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1
DiBenedetto, Michelle H., Nicholas T. Ouellette e Jeffrey R. Koseff. "Transport of anisotropic particles under waves". Journal of Fluid Mechanics 837 (21 dicembre 2017): 320–40. http://dx.doi.org/10.1017/jfm.2017.853.
Testo completoAbstract (sommario):
Using a numerical model, we analyse the effects of shape on both the orientation and transport of anisotropic particles in wavy flows. The particles are idealized as prolate and oblate spheroids, and we consider the regime of small Stokes and particle Reynolds numbers. We find that the particles preferentially align into the shear plane with a mean orientation that is solely a function of their aspect ratio. This alignment, however, differs from the Jeffery orbits that occur in the residual shear flow (that is, the Stokes drift velocity field) in the absence of waves. Since the drag on an anisotropic particle depends on its alignment with the flow, this preferred orientation determines the effective drag on the particles, which in turn impacts their net downstream transport. We also find that the rate of alignment of the particles is not constant and depends strongly on their initial orientation; thus, variations in initial particle orientation result in dispersion of anisotropic-particle plumes. We show that this dispersion is a function of the particle’s eccentricity and the ratio of the settling and wave time scales. Due to this preferential alignment, we find that a plume of anisotropic particles in waves is on average transported farther but dispersed less than it would be if the particles were randomly oriented. Our results demonstrate that accurate prediction of the transport of anisotropic particles in wavy environments, such as microplastic particles in the ocean, requires the consideration of these preferential alignment effects.
2
Hofmann, Eileen E., John M. Klinck, Ricardo A. Locarnini, Bettina Fach e Eugene Murphy. "Krill transport in the Scotia Sea and environs". Antarctic Science 10, n. 4 (dicembre 1998): 406–15. http://dx.doi.org/10.1017/s0954102098000492.
Testo completoAbstract (sommario):
Historical observations of the large-scale flow and frontal structure of the Antarctic Circumpolar Current in the Scotia Sea region were combined with the wind-induced surface Ekman transport to produce a composite flow field. This was used with a Lagrangian model to investigate transport of Antarctic krill. Particle displacements from known krill spawning areas that result from surface Ekman drift, a composite large-scale flow, and the combination of the two were calculated. Surface Ekman drift alone only transports particles a few kilometres over the 150-day krill larval development time. The large-scale composite flow moves particles several hundreds of kilometres over the same time, suggesting this is the primary transport mechanism. An important contribution of the surface Ekman drift on particles released along the continental shelf break west of the Antarctic Peninsula is moving them north-northeast into the high-speed core of the southern Antarctic Circumpolar Current Front, which then transports the particles to South Georgia in about 140–160 days. Similar particle displacement calculations using surface flow fields obtained from the Fine Resolution Antarctic Model do not show overall transport from the Antarctic Peninsula to South Georgia due to the inaccurate position of the southern Antarctic Circumpolar Current Front in the simulated circulation fields. The particle transit times obtained with the composite large-scale flow field are consistent with regional abundances of larval krill developmental stages collected in the Scotia Sea. These results strongly suggest that krill populations west of the Antarctic Peninsula provide the source for the krill populations found around South Georgia.
3
Won, Jongmuk, Dongseop Lee, Khanh Pham, Hyobum Lee e Hangseok Choi. "Impact of Particle Size Distribution of Colloidal Particles on Contaminant Transport in Porous Media". Applied Sciences 9, n. 5 (5 marzo 2019): 932. http://dx.doi.org/10.3390/app9050932.
Testo completoAbstract (sommario):
The presence of retained colloidal particles causes the retardation of contaminant transport when the contaminant is favorably adsorbed to colloidal particles. Although the particle size distribution affects the retention behavior of colloidal particles, the impact of particle size distribution on contaminant transport has not been reported to date. This study investigates the impact of the particle size distribution of the colloidal particles on contaminant transport through numerical simulation by representing the particle size distribution as a lognormal distribution function. In addition, the bed efficiency and contaminant saturation of simulated breakthrough curves were calculated, and a contaminant transport model with the Langmuir isotherm for the reaction between the contaminant–sand and contaminant–colloidal particle was introduced and validated with experimental data. The simulated breakthrough curves, bed efficiency, and contaminant saturation indicated that an increase in the mean and standard deviation of the particle size distribution causes the retardation of contaminant transport.
4
Douglas-Hamilton, D. H., e C. Taylor. "Particles and particle transport in ion implanters". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 6, n. 1-2 (gennaio 1985): 196–201. http://dx.doi.org/10.1016/0168-583x(85)90633-0.
Testo completo
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Kim, T., H. S. Ko e Oh Chae Kwon. "Simulation Assisted Measurement of Nanoparticle Concentration Generated during High-Density Plasma CVD of Poly-Silicon Films". Key Engineering Materials 326-328 (dicembre 2006): 349–52. http://dx.doi.org/10.4028/www.scientific.net/kem.326-328.349.
Testo completoAbstract (sommario):
To study nanoparticles generated within the high-density plasma system, it is necessary to know the particle concentration (#/cm3), which is typically measured using laser light scattering of particles trapped inside the plasma. This technique has limitations because particles are localized due to the forces that act on the trapped particles inside the plasma and the localization point varies as the particles grow. Unless spatially averaged particle concentrations are obtained by scanning through the plasma, laser light scattering measurements of particle concentration might represent only the local variation of particle concentration. In this paper, novel method is presented to measure the particle concentration employing TEM measurement results and the simulation of particle transport for calculation of transport efficiency from the plasma region where the particles are generated to the TEM grid. As the particles were collected on the TEM grid after the plasma was extinguished, the simulation includes the effects of Brownian diffusion, aerodynamic drag and gravitational sedimentation but not electrostatic or ion drag force. Simulation results were obtained for particles ranging from 5 to 100 nm. For each particle size, transport efficiencies from 56 different starting positions were evaluated. It was found that transport efficiencies of particles in the 20 to 50 nm diameter range were highest, since these particles tend to follow the gas flow. Sampling efficiencies of particles smaller than this decreased due to Brownian diffusion. For larger particles, sampling efficiencies also decreased, due to gravitational sedimentation. The measured particle concentrations were found to be ~108 #/cm3 and roughly constant over time.
6
Jones, Benjamin T., Andrew Solow e Rubao Ji. "Resource Allocation for Lagrangian Tracking". Journal of Atmospheric and Oceanic Technology 33, n. 6 (giugno 2016): 1225–35. http://dx.doi.org/10.1175/jtech-d-15-0115.1.
Testo completoAbstract (sommario):
AbstractAccurate estimation of the transport probabilities among regions in the ocean provides valuable information for understanding plankton transport, the spread of pollutants, and the movement of water masses. Individual-based particle-tracking models simulate a large ensemble of Lagrangian particles and are a common method to estimate these transport probabilities. Simulating a large ensemble of Lagrangian particles is computationally expensive, and appropriately allocating resources can reduce the cost of this method. Two universal questions in the design of studies that use Lagrangian particle tracking are how many particles to release and how to distribute particle releases. A method is presented for tailoring the number and the release location of particles to most effectively achieve the objectives of a study. The method detailed here is a sequential analysis procedure that seeks to minimize the number of particles that are required to satisfy a predefined metric of result quality. The study assesses the result quality as the precision of the estimates for the elements of a transport matrix and also describes how the method may be extended for use with other metrics. Applying this methodology to both a theoretical system and a particle transport model of the Gulf of Maine results in more precise estimates of the transport probabilities with fewer particles than from uniformly or randomly distributing particle releases. The application of this method can help reduce the cost of and increase the robustness of results from studies that use Lagrangian particles.
7
Wang, Jiayi, Yitian Li, Zhiqiang Lai, Lianjun Zhao e Zhongmei Wang. "Study on the Motion Characteristics of Particles Transported by a Horizontal Pipeline in Heterogeneous Flow". Water 14, n. 19 (9 ottobre 2022): 3177. http://dx.doi.org/10.3390/w14193177.
Testo completoAbstract (sommario):
The worldwide problem of reservoir sedimentation has perplexed the water conservancy industry. The problem of reservoir sedimentation is particularly serious in sandy rivers in China and directly affects the normal function of reservoirs. Due to its effect on the economy and environmental protection, the self-priming pipeline dredging and sediment discharge technology has broad application prospects. Nevertheless, there are pressing problems in the transportation of slurry particles in the pipeline system of this new technology. The purpose of this study is to use physical model tests to analyze the influence of the sediment transport rate and pipeline velocity on the motion state of particles (aggregation transport, jump transport, and suspension transport) when a heterogeneous flow with different particle sizes is transported in the pipeline. The results indicate that under the same pipeline velocity and sediment transport rate, the thickness of the static particle accumulation layer decreases with the increase in particle size in the state of aggregation and transportation, and the smaller the particle size, the greater the particle movement speed in the case of aggregation and suspension transportation. During jump transportation, the velocity of particles above the critical inflection point Y’ increases with the decrease in particle size. The opposite is found below the critical inflection point Y’. At the same particle size and sediment transport rate, when the pipeline velocity increases, the particle transport transits from aggregation transport to jump transport and then to suspension transport. The larger the pipeline velocity, the greater the overall movement speed of particles. When gathering and conveying, if the pipeline flow rate increases by 1.5, the maximum movement speed of particles increases by 3.3. The curvature of the vertical velocity curve of the particles during jump transportation is not affected by the pipeline velocity. The particle velocity at the highest point increases with the increase in the pipeline velocity. During suspension transportation, the difference between the maximum and minimum vertical particle distribution velocities is exponentially related to the pipeline velocity. At the same pipe velocity and particle size, the overall particle velocity decreases with the increase in sediment transport rate.
