Effects Of External Perturbations Research Articles

Regulating lamellar eutectic trajectory through external perturbations.

The present understanding of asymmetric lamellar eutectics focuses on pure diffusive transport, and how the external perturbations cause asymmetric pattern transitions remains unclear. In this work, the effect of external perturbations is discussed in terms of both thermal and convective effects via phase-field modeling. The presence of thermal perturbation distorts eutectic lamellae, while the convective perturbation causes a tilt band. Both can adjust the eutectic trajectory to accommodate newly established thermodynamics by reconstructing the transport equilibrium. Furthermore, how to regulate the eutectic growth (eutectic colony, zigzag, and snakelike patterns) by altering external perturbations is investigated, which provides information on how to control eutectic evolution.

Disentangling the effects of external perturbations on coexistence and priority effects

Abstract A major challenge in ecological research is to identify the tolerance of ecological communities to external perturbations. Modern coexistence theory (MCT) has been widely adopted as a framework to investigate the tolerance to perturbations in relative reductions of per capita growth rates, often using metrics that explicitly eliminate the independent role of intrinsic growth rates. More recently, the structural approach (SA) was introduced to investigate the tolerance of communities to perturbations in intrinsic growth rates as a function of the strength of intraspecific and interspecific competition. Because the external perturbations are likely to happen in both intrinsic growth rates and competition strengths, no framework alone can fully disentangle the effects of external perturbations. Here we combine MCT and SA to disentangle the tolerance in coexistence and priority effects of a pair of competing species when subject to perturbations in intrinsic growth rates and competition strengths. Through this combination, we reveal the emergence of a key trade‐off: increasing the tolerance to perturbations in intrinsic growth rates typically decreases the tolerance in competition strengths, and vice versa. Furthermore, this trade‐off is stronger under coexistence than under priority effects. We test this combined framework on competing pairs of 18 California annual plant species. For both coexistence and priority effects, we find that the tolerance to perturbations in intrinsic growth rates is maximized instead of that to perturbations in competition strengths in the studied annual plant communities. Synthesis. Our combined framework of modern coexistence theory and structural approach illustrates that it is possible to disentangle the impact of different external perturbations on the persistence of species. Importantly, our findings show that species interactions may reveal whether communities are dominated either by changes in intrinsic growth rates or by competition strengths. Overall, this combined framework can open a new perspective to understand and predict the response of populations to changing environmental conditions.

Вплив зміни збурюючих факторів на рівень коефіцієнтів тепловіддачі на зовнішніх поверхнях будинків

This article analyzes the impact on the level of heat transfer coefficients of such factors as: outside air temperature and change in its speed. The object of study is a complex of buildings of the A. Pidgorny Institute of Mechanical Engineering Problems of the National Academy of Sciences of Ukraine. To reduce energy consumption, it is necessary to determine the heat loss through the external enclosing structures of the A. Pidgorny Institute of Mechanical Engineering Problems of the National Academy of Sciences of Ukraine, taking into account the temperature of outdoor and indoor air, wind speed and direction. To correctly determine the heat loss, it is necessary to determine the specified heat transfer resistance coefficient. Therefore, at the first stage, the coefficients of heat transfer on the external structures of A. Pidgorny Institute of Mechanical Engineering Problems of the National Academy of Sciences of the Ukraine are determined, which depend on the wind speed, its direction, changes in height, as well as the temperature of the outside air. Project documentation of the A. Pidgorny Institute of Mechanical Engineering Problems of the National Academy of Sciences of Ukraine provided the following buildings: 16-storey building (building № 1); 2-storey laboratory (bench) building (building № 2); conference hall for 500 seats, building № 3; housing № 4, as well as the following ancillary facilities: air blower station (its compressor, dismantled); pumping circulating water supply; cooling tower; a separate checkpoint, a structure for civil defense vehicles. On the basis of numerical modeling the analysis of character of flow around by a wind stream of the given building is carried out. The sizes of a zone of braking of a wind stream and also the sizes of a zone of its separation are defined. The formula for determining the specified heat transfer coefficient on the roof is given. Heat transfer coefficients are determined for each type of panel. As a result, on the windward side of the building, the heat transfer coefficients are determined depending on the pulsating component of the wind speed, taking into account the change in the latter in height. The heat transfer coefficients in the separation zone are determined depending on its size and speed in this area. To determine the effect of external perturbations, the calculation of heat transfer coefficients is performed at t = –23 °С and t = –7 °С. As a result of the research it is shown that the specified heat transfer coefficient on the outer panels of the high-rise building of SP Mash NAS of Ukraine significantly depends on the speed and direction of the wind and its change in height.

