Página 1 dos resultados de 1726 itens digitais encontrados em 0.016 segundos

Chaotic phase synchronization and desynchronization in an oscillator network for object selection

Breve, Fabricio Aparecido; Liang, Zhao; Quiles, Marcos Gonçalves; Macau, Elbert E. N.
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.38%
Object selection refers to the mechanism of extracting objects of interest while ignoring other objects and background in a given visual scene. It is a fundamental issue for many computer vision and image analysis techniques and it is still a challenging task to artificial Visual systems. Chaotic phase synchronization takes place in cases involving almost identical dynamical systems and it means that the phase difference between the systems is kept bounded over the time, while their amplitudes remain chaotic and may be uncorrelated. Instead of complete synchronization, phase synchronization is believed to be a mechanism for neural integration in brain. In this paper, an object selection model is proposed. Oscillators in the network representing the salient object in a given scene are phase synchronized, while no phase synchronization occurs for background objects. In this way, the salient object can be extracted. In this model, a shift mechanism is also introduced to change attention from one object to another. Computer simulations show that the model produces some results similar to those observed in natural vision systems.

Repetitive transcranial magnetic stimulation interrupts phase synchronization during rhythmic motor entrainment

Malcolm, Matthew P.; Lavine, Andrea; Kenyon, Gary; Massie, Crystal; Thaut, Michael
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.36%
Rhythmic stimuli delivered through the auditory system can facilitate improved motor control following a motor impairment. The synchronization of movement to rhythmic auditory cues is characterized by quick, stable coupling of motor responses to rhythmic auditory cues. The exact neural sites responsible for this transformation of auditory input into timed rhythmic motor output are not clear. Neuroimaging studies have identified left ventral premotor cortex (vPMC) and left superior temporal–parietal (STP) activation during rhythmic auditory–motor synchronization. To investigate brain areas necessary for different types of rhythmic auditory–motor synchronization, we delivered repetitive transcranial magnetic stimulation (rTMS) to 15 healthy individuals prior to a rhythmic–auditory tapping task. Subthreshold rTMS was administered separately to the left vPMC and STP at a frequency of 0.9 Hz for 15 min. Phase synchronization error (difference between auditory stimulus and response onsets) significantly increased after rTMS to STP as compared to baseline. Synchronization error also increased after rTMS to vPMC as compared to baseline, but not significantly. Absolute period error, (absolute difference between metronome interval and response interval) was not affected by rTMS. The significant effect of rTMS at the STP expands upon previous imaging research...

Inferring Functional Neural Connectivity with Phase Synchronization Analysis: A Review of Methodology

Sun, Junfeng; Li, Zhijun; Tong, Shanbao
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.44%
Functional neural connectivity is drawing increasing attention in neuroscience research. To infer functional connectivity from observed neural signals, various methods have been proposed. Among them, phase synchronization analysis is an important and effective one which examines the relationship of instantaneous phase between neural signals but neglecting the influence of their amplitudes. In this paper, we review the advances in methodologies of phase synchronization analysis. In particular, we discuss the definitions of instantaneous phase, the indexes of phase synchronization and their significance test, the issues that may affect the detection of phase synchronization and the extensions of phase synchronization analysis. In practice, phase synchronization analysis may be affected by observational noise, insufficient samples of the signals, volume conduction, and reference in recording neural signals. We make comments and suggestions on these issues so as to better apply phase synchronization analysis to inferring functional connectivity from neural signals.

Equilibrium analysis and phase synchronization of two coupled HR neurons with gap junction

Wang, Haixia; Wang, Qingyun; Lu, Qishao; Zheng, Yanhong
Fonte: Springer Netherlands Publicador: Springer Netherlands
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.37%
The properties of equilibria and phase synchronization involving burst synchronization and spike synchronization of two electrically coupled HR neurons are studied in this paper. The findings reveal that in the non-delayed system the existence of equilibria can be turned into intersection of two odd functions, and two types of equilibria with symmetry and non-symmetry can be found. With the stability and bifurcation analysis, the bifurcations of equilibria are investigated. For the delayed system, the equilibria remain unchanged. However, the Hopf bifurcation point is drastically affected by time delay. For the phase synchronization, we focus on the synchronization transition from burst synchronization to spike synchronization in the non-delayed system and the effect of coupling strength and time delay on spike synchronization in delayed system. In addition, corresponding firing rhythms and spike synchronized regions are obtained in the two parameters plane. The results allow us to better understand the properties of equilibria, multi-time-scale properties of synchronization and temporal encoding scheme in neuronal systems.

