FCEN

Buenos Aires, Argentina
Buenos Aires, Argentina
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Medeiros B.N.S.,Federal University of Pernambuco | Minces V.,University of California at San Diego | Mindlin G.B.,FCEN | Copelli M.,Federal University of Pernambuco | Leite J.R.R.,Federal University of Pernambuco
International Journal of Bifurcation and Chaos | Year: 2012

An electronic circuit device, inspired on the FitzHughNagumo model of neuronal excitability, was constructed and shown to operate with characteristics compatible with those of biological sensory neurons. The nonlinear dynamical model of the electronics quantitatively reproduces the experimental observations on the circuit, including the Hopf bifurcation at the onset of tonic spiking. Moreover, we have implemented an analog noise generator as a source to study the variability of the spike trains. When the circuit is in the excitable regime, coherence resonance is observed. At sufficiently low noise intensity the spike trains have Poisson statistics, as in many biological neurons. The transfer function of the stochastic spike trains has a dynamic range of 6 dB, close to experimental values for real olfactory receptor neurons. © 2012 World Scientific Publishing Company.


Camjayi A.,FCEN | Acha C.,FCEN | Weht R.,Comision Nacional de la Energia Atomica | Weht R.,National University of San Martín of Argentina | And 5 more authors.
Physical Review Letters | Year: 2014

The nature of the Mott transition in the absence of any symmetry breaking remains a matter of debate. We study the correlation-driven insulator-to-metal transition in the prototypical 3D Mott system GaTa4Se8, as a function of temperature and applied pressure. We report novel experiments on single crystals, which demonstrate that the transition is of first order and follows from the coexistence of two states, one insulating and one metallic, that we toggle with a small bias current. We provide support for our findings by contrasting the experimental data with calculations that combine local density approximation with dynamical mean-field theory, which are in very good agreement. © 2014 American Physical Society.


Caputo M.C.,FCEN | Provasi P.F.,Northeastern University | Benitez L.,Northeastern University | Georg H.C.,Federal University of Goais | And 2 more authors.
Journal of Physical Chemistry A | Year: 2014

A theoretical study of magnetic properties of hydrogen peroxide in water has been carried out by means of Monte Carlo simulation and quantum mechanics calculations. The solvent effects were evaluated in supermolecular structures generated by simulations in the NPT ensemble. The solute-solvent structure was analyzed in terms of radial distribution functions, and the solute-solvent hydrogen bonds were identified with geometric and energetic criteria. Approximately three water molecules are hydrogen bonded to H2O 2 (0.6 and 0.8 in each hydrogen and oxygen atom, respectively, of the H2O2). Although, on average, both hydroxyls of the peroxide are equivalent, the distribution of hydrogen-bonded water molecules is highly asymmetric. Analyzing the statistics of the hydrogen bonds, we identify that only 34% of the configurations give symmetric distributions around the two hydroxyls of the H2O2 simultaneously. The magnetic shieldings and the indirect spin-spin coupling constants were calculated at the B3LYP/aug-cc-pVTZ and aug-cc-pVTZ-J computational level. We find that the solvent shields the oxygen and unshields the hydrogen atoms of the peroxide (+5.5 and -2.9 ppm, respectively), with large fluctuation from configuration to configuration in the oxygen case, an effect largely accounted for in terms of a single hydrogen bond with H2O2 as the proton donor. The most sensitive coupling in the presence of the solvent is observed to be the one-bond J(O,H). © 2014 American Chemical Society.


Pazos P.J.,FCEN | Pazos P.J.,CONICET | Rapalini A.,FCEN | Rapalini A.,CONICET
Geological Society Memoir | Year: 2011

In the Ediacaran-Cambrian Tandilia System of central Argentina, the glacial origin of the thin (10 m) Sierra del Volcán Formation (Fm.) has been recognized for many years (Spalletti & del Valle 1984), being the first undisputed glacial deposits recorded in the Río de la Plata craton. It consists of three units: (i) a basal polymictic diamictite with a kaolin-rich matrix, (ii) a middle pelite with heterolithic levels, undulatory stratification, symmetric ripples, and outsized clasts previously interpreted as dropstones, and (iii) an upper polymictic diamictite with subtle normal grading. Here, this poorly age-constrained formation is reviewed from a stratigraphic and regional context and compared with other putative glaciogenic intervals at the base of the Cerro Largo Fm. and in the Punta Mogotes borehole. © The Geological Society of London 2011.


