High-density Particles Research Articles

Self-assembly in two-dimensional mixtures of Janus disks and isotropic particles.

Using Monte Carlo simulations, we investigate the self-organization of Janus disks and small isotropic particles in two-dimensional systems. In our model, a Janus particle contains an attractive part, A, and an repulsive part, R. The isotropic particles are strongly attracted by the R-part and repelled by the A-part. The number of Janus particles is fixed, while the number of isotropic particles varies. As the concentration of isotropic particles increases, the system structure changes. We show that the size of Janus disks strongly affects the system morphology. In the case of big Janus particles, we have found a lamellar-like phase and a gel-like structure. Different structures are formed in mixtures with smaller Janus particles. At sufficiently high densities of isotropic particles, Janus particles always aggregate into small clusters that are evenly dispersed in the "sea" of isotropic particles. The energies of interactions between both species are analyzed. The mechanism of co-assembly is discussed.

Mechanics of composite hydrogels approaching phase separation.

For polymer-particle composites, limited thermodynamic compatibility of polymers and particles often leads to poor dispersal and agglomeration of the particles in the matrix, which negatively impacts the mechanics of composites. To study the impact of particle compatibility in polymer matrices on the mechanical properties of composites, we here study composite silica- protein based hydrogels. The polymer used is a previously studied telechelic protein-based polymer with end groups that form triple helices, and the particles are silica nanoparticles that only weakly associate with the polymer matrix. At 1mM protein polymer, up to 7% of silica nanoparticles can be embedded in the hydrogel. At higher concentrations the system phase separates. Oscillatory rheology shows that at high frequencies the particles strengthen the gels by acting as short-lived multivalent cross-links, while at low frequencies, the particles reduce the gel strength, presumably by sequestering part of the protein polymers in such a way that they can no longer contribute to the network strength. As is generally observed for polymer/particle composites, shear-induced polymer desorption from the particles leads to a viscous dissipation that strongly increases with increasing particle concentration. While linear rheological properties as function of particle concentration provide no signals for an approaching phase separation, this is very different for the non-linear rheology, especially fracture. Strain-at-break decreases rapidly with increasing particle concentration and vanishes as the phase boundary is approached, suggesting that the interfaces between regions of high and low particle densities in composites close to phase separation provide easy fracture planes.

Photon detectors and front-end electronics for RICH detectors in high particle density environments

Abstract Photon detectors capable of operating in high photon rate environments are required for next generation ring imaging Cherenkov (RICH) detectors at high luminosity accelerators, like HL-LHC. These photodetectors will have to sustain single photon rate in excess of 1 GHz∕cm 2 , while being able to resist to high radiation levels of several Mrad and a 1 MeV-equivalent neutron fluence up to 10 14 n eq ∕ cm 2 . The characteristics of latest models of commercial silicon photomultipliers (SiPMs) and micro-channel plates photomultiplier tubes (MCP-PMT) are investigated in order to verify whether they satisfy the required performance, with particular emphasis on radiation hardness and high rate operation. Their innovative characteristics require tailored front-end electronics, whose architecture can be adapted to deal with higher pixel occupancy, as it will be described.

Effects of Light Dispersed Particles on the Stability of Dense Suspended Particles Against Sedimentation.

A novel method in which vesicular dispersions of the double-chain cationic surfactant DDAB (didodecyldimethylammonium bromide) stabilize suspensions of high density titania particles was recently presented (Yang, Y.-J; Corti, D.S.; Franses, E. I. Langmuir 2015, 31, 8802-8808). At high enough DDAB concentration, the vesicles form a close-packed structure, providing strong resistance to the sedimentation of the titania particles, while the dispersions remain highly shear-thinning with moderate limiting viscosities. Here, to elucidate the key factors of the mechanism by which vesicles or other nonsettling particles stabilize high density particles against sedimentation, we use Brownian dynamics simulations (BDS) to examine the sedimentation behavior of mixtures of "dense particles" that settle rapidly on their own and "light particles" that represent nonsettling "rigid vesicles". BDS confirm that for large enough values of the volume fraction ϕ2 of the light particles, the dense particles should remain suspended. The rheological behavior of the mixtures is also computed with BDS. The observed shear-thinning behavior of the light particle dispersion suggests that the suspensions of the dense particles are still flowable at high shear stresses. Furthermore, the local viscosity of light particles around the dense particles significantly increases with increasing ϕ2, particularly when the same gravitational force applied in the BDS is exerted on a dense particle. The arrangement of light particles around the moving dense particles is an important factor in determining the stability of the dense particles against sedimentation. The BDS results indicate that dispersions of nonsettling particles provide a general method for the stabilization against sedimentation of high density particles.

