Effects Of External Perturbations Research Articles

Brownian colloids in optothermal field: An experimental perspective

Colloidal matter undergoing Brownian motion serves as a model system to study various physical phenomena. Understanding the effect of external perturbation on the assembly and dynamics of “Brownian colloids” has emerged as a relevant research issue in soft matter and biological physics. Optical perturbation in the form of photonic forces and torques has added impetus to this exploration. In recent years, optothermal effects arising due to optical excitation of mesoscale matter have expanded the toolbox of light–colloidal matter interactions. In this perspective, we present an experimental viewpoint on some of the developments related to the assembly and dynamics of Brownian colloids driven by the optothermal field. Furthermore, we discuss some interesting prospects on driven colloidal matter that can have implications on soft matter physics and soft photonics.

Can local heating and molecular crowders disintegrate amyloid aggregates?

The present study employs a blend of molecular dynamics simulations and a theoretical model to explore the potential disintegration mechanism of a matured Aβ octamer, aiming to offer a strategy to combat Alzheimer's disease. We investigate local heating and crowding effects on Aβ disintegration by selectively heating key Aβ segments and varying the concentration of sodium dodecyl sulphate (SDS), respectively. Despite initiation of disruption, Aβ aggregates resist complete disintegration during local heating due to rapid thermal energy distribution to the surrounding water. Conversely, although SDS molecules effectively inhibit Aβ aggregation at higher concentration through micelle formation, they fail to completely disintegrate the aggregate due to the exceedingly high energy barrier. To address the sampling challenge posed by the formidable energy barrier, we have performed well-tempered metadynamics simulations. Simulations reveal a multi-step disintegration mechanism for the Aβ octamer, suggesting a probable sequence: octamer → pentamer/hexamer ⇌ tetramer → monomer, with a rate-determining step constituting 45 kJ mol-1 barrier during the octamer to pentamer/hexamer transition. Additionally, we have proposed a novel two-state mean-field model based on Ising spins that offers an insight into the kinetics of the Aβ growth process and external perturbation effects on disintegration. Thus, the current simulation study, coupled with the newly introduced mean-field model, offers an insight into the detailed mechanisms underlying the Aβ aggregation process, guiding potential strategies for effective disintegration of Aβ aggregates.

Output-Feedback Stabilization of the Reaction Wheel Pendulum Via Active Disturbance Rejection Control

This work presents a continuous robust control method for stabilizing the reaction wheel pendulum, despite the effect of external perturbations and using only output information. To achieve this, first, an extended high-order sliding-modes observer estimates the states and identifies the perturbations, theoretically, in finite time. Then, an active disturbance rejection scheme considers the estimated states and the identified perturbation. As a result, the closed-loop system is robust against external perturbations, and the system trajectories converge to the origin. Experimental results illustrate the performance and advantages of the presented algorithm.

Hiccups are a manifestation of central respiratory arrhythmias

Hiccups (singultus) comprise repeated episodes of sharp, large-volume inspiration followed by glottic closure, interspersed among normal inspiration. Hiccupping causes involuntary contractions of diaphragm and thoracic musculature. While generally short-lived and self-limiting, hiccupping can last hours, or days, or longer, and cause wide-ranging medical, quality of life, and economic burdens. A proposed mechanism for hiccups is a pathway comprising: 1) an afferent limb including ascending fibers of the vagus nerve, 2) a central processing component in the midbrain and brainstem, and 3) an efferent limb including motorneurons of the diaphragm, glottis, and intercostal muscles. We hypothesize that hiccups represent a disinhibition of vestigial neural circuitry in the central processing component, manifesting as a multi-stable state of abnormal respiratory rhythm: a “respiratory arrhythmia”. This hypothesis applies the concept of multi-stable (chaotic) systems to the respiratory cycle and stable, but aberrant, breathing rhythms. A system is multi-stable if, for a set of inputs, it has multiple potential stable states, depending on the system’s prior state and the effects of external perturbations. This hypothesis is predicated on Straus et al.’s suggestion that hiccups are an evolutionary preservation of gill ventilation, normally suppressed by neural circuitry controlling mammalian breathing. The respiratory system, it is proposed, could stably exhibit eupneic breathing motor patterns or a mix of eupneic and aquatic-like patterns (hiccups). That is, eupnea alone, or eupnea plus gill ventilation are alternative stable equilibrium points of a multi-stable system. Evidence supporting the hypothesis includes computational models of the respiratory control center manifesting hiccup-like patterns, and experimental data showing that medullary stimulation induces hiccups-like breathing in cats. Additional evidence includes clinical reports of therapeutic perturbations to, or near, the putative respiratory pattern generator resetting the breathing pattern to the default stable state, eupnea. These approaches, which provide strong afferent input to the brainstem regulatory network rather than disrupting aberrant afferent signaling, include elevating CO2 concentrations to excite central and peripheral chemoreceptors increasing respiratory drive. Other examples include nasopharyngeal stimulation or sudden administration of strong sweet or sour tastes. Viewing hiccups as a respiratory arrhythmia could prove helpful in developing targeted interventions.

