Spatial Distribution Of Particles Research Articles

Effect of a barrier on spatial distribution of respiratory particles in a room

Barriers have been widely used to mitigate transmission of Covid-19 and other diseases. Their efficacy for aerosol particles is not well established. The objective of this study was to quantify the impact of a barrier on the spatial distribution of particles released by speaking in a room with a low air-change rate (0.6 ± 0.2 h−1). The source was a nebulizer that released fluorescent microspheres of diameters 0.5, 1, 6, 10, or 20 µm for 20 min, and the room was outfitted with 108 passive sampling sites. We counted the number of microspheres deposited on slides at sampling locations after >1 h. The presence of a barrier 0.46 m in front of the source resulted in an increase in 0.5 µm particles deposited on the source-side of the barrier and an increase in 0.5 µm particles around the sides of the barrier laterally and at certain locations 4–6 m from the source. The barrier had a minor effect on the distribution of 1 µm particles. There was no observable effect of the barrier on the distribution of 6, 10, and 20 µm particles. Most 10 and 20 µm particles deposited within 0.3 m of the source, although some were found at locations >3 m from the source. These results indicate that barriers may not serve as adequate protection to others in the room, depending on their location relative to the barrier and the exposure timescale. A limitation is that our study utilized only one barrier configuration at one air-change rate.

Caustics in turbulent aerosols form along the Vieillefosse line at weak particle inertia

Caustic singularities of the spatial distribution of particles in turbulent aerosols enhance collision rates and accelerate coagulation. Here we investigate how and where caustics form at weak particle inertia, by analysing a three-dimensional Gaussian statistical model for turbulent aerosols in the persistent limit, where the flow varies slowly compared with the particle relaxation time. In this case, correlations between particle- and fluid-velocity gradients are strong, and caustics are induced by large, strain-dominated excursions of the fluid-velocity gradients. These excursions must cross a characteristic threshold in the plane spanned by the invariants $Q$ and $R$ of the fluid-velocity gradients. Our method predicts that the most likely way to reach this threshold is by a unique ``optimal fluctuation'' that propagates along the Vieillefosse line, $27R^2/4 +Q^3=0$. We determine the shape of the optimal fluctuation as a function of time and show that it is dominant in numerical statistical-model simulations even for moderate particle inertia.

Spatial migration and distribution of suspended particles in saturated sand layer under the impact of temperature

AbstractThe migration, deposition and detachment of suspended particles in saturated sands are used in many fields. Temperature is an important influencing factor in the transport and deposition process of particles in porous media, and it plays an important role in ground‐water heat pump (GWHP) projects. This article discusses the independent development of a three‐dimensional percolation sandbox test device and the design of a particle migration test based on the Reynolds number in the context of the backfilling process of GWHP systems as the experimental background. The effects of various temperatures (10, 25, and 40°C) on the movement of suspended particles in porous media were studied. The experimental results showed that as the temperature rose, more particles were deposited in the sand layer, the uneven flow of particles in the sand layer accelerated, and the particles spread out in the direction opposite to the non‐percolation direction with a wider distribution range in the sandbox. Increased temperature also promoted the percolation of smaller particles, causing the diffusion zone to terminate sooner and the deposition zone to last longer, resulting in the capture of more particles on the surface and in the pore channels of the sand layer.

Occurrence, spatial distribution, and characterization of microplastic particles in the salt pans from the Southeastern part of the Bay of Bengal

The occurrence and spatial distribution of microplastics (MPs) in 12 salt pans from the southeastern part of Bangladesh were investigated. A total of 9640 MPs particles were found in the samples collected, ranging from 560 to 1253.33 particles kg −1 in each salt pan. The highest amount of microplastic (MPs) was found in the salt pans from South Kutubdia (1253.33 ± 128.58 particles kg −1) and North Kutubdia (1026.67 ± 189.03 particles kg −1), indicating that the sites that are linked to open seawater contain a greater amount of MPs than the sites connected to the sea through channels or creeks. The maximum number of MPs (88%) accounted for in the 300–1500μm size class. Based on colour, black (24%), transparent (17%) and yellow (15%) were the most dominant MPs in the collected samples. Among the six different shapes, fibres (43%) and foams (21%) were the most dominant shapes of MPs. The most abundant polymer types of MPs were polypropylene (40.63%), polyethylene (31.25%), polyethylene terephthalate (18.75%) and polystyrene (9.38%). This study indicated that the surface seawater of the southeastern coast of Bangladesh is highly contaminated by MPs. The presence of MPs in sea salt might pose a significant threat and risk to food safety, food security and thus public health. Therefore, ongoing monitoring should be in place to monitor MPs levels in local sea salts.