Giant Molecular Clouds as probes of of Galactic Cosmic Rays with Fermi-LAT

Direct measurements of Cosmic Rays (CRs) can not extend much further than the Solar System. In order to probe the so-called “sea” of Galactic Cosmic Rays, one should rely on secondary emission. Gamma rays produced in the interstellar gas, when hit by high energy particles, trace the energy distribution of the parent CRs. Giant Molecular Clouds, being huge reservoirs of hydrogen, serve as perfect targets for interaction with CRs. The high particle density in these objects enables to have enhanced  emission from small isolated location, and hence to derive information about single spots of the Milky Way. We analyzed more than 9 years data of Fermi-LAT from 18 molecular clouds, located in different regions from 100 pc to more than 10 kpc from us, allowing us to have the most comprehensive study on Galactic Cosmic Rays from Molecular Clouds ever.

The Dependence of Microstructural Evolution and Corrosion Resistance of a Sandwich Multi-Layers Brazing Sheets on the Homogenization Annealing

The influence of the microstructure on the corrosion susceptibility and mechanism of aluminum sheet was studied. The homogenization annealing treatment results in the segregation of copper on the surface of the re-solidified clad material and the increase of the diffusion depth of Si during brazing. The band of dense precipitates has a higher corrosion potential than clad and core material, and the high density particles in the diffusion zone (40 um<;depth<;70 um) are identified as α-Al(Fe-Mn)Si particles. Thus, the band of dense precipitates are catalytic sites for cathodic reduction reactions. Moreover, the effect of homogenization annealing treatment on the local electrochemical activity and corrosion properties are studied. The results indicate that the band of dense precipitates formed in the diffusion zone in the sample without homogenization annealing during brazing process, which improves the corrosion resistance of the material. Compared with sample with homogenization annealing at the same thickness, the time for the perforation during seawater acetic acid test of the sample without homogenization is longer than that of the homogenization annealed sample.

Observation of particles behavior near the wall using a narrow channel

Particle behavior on flat plate in narrow flow channel was experimentally investigated. As the test particle, polystyrene particle, glass particle, TiO2 and SiO2 powder were used and compared differences in behaviors for each particle. Number density of particles was measured using the microscope camera. Relatively large particles were removed from the wall surface to upper layer of the flow by the effect of lift force. However, the small and high density particles such as the TiO2 powder, could not remove from the wall surface. In addition, the difference in particle velocity for each particle diameter in a steady flow was measured using polystyrene at near the wall surface and center of narrow flow channel. At near the wall surface, large particles trended to move faster than small particles. At center of narrow flow channel, particle velocity was constant regardless of particle diameter. At near the wall surface, large particles was affected by the velocity distribution by shear layer and move faster than small particles.

Measurement of Microwave Propagation in Weakly Ionized Dusty Plasma

An experimental method of producing dusty plasma with high dusty particle density is proposed and implemented. Microdusty particles are immersed into an ac glow discharge plasma with large scale by applying electronically controlled vibratory screen mesh and continuous equidistributional dusty environment is formed. The impact of dusty particles on microwave propagation in a laboratory plasma device can be observed. The gigahertz microwave transmittance through the dusty plasma region is measured with vector network analyzer and horn antenna placed in the sides of plasma region. The results show that the dusty particles can synergize the influence on propagation of microwave in plasma.

Microstructure development and high tensile properties of He/H2 milled oxide dispersion strengthened copper

This study describes the effect of microstructural development on high tensile properties of a newly developed He/H2 milled oxide dispersion strengthened copper in a large centimeter sized spherical morphology. Electron back scattered diffraction showed development of a strong texture of (110) plane in micron sized (1.2 μm) grains on the surface of milled spheres. A combination of microstructural features of inhomogeneous grain size, nanoscale lenticular/rectangular deformation twins, high dislocation density and fine oxide particles distribution induced a very high ultimate tensile strength (688 MPa)-ductility (8.6% elongation).

