FISICA ESTADÍSTICA E INTERDISCIPLINARIA
URI permanente para esta comunidad
Las publicaciones de esta colección son parte de la producción intelectual del Grupo de Física Estadística e Interdisciplinaria del Centro Atómico Bariloche, área que se dedica a la teórica y experimental de sistemas complejos. Aprovechando la universalidad de los fenómenos fuera de equilibrio, se aplican técnicas propias del estudio de sistemas físicos a problemas relacionados con otras áreas de la ciencia, tales como la biología y los procesos socioeconómicos.
Las publicaciones son el resultado de las siguientes líneas de trabajo:
1.Sistemas complejos y fuera de equilibrio: Comportamiento colectivo, autoorganización, sincronización. Procesos estocásticos, fenómenos críticos. Sistemas cuánticos abiertos.
2.Biología matemática: Dinámica de ecosistemas, movimiento animal. Procesos epidémicos. Evolución biológica.
3.Sistemas socioeconómicos: Dinámica de redes sociales. Distribución de riqueza, mercados financieros. Formación de opinión.
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Ítem Acceso Abierto Directed transport induced by α-stable Lévy noises in weakly asymmetric periodic potentials(American Physical Society, 2013-02) Risau Gusman, Sebastian Luis; Ibáñez, Santiago Agustín; Bouzat, SebastianWe study the motion of a particle in spatially periodic potentials with broken mirror symmetry under the influence of white α-stable Lévy noises. We consider both time-independent and fluctuating potentials. We focus on cases in which the spatial asymmetry of the potential is due not to a difference between the distances from an absolute minimum to the absolute maximum on its left and to the absolute maximum on its right but only to the curvatures of the potential profiles. The analysis is performed using the fractional Fokker-Planck formalism. Consistent results from Langevin simulations are also presented. We analyze the influence of the symmetry properties of the potentials in combination with the fluctuating characteristics of the system in the determination of the current. We find different situations in which both the absolute value and the direction of the current depend not only on the properties of the potential but also on the parameters characterizing the α-stable Lévy noise. Among other features, we analyze the case of supersymmetric potentials. In particular, we show that a static supersymmetric potential produces no current, and we analyze the conditions for observing a nonvanishing current when the potential fluctuates between different supersymmetric profiles.Ítem Acceso Abierto Synchronization properties of self-sustained mechanical oscillators(Amer Physical Soc, 2013-05) Arroyo, Sebastián Ismael; Zanette, Damian HoracioWe study, both analytically and numerically, the dynamics of mechanical oscillators kept in motion by a feedback force, which is generated electronically from a signal produced by the oscillators themselves. This kind of self-sustained systems may become standard in the design of frequency-control devices at microscopic scales. Our analysis is thus focused on their synchronization properties under the action of external forces and on the joint dynamics of two to many coupled oscillators. Existence and stability of synchronized motion are assessed in terms of the mechanical properties of individual oscillators, namely, their natural frequencies and damping coefficients, and synchronization frequencies are determined. Similarities and differences with synchronization phenomena in other coupled oscillating systems are emphasized.Ítem Acceso Abierto Backbone structure of the Edwards-Anderson spin-glass model(Amer Physical Soc, 2013-10) Romá, Federico José; Risau-Gusman, S.We study the ground-state spatial heterogeneities of the Edwards-Anderson spin-glass model with both bimodal and Gaussian bond distributions. We characterize these heterogeneities by using a general definition of bond rigidity, which allows us to classify the bonds of the system into two sets, the backbone and its complement, with very different properties. This generalizes to continuous distributions of bonds the well-known definition of a backbone for discrete bond distributions. By extensive numerical simulations we find that the topological
structure of the backbone for a given lattice dimensionality is very similar for both discrete and continuous bond distributions. We then analyze how these heterogeneities influence the equilibrium properties at finite temperature and we discuss the possibility that a suitable backbone picture can be relevant to describe spin-glass phenomena.Ítem Acceso Abierto Epidemic thresholds for bipartite networks(Amer Physical Soc, 2013-11) Hernandez, Damián G.; Risau Gusman, Sebastian LuisIt is well known that sexually transmitted diseases (STD) spread across a network of human sexual contacts. This network is most often bipartite, as most STD are transmitted between men and women. Even though network models in epidemiology have quite a long history now, there are few general results about bipartite networks. One of them is the simple dependence, predicted using the mean field approximation, between the epidemic threshold and the average and variance of the degree distribution of the network. Here we show that going beyond this