NanoSpot™ collector for aerosol sample collection for direct microscopy and spectroscopy analysis.

We describe design and characterization of an aerosol NanoSpot™ collector, designed for collection of airborne particles on a microscopy substrate for direct electron and optical microscopy, and laser spectroscopy analysis. The collector implements a water-based, laminar-flow, condensation growth technique, followed by impaction onto an optical/electron microscopy substrate or a transmission electron microscopy grid for direct analysis. The compact design employs three parallel growth tubes allowing a sampling flow rate of 1.2 L min-1. Each growth tube consists of three-temperature regions, for controlling the vapor saturation profile and exit dew point. Following the droplet growth, the three streams merge into one flow and a converging nozzle enhances focusing of grown droplets into a tight beam, prior to their final impaction on the warm surface of the collection substrate. Experiments were conducted for the acquisition of the size-dependent collection efficiency and the aerosol concentration effect on the NanoSpot™ collector. Particles as small as 7 nm were activated and collected on the electron microscopy stub. The collected particle samples were analyzed using electron microscopy and Raman spectroscopy for the acquisition of the particle spatial distribution, the spot sample uniformity, and the analyte concentration. A spot deposit of approximately 0.7-mm diameter is formed for particles over a broad particle diameter range, for effective coupling with microscopic and spectroscopic analysis. Finally, the NanoSpot™ collector's analytical measurement sensitivity for laser Raman analysis and counting statistics for fiber count measurement using optical microscopy were calculated and were compared with those of the conventional aerosol sampling methods.

Gradient characterization of steel-concrete interface at early ages

Steel-Concrete Interface (SCI) refers to the porous weak area at the interface between steel bar and cement matrix. This study proposes sophisticated methods for quantifying gradient properties and their evolution of SCI using back-scattered electron (BSE) imaging and nano-indentation. The gradient of SCI is identified through a robust statistical analysis. Distinct stratification structure of SCI is discovered, which can be demonstrated from the grayscale of BSE as well as the indentation modulus and hardness. The thickness of SCI increases with age and the increasing rates roughly decline with the increase of w/c. SCI can be divided into highly porous layer I and transition layer II according to the hierarchically porosity. The layer II is subdivided into II(a) and II(b) based on the gradient of mechanical properties, which is mainly caused by the spatial distribution of cement particles within SCI.

A Novel Droplet Generator and a Bench-Testing Rig Enabling Research on Suspension Droplet Wall Impingement and Particle Deposition

We present a novel device for generating suspension droplets and studying droplet impact against solid substrates. The proposed droplet generator extends beyond previous designs by introducing hydraulic machinery that includes separate hydraulic and test containers. This eliminates mixing between the test liquid and the hydraulic liquid above the latch that connects the two containers, thus ensuring reliable clogless operation. The device can produce droplets of controllable sizes between 0.75 and 4.4 mm, and droplets can contain suspension particles of 45 μm to 300 μm size. Repeatability tests show that, at constant control parameters, the median relative droplet size deviation from the target value is ±0.9% and the maximum relative deviation is ±9.1%. We also explore different collision scenarios, which we change from spreading to bouncing by varying the substrate wettability. In addition, the shape of the stain and the resulting spatial distribution of particles are found to be sensitive to particle size.

Interrelationships among Adjustable Design Parameters and Rate Performance of Porous Electrodes in Lithium‐Ion Batteries

A combination of experiments and physics-based modeling is used to highlight the complex interaction among the adjustable design parameters of porous electrodes in determining the capacity and rate performance of lithium-ion batteries (LIBs). A series of 52 LiMn2O4 electrodes are prepared with loading and porosity in the range of 10 to 30 mg cm−2 and 0.2 to 0.5, respectively, and cycled at different C-rates in front of Li. A detailed polarization analysis of the 96 discharge profiles points to the absence of any ubiquitous sharp and universal correlation between the lumped macroscopic indexes such as the electrode thickness and the battery performance. The results call for a careful attention to the nonlinear response of the LIBs to the design variations and the significance of big data analysis to reveal the peculiar interrelationships between the battery performance and the detailed features of the electrodes such as the configuration and spatial distribution of the (in)active particles.

