Articles de revues : « Active particle »

1

Arkar, Kyaw, Mikhail M. Vasiliev, Oleg F. Petrov, Evgenii A. Kononov et Fedor M. Trukhachev. « Dynamics of Active Brownian Particles in Plasma ». Molecules 26, n^o 3 (21 janvier 2021) : 561. http://dx.doi.org/10.3390/molecules26030561.

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Experimental data on the active Brownian motion of single particles in the RF (radio-frequency) discharge plasma under the influence of thermophoretic force, induced by laser radiation, depending on the material and type of surface of the particle, are presented. Unlike passive Brownian particles, active Brownian particles, also known as micro-swimmers, move directionally. It was shown that different dust particles in gas discharge plasma can convert the energy of a surrounding medium (laser radiation) into the kinetic energy of motion. The movement of the active particle is a superposition of chaotic motion and self-propulsion.

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Datt, Charu, Giovanniantonio Natale, Savvas G. Hatzikiriakos et Gwynn J. Elfring. « An active particle in a complex fluid ». Journal of Fluid Mechanics 823 (23 juin 2017) : 675–88. http://dx.doi.org/10.1017/jfm.2017.353.

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In this work, we study active particles with prescribed surface velocities in non-Newtonian fluids. We employ the reciprocal theorem to obtain the velocity of an active spherical particle with an arbitrary axisymmetric slip velocity in an otherwise quiescent second-order fluid. We then determine how the motion of a diffusiophoretic Janus particle is affected by complex fluid rheology, namely viscoelasticity and shear-thinning viscosity, compared to a Newtonian fluid, assuming a fixed slip velocity. We find that a Janus particle may go faster or slower in a viscoelastic fluid, but is always slower in a shear-thinning fluid as compared to a Newtonian fluid.

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Speck, Thomas. « Collective forces in scalar active matter ». Soft Matter 16, n^o 11 (2020) : 2652–63. http://dx.doi.org/10.1039/d0sm00176g.

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Moran, Shannon E., Isaac R. Bruss, Philipp W. A. Schönhöfer et Sharon C. Glotzer. « Particle anisotropy tunes emergent behavior in active colloidal systems ». Soft Matter 18, n^o 5 (2022) : 1044–53. http://dx.doi.org/10.1039/d0sm00913j.

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Nourhani, Amir, Daniel Brown, Nicholas Pletzer et John G. Gibbs. « Engineering Contactless Particle-Particle Interactions in Active Microswimmers ». Advanced Materials 29, n^o 47 (2 novembre 2017) : 1703910. http://dx.doi.org/10.1002/adma.201703910.

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Cho, Durkhyun, Sanghoon Lee et Il Hong Suh. « Facial Feature Tracking Using Adaptive Particle Filter and Active Appearance Model ». Journal of Korea Robotics Society 8, n^o 2 (31 mai 2013) : 104–15. http://dx.doi.org/10.7746/jkros.2013.8.2.104.

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Gulin-Sarfraz, Tina, Jawad Sarfraz, Didem Şen Karaman Didem Şen Karaman, Jixi Zhang, Christina Oetken-Lindholm, Alain Duchanoy, Jessica M. Rosenholm et Daniel Abankwa. « FRET-reporter nanoparticles to monitor redox-induced intracellular delivery of active compounds ». RSC Adv. 4, n^o 32 (2014) : 16429–37. http://dx.doi.org/10.1039/c4ra00270a.

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FRET-reporter particles for redox-induced release of active compounds in cells were developed. This particle system allowed following the intracellular cleavage of delivered compounds after particle internalization.

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Steimel, Joshua P., Juan L. Aragones, Helen Hu, Naser Qureshi et Alfredo Alexander-Katz. « Emergent ultra–long-range interactions between active particles in hybrid active–inactive systems ». Proceedings of the National Academy of Sciences 113, n^o 17 (11 avril 2016) : 4652–57. http://dx.doi.org/10.1073/pnas.1520481113.

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Particle–particle interactions determine the state of a system. Control over the range of such interactions as well as their magnitude has been an active area of research for decades due to the fundamental challenges it poses in science and technology. Very recently, effective interactions between active particles have gathered much attention as they can lead to out-of-equilibrium cooperative states such as flocking. Inspired by nature, where active living cells coexist with lifeless objects and structures, here we study the effective interactions that appear in systems composed of active and passive mixtures of colloids. Our systems are 2D colloidal monolayers composed primarily of passive (inactive) colloids, and a very small fraction of active (spinning) ferromagnetic colloids. We find an emergent ultra–long-range attractive interaction induced by the activity of the spinning particles and mediated by the elasticity of the passive medium. Interestingly, the appearance of such interaction depends on the spinning protocol and has a minimum actuation timescale below which no attraction is observed. Overall, these results clearly show that, in the presence of elastic components, active particles can interact across very long distances without any chemical modification of the environment. Such a mechanism might potentially be important for some biological systems and can be harnessed for newer developments in synthetic active soft materials.

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Zhang, Ying-Nan, Qing-Ni Hu et Hong-Fei Teng. « Active target particle swarm optimization ». Concurrency and Computation : Practice and Experience 20, n^o 1 (2007) : 29–40. http://dx.doi.org/10.1002/cpe.1207.

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Orozco, Luisa Fernanda, Jean-Yves Delenne, Philippe Sornay et Farhang Radjai. « Effect of particle shape on particle breakage inside rotating cylinders ». EPJ Web of Conferences 249 (2021) : 07002. http://dx.doi.org/10.1051/epjconf/202124907002.

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We study the influence of particle shape on the evolution of particle breakage process taking place inside rotating cylinders. Extensive particle dynamics simulations taking into account the dynamics of the granular flow, particle breakage, and polygonal particle shapes were carried out. We find that the rate of particle breakage is faster in samples composed of initially rounder particles. The analysis of the active flowing layer thickness suggests that for samples composed of rounder particles a relatively lower dilatancy and higher connectivity lead to a less curved free surface profile. As a result, rounder particles rolling down the free surface have a higher mobility and thus higher velocities. In consequence, the faster breakage observed for rounder initial particles is due to the larger particles kinetic energy at the toe of the flow.

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Clerici, Davide, Francesco Mocera et Aurelio Somà. « Shape Influence of Active Material Micro-Structure on Diffusion and Contact Stress in Lithium-Ion Batteries ». Energies 14, n^o 1 (29 décembre 2020) : 134. http://dx.doi.org/10.3390/en14010134.

