Articles de revista
http://hdl.handle.net/2117/3215
Sun, 29 Nov 2015 04:19:56 GMT2015-11-29T04:19:56ZLangevin equation approach for slow dynamics in magnetic systems
http://hdl.handle.net/2117/79563
Langevin equation approach for slow dynamics in magnetic systems
Sancho, Jose Maria; Lacasta Palacio, Ana María; Torrent Serra, Maria del Carmen; García Ojalvo, Jordi; Tejeda Gómez, José Arturo
We present a magnetic model based on a Langevin equation which exhibits slow relaxation dynamics of ln(t) type. The system is composed of magnetic particles which are under the influence of a local potential and interact through a mean field. Recent experimental data are interpreted within this model.
Mon, 23 Nov 2015 12:56:01 GMThttp://hdl.handle.net/2117/795632015-11-23T12:56:01ZSancho, Jose MariaLacasta Palacio, Ana MaríaTorrent Serra, Maria del CarmenGarcía Ojalvo, JordiTejeda Gómez, José ArturoWe present a magnetic model based on a Langevin equation which exhibits slow relaxation dynamics of ln(t) type. The system is composed of magnetic particles which are under the influence of a local potential and interact through a mean field. Recent experimental data are interpreted within this model.Taming of modulation instability by spatio-temporal modulation of the potential
http://hdl.handle.net/2117/79387
Taming of modulation instability by spatio-temporal modulation of the potential
Kumar, Shubham; Herrero Simon, Ramon; Botey Cumella, Muriel; Staliunas, Kestutis
Spontaneous pattern formation in a variety of spatially extended nonlinear systems always occurs through a modulation instability, sometimes called Turing instability: the homogeneous state of the system becomes unstable with respect to growing modulation modes. Therefore, the manipulation of the modulation instability is of primary importance in controlling and manipulating the character of spatial patterns initiated by that instability. We show that a spatio-temporal periodic modulation of the potential of spatially extended systems results in a modification of its pattern forming instability. Depending on the modulation character the instability can be partially suppressed, can change its spectrum (for instance the long wave instability can transform into short wave instability), can split into two, or can be completely eliminated. The latter result is of special practical interest, as it can be used to stabilize the intrinsically unstable system. The result bears general character, as it is shown here on a universal model of the Complex Ginzburg-Landau equation in one and two spatial dimensions (and time). The physical mechanism of the instability suppression can be applied to a variety of intrinsically unstable dissipative systems, like self-focusing lasers, reaction-diffusion systems, as well as in unstable conservative systems, like attractive Bose Einstein condensates.
Wed, 18 Nov 2015 07:53:33 GMThttp://hdl.handle.net/2117/793872015-11-18T07:53:33ZKumar, ShubhamHerrero Simon, RamonBotey Cumella, MurielStaliunas, KestutisSpontaneous pattern formation in a variety of spatially extended nonlinear systems always occurs through a modulation instability, sometimes called Turing instability: the homogeneous state of the system becomes unstable with respect to growing modulation modes. Therefore, the manipulation of the modulation instability is of primary importance in controlling and manipulating the character of spatial patterns initiated by that instability. We show that a spatio-temporal periodic modulation of the potential of spatially extended systems results in a modification of its pattern forming instability. Depending on the modulation character the instability can be partially suppressed, can change its spectrum (for instance the long wave instability can transform into short wave instability), can split into two, or can be completely eliminated. The latter result is of special practical interest, as it can be used to stabilize the intrinsically unstable system. The result bears general character, as it is shown here on a universal model of the Complex Ginzburg-Landau equation in one and two spatial dimensions (and time). The physical mechanism of the instability suppression can be applied to a variety of intrinsically unstable dissipative systems, like self-focusing lasers, reaction-diffusion systems, as well as in unstable conservative systems, like attractive Bose Einstein condensates.Synchronization-based computation through networks of coupled oscillators
http://hdl.handle.net/2117/79093
Synchronization-based computation through networks of coupled oscillators
Malagarriga Guasch, Daniel; Garcia Vellisca, Mariano A.; Villa, Alessandro; Martín Buldú, Javier; García Ojalvo, Jordi; Pons Rivero, Antonio Javier
The mesoscopic activity of the brain is strongly dynamical, while at the same time exhibits remarkable computational capabilities. In order to examine how these two features coexist, here we show that the patterns of synchronized oscillations displayed by networks of neural mass models, representing cortical columns, can be used as substrates for Boolean-like computations. Our results reveal that the same neural mass network may process different combinations of dynamical inputs as different logical operations or combinations of them. This dynamical feature of the network allows it to process complex inputs in a very sophisticated manner. The results are reproduced experimentally with electronic circuits of coupled Chua oscillators, showing the robustness of this kind of computation to the intrinsic noise and parameter mismatch of the coupled oscillators. We also show that the information-processing capabilities of coupled oscillations go beyond the simple juxtaposition of logic gates.
