Influence Of External Perturbations Research Articles

The impact of external perturbations on postural control

Purpose External factors can disrupt postural control, but the intricate workings of the postural control system enable an appropriate response. This study seeks to assess how external perturbations affect postural control. Methods Twenty women participated in study, which consisted four trials involved quiet standing and experiencing induced perturbations by being struck with a boxing bag from the back, right, and left sides, respectively. The center of pressure (CoP) path length was recorded for each of the mentioned trials. Sample Entropy (SampEn), Lyapunov Exponent (LyE), and Fractal Dimension (FD) were computed for the CoP time series, separately for the anterior-posterior (AP) and mediolateral (ML) directions. The nonparametric Friedman ANOVA with Dunn-Bonferroni post-hoc analysis was employed to investigate the influence of external perturbations on both linear and nonlinear parameters on postural control. Results The post-hoc analysis showed for LyE_AP_quiet (1.02 ± 0.18) significantly higher values than for LyE_AP_right (0.92 ± 0.22) and significantly higher for LyE_AP_left. Lyapunov Exponent was the parameter that differentiated the most between samples. Conclusions The greatest number of significant differences between samples were demonstrated by the Lyapunov Exponent. This nonlinear parameter should be used to evaluate various perturbations during upright position in healthy subjects.

Sliding-mode observer-based fault diagnosis and fault-tolerant control of the main drive system of rolling mill

In order to address the problem that the main drive system of rolling mill is easily affected by the impact of biting steel, and considering the nonlinear friction damping and the external perturbations of the main drive system of rolling mill during the rolling process, a fault model of the main drive system of rolling mill is established, and a fault diagnosis and fault tolerance control method of the main drive system of rolling mill based on the nonlinear sliding-mode observer is proposed. In order to suppress the influence of external perturbations on fault diagnosis, a nonlinear sliding-mode observer is constructed for fault diagnosis and fault reconfiguration of the system, and the robustness of the observer to fault reconfiguration is improved by using the sliding-mode control rate [Formula: see text], and the stability of the designed nonlinear sliding-mode observer is proved using Lyapunov’s stability theorem. In order to ensure that the system can operate normally even after a fault occurs, a reference model is designed, and a new controller is redesigned for fault-tolerant control of the system by adding a fault compensation term to the original control scheme using fault estimation information. Through the simulation study of the main drive system of stand F4 of 2030 mm cold rolling mill, it is verified that the observer can accurately track the system state with an angular velocity error of 2.45% and detect and estimate the main drive system failure of rolling mill with an estimation error of no more than 0.04% after a fault occurs; the fault-tolerant control of the main drive system of rolling mill is carried out by using the fault information to restore the system to its normal state, and the angular velocity error is 1.89%.

The response of small-scale shear layers to perturbations in turbulence

The perturbation response of small-scale shear layers in turbulence is investigated with direct numerical simulations (DNS). The analysis of shear layers in isotropic turbulence suggests that the typical layer thickness is about four times the Kolmogorov scale $\eta$ . Response for sinusoidal perturbations is investigated for an isolated shear layer, which models a mean flow around the shear layers in turbulence. The vortex formation in the shear layer is optimally promoted by the perturbation whose wavelength divided by the layer thickness is about 7. These results indicate that the small-scale shear instability in turbulence is efficiently promoted by velocity fluctuations with a wavelength of about $30\eta$ . Furthermore, DNS are carried out for decaying turbulence initialised by the artificially modified velocity field of isotropic turbulence. The vortex formation from shear layers is accelerated under the influence of external perturbations with the efficient wavelength to promote the instability. When velocity fluctuations with this wavelength are eliminated by a band-cut filter, the shear layers tend to persist for a long time without producing vortices. These behaviours affect the number of vortices in turbulence, which increases and decreases when velocity perturbations with the unstable wavelength of the instability are artificially amplified and damped, respectively. The increase in the number of vortices results in the enhancement of kinetic energy dissipation, enstrophy production and strain self-amplification. These results indicate that the perturbation response of shear layers is important in the small-scale dynamics of turbulence as well as the modulation of small-scale turbulent motions by external disturbance.