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Electrochemical-mechanical modelling is a key issue to estimate the damage of active material, as direct measurements cannot be performed due to the particles nanoscale. The aim of this paper is to overcome the common assumptions of spherical and standalone particle, proposing a general approach that considers a parametrized particle shape and studying its influence on the mechanical stresses which arise in active material particles during battery operation. The shape considered is a set of ellipsoids with variable aspect ratio (elongation), which aims to approximate real active material particles. Active material particle is divided in two domains: non-contact domain and contact domain, whether contact with neighbouring particles affects stress distribution or not. Non-contact areas are affected by diffusion stress, caused by lithium concentration gradient inside particles. Contact areas are affected simultaneously by diffusion stress and contact stress, caused by contact with neighbouring particles as a result of particle expansion due to lithium insertion. A finite element model is developed in Ansys™APDL to perform the multi-physics computation in non-spherical domain. The finite element model is validated in the spherical case by analytical models of diffusion and contact available for simple geometry. Then, the shape factor is derived to describe how particle shape affects mechanical stress in non-contact and contact domains.

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Kubota, Naoki. « Deviation bounds for the first passage time in the frog model ». Advances in Applied Probability 51, n^o 01 (mars 2019) : 184–208. http://dx.doi.org/10.1017/apr.2019.8.

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AbstractWe consider the so-called frog model with random initial configurations. The dynamics of this model are described as follows. Some particles are randomly assigned to any site of the multidimensional cubic lattice. Initially, only particles at the origin are active and these independently perform simple random walks. The other particles are sleeping and do not move at first. When sleeping particles are hit by an active particle, they become active and start moving in a similar fashion. The aim of this paper is to derive large deviation and concentration bounds for the first passage time at which an active particle reaches a target site.

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Lebensztayn, Elcio, Fábio Prates Machado et Mauricio Zuluaga Martinez. « Nonhomogeneous random walks systems on ℤ ». Journal of Applied Probability 47, n^o 2 (juin 2010) : 562–71. http://dx.doi.org/10.1239/jap/1276784909.

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We consider a random walks system on ℤ in which each active particle performs a nearest-neighbor random walk and activates all inactive particles it encounters. The movement of an active particle stops when it reaches a certain number of jumps without activating any particle. We prove that if the process relies on efficient particles (i.e. those particles with a small probability of jumping to the left) being placed strategically on ℤ, then it might survive, having active particles at any time with positive probability. On the other hand, we may construct a process that dies out eventually almost surely, even if it relies on efficient particles. That is, we discuss what happens if particles are initially placed very far away from each other or if their probability of jumping to the right tends to 1 but not fast enough.

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Lebensztayn, Elcio, Fábio Prates Machado et Mauricio Zuluaga Martinez. « Nonhomogeneous random walks systems on ℤ ». Journal of Applied Probability 47, n^o 02 (juin 2010) : 562–71. http://dx.doi.org/10.1017/s0021900200006811.

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We consider a random walks system on ℤ in which each active particle performs a nearest-neighbor random walk and activates all inactive particles it encounters. The movement of an active particle stops when it reaches a certain number of jumps without activating any particle. We prove that if the process relies on efficient particles (i.e. those particles with a small probability of jumping to the left) being placed strategically on ℤ, then it might survive, having active particles at any time with positive probability. On the other hand, we may construct a process that dies out eventually almost surely, even if it relies on efficient particles. That is, we discuss what happens if particles are initially placed very far away from each other or if their probability of jumping to the right tends to 1 but not fast enough.

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15

Lou, Xin, Rui Liu, Ke Chen, Xin Zhou, Rudolf Podgornik et Mingcheng Yang. « Diffusion of a chemically active colloidal particle in composite channels ». Chinese Physics B 31, n^o 4 (1 avril 2022) : 044704. http://dx.doi.org/10.1088/1674-1056/ac381b.

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Diffusion of colloidal particles in microchannels has been extensively investigated, where the channel wall is either a no-slip or a slip-passive boundary. However, in the context of active fluids, driving boundary walls are ubiquitous and are expected to have a substantial effect on the particle dynamics. By mesoscale simulations, we study the diffusion of a chemically active colloidal particle in composite channels, which are constructed by alternately arranging the no-slip and diffusio-osmotic boundary walls. In this case, the chemical reaction catalyzed by the active colloidal particle creates a local chemical gradient along the channel wall, which drives a diffusio-osmotic flow parallel to the wall. We show that the diffusio-osmotic flow can significantly change the spatial distribution and diffusion dynamics of the colloidal particle in the composite channels. By modulating the surface properties of the channel wall, we can achieve different patterns of colloidal position distribution. The findings thus propose a novel possibility to manipulate colloidal diffusion in microfluidics, and highlight the importance of driving boundary walls in dynamics of colloidal particles in microchannels.

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Dolai, Pritha, Arghya Das, Anupam Kundu, Chandan Dasgupta, Abhishek Dhar et K. Vijay Kumar. « Universal scaling in active single-file dynamics ». Soft Matter 16, n^o 30 (2020) : 7077–87. http://dx.doi.org/10.1039/d0sm00687d.

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The single-file dynamics of various models of interacting scalar active particles shows universality. The cluster size distribution and tagged-particle MSD scale with density and activity parameters with the same scaling functions across all models.

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17

Nguyen, G. H. Philipp, René Wittmann et Hartmut Löwen. « Active Ornstein–Uhlenbeck model for self-propelled particles with inertia ». Journal of Physics : Condensed Matter 34, n^o 3 (2 novembre 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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Kim, Jeong-Soo, Heejun Park, Eun-Sol Ha, Kyu-Tae Kang, Min-Soo Kim et Sung-Joo Hwang. « Preparation and Characterization of Fenofibrate Microparticles with Surface-Active Additives : Application of a Supercritical Fluid-Assisted Spray-Drying Process ». Pharmaceutics 13, n^o 12 (2 décembre 2021) : 2061. http://dx.doi.org/10.3390/pharmaceutics13122061.

