Zeitschriftenartikel zum Thema „Particles flux“
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Tanis-Kanbur, Melike Begum, Navin Raj Tamilselvam, Hsiao Yu Lai und Jia Wei Chew. „Impact of Particle Shape and Surface Group on Membrane Fouling“. Membranes 12, Nr. 4 (04.04.2022): 403. http://dx.doi.org/10.3390/membranes12040403.
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Membrane fouling remains one of the most critical drawbacks in membrane filtration processes. Although the effect of various operating parameters—such as flow velocity, concentration, and foulant size—are well-studied, the impact of particle shape is not well understood. To bridge this gap, this study investigated the effect of polystyrene particle sphericity (sphere, peanut and pear) on external membrane fouling, along with the effect of particle charge (unmodified, carboxylated, and aminated). The results indicate that the non-spherical particles produce higher critical fluxes than the spherical particles (i.e., respectively 24% and 13% higher for peanut and pear), which is caused by the looser packing in the cake due to the varied particle orientations. Although higher crossflow velocities diminished the differences in the critical flux values among the particles of different surface charges, the differences among the particle shapes remained distinct. In dead-end filtration, non-spherical particles also produced lower flux declines. The shear-induced diffusion model predicts all five particle types well. The Derjaguin-Landau-Verwey-Overbeek (DLVO) and extended DLVO (XDLVO) models were used to quantify the interaction energies, and the latter agreed with the relative critical flux trends of all of the PS particles. As for the flux decline trends, both the DLVO and XDLVO results are in good agreement.
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Vigneswaran, S., D. Y. Kwon, H. H. Ngo und J. Y. Hu. „Improvement of microfiltration performance in water treatment: is critical flux a viable solution?“ Water Science and Technology 41, Nr. 10-11 (01.05.2000): 309–15. http://dx.doi.org/10.2166/wst.2000.0669.
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In this study, three definitions for critical flux were introduced based on the crossflow microfiltration (CFMF) experiments conducted under an operational mode of constant permeate flux. The critical flux based on material balance was calculated from the rate of particles deposition. The highest permeate flux results in no particle deposition being taken at the critical flux. The second definition was based on the increase in transmembrane pressure (TMP). The critical flux based on the TMP increase is the flux below which the membrane fouling does not occur. The third definition was based on the direct observation of particles deposition through microscope. Detailed experiments were conducted with synthetic suspension of different sizes of latex particles. Long term experiments conducted with polydispersed kaolin clay suspension indicated that the critical flux based on material balance concept is more realistic in field conditions.
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Kwon, D. Y., und S. Vigneswaran. „Influence of particle size and surface charge on critical flux of crossflow microfiltration“. Water Science and Technology 38, Nr. 4-5 (01.08.1998): 481–88. http://dx.doi.org/10.2166/wst.1998.0701.
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The effect of particle size and ionic strength of the feed suspension on critical flux was studied. The critical flux was defined in two different ways (strong and mild definition). The fouling, the increase of resistance (which is the basis of the mild definition of the critical flux) was relatively sensitive to the deposition of particles of 0.46 μm on the membrane of 0.2 μm mean pore. On the other hand, the deposition of large particles of 3.2 μm to a certain value on the membrane surface of 0.2 μm mean pore did not lead to the increase in resistance. In case of 11.9 μm particles, the transmembrane pressure did not increase even with significant amount of deposition of particles. The ionic strength of suspension had significant effect on the critical flux. For an ionic strength less than 1×10−1.5 M, there was a decrease in the critical flux. This could be due to the dense layer of deposit which is the result of less diffuse layer thickness of particles. Above this ionic strength, a significant increase in critical flux was noticed which may be due to the aggregation of particles.
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KIM, DAE-GEUN, und JAE-HO LEE. „KINETIC STUDY OF WC PARTICLES INCORPORATION IN NICKEL COMPOSITE PLATING“. Surface Review and Letters 17, Nr. 03 (Juni 2010): 359–62. http://dx.doi.org/10.1142/s0218625x10014089.
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The particles, suspended in the electrolyte, can be co-deposited with metal. The co-deposition behaviors of WC and Co-coated WC particles on nickel matrix were investigated. Many operating parameters that influence on the quantity of incorporated particles, including current density, bath agitation and electrolyte composition were investigated. The co-deposition of particles during electroplating depends on the rate of metal deposition and on the flux of particles to the film surface. The growth rate of the metal film is determined by the current density, whereas the flux of particles to the electrode surface is dependent on the particle size, particle concentration in solution, the electrode rotation rate, the particle diffusion coefficient, and the electrode geometry. The kinetic parameters in the co-deposition were calculated from the experimental results. Co-coated WC particles were easily incorporated in the matrix than WC particles from the calculated and experimental results.
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Wang, Yi, Wen Yang und Lifeng Zhang. „Interaction between Ti-bearing ultra-low carbon solid steel and mold flux at 1400 °C“. Metallurgical Research & Technology 116, Nr. 4 (2019): 423. http://dx.doi.org/10.1051/metal/2019023.
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Laboratory scale experiments on the reaction between mold flux and solid titanium (Ti) bearing ultra low carbon (ULC) steel were carried out at 1400 °C. It was found that the composition of mold flux particles changed after the interactions, which was resulted from the reduction of flux components by the aluminum (Al) and Ti in steel, leading to the decrease of SiO2 and the increase of Al2O3 and TiOx in flux particles. A layer of oxides was precipitated in the steel near the steel-flux interface. Al2O3 particles were firstly precipitated and then transformed into Ti-Al-O type with the decrease of the distance from the interface and the increase of reheating time, accompanying with the increase of the particle size. The precipitation of particles was estimated to result from the reoxidation of the steel matrix by the oxygen diffused from the mold flux, which would further increase the detriment of the entrapped mold flux to the cleanliness and surface quality of the rolled sheets of ULC steel.
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Pierce, J. Kevin, Marwan A. Hassan und Rui M. L. Ferreira. „Probabilistic description of bedload fluxes from the aggregate dynamics of individual grains“. Earth Surface Dynamics 10, Nr. 4 (03.08.2022): 817–32. http://dx.doi.org/10.5194/esurf-10-817-2022.
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Abstract. We formulate the bedload sediment flux probability distribution from the Lagrangian dynamics of individual grains. Individual particles obey Langevin equations wherein the stochastic forces driving particle motions are switched on and off by particle entrainment and deposition. The flux is calculated as the rate of many such particles crossing a control surface within a specified observation time. Flux distributions inherit observation time dependence from the on–off motions of particles. At the longest observation times, distributions converge to sharp peaks around classically expected values, but at short times, fluctuations are erratic. We relate this scale dependence of bedload transport rates to the movement characteristics of individual sediment grains. This work provides a statistical mechanics description for the fluctuations and observation-scale dependence of sediment transport rates.
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Bahari, A., S. Mohammadi, N. S. Shakib, M. R. Benam und Z. Sajjadi. „Monte Carlo Methods to Simulate the Propagation of the Created Atomic/ Nuclear Particles from Underground Piezoelectric Rocks through the Fractures Before the Earthquakes“. Atom Indonesia 1, Nr. 1 (28.02.2024): 27–35. http://dx.doi.org/10.55981/aij.2024.1311.
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Until now, many studies have been performed on particle radiations before or during earthquakes (EQs). Neutron, gamma, electron, proton, and ultra-low frequency (ULF) photons are among the particles, detected during EQs. In our previous study, with the help of piezoelectricity relationships and the elastic energy formula, the Monte Carlo N‐Particle eXtended (MCNPX) simulation code was applied to find the amount of created atomic/nuclear particles, the dominant interactions; and the energy of the particles for various sizes of quartz and granite blocks. In this study, using the MCNPX simulation code, we have estimated the flux of the particles (created from under-stressed granitic rocks) at different distances from the EQ hypocenter inside the fractures, filled with air, water, and CO2. It was found that inside a water-filled fracture, the particles do not show the flux far from the EQ hypocenter. However, inside the gases like air and CO2 with the normal condition density, different types of particles can have a flux far from the source (more than a kilometer) and they might reach themselves to the surface in the case that the EQ hypocenter is very shallow (0-5 km). However, for deep EQs, it seems that the most detected nuclear particles on the surface should pass via the vacuum-filled fractures and reach the surface. Moreover, it was concluded that the higher the density of the fracture’s filling fluid, the less distance that the particles can have a flux.
