Coupling Of Motion Research Articles

Numerical Study of Pressure Response to Action Potential by Water Permeation With Ion Transports

Abstract While the permeation mechanism of solute (e.g., ions and glucose) through biological membrane has been studied extensively, the mechanical role of water transport in intracellular phenomena has not received much attention. In the present study, to investigate the effect of water permeation on the intracellular pressure response, a novel permeation flux model through a biological membrane is developed by incorporating the coupling permeabilities (between water and ion fluxes) as the water–ion interaction in the ion channels. The proposed model is applied to a two–dimensional permeation problem of water and ions in a closed cell separated by a thin membrane. The permeation flux model reproduces the typical time response of intracellular pressure to action potentials with reasonable agreement with experimental results in the literature, indicating that the pressure response can be characterized by the following three parameters: water permeability, the mass ratio of water and ion, and the ratio of the permeation fluxes of water and ion. In particular, the permeation flux ratio plays an essential role in intracellular phenomena; depending on the value of the permeation flux ratio, the time lag between the action potential and the pressure response is 0.1 times smaller than that expected by the previous researchers, indicating that water transport associated with ions may trigger a pressure response. This study demonstrates the importance of water permeation in intracellular mechanical response through coupling of the fluid motion and electric fields.

Charge carrier motion and Mn-spin coupling defining the transport behaviors and the magnetic order at DySrCaMnO3 polycrystalline ceramic

The Ca-doped Dy0.5Sr0.5MnO3 manganite was synthesized using the Sol-Gel technique. The material demonstrates semiconducting behavior across a wide range of temperatures. This behavior could be attributed to the involvement of small polaron hopping, Shklovskii-Efros variable range hopping, and Mott-variable range hopping mechanisms. The Shimakawa Model is used in the intermediate temperature range to verify the existence of multiphonons in the compound. The conductance spectra adhere to the Jonscher power law and can be elucidated by the utilization of the Jump relaxation model. The manganite structure deviated from Summerfield scaling, indicating that numerous crystalline-ordered materials possess unexplored conduction and relaxation mechanisms, unlike amorphous systems. Magnetic anomalies at around 6K were observed, indicating antiferromagnetic (AFM) interactions between Dy–Dy pairs. Another anomaly occurs at approximately 40K, indicating AFM coupling between Mn-spins.

Revealing the mechanism and function underlying pairwise temporal coupling in collective motion

Coordinated motion in animal groups has predominantly been studied with a focus on spatial interactions, such as how individuals position and orient themselves relative to one another. Temporal aspects have, by contrast, received much less attention. Here, by studying pairwise interactions in juvenile zebrafish (Danio rerio)—including using immersive volumetric virtual reality (VR) with which we can directly test models of social interactions in situ—we reveal that there exists a rhythmic out-of-phase (i.e., an alternating) temporal coordination dynamic. We find that reciprocal (bi-directional) feedback is both necessary and sufficient to explain this emergent coupling. Beyond a mechanistic understanding, we find, both from VR experiments and analysis of freely swimming pairs, that temporal coordination considerably improves spatial responsiveness, such as to changes in the direction of motion of a partner. Our findings highlight the synergistic role of spatial and temporal coupling in facilitating effective communication between individuals on the move.

Development and Optimization of a Noncircular Pulley for Motion Decoupling in Cable-Driven Serial Robots

Abstract Cable-driven serial robots have emerged with high potential for wide applications due to their compact size and low inertia properties. However, developing this type of robot encounters a motion coupling issue that the movement of one joint leads to the motion of other joints, resulting in complex control. In this paper, we proposed a novel approach for motion decoupling based on a noncircular pulley. The length change of the driving cable caused by the motion coupling problem is resolved by using the noncircular pulley. The calculation process of the profile for the noncircular pulley is illustrated in detail. An optimization process based on the brute force method is presented to identify the optimal parameters to minimize the compensation error. A cable-driven serial robot based on the decoupling method is prototyped for assessments. Experiments are conducted to evaluate the performance of the proposed motion decoupling method. The results reveal that the proposed method can effectively resolve the motion coupling issue by maintaining almost constant cable length with a maximum accumulative error only as 0.086 mm, demonstrating the effectiveness of the method.

