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Journal articles on the topic 'Perturbation externe'

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Published: 7 July 2024

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1

Schuurman, F., M. G. Kleinhans, and H. Middelkoop. "Network response to internal and external perturbations in large sand-bed braided rivers." Earth Surface Dynamics Discussions 3, no. 1 (March 27, 2015): 197–250. http://dx.doi.org/10.5194/esurfd-3-197-2015.

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Abstract. The intrinsic instability of bars, bifurcations and branches in large braided rivers is a challenge to understand and predict. Even more, the reach-scale effect of human-induced perturbations on the braided channel network is still unresolved. In this study, we used a physics-based model to simulate the hydromorphodynamics in a large braided river and applied different types of perturbations. We analyzed the propagation of the perturbations through the braided channel network. The results showed that the perturbations initiate an instability that propagates in downstream direction by means of bifurcation instability. It alters and rotates the approaching flow of the bifurcations. The propagation celerity is in the same order of magnitude as the theoretical sand wave propagation rate. The adjustments of the bifurcations also change bar migration and reshape, with a feedback to the upstream bifurcation and alteration of the approaching flow to the downstream bifurcation. This way, the morphological effect of a perturbation amplifies in downstream direction. Thus, the interplay of bifurcation instability and asymmetrical reshaping of bars was found to be essential for propagation of the effects of a perturbation. The study also demonstrated that the large-scale bar statistics are hardly affected.

2

Kazantsev, E. "Sensitivity of the attractor of the barotropic ocean model to external influences: approach by unstable periodic orbits." Nonlinear Processes in Geophysics 8, no. 4/5 (October 31, 2001): 281–300. http://dx.doi.org/10.5194/npg-8-281-2001.

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Abstract. A description of a deterministic chaotic system in terms of unstable periodic orbits (UPO) is used to develop a method of an a priori estimate of the sensitivity of statistical averages of the solution to small external influences. This method allows us to determine the forcing perturbation which maximizes the norm of the perturbation of a statistical moment of the solution on the attractor. The method was applied to the barotropic ocean model in order to determine the perturbation of the wind field which provides the greatest perturbation of the model's climate. The estimates of perturbations of the model's time mean solution and its mean variance were compared with directly calculated values. The comparison shows that some 20 UPOs is sufficient to realize this approach and to obtain a good accuracy.

3

Ma, Yan, Weiming Sun, Nanrun Zhou, Jiping He, and Chaolin Ma. "Neurons in Primary Motor Cortex Encode External Perturbations during an Orientation Reaching Task." Brain Sciences 11, no. 9 (August 25, 2021): 1125. http://dx.doi.org/10.3390/brainsci11091125.

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When confronting an abrupt external perturbation force during movement, subjects continuously adjust their behaviors to adapt to changes. Such adaptation is of great importance for realizing flexible motor control in varied environments, but the potential cortical neuronal mechanisms behind it have not yet been elucidated. Aiming to reveal potential neural control system compensation for external disturbances, we applied an external orientation perturbation while monkeys performed an orientation reaching task and simultaneously recorded the neural activity in the primary motor cortex (M1). We found that a subpopulation of neurons in the primary motor cortex specially created a time-locked activity in response to a “go” signal in the adaptation phase of the impending orientation perturbation and did not react to a “go” signal under the normal task condition without perturbation. Such neuronal activity was amplified as the alteration was processed and retained in the extinction phase; then, the activity gradually faded out. The increases in activity during the adaptation to the orientation perturbation may prepare the system for the impending response. Our work provides important evidence for understanding how the motor cortex responds to external perturbations and should advance research about the neurophysiological mechanisms underlying motor learning and adaptation.

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Borkowski, Rafał, and Michalina Błażkiewicz. "Postural Reactions to External Mediolateral Perturbations: A Review." Applied Sciences 13, no. 3 (January 29, 2023): 1696. http://dx.doi.org/10.3390/app13031696.

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Background: Mediolateral perturbations caused by external pulling and pushing forces can occur in everyday living. Although the loss of balance can appear in all directions, coping with frontal plane perturbations is more challenging. In literature, it is common to compare postural responses between the elderly and the young, but the accurate description of reactions in the young is lacking. This manuscript aims to review all previous papers investigating how healthy young adults deal with mediolateral perturbations in a standing position, including reviewing the methodology, outcomes, and sequence of responses in these studies. Methods: A systematic review was conducted of papers published from 1999 to 2022. The databases searched were PubMed, Google Scholar, ScienceDirect, and EBSCO. Eight publications met the inclusion criteria. Results: There is no consensus on the methodology for conducting this type of research and how to collect the data, as it varies between authors. Many papers lack an accurate description and justification of the magnitude of imposed perturbations. It has been shown that the first joint torque and muscle response on perturbation may not be produced by active and voluntary muscle contraction, but are due to tissue stiffness. Such stiffness-based balance control does not directly involve the CNS and provides an immediate and appropriate corrective response. Conclusions: Postural reactions to mediolateral perturbations are a complicated process that still need further, systematized investigation.