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ZAKAULLAH, M., IMTIAZ AHMAD, KHAIRUR REHMAN und G. MURTAZA. „USE OF SOLID STATE NUCLEAR TRACK DETECTORS CR-39 TO STUDY CHARGED PARTICLES EMISSION FROM A 3 kJ PLASMA FOCUS“. Modern Physics Letters B 09, Nr. 16 (10.07.1995): 1033–37. http://dx.doi.org/10.1142/s0217984995001005.
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The CR-39 solid state nuclear track detectors are employed to investigate the fluence anisotropy of charged particles (protons, deuterons and tritons) emitted from the focus region of a low energy Mather-type plasma focus energized by a single 32 μF, 15 kV (3.6 kJ) capacitor. The charged particle flux is the highest in the axial direction, and decreases towards the radial direction. The radial charged particles flux is six times smaller than the flux in the axial direction.
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SHIM, JEONGHEE, MYUNG WOO HAN, YOUNG CHUL KANG und DONGSEON KIM. „Biogeochemical cycle of organic matter in a subtidal benthic environment in Marian Cove, King George Island, Antarctica“. Antarctic Science 17, Nr. 2 (Juni 2005): 193–204. http://dx.doi.org/10.1017/s0954102005002592.
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The flux and composition of settling particles were measured in a subtidal benthic environment of Marian Cove, King George Island, from February 1998–January 2000. The total mass flux ranged between 2.47 g m−2 d−1 (August and September 1998) and 21.97 g m−2 d−1 (February 1999), and showed distinct seasonal variation: high in the summer and low in winter. Lithogenic particles constituted 70–95% of the total particles, while biogenic particles represented only 10%, except in spring when biogenic particles made up more than 30%. The fluxes of organic carbon, biogenic silica, nitrogen, and organic phosphorus all peaked in spring rather than in summer, with ranges of 4.4–34.0, 1.2–23.5, 0.48–5.56, and 0.01–0.15 mmol m−2 d−1, respectively. Fluxes of metals (Al, Ti, Cu, Cd, and Pb) showed temporal variability, similar to that of the total mass flux, but each metal had different enrichment factor (EF) values. The EF value of Cu correlated positively with fluxes in lithogenic components, while the EF value of Cd correlated with biogenic particle fluxes. The Cu flux is mainly related to substantial inflows of melt water laden with Cu- enriched lithogenic particles. The Cd flux is probably associated with organic matter deposition following phytoplankton blooms in the water column.
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Singh, R. N., und R. Prasad. „Wave–particle interaction and enhanced precipitation of charged particles“. Canadian Journal of Physics 63, Nr. 4 (01.04.1985): 445–52. http://dx.doi.org/10.1139/p85-070.
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In addition to parallel electric fields, the distortions in the geomagnetic field have been considered in the study of resonant whistler wave interaction with gyrating charged particles. Mead axisymmetric distortions in the geomagnetic field have been considered and new expressions for the inhomogeneity parameter, αd, have been obtained. Considering the diffusion of charged particles in pitch angle, the variation in the precipitating electron flux under varying magnetospheric conditions has been computed. The variation in the distribution of trapped charged particles is shown to play an important role in controlling the electron flux precipitated into the lower ionosphere.
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Malinouski, A. I. „Method for calculation of radiative heat transfer in beds of spherical particles“. Doklady of the National Academy of Sciences of Belarus 63, Nr. 6 (07.01.2020): 680–88. http://dx.doi.org/10.29235/1561-8323-2019-63-6-680-688.
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A new technique for implementing external (particle-to-wall) and particle-to-particle radiative heat transfer in discrete elements method (DEM) simulations is proposed. It is based on the idea that an expected view factor value depends on relevant local bed parameters (distance between particles, particle radius ratio, and local bed porosity). Calculation of average view factors via the formula requires considerably less computational effort than direct in situ integration, when this happens a reasonable average value and an overall accuracy comparable to direct calculation are provided. Both mono- and polydisperse mixtures of spherical opaque particles were considered. It was shown that using nondimensional parameters, a simple general dependence for an external radiative heat flux may be introduced. Exponential and linear fits were proposed for estimating the particle-particle radiative heat flux. The generalization of the obtained formulas for various bed porosities is proposed. The distribution of cumulative transferred heat flux across the particles up to a certain distance was found, and the recommendations regarding the choice of that parameter to achieve a desired accuracy were formulated. Also, the method to account for the particle emissivity was proposed on the basis of the empirical dependence between emissivity and radiative heat flux in porous materials. The proposed method satisfies all the requirements to become a standard implementation of radiative heat transfer calculation in DEM.
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Johnson, Grant, Patrick Kilian, Fan Guo und Xiaocan Li. „Particle Acceleration in Magnetic Reconnection with Ad Hoc Pitch-angle Scattering“. Astrophysical Journal 933, Nr. 1 (01.07.2022): 73. http://dx.doi.org/10.3847/1538-4357/ac7143.
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Abstract Particle acceleration during magnetic reconnection is a long-standing topic in space, solar, and astrophysical plasmas. Recent 3D particle-in-cell simulations of magnetic reconnection show that particles can leave flux ropes due to 3D field-line chaos, allowing particles to access additional acceleration sites, gain more energy through Fermi acceleration, and develop a power-law energy distribution. This 3D effect does not exist in traditional 2D simulations, where particles are artificially confined to magnetic islands due to their restricted motions across field lines. Full 3D simulations, however, are prohibitively expensive for most studies. Here, we attempt to reproduce 3D results in 2D simulations by introducing ad hoc pitch-angle scattering to a small fraction of the particles. We show that scattered particles are able to transport out of 2D islands and achieve more efficient Fermi acceleration, leading to a significant increase of energetic particle flux. We also study how the scattering frequency influences the nonthermal particle spectra. This study helps achieve a complete picture of particle acceleration in magnetic reconnection.
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Müller, Thomas, Paolo Arosio, Luke Rajah, Samuel I. A. Cohen, Emma V. Yates, Michele Vendruscolo, Christopher M. Dobson und Tuomas P. J. Knowles. „Particle-Based Monte-Carlo Simulations of Steady-State Mass Transport at Intermediate Péclet Numbers“. International Journal of Nonlinear Sciences and Numerical Simulation 17, Nr. 3-4 (01.06.2016): 175–83. http://dx.doi.org/10.1515/ijnsns-2015-0056.
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AbstractConventional approaches for simulating steady-state distributions of dilute particles under diffusive and advective transport involve solving the diffusion and advection equations in at least two dimensions. Here, we present an alternative computational strategy by combining a particle-based rather than a field-based approach with the initialisation of particles in proportion to their flux. This method allows accurate prediction of the steady state and is applicable even at intermediate and high Péclet numbers $ (Pe \gt 1)$ where traditional particle-based Monte-Carlo methods starting from randomly initialised particle distributions fail. We demonstrate that generating a flux of particles according to a predetermined density and velocity distribution at a single fixed time and initial location allows for accurate simulation of mass transport under flow. Specifically, upon initialisation in proportion to their flux, these particles are propagated individually and detected by summing up their Monte-Carlo trajectories in predefined detection regions. We demonstrate quantitative agreement of the predicted concentration profiles with the results of experiments performed with fluorescent particles in microfluidic channels under continuous flow. This approach is computationally advantageous and readily allows non-trivial initial distributions to be considered. In particular, this method is highly suitable for simulating advective and diffusive transport in microfluidic devices, for instance in the context of diffusive sizing.
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Ahlm, L., E. D. Nilsson, R. Krejci, E. M. Mårtensson, M. Vogt und P. Artaxo. „Aerosol number fluxes over the Amazon rain forest during the wet season“. Atmospheric Chemistry and Physics Discussions 9, Nr. 4 (19.08.2009): 17335–83. http://dx.doi.org/10.5194/acpd-9-17335-2009.
