Significant Number Of Particles Research Articles

Simulation of Biomass Combustion with Modified Flue Gas Tract

The combustion of biomass is accompanied by the formation of particulate matter, the presence of which in the atmosphere harms human health. It is important to show the issues of reducing these pollutants and their impact on human health. This article focuses on the process of biomass combustion. The used model consists of two parts: the combustion chamber and the flue gas tract. The article shows four types of modification of the flue gas tract designed to reduce the amount of particulate matter in the atmosphere. Baffles are located in the flue gas tract, which is designed to capture the particulate matter. The final model is simulated by turbulent–viscosity models, k-ε realizable model, and then k-ω shear stress transport model. The interaction between turbulence and chemical reactions is expressed by using the Eddy Dissipation Concept model. The results then show different profiles of temperature, velocity, and particle distribution. Based on the evaluated data from two different calculations, it can be concluded that the baffles have a significant effect on the reduction of particulate matter in the atmosphere. The used baffles are able to capture mainly particles with a diameter greater than 100 µm. A significant number of particles with a diameter lower than 100 µm flows from the flue gas tract to the surrounding environment.

Carbon nanotube accelerator — Path toward TeV/m acceleration: Theory, experiment, and challenges

Aspirations of modern high energy particle physics call for compact and cost efficient lepton and hadron colliders with energy reach and luminosity significantly beyond the modern HEP facilities. Strong interplanar fields in crystals of the order of 10–100 V/Å can effectively guide and collimate high energy particles. Besides continuous focusing crystals plasma, if properly excited, can be used for particle acceleration with exceptionally high gradients [Formula: see text](TeV/m). However, the angstrom-scale size of channels in crystals might be too small to accept and accelerate significant number of particles. Carbon-based nano-structures such as carbon-nanotubes (CNTs) and graphenes have a large degree of dimensional flexibility and thermo-mechanical strength and thus could be more suitable for channeling acceleration of high intensity beams. Nano-channels of the synthetic crystals can accept a few orders of magnitude larger phase-space volume of channeled particles with much higher thermal tolerance than natural crystals. This paper presents conceptual foundations of the CNT acceleration, including underlying theory, practical outline and technical challenges of the proof-of-principle experiment. Also, an analytic description of the plasmon-assisted laser acceleration is detailed with practical acceleration parameters, in particular with specifications of a typical tabletop femtosecond laser system. The maximally achievable acceleration gradients and energy gains within dephasing lengths and CNT lengths are discussed with respect to laser-incident angles and the CNT-filling ratios.

Analysis of mass transfer behavior in membrane distillation: Mathematical modeling under various conditions

Four commercially available hydrophobic membranes with different pore sizes were separately used in a direct contact membrane distillation (DCMD) apparatus to investigate the effect of fouling on the mass transfer coefficient, and the dominant mass transport mode under different conditions defined by the temperature, membrane material, flow regime, and membrane pore size. Both ultrapure deionized water and simulated industrial wastewater were considered as the feed water. The results of the investigation confirmed that the fouling layer impacted the mass transport directly by resisting it, and indirectly by altering the heat transfer mechanism. In addition to the surface fouling layer, a significant number of particles were also observed to accumulate in the membrane pores. It was further determined that the contribution of Poiseuille flow to the entire mass transport was significant at higher temperatures when using a membrane with large pores. This highlighted the need for careful consideration of Poiseuille flow in the modeling and simulation of a membrane distillation (MD) mass transport process. It was also observed that the flow rate did not affect the Poiseuille flow and therefore did not directly impact the entire mass transfer. The study findings provide systematic insight for the development of a strategy for selecting an appropriate operating feed for DCMD and adjusting the permeate temperature to fit the prevailing water demand and environmental conditions.

