Influence Of Perturbations Research Articles

Influence of Perturbation’s Type and Location on Treadmill Gait Regularity

Background: This study aimed to investigate how —external perturbations caused by a treadmill belt’s acceleration (Acc) and deceleration (Dec) during the Initial-Contact (Initial), Mid-Stance (Mid), and Pre-Swing (ToeOff) phases affect gait regularity in young adults. Methods: Twenty-one healthy young females walked on a treadmill in a virtual environment (Motek GRAIL), in which four unexpected perturbations were applied to the left belt at the Initial, Mid, and ToeOff stages. Sample entropy (SampEn) was calculated for the center of mass (CoM) displacements for six perturbation scenarios in three directions—anterior–posterior (AP), medial–lateral (ML), and vertical (vert)—with SampEn vector lengths (m) ranging from 2 to 10. Results: The CoM displacement exhibited its highest regularity (low SampEn values) in the AP and vert directions during Dec–ToeOff, across all m values. Similarly, this pattern was observed in the ML direction, but exclusively for m = 2 and 4. The least-regular CoM trajectories (high SampEn values) were for Dec–Mid in the AP direction, across all m values. This trend persisted in the ML direction only for m = 2 and 4. However, the most irregular CoM displacements in the ML direction occurred during Dec–ToeOff for the remaining m values. Vertical CoM displacements exhibited the highest irregularities during Dec–Initial for m ≥ 4. Conclusions: Evaluating the regularity of CoM displacements using SampEn can be a useful tool for assessing how gait perturbations are handled.

Urbanization-Driven Anthropogenic and Environmental Factors Shape Soil Dissolved Organic Matter in Mangrove Ecosystems

Mangrove ecosystems play a critical role in supporting ecological service values and regulating the global carbon cycle. They have become one of the most highly vulnerable ecosystems in the Anthropocene under the long-term influence of diverse human perturbations. Soil dissolved organic matter (DOM) is an active fraction within the carbon cycle in mangrove ecosystems. However, it remains unclear how human perturbations regulate DOM dynamics. Here, we used the fluorescence method and structural equation modeling to quantify the anthropogenic and environmental influence on soil DOM across the urban development gradient on a national scale in China. Anthropogenic activities (urban construction and sewage discharge) and environmental factors (salinity, metals, pH, and soil organic carbon) were striking forces that shaped DOM quality in mangrove soils. Both indirect and direct effects played critical roles in the soil DOM heterogeneity across the gradient of urbanization. Environmental factors can act as cofactors mediating human impact on DOM pools and as promoters transforming soil DOM in mangroves. Our study provided novel insights into the relationship between coastal developments and mangrove soil DOM heterogeneity and improved knowledge of coastal ecosystems as blue carbon sinks.

The interface instability development induced by the bulk density perturbations in accelerated media

The development of hydrodynamic instabilities has a significant impact on the operation of laser fusion systems. During radiation compression, the shells of a target are accelerated, resulting in the growth of perturbations at their interfaces. In this paper, we study the influence of density perturbations on the stability of the contact boundary during accelerated motion. The analysis is performed in a two-dimensional planar formulation using the linear approximation and assuming a weak spatial dependence on the temperature near the contact boundary. Due to the consideration of small time intervals, the phenomenon of heat conduction is not taken into account. The cases of acceleration of a medium described by the Mie–Grüneisen equation of state (EoS) into a vacuum and of acceleration of two contacting media, each described by the ideal plasma EoS, are considered. The time dependence of the amplitude of the boundary perturbation on time is obtained. The obtained values are in agreement with the results of numerical analysis. It is shown that the boundary curvature occurs independently of the acceleration direction. The theoretical results are compared with numerical results for laser fusion systems.

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.

Constellation attitude tracking control of the space gravitational wave observatory under configuration disturbances

Space based gravitational wave detectors require a precision relative attitude pointing control in science mode. Their configuration drifts under the influence of perturbations. The spacecraft and telescope optical assembly attitude control loops need to respond to this change in real time. In particular, the constellation reference attitude of the detectors orbiting the earth changes much more than the detectors orbiting the sun, which posing a great challenge to the control system. This article focuses on the constellation attitude tracking problem of the space gravitational wave observatory under configuration disturbances, and systematically analyzes the evolution of the constellation reference attitude. A control method based on finite frequency optimization combine with an improved error-disturbance based observer is proposed. Numerical algorithm simulations show that the method can obtain precise attitude tracking in the measurement bandwidth while effectively suppress the unknown disturbances. Compare with the disturbance based observer controller, the overall error can be reduced by 55% of the original.