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Tajali, Shirin, Mina Rouhani, Mohammad Mehravar, Hossein Negahban, Elham Sadati, and Ali E. Oskouei. "Effects of External Perturbations on Anticipatory and Compensatory Postural Adjustments in Patients with Multiple Sclerosis and a Fall History." International Journal of MS Care 20, no. 4 (July 1, 2018): 164–72. http://dx.doi.org/10.7224/1537-2073.2016-098.

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Abstract Background: 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. Methods: 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. Results: 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. Conclusions: 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.

6

Ivanov, N. V., A. M. Kakurin, and S. V. Konovalov. "MAGNETIC ISLAND DYNAMICS UNDER EXTERNAL MAGNETIC PERTURBATION IN ROTATING RESISTIVE ITER PLASMA." Problems of Atomic Science and Technology, Ser. Thermonuclear Fusion 36, no. 2 (2013): 55–64. http://dx.doi.org/10.21517/0202-3822-2013-36-2-55-64.

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Sharma, Himakshi, Bhabesh Chandra Deka, and Pradip Kr Bhattacharyya. "Behavior of potential energy surface of C–X bonds in presence of solvent and external electric field: A DFT study." Journal of Theoretical and Computational Chemistry 15, no. 06 (September 2016): 1650051. http://dx.doi.org/10.1142/s0219633616500516.

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The effect of external perturbations, namely solvent and external electric field on potential energy surface (PES) and bond dissociation energy of C–X (X[Formula: see text]F, Cl, Br, N, O) bonds has been studied in the light of density functional theory (DFT). The study reveals that presence of solvent as well as external electric field changes the curvature of the PES significantly. Bond dissociation energy significantly drops in presence of both the external perturbation.

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Petrov A.V., Chapalo I.E., Bisyarin M.A., and Kotov O.I. "Intermodal fiber interferometer based on broadband light source and optical spectrum analyzer for external perturbations measurement." Technical Physics Letters 48, no. 15 (2022): 7. http://dx.doi.org/10.21883/tpl.2022.15.53809.18968.

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An intermodal fiber interferometer based on broadband light source and spectral signal processing is proposed and experimentally investigated. The perturbation of the parameters of the spectrum analyzer (scanning range and width of the instrumental spectral response function) on the output signal is demonstrated. It is shown that the method of correlation signal processing makes it possible to obtain linear and stable response to external fiber perturbations. The proposed interferometer scheme can be prospective for development of real-time sensors of physical quantities. Keywords: intermodal fiber interferometer, fiber-optic sensors, fiber optics, multimode fiber, interferometers.

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Beretta, Victor Spiandor, Rodrigo Vitório, Priscila Nóbrega-Sousa, Núbia Ribeiro Conceição, Diego Orcioli-Silva, Marcelo Pinto Pereira, and Lilian Teresa Bucken Gobbi. "Effect of Different Intensities of Transcranial Direct Current Stimulation on Postural Response to External Perturbation in Patients With Parkinson’s Disease." Neurorehabilitation and Neural Repair 34, no. 11 (October 1, 2020): 1009–19. http://dx.doi.org/10.1177/1545968320962513.

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Background Habituation of postural response to perturbations is impaired in people with Parkinson’s disease (PD) due to deficits in cortico-basal pathways. Although transcranial direct current stimulation (tDCS) modulate cortico-basal networks, it remains unclear if it can benefit postural control in PD. Objective To analyze the effect of different intensities of anodal tDCS on postural responses and prefrontal cortex (PFC) activity during the habituation to the external perturbation in patients with PD (n = 24). Methods Anodal tDCS was applied over the primary motor cortex (M1) with 1 mA, 2 mA, and sham stimulation in 3 different sessions (~2 weeks apart) during 20 minutes immediately before the postural assessment. External perturbation (7 trials) was applied by a support base posterior translation (20 cm/s and 5 cm). Primary outcome measures included lower limb electromyography and center of pressure parameters. Measures of PFC activity are reported as exploratory outcomes. Analyses of variance (Stimulation Condition × Trial) were performed. Results Habituation of perturbation was evidenced independent of the stimulation conditions. Both active stimulation intensities had shorter recovery time and a trend for lower cortical activity in the stimulated hemisphere when compared to sham condition. Shorter onset latency of the medial gastrocnemius as well as lower cortical activity in the nonstimulated hemisphere were only observed after 2 mA concerning the sham condition. Conclusions tDCS over M1 improved the postural response to external perturbation in PD, with better response observed for 2 mA compared with 1 mA. However, tDCS seems to be inefficient in modifying the habituation of perturbation.

10

Sokolov, V. "Adaptive optimal robust stabilization of autoregressive plant under biased external disturbance." Proceedings of the Komi Science Centre of the Ural Division of the Russian Academy of Sciences, no. 5 (December 20, 2022): 20–27. http://dx.doi.org/10.19110/1994-5655-2022-5-20-27.

