Готові списки джерел за темами / Perturbation externe

Добірка наукової літератури з теми "Perturbation externe"

Автор: Grafiati

Опубліковано: 7 липня 2024

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Статті в журналах з теми "Perturbation externe":

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.

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.

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.

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.

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.

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.

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.

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.

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.

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Дисертації з теми "Perturbation externe":

Rao, Guillaume. "Biomécanique de la coordination motrice : Modélisations et analyses en réponse à une perturbation interne ou externe." Phd thesis, Aix-Marseille Université, 2006. http://tel.archives-ouvertes.fr/tel-00908210.

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Ce travail doctoral poursuivait deux objectifs : D'une part, proposer une triple contribution méthodologique à l'analyse de la coordination motrice. Cette contribution consiste premièrement à analyser la sensibilité des résultats d'une procédure de dynamique inverse à la qualité des données d'entrée anthropométriques et à proposer une recommendation quant à la méthode d'estimation des BSP à utiliser pour déterminer au mieux les moments musculaires nets. Deuxièmement, une évolution d'un modèle biomécanique associant des données périphériques de différente nature (cinématique, anthropométrie, torseur dynamique externe, EMG) dans une procédure d'optimisation numérique et permettant d'estimer les moments développés par les groupes musculaires agoniste et antagoniste de l'articulation du genou est présentée. Les évolutions apportées visent à prendre en compte la baisse de capacit'e de production de force du groupe musculaire dûe à la fatigue en se basant sur une analyse fréquentielle du signal EMG réalisée par une transformée en ondelettes. Troisièmement, une méthode d'estimation des tensions musculaires est développée avec pour objectif une prédiction optimale de l'activité musculaire antagoniste. D'autre part, analyser la coordination musculaire lors d'une tâche de "squat" réalisée en présence d'une perturbation interne ou externe des conditions de réalisation de la tâche. L'ajout d'une charge supplémentaire modifiait les conditions externes de réalisation de la tâche tandis que la présence d'une fatigue musculaire représentait une perturbation interne. Les résultats de l'analyse de la coordination musculaire montrent une exploitation de la redondance musculaire orientée vers la stabilité de l'articulation et la production de mouvements coordonnés. De plus, la gestion de cette redondance en présence de fatigue diffère de celle observée lors de l'ajout d'une charge. Le Système Nerveux Central exploite donc différemment, mais toujours de manière optimale, la redondance musculaire pour faire face à une perturbation.

Corbeil, Philippe. "Études des mécanismes adaptatifs du maintien de l'équilibre orthostatique. Effets d'une fatigue musculaire, d'une douleur expérimentale et d'une perturbation externe." Thesis, Université Laval, 2003. http://www.theses.ulaval.ca/2003/21104/21104.pdf.

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Le maintien de l’équilibre orthostatique est une activité motrice primordiale parce qu’elle permet de préserver l’autonomie de chaque individu. Les études présentées dans cette thèse traitent comment diverses contraintes influencent les mécanismes de contrôle impliqués lors du maintien de l’équilibre en station debout. Cette thèse a donc pour objectifs de vérifier : (1) Les effets de la fatigue de certains muscles impliqués dans le contrôle du maintien orthostatique. (2) Les effets d’une douleur expérimentale sur les mécanismes de régulation de l’équilibre orthostatique. (3) Les effets d’une perturbation externe pouvant causer une perte d’équilibre. (4) La validité d’un modèle mathématique démontrant l’importance d’une troisième variable nécessaire pour prédire la stabilité en station debout : le temps de développement du moment de force aux chevilles. En conclusion, cette thèse permet d’éclaircir l’implication des mécanismes adaptatifs du système nerveux dans différents contextes. Premièrement, le système nerveux s’adapteraient à la fatigue des triceps suraux en augmentant la fréquence des ajustements posturaux afin d’éviter des déplacements plus excentriques du centre de masse du corps ou en augmentant les propriétés mécaniques des articulations (i.e. la rigidité). Deuxièmement, une stimulation des nocicepteurs altère principalement les processus sensori-moteurs du système de contrôle postural. La détérioration de la stabilité est fonction de la localisation et de l’intensité de la stimulation douloureuse. La perception de la douleur nécessite des ressources attentionnelles qui ne nuisent pas au contrôle du maintien de l’équilibre en station debout. Troisièmement, l’incertitude reliée à l’avènement probable d’une perturbation provoque une altération des processus de contrôle du maintien de l’équilibre dans les situations sans perturbation et avec perturbation. Quatrièmement, le temps de développement du moment de force aux chevilles contraint la capacité d’une personne à retrouver l’équilibre en station debout suite à une déstabilisation vers l’avant. En ajoutant cette variable à un modèle mathématique, celui-ci permet de prédire 73.3 % des chutes et 73.3 % des stabilisations observées expérimentalement.