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Abstract. Number fluxes of particles with diameter larger than 10 nm were measured with the eddy covariance method over the Amazon rain forest during the wet season as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) campaign 2008. The primary goal was to investigate whether sources or sinks dominate the aerosol number flux in the tropical rain forest-atmosphere system. During the measurement campaign, from 12 March to 18 May, 60% of the particle fluxes pointed downward, which is a similar fraction to what has been observed over boreal forests. The particle transfer velocity vt increased with increasing friction velocity and the relation is described by the equation vt=2.4×10−3·u∗ where u∗ is the friction velocity. Upward particle fluxes often appeared in the morning hours and seem to a large extent to be an effect of entrainment fluxes into a growing mixed layer rather than primary aerosol emission. In general, primary aerosol emission had a limited impact on the total aerosol number population in this study, possibly because the measured particle number fluxes reflect mostly particles less than approximately 200 nm. The net deposition flux prevailed even in the absolute cleanest atmospheric conditions during the campaign and therefore cannot be explained only by deposition of anthropogenic particles. It seems that a significant contribution of secondary aerosol particles to the aerosol population is the most reasonable explanation for the net downward flux. This is an indication that secondary aerosol particles may dominate the aerosol number population in the Amazon boundary layer and that the contribution of primary aerosol particles may be low in terms of numbers. However, aerosol flux measurements should be repeated in a more remote area of the Amazon with less influence from anthropogenic sources before any final conclusions may be drawn.
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Tung, V. X., und V. K. Dhir. „Experimental Study of Boiling Heat Transfer From a Sphere Embedded in a Liquid-Saturated Porous Medium“. Journal of Heat Transfer 112, Nr. 3 (01.08.1990): 736–43. http://dx.doi.org/10.1115/1.2910448.
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Boiling heat transfer from a sphere embedded in a porous medium composed of nonheated glass particles was studied under steady-state and transient quenching conditions. In the experiments, the diameter of the nonheated glass particles forming the porous layers was varied parametrically. Freon-113 was used as the test liquid. Experimental results showed that the maximum heat flux increased monotonically with increasing glass particle diameter and approached an asymptotic value corresponding to the maximum heat flux obtained in a pool free of glass particles. It was also observed that the minimum heat flux was nearly insensitive to the particle size and the film boiling heat transfer coefficient increased slightly with decreasing particle size. In the nucleate boiling region, the heat transfer coefficient showed a much weaker dependence on wall superheat in the presence of particles. Transient data indicated that the surface temperature was not uniform during quenching. Therefore, different maximum heat fluxes were obtained depending on the location of the thermocouple whose temperature history was employed in recovering the transient boiling curve. However, for some applications, cooling rates predicted by imposing the steady-state boiling curve may not be in large error.
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Cainey, Jill M., Melita Keywood, E. Keith Bigg, Michael R. Grose, Rob W. Gillett und Mick Meyer. „Flux chamber study of particle formation from Durvillaea potatorum“. Environmental Chemistry 4, Nr. 3 (2007): 151. http://dx.doi.org/10.1071/en07006.
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Environmental context. Kelp at Mace Head, Ireland, produces large quantities of iodine when exposed to sunlight at low tide and this iodine results in the rapid production of particles. Cape Grim, Tasmania, also has large colonies of kelp (Durvillaea potatorum) but its role in particle formation appears limited. A flux chamber was used to better understand the response of Durvillaea potatorum to light stress and ozone. Abstract. Brown kelp, in particular Laminara digitata at Mace Head, Ireland, has been shown to emit iodine when under stress, resulting in new particle formation. The Cape Grim Baseline Air Pollution Station, Tasmania, is surrounded by rocky reefs that support large colonies of the brown kelp Durvillaea potatorum. During an intensive campaign in February 2006 at Cape Grim, levels of IO, OIO and methyl iodide remained at background levels and no particle formation events could be associated with locally generated precursor iodine species. In order to better understand the limitations of the local kelp to provide a source of precursor species, samples of Durvillaea potatorum were collected from the beach below the Cape Grim Station and tested for their capacity to initiate particle formation using a flux chamber technique. Particles were observed only when the kelp was exposed to both very high levels (>100 ppb) of ozone and natural solar radiation. There was a high correlation between ozone level and particles produced. The particles resulting from exposure to high levels of ozone were aromatic and volatile. Durvillaea potatorum appears to plays a very limited role in contributing to particle formation at Cape Grim, but it does represent a source of atmospheric iodine under photo-oxidative stress, of 18 pmol g–1 (fresh weight) min–1 and is likely to have a significant role in atmospheric chemistry at this site.
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Ren, J., D. C. Donovan, J. G. Watkins, H. Q. Wang, C. Lasnier, T. Looby, J. Canik et al. „Measurements of multiple heat flux components at the divertor target by using surface eroding thermocouples (invited)“. Review of Scientific Instruments 93, Nr. 10 (01.10.2022): 103541. http://dx.doi.org/10.1063/5.0101719.
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The Surface Eroding Thermocouple (SETC) is a robust diagnostic utilized in DIII-D to provide fast, edge-localized modes (ELMs) resolved heat flux measurements, in particular in geometric regions that are too shadowed for traditional infrared thermography. In order to further investigate the power dissipation in the divertor region, a combination of flush-mounted and recessed SETCs was developed to assess the effect on surface heating from non-charged particles at the divertor target. Utilizing the Divertor Materials Evaluation System sample exposure platform, the first demonstration of the feasibility of using this new method to distinguish between the heat flux from charged particles and that from neutrals and radiative heating was achieved. This paper details the process of using the combination of flush SETCs and recessed SETCs to measure the multiple heat flux components at the divertor target and further discusses how to determine two important ratios, α (ratio of heat flux from charged particles deposit on recessed SETC to that deposit on flush SETC) and β (ratio of heat flux from non-charged particles deposit on recessed SETC to that deposit on flush SETC), in the estimation of the heat flux from non-charged particle sources. Using a time dependent ratio α, it was found that ∼50% of the total incident heat flux is attributable to the non-charged particles in the fully detached open divertor in DIII-D. Finally, the new application of similar SETC diagnostics in the Small Angle Slot divertor with a V-like configuration and partial tungsten coated surface (SAS-VW) is also introduced.
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Gorchakov, G. I., D. V. Buntov, A. V. Karpov, V. M. Kopeikin, S. F. Mirsaitov, R. A. Gushchin und O. I. Datsenko. „Saltating particle aleurite mode in windsand flux over desertified area“. Доклады Академии наук 488, Nr. 2 (24.09.2019): 193–96. http://dx.doi.org/10.31857/s0869-56524882193-196.
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Saltating particle aleurite mode is discovered in the windsand flux over desertified area. Approximation of the saltating particle distribution measured is received using two lognormal distribution functions. It is shown that aleurite and sand number concentration particles in the windsand flux depends on wind velocity in the surface layer in different way.
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Yakovchuk, Olesya, und Jan Maik Wissing. „Magnetic local time asymmetries in precipitating electron and proton populations with and without substorm activity“. Annales Geophysicae 37, Nr. 6 (28.11.2019): 1063–77. http://dx.doi.org/10.5194/angeo-37-1063-2019.
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Abstract. The magnetic local time (MLT) dependence of electron (0.15–300 keV) and proton (0.15–6900 keV) precipitation into the atmosphere based on National Oceanic and Atmospheric Administration POES and METOP satellite data during 2001–2008 was described. Using modified APEX coordinates the influence of particle energy, substorm activity and geomagnetic disturbance on the MLT flux distribution was statistically analysed. Some of the findings are the following. a. Substorms mostly increase particle precipitation in the night sector by about factor 2–4, but can also reduce it in the day sector.b. MLT dependence can be assigned to particles entering the magnetosphere at the cusp region and magnetospheric particles in combination with energy-specific drifts (in agreement with Newell et al., 2009).c. MLT flux differences of up to 2 orders of magnitude have been identified inside the auroral oval during geomagnetically disturbed conditions. The novelty here is the comprehensive coverage of energy bands and the focus on asymmetry.d. The maximum flux asymmetry ratio depends on particle energy, decreasing with Kp for low energetic particles and increasing with Kp for higher energy electrons, while high energy protons show a more complex dependency. While some aspects may already have been known, the quantification of the flux asymmetry sheds new light on MLT variation.