Characteristics of medial-lateral postural control while exposed to the external perturbation in step initiation

Controllability of posture in the medial-lateral direction is critical for balance maintenance, particularly in step initiation. The objective of the current study was to examine the effects of external perturbation and landing orientation on medial-lateral control stability in step initiation. Eleven young healthy participants stood on the force platform and waited for the instruction of taking a step while experiencing a pendulum perturbation applied at the lateral side of the right shoulder. Eight experimental conditions were conducted by two levels of step side (right or left), two levels of perturbation (with or without), and two levels of landing orientation (forward or diagonal). The center of pressure (COP), pelvic movements, and muscle activities were recorded and analyzed as the onset of COP and pelvic movement, the COP displacement, and cocontraction and reciprocal muscle activation pattern. The temporal events of COP and pelvic movement were not significantly different in all experimental conditions. However, COP and pelvic movement were significantly later in the diagonal condition. Most of the segments showed reciprocal muscle activation patterns in relation to the perturbation released time. Subsequently, all segments showed cocontraction muscle activation patterns, which was significantly affected by step side, perturbation, and orientation. The results suggest that how the CNS initiated a step was identical with the COP then pelvic movement. The outcome highlights the importance of external perturbation and foot landing orientation effects on postural adjustments, which may provide a different approach to help step initiation.

Simulation and experimental investigation about interferometric optical fiber acoustic sensor for sensitivity enhancement

In this paper, the results of simulation and experimental investigation of interferometric optical fiber acoustic sensing are primarily presented, and the main area of interest is studying the different algorithms for enhancement of sensor sensitivity. In fact, when light propagates through optical fiber, in a Michelson interferometer, the phase of light changes due to effect of external perturbation as acoustic wave on optical path length and this phase change is detected by demodulation algorithm. It is strived to present the Phase Generated Carrier (PGC) demodulation algorithm based on Differential-Cross-Multiplying (DCM), Arctangentfunction (ATAN) and ATAN based on Coordinate Rotation Digital Computer CORDIC algorithm. Simulation results reveal that PGC demodulation method based on ATAN CORDIC algorithm has better result (signal to noise ratio) than DCM and ATAN without using CORDIC algorithm. On this account, PGC demodulation algorithm based on ATAN method with CORDIC algorithm is applied in the experimental investigation due to simulation results and simpler digital implementation on Field Programmable Gate Array (FPGA). Moreover, acoustic frequency is detected as sidebands of harmonics of phase modulator frequencies. The sensitivity of digital circuit is 5μradHz-0.5 and the minimum detectable phase is 50μrad Acoustic frequency is detected as sidebands of harmonics of phase modulator frequencies, and consequently, the system allows detecting the sinusoidal acoustic wave with different frequencies. It is also detected acoustic frequency by measurement of the reflected optical power. Moreover, in this part, it is packaged sensing arm of interferometer with polymer material (polyurethane) for investigation the effect of polymer on sensitivity enhancement of sensor. It is observed with applying of acoustic wave, the reflected optical power decreases and this reduction is more, when sensing arm is packaged with polymer.

