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A modified phase-field model is presented to numerically study the dynamics of flowing foam in an obstructed channel. The bubbles are described as smooth deformable fields interacting with one another through a repulsive potential. A strength of the model lies in its ability to simulate foams with wide range of gas fraction. The foam motion, composed of about hundred two-dimensional gas elements, was analyzed for gas fractions ranging from 0.4 to 0.99, that is below and beyond the jamming transition. Simulations are preformed near the quasi-static limit, indicating that the bubble rearrangement in the obstructed channel is primarily driven by the soft collisions and not by the hydrodynamics. Foam compression and relaxation upstream and downstream of the obstacle are reproduced and qualitatively match previous experimental and numerical observations. Striking dynamics, such as bubbles being squeezed by their neighbors in negative flow direction, are also revealed at intermediate gas fractions.

Macroscopic nonlinearity and hysteresis observed in the piezoelectric and dielectric responses of ferroelectric materials to external stimuli are commonly attributed to localized displacements of domain walls (DWs). The link between the macroscopic response and microscopic DW dynamics is provided by the well-known Rayleigh relations, extensively used to quantify the electrical and electromechanical behavior of ferroelectric ceramics and thin films under subswitching conditions. In this chapter, I will present an intriguing case where DWs exhibit enhanced electrical conductivity with respect to the bulk conductivity. By combining experimental data and modeling, it will be shown that the local conductivity, related to accumulation of charged points defect at DWs, does not only affect DW dynamics through DW-defect pinning interactions, as we may expect, but goes beyond it by affecting the macroscopic nonlinearity and hysteresis in a more complex manner. The major characteristics and implications of the underlying nonlinear Maxwell-Wagner piezoelectric relaxation, triggered by the presence and dynamics of conducting DWs, will be presented, reviewed and discussed in the framework of systematic multiscale analyses on BiFeO3 ceramics. The result may have implications in the development of promising BiFeO3-based compositions for high-temperature piezoelectric applications.

In this paper, we study the dynamics of a single vortex and a corotating vortex pair in a quasi-two-dimensional Bose–Einstein condensate. The numerical results are obtained by solving the Gross–Pitaevskii equation. It is shown that the vortex motion is strongly dependent on the dipole–dipole interaction (DDI). For a single vortex, the periodic motion occurs with increasing dipole strength. The x-coordinate and y-coordinate as a function of time close to the shape of cosine wave and triangular wave when DDI is an isotropic repulsive interaction, respectively. In addition, it is evident that strong and anisotropic DDI makes the movement of vortex become fast and the amplitude enlarges. In the case of a corotating vortex pair, the dynamics is qualitatively consistent with a single vortex for weak dipole strength. Moreover, the periodic dynamics only appears for strong and anisotropic DDI and more rapid vortex motion is indicated.

A method for designing the key parameters of rotational centrifugal pendulum vibration absorbers is proposed herein. The vibration equations of the pendulum and rotor were established by utilizing Lagrange’s equations. It was found that there were two kinds of rotational centrifugal pendulum vibration absorbers (CPVAs): a linear rotational CPVA and a nonlinear rotational CPVA, which both behaved approximately as linear oscillators. The choice of the linear rotational coefficient and the nonlinear rotational coefficient (only for the nonlinear rotational CPVA) was analyzed, and the selection of the tuning order and trajectories of the centroid of the pendulum was investigated based on tautochronic design theory. In this study, the time variables were transformed to angle variables in the vibration equations. The parameters in the equations were then non-dimensionalized, and the equations were decoupled. Finally, the vibration responses of the pendulum and rotor were solved using the harmonic balance method. The results demonstrated that the linear rotational CPVA designed by utilizing tautochronic theory provided a better damping effect than the nonlinear rotational and non-rotational CPVAs. Furthermore, the linear rotational CPVA could decrease the impact effect on the rotor by adjusting the linear rotational angle and ensure its damping performance.

The structure and magnetization dynamics are investigated in a vortex spin-transfer nanooscillator, which is a three-layer spin-valve magnetic nanocolumn with a large diameter of 400 nm, under flowing spin-polarized current through it. The dynamic variation in the structure of vortices and their trajectory of motion are studied, using micromagnetic modeling, as a function of the value of the spin-polarized current. It is demonstrated that different modes of motion of vortices may exist: decaying oscillations of vortices, stationary oscillations of vortices, and the mode of switching polarity of one of vortices. The time for which different dynamic modes are settled is determined. The dependence of the oscillation frequency on the value of spin-polarized current is determined for the case of stationary dynamics of coupled vortices. It is shown that, at large values of current, switching of vortex polarity is only possible in a thick layer with the dynamic switching mechanism accompanied by generation of a vortex–antivortex pair. The software package for micromagnetic simulation, SpinPM, is used for numerical calculations of the dynamics of magnetic vortices.

