High-density Particles Research Articles

Classification and Quantification of Snow Based on Spatial Variability of Radar Reflectivity

In this study, a classification methodology of snow particle types, i.e., crystals, aggregates, rimed snow, and graupel, by using spatial variability of the equivalent radar reflectivity factor is proposed. The methodology is formulated on the basis of the analysis of vertically pointing Doppler radar, scanning dual-polarization weather radar, and supporting surface observations. It is arguedthat by using the proposedsnow-type identification methodology, it is possible to guide the choice of the particular parameters of power law relations of equivalent radar reflectivity factorliquid equivalent snowfall rate. The validity of the classification results are demonstrated by comparing the classification output to Vaisala WXT observations, which can be used to detect presence of high-density particles in snow. The performance of the proposedquantitative snowfall estimation algorithm is illustratedusing an example of the d ata collectedfrom the C-bandoperational Helsinki Vantaa rad ar andgroundinstruments (Vaisala PWD-11, Pluvio).

Study of Adhesion and Friction Properties on a Nanoparticle Gradient Surface: Transition from JKR to DMT Contact Mechanics

We have previously investigated the dependence of adhesion on nanometer-scale surface roughness by employing a roughness gradient. In this study, we correlate the obtained adhesion forces on nanometer-scale rough surfaces to their frictional properties. A roughness gradient with varying silica particle (diameter ≈ 12 nm) density was prepared, and adhesion and frictional forces were measured across the gradient surface in perfluorodecalin by means of atomic force microscopy with a polyethylene colloidal probe. Similarly to the pull-off measurements, the frictional forces initially showed a reduction with decreasing particle density and later an abrupt increase as the colloidal sphere began to touch the flat substrate beneath, at very low particle densities. The friction-load relation is found to depend on the real contact area (A(real)) between the colloid probe and the underlying particles. At high particle density, the colloidal sphere undergoes large deformations over several nanoparticles, and the contact adhesion (JKR type) dominates the frictional response. However, at low particle density (before the colloidal probe is in contact with the underlying surface), the colloidal sphere is suspended by a few particles only, resulting in local deformations of the colloid sphere, with the frictional response to the applied load being dominated by long-range, noncontact (DMT-type) interactions with the substrate beneath.

Synthesis, surface characteristics, and electrochemical capacitance of Cu-doped carbon xerogel microspheres

Small-amplitude oscillatory shear tests were used to determine the rheological properties of a copper acetate-doped resorcinol–formaldehyde mixture at between 30 and 40°C. The apparent activation energy of the sol–gel transition was 76.6±0.6kJ/mol. Organic gel microspheres were only obtained when the sol was emulsified immediately before the gelation point and not at the gelation point itself, due to the fast gelation kinetics of the copper acetate-doped resorcinol–formaldehyde mixture. The microspherical shape was preserved after carbonization. Cu-doped carbon xerogel microspheres were steam-activated at 840°C. All samples comprised isolated well-formed microspheres, whose size increased with higher degree of activation. The surface area and porosity varied with the activation degree. Copper was detected as CuO, which acted as gasification catalyst during activation, and its size increased with higher activation degree. Electrochemical measurements were conducted with a three-electrode cell in 1M H2SO4. A very large volumetric capacitance, 146F/cm3, was found for the 30%-activated Cu-doped activated carbon xerogel, attributable to the high particle density resulting from the very compact packing of the microspheres. This sample also showed the lowest equivalent series resistance, due to its pore texture and high surface Cu content.

Polyurethane seismic streamer skins: an application of cold spray metal embedment

Cold spray metal embedment is an innovative antifouling (AF) technology that delivers metal particles with AF properties into many thermoplastic polymers. AF efficacy was quantified for low (22.1 ± 4.8 g m−2) and high (101.1 ± 10.8 g m−2) densities of copper particles embedded into polyurethane (PU) seismic streamer skins, which are used in geophysical exploration. Failure of each Cu-embedded treatment was defined as settlement of hard foulers. Low-density streamers failed after 42 days while high-density streamers failed after 210 days. Most importantly, the high-density streamers were completely free of hard foulers including the barnacle Amphibalanus reticulatus during this time period. In conclusion, cold-spray metal embedment is an effective AF technology for PU seismic streamer skins, under intense fouling conditions. Higher copper particle densities enhance AF longevity and the effect of density provides a tool to extend efficacy and enhance AF performance for specific polymers.