Adaptive controller based on barrier Lyapunov function for a composite Cartesian-delta robotic device for precise time-varying position tracking

This study presents the design of an adaptive event-driven controller for solving the trajectory tracking problem of a composite robotic device made up of a three-dimensional Cartesian and a parallel Delta robot. The proposed composite device has a mathematical model satisfying a standard Lagrangian structure affected by modeling uncertainties and external perturbations. The adaptive gain of the controller is considered to enforce the convergence of the tracking error while the state bounds are satisfied. The barrier Lyapunov function addresses the preconceived state constraints for both robotic devices by designing a time-varying gain that guarantees the ultimate boundedness of the tracking error under the effect of external perturbations. The event-driven approach considers that the Cartesian robot is moving into a predefined invariant zone near to the origin. In contrast, the delta robot can complete the tracking problem once the end-effector is inside the given zone. The suggested controller was evaluated using a virtual representation of the composite robotic device showing better tracking performance (while the restrictions are satisfied) than the performances obtained with the traditional linear state feedback controllers. Analyzing the mean square error and its integral led to confirming the benefits of using the adaptive barrier control.

Flow dynamics of an axisymmetric impinging jet under two-frequency external forcing. A study by time-resolved PIV and DMD

The present paper reports on the experimental study of the dynamics of large-scale vortex structures in an axisymmetric impinging jet forced periodically with amplitude modulation. The velocity field measurements are conducted by the particle image velocimetry method. IR imaging is applied to evaluate the effect of external perturbations on local heat transfer coefficient. The Reynolds number of the jet flow is 12,500 and the distance between the nozzle and flat impingement plate is two nozzle diameters. The amplitude modulation corresponds to two-frequency forcing with a main harmonic (for the Strouhal number 0.5) and different sub-harmonics. To analyze quasi-periodic formation and near-wall merging of primary vortex structures and induced secondary vortices in the near-wall boundary layer, the obtained time-resolved velocity data sets are processed by the dynamic mode decomposition method. It is shown that the amplitude modulation can be efficiently used to attenuate the strength of the forced vortices due to the produced blowing events with different momenta and to control vortices pairing process in the near-wall region. It is also shown that two-frequency forcing can provide slightly greater intensification of heat transfer around the stagnation point with considerably smaller energy, consumed during the forcing.

A novel robust extended dissipativity state feedback control system design for interval type-2 fuzzy Takagi-Sugeno large-scale systems

Recently, systems have become large in their model and dynamic. To apply control algorithms, serious problems appear that need to be solved. Two significant problems are modelling the dynamics of the large-scale system and reducing effects of perturbations. In this paper, we use the advantage of large-scale systems modelling based on the type-2 fuzzy Takagi–Sugeno model to cover the uncertainties caused by large-scale systems modelling. The advantage of using membership function information is the reduction of conservatism resulting from stability analysis. Also, this paper uses the extended dissipativity robust control performance index to reduce the effect of external perturbations on the large-scale system, which is a generalization of , , passive and dissipativity performance indexes and control gains can be achieved through solving linear matrix inequalities (LMIs). Hence, the whole closed-loop system is asymptotically stable. Finally, the effectiveness of the proposed method is demonstrated by two practical examples.

Robust Control Based on Modeling Error Compensation of Microalgae Anaerobic Digestion

Microalgae are used to produce renewable biofuels (biodiesel, bioethanol, biogas, and biohydrogen) and high-value-added products, as well as in bioremediation and CO2 sequestration tasks. In the case of anaerobic digestion of microalgae, biogas can be produced from mainly proteins and carbohydrates. Anaerobic digestion is a complex process that involves several stages and is susceptible to operational instability due to various factors. Robust controllers with simple structure and design are necessary for practical implementation purposes and to achieve a proper process operation despite process variabilities, uncertainties, and complex interactions. This paper presents the application of a control design based on the modeling error compensation technique for the anaerobic digestion of microalgae. The control design departs from a low-order input–output model by enhancement with uncertainty estimation. The results show that achieving desired organic pollution levels and methanogenic biomass concentrations as well as minimizing the effect of external perturbations on a benchmark case study of the anaerobic digestion of microalgae is possible with the proposed control design.