8
Noorani, Azad, Gaetano Sardina, Luca Brandt e Philipp Schlatter. "Particle transport in turbulent curved pipe flow". Journal of Fluid Mechanics 793 (15 marzo 2016): 248–79. http://dx.doi.org/10.1017/jfm.2016.136.
Testo completoAbstract (sommario):
Direct numerical simulations (DNS) of particle-laden turbulent flow in straight, mildly curved and strongly bent pipes are performed in which the solid phase is modelled as small heavy spherical particles. A total of seven populations of dilute particles with different Stokes numbers, one-way coupled with their carrier phase, are simulated. The objective is to examine the effect of the curvature on micro-particle transport and accumulation. It is shown that even a slight non-zero curvature in the flow configuration strongly impact the particle concentration map such that the concentration of inertial particles with bulk Stokes number $0.45$ (based on bulk velocity and pipe radius) at the inner bend wall of mildly curved pipe becomes $12.8$ times larger than that in the viscous sublayer of the straight pipe. Near-wall helicoidal particle streaks are observed in the curved configurations with their inclination varying with the strength of the secondary motion of the carrier phase. A reflection layer, as previously observed in particle laden turbulent S-shaped channels, is also apparent in the strongly curved pipe with heavy particles. In addition, depending on the curvature, the central regions of the mean Dean vortices appear to be completely depleted of particles, as observed also in the partially relaminarised region at the inner bend. The turbophoretic drift of the particles is shown to be affected by weak and strong secondary motions of the carrier phase and geometry-induced centrifugal forces. The first- and second-order moments of the velocity and acceleration of the particulate phase in the same configurations are addressed in a companion paper by the same authors. The current data set will be useful for modelling particles advected in wall-bounded turbulent flows where the effects of the curvature are not negligible.
9
Yang, Wenwu, Bo-Fu Wang, Shuai Tang, Quan Zhou e Yuhong Dong. "Transport modes of inertial particles and their effects on flow structures and heat transfer in Rayleigh–Bénard convection". Physics of Fluids 34, n. 4 (aprile 2022): 043309. http://dx.doi.org/10.1063/5.0086017.
Testo completoAbstract (sommario):
We investigate the flow characteristics and kinetic behaviors of particles in turbulent Rayleigh–Bénard convection particulate flows. Direct numerical simulations combined with a Lagrangian point-particle strategy were carried out in the range of Stokes numbers [Formula: see text] for Rayleigh numbers from [Formula: see text] to [Formula: see text] at the Prandtl number [Formula: see text]. A two-way coupling model is employed in which the momentum exchange between the dispersed particles and the carrier fluid is taken fully into account. Based on various patterns of particle motion, we find three transport modes of inertial particles which are labeled as the circling transport (CCT) mode, the channel transport (CNT) mode, and the downpour transport (DPT) mode, respectively. These modes can switch to each other when Stokes numbers and Rayleigh numbers vary and exhibit different effects of particle motions on the flow field and heat transfer. For the CCT and DPT modes, compared with the CNT, a weakening alteration of flow structures and thermal plumes leads to no significant effect on the transport of momentum and heat. For the CNT mode, a pronounced effect of particles on enhancements of the turbulent momentum transport and heat transfer relates to the strong interaction between the particle clusters and the chaotic structures of eddies. What is more, the particles tend to homogeneously distribute for the CCT and DPT modes, although the particles exhibit different transport states. As for the CNT mode, under both preferential sweeping and centrifugal effects, particles accumulate into clusters that hover toward the region of high strain rate and the edges of eddies. We found that the averaged particle settling speeds are almost proportional to the Stokes number. The particle settling speeds are larger than the terminal velocity of Stokesian particles for the CCT and CNT modes as particles tend to settle in the downward fluid. In contrast, it becomes smaller than the terminal velocity for the DPT mode due to the drag of the upward fluid.
10
Yang, Chun-bo, Lin-bing Wang, Yuan Wang, Qing-wen Li e Jing-qi Huang. "Transport Characteristics of Tailing Sand Particles under Slotted Tube Overlapped with Geotextile and Steel Mesh". Geofluids 2023 (16 gennaio 2023): 1–15. http://dx.doi.org/10.1155/2023/1270931.
Testo completoAbstract (sommario):
Compared with a one-dimensional test, a two-dimensional test has the potential to study the transport characteristics of particles in tailings under different filtration materials. Due to the different test conditions and the complex test environment, the existing devices generally have limited measuring range or high accuracy. Thus, it is urgent to develop an advanced device to improve the ability of the transport characteristics of particles. In this study, a two-dimensional radial flow device is designed for analyzing the transport characteristics of particles which combine the water tank with adjustable pressure and the seepage body providing a tailing sand environment. An experimental system is built, and a seepage process is carried out to explore the transport characteristics of particles. The results indicate that when head difference remains stable, the mixture consisting of the tailing sand and water gradually transports to the vicinity of the slotted tube along the diameter direction. With an increase in head difference, the tailing sand particle size in the mixture shows a slow upward trend, which migrates in the tailing sand. And the proportion of tailing sand particles with different sizes varies under different head differences. Separation of the mixture consisting of tailing sand particles and water occurs near infiltration material, while the mixture has different transportation laws under different filtration materials. Under geotextile, most fine tailing sand particles which transport from the edge remain in geotextiles, causing an increase in the proportion of fine particles around the slotted tube. However, most fine particles pass through steel mesh, leading to a decrease in the proportion of fine particles.
11
Machunsky, Stefanie, e Urs Alexander Peuker. "Liquid-Liquid Interfacial Transport of Nanoparticles". Physical Separation in Science and Engineering 2007 (8 gennaio 2007): 1–7. http://dx.doi.org/10.1155/2007/34832.
Testo completoAbstract (sommario):
The study presents the transfer of nanoparticles from the aqueous phase to the second nonmiscible nonaqueous liquid phase. The transfer is based on the sedimentation of the dispersed particles through a liquid-liquid interface. First, the colloidal aqueous dispersion is destabilised to flocculate the particles. The agglomeration is reversible and the flocs are large enough to sediment in a centrifugal field. The aqueous dispersion is laminated above the receiving organic liquid phase. When the particles start to penetrate into the liquid-liquid interface, the particle surface is covered with the stabilising surfactant. The sorption of the surfactant onto the surface of the primary particles leads to the disintegration of the flocs. This phase transfer process allows for a very low surfactant concentration within the receiving organic liquid, which is important for further application, that is, synthesis for polymer-nanocomposite materials. Furthermore, the phase transfer of the nanoparticles shows a high efficiency up to 100% yield. The particle size within the organosol corresponds to the primary particle size of the nanoparticles.
12
Trotta, D., D. Burgess, G. Prete, S. Perri e G. Zimbardo. "Particle transport in hybrid PIC shock simulations: A comparison of diagnostics". Monthly Notices of the Royal Astronomical Society 491, n. 1 (12 ottobre 2019): 580–95. http://dx.doi.org/10.1093/mnras/stz2760.
Testo completoAbstract (sommario):
ABSTRACT Recent in situ and remote observations suggest that the transport regime associated with shock-accelerated particles may be anomalous i.e. the mean square displacement (MSD) of such particles scales non-linearly with time. We use self-consistent hybrid particle-in-cell plasma simulations to simulate a quasi-parallel shock with parameters compatible with heliospheric shocks, and gain insights about the particle transport in such a system. For suprathermal particles interacting with the shock we compute the MSD separately in the upstream and downstream regions. Tracking suprathermal particles for sufficiently long times up and/or downstream of the shock poses problems in particle plasma simulations, such as statistically poor particle ensembles and trajectory fragments of variable length in time. Therefore, we introduce the use of time-averaged mean square displacement (TAMSD), which is based on single-particle trajectories, as an additional technique to address the transport regime for the upstream and the downstream regions. MSD and TAMSD are in agreement for the upstream energetic particle population, and both give a strong indication of superdiffusive transport, consistent with interplanetary shock observations. MSD and TAMSD are also in reasonable agreement downstream, where indications of anomalous transport are also found. TAMSD shows evidence of heterogeneity in the diffusion properties of the downstream particle population, ranging from subdiffusive behaviour of particles trapped in the strong magnetic field fluctuations generated at the shock to superdiffusive behaviour of particles transmitted and moving away from the shock.
13
Ancey, C., e J. Heyman. "A microstructural approach to bed load transport: mean behaviour and fluctuations of particle transport rates". Journal of Fluid Mechanics 744 (10 marzo 2014): 129–68. http://dx.doi.org/10.1017/jfm.2014.74.