Robust observer-based synchronisation of chaotic oscillators with structural perturbations and input nonlinearity

This paper presents a generalised robust adaptive chaotic synchronisation method for chaotic systems with structural perturbations. One control input is used to synchronise both systems exponentially fast based on Lyapunov theory. This approach cannot only make the outputs of both master and slave systems reach synchronisation with the passage of time between both systems but it can also reduce the effect of external perturbations and input nonlinearities. By assuming bounded solutions of the nominal uncoupled systems, sufficient conditions have been derived for boundedness of the solutions of two different classes of chaotic systems with input nonlinearity affected by structural perturbations. The propose approach offers a systematic design procedure for robust adaptive synchronisation of a large class of chaotic systems in the chaos research literature. As an illustration of the effectiveness and robustness of the proposed strategy, synchronisation problem of a master system consists of a perturbed modified Colpitts oscillator and an observer consisting of a Chua oscillator. It was found that the controller maintains robust stable synchronisation in the presence of exoteric perturbations and structural uncertainties.

Normal mode analysis and beyond.

Normal mode analysis provides a powerful tool in biophysical computations. Particularly, we shed light on its application to protein properties because they directly lead to biological functions. As a result of normal mode analysis, the protein motion is represented as a linear combination of mutually independent normal mode vectors. It has been widely accepted that the large amplitude motions throughout the entire protein molecule can be well described with a few low-frequency normal modes. Furthermore, it is possible to represent the effect of external perturbations, e.g., ligand binding, hydrostatic pressure, as the shifts of normal mode variables. Making use of this advantage, we are able to explore mechanical properties of proteins such as Young’s modulus and compressibility. Within thermally fluctuating protein molecules under physiological conditions, tightly packed amino acid residues interact with each other through heat and energy exchanges. Since the structure and dynamics of protein molecules are highly anisotropic, the flow of energy and heat should also be anisotropic. Based on the harmonic approximation of the heat current operator, it is possible to analyze the communication map of a protein molecule. By using this method, the energy transfer pathways of photoactive yellow protein were calculated. It turned out that these pathways are similar to those obtained via the Green-Kubo formalism with equilibrium molecular dynamics simulations, indicating that normal mode analysis captures the intrinsic nature of the transport properties of proteins.

Multi-Scenarios Attitude Control of a Satellite with Flexible Solar Panels

The development of space mission design requires mathematical modelling and related numerical simulations. These latter are very important to select the Attitude Determination and Control Subsystem hardware against the mission requirements for attitude and orbit specifications. In this paper, a nonlinear dynamic modelling framework is presented for one degree of freedom of a flexible spacecraft. The dynamics of the structure are derived in the nonlinear Euler equations form for a circular orbit; the gravity-gradient torque is introduced as an external perturbation. The resulting model is used to perform attitude control precision of the pitch axis rotational manoeuvre, via several simulations for various in-orbit operating scenarios, to highlight the coupling effect between the main body and the flexible panels. For this purpose, the spacecraft is considered as a rigid cubic-body with two flexible solar panels deployed on each side of its roll axis. The simulation results show that the flexible motion of the panels has a substantial impact on the spacecraft dynamical responses, especially when considering the external perturbation effects. A classical controller is implemented to control the system three axes manoeuvres and to suppress the flexible panels’ distortions. Numerical results confirm the effectiveness of the proposed model to demonstrate the coupling effects and the control strategy.

MDPbiome: microbiome engineering through prescriptive perturbations.

MotivationRecent microbiome dynamics studies highlight the current inability to predict the effects of external perturbations on complex microbial populations. To do so would be particularly advantageous in fields such as medicine, bioremediation or industrial scenarios.ResultsMDPbiome statistically models longitudinal metagenomics samples undergoing perturbations as a Markov Decision Process (MDP). Given a starting microbial composition, our MDPbiome system suggests the sequence of external perturbation(s) that will engineer that microbiome to a goal state, for example, a healthier or more performant composition. It also estimates intermediate microbiome states along the path, thus making it possible to avoid particularly undesirable/unhealthy states. We demonstrate MDPbiome performance over three real and distinct datasets, proving its flexibility, and the reliability and universality of its output ‘optimal perturbation policy’. For example, an MDP created using a vaginal microbiome time series, with a goal of recovering from bacterial vaginosis, suggested avoidance of perturbations such as lubricants or sex toys; while another MDP provided a quantitative explanation for why salmonella vaccine accelerates gut microbiome maturation in chicks. This novel analytical approach has clear applications in medicine, where it could suggest low-impact clinical interventions that will lead to achievement or maintenance of a healthy microbial population, or alternately, the sequence of interventions necessary to avoid strongly negative microbiome states.Availability and implementationCode (https://github.com/beatrizgj/MDPbiome) and result files (https://tomdelarosa.shinyapps.io/MDPbiome/) are available online.Supplementary information Supplementary data are available at Bioinformatics online.