An understanding of nucleation, growth and coalescence of voids is required to predict the spall fracture. We employ molecular dynamics simulations to investigate the effect of temperature on the n...

We employ molecular dynamics simulations to investigate the evolution dynamics of {101¯2} twinning in single-crystal Ti under shock loading. The shock compression applied perpendicular to the c-axi...

The investigation of planetary gear dynamics including dynamic modeling and dynamic response analysis is a crucial approach in vibration reduction of industrial power transmission systems. In this paper, the nonlinear, time-varying dynamic model of a spur planetary gear system under consideration of the translational and rotational motions is investigated. The three subsystems for sun-planet, ring-planet and planet-carrier are analyzed subsequently, and the dynamic equations of the system are obtained. Moreover, different planet phasing and spacing configurations can be described by means of this model. In addition, the dynamic response is investigated by the multiple-scale method. First, the analytical solutions of the primary, superharmonic and subharmonic resonances are obtained. Then the frequency amplitude curves of different resonance modes are compared and the influence of some parameters on the vibration amplitude is studied. Meanwhile, the accuracy of the analytical solutions is evaluated by the numerical integration simulations. The results show that the frequency-amplitude curves of the primary and superharmonic resonance are similar in shape, the three solutions coexist, and the types of unstable solutions and stable solutions are identical. Furthermore, the softening nonlinearity of the subharmonic amplitude-frequency curve is more obvious under the three-dimensional model. This research is an important development of three-dimensional dynamic modeling and vibration prediction of planetary gears, and also improves the efficiency and accuracy of dynamic response calculation.

This study is concerned with modelling and analyses of a vibro-impact system consisting of a crank-slider mechanism and one oscillator attached to it, where the system is exposed to a non-ideal excitation. The impact occurs during the motion of the oscillator when it fits a base, and the excitation of the driving source is affected by this behaviour. The aim is to determine the interaction between a driving torque and the motion of the oscillator. To achieve this aim in a methodologically sound manner, both vibrating and vibro-impact systems with an ideal and non-ideal excitation are analysed. Analytical and numerical solutions are obtained for the vibrating system with the ideal excitation. Numerical analyses of the vibrating system with the non-ideal excitation is then conducted, where the characteristic curves for this system are found analytically. Numerical simulations are also carried out for other two systems and the results obtained are shown in terms of frequency–response diagrams, time-displacement diagrams and basins of attraction. The results found for different systems are compared mutually, and the differences between them are pointed out. Impact solutions for different regions of the excitation frequency are shown. For the vibro-impact system with the non-ideal excitation, the average value of its frequency is used.

Lab-on-a-chip devices based on inertial microfluidics have emerged as a promising technique to manipulate particles in a precise way. Inertial microfluidics exploits internal hydrodynamic forces and the mechanical structure of particles to achieve separation and focusing. The article focuses on the hydrodynamic interaction of two particles. This will help to develop an understanding of the dynamics of particle trains in inertial microfluidics, which are typical structures in multi-particle systems. We perform three-dimensional lattice Boltzmann simulations combined with the immersed boundary method to unravel the dynamics of various mono- and bi-dispersed pairs in inertial microfluidics. We study the influence of different starting positions for mono- and bi-dispersed pairs. We also change their deformability from relatively soft to rigid and choose spherical and biconcave particle shapes. The observed two-particle motions in the present work can be categorized into four types: stable pair, stable pair with damped oscillations, stable pair with bounded oscillations, and unstable pair. We show that stable pairs become unstable when increasing the particle stiffness. Furthermore, a pair with both capsules in the same channel half is more prone to become unstable than a pair with capsules in opposite channel halves.

A high-temperature superconducting (HTS) magnetic levitation (maglev), based on YBaCuO bulk superconductors and permanent magnet guideways, shows the potential to be applied in the future rail transportation. The maglev forces (levitation and guidance force) of the HTS maglev system, which bond the vehicle and the guideway, are the key factors of its dynamics studies. In practical operation, the HTS maglev vehicle moves in both the vertical and lateral directions, but the previous force models are in single degree of freedom. In this article, an experiment was designed to study the vertical–lateral coupled effect of the levitation and guidance force. A 2-D coupling model was proposed to fit the experimental data. Furthermore, the motion stability and the dynamical characteristics of the HTS maglev system in 2-D space were studied. The simulation results show that the vertical–lateral coupling effect in maglev forces cannot be neglected, and one direction motion can affect the motion in the other direction. It also shows that the proposed force model is suitable for HTS maglev dynamics’ calculations.

