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Aerospace thin-walled parts vibrates during the process of milling due to their characteristics of low rigidity, which influences the machining quality of the workpiece. Based on the characteristics of magnetorheological fluid excitation solidification, a magnetorheological damping fixture is designed to semi-actively suppress the vibration generated during the machining process. This paper simplifies the multi-characteristic structure of aerospace thin-walled parts into rectangular thin plates. In accordance with Kirchhoff G.’s small deflection bending theory of elastic thin-plates and Daramberg’s principle, the differential equations for the transverse vibration of the thin-walled parts are established, which aims to obtain the natural frequency as well as vibration mode function of the thin-walled parts. In consideration of damping characteristics and the external dynamic milling force after the magnetorheological fluid excitation solidification, this paper uses the mode superposition method and an improved dynamic response mathematical model of the magnetorheological damping fixture thin-walled parts system of the linear multiple degrees of freedom, which has different volumes of magnetorheological fluids under forced vibration, was established. The maximum error between the predicted and measured values ​​of the fixture-workpiece system dynamic response of displacement and acceleration is 16.2% and 15.5%, respectively. Finally, this paper verifies the feasibility as well as the effectiveness of the model through dynamics experiment and milling machining experiment.

In Laser Powder Bed Fusion (LPBF), melt pool dynamics stability determines the overall quality of a manufactured component. In this work, a numerical model of the LPBF process was developed in order to study and fully understand the behavior of the melt pool dynamics. The numerical model takes into account most of the manufacturing parameters, thermophysical properties, an enhanced thermal conductivity approach and a volumetric heat source in order to precisely mimic LPBF. This research assumes that the energy emitted by the laser interacts with the metal powder with an absorptivity gradient through the layer thickness in order to calculate the thermal history of the process and the evolution of the melt pool dimensions. The obtained results determined that melt pool dimensions follow a thermal pattern, which is caused by the laser scanning strategy of the LPBF process. A new effective width criterion was proposed in the present research in order to accurately relate both calculated and measured dimensions of the melt pool, reducing the relative error of the model and obtaining data scattering with a standard deviation of ±7.21 µm and a relative error of 2.92%.

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 stalk of Vorticella convallaria, a sessile microorganism, is a model for calcium-powered cellular contraction and biomimetic actuators because of its high contraction speed and unique energy source. Usually, the stalk coiling follows the contraction of the cell body with a time delay (latent period), and it propagates from the cell body side to the root side. The dynamics and energetics of contracting V. convallaria have been studied by applying a stall force to the cell and thus slowing down the stalk contraction. This study exerted an extrinsic stall force to V. convallaria by applying drag force to V. convallaria cells using a microchannel and found that the propagation speed of the stalk coiling was not affected by the stall force, which is similar to the stalk coiling propagation of V. convallaria contracting in a stagnant viscous liquid. In contrast, the minimum latent period increased with the stall force, which enabled estimation of the maximum rate of contraction force development of the V. convallaria stalk.

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.

The onset of dynamic friction plays an important role in the study of sliding interfaces. Previously, the sliding precursors in the form of crack-like defects have been detected in experiments and their strain fields have been measured to be comparable to those of moving cracks. In the present work, we considered the dynamics of sliding precursors by solving the elastic problem due to a moving dislocation in a half-plane and the transient emission of a dislocation at the edge. It has been found that both the strain field of a moving dislocation and the spatiotemporal evolution agree well with those of a sliding precursor detected in experiments. The results may cast new light to the dynamics of sliding onset.

To assess the meshing quality of spiral bevel gears, the static meshing characteristics are usually checked under different contact paths to simulate the deviation in the footprint from the design point to the heel or toe of the gear flank caused by the assembly error of two gear axes. However, the effect of the contact path on gear dynamics under lubricated conditions has not been reported. In addition, most studies regarding spiral bevel gears disregard the lubricated condition because of the complicated solutions of mixed elastohydrodynamic lubrication (EHL). Hence, an analytical friction model with a highly efficient solution, whose friction coefficient and film thickness predictions agree well with the results from a well-validated mixed EHL model for spiral bevel gears, is established in the present study to facilitate the study of the dynamics of lubricated spiral bevel gears. The obtained results reveal the significant effect of the contact path on the dynamic response and meshing efficiency of gear systems. Finally, a comparison of the numerical transmission efficiency under different contact paths with experimental measurements indicates good agreement.