Effects of external perturbations on dynamic performance of carbon dioxide transcritical power cycles for truck engine waste heat recovery

Carbon dioxide transcritical power cycle (CTPC) systems are dynamically tested on a constructed test bench using an expansion valve. Effects of external perturbations of pump speed, expansion valve opening and engine conditions on dynamic performance of the CTPC systems are investigated with step changes. Dynamic characteristics are identified with rise time, settling time and overshoot. Results show that both a basic CTPC system and a CTPC system with a recuperator (R-CTPC) behave as a second-order underdamped system with the perturbations of pump speed and expansion valve opening. Overshoot or undershoot tends to appear in pressures when pump speed changes, while overshoot or undershoot occurs more noticeably in temperatures when expansion valve opening varies. Although the CTPC systems respond slowly with the perturbations of engine conditions, they have the ability to operate safely and produce power continuously. Therefore, the CTPC systems are robust when facing narrow fluctuations of heat sources while swift when required to make adjustments, showing great potential for truck engine waste heat recovery. Overall, current research gives a full understanding of the dynamic performance of the CTPC systems, which will provide references for dynamic model validation and possible control strategy identification.

Planetary Systems in Star Clusters: the dynamical evolution and survival

AbstractMost stars form in crowded stellar environments. Such star forming regions typically dissolve within ten million years, while others remain bound as stellar groupings for hundreds of millions to billions of years, and then become the open clusters or globular clusters that are present in our Milky Way galaxy today. A large fraction of stars in the Galaxy hosts planetary companions. To understand the origin and dynamical evolution of such exoplanet systems, it is necessary to carefully study the effect of their environments. Here, we combine theoretical estimates with state-of-the-art numerical simulations of evolving planetary systems similar to our own solar system in different star cluster environments. We combine the planetary system evolution code, and the star cluster evolution code, integrated in the multi-physics environment. With our study we can constrain the effect of external perturbations of different environments on the planets and debris structures of a wide variety of planetary systems, which may play a key role for the habitability of exoplanets in the Universe.

A Framework for Engineering Stress Resilient Plants Using Genetic Feedback Control and Regulatory Network Rewiring.

Crop disease leads to significant waste worldwide, both pre- and postharvest, with subsequent economic and sustainability consequences. Disease outcome is determined both by the plants' response to the pathogen and by the ability of the pathogen to suppress defense responses and manipulate the plant to enhance colonization. The defense response of a plant is characterized by significant transcriptional reprogramming mediated by underlying gene regulatory networks, and components of these networks are often targeted by attacking pathogens. Here, using gene expression data from Botrytis cinerea-infected Arabidopsis plants, we develop a systematic approach for mitigating the effects of pathogen-induced network perturbations, using the tools of synthetic biology. We employ network inference and system identification techniques to build an accurate model of an Arabidopsis defense subnetwork that contains key genes determining susceptibility of the plant to the pathogen attack. Once validated against time-series data, we use this model to design and test perturbation mitigation strategies based on the use of genetic feedback control. We show how a synthetic feedback controller can be designed to attenuate the effect of external perturbations on the transcription factor CHE in our subnetwork. We investigate and compare two approaches for implementing such a controller biologically-direct implementation of the genetic feedback controller, and rewiring the regulatory regions of multiple genes-to achieve the network motif required to implement the controller. Our results highlight the potential of combining feedback control theory with synthetic biology for engineering plants with enhanced resilience to environmental stress.