We employ molecular dynamics simulations to investigate the role of temperature on the evolution dynamics of the voids in single crystal iron. We simulate isotropic tension in single crystal iron a...

The dynamics of ferroelectrics domain walls is modeled by the equation of a particle in a force field. It is considered that over the domain walls act the forces due to the interaction with an exte...

The dynamical evolution of smectic-C liquid crystals in the presence of a magnetic field is studied. The theoretical analysis is based on dynamic renormalisation group techniques. The starting poin...

We present a picture of flux-driven ITG turbulence and associated transport with heat source and sink which reveals resilience and stiffness coupled with SOC type intermittent bursts. The transport...

A detailed analysis of solutions to the Landau–Lifshitz equation describing solitons in a physically selected domain structure of a biaxial ferromagnet is presented. The structure and properties of new types of solitons that are strongly bound to the domain structure are investigated. Soliton behavior near the boundaries of their region of existence is considered. A comparative analysis of soliton cores in the domain structures of easy-axis and biaxial ferromagnets is performed, and their connection with solitons against a uniformly magnetized background is established.

Based on an algebraic model of Reynolds stresses and fluxes, a numerical model of the dynamics of a flat localized region of turbulent perturbations of non-zero buoyancy in a linearly stratified medium was constructed. The evolution of a weakly heated turbulent spot was considered. Presence of non-zero buoyancy leads to increase in the geometrical dimensions of the turbulent spot and generation of internal waves of greater amplitude.

The paper presents results of an experimental study of the effect of pin microstructures on the wetting front propagation and its structure under adiabatic conditions and on strongly pre-heated surfaces, as well as the heat transfer and critical heat fluxes under steady-state heat release with liquid nitrogen film flowing. The surface structuring was created by the deformational cutting method (DCM). Comparison with data obtained on a smooth heater is presented. It is shown that the microstructures created by the DCM may have a significant effect on the nature of the temperature curves, reducing the total time of plate cooling at rewetting up to 2 times, and significantly change the structure and dynamics of the wetting front under adiabatic conditions. At the same time, such microstructuring with preset parameters of microfinning has weak influence on the heat transfer under steady-state heat release. High-speed video data of the processes are presented.

To ascertain the effect of transverse dissipative particle dynamics (DPD), which includes lateral dissipative forces in addition to the central ones in the standard DPD, on dynamics of systems involving interfaces, we compare dynamic properties derived from coarse-grained (CG) molecular dynamics simulations with the standard and transverse DPD for nanometer-thick liquid films on solid surfaces. The dynamic properties include relaxation times of the film thickness distribution and molecular rotational motion, and transport properties associated with molecular translational motion. Our results show that these dynamic properties are tuneable by changing friction coefficients in the transverse DPD, whereas this is not the case in the standard DPD. We also confirm that the transverse DPD applied to liquid–solid CG bead pairs can tune dynamic properties of nanometer-thick liquid films on solid surfaces, though it is less effective than when applied to liquid–liquid CG bead pairs. Moreover, we reveal that the dissipative forces are isotropic in transverse DPD, whereas the liquid–solid dissipative forces are highly anisotropic and nearly along the direction perpendicular to solid surfaces in standard DPD. This suggests that the transverse liquid–solid DPD might be crucial for modelling the in-plane energy dissipation at liquid–solid interfaces., ファイル公開：2021/09/16

The shaft and pedestal deformations can produce large misalignments and displacements of shaft-bearing-pedestal systems (SBPSs). The phenomena have a great influence on the working performances of the SBPS. Thus, the shaft and pedestal stiffness should be properly optimized to minimize the system vibrations during the design process of the SBPSs. To overcome this issue, a new shaft and pedestal stiffness optimization strategy of a SBPS based on both the time- and frequency-domain vibrations is conducted in this work, which cannot be addressed by the previous methods considering single shaft or pedestal stiffness. Moreover, this method can be used to avoid the unexpected resonance frequencies of the rotor system during the design processing. A dynamic model of the SBPS considering both the flexible deformations of shaft and pedestal is presented. The effects of the shaft and pedestal stiffness on the vibration performances of the SBPS are discussed. The results give that the shaft and pedestal stiffness have a great effect on the time-domain waveform, magnitude, and peak frequencies of the vibrations of the SBPS. The relationships between the peak frequencies in the spectra of SBPS and two stiffness coefficients are nonlinear ones. However, they have no effect on the bearing passing frequency and its harmonics in the envelop spectra. It represents that the SBPS with the larger shaft and pedestal stiffness has a smaller vibration level. The obtained results can provide some guidance for the SBPS design with a low vibration level.