Modelling Rigid Body Potential of Small Celestial Bodies for Analyzing Orbit–Attitude Coupled Motions of Spacecraft

The present study aims to propose a general framework of modeling rigid body potentials (RBPs) suitable for analyzing the orbit–attitude coupled motion of a spacecraft (S/C) near small celestial bodies, regardless of gravity estimation models. Here, ‘rigid body potential’ refers to the potential of a small celestial body integrated across the finite volume of an S/C, assuming that the mass of the S/C has no influence on the motion of the small celestial body. First proposed is a comprehensive formulation for modeling the RBP including its associated force, torque, and Hessian matrix, which is then applied to three gravity estimation models. The Hessian of potential plays a crucial role in calculating the RBP. This study assesses the RBP via numerical simulations for the purpose of determining proper gravity estimation models and seeking modeling conditions. The gravity estimation models and the associated RBP are tested for eight small celestial bodies. In this study, we utilize distance units (DUs) instead of SI units, where the DU is defined as the mean radius of the given small celestial body. For a given specific distance in Dus, the relative error of the gravity estimation model at this distance has a similar value regardless of the small celestial body. However, the difference value between the potential and RBP depends on the DU; in other words, it depends on the size of the small celestial body. This implies that accurate gravity estimation models are imperative for conducting RBP analysis. The overall results can help develop a propagation system for orbit–attitude coupled motions of an S/C in the vicinity of small celestial bodies.

Gravitational radiation from eccentric binary black hole system in dynamical Chern-Simons gravity

Dynamical Chern-Simons (DCS) gravity, a typical parity-violating gravitational theory, modifies both the generation and propagation of gravitational waves from general relativity (GR). In this work, we derive the gravitational waveform radiated from a binary slowly-rotating black hole system with eccentric orbits under the spin-aligned assumption in the DCS theory. Compared with GR, DCS modification enters the second-order post-Newtonian (2PN) approximation, affecting the spin-spin coupling and monopole-quadrupole coupling of binary motion. This modification produces an extra precession rate of periastron. This effect modulates the scalar and gravitational waveform through a quite low frequency. Additionally, the dissipation of conserved quantities results in the secular evolution of the semimajor axis and the eccentricity of binary orbits. Finally, the frequency-domain waveform is given in the post-circular scheme, requiring the initial eccentricity to be ≲ 0.3. This ready-to-use template will benefit the signal searches and improve the future constraint on DCS theory.

Deep reinforcement learning and decoupling proportional-integral-derivative control of a humanoid cable-driven hybrid robot

Aiming at the application of robots in service, medical treatment, rehabilitation, and other fields, a humanoid cable-driven hybrid robot by imitating the structure of human arm is designed in this article. The robot is composed of a cable–spool–pulley system, series mechanism, and coaxial spherical parallel mechanism, which can achieve six degrees of freedom movement in space. A challenge with cable driving is that the movement of the rear end joints (such as pitch and roll) can alter the length or tension of the cable driven by the frontend joints, resulting in joint coupling. This interference can lead to a decrease in the motion accuracy of the robotic arm. In addition, it also affects the durability of cables or mechanical components such as bearings and pulleys. Considering the joint motion coupling phenomenon caused by the cable-driven, the decoupling method is proposed, and the kinematic model of the robot is established. To solve the nonlinear coupling characteristics and the uncertainty of the dynamics parameters, a controller is proposed for the humanoid cable-driven hybrid robot, combining proportional-integral-derivative (PID) control based on decoupling method (DC-PID) and the double delay deep deterministic policy gradient (TD3) deep reinforcement learning algorithm. The trajectory tracking of the end-effector position and orientation are controlled by using DC-PID and TD3. And the simulation results show that the proposed control method has good trajectory tracking and convergence performance according to trajectory tracking error and training reward. Finally, the humanoid cable-driven hybrid robot prototype is developed. The experimental results of coupling compensation show that the average maximum error of the joint is reduced by 77.58% after considering the coupling compensation of the joint. The results of the controller validation experiments show that the DC-PID controller reduces the maximum error in each axis by 11.54%, 35.29%, and 40.16%, respectively, compared to the open-loop experiments.

