenmode can be found. The quantitative correspondence of experimental results with the predictions of the proposed model is analysed.

Computational investigation of a novel hydrocyclone for fines bypass reduction

Hydrocylones offer a process intensified environment for rapid, high-throughput and relatively sharp particle classification or phase separation. One of the main performance limitations of hydrocyclone is bypassing of fines to the underflow. To address this limitation, a novel design modification of fitting thin concentric rings to the cylindro-conical section has been proposed. The Computational Fluid Dynamics (CFD) modeling based methodology has been adopted to validate the hypothesis. Predictions using Realizable k-ε, Reynolds Stress Model (RSM), and Large Eddy Simulation Wall Adopting Local Eddy viscosity (LES-WALE) turbulence models has revealed that LES-WALE matched better with the experimental observations. The experimental data included overall performance parameters and detailed observations of axial and tangential velocity profiles across the hydrocyclone. The validated CFD model and the methodology was then used to predict the behavior of the proposed designs. They established that the modifications held promise in reducing the bypass with additional benefits of sharper separation curve and finer D50.

Oscillations in the stochastic gravitational wave background from sharp features and particle production during inflation

We identify a characteristic pattern in the scalar-induced stochastic gravitational wave background from particle production during inflation.If particle production is sufficiently efficient, the scalar power spectrum exhibits \U0001d4aa(1) oscillations periodic in k, characteristic of a sharp feature, with an exponentially enhanced envelope. We systematically study the properties of the induced spectrum of gravitational waves sourced after inflation and find that this inherits the periodic structure in k, resulting in a peak in the gravitational wave energy density spectrum with \U0001d4aa(10 %) modulations. The frequency of the oscillation in the scalar power spectrum is determined by the scale of the feature during inflation and in turn sets the frequency of modulations in the gravitational wave signal. We present an explicit realisation of this phenomenon in the framework of multifield inflation, in the form of a strong sharp turn in the inflationary trajectory. The resulting stochastic background is potentially detectable in future gravitational wave observatories, and considerations of backreaction and perturbativity can be used to constrain the parameter space from the theoretical side. Our work motivates more extensive research linking primordial features to observable properties of the stochastic background of gravitational waves, and dedicated development in data analysis for their detection.

Experimental study on the repeated impact of sharp particles on metal surface

Particles (such as sand and debris) employed in exploitation and conveying systems in oil and gas industry often cause erosion in equipment and pipe fittings. Since erosion is a complex and poorl understood process that can result in economic losses, operation risks and pollution, studying the mechanisms causing it is within the scope of various researches. In this paper, a modified particle launcher is designed to conduct the particle-wall collision experiments. Special attention is paid to the effects of repeated impacts of sharp particles on the pit depth and pit width for better understanding the mechanisms of erosion. The results reveal that the rebound particles begin to rotate when the impact angle deviates from their main diagonal, squeezing or prying the piled lips. The surface damaged by the sharp particles exhibits two types of morphologies: the corrugated one occurring at a small impact angle and another presented by deep craters surrounded by piled lips at a large impact angle. An increase in the impact number is shown to reduce the sharp particle penetration depth. In this respect, the current work is important in terms of elucidation of erosion mechanisms and erosion modeling.

Physical and elemental analysis of Middle East sands from recent combat zones

Objective: The lungs are uniquely exposed to the external environment. Sand and dust exposures in desert regions are common among deployed soldiers. A significant number of Veterans deployed to the Middle East report development of respiratory disorders and diseases.Materials and methods: Sand collected from Fallujah, Iraq and Kandahar, Afghanistan combat zones was analyzed and compared to a sand sample collected from an historic United States (U.S.) battle region (Fort Johnson, James Island, SC, Civil War battle site). Sand samples were analyzed to determine the physical and elemental characteristics that may have the potential to contribute to development of respiratory disease.Results: Using complementary scanning electron microscopy (SEM) imaging and analysis, and inductively coupled plasma mass spectrometry (ICP-MS), it was determined that Iraq sand contained elevated levels of calcium and first row transition metals versus Afghanistan and U.S. sand. Iraq sand particle texture was smooth and round, and particles were considerably smaller than Afghanistan sand. Afghanistan sand was elevated in rare earth metals versus Iraq or U.S. sands and had sharp edge features and larger particle size than Iraq sand.Conclusions: These data demonstrate significant differences in Iraq and Afghanistan sand particle size and characteristics. Middle East sands contained elevated levels of elements that have been associated with respiratory disease versus control site sand, suggesting the potential of sand/dust storm exposure to promote adverse respiratory symptoms. Data also demonstrate the potential for variation based on geographical region or site of exposure. The data generated provide baseline information that will be valuable in designing future exposure studies.

