Artykuły w czasopismach na temat „Particles”
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Zhang, Shangjia, Zhaohuan Zhu, Takahiro Ueda, Akimasa Kataoka, Anibal Sierra, Carlos Carrasco-González i Enrique Macías. "Porous Dust Particles in Protoplanetary Disks: Application to the HL Tau Disk". Astrophysical Journal 953, nr 1 (1.08.2023): 96. http://dx.doi.org/10.3847/1538-4357/acdb4e.
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Abstract Dust particle sizes constrained from dust continuum and polarization observations by radio interferometry are inconsistent by at least an order of magnitude. Motivated by porous dust observed in small solar system bodies (e.g., from the Rosetta mission), we explore how the dust particle’s porosity affects the estimated particle sizes from these two methods. Porous particles have lower refractive indices, which affect both opacity and polarization fraction. With weaker Mie interference patterns, the porous particles have lower opacity at millimeter wavelengths than the compact particles if the particle size exceeds several hundred microns. Consequently, the inferred dust mass using porous particles can be up to a factor of six higher. The most significant difference between compact and porous particles is their scattering properties. The porous particles have a wider range of particle sizes with high linear polarization from dust self-scattering, allowing millimeter- to centimeter-sized particles to explain polarization observations. With a Bayesian approach, we use porous particles to fit HL Tau disk’s multiwavelength continuum and millimeter-polarization observations from the Atacama Large Millimeter/submillimeter Array (ALMA) and the Very Large Array (VLA). The moderately porous particles with sizes from 1 mm–1 m can explain both continuum and polarization observations, especially in the region between 20 and 60 au. If the particles in HL Tau are porous, the porosity should be from 70%–97% from current polarization observations. We also predict that future observations of the self-scattering linear polarization at longer wavelengths (e.g., ALMA B1 and ngVLA) have the potential to further constrain the particle’s porosity and size.
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Zhao, Zhen Kai, Yan Pei Song i Zhi Ming Feng. "Study on the Migration Law of Unmelted WC Particles during the Process of Centrifugal Casting". Advanced Materials Research 320 (sierpień 2011): 394–98. http://dx.doi.org/10.4028/www.scientific.net/amr.320.394.
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A model of the movement of WC reinforcing particles with the effect of centrifugal force during the process of centrifugal casting was established. The motion equations of the WC particles were solved in this model. The motion curve of the WC particles WC particle was drawn according to the motion equation, and the influential factors of WC particle's movement are analyzed. The conclusions show that: the radical movement speed of the WC particles increases with the increase of time, and the movement distance increases by exponentially at the same time. The particle movement distance at the same time increases due to the larger diameter, the quicker centrifugal speed and the higher the casting temperature. The radial pitch of the particle with different initial position becomes lager with the increase of time. Centrifugal Casting formed the final particle reinforced composites, in which the volume fraction of WC particles gradient increased from the inner surface to the outer surface.
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Li, Xiang, i Ying Lin. "Fluid-Structure Interaction Approach to Single Particle in a Square Microchannel". Journal of Physics: Conference Series 2097, nr 1 (1.11.2021): 012002. http://dx.doi.org/10.1088/1742-6596/2097/1/012002.
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Abstract Inertial microfluidic technique has been widely applied on particle/cell manipulation and detection. To understand the physical principle of this technique more detailed, the interaction of fluid and particle was studied through the Fluid-Structure Interaction (FSI) method. The equilibrium positions of finite-size particles with different diameters were simulated at moderate Reynolds numbers. The flow structure around two typical particles was analysed. The vortex in the front of the particle retards particle’s translation leading to the lag velocity increasing. Finally, the rotation velocity and the rotational-induced force analysed quantitatively to demonstrate that particle’s self-rotation significantly promotes its inertial migration.
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Ohshima, Hiroyuki. "Diffusiophoresis of a Soft Particle as a Model for Biological Cells". Colloids and Interfaces 6, nr 2 (14.04.2022): 24. http://dx.doi.org/10.3390/colloids6020024.
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We derive the general expression for the diffusiophoretic mobility of a soft particle (i.e., polyelectrolyte-coated hard particle) in a concentration gradient of electrolytes for the case in which the particle’s core size is large enough compared with the Debye length. Therefore, the particle surface can be regarded as planar, and the electrolyte concentration gradient is parallel to the core surface. The obtained expression can be applied for arbitrary values of the fixed charge density of the polyelectrolyte layer and the surface charge density of the particle core. We derive approximate analytic mobility expressions for soft particles of three types, i.e., (i) weakly charged soft particles, (ii) soft particles with a thick polyelectrolyte layer, in which the equilibrium electric potential deep inside the polyelectrolyte layer is equal to the Donnan potential, and (iii) soft particles with an uncharged polymer layer of finite thickness.
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DiBenedetto, Michelle H., Nicholas T. Ouellette i Jeffrey R. Koseff. "Transport of anisotropic particles under waves". Journal of Fluid Mechanics 837 (21.12.2017): 320–40. http://dx.doi.org/10.1017/jfm.2017.853.
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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.
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Yu, Chengcheng, i Laijun Zhao. "Multi-Objective Particle Swarm Optimization Algorithm based on Position Vector Offset". International Journal of Mechanical and Electrical Engineering 2, nr 2 (15.04.2024): 131–35. http://dx.doi.org/10.62051/ijmee.v2n2.15.
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In response to the issue that particle swarm optimization algorithms tend to fall into local optima when dealing with multi-objective optimization tasks, a multi-objective optimization algorithm based on particle swarm is proposed. This algorithm is based on the relationship between the position vectors of particles, changing the selection and movement strategies of particles to find the true Pareto front. Firstly, two additional position vectors are added around the iterating particles to enhance their search capability; then, a non-dominated vector archive is established to record the non-dominated solutions of the iterating particles and the additional position vectors, increasing particle diversity. Finally, additional position vectors with high fitness are selected to produce a shift in the iterating particle's position, accelerating particle convergence. Comparing this algorithm with dMOPSO, SMPSO, NMPSO, and MOPSOCD algorithms, simulation experiments show that the proposed PVSPSO algorithm has stronger optimization ability.
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Crutcher, Russ. "Scotch® Magic Tape™ and the Analysis of Settled Dust". Microscope 70, nr 4 (2023): 177–83. http://dx.doi.org/10.59082/akyo4067.
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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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Liu, Yanmin, i Ben Niu. "A Novel PSO Model Based on Simulating Human Social Communication Behavior". Discrete Dynamics in Nature and Society 2012 (2012): 1–21. http://dx.doi.org/10.1155/2012/791373.
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In order to solve the complicated multimodal problems, this paper presents a variant of particle swarm optimizer (PSO) based on the simulation of the human social communication behavior (HSCPSO). In HSCPSO, each particle initially joins a default number of social circles (SC) that consist of some particles, and its learning exemplars include three parts, namely, its own best experience, the experience of the best performing particle in all SCs, and the experiences of the particles of all SCs it is a member of. The learning strategy takes full advantage of the excellent information of each particle to improve the diversity of the swarm to discourage premature convergence. To weight the effects of the particles on the SCs, the worst performing particles will join more SCs to learn from other particles and the best performing particles will leave SCs to reduce their strong influence on other members. Additionally, to insure the effectiveness of solving multimodal problems, the novel parallel hybrid mutation is proposed to improve the particle’s ability to escape from the local optima. Experiments were conducted on a set of classical benchmark functions, and the results demonstrate the good performance of HSCPSO in escaping from the local optima and solving the complex multimodal problems compared with the other PSO variants.
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Yu, Chi, Runhui Geng i Xinwen Wang. "A Numerical Study of Separation Performance of Vibrating Flip-Flow Screens for Cohesive Particles". Minerals 11, nr 6 (14.06.2021): 631. http://dx.doi.org/10.3390/min11060631.