Asymmetry in particle transport in slightly non-homogeneously doped silicon layers in low injection regime and quasi-neutrality condition

In this work a 1D slightly doped n-type Silicon layer is considered. Irreversible thermodynamics transport equations are used to obtain the spatial particle distribution in isothermal stationary state. The excess particle transport is studied in low injection regime and quasineutrality condition. The material is subjected to Dirichlet-Neumann (N-D) conditions at the boundaries. We wonder if an asymmetry of the particle flux exists when the boundary conditions are inverted. We find that the asymmetry does exist and a rectification factor may reach the value 0.35. We conclude that particle flux rectification seems to be featuring the particle transport in slightly non-homogeneously doped semiconductor when the excess hole concentration is smaller than the equilibrium hole concentration

STRUCTURE, MARTENSITIC TRANSFORMATIONS AND MECHANICAL PROPERTIES OF AGING NANOCRYSTALLINE TI-50.9 AT % NI ALLOY

The effect of aging temperature in the range of 300-500°C on the structure, R martensitic transformations and mechanical characteristics of nanocrystalline Ti-50.9 at % Ni alloy with a grain/subgrain structure was studied. It was found that variation in the spatial distribution of coherent Ti3Ni4 particles in the nanostructure from their location on dislocations during low-temperature aging to precipitation at dislocation boundaries under intense aging is accompanied by a change in the morphology of the R phase from a nanodomain to a self-accommodating lamellar structure. The nanodomain structure of the R phase contributes to uniform deformation of the alloy during loading/unloading and stabilization of superelasticity. When loading the alloy with a lamellar R-phase morphology, localized deformation bands are formed by the R-phase reorientation in a Luders deformation manner.

Modeling the dynamics of fine dust fraction in the surface layer of the atmosphere

We investigated the operating conditions of excavator equipment, leading to unsteady dynamics of dust far from the pollution source. Wind transport of dust takes into account the non-uniform vertical wind profile. Diffusion movement is also determined by the inhomogeneous coefficient of turbulent diffusion with a nonmonotonic dependence on height. The Earth’s surface is given by a digital elevation model, which allows calculations for a specific area with complex topography. Vertical inhomogeneities of wind and turbulence significantly change the nature of the spatial distributions of dust particles. Our approach makes it possible to determine changes in the disperse composition of particles with distance from the dust source.

Two-dimensional fluid simulation of spatial distribution of dust particles in a capacitively coupled silane plasma

In this work, we develop a two-dimensional fluid model to study the spatial density distributions of dust particles in a radio frequency capacitively coupled silane plasma. Unlike those scenarios based on the one-dimensional fluid model, in this work, the nonuniformity of the radial density distributions of dust particles is attributed mainly to the radial components of the electric field force and the ion drag force acting on the dust particles, leading to the two local density peaks near the electrode edges. It seems that dust particles tend to overcome the support of the electric field force and move much closer to the electrodes, as one of the density peaks indicates. Moreover, with the decrease of the radii of the discharge electrodes or the distance between them, the radial component of the ion drag force is enhanced, resulting in more dust particles gathering near the electrode edge region, and forming a ring-shaped particle density distribution. In the case of the discharge electrodes wrapped with dielectric materials, the uniformity of the radial density distributions of dust particles between the two electrodes is improved. Finally, the vortex motion of a single dust particle near the electrode edge region is also simulated in this work.

Statistical characterization of spatial and size distributions of particles in composite materials used in the manufacturing of biomedical instruments

Aluminium is extensively used in many manufacturing processes because of its intrinsic properties like soft, ductile, high electrical conductivity and highly corrosion resistant. Unfortunately, pure aluminium cannot give a required tensile strength, whereas by adding some other materials like particles of silicon carbide can give a proper strength and converted into a composite with adequate properties which is most suitable in the manufacturing of some specific biomedical instruments. It is well known that size and spatial distributions of particles are both influential in determining the mechanical properties of composite materials and, therefore, statistical characterization of these distributions is of prime importance if we wish to control the quality of the manufacturing processes for these materials. Many researchers have considered quantitative analysis of these features separately, but here we investigate the relationship between size and spatial distribution of the particles over an aluminium matrix. We have considered the actual sizes simply as ‘large’ or ‘small’ and, consequently, the characterization of the particle distribution patterns in the aluminium matrix can be carried out using statistical methods based on the theory of bivariate spatial point processes. We have applied this statistical approach to a sample of an aluminium alloy reinforced with silicon carbide particles. It is shown that the methods provide a complete characterization on the spatial interaction between small and large silicon carbide particles and it can be successfully used in a quality control step for the production of particulate composite materials used in the manufacturing of biomedical instruments.

