Constant External Force Research Articles

Diffusion dynamics of an overdamped active ellipsoidal Brownian particle in two dimensions

Shape asymmetry is the most abundant in nature and has attracted considerable interest in recent research. The phenomenon is widely recognized: a free ellipsoidal Brownian particle displays anisotropic diffusion during short time intervals, which subsequently transitions to an isotropic diffusion pattern over longer timescales. We have further expanded this concept to incorporate active ellipsoidal particles characterized by an initial self-propelled velocity. This paper provides analytical and simulation results of diffusion dynamics of an active ellipsoidal particle. The active ellipsoidal particle manifests three distinct regimes in its diffusion dynamics over time. In the transient regime, it displays diffusive behavior followed by a super-diffusive phase, and in the longer time duration, it transitions to purely diffusive dynamics. We investigated the diffusion dynamics of a free particle as well as a particle in a harmonic trap, and a particle subject to a constant field force. Moreover, we have studied the rotational diffusion dynamics and torque production resulting from an external constant force field. Furthermore, our investigation extends to the examination of the scaled average velocity of an ellipsoidal active particle, considering both a constant force field and a one-dimensional ratchet.

Numerical simulation of nanoneedle-cell membrane collision: minimum magnetic force and initial kinetic energy for penetration

Aims and objectives: This research aims to develop a kinetic model that accurately captures the dynamics of nanoparticle impact and penetration into cell membranes, specifically in magnetically-driven drug delivery. The primary objective is to determine the minimum initial kinetic energy and constant external magnetic force necessary for successful penetration of the cell membrane. Model Development: Built upon our previous research on quasi-static nanoneedle penetration, the current model development is based on continuum mechanics. The modeling approach incorporates a finite element method and explicit dynamic solver to accurately represent the rapid dynamics involved in the phenomenon. Within the model, the cell is modeled as an isotropic elastic shell with a hemiellipsoidal geometry and a thickness of 200 nm, reflecting the properties of the lipid membrane and actin cortex. The surrounding cytoplasm is treated as a fluid-like Eulerian body. Scenarios and Results: This study explores three distinct scenarios to investigate the penetration of nanoneedles into cell membranes. Firstly, we examine two scenarios in which the particles are solely subjected to either a constant external force or an initial velocity. Secondly, we explore a scenario that considers the combined effects of both parameters simultaneously. In each scenario, we analyze the critical values required to induce membrane puncture and present comprehensive diagrams illustrating the results. Findings and significance: The findings of this research provide valuable insights into the mechanics of nanoneedle penetration into cell membranes and offer guidelines for optimizing magnetically-driven drug delivery systems, supporting the design of efficient and targeted drug delivery strategies.

Mechanotransduction in the Vocal Fold Microenvironment: A Narrative Review.

The vocal fold tissues undergo nearly continuous and repeated cycles of injury and repair throughout the course of an individual's lifetime. It is well established that certain individuals are at greater risk of lesion development based on personality and behavioral classification. However, these characteristics alone do not wholly predict or explain lesion development or severity. In this review, we discuss current knowledge of mechanotransduction proteins and their potential relevance to tissue homeostasis in the vocal folds. A review of literature surrounding mechanotransduction and tissue homeostasis as it relates to the vocal folds was conducted. Review of the literature included searches of PubMed, Google Scholar, and other various online peer-reviewed sources. Search terms pertained to mechanosensation, mechanotransduction, mechanically activated channels, mechanical cellular regulation, and other associated concepts and terms. Additional literature was identified through the reference lists of identified papers. Findings of this literature review were then applied to known physiology and pathophysiology of the vocal folds in order to speculate on the contribution of mechanically mediated mechanisms within the vocal fold. Because the vocal folds are such mechanically active structures, withstanding nearly constant external forces, there is strong support for the idea that mechanically sensitive molecular pathways within the vocal fold tissue play a major role in tissue homeostasis in the presence of these considerable forces. As such, mechanotransduction within the vocal fold should be considered and targeted in future biological studies of vocal fold physiology.

Constructing critical control parameters to keep vehicle away from divergent loss of stability

This paper describes a proposed methodology for the vehicle dynamics modelling and analysis of the stationary states for a two-axle road vehicle subject to a constant external lateral force and a resulting moment acting about a vertical axis passing through the mass centre of the vehicle. The classic nonlinear bicycle model is used and analyses are performed to investigate the stabilisation of straight-line motion through the automated correction of steering inputs to the front wheels. The approach taken here is based on the Pevsner-Pacejka graph-analytical method analysis of a stability set of stationary states in combination with an applicable theory of bifurcation. The disturbing lateral force is typically due to the pressure resulting from a strong side wind gust. The resolution of this force will act through the centre of pressure, taking the vehicle in side profile. The centre of pressure is unlikely to coincide with the centre of mass. This results in the additional disturbing yaw moment acting about a vertical axis through the centre of mass of the vehicle. Depending on the vehicle configuration this moment may introduce a dangerous oversteer response that most drivers would find difficult to manage.