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Vibrating flip-flow screens (VFFS) are widely used to separate high-viscosity and fine materials. The most remarkable characteristic is that the vibration intensity of the screen frame is only 2–3 g (g represents the gravitational acceleration), while the vibration intensity of the screen surface can reach 30–50 g. This effectively solves the problem of the blocking screen aperture in the screening process of moist particles. In this paper, the approximate state of motion of the sieve mat is realized by setting the discrete rigid motion at multiple points on the elastic sieve mat of the VFFS. The effects of surface energy levels between particles separated via screening performance were compared and analyzed. The results show that the flow characteristics of particles have a great influence on the separation performance. For 8 mm particle screening, the particle’s velocity dominates its movement and screening behavior in the range of 0–8 J/m2 surface energy. In the feeding end region (Sections 1 and 2), with the increase in the surface energy, the particle’s velocity decreases, and the contact time between the particles and the screen surface increases, and so the passage increases. When the surface energy level continues to increase, the particles agglomerate together due to the effect of the cohesive force, and the effect of the particle’s agglomeration is greater than the particle velocity. Due to the agglomeration of particles, the difficulty of particles passing through the screen increases, and the yields of various size fractions in the feeding end decrease to some extent. In the transporting process, the agglomerated particles need to travel a certain distance before depolymerization, and the stronger the adhesive force between particles, the larger the depolymerization distance. Therefore, for the case of higher surface energy, the screening percentage near the discharging end (Sections 3 and 4) is greater. The above research is helpful to better understand and optimize the screening process of VFFS.
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Tiwari, Aishwarya. "Calculations of the Average Number of Radicals per Particle in Emulsion Polymerization". International Journal for Research in Applied Science and Engineering Technology 9, nr VI (15.06.2021): 1056–59. http://dx.doi.org/10.22214/ijraset.2021.35189.
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In emulsion polymerization, the free radicals enter the particles intermittently from the aqueous phase. The number of radicals per particleis given by the Smith-Ewart recursion relation which balances the rate of radical entry into, the rate of radical exit from and the rate of radical termination inside the particle. Models for emulsion polymerisation are based on the 0-1 kinetics or the pseudo-bulk kinetics. Small particles, low initiator concentrations and large number of particles favour the 0–1 kinetics, whereas the large particles, high initiator concentrations and small number of particles will favour pseudo-bulk kinetics. A given polymerization system may exhibit both these kinetic behaviours, initially following the 0-1 kinetics and during the later stages of polymerization following the pseudo-bulk kinetics. The aim of this work is to calculate the time dependent values of the average number of radicals per particle in emulsion polymerization for the pseudo-bulk kinetics.
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KANU, REX C., i MONTGOMERY T. SHAW. "STUDIES OF ER FLUIDS FEATURING RODLIKE PARTICLES". International Journal of Modern Physics B 10, nr 23n24 (30.10.1996): 2925–32. http://dx.doi.org/10.1142/s0217979296001379.
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Chaining of micron-sized polarizable particles in ER fluids is generally accepted to be responsible for the liquid-to-solid transitions on the application of an external electric field. It has been hypothesized that the strength of the particle-particle interactions solely determines the rheological properties of ER fluids. In our work, the particle’s structure has been used to control interactions; for example, we have developed systems featuring rodlike particles. With such particles it should be possible to enhance the dielectric interaction of the particles as well as their mechanical interaction. The main goal of our effort has been to distinguish between these two mechanisms through measurements of the dielectric properties in conjunction with the rheological responses. Based on the experimental evidence thus far gathered, we can state that most, but not all, of the rheological effects are explainable in terms of the dielectric changes in the fluid.
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Ali, Usman, Mamoru Kikumoto, Ying Cui, Matteo Ciantia i Marco Previtali. "Micromechanical observation of kinematics of sheared circular discs". E3S Web of Conferences 544 (2024): 05007. http://dx.doi.org/10.1051/e3sconf/202454405007.
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Particle rolling is an essential microscopic mechanism that governs macroscopic behavior. This study conducts biaxial shearing tests on bi-dispersed circular discs at different confining pressures. A novel 2D image analysis technique is employed to measure the rolling of all the particles. It is observed that most of the particles exhibit significant rolling during shearing. Rollings are normally distributed in clockwise and counterclockwise directions, and the net rolling of the granular assembly is almost zero. Generally, the rolling of a particle is accompanied by its neighboring particle’s opposite rolling in a similar magnitude. In some cases, a group of particles is observed to exhibit rolling in the same direction, accompanied by another opposite rolling group in the neighboring regions. Particles inside the shear band tend to show significant rolling. The rolling rate is prominent at the beginning of the shearing and gradually decreases towards the end. Small particles exhibit significantly higher rotations, while larger particles are relatively resistant to rolling. Small particles work as ball bearings between two big particles, reducing the shear strength of the granular materials. The experimental data obtained in this study can be used to perform detailed validation of numerical models to simulate realistic granular behavior such as DEM.
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Nguyen, G. H. Philipp, René Wittmann i Hartmut Löwen. "Active Ornstein–Uhlenbeck model for self-propelled particles with inertia". Journal of Physics: Condensed Matter 34, nr 3 (2.11.2021): 035101. http://dx.doi.org/10.1088/1361-648x/ac2c3f.
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Abstract Self-propelled particles, which convert energy into mechanical motion, exhibit inertia if they have a macroscopic size or move inside a gaseous medium, in contrast to micron-sized overdamped particles immersed in a viscous fluid. Here we study an extension of the active Ornstein–Uhlenbeck model, in which self-propulsion is described by colored noise, to access these inertial effects. We summarize and discuss analytical solutions of the particle’s mean-squared displacement and velocity autocorrelation function for several settings ranging from a free particle to various external influences, like a linear or harmonic potential and coupling to another particle via a harmonic spring. Taking into account the particular role of the initial particle velocity in a nonstationary setup, we observe all dynamical exponents between zero and four. After the typical inertial time, determined by the particle’s mass, the results inherently revert to the behavior of an overdamped particle with the exception of the harmonically confined systems, in which the overall displacement is enhanced by inertia. We further consider an underdamped model for an active particle with a time-dependent mass, which critically affects the displacement in the intermediate time-regime. Most strikingly, for a sufficiently large rate of mass accumulation, the particle’s motion is completely governed by inertial effects as it remains superdiffusive for all times.
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Yi-Fang, Chang. "Final Simplest Model of Smallest Particles and Possibly Developed Directions of Particle Physics". Physical Science & Biophysics Journal 5, nr 2 (2021): 1–12. http://dx.doi.org/10.23880/psbj-16000196.
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First, so far the high energy experiments in the past sixty years have shown that the smallest mass fermions are proton, electron, neutrino and photon, which form the simplest model of particles. These fermions seem to be inseparable truth “atoms” (elements), because further experiments derive particles with bigger mass. They correspond to four interactions, and are also only stable particles. Next, the final simplest theory is based on leptons (e- e ν ) and nucleons (p-n) or (u-d) in quark model with SU(2) symmetry and corresponding Yang-Mills field. Other particles and quark-lepton are their excited states. Their spectrum is mass formula and symmetric lifetime formula. Some applications are discussed. Further, the simplest interactions and unification of weak-strong interactions by QCD are discussed. We research opposite continuous separable models. Finally, we propose some possibly developed directions of particle physics, for example, violation of basic principles, in particular, the uncertainty principle, and precision and systematization of the simplest model, etc.
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Chatain, Mélodie, Raphaël Alvarez, Aurélien Ustache, Emmanuel Rivière, Olivier Favez i Cyril Pallares. "Simultaneous Roadside and Urban Background Measurements of Submicron Aerosol Number Concentration and Size Distribution (in the Range 20–800 nm), along with Chemical Composition in Strasbourg, France". Atmosphere 12, nr 1 (6.01.2021): 71. http://dx.doi.org/10.3390/atmos12010071.
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The adverse health impact of particles and ultrafine particles (UFP) is proven, highlighting the need of measuring the particle number concentration (PNC) dominated by UFP. So far, PNC had never been measured in the Strasbourg urban area (France). The present study on particle size distribution and PNC measurements by an UFP-3031 analyzer was conducted during winter 2019 on a background and a roadside multi-instrumented sites (Black Carbon, chemical speciation, particulate matter 10 μm or less in diameter—PM10 mass). This paper shows significantly higher particle number concentrations of particles below 100 nm at the traffic site compared to the background site. The presence of a road axis thus mainly influences UFP, contrary to larger particles whose levels are more homogeneous over the agglomeration. During the measurement period, the nature of the particles (particle size contribution and chemical composition) was different between periods of high PM10 mass concentrations and periods of high PNC. High PM10 mass concentrations were associated with a high contribution of particles larger than 100 nm but they did not show specific chemical signature. On the other hand, during the periods with high PNC, the chemical composition was modified with an increase of the primary carbonaceous fraction compared to the periods with low PNC, but there was then no clear change in size distribution. Overall, this study illustrates that PM10 mass concentrations were barely representative of UFP and PNC variations, confirming that the monitoring of the latter metrics is necessary to better evaluate the particles toxicity, knowing that this toxicity also depends on the particle’s chemical composition.