Corbeil, Philippe. "Etude des mécanismes adaptatifs du maintien de l'équilibre orthostatique : effets d'une fatigue musculaire, d'une douleur expérimentale et d'une perturbation externe." Université Joseph Fourier (Grenoble), 2003. http://www.theses.fr/2003GRE10062.

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Chatagnon, Thomas. "Standing balance recovery strategies following external perturbations : a multiscale approach with applications to dense crowds." Electronic Thesis or Diss., Université de Rennes (2023-....), 2023. http://www.theses.fr/2023URENE007.

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Chaque année dans le monde on rapporte plusieurs accidents liés aux foules denses. Ces accidents peuvent entraîner des blessures et même des décès dans les cas les plus extrêmes. Les chutes dans les foules denses ont été observées comme l’un des éléments déclencheurs possibles de ces accidents. De telles chutes résultent des difficultés de recouvrement de l’équilibre postural dans ce contexte particulier. Cependant, les connaissances concernant l’équilibre postural dans ce contexte sont très limitées en raison de la nature complexe des environnements liés aux foules denses. Dans cette thèse, nous proposons une approche expérimentale pour étudier le rétablissement d’équilibre postural suite à des perturbations externes dans des environnements de foules humaines avec différents niveaux de densité. En particulier, comme les perturbations peuvent survenir de n’importe quelle direction dans les foules, nous étudions dans un premier temps la réaction d’individus isolés à des perturbations externes provenant de plusieurs directions. Nous proposons ensuite une méthode permettant de prédire les stratégies de recouvrement d’équilibre des participants sur la base d’informations cinématiques uniquement. Des expériences impliquant plusieurs individus sont par la suite étudiées. En particulier, nous avons étudié l’effet de la densité de la foule sur l’initiation et les caractéristiques des pas de récupération d’équilibre. Finalement, un nouveau paradigme expérimental a été proposé pour étudier l’équilibre postural en conditions réelles lors d’événements impliquant des foules denses. Cette approche a ensuite été utilisée au sein de foules durant des concerts de musique punk rock. Les résultats fournissent de nouvelles informations concernant la nature des interactions physiques et les stratégies de récupération d’équilibre utilisées dans ce contexte
Every year, several crowd accidents are reported around the world. These accidents can result in injuries and even fatalities. One of the triggering element of these accidents has been reported to result from falls associated with loss of standing balance in this dense crowd context. However, knowledge regarding human standing balance in dense crowd is very limited due the complex nature of this environment. In this thesis we proposed an experimental approach to study standing balance recovery of individuals following external perturbations in environments with different crowd density. In particular, as perturbation may occur from any direction in dense crowds we first study the reaction to single individuals to external perturbations arising from different directions. Based on the data collected during of this experiment, we were able to propose a method to predict participants’ recovery strategies following external perturbations based on kinematic information. Experiment involving multiple individuals were then considered. In particular, we study the effect of the crowd density on the initiation and the characteristics of recovery steps. Eventually, a novel experimental paradigm was proposed to study standing balance during real crowded events. This approach was then used within punk rock concert crowds. Results provided new insights regarding the physical interactions and recovery strategies observed in this context

Zhang, Lei. "Rapid motor responses to external perturbations during reaching movements." Diss., Ludwig-Maximilians-Universität München, 2015. http://nbn-resolving.de/urn:nbn:de:bvb:19-184803.

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Bouattour, Jouda. "Etude des perturbations électromagnétiques externes et internes engendrées sur du matériel ferroviaire RATP." Paris 6, 1986. http://www.theses.fr/1986PA066200.

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Le matériel roulant du RER, MI 79, construit en 1979 pour desservir la ligne B SNCF/RATP reliant Roissy Charles de Gaulle à St-Remy-les-Chevreuse a perturbé, dès sa mise en service, la réception des émissions radiophoniques des riverains. L'exploitation du matériel a provoqué le rayonnement vers l'extérieur d'un niveau de bruit dépassant la norme prescrite par les organismes intéressés (TDF). Une première tentative de parade a consisté à placer une série de condensateurs de filtrage à haute fréquence aux points du circuit juges les plus favorables. Mais, une contrepartie inattendue s'est manifestée, sous forme de perturbations internes à la rame. Ceci a justifié l'engagement du présent travail et a permis d'en définir les objectifs: 1) localiser les sources et les modes de propagation des perturbations électromagnétiques sur les rames, 2) optimiser les valeurs et les emplacements des condensateurs sur une rame, 3) proposer un ensemble de spécifications RATP, en matière de perturbations électromagnétiques auquel devrait satisfaire toute rame avant sa mise en exploitation, le but étant: 1. De limiter le niveau de perturbation a sa source, 2. D'immuniser les circuits sensibles par la mise en œuvre de protections adéquates. La première étape a consisté à caracteriser expérimentalement le niveau et la bande de fréquences des perturbations. Des mesures sur les composants de puissance de la rame ont été nécessaires en vue d'établir les bases d'une simulation numérique de la propagation des perturbations sur la rame. Ensuite, des mesures de perturbations sur la rame ont permis de comparer les résultats théoriques et expérimentaux. La portée de ce travail ne se limite pas à la résolution des problèmes actuels; en effet, il est important d'avancer quelques propositions visant à assurer dès la conception, la compatibilité électromagnétique dans le domaine du matériel ferroviaire, car l'utilisation future des circuits de traitement numérique a microprocesseur ne peut qu'accroitre les difficultés actuelles.