Relaxation dynamics of unentangled polymer melts (with a chain length below N = 100 for polyethylene) can be studied by performing either Rouse mode or relaxation mode analysis, such as proper orth...

The change in the carrier mobility in GaAs structures after irradiation is numerically simulated. For each investigated scattering potential, the model parameters are determined at which the calculation data are consistent with the results of the experiment. It is shown for the first time that the form of the potential of scattering at radiation-induced defects determines the time and space dynamics of the velocity overshoot in short structures.

Results of experimental investigation of the floating-up of a cluster of air bubbles in a viscous fluid by an optical method are presented. A setup has been developed for formation of a compact cluster of monodisperse bubbles with assigned diameter and volume concentration. It is shown that the velocity of the floating-up of a cluster of bubbles is higher than the velocity of the floating-up of a single bubble and depends on their number, diameter, and the distance between the bubbles. An empirical dependence of the resistance coefficient of a cluster of air bubbles floating up in glycerin on the Reynolds number has been obtained.

Scripta materialia 186, 268 - 271 (2020). doi:10.1016/j.scriptamat.2020.05.002, We reveal a slow-to-fast dynamics transition in the as-cast Cu$_{46}$Zr$_{46}$Al$_8$ (at.%) metallic glass (MG) at a temperature below the glass transition upon heating, which depends on the competition between free volume annihilation and thermally-activated atomic mobility, well consistent with the bond-length change of Cu-Cu pairs. The activation of $��$-relaxation at high temperatures could be related to the bond-length extension of Cu-Cu and Zr-Zr like-atom pairs together with the shortening of Cu-Zr unlike-atom pairs. Our results provide new insights into the correlation of dynamics with atomic structure in MGs and will be helpful to the understanding of ageing behaviors in MGs., Published by Elsevier Science, Amsterdam [u.a.]

The equations governing the dynamics of a periodically driven micro-spheroid in an unsteady viscous fluid at low Reynolds number are derived. Its oscillation properties in the presence/absence of memory forces are reported. The core part of the derivation is a perturbation analysis of motion of a sphere. The calculated solutions match with those available in the literature in the limiting case of a sphere. The dependence of the solutions on shape ( $$\alpha $$ ), free oscillation frequency ( $$\omega _0$$ ) and particle–fluid density ratio ( $$d_r$$ ) is calculated. The maximum amplitude of the oscillations of an oblate spheroid is greater than that of a prolate spheroid, showing that the velocity disturbance for an oblate spheroid is higher in the presence/absence of the memory force. The increase in $$\alpha $$ leads to the enhancement(reduction) of amplitude peaks in the case of the oblate (prolate) spheroid in the presence and more dominantly in the absence of the force. There is also a reduction in the amplitude of spheroid oscillations of many multiples due to the presence of the memory force. Stronger oscillation variations are observed on changing $$\omega _0$$ or $$d_r$$ compared to $$\alpha .$$ The variations of the value of the phase are similar for both the spheroids on varying $$\omega _0$$ and $$d_r$$ , whereas they are reversed on varying $$\alpha .$$ The linear scaling of amplitude on $$\alpha $$ observed for the spheroids may give insight into the physics, especially regarding the quantum of velocity disturbances due to particle size. The slopes are high in the absence of the force, confirming that the presence of the force increases the resistance of spheroid motion, largely. The dependencies of oscillations on the parameters can be utilized for better separation of particles or for characterizing the suspension. The novelty of the problem and its analytical solutions might have value as tests in software for more complicated and realistic systems and hence strikes a good balance between complication and tractability.

On the basis of the quantum model taking into account the Zeeman energy and the energy of the crystal field, dynamic equations of Landau — Lifshitz — Hilbert type for the magnetization of the deformed singledomain α-Fe crystal are obtained. The domain deformation is taken into account in the framework of a linear approximation. The equations of motion are solved numerically using the Adams — Multon, Rosenbrock, and RADAU5 methods. It is shown that for some values of the model parameters, the dependence of the magnetization on the strength of an external magnetic field has the characteristic form of a hysteresis loop. Qualitative agreement of the model dependence of the coercive force on the applied longitudinal pressure with similar experimental data for various steel grades Durehete 1055, AS1548746OR, X70, 11HN3D is obtained.