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Singh, John P., Sourav Padhy, Eric S. G. Shaqfeh i Donald L. Koch. "Flow of power-law fluids in fixed beds of cylinders or spheres". Journal of Fluid Mechanics 713 (29.10.2012): 491–527. http://dx.doi.org/10.1017/jfm.2012.471.
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AbstractAn ensemble average of the equations of motion for a Newtonian fluid over particle configurations in a dilute fixed bed of spheres or cylinders yields Brinkman’s equations of motion, where the disturbance velocity produced by a test particle is influenced by the Newtonian fluid stress and a body force representing the linear drag on the surrounding particles. We consider a similar analysis for a power-law fluid where the stress $\boldsymbol{\tau} $ is related to the rate of strain $ \mathbisf{e} $ by $\boldsymbol{\tau} = 2m \mathop{ \vert \mathbisf{e} \vert }\nolimits ^{n\ensuremath{-} 1} \mathbisf{e} $, where $m$ and $n$ are constants. In this case, the ensemble-averaged momentum equation includes a body force resulting from the nonlinear drag exerted on the surrounding particles, a power-law stress associated with the disturbance velocity of the test particle, and a stress term that is linear with respect to the test particle’s disturbance velocity. The latter term results from the interaction of the test particle’s velocity disturbance with the random straining motions produced by the neighbouring particles and is important only in shear-thickening fluids where the velocity disturbances of the particles are long-ranged. The solutions to these equations using scaling analyses for dilute beds and numerical simulations using the finite element method are presented. We show that the drag force acting on a particle in a fixed bed can be written as a function of a particle-concentration-dependent length scale at which the fluid velocity disturbance produced by a particle is modified by hydrodynamic interactions with its neighbours. This is also true of the drag on a particle in a periodic array where the length scale is the lattice spacing. The effects of particle interactions on the drag in dilute arrays (periodic or random) of cylinders and spheres in shear-thickening fluids is dramatic, where it arrests the algebraic growth of the disturbance velocity with radial position when $n\geq 1$ for cylinders and $n\geq 2$ for spheres. For concentrated random arrays of particles, we adopt an effective medium theory in which the drag force per unit volume in the medium surrounding a test particle is assumed to be proportional to the local volume fraction of the neighbouring particles, which is derived from the hard-particle packing. The predictions of the averaged equations of motion are validated by comparison with simulations of randomly distributed hydrodynamically interacting cylinders.
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Martynov, S. I., T. V. Pronkina, N. V. Dvoryaninova i T. V. Karyagina. "Dynamics of sedimentation of particle in a viscous fluid in the presence of two flat walls". Zhurnal Srednevolzhskogo Matematicheskogo Obshchestva 20, nr 3 (6.09.2018): 318–26. http://dx.doi.org/10.15507/2079-6900.20.201802.318-326.
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The model problem of sedimentation of a solid spherical particle in a viscous fluid bordering two solid planar surfaces is considered. To find the solution of the hydrodynamic equations in the approximation of small Reynolds numbers with boundary conditions on a particle and on two planes, a procedure developed for numerical simulation of the dynamics of a large number of particles in a viscous fluid with one plane wall is used. The procedure involves usage of fictive particles located symmetrically to real ones with respect to the plane. To solve the problem of the real particle’s sedimentation in the presence of two planes, a system of fictive particles is introduced. An approximate solution was found using four fictive particles. Basing on this solution, numerical results are obtained on dynamics of particle deposition for the cases of planes oriented parallel and perpendicular to each other. In particular, the values of linear and angular velocities of a particle are found, depending on the distance to each plane and on the direction of gravity. In the limiting case, when one of the planes is infinitely far from the particle, we obtain known results on the dynamics of particle sedimentation along and perpendicular to one plane.
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Martynov, Sergey I., Tatyana V. Pronkina, Natalya V. Dvoryaninova i Tatyana V. Karyagina. "Dynamics of sedimentation of particle in a viscous fluid in the presence of two flat walls". Zhurnal Srednevolzhskogo Matematicheskogo Obshchestva 20, nr 3 (6.09.2018): 318–26. http://dx.doi.org/10.15507/2079-6900.20.201803.318-326.
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The model problem of sedimentation of a solid spherical particle in a viscous fluid bordering two solid planar surfaces is considered. To find the solution of the hydrodynamic equations in the approximation of small Reynolds numbers with boundary conditions on a particle and on two planes, a procedure developed for numerical simulation of the dynamics of a large number of particles in a viscous fluid with one plane wall is used. The procedure involves usage of fictive particles located symmetrically to real ones with respect to the plane. To solve the problem of the real particle’s sedimentation in the presence of two planes, a system of fictive particles is introduced. An approximate solution was found using four fictive particles. Basing on this solution, numerical results are obtained on dynamics of particle deposition for the cases of planes oriented parallel and perpendicular to each other. In particular, the values of linear and angular velocities of a particle are found, depending on the distance to each plane and on the direction of gravity. In the limiting case, when one of the planes is infinitely far from the particle, we obtain known results on the dynamics of particle sedimentation along and perpendicular to one plane.
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Ma, Zhen Zhong, Yang Zhang i Bin Bin Wang. "Experimental Research on the Particles Reflux in the Particle Impact Drilling System". Advanced Materials Research 361-363 (październik 2011): 381–85. http://dx.doi.org/10.4028/www.scientific.net/amr.361-363.381.
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Particle Impact Drilling technology (PID) is a new drilling technology, which is designed especially to solve the oil and gas exploration under hard terrane. In PID system, the steel particles were added in the drilling fluid to impact rock. The particles would be recycled and put to use again, thus it is of great significance to adjust proper drilling fluid flow rate for steel particle’s reflux. The flow rate of drilling fluids carrying particles is influenced by the fluid viscosity, the annular gap between drill pipe and wellbore, the particle volume fraction and particle size, etc. This paper mainly studied the influence of the annular gap and the flow rate, while the other factors keep constant. Both experimental method and dimension theory were employed in the research. Furthermore, empirical formula was proposed to describe the mechanism.
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Denjean, C., P. Formenti, B. Picquet-Varrault, Y. Katrib, E. Pangui, P. Zapf i J. F. Doussin. "A new experimental approach to study the hygroscopic and optical properties of aerosols: application to ammonium sulfate particles". Atmospheric Measurement Techniques 7, nr 1 (23.01.2014): 183–97. http://dx.doi.org/10.5194/amt-7-183-2014.
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Abstract. A new methodology for the determination of the changes due to hygroscopic growth with relative humidity of the number size distribution and optical properties of polydispersed aerosols is described. This method uses the simulation chamber CESAM where the hygroscopic properties of polydispersed aerosol particles can be investigated in situ by exposing them to RH ranging from 0 to 100% for approximately 1 h. In situ humidification is used to provide simultaneous information on the RH-dependence of the particle size and the corresponding scattering coefficient (σscat), and that for the entire size distribution. Optical closure studies, based on integrated nephelometer and aethalometer measurements, Mie scattering calculations and measured particle size distributions, can therefore be performed to yield derived parameters such as the complex refractive index (CRI) at λ = 525 nm. The CRI can also be retrieved in the visible spectrum by combining differential mobility analyzer (DMA) and white light aerosol spectrometer (Palas Welas®) measurements. We have applied this methodology to ammonium sulfate particles, which have well known optical and hygroscopic properties. The CRI obtained from the two methods (1.54–1.57) compared favourably to each other and are also in reasonable agreement with the literature values. The particle's growth was compared to values obtained for one selected size of particles (150 nm) with a H-TDMA and the effect of the residence time for particles humidification was investigated. When the humidification was performed in the chamber for a few minutes, a continuous increase of the ammonium sulfate particle's size and σscat was observed from RH values as low as 30% RH. Comparison of the measured and modelled values based on Köhler and Mie theories shows that layers of water are adsorbed on ammonium sulfate particles below the deliquescence point. In contradiction, the particle's growth reported with H-TDMAs showed a prompt deliquescence of ammonium sulfate particles with no continuous growth in size at low RH. These findings highlight the need to allow sufficient time for particle-water vapour equilibrium in investigating the aerosols hygroscopic properties. H-TDMA instruments induce limited residence time for humidification and seem to be insufficient for water adsorption on ammonium sulfate particles.