Analysis of Critical Phenomena in a Dynamic System Under the Influence of Random Perturbations

The paper is devoted to the study of stochastic models of an electrochemical reaction with a perturbation described by a generalized white-noise random process. Noise-induced transitions are analyzed, the influence of external perturbations on limit cycles is examined, and the sensitivity of the cycle to noise was found. The dependence of the threshold value of the noise intensity on the control parameter of the system is established. The critical value of the noise intensity at which small-amplitude oscillations turn into mixed-type oscillations is obtained. The critical value of noise corresponding to the transition from canard trajectories to relaxation oscillations in the model is found. It is shown that an increase in the intensity of random perturbations can lead to significant changes of oscillation modes of the model up to their destruction.

Alteration of ankle proprioceptive threshold during gait in the presence of acute experimental pain.

ObjectiveHuman gait requires complex somatosensory processing of various inputs such as proprioception. Proprioception can be altered in the presence of pain. This has been shown mostly during controlled tasks, thereby limiting the influence of external perturbations. While controlling the environment is sometimes warranted, it limits the ecological validity of the data. Using robotic orthoses to apply perturbations during movements seems a promising tool to functionally assess proprioception, where the complex somatosensory processing required in real-life situations is at play. The main objective of this study was to compare the proprioceptive threshold of healthy participants during gait in the presence and absence of an acute experimental pain.Methods36 healthy participants walked on a treadmill while wearing a robotized ankle–foot orthosis (rAFO) around their right ankle. The rAFO applied torque perturbations of graded magnitudes during the swing phase of gait. Participants had to report the presence/absence of such perturbations, as a measure of proprioceptive threshold. Following initial assessment, they were randomly assigned to one of three experimental groups: Control (no stimulation), Painless (non-nociceptive stimulation) and Painful (nociceptive stimulation). Electrodes placed on the right lateral malleolus delivered an electrical stimulation during the second assessment for Painless and Painful groups. A Kruskal-Wallis was used to compare the percentage of change of the three groups between the two assessments.ResultsA 31.80±32.94% increase in proprioceptive threshold, representing an increase of 1.3±1.2 Nm in the detection threshold, was observed for the Painful group only (p<0.005), with an effect size of 1.6.ConclusionFindings show that the presence of pain at the ankle can alter participants’ proprioceptive threshold during gait. Clinical assessment of proprioception should therefore carefully consider the presence of pain when evaluating a patient’s performance using clinical proprioceptive test and consider the negative effect of pain on proprioceptive threshold for test interpretation.

A study on the effects of anion, cation, organic compounds, and pH on the release behaviors of As and Sb from sediments.

The trace element of As and Sb have resulted in serious threats to ecological sustainability and human health in the Xijiang River basin, China. The geoaccumulation index (Igeo) results showed the sediment of Xijiang River was heavily contaminated by Sb as well as moderately contaminated by As. The effect of inorganic anions on the released As and Sb from the sediment increases in the following sequence: Cl- < SO42- < CO32- < PO43-. The presence of PO43- and CO32- had the greater effect over As mobility from the sediment compared to Sb. The effect of Ca(II), Al(III), and Mg(II) on the released amount of Sb from the sediment is negligible. Meanwhile, in the case of As, Ca(II) and Mg(II) had small impacts, but the released amount of As increased slightly with an increase of Al(III) concentration. The stability of As and Sb in the sediment was found to be the best at pH 5. The effect of organic compounds (≤ 0.05 mol/L) on the dissolved As percentages from the sediment increased in the following sequence: ethylenediaminetetraacetate (EDTA) < oxalate < citrate, and the effect on Sb release was oxalate < EDTA < citrate at concentrations (≤ 0.025 mol/L). This study provides the basic theoretical basis to manage the mobilization of co-contamination of sediments with As and Sb under the influence of external perturbations.

Correction of Human Forehead Temperature Variations Measured by Non-Contact Infrared Thermometer

Elevated body temperature (fever) can be a common symptom of a medical condition, such as a viral or bacterial infection, including SARS-CoV-2 or influenza. Non-contact infrared thermometers are able to measure forehead temperature in a timely manner and were used to perform a fast fever screening in a population. However, forehead temperature measurements differ greatly from basal body temperatures, and are the target of massive perturbations from the environment. Here we gathered a dataset of N=18024 measurements using the same precision infrared sensor in different locations while tracking both outside temperature, room temperature, time of measurement, and identity. Herein, we propose a method able to extract and remove the influence of external perturbations, and set the threshold for fever detection to 37.38 °C, after calibration and temperature correction. This method can help manufacturers and decision-makers to build and use more accurate tools so as to maximize both sensitivity and specificity of the screening protocol.