Model-based design optimization for motion decoupling in dual-segment flexible robots

The design of a multiple-segment notched tube is distinctively appropriate for miniature surgical robots, attributing to its superior structural compliance and the provision of a substantial lumen within a constrained diameter. However, the cable-driven mechanism commonly adopted in this design naturally leads to inter-segment motion coupling, limiting its clinical potential. This study introduces a model-based design optimization method aimed at concurrently minimizing the coupled motion of a two-segment notched flexible robot and meeting diverse design and performance criteria. In the design optimization framework, a single-segment mechanics model, a 3-dimensional (3D) coupled mechanics model, and a 3D stiffness model have been developed and integrated to simultaneously minimize the coupled bending angle and satisfy surgery-specific performance requirements. A back propagation neural network (BPNN) has also been adopted to achieve computationally efficient optimization process. A case study is conducted on two-segment notched flexible robot optimization design for maxillary sinus surgery, with the mechanics models being verified experimentally. Ultimately, the optimized robot demonstrates its ability to provide visualization of the maxillary sinus cavity, including the blind spots. The proposed robot design optimization approach offers a systematic and efficient methodology to minimize motion coupling without compromising robot performance, thus fundamentally enabling procedure-specific design of multi-segment flexible surgical robots.

Maritime Moving Target Reconstruction via MBLCFD in Staggered SAR System

Imaging maritime targets requires a high resolution and wide swath (HWRS) in a synthetic aperture radar (SAR). When operated with a variable pulse repetition interval (PRI), a staggered SAR can realize HRWS imaging, which needs to be reconstructed due to echo pulse loss and a nonuniformly sampled signal along the azimuth. The existing reconstruction algorithms are designed for stationary scenes in a staggered SAR mode, and thus, produce evident image defocusing caused by complex target motion for moving targets. Typically, the nonuniform sampling and complex motion of maritime targets aggravate the spectrum aliasing in a staggered SAR mode, causing inevitable ambiguity and degradation in its reconstruction performance. To this end, this study analyzed the spectrum of maritime targets in a staggered SAR system through theoretical derivation. After this, a reconstruction method named MBLCFD (Modified Best Linear Unbaised and Complex-Lag Time-Frequency Distribution) is proposed to refocus the blurred maritime target. First, the signal model of the maritime target with 3D rotation accompanying roll–pitch–yaw movement was established under the curved orbit of the satellite. The best linear unbiased (BLU) method was modified to alleviate the coupling of nonuniform sampling and target motion. A precise SAR algorithm was performed based on the method of inverse reversion to counteract the effect of a curved orbit and wide swath. Based on the hybrid SAR/ISAR technique, the complex-lag time-frequency distribution was exploited to refocus the maritime target images. Simulations and experiments were carried out to verify the effectiveness of the proposed method, providing precise refocusing performance in staggered mode.

Decoupled incremental nonlinear dynamic inversion control for aircraft autonomous landing with ground-effect

Due to motion coupling and increased model dependence, the use of nonlinear controllers in real-time applications for aircraft is extremely constrained. This explains why proportional, derivative, and integral (PID) controls are frequently used in practice. However, fast changes in the commanded path and the requirement for high accuracy and tracking performance limit use of PID in landing. This paper presents a design of a decoupled incremental nonlinear dynamic inversion (INDI) controller for performing autonomous landing of a fixed-wing aircraft. The investigation is carried out using the ground effect model and is compared without it. A carrot chasing guidance algorithm is implemented for waypoint navigation to generate the command for the proposed controller's outer loop. The navigational state estimate issue has been resolved using the Cubature Kalman Filter (CKF) approach. Two decoupled CKF algorithms named complementary Cubature Kalman Filter (CCKF) and Integrated Cubature Kalman Filter (I-CKF) are proposed to estimate aircraft navigational states comprised of attitudes, navigational position in terms of latitude, longitude altitudes, and North-East-down velocities. The mathematical model for flare and approach trajectory is designed and commanded to follow the same by the proposed INDI controller. The effectiveness of INDI have been evaluated in a simulation environment by landing the aircraft in the same runway position at arbitrary wind conditions. The performance of the proposed INDI controller is juxtaposed with a conventional proportional integrator and derivative (PID) based landing controller. The simulation findings demonstrate that the INDI has a competitive edge over traditional PID approaches due to its robust performance, less dependence on model dynamics, and fast command tracking capability required during the flare phase.