Vorticity-Aligned Droplet Bands in Sheared Immiscible Polymer Blends Induced by Solid Particles

The spatiotemporal organization of complex fluids under flow can be strongly affected by incorporating solid particles. Here, we report that a monolayer of interfacially active microspheres preferentially wetted by the matrix phase can bridge droplets into vorticity-aligned bands in immiscible polymer blends at intermediate particle concentrations and low shear rates. Strong particle bridging ability and the formation of rigid anisotropic droplet bands with a negligible inertia effect in the Newtonian matrix are suggested to be responsible for the vorticity orientation of droplet bands during slow shear flow, which could be understood based on Jeffery orbit theory in the framework of fluid mechanics and strong confinement effect acted by shear walls and adjacent bands. However, increasing the aspect ratio of particles could restrain the formation of anisotropic bands because of reduced particle coverage and promoted droplet coalescence induced by sharp particle corners, increased and uneven distribution of particle aggregates in the matrix phase, and weakened particle bridging ability.

Synthesis of Embryonic Zeolites with Controlled Physicochemical Properties

Colloidal zeolite precursors with sharp particle size distributions (ca. 3–5 nm) and identical chemical compositions, so called embryonic zeolites (EZs), are prepared by strict control of aluminosi...

Incoherent ultrarelativistic particle scattering by nuclei at planar channeling

The problem of high-energy charged particle motion in the field of atomic planes of oriented crystals, essential for particle beam manipulation, intensive gamma-radiation generation and prepared measurements of short-living elementary particle properties, such as magnetic and electric dipole momenta, is considered. A rigorously evaluated instant change of transverse channeling motion energy under the scattering by an atomic core is applied to deduce an expression for the average transverse energy growth rate, which takes into consideration both the quantum effects and sharp particle density variation inside an inter-plane channel. The latter makes it possible for the first time to describe numerically the key limitations of multiple applications of the channeling effects in high-energy physics, not involving the parameters, introduces earlier through the arbitrary qualitative considerations. Also, the expressions of both the large angle scattering cross section and average square of small scattering angles are obtained, making possible to formulate a consistent simulation method of both positively and negatively charged particles propagation both in and out of the channeling conditions, taking into consideration both quantum nature of incoherent and classical one of the coherent scattering of ultra-relativistic particles by crystal plane atoms.

Densified W[sbnd]Cu composite fabricated via laser additive manufacturing

Tungsten-Copper (WCu) composites are promising materials for electrical and thermal applications. However, their fabrication remains limited using conventional techniques, such as powder metallurgy, which are not suitable for manufacturing densified complex WCu components. In this work, laser additive manufacturing (LAM) technology was introduced for fabricating W-25 wt%Cu composites. A densified WCu composite, free of apparent cracks and pores, is successfully synthesized using optimum process parameters of laser power 2000 W and laser scan speed 360 mm/min in an Ar atmosphere with less than 10 ppm O. The densification of WCu composites is owing to the sufficient wetting of solid W particles by the molten liquid Cu and the surface smoothing of the W particles. The good wetting of the solid W particles by the liquid Cu is due to the low oxygen content and the combined effect of increased capillary force and reduced friction force. The W grains are rounded, indicating some solution-reprecipitation of sharp particle edges originating from the increase in solubility from curvature effects.

DEVELOPMENT OF A PELTIER TYPE CLOUD CHAMBER WITH WIDE VIEW FIELD.

Cloud chamber contributes to radiation education by facilitating observation of particle tracks formed by radiation. Peltier-based chamber achieves cooling without the need for dry ice,. we developed a cloud chamber based on peltier thermoelectric modules and has a multilayered heat insulation system to maintain a stable cool environment. It produces sharp particle tracks without requiring a dark room for observing the tracks. Its large top window (diameter of 12.5 cm) provides a relatively wider observation field capable of accommodating five to six students at a time.

Enhanced CO2/CH4 separation performance of mixed-matrix membranes through dispersion of sorption-selective MOF nanocrystals

Mixed matrix membranes (MMMs) derived from metal-organic frameworks (MOFs) nanocrystals represent a promising alternative for overcoming the trade-off between permeability and selectivity derived from the pristine polymeric membrane. The selection of MOFs fillers are mainly focused on their diffusion-selectivity property for gas-pairs. However, the improvement of both gas-permeability and selectivity through addition of sorption-selective MOFs are rarely reported. Herein, the incorporation of CO2-philic KAUST-7 (also referred to as NbOFFIVE-1-Ni) nanocrystals makes the neat 6FDA-Durene polyimide membrane more permeable and more selective, surpassing the state-of-the-art 2008 Robeson upper bound for CO2/CH4. Nano-sized (~ 80 nm) KAUST-7 crystals with sharp particle size distribution were first fabricated through a co-solvent synthesis method. The explored gas transportation mechanism indicates that the improvement of CO2/CH4 selectivity on MMMs are attributed to the significant raise of the sorption-selectivity rather than the diffusion-selectivity. The favorable interfacial interaction between the imide groups of the 6FDA and the H of the pyrazine in the KAUST-7 enhances plasticization resistance of the neat polymer membrane. The developed MMMs exhibit a promising application in CO2 capture from natural- and bio-gas.