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In this study, supercritical fluid-assisted spray-drying (SA-SD) was applied to achieve the micronization of fenofibrate particles possessing surface-active additives, such as d-α-tocopheryl polyethylene glycol 1000 succinate (TPGS), sucrose mono palmitate (Sucroester 15), and polyoxyethylene 52 stearate (Myrj 52), to improve the pharmacokinetic and pharmacodynamic properties of fenofibrate. For comparison, the same formulation was prepared using a spray-drying (SD) process, and then both methods were compared. The SA-SD process resulted in a significantly smaller mean particle size (approximately 2 μm) compared to that of unprocessed fenofibrate (approximately 20 μm) and SD-processed particles (approximately 40 μm). There was no significant difference in the effect on the particle size reduction among the selected surface-active additives. The microcomposite particles prepared with surface-active additives using SA-SD exhibited remarkable enhancement in their dissolution rate due to the synergistic effect of comparably moderate wettability improvement and significant particle size reduction. In contrast, the SD samples with the surface-active additives exhibited a decrease in dissolution rate compared to that of the unprocessed fenofibrate due to the absence of particle size reduction, although wettability was greatly improved. The results of zeta potential and XPS analyses indicated that the surface-active additive coverage on the surface layer of the SD-processed particles with a better wettability was higher than that of the SA-SD-processed composite particles. Additionally, after rapid depletion of hydrophilic additives that were excessively distributed on the surfaces of SD-processed particles, the creation of a surface layer rich in poorly water-soluble fenofibrate resulted in a decrease in the dissolution rate. In contrast, the surface-active molecules were dispersed homogeneously throughout the particle matrix in the SA-SD-processed microparticles. Furthermore, improved pharmacokinetic and pharmacodynamic characteristics were observed for the SA-SD-processed fenofibrate microparticles compared to those for the SD-processed fenofibrate particles. Therefore, the SA-SD process incorporating surface-active additives can efficiently micronize poorly water-soluble drugs and optimize their physicochemical and biopharmaceutical characteristics.

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Sharifi-Mood, Nima, Ali Mozaffari et Ubaldo M. Córdova-Figueroa. « Pair interaction of catalytically active colloids : from assembly to escape ». Journal of Fluid Mechanics 798 (16 juin 2016) : 910–54. http://dx.doi.org/10.1017/jfm.2016.317.

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The dynamics and pair trajectories of two self-propelled (active) colloids in a quiescent fluid for both axisymmetric and asymmetric cases are reported. The autonomous motions of the colloids are due to a catalytic chemical reaction taking place asymmetrically on their surfaces that generates a concentration gradient of interactive solutes around the particles and actuates particle propulsion. A combined analytical–numerical technique was developed to solve the coupled mass conservation equation for the solute and the hydrodynamics between the colloids in the Stokes flow regime. For axisymmetric motions, the translational swimming velocities of the particles in the near field can be enhanced or weakened (compared to their motions when they are far apart) depending on the relative orientations of their active sections. Moreover, it can be shown that different surface activities of two symmetric particles, e.g. an inert versus a catalytic particle or two catalytic particles, can also lead to a propulsion where the far-field swimming velocity for the inert and the catalytic particle attenuate as ${\sim}1/{\it\Delta}^{2}$ and ${\sim}1/{\it\Delta}^{5}$ respectively, ${\it\Delta}$ is the non-dimensional centre-to-centre distance. For asymmetric motions, our analysis indicates two possible scenarios for pair trajectories of catalytically active particles: either the particles approach, come into contact and assemble or they interact and move away from each other (escape). It is found that the direction of particle rotations is the key factor in determining the escape or assembly scenario due to an interplay between both hydrodynamic and phoretic effects. Based on the analysis, a phase diagram is sketched for the pair trajectory of the catalytically active particles as a function of reacting surface coverages and their initial relative orientations with respect to each other. We believe this study has important implications in elucidation of collective behaviours of autophoretically self-propelled colloids and would be certainly a guide for experimentalists to design and control active systems.

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Nosenko, V. « Two-dimensional complex (dusty) plasma with active Janus particles ». Physics of Plasmas 29, n^o 12 (décembre 2022) : 123701. http://dx.doi.org/10.1063/5.0121734.

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A two-dimensional complex plasma containing active Janus particles was experimentally studied. A single layer of micrometer-sized plastic microspheres was suspended in the plasma sheath of a radio frequency discharge in argon at low pressure. The particle sample used was a mixture of regular particles and Janus particles, which were coated on one side with a thin layer of platinum. Unlike a suspension consisting of regular particles only, the suspension with the inclusion of Janus particles did not form an ordered lattice in the experimental conditions used. Instead, the particles moved around with high kinetic energy in a disordered suspension. Unexpectedly, the mean kinetic energy of the particles declined as the illumination laser power was increased. This is explained by the competition of two driving forces: the photophoretic force and the oppositely directed ion drag force. The mean-squared displacement of the particles scaled as [Formula: see text] with α = 2 at small times t indicating ballistic motion and [Formula: see text] at longer times due to the combined effect of the Janus particle propensity to move in circular trajectories and external confinement.

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Bertacchi, Daniela, Fábio Prates Machado et Fabio Zucca. « Local and Global Survival for Nonhomogeneous Random Walk Systems on Z ». Advances in Applied Probability 46, n^o 1 (mars 2014) : 256–78. http://dx.doi.org/10.1239/aap/1396360113.

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We study an interacting random walk system on ℤ where at time 0 there is an active particle at 0 and one inactive particle on each site n ≥ 1. Particles become active when hit by another active particle. Once activated, the particle starting at n performs an asymmetric, translation invariant, nearest neighbor random walk with left-jump probability ln. We give conditions for global survival, local survival, and infinite activation both in the case where all particles are immortal and in the case where particles have geometrically distributed lifespan (with parameter depending on the starting location of the particle). More precisely, once activated, the particle at n survives at each step with probability pn ∈ [0, 1]. In particular, in the immortal case, we prove a 0-1 law for the probability of local survival when all particles drift to the right. Besides that, we give sufficient conditions for local survival or local extinction when all particles drift to the left. In the mortal case, we provide sufficient conditions for global survival, local survival, and local extinction (which apply to the immortal case with mixed drifts as well). Analysis of explicit examples is provided: we describe completely the phase diagram in the cases ½ - ln ~ ± 1 / nα, pn = 1 and ½ - ln ~ ± 1 / nα, 1 - pn ~ 1 / nβ (where α, β > 0).