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YEN, GARY G., i MOAYED DANESHYARI. "DIVERSITY-BASED INFORMATION EXCHANGE AMONG MULTIPLE SWARMS IN PARTICLE SWARM OPTIMIZATION". International Journal of Computational Intelligence and Applications 07, nr 01 (marzec 2008): 57–75. http://dx.doi.org/10.1142/s1469026808002144.
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This paper proposes a method to exchange information among multiple swarms in particle swarm optimization (PSO) to facilitate evolutionary search. The algorithm is developed to solve problems having landscapes with a large number of local optima. Each swarm maintains two sets of particles; one set includes the particles to be shared with other swarms, while the other involves the particles to be replaced by individuals from other swarms. The proposed algorithm also provides a new design to search for neighboring swarms in order to share common interests among the swarm's neighborhood. The particle's movement is according to one variation of PSO with three basic terms, each one to lead the particles toward the best particle in the swarm, in the neighborhood, and in the whole population. Demonstrated through a suite of benchmark test functions, the proposed algorithm shows competitive performance with improved convergence speed.
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Daghooghi, Mohsen, i Iman Borazjani. "A kinematics-based model for the settling of gravity-driven arbitrary-shaped particles on a surface". PLOS ONE 16, nr 2 (9.02.2021): e0243716. http://dx.doi.org/10.1371/journal.pone.0243716.
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A discrete model is proposed for settling of an arbitrary-shaped particle onto a flat surface under the gravitational field. In this method, the particle dynamics is calculated such that (a) the particle does not create an overlap with the wall and (b) reaches a realistic equilibrium state, which are not guaranteed in the conventional discrete element methods that add a repulsive force (torque) based on the amount of overlap between the particle and the wall. Instead, upon the detection of collision, the particle’s kinematics is modified depending on the type of contact, i.e., point, line, and surface types, by assuming the contact point/line as the instantaneous center/line of rotation for calculating the rigid body dynamics. Two different stability conditions are implemented by comparing the location of the projection of the center of mass on the wall along gravity direction against the contact points to identify the equilibrium (stable) state on the wall for particles with multiple contact points. A variety of simulations are presented, including smooth surface particles (ellipsoids), regular particles with sharp edges (cylinders and pyramids) and irregular-shaped particles, to show that the method can provide the analytically-known equilibrium state.
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Bordoloi, Ankur D., i Evan Variano. "Rotational kinematics of large cylindrical particles in turbulence". Journal of Fluid Mechanics 815 (20.02.2017): 199–222. http://dx.doi.org/10.1017/jfm.2017.38.
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The rotational kinematics of inertial cylinders in homogeneous isotropic turbulence is investigated via laboratory experiments. The effects of particle size and shape on rotation statistics are measured for near-neutrally buoyant particles whose sizes are within the inertial subrange of turbulence. To examine the effects of particle size, three right-circular cylinders (aspect ratio $\unicode[STIX]{x1D706}=1$) are considered, with size $d_{eq}=16\unicode[STIX]{x1D702}$, $27\unicode[STIX]{x1D702}$ and $67\unicode[STIX]{x1D702}$. Here, $d_{eq}$ is the diameter of a sphere whose volume is equal to that of the particle and $\unicode[STIX]{x1D702}$ is the Kolmogorov length scale. Results show that the variance of the particle rotation rate follows a $-4/3$ power-law scaling with respect to $d_{eq}$. To examine the effect of particle shape, two cylinders with identical volumes and different aspect ratios ($\unicode[STIX]{x1D706}=1$ and $\unicode[STIX]{x1D706}=4$) are measured. Their motion also scales with $d_{eq}$ regardless of shape. Simultaneous measurements of orientation and rotation for $\unicode[STIX]{x1D706}=4$ particles allows a decomposition of rotation along the primary axes of each particle. This analysis shows that there is no preference for rotation about a particle’s symmetry axis, unlike the preference displayed by sub-Kolmogorov-scale particles in previous studies.
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Guo, Jiachen, Zhirong Zhong, Heng Jiang i Hongfu Zuo. "Identification methods of charged particles based on aero-engine exhaust gas electrostatic sensor array". Science Progress 104, nr 2 (kwiecień 2021): 003685042110236. http://dx.doi.org/10.1177/00368504211023691.
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This paper presents a study of aero-engine exhaust gas electrostatic sensor array to estimate the spatial position, charge amount and velocity of charged particle. Firstly, this study establishes a mathematical model to analyze the inducing characteristics and obtain the spatial sensitivity distribution of sensor array. Then, Tikhonov regularization and compressed sensing are used to estimate the spatial position and charge amount of particle based on the obtained sensitivity distribution; cross-correlation algorithm is used to determine particle’s velocity. An oil calibration test rig is established to verify the proposed methods. Thirteen spatial positions are selected as the test points. The estimation errors of spatial positions and charge amounts are both within 5% when the particles are locating at central area. The errors are higher when the particles are closer to the wall and may exceed 10%. The estimation errors of velocities by using cross-correlation are all within 2%. An air-gun test rig is further established to simulate the high velocity condition and distinguish different kinds of particles such as metal particles and non-metal particles.
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Zimmermann, Ralf, Johannes Passig, Robert Irsig, Hendryk Czech, Patrick Martens, Thomas Adam, Julian Schade i Sven Ehlert. "150 Keynote: A New Aerosol Mass-Spectrometer for Simultaneous Detection of Health-Relevant Polycyclic Aromatic Hydrocarbons, Soot and Inorganic Components from Individual Airborne Particles". Annals of Work Exposures and Health 67, Supplement_1 (1.05.2023): i2—i3. http://dx.doi.org/10.1093/annweh/wxac087.006.
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Abstract Air pollution by fine particles represents a severe environmental health-risk. The particle’s content of toxic compounds, such as polycyclic aromatic hydrocarbons (PAH), elemental carbon/soot or redox-active transition metals (e.g. Fe), is highly relevant for their toxicity. The particulate matter (PM) composition can be determined by chemical analysis of PM-loaded filter samples but no information on the mixing state of toxicants, i.e. the distribution of toxicants within the particle ensemble, is obtainable by this approach. The mixing state, however, is a crucial parameter to assess health effects as the toxicants may either be equally distributed over many particles (internally mixed) or could be highly concentrated within a small particle sub-population (externally mixed). In the latter case, the few particles with a very high concentration of toxicants can induce stronger cellular effects at the lung-deposition site. A new approach is based on single particle mass spectrometry (SPMS) but introduces a novel, tailored laser ionisation process. Aerosol particles are on-line sampled from the air and size-characterized by laser velocimetry. The organic coating of individual particles is desorbed by intense IR-laser pulses and subsequently the relevant toxicants (transition metals, PAH and soot) are ionized and MS-detected particle-by-particle, using a novel combined UV-laser ionization scheme (Schade et al. Anal., Chem. 2019; Passig et al. ACP 2022). The novel SPMS system offers the characterisation of the most relevant PM-toxicants (soot, metals, PAH) on a sized-resolved, single particle-basis and gives insight into their mixing state. First SPMS-ambient air monitoring results for PAH or metals show that, depending on conditions, the toxicants indeed either are concentrated on a very small fraction of the particle-ensemble or are rather uniformly distributed over all particles. Future application concepts of the new SPMS-technology in air monitoring and environmental health research are discussed.
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Riabinkina, Polina A., Ivan A. Bataev, Igor S. Batraev, Alexey A. Ruktuev, Vladimir Yu Ulianitsky, Shigeru Tanaka, Yulia Yu Emurlaeva, Tatiana S. Ogneva i Vladimir A. Bataev. "An Experimental and Numerical Simulation Study of Single Particle Impact during Detonation Spraying". Metals 12, nr 6 (15.06.2022): 1013. http://dx.doi.org/10.3390/met12061013.