Magnetic skyrmions are topological magnetic spin structures exhibiting particle-like behaviour. They are of strong interest from a fundamental viewpoint and for application, where they have potential to act as information carriers in future low-power computing technologies. Importantly, skyrmions have high physical stability because of topological protection. However, they have potential to deform according to their local energy environment. Here we demonstrate that, in regions of high exchange energy density, skyrmions may exhibit such extreme deformation that spontaneous merging with nearest neighbours or spawning new skyrmions is favoured to attain a lower energy state. Using transmission electron microscopy and a high-speed imaging detector, we observe dynamics involving distinct configurational states, in which transitions are accompanied by spontaneous creation or annihilation of skyrmions. These observations raise important questions regarding the limits of skyrmion stability and topological charge conservation, while also suggesting a means of control of skyrmion creation and annihilation., 19 pages total. 4 figures at the end of the main text, supplementary material follows

A hydrodynamic model of motion of compressible liquid in a complex profile pipeline has been built and the resulting coupled equations have been solved. The dynamics of the liquid flow rate was determined in dependence on parameters of the system and inlet and outlet pressure variation.

In order to enhance sampling efficiency and security when robot maintains power transmission line (PTL), this article develops a new approach for the rigid-flexible coupling dynamics of robot/PTL system, which decouples the large system into two small systems and solves them separately by estimating the contact force. The robot is modelled as a system of rigid bodies by screw theory, while the PTL system is modelled using absolute node coordinate formulation (ANCF). The integration of screw theory, ANCF and contact estimator trained by artificial neural network has not been accomplished before in the literature. The main contribution of this paper is to achieve this integration with the goal of developing a new and general approach for the nonlinear dynamic analysis of the interaction of the rigid maintenance robot with flexible PTL cable. A simplified two-dimensional example is used to compute the effect of the robot/PTL interaction under different operating conditions to have an understanding of the coupling approach between the two systems. A more detailed three-dimensional model was developed, and the results obtained validate the utility and effectiveness of our approach.

The paper presents the investigation results of a metal plate re-melting process by a fiber laser beam using a high-speed video camera. The obtained video materials allow observing the transition process of molten metal to a solid state. The dependence of the molten metal transition to the solid state on the laser welding speed and on the focal distance (in the range of ± 20 mm) is analyzed. A quantitative analysis of the geometric dimensions of the microstructural components of the re-melted metal was carried out. When comparing the processed video material and microstructure elements of the molten pool, the similar trends are observed depending on the re-melting speed by a laser beam in a certain range of speeds from 20 to 45 mm/s. The obtained results can be used to develop a technique for estimating the presence of a key-hole depending on the laser focal distance.

The problem of harmonic oscillations in electro-electromagnetic composites is studied. Oscillations can be initiated by the extended load vector, including the horizontal and vertical components of mechanical displacements, and electrical induction distributed on top of the surface. Boundary conditions assume full mechanical coupling for all layers of the structure. Electrical conditions on the surface top can be both electrically open, and electrically shorted. Magnetic conditions are similar to electric ones and describe the continuity of fields in between two mediums, or indicate the isolation of the magnetic field between them. The Green's function of electro–magneto–elastic medium is constructed. Phase velocities are obtained for various geometric proportions and materials.

We perform molecular dynamics simulations to investigate the void evolution dynamics in single-crystal iron deformed under uniaxial, biaxial and triaxial loading conditions. We find that the void d...

Effect of precipitation strengthening on metal is generally attributed to the dislocation interaction with the precipitate which acts as the barrier to the dislocation motion on the slip plane. In order to achieve better understanding of critical events of dislocation motion and evolution of dislocation microstructure, we have developed numerical simulation method of dislocation-dislocation and dislocation-particle interactions by means of discrete dislocation dynamics at mesoscopic scale. In this work, Green’s function method is utilized for the computation of the stress fields of dislocation and misfitting particle, and the interaction forces acting on the dislocation. We also proposed the efficient algorithm of the connectivity vector for the dislocation line elements, linked-list data structure, to deal with the flexible interaction of dislocation line elements. The geometrical effect of dislocation slip planes on the dislocation bypassing behaviors is tested by changing the relative height of dislocation slip plane against the center plane of spherical particle, where cross slip event is also taken into account for the dislocation motion. Simulation results show a wide variety of topological changes of dislocation during motion on the slip planes around the particle, which results from the stress field of the particle varied with the relative height between the dislocation slip plane and center plane of particle. The full analysis of the mechanisms of dislocation line bypassing misfitting particle has been explained in this study.