Research on constellation attitude synchronous tracking control for space gravitational wave measurement

Space based gravitational wave detectors require a precision relative attitude pointing control in science mode. Their configuration drifts sensitively under the influence of perturbations. The spacecraft and telescope optical assembly attitude control loops need to respond to this change in real time to maintain an ultra-high precision laser pointing. To implement precision gravitational wave scientific measurement, distributed detector systems need to coordinate the relative attitude pointing between spacecrafts in the constellation. This article proposes a synchronization coordination control method based on state estimation feedforward and finite frequency domain optimization. The simulation results show that the synchronization and coordination tracking of the relative attitude between satellites can be achieved under configuration perturbations, and the jitter in the ultra-low frequency range can be effectively reduced. Especially in the frequency range below 10−3 Hz, the stability of the line of sight attitude pointing is improved from 10−6 rad/Hz1/2 to 10−9 rad/Hz1/2. The absolute attitude pointing performance and stability are greatly improved.

Magnetic field influence on the light yield from fiber-coupled BCF-60 plastic scintillators of relevance for output factor dosimetry in MR-linacs

Organic plastic scintillators are of interest for ionizing radiation dosimetry in megavoltage photon beams because plastic scintillators have a mass density very similar to that of water. This leads to insignificant perturbation of the electron fluence at the point of measurement in a water phantom. This feature is a benefit for dosimetry in strong magnetic fields (e.g., 1.5 T) as found in linacs with magnetic resonance imaging. The objective of this work was to quantify if the light yield per dose for the scintillating fiber BCF-60 material from Saint-Gobain Ceramics and Plastics Inc. is constant regardless of the magnetic flux density. This question is of importance for establishing traceable measurement in MR linacs using this detector type. Experiments were carried out using an accelerator combined with an electromagnet (max 0.7 T). Scintillator probes were read out using chromatic stem-removal techniques based on two optical channels or full spectral information. Reference dosimetry was carried out with PTW31010 and PTW31021 ionization chambers. TOPAS/GEANT4 was used for modelling. The light yield per dose for the BCF-60 was found to be strongly influenced by the magnitude of the magnetic field from about 1 mT to 0.7 T. The light yield per dose increased (1.3 ± 0.2)% (k = 1) from 1 mT to 10 mT and it increased (4.5 ± 0.9)% (k = 1) from 0 T to 0.7 T. Previous studies of the influence of magnetic fields on medical scintillator dosimetry have been unable to clearly identify if observed changes in scintillator response with magnetic field strength were related to changes in dose, stem signal removal, or scintillator light yield. In the current study of BCF-60, we see a clear change in light yield with magnetic field, and none of the other effects.

Adaptive active and reactive power control strategy for virtual synchronous generator

SummaryWith the increase in the penetration level of renewables into the grid, the virtual synchronous generator (VSG) concept has emerged as an attractive solution for controlling grid‐tied inverters. The variation in reactive power also affects the real power of the system as well. To address the voltage variations and phase angle variations occurring because of the energy storage elements, the control of the reactive power loop (RPL) is important. Also, it is used to maintain voltage regulation and improve the power factor of the VSG system. This paper focuses on the damping of oscillations occurring because of load variation by proper adjustment of the rotational inertia, damping coefficient, droop coefficient, and regulatory coefficient of reactive power with a proposed adaptive control strategy. Small‐signal analysis of the active and reactive power and point of common coupling (PCC) have been derived, and the detailed dynamic performances are analyzed. The influences of parameters perturbation on PCC voltage and reactive power were investigated. Furthermore, adaptive control includes optimizing dynamic indexes such as rise time, delay time, and response settling time. Finally, the performance and improvement in the results of VSG with and without adaptive control are compared.

An adaptive feed-forward active vibration isolation algorithm for input disturbance unbalanced MIMO systems

Multi-axis active vibration isolation systems often encounter order-of-magnitude differences in the perturbations in each input direction. This causes adaptive feedforward control systems to converge at a relatively slow rate, or possibly even diverge. To solve this problem, we propose an improved adaptive feedforward vibration isolation technique based on the classical FxLMS algorithm. Our approach constructs a weighted transformation matrix based on singular value decomposition, attenuates the uneven influence of the input perturbations, and effectively avoids the problems of slow convergence and poor stability faced by existing adaptive algorithms. This paper first describes the parameter update algorithm and the structure of adaptive feedforward algorithms. The convergence of the proposed algorithm is then analyzed, and the method for constructing the weighting matrix is introduced. Finally, the feasibility of the algorithm is verified using a multi-axis vibration isolation system simulation model. The simulation results show that the power spectrum of acceleration in the frequency domain from 0.1 to 100 Hz is attenuated by up to 70 dB under the condition of no excitation in a specific direction, demonstrating the vibration isolation effect of the algorithm. The relative deviation between the predicted and actual parameter error is no more than 6 %, which shows that the algorithm achieves good convergence. The proposed algorithm has potential applications in the active vibration isolation of space telescopes and high-precision optical equipment.