This study illustrates pervasive challenges in studying wetting dynamics, including dynamic contact angles, on irregularly roughened surfaces. We demonstrate that asymmetric water droplet shapes occur more than 50% of the time during static and dynamic contact angle measurements on sandblasted Zn-plated stainless steel with a polymeric overcoat. The pinning that causes the asymmetric drop shape distortion on horizontal surfaces also influences the sliding behavior on inclined surfaces. These effects lead to a poor correlation between the measured dynamic contact angles and the observed sliding angles (critical tilt angles). Our work emphasizes that large variations in the values of these dynamic wetting parameters are inherent to the heterogeneity of the surface roughness, and thus they limit the usefulness of standard dynamic wetting criteria. These findings have implications for academic and industrial research focused on making coated materials that have consistent wettability properties throughout their usage life cycle.

From the understanding of dynamics and processes of rapid granular flows and the granular-segregation mechanism in gravity-driven flow, we can clarify the particle-composition structure in the downstream areas of avalanches in geophysical contexts, such as landslides, rock falls, and snow-slab avalanches. Such dynamics also provide a basis for geophysical studies. This study experimentally investigates the dynamic behavior and segregation phenomena of a density-bidisperse, rapid, granular flow down a quasi-2D, rough, inclined rectangular chute. Particles with two density ratios are used to investigate the mechanism of density-induced segregation, and four chute-inclination angles are tested to examine the influence of driving forces. The dynamics of the mixture flow—which includes the flow-depth evolution, stream-wise and depth-wise velocity profiles, shear rate, and granular temperature in the upper high-shear band of the flow—are obtained from particle image velocimetry (PIV) measurements. The two-dimensional concentration distributions of the particles in the stream-wise direction are also obtained using 2D image processing to determine the segregation state. In the upstream region, the variation in the concentration of heavier particles is defined as the strength of the density-induced segregation state, Sd. Our results indicate that the mixture-flow parameter—particularly the shear rate and the granular temperature in the upper high-shear band—crucially influence the strength of particle segregation in granular avalanches. In the upstream region, a higher shear rate and a higher granular temperature in the upper high-velocity band result in a smaller drag force in the mixture flow, causing stronger density-induced particle segregation. These results well describe the entire processes of dense granular flows, from upstream initiation to the downstream steady state. Therefore, they reveal the structure of the mixed flow in the depth direction and are expected to explain various gravity-driven mixture granular flows.

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.

The thermal and mechanical properties of angular contact ball bearings are critical to their operating accuracy and service life. On the basis of the theory of dynamics and frictional heat generation, this work establishes a thermal-mechanical fully coupled model. The high-speed motion characteristics, temperature, and dynamic stiffness are analyzed, and the simulation results are compared with the theoretical calculation and experimental results. Then, the temperature and axial deformation of the bearings under different rotation speeds are analyzed, and the laws of mechanical and thermal characteristics of the bearings are obtained. Results show that an increase in the rotation speed of the inner ring causes the temperature of each component to increase, with the contact area of the balls showing the greatest increase in temperature. An increase in rotation speed also increases the axial deformation of the inner ring.

Interfacial behaviour of stratified and wavy-stratified flow is analysed in terms of measured velocity signals in liquid phase using Laser Doppler Velocimetry. Measurement of liquid height (interface level) is achieved using Laser Doppler Velocimetry synchronized with a computerised 3-dimensional traverse system. The precision obtained in measurement of air sheared interface level (liquid height) in this approach is 0.032±0.01 mm. First part of this paper deals with influence of gas and liquid superficial Reynolds numbers on the liquid height for stratified and wavy-stratified flow. With increase in liquid depth, waves are initiated at the gas-liquid interface which is precursor to slug formation. A critical liquid height for onset of slug formation is obtained in this part. The second part deals with the measurement of fluctuations occurring near to the air-sheared interface. These fluctuations are recorded in terms of local velocity of liquid phase and have been used to characterize the behaviour of air-water interface for stratified and wavy-stratified flow. Furthermore, influence of gas and liquid flow rates on local liquid velocity for different stratified and wavy-stratified flow conditions is analysed by plotting the axial velocity profiles in radial direction.