Fronto-parietal and fronto-temporal theta phase synchronization for visual and auditory-verbal working memory

Kawasaki, Masahiro; Kitajo, Keiichi; Yamaguchi, Yoko
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 18/03/2014 EN
Relevância na Pesquisa
46.41%
In humans, theta phase (4–8 Hz) synchronization observed on electroencephalography (EEG) plays an important role in the manipulation of mental representations during working memory (WM) tasks; fronto-temporal synchronization is involved in auditory-verbal WM tasks and fronto-parietal synchronization is involved in visual WM tasks. However, whether or not theta phase synchronization is able to select the to-be-manipulated modalities is uncertain. To address the issue, we recorded EEG data from subjects who were performing auditory-verbal and visual WM tasks; we compared the theta synchronizations when subjects performed either auditory-verbal or visual manipulations in separate WM tasks, or performed both two manipulations in the same WM task. The auditory-verbal WM task required subjects to calculate numbers presented by an auditory-verbal stimulus, whereas the visual WM task required subjects to move a spatial location in a mental representation in response to a visual stimulus. The dual WM task required subjects to manipulate auditory-verbal, visual, or both auditory-verbal and visual representations while maintaining auditory-verbal and visual representations. Our time-frequency EEG analyses revealed significant fronto-temporal theta phase synchronization during auditory-verbal manipulation in both auditory-verbal and auditory-verbal/visual WM tasks...

Markers of criticality in phase synchronization

Botcharova, Maria; Farmer, Simon F.; Berthouze, Luc
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 24/09/2014 EN
Relevância na Pesquisa
46.4%
The concept of the brain as a critical dynamical system is very attractive because systems close to criticality are thought to maximize their dynamic range of information processing and communication. To date, there have been two key experimental observations in support of this hypothesis: (i) neuronal avalanches with power law distribution of size and (ii) long-range temporal correlations (LRTCs) in the amplitude of neural oscillations. The case for how these maximize dynamic range of information processing and communication is still being made and because a significant substrate for information coding and transmission is neural synchrony it is of interest to link synchronization measures with those of criticality. We propose a framework for characterizing criticality in synchronization based on an analysis of the moment-to-moment fluctuations of phase synchrony in terms of the presence of LRTCs. This framework relies on an estimation of the rate of change of phase difference and a set of methods we have developed to detect LRTCs. We test this framework against two classical models of criticality (Ising and Kuramoto) and recently described variants of these models aimed to more closely represent human brain dynamics. From these simulations we determine the parameters at which these systems show evidence of LRTCs in phase synchronization. We demonstrate proof of principle by analysing pairs of human simultaneous EEG and EMG time series...

Investigation of atrial vulnerability by analysis of the sinus node EG from atrial fibrillation models using a phase synchronization method

Chen, Y.; Wu, Z.; Yang, C.; Shao, J.; Wong, K.; Abbott, D.
Fonte: IEEE-Inst Electrical Electronics Engineers Inc Publicador: IEEE-Inst Electrical Electronics Engineers Inc
Tipo: Artigo de Revista Científica
Publicado em //2012 EN
Relevância na Pesquisa
66.28%
Atrial fibrillation (AF) can result in life-threatening arrhythmia, and a clinically convenient means for detecting vulnerability remains elusive. We investigated atrial vulnerability by analyzing the sinus electrogram (EG) from AF animal models using a phase synchronizationmethod. Using acetylcholine (ACh)-induced acute canine AF models (n= 4), a total of 128 electrical leads were attached to the surface of the anterior and posterior atria, and the pulmonary veins to form an electrocardiological mapping system. ACh was injected at varying concentrations with ladder-type adjustments. Sinus EGs and induced AF EGs that pertain to specific ACh concentrations were recorded.We hypothesize that the atrial vulnerability may be correlated with the Shannon entropy (SE) of the phase difference matrix that is extracted from the sinus EG. Our research suggests that the combination of SE with the synchronization method enables the sinus node EG to be analyzed and used to estimate atrial vulnerability. Index Terms—Atrial fibrillation (AF), electrophysiologicalmapping, phase synchronization, Shannon entropy, sinus rhythm.; Ying Chen, Zhong Wu, Cuiwei Yang, Jun Shao, Kelvin Kian Loong Wong and Derek Abbott

Development of the phase synchronization circuit for wirelessly distributed digital phased array

