Search

Dynamic variables of drop impact such as force, drag, pressure, and stress distributions are key to understanding a wide range of natural and industrial processes. While the study of drop impact kinematics has been in constant progress for decades thanks to high-speed photography and computational fluid dynamics, research on drop impact dynamics has only peaked in the last 10 years. Here, we review how recent coordinated efforts of experiments, simulations, and theories have led to new insights on drop impact dynamics. Particularly, we consider the temporal evolution of the impact force in the early- and late-impact regimes, as well as spatiotemporal features of the pressure and shear-stress distributions on solid surfaces. We also discuss other factors, including the presence of water layers, air cushioning, and nonspherical drop geometry, and briefly review granular impact cratering by liquid drops as an example demonstrating the distinct consequences of the stress distributions of drop impact.

In conventional Finite Element – Lagrangian methods, the dynamics model of a flexible robot is usually formulated based on a critical assumption that the kinetic energy of an element is approximately calculated with an integral of mass point energy. Since the energy integral is implicit, the formulation of the dynamics model is also very complex and implicit. Hence, this paper develops a new mathematical approach for the dynamic modelling of a general flexible/rigid robot. The proposed method is more comprehensive and efficient in comparison with the previous ones because it no longer requires the calculation of the symbolic integrals and the implicit expressions of the elemental and global mass matrices. Besides, the proposed approach is applicable for both the flexible robots and the hybrid flexible/rigid robots. To validate the proposed method, numerical simulations and experimental results are presented.

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.

A Free Energy Lattice Boltzmann Method has been developed to characterize dominant forces and regimes involved in the capillary rise imbibition process. The comparison of the capillary rise behavior at the initial stages, reveals significant differences between numerical and theoretical models. This is attributed to the simplifying assumptions, ignoring the entrance region, dynamic contact angle, and inertial term in the theoretical model. By relaxing these assumptions in numerical formulations, the proposed model prevails the theoretical model limitations and shows closer results to the experimental records. However, as the capillary tube size decreases, the capillary force overcomes the inertia and the theoretical and numerical curves converge. Comparing the numerical curves and the experimental results indicates that the dynamics of the capillary ascent predicted by the present model is similar to the dry tube data. It should be mentioned that the inertial regime, the viscous regime, and the gravity-viscous regime can be considered as the successive regimes involved. Further investigations reveal a transition regime at the beginning of the process, which appears due to singular pressure loss. Therefore, the capillary rise phenomenon develops during these regimes as h ~ t2, h ~ t, h ~ t1/2 and relaxing to a constant value, respectively. Finally, for better understanding of the phenomenon, sensitivity analysis on the dominant forces has been performed.

Controlling the drop impact behaviors plays an important role in both designing surface functional materials and improving industrial techniques. Here, the impact dynamics of nanodroplets on "V-shaped" substrates is studied, which is manifested as asymmetrical spreading and retraction behaviors that could be weakened by increasing the angles of the "V" shape, accompanied by the evolution of the shape from leaf-like, stripe-like, to dumbbell-like at v = 20 A/ps. When v increases to 40 A/ps, the previously deposited nanodroplets could be transformed to a rebound one at α = 60 and 90°, which is ascribed to the combined effect of the confinement conditions and the extrusion force. Furthermore, an impact behavior map as a function of impact velocity and angle is depicted, which suggests that a decrease in angles or an increase in the impact velocity is likely to cause the nanodroplets to rebound. More importantly, the results give visible evidence that compared to the flat substrates, the V-shaped structure is advantageous for achieving a fast-rebound behavior even at a low speed of impact, which should be good news for practical applications in many multidisciplinary fields, such as self-cleaning, anti-icing/fogging, pollution prevention, energy storage, and so forth.

In this study, a new controller to prevent the yaw instability and rollover of a three-wheeled vehicle has been proposed. This controller offers the most obvious opportunity for affecting the vehicle's lateral dynamics performance on the full range of nonlinearities during various operating boundaries. The active combined controller has been designed based on sliding mode control method using an active roll system and an active braking system to dominate the uncertainties of the nonlinear dynamic model. Firstly, to avoid rollover of the three-wheeled vehicle, the roll angle was considered as the control objective, and the anti-roll bar was employed as an actuator to produce the roll moment. Secondly, to increase the maneuverability and lateral dynamics enhancement, an active braking system was designed. In the control system, the yaw rate and the lateral velocity were regarded as the control variables to track their references. Moreover, to verify the performance of the mentioned combined controller, another control system has been designed using the linearization feedback control method. Then, computer simulation has been carried out with a 12 degrees of freedom dynamic model of the three-wheeled vehicle called the delta. Furthermore, a nonlinear tire model has been utilized to compute the longitudinal and the lateral forces. Next, the comparative simulation results confirmed the effectiveness of the robust control system to raise the vehicle's maneuverability and its rollover stability in comparison with the linearization feedback control method, especially when the three-wheeled vehicle is subjected to critical conditions.