Adaptive control algorithm for quadruped robots in unknown high-slope terrain

The capability to navigate high-slope terrains is crucial for quadruped robots engaged in field operations. We propose a novel terrain estimation and adaptation strategy tailored for facilitating quadruped robot locomotion on complex slope terrains. Our approach involves predicting terrain slopes by analyzing foot positions and IMU data, subsequently adjusting the robot’s body orientation and height in real-time to accommodate varying slope conditions. To effectively control the motion of quadruped robots on such challenging terrains, we introduce a multimodal motion control algorithm that integrates Model Predictive Control (MPC) with Quadratic Programming (QP) torque control. This combined approach ensures stable and efficient locomotion even on steep slopes. Furthermore, we present a state estimation method based on Kalman filtering, enabling accurate self-assessment by the robot without heavy reliance on visual sensors. In simulation validation, our quadruped robot achieved notable performance metrics. It achieved a forward speed of 0.7 m/s on slopes with angles up to 43∘ and demonstrated stable rotational capability at a speed of 2 rad/s on a 32∘ slope. When subjected to external force interference, the robot exhibited resilience, withstanding constant external forces of up to 60Nm and external torques of up to 35Nm on flat ground. Moreover, on a 30∘ slope, the robot maintained stable locomotion in the face of impulses reaching 64Nm ⋅ s along the x and y directions of its body coordinate system and 7Nm ⋅ s along the z-axis. This comprehensive strategy and experimental validation highlight the efficacy and robustness of our adaptive control algorithm, paving the way for enhanced performance of quadruped robots navigating high-slope terrains with unpredictable characteristics.

Langevin picture of subdiffusive particles under the joint influence of an expanding medium and an external constant force

It has been found that expanding medium has a nonnegligible influence on particle’s diffusion, the physical mechanism of which is quite different from an external force field. To study the joint influence of the expanding medium and the constant force, we start from the Langevin picture of the subdiffusive particles in the expanding medium, and then introduce the effect of the external constant force in two ways, which are sustainedly or intermittently acting on the particle’s motion. Therefore, we get two models with the only difference on the force terms. Then under the framework of the Langevin equation, we conduct detailed analyses and derive the corresponding Fokker–Planck equations and the moments for the two models. In the case with the sustained constant force, the force behaves as a decoupled force, which is called Galilei invariant. While for the intermittent case, the force changes the diffusion behavior, and the specific effects vary according to the expanding rate of the medium. Our detailed theoretical analyses and simulations present a consistent Langevin framework of investigating anomalous diffusion phenomena in the expanding medium together with the external force.

Numerical Investigation of the Evolving Inelastic Deformation Path of a Solder Ball Joint under Various Loading Conditions

Solder joints of ball grid arrays (BGA) have been widely used to connect electronic components to printed circuit boards (PCBs) and are often subjected to mechanical stress. Several studies have been conducted on the mechanical reliability of solder joints. While these studies have been useful in the industry, detailed studies on how the inelastic deformation path of the solder ball joints evolves under specific loading conditions have not been sufficiently reported. This study aims to understand how the inelastic deformation path evolves when a solder joint is subjected to a constant external force by utilizing the theory of mechanics. It has also been found that the mechanical failure is strongly influenced by the evolution history of the deformation modes in materials. For this study, an elastoplastic constitutive model and a ductile fracture criterion were implemented into the vectorized user-defined material (VUMAT) subroutine of the ABAQUS program for finite element (FE) analysis. With the model, the evolution of the inelastic deformation path of a single solder ball under different loading conditions was numerically analyzed. Three loadings (shear, compression, and bending) were chosen as the basic loading conditions. In addition, combinations of the basic loadings resulted in three dual loadings and one complex loading. The simulation results showed that the shear and bending caused the fracture for both single and dual loadings, but when combined with compression, the fracture was suppressed. The results indicate that fracture is not solely determined by the magnitude of equivalent plastic strain but also by the evolution of inelastic deformation mode. This research offers an improved understanding of the significance of the inelastic deformation path and fracture.

An overdamped Langevin approach to parallel diffusion and energy dissipation in the presence of low-frequency circularly polarized electromagnetic waves

Brownian motion of charged particles in the presence of low-frequency, circularly polarized electromagnetic waves is discussed. By using the wave rest frame, the Langevin system including low-frequency waves can be treated as a periodic system with a constant external force. In an overdamped limit, parallel diffusion is formulated by the Brownian motion whose diffusion coefficient includes wave amplitude. The nonequilibrium work by low-frequency waves satisfies a nonequilibrium relation corresponding to the fluctuation–dissipation relation with the effective temperature defined by wave amplitude.