Effects of External Perturbations on Protein Systems: A Microscopic View.

Protein folding can be viewed as the origami engineering of biology resulting from the long process of evolution. Even decades after its recognition, research efforts worldwide focus on demystifying molecular factors that underlie protein structure-function relationships; this is particularly relevant in the era of proteopathic disease. A complex co-occurrence of different physicochemical factors such as temperature, pressure, solvent, cosolvent, macromolecular crowding, confinement, and mutations that represent realistic biological environments are known to modulate the folding process and protein stability in unique ways. In the current review, we have contextually summarized the substantial efforts in unveiling individual effects of these perturbative factors, with major attention toward bottom-up approaches. Moreover, we briefly present some of the biotechnological applications of the insights derived from these studies over various applications including pharmaceuticals, biofuels, cryopreservation, and novel materials. Finally, we conclude by summarizing the challenges in studying the combined effects of multifactorial perturbations in protein folding and refer to complementary advances in experiment and computational techniques that lend insights to the emergent challenges.

Effects of external perturbations on light absorption by light/heavy hole excitons in a semi-parabolic quantum well

The effects of electric, magnetic, and intense terahertz laser fields on optoelectronic properties are investigated in a GaAs/AlxGa1-xAs semi-parabolic quantum well. The binding energy, exciton light absorption coefficients, interband transition energies, and dipole elements in the matrix are studied within the structure of the parabolic band and effective-mass approximations. The transition energy difference between the ground-state electron energy level and the ground-state heavy hole (light hole) energy level and matrix elements are carried out as functions of external perturbations with a constant well size. The results exhibit that the exciton binding energies of heavy and light holes reduce as long as the laser dressing parameter is larger. The optical absorption of light hole exciton in the system is stronger than the heavy hole exciton. And the excitonic energies, transition energies, and absorption coefficients are much more sensitive and controlled by changing the external perturbations.

Motion of a swimming droplet under external perturbations: A model-based approach.

Microdroplets driven by the Marangoni effect are known to continue to swim for hours despite their simple composition. This swimming microdroplet changes its motion from straight to curvilinear and further to chaotic as the Péclet number increases. In this study, we investigate the effect of external perturbations on the three-dimensional axis-asymmetric model of a droplet driven by the Marangoni effect. The aim here is to elucidate the contribution of external perturbation to the complex motion of the droplet and the change in its effect according to the droplet size. In this paper, first we provide a detailed explanation on the derivation of the model introduced in our previous work, which is next used to describe the motion of the droplet in the numerical study of the angular response to random perturbations. The numerical simulation of droplet motion with different types of noise indicates that the model does not converge them into a certain type of motion but rather helps to reflect the external perturbations. The obtained results suggest that the types and properties of external perturbation have a considerable effect on the droplet motion.

The effect of external perturbations on nonlinear panel flutter at low supersonic speed

We studied two-dimensional nonlinear flutter oscillations of a flat elastic panel in a low supersonic flow, where several panel eigenmodes are simultaneously unstable, and resulting nonlinear oscillations are governed by the nonlinear interaction of growing modes. The objective of our work was to study the dependence of limit cycle oscillations of the panel on an external disturbance. To analyse possible limit cycle oscillations, we first investigated the effect of the spatial distribution and amplitude of the initial excitation loading. We show that, depending on the initial perturbation, different modes of limit cycle oscillations can develop, in which the cyclic stress amplitude differs by an order of magnitude. Second, we investigated the effect of a short strong perturbation applied to the developed limit cycle oscillations and show the possibility of switching the limit cycle mode from high- to low-energy oscillations, thus providing the ability to control oscillations of the fluttering panel.

Pressure-induced collapse of ferromagnetism in nickel

Transition metals Fe, Co, and Ni are the canonical systems for studying the effect of external perturbations on ferromagnetism. Among these, Ni stands out as it undergoes no structural phase transition under pressure. Here we have investigated the long-debated issue of the pressure-induced magnetization drop in Ni from first principles. Our calculations confirm an abrupt quenching of magnetization at high pressures not associated with any structural phase transition. We find that the pressure substantially enhances the crystal-field splitting of Ni-$3d$ orbitals, driving the system toward a new metallic phase violating the Stoner Criterion for ferromagnetic (FM) ordering. Analyzing the charge populations in each spin channel, we show that the next-nearest-neighbor interactions play a crucial role in quenching FM ordering in Ni and materials alike.

