Articles de revista
http://hdl.handle.net/2117/3215
Sun, 07 Feb 2016 04:14:43 GMT2016-02-07T04:14:43ZControllable light diffraction in woodpile photonic crystals filled with liquid crystal
http://hdl.handle.net/2117/82238
Controllable light diffraction in woodpile photonic crystals filled with liquid crystal
Ho, Chih-Hua; Cheng, Yu Chieh; Maigyte, Lina; Zeng, H; Trull Silvestre, José Francisco; Cojocaru, Crina; Wiersma, D.S.; Staliunas, Kestutis
An approach to switching between different patterns of light beams transmitted through the woodpile photonic crystals filled with liquid crystals is proposed. The phase transition between the nematic and isotropic liquid crystal states leads to an observable variation of the spatial pattern transmitted through the photonic structure. The transmission profiles in the nematic phase also show polarization sensibility due to refractive index dependence on the field polarization. The experimental results are consistent with a numerical calculation by Finite Difference Time Domain method.
Thu, 28 Jan 2016 16:16:52 GMThttp://hdl.handle.net/2117/822382016-01-28T16:16:52ZHo, Chih-HuaCheng, Yu ChiehMaigyte, LinaZeng, HTrull Silvestre, José FranciscoCojocaru, CrinaWiersma, D.S.Staliunas, KestutisAn approach to switching between different patterns of light beams transmitted through the woodpile photonic crystals filled with liquid crystals is proposed. The phase transition between the nematic and isotropic liquid crystal states leads to an observable variation of the spatial pattern transmitted through the photonic structure. The transmission profiles in the nematic phase also show polarization sensibility due to refractive index dependence on the field polarization. The experimental results are consistent with a numerical calculation by Finite Difference Time Domain method.Assessing the direction of climate interactions by means of complex networks and information theoretic tools
http://hdl.handle.net/2117/81989
Assessing the direction of climate interactions by means of complex networks and information theoretic tools
Deza, Juan Ignacio; Barreiro, Marcelo; Masoller Alonso, Cristina
An estimate of the net direction of climate interactions in different geographical regions is made by constructing a directed climate network from a regular latitude-longitude grid of nodes, using a directionality index (DI) based on conditional mutual information (CMI). Two datasets of surface air temperature anomalies-one monthly averaged and another daily averaged-are analyzed and compared. The network links are interpreted in terms of known atmospheric tropical and extratropical variability patterns. Specific and relevant geographical regions are selected, the net direction of propagation of the atmospheric patterns is analyzed, and the direction of the inferred links is validated by recovering some well-known climate variability structures. These patterns are found to be acting at various time-scales, such as atmospheric waves in the extratropics or longer range events in the tropics. This analysis demonstrates the capability of the DI measure to infer the net direction of climate interactions and may contribute to improve the present understanding of climate phenomena and climate predictability. The work presented here also stands out as an application of advanced tools to the analysis of empirical, real-world data. (C) 2015 AIP Publishing LLC.
Mon, 25 Jan 2016 15:08:37 GMThttp://hdl.handle.net/2117/819892016-01-25T15:08:37ZDeza, Juan IgnacioBarreiro, MarceloMasoller Alonso, CristinaAn estimate of the net direction of climate interactions in different geographical regions is made by constructing a directed climate network from a regular latitude-longitude grid of nodes, using a directionality index (DI) based on conditional mutual information (CMI). Two datasets of surface air temperature anomalies-one monthly averaged and another daily averaged-are analyzed and compared. The network links are interpreted in terms of known atmospheric tropical and extratropical variability patterns. Specific and relevant geographical regions are selected, the net direction of propagation of the atmospheric patterns is analyzed, and the direction of the inferred links is validated by recovering some well-known climate variability structures. These patterns are found to be acting at various time-scales, such as atmospheric waves in the extratropics or longer range events in the tropics. This analysis demonstrates the capability of the DI measure to infer the net direction of climate interactions and may contribute to improve the present understanding of climate phenomena and climate predictability. The work presented here also stands out as an application of advanced tools to the analysis of empirical, real-world data. (C) 2015 AIP Publishing LLC.Stochasticity enhances the gaining of bet-hedging strategies in contact-process-like dynamics
http://hdl.handle.net/2117/81930
Stochasticity enhances the gaining of bet-hedging strategies in contact-process-like dynamics
Hidalgo, Juan J.; Pigolotti, Simone; Muñoz Martínez, Miguel Ángel
Mon, 25 Jan 2016 08:56:17 GMThttp://hdl.handle.net/2117/819302016-01-25T08:56:17ZHidalgo, Juan J.Pigolotti, SimoneMuñoz Martínez, Miguel ÁngelEnhanced transmission band in periodic media with loss modulation
http://hdl.handle.net/2117/81684
Enhanced transmission band in periodic media with loss modulation
Cebrecos, A.; Pico Vila, Rubén; Romero García, Vicenç; Yasser, A.M.; Maigyte, Lina; Herrero Simon, Ramon; Botey Cumella, Muriel; Sánchez Morcillo, Victor José; Staliunas, Kestutis
We study the propagation of waves in a periodic array of absorbing layers. We report an anomalous increase of wave transmission through the structure related to a decrease of the absorption around the Bragg frequencies. The effect is first discussed in terms of a generic coupled wave model extended to include losses, and its predictions can be applied to different types of waves propagating in media with periodic modulation of the losses at the wavelength scale. The particular case of sound waves in an array of porous layers embedded in air is considered. An experiment designed to test the predictions demonstrates the existence of the enhanced transmission band.