Impact of the external window crack structure on indoor PM2.5 mass concentration

The fine particulate matter, generally known as PM2.5, has great impact on the air quality and human health. Although closing external windows can help prevent outdoor PM2.5 going into indoors, many studies have shown that a significant number of particles can still pass the building façade through the cracks around the window. In order to quantify the influence of the external window crack structure and some relevant parameters, such as room dimension, on the indoor PM2.5 mass concentration, this paper introduces an updated model from a previously published paper by the authors [18]. The model was developed based on two-month field measured data from five unoccupied offices located in the central area of Beijing (capital city located in northern China), and then was validated against a new dataset measured in Guangzhou (a major city located in southern China). The model can be used to quantify the indoor PM2.5 mass concentration based on the instant outdoor PM2.5 level, considering influences from external window crack structure, room dimension and outdoor meteorological conditions, i.e. outdoor wind speed and relative humidity.

Microfluidic Buffer Exchange for Interference-free Micro/Nanoparticle Cell Engineering

Engineering cells with active-ingredient-loaded micro/nanoparticles (NPs) is becoming an increasingly popular method to enhance native therapeutic properties, enable bio imaging and control cell phenotype. A critical yet inadequately addressed issue is the significant number of particles that remain unbound after cell labeling which cannot be readily removed by conventional centrifugation. This leads to an increase in bio imaging background noise and can impart transformative effects onto neighboring non-target cells. In this protocol, we present an inertial microfluidics-based buffer exchange strategy termed as Dean Flow Fractionation (DFF) to efficiently separate labeled cells from free NPs in a high throughput manner. The developed spiral microdevice facilitates continuous collection (>90% cell recovery) of purified cells (THP-1 and MSCs) suspended in new buffer solution, while achieving >95% depletion of unbound fluorescent dye or dye-loaded NPs (silica or PLGA). This single-step, size-based cell purification strategy enables high cell processing throughput (106 cells/min) and is highly useful for large-volume cell purification of micro/nanoparticle engineered cells to achieve interference-free clinical application.

Microfluidic Buffer Exchange for Interference-free Micro/Nanoparticle Cell Engineering.

Engineering cells with active-ingredient-loaded micro/nanoparticles (NPs) is becoming an increasingly popular method to enhance native therapeutic properties, enable bio imaging and control cell phenotype. A critical yet inadequately addressed issue is the significant number of particles that remain unbound after cell labeling which cannot be readily removed by conventional centrifugation. This leads to an increase in bio imaging background noise and can impart transformative effects onto neighboring non-target cells. In this protocol, we present an inertial microfluidics-based buffer exchange strategy termed as Dean Flow Fractionation (DFF) to efficiently separate labeled cells from free NPs in a high throughput manner. The developed spiral microdevice facilitates continuous collection (>90% cell recovery) of purified cells (THP-1 and MSCs) suspended in new buffer solution, while achieving >95% depletion of unbound fluorescent dye or dye-loaded NPs (silica or PLGA). This single-step, size-based cell purification strategy enables high cell processing throughput (10(6) cells/min) and is highly useful for large-volume cell purification of micro/nanoparticle engineered cells to achieve interference-free clinical application.

Statistical mechanics of dust charging in a multi-ion plasma with negative and positive ionic species

On the basis of statistical mechanics and charging kinetics, the charge distribution over uniform size spherical dust particles in a multi-ion plasma comprising of multiple charged negative and positive ions is investigated. Two specific situations where the complex plasma is viz., (i) dark (no emission from dust) and (ii) irradiated by laser light (causing photoemission from dust) have been taken into account. The analytical formulation includes the population balance equation for the charged dust particles along with number and energy balance of the complex plasma constituents. The departure of the results for multi-ion plasma from that in case of usual singly charged positive ion plasma is graphically illustrated and discussed. In contrast to electron-ion plasma, significant number of particles is seen to acquire opposite charge in case of pure positive-negative ion plasma, even in the absence of electron emission from the dust grains. The effects of various plasma parameters viz., number density, particle size, and work function of dust on charge distribution have also been examined.