Magnetorheological response of soft-magnetic carbonyl iron microbeads dispersed in a poly(ethylene oxide) solution

A magnetorheological (MR) fluid is a smart magnetic particle suspension with the ability of being transformed from a liquid-like to a solid-like state under the stimulus of a magnetic field. However, in the absence of the magnetic field, dispersed magnetic particles of high density are apt to settle, resulting in poor dispersion stability. In this study, we introduced an aqueous poly(ethylene oxide) (PEO) solution with controlled shear viscosity as a medium fluid for a carbonyl-iron-based MR fluid. Its rheological and dispersion properties were studied by varying the molecular weight of the PEO. Field dependences of its MR properties were observed by using a rotational rheometer with an attached MR device.

Simulating sinking satellites with superbox-10

SUPERBOX-10 is the successor of SUPERBOX, a particle-mesh code where additional grids and sub-grids are applied to regions of high particle density. Previous limitations have been solved. For instance, the vertical resolution is improved considerably when flattened grids are used. Since the computationally most intensive part is the Fast Fourier Transform, we introduce a parallelised version using the library FFTW, resulting in a speed-up of a few. The new features are tested using a galaxy model consisting of an exponential disc, a bulge and a dark matter halo. We demonstrate that the use of flattened grids efficiently reduces numerical heating. We simulate the merging of disc-bulge-halo galaxies with small spherical satellites. As a result, satellites on orbits with both low eccentricity and inclination heat the disc most efficiently. Moreover, we find that most of the satellite's energy and angular momentum is transfered to the halo.

Observed Mixing Behavior of Single Particles in a Bubbling Fluidized Bed of Higher-Density Particles

We report experimental observations of the dynamic behavior of single, magnetically tagged 3—4 mm particles varying in density from 0.55 g/cm 3 to 1.2 g/cm 3 as they migrate freely in a bubbling air-fluidized bed of 177—250 μm glass beads of 2.5 g/cm 3 density over a range of air flows. The densities of the tracer particles (made by imbedding small magnets in wooden particles) were chosen to span a range typical for many biomass materials and exhibited both segregated and well-mixed behavior. Using high-speed measurements from externally mounted magnetic probes, we were able to reconstruct three-dimensional spatial and temporal information about the tracers' trajectories over periods of five minutes. Based on this information, we describe general trends in how the tracers moved and redistributed themselves as functions of their density, fluidization air flow, and the overall concentration of low density particles present. One key finding was that the time average vertical probability distribution of the tracer particles locations is consistent with a Weibull distribution. The effective Weibull parameters appear to vary systematically with the degree of fluidization and particle density. Also, we observed that temporal autocorrelations in the vertical position of the tracer particles vary systematically with fluidization intensity and reveal important information about the dominant bed circulation time scales. Our results suggest that it may be possible to develop relatively simple statistical models or correlations for describing the spatial distribution and circulation of mm sized particles in bubbling beds of this type. Such tools should be useful for simulating some types of fluidized biomass processing and for validating kinetic-theory models of fluidized bed systems.

Bimodal Momentum Distribution of the High-Density Supersolid State

By performing exact quantum Monte Carlo simulations, we study the momentum distribution of the supersolid state in the two-dimensional extended Bose-Hubbard model with the nearest-neighbor repulsion. For strong nearest-neighbor repulsions, the supersolid state is stable in a broad region up to large hopping amplitudes and high particle densities. In the supersolid state, the momentum distribution shows a bimodal structure with two peaks related to the superfluidity and solidity respectively. By our calculations, we show that the bimodal structure becomes clearer as the chemical potential (or the particle density) is increased.