Thu, 12 Nov 2015 09:56:16 GMThttp://hdl.handle.net/2117/790932015-11-12T09:56:16ZMalagarriga Guasch, DanielGarcia Vellisca, Mariano A.Villa, AlessandroMartín Buldú, JavierGarcía Ojalvo, JordiPons Rivero, Antonio JavierThe mesoscopic activity of the brain is strongly dynamical, while at the same time exhibits remarkable computational capabilities. In order to examine how these two features coexist, here we show that the patterns of synchronized oscillations displayed by networks of neural mass models, representing cortical columns, can be used as substrates for Boolean-like computations. Our results reveal that the same neural mass network may process different combinations of dynamical inputs as different logical operations or combinations of them. This dynamical feature of the network allows it to process complex inputs in a very sophisticated manner. The results are reproduced experimentally with electronic circuits of coupled Chua oscillators, showing the robustness of this kind of computation to the intrinsic noise and parameter mismatch of the coupled oscillators. We also show that the information-processing capabilities of coupled oscillations go beyond the simple juxtaposition of logic gates.Two-dimensional complex parity-time-symmetric photonic structures
http://hdl.handle.net/2117/76568
Two-dimensional complex parity-time-symmetric photonic structures
Turduev, M.; Botey Cumella, Muriel; Giden, I.; Herrero Simon, Ramon; Kurt, H.; Ozbay, E; Staliunas, Kestutis
We propose a simple realistic two-dimensional complex parity-time-symmetric photonic structure that is described by a non-Hermitian potential but possesses real-valued eigenvalues. The concept is developed from basic physical considerations to provide asymmetric coupling between harmonic wave components of the electromagnetic field. The structure results in a nonreciprocal chirality and asymmetric transmission between in- and out-coupling channels into the structure. The analytical results are supported by a numerical study of the Bloch-like mode formations and calculations of a realistic planar semiconductor structure.
Thu, 03 Sep 2015 08:13:45 GMThttp://hdl.handle.net/2117/765682015-09-03T08:13:45ZTurduev, M.Botey Cumella, MurielGiden, I.Herrero Simon, RamonKurt, H.Ozbay, EStaliunas, KestutisWe propose a simple realistic two-dimensional complex parity-time-symmetric photonic structure that is described by a non-Hermitian potential but possesses real-valued eigenvalues. The concept is developed from basic physical considerations to provide asymmetric coupling between harmonic wave components of the electromagnetic field. The structure results in a nonreciprocal chirality and asymmetric transmission between in- and out-coupling channels into the structure. The analytical results are supported by a numerical study of the Bloch-like mode formations and calculations of a realistic planar semiconductor structure.Quantifying sudden changes in dynamical systems using symbolic networks
http://hdl.handle.net/2117/76333
Quantifying sudden changes in dynamical systems using symbolic networks
Masoller Alonso, Cristina; Hong, Yanhua; Ayad, Sarah; Gustave, Francois; Barland, Stéphane; Pons Rivero, Antonio Javier; Gómez, Sergio; Arenas, Alex
We characterize the evolution of a dynamical system by combining two well-known complex systems' tools, namely, symbolic ordinal analysis and networks. From the ordinal representation of a time series we construct a network in which every node weight represents the probability of an ordinal pattern (OP) to appear in the symbolic sequence and each edge's weight represents the probability of transitions between two consecutive OPs. Several network-based diagnostics are then proposed to characterize the dynamics of different systems: logistic, tent, and circle maps. We show that these diagnostics are able to capture changes produced in the dynamics as a control parameter is varied. We also apply our new measures to empirical data from semiconductor lasers and show that they are able to anticipate the polarization switchings, thus providing early warning signals of abrupt transitions.
Mon, 27 Jul 2015 10:42:08 GMThttp://hdl.handle.net/2117/763332015-07-27T10:42:08ZMasoller Alonso, CristinaHong, YanhuaAyad, SarahGustave, FrancoisBarland, StéphanePons Rivero, Antonio JavierGómez, SergioArenas, AlexWe characterize the evolution of a dynamical system by combining two well-known complex systems' tools, namely, symbolic ordinal analysis and networks. From the ordinal representation of a time series we construct a network in which every node weight represents the probability of an ordinal pattern (OP) to appear in the symbolic sequence and each edge's weight represents the probability of transitions between two consecutive OPs. Several network-based diagnostics are then proposed to characterize the dynamics of different systems: logistic, tent, and circle maps. We show that these diagnostics are able to capture changes produced in the dynamics as a control parameter is varied. We also apply our new measures to empirical data from semiconductor lasers and show that they are able to anticipate the polarization switchings, thus providing early warning signals of abrupt transitions.Ultrashort pulse chirp measurement via transverse second-harmonic generation in strontium barium niobate crystal
http://hdl.handle.net/2117/28568
Ultrashort pulse chirp measurement via transverse second-harmonic generation in strontium barium niobate crystal
Trull Silvestre, José Francisco; Sola, Ïñigo; Wang, Bingxia; Parra, Albert; Krolikowski, W.; Sheng, Y.; Vilaseca Alavedra, Ramon; Cojocaru, Crina
Pulse compression in dispersive strontium barium niobate crystal with a random size and distribution of the anti-parallel orientated nonlinear domains is observed via transverse second harmonic generation. The dependence of the transverse width of the second harmonic trace along the propagation direction allows for the determination of the initial chirp and duration of pulses in the femtosecond regime. This technique permits a real-time analysis of the pulse evolution and facilitates fast in-situ correction of pulse chirp acquired in the propagation through an optical system.