Testo completoAbstract (sommario):
AbstractThis paper concerns a model of bed load transport, which describes the advection and dispersion of coarse particles carried by a turbulent water stream. The challenge is to develop a microstructural approach that, on the one hand, yields a parsimonious description of particle transport at the microscopic scale and, on the other hand, leads to averaged equations at the macroscopic scale that can be consistently interpreted in light of the continuum equations used in hydraulics. The cornerstone of the theory is the proper determination of the particle flux fluctuations. Apart from turbulence-induced noise, fluctuations in the particle transport rate are generated by particle exchanges with the bed consisting of particle entrainment and deposition. At the particle scale, the evolution of the number of moving particles can be described probabilistically using a coupled set of reaction–diffusion master equations. Theoretically, this is interesting but impractical, as solving the governing equations is fraught with difficulty. Using the Poisson representation, we show that these multivariate master equations can be converted into Fokker–Planck equations without any simplifying approximations. Thus, in the continuum limit, we end up with a Langevin-like stochastic partial differential equation that governs the time and space variations of the probability density function for the number of moving particles. For steady-state flow conditions and a fixed control volume, the probability distributions of the number of moving particles and the particle flux can be calculated analytically. Taking the average of the microscopic governing equations leads to an average mass conservation equation, which takes the form of the classic Exner equation under certain conditions carefully addressed in the paper. Analysis also highlights the specific part played by a process we refer to as collective entrainment, i.e. a nonlinear feedback process in particle entrainment. In the absence of collective entrainment the fluctuations in the number of moving particles are Poissonian, which implies that at the macroscopic scale they act as white noise that mediates bed evolution. In contrast, when collective entrainment occurs, large non-Poissonian fluctuations arise, with the important consequence that the evolution at the macroscopic scale may depart significantly that predicted by the averaged Exner equation. Comparison with experimental data gives satisfactory results for steady-state flows.
14
Cui, Xianze, Quansheng Liu e Chengyuan Zhang. "Physical factors affecting the transport and deposition of particles in saturated porous media". Water Supply 17, n. 6 (13 aprile 2017): 1616–25. http://dx.doi.org/10.2166/ws.2017.065.
Testo completoAbstract (sommario):
Abstract Saturated sand box experiments were conducted to explore the effect of various physical factors on the transport and deposition of suspended particles in porous media. Red quartz powder and natural quartz sand were employed in the study and acted as suspended particles and porous media, respectively. Particles were injected into the sand box in two modes, i.e., pulse injection and continuous injection. Tests were performed at various particle concentrations, flow velocities, deposition rate coefficient and longitudinal dispersion coefficient by both injection modes. The breakthrough curves were described with the analytical solution of a convection–dispersion equation, in which first-order deposition kinetics were taken into account. Different behavior of suspended-particle transport and deposition in porous media was observed under different injection modes and experimental conditions. The results show that effluent concentration was approximately linear with the initial particle concentration. The deposition rate coefficient depends strongly on particle size and flow velocity, and the transport and deposition process was very sensitive to it. Furthermore, the longitudinal dispersion coefficient increases with increasing flow rate, and particles are easier to transport through pores as the longitudinal dispersion coefficient increases. This study shows the importance of particle concentration, flow velocity, deposition rate coefficient and longitudinal dispersion coefficient in the transport and deposition process of suspended particles.
15
Torsti, J., E. Valtonen, L. Kocharov, M. Lumme, T. Eronen, M. Louhola, E. Riihonen et al. "Energetic particle investigation using the ERNE instrument". Annales Geophysicae 14, n. 5 (31 maggio 1996): 497–502. http://dx.doi.org/10.1007/s00585-996-0497-5.
Testo completoAbstract (sommario):
Abstract. During solar flares and coronal mass ejections, nuclei and electrons accelerated to high energies are injected into interplanetary space. These accelerated particles can be detected at the SOHO satellite by the ERNE instrument. From the data produced by the instrument, it is possible to identify the particles and to calculate their energy and direction of propagation. Depending on variable coronal/interplanetary conditions, different kinds of effects on the energetic particle transport can be predicted. The problems of interest include, for example, the effects of particle properties (mass, charge, energy, and propagation direction) on the particle transport, the particle energy changes in the transport process, and the effects the energetic particles have on the solar-wind plasma. The evolution of the distribution function of the energetic particles can be measured with ERNE to a better accuracy than ever before. This gives us the opportunity to contribute significantly to the modeling of interplanetary transport and acceleration. Once the acceleration/transport bias has been removed, the acceleration-site abundance of elements and their isotopes can be studied in detail and compared with spectroscopic observations.
16
Abdull, Norhidayah, Nur Sarah Irina Muhammad, Khairiah Mohd Mokhtar e Zarifah Shahri. "Occurrence, characterization, and transport mechanism of welding fumes particles emitted during the welding process". Journal of Physics: Conference Series 2688, n. 1 (1 gennaio 2024): 012010. http://dx.doi.org/10.1088/1742-6596/2688/1/012010.
Testo completoAbstract (sommario):
Abstract In metalworking processes, welding fumes are a prevalent type of particle aerosols. Particle characteristics, physical factors, and the generation process influence the transport of welding fumes in the air. This research delves into the investigation of welding fumes particles during two types of currents: low current (60A) and high current (130A). The study encompasses the determination of the occurrence and characterization of these particles, as well as estimating their transport mechanisms during the welding process. Direct reading instruments were utilized to measure the mass concentration and the number concentration of welding fumes particles alongside environmental parameters such as relative humidity, air velocity, and air temperature. The size distribution and morphology of the particles were collected through a sampling pump and subsequently analyzed using a Field Emission Scanning Electron Microscope (FESEM). Welding fumes particle transport was predicted by employing variables such as Reynolds number (Re), settling velocity, mechanical velocity, and stopping distance. The welding process’s high current (130 A) generates a higher mass concentration (0.122mg/m3) than the low current (60 A) (0.064mg/m3). Notably, for particle size fractions ranging from 0.5μm to 2.0μm, the number of particles generated during high current surpassed that of low current, except for the 0.3μm size fraction. Analysis of the size distribution through FESEM revealed particle sizes of 2.25μm, 2.33μm, and 2.63μm for welding fumes collected during 130A. In contrast, fumes collected during 60A exhibited sizes of 0.45μm, 0.61μm, and 0.60μm. Notably, accumulation of particles were observed, indicating that the fumes collected during 60A consisted of smaller particles classified as fine particles. The particle counts for high and low currents were 283,232,661 count/m3 and 300,604,341 count/m3, respectively. The observed particle shapes appeared agglomerate, comprised of primary spherical particles adhering together through Van Der Waals forces. Reynolds number values (Re=0.0046-0.0223, less than 1) indicated that the motion of fume particles occurred within a laminar flow regime. Furthermore, the movement of particles was influenced by their diameter, with larger particles exhibiting higher settling velocities, smaller mechanical mobility, and shorter travelled distances. In summary, this research sheds light on the intricate transport mechanisms of welding fumes, providing insights into their occurrence, characterization, and transport during the metalworking process.
17
Bohrmann, J., e K. Biber. "Cytoskeleton-dependent transport of cytoplasmic particles in previtellogenic to mid-vitellogenic ovarian follicles of Drosophila: time-lapse analysis using video-enhanced contrast microscopy". Journal of Cell Science 107, n. 4 (1 aprile 1994): 849–58. http://dx.doi.org/10.1242/jcs.107.4.849.
Testo completoAbstract (sommario):
In Drosophila oogenesis, several morphogenetic determinants and other developmental factors synthesized in the nurse cells have been shown to accumulate in the oocyte during pre- to mid-vitellogenic stages. However, the mechanisms of the involved intercellular transport processes that seem to be rather selective have not been revealed so far. We have investigated in vitro, by means of video-enhanced contrast time-lapse microscopy, the transport of cytoplasmic particles from the nurse cells through ring canals into the oocyte during oogenesis stages 6–10A. At stage 7, we first observed single particles moving into the previtellogenic oocyte. The particle transfer was strictly unidirectional and seemed to be selective, since only some individual particles moved whereas other particles lying in the vicinity of the ring canals were not transported. The observed transport processes were inhibitable with 2,4-dinitrophenol, cytochalasin B or N-ethylmaleimide, but not with microtubule inhibitors. At the beginning of vitellogenesis (stage 8), the selective translocation of particles through the ring canals became faster (up to 130 nm/second) and more frequent (about 1 particle/minute), whereas during mid-vitellogenesis (stages 9–10A) the velocity and the frequency of particle transport decreased again. Following their more or less rectilinear passage through the ring canals, the particles joined a circular stream of cytoplasmic particles in the oocyte. This ooplasmic particle streaming started at stage 6/7 with velocities of about 80 nm/second and some reversals of direction at the beginning. The particle stream in the oocyte was sensitive to colchicine and vinblastine, but not to cytochalasin B, and we presume that it reflects the rearrangement of ooplasmic microtubules described recently by other authors. We propose that during stages 7–10A, a selective transport of particles into the oocyte occurs through the ring canal along a polarized scaffold of cytoskeletal elements in which microfilaments are involved. This transport might be driven by a myosin-like motor molecule. Either attached to, or organized into, such larger particles or organelles, specific mRNAs and proteins might become selectively transported into the oocyte.