Modeling of Ni4Ti3 precipitation during stress-free and stress-assisted aging of bi-crystalline NiTi shape memory alloys

The phase field method was applied to study the microstructure evolution of Ni4Ti3 precipitates during stress-free and stress-assisted aging of bi-crystalline NiTi shape memory alloys (SAMs) with two different initial Ni-contents of 51.5% and 52.5% (mole fraction), respectively. The simulation results show that, during stress-free aging of the NiTi alloy with a low supersaturation of Ni (i.e., Ti-51.5%Ni), the Ni4Ti3 precipitates exhibit a heterogeneous distribution with a high number density of particles at the grain boundary, leaving most of the grain interiors free of precipitates; while for the NiTi alloy with a high supersaturation of Ni (i.e., Ti-52.5%Ni), the Ni4Ti3 precipitates show a homogeneous distribution across the entire simulation system. The stress-assisted aging can give rise to homogeneous distribution of the precipitates, regardless of the initial Ni-content; however, the distribution of variant type within the two grains is heterogeneous.

Increase in Standard Cholesterol and Large HDL Particle Subclasses in Antiretroviral-Naïve Patients Prescribed Efavirenz Compared to Atazanavir/Ritonavir

Background: Cardiovascular risk in HIV-infected patients is related, at least in part, to serum lipid alterations before and after HAART. Lipoprotein-particle subclasses may also have an effect, but comparative data after standard HAART regimens are limited.Methods: This was a substudy of a trial in 91 antiretroviral-naïve patients randomized to tenofovir + emtricitabine + atazanavir/ritonavir (ATV/r) or efavirenz (EFV). Over-time trends from baseline to week 48 in total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), HDL particles (HDLp), and TC:HDL-C and TG:HDL-C ratios were analyzed by analysis of covariance (ANCOVA). Furthermore, confidence intervals for differences between the 2 groups at week 48 were calculated. Indications for lipid-lowering interventions and low HDL-C were also studied.Results: ANCOVA showed that, with respect to patients receiving ATV/r, those prescribed efavirenz (EFV) had greater increases reported as mean differences in lipid values at week 48: 14 mg/dL (95% CI, 0.2 to 27) for TC, 14 mg/dL (95% CI, 4 to 25) for LDL-C, 5 mg/dL (95% CI, 2 to 9) for HDL-C, and 2.2 mg/dL (95% CI, 0.4 to 4) for large HDLp. Proportions of subjects with indications for lipid-lowering interventions and with HDL-C <40 mg/dL did not differ significantly.Conclusions: Patients prescribed EFV had greater increases in TC, LDL-C, and HDL-C. Although no significant differences were detected between the 2 groups for the TC:HDL ratio and for indications to start lipid-lowering interventions, large HDLp increased more in the EFV group compared to the ATV/r group, suggesting a protective effect associated with EFV use.

Advanced alignment of the ATLAS inner detector

The primary goal of the ATLAS inner detector (ID) is to accurately measure the trajectories of charged particles in the high particle density environment of the large hadron collider (LHC) collisions. This is achieved using a combination of different technologies, including silicon pixels, silicon microstrips, and gaseous drift-tubes, all immersed in a 2Tesla magnetic field. With nearly 750k alignable degrees of freedom, it is crucial that an accurate model of the detector positions be produced using an automated and robust algorithm in order to achieve good tracking performance. This has been accomplished using a variety of alignment techniques resulting in near optimal hit and momentum resolutions.

Modeling of the heat transfer in laser-heated small particles on surfaces

Motivated by new photothermal techniques to detect trace quantities of illicit substances, we are examining the heat transfer of small particles randomly distributed on surfaces that are selectively heated by a laser beam. For an optimal choice of laser power, illumination time and other parameters, we need formulas describing how the thermal signal depends on particle size, their distribution on the substrate surface and thermo-physical properties of the materials involved.In this manuscript we compare very simple physical models and computational simulations with experimental data from polyethylene microspheres on a polished copper surface, with diameters ranging from 20 to 200μm. Heat transfer through air dominates the process, both for single particles and between particles in clusters. The influence of high particle densities per substrate area on the heat transfer process is factored into the simulation by using a cell with just one particle and symmetric boundary conditions. Further simulations where irregular-shaped carbon pieces were approximated as lying cylinders indicate that our simple model can also describe the thermal behavior of a wider class of realistic particles on solid surfaces.