Synchronous and Fully Steerable Active Particle Systems for Enhanced Mimicking of Collective Motion in Nature.

The collective motion observed in living active matter, such as fish schools and bird flocks, is characterized by its dynamic and complex nature, involving various moving states and transitions. By tailoring physical interactions or incorporating information exchange capabilities, inanimate active particles can exhibit similar behavior. However, the lack of synchronous and arbitrary control over individual particles hinders their use as a test system for the study of more intricate collective motions in living species. Herein, a novel optical feedback control system that enables the mimicry of collective motion observed in living objects using active particles is proposed. This system allows for the experimental investigation of the velocity alignment, a seminal model of collective motion (known as the Vicsek model), in a microscale perturbed environment with controllable and realistic conditions. The spontaneous formation of different moving states and dynamic transitions between these states is observed. Additionally, the high robustness of the active-particle group at the critical density under the influence of different perturbations is quantitatively validated. These findings support the effectiveness of velocity alignment in real perturbed environments, thereby providing a versatile platform for fundamental studies on collective motion and the development of innovative swarm microrobotics.

Quasi discreteness analysis of a 2-dimensional Heisenberg ferromagnetic spin system with biquadratic interactions

The dynamical theory of soliton excitations in two-dimensional ferromagnets is studied by introducing a Hamiltonian that includes biquadratic interaction along with uniaxial anisotropy. To obtain a dynamical equation of motion, we use the Dyson-Maleev transformation and the coherent state ansatz. We obtain a Nonlinear Schrdinger equation by applying the multiple-scale and quasi-discreteness methods. For the more general nonintegrable case, we perform a multiple scale perturbation analysis to determine the discreteness effect on the soliton excitations. Finally, we examine modulational instability (MI) under the influence of small perturbations.

A co-design condition for dynamic event-triggered feedback linearization control

This paper presents a novel approach for dynamic event-triggered feedback linearization control of nonlinear systems. Two main aspects should be accounted for in this context: the internal perturbation induced by the sampling error and the stability of the internal dynamics. To deal with the first aspect, a trigger function is designed to cancel out the influence of the internal perturbation completely. Concerning the second one, a sufficient stability analysis condition is derived by representing the internal dynamics as a polytopic differential inclusion. These two ingredients allow for performing the co-design of dynamic event-triggered feedback linearization controllers. A multi-objective optimization problem with linear matrix inequality constraints is formulated to achieve the maximization of the estimate of the region of attraction and the minimization of the number of transmissions. Numerical examples illustrate the effectiveness of the proposed approach.

Analysis of the impact of treatments on HIV/AIDS and Tuberculosis co-infected population under random perturbations

In this work, we study the impact of treatments at different stages of Human Immunodeficiency Virus (HIV) and Tuberculosis (TB) co-infection in a population under the influence of random perturbations. This is achieved by constructing a stochastic epidemic model describing the transmission and treatment of the diseases. The model is created with the assumption that transmission rates fluctuate rapidly compared to the evolution of the untreated diseases. The basic reproduction numbers corresponding to the population with HIV infection only (with n stages of infections and treatments), the population with tuberculosis infection only, and the overall population with co-infection (with n stages of infection/treatments) are derived in the presence and absence of noise perturbations. These are used to discuss the long term behavior of the population around a disease-free equilibrium and an endemic equilibrium, and to analyze the effect of noise and treatments on the system. We also showed conditions under which TB infected population dynamic undergoes backward bifurcation and give conditions for disease eradication in the entire population. Analysis shows that small perturbations to the disease-free equilibrium can initially grow under certain conditions, and the introduction of TB treatment is effective in eliminating the co-infection. Numerical simulations are presented for validation of our results using published parameters.

Influence of structural variables and external perturbations on the nonlinear optical rectification, second, and third-harmonic generation in the InP/InGaAs triple quantum well structure

Influence of structural variables and external perturbations on the nonlinear optical rectification, second, and third-harmonic generation in the InP/InGaAs triple quantum well structure

The transcriptional legacy of developmental stochasticity

Genetic and environmental variation are key contributors during organism development, but the influence of minor perturbations or noise is difficult to assess. This study focuses on the stochastic variation in allele-specific expression that persists through cell divisions in the nine-banded armadillo (Dasypus novemcinctus). We investigated the blood transcriptome of five wild monozygotic quadruplets over time to explore the influence of developmental stochasticity on gene expression. We identify an enduring signal of autosomal allelic variability that distinguishes individuals within a quadruplet despite their genetic similarity. This stochastic allelic variation, akin to X-inactivation but broader, provides insight into non-genetic influences on phenotype. The presence of stochastically canalized allelic signatures represents a novel axis for characterizing organismal variability, complementing traditional approaches based on genetic and environmental factors. We also developed a model to explain the inconsistent penetrance associated with these stochastically canalized allelic expressions. By elucidating mechanisms underlying the persistence of allele-specific expression, we enhance understanding of development’s role in shaping organismal diversity.