Revised electrochemical etching system for a reproducible fabrication of ultra-sharp tungsten tips

This article proposes an improved version of the drop-off electrochemical etching technique, developed for a reproducible production of ultra-sharp metal tips. Firstly, a comprehensive survey of other mechanical and physicochemical procedures is made in order to individuate three issues commonly neglected: (i) the influence of external perturbations, (ii) the positions of the electrode (a W wire) and counter-electrode (a Pt ring) and (iii) the counter-electrode shape. These issues need to be carefully fixed, in an enclosed and geometrically well-defined configuration, to better control the opening angle, radius of curvature and aspect ratio. The quality of the tips produced is evaluated comparing their performances, in imaging a reference sample with scanning tunnelling microscopy, to those of commercial tips. Using established procedures and data reported in the literature, an optimal set of the parameters can be identified obtaining high-quality tips with an opening angle < 10° and a radius of curvature ~ 30 nm. Furthermore, achieving a higher reproducibility allows us to investigate the electrochemical process monitoring the time dependence of the current from the etching parameters, such as the wire immersion, electrolyte concentration and applied bias voltage. Thus, the current versus time curves can be analysed in terms of linear scan voltammetry and electrochemical impedance spectroscopy, in order to investigate the phenomena occurring during the wire etching. In particular, at the beginning of the electrochemical process, the replacement of the native W oxide with a thicker layer of WO3(H2O)x oxide is observed, in agreement with previous observations.

Improvement of the transfer function quality indicators of the power control system at the electric drill engine shaft

In order to get better rigs performance the authors improve the schematic diagram of the power control system at the electric drill engine shaft using control input transfer function, where the electric drill is considered to be the control object which operates in conditions of a priori and current uncertainty under the influence of external perturbations. To improve the quality of the transient process under the conditions of changes in the parameters of the control object (when these parameters cannot be checked on), the authors have developed the algorithm of tuning the adaptive fuzzy PID controller based on the hybrid adaptive system. This algorithm includes the advantages of artificial neural networks and fuzzy logic. The efficiency of the algorithm with the parametric disturbance has been shown. It is concluded that the implementation of adaptive fuzzy PID controllers makes it possible to improve the quality of the transfer function of the power control system at the electric drill engine shaft when this drill operates in the indefinite conditions. The advantage of the developed algorithm is that it does not require special methods of the object parameters identification. Its implementation using modern microcontrollers is quite simple and accessible.

The electron-related optical responses for the square tangent quantum well: Role of applied external fields

In the present work, a detailed investigation of the influence of external perturbations, in particular intense terahertz radiation, static electric and magnetic fields on the electron-related optical responses such as total optical absorption coefficients and relative refractive index changes for a quantum well with the square tangent potential is presented. The subband energy levels and their corresponding wave functions are obtained by solving the one-electron Hamiltonian of the system under the framework of the effective-mass and parabolic band approximations. Optical coefficients are reported for varying incident photon energies. The numerical results show that the optical response is shifted towards the blue with the increase in the magnitude of the applied external fields. These results can provide an input for use in optoelectronic device applications.

Application-oriented type synthesis and coupling kinematics analysis of a 1Rx2Tyz parallel stabilized platform for tunnel detection system

For collecting image high precisely, the application-oriented type synthesis and kinematics analysis for parallel vehicle-based stabilized platform are systematically carried out. Firstly, taking multi-camera install center and vehicle trajectory offset as research objects, the influence of external perturbation on visual system is analyzed quantitatively by numerical calculation and field testing. On this basis, a new type of 2SPR/RPS parallel mechanism with two-translational and one-rotational degree of freedoms is presented. Secondly, by analyzing the motion characteristic of 2SPR/RPS parallel mechanism, the motion adjoint transformation and input–output mapping for parallel vehicle-based stabilized platform are proposed by screw description of rigid-body movement. In addition, an experimental prototype is developed, and the results between numerical examples and semi-physical simulations are compared in order to prove the validity of theoretical analysis. Finally, based on the concept of influence of external perturbations on tunnel detecting system, an external parameter identify method for coupling pose and object distance of visual system is studied. The results can be extended to development, application, and performance evaluation for parallel vehicle-based stabilized platform in next step.