Numerical Simulation of 2D Shallow water equation with constant external body force by using Finite difference method

Numerical Simulation of 2D Shallow water equation with constant external body force by using Finite difference method

Diffusion Properties of a Brownian Ratchet with Coulomb Friction

The motion of a Brownian particle in the presence of Coulomb friction and an asymmetric spatial potential was evaluated in this study. The system exhibits a ratchet effect, i.e., an average directed motion even in the absence of an external force, induced by the coupling of non-equilibrium conditions with the spatial asymmetry. Both the average motion and the fluctuations of the Brownian particle were analysed. The stationary velocity shows a non-monotonic behaviour as a function of both the temperature and the viscosity of the bath. The diffusion properties of the particle, which show several time regimes, were also investigated. To highlight the role of non-linear friction in the dynamics, a comparison is presented with a linear model of a Brownian particle driven by a constant external force, which allows for analytical treatment. In particular, the study unveils that the passage times between different temporal regimes are strongly affected by the presence of Coulomb friction.

CO2 adsorption-deformation-percolation characteristics of coals with different degrees of metamorphism and improvement of dynamic prediction model

The deformation and permeability changes occurring during CO2 adsorption in the coal body are important factors affecting CO2 injectability. In order to reveal the characteristic laws of adsorption, deformation and permeability of coal in the process of CO2 adsorption by different coal rank coals, the test experiments of adsorption, deformation and permeability of different coal rank coals under the condition of constant external force were carried out. The adsorption capacity of different coal samples for CO2 was obtained as anthracite > coking coal > long flame coal; The radial deformation ɛ2 and axial deformation ɛ1 of coal after CO2 gas adsorption by anthracite are the closest (ɛ2/ɛ1 is about 1.37), coking coal is the second (ɛ2/ɛ1 is about 1.73), long-flame coal is the largest (ɛ2/ɛ1 is about 2.72), In other words, the higher the coal rank, the more significant the degree of internal homogeneity and isotropy of the coal body, and the mean value of the volume deformation of CO2 adsorbed by long-flame coal is 1.07 and 1.17 times higher than that of coking coal and anthracite. The permeability curves of CO2 adsorption in all three coal samples decreased first and then increased, and the permeability of CO2 in coking coal was the largest, and the sensitivity coefficient of CO2 permeability in coal to adsorption pressure showed a trend of rapid decrease and then small increase. Based on the CO2 adsorption-deformation-percolation variation law of coal, an improved dynamic prediction model of adsorption (fitting accuracy 0.9850 ∼ 0.9963), an improved dynamic prediction model of coal body deformation (fitting accuracy 0.9889 ∼ 0.9921) and an improved dynamic prediction model of permeability (fitting accuracy 0.9848 ∼ 0.9914).

Relativistic linear oscillator under the action of a constant external force. Transition amplitudes and the Green’s function

Relativistic linear oscillator under the action of a constant external force. Transition amplitudes and the Green’s function

Steady state propulsion of isotropic active colloids along a wall

Active drops emit/absorb chemical solutes, whose concentration gradients cause interfacial flows driving their own transport and the propulsion of the droplet. Such non-linear coupling enables active drops to achieve directed self-propulsion despite their isotropy, if the ratio of advective-to-diffusive solute transport, i.e. the Peclet number Pe, is larger than a finite critical threshold. In most experimental situations, active drops are non-neutrally buoyant and thus swim along rigid surfaces; yet theoretical descriptions of their non-linear motion focus almost exclusively on unbounded domains to circumvent geometric complexity. To overcome this gap in understanding, we investigate the spontaneous emergence and nonlinear saturation of propulsion of an isotropic phoretic colloid along a rigid wall, to which it is confined by a constant external force (e.g., gravity). This phoretic particle model is considered here as a limiting case for a viscous active drop. We show that, for moderate Pe, the particle motion and associated chemical transport reduce the chemically-induced wall repulsion, thereby causing the particle to swim progressively closer to the wall as Pe increases. Far from hindering self-propulsion, this reduction in the particle-wall separation is accompanied by a wall-induced efficient rearrangement of the solute concentration gradients driving the particle, thus augmenting its swimming speed.

Lévy Walk Dynamics in an External Constant Force Field in Non-Static Media.

Based on the recognition of the huge change of the transport properties for diffusion particles in non-static media, we consider a Lévy walk model subjected to an external constant force in non-static media. Since the physical and comoving coordinates of non-static media are related by scale factor, we equivalently transfer the process from physical coordinate into comoving coordinate and derive the master equation governing the probability density function of the position of the particles in comoving coordinate. Utilizing the Hermite orthogonal polynomial expansions, some statistical properties are obtained, including the asymptotic behaviors of the first two moments in both coordinates and kurtosis. For some representative types of non-static media and Lévy walks, the striking and interesting phenomena originating from the interplay between non-static media, external force, and intrinsic stochastic motion are observed. The stationary distribution are also analyzed for some cases through numerical simulations.