Tsai, Yen-Chang
Fonte: Monterey, California: Naval Postgraduate School Publicador: Monterey, California: Naval Postgraduate School
Tipo: Tese de Doutorado
Relevância na Pesquisa
46.36%
Approved for public release, distribution unlimited; The Wirelessly Distributed Digital Phased Array (WDDPA) is an ongoing research program at the Naval Postgraduate School (NPS) which has numerous possible applications in radar and communication systems. The WDDPA incorporates many array elements randomly or nonuniformly in the environment or on a platform. Array elements are synchronized and controlled over a wireless channel. Compared to conventional phased array systems, its advantages are adaptability, survivability and flexibility. Phase synchronization is a critical component of the WDDPA development. The common phase reference is vital to steer the beam and control the radiation pattern for the phased array system. The objective of this paper is to improve the WDDPA synchronization operation. Previous hardware and software architectures were replaced or modified to improve the accuracy and speed of the phase synchronization. A series of experiments, first for hardwired channels, then for wireless channels, were conducted successfully to verify the synchronization operation for two elements. Several problems with the circuit were diagnosed and then addressed. The overall performance of the improved synchronization circuit for the demonstration array was satisfactory...

Ferramenta para avaliação do padrão de conectividade cortical funcional baseada na sincronização de fase

Melo, Mariana Cardoso
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Dissertação
POR
Relevância na Pesquisa
46.38%
O estudo de processos corticais é importante para a compreensão de déficits neurológicos, e assim, permite o desenvolvimento de estratégias para auxiliar no tratamento dessas doenças. Os mecanismos de integração e coordenação das atividades de diversas regiões corticais podem ser estudados por meio da análise da sincronização entre as fases dos sinais obtidos das múltiplas áreas do córtex. A sincronização de fase é um método que mede a conectividade funcional entre as regiões corticais, isto é, a correlação temporal entre essas áreas, entretanto, não é capaz de identificar a relação causal entre duas regiões, definida como conectividade efetiva. No cenário nacional, ainda existe carência, de conhecimento mais profundo das técnicas a serem empregadas para avaliação do padrão de sincronização cortical funcional, especialmente a partir de dados coletados por eletroencefalografia de superfície. Com isso, esse trabalho propõe o desenvolvimento de uma plataforma para avaliação do padrão de conectividade funcional, baseado em técnicas de análise de sincronização de fase, a partir de sinais eletroencefalográficos. A ferramenta foi desenvolvida em MATLAB e realiza o cálculo do índice de sincronização de fase dos sinais eletroencefalográficos pela Transformada de Hilbert. Na etapa de validação do estudo com sinais sintéticos...

Phase synchronization between collective rhythms of globally coupled oscillator groups: noiseless non-identical case

Kawamura, Yoji; Nakao, Hiroya; Arai, Kensuke; Kori, Hiroshi; Kuramoto, Yoshiki
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 29/07/2010
Relevância na Pesquisa
46.34%
Phase synchronization between collective oscillations exhibited by two weakly interacting groups of non-identical phase oscillators with internal and external global sinusoidal coupling of the groups is analyzed theoretically. Coupled amplitude equations describing the collective oscillations of the oscillator groups are obtained by using the Ott-Antonsen ansatz, and then coupled phase equations for the collective oscillations are derived by phase reduction of the amplitude equations. The collective phase coupling function, which determines the dynamics of macroscopic phase differences between the groups, is calculated analytically. It is demonstrated that the groups can exhibit effective anti-phase collective synchronization even if the microscopic external coupling between individual oscillator pairs belonging to different groups is in-phase, and similarly effective in-phase collective synchronization in spite of microscopic anti-phase external coupling between the groups.; Comment: 11 pages, 3 figures

Phase Synchronization in Temperature and Precipitation Records

Rybski, Diego; Havlin, Shlomo; Bunde, Armin
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/11/2002
Relevância na Pesquisa
46.36%
We study phase synchronization between atmospheric variables such as daily mean temperature and daily precipitation records. We find significant phase synchronization between records of Oxford and Vienna as well as between the records of precipitation and temperature in each city. To find the time delay in the synchronization between the records we study the time lag phase synchronization when the records are shifted by a variable time interval of days. We also compare the results of the method with the classical cross-correlation method and find that in certain cases the phase synchronization yields more significant results.; Comment: 11 pages including 8 figures

An Analysis of Phase Synchronization Mismatch Sensitivity for Coherent MIMO Radar Systems