Mon, 13 Jul 2015 10:31:50 GMThttp://hdl.handle.net/2117/285682015-07-13T10:31:50ZTrull Silvestre, José FranciscoSola, ÏñigoWang, BingxiaParra, AlbertKrolikowski, W.Sheng, Y.Vilaseca Alavedra, RamonCojocaru, CrinaPulse compression in dispersive strontium barium niobate crystal with a random size and distribution of the anti-parallel orientated nonlinear domains is observed via transverse second harmonic generation. The dependence of the transverse width of the second harmonic trace along the propagation direction allows for the determination of the initial chirp and duration of pulses in the femtosecond regime. This technique permits a real-time analysis of the pulse evolution and facilitates fast in-situ correction of pulse chirp acquired in the propagation through an optical system.Acoustically penetrable sonic crystals based on fluid-like scatterers
http://hdl.handle.net/2117/28088
Acoustically penetrable sonic crystals based on fluid-like scatterers
Cebrecos, A.; Romero García, Vicenç; Pico Vila, Rubén; Sánchez Morcillo, Victor José; Botey Cumella, Muriel; Herrero Simon, Ramon; Cheng, Yu Chieh; Staliunas, Kestutis
We propose a periodic structure that behaves as a fluid-fluid composite for sound waves, where the building blocks are clusters of rigid scatterers. Such building-blocks are penetrable for acoustic waves, and their properties can be tuned by selecting the filling fraction. The equivalence with a fluid-fluid system of such a doubly periodic composite is tested analytical and experimentally. Because of the fluid-like character of the scatterers, sound structure interaction is negligible, and the propagation can be described by scalar models, analogous to those used in electromagnetics. As an example, the case of focusing of evanescent waves and the guided propagation of acoustic waves along an array of penetrable elements is discussed in detail. The proposed structure may be a real alternative to design a low contrast and acoustically penetrable medium where new properties as those shown in this work could be experimentally realized.
Thu, 28 May 2015 09:24:54 GMThttp://hdl.handle.net/2117/280882015-05-28T09:24:54ZCebrecos, A.Romero García, VicençPico Vila, RubénSánchez Morcillo, Victor JoséBotey Cumella, MurielHerrero Simon, RamonCheng, Yu ChiehStaliunas, KestutisWe propose a periodic structure that behaves as a fluid-fluid composite for sound waves, where the building blocks are clusters of rigid scatterers. Such building-blocks are penetrable for acoustic waves, and their properties can be tuned by selecting the filling fraction. The equivalence with a fluid-fluid system of such a doubly periodic composite is tested analytical and experimentally. Because of the fluid-like character of the scatterers, sound structure interaction is negligible, and the propagation can be described by scalar models, analogous to those used in electromagnetics. As an example, the case of focusing of evanescent waves and the guided propagation of acoustic waves along an array of penetrable elements is discussed in detail. The proposed structure may be a real alternative to design a low contrast and acoustically penetrable medium where new properties as those shown in this work could be experimentally realized.Exact detection of direct links in networks of interacting dynamical units
http://hdl.handle.net/2117/27390
Exact detection of direct links in networks of interacting dynamical units
Rubido, Nicolas; Marti, Arturo; Bianco-Martinez, Ezequiel; Grebogi, Celso; Baptista, Murilo; Masoller Alonso, Cristina
The inference of an underlying network topology from local observations of a complex system composed of interacting units is usually attempted by using statistical similarity measures, such as cross-correlation (CC) and mutual information (MI). The possible existence of a direct link between different units is, however, hindered within the time-series measurements. Here we show that, for the class of systems studied, when an abrupt change in the ordered set of CC or MI values exists, it is possible to infer, without errors, the underlying network topology from the time-series measurements, even in the presence of observational noise, non-identical units, and coupling heterogeneity. We find that a necessary condition for the discontinuity to occur is that the dynamics of the coupled units is partially coherent, i.e., neither complete disorder nor globally synchronous patterns are present. We critically compare the inference methods based on CC and MI, in terms of how effective, robust, and reliable they are, and conclude that, in general, MI outperforms CC in robustness and reliability. Our findings could be relevant for the construction and interpretation of functional networks, such as those constructed from brain or climate data.
