Física

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The evolutionary minority game with local coordination
(2003) Burgos, Enrique; Ceva, Horacio; Perazzo, Roberto P. J.
"We discuss a modification of the evolutionary minority game (EMG) in which agents are placed in the nodes of a regular or a random graph. A neighborhood for each agent can thus be defined and a modification of the usual relaxation dynamics can be made in which each agent updates her decision depending upon her neighborhood. We report numerical results for the topologies of a ring, a torus and a random graph changing the size of the neighborhood. We find the surprising result that in the EMG a better coordination (a lower frustration) can be achieved if agents base their actions on local information disregarding the global trend in the self-segregation process."
Performance of non-fibre based dispersion compensation for long-haul 10.7 Gbit/s DWDM transmission
(2004) Grosz, Diego; Maywar, D. N.; Küng, A. P.; Agarwal, A.; Banerjee, S.
"Non-fibre based in-line dispersion compensation is employed to achieve long-haul transmission of 80 channels at 10.7 Gbit=s bit rate over 1200 km of LEAF fibre. Average system margins of more than 4 dB and small transmission are demonstrated. The additional penalty incurred by the periodic nature of the dispersion compensator is assessed."
Uncertainty relation for the optimization of optical-fiber transmission systems simulations
(2005) Tolisano, T.; Callegari, Fulvio A.; Grosz, Diego; Fragnito, Hugo L.; Rieznik, Andrés
“The mathematical inequality which in quantum mechanics gives rise to the uncertainty principle between two non commuting operators is used to develop a spatial step-size selection algorithm for the Split-Step Fourier Method (SSFM) for solving Generalized Non-Linear Schrödinger Equations (G-NLSEs). Numerical experiments are performed to analyze the efficiency of the method in modeling optical-fiber communications systems, showing its advantages relative to other algorithms.”
Stochastic resonance and brownian ratchets
(2005) Fendrik, Alejandro J.; Romanelli, Lilia; Perazzo, Roberto P. J.
"We discuss the connections between Brownian ratchets (BR) and stochastic resonance (SR). We consider a periodic potential energy landscape with no left–right symmetry that is driven by an external force which can be derived from a potential that is periodic both in time and space. We show that this system presents two thermal enhancements within two different windows of the temperature. One is associated with a ‘‘coherent diffusion’’ by which particles jump back and forth between the minima of the periodic potential in synchrony with the external driving. The other is instead associated with a ‘‘coherent directional transport’’ by which particles hop synchronically from one minimum of the ratchet to the next. We calculate the current and the diffusion coefficients and show how transport undergoes a resonant enhancement. While the former is always present, the second only appears when left–right symmetry is broken."
Order and disorder in the local evolutionary minority game
(2005) Burgos, Enrique; Ceva, Horacio; Perazzo, Roberto P. J.
"We study a modification of the Evolutionary Minority Game (EMG) in which agents are placed in the nodes of a regular or a random graph. A neighborhood for each agent can thus be defined and a modification of the usual relaxation dynamics can be made in which each agent updates her decision scheme depending upon the options made in her immediate neighborhood. We name this model the Local Evolutionary Minority Game (LEMG). We report numerical results for the topologies of a ring, a torus and a random graph changing the size of the neighborhood.We focus our discussion in a one-dimensional system and perform a detailed comparison of the results obtained from the random relaxation dynamics of the LEMG and from a linear chain of interacting spin-like variables with temperature. We provide a physical interpretation of the surprising result that in the LEMG a better coordination (a lower frustration) is achieved if agents base their actions on local information.We show how the LEMG can be regarded as a model that gradually interpolates between a fully ordered, antiferromagnetic-like system, and a fully disordered system that can be assimilated to a spin glass."
Impact of DCF properties on system design
(2006) Essiambre, René-Jean; Winzer, Peter J.; Grosz, Diego
"The dispersion-compensating ﬁber is an important optical element of current and future optical networks. In this paper, we review the impact that various properties of dispersion-compensating ﬁbers has on the performance of optical communication systems."
The power of dispersion management for 10-Gb/s and 40-Gb/s systems
(2006) Grosz, Diego; Agarwal, A.; Küng, A. P.; Maywar, D. N.; Lakoba, T. I.
"We review applications and requirements of dispersion compensation that enable highcapacity, long-haul, and ultra-long-haul 10-Gb/s and 40-Gb/s DWDM transmission. We briefly describe their impact on system performance and present sorne future perspectives."
Why nestedness in mutualistic networks?
(2007) Burgos, Enrique; Ceva, Horacio; Perazzo, Roberto P. J.; Devoto, Mariano; Medan, Diego; Zimmermann, Martín; Delbue, Ana María
"We investigate the relationship between the nested organization of mutualistic systems and their robustness against the extinction of species. We establish that a nested pattern of contacts is the best possible one as far as robustness is concerned, but only when the least linked species have the greater probability of becoming extinct. We introduce a coefficient that provides a quantitative measure of the robustness of a mutualistic system."