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A comparison of the numerical simulation and an experimental study of the collision of the particles and the substrate during detonation spraying is presented. The spraying regimes were chosen to provide unmelted, partially melted, and completely molten particles. The numerical simulation was performed using the smoothed particle hydrodynamics (SPH) method with velocity and temperature settings as initial conditions. Good agreement was obtained between the simulation results and the experimental data, making the SPH simulation suitable for analysis of the deformation of particles and the substrate during detonation spraying. Information about the particle’s shape evolution during the collision is presented. An increase in temperature and plastic strain is analyzed at different points of the particle and substrate. Under certain spraying regimes, it is possible to melt a solid particle due to its high-strain-rate deformation, but no melting of the substrate was observed during the simulation.
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Lin, Jian-Hung, i Keh-Chin Chang. "A Modeling Study on Particle Dispersion in Wall-Bounded Turbulent Flows". Advances in Applied Mathematics and Mechanics 6, nr 06 (grudzień 2014): 764–82. http://dx.doi.org/10.4208/aamm.2014.m533.
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AbstractThree physical mechanisms which may affect dispersion of particle’s motion in wall-bounded turbulent flows, including the effects of turbulence, wall roughness in particle-wall collisions, and inter-particle collisions, are numerically investigated in this study. Parametric studies with different wall roughness extents and with different mass loading ratios of particles are performed in fully developed channel flows with the Eulerian-Lagrangian approach. A low-Reynolds-numberk–εturbulence model is applied for the solution of the carrier-flow field, while the deterministic Lagrangian method together with binary-collision hard-sphere model is applied for the solution of particle motion. It is shown that the mechanism of inter-particle collisions should be taken into account in the modeling except for the flows laden with sufficiently low mass loading ratios of particles. Influences of wall roughness on particle dispersion due to particle-wall collisions are found to be considerable in the bounded particle–laden flow. Since the investigated particles are associated with large Stokes numbers, i.e., larger thanO(1), in the test problem, the effects of turbulence on particle dispersion are much less considerable, as expected, in comparison with another two physical mechanisms investigated in the study.
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Lv, Xiaofang, Bohui Shi, Shidong Zhou, Shuli Wang, Weiqiu Huang i Xianhang Sun. "Study on the Decomposition Mechanism of Natural Gas Hydrate Particles and Its Microscopic Agglomeration Characteristics". Applied Sciences 8, nr 12 (3.12.2018): 2464. http://dx.doi.org/10.3390/app8122464.
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Research on hydrate dissociation mechanisms is critical to solving the issue of hydrate blockage and developing hydrate slurry transportation technology. Thus, in this paper, natural gas hydrate slurry decomposition experiments were investigated on a high-pressure hydrate experimental loop, which was equipped with two on-line particle analyzers: focused beam reflectance measurement (FBRM) and particle video microscope (PVM). First, it was observed from the PVM that different hydrate particles did not dissociate at the same time in the system, which indicated that the probability of hydrate particle dissociation depended on the particle’s shape and size. Meanwhile, data from FBRM presented a periodic oscillating trend of the particle/droplet numbers and chord length during the hydrate slurry dissociation, which further demonstrated these micro hydrate particles/droplets were in a dynamic coupling process of breakage and agglomeration under the action of flow shear during the hydrate slurry dissociation. Then, the influences of flow rate, pressure, water-cut, and additive dosage on the particles chord length distribution during the hydrate decomposition were summarized. Moreover, two kinds of particle chord length treatment methods (the average un-weighted and squared-weighted) were utilized to analyze these data onto hydrate particles’ chord length distribution. Finally, based on the above experimental data analysis, some important conclusions were obtained. The agglomeration of particles/droplets was easier under low flow rate during hydrate slurry dissociation, while high flow rate could restrain agglomeration effectively. The particle/droplet agglomerating trend and plug probability went up with the water-cut in the process of hydrate slurry decomposition. In addition, anti-agglomerates (AA) greatly prohibited those micro-particles/droplets from agglomeration during decomposition, resulting in relatively stable mean and square weighting chord length curves.
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Koleda, Pavol, Peter Koleda, Mária Hrčková, Martin Júda i Áron Hortobágyi. "Experimental Granulometric Characterization of Wood Particles from CNC Machining of Chipboard". Applied Sciences 13, nr 9 (28.04.2023): 5484. http://dx.doi.org/10.3390/app13095484.
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The aim of this paper is to determine the particle size composition of the wood particles obtained from CNC milling the chipboard using an experimental optical granulometric method. Composite materials (chipboard) are the most-used materials in the woodworking and furniture industries. The proposed optical method of measuring particles’ dimensions is compared to the sieving technique. The researched experimental method allows for the determination of not only the size of the fraction of an individual particle’s fraction but also more detailed information about the analyzed wood dust emission, for example, the largest and smallest dimension of each single particle; its circularity, area, perimeter, eccentricity, and convex hull major and minor axis length; or the color of the particle.
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Yu-Sandstrom, Yansha. "Differentiating Commonality Particles from Individuality Particles". British Journal of Multidisciplinary and Advanced Studies 5, nr 2 (30.03.2024): 1–12. http://dx.doi.org/10.37745/bjmas.2022.0457.
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The Same Completely Inclusive Faith with Its Principium of Natural Laws of the Compounding-Corresponding-Trinity Presents and Unfolds Through Different Ways and Methods in Science, Philosophy, Religion, etc.” (Abbreviated as Principium. clarify that: The particles not only have the distinction between Commonality Particles and Individuality Particle; any particle compounding and corresponding, also have four major natural standpoint- attributes. Among them, “The Commonality Particle” consistently demonstrate higher stability than “The Individuality Particle” through compounding and corresponding. Similarly, the destruction of “The Commonality Particles” would cause greater harm to humans and nature, potentially even leading to human destruction. Only by adhering to “The Three Great Natural Complementary Laws” of Principium, can humans expand their lives and human society with clarity of mind, saving time and effort while ensuring safe operations
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Thiede, Tobias, Tatiana Mishurova, Sergei Evsevleev, Itziar Serrano-Munoz, Christian Gollwitzer i Giovanni Bruno. "3D Shape Analysis of Powder for Laser Beam Melting by Synchrotron X-ray CT". Quantum Beam Science 3, nr 1 (19.02.2019): 3. http://dx.doi.org/10.3390/qubs3010003.
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The quality of components made by laser beam melting (LBM) additive manufacturing is naturally influenced by the quality of the powder bed. A packing density <1 and porosity inside the powder particles lead to intrinsic voids in the powder bed. Since the packing density is determined by the particle size and shape distribution, the determination of these properties is of significant interest to assess the printing process. In this work, the size and shape distribution, the amount of the particle’s intrinsic porosity, as well as the packing density of micrometric powder used for LBM, have been investigated by means of synchrotron X-ray computed tomography (CT). Two different powder batches were investigated: Ti–6Al–4V produced by plasma atomization and stainless steel 316L produced by gas atomization. Plasma atomization particles were observed to be more spherical in terms of the mean anisotropy compared to particles produced by gas atomization. The two kinds of particles were comparable in size according to the equivalent diameter. The packing density was lower (i.e., the powder bed contained more voids in between particles) for the Ti–6Al–4V particles. The comparison of the tomographic results with laser diffraction, as another particle size measurement technique, proved to be in agreement.
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Liu, Hong, Haijun Wei, Lidui Wei, Jingming Li i Zhiyuan Yang. "The Segmentation of Wear Particles Images UsingJ-Segmentation Algorithm". Advances in Tribology 2016 (2016): 1–10. http://dx.doi.org/10.1155/2016/4931502.
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This study aims to use a JSEG algorithm to segment the wear particle’s image. Wear particles provide detailed information about the wear processes taking place between mechanical components. Autosegmentation of their images is key to intelligent classification system. This study examined whether this algorithm can be used in particles’ image segmentation. Different scales have been tested. Compared with traditional thresholding along with edge detector, the JSEG algorithm showed promising result. It offers a relatively higher accuracy and can be used on color image instead of gray image with little computing complexity. A conclusion can be drawn that the JSEG method is suited for imaged wear particle segmentation and can be put into practical use in wear particle’s identification system.
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Coulson, S. G. "On the deceleration of cometary fragments in aerogel". International Journal of Astrobiology 8, nr 1 (22.12.2008): 9–17. http://dx.doi.org/10.1017/s147355040800431x.