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This paper addresses the problem of adaptive optimal robust control of a discrete-time plant with unknown parameters of autoregressive nominal model, unknown upper bound and bias of external disturbance, and unknown gains of coprime factor perturbations. The control criterion is the worst-case steady-state upper bound of the output. Solution of the problem is based on an optimal polyhedral estimation of unknown non-identifiable parameters with the control criterion treated as the identification criterion. A replacement of unknown parameters is proposed that modifies the plant model to a model without perturbation in control. This transforms the nonconvex control criterion to a linear fractional one and thus makes possible online computation of optimal estimates.

11

Pollock, C. L., T. D. Ivanova, M. A. Hunt, and S. J. Garland. "Motor unit recruitment and firing rate in medial gastrocnemius muscles during external perturbations in standing in humans." Journal of Neurophysiology 112, no. 7 (October 1, 2014): 1678–84. http://dx.doi.org/10.1152/jn.00063.2014.

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There is limited investigation of the interaction between motor unit recruitment and rate coding for modulating force during standing or responding to external perturbations. Fifty-seven motor units were recorded from the medial gastrocnemius muscle with intramuscular electrodes in response to external perturbations in standing. Anteriorly directed perturbations were generated by applying loads in 0.45-kg increments at the pelvis every 25–40 s until 2.25 kg was maintained. Motor unit firing rate was calculated for the initial recruitment load and all subsequent loads during two epochs: 1) dynamic response to perturbation directly following each load drop and 2) maintenance of steady state between perturbations. Joint kinematics and surface electromyography (EMG) from lower extremities and force platform measurements were assessed. Application of the external loads resulted in a significant forward progression of the anterior-posterior center of pressure (AP COP) that was accompanied by modest changes in joint angles (<3°). Surface EMG increased more in medial gastrocnemius than in the other recorded muscles. At initial recruitment, motor unit firing rate immediately after the load drop was significantly lower than during subsequent load drops or during the steady state at the same load. There was a modest increase in motor unit firing rate immediately after the load drop on subsequent load drops associated with regaining balance. There was no effect of maintaining balance with increased load and forward progression of the AP COP on steady-state motor unit firing rate. The medial gastrocnemius utilized primarily motor unit recruitment to achieve the increased levels of activation necessary to maintain standing in the presence of external loads.

12

Crevecoeur, F., I. Kurtzer, T. Bourke, and S. H. Scott. "Feedback responses rapidly scale with the urgency to correct for external perturbations." Journal of Neurophysiology 110, no. 6 (September 15, 2013): 1323–32. http://dx.doi.org/10.1152/jn.00216.2013.

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Healthy subjects can easily produce voluntary actions at different speeds and with varying accuracy requirements. It remains unknown whether rapid corrective responses to mechanical perturbations also possess this flexibility and, thereby, contribute to the capability expressed in voluntary control. Paralleling previous studies on self-initiated movements, we examined how muscle activity was impacted by either implicit or explicit criteria affecting the urgency to respond to the perturbation. Participants maintained their arm position against torque perturbations with unpredictable timing and direction. In the first experiment, the urgency to respond was explicitly altered by varying the time limit (300 ms vs. 700 ms) to return to a small target. A second experiment addresses implicit urgency criteria by varying the radius of the goal target, such that task accuracy could be achieved with less vigorous corrections for large targets than small target. We show that muscle responses at ∼60 ms scaled with the task demand. Moreover, in both experiments, we found a strong intertrial correlation between long-latency responses (∼50–100 ms) and the movement reversal times, which emphasizes that these rapid motor responses are directly linked to behavioral performance. The slopes of these linear regressions were sensitive to the experimental condition during the long-latency and early voluntary epochs. These findings suggest that feedback gains for very rapid responses are flexibly scaled according to task-related urgency.

13

Curuk, Etem, Yunju Lee, and Alexander S. Aruin. "Individuals With Stroke Use Asymmetrical Anticipatory Postural Adjustments When Counteracting External Perturbations." Motor Control 23, no. 4 (October 1, 2019): 461–71. http://dx.doi.org/10.1123/mc.2018-0083.

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The authors investigated anticipatory postural adjustments in persons with unilateral stroke using external perturbations. Nine individuals with stroke and five control subjects participated. The electromyographic activity of 16 leg and trunk muscles was recorded. The onsets of muscle activity during the anticipatory phase of postural control were analyzed. The individuals with stroke did not show an anticipatory activation of leg and trunk muscles on the affected side; instead, the muscle onsets were seen after the perturbation, during the balance restoration phase. However, an anticipatory activation of muscles on the unaffected side was seen in individuals with stroke, and it was observed earlier compared with healthy controls (p < .05). The individuals with stroke showed a distal to proximal order of anticipatory activation of muscles on the unaffected side. The outcome of the study provides a basis for future investigations regarding ways of improving balance control in people with stroke.

14

Kunimura, Hiroshi, Masakazu Matsuoka, Naoki Hamada, and Koichi Hiraoka. "Effects of Internal and External Attentional Focus on Postural Response to a Sliding Stance Surface." Perceptual and Motor Skills 126, no. 3 (April 5, 2019): 446–61. http://dx.doi.org/10.1177/0031512519838688.