In the paper, a combined model of traction and ball bearings dynamics is established, considering the interaction among the cage, races, and balls. A curve-fitted traction model, which can be used to analyze the effect of the geometry of the bearing and parameters of the lubricant, is applied. The traction that is affected by certain parameters is analyzed; then, the effect of the traction on ball bearings is investigated. The displacements of balls and contact angles are different under different surface roughness. The changes in displacements of balls and contact angles are obtained with different roughness, load, and velocities. The amplitudes of axial displacement of balls are bigger with the roughness being higher. The amplitudes of ball-inner contact angles increase with greater roughness, and the amplitudes of ball-outer race contact angles decrease with greater roughness. The simulated vibration results of ball bearings under different levels agree with the actual by the model.

In this paper, we study the geometric quantum discord dynamics of the double quantum dot charge qubit in the non-Markovian environment. We apply the non-perturbative non-Markovian quantum state diffusion method to obtain the exact master equation of the double quantum dot system coupled to two independent non-zero temperature electronic baths. Then, we use this master equation to investigate the effects of non-Markovianity, inter-dot coupling strength and bath temperature on the dynamics of geometric quantum discord. Our studies show that the geometric quantum discord of a double quantum dot system can be modified and enhanced in some cases via these factors.

The dynamics of water droplets on fiber layers are investigated by fiber-scale simulation using volume of fluid (VOF) method. The effects of fiber spaces, contact angles at fibers and numbers of layers on droplet dynamics are investigated. Force analysis for the pinned and moving droplets on fiber layers shows that the resistant forces from the wetted fibers at the edge positions rather than middle positions are the dominant force to control the droplet mobility. Force analysis for droplets on the dual-layers fiber layer are also conducted. The results show that the second layer contributes little to hinder the droplet directly due to the insignificant resistant force they provided. However, the second fiber layer enhances the total resistant force from the first layer. Furthermore a simplified model is used to compare with the fiber model. The results indicate that the simplified model can also be used to predict the droplet mobility once the contact angle is given.

In the second part of this series, we propose a physics-based model for describing the temperature dependence of TiO x -based memristors, both switching and static. We show that the current–voltage ( ${I}$ – ${V}$ ) characteristics of memristor in the nonswitching regime, indicating a Schottky emission mechanism, can be described by minor modifications to the Schottky current equation. This leads to a physics-based static ${I}$ – ${V}$ compact model. Simultaneously, we show that the temperature dependence of the switching dynamics model parameters naturally emerges as a mere scaling factor from the static ${I}$ – ${V}$ model. This is a computationally efficient approach, which does not require any additional parameters to extend the switching dynamics model for incorporating thermal dependence.

The control of coalescence and motion of droplets play a significant role in advanced technology and our daily life, and one of the most important approaches is surface design. Here, the microtextured surfaces decorated with wrinkled substrates are designed and studied for coalescence behaviors. The simulation results show that the coalescence speed would be slower on such surfaces due to the downward movement of the droplets induced by the penetration of atoms into the grooves that delays their movement along the coalescence direction, which is considered as a restriction effect. With the increase of the angles and the interval distance of wrinkled structures, the coalescence time becomes longer and the coalescing process becomes unfavorable, resulting from the enhanced restriction effect. More importantly, a composite substrate possessing the original and sub-wrinkled structures has been designed to tune the coalescence dynamics. The results of this work may not only help shed light on understanding the coalescence behaviors on the wrinkled substrates but also propose a feasible method for controlling the liquid coalescence behavior, which is expected to provide some useful implications for practical applications.

Direct numerical simulations of a turbulent channel with liquid infused surfaces made of longitudinal micro-ridges have been performed to study the effect of texture geometry and interface deformat...

The nonlinear absorption of two-dimensional (2 D) Nb2CTx (MXene) nanosheets were investigated by using nanosecond Z-scan measurements in 532 nm under different laser intensities. It was found that,...