The structural dynamics depend on a series of factors that revolves around the chemical stability of the compound. In superconductivity, surface deformation occurs due to chemical instabilities and continuous magnetic or thermal excitations. In this research, a new cuprates compound was proposed. The microstructural and ion bombardment analysis were used extensively to investigate the structural faults in the material. It was discovered that the material had electron and phonon ratio of 6:1. This result denotes the predictability of its lattice system. More so, there is the possibility of knowing its electronic mechanism and structural variation.

There are two types of pop-in mode that have been widely observed in nanoindentation experiments: the single pop-in, and the successive pop-in modes. Here we employ the molecular dynamics (MD) mode...

A coupled nonlinear nonlocal strain gradient theory (NSGT) is developed for functionally graded Timoshenko nanoscale (FGTN) beams. This highly nonlinear-scale-dependent continuum model is solved numerically for dynamical responses for the first time. Hamilton’s energy minimisation technique is used for rotation-equation of the nanobeam in addition to axial-displacement and transverse-displacement equations; these equations are coupled both nonlinearly and linearly, where decoupling is not possible. The functional nature of the material of the nanobeam is incorporated via the Mori–Tanaka mixture scheme. Small-scale influences are taken into account via the NSGT which is able to incorporate both softening/hardening effects. The coupled/nonlinear model is reduced to a high-dimensional system using Galerkin’s method. The dynamics of the FGTN beam is analysed and the influence of functionally graded nature as well as the softening/hardening effects due to the NSGT is highlighted.

We investigate the transport of excitons and trions in monolayer semiconductor WS$_2$ subjected to controlled non-uniform mechanical strain. We actively control and tune the strain profiles with an AFM-based setup in which the monolayer is indented by an AFM tip. Optical spectroscopy is used to reveal the dynamics of the excited carriers. The non-uniform strain configuration locally changes the valence and conduction bands of WS$_2$, giving rise to effective forces attracting excitons and trions towards the point of maximum strain underneath the AFM tip. We observe large changes in the photoluminescence spectra of WS$_2$ under strain, which we interpret using a drift-diffusion model. We show that the transport of neutral excitons, a process that was previously thought to be efficient in non-uniformly strained 2D semiconductors and termed as "funneling", is negligible at room temperature in contrast to previous observations. Conversely, we discover that redistribution of free carriers under non-uniform strain profiles leads to highly efficient conversion of excitons to trions. Conversion efficiency reaches $\simeq 100\%$ even without electrical gating. Our results explain inconsistencies in previous experiments and pave the way towards new types of optoelectronic devices., 6 pages, 4 figures

Microswimmers such as E. coli bacteria accumulate and exhibit an intriguing dynamics near walls, governed by hydrodynamic and steric interactions. Insight into the underlying mechanisms and predominant interactions demand a detailed characterization of the entrapment process. We employ a mesoscale hydrodynamics simulation approach to study entrapment of an E. coli-type cell at a no-slip wall. The cell is modeled by a spherocylindrical body with several explicit helical flagella. Three stages of the entrapment process can be distinguished: the approaching regime, where a cell swims toward a wall on a nearly straight trajectory; a scattering regime, where the cell touches the wall and reorients; and a surface-swimming regime. Our simulations show that steric interactions may dominate the entrapment process, yet, hydrodynamic interactions slow down the adsorption dynamics close to the boundary and imply a circular motion on the wall. The locomotion of the cell is characterized by a strong wobbling dynamics, with cells preferentially pointing toward the wall during surface swimming.

The dynamics of passive micro-objects in an active bath has been receiving much attention. However, the influence of the shapes of micro-objects remains unclear. Here, we use 2D simulation to investigate the interaction between active Brownian particles and different-shaped passive micro-objects. We show that active particles accumulate around micro-objects and self-assemble into living aggregations at a high active velocity and high volume fraction. The shapes of micro-objects affect the distributions of the aggregations. In turn, the different distribution of aggregations influences the motion of micro-objects and induces abnormal diffusive behaviors. We further demonstrate that polar distributed aggregations at a high active velocity and the inhibition of the active bath at a low active velocity induce the counterintuitive anisotropic enhanced diffusion of rods, and the steric interaction between active particles induces the reverse translation-rotation coupled diffusion of chevrons.