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The present study examined whether an internal or external attentional focus would affect participants’ feet-in-place balance response to postural stance perturbations. A movable platform automatically slid forward or backward while healthy participants stood on it and (a) performed no cognitive activity (control), (b) focused on the pelvis or upper body sway (internal focus), (c) memorized a number displayed immediately before the platform slid (external focus), or (d) kept the equilibrium of an unstable cylinder over the arm (external focus). The forward displacement of the pelvis induced by the platform sliding forward was smaller when participants focused on their pelvic sway, although such effect was absent when they focused on their upper body sway, indicating that the internal focus was effective for the postural response when attention was paid to the pelvic sway. Regarding an external attention focus, the forward displacement of the pelvis induced by the platform sliding forward was smaller when participants focused on the equilibrium of an unstable object over the arm, but this effect was absent when they focused on the number, indicating that an external focus was only effective when the unstable object focused upon was relevant to the equilibrium of one’s own body. No attentional intervention was effective during backward sliding of the support surface, indicating that central set for responding to postural perturbation depends on the direction of the postural perturbation.

15

Li, Jian, Yang Xu, Mingjiang Zhang, Jianzhong Zhang, Lijun Qiao, and Tao Wang. "Performance improvement in double-ended RDTS by suppressing the local external physics perturbation and intermodal dispersion." Chinese Optics Letters 17, no. 7 (2019): 070602. http://dx.doi.org/10.3788/col201917.070602.

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Klapp, Sabine H. L. "Dipolar fluids under external perturbations." Journal of Physics: Condensed Matter 17, no. 15 (April 2, 2005): R525—R550. http://dx.doi.org/10.1088/0953-8984/17/15/r02.

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MOUS, SIPKO L. J., and JOHAN GRASMAN. "TWO METHODS FOR ASSESSING THE SIZE OF EXTERNAL PERTURBATIONS IN CHAOTIC PROCESSES." Mathematical Models and Methods in Applied Sciences 03, no. 04 (August 1993): 577–93. http://dx.doi.org/10.1142/s0218202593000291.

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This paper deals with the assessment of an external perturbation in nonlinear chaotic dynamical processes using either a modified sentinel function or an extended Kalman filter treatment. We consider processes that can be modeled by a system of nonlinear ordinary differential equations. The sentinel function is used to detect an external perturbation, that is not included in the model of the process. In cases where the time dependency of the external perturbation is known but the size of the perturbation is unknown, the sentinel function is also used to estimate the size of this perturbation. We have compared this approach to estimate the size of a perturbation with an extended Kalman filter treatment and as an example to illustrate these two approaches we have analyzed a lower order spectral model of the atmospheric circulation with a perturbed equator-pole temperature gradient.

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Stouffer, Ronald J., Dan Seidov, and Bernd J. Haupt. "Climate Response to External Sources of Freshwater: North Atlantic versus the Southern Ocean." Journal of Climate 20, no. 3 (February 1, 2007): 436–48. http://dx.doi.org/10.1175/jcli4015.1.

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Abstract The response of an atmosphere–ocean general circulation model (AOGCM) to perturbations of freshwater fluxes across the sea surface in the North Atlantic and Southern Ocean is investigated. The purpose of this study is to investigate aspects of the so-called bipolar seesaw where one hemisphere warms and the other cools and vice versa due to changes in the ocean meridional overturning. The experimental design is idealized where 1 Sv (1 Sv ≡ 106 m3 s−1) of freshwater is added to the ocean surface for 100 model years and then removed. In one case, the freshwater perturbation is located in the Atlantic Ocean from 50° to 70°N. In the second case, it is located south of 60°S in the Southern Ocean. In the case where the North Atlantic surface waters are freshened, the Atlantic thermohaline circulation (THC) and associated northward oceanic heat transport weaken. In the Antarctic surface freshening case, the Atlantic THC is mainly unchanged with a slight weakening toward the end of the integration. This weakening is associated with the spreading of the fresh sea surface anomaly from the Southern Ocean into the rest of the World Ocean. There are two mechanisms that may be responsible for such weakening of the Atlantic THC. First is that the sea surface salinity (SSS) contrast between the North Atlantic and North Pacific is reduced. And, second, when freshwater from the Southern Ocean reaches the high latitudes of the North Atlantic Ocean, it hinders the sinking of the surface waters, leading to the weakening of the THC. The spreading of the fresh SSS anomaly from the Southern Ocean into the surface waters worldwide was not seen in earlier experiments. Given the geography and climatology of the Southern Hemisphere where the climatological surface winds push the surface waters northward away from the Antarctic continent, it seems likely that the spreading of the fresh surface water anomaly could occur in the real world. A remarkable symmetry between the two freshwater perturbation experiments in the surface air temperature (SAT) response can be seen. In both cases, the hemisphere with the freshwater perturbation cools, while the opposite hemisphere warms slightly. In the zonally averaged SAT figures, both the magnitude and the pattern of the anomalies look similar between the two cases. The oceanic response, on the other hand, is very different for the two freshwater cases, as noted above for the spreading of the SSS anomaly and the associated THC response. If the differences between the atmospheric and oceanic responses apply to the real world, then the interpretation of paleodata may need to be revisited. To arrive at a correct interpretation, it matters whether or not the evidence is mainly of atmospheric or oceanic origin. Also, given the sensitivity of the results to the exact details of the freshwater perturbation locations, especially in the Southern Hemisphere, a more realistic scenario must be constructed to explore these questions.