Pollock, Courtney L. "Motor control of response to external perturbations in people post-stroke." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/51595.

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Mechanisms underpinning motor control of standing balance post-stroke remain unclear. Following stroke, ankle plantarflexor muscles demonstrate impairment associated with asymmetrical postural control and decreased balance. Stroke also results in increased attentional demands during challenges to standing balance. This thesis examined motor control impairment post-stroke from medial gastrocnemius motor units to the tri-muscle plantarflexor complex. Investigation of motor, kinematic and kinetic parameters of postural control during external perturbations in standing and associated levels of physiological arousal have furthered understanding of balance impairment post-stroke. Methods: Medial gastrocnemius motor units were recorded in controls (Chapter 2) and people post-stroke (Chapter 3) in standing as perturbations were sequentially applied at the pelvis under conditions of increased anteriorly-directed challenge. In both studies, motor unit firing rate was calculated during dynamic response to perturbation, and maintenance of steady state between perturbations. Joint kinematics, surface electromyography and movements of the centre of pressure were assessed. In Chapter 4, this methodology was expanded to cross-correlation analysis of electromyography activity of the three plantarflexor muscles with anterior-posterior centre of pressure during steady state. In Chapter 5, attentional demands surrounding timing of external perturbation were manipulated to investigate effects of stroke on physiological arousal and postural reactions. Results: In healthy subjects, medial gastrocnemius utilized primarily motor unit recruitment to maintain standing with a modest increase in motor unit firing rate only during the dynamic response to external perturbations. The paretic medial gastrocnemius also primarily used motor unit recruitment; however, lacked firing rate modulation during the dynamic response, albeit firing rate was related to kinematic variables of postural control. In people post-stroke, the three plantarflexors demonstrated asymmetrical motor control of postural sway between-legs but symmetry was improved under conditions of increased challenge to standing balance. Finally, knowledge of timing of perturbations did not decrease the heightened anticipatory postural strategy and level of physiological arousal exhibited post-stroke. Conclusions: This dissertation provides new understanding of motor control of standing balance post-stroke and reveals anticipatory postural strategies adopted post-stroke under conditions challenging balance. These findings implicate the importance of introducing challenge to standing balance post-stroke in the assessment and rehabilitation of postural control post-stroke.
Medicine, Faculty of
Graduate