Intronati G.A.,FCEN | Intronati G.A.,CNRS Institute of Genetics and of Molecular and Cellular Biology | Intronati G.A.,CEA Saclay Nuclear Research Center | Tamborenea P.I.,FCEN | And 3 more authors.
Physica B: Condensed Matter | Year: 2012

We study numerically the effects of an extrinsic spin-orbit interaction on the model of electrons in n-doped semiconductors of Matsubara and Toyozawa (MT). We focus on the analysis of the density of states (DOS) and the inverse participation ratio (IPR) of the spin-orbit perturbed states in the MT set of energy eigenstates in order to characterize the eigenstates with respect to their extended or localized nature. The finite sizes that we are able to consider necessitate an enhancement of the spin-orbit coupling strength in order to obtain a meaningful perturbation. The IPR and DOS are then studied as a function of the enhancement parameter. © 2012 Elsevier B.V.


Delle Donne D.,FCEN | Delle Donne D.,National University of General Sarmiento | Marenco J.,FCEN | Marenco J.,National University of General Sarmiento
Discrete Optimization | Year: 2011

In this work we study a particular way of dealing with interference in combinatorial optimization models representing wireless communication networks. In a typical wireless network, co-channel interference occurs whenever two overlapping antennas use the same frequency channel, and a less critical interference is generated whenever two overlapping antennas use adjacent channels. This motivates the formulation of the minimum-adjacency vertex coloring problem which, given an interference graph G representing the potential interference between the antennas and a set of prespecified colors/channels, asks for a vertex coloring of G minimizing the number of edges receiving adjacent colors. We propose an integer programming model for this problem and present three families of facet-inducing valid inequalities. Based on these results, we implement a branch-and-cut algorithm for this problem, and we provide promising computational results. © 2011 Elsevier B.V. All rights reserved.


Heas P.,French Institute for Research in Computer Science and Automation | Herzet C.,French Institute for Research in Computer Science and Automation | Memin E.,French Institute for Research in Computer Science and Automation | Heitz D.,IRSTEA | And 2 more authors.
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2013

Based on physical laws describing the multiscale structure of turbulent flows, this paper proposes a regularizer for fluid motion estimation from an image sequence. Regularization is achieved by imposing some scale invariance property between histograms of motion increments computed at different scales. By reformulating this problem from a Bayesian perspective, an algorithm is proposed to jointly estimate motion, regularization hyperparameters, and to select the most likely physical prior among a set of models. Hyperparameter and model inference are conducted by posterior maximization, obtained by marginalizing out non-Gaussian motion variables. The Bayesian estimator is assessed on several image sequences depicting synthetic and real turbulent fluid flows. Results obtained with the proposed approach exceed the state-of-the-art results in fluid flow estimation. © 2013 IEEE.


Sitt J.D.,FCEN | Arneodo E.M.,FCEN | Goller F.,University of Utah | Mindlin G.B.,FCEN
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

In this work, we build an electronic syrinx, i.e., a programmable electronic device capable of integrating biomechanical model equations for the avian vocal organ in order to synthesize song. This vocal prosthesis is controlled by the bird's neural instructions to respiratory and the syringeal motor systems, thus opening great potential for studying motor control and its modification by sensory feedback mechanisms. Furthermore, a well-functioning subject-controlled vocal prosthesis can lay the foundation for similar devices in humans and thus provide directly health-related data and procedures. © 2010 The American Physical Society.


Moreira D.,CONICET | Simionato C.G.,CONICET | Dragani W.,FCEN | Dragani W.,CONICET
Journal of Coastal Research | Year: 2011

During the last decade, global tidal models have spectacularly improved. However, they still have difficulties in resolving tides over continental shelves and near coastlines. This study of tidal propagation from the continental shelf to the North Patagonia Gulfs of Argentina applies a set of three nested high resolution models based on the Hamburg shelf ocean model (HamSOM), where particular attention was paid to the bathymetry and the coast line. The study is complemented by the use of all the tidal gauge and tidal current observations available. Simulations display good agreement with observations, permitting the construction of higher resolution and more reliable cotidal and corange charts. The tidal regime in the area is essentially semidiurnal and dominated by M2. This constituent propagates northward as a Kelvin wave and reaches the gulfs from the south. In their interior an important amplification is observed. Tidal currents are large at the mouths of the gulfs, and weaken toward their interior. The nonlinear transfer of energy from the semidiurnal to higher order harmonics was analyzed. This can be very important in the interior of the gulfs, particularly in Nuevo Gulf and in the northwestern San Matías Gulf, close to San Antonio. Energy flux and energy dissipation by bottom friction has been computed and indicate that this region dissipates 17% of the total energy dissipated on the Patagonian Shelf which, in turn, is one of the most dissipative areas of the world ocean. The Simpson-Hunter parameter computed from the simulations shows that in the mouth of the gulfs, particularly in San Matías and east of the Península de Valdés, the tides are energetic enough to overcome stratification and produce tidal fronts. The locations where tidal fronts are located are highly consistent with results from sea surface temperature and primary productivity data analyzed by other authors. © Coastal Education & Research Foundation 2011.

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