Tue, 19 Jan 2016 14:58:55 GMThttp://hdl.handle.net/2117/816842016-01-19T14:58:55ZCebrecos, A.Pico Vila, RubénRomero García, VicençYasser, A.M.Maigyte, LinaHerrero Simon, RamonBotey Cumella, MurielSánchez Morcillo, Victor JoséStaliunas, KestutisWe study the propagation of waves in a periodic array of absorbing layers. We report an anomalous increase of wave transmission through the structure related to a decrease of the absorption around the Bragg frequencies. The effect is first discussed in terms of a generic coupled wave model extended to include losses, and its predictions can be applied to different types of waves propagating in media with periodic modulation of the losses at the wavelength scale. The particular case of sound waves in an array of porous layers embedded in air is considered. An experiment designed to test the predictions demonstrates the existence of the enhanced transmission band.Inferring the connectivity of coupled oscillators from time-series statistical similarity analysis
http://hdl.handle.net/2117/81536
Inferring the connectivity of coupled oscillators from time-series statistical similarity analysis
Tirabassi, Giulio; Sevilla Escoboza, Ricardo; Martín Buldú, Javier; Masoller Alonso, Cristina
A system composed by interacting dynamical elements can be represented by a network, where the nodes represent the elements that constitute the system, and the links account for their interactions, which arise due to a variety of mechanisms, and which are often unknown. A popular method for inferring the system connectivity (i.e., the set of links among pairs of nodes) is by performing a statistical similarity analysis of the time-series collected from the dynamics of the nodes. Here, by considering two systems of coupled oscillators (Kuramoto phase oscillators and Rossler chaotic electronic oscillators) with known and controllable coupling conditions, we aim at testing the performance of this inference method, by using linear and non linear statistical similarity measures. We find that, under adequate conditions, the network links can be perfectly inferred, i.e., no mistakes are made regarding the presence or absence of links. These conditions for perfect inference require: i) an appropriated choice of the observed variable to be analysed, ii) an appropriated interaction strength, and iii) an adequate thresholding of the similarity matrix. For the dynamical units considered here we find that the linear statistical similarity measure performs, in general, better than the non-linear ones.
Fri, 15 Jan 2016 14:51:36 GMThttp://hdl.handle.net/2117/815362016-01-15T14:51:36ZTirabassi, GiulioSevilla Escoboza, RicardoMartín Buldú, JavierMasoller Alonso, CristinaA system composed by interacting dynamical elements can be represented by a network, where the nodes represent the elements that constitute the system, and the links account for their interactions, which arise due to a variety of mechanisms, and which are often unknown. A popular method for inferring the system connectivity (i.e., the set of links among pairs of nodes) is by performing a statistical similarity analysis of the time-series collected from the dynamics of the nodes. Here, by considering two systems of coupled oscillators (Kuramoto phase oscillators and Rossler chaotic electronic oscillators) with known and controllable coupling conditions, we aim at testing the performance of this inference method, by using linear and non linear statistical similarity measures. We find that, under adequate conditions, the network links can be perfectly inferred, i.e., no mistakes are made regarding the presence or absence of links. These conditions for perfect inference require: i) an appropriated choice of the observed variable to be analysed, ii) an appropriated interaction strength, and iii) an adequate thresholding of the similarity matrix. For the dynamical units considered here we find that the linear statistical similarity measure performs, in general, better than the non-linear ones.Far-field narrowing in spatially modulated broad-area edge-emitting semiconductor amplifiers
http://hdl.handle.net/2117/81487
Far-field narrowing in spatially modulated broad-area edge-emitting semiconductor amplifiers
Radziunas, Mindaugas; Herrero Simon, Ramon; Botey Cumella, Muriel; Staliunas, Kestutis
We perform a detailed theoretical analysis of the far-field narrowing in broad-area edge-emitting semiconductor amplifiers that are electrically injected through contacts periodically modulated in both longitudinal and transverse directions. The beam propagation properties within the semiconductor amplifier are explored by a (1 + 2)-dimensional traveling wave model and its coupled-mode approximation. Assuming a weak field regime, we analyze the impact of different parameters and modulation geometry on the narrowing of the principal far-field component.