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Wu, Yan, und Wei-Tao Wu. „Modeling on Effect of Particle Sediment on Fluid Flow and Heat Transfer of Solid–Fluid Suspension“. Energies 14, Nr. 2 (18.01.2021): 487. http://dx.doi.org/10.3390/en14020487.
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A two-way coupling particle flux model is proposed for studying the multi-component solid–fluid suspension. The suspension mixture is treated as a non-linear single-phase fluid and the migration of the solid particles is modeled by a particle flux equation. The proposed particle flux model takes the effects of the particle migration on the transport of the suspension’s momentum and internal energy into account. Two benchmark problems are calculated to study the performance of the proposed particle flux model, i.e., flow in a sudden expansion straight channel and flow between two rotating cylinders. It is found that the particle flux model converges without numerical stability issue with the commonly used PISO-SIMPLE transient solver, and the effect of the particle migration is evident on both velocity profile and temperature distribution.
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Tarabara, V., R. Hovinga und M. R. Wiesner. „Transient permeate flux analysis: model validation“. Water Supply 1, Nr. 5-6 (01.06.2001): 21–30. http://dx.doi.org/10.2166/ws.2001.0096.
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An extended model integrating several particle back-transport theories has been proposed by Sethi and Wiesner to predict transient permeate flux as a function of operational parameters for constant permeate flux (CF) and constant transmembrane pressure (CP) cross-flow regimes. Filtration experiments using monodisperse latex suspensions of particles 0.02 μm, 0.12 μm and 0.68 μm in diameter in a cross-flow flat slit membrane were carried out for model validation. In a separate set of filtration experiments with monodisperse latex particles 0.10 μm, 0.43 μm and 1.00 μm in diameter, the transient behavior of permeate flux in CP and CF modes of operation was compared. Significant differences between model calculations and experiments were observed. A slightly more complex structure at the cake-suspension interface was hypothesized to explain these differences. A representation of the cake with a gradually changing solids concentration allowed for better matching of the extended model and experimental results. The CP operation mode yielded a higher specific permeate flux resulting from a thinner cake or a cake with a lower average specific resistance. Experimentally observed differences between performance in CP and CF modes were less sensitive to the size of particles in the suspension than predicted by theory.
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Kim, S., S. H. Cho und H. Park. „Reduction of cake layer by re-aggregation in coagulation-crossflow microfiltration process“. Water Supply 2, Nr. 5-6 (01.12.2002): 329–36. http://dx.doi.org/10.2166/ws.2002.0187.
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Cake layer in crossflow microfiltration(CFMF) can be reduced by coagulation, enhancing membrane flux. This is because enlarging particle size by coagulation increases shear-induced diffusivity and the back-transport of rejected particles. However, it is known that the enlarged particles are disaggregated by the shear force of the pump while passing through it. This study looks at the disaggregation in relation to cake layer reduction. Kaolin and polysulfon hollow fiber microfilters are used for experiments. The reduction of cake resistance by coagulation is observed in a range of 17% to 53% at the various coagulation conditions. Particle size analysis results of the experiments show that aggregated particles in feed are completely disaggregated by the pump but re-aggregation of particles occurs in the membrane. This suggests that the re-aggregation of particles is critical to cake reduction and flux enhancement, since the aggregated particles are completely broken. The mechanisms for re-aggregation in the membrane are the same as those for coagulation in the feed tank. Charge neutralization is better for CCFMF than sweep flocculation although it has two drawbacks in operation.
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Yang, Fan, Bhargav Rallabandi und Howard A. Stone. „Autophoresis of two adsorbing/desorbing particles in an electrolyte solution“. Journal of Fluid Mechanics 865 (20.02.2019): 440–59. http://dx.doi.org/10.1017/jfm.2019.61.
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Classical diffusiophoresis describes the motion of particles in an electrolyte or non-electrolyte solution with an imposed concentration gradient. We investigate the autophoresis of two particles in an electrolyte solution where the concentration gradient is produced by either adsorption or desorption of ions at the particle surfaces. We find that when the sorption fluxes are large, the ion concentration near the particle surfaces, and consequently the Debye length, is strongly modified, resulting in a nonlinear dependence of the phoretic speed on the sorption flux. In particular, we show that the phoretic velocity saturates at a finite value for large desorption fluxes, but depends superlinearly on the flux for adsorption fluxes, where both conclusions are in contrast with previous results that predict a linear relationship between autophoretic velocity and sorption flux. Our theory can also be applied to precipitation/dissolution and other surface chemical processes.
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Joo, Hye Sook, Han Shin Choi, Hyung Ho Jo, Hoon Cho, June Seob Kim und Chang Hee Lee. „Alumina-Titania Spot Spraying Bead Formation and Characteristics in Atmospheric Plasma Spraying“. Materials Science Forum 534-536 (Januar 2007): 401–4. http://dx.doi.org/10.4028/www.scientific.net/msf.534-536.401.
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Fine and coarse alumina-titania composite particles were overlaid by allowing the particles to be deposited for a short time without moving a plasmatron [spot spraying bead]. Both the deposition efficiency and maximum deposition rate were measured at the different plasma gas composition. Considering the normalized maximum deposition rate [(maximum deposition rate)x(deposition efficiency)-1], effects of particle size and plasma gas composition on the particle segregation within a cross-section of mass flux could be estimated. Also, particle melting state according to the position within a mass flux at the moment of impact could be also estimated through the investigations of microstructure and phase composition of the spot spraying bead.
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Diaz, Dominic, Jessica Bojorquez, Joshua Crasto, Margaret Koulikova, Tameez Latib, Aviva Prins, Andrew Shapiro et al. „Investigation of Constant Volume and Constant Flux Initial Conditions on Bidensity Particle-Laden Slurries on an Incline“. American Journal of Undergraduate Research 16, Nr. 3 (29.12.2019): 42–57. http://dx.doi.org/10.33697/ajur.2019.029.
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Particle-laden slurries are pervasive in both natural and industrial settings, whenever particles are suspended or transported in a fluid. Previous literature has investigated the case of a single species of negatively buoyant particles suspended in a viscous fluid. On an incline, three distinct regimes emerge depending on the particle concentration and inclination angle: settled (where particles settle and there is a pure fluid front), well-mixed (where particle concentration is constant throughout), and ridged (where a particle-rich ridge leads the flow). Recently, the same three regimes were also found for constant volume two species bidensity slurries. We extend the literature on bidensity slurries by presenting results on constant volume and a new type of initial condition: constant flux, where slurry is pumped onto the incline at a constant rate. We present front positions of the slurries and compare them to theoretical predictions. In addition, height profiles (film thicknesses) are also presented for the constant flux case, showing the distinct behavior of the ridged regime. We find that for constant flux conditions the settled regime forms for small particle volume fractions and inclination angles while the ridged regime forms for large corresponding values. Intermediate values of these two parameters are shown to produce a well-mixed regime. KEYWORDS: Thin Films; Particle-Laden Flow; Multiphase Fluids; Interfacial Flows; Particle Segregation
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Park, Hyungwon John, Jeffrey S. Reid, Livia S. Freire, Christopher Jackson und David H. Richter. „In situ particle sampling relationships to surface and turbulent fluxes using large eddy simulations with Lagrangian particles“. Atmospheric Measurement Techniques 15, Nr. 23 (13.12.2022): 7171–94. http://dx.doi.org/10.5194/amt-15-7171-2022.
