TY  - JOUR
A1  - Baptista, Murilo da Silva
A1  - Pereira, Tiago
A1  - Kurths, Jürgen
T1  - Upper bounds in phase synchronous weak coherent chaotic attractors
N2  - An approach is presented for coupled chaotic systems with weak coherent motion, from which we estimate the upper bound value for the absolute phase difference in phase synchronous states. This approach shows that synchronicity in phase implies synchronicity in the time of events, a characteristic explored to derive an equation to detect phase synchronization, based on the absolute difference between the time of these events. We demonstrate the potential use of this approach for the phase coherent and the funnel attractor of the Rossler system, as well as for the spiking/bursting Rulkov map.
Y1  - 2006
UR  - http://www.sciencedirect.com/science/journal/01672789
U6  - https://doi.org/10.1016/j.physd.2006.02.007
SN  - 0167-2789
ER  - 
TY  - JOUR
A1  - Baptista, Murilo da Silva
A1  - Pereira, Tiago
A1  - Sartorelli, J. C.
A1  - Caldas, Ibere Luiz
A1  - Kurths, Jürgen
T1  - Non-transitive maps in phase synchronization
N2  - Concepts from Ergodic Theory are used to describe the existence of special non-transitive maps in attractors of phase synchronous chaotic oscillators. In particular, it is shown that, for a class of phase-coherent oscillators, these special maps imply phase synchronization. We illustrate these ideas in the sinusoidally forced Chua's circuit and two coupled Rossler oscillators. Furthermore, these results are extended to other coupled chaotic systems. In addition, a phase for a chaotic attractor is defined from the tangent vector of the flow. Finally, it is discussed how these maps can be used for the real-time detection of phase synchronization in experimental systems. (c) 2005 Elsevier B.V. All rights reserved
Y1  - 2005
ER  - 
TY  - THES
A1  - Pereira da Silva, Tiago
T1  - Synchronization in active networks
T1  - Synchronisation in Aktiven Netzwerken
N2  - In nature one commonly finds interacting complex oscillators which by the coupling scheme form small and large networks, e.g. neural networks. Surprisingly, the oscillators can synchronize, still preserving the complex behavior. Synchronization is a fundamental phenomenon in coupled nonlinear oscillators. Synchronization can be enhanced at different levels, that is, the constraints on which the synchronization appears. Those can be in the trajectory amplitude, requiring the amplitudes of both oscillators to be equal, giving place to complete synchronization. Conversely, the constraint could also be in a function of the trajectory, e.g. the phase, giving place to phase synchronization (PS). In this case, one requires the phase difference between both oscillators to be finite for all times, while the trajectory amplitude may be uncorrelated. The study of PS has shown its relevance to important technological problems, e.g. communication, collective behavior in neural networks, pattern formation, Parkinson disease, epilepsy, as well as behavioral activities. It has been reported that it mediates processes of information transmission and collective behavior in neural and active networks and communication processes in the Human brain. In this work, we have pursed a general way to analyze the onset of PS in small and large networks. Firstly, we have analyzed many phase coordinates for compact attractors. We have shown that for a broad class of attractors the PS phenomenon is invariant under the phase definition. Our method enables to state about the existence of phase synchronization in coupled chaotic oscillators without having to measure the phase. This is done by observing the oscillators at special times, and analyzing whether this set of points is localized. We have show that this approach is fruitful to analyze the onset of phase synchronization in chaotic attractors whose phases are not well defined, as well as, in networks of non-identical spiking/bursting neurons connected by chemical synapses. Moreover, we have also related the synchronization and the information transmission through the conditional observations. In particular, we have found that inside a network clusters may appear. These can be used to transmit more than one information, which provides a multi-processing of information. Furthermore, These clusters provide a multichannel communication, that is, one can integrate a large number of neurons into a single communication system, and information can arrive simultaneously at different places of the network.
N2  - In oder Natur sind interagierende komplexe Oszillatoren, die Netzwerke bilden, häufig anzutreffen. Erstaunlich ist, dass sich diese Oszillatoren synchronisieren, ohne ihr eigenes komplexes Verhalten zu verlieren. Diese Fähigkeit zur Synchronisation ist eine wesentliche Eigenschaft von gekoppelten nichtlinearen Oszillatoren. Die Fähigkeit zur Synchronisation kann auf unterschiedliche Weise durch Eingriff in die Bedingungen, die zur Synchronisation führen, verbessert werden. Es kann sowohl eine Synchronisation der Amplituden als auch der Phasen stattfinden bzw. erzwungen werden. Insbesondere Phase Synchronisation über die Phase (PS) hat sich in den wichtigen Bereichen der Technik, Kommunikation, Soziologie und Neurologie als Modellierungsgrundlage bewiesen. Bekannte Beispiele aus der Neurologie sind Parkinson und Epilepsie. In der vorliegenden Arbeit haben wir nach einem verallgemeinerten Weg gesucht, das Phänomen der PS in Netzwerken analysieren zu können. Zuerst haben wir viele Phasendefinitionen für einfache Attraktoren (Oszillatoren mit definierten Phaseneigenschaften) untersucht und festgestellt, dass das Phänomen der PS unabhängig von der Definition der Phase ist. Als nächstes haben wir begonnen, die maximale Abweichungen abzuschätzen, bei der die Synchronisation für bei einer gegebene Phase nicht verlorengeht. Abschließend haben wir eine Methode entwickelt, mittels derer Synchronisation in chaotischen System festgestellt werden kann, ohne die Phase selbst messen zu müssen. Dazu wird zu geeigneten Zeitpunkten der Zustandsraum untersucht. Wir können zeigen, dass mittels dieser Methode in chaotisch Systemen sowohl die Grössenordnung der Synchronisation als auch die Bereiche, in denen Synchronisation stattfindet, untersucht werden können. Dabei kann festgestellt werden, dass der Grad der Synchronisation mit der Menge an Information in Beziehung steht, die an verschieden Stellen eines Netzwerks gleichzeitig übermittelt wird. Dies kann zur Modellierung der Informationsübertragung über die Synapsen im Gehirn verwendet werden.