approximation can lead to qualitatively different results that are supported by numerical simulations. One of the new features, that can be relevant for applications, is the existence of a critical value for the infectivity of each population, below which no epidemics can arise, regardless of the value of the infectivity of the other population.Ítem Acceso Abierto Peculiar: Centaurus A(Planetario de la Ciudad de Buenos Aires Galileo Galilei, 2014-03) Abramson, GuillermoHe aquí Centaurus A, también conocida como NGC 5128. Es una de las galaxias más brillantes, una de las joyitas del cielo austral. Los astrónomos clasifican a esta galaxia como “peculiar”. Aún para un ocasional astrónomo aficionado, una foto como ésta no deja lugar a dudas: es peculiarÍtem Acceso Abierto Critical phenomena in the spreading of opinion consensus and disagreement(Papers in Physics, 2014-08-29) Chacoma, Andrés Alberto; Zanette, Damian HoracioWe consider a class of models of opinion formation where the dissemination of individual opinions occurs through the spreading of local consensus and disagreement. We study the emergence of full collective consensus or maximal disagreement in one- and two-dimensional arrays. In both cases, the probability of reaching full consensus exhibits well-defined scaling properties as a function of the system size. Two-dimensional systems, in particular, possess nontrivial exponents and critical points. The dynamical rules of our models, which emphasize the interaction between small groups of agents, should be considered as complementary to the imitation mechanisms of traditional opinion dynamics.Ítem Acceso Abierto A corpus analysis of rubato in Bach's C major prelude, WTC I(Royal Northern College of Music, 2015) Benadon, Fernando; Zanette, Damian HoracioWe examined microtiming properties in a corpus of 48 recorded performances of J.S. Bach's C Major Prelude from The Well Tempered Clavier, Book I. Drawing on the results of a listening experiment and from wavelet analysis, we derived a quantitative measure of rubato 'depth' that was used to assess timing trends across performances. In addition to highlighting important structural moments in the Prelude, rubato was used to bring melodic elements into relief as well as to generate grouping segmentations that may contradict the Prelude's inherent phrase structure. We then applied the statistical method of principal components analysis (PCA) to examine timing contours specific to individual performers. Repetitively consistent microrhythmic patterns, which we qualified as groove-like, differed from non-consistent and non-repetitive timing inflections, which we qualified as rubatoSlike.Ítem Acceso Abierto The effect of synaptic plasticity on orientation selectivity in a balanced model of primary visual cortex(Frontiers Media S.A., 2015- 08-20) Gonzalo Cogno, Ximena Soledad; Mato, GermanOrientation selectivity is ubiquitous in the primary visual cortex (V1) of mammals. In cats and monkeys, V1 displays spatially ordered maps of orientation preference. Instead, in mice, squirrels, and rats, orientation selective neurons in V1 are not spatially organized, giving rise to a seemingly random pattern usually referred to as a salt-and-pepper layout. The fact that such different organizations can sharpen orientation tuning leads to question the structural role of the intracortical connections; specifically the influence of plasticity and the generation of functional connectivity. In this work, we analyze the effect of plasticity processes on orientation selectivity for both scenarios. We study a computational model of layer 2/3 and a reduced one-dimensional model of orientation selective neurons, both in the balanced state. We analyze two plasticity mechanisms. The first one involves spike-timing dependent plasticity (STDP), while the second one considers the reconnection of the interactions according to the preferred orientations of the neurons. We find that under certain conditions STDP can indeed improve selectivity but it works in a somehow unexpected way, that is, effectively decreasing the modulated part of the intracortical connectivity as compared to the non-modulated part of it. For the reconnection mechanism we find that increasing functional connectivity leads, in fact, to a decrease in orientation selectivity if the network is in a stable balanced state. Both counterintuitive results are a consequence of the dynamics of the balanced state. We also find that selectivity can increase due to a reconnection process if the resulting connections give rise to an unstable balanced state. We compare these findings with recent experimental results.Ítem Acceso Abierto ¿Sustentabilidad?(Red latinoamericana y del Caribe de bioética-UNESCO, 2015-01-01) Monjeau, Jorge Adrian; Lanata, Jose Luis; Kuperman, Marcelo Nestor; Abramson, Guillermo; Laguna, Maria FabianaAbordamos el problema de la sustentabilidad desde la teoría de la construcción de nicho sumando a ésta un enfoque biofísico y energético. Presentamos el desarrollo teórico de un modelo matemático que acopla el crecimiento poblacional con el hábito en el uso de los recursos. En el modelo, cada individuo representa un factor de conversión y disipación de materia y energía de la biósfera en biomasa de Homo sapiens y en cultura material, estableciendo una vinculación matemática entre demografía, consumo, y deterioro de los recursos, escenario a ser heredado por las generaciones futuras. Ejemplificamos distintos escenarios de población y consumo y alternativas matemáticas para resolver la sustentabilidad. Una nueva sociedad futura justa, que satisfaga las necesidades de calidad de vida de todos los individuos presentes y futuros evitando la destrucción de especies y ecosistemas será aquella que pueda subordinar las leyes humanas a las leyes naturales, cualquier otro modo es inviable.