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Abstract. Source functions for mechanically driven coarse-mode sea spray and dust aerosol particles span orders of magnitude owing to a combination of physical sensitivity in the system and large measurement uncertainty. Outside special idealized settings (such as wind tunnels), aerosol particle fluxes are largely inferred from a host of methods, including local eddy correlation, gradient methods, and dry deposition methods. In all of these methods, it is difficult to relate point measurements from towers, ships, or aircraft to a general representative flux of aerosol particles. This difficulty is from the particles' inhomogeneous distribution due to multiple spatiotemporal scales of an evolving marine environment. We hypothesize that the current representation of a point in situ measurement of sea spray or dust particles is a likely contributor to the unrealistic range of flux and concentration outcomes in the literature. This paper aims to help the interpretation of field data: we conduct a series of high-resolution, cloud-free large eddy simulations (LESs) with Lagrangian particles to better understand the temporal evolution and volumetric variability of coarse- to giant-mode marine aerosol particles and their relationship to turbulent transport. The study begins by describing the Lagrangian LES model framework and simulates flux measurements that were made using numerical analogs to field practices such as the eddy covariance method. Using these methods, turbulent flux sampling is quantified based on key features such as coherent structures within the marine atmospheric boundary layer (MABL) and aerosol particle size. We show that for an unstable atmospheric stability, the MABL exhibits large coherent eddy structures, and as a consequence, the flux measurement outcome becomes strongly tied to spatial length scales and relative sampling of crosswise and streamwise sampling. For example, through the use of ogive curves, a given sampling duration of a fixed numerical sampling instrument is found to capture 80 % of the aerosol flux given a sampling rate of zf/w∗∼ 0.2, whereas a spanwise moving instrument results in a 95 % capture. These coherent structures and other canonical features contribute to the lack of convergence to the true aerosol vertical flux at any height. As expected, sampling all of the flow features results in a statistically robust flux signal. Analysis of a neutral boundary layer configuration results in a lower predictive range due to weak or no vertical roll structures compared to the unstable boundary layer setting. Finally, we take the results of each approach and compare their surface flux variability: a baseline metric used in regional and global aerosol models.
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Chen, Zhi Li, Wen Biao Wang, Li An Hou, Hong Xia Liu und Zhen Jie Ren. „Comparative Study of the Flux of Filamentous Bulking MBR and Non-Bulking MBR“. Advanced Materials Research 368-373 (Oktober 2011): 3809–15. http://dx.doi.org/10.4028/www.scientific.net/amr.368-373.3809.
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Under the same operating mode, the flux of non-bulking MBR（1#） descends much faster than the flux of filamentous bulking MBR（3#）, mainly because the particles adhered to membrane 1# become smaller much more quickly，provided that spherical particles tend to be rushed off into the mixed liquid more easily than filamentous particles. The falling of particles diameter is caused by the decline of flux, which can be interpreted with the formulation for critical diameter and flux as well as Critical Flux Theory.
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Aryal, Rupak, Saravanamuthu Vigneswaran, Jaya Kandasamy, Bivek Baral und Alain Grasmick. „Influence of aeration and permeate flux on deposition of particulates on membrane surface“. Water Supply 10, Nr. 6 (01.12.2010): 979–86. http://dx.doi.org/10.2166/ws.2010.515.
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In microfiltration, a deposit of foulant tends to form on the membrane surface and this usually controls the performance of the filtration process. This paper discusses the influence of physical parameters such as aeration and permeates flux on migration and deposition of above micron particles on the membrane surface. Kaolin clay suspension of particle 3.7–8 μm with mean particle diameter 4.1 μm was used in this study. Equal amount of mass of deposited particles on the membrane surface created different transmembrane pressure (TMP) when operated at different aeration rates and permeate flux showing that there is a composite effect. The particle deposition rate at the beginning at lower flux was almost linear which changed to a sharp logarithamic rise at higher flux. The difference in TMP rise for the same amount of deposit demonstrated the selective nature of particle deposition. The mass of the particle deposition on the membrane surface could be described by two parameters: maximum deposition and time using a simple empirical logarithamic equation y=k/[1+exp(b−at)], where k, a, and b are constant; y is the particulate mass deposit (g/m2) and t is the time. The maximum particle mass deposition growth could be described by the equation dy/dt=1/4ka.
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Flanagan, Robert J., Michael Geever und Colin D. O'Dowd. „Direct Measurements of New-Particle Fluxes in the Coastal Environment“. Environmental Chemistry 2, Nr. 4 (2005): 256. http://dx.doi.org/10.1071/en05069.
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Environmental Context.The formation of new secondary aerosol particles in the natural atmosphere is important in terms of controlling the background aerosol population, which significantly impacts on climate. The coastal zone is perhaps the strongest natural source of new secondary aerosol particles, driven by the release of biogenic vapours, which, after undergoing photochemical reactions, lead to the massive production of nucleation mode aerosols, with concentrations often reaching in excess of 106 cm−3. Quantification of this source strength is important, particularly on a regional scale, in terms of estimating the impact of aerosols on climate. Abstract.Measurements of the flux of new secondary aerosol particles during nucleation events in the coastal environment using an eddy-correlation technique are reported for the first time. Events are divided into two types based on the prevailing wind direction. During tidal-related nucleation events, new-particle upward fluxes are typically of the order of 109–1010 particles m−2 s−1. A close correlation (r2 = 0.86) was found between total particle concentration and total (positive) flux when air masses were not affected by multiple sources. This would suggest that continuous measurements of particle number concentration at Mace Head can be translated into a flux using the resulting parameterization. It is expected that parameterizations obtained from similar data and analysis would be equally feasible at other coastal locations.
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Poff, Kirsten E., Andy O. Leu, John M. Eppley, David M. Karl und Edward F. DeLong. „Microbial dynamics of elevated carbon flux in the open ocean’s abyss“. Proceedings of the National Academy of Sciences 118, Nr. 4 (21.01.2021): e2018269118. http://dx.doi.org/10.1073/pnas.2018269118.
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In the open ocean, elevated carbon flux (ECF) events increase the delivery of particulate carbon from surface waters to the seafloor by severalfold compared to other times of year. Since microbes play central roles in primary production and sinking particle formation, they contribute greatly to carbon export to the deep sea. Few studies, however, have quantitatively linked ECF events with the specific microbial assemblages that drive them. Here, we identify key microbial taxa and functional traits on deep-sea sinking particles that correlate positively with ECF events. Microbes enriched on sinking particles in summer ECF events included symbiotic and free-living diazotrophic cyanobacteria, rhizosolenid diatoms, phototrophic and heterotrophic protists, and photoheterotrophic and copiotrophic bacteria. Particle-attached bacteria reaching the abyss during summer ECF events encoded metabolic pathways reflecting their surface water origins, including oxygenic and aerobic anoxygenic photosynthesis, nitrogen fixation, and proteorhodopsin-based photoheterotrophy. The abundances of some deep-sea bacteria also correlated positively with summer ECF events, suggesting rapid bathypelagic responses to elevated organic matter inputs. Biota enriched on sinking particles during a spring ECF event were distinct from those found in summer, and included rhizaria, copepods, fungi, and different bacterial taxa. At other times over our 3-y study, mid- and deep-water particle colonization, predation, degradation, and repackaging (by deep-sea bacteria, protists, and animals) appeared to shape the biotic composition of particles reaching the abyss. Our analyses reveal key microbial players and biological processes involved in particle formation, rapid export, and consumption, that may influence the ocean’s biological pump and help sustain deep-sea ecosystems.
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Woo, S. H., Min Ku Lee und Chang Kyu Rhee. „Sedimentation Properties of TiO2 Nanoparticles in Organic Solvents“. Solid State Phenomena 119 (Januar 2007): 267–70. http://dx.doi.org/10.4028/www.scientific.net/ssp.119.267.
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In this study, the colloidal stability and sedimentation behavior of crystalline TiO2 particles (∼300nm) in various organic solvents have been investigated by means of a backscattered light flux profile (Turbiscan) and a zeta potential measurement. The backscattered light flux profiles revealed that the TiO2 nanoparticles were readily sedimented in water, methyl alcohol, and ethyl alcohol due to a flocculation-induced particle growth, while a particle coalescence and a sedimentation of the TiO2 nanoparticles were hardly observed in isopropyl alcohol. The measured ζ potentials verified the differences of the colloidal stabilities of the TiO2 particles in the organic solvents, showing a good correlation with the migration velocity.