18
Dröge, Wolfgang. "Transport of Solar Energetic Particles". International Astronomical Union Colloquium 142 (1994): 567–76. http://dx.doi.org/10.1017/s0252921100077824.
Testo completoAbstract (sommario):
AbstractNew developments in the understanding of the interplanetary transport of solar cosmic rays are reviewed. Based on carefully analyzed solar particle events observed on the Helios and ISEE 3 spacecraft, the relation of transport parameters to the structure of the interplanetary magnetic field is discussed. Special emphasis is given to a comparison of particle mean free paths determined from fits to intensity and anisotropy profiles with theoretical predictions derived from magnetic field spectra measured at the time of the solar particle event. Different aspects of the turbulence and wave models for the magnetic fluctuations are considered, including the effects resulting from the finite temperature of the plasma and of resonance broadening. It is found that a modified quasi-linear theory of particle scattering taking into account the effects of plasma waves propagating with respect to the average solar wind flow and the proper treatment of the dispersion relation at high wavenumber gives results which are in several cases in good agreement with particle observations in the interplanetary medium between 0.3 and 1 AU, indicating that quasi-linear theory is probably a good approximation to a full theory of solar particle transport. This has important implications for other astrophysical problems where quasi-linear theory is often used, such as the propagation and acceleration of Galactic cosmic rays and particle acceleration at shock waves.Subject headings: acceleration of particles — cosmic rays — interplanetary medium — MHD — solar wind — Sun: particle emission
19
Lajeunesse, E., O. Devauchelle, M. Houssais e G. Seizilles. "Tracer dispersion in bedload transport". Advances in Geosciences 37 (17 dicembre 2013): 1–6. http://dx.doi.org/10.5194/adgeo-37-1-2013.
Testo completoAbstract (sommario):
Abstract. Bedload particles entrained by rivers tends to disperse as they move downstream. In this paper, we use the erosion-deposition model of Charru et al. (2004) to describe the velocity and the spreading of a plume of tracer particles. We restrict our analysis to steady-state transport above a flat bed of uniform sediment. The transport of tracer particles is then controlled by downstream advection and particle exchange with the immobile bed. After a transitional regime dominated by initial conditions, the evolution of a plume of markers tends asymptotically towards classical advection-diffusion: its average position grows linearly with time, whereas it spreads like the square root of time.
20
Dentler, William. "Intraflagellar transport (IFT) during assembly and disassembly of Chlamydomonas flagella". Journal of Cell Biology 170, n. 4 (15 agosto 2005): 649–59. http://dx.doi.org/10.1083/jcb.200412021.
Testo completoAbstract (sommario):
Intraflagellar transport (IFT) of particles along flagellar microtubules is required for the assembly and maintenance of eukaryotic flagella and cilia. In Chlamydomonas, anterograde and retrograde particles viewed by light microscopy average 0.12-μm and 0.06-μm diameter, respectively. Examination of IFT particle structure in growing flagella by electron microscopy revealed similar size aggregates composed of small particles linked to each other and to the membrane and microtubules. To determine the relationship between the number of particles and flagellar length, the rate and frequency of IFT particle movement was measured in nongrowing, growing, and shortening flagella. In all flagella, anterograde and retrograde IFT averaged 1.9 μm/s and 2.7 μm/s, respectively, but retrograde IFT was significantly slower in flagella shorter than 4 μm. The number of flagellar IFT particles was not fixed, but depended on flagellar length. Pauses in IFT particle entry into flagella suggest the presence of a periodic “gate” that permits up to 4 particles/s to enter a flagellum.
21
Won, Jongmuk, e Susan E. Burns. "Stochastic modeling of kaolinite transport through a sand filter". Canadian Geotechnical Journal 56, n. 11 (novembre 2019): 1573–83. http://dx.doi.org/10.1139/cgj-2018-0394.
Testo completoAbstract (sommario):
Accurately modeling the transport of clay particles through coarse-grained porous media is essential to engineering applications ranging from filtration and drainage, groundwater flow modeling, to contaminant transport. However, predicting the retention and clogging behavior of clay particles within a coarse-grained soil matrix is extremely challenging because clay particles can aggregate and form clusters with a variety of fabrics depending on the prevailing geochemistry of the pore fluid (i.e., pH and ionic strength). The work performed in this study developed a stochastic model to investigate the uncertainty of clay particle transport in porous media using random sampling at a given grain-size distribution to account for inherent uncertainty of the size of clay clusters being transported. Results demonstrated that the model proposed in this work can evaluate upper and lower boundaries of retention profiles of clay particles in a sand medium at given mean and standard deviation of grain-size distributions. In addition, the deterministic approach (using median sizes of sand and clay particles in the simulation) underestimated the mass of retained particles at small size ratios of clay particle size/sand particle size when compared with the stochastic prediction, which would result in nonconservative design.
22
Abedini-Nassab, Roozbeh, e Ali Emamgholizadeh. "Controlled Transport of Magnetic Particles and Cells Using C-Shaped Magnetic Thin Films in Microfluidic Chips". Micromachines 13, n. 12 (8 dicembre 2022): 2177. http://dx.doi.org/10.3390/mi13122177.
Testo completoAbstract (sommario):
Single-cell analysis is an emerging discipline that has shown a transformative impact in cell biology in the last decade. Progress in this field requires systems capable of accurately moving the cells and particles in a controlled manner. Here, we present a microfluidic platform equipped with C-shaped magnetic thin films to precisely transport magnetic particles in a tri-axial rotating magnetic field. This innovative system, compared to the other rivals, offers numerous advantages. The magnetic particles repel each other to prevent undesired cluster formation. Many particles move synced with the external rotating magnetic field, which results in highly parallel controlled particle transport. We show that the particle transport in this system is analogous to electron transport and Ohm’s law in electrical circuits. The proposed magnetic transport pattern is carefully studied using both simulations and experiments for various parameters, including the magnetic field characteristics, particle size, and gap size in the design. We demonstrate the appropriate transport of both magnetic beads and magnetized living cells. We also show a pilot mRNA-capturing experiment with barcode-carrying magnetic beads. The introduced chip offers fundamental potential applications in the fields of single-cell biology and bioengineering.
23
Landa, Polina. "Noise-induced transport of Brownian particles". Izvestiya VUZ. Applied Nonlinear Dynamics 6, n. 5 (1998): 3–18. http://dx.doi.org/10.18500/0869-6632-1998-6-5-3-18.
Testo completoAbstract (sommario):
А number of examples of the transport of Brownian particles induced by nonequilibrium fluctuations is considered. The results of approximate analytical calculations for the averaged particle velocity in periodic ratchei—like potential are presented. An analogy between fluctnation—induced transport and well known in mechanics vibrational transport is discussed.
24
Shah, Anant, e Danesh K. Tafti. "Transport of Particulates in an Internal Cooling Ribbed Duct". Journal of Turbomachinery 129, n. 4 (4 agosto 2006): 816–25. http://dx.doi.org/10.1115/1.2720509.
Testo completoAbstract (sommario):
A ribbed square duct (P∕e=10, e∕Dh=0.10) subjected to sand ingestion is studied using large-eddy simulations (LES). Particle sizes of 10μm, 50μm, and 100μm with nondimensional response times (normalized by friction velocity and hydraulic diameter) of 0.06875, 1.71875, and 6.875, respectively are considered. The calculations are performed for a nominal bulk Reynolds number of 20,000 under fully-developed conditions. Distributions of impingement density, impingement velocities and angles, together with fractional energy transfer are presented for each surface. It is found that about 40% of the total number of 10micron particles are concentrated in the vicinity (within 0.05 Dh) of the duct surfaces, compared to 25–30% of the 50 and 100micron particles. The 10micron particles are more sensitive to the primary and secondary flow velocities than the larger particles. While the 10micron particles exhibit high energy transfer to the surface near the rib side-wall junction and immediately upstream of the rib, the larger particles exhibit more uniform distributions. The largest fraction of incoming particulate energy is transferred to the front face of the rib and is between one to two orders of magnitude larger than the other surfaces. As particle size increases, substantial particle energy is also transferred to the back face of the rib by particles bouncing off the front face and carrying enough momentum to impinge on the back face of the preceding rib.
25
Zhan, Xia, Kaixiang Gao, Yucheng Jia, Wen Deng, Ning Liu, Xuebin Guo, Hehe Li e Jiding Li. "Enhanced Desulfurization Performance of ZIF−8/PEG MMMs: Effect of ZIF−8 Particle Size". Membranes 13, n. 5 (15 maggio 2023): 515. http://dx.doi.org/10.3390/membranes13050515.