An extended continuum model incorporating the electronic throttle dynamics for traffic flow

This study develops a novel continuum model with consideration of the effect of electronic throttle (ET) dynamics to capture the behaviour of vehicles in traffic flow. In particular, the continuum model is proposed by incorporating the opening angle of ET based on the throttle-based full velocity difference model. Theoretical analyses including stability, negative velocity and shock wave are performed systematically. Numerical experiments and comparisons are conducted to verify the performance of the proposed continuum model. Results show that the steady-state performance of the proposed model is improved with respect to the stability. In addition, the proposed model is effective to rapidly dissipate the effect of external perturbation. Also, the phenomenon of negative velocity can be avoided by the proposed model.

Modelling and Control of Gene Regulatory Networks for Perturbation Mitigation.

Synthetic Biologists are increasingly interested in the idea of using synthetic feedback control circuits for the mitigation of perturbations to gene regulatory networks that may arise due to disease and/or environmental disturbances. Models employing Michaelis-Menten kinetics with Hill-type nonlinearities are typically used to represent the dynamics of gene regulatory networks. Here, we identify some fundamental problems with such models from the point of view of control system design, and argue that an alternative formalism, based on so-called S-System models, is more suitable. Using tools from system identification, we show how to build S-System models that capture the key dynamics of an example gene regulatory network, and design a genetic feedback controller with the objective of rejecting an external perturbation. Using a sine sweeping method, we show how the S-System model can be approximated by a linear transfer function and, based on this transfer function, we design our controller. Simulation results using the full nonlinear S-System model of the network show that the synthetic control circuit is able to mitigate the effect of external perturbations. Our study is the first to highlight the usefulness of the S-System modelling formalism for the design of synthetic control circuits for gene regulatory networks.

Unravelling external perturbation effects on the optical phonon response of graphene

Raman spectroscopy is a powerful and nondestructive probe that demonstrates its efficiency in revealing the physical properties of low‐dimensional sp2 carbon systems. It gives access to the number of layers, the quality and the nature of defects of all carbon allotropes, but also to the understanding of the influence of perturbations such as strain and/or doping. In this paper, we review the state of the art regarding the effect of external perturbations on the optical phonons of graphene. We describe how doping can tune the unusual electron–phonon coupling in graphene and thus modify not only the resonance conditions but also the phonon intensities thanks to quantum interferences. We also review the impact of strain on optical phonons and how one can disentangle strain and doping thanks to optical phonons. Last, implementations of this field to strain engineering or to graphene‐based mechanical resonators will be presented. Copyright © 2018 John Wiley & Sons, Ltd.

Surface-enhanced FAST CARS: en route to quantum nano-biophotonics

AbstractQuantum nano-biophotonics as the science of nanoscale light-matter interactions in biological systems requires developing new spectroscopic tools for addressing the challenges of detecting and disentangling weak congested optical signals. Nanoscale bio-imaging addresses the challenge of the detection of weak resonant signals from a few target biomolecules in the presence of the nonresonant background from many undesired molecules. In addition, the imaging must be performed rapidly to capture the dynamics of biological processes in living cells and tissues. Label-free non-invasive spectroscopic techniques are required to minimize the external perturbation effects on biological systems. Various approaches were developed to satisfy these requirements by increasing the selectivity and sensitivity of biomolecular detection. Coherent anti-Stokes Raman scattering (CARS) and surface-enhanced Raman scattering (SERS) spectroscopies provide many orders of magnitude enhancement of chemically specific Raman signals. Femtosecond adaptive spectroscopic techniques for CARS (FAST CARS) were developed to suppress the nonresonant background and optimize the efficiency of the coherent optical signals. This perspective focuses on the application of these techniques to nanoscale bio-imaging, discussing their advantages and limitations as well as the promising opportunities and challenges of the combined coherence and surface enhancements in surface-enhanced coherent anti-Stokes Raman scattering (SECARS) and tip-enhanced coherent anti-Stokes Raman scattering (TECARS) and the corresponding surface-enhanced FAST CARS techniques. Laser pulse shaping of near-field excitations plays an important role in achieving these goals and increasing the signal enhancement.