Modelling the accumulation and transport of floating marine micro-plastics around South Africa

Plastic pollution of South Africa's marine environment is widespread, yet limited research exists on the distribution, accumulation and transport of plastic debris around South Africa. In this paper, numerical modelling is used to provide a first approximation of the pathways and accumulation of marine micro-plastics around South Africa. To account for a range of plastic classes, particles with two different densities are considered. Low-density (LD) particles represent low- and high-density polyethylene while high-density (HD) particles are representative of Polyethylene terephthalate and Polyvinyl chloride. While the majority of micro-plastic particles that enter the ocean from the five major coastal urban-industrialised centers beach along the coastline of South Africa, a third is exported to the open ocean. LD and HD particles are primarily exported to the South Atlantic and South Indian Ocean, respectively. Particles that beach along South Africa's coastline tend to accumulate in close proximity to the coastal urban-industrialised centers.

Numerical study on gas-solid flow characteristics of ultra-light particles in a cyclone separator

Cyclone separator is a widely used mechanical equipment that removes solid materials from transport gas, and the separation characteristics depends heavily on material properties. Most separation objects commonly studied are micron-sized powders or particles of high density with the magnitude ranging from 102 to 103kg/m3. While the particle density of expanded graphite (EG), a new type of material that is widely used in industry, is only a few tenths of conventional materials. However, the cyclone separation of such ultra-light particle has not been studied so far. This paper, based on the computational fluid dynamics and discrete element (CFD-DEM) coupling method, performs simulation experiments of the ultra-light particle cyclone separation at different inlet velocities. The pressure and velocity distribution of the continuous phase in the separator are studied. The effects of ultra-light particles on the flow field are revealed. The particle flow patterns are obtained and the force characteristics of the ultra-light particle are analyzed. Simulation results are verified experimentally. The results show that the separation characteristics of ultra-light particles are different from that of conventional materials: a) the appearance of ultra-light particles has negligible effect on the flow field in the separator; b) the ultra-light particles can be completely separated even if the inlet velocity is low; c) when the inlet velocity is higher than 7.5m/s, "top ash ring" composed of ultra-light particles appears under the roof of the cyclone, and multi-helical particle stream is observed in the cylinder region; besides,some "stagnant" particles rotate horizontally in the cone separation zone; d) particle turbulent diffusions in the upper part of the cyclone become stronger first and then weaker as the inlet velocity increases; e) the gas-particle coupling force and collision force are much larger than the particle gravity, and collisions of particles with different sizes are the main cause of secondary particle breakage.

A novel modifier on eutectic Si and mechanical properties of Al-Si alloy

In this study, a novel Al-Si alloy eutectic Si modifier was proposed and prepared. The microstructure, metamorphism mechanism and mechanical properties of the eutectic Si of the alloy after adding Mg-15La master alloy were investigated. The results show that high-density nano-cluster particles appear within the eutectic Si after Mg-15La master alloy addition. After adding the master alloy, the eutectic Si morphology changes from strip to fiber or granular. The average length of eutectic Si changed from 6.04 µm to 1.04 µm. The mechanical properties after casting and heat treatment have been significantly improved.

Synaptic distributions of pS214-tau in rhesus monkey prefrontal cortex are associated with spine density, but not with cognitive decline.

Female rhesus monkeys and women are subject to age- and menopause-related deficits in working memory, an executive function mediated by the dorsolateral prefrontal cortex (dlPFC). Long-term cyclic administration of 17β-estradiol improves working memory, and restores highly plastic axospinous synapses within layer III dlPFC of aged ovariectomized monkeys. In this study, we tested the hypothesis that synaptic distributions of tau protein phosphorylated at serine 214 (pS214-tau) are altered with age or estradiol treatment, and couple to working memory performance. First, ovariectormized young and aged monkeys received vehicle or estradiol treatment, and were tested on the delayed response (DR) test of working memory. Serial section electron microscopic immunocytochemistry was then performed to quantitatively assess the subcellular synaptic distributions of pS214-tau. Overall, the majority of synapses contained pS214-tau immunogold particles, which were predominantly localized to the cytoplasm of axon terminals. pS214-tau was also abundant within synaptic and cytoplasmic domains of dendritic spines. The density of pS214-tau immunogold within the active zone, cytoplasmic, and plasmalemmal domains of axon terminals, and subjacent to the postsynaptic density within the subsynaptic domains of dendritic spines, were each reduced with age. None of the variables examined were directly linked to cognitive status, but a high density of pS214-tau immunogold particles within presynaptic cytoplasmic and plasmalemmal domains, and within postsynaptic subsynaptic and plasmalemmal domains, accompanied high synapse density. Together, these data support a possible physiological, rather than pathological, role for pS214-tau in the modulation of synaptic morphology in monkey dlPFC.