Stochastic modeling of the Monkeypox 2022 epidemic with cross-infection hypothesis in a highly disturbed environment.

Monkeypox 2022, a new re-emerging disease, is caused by the Monkeypox virus. Structurally, this virus is related to the smallpox virus and infects the host in a similar way; however, the symptoms of Monkeypox are more severe. In this research work, a mathematical model for understanding the dynamics of Monkeypox 2022 is suggested that takes into account two modes of transmission: horizontal human dissemination and cross-infection between animals and humans. Due to lack of substantial knowledge about the virus diffusion and the effect of external perturbations, the model is extended to the probabilistic formulation with Lévy jumps. The proposed model is a two block compartmental system that requires the form of Itô-Lévy stochastic differential equations. Based on some assumptions and nonstandard analytical techniques, two principal asymptotic properties are proved: the eradication and continuation in the mean of Monkeypox 2022. The outcomes of the study reveals that the dynamical behavior of the proposed Monkeypox 2022 system is chiefly governed by some parameters that are precisely correlated with the noise intensities. To support the obtained theoretical finding, examples based on numerical simulations and real data are presented at the end of the study. The numerical simulations also exhibit the impact of the innovative adopted mathematical techniques on the findings of this work.

Dynamic evolution of hyperuniformity in a driven dissipative colloidal system

Hyperuniformity is evolving to become a unifying concept that can help classify and characterize equilibrium and nonequilibrium states of matter. Therefore, understanding the extent of hyperuniformity in dissipative systems is critical. Here, we study the dynamic evolution of hyperuniformity in a driven dissipative colloidal system. We experimentally show and numerically verify that the hyperuniformity of a colloidal crystal is robust against various lattice imperfections and environmental perturbations. This robustness even manifests during crystal disassembly as the system switches between strong (class I), logarithmic (class II), weak (class III), and non-hyperuniform states. To aid analyses, we developed a comprehensive computational toolbox, enabling real-time characterization of hyperuniformity in real- and reciprocal-spaces together with the evolution of several order metric features, and measurements showing the effect of external perturbations on the spatiotemporal distribution of the particles. Our findings provide a new framework to understand the basic principles that drive a dissipative system to a hyperuniform state.

The outer disc in shambles: Blind detection of Monoceros and the ACS with Gaia’s astrometric sample

Context. The Gaia astrometric sample allows us to study the outermost Galactic disc, the halo, and their interface. It is precisely at the very edge of the disc where the effects of external perturbations are expected to be the most noticeable. Aims. Our goal is to detect the kinematic substructure present in the halo and at the edge of the Milky Way (MW) disc and provide observational constraints on their phase-space distribution. Methods. We download, one HEALpix at a time, the proper motion histogram of distant stars, to which we apply a wavelet transformation to reveal the significant overdensities. We then analyse the large coherent structures that appear in the sky. Results. We reveal a sharp yet complex anticentre dominated by Monoceros (MNC) and the Anticentre Stream (ACS) in the north – which we find have intensities comparable to the Magellanic Clouds and the Sagittarius stream – and by MNC South and TriAnd at negative latitudes. Our method allows us to perform a morphological analysis of MNC and the ACS, both of which span more than 100° in longitude, and to provide a high purity sample of giants with which we track MNC down to latitudes as low as ∼5°. Their colour-magnitude diagram is consistent with extended structures at a distance of ∼10−11 kpc that originated in the disc, with a very low ratio of RR Lyrae over M giants, and with kinematics compatible with the rotation curve at those distances or slightly slower. Conclusions. We present a precise characterisation of MNC and the ACS, two previously known structures that our method reveals naturally, allowing us to detect them without limiting ourselves to a particular stellar type and, for the first time, using only kinematics. Our results will allow future studies to model their chemo-dynamics and evolution, thus constraining some of the most influential processes that shaped the MW.