Adaptive EKF enhanced fault diagnosis and fault tolerant control for space manipulators with position measurements only

Space manipulators play a critical role in the operation of space robots. However, the failure of these manipulators can affect the control performance and even lead to instability. To improve the safety and robustness of space manipulators, this paper presents an efficient fault diagnosis and fault tolerant control method by integrating adaptive extended Kalman filter (AEKF) and sliding mode control (SMC). The proposed method uses AEKF for system estimation, taking into account uncertainties in the process and measurement noise, as well as sensor limitations. By detecting the failure of angle sensors timely, the trajectory tracking performance can be guaranteed by the robustness of AEKF. In cases where a joint experiences free-swinging, the failure can be identified based on the estimated control effectiveness coefficients from AEKF. Then, once the failure is identified, the joint angle can be regulated by exploiting the motion coupling between the joints. Furthermore, SMC is employed to mitigate the effects of unknown disturbances in the joints. The effectiveness of the proposed method is demonstrated through numerical simulation, which illustrates its ability to diagnose failures and maintain control performance under various failure scenarios. In addition, the robustness of the method is verified through Monte Carlo simulation, demonstrating its reliability in dealing with various uncertainties.

Dynamic characteristics testing and modeling in electromagnetic-thermal-force coupling of electromagnetic devices using parallel finite element simulation

Electromagnetic systems of Electromagnetic devices involve multiphysics coupling of electromagnetic fields, electrical circuits, mechanical motion, and temperature fields. When the digital prototype model has a large number of meshes, the commercial finite element software also has the disadvantage of long computation time in the simulation of dynamic characteristics of electrical apparatus. This paper proposes a transmission line method (TLM) based digital modeling method for the electromagnetic-thermal-force coupling to test and evaluate the static and dynamic characteristics of electromagnetic devices more accurately and efficiently. The case study is developed on a direct current (DC) contactor, and the dynamic characteristics testing and modeling in the electromagnetic-thermal-force coupling of the contactor are investigated. The numerical results of the finite element method (FEM) model for the electromagnetic system of the contactor are compared with the commercial FEM software Altair Flux and the experimental results, which demonstrate the exceptional accuracy of the proposed digital modeling method for the multiphysics coupling of the DC contactor. Meanwhile, the dynamic characteristics of the DC contactor at different ambient temperatures are measured and evaluated, and the comparison with the experimental measurements shows the applicability of the proposed digital prototype model at different ambient temperatures. Compared with the conventional Newton-Raphson (NR) iteration, when dividing fine mesh and extremely fine mesh, the TLM parallel computing significantly improves the efficiency of solving the dynamic characteristics of multiphysics coupling by about 35 % and 44 % with the same computational accuracy, respectively. The dynamic characteristics evaluation method combined with digital modeling technology and experimental measurements proposed in this paper demonstrates high accuracy and solving efficiency, making a notable contribution to the field of design and optimization of electromagnetic devices.

Coupled surface diffusion and mean curvature motion: An axisymmetric system with two grains and a hole

Thin polycrystalline solid state films, which are used in many technological applications, can exhibit various phenomena, such as wetting, dewetting, and hole formation. We focus on a model system containing two contacting grains which surround a hole. For simplicity, the system is assumed to be axisymmetric, to be supported by a planar substrate and to be bounded within an inert semi-infinite cylinder. We assume that the exterior surfaces of the grains evolve by surface diffusion and the grain boundary between the adjacent grains evolve by motion by mean curvature. Boundary conditions are imposed following W.W. Mullins, 1958. Parametric formulas are derived for the steady states, which contain two nodoids describing the exterior surfaces, which are coupled to a catenoid which describes the grain boundary. At steady state, the physical parameters of the system may be prescribed via two angles, β \beta , the angle between the exterior surface and the grain boundary, and θ c \theta _c , the contact angle between the exterior surface and the substrate; additionally, there are two dimensionless geometric parameters which must satisfy certain constraints. We prove that if β ∈ ( π / 2 , π ) \beta \in (\pi /2, \pi ) and θ c = π \theta _c=\pi , then there exists a continuum of steady states. Numerical calculations indicate that steady state profiles can exhibit physical features, such as hillock formation; a fuller numerical study of the steady states and their properties recently appeared in Zigelman and Novick-Cohen [J. Appl. Phys. 134 (2023), 135302], which relies on the formulas and results derived here.