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Ahlm, L., E. D. Nilsson, R. Krejci, E. M. Mårtensson, M. Vogt und P. Artaxo. „A comparison of dry and wet season aerosol number fluxes over the Amazon rain forest“. Atmospheric Chemistry and Physics 10, Nr. 6 (31.03.2010): 3063–79. http://dx.doi.org/10.5194/acp-10-3063-2010.
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Abstract. Vertical number fluxes of aerosol particles and vertical fluxes of CO2 were measured with the eddy covariance method at the top of a 53 m high tower in the Amazon rain forest as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) experiment. The observed aerosol number fluxes included particles with sizes down to 10 nm in diameter. The measurements were carried out during the wet and dry season in 2008. In this study focus is on the dry season aerosol fluxes, with significant influence from biomass burning, and these are compared with aerosol fluxes measured during the wet season. Net particle deposition fluxes dominated in daytime in both seasons and the deposition flux was considerably larger in the dry season due to the much higher dry season particle concentration. The particle transfer velocity increased linearly with increasing friction velocity in both seasons. The difference in transfer velocity between the two seasons was small, indicating that the seasonal change in aerosol number size distribution is not enough for causing any significant change in deposition velocity. In general, particle transfer velocities in this study are low compared to studies over boreal forests. The reasons are probably the high percentage of accumulation mode particles and the low percentage of nucleation mode particles in the Amazon boundary layer, both in the dry and wet season, and low wind speeds in the tropics compared to the midlatitudes. In the dry season, nocturnal particle fluxes behaved very similar to the nocturnal CO2 fluxes. Throughout the night, the measured particle flux at the top of the tower was close to zero, but early in the morning there was an upward particle flux peak that is not likely a result of entrainment or local pollution. It is possible that these morning upward particle fluxes are associated with emission of primary biogenic particles from the rain forest. Emitted particles may be stored within the canopy during stable conditions at nighttime, similarly to CO2, and being released from the canopy when conditions become more turbulent in the morning.
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Mingotti, Nicola, und Andrew W. Woods. „Multiphase plumes in a stratified ambient“. Journal of Fluid Mechanics 869 (23.04.2019): 292–312. http://dx.doi.org/10.1017/jfm.2019.198.
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We report on experiments of turbulent particle-laden plumes descending through a stratified environment. We show that provided the characteristic plume speed $(B_{0}N)^{1/4}$ exceeds the particle fall speed, where the plume buoyancy flux is $B_{0}$ and the Brunt–Väisälä frequency is $N$, then the plume is arrested by the stratification and initially intrudes at the neutral height associated with a single-phase plume of the same buoyancy flux. If the original fluid phase in the plume has density equal to that of the ambient fluid at the source, then as the particles sediment from the intruding fluid, the fluid finds itself buoyant and rises, ultimately intruding at a height of about $0.58\pm 0.03$ of the original plume height, consistent with new predictions we present based on classical plume theory. We generalise this result, and show that if the buoyancy flux at the source is composed of a fraction $F_{s}$ associated with the buoyancy of the source fluid, and a fraction $1-F_{s}$ from the particles, then following the sedimentation of the particles, the plume fluid intrudes at a height $(0.58+0.22F_{s}\pm 0.03)H_{t}$, where $H_{t}$ is the maximum plume height. This is key for predictions of the environmental impact of any material dissolved in the plume water which may originate from the particle load. We also show that the particles sediment at their fall speed through the fluid below the maximum depth of the plume as a cylindrical column whose area scales as the ratio of the particle flux at the source to the fall speed and concentration of particles in the plume at the maximum depth of the plume before it is arrested by the stratification. We demonstrate that there is negligible vertical transport of fluid in this cylindrical column, but a series of layers of high and low particle concentration develop in the column with a vertical spacing which is given by the ratio of the buoyancy of the particle load and the background buoyancy gradient. Small fluid intrusions develop at the side of the column associated with these layers, as dense parcels of particle-laden fluid convect downwards and then outward once the particles have sedimented from the fluid, with a lateral return flow drawing in ambient fluid. As a result, the pattern of particle-rich and particle-poor layers in the column gradually migrates upwards owing to the convective transport of particles between the particle-rich layers superposed on the background sedimentation. We consider the implications of the results for mixing by bubble plumes, for submarine blowouts of oil and gas and for the fate of plumes of waste particles discharged at the ocean surface during deep-sea mining.
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Clay, R. W., und A. G. K. Smith. „The Extragalactic Flux of Cosmic Rays“. Publications of the Astronomical Society of Australia 13, Nr. 2 (Mai 1996): 121–26. http://dx.doi.org/10.1017/s1323358000020658.
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AbstractThe propagation of extragalactic particles within our Galaxy has been modelled. The flux of such particles is below the observed cosmic ray flux at most energies when their power-law spectrum is extrapolated back from the highest energies. Also, we expect that the propagation of extragalactic particles through static magnetic fields in the Galaxy will not result in a flux change to match the flux of particles measured here within the Galaxy. However, if we were to consider the observed cosmic rays to be of Galactic origin, there would be a remarkable similarity between the required Galactic injection flux and the extrapolated extragalactic flux. We consider here whether the scattering of extragalactic particles in the Galaxy together with an associated energy perturbation might be sufficient for the extragalactic beam to result in the production of ‘Galactic’ particles and, hence, essentially all of the observed cosmic rays. This appears to be possible.
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Kiat, W. Y., K. Yamamoto und S. Ohgaki. „Optimal Fiber Spacing in Externally Pressurized Hollow Fiber Module for Solid Liquid Separation“. Water Science and Technology 26, Nr. 5-6 (01.09.1992): 1245–54. http://dx.doi.org/10.2166/wst.1992.0567.
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Flux decline and clogging mechanism in hollow fiber bundle by activated sludge and kaolin clay suspensions were investigated experimentally. Filtration characteristics of hollow fiber bundles consisting of 10 fiber threads but different in packing density were observed. The main reason for severe flux decline was due to the accumulation of particles at the space in between fibers. The results showed that there was no particle accumulation when fiber packing density β was lower than a critical value βa. Maximum filtration flux and maximum membrane productivity Q/Vr,which is defined as the filtration rate per unit volume of bundle, were obtained below and at this point, respectively. When fiber packing density β was increased, accumulation of particles happened and flux declined rapidly to a minimum, then increased to a maximum and then decreased when surface clogging predominated in the case of activated sludge filtration, but remained almost constant for the case of kaolin clay suspensions. The critical point where accumulation of particles started was related to cross flow velocity. The higher the cross flow velocity, the higher the value of βa obtained.
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Gajjar, P., und J. M. N. T. Gray. „Asymmetric flux models for particle-size segregation in granular avalanches“. Journal of Fluid Mechanics 757 (19.09.2014): 297–329. http://dx.doi.org/10.1017/jfm.2014.503.
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AbstractParticle-size segregation commonly occurs in both wet and dry granular free-surface flows through the combined processes of kinetic sieving and squeeze expulsion. As the granular material is sheared downslope, the particle matrix dilates slightly and small grains tend to percolate down through the gaps, because they are more likely than the large grains to fit into the available space. Larger particles are then levered upwards in order to maintain an almost uniform solids volume fraction through the depth. Recent experimental observations suggest that a single small particle can percolate downwards through a matrix of large particles faster than a large particle can be levered upwards through a matrix of fines. In this paper, this effect is modelled by using a flux function that is asymmetric about its maximum point, differing from the symmetric quadratic form used in recent models of particle-size segregation. For illustration, a cubic flux function is examined in this paper, which can be either a convex or a non-convex function of the small-particle concentration. The method of characteristics is used to derive exact steady-state solutions for non-diffuse segregation in two dimensions, with an inflow concentration that is (i) homogeneous and (ii) normally graded, with small particles above the large. As well as generating shocks and expansion fans, the new asymmetric flux function generates semi-shocks, which have characteristics intersecting with the shock just from one side. In the absence of diffusive remixing, these can significantly enhance the distance over which complete segregation occurs.