Testo completoAbstract (sommario):
Constructing efficient and continuous transport pathways in membranes is a promising and challenging way to achieve the desired performance in the pervaporation process. The incorporation of various metal–organic frameworks (MOFs) into polymer membranes provided selective and fast transport channels and enhanced the separation performance of polymeric membranes. Particle size and surface properties are strongly related to the random distribution and possible agglomeration of MOFs particles, which may lead to poor connectivity between adjacent MOFs-based nanoparticles and result in low-efficiency molecular transport in the membrane. In this work, ZIF−8 particles with different particle sizes were physically filled into PEG to fabricate mixed matrix membranes (MMMs) for desulfurization via pervaporation. The micro-structures and physi-/chemical properties of different ZIF−8 particles, along with their corresponding MMMs, were systematically characterized by SEM, FT-IR, XRD, BET, etc. It was found that ZIF−8 with different particle sizes showed similar crystalline structures and surface areas, while larger ZIF−8 particles possessed more micro-pores and fewer meso-/macro-pores than did the smaller particles. ZIF−8 showed preferential adsorption for thiophene rather than n−heptane molecules, and the diffusion coefficient of thiophene was larger than that of thiophene in ZIF−8, based on molecular simulation. PEG MMMs with larger ZIF−8 particles showed a higher sulfur enrichment factor, but a lower permeation flux than that found with smaller particles. This might be ascribed to the fact that larger ZIF−8 particles provided more and longer selective transport channels in one single particle. Moreover, the number of ZIF−8−L particles in MMMs was smaller than the number of smaller ones with the same particle loading, which might weaken the connectivity between adjacent ZIF−8−L nanoparticles and result in low-efficiency molecular transport in the membrane. Moreover, the surface area available for mass transport was smaller for MMMs with ZIF−8−L particles due to the smaller specific surface area of the ZIF−8−L particles, which might also result in lower permeability in ZIF−8−L/PEG MMMs. The ZIF−8−L/PEG MMMs exhibited enhanced pervaporation performance, with a sulfur enrichment factor of 22.5 and a permeation flux of 183.2 g/(m−2·h−1), increasing by 57% and 389% compared with the results for pure PEG membrane, respectively. The effects of ZIF−8 loading, feed temperature, and concentration on desulfurization performance were also studied. This work might provide some new insights into the effect of particle size on desulfurization performance and the transport mechanism in MMMs.
26
Xie, Peng, Lianghai Lv, Juntong Liu e Kechao Chen. "Study on the Optical Parameters of Different Particle Sizes Considering Particle Group Reflectivity". Journal of Nanoelectronics and Optoelectronics 18, n. 4 (1 aprile 2023): 417–27. http://dx.doi.org/10.1166/jno.2023.3404.
Testo completoAbstract (sommario):
With the rapid advancements in laser and detection technology, it is now possible to obtain the physical properties of particles. Analyzing the physical properties of particles can establish the foundation for further research on the optical field transmission of particles in the micron range. The transport model of unpolarized particles is constructed by applying the unpolarized transport technology, and the Stokes vector is used to calculate the transport characteristics of the particle to obtain the four-dimensional mathematical vector that represents average light intensity. A random matrix is established with the help of the Markov chain to transmit unpolarized characteristic parameters of particles and to investigate the energy levels of a vast number of particles. According to the Mie scattering theory, the spatial intensity distribution function of light scattering is calculated, and the experiment on the characteristic parameter of the particle is carried out based on the results of a photoelectric detector, and compared with the numerical simulation. By analyzing the mathematical model, the accuracy and effectiveness of the model are verified, which provides theoretical support for further research on particle physics.
27
Bogomolov, S. V., e A. E. Kuvshinnikov. "A discontinuous shapeless particle method for the quasi-linear transport". Journal of Physics: Conference Series 2099, n. 1 (1 novembre 2021): 012009. http://dx.doi.org/10.1088/1742-6596/2099/1/012009.
Testo completoAbstract (sommario):
Abstract This paper considers a new version of the discontinuous particle method, whose higher accuracy is based on the “predictor-corrector” scheme. The peculiarity of this version is a new criterion of rearranging particles at the “corrector” stage. In contrast to the previously used version with the analysis of overlapping particles, which required an assumption about their form, we use another key characteristic of particles, namely, their mass, more precisely, the assumption that in the nonlinear elastic transport not only particle masses are conserved but also the mass located between the centers of these particles. This requirement leads to the fact that changing a distance between particles in the process of their movement and conservation of mass in the space between them, lead to a change in the density of one of the particles. A new version arose in the solution of the two-dimensional transport problems. We emphasize that the discontinuity is smeared into a single particle, which indicates to a high accuracy of the method. The construction of the method for a simple nonlinear transport problem is a necessary step to simulate the complex gas dynamics problems.
28
Tewari, Deepti, Arturo Gutierrez, Jason R. Croy e Venkat Srinivasan. "Designing Cathode Morphology for Materials with Solid Transport Limitation". ECS Meeting Abstracts MA2022-02, n. 3 (9 ottobre 2022): 295. http://dx.doi.org/10.1149/ma2022-023295mtgabs.
Testo completoAbstract (sommario):
Lithium manganese rich (LMR-NMC) material is a great candidate for next generation high energy density cathodes. It has high specific capacity, low cost, and decreased usage of Cobalt. However, these materials display poor rate capabilities attributed in part due to low lithium diffusion in cathode particle. The LMR-NMC cathode particles (size ~ 5 to 15 microns) are agglomeration of nanoscale primary particles. In this work, we focus on the link between morphology and performance. There are two characteristic diffusion lengths associated with the morphology of LMR-NMC. The diffusion length associated with primary particle radius and the diffusion length associated with the agglomeration of primary particles. The agglomerate diffusion length varies significantly with how the primary particles agglomerate. Presence of intra-agglomerate closed pores results in higher agglomerate diffusion length compared to open and well dispersed arrangement of primary particles. The electrochemical performance is better with smaller primary and agglomerate diffusion lengths. Tailoring the synthesis of cathode particles to obtain the desired diffusion characteristics is promising avenue to optimize the performance of LMR-NMC cathode materials. Figure 1
29
Wang, Xiaoyu, Jun Yao, Liang Gong, Hai Sun, Yongfei Yang, Wenchao Liu e Yang Li. "Numerical study on particle transport and deposition in rough fractures". Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles 75 (2020): 23. http://dx.doi.org/10.2516/ogst/2020015.
Testo completoAbstract (sommario):
The transport and deposition of particulate materials through fractures is widely involved in environmental engineering and resource development engineering. A 3D Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) coupling method was used to investigate the particle and fluid flow. The Gauss Model was applied to construct the rough surfaces. First, the numerical results were compared with the previous results and reasonable agreements were obtained. Second, the results indicated a novel flow pattern of particles in rough fractures. Then, a comprehensive particle sedimentary analysis indicated that the deposition distance of particles was inversely proportional to the particle size and density ratio. In addition, the particle deposition rates were increased by the mean roughness and there was an uneven sediment distribution impacted by roughness. Reasons for this uneven sediment distribution were analyzed in detail. Moreover, the bridge plugs of particles considering the closure of fractures were simulated as well. A part of particulate materials would be filtered at the inlet due to size effect and the transport distance of entered particles decreased significantly when the particle was large. A critical particle radius (R < 0.27 mm) that can flow through closure fracture in this work was found. This work can provide a clear insight into the migration and deposition characteristics of particles in the rough fractures underground.
30
Wu, Shixian, Hui Zhu, Yongping Chen, Can Qi e Gang Li. "A 3D Monte Carlo Simulation for Aerosol Deposition onto Horizontal Surfaces by Combined Mechanisms of Brownian Diffusion and Gravity Sedimentation". Atmosphere 13, n. 9 (31 agosto 2022): 1408. http://dx.doi.org/10.3390/atmos13091408.
Testo completoAbstract (sommario):
A three-dimensional Monte Carlo model was developed to simulate the deposition of aerosol particles onto horizontal solid surfaces. The random walk method was employed to solve the particle transport equation, which allowed obtaining the trajectory of particle motion by a combined mechanism of Brownian diffusion and gravity sedimentation. The particle transport mechanism was described in terms of a Peclet number (Pe). The local structures of the dust layer, the relationship between the structure of the dust layer and particle transport mechanisms, and the number of the particles attached to the solid surface were investigated. The results showed that for a small Pe, when Brownian diffusion was a controlling mechanism for aerosol transport, the dust layer might exhibit a more open and looser structure, while for a large Pe, the dust layer was dense and tight. The differences of deposition morphologies under different transport mechanisms were caused by the different random intensities of particle motion. There was an upper limit of the maximum number of particles attached to the surface, and it strongly depended on particle transport mechanisms and size distributions. Additionally, the deposit morphologies obtained with the 3D Monte Carlo model were in good agreement with the experimental results found in the literature.
31
Nikpour, M., B. A. Mazzeo e D. R. Wheeler. "A Model for Investigating Sources of Li-Ion Battery Electrode Heterogeneity: Part II. Active Material Size, Shape, Orientation, and Stiffness". Journal of The Electrochemical Society 168, n. 12 (1 dicembre 2021): 120518. http://dx.doi.org/10.1149/1945-7111/ac3c1f.