On the spatial characteristics of the flame transfer function for a GCH4-GO2 swirl coaxial flame

In this study, the combustion instability characteristics of gaseous methane–gaseous oxygen atmospheric flame were investigated. A swirl coaxial injector was used under external modulation with a central methane flow and a loudspeaker. The flame transfer function with a photomultiplier tube was examined for possible errors, and an injector transfer function was defined to study the influence of the input perturbation on the cold gas flow without combustion. Both the results of flame transfer function and injector transfer function were affected by acoustic resonance. However, a higher mode of resonance did not appear in the flame transfer function. To analyze this difference, the flame movement was visualized using a high-speed camera by capturing the OH* chemiluminescence signal. Furthermore, a local flame transfer function was defined to examine the flame response zone-by-zone through a light signal. A higher-mode reaction appeared again in the local flame transfer function. It was found that flame separation due to modulation was the cause of the difference among the flame transfer function, injector transfer function, and local flame transfer function. By capturing the entire flame, its periodicity could be lost; hence, the local flame transfer function could prevent misinterpretation of the flame fluctuation.

The influence of physiological and pathological perturbations on blood-brain barrier function.

The blood-brain barrier (BBB) is located at the interface between the vascular system and the brain parenchyma, and is responsible for communication with systemic circulation and peripheral tissues. During life, the BBB can be subjected to a wide range of perturbations or stresses that may be endogenous or exogenous, pathological or therapeutic, or intended or unintended. The risk factors for many diseases of the brain are multifactorial and involve perturbations that may occur simultaneously (e.g., two-hit model for Alzheimer's disease) and result in different outcomes. Therefore, it is important to understand the influence of individual perturbations on BBB function in isolation. Here we review the effects of eight perturbations: mechanical forces, temperature, electromagnetic radiation, hypoxia, endogenous factors, exogenous factors, chemical factors, and pathogens. While some perturbations may result in acute or chronic BBB disruption, many are also exploited for diagnostic or therapeutic purposes. The resultant outcome on BBB function depends on the dose (or magnitude) and duration of the perturbation. Homeostasis may be restored by self-repair, for example, via processes such as proliferation of affected cells or angiogenesis to create new vasculature. Transient or sustained BBB dysfunction may result in acute or pathological symptoms, for example, microhemorrhages or hypoperfusion. In more extreme cases, perturbations may lead to cytotoxicity and cell death, for example, through exposure to cytotoxic plaques.

Cosmic masses escape from the vicinity of a massive body under the influence of external gravitational perturbation

In the era of practical space exploration, a sufficient amount of artificial objects remnants has accumulated in near-Earth space, ground control of which is lost. So, the important applied aspects of the numerous scientific problems are the issues of safety of space missions.When solving the practical problems of cleaning the near-Earth space from space debris, an important fundamental problem arises - the study of the evolution and the stability of a space debris cloud under the influence of lunar perturbation.Within the Chazy classification of final motions in the three-body problem we consider the case of the final hyperbolic-ellipticity of the motion, discuss the possible capture of cosmic masses and vice versa, the possible escape of cosmic masses. This mathematical model let us to understand, why there is no space debris of extra-terrestrial origin in the near-Earth space between the Earth and the Moon, and why so much debris of terrestrial origin remains near the Earth.

Influence of perturbations on linear and nonlinear optical properties of quantum dot

Influence of perturbations on linear and nonlinear optical properties of quantum dot

Nonparametric three-vector model predictive current control for permanent magnet synchronous motor

Multi-vector model predictive control of permanent magnet synchronous motor can effectively overcome the shortcomings of conventional single-vector model predictive control such as large motor current ripples and limited control accuracy, but its control performance is more susceptible to the influence of motor parameter perturbation. To improve the robustness of the multi-vector predictive control algorithm under the motor parameter perturbation, a novel nonparametric three-vector model predictive current control method for permanent magnet synchronous motors is proposed in this paper. Through constructing an ultra-local predictive current model based on the input and output signals of the permanent magnet synchronous motor, the influence of motor parameter perturbation on current prediction is avoided, and a disturbance observer is designed to estimate the non-modeled and perturbed parts of the ultra-local model. In addition, the direct calculation method of vector duty cycles based on current error is introduced to suppress the influence of motor parameter uncertainty on the duty cycle calculation link, which further improves the system robustness. Finally, simulations and experiments of the proposed method are demonstrated to compare with the conventional parametric three-vector model predictive current control, and the results show that the proposed control strategy can effectively suppress the disturbances caused by the motor parameters and ensure the steady-state performance during motor operation.