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Holmes, Michael W. R., and Peter J. Keir. "Muscle Contributions to Elbow Joint Rotational Stiffness in Preparation for Sudden External Arm Perturbations." Journal of Applied Biomechanics 30, no. 2 (April 2014): 282–89. http://dx.doi.org/10.1123/jab.2013-0135.

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Understanding joint stiffness and stability is beneficial for assessing injury risk. The purpose of this study was to examine joint rotational stiffness for individual muscles contributing to elbow joint stability. Fifteen male participants maintained combinations of three body orientations (standing, supine, sitting) and three hand preloads (no load, solid tube, fluid filled tube) while a device imposed a sudden elbow extension. Elbow angle and activity from nine muscles were inputs to a biomechanical model to determine relative contributions to elbow joint rotational stiffness, reported as percent of total stiffness. A body orientation by preload interaction was evident for most muscles (P< .001). Brachioradialis had the largest change in contribution while standing (no load, 18.5%; solid, 23.8%; fluid, 26.3%). Across trials, the greatest contributions were brachialis (30.4 ± 1.9%) and brachioradialis (21.7 ± 2.2%). Contributions from the forearm muscles and triceps were 5.5 ± 0.6% and 9.2 ± 1.9%, respectively. Contributions increased at time points closer to the perturbation (baseline to anticipatory), indicating increased neuromuscular response to resist rotation. This study quantified muscle contributions that resist elbow perturbations, found that forearm muscles contribute marginally and showed that orientation and preload should be considered when evaluating elbow joint stiffness and safety.

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Roques, Lionel, and Mickaël D. Chekroun. "On Population Resilience to External Perturbations." SIAM Journal on Applied Mathematics 68, no. 1 (January 2007): 133–53. http://dx.doi.org/10.1137/060676994.

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Stout, Eric, and Fazle Hussain. "External turbulence-induced axial flow and instability in a vortex." Journal of Fluid Mechanics 793 (March 16, 2016): 353–79. http://dx.doi.org/10.1017/jfm.2016.123.

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External turbulence-induced axial flow in an incompressible, normal-mode stable Lamb–Oseen (two-dimensional) vortex column is studied via direct numerical simulations of the Navier–Stokes equations. Azimuthally oriented vorticity filaments, formed from external turbulence, advect radially towards or away from the vortex axis (depending on the filament’s swirl direction), resulting in a net induced axial flow in the vortex core; axial flow increases with increasing vortex Reynolds number ($Re=$ vortex circulation/viscosity). This contrasts the viscous mechanism for axial flow generation downstream of a lifting body, wherein an axial pressure gradient is produced by viscous diffusion of the swirl (Batchelor, J. Fluid Mech., vol. 20, 1964, pp. 645–658). Analysis of the self-induced motion of an arbitrarily curved external filament shows that any non-axisymmetric filament undergoes radial advection. We then studied the evolution of a vortex column starting with an imposed optimal transient growth perturbation. For a range of Re values, axial flow develops and initially grows as (time)$^{5/2}$ before decreasing after two turnover times; for $Re=10\,000$ – the highest computationally achievable – axial flow at late times becomes sufficiently strong to induce vortex instability. Contrary to a prior claim of a parent–offspring mechanism at the outer edge of the core, vorticity tilting within the core by axial flow is the underlying mechanism producing energy growth. Thus, external perturbations in practical flows (at $Re\sim 10^{7}$) produce destabilizing axial flow, possibly leading to the sought-after vortex breakup.

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Andrianov, Igor I. "Analytical investigation of buckling of a cylindrical shell subjected to nonuniform external pressure." Mathematics and Mechanics of Solids 24, no. 3 (March 15, 2018): 874–83. http://dx.doi.org/10.1177/1081286518756179.

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An analytical algorithm is proposed for studying the stability of a cylindrical shell subjected to nonuniform external pressure. The algorithm is based on a perturbation procedure and Padé approximants. Unlike the commonly used perturbation method, this approach is not limited by the smallness of the perturbation parameter. The approximate formulas obtained are sufficiently accurate and can be used in engineering practice.

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Bilskiy, Artur, Yuriy Lozhkin, and Aleksandr Nebuchinov. "Study of the effect of external periodic flow perturbations on heat transfer intensity in the impact jet." Modern science: researches, ideas, results, technologies 8, no. 2 (June 15, 2017): 9–18. http://dx.doi.org/10.23877/ms.ts.39.002.

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Handelzalts, Shirley, Flavia Steinberg-Henn, Sigal Levy, Guy Shani, Nachum Soroker, and Itshak Melzer. "Insufficient Balance Recovery Following Unannounced External Perturbations in Persons With Stroke." Neurorehabilitation and Neural Repair 33, no. 9 (July 17, 2019): 730–39. http://dx.doi.org/10.1177/1545968319862565.