Beretta, Victor Spiandor [UNESP]. "Ajustes posturais sob perturbação externa em indivíduos com doença de Parkinson e neurologicamente sadios." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/151770.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Introdução: A manutenção da postura emprega mecanismos de controle preditivos e reativos. Indivíduos com doença de Parkinson (DP) apresentam declínio no controle postural, principalmente na presença de perturbações externas. O uso de informações adicionais sobre a perturbação postural parece ser eficiente para melhorar o controle postural de idosos neurologicamente sadios, porém, na DP ainda é pouco conhecido. Objetivos: a) comparar as respostas dos ajustes posturais preditivos e reativos em idosos neurologicamente sadios (GC) e com DP (Estudo 1); b) verificar o efeito do fornecimento de informações adicionais nos ajustes posturais preditivos e reativos (Estudo 2). Metodologia: Participaram do Estudo 1, 39 (19 com DP e 20 GC) e do Estudo 2, 36 (17 com DP e 19 GC) selecionados na comunidade. Os indivíduos ficaram em pé sobre um equipamento que provocou a perturbação pelo deslocamento da base de suporte com intensidade de 15 cm/s e deslocamento de 5 cm. A perturbação inesperada foi apenas a primeira tentativa e, posteriormente, foram realizadas mais 15 tentativas em que apenas 5 ocorreram a perturbação de maneira imprevisível para análise da habituação à tarefa (Estudo 1). Para o Estudo 2 foram realizadas 20 tentativas com o fornecimento de informações adicionais sobre a perturbação, visual, verbal e somatossensorial do músculo requerido. Os dados EMG e CoP na condição inesperada foram analisados por meio de ANOVA one-way e nas perturbações imprevisíveis (Estudo 1 e 2) por meio de ANOVAs two-way. Resultados: Na perturbação inesperada, os idosos com DP apresentaram maiores valores nos parâmetros da EMG e do CoP em relação ao GC. Na habituação à perturbação, os idosos com DP adaptaram os padrões nos ajustes posturais reativos de forma tardia quando comparados ao GC. Em relação ao efeito das informações adicionais no controle postural, os idosos com DP apresentaram menor oscilação do CoP nos ajustes posturais preditivos em todas as condições de informações quando comparados ao GC. Já o GC aumentou a oscilação do CoP nos ajustes preditivos, considerando as mesmas condições. Nos ajustes posturais reativos, ambos os grupos apresentaram efeitos positivos das informações verbais e somatossensoriais, diminuindo os parâmetros temporais, de amplitude da EMG e espaciais do CoP em relação ás tentativas sem o seu fornecimento ou com o as demais informações (sobre a perturbação e visual). Além disso, os idosos com DP apresentaram controle postural mais adequado quando fornecida informação somatossensorial em relação às demais informações. Por fim, apesar das alterações positivas nos ajustes reativos, os idosos com DP apresentaram maior coativação muscular e tempo para recuperar a posição estável em relação ao GC. Conclusão: Idosos com DP possuem pior controle postural em situações com perturbações externas inesperada e imprevisível, evidenciando alterações temporais, na amplitude da EMG e espaciais do CoP. Além disso, idosos neurologicamente sadios e com DP conseguem alterar os padrões dos ajustes posturais com a exposição de perturbações externas, porém, na DP essa habituação é mais atrasada. As informações adicionais somatossensoriais parecem ter efeito positivo no controle postural dos idosos, principalmente na DP, diminuindo os parâmetros EMG e do CoP nos ajustes preditivos e reativos.
Introduction: Predictive and reactive postural mechanisms are necessary to maintain the posture. Patients with Parkinson's disease (PD) have a decline in postural control, mainly when occur an external perturbation. The use of additional information about the postural perturbation seems to be efficient to improve the postural control of neurotypical older people, but in PD it is still unclear. Aims: a) To compare the predictive and reactive postural adjustments responses in the neurotypical older people (CG) and the PD patients (Study 1); b) To verify the effect of additional information on predictive and reactive postural adjustments (Study 2). Methods: Participated thirty-nine (19 with PD and 20 GC) in the Study 1 and 36 (17 with PD and 19 GC) in the Study 2, selected in the community. The individuals stood on equipment that caused the perturbation by the displacement of the support base with the velocity of 15 cm/s and the range of 5 cm. The unexpected perturbation was the first trial, and 15 trials were realized in which in just 5 occurred the unpredictably perturbation to analyze the habituation to the task (Study 1). In the Study 2, 20 trail were realized with the additional information about the perturbation characteristics, visual, verbal, and somatosensory of the required muscle. The EMG and CoP data in the unexpected condition were analyzed by ANOVA one-way and in the unpredictable perturbations (Study 1 and 2) by the ANOVAs two-way. Results: In the unexpected perturbation, the PD patients presented higher temporal, range of EMG and spatial of CoP in relation to the CG. For the habituation to the perturbation, the patients with PD adapted the patterns in the reactive postural adjustments of delayed form when compared to the GC. In relation to the effect of the additional information on postural control, the PD patients presented lower CoP oscillation in the predictive postural adjustments in all the information conditions when compared to the CG. The GC increased the CoP oscillation in the predictive adjustments, considering the same information conditions. Both groups presented positive effects of verbal and somatosensory information in the reactive postural adjustments, decreasing temporal, range of EMG and spatial parameters of CoP in relation to trial without the information or with other information (about perturbation and visual). In addition, the PD patients presented more adequate postural control when somatosensory information was provided in relation to the other information. Finally, despite of the improvement in the reactive adjustments, patients with PD have a greater muscular coactivation and time to recover the stable position in relation to the CG. Conclusion: Patients with PD have worse postural control in situations with unexpected and unpredictable external perturbation, evidencing changes in the temporal, range of EMG and spatial of CoP parameters. In addition, neurotypical older people and PD patients can change the patterns of postural adjustments with the exposure of external perturbation, but in PD this habituation is more delayed. Besides that, somatosensory information seems to have a positive effect on the postural control of the older people, mainly in the PD, decreasing the EMG and CoP parameters in the predictive and reactive postural adjustments.
FAPESP: 2016/00503-0
CNPq: 159381/2015-0

Cervantes, Chia Carlos Andres, and Weronika Maria Lewandowska. "Optical Characterization of Quantum-Dots-in-a-Well Infrared Photodetectors Under External Perturbations." Thesis, Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-1659.