Godrich, Hana; Haimovich, Alexander M.; Poor, H. Vincent
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/10/2009
Relevância na Pesquisa
46.35%
In this study, the hybrid Cramer-Rao bound (CRB) is developed for target localization, to establish the sensitivity of the estimation mean-square error (MSE) to the level of phase synchronization mismatch in coherent Multiple-Input Multiple-Output (MIMO) radar systems with widely distributed antennas. The lower bound on the MSE is derived for the joint estimation of the vector of unknown parameters, consisting of the target location and the mismatch of the allegedly known system parameters, i.e., phase offsets at the radars. Synchronization errors are modeled as being random and Gaussian. A closed-form expression for the hybrid CRB is derived for the case of orthogonal waveforms.The bound on the target localization MSE is expressed as the sum of two terms - the first represents the CRB with no phase mismatch, and the second captures the mismatch effect. The latter is shown to depend on the phase error variance, the number of mismatched transmitting and receiving sensors and the system geometry. For a given phase synchronization error variance, this expression offers the means to analyze the achievable localization accuracy. Alternatively, for a predetermined localization MSE target value, the derived expression may be used to determine the necessary phase synchronization level in the distributed system.; Comment: To be presented at CAMSAP 2009

Two Scenarios of Breaking Chaotic Phase Synchronization

Koronovskii, A. A.; Kurovskaya, M. K.; Moskalenko, O. I.; Hramov, A. E.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/05/2007
Relevância na Pesquisa
46.38%
Two types of phase synchronization (accordingly, two scenarios of breaking phase synchronization) between coupled stochastic oscillators are shown to exist depending on the discrepancy between the control parameters of interacting oscillators, as in the case of classical synchronization of periodic oscillators. If interacting stochastic oscillators are weakly detuned, the phase coherency of the attractors persists when phase synchronization breaks. Conversely, if the control parameters differ considerably, the chaotic attractor becomes phase-incoherent under the conditions of phase synchronization break.; Comment: 8 pages, 7 figures

Bistable analytic-phase synchronization in strongly-competing chaotic lasing modes

Wieczorek, Sebastian; Chow, Weng W.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.34%
We theoretically study analytic-phase synchronization in strongly-competing oscillator systems. Using the example of composite-cavity modes coupled via a class-B laser active medium, we discover that inherent chaotic phase synchronization can arise concurrently at two different chaotic attractors, leading to bistable phase-synchronized solutions. In our example, the underlying mechanism for bistability and inherent phase synchronization is population pulsation within the active medium.; Comment: 6 pages, revised mechanism for the loss of chaotic phase synchronization, changed Fig.2, three new figures: Figs.3-5

Frequency and Phase Synchronization in Stochastic Systems

Freund, Jan A.; Schimansky-Geier, Lutz; Haenggi, Peter
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 24/06/2002
Relevância na Pesquisa
46.35%
The phenomenon of frequency and phase synchronization in stochastic systems requires a revision of concepts originally phrased in the context of purely deterministic systems. Various definitions of an instantaneous phase are presented and compared with each other with special attention payed to their robustness with respect to noise. We review the results of an analytic approach describing noise-induced phase synchronization in a thermal two-state system. In this context exact expressions for the mean frequency and the phase diffusivity are obtained that together determine the average length of locking episodes. A recently proposed method to quantify frequency synchronization in noisy potential systems is presented and exemplified by applying it to the periodically driven noisy harmonic oscillator. Since this method is based on a threshold crossing rate pioneered by S.O. Rice the related phase velocity is termed Rice frequency. Finally, we discuss the relation between the phenomenon of stochastic resonance and noise-enhanced phase coherence by applying the developed concepts to the periodically driven bistable Kramers oscillator.; Comment: to appear in the Chaos focus issue on "Control, communication, and synchronization in chaotic dynamical systems"

Phase synchronization between collective rhythms of globally coupled oscillator groups: noisy identical case

Kawamura, Yoji; Nakao, Hiroya; Arai, Kensuke; Kori, Hiroshi; Kuramoto, Yoshiki
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 26/07/2010
Relevância na Pesquisa
46.35%
We theoretically investigate collective phase synchronization between interacting groups of globally coupled noisy identical phase oscillators exhibiting macroscopic rhythms. Using the phase reduction method, we derive coupled collective phase equations describing the macroscopic rhythms of the groups from microscopic Langevin phase equations of the individual oscillators via nonlinear Fokker-Planck equations. For sinusoidal microscopic coupling, we determine the type of the collective phase coupling function, i.e., whether the groups exhibit in-phase or anti-phase synchronization. We show that the macroscopic rhythms can exhibit effective anti-phase synchronization even if the microscopic phase coupling between the groups is in-phase, and vice versa. Moreover, near the onset of collective oscillations, we analytically obtain the collective phase coupling function using center-manifold and phase reductions of the nonlinear Fokker-Planck equations.; Comment: 15 pages, 7 figures

On the relationship between the theory of cointegration and the theory of phase synchronization