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Bertacchi, Daniela, Fábio Prates Machado et Fabio Zucca. « Local and Global Survival for Nonhomogeneous Random Walk Systems on Z ». Advances in Applied Probability 46, n^o 01 (mars 2014) : 256–78. http://dx.doi.org/10.1017/s0001867800007035.

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We study an interacting random walk system on ℤ where at time 0 there is an active particle at 0 and one inactive particle on each site n ≥ 1. Particles become active when hit by another active particle. Once activated, the particle starting at n performs an asymmetric, translation invariant, nearest neighbor random walk with left-jump probability l n . We give conditions for global survival, local survival, and infinite activation both in the case where all particles are immortal and in the case where particles have geometrically distributed lifespan (with parameter depending on the starting location of the particle). More precisely, once activated, the particle at n survives at each step with probability p n ∈ [0, 1]. In particular, in the immortal case, we prove a 0-1 law for the probability of local survival when all particles drift to the right. Besides that, we give sufficient conditions for local survival or local extinction when all particles drift to the left. In the mortal case, we provide sufficient conditions for global survival, local survival, and local extinction (which apply to the immortal case with mixed drifts as well). Analysis of explicit examples is provided: we describe completely the phase diagram in the cases ½ - l n ~ ± 1 / n α, p n = 1 and ½ - l n ~ ± 1 / n α, 1 - p n ~ 1 / n β (where α, β > 0).

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Nikpour, M., B. A. Mazzeo et D. R. Wheeler. « A Model for Investigating Sources of Li-Ion Battery Electrode Heterogeneity : Part II. Active Material Size, Shape, Orientation, and Stiffness ». Journal of The Electrochemical Society 168, n^o 12 (1 décembre 2021) : 120518. http://dx.doi.org/10.1149/1945-7111/ac3c1f.

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This work is the extension of our previous paper [Nikpour et al., J. Electrochem. Soc. 168, 060547, (2021)] which introduced the multi-phase smoothed particle (MPSP) model. This model was used to simulate the evolution of the microstructure during the drying and calendering manufacturing processes of four different electrodes. The MPSP model uses particle properties to predict overall film properties such as conductivities and elastic moduli and is validated by multiple experiments. In this work, the model is used to investigate the effects of active material particle size, shape, orientation, and stiffness on graphitic anodes. The model predicts that smaller active particles produce higher calendered film density, electronic conductivity, MacMullin number, and Young’s modulus, as compared to larger active particles. Rod-shaped active materials have greater ionic transport and lower electronic transport compared to the disk and sphere shapes, which have similar transport properties. During calendering, disk-shaped particles tend to be oriented horizontally, which decreases through-plane ionic transport. Increasing the stiffness of the active material increases film porosity and composite Young’s modulus, while lowering electronic transport and increasing ionic transport.

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Ibrahim, Yahaya, et Saratu Abddulfatah. « PAIR INTERACTION OF ACTIVE COLLOIDS IN AN EXTERNAL CHEMICAL GRADIENT ». FUDMA JOURNAL OF SCIENCES 6, n^o 3 (6 juillet 2022) : 271–77. http://dx.doi.org/10.33003/fjs-2022-0603-999.

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We study the pair interaction of chemically isotropic active colloidal particles in an externally imposed chemical gradient. Colloid particles migrate in response to a gradient of chemical solutes (i.e., via the diffusiophoresis mechanism). The particles motion induces fluid flow and distort locally the background chemical concentration field. Using the methods of images, we calculate the phoretic inter-particle interaction between two symmetric active colloids in the presence of an externally applied gradient. We highlight an interesting colloidal dipole that would arise from tuning the surface and chemical activity of the colloids. The colloidal phoretic dipoles share similar properties to the electrostatic dipoles. The inter-particle interaction we obtained is an important component for a large-scale simulation of the active colloid suspension. It may also help towards better understanding of the active systems’ emergent phenomena

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Dulaney, Austin R., et John F. Brady. « Machine learning for phase behavior in active matter systems ». Soft Matter 17, n^o 28 (2021) : 6808–16. http://dx.doi.org/10.1039/d1sm00266j.

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We demonstrate that deep learning techniques can be used to predict motility-induced phase separation (MIPS) in suspensions of active Brownian particles (ABPs) by creating a notion of phase at the particle level.

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Mosa, Qusay O., Ali Saeed Alfoudi, Ahmed A. Brisam, Abayomi M. Otebolaku et Gyu Myoung Lee. « Driving Active Contours to Concave Regions ». Webology 19, n^o 1 (20 janvier 2022) : 5131–40. http://dx.doi.org/10.14704/web/v19i1/web19345.

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Broken characters restoration represents the major challenge of optical character recognition (OCR). Active contours, which have been used successfully to restore ancient documents with high degradations have drawback in restoring characters with deep concavity boundaries. Deep concavity problem represents the main obstacle, which has prevented Gradient Vector Flow active contour in converge to objects with complex concavity boundaries. In this paper, we proposed a technique to enhance (GVF) active contour using particle swarm optimization (PSO) through directing snake points (snaxels) toward correct positions into deep concavity boundaries of broken characters by comparing with genetic algorithms as an optimization method. Our experimental results showed that particle swarm optimization outperform on genetic algorithm to correct capturing the converged areas and save spent time in optimization process.

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Сергеев, К. С., et K. S. Sergeev. « Dynamics of Ensemble of Active Brownian Particles Controlled by Noise ». Mathematical Biology and Bioinformatics 10, n^o 1 (16 février 2015) : 72–87. http://dx.doi.org/10.17537/2015.10.72.

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Dynamics of an ensemble of small number of active Brownian particles is studied by means of numerical simulations. The particles are influenced by independent sources of noise, passive and active, and interact with each other through a global velocity field. We suppose that active noise affects to direction of the particle velocity only. Behaviour of the large ensemble and behaviour of the small one are compared. Mean velocity of particles of the large ensemble was analytically estimated earler. We show that a noise-induced "order- disorder" transition accompaniated by a bistability phenomena is observed in a small ensemble. A borderline of a coupling coefficient moves up while reducing the number of particles. Influence of passive noise leads to conversion of bistability to bimodality. There are two most probable values of a particle velocity in the last case. Borders of regions of bistability and bimodality are defined by the stochastic bifurcations of different kinds.