Design and Analysis of a Spatial 2R1T Remote Center of Motion Mechanism for a Subretinal Surgical Robot

With advances in minimally invasive ophthalmic surgery (MIOS), novel vitreoretinal surgeries have been proposed to treat retinal diseases. Due to the limitations of manual techniques, surgical robots have been introduced for such surgeries. Among ophthalmic surgical robots, the remote center of motion (RCM) mechanism is widely used due to its unique advantages. In this paper, a novel RCM is proposed. Based on the configuration, the kinematics and singularity are analyzed. Subsequently, the planar workspace is analyzed based on ocular anatomy and the requirements of MIOS. The optimal configuration is selected according to the workspace coverage analysis, and the three-dimensional workspace is obtained. Finally, a prototype is built, and the motion is validated. When compared with the related prior RCM mechanisms, the resulting design has qualified workspace coverage, more concise kinematics, and reduced motion coupling with all actuators placed at the distal end of the base. The proposed RCM mechanism is suitable for common MIOS. Future research will further optimize the mechanical structure and control algorithm to improve the accuracy of the prototype.

Optimization of wind‐wave hybrid system based on wind‐wave coupling model

AbstractThe integration of wave energy converters (WECs) into floating offshore wind turbine (FOWT) can effectively reduce costs and increase power generation. When WECs are integrated into FOWT, the hydrodynamic interference, motion coupling, and other factors contribute to the high spatial dimension of the coupled optimization, making it difficult to find the globally optimal solution. Therefore, this study proposes an optimization method based on a wind‐wave coupling model, and takes a new wind‐wave hybrid system as an example for verification and analysis. First, the experimental design is completed through random sampling, and the corresponding WECs and wind turbine power of each sample point are calculated using full coupling simulation. And then according to the design input and simulation results, the wind‐wave coupling model is obtained by training the elliptical basis functions neural network (EBFNN). At last, based on this model, the non‐dominated sorting genetic algorithm II (NSGA‐II) is used to optimize the WECs microarray. The results show that the prediction model established in this paper has high accuracy and is used with the NSGA‐II to effectively improve the wind‐wave coupling energy harvesting. This method can effectively solve the problem of high coupling dimensions in the process of hybrid system design.

Effect of penetrant-polymer interactions and shape on the motion of molecular penetrants in dense polymer networks.

The diffusion of dilute molecular penetrants within polymers plays a crucial role in the advancement of material engineering for applications such as coatings and membrane separations. The potential of highly cross-linked polymer networks in these applications stems from their capacity to adjust the size and shape selectivity through subtle changes in network structures. In this paper, we use molecular dynamics simulation to understand the role of penetrant shape (aspect ratios) and its interaction with polymer networks on its diffusivity. We characterize both local penetrant hopping and the long-time diffusive motion for penetrants and consider different aspect ratios and penetrant-network interaction strengths at a variety of cross-link densities and temperatures. The shape affects the coupling of penetrant motion to the cross-link density- and temperature-dependent structural relaxation of networks and also affects the way a penetrant experiences the confinement from the network meshes. The attractive interaction between the penetrant and network primarily affects the former since only the system of dilute limit is of present interest. These results offer fundamental insights into the intricate interplay between penetrant characteristics and polymer network properties and also suggest future directions for manipulating polymer design to enhance the separation efficiency.

A torsion balance as a weak-force testbed for novel optical inertial sensors

Torsion balances (TBs) are versatile instruments known for their ability to measure tiny forces and accelerations with high precision. We are currently commissioning a new TB facility to support the development and testing of novel optical inertial sensor units for future gravity-related space missions. Here, we report on the status of our apparatus and present first sensitivity curves that demonstrate acceleration and torque sensitivities of 5⋅10−11ms−2 and 1⋅10−12NmHz−1 at frequencies around 4mHz , respectively. Capacitive sensors and optical levers measure the dynamics of the system with a displacement sensitivity of down to 9⋅10−10mHz−1 for the former and 2⋅10−11mHz−1 for the latter. Combining the readout of the suspended inertial member (IM) with environmental sensor signals, the system is characterized, and limiting noise sources are identified. We find that, in particular, the coupling of ambient seismic motion is limiting over a broad frequency range and show that due to its high susceptibility to ground motion, our TB is also a promising platform for exploring ground motion sensing in multiple degrees of freedom. Future upgrades will focus on mitigating seismic noise by controlling the torsion fiber suspension point using piezoelectric actuators and the integration of precision interferometric readout of the IM. These improvements will further increase the sensitivity towards the thermal noise limit which constrains the performance to 1⋅10−13ms−2Hz−1 at 4mHz .