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In this project we have used Fourier transform infrared spectroscopy to study the photoresponse of two different types of quantum dot-in-a-well infrared photodetectors (DWELL QDIPs). The basic task was to compare the photoresponse of these two detectors, and to study the influence of external resonant laser pumping on the photoresponse. Series of measurements were done at 77K. In the first measurements we investigated the photoresponse for different applied voltages at 77K.

In a second run of experiments, we used a 1064 nm infrared semiconductor laser to resonantly

pump the fundamental transition of the quantum dots. The results show that by using this

additional illumination the photoresponse was dramatically increased by creating additional

charge carriers in the quantum dots. This could be used to increase the sensitivity of infrared

detectors based on QDs.

Keil, Julian [Verfasser]. "Use your illusion : audiovisual perception and external perturbation are influenced by oscillatory activity / Julian Keil." Konstanz : Bibliothek der Universität Konstanz, 2012. http://d-nb.info/1026012759/34.

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Книги з теми "Perturbation externe":

Rainone, Corrado. Metastable Glassy States Under External Perturbations. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-60423-7.

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Rainone, Corrado. Metastable Glassy States Under External Perturbations: Monitoring the Effects of Compression and Shear-strain. Springer, 2017.

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Rainone, Corrado. Metastable Glassy States Under External Perturbations: Monitoring the Effects of Compression and Shear-strain. Springer, 2018.

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Plume diagnostics of the RSRM static firings for the pressure perturbation studies. [Washington, D.C: National Aeronautics and Space Administration, 1995.

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Bertola, Marco. Chain of matrices, loop equations, and topological recursion. Edited by Gernot Akemann, Jinho Baik, and Philippe Di Francesco. Oxford University Press, 2018. http://dx.doi.org/10.1093/oxfordhb/9780198744191.013.16.

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This article considers the so-called loop equations satisfied by integrals over random matrices coupled in a chain as well as their recursive solution in the perturbative case when the matrices are Hermitian. Random matrices are used in fields such as the study of multi-orthogonal polynomials or the enumeration of discrete surfaces, both of which are based on the analysis of a matrix integral. However, this term can be confusing since the definition of a matrix integral in these two applications is not the same. The article discusses these two definitions, perturbative and non-perturbative, along with their relationship. It first provides an overview of a matrix integral before comparing convergent and formal matrix integrals. It then describes the loop equations and their solution in the one-matrix model. It also examines matrices coupled in a chain plus external field and concludes with a generalization of the topological recursion.

Taylor, Kenneth A. Referring to the World. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780195144741.001.0001.

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Our words and ideas refer to objects and properties in the external world; this phenomenon is central to thought, language, communication, and science. But great works of fiction are full of names that don’t seem to refer to anything! This book explores the myriad of problems that surround the phenomenon of reference. How can words in language and perturbations in our brains come to stand for external objects? Reference is essential to truth, but which is more basic: reference or truth? How can fictional characters play such an important role in imagination and literature, and how does this use of language connect with more mundane uses? The book develops a framework for understanding reference, and the theories that other thinkers—past and present—have developed about it. But it doesn’t simply tell us what others thought; the book is full of new ideas and analyses, making for a vital final contribution from a seminal philosopher.

Launay, Jean-Pierre, and Michel Verdaguer. The localized electron: magnetic properties. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198814597.003.0002.

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After preliminaries about electron properties, and definitions in magnetism, one treats the magnetism of mononuclear complexes, in particular spin cross-over, showing the role of cooperativity and the sensitivity to external perturbations. Orbital interactions and exchange interaction are explained in binuclear model systems, using orbital overlap and orthogonality concepts to explain antiferromagnetic or ferromagnetic coupling. The phenomenologically useful Spin Hamiltonian is defined. The concepts are then applied to extended molecular magnetic systems, leading to molecular magnetic materials of various dimensionalities exhibiting bulk ferro- or ferrimagnetism. An illustration is provided by Prussian Blue analogues. Magnetic anisotropy is introduced. It is shown that in some cases, a slow relaxation of magnetization arises and gives rise to appealing single-ion magnets, single-molecule magnets or single-chain magnets, a route to store information at the molecular level.

Glazov, M. M. Electron Spin Decoherence by Nuclei. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198807308.003.0007.