Thu, 14 Jan 2016 16:17:19 GMThttp://hdl.handle.net/2117/814872016-01-14T16:17:19ZRadziunas, MindaugasHerrero Simon, RamonBotey Cumella, MurielStaliunas, KestutisWe perform a detailed theoretical analysis of the far-field narrowing in broad-area edge-emitting semiconductor amplifiers that are electrically injected through contacts periodically modulated in both longitudinal and transverse directions. The beam propagation properties within the semiconductor amplifier are explored by a (1 + 2)-dimensional traveling wave model and its coupled-mode approximation. Assuming a weak field regime, we analyze the impact of different parameters and modulation geometry on the narrowing of the principal far-field component.Coherent amplification of attosecond light pulses in the water-window spectral region
http://hdl.handle.net/2117/81459
Coherent amplification of attosecond light pulses in the water-window spectral region
Serrat Jurado, Carles; Roca, David; Seres, Jozsef
We present a theoretical study on coherent extreme ultraviolet (XUV) attosecond pulse amplification mediated by nonlinear parametric enhanced forward scattering occurring in the interaction of a strong femtosecond infrared (IR) laser pulse combined with a weak attosecond XUV pulse train with an atom. We predict large amplification of XUV radiation when the IR strong pulse and the XUV weak pulse are optimally phased. We study high-order harmonic processes (HHG) in He, He+ and Ne++, and show how although the HHG yield is largely affected by the particular atom used as target, nonlinear parametric XUV amplification is only weakly affected. We conclude that XUV nonlinear parametric attosecond pulse amplification can be most efficiently observed by using atoms with a high ionization potential and that the nonlinear amplification is robust at high photon energies where HHG is not efficient, such as in the water-window spectral region.
Thu, 14 Jan 2016 14:13:52 GMThttp://hdl.handle.net/2117/814592016-01-14T14:13:52ZSerrat Jurado, CarlesRoca, DavidSeres, JozsefWe present a theoretical study on coherent extreme ultraviolet (XUV) attosecond pulse amplification mediated by nonlinear parametric enhanced forward scattering occurring in the interaction of a strong femtosecond infrared (IR) laser pulse combined with a weak attosecond XUV pulse train with an atom. We predict large amplification of XUV radiation when the IR strong pulse and the XUV weak pulse are optimally phased. We study high-order harmonic processes (HHG) in He, He+ and Ne++, and show how although the HHG yield is largely affected by the particular atom used as target, nonlinear parametric XUV amplification is only weakly affected. We conclude that XUV nonlinear parametric attosecond pulse amplification can be most efficiently observed by using atoms with a high ionization potential and that the nonlinear amplification is robust at high photon energies where HHG is not efficient, such as in the water-window spectral region.Organization and identification of solutions in the time-delayed Mackey-Glass model
http://hdl.handle.net/2117/81311
Organization and identification of solutions in the time-delayed Mackey-Glass model
Amil, Pablo; Cabeza, Cecilia; Masoller Alonso, Cristina; Marti, Arturo C
Multistability in the long term dynamics of the Mackey-Glass (MG) delayed model is analyzed by using an electronic circuit capable of controlling the initial conditions. The system's phase-space is explored by varying the parameter values of two families of initial functions. The evolution equation of the electronic circuit is derived and it is shown that, in the continuous limit, it exactly corresponds to the MG model. In practice, when using a finite set of capacitors, an excellent agreement between the experimental observations and the numerical simulations is manifested. As the delay is increased, different periodic or aperiodic solutions appear. We observe abundant periodic solutions that have the same period but a different alternation of peaks of dissimilar amplitudes and propose a novel symbolic method to classify these solutions.
Tue, 12 Jan 2016 15:48:22 GMThttp://hdl.handle.net/2117/813112016-01-12T15:48:22ZAmil, PabloCabeza, CeciliaMasoller Alonso, CristinaMarti, Arturo CMultistability in the long term dynamics of the Mackey-Glass (MG) delayed model is analyzed by using an electronic circuit capable of controlling the initial conditions. The system's phase-space is explored by varying the parameter values of two families of initial functions. The evolution equation of the electronic circuit is derived and it is shown that, in the continuous limit, it exactly corresponds to the MG model. In practice, when using a finite set of capacitors, an excellent agreement between the experimental observations and the numerical simulations is manifested. As the delay is increased, different periodic or aperiodic solutions appear. We observe abundant periodic solutions that have the same period but a different alternation of peaks of dissimilar amplitudes and propose a novel symbolic method to classify these solutions.Nonlinear self-collimated sound beams in sonic crystals
http://hdl.handle.net/2117/81132
Nonlinear self-collimated sound beams in sonic crystals
Hamham, El Mokhtar; Jimenez, Noe; Pico Vila, Rubén; Sánchez Morcillo, Victor José; Garcia Raffi, Luis Miguel; Staliunas, Kestutis
Fri, 08 Jan 2016 08:48:03 GMThttp://hdl.handle.net/2117/811322016-01-08T08:48:03ZHamham, El MokhtarJimenez, NoePico Vila, RubénSánchez Morcillo, Victor JoséGarcia Raffi, Luis MiguelStaliunas, KestutisLangevin 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.