Non-steady relaxation and critical exponents at the depinning transition

We study the non-steady relaxation of a driven one-dimensional elastic interface at the depinning transition by extensive numerical simulations concurrently implemented on graphics processing units (GPUs). We compute the time-dependent velocity and roughness as the interface relaxes from a flat initial configuration at the thermodynamic random-manifold critical force. Above a first, non-universal microscopic time-regime, we find a non-trivial long crossover towards the non-steady macroscopic critical regime. This "mesoscopic" time-regime is robust under changes of the microscopic disorder including its random-bond or random-field character, and can be fairly described as power-law corrections to the asymptotic scaling forms yielding the true critical exponents. In order to avoid fitting effective exponents with a systematic bias we implement a practical criterion of consistency and perform large-scale (L~2^{25}) simulations for the non-steady dynamics of the continuum displacement quenched Edwards Wilkinson equation, getting accurate and consistent depinning exponents for this class: \beta = 0.245 \pm 0.006, z = 1.433 \pm 0.007, \zeta=1.250 \pm 0.005 and \nu=1.333 \pm 0.007. Our study may explain numerical discrepancies (as large as 30% for the velocity exponent \beta) found in the literature. It might also be relevant for the analysis of experimental protocols with driven interfaces keeping a long-term memory of the initial condition.Comment: Published version (including erratum). Codes and Supplemental Material available at https://bitbucket.org/ezeferrero/qe

Alexis de Tocqueville: opinión pública y declinación del discurso revolucionario

El objetivo de este trabajo consiste en reconstruir una visión que aparece fragmentada en su obra: cómo los mecanismos de opinión en las sociedades democráticas debilitarían la propagación de las doctrinas revolucionarias. Entre sus diversas anticipacion

Short time relaxation of a driven elastic string in a random medium

We study numerically the relaxation of a driven elastic string in a two dimensional pinning landscape. The relaxation of the string, initially flat, is governed by a growing length $L(t)$ separating the short steady-state equilibrated lengthscales, from the large lengthscales that keep memory of the initial condition. We find a macroscopic short time regime where relaxation is universal, both above and below the depinning threshold, different from the one expected for standard critical phenomena. Below the threshold, the zero temperature relaxation towards the first pinned configuration provides a novel, experimentally convenient way to access all the critical exponents of the depinning transition independently.Comment: 4.2 pages, 3 figure

Evaluation of the particle geometry and interphase influence on the filler-matrix debonding process

Incorporation of rigid fillers into polymer matrices represents a widely used technique to obtain improved performance. The mechanical behavior finally obtained is closely related to a wide range of involved factors (filler type and size, internal structure, filler-matrix interaction, among others) and to activated dissipative mechanisms (debonding, plastic void growth, crazing, matrix yielding, etc). In this work, a debonding strength approach was applied for rigid particles (spherical, elliptical and fiber) surrounded by an interphase. The effect of interphase mechanical properties and thickness on the debonding process was investigated. The obtained results suggested a significant influence of the transition rigidity. In general, stiffer interphases promoted higher critical strength values. On the other hand, particle surrounded by a softer transition region displayed higher dissipated energy for all examined particle, except for spheres.Fil: Perez, Ezequiel Martin. Instituto Nacional de Tecnología Industrial; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lauke, B.. No especifíca

What makes us conscious is not what makes us human

Consistent with the promising proposal of Klein & Barron (K & B), we discuss how what makes us conscious appears to be distinct from and more widespread in the animal kingdom than what distinguishes us from other species. Many of the abilities that do distinguish humans from other species (e.g., syntax and co-articulation in speech production) can be mediated unconsciously. The kind of functional architecture proposed by K & B may engender an “action selection bottleneck” in both humans and nonhuman species. As noted by K & B, this bottleneck is intimately related to conscious processing

The Effect of Fertiliser Treatment on the Development of Rangelands in Argentina

In Argentina grazing of rangelands may result in a decrease in winter gramineous species with an increase in summer weeds such as Cynodon dactylon. Lolium multiflorum is an important forage resource for grazing in the autumn, winter and spring. A delay in its emergence may occur because of summer weeds, which reduces the germination rate. The proportion of the seed bank as ryegrass allows the recovery of natural grassland and facilitates an increase in the productivity of livestock. The objective of this study was the evaluation of the impact of application of fertiliser in the short term on the relationship with botanical composition at different herbage availabilities