AUV Single Beacon Range-Only SLAM with a SOG Filter

This paper presents a solution to the Simultaneous Localization and Mapping (SLAM) problem of an AUV which uses range-only measurements towards a single beacon. It simultaneously estimates the beacon (a priori unknown) and AUV (a priori known) positions. Conventional EKF-SLAM methods cannot deal with this problem since the resultant probability density function (pdf) of the beacon-position is severely non-Gaussian during the initialization. Particle filters can do the job but, depending on the size of the space where the beacon lays, a significant number of particles may be required to populate the solution domain, making difficult to achieve real-time performance. In this paper we present a filter which represents the joint pdf of the robot and beacon positions as a Multivariate Gaussian Mixture which has the potential to represent an arbitrary pdf with a number of Gaussian 'particles' significantly smaller than the one that would be necessary if conventional particles were used instead. In our method, each particle contains a full EKF over vehicle position/velocity and the beacon position. The method is applied to locate a sub-sea panel and home to it autonomously in order to establish visual contact to later launch a visual servoing based docking task. The method is demonstrated through real-time Hardware-in-the-loop experiments (HIL) where the robot follows an observable trajectory.

An experimental investigation of the indirect transfer and deposition of gunshot residue: Further studies carried out with SEM–EDX analysis

Experiments were undertaken in order to explore the potential for gunshot residue (GSR) particles to undergo tertiary transfer, and to be deposited on individuals in the vicinity of a firearm discharge. Samples were taken from hands following a series of test-firings. SEM-EDX with automated detection and analysis software was used to determine the presence of GSR on these samples. As many as 22 particles were found to have undergone tertiary transfer via a series of handshakes following a firearm discharge. In one run, a particle measuring 49.19 μm was recovered from a tertiary transfer recipient. Significant numbers of particles were also recovered from bystanders, with as many as 36 being detected on a sample taken from an individual who was in the proximity of a firearm discharge. The implications of these observations for forensic investigations are considered. In particular, the need to prevent unwanted transfer during the collection phase is highlighted, and the importance of acknowledging the possibility of secondary and tertiary transfers when reconstructing firearms incidents is also stressed. Experimental studies offer a means of improving our understanding of the dynamics of GSR transfer and deposition, and assisting the forensic reconstruction of firearms incidents.

Particle Release from Respirators, Part II: Determination of the Effect of Tension Applied in Simulation of Removal

This study evaluated the potential for disposable filtering facepiece respirators (hereafter termed masks) contaminated with 1-μ m particles to release particles as a result of lateral tension applied to the mask. The lateral tension was designed to simulate the removal of a contaminated mask from a user's head. Four brands of filtering facepieces were loaded with approximately 20 million 1.0-μ m polystyrene latex (PSL) microspheres. The respirators were then placed in a test chamber and subjected to lateral tension between 17.8–26.7 N (4–6 lbs) for 1 to 2 sec. The findings suggest that neither mask type nor loading condition affects particle release. This supports our hypothesis that when filtering facepiece respirators are properly removed from the head they will not release a significant number of particles.

Numerical methods for particle-laden DNS of homogeneous isotropic turbulence

Particle-laden direct numerical simulations (DNS) are a valuable research tool for the calculation of turbulent particle dispersion. Since the first particle-laden DNS was performed, there has been a vast amount of information gained on the physics of how particles disperse in turbulent flow. However, there appears to be a lack of consensus regarding several issues involved in performing a particle-laden DNS. These issues include: selecting a statistically significant number of particles to track, determining the most accurate yet computationally efficient particle velocity interpolation scheme and deciding on a virtual release time for the particles such that the particle trajectories are independent of their initial conditions. To illustrate the lack of consensus in the scientific community, a survey of the literature is presented and an analysis of the various issues is performed. In addition, new methods for determining the statistically significant number of particles to track are proposed and improvements are made to the existing method for selecting a virtual release time in decaying isotropic turbulence.