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Liu, Peng, Hongwei Zhu, Ying Zeng, Guangle Du, Luhui Ning, Dunyou Wang, Ke Chen et al. « Oscillating collective motion of active rotors in confinement ». Proceedings of the National Academy of Sciences 117, n^o 22 (19 mai 2020) : 11901–7. http://dx.doi.org/10.1073/pnas.1922633117.

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Due to its inherent out-of-equilibrium nature, active matter in confinement may exhibit collective behavior absent in unconfined systems. Extensive studies have indicated that hydrodynamic or steric interactions between active particles and boundary play an important role in the emergence of collective behavior. However, besides introducing external couplings at the single-particle level, the confinement also induces an inhomogeneous density distribution due to particle-position correlations, whose effect on collective behavior remains unclear. Here, we investigate this effect in a minimal chiral active matter composed of self-spinning rotors through simulation, experiment, and theory. We find that the density inhomogeneity leads to a position-dependent frictional stress that results from interrotor friction and couples the spin to the translation of the particles, which can then drive a striking spatially oscillating collective motion of the chiral active matter along the confinement boundary. Moreover, depending on the oscillation properties, the collective behavior has three different modes as the packing fraction varies. The structural origins of the transitions between the different modes are well identified by the percolation of solid-like regions or the occurrence of defect-induced particle rearrangement. Our results thus show that the confinement-induced inhomogeneity, dynamic structure, and compressibility have significant influences on collective behavior of active matter and should be properly taken into account.

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Zhang, Weitao, Yunyun Li, Fabio Marchesoni, Vyacheslav R. Misko et Pulak K. Ghosh. « Narrow Pore Crossing of Active Particles under Stochastic Resetting ». Entropy 25, n^o 2 (1 février 2023) : 271. http://dx.doi.org/10.3390/e25020271.

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We propose a two-dimensional model of biochemical activation process, whereby self-propelling particles of finite correlation times are injected at the center of a circular cavity with constant rate equal to the inverse of their lifetime; activation is triggered when one such particle hits a receptor on the cavity boundary, modeled as a narrow pore. We numerically investigated this process by computing the particle mean-first exit times through the cavity pore as a function of the correlation and injection time constants. Due to the breach of the circular symmetry associated with the positioning of the receptor, the exit times may depend on the orientation of the self-propelling velocity at injection. Stochastic resetting appears to favor activation for large particle correlation times, where most of the underlying diffusion process occurs at the cavity boundary.

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Kwee, Darren W., Taehoon Lim et Alfredo Martinez-Morales. « Analysis of LiFePO4 Cathodic Active Material Synthesized in Open Environment Conditions through Ionic Medium ». MRS Proceedings 1774 (2015) : 1–6. http://dx.doi.org/10.1557/opl.2015.576.

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ABSTRACTIn this work, LiFePO4 (LFP) particles were synthesized through an ionic liquid medium. Through the fabrication of LFP particles, we observed the formation of quasi-1−dimensional (1D) structures. The characterization of phases found in the reaction, through time-dependent studies, have led us to propose a possible scheme for particle formation.Synthesized material was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD). We also report our analysis on particle morphology and crystallinity of LFP particles synthesized through an ionic liquid−mediated process.

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Wagner, Caleb G., Michael F. Hagan et Aparna Baskaran. « Steady states of active Brownian particles interacting with boundaries ». Journal of Statistical Mechanics : Theory and Experiment 2022, n^o 1 (1 janvier 2022) : 013208. http://dx.doi.org/10.1088/1742-5468/ac42cf.

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Abstract An active Brownian particle is a minimal model for a self-propelled colloid in a dissipative environment. Experiments and simulations show that, in the presence of boundaries and obstacles, active Brownian particle systems approach nontrivial nonequilibrium steady states with intriguing phenomenology, such as accumulation at boundaries, ratchet effects, and long-range depletion interactions. Nevertheless, theoretical analysis of these phenomena has proven difficult. Here, we address this theoretical challenge in the context of non-interacting particles in two dimensions, basing our analysis on the steady-state Smoluchowski equation for the one-particle distribution function. Our primary result is an approximation strategy that connects asymptotic solutions of the Smoluchowski equation to boundary conditions. We test this approximation against the exact analytic solution in a 2D planar geometry, as well as numerical solutions in circular and elliptic geometries. We find good agreement so long as the boundary conditions do not vary too rapidly with respect to the persistence length of particle trajectories. Our results are relevant for characterizing long-range flows and depletion interactions in such systems. In particular, our framework shows how such behaviors are connected to the breaking of detailed balance at the boundaries.

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Mohan, Lavanya, Michel Cloitre et Roger T. Bonnecaze. « Active microrheology of soft particle glasses ». Journal of Rheology 58, n^o 5 (septembre 2014) : 1465–82. http://dx.doi.org/10.1122/1.4887535.

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Schächter, Levi. « Particle acceleration in an active medium ». Physical Review E 53, n^o 6 (1 juin 1996) : 6427–34. http://dx.doi.org/10.1103/physreve.53.6427.

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Katuri, Jaideep, William E. Uspal, Mihail N. Popescu et Samuel Sánchez. « Inferring non-equilibrium interactions from tracer response near confined active Janus particles ». Science Advances 7, n^o 18 (avril 2021) : eabd0719. http://dx.doi.org/10.1126/sciadv.abd0719.

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Chemically active Janus particles sustain non-equilibrium spatial variations in the chemical composition of the suspending solution; these induce hydrodynamic flow and (self-)motility of the particles. Direct mapping of these fields has so far proven to be too challenging. Therefore, indirect methods are needed, e.g., deconvolving the response of “tracer” particles to the activity-induced fields. Here, we study experimentally the response of silica particles, sedimented at a wall, to active Pt/silica Janus particles. The latter are either immobilized at the wall, with the symmetry axis perpendicular or parallel to the wall, or motile. The experiments reveal complex effective interactions that are dependent on the configuration and on the state of motion of the active particle. Within the framework of a coarse-grained model, the behavior of tracers near an immobilized Janus particle can be captured qualitatively once activity-induced osmotic flows on the wall are considered.

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Brooks, Allan M., Syeda Sabrina et Kyle J. M. Bishop. « Shape-directed dynamics of active colloids powered by induced-charge electrophoresis ». Proceedings of the National Academy of Sciences 115, n^o 6 (22 janvier 2018) : E1090—E1099. http://dx.doi.org/10.1073/pnas.1711610115.