In this work, we numerically study the impact of a water droplet onto a deep oil pool. Two fluids are immiscible and the viscosity of the pool liquid is changed systematically. We focus on the cavity dynamics during the impact and especially the effects of the pool liquid viscosity and the impacting velocity. For the parameter range explored, we identify the regime where splashing occurs with corolla breaking into droplets, and the regime where no splashing is observed. Similarity is found for the time evolution of cavity depth for fixed impact velocity and different viscosity, if the cavity depth and time are nondimensionalized by the maximal depth and the time when the maximal depth is reached. Effective power-law scalings are also proposed to describe the dependence of the maximal cavity depth and the corresponding time on the impact velocity and pool liquid viscosity, in the term of Froude and Reynolds numbers.

Computational simulation provides an effective way of understanding the disordered structure and structure-property relationships for metallic glass systems. Here, we systematically investigated the finite-size effects of the static structure and dynamical behaviors in a three-dimensional Cu50Zr50 model metallic glass via classical molecular dynamics (MD) simulations. It was found that the local structure is insensitive to the system size while the dynamical properties present evident finite-size effects. The decoupling between local structure and relaxation dynamics in the investigated supercooling emerges when the system contains less than ~2000 atoms. However, the collapse can be observed between the structural relaxation time and the dynamical heterogeneity for different sized systems across the whole range of our investigation. Our results support the intrinsic link between the structural relaxation time and dynamic heterogeneity and reveal the critical simulated system size for representing the structural origins of dynamics in bulk metallic glass with ignorable surface effects.

The investigation in the mixing characteristics of microscale shock cylindrical bubble interaction (SBI) provides a fundamental perspective into the microscale fuel injection. In present paper, the mixing performance of multi-scale SBI is numerically studied based on compressible Navier–Stokes equation. Starting from the bubble morphology, a scaling behavior of concentration distribution is exhibited in macroscale dynamics, whereas a superior capability of concentration decaying is observed in microscale cases. On the basis of mixedness evaluation, the mixing property of microscale bubbles is reinforced in the pre-interaction stage with notable viscous diffusion, and suppressed in the later evolution in the absence of vortex formation. Resorting to the Lagrangian coherent structure, a spatial coincidence between fluid stretching and mixing extent is visualized. The present study attempts to clarify the physical rationality of microscale injection strategies such as the atomization process and multiple micro-nozzles for mixing enhancement. Further efforts are devoted to physically modelling the competing mechanism of stirring effect (macroscale dynamics) and viscous diffusion (microscale dynamics) for optimal mixing performance.

Two-coupled excitatory neurons model containing both calcium-activated non-specific cationic and persistent sodium current in the pre-Botzinger complex (pre-BotC) is studied. A new type of mixed burst similar to a depolarization block bursting (DB-bursting) is observed in the model of pre-BotC neurons. The multi-time scale dynamics, one- and two-parameter bifurcation analysis, are used to study the types of mixed burst and their transition mechanisms. The results show that the periodic fluctuation of calcium concentration has a great influence on the generation of mixed bursting. The change of time scale caused by fluctuation of calcium concentration and the relative position of bifurcation curves have great influence on patterns of bursting.

Investigated in this paper is the coupled fluid–body motion of a thin solid body undergoing a skimming impact on a shallow-water layer. The underbody shape (the region that makes contact with the liquid layer) is described by a smooth polynomic curve for which the magnitude of underbody thickness is represented by the scale parameter C. The body undergoes an oblique impact (where the horizontal speed of the body is much greater than its vertical speed) onto a liquid layer with the underbody’s trailing edge making the initial contact. This downstream contact point of the wetted region is modelled as fixed (relative to the body) throughout the skimming motion with the liquid layer assumed to detach smoothly from this sharp trailing edge. There are two geometrical scenarios of interest: the concave case ($$C C < 0 producing a hooked underbody) and the convex case ($$C > 0$$ C > 0 producing a rounded underbody). As C is varied the rebound dynamics of the motion are predicted. Analyses of small-time water entry and of water exit are presented and are shown to be broadly in agreement with the computational results of the shallow-water model. Reduced analysis and physical insights are also presented in each case alongside numerical investigations and comparisons as C is varied, indicating qualitative analytical/numerical agreement. Increased body thickness substantially changes the interaction structure and accentuates inertial forces in the fluid flow.