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AbstractDetermining the thermal history of the cometary grains captured by the Stardust mission presents a difficult problem. We consider two simplified models for the deceleration of hypervelocity particles captured in aerogel; both models assume a velocity squared drag force. The first model assumes that the mass of the particle remains constant during capture and the second that mass is lost due to ablation of the particle through interactions with the aerogel. It is found that the constant mass model adequately reproduces the track lengths, found from experiments by Hörz et al. in 2008, that impacted aluminium oxide spheres into aerogel at hypervelocities ~6 km s−1.Deceleration in aerogel heats volatile particles such as organic ices to high temperatures greater than 1,000 K, for durations of ~1 μs: more than sufficient to completely ablate the particle. Refractory particles also experience significant heating greater than 2500 K, greater than the particle's melting point, over similar timescales. This suggests that the fragments recovered to Earth by the Stardust mission were considerably altered by hypersonic capture by aerogel, and so limits the amount of information that can be obtained regarding the formation of mineral and organic particles within Kuiper Belt comets.
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Stetsenko, V. Yu. "About elementary particles". Litiyo i Metallurgiya (FOUNDRY PRODUCTION AND METALLURGY), nr 4 (15.12.2023): 127–30. http://dx.doi.org/10.21122/1683-6065-2023-4-127-130.
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It is shown that only stable particles can be elementary particles. The fundamental elementary particles are positive, negative and neutral particles of space. Photons and neutrinos are formed from them, which are elementary particles of electrons, positrons and protons. A neutral photon consists of a positive elementary particle of space, around which a negative elementary particle of space rotates. A neutrino consists of a negative elementary particle of space, around which a positive elementary particle of space rotates. An electron has a structure consisting of negative and neutral photons connected by negative elementary particles of space. The positron has a structure consisting of positive and neutral photons connected by negative elementary particles of space. A proton consists of a positively charged nucleus around which electrons rotate. The proton nucleus consists of positrons bound by neutrino particles. Atomic nuclei consist of positive and neutral protons connected by the exchange of electrons and neutrino particles. The carriers of electromagnetic interaction are positive and negative elementary particles of space. The carriers of the gravitational interaction are neutral elementary particles of space. Electromagnetic, gravitational and inertial forces are the forces of space. Space is an equilibrium system, just like the whole universe.
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Itoh, Yoshiaki, Colin Mallows i Larry Shepp. "Explicit sufficient invariants for an interacting particle system". Journal of Applied Probability 35, nr 3 (wrzesień 1998): 633–41. http://dx.doi.org/10.1239/jap/1032265211.
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We introduce a new class of interacting particle systems on a graph G. Suppose initially there are Ni(0) particles at each vertex i of G, and that the particles interact to form a Markov chain: at each instant two particles are chosen at random, and if these are at adjacent vertices of G, one particle jumps to the other particle's vertex, each with probability 1/2. The process N enters a death state after a finite time when all the particles are in some independent subset of the vertices of G, i.e. a set of vertices with no edges between any two of them. The problem is to find the distribution of the death state, ηi = Ni(∞), as a function of Ni(0).We are able to obtain, for some special graphs, the limiting distribution of Ni if the total number of particles N → ∞ in such a way that the fraction, Ni(0)/S = ξi, at each vertex is held fixed as N → ∞. In particular we can obtain the limit law for the graph S2, the two-leaf star which has three vertices and two edges.
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Itoh, Yoshiaki, Colin Mallows i Larry Shepp. "Explicit sufficient invariants for an interacting particle system". Journal of Applied Probability 35, nr 03 (wrzesień 1998): 633–41. http://dx.doi.org/10.1017/s0021900200016284.
Pełny tekst źródłaStreszczenie:
We introduce a new class of interacting particle systems on a graph G. Suppose initially there are N i (0) particles at each vertex i of G, and that the particles interact to form a Markov chain: at each instant two particles are chosen at random, and if these are at adjacent vertices of G, one particle jumps to the other particle's vertex, each with probability 1/2. The process N enters a death state after a finite time when all the particles are in some independent subset of the vertices of G, i.e. a set of vertices with no edges between any two of them. The problem is to find the distribution of the death state, η i = N i (∞), as a function of N i (0). We are able to obtain, for some special graphs, the limiting distribution of N i if the total number of particles N → ∞ in such a way that the fraction, N i (0)/S = ξ i , at each vertex is held fixed as N → ∞. In particular we can obtain the limit law for the graph S 2, the two-leaf star which has three vertices and two edges.
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GAVZE, EHUD, i MICHAEL SHAPIRO. "Motion of inertial spheroidal particles in a shear flow near a solid wall with special application to aerosol transport in microgravity". Journal of Fluid Mechanics 371 (25.09.1998): 59–79. http://dx.doi.org/10.1017/s0022112098002109.
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Trajectories of inertial spheroidal particles moving in a shear flow near a solid wall are calculated numerically from the Stokes flow equations by computing the hydrodynamic forces and torques acting on the particles. Near the wall these interactions cause coupling between the particle's rotational and translational motions. Due to this coupling an inertial spheroid is shown to move along an oscillatory trajectory, while simultaneously drifting towards the wall. This phenomenon occurs in the absence of gravity as a combined effect of three factors: particle non-spherical shape, its inertia and particle–wall hydrodynamic interactions. This drift is absent for inertialess spheroids, and also for inertial spherical particles which move along flow streamlines.The drift velocity is calculated for various particle aspect ratios γ and relaxation times τ. An approximate solution, valid for small particle inertia is developed, which allows the contribution of various terms to the drift velocity to be elucidated. It was found that the maximum value of the drift velocity prevails for N(γ)γ2τs∼4, where s is the shear rate and N(γ) is a decreasing function of γ, related to the particle–wall hydrodynamic interactions. In the limiting cases of large and small inertia and also of very long and thin spheroids, the drift vanishes.Possible applications of the results are discussed in the context of transport of micrometre particles in microgravity conditions. It is shown that the model used is applicable for analysis of the deposition of aerosol particles with sizes above 10 μm inhaled in the human respiratory tract in the absence of gravity.
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Xiao, Qin, i Pratomo Widodo. "CONTRASTIVE ANALYSIS OF PARTICLES IN CHINESE AND INDONESIAN LANGUAGE". LITERA 18, nr 3 (19.11.2019): 361–78. http://dx.doi.org/10.21831/ltr.v18i3.24223.
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In Chinese and Indonesian, particles are often used and occupying an important place specifically in daily conversation. The study distinguishes ways of using particles in order to propose suggestions that can be useful for Chinese learners in Indonesia. In this article, the author describe the four pairs of particles to compare the similarities and differences in terms of syntax, semantics, pragmatics and analyzing the types and reasons in particle’s using error for Indonesian learners based on corpus HSK. Where the data sources are the examples of a sentence containing particles, the technique of data collection is the technique of reading and taking notes, and the instrument is a human instrument. The authors found that the four pairs of particles have similarities and differences in syntax, semantics and pragmatics: all of them can be used at the end and middle of the sentence, but not all can be used with other particles; all the pairs can translate to one another and can also be translated into other particles or adverbs, but there are some particles sometimes don’t need to be translated; in different contexts, the four pairs of modal particles have different pragmatic functions. Keywords: particle, Chinese, Indonesian, contrastive analysis
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Zid, Maha, Kaushik Pal, Saša Harkai, Andreja Abina, Samo Kralj i Aleksander Zidanšek. "Qualitatively and Quantitatively Different Configurations of Nematic–Nanoparticle Mixtures". Nanomaterials 14, nr 5 (27.02.2024): 436. http://dx.doi.org/10.3390/nano14050436.
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We consider the influence of different nanoparticles or micrometre-scale colloidal objects, which we commonly refer to as particles, on liquid crystalline (LC) orientational order in essentially spatially homogeneous particle–LC mixtures. We first illustrate the effects of coupling a single particle with the surrounding nematic molecular field. A particle could either act as a “dilution”, i.e., weakly distorting local effective orientational field, or as a source of strong distortions. In the strong anchoring limit, particles could effectively act as topological point defects, whose topological charge q depends on particle topology. The most common particles exhibit spherical topology and consequently act as q = 1 monopoles. Depending on the particle’s geometry, these effective monopoles could locally induce either point-like or line-like defects in the surrounding LC host so that the total topological charge of the system equals zero. The resulting system’s configuration is topologically equivalent to a crystal-like array of monopole defects with alternating topological charges. Such configurations could be trapped in metastable or stable configurations, where the history of the sample determines a configuration selection.