A data-driven framework is presented for building magneto-elastic machine-learning interatomic potentials (ML-IAPs) for large-scale spin-lattice dynamics simulations. The magneto-elastic ML-IAPs are constructed by coupling a collective atomic spin model with an ML-IAP. Together they represent a potential energy surface from which the mechanical forces on the atoms and the precession dynamics of the atomic spins are computed. Both the atomic spin model and the ML-IAP are parametrized on data from first-principles calculations. We demonstrate the efficacy of our data-driven framework across magneto-structural phase transitions by generating a magneto-elastic ML-IAP for α-iron. The combined potential energy surface yields excellent agreement with first-principles magneto-elastic calculations and quantitative predictions of diverse materials properties including bulk modulus, magnetization, and specific heat across the ferromagnetic–paramagnetic phase transition.

A differential mechanism is an essential component in the majority of automotive applications. Its vitality stems from the fact that it allows a wheel-drive vehicle to take a curve safely. On the other hand, it can ratchet up the vibration in the wheel-drive vehicle due to the excessive gear tooth deflection from applied torque. Some gear tooth modifications can increase or decrease the level of vibration in the mechanism. So far, very little attention has been paid to the effects of the uncertain geometric deviation of the tooth profile and uncertain crowning parameters on the dynamic performance of the mechanism. This study aims to investigate the impacts of these uncertain parameters on the gear systems’ dynamic performance. To this end, the nonlinear interval model of the differential mechanism is proposed. The mesh stiffness for straight bevel gear is modelled through the potential energy method and slice theory, while bearing stiffness elements are calculated at each time step. A refined computational algorithm is proposed to deal with any gear system with multiple interval variables. The scanning method is used as a reference method in this paper. The main outcomes of this study are that the crowning design can slightly reduce the vibration in the mechanism, and the profile errors can increase its vibration level excessively. Besides, the results derived from the refined algorithm show similarities to those determined by the scanning method, and the study shows that the refined algorithm can handle any gear system with uncertain static or time-varying parameters.

In the framework of the classical equations for the magnetization dynamics and the collective variables approximation, the dynamics of magnetic vortices in two-dimensional ferromagnets with the easy-plane anisotropy and spatially inhomogeneous exchange interaction is considered. In the case of a wide straight line of the interface between magnetic media with different but slightly different exchange interaction, the dependence of the magnetic vortex velocity on its distance to the structure defect and position inside the interface domain is obtained.

A complete phenomenological description for the relaxation dynamics of the Ising ferromagnets in the presence of external magnetic field h is given by using the pair approximation. To study the relaxation dynamics, we calculate two characteristic times (denoted as τS, τF ) using the rate constants which satisfy the Onsager reciprocity theorem. Temperature/magnetic field variations of τS and τF are investigated. We have shown that the extrema of the curves obtained for τS when h 6= 0 determine the loci of correlation length maxima or the Widom lines. The results are compared with those of response functions and thermodynamic curvature. We observe that they exactly match that for the magnetic susceptibility. 000713033100009

In this study, an equivalent multi-body dynamics model of a rotary compressor for a household air-conditioner is established to predict its vibration responses when eccentric masses on the cranksha...

Through its ability to image liquid-phase dynamics at nano/atomic-scale resolution, liquid-cell electron microscopy is essential for a wide range of applications, including wet-chemical synthesis, catalysis, and nanoparticle tracking, for which involved structural features are critical. However, statistical investigations by usual techniques remain challenging because of the difficulty in fabricating substantial liquid cells with appreciable efficiency. Here, we report a general approach for efficiently printing huge numbers of ready-to-use liquid cells (∼9000) within 30 s by electrospinning, with the unique feature of statistical liquid-phase studies requiring only one experimental time slot. Our solution efficiently resolves a complete transition picture of bubble evolution and also the induced nanoparticle motion. We statistically quantify the effect of the electron dose rate on the bubble variation and conclude that the bubble-driven nanoparticle motion is a ballistic-like behavior insignificant to morphological asymmetries. The versatile approach here is critical for statistical research, offering great opportunities in liquid-phase-associated dynamic studies.

Dynamic responses and vibration characteristics of a rotating functionally graded material (FGM) beam with a hollow circular cross-section in the temperature field are investigated in this paper. The material properties of the FGM beam are assumed to be temperature-dependent and vary along the thickness direction of the beam. By considering the rigid-flexible coupling effect, the geometrically nonlinear dynamic equations of a hub–FGM beam system are derived by employing the assumed modes method and Lagrange’s equations. With the high-order coupling dynamic model, the effect of temperature variations under two different laws of motion is discussed, and the free vibration of the system is studied based on the first-order approximate coupling model. This research can provide ideas for the design of space thermal protection mechanisms.

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.