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Background. Persons with stroke (PwS) are at increased risk of falls, especially toward the paretic side, increasing the probability of a hip fracture. The ability to recover from unexpected loss of balance is a critical factor in fall prevention. Objectives. We aimed to compare reactive balance capacity and step kinematics between PwS and healthy controls. Methods. Thirty subacute PwS and 15 healthy controls were exposed to forward, backward, right, and left unannounced surface translations in 6 increasing intensities while standing. Single step threshold, multiple step threshold, and fall threshold (ie, perturbation intensity leading to a fall into harness system) were recorded as well as reactive step initiation time, step length, and step velocity. Results. Twenty-five PwS fell into harness system during the experiment while healthy controls did not fall. Fourteen out of 31 falls occurred in response to surface translations toward the nonparetic side, that is, falling toward the paretic side. Compared with healthy controls, PwS demonstrated significantly lower fall threshold and multiple step threshold in response to forward, backward, and lateral surface translations. Impairments were more pronounced in response to forward surface translation and toward the nonparetic side (ie, loss of balance toward the paretic side). A trend toward significant shorter step length in response to lateral surface translations was found in PwS compared with healthy controls. Conclusions. Findings highlight the importance of assessing reactive balance capacity in response to perturbations in different directions and intensities in addition to the routine assessment in PwS.

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TAGHIPOOR, M., Sophie LEMOSQUET, J. VAN MILGEN, A. SIEGEL, D. SAUVANT, and F. GONDRET. "Modélisation de la flexibilité métabolique : vers une meilleure compréhension des capacités adaptatives de l’animal." INRA Productions Animales 29, no. 3 (December 12, 2019): 201–16. http://dx.doi.org/10.20870/productions-animales.2016.29.3.2960.

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Une production durable nécessite de disposer d’animaux capables de s’adapter à une diversité croissante de contraintes et perturbations environnementales pour maintenir leurs performances de production. La flexibilité métabolique est un des leviers importants pour la compréhension de l’adaptation individuelle aux perturbations externes. Les éléments du métabolisme sont organisés en un réseau biologique vaste et complexe, recouvrant différentes échelles d’organisations spatiales et temporelles. Cet article présent trois formalismes de modélisation permettant de décrire ce réseau et y associe trois exemples illustratifs du comportement de ce réseau face à des perturbations telles que rencontrées en production animale. Ces formalismes dépendent de la taille du (sous)-réseau que l’on souhaite considérer et du type de prédictions souhaitées (qualitatives, quantitatives) : i) la modélisation structurelle qui se base sur l’étude des propriétés topologiques d’un réseau de grande taille, ii) la modélisation stœchiométrique qui permet d’analyser les flux métaboliques dans un état stationnaire et iii) la modélisation dynamique qui permet d’observer l’évolution des acteurs d’un réseau biologique dans le temps.

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Wang, Qing-Jun, and Jiping He. "Fuzzy control of postural stability under external perturbation." IFAC Proceedings Volumes 32, no. 2 (July 1999): 5719–24. http://dx.doi.org/10.1016/s1474-6670(17)56976-1.

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Pepyolyshev, Yu N., and A. K. Popov. "Safe external reactivity perturbation limits in IBR-2." Annals of Nuclear Energy 38, no. 5 (May 2011): 1109–14. http://dx.doi.org/10.1016/j.anucene.2010.12.016.

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Maslov, E. M., L. A. Kalyakin, and A. G. Shagalov. "Breather resonant phase locking by an external perturbation." Theoretical and Mathematical Physics 152, no. 2 (August 2007): 1173–82. http://dx.doi.org/10.1007/s11232-007-0100-6.

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29

JING, ZHUJUN, and JIANPING YANG. "COMPLEX DYNAMICS IN PENDULUM EQUATION WITH PARAMETRIC AND EXTERNAL EXCITATIONS II." International Journal of Bifurcation and Chaos 16, no. 10 (October 2006): 3053–78. http://dx.doi.org/10.1142/s0218127406016653.

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Abstract:

This paper (II) is a continuation of "Complex dynamics in pendulum equation with parametric and external excitations (I)." By applying second-order averaging method and Melnikov's method, we obtain the criterion of existence of chaos in an averaged system under quasi-periodic perturbation for Ω = nω + ∊ν, n = 1, 2, 4 and cannot prove the criterion of existence of chaos in averaged system under quasi-periodic perturbation for Ω = nω + ∊ν, n = 3, 5–15 by Melnikov's method, where ν is not rational to ω. However, we show the occurrence of chaos in the averaged and original systems under quasi-periodic perturbation for Ω = nω + ∊ν, n = 3, 5 by numerical simulation. The numerical simulations, include the bifurcation diagram of fixed points, bifurcation diagrams in three- and two-dimensional spaces, homoclinic bifurcation surface, maximum Lyapunov exponent, phase portraits, Poincaré map, are plotted to illustrate theoretical analysis, and to expose the complex dynamical behaviors, including period-3 orbits in different chaotic regions, interleaving occurrence of chaotic behaviors and quasi-periodic behaviors, a different kind of interior crisis, jumping behavior of quasi-periodic sets, different nice quasi-periodic attractors, nonchaotic attractors and chaotic attractors, coexistence of three quasi-periodic sets, onset of chaos which occurs more than once for a given external frequency or amplitudes, and quasi-periodic route to chaos. We do not find the period-doubling cascade. The dynamical behaviors under quasi-periodic perturbation are different from that of periodic perturbation.