Ítem Acceso Abierto Random-walk model to study cycles emerging from the exploration-exploitation trade-off(American Physical Society, 2015-01-13) Kazimierski, Laila Daniela; Abramson, Guillermo; Kuperman, Marcelo NestorWe present a model for a random walk with memory, phenomenologically inspired in a biological system. The walker has the capacity to remember the time of the last visit to each site and the step taken from there. This memory affects the behavior of the walker each time it reaches an already visited site modulating the probability of repeating previous moves. This probability increases with the time elapsed from the last visit. A biological analog of the walker is a frugivore, with the lattice sites representing plants. The memory effect can be associated with the time needed by plants to recover its fruit load. We propose two different strategies, conservative and explorative, as well as intermediate cases, leading to nonintuitive interesting results, such as the emergence of cycles.Ítem Acceso Abierto Analysis of the role of the low threshold currents IT and Ih in intrinsic delta oscillations of thalamocortical neurons(Frontiers Media S.A., 2015-05-07) Amarillo Gomez, Yimy; Mato, German; Nadal, MarcelaThalamocortical neurons are involved in the generation and maintenance of brain rhythms associated with global functional states. The repetitive burst firing of TC neurons at delta frequencies (1-4 Hz) has been linked to the oscillations recorded during deep sleep and during episodes of absence seizures. To get insight into the biophysical properties that are the basis for intrinsic delta oscillations in these neurons, we performed a bifurcation analysis of a minimal conductance-based thalamocortical neuron model including only the IT channel and the sodium and potassium leak channels. This analysis unveils the dynamics of repetitive burst firing of TC neurons, and describes how the interplay between the amplifying variable mT and the recovering variable hT of the calcium channel IT is sufficient to generate low threshold oscillations in the delta band. We also explored the role of the hyperpolarization activated cationic current Ih in this reduced model and determine that, albeit not required, Ih amplifies and stabilizes the oscillation.Ítem Acceso Abierto Mathematical model of livestock and wildlife: Predation and competition under environmental disturbances(Elsevier Science, 2015-08-10) Laguna, Maria Fabiana; Abramson, Guillermo; Kuperman, Marcelo Nestor; Lanata, Jose Luis; Monjeau, Jorge AdrianInspired by real scenarios in Northern Patagonia, we analyze a mathematical model of a simple trophic web with two herbivores and one predator. The studied situations represent a common practice in the steppes of Argentine Patagonia, where livestock are raised in a semi-wild state, either on the open range or enclosed, coexisting with competitors and predators. In the present work, the competing herbivores represent sheep and guanacos, while the predator is associated with the puma. The proposed model combines the concepts of metapopulations and patches dynamics, and includes an explicit hierarchical competition between species, which affects their prospect to colonize an empty patch when having to compete with other species. We perform numerical simulations of spatially extended metapopulations assemblages of the system, which allow us to incorporate the effects of habitat heterogeneity and destruction. The numerical results are compared with those obtained from mean field calculations. We find that the model provides a good theoretical framework in several situations, including the control of the wild populations that the ranchers exert to different extent. Furthermore, the present formulation incorporates new terms in previously analyzed models that help to reveal the important effects due to the heterogeneous nature of the system.Ítem Acceso Abierto Thalamic neuron models encode stimulus information by burst-size modulation(Frontiers Media S.A., 2015-09-23) Elijah, Daniel H.; Samengo, Ines; Montemurro, Marcelo AlejandroThalamic neurons have been long assumed to fire in tonic mode during perceptive states, and in burst mode during sleep and unconsciousness. However, recent evidence suggests that bursts may also be relevant in the encoding of sensory information. Here, we explore the neural code of such thalamic bursts. In order to assess whether the burst code is generic or whether it depends on the detailed properties of each bursting neuron, we analyzed two neuron models incorporating different levels of biological detail. One of the models contained no information of the biophysical processes entailed in spike generation, and described neuron activity at a phenomenological level. The second model represented the evolution of the individual ionic conductances involved in spiking and bursting, and required a large