Graphene and related 2D materials: An overview of the Raman studies

After a brief overview of the discovery and the Raman study of new forms of carbons (intercalated graphite, carbon fiber, fullerenes, carbon nanotubes), the invaluable contribution of late Professor M. Dresselhaus is noted, and the 10 reviews and 9 contributions collected to present a picture of the current Raman investigations of graphene and related 2D materials (such as black phosphorus, MoS2) are introduced. Methods for numbering the graphene layers, the effects of external perturbations (temperature, pressure, doping, and magnetic field) on the phonons of graphene, characterization of the chemical and structural properties of graphene at the nanoscale level by tip‐enhanced Raman spectroscopy, surface enhanced Raman spectroscopy and hyperspectral imaging, and applications combining graphene and Raman spectroscopy are addressed. Copyright © 2017 John Wiley & Sons, Ltd.

Electron–hole liquid in semiconductors and low-dimensional structures

The condensation of excitons into an electron–hole liquid (EHL) and the main EHL properties in bulk semiconductors and low-dimensional structures are considered. The EHL properties in bulk materials are discussed primarily in qualitative terms based on the experimental results obtained for germanium and silicon. Some of the experiments in which the main EHL thermodynamic parameters (density and binding energy) have been obtained are described and the basic factors that determine these parameters are considered. Topics covered include the effect of external perturbations (uniaxial strain and magnetic field) on EHL stability; phase diagrams for a nonequilibrium exciton-gas–EHL system; information on the size and concentration of electron–hole drops (EHDs) under various experimental conditions; the kinetics of exciton condensation and of recombination in the exciton-gas–EHD system; dynamic EHD properties and the motion of EHDs under the action of external forces; the properties of giant EHDs that form in potential wells produced by applying an inhomogeneous strain to the crystal; and effects associated with the drag of EHDs by nonequilibrium phonons (phonon wind), including the dynamics and formation of an anisotropic spatial structure of the EHD cloud. In discussing EHLs in low-dimensional structures, a number of studies are reviewed on the observation and experimental investigation of phenomena such as spatially indirect (dipolar) electron–hole and exciton (dielectric) liquids in GaAs/AlGaAs structures with double quantum wells (QWs), EHDs containing only a few electron–hole pairs (dropletons), EHLs in type-I silicon QWs, and spatially direct and dipolar EHLs in type-II silicon–germanium heterostructures.

Investigation of high frequency external perturbation effects on flow in a T-shape microchannel by μLIF technique

Investigation of high frequency external perturbation effect on flow inside T-shape microchannel was examined. In-phase pulsations of different frequencies were added to both inlets of the T-shaped microchannel to study mixing by means of Micro Laser Induced Fluorescence (μLIF) technique. For all flow regimes studied, mixing enhancement was obtained. Significant enhancement can be achieved at the beginning of the outlet channel operating in steady asymmetric regime (Re=186) by forcing at certain frequency ranges (f = 500Hz, f = 800Hz). Mixing suppression was also observed for two flow regimes (Re = 400, f = 1000Hz) and (Re = 120, f = 700Hz).

Effects of External Perturbations on Anticipatory and Compensatory Postural Adjustments in Patients with Multiple Sclerosis and a Fall History.

Although previous studies have investigated postural adjustment mechanisms in patients with multiple sclerosis (MS), it seems that no study has yet investigated the relationship between anticipatory and compensatory postural adjustments (APAs and CPAs, respectively) and falls. Seventeen MS fallers, 17 MS nonfallers, and 15 controls were exposed to a series of expected and unexpected backward pull perturbations applied at the trunk level. The electrical activity of 12 leg and trunk muscles as well as center of pressure displacement were recorded. The MS fallers had delayed muscle activity onsets compared with MS nonfallers and controls. In addition, a significantly lower level of muscle activity during APAs was detected in MS fallers compared with controls. Moreover, in the unexpected condition of perturbation, significantly smaller CPA was observed in MS fallers compared with controls. Both groups of patients with MS required more time to stabilize their center of pressure after both types of perturbations compared with controls. The inability to produce efficient APAs and CPAs during perturbations may explain the high rates of postural instability and falls in patients with MS. Findings from this study provide a background for the development of perturbation-based training programs aimed at balance improvement and fall prevention by restoring mechanisms underlying balance impairments.