Testo completoAbstract (sommario):
This work is the extension of our previous paper [Nikpour et al., J. Electrochem. Soc. 168, 060547, (2021)] which introduced the multi-phase smoothed particle (MPSP) model. This model was used to simulate the evolution of the microstructure during the drying and calendering manufacturing processes of four different electrodes. The MPSP model uses particle properties to predict overall film properties such as conductivities and elastic moduli and is validated by multiple experiments. In this work, the model is used to investigate the effects of active material particle size, shape, orientation, and stiffness on graphitic anodes. The model predicts that smaller active particles produce higher calendered film density, electronic conductivity, MacMullin number, and Young’s modulus, as compared to larger active particles. Rod-shaped active materials have greater ionic transport and lower electronic transport compared to the disk and sphere shapes, which have similar transport properties. During calendering, disk-shaped particles tend to be oriented horizontally, which decreases through-plane ionic transport. Increasing the stiffness of the active material increases film porosity and composite Young’s modulus, while lowering electronic transport and increasing ionic transport.
32
Grosshans, Holger, e Miltiadis V. Papalexandris. "Exploring the mechanism of inter-particle charge diffusion". European Physical Journal Applied Physics 82, n. 1 (aprile 2018): 11101. http://dx.doi.org/10.1051/epjap/2018170360.
Testo completoAbstract (sommario):
Dispersed solid particles in wall-bounded flows may get electrified during particle-wall collisions due to triboelectric effects. Subsequently, the electrostatic charge migrates from the near-wall regions to the bulk of the flow through the dynamics of the particles (particle-bound charge transport) and charge transfer during collisions between particles (inter-particle charge diffusion). In this paper, we explore the physics underlying the mechanism of inter-particle charge diffusion, which remains not well understood, by means of numerical simulations. We investigated the efficiency of the charge transport within the particulate phase via this mechanism and propose a time-scale for its characterization for particular systems. The considered parameters of these systems included the particle number density and charge as well as their mechanical and electrical properties. It was found that both an increase of the material density of the particles or of their number density results in an enhanced inter-particle charge diffusion and, thus, a reduction of its time scale. Moreover, if only the number density is high but the material density is kept low, then inter-particle charge diffusion may even become the dominant wall-normal charge transport mechanism. Further, in case some particles carry a high charge they are accelerated towards uncharged particles through electrostatic forces which leads to an efficient charge redistribution.
33
Yang, Yuguang, e Michael A. Bevan. "Cargo capture and transport by colloidal swarms". Science Advances 6, n. 4 (gennaio 2020): eaay7679. http://dx.doi.org/10.1126/sciadv.aay7679.
Testo completoAbstract (sommario):
Controlling active colloidal particle swarms could enable useful microscopic functions in emerging applications at the interface of nanotechnology and robotics. Here, we present a computational study of controlling self-propelled colloidal particle propulsion speeds to cooperatively capture and transport cargo particles, which otherwise produce random dispersions. By sensing swarm and cargo coordinates, each particle’s speed is actuated according to a control policy based on multiagent assignment and path planning strategies that navigate stochastic particle trajectories to targets around cargo. Colloidal swarms are shown to dynamically cage cargo at their center via inward radial forces while simultaneously translating via directional forces. Speed, power, and efficiency of swarm tasks display emergent coupled dependences on swarm size and pair interactions and approach asymptotic limits indicating near-optimal performance. This scheme exploits unique interactions and stochastic dynamics in colloidal swarms to capture and transport microscopic cargo in a robust, stable, error-tolerant, and dynamic manner.
34
Kucik, D. F., S. C. Kuo, E. L. Elson e M. P. Sheetz. "Preferential attachment of membrane glycoproteins to the cytoskeleton at the leading edge of lamella." Journal of Cell Biology 114, n. 5 (1 settembre 1991): 1029–36. http://dx.doi.org/10.1083/jcb.114.5.1029.
Testo completoAbstract (sommario):
The active forward movement of cells is often associated with the rearward transport of particles over the surfaces of their lamellae. Unlike the rest of the lamella, we found that the leading edge (within 0.5 microns of the cell boundary) is specialized for rearward transport of membrane-bound particles, such as Con A-coated latex microspheres. Using a single-beam optical gradient trap (optical tweezers) to apply restraining forces to particles, we can capture, move and release particles at will. When first bound on the central lamellar surface, Con A-coated particles would diffuse randomly; when such bound particles were brought to the leading edge of the lamella with the optical tweezers, they were often transported rearward. As in our previous studies, particle transport occurred with a concurrent decrease in apparent diffusion coefficient, consistent with attachment to the cytoskeleton. For particles at the leading edge of the lamella, weak attachment to the cytoskeleton and transport occurred with a half-time of 3 s; equivalent particles elsewhere on the lamella showed no detectable attachment when monitored for several minutes. Particles held on the cell surface by the laser trap attached more strongly to the cytoskeleton with time. These particles could escape a trapping force of 0.7 X 10(-6) dyne after 18 +/- 14 (sd) s at the leading edge, and after 64 +/- 34 (SD) s elsewhere on the lamella. Fluorescent succinylated Con A staining showed no corresponding concentration of general glycoproteins at the leading edge, but cytochalasin D-resistant filamentous actin was found at the leading edge. Our results have implications for cell motility: if the forces used for rearward particle transport were applied to a rigid substratum, cells would move forward. Such a mechanism would be most efficient if the leading edge of the cell contained preferential sites for attachment and transport.
35
Zhu, Wen Kui, Bin Li, Chuan Fang Yu e Liang Yuan Chen. "Investigation on the Transport Characteristics of Typical Biological Slender Particles in a Pilot-Scale Rotary Dryer". Advanced Materials Research 396-398 (novembre 2011): 315–21. http://dx.doi.org/10.4028/www.scientific.net/amr.396-398.315.
Testo completoAbstract (sommario):
The transport characteristics of cut tobacco as a typical biological wet slender particle were investigated in a pilot-scale rotary cylinder. Effect of solids and gas flow rate, moisture content of particles and rotating speed of cylinder was analyzed. The adaptability of the classical Friedman model for predicting average residence time of these type particles was also investigated. The result shows that the gas flow rate, moisture content of particles as well as rotating speed of cylinder have a significant influence on the axis transport velocity and forward step per cycle of cut tobacco in rotary cylinder. It’s difficult for Friedman model to accurately describe influence of gas flow rate and moisture content on transport of cut tobacco, which was associated with the particle characterize and influence of moisture content on the fluidity of particles.
36
Yang, Jinduo, Xi’an Li, Weiping Wang, Hao Chai, Mingxiao An e Qianyi Dai. "The Mechanism of Dust Transportation Based on Wind Tunnel Experiments and Numerical Simulations". Water 16, n. 7 (29 marzo 2024): 1006. http://dx.doi.org/10.3390/w16071006.
Testo completoAbstract (sommario):
The process of dust transportation is widespread, leading to the formation of regions such as the Loess Plateau. In order to understand the mechanisms of dust particle transportation, this study conducted wind tunnel experiments to simulate natural wind-driven dust transport processes. Theoretical derivations were carried out to establish the relationship between particle size and transportation distance, which was then validated through numerical simulations. The following conclusions were drawn: (1) wind tunnel experiments, theoretical derivations, and numerical simulations yielded consistent results, indicating the effectiveness of the wind tunnel experiments; (2) Under the influence of wind forces, the ideal transportation distance of particles is inversely proportional to the square of their size; (3) turbulent wind fields have a minor impact on dust transport, while particle roundness has a significant effect on transport; (4) clay particles and dust particles in loess regions share the same source areas and transport pathways.
37
Daubner, Simon, Marcel Weichel, Paul W. Hoffrogge, Daniel Schneider e Britta Nestler. "Modeling Anisotropic Transport in Polycrystalline Battery Materials". Batteries 9, n. 6 (5 giugno 2023): 310. http://dx.doi.org/10.3390/batteries9060310.
Testo completoAbstract (sommario):
Hierarchical structures of many agglomerated primary crystals are often employed as cathode materials, especially for layered-oxide compounds. The anisotropic nature of these materials results in a strong correlation between particle morphology and ion transport. In this work, we present a multiphase-field framework that is able to account for strongly anisotropic diffusion in polycrystalline materials. Various secondary particle structures with random grain orientation as well as strongly textured samples are investigated. The observed ion distributions match well with the experimental observations. Furthermore, we show how these simulations can be used to mimic potentiostatic intermittent titration technique (PITT) measurements and compute effective diffusion coefficients for secondary particles. The results unravel the intrinsic relation between particle microstructure and the apparent diffusivity. Consequently, the modeling framework can be employed to guide the microstructure design of secondary battery particles. Furthermore, the phase-field method closes the gap between computation of diffusivities on the atomistic scale and the effective properties of secondary particles, which are a necessary input for Newman-type cell models.
38
Tohme, Tohme, Pascale Magaud e Lucien Baldas. "Transport of Non-Spherical Particles in Square Microchannel Flows: A Review". Micromachines 12, n. 3 (7 marzo 2021): 277. http://dx.doi.org/10.3390/mi12030277.