Frequency-modulated ratchet with autoresonance

Motion of an ensemble of non-interacting classical particles in a space-periodic potential subjected to a weak external wave-like perturbation is considered. With large values of the wavenumber, the perturbation causes a resonance-induced chaotic layer in a certain area of phase space. Different scenarios of the emergence of chaos are considered. Adiabatic space or time modulation of the phase of the perturbation changes the location of the chaotic layer. A significant number of particles trapped within the chaotic layer is retained inside in course of the adiabatic modulation, revealing autoresonant behavior. We show that this phenomenon can be used to generate a directed ballistic current using a weak perturbation, even if particle’s energies are initially close to the minimal value.

Mild steel welding fume causes manganese accumulation and subtle neuroinflammatory changes but not overt neuronal damage in discrete brain regions of rats after short-term inhalation exposure

Serious questions have been raised by occupational health investigators regarding a possible causal association between neurological effects in welders and the presence of manganese (Mn) in welding fume. Male Sprague–Dawley rats were exposed by inhalation to 40 mg/m 3 of gas metal arc-mild steel (MS) welding fume for 3 h/day for 10 days. Generated fume was collected in the animal chamber during exposure, and particle size, composition, and morphology were characterized. At 1 day after the last exposure, metal deposition in different organ systems and neurological responses in dopaminergic brain regions were assessed in exposed animals. The welding particles were composed primarily of a complex of iron (Fe) and Mn and were arranged as chain-like aggregates with a significant number of particles in the nanometer size range. Mn was observed to translocate from the lungs to the kidney and specific brain regions (olfactory bulb, cortex, and cerebellum) after MS fume inhalation. In terms of neurological responses, short-term MS fume inhalation induced significant elevations in divalent metal ion transporter 1 (Dmt1) expression in striatum and midbrain and significant increases in expression of proinflammatory chemokines (Ccl2, Cxcl2) and cytokines (IL1β, TNFα) in striatum. In addition, mRNA and protein expression of glial fibrillary acidic protein (GFAP) was significantly increased in striatum after MS fume exposure. However, the 10-day MS welding fume inhalation did not cause any changes in dopamine and its metabolites or GABA in dopaminergic brain regions nor did it produce overt neural cell damage as assessed by histopathology. In summary, short-term MS welding fume exposure led to translocation of Mn to specific brain regions and induced subtle changes in cell markers of neuroinflammatory and astrogliosis. The neurofunctional significance of these findings currently is being investigated in longer, more chronic welding fume exposure studies.

Dynamic facilitation explains ‘democratic’ particle motion of metabasin transitions

Transitions between metabasins in supercooled liquids seem to occur through rapid collective particle rearrangements. These events have been called ‘democratic’ as they appear homogeneous over a significant number of particles. This could suggest that ‘democratic’ rearrangements are fundamentally distinct to those leading to dynamic heterogeneity. Here we show, however, that this apparent homogeneous particle motion can be explained solely in terms of dynamic facilitation, and is therefore intriniscally heterogeneous. We do so by studying metabasin transitions in facilitated spin models and constrained lattice gases. We find that metabasin transitions occur through a sequence of locally facilitated events taking place over a relatively short time frame. When observed on small enough spatial windows these events appear sudden and homogeneous. Our results indicate that metabasin transitions, while apparently homogeneous and ‘democratic’, are yet another manifestation of dynamical heterogeneity in glass formers.

Conceiving a high resolution and fast X-ray CT system for imaging fine multi-phase mineral particles and retrieving mineral liberation spectra

Mineral liberation studies on fine particulate systems require high resolution and fast examination of a (statistically) significant number of particles. Commercial X-ray computed tomography systems allow high resolution on very small samples (say few micrometers on single particles) and only limited resolution on large particulate samples: thus they are unsuitable for fine particle liberation studies. A computed tomography system was conceived that is capable of high resolution (say micrometric or sub-micrometric) and allows imaging at once a large number of particles. It uses a detector design with a fiber optic bundle that allows enlarging the Field of View of a standard high resolution CCD in one direction. The thin particle multi-layer in a straw offers low X-ray attenuation and permits scanning with low current and voltages that in turn allows keeping small the size of X-ray focal spot and the induced geometrical un-sharpness of the projected particles. At low magnification values (i.e., with the sample close to the detector fiber optic input end) the overall resolution is controlled by CCD pixel size and the detector allows to scan more particles. At higher magnification values the detector design allows also improvements in resolutions. The system allows studying directly in 3D those liberation problems that require micrometer-size resolution.