Optical properties of two-dimensional black phosphorus

Recently, black phosphorus (BP), an emerging layered two-dimensional (2D) material, has aroused much research interest. Distinguished from most of other 2D materials, BP is always a direct bandgap semiconductor regardless of the thickness, with the bandgap ranging from 0.3 eV (bulk) to 1.7 eV (monolayer), which is just fill the gap in the bandgap between graphene and transition metal dichalcogenides (TMDCs) in this frequency range. Besides, the BP exhibits many intriguing properties, such as high carrier mobility, highly tunable and anisotropic physical properties, which render the BP another star 2D material following graphene and TMDCs. In this review, we mainly focus on the advances in the optical properties of 2D BP, with the content covering the intrinsic optical properties and external perturbation effects on optical properties. Regarding the intrinsic optical properties, we introduce the anisotropic and layer-dependent optical absorption from interband transitions, the layer-dependent exciton binding energy and exciton absorption, visible-to-infrared photoluminescence, and stability of absorption and photoluminescence. As for external perturbation effects on optical properties, we introduce in-plane uniaxial and biaxial strain effects, gate-induced quantum confined Franz-Keldysh effect and Burstein-Moss effect. And finally we give a brief summary and outlook, pointing out some several interesting and important issues of BP, which need further studying urgently such as hyperbolic plasmons, intersubband transitions, optical properties in heterostructures and twist angle moiré superlattice and so on. This review gives an overview of the optical properties of BP and is expected to arouse the interest in further studying the BP.

Controlling the Effects of External Perturbations on a Gene Regulatory Network Using Proportional-Integral-Derivative Controller.

Gene regulatory networks are biologically robust, which imparts resilience to living systems against most external perturbations affecting them. However, there is a limit to this and disturbances beyond this limit can impart unwanted signalling on one or more master regulators in a network. Certain disturbances may affect the functioning of other constituent genes of the same network. In most cases, this phenomenon can have some effect on the functioning of the living organism. In this investigation, we have proposed a methodology to mitigate the effects of external perturbations on a genetic network using a proportional-integral-derivative controller. The proposed controller has been used to perturb one or more of the other unaffected master regulators such that the most affected gene/s of the network revert to their normal state. The only required condition of such type of manoeuvring is that there should be multiple master regulators in a network. The proposed technique has been experimented on a 10-gene DREAM4 benchmark network and also on a larger 20-gene network, where only downregulation has been considered due to data constraints. Simulation results indicate that the most vulnerable genes can be reverted to their normal expression levels in 10 out of the 16 simulations performed.

How Do Metal Ions Modulate the Rate-Determining Electron-Transfer Step in Cytochrome P450 Reactions?

Cytochrome P450 (CYP450) enzymes play important roles in maintaining human health and their reaction rates are dependent on the first electron transfer from the reduction partner. Interestingly, experimental work has shown that this step is highly influenced by the addition of metal ions. To understand the effect of external perturbations on the CYP450 first reduction step, we have performed a computational study with model complexes in the presence of metal and organic ions, solvent molecules, and an electric field. The results show that these medium-range interactions affect the driving force as well as electron-transfer rates dramatically. Based on the location, distance, and direction of the ions/electric field, the catalytic reaction rates are enhanced or impaired. Calculations on a large crystal structure with bonded alkali metal ions indicated inhibition patterns of the ions. Therefore, we predict that the active forms of the natural CYP450 isozymes will not have more than one alkali metal ion bound in the second-coordination sphere. As such, this study provides an insight into the activity of CYP450 enzymes and the effects of ions and electric field perturbations on their activity.

The Effect of Eight Weeks of Training on Head and Neck Stability in Tsuki Punch after Neck Muscle Fatigue

Introduction : Muscular fatigue can interfere with the proper functioning of postural stability strategies, hence decreasing stability and increasing the risk of injuries in athletes. The aim of this study is to examine the effect of training on head and neck stability against Tsuki punch during the neck muscle fatigue in male athletes. Materials and Methods: 24 professional male karate athletes were selected and randomly divided into the experimental [n = 12, age: 20.92 ± 2.62 (y), weight: 71.00 ± 11.68 (kg), height: 1.77 ± 0.05 (m)] and control [n = 12, age: 22.08 ± 2.21 (y), weight: 72.15 ± 13.24 (kg), height: 1.78 ± 0.06 (m)] groups. The experimental group performed a training program for eight weeks, three times per week. Moreover, the angular displacement and acceleration of head and neck in Tsuki punch during muscular fatigue were measured by motion analysis system before and after the training protocol. Data were analyzed by paired t-test, independent t-test, and analysis of covariance (ANCOVA) at the significance level of 0.05. Results: There was a significant difference in angular displacement (Experimental: 2.95 ± 1.85, Control: 4.15 ± 2.15) and acceleration before (Experimental: 16.29 ± 9.62, Control: 70.17 ± 12.23) and after (Experimental: 24.69 ± 15.98, Control: 70.86 ± 14.92) hitting the punching bag. Conclusion: The outcome of this study showed that proprioception training can improve head and neck postural stability during muscular fatigue against external perturbation in Karate athletes. Therefore, these exercises can be used to reduce the effect of external perturbation on the head and neck of these athletes.