We study the single-file dynamics of three classes of active particles: run-and-tumble particles, active Brownian particles and active Ornstein-Uhlenbeck particles. At high activity values, the particles, interacting via purely repulsive and short-ranged forces, aggregate into several motile and dynamical clusters of comparable size, and do not display bulk phase-segregation. In this dynamical steady-state, we find that the cluster size distribution of these aggregates is a scaled function of the density and activity parameters across the three models of active particles with the same scaling function. The velocity distribution of these motile clusters is non-Gaussian. We show that the effective dynamics of these clusters can explain the observed emergent scaling of the mean-squared displacement of tagged particles for all the three models with identical scaling exponents and functions. Concomitant with the clustering seen at high activities, we observe that the static density correlation function displays rich structures, including multiple peaks that are reminiscent of particle clustering induced by effective attractive interactions, while the dynamical variant shows non-diffusive scaling. Our study reveals a universal scaling behavior in the single-file dynamics of interacting active particles., Accepted for publication in Soft Matter

Tissues transition between solid-like and fluid-like behavior, which has major implications for morphogenesis and disease. These transitions can occur due to changes in the intrinsic shape of constituent cells and cell motility. We consider an alternative mechanism by studying tissues that explore the energy landscape through stochastic dynamics, driven by turnover of junctional molecular motors. To identify the solid-fluid transition, we start with single-component tissues and show that the mean cell-shape index uniquely describes the effective diffusion coefficient of cell movements, which becomes finite at the transition. We generalize our approach to two-component tissues, and explore cell-sorting dynamics both due to differential adhesion and due to differential degree of junctional fluctuations. We recover some known characteristic scaling relations describing the sorting kinetics, and discover some discrepancies from these relations in the case of differential-fluctuations-driven sorting. Finally, we show that differential fluctuations efficiently sort two solid-like tissues with a fluid intercompartmental boundary.

We demonstrate the emergence of circular collective motion in a system of spherical light-propelled Brownian particles. Light-propulsion occurs as consequence of the coupling between the chirality of polymeric particles - left (L)- or right (R)-type - and the circularly-polarized light that irradiates them. Irradiation with light that has the same helicity as the particle material leads to a circular cooperative vortical motion between the chiral Brownian particles. In contrast, opposite circular-polarization does not induce such coupling among the particles but only affects their Brownian motion. The mean angular momentum of each particle has a value and sign that distinguishes between chiral activity dynamics and typical Brownian motion. These outcomes have relevant implications for chiral separation technologies and provide new strategies for optical torque tunability in mesoscopic optical array systems, micro- and nanofabrication of light-activated engines with selective control and collective motion.

We study the dynamics of a polymer, described as a variant of a Rouse chain, driven by an active terminal monomer (head). The local active force induces a transition from a globule-like to an elongated state, as revealed by the study of the end-to-end distance, the variance of which is analytically predicted under suitable approximations. The change in the relaxation times of the Rouse-modes produced by the local self-propulsion is consistent with the transition from globule to elongated conformations. Moreover, also the bond-bond spatial correlation for the chain head are affected by the self-propulsion and a gradient of over-stretched bonds along the chain is observed. We compare our numerical results both with the phenomenological stiff-polymer theory and several analytical predictions in the Rouse-chain approximation.

A 3-D simulation of red blood cells (RBCs) described as deformable cells in plasma flow is an indispensable element of blood flow analysis in the human vessels. To numerically investigate RBC motio...

The dynamics and wall collision of inertial particles were investigated in non-isotropic turbulence of a horizontal liquid channel flow. The inertial particles were $125~\unicode[STIX]{x03BC}\text{m}$ glass beads at a volumetric concentration of 0.03 %. The bead-laden flow and the unladen base case had the same volumetric flow rates, with a shear Reynolds number, $Re_{\unicode[STIX]{x1D70F}}$, of the unladen flow equal to 410 based on the half-channel height and friction velocity. Lagrangian measurements of three-dimensional trajectories of both fluid tracers and glass beads were obtained using time-resolved particle tracking velocimetry based on the shake-the-box algorithm of Schanz et al. (Exp. Fluids, vol. 57, no. 5, 2016, pp. 1–27). The analysis showed that on average the near-wall glass beads decelerate in the streamwise direction, while farther away from the wall, the streamwise acceleration of the glass beads became positive. The ejection motions provided a local maximum streamwise acceleration above the buffer layer by transporting glass beads to high velocity layers and exposing them to a high drag force in the streamwise direction. Conversely, the sweep motion made the maximum contribution to the average streamwise deceleration of glass beads in the near-wall region. The wall-normal acceleration of the beads was positive in the vicinity of the wall, and it became negative farther from the wall. The investigation showed that the glass beads with sweeping motion had the maximum momentum, streamwise deceleration, and wall-normal acceleration among all the beads close to the wall and these values increased with increasing their trajectory angle. The investigation of the beads that collided with the wall showed that those with shallow impact angles (less than $1.5^{\circ }$) typically slide along the wall. The sliding beads had a small streamwise momentum exchange of ${\sim}5\,\%$ during these events. The duration of their sliding motion could be as much as five times the inner time scale of the unladen flow. The wall-normal velocity of these beads after sliding was greater than their wall-normal velocity before sliding, and was associated with the rotation induced lift force. Beads with impact angles greater than $1.5^{\circ }$ had shorter interaction times with the wall and smaller streamwise and wall-normal restitution ratios.