KW  - Synchronisation
KW  - Netzwerk
KW  - Phase
KW  - Information
KW  - Synchronization
KW  - Networks
KW  - Phase
KW  - Information
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-14347
ER  - 
TY  - JOUR
A1  - Pereira, Tiago
A1  - Baptista, Murilo da Silva
A1  - Reyes, Marcelo B.
A1  - Caldas, Ibere Luiz
A1  - Sartorelli, José Carlos
A1  - Kurths, Jürgen
T1  - A scenario for torus T-2 destruction via a global bifurcation
N2  - We show a scenario of a two-frequeney torus breakdown, in which a global bifurcation occurs due to the collision of a quasi-periodic torus T-2 with saddle points, creating a heteroclinic saddle connection. We analyze the geometry of this torus-saddle collision by showing the local dynamics and the invariant manifolds (global dynamics) of the saddle points. Moreover, we present detailed evidences of a heteroclinic saddle-focus orbit responsible for the type- if intermittency induced by this global bifurcation. We also characterize this transition to chaos by measuring the Lyapunov exponents and the scaling laws.
Y1  - 2009
UR  - http://www.sciencedirect.com/science/journal/09600779
U6  - https://doi.org/10.1016/j.chaos.2007.06.115
SN  - 0960-0779
ER  - 
TY  - JOUR
A1  - Pereira, Tiago
A1  - Baptista, Murilo da Silva
A1  - Reyes, Marcelo Bussotti
A1  - Caldas, Ibere Luiz
A1  - Sartorelli, José Carlos
A1  - Kurths, Jürgen
T1  - Global bifurcation destroying the experimental torus T-2
N2  - We show experimentally the scenario of a two-frequency torus T-2 breakdown, in which a global bifurcation occurs due to the collision of a torus with an unstable periodic orbit, creating a heteroclinic saddle connection, followed by an intermittent behavior
Y1  - 2006
UR  - http://pre.aps.org/
U6  - https://doi.org/10.1103/Physreve.73.017201
ER  - 
TY  - JOUR
A1  - Pereira, Rui F. P.
A1  - Zehbe, Kerstin
A1  - Günter, Christina
A1  - dos Santos, Tiago
A1  - Nunes, Silvia C.
A1  - Almeida Paz, Filipe A.
A1  - Silva, Maria M.
A1  - Granja, Pedro L.
A1  - Taubert, Andreas
A1  - de Zea Bermudez, Verónica
T1  - Ionic liquid-assisted synthesis of mesoporous silk fibroin/silica hybrids for biomedical applications
JF  - ACS Omega
N2  - New mesoporous silk fibroin (SF)/silica hybrids were processed via a one-pot soft and energy-efficient sol-gel chemistry and self-assembly from a silica precursor, an acidic or basic catalyst, and the ionic liquid 1-butyl-3-methylimidazolium chloride, acting as both solvent and mesoporosity-inducer. The as-prepared materials were obtained as slightly transparent-opaque, amorphous monoliths, easily transformed into powders, and stable up to ca. 300 degrees C. Structural data suggest the formation of a hexagonal mesostructure with low range order and apparent surface areas, pore volumes, and pore radii of 205-263 m(2) g(-1), 0.16-0.19 cm(3) g(-1), and 1.2-1.6 nm, respectively. In all samples, the dominating conformation of the SF chains is the beta-sheet. Cytotoxicity/bioactivity resazurin assays and fluorescence microscopy demonstrate the high viability of MC3T3 pre-osteoblasts to indirect (>= 99 +/- 9%) and direct (78 +/- 2 to 99 +/- 13%) contact with the SF/silica materials. Considering their properties and further improvements, these systems are promising candidates to be explored in bone tissue engineering. They also offer excellent prospects as electrolytes for solid-state electrochemical devices, in particular for fuel cells.
Y1  - 2018
U6  - https://doi.org/10.1021/acsomega.8b02051
SN  - 2470-1343
VL  - 3
IS  - 9
SP  - 10811
EP  - 10822
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Tönjes, Ralf
A1  - Fiore, Carlos E.
A1  - Pereira da Silva, Tiago
T1  - Coherence resonance in influencer networks
JF  - Nature Communications
N2  - Complex networks are abundant in nature and many share an important structural property: they contain a few nodes that are abnormally highly connected (hubs). Some of these hubs are called influencers because they couple strongly to the network and play fundamental dynamical and structural roles. Strikingly, despite the abundance of networks with influencers, little is known about their response to stochastic forcing. Here, for oscillatory dynamics on influencer networks, we show that subjecting influencers to an optimal intensity of noise can result in enhanced network synchronization. This new network dynamical effect, which we call coherence resonance in influencer networks, emerges from a synergy between network structure and stochasticity and is highly nonlinear, vanishing when the noise is too weak or too strong. Our results reveal that the influencer backbone can sharply increase the dynamical response in complex systems of coupled oscillators. Influencer networks include a small set of highly-connected nodes and can reach synchrony only via strong node interaction. Tonjes et al. show that introducing an optimal amount of noise enhances synchronization of such networks, which may be relevant for neuroscience or opinion dynamics applications.
Y1  - 2021
U6  - https://doi.org/10.1038/s41467-020-20441-4
SN  - 2041-1723
VL  - 12
IS  - 1
PB  - Nature Publishing Group UK
CY  - London
ER  -