Particle generation by laser ablation during surface decontamination

Abstract Laser ablation allows significant number of particles to be generated from the surfaces of cement, chromium-embedded cement, stainless steel, or alumina. The number concentrations and size distributions of the particles were experimentally investigated with respect to applied laser fluence (mJ cm - 2 ) and wavelength. Based on the measurements, 266-nm laser ablation generates particles most efficiently. Of the three materials tested, cement was the most favorable for material removal, stainless steel was the next, and alumina was the least. The removal of particles from chromium-embedded cement by 532- and 1064-nm-wavelength lasers was less effective than from stainless steel, but more effective than from alumina. For ablation with a 266-nm laser, chromium enhanced the removal above 20 J cm - 2 . Comparisons of other characteristics such as the size and removal rate of these particles are also discussed in this paper.

In situ measurements of background aerosol and subvisible cirrus in the tropical tropopause region

In situ aerosol measurements were performed in the Indian Ocean Intertropical Convergence Zone (ITCZ) region during the Airborne Polar Experiment‐Third European Stratospheric Experiment on Ozone (APE‐THESEO) field campaign based in Mahé, Seychelles between 24 February and 6 March 1999. These are measurements of particle size distributions with a laser optical particle counter of the Forward Scattering Spectrometer Probe (FSSP)‐300 type operated on the Russian M‐55 high‐altitude research aircraft Geophysica in the tropical upper troposphere and lower stratosphere up to altitudes of 21 km. On 24 and 27 February 1999, ultrathin layers of cirrus clouds were penetrated by Geophysica directly beneath the tropical tropopause at 17 km pressure altitude and temperatures below 190 K. These layers also were concurrently observed by the Ozone Lidar Experiment (OLEX) lidar operating on the lower‐flying German DLR Falcon research aircraft. The encountered ultrathin subvisual cloud layers can be characterized as (1) horizontally extending over several hundred kilometers, (2) persisting for at least 3 hours (but most likely much longer), and (3) having geometrical thicknesses of 100–400 m. These cloud layers belong to the geometrically and optically thinnest ever observed. In situ particle size distributions covering diameters between 0.4 and 23 μm obtained from these layers are juxtaposed with those obtained inside cloud veils around cumulonimbus (Cb) anvils and also with background aerosol measurements in the vicinity of the clouds. A significant number of particles with size diameters around 10 μm were detected inside these ultrathin subvisible cloud layers. The cloud particle size distribution closely resembles a background aerosol onto which a modal peak between 2 and 17 μm is superimposed. Measurements of particles with sizes above 23 μm could not be obtained since no suitable instrument was available on Geophysica. During the flight of 6 March 1999, upper tropospheric and lower stratospheric background aerosol was measured in the latitude band between 4°S and 19°S latitude. The resulting particle number densities along the 56th meridian exhibit very little latitudinal variation. The concentrations for particles with sizes above 0.5 μm encountered under these background conditions varied between 0.1 and 0.3 particles/cm3 of air in altitudes between 17 and 21 km.

STAAARTE‐MED 1998 summer airborne measurements over the Aegean Sea 1. Aerosol particles and trace gases