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The symmetry and shape of colloidal particles can direct complex particle motions through fluid environments powered by simple energy inputs. The ability to rationally design or “program” the dynamics of such active colloids is an important step toward the realization of colloidal machines, in which components assemble spontaneously in space and time to perform dynamic (dissipative) functions such as actuation and transport. Here, we systematically investigate the dynamics of polarizable particles of different shapes moving in an oscillating electric field via induced-charge electrophoresis (ICEP). We consider particles from each point group in three dimensions (3D) and identify the different rotational and translational motions allowed by symmetry. We describe how the 3D shape of rigid particles can be tailored to achieve desired dynamics including oscillatory motions, helical trajectories, and complex periodic orbits. The methodology we develop is generally applicable to the design of shape-directed particle motions powered by other energy inputs.

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Smanova, Zulayho A., Tokhir Kh Rakhimov, Muxtarjan Mukhamediev, Dilfuza Gafurova et Dilbar Shaxidova. « Calculation of the Boundary Dimensions of Functionally Active Nanoparticles ». International Journal of Applied Nanotechnology Research 5, n^o 1 (janvier 2020) : 1–9. http://dx.doi.org/10.4018/ijanr.20200101.oa1.

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Size is a key characteristic of nanoparticles that determines whether the objects belong to this category. Currently, there are not enough experiments on materials of the same chemical composition but of different dispersion in particle size, with equal size of the particles or grains of each sample of material investigated. In the present article, the authors show that the effect of the dispersion of the particle size determines whether the size dependence of a specific property can be calculated alternatively to the direct measurements. By finding the correlations between nano-properties and content of nanoparticles' fractions of different sizes, the boundary conditions can be calculated.

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Iwata, Ayumi, et Atsushi Matsuki. « Characterization of individual ice residual particles by the single droplet freezing method : a case study in the Asian dust outflow region ». Atmospheric Chemistry and Physics 18, n^o 3 (7 février 2018) : 1785–804. http://dx.doi.org/10.5194/acp-18-1785-2018.

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Abstract. In order to better characterize ice nucleating (IN) aerosol particles in the atmosphere, we investigated the chemical composition, mixing state, and morphology of atmospheric aerosols that nucleate ice under conditions relevant for mixed-phase clouds. Five standard mineral dust samples (quartz, K-feldspar, Na-feldspar, Arizona test dust, and Asian dust source particles) were compared with actual aerosol particles collected from the west coast of Japan (the city of Kanazawa) during Asian dust events in February and April 2016. Following droplet activation by particles deposited on a hydrophobic Si (silicon) wafer substrate under supersaturated air, individual IN particles were located using an optical microscope by gradually cooling the temperature to −30 ∘C. For the aerosol samples, both the IN active particles and non-active particles were analyzed individually by atomic force microscopy (AFM), micro-Raman spectroscopy, and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). Heterogeneous ice nucleation in all standard mineral dust samples tested in this study was observed at consistently higher temperatures (e.g., −22.2 to −24.2 ∘C with K-feldspar) than the homogeneous freezing temperature (−36.5 ∘C). Meanwhile, most of the IN active atmospheric particles formed ice below −28 ∘C, i.e., at lower temperatures than the standard mineral dust samples of pure components. The most abundant IN active particles above −30 ∘C were predominantly irregular solid particles that showed clay mineral characteristics (or mixtures of several mineral components). Other than clay, Ca-rich particles internally mixed with other components, such as sulfate, were also regarded as IN active particle types. Moreover, sea salt particles were predominantly found in the non-active fraction, and internal mixing with sea salt clearly acted as a significant inhibiting agent for the ice nucleation activity of mineral dust particles. Also, relatively pure or fresh calcite, Ca(NO3)2, and (NH4)2SO4 particles were more often found in the non-active fraction. In this study, we demonstrated the capability of the combined single droplet freezing method and thorough individual particle analysis to characterize the ice nucleation activity of atmospheric aerosols. We also found that dramatic changes in the particle mixing states during long-range transport had a complex effect on the ice nucleation activity of the host aerosol particles. A case study in the Asian dust outflow region highlighted the need to consider particle mixing states, which can dramatically influence ice nucleation activity.

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Agarwal, Pradeep K., William J. Mitchell et Robert D. La Nauze. « Transport phenomena in multi-particle systems—III. Active particle mass transfer in fluidized beds of inert particles ». Chemical Engineering Science 43, n^o 9 (1988) : 2511–21. http://dx.doi.org/10.1016/0009-2509(88)85185-6.

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Lambert, Ruth A., Francesco Picano, Wim-Paul Breugem et Luca Brandt. « Active suspensions in thin films : nutrient uptake and swimmer motion ». Journal of Fluid Mechanics 733 (25 septembre 2013) : 528–57. http://dx.doi.org/10.1017/jfm.2013.459.

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AbstractA numerical study of swimming particle motion and nutrient transport is conducted for a semidilute to dense suspension in a thin film. The steady squirmer model is used to represent the motion of living cells in suspension with the nutrient uptake by swimming particles modelled using a first-order kinetic equation representing the absorption process that occurs locally at the particle surface. An analysis of the dynamics of the neutral squirmers inside the film shows that the vertical motion is reduced significantly. The mean nutrient uptake for both isolated and populations of swimmers decreases for increasing swimming speeds when nutrient advection becomes relevant as less time is left for the nutrient to diffuse to the surface. This finding is in contrast to the case where the uptake is modelled by imposing a constant nutrient concentration at the cell surface and the mass flux results to be an increasing monotonic function of the swimming speed. In comparison to non-motile particles, the cell motion has a negligible influence on nutrient uptake at lower particle absorption rates since the process is rate limited. At higher absorption rates, the swimming motion results in a large increase in the nutrient uptake that is attributed to the movement of particles and increased mixing in the fluid. As the volume fraction of swimming particles increases, the squirmers consume slightly less nutrients and require more power for the same swimming motion. Despite this increase in energy consumption, the results clearly demonstrate that the gain in nutrient uptake make swimming a winning strategy for micro-organism survival also in relatively dense suspensions.

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A. Balakrishna, A. Balakrishna, B. Mahesh Babu, Dr L. Ravi Srinivas et Dr S. S. Tulasi Ram. « Particle Swarm Optimization For Power Quality Improvement Based on Shunt Active Power Filter ». International Journal of Scientific Research 3, n^o 1 (1 juin 2012) : 158–63. http://dx.doi.org/10.15373/22778179/jan2014/51.