Normalized Ratcheting Diagram Under Sinusoidal Vibration Waves

Abstract Ratcheting is a progressive incremental inelastic deformation or strain which can occur in a component that is subjected to variations of mechanical stress, thermal stress, or both. This study concentrated on the ratcheting occurrence of the piping model under the combined effect of constant external force and dynamic cyclic vibrations. Bent solid bars represented piping models, and sinusoidal acceleration waves were loaded. Characteristics of seismic loads between load-controlled and displacement-controlled properties were studied from the viewpoint of the frequency ratio of the forcing frequency to the natural frequency of the piping model. Besides, the ratcheting occurrence conditions of the beam and the piping model were compared in one normalized diagram to display the general mechanism of ratcheting with the consideration of the effect from the difference of shape and material. Results show that ratcheting occurs easily with a lower frequency ratio in both beam and piping models. In addition, it is meaningful to use beam models to understand the ratcheting mechanism of piping models. Describing the occurrence of ratcheting using the normalized ratcheting diagram for different components is feasible.

Enhancing particle transport in deformable micro-channels.

It is shown that the action of an oscillating force on particles moving through a deformable-walled channel causes them to travel greater distances than in the case of a rigid channel. This increase in the transport efficiency is due to an intensification of the stochastic resonance effect observed in corrugated rigid channels, for which the response to the force is maximal for an optimal value of the thermal noise. The distances traveled by the particles are even larger when the oscillation of the micro-channel is synchronized with that of an applied transverse force and also when a constant external force is considered. The phenomenon found could be observed in the transport of particles through elastic porous media, in drug delivery to cancerous tissues, and in the passage of substrates through transporters in biological membranes. Our results indicate that an appropriate channel design and a suitable choice of applied forces lead to optimal scenarios for particle transport.

Синтез адаптивного скользящего режима управления полетом квадрокоптера в условиях переменной нагрузки и помех

Adaptive sliding control mode of an unmanned aerial vehicle (UAV) has been synthesized using neural networks to identify unknown factors acting on UAV. The MATLAB SIMULINK software was used to simulate the operation of the UAV control system. The simulation of the operation of the UAV location tracking system and UAV movement under the influence of unknown external forces of both constant magnitude and external forces varying according to a linear law is performed. An assessment of the performance of the UAV control system under the influence of random interference is given.

Experimental and numerical investigation of thermomechanical cycling of notched NiTi shape memory ribbon using SMA model accounting for plastic deformation

Shape memory alloys (SMAs) are being increasingly applied as thermally driven actuators. The commercially available SMA elements, however, frequently contain stress risers, either due to internal or surface defects or due to the required component shape. Stress risers represent a potential danger for the preliminary fatigue failure of such actuators but its actual mechanism is not very clear. This paper presents a combined experimental (2D DIC analysis of surface strains) and numerical analysis (SMA model with plastic deformation) of the stress, strain and phase fraction fields evolving in a thin NiTi shape memory ribbon with an artificial notch subjected to cyclic cooling-heating through transformation range under constant external force. It appeared that, even if only very low tensile stress is externally applied upon thermal cycling, local tensile stress at the notch tip sharply increases during the first cooling due to the forward martensitic transformation (MT) proceeding heterogeneously in space. This heterogeneity gives rise to plastic deformation at the notch-tip, which gradually accumulates upon thermal cycling and shields the notch tip from tensile overloading. Hence, fatigue performance of thermal NiTi actuator with stress riser depends very much on the plastic deformability of the alloy.

Relativistic linear oscillator under the action of a constant external force. Wave functions and dynamical symmetry group

Relativistic linear oscillator under the action of a constant external force. Wave functions and dynamical symmetry group

Thermodynamic Uncertainty Relation Bounds the Extent of Anomalous Diffusion.

In a finite system driven out of equilibrium by a constant external force the thermodynamic uncertainty relation (TUR) bounds the variance of the conjugate current variable by the thermodynamic cost of maintaining the nonequilibrium stationary state. Here we highlight a new facet of the TUR by showing that it also bounds the timescale on which a finite system can exhibit anomalous kinetics. In particular, we demonstrate that the TUR bounds subdiffusion in a single file confined to a ring as well as a dragged Gaussian polymer chain even when detailed balance is satisfied. Conversely, the TUR bounds the onset of superdiffusion in the active comb model. Remarkably, the fluctuations in a comb model evolving from a steady state behave anomalously as soon as detailed balance is broken. Our work establishes a link between stochastic thermodynamics and the field of anomalous dynamics that will fertilize further investigations of thermodynamic consistency of anomalous diffusion models.