Experimental investigation of noise-assisted information transmission and storage via stochastic resonance
(2010-05) Patterson, Germán; Goya, Andrés F.; Fierens, Pablo Ignacio; Ibáñez, Santiago Agustín; Grosz, Diego
"We present experimental results on the information transmission and storage via stochastic resonance in circuits designed and built around Schmitt triggers (STs). First, we investigate the performance of a transmission line comprised of five STs and show it to exhibit stochastic resonance. Each ST in the line is fed with white Gaussian noise, and the first ST is driven by a non-return-to-zero pseudo-random bit sequence with sub-threshold amplitude. Parameters such as bit error rate (Q-factor) are measured (calculated) and shown to exhibit a minimum (maximum) for an optimum amount of noise. Interestingly, we find that system performance degrades with the number of STs as if the system were linear and impaired only by additive Gaussian noise. We then propose and build a 1-bit storage device based on two STs in a loop configuration. We demonstrate that such a system is capable of storing one bit of information only in the presence of noise, and that there is a regime where the efficiency of such a device increases with increasing noise. Our results point to the feasibility of building 'blocks' that can transmit, store and eventually process information, whose performance is not only robust against noise, but can actually benefit from it. © 2010 Elsevier B.V. All rights reserved."
PCF-based tunable source of femtosecond pulses in the visible region
(2010-06) Rieznik, Andrés; Bettachini, Víctor A.; König, Pablo; Grosz, Diego; Masip, Martin Eduardo; Caldarola, Martín; Bragas, Andrea
"Blue-shifting dispersive waves and soliton trapping in a PCF pumped with a Ti:Sa laser are shown to produce tunable femtosecond pulses in the visible region, with a central wavelength depending upon the input pump power."
Tilt dynamics of an electrostatically actuated microoscillator at a liquid-liquid interface
(2011) Allievi, Alejandro
"We investigate the time-domain tilt response of an electrostatically actuated mechanical microoscillator positioned at a liquid-liquid interface. An analytical model is presented to simulate the microoscillator’s rotational motion inside a microchannel completely ﬁlled with two immiscible liquids. The model considers two coupled ordinary diﬀerential equations; one simulates the mechanical response of the microplate-microbeam assembly making-up the microoscillator and the other provides the behaviour of the electrical charge responsible for the electrostatic moment that tilts the microplate. Results show that remarkable improvements in sampling time and sensitivity can be obtained using a bi-liquid conﬁguration versus its singleliquid counterpart. Therefore, enhanced performance of mechanical microsensors for liquids could be achieved."
Continuous-space automaton model for pedestrian dynamics
(2011-05-11) Baglietto, Gabriel; Parisi, Daniel
An off-lattice automaton for modeling pedestrian dynamics is presented. Pedestrians are represented by disks with variable radius that evolve following predefined rules. The key feature of our approach is that although positions and velocities are continuous, forces do not need to be calculated. This has the advantage that it allows using a larger time step than in force-based models. The room evacuation problem and circular racetrack simulations quantitatively reproduce the available experimental data, both for the specific flow rate and for the fundamental diagram of pedestrian traffic with an outstanding performance. In this last case, the variation of two free parameters (r min and rmax) of the model accounts for the great variety of experimental fundamental diagrams reported in the literature. Moreover, this variety can be interpreted in terms of these model parameters.
Noise-assisted multibit storage device
(2011-08-29) Bellomo, Guido; Patterson, Germán; Fierens, Pablo Ignacio; Grosz, Diego
In this Letter we extend our investigations on noise-assisted storage devices through the experimental study of a loop composed of a single Schmitt trigger and an element that introduces a finite delay. We show that such a system allows the storage of several bits and does so more efficiently for an intermediate range of noise intensities. Finally, we study the probability of erroneous information retrieval as a function of elapsed time and show a way for predicting device performance independently of the number of stored bits.
Optimum integration procedures for supercontinuum simulation
(2012) Rieznik, Andrés; Heidt, Alexander M.; König, Pablo; Bettachini, Víctor A.; Grosz, Diego
"We study numerical solutions of the generalized nonlinear Schrödinger equation (GNLSE), focusing on the advantage of integrating the nonlinear part of the equation in the frequency domain (FD), rather than in the time domain (TD), when simulating supercontinuum generation in optical fibers. We show that integration of the nonlinear operator in the FD is more efficient than its integration in the TD. We analyze different adaptive stepsize algorithms in combination with the interaction picture integration method and show that their performance strongly depends on whether integration of the nonlinear operator is performed in the FD or TD. We find that the most efficient procedure for supercontinuum simulation in optical fibers results from solving the nonlinearity in the FD and applying the recently introduced conservation quantity error adaptive step-size algorithm."