Nucleate boiling is an important part of the pool boiling phenomenon which occurs in various processes involving heat transfer, such as, steam production, chemical processes, etc. The inclination of the heated surface, where bubbles nucleates, significantly affects the bubble growth dynamics as well as the heat transfer rate from the microlayer underneath the bubble during the nucleate boiling. In this study, the effect of the surface inclination on the bubble growth and detachment during the nucleate boiling is investigated numerically. For this purpose, the proposed model of Lay and Dhir for the microlayer is modified to include the effect of the inclination of the heated surface. The resulting equations are solved numerically, and the effect of varying the inclination of the heated surface on the bubble growth and heat transfer is investigated. The results show that the largest bubble size and the highest heat transfer from the heated surface occur when the inclination of the heated surface is 30°; while, the smallest bubble size and the lowest heat transfer from the heated surface are observed for the horizontal surface. Furthermore, the total heat transfer from the inclined surface during the bubble growth increases up to 32% compared to that for the horizontal surface.

An attempt has been made to perform a comparative study on advances in the shear deformation theory for analyzing the statics and dynamics of different plates with the use of numerical examples. Initially, shape functions for the displacement field across the plate thickness are compared, and then, the stresses, deflections, and natural frequencies of laminated composite plates are also compared.

Suppression of self-excited vibrations in their design and incipient stages is vital for assuring surface finish and machining efficiency in the precision machining process. Various cutting vibration suppression methods (e.g., variable tooth pitch and variable spindle speed) have been designed for suppressing regenerative chatter. However, variable parameter-based cutting vibration suppression models have mostly been developed separately with the other parameter assumed to be constant. In addition, these methods failed to provide detailed helix angle information required by a machining practitioner to determine which helix angle degree or group of helix angle degrees would have matched the stability of milling cutters. Moreover, only a single degree of freedom (1-DOF) milling system was adopted; thus, these methods cannot account for two degrees of freedom (2-DOF) and higher milling system. This study proposes a helix angle-based 2-DOF milling model with simultaneous tooth pitch and spindle speed variation to deal with these aforementioned problems. Experimental results showed that the proposed model can be effectively and efficiently applied to the prediction of the regenerative chatter stability for not only 1-DOF but also 2-DOF milling system. Empirical comparisons indicated that the proposed model outperformed the existing methods in stability prediction, while also offering stable area enlargement capability that facilitates cutting vibration suppression. A numerical example is presented to illustrate the usage of the proposed model.

A mesoscopic simulation is applied to investigate the effects of hydrodynamic interactions and axial chains on the dynamics of threaded rings. The hydrodynamic interactions significantly speed up the diffusion and relaxation of both free and threaded rings. The decoupled diffusion and relaxation dynamics indicate the broken of the Einstein-Stokes relationship. The diffusion of a ring threaded on a flexible chain exhibits a synergism effect compared to that on an axial rod, which originates from the self-diffusion of the ring and the reptation-like motion of the axial chain. Meanwhile, hydrodynamic interactions significantly improve the synergism effect, leading to an enhanced sliding motion of the threaded ring. The faster sliding of threaded rings suggests that the entropic barrier is negligible, which agrees well with the basic assumption of barrier-less confining tube at equilibrium in tube theory. Our results provide a new perspective on analysis of the effects of topology constraints on polymer dynamics.

Swimming microorganisms can influence the diffusion of passive particles. The effect of this swimmer-particle interaction depends on different properties, such as the hydrodynamic field of the swimmer and the relative sizes of microorganisms and particles. We investigated an enhancement of the diffusion of silica doublets in a suspension of microalgae Chlamydomonas reinhardtii in a flat capillary. Depending on the concentration of microswimmers, the translational and rotational diffusion constants increase by several orders of magnitude in the presence of the swimming algae. For low concentrations of algae, the doublets exhibit Brownian motion in a fluctuating flow field generated by multiple swimmers. One can observe strong, diffusive transport caused by occasional large displacements. At high swimmer concentration, the algae form dense clusters, where the rotational motion of the doublets shows a subdiffusive behaviour while the translational motion remains diffusive.

We present here the results of studies of laser-induced shockwave destruction of biological tissues obtained experimentally and by computation. In the experiments, microexplosion dynamics were studied by analysis of acoustic pulses induced by explosion of activated charcoal during laser heating of unbound water. The computational method was based on automodel solution of the Stefan problem using a quasilinear approximation. Good agreement was obtained between computation and experimental data for assessment of the main parameters of acoustic waves arising as a result of thermal explosion of microparticles. Morphological studies and clinical testing of the method provided the evidential aspect of the proposed description of the mechanism of shockwave actions.