We performed airborne measurements of sulfur dioxide (SO2), carbon monoxide (CO), and aerosol chemical/microphysical properties over the Aegean Sea. The data were collected on board the Met Office C‐130 research aircraft in August 1998. High SO2 mixing ratios up to 18 ppb and aerosol sulfate levels up to 500 ppt were measured near Thessaloniki in northern Greece. The highest concentrations were observed at altitudes between 1 and 2 km, while near the surface much lower SO2 mixing ratios between 1 and 4 ppb were found. The pollution was transported southward over the Aegean Sea as far south as Crete, where SO2 mixing ratios up to 5 ppb were observed. The combined results of the SO2, aerosol sulfate, and particle size distribution measurements indicate air masses containing emissions with different ages, which range from a few hours to several days. Fossil fuel pollution observed over northern Greece is transported from eastern Europe (Bulgaria, Romania, and Turkey). Additionally, our measurements indicate significant contributions from forest fires, in particular from haze layers that originated ten days earlier from fires over the Northwestern Canadian territories, and had crossed the Atlantic and passed over Europe. CO layers 1 to 2 km deep were observed above 1 km. Often a double‐layer structure with a secondary CO layer above 3.5 km was also observed. We estimate that the contribution of biomass burning to the CO measured over Greece is fourfold that of fossil fuel. The lower layer had a significant number of particles in the accumulation mode (Np, size range 0.1–1 μm, ratio Np/CO of the order of 2–6 cm−3 (STP) ppb−1), while the upper layers were particle‐depleted by convection and wet scavenging. The Aitken particle mode (size range 5–100 nm) was depleted both in the lower and in the upper layers. This suggests that the Aitken particles originally present in the lower layers had already grown to the accumulation mode size when detected.

Environmental tobacco smoke removal capability of activated carbon

Removal of gaseous and vapor constituents of environmental tobacco smoke (ETS) by activated carbons in a packed bed arrangement was studied under dynamic conditions and was compared with that by silica gel and molecular sieve 13X. ETS is a mixture of sidestream smoke and exhaled mainstream smoke, and it consists of various organic and inorganic compounds, trace heavy metals, and particulate matters. Due to the complex nature of ETS-air mixture, its removal from indoors is a challenging task. For experimentation in a laboratory, the ETS was produced from a specially designed smoking apparatus that simulated the puffng of a cigarette by a person. Air containing ETS was passed through a bed containing about 25 grams of activated carbon at room temperature. The flow rate of air-ETS mixture through the bed was 4000 cm3/min. The relative humidity of the air was 50% and contained about 35 to 40 ppm of hydrocarbons as measured as methane-equivalent. The number of particles in the inlet air stream were in the range of 30,000 to 35,000 particles/cm3. About 60% of hydrocarbons present in ETS were removed at these operating conditions for a period of about 70 hours. Based on 15 adsorption and regeneration cycles, it was noted that the carbon bed did not loose its capacity for ETS significantly as indicated by the BET surface area and water adsorption data. At the beginning of an adsorption cycle, the carbon bed captured a significant number of particles. However, the bed rapidly lost its particle capture effciency as the experiment progressed. The number of particles in the outlet air stream was found to be the same as that of the inlet stream within five minutes.

Model for growth and coarsening of two phase systems under diffusional control

A model is described which is capable of simulating the two-dimensional evolution of microstructure in two phase systems undergoing diffusion controlled growth and surface tension driven coarsening. To solve the diffusion equation in the matrix phase, an integral equation method is employed. Thus, although it is necessary to describe the shapes of the second phase particles using a number of elements, it is not necessary to discretise the matrix phase as the particles evolve. This allows the computation times to be kept within reasonable limits. The boundary condition at the interface and the variation of the interfacial concentration with interface curvature are accounted for in a rigorous fashion. It is shown that the method can handle the ‘soft’ impingement of overlapping diffusion fields. A treatment of the ‘hard'’ physical impingement of particles is developed. To demonstrate the accuracy and stability of the method, the results from the model are compared with the exact solution for a spherical particle growing in a circular domain; it is shown that the agreement is reasonable. The results from a number of example computations are presented, which include (a) growth of a single particle in a finite domain, (b) soft and hard impingement of two particles in a finite domain, (c) coarsening of a significant number of particles at constant volume fraction, and (d) simultaneous nucleation, growth, and coarsening of second phase particles. Where appropriate, the results are compared with those from other models which have been published in the literature. The advantages and disadvantages of the present model are discussed.