Fractional Extended Diffusion Theory to capture anomalous relaxation from biased/accelerated molecular simulations.

Biased and accelerated molecular simulations (BAMS) are widely used tools to observe relevant molecular phenomena occurring on time scales inaccessible to standard molecular dynamics, but evaluation of the physical time scales involved in the processes is not directly possible from them. For this reason, the problem of recovering dynamics from such kinds of simulations is the object of very active research due to the relevant theoretical and practical implications of dynamics on the properties of both natural and synthetic molecular systems. In a recent paper [A. Rapallo et al., J. Comput. Chem. 42, 586-599 (2021)], it has been shown how the coupling of BAMS (which destroys the dynamics but allows to calculate average properties) with Extended Diffusion Theory (EDT) (which requires input appropriate equilibrium averages calculated over the BAMS trajectories) allows to effectively use the Smoluchowski equation to calculate the orientational time correlation function of the head-tail unit vector defined over a peptide in water solution. Orientational relaxation of this vector is the result of the coupling of internal molecular motions with overall molecular rotation, and it was very well described by correlation functions expressed in terms of weighted sums of suitable time-exponentially decaying functions, in agreement with a Brownian diffusive regime. However, situations occur where exponentially decaying functions are no longer appropriate to capture the actual dynamical behavior, which exhibits persistent long time correlations, compatible with the so called subdiffusive regimes. In this paper, a generalization of EDT will be given, exploiting a fractional Smoluchowski equation (FEDT) to capture the non-exponential character observed in the relaxation of intramolecular distances and molecular radius of gyration, whose dynamics depend on internal molecular motions only. The calculation methods, proper to EDT, are adapted to implement the generalization of the theory, and the resulting algorithm confirms FEDT as a tool of practical value in recovering dynamics from BAMS, to be used in general situations, involving both regular and anomalous diffusion regimes.

Classical ‘Spin’ Filtering with Two Degrees of Freedom and Dissipation

Coupling of orbital motion to a spin degree of freedom gives rise to various transport phenomena in quantum systems that are beyond the standard paradigms of classical physics. Here, we discuss features of spin-orbit dynamics that can be visualized using a classical model with two coupled angular degrees of freedom. Specifically, we demonstrate classical ‘spin’ filtering through our model and show that the interplay between angular degrees of freedom and dissipation can lead to asymmetric ‘spin’ transport.

Coupled Rotary Motion in Molecular Motors.

Biological molecular machines play a pivotal role in sustaining life by producing a controlled and directional motion. Artificial molecular machines aim to mimic this motion, to exploit and tune the nanoscale produced motion to power dynamic molecular systems. The precise control, transfer, and amplification of the molecular-level motion is crucial to harness the potential of synthetic molecular motors. It is intriguing to establish how directional motor rotation can be utilized to drive secondary motions in other subunits of a multicomponent molecular machine. The challenge to design sophisticated synthetic machines involving multiple motorized elements presents fascinating opportunities for achieving unprecedented functions, but these remain almost unexplored due to their extremely intricate behavior. Here we show intrinsic coupled rotary motion in light-driven overcrowded-alkene based molecular motors. Thus far, molecular motors with two rotors have been understood to undergo independent rotation of each subunit. The new bridged-isoindigo motor design revealed an additional dimension to the motor's unidirectional operation mechanism where communication between the rotors occurs. An unprecedented double metastable state intermediate bridges the rotation cycles of the two rotor subunits. Our findings demonstrate how neighboring motorized subunits can affect each other and thereby drastically change the motor's functioning. Controlling the embedded entanglement of active intramolecular components sets the stage for more advanced artificial molecular machines.