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.

Extensive investigations have been carried out on the thermo-hydrodynamics of nanofluid droplet interaction with heated and non-heated flat surfaces. However, the influence of shape of nanoparticles on the dynamics of droplet impingement on heated flat surfaces is yet to be explored in detail. In this study, hydrodynamics of nanofluid droplet impingement process on heated and mechanically polished aluminum substrate was studied using dissolved Al2O3 nanoparticles having spherical as well as cylindrical shapes. Nanofluids of 0.3% volume fractions were prepared from spherical Al2O3 particles of mean size less than 50 nm and from cylindrical Al2O3 particles of 2–6 nm in diameter and 200–400 nm in length. It was observed that, the impact dynamics is different from that of base pure fluid owing to the presence of nanoparticles. Leidenfrost temperatures of both nanofluids were dropped drastically in comparison with pure liquid. Further, the residence time, spread factor as well as retraction height also exhibit a different behavior against the base fluid. Detailed investigations were carried out for different Weber numbers (We = 18–159) and surface superheat and resul ts obtained were compared with de-ionized (DI) water.

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

Surfactant-induced Marangoni flows can alter the typical outward capillary flows in a drying droplet. Previous studies show that intricate time-dependent periodic motions of colloidal particles, such as Marangoni eddies and back-and-forth oscillatory motions, can be developed due to the coupled dynamics of surfactant and evaporation. Here, the temporal motions are investigated using a coarse-grained lattice model. We show that during the evaporation, aggregation and depletion zones of colloidal particles emerge close to the contact line when the capillary and Marangoni flows are comparable in the opposite directions. It is found that the type of periodic motions is determined by the initial surfactant concentration. When the strength of the Marangoni flows is sufficiently large at the early stage of evaporation swirling motions rather than oscillatory motions are developed. The periodic motions of particles persist until the surfactant concentration on the surface is saturated. Also, the onset and terminate times of the motions decrease with the initial surfactant concentration.

This article presents an analytical method for calculating a transient dynamic regime that precedes a formation of periodic impurity bands during a rapid crystallization of dilute binary melts. Obtained results may be used for creating impurity superstructures with prescribed impurity profiles.

Using an advancement of a phase field model of multi-grain crystallization developed by Moelans et al., a system of governing equations describing the evolution of multiple crystals in rapidly solidifying samples is formulated. The dynamics of the moving interface is analysed, and an analytical solution in form of traveling wave is obtained for the phase field profile and its velocity.

Current-induced spin-transfer torques (STT) and spin-orbit torques (SOT) enable the electrical switching of magnetic tunnel junctions (MTJs) in non-volatile magnetic random access memories. To develop faster memory devices, an improvement in the timescales that underlie the current-driven magnetization dynamics is required. Here we report all-electrical time-resolved measurements of magnetization reversal driven by SOT in a three-terminal MTJ device. Single-shot measurements of the MTJ resistance during current injection reveal that SOT switching involves a stochastic two-step process that consists of a domain nucleation time and propagation time, which have different genesis, timescales and statistical distributions compared to STT switching. We further show that the combination of SOT, STT and the voltage control of magnetic anisotropy leads to reproducible subnanosecond switching with the spread of the cumulative switching time smaller than 0.2 ns. Our measurements unravel the combined impact of SOT, STT and the voltage control of magnetic anisotropy in determining the switching speed and efficiency of MTJ devices.

In this study, we investigated droplet impact dynamics offalling water drops (D0 ~ 2.3 mm ) on slippery oil-infused surfaces and compared them to other features of the surfaces, to elucidate the wettability- and roughness-controlled characteristics. We prepared transparent substrates with the designed characteristics, so it would be feasible to visualize the droplet impact dynamics in detail. A wide range of impact kinetics (We ~ 800 (=ρD0Vi2/σw)) was covered, which gave rise to several types of droplet-impact: gentle spreading, wavy (undulated fingers of spreading edges), droplet break-up, and splashing with small secondary droplets. The basic parameters of the droplet-solid interactions were measured, and events were mapped with respect to the sample surface and impact kinetic conditions. We found that, generally, surface wettability has a major influence on the triple line shape and instability during the impact and retraction process, and thus determines events in of the framework of the dynamic wetting-failure model. Furthermore, while rough conditions promote instability of the impacted droplet, slippery lubricant-infused features tend to dampen perturbations of the spreading/retracting edge.