The distribution of neodymium isotopes and concentrations in the Eastern Equatorial Pacific: Water mass advection versus particle exchange

The radiogenic isotope composition of the Rare Earth Element (REE) neodymium (Nd) is a powerful water mass proxy for present and past ocean circulation. The processes controlling the Nd budget of the global ocean are not quantitatively understood and in particular source and sink mechanisms are still under debate.In this study we present the first full water column data set of dissolved Nd isotope compositions and Nd concentrations for the Eastern Equatorial Pacific (EEP), where one of the globally largest Oxygen Minimum Zones (OMZ) is located. This region is of particular interest for understanding the biogeochemical cycling of REEs because anoxic conditions may lead to release of REEs from the shelf, whereas high particle densities and fluxes potentially remove the REEs from the water column. Data were obtained between 1°40′N and 16°S along a nearshore and an offshore transect. Near surface zonal current bands, such as the Equatorial Undercurrent (EUC) and the Subsurface Countercurrent (SSCC), which are supplying oxygen-rich water to the OMZ are characterized by radiogenic Nd isotope signatures (εNd=−2). Surface waters in the northernmost part of the study area are even more radiogenic (εNd=+3), most likely due to release of Nd from volcanogenic material. Deep and bottom waters at the southernmost offshore station (14°S) are clearly controlled by advection of water masses with less radiogenic signatures (εNd=−7) originating from the Southern Ocean. Towards the equator, however, the deep waters show a clear trend towards more radiogenic values of up to εNd=−2. The northernmost station located in the Panama basin shows highly radiogenic Nd isotope signatures in the entire water column, which indicates that particle scavenging, downward transport and release processes play an important role. This is supported by relatively low Nd concentrations in deep waters (3000–6000m) in the EEP (20pmol/kg) compared to locations in the Northern and Central Pacific (40–60pmol/kg), which suggests enhanced removal of Nd in the EEP.

Radial Distributions of Dusty Plasma Parameters in a DC Glow Discharge

AbstractA non‐stationary non‐local kinetic model for radial distributions of dusty plasma parameters based on the solution of Boltzmann equation for electron energy distribution function is presented. Electrons and ions production in ionizing collisions and their recombination on dust particle surface were taken into account. The drift‐diffusion approximation for ions was used. To obtain the self‐consistent radial distribution of electric potential the Poisson equation was used. It is shown that at high dust particle density the recombination of electrons and ions can exceed their production in ionization collisions in the region of dusty cloud. In this case the non‐monotonous radial distribution of the electric field is formed, the radial electric field becomes reversed and the radial electron and ion fluxes change their direction toward the center of the tube (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Driving kinetically constrained models into nonequilibrium steady states: Structural and slow transport properties

Complex fluids in shear flow and biased dynamics in crowded environments exhibit counterintuitive features which are difficult to address both at a theoretical level and by molecular dynamic simulations. To understand some of these features we study a schematic model of a highly viscous liquid, the two-dimensional Kob-Andersen kinetically constrained model, driven into nonequilibrium steady states by a uniform non-Hamiltonian force. We present a detailed numerical analysis of the microscopic behavior of the model, including transversal and longitudinal spatial correlations and dynamic heterogeneities. In particular, we show that at high particle density the transition from positive to negative resistance regimes in the current vs field relation can be explained via the emergence of nontrivial structures that intermittently trap the particles and slow down the dynamics. We relate such spatial structures to the current vs field relation in the different transport regimes.