The benefits of nucleate pool boiling phenomena and their potential applications on thermal management of various microelectronic devices have triggered the development of new approaches that augment the magnitude of heat transfer rate. To implement these approaches, an accurate estimation of the boiling heat transfer coefficient between the fluid and the heated surface is often required. The acquisition of the boiling heat transfer coefficient must follow a better understanding of the bubble ebullition cycle because of its inherent coupling with heat transfer mechanisms involved in this cycle. Bubble ebullition occurs by periodic bubble nucleation on a boiling surface, bubble growth, and subsequent bubble departure from the surface. Different parameters related to the dynamics of the bubble ebullition cycle, including bubble departure diameter, bubble waiting period, active nucleation site density, bubble growth period, bubble departure frequency, and bubble growth rate govern the heat transfer rate in the nucleate pool boiling. Thus, numerous empirical correlations that determine the boiling heat transfer coefficient have been proposed by many researchers according to different bubble dynamics parameters. To accurately predict the boiling heat transfer coefficient and boiling heat flux based on the bubble ebullition cycle, understanding bubble growth mechanisms and associated dominant parameters is crucial. In this review, different bubble growth mechanisms during nucleate pool boiling are thoroughly reviewed. Then, bubble dynamics parameters used in different correlations for determining the boiling heat transfer coefficient are discussed. Semi-empirical and empirical correlations for determining these parameters are also extensively provided. Additionally, a detailed review of factors affecting bubble dynamics parameters is provided. Next, different applications of nucleate boiling in cooling systems are reviewed. Overall, this review includes various correlations from experimental and numerical data, which can be used to better predict the heat transfer during nucleate boiling.

Active matter systems[1–3] are made of self-propelling particles and make ideal ground for studies of out-of-equilibrium phenomena. The self-propulsion is fueled by continuous drawing of energy fro...

Two-dimensional dynamics of the wake in transitional flow around a circular cylinder is studied using weakly compressible smoothed particle hydrodynamics scheme up to 10 cylinder diameters downstre...

The influence of an external flow on the dynamics of active deformable particles demands a detailed understanding of the involved mechanism due to their prominent applications in medical and indust...

In this study, the friction properties of emulsions in an oral environment were investigated to understand the food-texture recognition mechanisms occurring on biological surfaces. Numerous publications have suggested that the friction phenomena depend on friction conditions, such as the surface characteristics, as well as the shape and movement of contact probes. Traditional friction evaluation systems are unsuitable for mimicking the oral environment. Thus, in this study, the friction forces between two fractal agar gel substrates in an emulsion were examined using a sinusoidal motion friction evaluation system that effectively mimics the oral environment. The physical properties of the fractal agar gel, including the elasticity, hydrophilicity, and surface roughness, were analogous to those of the human tongue. Furthermore, the sinusoidal motion imitated the movements of living organisms. Depending on the samples, three friction profiles were observed. For water, the surfactant aqueous solution, and olive oil, the friction profiles of the outward and homeward processes were symmetric (stable pattern). Interestingly, for an oil-in-water (O/W) emulsion, friction behaviors with not only an asymmetric friction profile (unstable pattern I) but also a lubrication phenomenon, which temporarily decreased the friction force (unstable pattern II), were noted. The probability for the appearance of unstable patterns and adhesion force between the gel substrates increased with the oil content of the O/W emulsions. These characteristic friction phenomena were attributed to the strong adhesive force in the emulsion, which was sandwiched between the agar gel substrates. The findings obtained in this study would contribute significantly to understanding the food-texture recognition mechanisms and dynamic phenomena occurring on biological surfaces.

We applied a new large two membrane model of human urea transporter B (UT-B) with urea concentration gradient between intracellular and extracellular solution to explore the structure and dynamics ...

Linear theory continues to play a critical role in extracting the underlying primary instability dynamics of boundary layer transition. However, such methods have difficulty in isolating the dynami...

In this research, frequency and resonance area information of a size-dependent electro-elastic rotary non-classical piezoelectric microdisk via modified couple stress theory (MCST) is presented. Th...

In this technical brief, a simple concise derivation of the Gibbs-Appell equations for the dynamics of a constrained rigid body is presented.

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.

To design anticancer drug Taxol working more efficiently, looking at details of microtubules' dynamic behavior has become more important for researchers worldwide. According to this issue, dynamic ...

The accuracy of numerical calculations of the dynamics of vortex filaments is estimated via the cutoff method using the example of the motion of helical vortices. In the case of helical vortices with uniform vorticity distribution of a Rankine core, there are two analytical approaches to solving the problem. These approaches are used to determine the minimum admissible distance between vortex filaments or their elements to ensure the accuracy of calculations when using the cutoff method. There is an established error that occurs in the calculations based on the cutoff method in the case of convergence of the rounds of a helical vortex.