number of parameters. We analyzed the models' input selectivity using reverse correlation methods and information theory. We found that n-spike bursts from both models transmit information by modulating their spike count in response to changes to instantaneous input features, such as slope, phase, amplitude, etc. The stimulus feature that is most efficiently encoded by bursts, however, need not coincide with one of such classical features. We therefore searched for the optimal feature among all those that could be expressed as a linear transformation of the time-dependent input current. We found that bursting neurons transmitted 6 times more information about such more general features. The relevant events in the stimulus were located in a time window spanning 〜100 ms before and 〜20 ms after burst onset. Most importantly, the neural code employed by the simple and the biologically realistic models was largely the same, implying that the simple thalamic neuron model contains the essential ingredients that account for the computational properties of the thalamic burst code. Thus, our results suggest the n-spike burst code is a general property of thalamic neurons.Ítem Acceso Abierto Models for microtubule cargo transport coupling the Langevin equation to stochastic stepping motor dynamics: Caring about fluctuations(American Physical Society, 2016-01-04) Bouzat, SebastianOne-dimensional models coupling a Langevin equation for the cargo position to stochastic stepping dynamics for the motors constitute a relevant framework for analyzing multiple-motor microtubule transport. In this work we explore the consistence of these models focusing on the effects of the thermal noise. We study how to define consistent stepping and detachment rates for the motors as functions of the local forces acting on them in such a way that the cargo velocity and run-time match previously specified functions of the external load, which are set on the base of experimental results. We show that due to the influence of the thermal fluctuations this is not a trivial problem, even for the single-motor case. As a solution, we propose a motor stepping dynamics which considers memory on the motor force. This model leads to better results for single-motor transport than the approaches previously considered in the literature. Moreover, it gives a much better prediction for the stall force of the two-motor case, highly compatible with the experimental findings. We also analyze the fast fluctuations of the cargo position and the influence of the viscosity, comparing the proposed model to the standard one, and we show how the differences on the single-motor dynamics propagate to the multiple motor situations. Finally, we find that the one-dimensional character of the models impede an appropriate description of the fast fluctuations of the cargo position at small loads. We show how this problem can be solved by considering two-dimensional models.Ítem Acceso Abierto Duffing revisited: Phase-shift control and internal resonance in self-sustained oscillators(Springer, 2016-01-20) Arroyo, Sebastián Ismael; Zanette, Damian HoracioWe address two aspects of the dynamics of the forced Duffing oscillator which are relevant to the technology of micromechanical devices and, at the same time, have intrinsic significance to the field of nonlinear oscillating systems. First, we study the stability of periodic motion when the phase shift between the external force and the oscillation is controlled-contrary to the standard case, where the control parameter is the frequency of the force. Phase-shift control is the operational configuration under which self-sustained oscillators-and, in particular, micromechanical oscillators-provide a frequency reference useful for time keeping. We show that, contrary to the standard forced Duffing oscillator, under phaseshift control oscillations are stable over the whole resonance curve, and provide analytical approximate expressions for the time dependence of the oscillation amplitude and frequency during transients. Second, we analyze a model for the internal resonance between the main Duffing oscillation mode and a higherharmonic mode of a vibrating solid bar clamped at its two ends. We focus on the stabilization of the oscillation frequency when the resonance takes place, and present preliminary experimental results that illustrate the phenomenon. This synchronization process has been proposed to counteract the undesirable frequency-amplitude interdependence in nonlinear time-keeping micromechanical devices.Ítem Acceso Abierto Self-Sustained Micromechanical Oscillator with Linear Feedback(American Physical Society, 2016-07-01) Chen, Changyao; Zanette, Damian Horacio; Guest, Jeffrey R.; Czaplewski, David A.; López, DanielAutonomous oscillators, such as clocks and lasers, produce periodic signals without any external frequency reference. In order to sustain stable periodic motion, there needs to be an external energy supply as well as nonlinearity built into the oscillator to regulate the amplitude. Usually, nonlinearity is provided by the sustaining feedback mechanism, which also supplies energy, whereas the constituent resonator that determines the output frequency stays linear. Here, we propose a new self-sustaining scheme that relies on the nonlinearity originating from the resonator itself to limit the oscillation amplitude, while the feedback remains linear. We introduce a model for describing the working principle of the self-sustained oscillations and validate it with experiments performed on a nonlinear microelectromechanical oscillator.