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Liu, Yun, Zhe Liu i Ziyi Liu. "New Progress in the Study of Quark Mass Unlock the Secrets of Strong Force". Advances in Engineering Technology Research 4, nr 1 (20.03.2023): 132. http://dx.doi.org/10.56028/aetr.4.1.132.2023.
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The unification of the four forces is the ultimate goal of physics. At present, humans have not really unified the power and the strong force, and the source of the strong force remains a mystery. In 2018, Liu Yun proposed a new formula to accurately calculate the static mass of particles. Later, Liu Ziyi assumed that the particle was composed of three charges with integer 1, and believed that the particle's high rate spin produced the strong force. According to Coulomb's law and relativity, he deduced the formula for the strong force coefficient between particles and Λc(2287), and found that the strong force decreases with the increase of the distance and finally tends to a constant. By substituting the force value into Liu Yun's static mass formula, the mass spectrum obtained is in good agreement with that of J/ψ particles. After they have the same method, found that positive and negative Λb(5500) accidentally Υ particle particle mass spectra and the experimental mass spectrum highly accord with more, more surprisingly, almost coincide with triplet experimental data. These highly consistent simulations show that the strong force comes from the rapid rotation of the charges inside the particles, and strongly suggest that the so-called quarks are ordinary particles that already exist, making the catalytic development of nuclear energy possible.
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Wells, Craig C., Dmitriy V. Melnikov i Maria E. Gracheva. "Brownian dynamics of cylindrical capsule-like particles in a nanopore in an electrically biased solid-state membrane". Physical Chemistry Chemical Physics 24, nr 5 (2022): 2958–65. http://dx.doi.org/10.1039/d1cp03965b.
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Charged particles traversing an electrically biased nanopore tend to rotate the least where a larger net charge or particle length results in a smaller range of rotational movement and strongly affects the particle's translocation time.
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Hirosawa, Fumie, Tomohiro Iwasaki i Masashi Iwata. "Particle Impact Energy Variation with the Size and Number of Particles in a Planetary Ball Mill". MATEC Web of Conferences 333 (2021): 02016. http://dx.doi.org/10.1051/matecconf/202133302016.
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To investigate the mechanical energy applying to the particles in a grinding process using a planetary ball mill, the impact energy of particles was estimated by simulating the behavior of the particles and grinding balls using the discrete element method (DEM) under different conditions of the size and number of particles, corresponding to their variations during milling. As the impact energy contributing to the particle breakage, we focused on the particle impact energy generated at particle-to-grinding ball/wall and particle-to-particle collisions. The particle size and the number of particles affected the level of particle impact energy at a single collision and the number of collisions of particles, respectively, resulting in an increase of the total impact energy of particles with decreasing particle size and increasing number of particles. The result suggests that milling conditions such as the size of grinding balls should be adjusted appropriately based on the variation of the size and number of particles so that the particles can receive large amounts of the impact energy during milling.
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Hirosawa, Fumie, Tomohiro Iwasaki i Masashi Iwata. "Particle Impact Energy Variation with the Size and Number of Particles in a Planetary Ball Mill". MATEC Web of Conferences 333 (2021): 02016. http://dx.doi.org/10.1051/matecconf/202133302016.
Pełny tekst źródłaStreszczenie:
To investigate the mechanical energy applying to the particles in a grinding process using a planetary ball mill, the impact energy of particles was estimated by simulating the behavior of the particles and grinding balls using the discrete element method (DEM) under different conditions of the size and number of particles, corresponding to their variations during milling. As the impact energy contributing to the particle breakage, we focused on the particle impact energy generated at particle-to-grinding ball/wall and particle-to-particle collisions. The particle size and the number of particles affected the level of particle impact energy at a single collision and the number of collisions of particles, respectively, resulting in an increase of the total impact energy of particles with decreasing particle size and increasing number of particles. The result suggests that milling conditions such as the size of grinding balls should be adjusted appropriately based on the variation of the size and number of particles so that the particles can receive large amounts of the impact energy during milling.
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Poletaev, Gennady, Yuri Gafner, Svetlana Gafner, Yuriy Bebikhov i Alexander Semenov. "Molecular Dynamics Study of the Devitrification of Amorphous Copper Nanoparticles in Vacuum and in a Silver Shell". Metals 13, nr 10 (28.09.2023): 1664. http://dx.doi.org/10.3390/met13101664.
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The process of the devitrification of copper nanoparticles in vacuum and in a silver shell during heating was studied using a molecular dynamics simulation. The results show that there is an inverse relationship between the particle diameter and devitrification temperature. As the size of the particles decreases, the temperature at which devitrification occurs increases due to a higher fraction of atoms near the interface. The presence of a silver shell leads to a significant increase in the devitrification temperature of the copper nanoparticles. For the considered particle sizes, the difference between the devitrification temperatures without a shell and with a shell ranged from 130 K for copper particles with a diameter of 11 nm to 250 K for 3 nm particles. The mechanisms of the nucleation of a crystalline phase in particles in vacuum and in a silver shell are significantly different. In the first case, crystalline nuclei are predominantly formed near the surface, while in the second case, on the contrary, they are formed within the particle’s volume.
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Liu, H. J., C. S. Zhao, B. Nekat, N. Ma, A. Wiedensohler, D. van Pinxteren, G. Spindler, K. Müller i H. Herrmann. "Aerosol hygroscopicity derived from size-segregated chemical composition and its parameterization in the North China Plain". Atmospheric Chemistry and Physics 14, nr 5 (12.03.2014): 2525–39. http://dx.doi.org/10.5194/acp-14-2525-2014.
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Abstract. Hygroscopic growth of aerosol particles is of significant importance in quantifying the aerosol radiative effect in the atmosphere. In this study, hygroscopic properties of ambient particles are investigated based on particle chemical composition at a suburban site in the North China Plain during the HaChi campaign (Haze in China) in summer 2009. The size-segregated aerosol particulate mass concentration as well as the particle components such as inorganic ions, organic carbon and water-soluble organic carbon (WSOC) are identified from aerosol particle samples collected with a ten-stage impactor. An iterative algorithm is developed to evaluate the hygroscopicity parameter κ from the measured chemical composition of particles. During the HaChi summer campaign, almost half of the mass concentration of particles between 150 nm and 1 μm is contributed by inorganic species. Organic matter (OM) is abundant in ultrafine particles, and 77% of the particulate mass with diameter (Dp) of around 30 nm is composed of OM. A large fraction of coarse particle mass is undetermined and is assumed to be insoluble mineral dust and liquid water. The campaign's average size distribution of κ values shows three distinct modes: a less hygroscopic mode (Dp < 150 nm) with κ slightly above 0.2, a highly hygroscopic mode (150 nm < Dp < 1 μm) with κ greater than 0.3 and a nearly hydrophobic mode (Dp > 1 μm) with κ of about 0.1. The peak of the κ curve appears around 450 nm with a maximum value of 0.35. The derived κ values are consistent with results measured with a high humidity tandem differential mobility analyzer within the size range of 50–250 nm. Inorganics are the predominant species contributing to particle hygroscopicity, especially for particles between 150 nm and 1 μm. For example, NH4NO3, H2SO4, NH4HSO4 and (NH4)2SO4 account for nearly 90% of κ for particles of around 900 nm. For ultrafine particles, WSOC plays a critical role in particle hygroscopicity due to the predominant mass fraction of OM in ultrafine particles. WSOC for particles of around 30 nm contribute 52% of κ. Aerosol hygroscopicity is related to synoptic transport patterns. When southerly wind dominates, particles are more hygroscopic; when northerly wind dominates, particles are less hygroscopic. Aerosol hygroscopicity also has a diurnal variation, which can be explained by the diurnal evolution of planetary boundary layer, photochemical aging processes during daytime and enhanced black carbon emission at night. κ is highly correlated with mass fractions of SO42−, NO3− and NH4+ for all sampled particles as well as with the mass fraction of WSOC for particles of less than 100 nm. A parameterization scheme for κ is developed using mass fractions of SO42−, NO3−, NH4+ and WSOC due to their high correlations with κ, and κ calculated from the parameterization agrees well with κ derived from the particle's chemical composition. Further analysis shows that the parameterization scheme is applicable to other aerosol studies in China.