Testo completoAbstract (sommario):
Understanding the behavior of a single particle flowing in a microchannel is a necessary step in designing and optimizing efficient microfluidic devices for the separation, concentration, counting, detecting, sorting, or mixing of particles in suspension. Although the inertial migration of spherical particles has been deeply investigated in the last two decades, most of the targeted applications involve shaped particles whose behavior in microflows is still far from being completely understood. While traveling in a channel, a particle both rotates and translates: it translates in the streamwise direction driven by the fluid flow but also in the cross-section perpendicular to the streamwise direction due to inertial effects. In addition, particles’ rotation and translation motions are coupled. Most of the existing works investigating the transport of particles in microchannels decouple their rotational and lateral migration behaviors: particle rotation is mainly studied in simple shear flows, whereas lateral migration is neglected, and studies on lateral migration mostly focus on spherical particles whose rotational behavior is simple. The aim of this review is to provide a summary of the different works existing in the literature on the inertial migration and the rotational behavior of non-spherical particles with a focus and discussion on the remaining scientific challenges in this field.
39
Doroshenko, Yaroslav, Julia Doroshenko, Vasyl Zapukhliak, Lyubomyr Poberezhny e Pavlo Maruschak. "MODELING COMPUTATIONAL FLUID DYNAMICS OF MULTIPHASE FLOWS IN ELBOW AND T-JUNCTION OF THE MAIN GAS PIPELINE". Transport 34, n. 1 (16 gennaio 2019): 19–29. http://dx.doi.org/10.3846/transport.2019.7441.
Testo completoAbstract (sommario):
The research was performed in order to obtain the physical picture of the movement of condensed droplets and solid particles in the flow of natural gas in elbows and T-junctions of the linear part of the main gas pipeline. 3D modeling of the elbow and T-junction was performed in the linear part of the gas main, in particular, in places where a complex movement of multiphase flows occurs and changes its direction. In these places also occur swirls, collisions of discrete phases in the pipeline wall, and erosive wear of the pipe wall. Based on Lagrangian approach (Discrete Phase Model – DPM), methods of computer modeling were developed to simulate multiphase flow movement in the elbow and T-junction of the linear part of the gas main using software package ANSYS Fluent R17.0 Academic. The mathematical model is based on solving the Navier–Stokes equations, and the equations of continuity and discrete phase movement closed with Launder–Sharma (k–e) two-parameter turbulence model with appropriate initial and boundary conditions. In T-junction, we simulated gas movement in the run-pipe, and the passage of the part of flow into the branch. The simulation results were visualized in postprocessor ANSYS Fluent R17.0 Academic and ANSYS CFD-Post R17.0 Academic by building trajectories of the motion of condensed droplets and solid particles in the elbow and T-junction of the linear part of the gas main in the flow of natural gas. The trajectories were painted in colors that match the velocity and diameter of droplets and particles according to the scale of values. After studying the trajectories of discrete phases, the locations of their heavy collision with the pipeline walls were found, as well as the places of turbulence of condensed droplets and solid particles. The velocity of liquid and solid particles was determined, and the impact angles, diameters of condensed droplets and solid particles in the place of collision were found. Such results provide possibilities for a full and comprehensive investigation of erosive wear of the elbow and T-junction of the linear part of the gas main and adjacent sections of the pipeline, and for the assessment of their strength and residual life.
40
Meng, Zhaohui, Sihai Hu, Ran Sun, Chengzhen Meng, Yaoguo Wu e Xiaofeng Sun. "Co-Transport of Aniline and TNT with Loess Colloid Particles in Saturated Loess Columns: Mechanism and Processes". Water 16, n. 1 (4 gennaio 2024): 180. http://dx.doi.org/10.3390/w16010180.
Testo completoAbstract (sommario):
The transport of mobile colloidal particles with organic pollutants in porous media has attracted considerable attention. Aniline and 2,4,6-trinitrotoluene (TNT), as aromatic compounds and key components of energetic materials, are continuously released into the environment. This study compared the co-transport of loess colloidal particles with aniline and TNT, aiming to investigate the influence of structural and physicochemical properties of the pollutants. The colloids were prepared and characterized, and static adsorption and dynamic column experiments were conducted. The results indicate that the adsorption processes of aniline and TNT both conformed to the quasi-second-order kinetic and the intra-particle diffusion models, with aniline exhibiting higher rate constants than TNT. The main adsorption mechanism involved van der Waals force, hydrogen bonding, and electrostatic interaction. Response surface experiments indicated that the adsorption capacity increased with higher initial concentration of organic compound but decreased with larger particle size and higher Na+ concentration. In column experiments, the adsorption of loess colloid particles on aniline and TNT was strongly correlated with the concentration of loess colloid particles. Loess colloid particles could be used as carriers to enhance the co-transport, with aniline exhibiting a faster transport rate due to the differences in polarity and molecular structure compared to TNT. In summary, loess colloidal particles enhanced the transport behavior of aniline and TNT in saturated loess columns. The differences in polarity and molecular structure of aniline and TNT further affect their co-transport mechanism in loess.
41
Hofemeier, Philipp, e Josué Sznitman. "Revisiting pulmonary acinar particle transport: convection, sedimentation, diffusion, and their interplay". Journal of Applied Physiology 118, n. 11 (1 giugno 2015): 1375–85. http://dx.doi.org/10.1152/japplphysiol.01117.2014.
Testo completoAbstract (sommario):
It is largely acknowledged that inhaled particles ranging from 0.001 to 10 μm are able to reach and deposit in the alveolated regions of the lungs. To date, however, the bulk of numerical studies have focused mainly on micrometer-sized particles whose transport kinematics are governed by convection and sedimentation, thereby capturing only a small fraction of the wider range of aerosols leading to acinar deposition. Too little is still known about the local acinar transport dynamics of inhaled (ultra)fine particles affected by diffusion and convection. Our study aims to fill this gap by numerically simulating the transport characteristics of particle sizes spanning three orders of magnitude (0.01-5 μm) covering diffusive, convective, and gravitational aerosol motion across a multigenerational acinar network. By characterizing the deposition patterns as a function of particle size, we find that submicrometer particles [[Formula: see text] (0.1 μm)] reach deep into the acinar structure and are prone to deposit near alveolar openings; meanwhile, other particle sizes are restricted to accessing alveolar cavities in proximal generations. Our findings underline that a precise understanding of acinar aerosol transport, and ultrafine particles in particular, is contingent upon resolving the complex convective-diffusive interplay in determining their irreversible kinematics and local deposition sites.
42
Hou, Chaofeng, e Yufeng Huang. "Controllable transport and size segregation of tiny particles harnessing noise in 2D Brownian motor system". Journal of Applied Physics 132, n. 7 (21 agosto 2022): 074902. http://dx.doi.org/10.1063/5.0100636.
Testo completoAbstract (sommario):
Controllable transport and size segregation of tiny particles following the Brownian motor mechanism are investigated with pseudo-particle modeling (PPM), a simplified molecular simulation approach, in which the liquid surrounding the Brownian particle is discretized into many pseudo particles and naturally introduces thermal noise by hard-sphere interaction between the pseudo particles. An asymmetric periodic potential is applied to the Brownian particles acting as a flashing ratchet model. The macroscopic directional motion of a single Brownian particle in external non-equilibrium fluctuation is reproduced well by the method. Illustratively, the PPM method is successfully employed to conduct the simulations of Brownian motor and testify the adaptability of the method. The segregation of different-sized particles is also studied by varying the size ratio and operation conditions, such as temperature. The simulations will help a quantitative design of Brownian motors and their application in particle transport, separation, and segregation.
43
Deng, Liwen, Qiong Hu, Jun Chen, Yajuan Kang e Shaojun Liu. "Particle Distribution and Motion in Six-Stage Centrifugal Pump by Means of Slurry Experiment and CFD-DEM Simulation". Journal of Marine Science and Engineering 9, n. 7 (29 giugno 2021): 716. http://dx.doi.org/10.3390/jmse9070716.
Testo completoAbstract (sommario):
Six-stage centrifugal pumps are used in deep-sea mining lifting systems and are required to convey slurry containing coarse particles. A six-stage centrifugal pump suitable for operation in a natural mining system was manufactured. High-flow and full-scaled slurry conveying experiments at a 5% and 9% volume concentration of particles was carried out at a large modified test site with artificial nodules. CFD-DEM simulations were carried out to obtain slurry transport characteristic curves, particle transport and distribution characteristics, where the simulation method was validated by the experiment data. A clarified two-stage pump can be used instead of a multi-stage pump for simplified simulation calculations with acceptable accuracy. Local agglomeration of particles caused by backflow was found at the outlet of the diffuser, and such agglomeration decreased with increasing flow rates. It was found that particles are transported non-uniformly, particles transport in diffusers in strands. Particles are transported in a pulse-like mode within the pump, with the latter stage showing similar particle characteristics to those transported in the previous pump stage.
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Crutcher, Russ. "Scotch® Magic Tape™ and the Analysis of Settled Dust". Microscope 70, n. 4 (2023): 177–83. http://dx.doi.org/10.59082/akyo4067.