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Samal, Sneha, Marcela Kolinova et Ignazio Blanco. « The Magneto-Mechanical Behavior of Active Components in Iron-Elastomer Composite ». Journal of Composites Science 2, n^o 3 (6 septembre 2018) : 54. http://dx.doi.org/10.3390/jcs2030054.

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The magneto-rheological effects in iron-elastomer composites (IEC) were investigated by simulation, surface topography, and 3D representation. The simulated behavior of magneto-rheological elastomeric composites in the presence of an external magnetic field was determined and the influence of magnetic intensity on the isotropic distribution of iron filler particles in IECs was investigated. The magnetic intensity distribution was analyzed from the edge of the surface towards the center of the IEC. The samples were characterized for microstructural images after experimental tests using both micro-computed tomography (µCT) and scanning electron microscopy (SEM). The adhesion of filler particles within the matrix of the magneto-rheological elastomer (MRE) composite and their distributions were also investigated. µCT showed the overall 3D representation of IEC and the inner distribution of filler particles revealed the presence of some porosity which may be due to bubbles and voids in the matrix of the composite. Finally, a mechanism was established governing particle–particle interactions on the basis of dipole–dipole interactions.

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Ezhilan, Barath, et David Saintillan. « Transport of a dilute active suspension in pressure-driven channel flow ». Journal of Fluid Mechanics 777 (20 juillet 2015) : 482–522. http://dx.doi.org/10.1017/jfm.2015.372.

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Confined suspensions of active particles show peculiar dynamics characterized by wall accumulation, as well as upstream swimming, centreline depletion and shear trapping when a pressure-driven flow is imposed. We use theory and numerical simulations to investigate the effects of confinement and non-uniform shear on the dynamics of a dilute suspension of Brownian active swimmers by incorporating a detailed treatment of boundary conditions within a simple kinetic model where the configuration of the suspension is described using a conservation equation for the probability distribution function of particle positions and orientations, and where particle–particle and particle–wall hydrodynamic interactions are neglected. Based on this model, we first investigate the effects of confinement in the absence of flow, in which case the dynamics is governed by a swimming Péclet number, or ratio of the persistence length of particle trajectories over the channel width, and a second swimmer-specific parameter whose inverse measures the strength of propulsion. In the limit of weak and strong propulsion, asymptotic expressions for the full distribution function are derived. For finite propulsion, analytical expressions for the concentration and polarization profiles are also obtained using a truncated moment expansion of the distribution function. In agreement with experimental observations, the existence of a concentration/polarization boundary layer in wide channels is reported and characterized, suggesting that wall accumulation in active suspensions is primarily a kinematic effect that does not require hydrodynamic interactions. Next, we show that application of a pressure-driven Poiseuille flow leads to net upstream swimming of the particles relative to the flow, and an analytical expression for the mean upstream velocity is derived in the weak-flow limit. In stronger imposed flows, we also predict the formation of a depletion layer near the channel centreline, due to cross-streamline migration of the swimming particles towards high-shear regions where they become trapped, and an asymptotic analysis in the strong-flow limit is used to obtain a scale for the depletion layer thickness and to rationalize the non-monotonic dependence of the intensity of depletion upon flow rate. Our theoretical predictions are all shown to be in excellent agreement with finite-volume numerical simulations of the kinetic model, and are also supported by recent experiments on bacterial suspensions in microfluidic devices.

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Peng, Zhiwei, et John F. Brady. « Forced microrheology of active colloids ». Journal of Rheology 66, n^o 5 (septembre 2022) : 955–72. http://dx.doi.org/10.1122/8.0000504.

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Particle-tracking microrheology of dilute active (self-propelled) colloidal suspensions is studied by considering the external force required to maintain the steady motion of an immersed constant-velocity colloidal probe. If the probe speed is zero, the suspension microstructure is isotropic but exhibits a boundary accumulation of active bath particles at contact due to their self-propulsion. As the probe moves through the suspension, the microstructure is distorted from the nonequilibrium isotropic state, which allows us to define a microviscosity for the suspension using the Stokes drag law. For a slow probe, we show that active suspensions exhibit a swim-thinning behavior in which their microviscosity is gradually lowered from that of passive suspensions as the swim speed increases. When the probe speed is fast, the suspension activity is obscured by the rapid advection of the probe and the measured microviscosity is indistinguishable from that of passive suspensions. Generally for finite activity, the suspension exhibits a velocity-thinning behavior—though with a zero-velocity plateau lower than passive suspensions—as a function of the probe speed. These behaviors originate from the interplay between the suspension activity and the hard-sphere excluded-volume interaction between the probe and a bath particle.

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Boczkowska, Anna, et Stefan F. Awietjan. « Tuning Active Magnetorheological Elastomers for Damping Applications ». Materials Science Forum 636-637 (janvier 2010) : 766–71. http://dx.doi.org/10.4028/www.scientific.net/msf.636-637.766.

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Magnetorheological elastomers (MREs) were obtained by mixing soft polyurethane and carbonyl-iron particles. The effect of the volume fraction of the ferromagnetic particles on the MREs microstructure and properties, as well as their arrangement in relation to the external magnetic field were investigated. As a ferromagnetic component carbonyl–iron powder, with particle size from 6-9µm, was used. The amount of the carbonyl iron particles was varied from 1.5 to 33.0 %(v/v). The samples were produced with randomly dispersed and aligned carbonyl iron particles. Scanning electron and light microscopy techniques were used for the MRE microstructure observations. The rheological properties (G’, G’’ and tan δ) of the MRE were tested without and with the application of the magnetic field. It was found that the microstructure of MREs, particularly the amount and arrangement of the carbonyl-iron particles, has a significant influence on their rheological and damping properties.

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Back, Seung Wook. « Influence of nonuniform particle temperature on the radiatively active particle ignition ». Journal of Thermophysics and Heat Transfer 6, n^o 2 (avril 1992) : 382–84. http://dx.doi.org/10.2514/3.372.

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Johnson, Brian K., et Robert K. Prud'homme. « Flash NanoPrecipitation of Organic Actives and Block Copolymers using a Confined Impinging Jets Mixer ». Australian Journal of Chemistry 56, n^o 10 (2003) : 1021. http://dx.doi.org/10.1071/ch03115.