The mean dynamics in oscillatory channel flow is examined to investigate the dynamical mechanisms underlying the transition to turbulence in oscillatory wall-bounded flow. The analyses employ direct numerical simulation data acquired at three Stokes Reynolds numbers: $Re_{s}=648$, 801 and 1009, where the lower $Re_{s}$ flow is transitional over the entire cycle and the two higher $Re_{s}$ flows exhibit flow characteristics similar to steady turbulent wall-bounded flow during part of the cycle. The flow evolution over a half-period of oscillation for all three $Re_{s}$ is as follows: near-wall streamwise velocity streaks develop during the early accelerating portion of the cycle; then at some later point in the cycle that depends on $Re_{s}$, the near-wall streaks breakdown (demarking the onset of the nonlinear development stage), and the near-wall Reynolds stress grows explosively; the Reynolds stress remains elevated for part of the cycle before diminishing (yet remaining finite) during the late decelerating portion of the cycle. This process is then repeated indefinitely. The present findings demonstrate that transition to turbulence occurs when the nonlinear development stage begins during the accelerating portion of the cycle. This crucially leads to the diminishing importance of the centreline momentum source, the emergence of a locally accelerating/decelerating internal layer centred about the edge of the Stokes layer and the wall-normal rearrangement of the mean forces prior to the start of the decelerating portion of the cycle. The rearrangement of mean forces culminates in a four layer structure in the mean balance of forces. This is significant on a number of accounts since empirical and theoretical evidence suggests that the formation of a four layer structure is an important characteristic of a self-similar hierarchal structure that underlies logarithmic dependence of the mean velocity profile in steady turbulent wall-bounded flows (Klewicki et al., J. Fluid Mech., vol. 638, 2009, pp. 73–93). When the nonlinear development stage begins during the decelerating portion of the cycle (i.e. at $Re_{s}=648$), a four layer structure is not observed in the mean balance of forces and the flow remains weakly transitional over the entire cycle.

This work studies temperature dependent dynamics hysteresis scaling of Ba0.85Ca0.15Ti0.9–xSnxZr0.10O3 (BCT-BZT-Sn) bulk ferroelectric ceramics. The scaling relation are derived for coercive...

A set of ordinary differential equations governing the migration of an arbitrary forced spheroid in a quiescent flow at low Reynolds number is formulated and discussed, assuming a sufficiently diluted suspension to neglect the particle-particle interactions. The equations are non-linear and contain a history term of all the past position and velocity and hence impossible to solve symbolically. The spheroid transport is numerically investigated by varying Reynolds numbers, particle aspect ratios, and external forces. Interestingly, the size of the attractor increases as aspect ratio or/and force increases, whereas it decreases as Reynolds number increases. This decrement is due to the increase in the particle inertia. A delay with the velocity at maximum position is observed as evident from the respective time series. The reason for the delay could be the fact that in the absence of inertia, the time at which the velocity reaches its maximum, the position is at its minimum and when the particle experiences its maximum deviation, the velocity is at its minimum. Since position variation is almost sinusoidal, the velocity will also be sinusoidal with a phase shift of nearly π/2. The net migration at zero Reynolds number will be negligible and should increase with the number increases. Inertia should change this to a larger extent at higher values of Reynolds number. The dependence of the position and velocity on the parameters can be characterized for making use it as a potential application to particle separation.

HIV-1 infection is a major threat in the world and has drawn much attention. The emergence of drug-resistance to most of the HIV-1 inhibitors has led to the crucial call for new inhibitors that can...

The influence of sliding speed in the nanoscale friction forces between a silicon tip and monolayer and multilayer graphene were investigated with the use of an atomic force microscope. We found that the friction forces increase linearly with the logarithm of the sliding speed in a highly layer-dependent way. The increase in friction forces with velocity is amplified at the monolayer. The amplification of the friction forces with velocity results from the introduction of additional corrugation in the interaction potential driven by the tip movement. This effect can be interpreted as a manifestation of local thermally induced surface corrugations in nanoscale influencing the hopping dynamics of the atoms at the contact. These experimental observations were explained by modeling the friction forces with the thermally activated Prandtl-Tomlinson model. The model allowed determination of the interaction potential between tip and graphene, critical forces, and attempt frequencies of slip events. The latter was observed to be dominated by the effective contact stiffness and independent of the number of layers.