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Pu, Z. Y., R. H. W. Friedel, A. Korth, Q. G. Zong, Z. X. Chen, A. Roux und S. Perraut. „Evaluation of energetic particle parameters in the near-Earth magnetotail derived from flux asymmetry observations“. Annales Geophysicae 16, Nr. 3 (31.03.1998): 283–91. http://dx.doi.org/10.1007/s00585-998-0283-7.
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Abstract. The flux asymmetries measured by spectrometers on board spacecraft contain information on particle parameters. The net flux intensity (NFI) method provides a tool to evaluate these parameters. The NFI method is valid when both the spin period of the spacecraft and the time resolution of the particle spectrometers are much shorter than the characteristic time-scale of the particle flux variations. We apply the NFI analysis to the flux asymmetry measurements made by GEOS 2 at the nightside geosynchronous orbit in the late substorm growth phase. The cross-tail current of energetic ions, their pressure gradient and average drift velocity, as well as a field-aligned flows are investigated. Current disruption at substorm onset and the "convection surge" mechanism during dipolarization of the magnetic field are directly observed.Key words. Flux asymmetry · Net flux intensity · GEOS 2 · Energetic particles
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Mikhailov, G. A., und G. Z. Lotova. „NUMERICAL-STATISTICAL INVESTIGATION OF SUPEREXPONENTIAL GROWTH OF THE MEAN PARTICLE FLUX WITH MULTIPLICATION IN A HOMOGENEOUS RANDOM MEDIUM“. Доклады Российской академии наук. Математика, информатика, процессы управления 514, Nr. 1 (01.11.2023): 112–17. http://dx.doi.org/10.31857/s2686954323600210.
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The new correlative-grid approximation of a homogeneous random field is introduced for the effective numerically-analytical investigation of the superexponential growth of the mean particles flux with multiplication in a random medium. A complexity of particle trajectory realization is not dependent on the correlation scale. The test computations for a critical ball with isotropic scattering showed high accuracy of the corresponding mean flux estimates. For the correlative-grid approximation the possibility of Gaussian asymptotics of the mean particles multiplication rate when the correlation scale decreases is justified.
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Fromant, Guillaume, Peter D. Thorne und David Hurther. „An examination of point-particle Lagrangian simulations for assessing time-resolved hydroacoustic particle flux measurements in sediment-laden flows“. Journal of the Acoustical Society of America 155, Nr. 4 (01.04.2024): 2817–35. http://dx.doi.org/10.1121/10.0025766.
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Accurate modelling and prediction of sediment transport in aquatic environments is essential for sustainable coastal and riverine management. Current capabilities rely on physical process-based numerical models and fine-scale sediment flux measurements. High-resolution hydroacoustic instrumentation has emerged as a promising tool for such measurements. However, challenges arise due to the inherent complexity of ultrasound scattering processes. This study introduces a numerical modelling using a point-particle approach to simulate the echoes backscattered by such instrumentation in sediment-laden flow conditions. The model considers geometric, statistical, particle cloud, and flow-induced effects on sediment velocity, concentration, and flux estimates using an acoustic concentration and velocity profiler as a reference. The model performance is assessed here under unidirectional constant flow conditions in terms of velocity, concentration, and time-resolved sediment flux estimates for a large range of the particles' advection speed and sampled volume sizes. Application to the estimation of the measurement accuracy of sediment flux in these flows is also considered, with a final error on the flux seen to be partially controlled by the residence time of particles within the sampled volumes. The proposed model provides insights into scattering processes and offers a tool for investigating robust sediment flux estimation techniques in various flow conditions.
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Adel. „Absolute Flux Comparison of Magnetospheric Particles“. Physics International 3, Nr. 1 (01.01.2012): 1–8. http://dx.doi.org/10.3844/pisp.2012.1.8.
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Schimansky-Geier, Lutz, Maik Kschischo und Thomas Fricke. „Flux of Particles in Sawtooth Media“. Physical Review Letters 79, Nr. 18 (03.11.1997): 3335–38. http://dx.doi.org/10.1103/physrevlett.79.3335.
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Kryvdyk, Volodymyr. „Radiation Bursts from a Presupernova Collapsar“. International Astronomical Union Colloquium 192 (2005): 215–18. http://dx.doi.org/10.1017/s0252921100009210.
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SummaryThe radiation from the magnetic presupernova star is calculated. This radiation will generate when the magnetosphere of presupernova star compresses during collapse and its magnetic field increases considerably. The variable magnetic field will accelerate the charged particle, which generate radiation when moving in the magnetic field. The particles dynamics and their non-thermal emission in the magnetospheres of presupernova collapsing star with initial dipole magnetic fields and a certain initial energy distribution of charged particles in a magnetosphere are considered. The radiation flux depend on the distance to the star, its magnetic field, and the particle spectrum in the magnetosphere. This flux can be observed by means of modern instruments in broad band (from radio waves to gamma rays). The radiation flux grows with decreasing stellar radius and frequency and can be observed in the form of radiation bursts with duration equal to the stellar collapse time.
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Zhang, Yan Jie, Xue Yong Wang und Yan Fang Yang. „Experimental Research of Al2O3 Micro-Particles Production by Supercritical Hydrolysis“. Applied Mechanics and Materials 268-270 (Dezember 2012): 464–67. http://dx.doi.org/10.4028/www.scientific.net/amm.268-270.464.
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Because of the excellent specialties of intensity, rigidity, heat-durability, corrosion proof and wide uses in many fields, Al2O3 has a promising future. Supercritical hydrolysis is a new method to produce Al2O3 micro-particles whose average diameter is 537nm. The resulting samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Particle-size Analyzer. Its product is the high purity α-Al2O3 which is characterized by the features of the small particle size, the well developed dispersion, and the fine concentricity. The influences of process parameters, including pressure, temperature，total flux and ratio of branch flux, on particle size were investigated at the same time. The results indicated that the particle size has a significant increasing trend with an increase in the pressure and temperature; however, it decreased with an increase in the total flux, while it decreased slightly with an increase in the ratio of branch flux.
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Deventer, Malte Julian, Frank Griessbaum und Otto Klemm. „Size-resolved flux measurement of sub-micrometer particles over an urban area“. Meteorologische Zeitschrift 22, Nr. 6 (01.12.2013): 729–37. http://dx.doi.org/10.1127/0941-2948/2013/0441.
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Cisternas-Novoa, Carolina, Frédéric A. C. Le Moigne und Anja Engel. „Composition and vertical flux of particulate organic matter to the oxygen minimum zone of the central Baltic Sea: impact of a sporadic North Sea inflow“. Biogeosciences 16, Nr. 4 (27.02.2019): 927–47. http://dx.doi.org/10.5194/bg-16-927-2019.