Synthesis and technical realization of control systems with discrete fractional integral-differentiating controllers

Control systems with a fractional order which provide better dynamic and static indicators for many technical objects in comparison with systems with integer order of astaticism were studied. Based on the analysis of frequency characteristics, transient processes and a modified criterion for quality assessment, optimal relationships between parameters of the desired transfer function were obtained. Normalized transition functions of closed systems with the order of astaticism from 1 to 2 were presented with overregulation less than 2...5 % on the basis of which parameters can be chosen and the controller structure determined. The process of stabilizing cutting power was analyzed for a milling machine as an example of the systems with nonlinear parametric and structural dependences in control and perturbation channels. It was shown that fractional integral-differentiating controllers make it possible to provide the order of astaticism from 1.3 to 1.7 and permissible level of overregulation in a wide range of external perturbing influences. A method for approximate calculation of fractional integrals based on the approximation of the highest coefficients of expansion in a series of geometric progressions was developed. It provides reduction of the memory capacity required to store the coefficient arrays and the history of the input signal and requires significantly less CPU time to calculate the controller signal. For example, for controllers based on the Intel® Quark ™ SoC X1000 or FPGA Altera Cyclone V, the quantization period is 6...15 μs and several milliseconds for Atmega328. This makes it possible to implement fractional integral-differentiating controllers based on widely used modern processors and apply fractional-integral calculus methods for synthesis of high-speed automatic control systems. The proposed methods can be used in the control of the objects both with fractional and integer orders of differential equations.

Motor adaptations to trunk perturbation: effects of experimental back pain and spinal tissue creep.

In complex anatomical systems, such as the trunk, motor control theories suggest that many motor solutions can be implemented to achieve a similar goal. Although reflex mechanisms act as a stabilizer of the spine, how the central nervous system uses trunk redundancy to adapt neuromuscular responses under the influence of external perturbations, such as experimental pain or spinal tissue creep, is still unclear. The aim of this study was to identify and characterize trunk neuromuscular adaptations in response to unexpected trunk perturbations under the influence of spinal tissue creep and experimental back pain. Healthy participants experienced a repetition of sudden external trunk perturbations in two protocols: 1) 15 perturbations before and after a spinal tissue creep protocol and 2) 15 perturbations with and without experimental back pain. Trunk neuromuscular adaptations were measured by using high-density electromyography to record erector spinae muscle activity recruitment patterns and a motion analysis system. Muscle activity reflex attenuation was found across unexpected trunk perturbation trials under the influence of creep and pain. A similar area of muscle activity distribution was observed with or without back pain as well as before and after creep. No change of trunk kinematics was observed. We conclude that although under normal circumstances muscle activity adaptation occurs throughout the same perturbations, a reset of the adaptation process is present when experiencing a new perturbation such as experimental pain or creep. However, participants are still able to attenuate reflex responses under these conditions by using variable recruitment patterns of back muscles. NEW & NOTEWORTHY The present study characterizes, for the first time, trunk motor adaptations with high-density surface electromyography when the spinal system is challenged by a series of unexpected perturbations. We propose that the central nervous system is able to adapt neuromuscular responses by using a variable recruitment pattern of back muscles to maximize the motor performance, even under the influence of pain or when the passive structures of the spine are altered.

Phase oscillator model for noisy oscillators

The Kuramoto model has become a paradigm to describe the dynamics of nonlinear oscillator under the influence of external perturbations, both deterministic and stochastic. It is based on the idea to describe the oscillator dynamics by a scalar differential equation, that defines the time evolution for the phase of the oscillator. Starting from a phase and amplitude description of noisy oscillators, we discuss the reduction to a phase oscillator model, analogous to the Kuramoto model. The model derived shows that the phase noise problem is a drift-diffusion process. Even in the case where the expected amplitude remains unchanged, the unavoidable amplitude fluctuations do change the expected frequency, and the frequency shift depends on the amplitude variance. We discuss different degrees of approximation, yielding increasingly accurate phase reduced descriptions of noisy oscillators.

Geometrical Description of Chemical Equilibrium and Le Châtelier’s Principle: Two-Component Systems

Chemical equilibrium is one of the most important concepts in chemistry. The changes in properties of the chemical system at equilibrium induced by variations in pressure, volume, temperature, and concentration are always included in classroom teaching and discussions. This work introduces a novel, geometrical approach to understanding the chemical system at equilibrium with the example of a simple two-component system and shows how the equilibrium changes under the influence of external perturbations. The paper discusses how thermodynamic factors (contained in the equilibrium constant K) and the conservation of mass principle govern the equilibrium state. The equilibrium and its changes are described using the geometrical representation in concentration space. The goal of this work is to help students better understand the basis behind the well-known Le Châtelier’s principle and equilibrium in general.