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The discussion of the electron spin decoherence and relaxation phenomena via the hyperfine interaction with host lattice spins is presented here. The spin relaxation processes processes limit the conservation time of spin states as well as the response time of the spin system to external perturbations. The central spin model, where the spin of charge carrier interacts with the bath of nuclear spins, is formulated. We also present different methods to calculate the spin dynamics within this model. Simple but physically transparent semiclassical treatment where the nuclear spins are considered as largely static classical magnetic moments is followed by more advanced quantum mechanical approach where the feedback of electron spin dynamics on the nuclei is taken into account. The chapter concludes with an overview of experimental data and its comparison with model calculations.

Частини книг з теми "Perturbation externe":

Metral, E., G. Rumolo, and W. Herr. "Impedance and Collective Effects." In Particle Physics Reference Library, 105–81. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-34245-6_4.

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AbstractAs the beam intensity increases, the beam can no longer be considered as a collection of non-interacting single particles: in addition to the “single-particle phenomena”, “collective effects” become significant. At low intensity a beam of charged particles moves around an accelerator under the Lorentz force produced by the “external” electromagnetic fields (from the guiding and focusing magnets, RF cavities, etc.). However, the charged particles also interact with themselves (leading to space charge effects) and with their environment, inducing charges and currents in the surrounding structures, which create electromagnetic fields called wake fields. In the ultra-relativistic limit, causality dictates that there can be no electromagnetic field in front of the beam, which explains the term “wake”. It is often useful to examine the frequency content of the wake field (a time domain quantity) by performing a Fourier transformation on it. This leads to the concept of impedance (a frequency domain quantity), which is a complex function of frequency. The charged particles can also interact with other charged particles present in the accelerator (leading to two-stream effects, and in particular to electron cloud effects in positron/hadron machines) and with the counter-rotating beam in a collider (leading to beam–beam effects). As the beam intensity increases, all these “perturbations” should be properly quantified and the motion of the charged particles will eventually still be governed by the Lorentz force but using the total electromagnetic fields, which are the sum of the external and perturbation fields. Note that in some cases a perturbative treatment is not sufficient and the problem has to be solved self consistently. These perturbations can lead to both incoherent (i.e. of a single particle) and coherent (i.e. of the centre of mass) effects, in the longitudinal and in one or both transverse directions, leading to beam quality degradation or even partial or total beam losses. Fortunately, stabilising mechanisms exist, such as Landau damping, electronic feedback systems and linear coupling between the transverse planes (as in the case of a transverse coherent instability, one plane is usually more critical than the other).

Álvarez, Miguel Dovale. "Isolation from External Perturbations." In Optical Cavities for Optical Atomic Clocks, Atom Interferometry and Gravitational-Wave Detection, 63–89. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-20863-9_3.

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Kita, Takafumi. "Responses to External Perturbations." In Statistical Mechanics of Superconductivity, 159–74. Tokyo: Springer Japan, 2015. http://dx.doi.org/10.1007/978-4-431-55405-9_11.

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Rainone, Corrado. "Introduction." In Metastable Glassy States Under External Perturbations, 1–18. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-60423-7_1.

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Rainone, Corrado. "From Supercooled Liquids to RFOT." In Metastable Glassy States Under External Perturbations, 19–47. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-60423-7_2.

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Rainone, Corrado. "Metastable Glasses." In Metastable Glassy States Under External Perturbations, 49–83. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-60423-7_3.

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Rainone, Corrado. "The State Following Construction." In Metastable Glassy States Under External Perturbations, 85–97. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-60423-7_4.

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Rainone, Corrado. "The Replica Symmetric Ansatz." In Metastable Glassy States Under External Perturbations, 99–125. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-60423-7_5.

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Rainone, Corrado. "The Full Replica Symmetry Breaking Ansatz." In Metastable Glassy States Under External Perturbations, 127–43. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-60423-7_6.

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Rainone, Corrado. "Numerics in the Mari-Kurchan Model." In Metastable Glassy States Under External Perturbations, 145–57. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-60423-7_7.

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Тези доповідей конференцій з теми "Perturbation externe":

Beldiman, Octavian, Linda G. Bushnell, Gregory C. Walsh, Hua O. Wang, and Yiguang Hong. "Perturbations in Networked Control Systems." In ASME 2001 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/imece2001/dsc-24538.

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Abstract In this paper we study the effect of external perturbations on a networked control system. We start by assuming that the non-networked system without perturbation is exponentially stable. Then, for fast enough networks we show that if the perturbation is bounded the networked system is ultimately bounded and if the perturbation is vanishing then the networked system is asymptotically stable. We conclude the paper with simulations verifying the results.

Hahn, Steven R., and Aldo A. Ferri. "Effect of Large Structural Perturbations on Response of Structural-Acoustic Systems." In ASME 1999 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/imece1999-0177.