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Schäfer, Frank, Miguel A. Bastarrachea-Magnani, Axel U. J. Lode, Laurent de Forges de Parny i Andreas Buchleitner. "Spectral Structure and Many-Body Dynamics of Ultracold Bosons in a Double-Well". Entropy 22, nr 4 (26.03.2020): 382. http://dx.doi.org/10.3390/e22040382.
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We examine the spectral structure and many-body dynamics of two and three repulsively interacting bosons trapped in a one-dimensional double-well, for variable barrier height, inter-particle interaction strength, and initial conditions. By exact diagonalization of the many-particle Hamiltonian, we specifically explore the dynamical behavior of the particles launched either at the single-particle ground state or saddle-point energy, in a time-independent potential. We complement these results by a characterization of the cross-over from diabatic to quasi-adiabatic evolution under finite-time switching of the potential barrier, via the associated time evolution of a single particle’s von Neumann entropy. This is achieved with the help of the multiconfigurational time-dependent Hartree method for indistinguishable particles (MCTDH-X)—which also allows us to extrapolate our results for increasing particle numbers.
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Dezhkam, Rasool, Hoseyn A. Amiri, David J. Collins i Morteza Miansari. "Continuous Submicron Particle Separation via Vortex-Enhanced Ionic Concentration Polarization: A Numerical Investigation". Micromachines 13, nr 12 (12.12.2022): 2203. http://dx.doi.org/10.3390/mi13122203.
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Separation and isolation of suspended submicron particles is fundamental to a wide range of applications, including desalination, chemical processing, and medical diagnostics. Ion concentration polarization (ICP), an electrokinetic phenomenon in micro-nano interfaces, has gained attention due to its unique ability to manipulate molecules or particles in suspension and solution. Less well understood, though, is the ability of this phenomenon to generate circulatory fluid flow, and how this enables and enhances continuous particle capture. Here, we perform a comprehensive study of a low-voltage ICP, demonstrating a new electrokinetic method for extracting submicron particles via flow-enhanced particle redirection. To do so, a 2D-FEM model solves the Poisson–Nernst–Planck equation coupled with the Navier–Stokes and continuity equations. Four distinct operational modes (Allowed, Blocked, Captured, and Dodged) were recognized as a function of the particle’s charges and sizes, resulting in the capture or release from ICP-induced vortices, with the critical particle dimensions determined by appropriately tuning inlet flow rates (200–800 [µm/s]) and applied voltages (0–2.5 [V]). It is found that vortices are generated above a non-dimensional ICP-induced velocity of , which represents an equilibrium between ICP velocity and lateral flow velocity. It was also found that in the case of multi-target separation, the surface charge of the particle, rather than a particle’s size, is the primary determinant of particle trajectory. These findings contribute to a better understanding of ICP-based particle separation and isolation, as well as laying the foundations for the rational design and optimization of ICP-based sorting systems.
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Barbosa, Marcos V., Fernando C. De Lai i Silvio L. M. Junqueira. "Numerical Evaluation of CFD-DEM Coupling Applied to Lost Circulation Control: Effects of Particle and Flow Inertia". Mathematical Problems in Engineering 2019 (20.10.2019): 1–13. http://dx.doi.org/10.1155/2019/6742371.
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In the present study, the transport and deposition of solid particles to mitigate the loss circulation of fluid through a fracture transversely placed to a vertical channel is numerically investigated. These solid particles (commonly known in the industry as lost circulation materials—LCMs) are injected into the flow during the drilling operation in the petroleum industry, in hopes to control the fluid loss. The numerical simulation of the process follows a two-stage process: the first characterizes the lost circulation flow and the second the particle injection. The numerical model comprises an Eulerian–Lagrangian approach, in which the dense discrete phase model (DDPM) is combined with the discrete element method (DEM). A parametric analysis is done by varying the vertical channel Reynolds number, the particle-to-fluid density ratio, and the particle diameter. Results are shown in terms of the particle’s bed geometric characteristics, focusing on the location inside the fracture where the particles deposit, and the particle bed length, height, and time spent to fill the fracture. Also monitored are the fluid loss reduction over time and the fractured channel bottom pressure (which can be related to the fracture pressure). Results indicate that using a slow/intermediate flow velocity, associated with heavy particles with small diameters, provides the best combination for the efficient mitigation of the fluid loss process.
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PAN, LIUBIN, i PAOLO PADOAN. "Relative velocity of inertial particles in turbulent flows". Journal of Fluid Mechanics 661 (27.07.2010): 73–107. http://dx.doi.org/10.1017/s0022112010002855.
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We present a model for the relative velocity of inertial particles in turbulent flows that provides new physical insight into this problem. Our general formulation shows that the relative velocity has contributions from two terms, referred to as the ‘generalized acceleration’ and ‘generalized shear’, because they reduce to the well-known acceleration and shear terms in the Saffman–Turner limit. The generalized shear term represents particles' memory of the flow velocity difference along their trajectories and depends on the inertial particle pair dispersion backward in time. The importance of this backward dispersion in determining the particle relative velocity is emphasized. We find that our model with a two-phase separation behaviour, an early ballistic phase and a later tracer-like phase, as found by recent simulations for the forward (in time) dispersion of inertial particle pairs, gives good fits to the measured relative speeds from simulations at low Reynolds numbers. In the monodisperse case with identical particles, the generalized acceleration term vanishes and the relative velocity is determined by the generalized shear term. At large Reynolds numbers, our model gives a St1/2-dependence of the relative velocity on the Stokes number St in the inertial range for both the ballistic behaviour and the Richardson separation law. This leads to the same inertial-range scaling for the two-phase separation that well fits the simulation results. Our calculations for the bidisperse case show that, with the friction timescale of one particle fixed, the relative speed as a function of the other particle's friction time has a dip when the two timescales are similar. This indicates that similar-size particles tend to have stronger velocity correlation than different ones. We find that the primary contribution at the dip, i.e. for similar particles, is from the generalized shear term, while the generalized acceleration term is dominant for particles of very different sizes. Future numerical studies are motivated to check the accuracy of the assumptions made in our model and to investigate the backward-in-time dispersion of inertial particle pairs in turbulent flows.
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de Francisco, Marina, Sara Mira, Luisa Durães, Andreia Romeiro, Silvia Álvarez-Torrellas i Patricia Almendros. "Zn Oxide Nanoparticles and Fine Particles: Synthesis, Characterization and Evaluation of the Toxic Effect on Germination and Vigour of Solanum licopersicum L." Agronomy 14, nr 5 (7.05.2024): 980. http://dx.doi.org/10.3390/agronomy14050980.
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The micronutrient Zinc (Zn) is essential for the proper growth and development of crops. Zinc oxide nanoparticles (NPs) and fine particles are presented as an emerging alternative to more traditional fertilizers. In this study, the possible toxic effect of four laboratory-synthesized ZnO NPs and fine particles with different characteristics on tomato seed germination and vigor parameters was examined in comparison to bulk ZnO. Different metal precursors were used for the chemical synthesis of the particles: Zn(NO3)2 and ZnSO4, for particles named NIT-. and SUL-., respectively. In addition, the synthesis process was modified to obtain coated particles (denoted as UW-, NIT-UW and SUL-UW) and washed particles (denoted as W-, NIT-W and SUL-W). These particles were applied at different toxic doses (0, 1.4, 2.8, 5.6 and 11.2 g L−1). The results indicated that although the constant contact time between the ZnO particles did not affect the germination capacity of the seeds, it affected the growth of roots and hypocotyls, with a higher impact on the roots’ development. This toxicity was more evident from the lowest particle dose used, although it did not prevent radicle and hypocotyl elongation during the development period studied (14 days). The synthesized coated particles (NIT-UW, SUL-UW) generated high toxicity on radicle and hypocotyl development, and this effect was observed from the first days of contact with the particles. The observed toxic effects on radicle length were minimized by the application of bulk ZnO particles. In the case of hypocotyl growth, these minor toxic effects were observed by using NIT-W particles and bulk ZnO. The possibility of positive effects on seed germination and development (radicle and hypocotyl length) when in continuous contact with ZnO, whether in fine particles, nanoparticles, or bulk sizes, was excluded. Furthermore, no benefits on germination parameters were observed by suppressing the final washing step in the particle’s synthesis process, suggesting that particle coating did not provide any advantage for seed germination under these continuous contact conditions.