Extragradient method for finding a saddle point in a multicriteria problem with dynamics

We consider an optimal control problem for a linear system of ordinary differential equations with an implicitly given boundary condition connected with a multicriteria problem. Such problems arise, for example, in the study of controlled objects that lose their stability under the influence of external perturbations, where it is required to return an object to stability by means of an appropriate choice of the control. We describe a possible mathematical model of this kind, propose an extragradient method for recovering the stability, and investigate its convergence.

Discontinuous H ∞ control of underactuated mechanical systems with friction and backlash

Nonlinear H∞-control is extended to discontinuous mechanical systems with degree of underactuation one, where nonlinear phenomena such as Coulomb friction and backlash are considered. The problem in question is to design a feedback controller via output measurements so as to obtain the closed-loop system in which all trajectories are locally ultimate bounded, and the underactuated link is regulated to a desired position while also attenuating the influence of external perturbations and nonlinear phenomena. It is considered that positions are the only measurements available for feedback in the system. Performance issues of the discontinuous H∞-regulation controller are illustrated in an experimental study made for a rectilinear plant with friction modified to have a gap in the point of contact between bodies.

Information Transfer and Conformation Change in Network of Coupled Oscillator

Abstract: In this paper, we investigate the problem of conformation change in a network of coupled oscillator system with double well internal potential. Conformation change refers to the phenomena where all the oscillators in the network make a transition from one potential well to another potential well under the influence of external perturbation. We propose a novel approach based on information transfer in network dynamical systems to understand this phenomenon. We consider a heterogeneous network system where the internal dynamics of the oscillators are assumed to be nonidentical and the interconnecting Laplacian can also be asymmetric. The objective is to determine which of the network oscillator is most influential in driving the conformation dynamics. We show that the net information transfer of individual oscillators can be used to determine the most influential oscillator which can drive the entire network from one well to another well of the potential. We use three different network topologies to verify our proposed framework.

Edge states in graphene-like systems

The edges of graphene and graphene like systems can host localized states with evanescent wave function with properties radically different from those of the Dirac electrons in bulk. This happens in a variety of situations, that are reviewed here. First, zigzag edges host a set of localized non-dispersive state at the Dirac energy. At half filling, it is expected that these states are prone to ferromagnetic instability, causing a very interesting type of edge ferromagnetism. Second, graphene under the influence of external perturbations can host a variety of topological insulating phases, including the conventional quantum Hall effect, the quantum anomalous Hall (QAH) and the quantum spin Hall phase, in all of which phases conduction can only take place through topologically protected edge states. Here we provide an unified vision of the properties of all these edge states, examined under the light of the same one orbital tight-binding model. We consider the combined action of interactions, spin–orbit coupling and magnetic field, which produces a wealth of different physical phenomena. We briefly address what has been actually observed experimentally.

Исследование алгоритмов адаптации управляю- щего воздействия для приводов робототехнических систем с помощью симулятора межкоординатных возмущений

In this paper we review algorithms of technologic trajectory correction for coordinate actuators of robot effectors. The target of controlling these effectors is essentially the motion of controlled object along the given trajectory and also (if necessary) the adaptation of an programmed traectory to the actual one under the influence of perturbations from the object or from the technological process. The object of our research is the motion actuator with the feedback of the position of an effector. The adjacent coordinate actuator is implemented as a simulation of the intercoordinate perturbations. Control is based on a fourth form of invariance. The first algorithm in this article includes the synthesis of the additional component and its inclusion into the already devised control action. This additional component is a torque error function of an uncalculated perturbation. The second algorithm is a correction of derivative signal levels performed during a stage of the control action synthesis while the technological process executes. Correction of the control action in the control component is performed on a software level and does not involve changes in the main actuator circuit, i.e. the inner properties and therefore the dynamic characteristics of an actuator are not influenced. In this paper we provide an analysis of the control system precision in the mode of constant velocity motion, while processing the harmonic input signal for channels of the position, velocity and acceleration signal adaptation. The test actuator in constant velocity motion exhibits the positioning error ranging from 5% to 10% due to the influence of the adjacent coordinate simulation. Introducing the adaptation circuit allowed us to reduce the influence of external perturbations during the technological process execution to a minimum (positioning error is &lt;0.5%) Simulation results show that the link with variable transmission coefficient is essential. During the simulation we formulate dependences of the transmission coefficient in the adaptation channel. The results of the research confirm the efficiency of algorithms considered in this paper.