Application of Drift Chambers for Research of Cosmic-Ray Muon Bundles

The new coordinate-tracking detector based on drift chambers TREK, for research of ultrahighenergy cosmic rays is under development at National Research Nuclear University MEPhI. At the present, a prototype of the future detector—coordinate-tracking unit based on drift chambers (CTUDC)—is functioning. The prototype consists of 16 drift chambers. Results of experimental series have shown wide capabilities of this type of detectors for registration of muon bundles, including bundles with high density of particles. Results of operation of the prototype and prospects of developing a full-size detector TREK are presented.

Biomass-derived robust three-dimensional porous carbon for high volumetric performance supercapacitors

The inherent low volumetric performance of two-dimensional (2D) carbon materials hinders their practical usage in portable devices. Three-dimensional (3D) carbon materials derived from sustainable biomass have been widely investigated but also suffer from the moderate volumetric performance. In this work, using biomass (jujube) as carbon precursor, robust 3D porous carbon with a high particle density of 1.06 gcm−3 is synthesized through high-temperature carbonization and subsequent activation. In three-electrode system, the electrode exhibits an ultrahigh volumetric capacitance of 476 Fcm−3 in 6 M KOH electrolyte, which is much higher than previously reported results. The symmetrical two-electrode supercapacitor delivers excellent rate capability (75% capacitance retention at 20 Ag−1) as well as superior cycle stability (91% capacitance retention after 10,000 cycles) in 1 M H2SO4 electrolyte. Furthermore, an energy density as high as 13 WhL−1 at a power density of 477 WL−1 is demonstrated in 1 M Li2SO4 electrolyte. The high volumetric performance of our biomass-derived porous carbon meets the requirements of portable devices and the fabrication process can be scaled up easily to industrial levels.

Influence of lipid content and dilution on properties and stability of nanostructured lipid carriers (NLCs) prepared from rambutan (Nephelium lappaceum L.) kernel fat and evaluation of their β-carotene loading capacity

The effects of lipid content and dilution on the properties and stability of nanostructured lipid carriers (NLCs) prepared from rambutan (Nephelium lappaceum L.) kernel fat were investigated. The β-carotene-loading capacity of the NLCs was also evaluated. NLCs containing various lipid phase concentrations (5, 10, and 15 wt%) were prepared using Tween 80 as the emulsifier with a lipid to emulsifier weight ratio of 1:0.2. The results showed that an increase in the lipid content up to 15 wt% had no effect on the zeta-potential, particle size and polydispersity index but resulted in a higher particle density. All samples showed no phase separation during storage at 25 °C for 28 days; however, the relative recrystallization index (RRI) increased. Dilution of concentrated NLC (15 wt%) to a lower lipid content (5 and 10 wt%) produced no differences in the particle characteristics and stability during storage. NLCs loaded with β-carotene at different concentrations (0, 0.5, and 1 wt% of the lipid phase) exhibited desirable characteristics and had high encapsulation efficiency (∼97%) over 28 days of storage. These results demonstrated that NLC prepared from rambutan kernel fat can be used to entrap lipophilic bioactive components which could be used as ingredients in functional food products.

Primary aldosteronism is associated with decreased low-density and high-density lipoprotein particle concentrations and increased GlycA, a pro-inflammatory glycoprotein biomarker.

Primary aldosteronism (PA) may confer increased cardiovascular risk beyond effects on systemic blood pressure, but contributing mechanisms remain incompletely understood. We compared plasma (apo)lipoproteins and lipoprotein particle characteristics, GlycA, a pro-inflammatory glycoprotein biomarker of enhanced chronic inflammation, and plasma total branched-chain amino acids (BCAA), measured using nuclear magnetic resonance (NMR) spectroscopy, between patients with PA, control subjects without hypertension, subjects with untreated hypertension and subjects with treated hypertension. Twenty PA patients were individually matched with 2819 control subjects without hypertension, 501 subjects with untreated hypertension and 878 subjects with treated hypertension participating in the PREVEND (Prevention of Renal and Vascular End-Stage Disease) cohort study with respect to age, sex, body mass index, smoking and statin use. The Vantera® Clinical Analyzer was used to determine NMR-based laboratory parameters. Total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), apolipoprotein (apo) B, apolipoprotein A-I (apoA-I), LDL particle and HDL particle concentrations were all decreased in PA subjects vs control subjects and subjects with untreated hypertension (P<0.016). Triglycerides (TG) and triglyceride-rich lipoprotein (TRL) concentrations were lower in PA subjects vs subjects with (untreated) hypertension. GlycA was increased in PA vs the three comparator groups (P<0.016). Total BCAA concentrations were unaltered in PA. Primary aldosteronism is associated with lower concentrations of LDL and HDL particles and to some extent also with lower TG and TRL particle concentrations. PA is also characterized by increased GlycA levels, indicating enhanced low-grade chronic inflammation. Low HDL particle concentrations and increased GlycA could contribute to accelerated cardiovascular disease development in PA.