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A new technology to form nanoparticles of hydrophobic organic actives at high concentration and yield, as well as methods to characterize the process, are presented. In Flash NanoPrecipitation, an organic active and an amphiphilic diblock copolymer are molecularly dissolved in an organic phase and mixed rapidly with a miscible anti-solvent to afford precipitation of the active with a tunable, narrow submicron particle size distribution from 1 μm to 80 nm. The enabling components are a novel ‘analytical’ (quantified mixing time) confined impinging jets (CIJ) mixer for millisecond stream homogenization and amphiphilic diblock copolymers which alter the organic nucleation and growth, provide steric stabilization for the particles, and offer a functional surface for the particle. Applications in enhanced pharmaceutical delivery, dye preparation, and pesticide formulation are specifically targeted.

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Granados-Muñoz, M. J., F. Navas-Guzmán, J. A. Bravo-Aranda, J. L. Guerrero-Rascado, H. Lyamani, A. Valenzuela, G. Titos, J. Fernández-Gálvez et L. Alados-Arboledas. « Hygroscopic growth of atmospheric aerosol particles based on active remote sensing and radiosounding measurements ». Atmospheric Measurement Techniques Discussions 7, n^o 10 (10 octobre 2014) : 10293–326. http://dx.doi.org/10.5194/amtd-7-10293-2014.

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Abstract. A new methodology based on combining active and passive remote sensing and simultaneous and collocated radiosounding data to study the aerosol hygroscopic growth effects on the particle optical and microphysical properties is presented. The identification of hygroscopic growth situations combines the analysis of multiespectral aerosol particle backscatter coefficient and particle linear depolarization ratio with thermodynamic profiling of the atmospheric column. We analysed the hygroscopic growth effects on aerosol properties, namely the aerosol particle backscatter coefficient and the volume concentration profiles, using data gathered at Granada EARLINET station. Two study cases, corresponding to different aerosol loads and different aerosol types, are used for illustrating the potential of this methodology. Values of the aerosol particle backscatter coefficient enhancement factors range from 2.10 ± 0.06 to 3.90 ± 0.03, being similar to those previously reported in the literature. Differences in the enhancement factor are directly linked to the composition of the atmospheric aerosol. The largest value of the aerosol particle backscatter coefficient enhancement factor corresponds to the presence of sulphate and marine particles that are more affected by hygroscopic growth. On the contrary, the lowest value of the enhancement factor corresponds to an aerosol mixture containing sulphates and slight traces of mineral dust. The Hänel parameterization is applied to these case studies, obtaining results within the range of values reported in previous studies, with values of the γ exponent of 0.56 ± 0.01 (for anthropogenic particles slightly influenced by mineral dust) and 1.07 ± 0.01 (for the situation dominated by anthropogenic particles), showing the convenience of this remote sensing approach for the study of hygroscopic effects of the atmospheric aerosol under ambient unperturbed conditions. For the first time, the retrieval of the volume concentration profiles for these cases using the Lidar Radiometer Inversion Code (LIRIC) allows us to analyse the aerosol hygroscopic growth effects on aerosol volume concentration, observing a stronger increase of the fine mode volume concentration with increasing relative humidity.

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Wang, Wei-Kang, Jie-Jie Chen, Zai-Zhu Lou, Sooyeon Kim, Mamoru Fujitsuka, Han-Qing Yu et Tetsuro Majima. « Single-molecule and -particle probing crystal edge/corner as highly efficient photocatalytic sites on a single TiO2 particle ». Proceedings of the National Academy of Sciences 116, n^o 38 (4 septembre 2019) : 18827–33. http://dx.doi.org/10.1073/pnas.1907122116.

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The exposed active sites of semiconductor catalysts are essential to the photocatalytic energy conversion efficiency. However, it is difficult to directly observe such active sites and understand the photogenerated electron/hole pairs’ dynamics on a single catalyst particle. Here, we applied a quasi-total internal reflection fluorescence microscopy and laser-scanning confocal microscopy to identify the photocatalytic active sites at a single-molecule level and visualized the photogenerated hole–electron pair dynamics on a single TiO2 particle, the most widely used photocatalyst. The experimental results and density functional theory calculations reveal that holes and electrons tend to reach and react at the same surface sites, i.e., crystal edge/corner, within a single anatase TiO2 particle owing to the highly exposed (001) and (101) facets. The observation provides solid proof for the existence of the surface junction “edge or corner” on single TiO2 particles. These findings also offer insights into the nature of the photocatalytic active sites and imply an activity-based strategy for rationally engineering catalysts for improved photocatalysis, which can be also applied for other catalytic materials.

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Bertoluzzo, M. G., S. M. Bertoluzzo, J. A. Luisetti et C. A. Gatti. « A bidimensional simulation of particle-cluster aggregation with variable active sites particles ». Colloid & ; Polymer Science 276, n^o 5 (19 juin 1998) : 443–45. http://dx.doi.org/10.1007/s003960050264.

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Zybert, Magdalena, Aleksandra Tarka, Wojciech Patkowski, Hubert Ronduda, Bogusław Mierzwa, Leszek Kępiński et Wioletta Raróg-Pilecka. « Structure Sensitivity of Ammonia Synthesis on Cobalt : Effect of the Cobalt Particle Size on the Activity of Promoted Cobalt Catalysts Supported on Carbon ». Catalysts 12, n^o 10 (21 octobre 2022) : 1285. http://dx.doi.org/10.3390/catal12101285.

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This work presents a size effect, i.e., catalyst surface activity, as a function of active phase particle size in a cobalt catalyst for ammonia synthesis. A series of cobalt catalysts supported on carbon and doped with barium was prepared, characterized (TEM, XRPD, and H2 chemisorption), and tested in ammonia synthesis (9.0 MPa, 400 °C, H2/N2 = 3, 8.5 mol% of NH3). The active phase particle size was varied from 3 to 45 nm by changing the metal loading in the range of 4.9–67.7 wt%. The dependence of the reaction rate expressed as TOF on the active phase particle size revealed an optimal size of cobalt particles (20–30 nm), ensuring the highest activity of the cobalt catalyst in the ammonia synthesis reaction. This indicated that the ammonia synthesis reaction on cobalt is a structure-sensitive reaction. The observed effect may be attributed to changes in the crystalline structure, i.e., the appearance of the hcp Co phase for the particles with a diameter of 20–30 nm.

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