In this study, we investigate the motion of polymer segments in polymer/nanoparticle composites by varying nanoparticle (NP) volume fractions. By studying the probability distribution of segment displacement, segment trajectory, and the square displacement of segment, we find the intermittent motion of segments, accompanied with the coexistence of slow and fast segments in polymer nanocomposites (PNCs). The displacement distribution of segments exhibits an exponential tail, rather than a Gaussian form. The intermittent dynamics of chain segments is comprised of a long-range jump motion and a short-range localized motion, which is mediated by the weakly attractive interaction between NP and chain segment and the strong confinement induced by NPs. Meanwhile, the intermittent motion of chain segments can be described by the adsorption-desorption transition at low particle loading and confinement effect at high particle loading. These findings may provide important information for understanding the anomalous motion of polymer chains in the presence of NPs.

The propagation of acoustic waves in a porous medium partially filled with a gas hydrate was investigated with regard for the viscoelastic properties of the skeleton of this medium on the assumption that the gas hydrate is distributed homogeneously in the thin layer at the inner surface of pores of the medium. A system of equations defining the propagation of acoustic waves in a porous medium containing a gas hydrate is proposed. A dispersion relation has been derived for investigating the influence of different parameters of a porous medium on the propagation of acoustic waves in it.

A two-dimensional system of miniature Langmuir probes operating in the electron saturation current mode is proposed. With its help, the spatial distribution of plasma density near the discharge gap and the dynamics of cathode-plasma sheath extension are investigated after the high-current vacuum-arc discharge crosses zero current. The proposed methodology and the results obtained are urgent for investigating processes of current interruption in vacuum circuit breakers.

Modeling techniques applied to mechanical vibration damping problems in systems made of viscoelastic materials contribute to the development of compact and efficient industrial devices. To reduce the weight of rotors, polymeric materials and light metal alloys can be included in their manufacturing. The objectives of this study are to present analytical models that describe the dynamic behavior of rotors made of viscoelastic materials and to evaluate and compare their performances. Using the anelastic displacement fields method applied to the strain dynamics of the rotor material and introduced into Lagrange equations with a differential operator in the time domain, motion equations are obtained by Rayleigh–Ritz approximation. Based on the numerical solution of the motion equations, comparative analyses are performed for two rotors with different geometries, made of PVC and aluminum. Both models, the first for aluminum and the second for PVC, result in good approximations.

Cold shock protein (Csp) is a typical two-state folding model protein which has been widely studied by biochemistry and single molecule techniques. Recently two-state property of Csp was confirmed by atomic force microscopy (AFM) through direct pulling measurement, while several long-lifetime intermediate states were found by force-clamp AFM. We systematically studied force-dependent folding and unfolding dynamics of Csp using magnetic tweezers with intrinsic constant force capability. Here we report that Csp mostly folds and unfolds with a single step over force range from 5 pN to 50 pN, and the unfolding rates show different force sensitivities at forces below and above ~8 pN, which determines a free energy landscape with two barriers and a transient intermediate state between them along one transition pathway. Our results provide a new insight on protein folding mechanism of two-state proteins. Force-dependent transitions can provide insights into the free-energy landscape of proteins. Here, the authors observe the folding and unfolding dynamics of the model protein Csp using magnetic tweezers, from which a free-energy landscape with two energy barriers and a transient intermediate state is constructed.