Thu, 16 Apr 2015 13:34:48 GMThttp://hdl.handle.net/2117/273902015-04-16T13:34:48ZRubido, NicolasMarti, ArturoBianco-Martinez, EzequielGrebogi, CelsoBaptista, MuriloMasoller Alonso, CristinaThe inference of an underlying network topology from local observations of a complex system composed of interacting units is usually attempted by using statistical similarity measures, such as cross-correlation (CC) and mutual information (MI). The possible existence of a direct link between different units is, however, hindered within the time-series measurements. Here we show that, for the class of systems studied, when an abrupt change in the ordered set of CC or MI values exists, it is possible to infer, without errors, the underlying network topology from the time-series measurements, even in the presence of observational noise, non-identical units, and coupling heterogeneity. We find that a necessary condition for the discontinuity to occur is that the dynamics of the coupled units is partially coherent, i.e., neither complete disorder nor globally synchronous patterns are present. We critically compare the inference methods based on CC and MI, in terms of how effective, robust, and reliable they are, and conclude that, in general, MI outperforms CC in robustness and reliability. Our findings could be relevant for the construction and interpretation of functional networks, such as those constructed from brain or climate data.Flat focusing mirror
http://hdl.handle.net/2117/27287
Flat focusing mirror
Cheng, Yu Chieh; Kicas, Simonas; Trull Silvestre, José Francisco; Peckus, Martynas; Cojocaru, Crina; Vilaseca Alavedra, Ramon; Drazdys, Ramutis; Staliunas, Kestutis
The control of spatial propagation properties of narrow light beams such as divergence, focusing or imaging are main objectives in optics and photonics. In this letter, we propose and demonstrate experimentally a flat focusing mirror, based on an especially designed dielectric structure without any optical axis. More generally, it also enables imaging any light pattern in reflection. The flat focusing mirror with a transversal invariance can largely increase the applicability of structured photonic materials for light beam propagation control in small-dimension photonic circuits.
Mon, 13 Apr 2015 13:43:16 GMThttp://hdl.handle.net/2117/272872015-04-13T13:43:16ZCheng, Yu ChiehKicas, SimonasTrull Silvestre, José FranciscoPeckus, MartynasCojocaru, CrinaVilaseca Alavedra, RamonDrazdys, RamutisStaliunas, KestutisThe control of spatial propagation properties of narrow light beams such as divergence, focusing or imaging are main objectives in optics and photonics. In this letter, we propose and demonstrate experimentally a flat focusing mirror, based on an especially designed dielectric structure without any optical axis. More generally, it also enables imaging any light pattern in reflection. The flat focusing mirror with a transversal invariance can largely increase the applicability of structured photonic materials for light beam propagation control in small-dimension photonic circuits.Polarization switching and hysteresis in vertical-cavity surface-emitting lasers subject to orthogonal optical injection
http://hdl.handle.net/2117/27173
Polarization switching and hysteresis in vertical-cavity surface-emitting lasers subject to orthogonal optical injection
Salvide, Matias Fernando; Masoller Alonso, Cristina; Torre, Maria Susana
We study polarization switching and hysteresis in a vertical-cavity surface-emitting laser (VCSEL) subject to an orthogonal optical injection, such that the polarization of the injected light is perpendicular to that of the free-running VCSEL. We use the framework of the spin-flip model to characterize the polarization state of the VCSEL as a function of the frequency detuning. With appropriated injection conditions, the orthogonal polarization turns on and locks to the injected field. Increasing and decreasing the detuning across the two locking boundaries results either in narrow or wide hysteresis cycles, or even in irreversible switching. These results are in a good agreement with recent experimental observations.
Wed, 08 Apr 2015 14:33:32 GMThttp://hdl.handle.net/2117/271732015-04-08T14:33:32ZSalvide, Matias FernandoMasoller Alonso, CristinaTorre, Maria SusanaWe study polarization switching and hysteresis in a vertical-cavity surface-emitting laser (VCSEL) subject to an orthogonal optical injection, such that the polarization of the injected light is perpendicular to that of the free-running VCSEL. We use the framework of the spin-flip model to characterize the polarization state of the VCSEL as a function of the frequency detuning. With appropriated injection conditions, the orthogonal polarization turns on and locks to the injected field. Increasing and decreasing the detuning across the two locking boundaries results either in narrow or wide hysteresis cycles, or even in irreversible switching. These results are in a good agreement with recent experimental observations.