DONLL - Dinàmica no lineal, òptica no lineal i làsers
http://hdl.handle.net/2117/3214
2015-11-28T20:26:48ZLangevin 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.
2015-11-23T12:56:01ZSancho, 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.
2015-11-18T07:53:33ZKumar, 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.
2015-11-12T09:56:16ZMalagarriga 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.
2015-09-03T08:13:45ZTurduev, 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.Asymmetric light transmission by using 2D PT-symmetric photonic nanostructure
http://hdl.handle.net/2117/76340
Asymmetric light transmission by using 2D PT-symmetric photonic nanostructure
Turduev, M.; Botey Cumella, Muriel; Herrero Simon, Ramon; Kurt, H.; Staliunas, Kestutis; Giden, I.
We propose for the first time a simple realization of a two-dimensional Parity-Time symmetric hexagonal shaped photonic structure composed of honeycomb lattice. The structure has a symmetric periodic modulation of the refractive index on the wavelength scale, which is combined with an anti-symmetric gain/loss distribution on the same scale. That leads to non-reciprocal light coupling at resonant frequencies. The design of the realistic structure is based on a simple physical concept: alternating low index cylinders with gain and loss in a honeycomb configuration, embedded in a higher index dielectric background.
2015-07-27T11:42:50ZTurduev, M.Botey Cumella, MurielHerrero Simon, RamonKurt, H.Staliunas, KestutisGiden, I.We propose for the first time a simple realization of a two-dimensional Parity-Time symmetric hexagonal shaped photonic structure composed of honeycomb lattice. The structure has a symmetric periodic modulation of the refractive index on the wavelength scale, which is combined with an anti-symmetric gain/loss distribution on the same scale. That leads to non-reciprocal light coupling at resonant frequencies. The design of the realistic structure is based on a simple physical concept: alternating low index cylinders with gain and loss in a honeycomb configuration, embedded in a higher index dielectric background.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.
2015-07-27T10:42:08ZMasoller 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.
2015-07-13T10:31:50ZTrull 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.Suppression of modulation instability by spatio-temporal modulation
http://hdl.handle.net/2117/28105
Suppression of modulation instability by spatio-temporal modulation
Staliunas, Kestutis
Modulation Instability (MI) is at the basis of spontaneous pattern formation in many nonlinear spatially extended systems in Nature, technologies, and in everyday live. In spite of variety of spatial patterns in different systems, the very onset of a spatio-temporal dynamics, the breaking of initial spatial and temporal symmetry, is initiated by MI. The said is valid for dissipative nonlinear systems, where dissipative patterns set in, but also for conservative systems. The examples in latter case ranges from the filamentation of light in Kerr-nonlinear media, instabilities of Bose condensates with attractive interactions, to perhaps, the recently much discussed formation of the “rogue waves”.
2015-05-29T15:05:10ZStaliunas, KestutisModulation Instability (MI) is at the basis of spontaneous pattern formation in many nonlinear spatially extended systems in Nature, technologies, and in everyday live. In spite of variety of spatial patterns in different systems, the very onset of a spatio-temporal dynamics, the breaking of initial spatial and temporal symmetry, is initiated by MI. The said is valid for dissipative nonlinear systems, where dissipative patterns set in, but also for conservative systems. The examples in latter case ranges from the filamentation of light in Kerr-nonlinear media, instabilities of Bose condensates with attractive interactions, to perhaps, the recently much discussed formation of the “rogue waves”.Stochastic competition between two populations in space
http://hdl.handle.net/2117/28093
Stochastic competition between two populations in space
Pigolotti, Simone; Benzi, Roberto; Jensen, Mogens H.; Perlekar, Prasad; Toschi, Federico
2015-05-28T11:12:08ZPigolotti, SimoneBenzi, RobertoJensen, Mogens H.Perlekar, PrasadToschi, FedericoAcoustically 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.
2015-05-28T09:24:54ZCebrecos, 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.