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Abstract Due to high sensitivity, first-order perturbation analysis of structural-acoustic systems can be inaccurate for large perturbations. Using high-order derivatives to create a Taylor series approximation for the perturbed solution can result in slow convergence or even divergence. A rational polynomial or Padé approximation may overcome the poor convergence of the Taylor series by canceling out the poles causing the poor convergence. In this study, a finite element framework is used to describe the structural-acoustic system. External radiation and scattering problems are accommodated by truncating the infinite fluid region using exponential decay infinite elements. Changes to a nominal model are introduced through a structural perturbation to the nominal structural stiffness and/or mass matrices. An efficient method for calculating the solution derivatives with respect to the structural perturbation is presented. A Taylor series expansion is constructed using the derivative information and the convergence criteria for the series is examined. The local solution and derivatives are then used to construct a Padé approximation. The method is illustrated by considering what effect the addition of a rib stiffener to a plate in a rigid baffle has on the scattering of a plane wave. The approximation is shown to be quite accurate for large perturbations even when there are one or more nearby poles and the Taylor series fails to converge.

McGehee, Clark C., Si Mohamed Sah, and Brian P. Mann. "Refining the Method of Averaging for a More Accurate Analytical Approximation to the Behaviors of a Damped Pendulum." In ASME 2012 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/detc2012-70202.

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KBM averaging is a widely used technique in the analysis of nonlinear dynamical systems. The KBM method allows complex systems to be approximated as perturbations of simple harmonic oscillator. In many cases, such as in otherwise linear systems with various forms nonlinear damping, the KBM method performs exceptionally well, with error proportional to the size of the perturbations. However, when the largest perturbation in the system arises from nonlinearities in the restoring force, the KBM method falls short, and the interesting effects of other nonlinear terms are drowned out by the approximation errors generated by the KBM method. By generalizing the notion of KBM averaging and approximating systems as perturbations the isoenergy contours of their corresponding Hamiltonian, a greater degree of accuracy can be obtained. We extend the work of several authors to show that not only is this method more accurate, but it is also simple to implement and generalizable to a wide range of nonlinear systems. As an illustrative example, the motion of a pendulum on a tilted platform is studied.

Li, Hanlai, Bin Liu, and Lin Ji. "System size resonance induced by external perturbation." In 2012 8th International Conference on Natural Computation (ICNC). IEEE, 2012. http://dx.doi.org/10.1109/icnc.2012.6234539.

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Okulov, A. Yu. "Spiral cold atomic ensemble under external perturbations." In Conference on Coherence and Quantum Optics. Washington, D.C.: OSA, 2019. http://dx.doi.org/10.1364/cqo.2019.th2a.5.

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Blouin, Vincent. "Treatment of Damping in Structural Redesign by Large Admissible Perturbations." In ASME 1999 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/imece1999-0180.

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Abstract A method to solve redesign (inverse design) problems of complex structures with forced response amplitude constraints is developed. It is assumed that a structure is excited by harmonic external forces at a given frequency. The problem is to find optimum values of structural characteristics in order to achieve a desired level of forced response at one or several locations on the structure. The method of LargE Admissible Perturbations (LEAP) is used. Damping is shown to have an important impact on the redesign solution and must be considered in the redesign process. Two different treatments of the damping, leading to two different algorithms, are studied. In the case of structural damping, the commonly used Rayleigh formulation allows the damping matrix to be diagonalized by use of the real mode shapes of the undamped structure. This leads to the derivation of an exact perturbation equation with no loss of accuracy. When damping cannot be approximated by the Rayleigh model, the damping matrix must be treated externally and the perturbation equation is solved by means of an iterative process introduced into the redesign algorithm. The two algorithms are compared in terms of accuracy and limitations.

Jaroszewicz, Leszek R., Idzi Merta, and Aleksander Kiezun. "Fiber optic external perturbation sensor with ring-wedge photodetector." In Photonics China '98, edited by Shanglian Huang, Kim D. Bennett, and David A. Jackson. SPIE, 1998. http://dx.doi.org/10.1117/12.318214.

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Xia, Guang-Qiong, Tao Deng, and Zheng-Mao Wu. "Nonlinear dynamics of 1550nm VCSELs under external perturbations." In 2013 12th International Conference on Optical Communications and Networks (ICOCN). IEEE, 2013. http://dx.doi.org/10.1109/icocn.2013.6617203.

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Demyanov, D. N. "Analytical Synthesis of External Perturbation Observer for Bilinear Dynamic System." In 2018 International Conference on Industrial Engineering, Applications and Manufacturing (ICIEAM). IEEE, 2018. http://dx.doi.org/10.1109/icieam.2018.8728795.