We perform a numerical and experimental study of immiscible two-phase flows within predominantly 2D transparent PDMS microfluidic domains with disordered pillar-like obstacles, that effectively serve as artificial porous structures. Using a high sensitivity pressure sensor at the flow inlet, we capture experimentally the pressure dynamics under fixed flow rate conditions as the fluid-fluid interface advances within the porous domain, while also monitoring the corresponding phase distribution patterns using optical microscopy. Our experimental study covers 4 orders of magnitude with respect to the injection flow rate and highlights the characteristics of immiscible displacement processes during the transition from the capillarity-controlled interface displacement regime at lower flow rates, where the pores are invaded sequentially in the form of Haines jumps, to the viscosity-dominated regime, where multiple pores are invaded simultaneously. In the capillary regime, we recover a clear correlation between the recorded inlet pressure and the pore-throat diameter invaded by the interface that follows the Young-Laplace equation, while during the transition to the viscous regime such a correlation is no longer evident due to multiple pore-throats being invaded simultaneously (but also due to significant viscous pressure drop along the inlet and outlet channels, that effectively mask capillary effects). The performed experimental study serves for the validation of a robust Level-Set model capable of explicitly tracking interfacial dynamics at sub-pore scale resolutions under identical flow conditions. The numerical model is validated against both well-established theoretical flow models, that account for the effects of viscous and capillary forces on interfacial dynamics, and the experimental results obtained using the developed microfluidic setup over a wide range of capillary numbers. Our results show that the proposed numerical model recovers very well the experimentally observed flow dynamics in terms of phase distribution patterns and inlet pressures, but also the effects of viscous flow on the apparent (i.e. dynamic) contact angles in the vicinity of the pore walls. For the first time in the literature, this work clearly shows that the proposed numerical approach has an undoubtable strong potential to simulate multiphase flow in porous domains over a wide range of Capillary numbers.

We demonstrate label-free imaging of the functional and structural properties of microvascular complex in mice liver. The imaging was performed by a custom-built Jones-matrix based polarization sensitive optical coherence tomography (JM-OCT), which is capable of measuring tissue’s attenuation coefficient, birefringence, and tiny tissue dynamics. Two longitudinal studies comprising a healthy liver and an early fibrotic liver model were performed. In the healthy liver, we observed distinctive high dynamics beneath the vessel at the initial time point (0 hour) and reappearance of high dynamics at 32-hour time point. In the early fibrotic liver model, we observed high dynamics signal that reveals a clear network vascular structure by volume rendering. Longitudinal time-course imaging showed that these high dynamics signals faded and decreased over time.

Water droplets sitting between wires are ubiquitous in nature and industry, often showing irregular (non-spherical) droplet shapes. To understand their topological singularity and evaporation mechanism, measuring volume changes of irregular water droplets is essential but highly challenging for small-volume water droplets. Here we experimentally explore topological heterogeneity and evaporation dynamics for irregular water droplets between wires with four-dimensional X-ray microtomography that directly provides images in three spatial dimensions as a function of time, enabling us to get three-dimensional structural and geometric information changes with time. We find that the topological heterogeneity of an irregular droplet is due to the local contact lines and the evaporation dynamics of an irregular droplet is governed by the effective contact radius. This study may offer an opportunity to understand how the topological heterogeneity contributes to the evaporation dynamics of irregular water droplets.

Understanding liquid evaporation on surfaces is of utmost importance due to its impact on a plethora of industrial and natural processes. Over the past several decades, through chemical functionalization or surface structuring, wetting and non-wetting surfaces have been extensively developed and studied in an attempt to control liquid–surface interactions. More recently, surfaces with wettability patterns comprising of local wetting/non-wetting regions have received considerable attention. Although quantitative analytical models in parallel with scaling arguments have been developed to predict and understand liquid droplet evaporation on such micro-structured surfaces, consensus in the wider community is sparse. Developing a better understanding of the evaporation performance on structured surfaces is imperative for selecting optimal structure length scales and designs for specific applications. Here, we develop dual wettability or biphilic micropillar surfaces having various dimensions by utilizing lift-off microfabrication. We focus on studying the evaporation dynamics of sessile water droplets on such micropillared biphilic as well as hydrophobic surfaces. We start by investigating the evaporation of water droplets having a wide range of diameter ( $$100

The dynamics of the magnetocaloric effect (MCE) in a ribbon sample Ni50Mn35Al2Sn13 in a cyclic magnetic field of 1.8 T was studied by a direct method. It was shown that near magnetostructural phase transition (MSPT), due to the irreversibility of the MSPT in a magnetic field of 1.8 T, the value of the inverse effect depends on the rate of temperature change. The higher the scanning rate, the greater the value of the MCE, which is associated with the phase transition kinetics and with relaxation processes that manifest themselves in the first-order MSPT region. At scanning rates below 1 K/min, a direct MCE appears with ΔT = 0.21 K, at a maximum rate of 10 K/min, an inverse MCE appears with a value of ΔT = − 0.12 K.