Polarimetry of the Total Lunar Eclipse on 2022 November 8

Abstract We have measured the degree of linear polarization of the Moon during its total eclipse on 2022 November 8, and found P ≈ −2% in the V filter. The plane of preferential polarization was oriented at ∼36° counting clockwise from the lunar equator. These measurements suggest global asymmetry in the spatial distribution of aerosol particles in the uppermost atmosphere of Earth, with their net linear polarization being P ≈ −6.5%.

Human health risk perspective study on characterization, quantification and spatial distribution of microplastics in surface water, groundwater and coastal sediments of thickly populated Chennai coast of South India

Microplastics (MPs) are defined as plastic particles smaller than 5 mm in size. They are primarily derived from larger pieces of plastic debris that degrade into smaller pieces. The current study identified, characterized, and quantified MPs in Chennai coast coastal aquifers, seawater, and foreshore sediments. The spatial distribution and polymer composition of MP particles were studied to identify and evaluate their abundance and characteristics (composite, size, color, and shape of MPs). The foreshore and river mouth sediment samples were found to be contaminated by MPs with a total of 263 particles in 12 samples collected from different locations (average of 22 particles 5 g−1 of dry sediment (d.s.)). The surface water and groundwater samples were also contaminated by MPs with a total of 315 particles in 25 samples collected from different locations (average of 13 particles/L). Size of majorities of MPs ranged from 1 mm to 300 μm. The study also confirmed the presence of MPs in sediments and water samples collected from the study area using Fourier transform infrared spectroscopy (FTIR). FTIR results revealed that nylon, polyvinylchloride, and polyethylene terephthalate were the predominant types of MPs. The spatial variation map showed that high concentration of MPs was observed on tourist beaches. Remediation technologies are highly effective in eliminating and preventing MPs pollution in our environment. The existence of MPs in water samples suggests that it is essential to take preventive steps to avoid MPs causing health issues like neurotoxicity, Alzheimer, and cancer.

Improved Heat Transfer in Guar Gel Composites Reinforced with Randomly Distributed Glass Microspheres

Improved heat transfer in composites consisting of guar gel matrix and randomly distributed glass microspheres is extensively studied to predict the effective thermal conductivity of composites using the finite element method. In the study, the proper and probabilistic three-dimensional random distribution of microspheres in the continuous matrix is automatically generated by a simple and efficient random sequential adsorption algorithm which is developed by considering the correlation of three factors including particle size, number of particles, and particle volume fraction controlling the geometric configuration of random packing. Then the dependences of the effective thermal conductivity of composite materials on some important factors are investigated numerically, including the particle volume fraction, the particle spatial distribution, the number of particles, the nonuniformity of particle size, the particle dispersion morphology and the thermal conductivity contrast between particle and matrix. The related numerical results are compared with theoretical predictions and available experimental results to assess the validity of the numerical model. These results can provide good guidance for the design of advanced microsphere reinforced composite materials.

Network approach for the analysis of the irreversible deformation of solids with soft heterogeneities

We introduce the concept of shear band network (SBN) in ductile solids containing soft particles to investigate their irreversible deformation. Drawing on network science tools, we show that the evolution of the SBN explains the material strength at the coarse scale. To gain physical understanding of the activation order of the SBN links during tensile loading, we develop an analytical model based on the continuum theory of irreversible deformation. The results are used to construct an efficient, parameter-free indicator of the material strength that is solely based on the particle size and spatial distribution, thus proving that network science can advance the understanding of strength mechanisms in ductile solids.