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Zhang, Chaoning, Philipp Benz, Chenguo Lin, Adil Karjauv, Jing Wu, and In So Kweon. "A Survey on Universal Adversarial Attack." In Thirtieth International Joint Conference on Artificial Intelligence {IJCAI-21}. California: International Joint Conferences on Artificial Intelligence Organization, 2021. http://dx.doi.org/10.24963/ijcai.2021/635.

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The intriguing phenomenon of adversarial examples has attracted significant attention in machine learning and what might be more surprising to the community is the existence of universal adversarial perturbations (UAPs), i.e. a single perturbation to fool the target DNN for most images. With the focus on UAP against deep classifiers, this survey summarizes the recent progress on universal adversarial attacks, discussing the challenges from both the attack and defense sides, as well as the reason for the existence of UAP. We aim to extend this work as a dynamic survey that will regularly update its content to follow new works regarding UAP or universal attack in a wide range of domains, such as image, audio, video, text, etc. Relevant updates will be discussed at: https://bit.ly/2SbQlLG. We welcome authors of future works in this field to contact us for including your new findings.

Звіти організацій з теми "Perturbation externe":

Terry, M. R. Effects of an External Perturbation on a Cylindrical Spheromak. Office of Scientific and Technical Information (OSTI), May 2002. http://dx.doi.org/10.2172/15007468.

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Park, Jong-Kyu, Allen H. Boozer, Jonathan E. Menard, Stefan P. Gerhardt, and Steve A. Sabbagh. Shielding of External Magnetic Perturbations By Torque In Rotating Tokamak Plasmas. Office of Scientific and Technical Information (OSTI), August 2009. http://dx.doi.org/10.2172/963532.

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Fitzpatrick, R., and T. C. Hender. Effect of a static external magnetic perturbation on resistive mode stability in tokamaks. Office of Scientific and Technical Information (OSTI), March 1994. http://dx.doi.org/10.2172/10140470.

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Or, Dani, Shmulik Friedman, and Jeanette Norton. Physical processes affecting microbial habitats and activity in unsaturated agricultural soils. United States Department of Agriculture, October 2002. http://dx.doi.org/10.32747/2002.7587239.bard.

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experimental methods for quantifying effects of water content and other dynamic environmental factors on bacterial growth in partially-saturated soils. Towards this end we reviewed critically the relevant scientific literature and performed theoretical and experimental studies of bacterial growth and activity in modeled, idealized and real unsaturated soils. The natural wetting-drying cycles common to agricultural soils affect water content and liquid organization resulting in fragmentation of aquatic habitats and limit hydraulic connections. Consequently, substrate diffusion pathways to soil microbial communities become limiting and reduce nutrient fluxes, microbial growth, and mobility. Key elements that govern the extent and manifestation of such ubiquitous interactions include characteristics of diffusion pathways and pore space, the timing, duration, and extent of environmental perturbations, the nature of microbiological adjustments (short-term and longterm), and spatial distribution and properties of EPS clusters (microcolonies). Of these key elements we have chosen to focus on a manageable subset namely on modeling microbial growth and coexistence on simple rough surfaces, and experiments on bacterial growth in variably saturated sand samples and columns. Our extensive review paper providing a definitive “snap-shot” of present scientific understanding of microbial behavior in unsaturated soils revealed a lack of modeling tools that are essential for enhanced predictability of microbial processes in soils. We therefore embarked on two pronged approach of development of simple microbial growth models based on diffusion-reaction principles to incorporate key controls for microbial activity in soils such as diffusion coefficients and temporal variations in soil water content (and related substrate diffusion rates), and development of new methodologies in support of experiments on microbial growth in simple and observable porous media under controlled water status conditions. Experimental efforts led to a series of microbial growth experiments in granular media under variable saturation and ambient conditions, and introduction of atomic force microscopy (AFM) and confocal scanning laser microscopy (CSLM) to study cell size, morphology and multi-cell arrangement at a high resolution from growth experiments in various porous media. The modeling efforts elucidated important links between unsaturated conditions and microbial coexistence which is believed to support the unparallel diversity found in soils. We examined the role of spatial and temporal variation in hydration conditions (such as exist in agricultural soils) on local growth rates and on interactions between two competing microbial species. Interestingly, the complexity of soil spaces and aquatic niches are necessary for supporting a rich microbial diversity and the wide array of microbial functions in unsaturated soils. This project supported collaboration between soil physicists and soil microbiologist that is absolutely essential for making progress in both disciplines. It provided a few basic tools (models, parameterization) for guiding future experiments and for gathering key information necessary for prediction of biological processes in agricultural soils. The project sparked a series of ongoing studies (at DTU and EPFL and in the ARO) into effects of soil hydration dynamics on microbial survival strategy under short term and prolonged desiccation (important for general scientific and agricultural applications).