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Dagnino, Paulina Clara, Anira Escrichs, Ane López-González, Olivia Gosseries, Jitka Annen, Yonatan Sanz Perl, Morten L. Kringelbach, Steven Laureys, and Gustavo Deco. "Re-awakening the brain: Forcing transitions in disorders of consciousness by external in silico perturbation." PLOS Computational Biology 20, no. 5 (May 3, 2024): e1011350. http://dx.doi.org/10.1371/journal.pcbi.1011350.

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Abstract:

A fundamental challenge in neuroscience is accurately defining brain states and predicting how and where to perturb the brain to force a transition. Here, we investigated resting-state fMRI data of patients suffering from disorders of consciousness (DoC) after coma (minimally conscious and unresponsive wakefulness states) and healthy controls. We applied model-free and model-based approaches to help elucidate the underlying brain mechanisms of patients with DoC. The model-free approach allowed us to characterize brain states in DoC and healthy controls as a probabilistic metastable substate (PMS) space. The PMS of each group was defined by a repertoire of unique patterns (i.e., metastable substates) with different probabilities of occurrence. In the model-based approach, we adjusted the PMS of each DoC group to a causal whole-brain model. This allowed us to explore optimal strategies for promoting transitions by applying off-line in silico probing. Furthermore, this approach enabled us to evaluate the impact of local perturbations in terms of their global effects and sensitivity to stimulation, which is a model-based biomarker providing a deeper understanding of the mechanisms underlying DoC. Our results show that transitions were obtained in a synchronous protocol, in which the somatomotor network, thalamus, precuneus and insula were the most sensitive areas to perturbation. This motivates further work to continue understanding brain function and treatments of disorders of consciousness.

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Dvornichenko, A. V. "Influence of nonlinear dissipation and external perturbations on transition scenarios to the chaos in the Lorenz-Haken system." Functional materials 20, no. 2 (June 25, 2013): 227–33. http://dx.doi.org/10.15407/fm20.02.227.

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32

Upadhyay, R. K., V. Rai, and S. R. K. Iyengar. "How do ecosystems respond to external perturbations?" Chaos, Solitons & Fractals 11, no. 13 (October 2000): 1963–82. http://dx.doi.org/10.1016/s0960-0779(99)00086-7.

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33

Nakabayashi, Seiichiro, and Kohei Uosaki. "Synchronization of electrochemical oscillations with external perturbations." Chemical Physics Letters 217, no. 1-2 (January 1994): 163–66. http://dx.doi.org/10.1016/0009-2614(93)e1364-m.

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34

Masamune, S., M. Iida, Y. Ohfuji, K. Ohta, and H. Oshiyama. "RFP plasma response to external helical perturbations." Plasma Physics and Controlled Fusion 40, no. 1 (January 1, 1998): 127–37. http://dx.doi.org/10.1088/0741-3335/40/1/007.

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35

Sergeev, Oleg. "Bistable system with external dynamical influence." Izvestiya VUZ. Applied Nonlinear Dynamics 8, no. 5 (2001): 48–56. http://dx.doi.org/10.18500/0869-6632-2000-8-5-48-56.

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Abstract:

In this paper we have studied the influence of additive periodical and dynamical chaos perturbation on the location of the bifurcation boundary which separates mono— and bistable regimes in bistable one—dimensional dynamical system with cubic nonlinearity.

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Li, Mengyang, and Mingcong Deng. "Operator-based external disturbance rejection of perturbed nonlinear systems by using robust right coprime factorization." Transactions of the Institute of Measurement and Control 40, no. 10 (August 1, 2017): 3169–78. http://dx.doi.org/10.1177/0142331217718899.

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Abstract:

In this paper, a class of nonlinear systems with external disturbance and internal perturbation are considered by using operator-based robust right coprime factorization for guaranteeing robust stability, rejecting adverse effects resulting from the existing disturbance and perturbation quantitatively and, meanwhile, realizing output tracking performance. In detail, firstly, robust stability is guaranteed based on a Lipschitz norm inequation using robust right coprime factorization. Secondly, based on the proposed design scheme, a convenient framework is obtained for discussing rejection issues for external disturbance and internal perturbation. Thirdly, from an error signal point of view, the adverse effects resulting from the external disturbance and internal perturbation of the nonlinear system are removed by the designed nonlinear operator. Moreover, output tracking performance is realized using the proposed design scheme simultaneously. Finally, a simulation example is given to confirm the effectiveness of the proposed design scheme of this paper.

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Xie, Chengrong, Yuhua Xu, and Dongbing Tong. "Chaos Synchronization of Financial Chaotic System with External Perturbation." Discrete Dynamics in Nature and Society 2015 (2015): 1–7. http://dx.doi.org/10.1155/2015/731376.