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Abstract. Particle sinking is a major form of transport for photosynthetically fixed carbon to below the euphotic zone via the biological carbon pump (BCP). Oxygen (O2) depletion may improve the efficiency of the BCP. However, the mechanisms by which O2 deficiency can enhance particulate organic matter (POM) vertical fluxes are not well understood. Here, we investigate the composition and vertical fluxes of POM in two deep basins of the Baltic Sea (GB: Gotland Basin and LD: Landsort Deep). The two basins showed different O2 regimes resulting from the intrusion of oxygen-rich water from the North Sea that ventilated the water column below 140 m in GB, but not in LD, during the time of sampling. In June 2015, we deployed surface-tethered drifting sediment traps in oxic surface waters (GB: 40 and 60 m; LD: 40 and 55 m), within the oxygen minimum zone (OMZ; GB: 110 m and LD: 110 and 180 m) and at recently oxygenated waters by the North Sea inflow in GB (180 m). The primary objective of this study was to test the hypothesis that the different O2 conditions in the water column of GB and LD affected the composition and vertical flux of sinking particles and caused differences in export efficiency between those two basins. The composition and vertical flux of sinking particles were different in GB and LD. In GB, particulate organic carbon (POC) flux was 18 % lower in the shallowest trap (40 m) than in the deepest sediment trap (at 180 m). Particulate nitrogen (PN) and Coomassie stainable particle (CSP) fluxes decreased with depth, while particulate organic phosphorus (POP), biogenic silicate (BSi), chlorophyll a (Chl a) and transparent exopolymeric particle (TEP) fluxes peaked within the core of the OMZ (110 m); this coincided with the presence of manganese oxide-like (MnOx-like) particles aggregated with organic matter. In LD, vertical fluxes of POC, PN and CSPs decreased by 28 %, 42 % and 56 %, respectively, from the surface to deep waters. POP, BSi and TEP fluxes did not decrease continuously with depth, but they were higher at 110 m. Although we observe a higher vertical flux of POP, BSi and TEPs coinciding with abundant MnOx-like particles at 110 m in both basins, the peak in the vertical flux of POM and MnOx-like particles was much higher in GB than in LD. Sinking particles were remarkably enriched in BSi, indicating that diatoms were preferentially included in sinking aggregates and/or there was an inclusion of lithogenic Si (scavenged into sinking particles) in our analysis. During this study, the POC transfer efficiency (POC flux at 180 m over 40 m) was higher in GB (115 %) than in LD (69 %), suggesting that under anoxic conditions a smaller portion of the POC exported below the euphotic zone was transferred to 180 m than under reoxygenated conditions present in GB. In addition, the vertical fluxes of MnOx-like particles were 2 orders of magnitude higher in GB than LD. Our results suggest that POM aggregates with MnOx-like particles formed after the inflow of oxygen-rich water into GB, and the formation of those MnOx–OM-rich particles may alter the composition and vertical flux of POM, potentially contributing to a higher transfer efficiency of POC in GB. This idea is consistent with observations of fresher and less degraded organic matter in deep waters of GB than LD.
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Carfì, David. „Relativistic Schrödinger equation and probability currents for free particles“. Proceedings of the International Geometry Center 17, Nr. 1 (13.01.2024): 99–131. http://dx.doi.org/10.15673/pigc.v17i1.2597.
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In this work, we start from the problem of quantizing the relativistic Hamiltonian of a free massive particle (rest mass different from 0), a problem exceptionally difficult in the standard approaches to quantum mechanics. In fact, in tempered distribution state space, we find the natural way to define the relativistic Hamiltonian operator and its associated Schrödinger equation The existence of a linear continuous Hermitian operator associated with the Einstein's Hamiltonian of a free particle, defined on the entire tempered distribution space, automatically implies the conservation of Born probability flux (which doesn't mean the conservation of particles number, rather it implies the conservation of the total relativistic energy of the solution wave). We, then, deduce the continuity equation for the Born probability density and study some its different (but equivalent) expressions. We determine some possible forms of probability currents and flux velocity fields associated with the particle evolution. We provide the relativistic invariant expression for both Schrödinger equation and probability flux continuity equations.
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Takahashi, Sbuhei. „Characteristics of Drifting Snow at Mizuho Station, Antarctica“. Annals of Glaciology 6 (1985): 71–75. http://dx.doi.org/10.3189/1985aog6-1-71-75.
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Observations of drifting snow were carried out at Mizuho Station (70°42'S, 44°20'E, 2230 m above sea level), East Antarctica, in 1982. Drift flux was proportional to about the 8th power of wind velocity above 1 m and about the 4th power below 0.1 m, while snow drift transport rate was proportional to about the 5th power. For drift flux at 1 m height, the power had a temperature dependence, decreasing above -20 °C. Visibility was proportional to about the -8th power of wind velocity; this is explained by the power relation between drift flux and wind velocity. The repose angle of drifting snow particles was observed by the inclination of a cone-shaped deposit on a disk; it was more than 80° when snow was falling and less than 80° without precipitation. The fall velocity of drifting snow particles, obtained by time-marked trajectories of particles, was between 0.3 and 0.9 m/s, and depended on wind velocity and snow particle shape.
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Takahashi, Sbuhei. „Characteristics of Drifting Snow at Mizuho Station, Antarctica“. Annals of Glaciology 6 (1985): 71–75. http://dx.doi.org/10.1017/s0260305500010028.
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Observations of drifting snow were carried out at Mizuho Station (70°42'S, 44°20'E, 2230 m above sea level), East Antarctica, in 1982. Drift flux was proportional to about the 8th power of wind velocity above 1mand about the 4th power below 0.1 m, while snow drift transport rate was proportional to about the 5th power. For drift flux at 1 m height, the power had a temperature dependence, decreasing above -20 °C. Visibility was proportional to about the -8th power of wind velocity; this is explained by the power relation between drift flux and wind velocity. The repose angle of drifting snow particles was observed by the inclination of a cone-shaped deposit on a disk; it was more than 80° when snow was falling and less than 80° without precipitation. The fall velocity of drifting snow particles, obtained by time-marked trajectories of particles, was between 0.3 and 0.9 m/s, and depended on wind velocity and snow particle shape.
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Petters, Markus D., Tyas Pujiastuti, Ajmal Rasheeda Satheesh, Sabin Kasparoglu, Bethany Sutherland und Nicholas Meskhidze. „Wind-driven emissions of coarse-mode particles in an urban environment“. Atmospheric Chemistry and Physics 24, Nr. 1 (18.01.2024): 745–62. http://dx.doi.org/10.5194/acp-24-745-2024.
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Abstract. Quantifying surface–atmosphere exchange rates of particles is important for understanding the role of suspended particulate matter in radiative transfer, clouds, precipitation, and climate change. Emissions of coarse-mode particles with a diameter greater than 0.5 µm provide giant cloud condensation nuclei and ice nuclei. These emissions are critical for understanding the evolution of cloud microphysical properties yet remain poorly understood. Here we introduce a new method that uses lidar retrievals of the elastic backscatter and Doppler velocity to obtain surface number emissions of particles with a diameter greater than 0.53 µm. The technique is applied to study particle number fluxes over a 2-month period from 1 June to 10 August 2022 during the TRACER campaign at an urban site near Houston, TX, USA. We found that all the observed fluxes were positive (upwards), indicating particle emission from the surface. The fluxes followed a diurnal pattern and peaked near noon local time. Flux intensity varied through the 2 months with multi-day periods of strong fluxes and multi-day periods of weak fluxes. Emission particle number fluxes peaked near ∼ 100 cm−2 s−1. The daily averaged emission fluxes correlated with friction velocity and were anticorrelated with surface relative humidity. The emission flux can be parameterized as F= 3000 u*4, where u* is the friction velocity in m s−1 and the emission flux F is in cm−2 s−1. The u* dependence is consistent with emission from wind-driven erosion. Estimated values for the mass flux are in the lower range of literature values from non-urban sites. These results demonstrate that urban environments may play an important role in supplying coarse-mode particles to the boundary layer. We anticipate that quantification of these emissions will help constrain aerosol–cloud interaction models that use prognostic aerosol schemes.
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Carey, V. P., E. Markovitz und Y. K. Chuah. „The Effect of Turbulence-Suspended Light Particles on Dryout for Pool Boiling From a Horizontal Surface“. Journal of Heat Transfer 108, Nr. 1 (01.02.1986): 109–16. http://dx.doi.org/10.1115/1.3246874.
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Experimental measurements are reported which indicate the relationship between particle loading and dryout heat flux for pool boiling from a horizontal surface covered with a mixture of water and light particles. This study specifically examines the dryout conditions for particles which have low settling velocities and are easily suspended by the bubble-generated turbulence in the liquid pool above the surface. Dryout data are presented for pool boiling of mixtures of saturated water and glass beads with diameters ranging from 0.105 mm to 0.475 mm. Data are also presented for methanol and glass beads. At high particle loadings, a portion of the load is suspended, while the remainder forms a layer on the surface. The dryout mechanism apparently is similar to the Helmholtz instability mechanism previously identified as the cause of dryout in shallow beds of heavy particles. However, the suspension of particles in the liquid pool produces very unusual trends in the dryout data. In particular, conditions have been observed in which a decrease in the heat flux can cause dryout to occur. An approximate theoretical model of the particle suspension mechanism is proposed and used to predict the dryout conditions for very light particles. This model explains the trends in the data and predicts dryout conditions which compare favorably with the experimental results for very light particles.