Particle image reconstruction for particle detection in particle tracking velocimetry

A new methodology for particle identification and localization in the context of particle tracking velocimetry (PTV) is presented. The aim is to overcome the issue of inherent detection errors under high particle density conditions. The approach is based on the particle position reconstruction through the inversion of a linear model connecting the PTV signal with a particle-based representation of the 3D-to-2D projection. The inversion procedure accounts for both the non-negativity and the sparsity of the sought solution. Simulation tests using synthetically generated images are carried out to evaluate the sensitivity of the proposed method to characteristic parameters such as the particle image density, the particle image size, the model image size, and/or background noise. Its ability to provide better detection performances with higher reliability than conventional techniques is demonstrated.

The effects of particle density in moxa smoke on the ultrastructure of knee cartilage and expressions of TNF‐α, IL‐1b, BAX, and Bcl‐2 mRNA in a rat model for osteoarthritis

The effectiveness of smokeless moxa and other means to reduce exposure are extensively investigated with regards to the health consequences of inhalation of moxa smoke, and clinical studies indicate that classical moxibustion is superior to smokeless moxa. This study aims to quantify the effects of particle density in moxa smoke on the clinical outcome with an established model, demonstrated to be effective for classical moxibustion. The purpose of this study is to explore the effects of particle density in moxa smoke on the ultrastructure of knee cartilage and expression of cytokine, tissue necrosing factor-alpha (TNF-α), interleukin 1 beta (IL-1b), apoptosis regulator, B-cell lymphoma-2 (Bcl-2), and BAX in a rat model for inflammatory joint disease. Fifty healthy experimental rats were randomly divided into five groups, including normal control, model control, and moxa exposure groups with low, medium, and high particle density, and n = 10/group. In addition, a knee osteoarthritis model was duplicated in the model control and moxa exposure groups. Finally, the ultrastructure of knee cartilage was observed using transmission electron microscopy, and messenger RNA (mRNA) expressions of TNF-α, IL-1b, BAX, and Bcl-2 were determined with quantitative fluorescence methodology. In the model control and moxa exposure groups, knee cartilage indicated that histologic changes with the degree of injury were inversely proportional to moxa smoke density. The mRNA expressions of TNF-α, IL-1b, and BAX in synovial fluid, as an acute phase reactant, were similarly inversely related to moxa smoke density, but significantly increased. In contrast, Bcl-2, as an antiapoptotic, was substantially decreased in the model, while its levels were directly proportional to moxa smoke density. Besides, the ratio of Bcl-2/BAX mRNA was sharply decreased in the model group, but with levels proportional to moxa smoke density. A correlation was found between the particle density in moxa smoke and degree of injury to knee cartilage, favoring higher particle densities. This can be partially related to the suppression of the inflammatory effects of TNF-α, IL-1b, enhancement of the antiapoptotic effects of Bcl-2, and, nevertheless, suppression of the apoptotic effects of BAX. Finally, the protective effect of antiapoptotic is one of the key mechanisms for an ambient moxa smoking environment.

Detecting stability of conical spouted beds based on information entropy theory

Effects of particle size, particle density, gas inlet diameter and static bed height on the stability of operation in conical spouted beds were investigated through analyses of information entropy of pressure fluctuations. In this respect, the maximum information entropy of pressure fluctuations was used as a stability criterion. The results showed that stability of the bed increases with an increase in the maximum entropy. The maximum information entropy of pressure fluctuations increases with increasing particle size and bed height while decreases with increasing gas inlet diameter and particle density. A stability map was also prepared to present the effect of operating parameters on the maximum entropy. Moreover, a correlation for prediction of maximum information entropy was developed to determine the stable operation conditions of conical spouted beds operating with low as well as high density particles.