Numerical simulation and multi-process coupling analysis for biomass pyrolysis fluidized bed reactor based on synergistic effects between biomass and nitrogen inlet modes

Biomass fast pyrolysis fluidized bed reactor is regarded as one of the most promising technologies for high value utilization of biomass. In this work, one two-dimensional fluidized bed reactor model was established, coupling with multiphase CFD simulation method and pyrolysis reaction kinetics, and further verified by the experimental data. This work mainly investigated the effects of biomass inlet and nitrogen inlet modes on multi-process characteristics, such as flow behavior, heat transfer and pyrolysis reaction. The synergistic effects between the two inlet modes were further explored and thus would affect the three-phase pyrolysis product distribution. The results showed that the spatial particle distribution and temperature distribution in the dense phase zone were becoming more uniform and the tar yield increased when the biomass inlet mode changed from single nozzle to double nozzles jetting opposite. Besides, when the nitrogen nozzle number was set as one and the auxiliary gas velocity was set as 0.15 m/s, much larger local circulation formed in the dense phase zone, meanwhile the particle volume fraction and temperature became more evenly distributed, which was conducive to the biomass pyrolysis process. The nitrogen inlet mode was found to show a greater impact on the tar yield compared to the biomass inlet mode. For single gas inlet mode, one biomass nozzle should be preferred for lower auxiliary gas velocity and the opposite double nozzle would be better for higher auxiliary gas velocity. The synergistic effects between biomass and nitrogen inlet modes were further summarized, which were found to have a positive impact on the biomass pyrolysis reaction characteristics. Based on the above conclusions, this work could provide a feasible theoretical guidance for designing fluidized bed pyrolysis reactor and optimizing the biomass pyrolysis process.

A pairwise hydrodynamic theory for flow-induced particle transport in shear and pressure-driven flows

An exact pairwise hydrodynamic theory is developed for the flow-induced spatial distribution of particles in dilute polydisperse suspensions undergoing two-dimensional unidirectional flows, including shear and planar Poiseuille flows. Coupled diffusive fluxes and a drift velocity are extracted from a Boltzmann-like master equation. A boundary layer is predicted in regions where the shear rate vanishes with thickness set by the radii of the upstream collision cross-sections for pair interactions. An analysis of this region yields linearly vanishing drift velocities and non-vanishing diffusivities where the shear rate vanishes, thus circumventing the source of the singular particle distribution predicted by the usual models. Outside of the boundary layer, a power-law particle distribution is predicted with exponent equal to minus half the exponent of the local shear rate. Trajectories for particles with symmetry-breaking contact interactions (e.g. rough particles, permeable particles, emulsion drops) are analytically integrated to yield particle displacements given by quadratures of hard-sphere (or spherical drop) mobility functions. Using this analysis, stationary particle distributions are obtained for suspensions in Poiseuille flow. The scale for the particle distribution in monodisperse suspensions is set by the collision cross-section of the particles but its shape is almost universal. Results for polydisperse suspensions show size segregation in the central boundary layer with enrichment of smaller particles. Particle densities at the centreline scale approximately with the inverse square root of particle size. A superposition approximation reliably predicts the exact results over a broad range of parameters. The predictions agree with experiments in suspensions up to approximately 20 % volume fraction without fitting parameters.

Bayesian Inverse Modelling for Probabilistic Multi-Nuclide Source Term Estimation Using Observations of Air Concentration and Gamma Dose Rate

In case of a release of hazardous radioactive matter to the atmosphere from e.g., a nuclear power plant accident, atmospheric dispersion models are used to predict the spatial distribution of radioactive particles and gasses. However, at the early stages of an accident, only limited information about the release may be available. Thus, there is a need for source term estimation methods suitable for operational use shortly after an accident. We have developed a Bayesian inverse method for estimating the multi-nuclide source term describing a radioactive release from a nuclear power plant. The method provides a probabilistic source term estimate based on the early available observations of air concentration and gamma dose rate by monitoring systems. The method is intended for operational use in case of a nuclear accident, where no reliable source term estimate exists. We demonstrate how the probabilistic formulation can be used to provide estimates of the released amounts of each radionuclide as well as estimates of future gamma dose rates. The method is applied to an artificial case of a radioactive release from the Loviisa nuclear power plant in southern Finland, considering the most important dose-contributing nuclides. The case demonstrates that only limited air concentration measurement data may be available shortly after the release, and that to a large degree one will have to rely on gamma dose rate observations from a frequently reporting denser monitoring network. Further, we demonstrate that information about the core inventory of the nuclear power plant can be used to constrain the release rates of certain radionuclides, thereby decreasing the number of free parameters of the source term.