Formulation of a poorly water-soluble drug in sustained-release hollow granules with a high viscosity water-soluble polymer using a fluidized bed rotor granulator

Water-soluble polymers with high viscosity are frequently used in the design of sustained-release formulations of poorly water-soluble drugs to enable complete release of the drug in the gastrointestinal tract. Tablets containing matrix granules with a water-soluble polymer are preferred because tablets are easier to handle and the multiple drug-release units of the matrix granules decreases the influences of the physiological environment on the drug. However, matrix granules with a particle size of over 800 μm sometimes cause a content uniformity problem in the tableting process because of the large particle size. An effective method of manufacturing controlled-release matrix granules with a smaller particle size is desired. The aim of this study was to develop tablets containing matrix granules with a smaller size and good controlled-release properties, using phenytoin as a model poorly water-soluble drug. We adapted the recently developed hollow spherical granule granulation technology, using water-soluble polymers with different viscosities. The prepared granules had an average particle size of 300 μm and sharp particle size distribution (relative width: 0.52–0.64). The values for the particle strength of the granules were 1.86–1.97 N/mm2, and the dissolution profiles of the granules were not affected by the tableting process. The dissolution profiles and the blood concentration levels of drug released from the granules depended on the viscosity of the polymer contained in the granules. We succeeded in developing the desired controlled-release granules, and this study should be valuable in the development of sustained-release formulations of poorly water-soluble drugs.

Structural, microstructural and dielectric behavior of sol–gel grown nanostructured Y0.95Zr0.05MnO3

In this communication, we report the results of the studies on structural, microstructural and dielectric properties of nanostructured Y0.95Zr0.05MnO3 (YZMO) manganites synthesized by acetate precursor route based sol–gel method. Effect of sintering temperature and hence crystallite size on the room temperature dielectric behavior has been discussed on the basis of boundary density and electric phase coexistence. Temperature dependent dielectric vs. frequency behavior of all nanostructured YZMO suggests ferroelectric nature of the samples without any dielectric anomaly within the temperature range studied. Structural studies have been carried out by performing X–ray diffraction (XRD) measurements using CuKα X–ray source. Transmission electron microscopy (TEM) images reveal an increase in particle size with sintering temperature while for all the three samples understudy particles are grown with sharp particle boundaries. Particle size analyzer study shows a broad size distribution for the lower temperature sintered samples. Dielectric constant is found to decrease with sintering temperature for all the samples. Cole–cole plots have been studied for the relaxation mechanisms while various mechanisms, theories and models have been discussed to understand the dielectric behavior of the samples. Capacitance of the samples has been discussed in the context of electric phase coexistence, built–in potential and free charge carrier density.

Abrasion erosion modeling in particulate flow

Solid particle erosion is of great importance to many industries including oil and gas production, drilling, process and transportation of minerals including oil sands. The particles that may cause erosion are of various sizes, shapes and hardnesses. These particles may impact the surface at various speeds and angles, and the influence of these parameters is characterized to some extent in the literature. Experimental and numerical studies have shown that when particles are transported by liquid (e.g. slurry transport in the pipe) or dense gas, the particle impact angles are very low. The impact angles in these cases are sometimes less than the smallest value that can be obtained in a direct impingement erosion test in gas. In this work, the mechanistic erosion equation developed previously is extended to near zero impact angles for sharp particles. The abrasion erosion equation is developed by introducing an initial penetration of the sharp particle in the equation of the motion. This initial penetration may be attributed to the sharp particle rotation and/or turbulent flow fluctuations of the carrier fluid near the wall. The empirical constants are obtained from submerged erosion experiments in liquid. The equation has been implemented in a commercially available Computational Fluid Dynamics (CFD) code (ANSYS FLUENT) to calculate erosion for a submerged impingement jet geometry, and the result is compared with the experiment. It is shown that by neglecting the abrasive term in the erosion equation, the specimen mass loss does not match the experimental measured mass loss. While by including the abrasive term, the total mass loss of the specimen agrees well with the experimental data. Moreover, the erosion pattern becomes closer to the experimentally measured pattern especially farther from the center of the highly eroded area where abrasive wear is expected to dominate.