Experimental evidence of enhancement of thermoelectric properties in tellurium nanoparticle-embedded bismuth antimony telluride

Abstract

A vision-based hybrid particle tracking velocimetry (PTV) technique using a modified cascade correlation peak-finding method

A novel technique for particle tracking velocimetry is presented in this paper to overcome the issue of overlapping particle images encountered in the flows with high particle density or under volumetric illumination conditions. To achieve this goal, algorithms for particle identification and tracking are developed based on current methods and validated with both synthetic and experimental image sets. The results from synthetic image tests show that the particle identification algorithm is able to resolve overlapped particle images up to 50 % under noisy conditions, while keeping the root mean square peak location error under 0.07 pixels. The algorithm is also robust to the size changes up to a size ratio of 5. The tracking method developed from a classic computer vision matching algorithm is capable of capturing a velocity gradient up to 0.3 while maintaining the error under 0.2 pixels. Sensitivity tests were performed to describe the optimum conditions for the technique in terms of particle image density, particle image sizes and velocity gradients, also its sensitivity to errors of the PIV results that guide the tracking process. The comparison with other existing tracking techniques demonstrates that this technique is able to resolve more vectors out of a dense particle image field.

Porous media generated by using an immiscible lattice-gas model

To get a right structure–property relationship in porous media it is necessary to have an appropriate digital representation of the microstructure. In this paper a methodology based on a phase ordering dynamics, which it is possible to obtain digital representations of a great variety of isotropic and anisotropic microstructures, is presented. The ordering dynamics, guided by an immiscible lattice gas in a D3Q19 geometry, was characterized by using the structure factor. It was found that, for long times and high particle densities, the obtained patterns are similar to those observed in ordering processes under shear effects. The materials were characterized by means of their two-points correlation and chord length distribution functions. As an application of the model an approximated digital representation of the cubic section of a ceramic material is presented.

Optimisation of polymer coating process for microencapsulating ferrous fumarate for salt double fortification with iodine and iron

An extrusion-based encapsulation process has been developed for making salt grain-sized iron premix for salt fortification. The first step of extrusion agglomeration process has been studied and reported previously. The focus of this study is on the optimisation of the colour-masking and polymer coating steps. Several colour-masking techniques and polymer encapsulants were investigated at various encapsulation levels. Salt samples prepared by blending the resulting iron premixes with iodised salt retained more than 90% of the original iodine and more than 93% of the ferrous iron after 3 months storage at 35°C and 60% relative humidity (RH). Hydrophilic coatings such as hydroxypropyl methyl cellulose (HPMC) offered more protection at the 10% encapsulation level compared to other coating materials studied. All iron premix formulations exhibited high particle density, good bioavailability and acceptable organoleptic properties. The process using the most effective formulations and optimised operation parameters is ready for pilot scale testing and field studies.

Lipids ‒ A key for hepatitis C virus entry and a potential target for antiviral strategies

Viruses have evolved to complex relationship with their host cells. Many viruses modulate the lipid composition, lipid synthesis and signaling of their host cell. Lipids are also an essential part of the life cycle of the hepatitis C virus (HCV). HCV is a major human pathogen, persistently infecting 170 million people worldwide, with no currently effective treatment available for all patients. HCV appears to make use of the host lipid metabolism and one common feature of chronic hepatitis C is the steatosis, characterized by excessive accumulation of triglycerides and lipid content in the liver. Thus, HCV lifecycle appears to be closely connected to host cell lipid metabolism, from cell entry, through viral RNA replication to viral particle production and formation/assembly. HCV particles have a unique lipid composition, certainly distinct from other viruses. In the blood of chronically-infected patients, viral particles are bound to serum lipoproteins and are thus called lipo-viro-particles. The density of these circulating viral particles is heterogeneous. Specific infectivity and fusion of low density particles are greater than those of high density particles. Lipids and association to lipoproteins therefore play a key role in HCV life cycle. The purpose of this review is to make a state of the art on recent findings on the contribution of lipids in cell entry and membrane fusion of HCV. The influence of lipids as chemically-defined entities will be analyzed, as well as the role played by cholesterol transporters and lipoprotein receptors in HCV entry and fusion. Since viral entry would constitute a key target for antiviral strategies, inhibitor molecules interacting with viral and/or cellular membranes or interfering with the function of lipid metabolism regulators of HCV entry could offer strong antiviral potential. This will be lastly discussed in this review.