In this paper, a 3D laser plasma interaction system is presented, analysed, and implemented. The system has two unstable equilibria, and two types of coexisting attractors in which the coexistence of two periodic orbits and the coexistence of two chaotic attractors can be clearly observed. The multistability behaviours are determined by the bifurcation diagrams, largest Lyapunov exponents, and phase spaces. Moreover, the complexity performance of the laser plasma interaction system is investigated by the contour plot of the Sample Entropy.

Water management is crucial to achieve both high-performance and durability of proton exchange membrane fuel cell (PEMFC). Therefore, it is necessary to investigate the dynamic behavior of droplets in PEMFC channel for water management. In this paper, we explore the kinetics of droplets in a 3D flow field by experimental and theoretical analysis. More specifically, we examine the following four perspectives: 1) the movement and falling of droplets, and their force and deformation, 2) the superiority of 3D flow field drainage, 3) the pressure and viscous force under different scenarios including varying droplet sizes and velocities, and 4) the expression describing the shape change of droplets. The results show that the 3D flow field has a greater driving force on droplets and that their deformation affects the discharge of liquid water. Throughout the study, we provide better understanding of droplet dynamic in PEMFC gas channels. It enables to optimize the design and working conditions of these channels.

Non-premixed impinging jet flames with different coflow conditions are performed using PIV technology combined with numerical simulation to investigate flame instability in the vicinity of wall. Re...

The interest on closed-form analytical sensitivity equations based on the classical forward dynamics formulations, started shortly after the equations were ready and became popular. A vast effort w...

Bubble-bubble interactions are of great importance for bubble dynamics. A mathematical model describing the dynamics of a cluster in hydrodynamic cavitation is presented. The interaction strength (i.e. the number density of bubbles) is introduced into Keller-Misis equation. Using this model, numerical investigations of bubble dynamics (i.e. radial motion and internal energy) of single bubble in a cluster have been made due to linear pressure gradient. With the increase of interaction strength, the times of bubble reaching the maximum and minimum radii are delayed. The more of bubbles are in a cluster, the more significant of the delay effect is. The maximum internal energy inside the bubble is closely related to interaction strength (i.e. positive correlation). Furthermore, the initial bubble radius and final recovered pressure of the orifice on bubble dynamics are quantitatively discussed. Based on numerical results, some references are put forward for optimize and manipulate of hydrodynamic cavitation reactor.

A series of large-scale parallel simulations of flat-plate film cooling are performed to uncover the qualitative and quantitative relationship between coherent structure dynamics and heat-transfer ...

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.

Molecular fluctuations directly reflect the underlying energy landscape. Variance analysis examines protein dynamics in several biochemistry-driven approaches, yet measurement of probe-independent fluctuations in proteins exposed to mechanical forces remains only accessible through steered molecular dynamics simulations. Using single molecule magnetic tweezers, here we conduct variance analysis to show that individual unfolding and refolding transitions occurring in dynamic equilibrium in a single protein under force are hallmarked by a change in the protein's end-to-end fluctuations, revealing a change in protein stiffness. By unfolding and refolding three structurally distinct proteins under a wide range of constant forces, we demonstrate that the associated change in protein compliance to reach force-induced thermodynamically stable states scales with the protein's contour length increment, in agreement with the sequence-independent freely jointed chain model of polymer physics. Our findings will help elucidate the conformational dynamics of proteins exposed to mechanical force at high resolution which are of central importance in mechanosensing and mechanotransduction.

The kinetics of photoluminescence (PL) and time-resolved emission spectra (TRES) of melanin solutions with an effective electron acceptor 2,4,7-trinitrofluorenone (TNF) have been studied. Based on ...

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.

Topological defects are interesting phenomena which can be observed in ordered phases such as oriented active fluids or nematic liquid crystals. Topological defects are determined by the overall st...

Active materials are capable of converting free energy into mechanical work to produce autonomous motion, and exhibit striking collective dynamics that biology relies on for essential functions. Controlling those dynamics and transport in synthetic systems has been particularly challenging. Here, we introduce the concept of spatially structured activity as a means of controlling and manipulating transport in active nematic liquid crystals consisting of actin filaments and light-sensitive myosin motors. Simulations and experiments are used to demonstrate that topological defects can be generated at will and then constrained to move along specified trajectories by inducing local stresses in an otherwise passive material. These results provide a foundation for the design of autonomous and reconfigurable microfluidic systems where transport is controlled by modulating activity with light. Light-responsive myosin motors enable spatial and temporal control over the dynamics and transport of active nematic liquid crystals composed of actin filaments and myosin at an oil–water interface.

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...