Ítem Acceso Abierto Noise-induced interspike interval correlations and spike train regularization in spike-triggered adapting neurons(Europhysics Letters, 2016-10-27) Urdapilleta, EugenioSpike generation in neurons produces a temporal point process, whose statistics is governed by intrinsic phenomena and the external incoming inputs to be coded. In particular, spike-evoked adaptation currents support a slow temporal process that conditions spiking probability at the present time according to past activity. In this work, we study the statistics of interspike interval correlations arising in such non-renewal spike trains, for a neuron model that reproduces different spike modes in a small adaptation scenario. We found that correlations are stronger as the neuron fires at a particular firing rate, which is defined by the adaptation process. When set in a subthreshold regime, the neuron may sustain this particular firing rate, and thus induce correlations, by noise. Given that, in this regime, interspike intervals are negatively correlated at any lag, this effect surprisingly implies a reduction in the variability of the spike count statistics at a finite noise intensity.Ítem Acceso Abierto Assessing the growth rate of endangered Franciscana dolphin in Argentina, South America(Board, 2020) Caceres, Manuel Osvaldo; Cáceres-Saez, Iris; Secchi, Eduardo R.; Negri, María Fernanda; Panebianco, Maria Victoria; Cappozzo, Humberto LuisCetacean populations are vulnerable to decline due to anthropogenic threats and life history traits. The Franciscana dolphin (Pontoporia blainvillei) has been considered the most affected small dolphin in the Southwestern Atlantic Ocean. In this study a method is presented for estimating the growth rate of the Franciscana dolphin affected by incidental mortality (bycatch) in coastal marine areas of Argentina, South America. We used a general approach based on vital parameters information such as reproductive rates and survival probabilities for an age-structured population. The Franciscana’s growth rate was estimated using Leslie’s approach through an algorithm implemented in a 14 x 14 matrix model. Then, the population was characterized analysing the discrete-time evolution of the age–population vector. We found that the potential growth rate <1 indicates that Franciscanas in Argentina are susceptible to decline under current levels of incidental mortality.Ítem Acceso Abierto Tell me where you live and I'll tell you who you are: Spatial segregation of southern species of Eligmodontia Cuvier in Patagonia, Argentina(Elsevier, 2020) Ruiz Barlett, Trinidad; Martin, Gabriel; Laguna, María Fabiana; Abramson, Guillermo; Monjeau, AdrianEligmodontia morgani y E. typus son dos pequeños (<25 g) roedores sigmodontinos que habitan los ambientes áridos del sur de Argentina. Debido a que las especies son difíciles de distinguir en el campo, su delimitiación geográfica siempre ha sido controvertida. En este trabajo usamos registros donde las especies fueron identificadas por su cariotipo y ADN mitocondrial, y modelamos su distribución potencial usando análisis de máxima entropía. Nuestros resultados muestran una segregación en el nicho entre las especies, mayormente impulsado por la temperatura. Los modelos ecológicos de nicho muestran que E. morgani es un habitante del oeste y centro patagónico correspondientes con la ecorregión de la Estepa Patagónica, mientras E. typus es un habitante de las regiones centrales y el este patagónico, correspondientes con la ecorregión del Monte. En áreas de ecotono, nuestros modelos predicen que E. morgani ocupa las zonas altas y frías de las mesetas, mientras que E. typus ocupa zonas bajas con una matriz de vegetación de la Ecorregión del Monte. Nuestros modelos matemáticos muestran una selección de hábitat de temperaturas medias mínimas de 1 °C y 5 °C para E. morgani y E. typus, respectivamente, y de temperaturas máximas medias de 22 °C y de 27 °C para cada especie.Ítem Acceso Abierto Energy exchange in globally coupled mechanical phase oscillators(American Physical Society, 2020) Sosa, Raúl I.; Zanette, Damian HoracioWe study the stationary dynamics of energy exchange in an ensemble of phase oscillators, coupled through a mean-field mechanical interaction and added with friction and an external periodic excitation. The degree of entrainment between different parts of the ensemble and the external forcing determines three dynamical regimes, each of them characterized by specific rates of energy exchange. Using suitable approximations, we are able to obtain analytical expressions for those rates, which are in satisfactory agreement with results from numerical integration of the equations of motion. In some of the dynamical regimes, the rates of energy exchange show nontrivial dependence on the friction coefficients—in particular, nonmonotonic behavior and sign switching. This suggests that, even in this kind of stylized model, power transfer between different parts of the ensemble and to the environment can be manipulated by a convenient choice of the individual oscillator parameters.