Dahlhaus, Rainer; Neddermeyer, Jan C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.41%
The theory of cointegration has been the leading theory in econometrics with powerful applications to macroeconomics during the last decades. On the other hand the theory of phase synchronization for weakly coupled complex oscillators has been one of the leading theories in physics for some 15 years with many applications to different areas of science. For example in neuroscience phase synchronization is regarded as essential for functional coupling of different brain regions. In an abstract sense both theories describe the dynamic fluctuation around some equilibrium. In this paper we point out that there exists a very close connection between both theories. We show that there exists a system of stochastic difference equations which can be viewed as close to the Kuramoto equations, whose solution is a cointegrated system. As one consequence the rich theory on statistical inference for cointegrated systems can immediately be applied for statistical inference on phase synchronization based on empirical data. This includes tests for phase synchronization, tests for unidirectional coupling and the identification of the equilibrium from data including phase shifts. We give an example where an unidirectionally coupled Roessler-Lorenz system is identified with the methods from cointegration. The methods from cointegration may also be used to investigate phase synchronization in complex networks. On the contrary there are many interesting results on phase synchronization which may inspire new research on cointegration.

A new measure of phase synchronization for a pair of time series and seizure focus localization

Majumdar, Kaushik
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.4%
Defining and measuring phase synchronization in a pair of nonlinear time series are highly nontrivial. This can be done with the help of Fourier transform, when it exists, for a pair of stored (hence stationary) signals. In a time series instantaneous phase is often defined with the help of Hilbert transform. In this paper phase of a time series has been defined with the help of Fourier transform. This gives rise to a deterministic method to detect phase synchronization in its most general form between a pair of time series. Since this is a stricter method than the statistical methods based on instantaneous phase, this can be used for lateralization and source localization of epileptic seizures with greater accuracy. Based on this method a novel measure of phase synchronization, called syn function, has been defined, which is capable of quantifying neural phase synchronization and asynchronization as important parameters of epileptic seizure dynamics. It has been shown that such a strict measure of phase synchronization has potential application in seizure focus localization from scalp electroencephalogram (EEG) data, without any knowledge of electrical conductivity of the head.; Comment: 22 pages, 3 figures. A much more elaborate version with application

Comment on "Periodic Phase Synchronization in Coupled Chaotic Oscillators"

Pazó, Diego; Matías, Manuel A.
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Artículo Formato: 2373 bytes; 48239 bytes; text/plain; application/pdf
ENG
Relevância na Pesquisa
56.26%
2 pages.-- PACS numbers: 05.45.Xt, 05.45.Pq.-- Final full-text version of the paper available at: http://dx.doi.org/10.1103/PhysRevE.73.038201.; Kye et al. [Phys. Rev. E 68, 025201(R) (2003)] have recently claimed that, before the onset of Chaotic Phase Synchronization in coupled phase coherent oscillators, there exists a temporally coherent state called Periodic Phase Synchronization (PPS). Here we give evidence that some of their numerical calculations are flawed, while we provide theoretical arguments that indicate that PPS is not to be expected generically in this type of systems.; This work was supported by MEC (Spain) and FEDER under Grant Nos. BFM2001-0341-C02-02, FIS2004-00953 (CONOCE2), and FIS2004-05073-C04-03.; http://dx.doi.org/10.1103/PhysRevE.73.038201

Phase Synchronization and Polarization Ordering of Globally Coupled Oscillators

Scirè, Alessandro; Colet, Pere; San Miguel, Maxi
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Artículo Formato: 2373 bytes; 58548 bytes; text/plain; application/pdf
ENG
Relevância na Pesquisa
56.22%
4 pages, 2 figures.-- PACS nrs.: 82.40.Bj, 42.60.Da, 05.45.Xt, 42.25.Ja.-- PMID: 15524572 [PubMed].-- ArXiv pre-print available at: http://arxiv.org/abs/physics/0403038; We introduce a prototype model for globally-coupled oscillators in which each element is given an oscillation frequency and a preferential oscillation direction (polarization), both randomly distributed. We found two collective transitions: to phase synchronization and to polarization ordering. Introducing a global-phase and a polarization order parameters, we show that the transition to global-phase synchrony is found when the coupling overcomes a critical value and that polarization order enhancement can not take place before global-phase synchrony. We develop a self-consistent theory to determine both order parameters in good agreement with numerical results.; This work has been funded by the European Commission through VISTA HPRN-CT-2000-00034, the Spanish MCyT under project BFM2000-1108, MCyT and Feder SINFIBIO BFM 2001-0341-C02-02.; Peer reviewed