The phenomenon of a precursor spreading in front of an advancing droplet is still not fully understood. We recently used a driven lattice-gas model to study the microscopic dynamics of thin film spreading. We found that the scaling exponents describing the dynamics of both the precursor and the bulk layers are not universal, and strongly depend on the parameters describing the various interactions in the system. In this paper we show yet another nontrivial and rich behavior of the system. This is the non-monotonicity of the exponents, which reflects the competition between the various mechanisms that drive the system. In particular, we study the dependence of the scaling exponents on the ratio of the external substrate potential and the internal short-range interactions that drive the spreading in both layers.

PURPOSE: With new repair techniques of the aortic root and valve emerging, a detailed understanding of the dynamics of the aortic annulus and valve is required for optimal results. The objective of this study was to characterize geometrical changes and force distribution of the native porcine aortic annulus throughout the cardiac cycle.METHODS: Measurements were performed in an acute 80 kg porcine model (n = 7) using sonomicrometry crystals in the aortic annulus for evaluation of geometry and dynamics, annular force transducer evaluating force distribution, and pressure measurements and echocardiography evaluating valve performance.RESULTS: Overall, segmental force distribution and geometrical changes differed between different segments of the aortic annulus. The highest force development was found at the left/right interleaflet triangle (2.87 ± 2.1 N) and the largest segmental expansion was observed at the right-coronary and left-coronary sinus. The aortic annulus changed configuration throughout the cardiac cycle and became more oval in systole.CONCLUSIONS: This study is the first to describe detailed segmental dynamics and force distribution of the native aortic annulus in a porcine model in vivo. The heterogenous behavior of the aortic annulus suggests that different segments demand different support for repair of the aortic root and valve.

In ultra-precision machining (UPM), a brushless permanent magnet DC motor employed for an air bearing spindle exhibits unbalanced magnetic forces (UMFs). The UMFs exert on the spindle rotor to induce forced spindle vibration, named UMFs induced forced spindle vibration (UMF-FSV). It would significantly deteriorate surface quality in UPM. However, the UMF-FSV is not well understood with its effect on surface generation in UPM. In this study, an analysis model of magnetic forces for a spindle motor is developed along with a surface generation model to study dynamics of UMF-FSV and its effect in UPM. The theoretical and experimental results signify that UMF-FSV is harmonic at a fundamental frequency 2pω (motor’s pole number 2p and spindle speed ω), which produces 2p straight radial patterns without phase shift at a machined surface in UPM.

The formation of equally-spaced structures (trains) of rigid, spherical particles suspended in a viscoelastic fluid flowing in a cylindrical microchannel is investigated by numerical simulations. Direct Numerical Simulations (DNS) have been employed to accurately compute the translational velocities of a system made by three particles aligned along a cylindrical channel for different interparticle distances. A shear-thinning, elastic fluid, modeled by the Giesekus costitutive equation, is considered. The DNS results are collected in a database used for simulating the dynamics of a multi-particle system. The evolution of the particle microstructure through the channel is presented in terms of interparticle distance distributions. The effects of the Deborah number (defined as the ratio between the fluid and flow characteristic times), the volume fraction, and the initial particle distribution on the train dynamics are investigated.

Spindle-holder interface is the weakest part of the spindle system, and to some extent, determines the dynamics of spindle systems and strongly affects the cutting process stability. In order to improve the spindle system during the design stage and predict the tool point dynamics, this paper proposes modelling of spindle-holder assembly and presents an investigation on the contact characteristic under clamping and centrifugal forces. Modal test results show a good agreement with the simulated results. After that, contact pressure distribution under different clamping and centrifugal forces are investigated, which indicates a decrease of natural frequency of spindle-holder assembly caused by rotational speed. In the last, an improvement of holder dimensions based on the deformations of spindle and holder is presented, and the results show a significantly improved performance of spindle-holder assembly under the rotating condition.

In this work, we analyze an ensemble of dividing and growing living cells that maintain contact with each other. The dynamics of the cell area distribution in a confined system is theoretically investigated in both uniform and nonuniform settings. The effective pressure is introduced to model the experimentally observed phenomenon in which the average cell size dramatically decreases over time. For a nonuniform system, the cell shift due to the gradient of the effective pressure is considered and its effect on the average cell area profiles is examined.