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Abstract:

This paper investigates the problem of two kinds of function projective synchronization of financial chaotic system with definite integration scaling function, which are not fully considered in the existing research. Different from the previous methods, in this paper, the following two questions are investigated: (1) two kinds of the definite integration scaling function projective synchronization are given; (2) the upper and lower limit of the definite integral scaling function are the bound dynamical systems. Finally, illustrative example is provided to show the effectiveness of this method.

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Razdoburdin, D. N. "Perturbation dynamics in Keplerian flow under external stochastic forcing." Monthly Notices of the Royal Astronomical Society 492, no. 4 (February 14, 2020): 5366–76. http://dx.doi.org/10.1093/mnras/staa145.

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ABSTRACT We investigate the dynamics of linear perturbations in Keplerian flow under external stochastic force. To abstract from the details of flow structure and boundary conditions, we consider the problem in the shearing box approximation. An external force is assumed to have zero mean, even so, induced perturbations form a steady state, which provides angular momentum transfer to the periphery of the flow. The most effective scenario is based on the transient amplification of induced vortices with the following emission of a shearing sound wave, wherein the maximum of the flux linearly depends on Reynolds number. Thus such a mechanism is significant for astrophysical flows, for which enormous Reynolds numbers are typical. At the same time, addressing the problem analytically, we find that for incompressible fluid in the shearing box approximation stochastic forcing does not lead to average angular momentum transfer. Thus the compressibility of the fluid plays an important role here, and one cannot neglect it.

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Wang, Hongwei, Jon Fuller, Peng Chen, Sergey I. Morozov, and Qi An. "Characterizing local metallic bonding variation induced by external perturbation." Physical Chemistry Chemical Physics 22, no. 4 (2020): 2372–78. http://dx.doi.org/10.1039/c9cp05954g.

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40

Nagasaki, Kazunobu, and Kimitaka Itoh. "Decay Process of a Magnetic Islandby External Magnetic Perturbation." Journal of the Physical Society of Japan 60, no. 9 (September 15, 1991): 2966–76. http://dx.doi.org/10.1143/jpsj.60.2966.

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41

Yamada, Hiroshi, and Zensho Yoshida. "Saturated Island Width in Tokamak with External Helical Perturbation." Journal of the Physical Society of Japan 56, no. 7 (July 15, 1987): 2241–44. http://dx.doi.org/10.1143/jpsj.56.2241.

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42

Klinshov, Vladimir, and Vladimir Nekorkin. "Switching thresholds for multistable systems under strong external perturbation." Communications in Nonlinear Science and Numerical Simulation 83 (April 2020): 105067. http://dx.doi.org/10.1016/j.cnsns.2019.105067.

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43

Shin, Youngkyun, and Gu-Bum Park. "Analysis of Postural Stability During Continuous External Perturbations." Journal of the Korean Institute of Illuminating and Electrical Installation Engineers 27, no. 8 (August 31, 2013): 21–29. http://dx.doi.org/10.5207/jieie.2013.27.8.021.

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44

Aliev, K. M., I. K. Kamilov, Kh O. Ibragimov, and N. S. Abakarova. "Response of semiconductor nonlinear circuits to external perturbations." Semiconductors 49, no. 3 (March 2015): 401–5. http://dx.doi.org/10.1134/s1063782615030033.

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45

Kawano, Yozo, Masamune Oguri, Takahiko Matsubara, and Satoru Ikeuchi. "Galaxy Structures and External Perturbations in Gravitational Lenses." Publications of the Astronomical Society of Japan 56, no. 2 (April 25, 2004): 253–60. http://dx.doi.org/10.1093/pasj/56.2.253.

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46

Akhobadze, A. G., and S. A. Krasnova. "Tracking in linear MIMO systems under external perturbations." Automation and Remote Control 70, no. 6 (June 2009): 933–57. http://dx.doi.org/10.1134/s0005117909060034.

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47

Gu, Q., and F. A. Popp. "Nonlinear response of biophoton emission to external perturbations." Experientia 48, no. 11-12 (December 1992): 1069–82. http://dx.doi.org/10.1007/bf01947994.

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48

de Oliveira, G. I., and F. B. Rizzato. "Nonlinear spatiotemporal stability of solitons against external perturbations." Chaos, Solitons & Fractals 28, no. 5 (June 2006): 1347–55. http://dx.doi.org/10.1016/j.chaos.2005.08.011.

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49

Grosman, A., J. M. Ané, P. Barabaschi, K. H. Finken, A. Mahdavi, Ph Ghendrih, G. Huysmans, M. Lipa, P. R. Thomas, and E. Tsitrone. "H-mode barrier control with external magnetic perturbations." Journal of Nuclear Materials 313-316 (March 2003): 1314–20. http://dx.doi.org/10.1016/s0022-3115(02)01509-x.

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50

Wang, Xingyuan, and Na Wei. "Modified function projective lag synchronization of hyperchaotic complex systems with parameter perturbations and external perturbations." Journal of Vibration and Control 21, no. 16 (March 13, 2014): 3266–80. http://dx.doi.org/10.1177/1077546314521263.

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