Thermal effects on the switching kinetics of silver/manganite memristive systems
(2014-10) Stoliar, Pablo; Sánchez, M. J.; Patterson, Germán; Fierens, Pablo Ignacio
"We investigate the switching kinetics of oxygen vacancy (Ov) diffusion in La(5/8-y)Pr(y) Ca(3/8)MnO(3)-Ag (LPCMO–Ag) memristive interfaces by performing experiments on the temperature dependence of the high resistance state under thermal cycling. Experimental results are well reproduced by numerical simulations based on thermally activated Ov diffusion processes and fundamental assumptions relying on a recent model proposed to explain bipolar resistive switching in manganite-based cells. The confident values obtained for activation energies and the diffusion coefficient associated to Ov dynamics constitute a validation test for both model predictions and Ov diffusion mechanisms in memristive interfaces."
Permutation min-entropy: an improved quantifier for unveiling subtle temporal correlations
(2015-01) Zunino, Luciano; Olivares, Felipe; Rosso, Osvaldo A.
"The aim of this letter is to introduce the permutation min-entropy as an improved symbolic tool for identifying the existence of hidden temporal correlations in time series. On the one hand, analytical results obtained for the fractional Brownian motion stochastic model theoretically support this hypothesis. On the other hand, the analysis of several computer-generated and experimentally observed time series illustrate that the proposed symbolic quantifier is a versatile and practical tool for identifying the presence of subtle temporal structures in complex dynamical systems. Comparisons against the results obtained with other tools confirm its usefulness as an alternative and/or complementary measure of temporal correlations."
Time series characterization via horizontal visibility graph and Information theory
(2016) Gonçalves, Bruna Amin; Capri, Laura; Rosso, Osvaldo A.; Ravetti, Martín G.
"Complex networks theory have gained wider applicability since methods for transformation of time series to networks were proposed and successfully tested. In the last few years, horizontal visibility graph has become a popular method due to its simplicity and good results when applied to natural and artificially generated data. In this work, we explore different ways of extracting information from the network constructed from the horizontal visibility graph and evaluated by Information Theory quantifiers. Most works use the degree distribution of the network, however, we found alternative probability distributions, more efficient than the degree distribution in characterizing dynamical systems. In particular, we find that, when using distributions based on distances and amplitude values, significant shorter time series are required. We analyze fractional Brownian motion time series, and a paleoclimatic proxy record of ENSO from the Pallcacocha Lake to study dynamical changes during the Holocene."
Flow of pedestrians through narrow doors with dierent competitiveness
(2016) Garcimartín, Ángel; Parisi, Daniel; Pastor, José Martín; Martín-Gómez, César; Zuriguel, Iker
"We report a thorough analysis of the intermittent flow of pedestrians through a narrow door. The observations include five diferent sets of evacuation drills with which we have investigated the efect of door size and competitiveness on the flow dynamics. Although the outcomes are in general compatible with the existence of the faster-is-slower efect, the temporal evolution of the instantaneous flow rate provides evidence of new features. These stress the crucial role of the number of people performing the tests, which has an influence on the obtained results. Once the transients at the beginning and end of the evacuation are removed, we have found that the time lapses between the passage of two consecutive pedestrians display heavy-tailed distributions in all the scenarios studied. Meanwhile, the distribution of burst sizes decays exponentially; this can be linked to a constant probability of finding a long-lasting clog during the evacuation process. Based on these results, a discussion is presented on the caution that should be exercised when measuring or describing the intermittent flow of pedestrians through narrow doors."
Noise on resistive switching: a Fokker–Planck approach
(2016-05) Patterson, Germán; Grosz, Diego; Fierens, Pablo Ignacio
"We study the effect of internal and external noise on the phenomenon of resistive switching. We consider a non-harmonic external driving signal and provide a theoretical framework to explain the observed behavior in terms of the related Fokker–Planck equations. It is found that internal noise causes an enhancement of the resistive contrast and that noise proves to be advantageous when considering short driving pulses. In the case of external noise, however, noise only has the effect of degrading the resistive contrast. Furthermore, we find a relationship between the noise amplitude and the driving signal pulse width that constrains the persistence of the resistive state. In particular, results suggest that strong and short driving pulses favor a longer persistence time, an observation that may find applications in the field of high-integration high-speed resistive memory devices."
Libor at crossroads: stochastic switching detection using information theory quantifiers
(2016-07) Fernández Bariviera, Aurelio; Guercio, M. Belén; Martinez, Lisana B.; Rosso, Osvaldo A.
"This paper studies the 28 time series of Libor rates, classified in seven maturities and four currencies, during the last 14 years. The analysis was performed using a novel technique in financial economics: the Complexity-Entropy Causality Plane. This planar representation allows the discrimination of different stochastic and chaotic regimes. Using a temporal analysis based on moving windows, this paper unveils an abnormal movement of Libor time series around the period of the 2007 financial crisis. This alteration in the stochastic dynamics of Libor is contemporary of what press called "Libor scandal", i.e. the manipulation of interest rates carried out by several prime banks. We argue that our methodology is suitable as a market watch mechanism, as it makes visible the temporal redution in informational efficiency of the market."

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