Testo completoAbstract (sommario):
An environmental “sticky” tape lift contains hundreds to tens of thousands of individual particles. Each particle is unique, and its optical properties indicate the particle’s identity and history. Environmental particles are not isolated and by association occur with other particles, which may provide information on the source of an individual particle. The physical placement of particles on a surface carries information about the individual particles as well as the microenvironment associated with the surface at that location. Sampling is a destructive process because information is lost no matter how the surface is sampled. Therefore, the chosen sampling procedure must retain the data required for the analysis. Tape lifts can retain data on particle concentrations, particle identification, particle sources, transport mechanisms active at the sample location, and more. The type and quality of tape, how it is processed, and how it is analyzed will affect the extent to which the environment has been characterized. 3M Scotch® Magic™ Tape (Magic Tape) and the light microscope have been used to make tape lifts by the author since 1970 for characterizing environments. The advantages and disadvantages of using this sampling method are briefly discussed.
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Martinell, Julio J., e Andrés E. Medrano-Albarrán. "Model for plasma transport due to drift waves based on mappings including finite Larmor radius". Journal of Physics: Conference Series 2839, n. 1 (1 settembre 2024): 012015. http://dx.doi.org/10.1088/1742-6596/2839/1/012015.
Testo completoAbstract (sommario):
Abstract Turbulence in plasmas is modeled by fluctuating electric fields that determine particle motion through the E × B drift velocity which can lead to chaotic behavior. When applied to an ensemble of plasma particles in the chaotic regime their transport is studied: the anomalous plasma transport. The fluctuations are modeled by a spectrum of traveling waves with a wide frequency span which converts the equations of motion into an iterative mapping. The statistical properties of transport are derived. When the waves amplitude is small the particle orbits are regular, but as it is increased the behavior becomes increasingly chaotic. The effect of finite Larmor radius and the presence of a background plasma flow is also studied. We show that when a thermal population of particles is considered, the transport becomes non-local, as evidenced by a non-Gaussian particle distribution function (PDF). We have analyzed two different kinds of sheared flows: (1) a monotonic velocity shear and (2) a non-monotonic shear. The presence of transport barriers associated with the sheared velocity is also studied. We also present the application of the same techniques to study the transport of energetic particles that are born with a monoenergetic distribution.
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Suarez-Fernandez, William R., Juan D. G. Duran e Modesto T. Lopez-Lopez. "The role of thermal diffusion, particle clusters, hydrodynamic and magnetic forces on the flow behaviour of magneto-polymer composites". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 379, n. 2205 (19 luglio 2021): 20200302. http://dx.doi.org/10.1098/rsta.2020.0302.
Testo completoAbstract (sommario):
In this paper, we study the shear-induced flow of magneto-polymer composites, consisting of dispersions of magnetic particles in solutions of polymers, as a competition between the colloidal forces amid particles and their bulk transport induced by the hydrodynamic forces. For this aim, we analyse the role of different experimental parameters. Firstly, by using only solutions of a well-known anionic polymer (sodium alginate), we provoke a moderate hindering of particle movement, but keeping the liquid-like state of the samples. On the contrary, a gel-like behaviour is conferred to the samples when a cationic polymer (chitosan) is additionally added, which further reduces the particle movement. We analyse the effect of an applied magnetic field, which is opposed to particle transport by hydrodynamic forces, by inducing magnetic attraction between the particles. We perform the analysis under both stationary and oscillatory shear. We show that by using dimensionless numbers the differences between samples and experimental conditions are emphasized. In all cases, as expected, the transport of particles driven by bulk hydrodynamic forces dominates at high values of the shear rate. This article is part of the theme issue ‘Transport phenomena in complex systems (part 1)’.
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Stuhlmüller, Nico C. X., Thomas M. Fischer e Daniel de las Heras. "Competition between drift and topological transport of colloidal particles in twisted magnetic patterns". New Journal of Physics 26, n. 2 (1 febbraio 2024): 023056. http://dx.doi.org/10.1088/1367-2630/ad2a81.
Testo completoAbstract (sommario):
Abstract We simulate the motion of paramagnetic particles between two magnetic patterns with hexagonal symmetry that are twisted at a magic angle. The resulting Morié pattern develops flat channels in the magnetic potential along which colloidal particles can be transported via a drift force of magnitude larger than a critical value. Colloidal transport is also possible via modulation loops of a uniform external field with time varying orientation, in which case the transport is topologically protected. Drift and topological transport compete or cooperate giving rise to several transport modes. Cooperation makes it possible to move particles at drift forces weaker than the critical force. At supercritical drift forces the competition between the transport modes results e.g. in an increase of the average speed of the particles in integer steps and in the occurrence of subharmonic responses. We characterize the system with a dynamical phase diagram of the average particle speed as a function of the direction of the topological transport and the magnitude of the drift force.
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Mingotti, Nicola, e Andrew W. Woods. "On the transport of heavy particles through a downward displacement-ventilated space". Journal of Fluid Mechanics 774 (8 giugno 2015): 192–223. http://dx.doi.org/10.1017/jfm.2015.244.
Testo completoAbstract (sommario):
We investigate the transport of relatively heavy, small particles through a downward displacement-ventilated space. A flux of particles is supplied to the space from a localised source at a high level and forms a turbulent particle-laden plume which descends through the space. A constant flow of ambient fluid which does not contain particles is supplied to the space at a high level, while an equal amount of fluid is vented from the space at a low level. As a result of the entrainment of ambient fluid into the particle plume, a return flow is produced in the ambient fluid surrounding the plume in the lower part of the space. At steady state, particles are suspended by this return flow. An interface is formed which separates the ambient fluid in the lower part of the space, which contains particles, from the particle-free ambient fluid in the upper part of the space. New laboratory experiments show that the concentration of particles in the ambient fluid below the interface is larger than the average concentration of particles in the plume fluid at the level of the interface. Hence, as the plume fluid crosses the interface and descends through the particle-laden fluid underneath, it becomes relatively buoyant and forms a momentum-driven fountain. If the fountain fluid impinges on the floor, it then spreads radially over the surface until lifting off. We develop a quantitative model which can predict the height of the interface, the concentration of particles in the lower layer, and the partitioning of the particle flux between the fraction which sediments over the floor and that which is ventilated out of the space. We generalise the model to show that when particles and negatively buoyant fluid are supplied at the top of the space, a three-layer stratification develops in the space at steady state: the upper layer contains relatively low-density ambient fluid in which no particles are suspended; the central layer contains a mixture of ambient and plume fluid in which no particles are suspended; and the lower layer contains a suspension of particles in the same mixture of ambient and plume fluid. We quantify the heights of the two interfaces which separate the three layers in the space and the concentration of particles in suspension in the ambient fluid in the lower layer. We then discuss the relevance of the results for the control of airborne infections in buildings. Our experiments show that the three-layer stratification is subject to intermittent large-scale instabilities when the concentration of particles in the plume at the source is sufficiently small, or the rate of ventilation of the space is sufficiently large: we describe the transient concentration of particles in the space during one of these instabilities.
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Cao, Zhe, e Ming Li. "INCLUSION OF CONTACT FRICTION FOR PARTICLE-BASED SIMULATION OF SEDIMENT TRANSPORT OVER MOBILE BED". Coastal Engineering Proceedings, n. 37 (1 settembre 2023): 34. http://dx.doi.org/10.9753/icce.v37.sediment.34.
Testo completoAbstract (sommario):
The particle based approach, including the particle resolving method, such as CFD-DEM, e.g. Drake and Calantoni (2001), Schmeeckle (2014), and the Particle-In-Cell (PIC) method, e.g. Patankar and Joseph (2001); Finn, M. Li, and Apte (2016); Y. Li et al. (2014), has become important tool for simulation of sediment transport in recent years. The latter is advantageous in the required computing resources when large amount of particles are involved and hence is more suitable for simulation of sediment transport over mobile bed. However, unlike that in CFD-DEM, special treatment is needed in the PIC method in order to prevent overlap and over-packing of sediment particles in a computational cell. Most models so far ignore the contact friction force between particles that hinders relative movement but often is essential to maintain particles in static position, especially in the seabed where the contact forces between particles are the largest. An new friction force is proposed to simulate the particle interactions, similar to the collision used in previous studies, so that the kinetic energy driving particles motion can be effectively dissipated and over-packing can be minimised under either static or dynamic stages of the particle motion.
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Wang, J. F., e G. Qin. "The Effect of Solar Wind on Charged Particles’ Diffusion Coefficients". Astrophysical Journal 961, n. 1 (1 gennaio 2024): 6. http://dx.doi.org/10.3847/1538-4357/ad09b7.
Testo completoAbstract (sommario):
Abstract The transport of energetic charged particles through magnetized plasmas is ubiquitous in interplanetary space and astrophysics, and the important physical quantities are the parallel and perpendicular diffusion coefficients of energetic charged particles. In this paper, the influence of solar wind on particle transport is investigated. Using the focusing equation, we obtain parallel and perpendicular diffusion coefficients, accounting for the solar wind effect. For different conditions, the relative importance of the solar wind effect to diffusion is investigated. It is shown that, when energetic charged particles are close to the Sun, for parallel diffusion, the solar wind effect needs to be taken into account. These results are important for studying energetic charged particle transport processes in the vicinity of the Sun.