Effect of exogenous proline on physiological and growth traits of melon seedlings under salt stress

Proline is an amino acid that accumulates in plants in response to stress conditions. Exogenous application of proline has been reported to increase stress tolerance. An experiment was conducted to evaluate the effect of different exogenous proline solutions applied to melon seedlings grown under saline stress. Four concentrations of proline were evaluated: 0, 5, 10 and 20 mM. Plants were grown at 8.0 dS m-1 electrical conductivity. Plants treated with 10 and 20 mM proline showed higher proline content as well as increased growth parameters. Chlorophyll content was higher in the 10 mM treatment. The results suggest that exogenous application of 10 and 20 mM proline allows plants to increase salt tolerance response.La prolina es un aminoácido que se acumula en plantas en respuesta a condiciones de estrés. Se ha reportado que la aplicación exógena de prolina aumenta la tolerancia al estrés. Se realizó un experimento para evaluar el efecto de diferentes soluciones de prolina exógena aplicadas a plántulas de melón cultivadas en estrés salino. Se evaluaron cuatro concentraciones de prolina: 0, 5, 10 y 20 mM. Las plantas se cultivaron con una conductividad eléctrica de 8,0 dS m-1. Las plantas tratadas con prolina 10 y 20 mM tuvieron un mayor contenido de prolina así como un aumento de los parámetros de crecimiento. El contenido de clorofila tuvo el valor más alto para el tratamiento 10 mM. Los resultados sugieren que la aplicación exógena de prolina 10 y 20 mM permite aumentar la respuesta de tolerancia al estrés salino.EEA AMBAFil: Castañares, José Luis. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Area Metropolitana de Buenos Aires. Agencia de Extensión Rural Luján; ArgentinaFil: Castañares, José Luis. Universidad Nacional de Luján. Departamento de Ciencias Básicas. Laboratorio de Fisiología Vegetal; ArgentinaFil: Corvalán, B. Universidad Nacional de Luján. Departamento de Ciencias Básicas. Laboratorio de Fisiología Vegetal; ArgentinaFil: Larraburu, Ezequiel. Universidad Nacional de Luján. Departamento de Ciencias Básicas. Laboratorio de Fisiología Vegetal; Argentin

Depinning free of the elastic approximation

We model the isotropic depinning transition of a domain-wall using a two dimensional Ginzburg-Landau scalar field instead of a directed elastic string in a random media. An exact algorithm accurately targets both the critical depinning field and the critical configuration for each sample. For random bond disorder of weak strength $\Delta$, the critical field scales as $\Delta^{4/3}$ in agreement with the predictions for the quenched Edwards-Wilkinson elastic model. However, critical configurations display overhangs beyond a characteristic length $l_{\tt 0} \sim \Delta^{-\alpha}$, with $\alpha\approx 2.2$, indicating a finite-size crossover. At the large scales, overhangs recover the orientational symmetry which is broken by directed elastic interfaces. We obtain quenched Edwards-Wilkinson exponents below $l_{\tt 0}$ and invasion percolation depinning exponents above $l_{\tt 0}$. A full picture of domain wall isotropic depinning in two dimensions is hence proposed.Comment: 8 pages, 8 figure

Evaluating performance of neural codes in neural communication networks

Information needs to be appropriately encoded to be reliably transmitted over a physical media. Similarly, neurons have their own codes to convey information in the brain. Even though it is well-know that neurons exchange information using a pool of several protocols of spatial-temporal encodings, the suitability of each code and their performance as a function of the network parameters and external stimuli is still one of the great mysteries in Neuroscience. This paper sheds light into this problem considering small networks of chemically and electrically coupled Hindmarsh-Rose spiking neurons. We focus on the mathematical fundamental aspects of a class of temporal and firing-rate codes that result from the neurons' action-potentials and phases, and quantify their performance by measuring the Mutual Information Rate, aka the rate of information exchange. A particularly interesting result regards the performance of the codes with respect to the way neurons are connected. We show that pairs of neurons that have the largest rate of information exchange using the interspike interval and firing-rate codes are not adjacent in the network, whereas the spiking-time and phase codes promote large exchange of information rate from adjacent neurons. This result, if possible to extend to larger neural networks, would suggest that small microcircuits of fully connected neurons, also known as cliques, would preferably exchange information using temporal codes (spiking-time and phase codes), whereas on the macroscopic scale, where typically there will be pairs of neurons that are not directly connected due to the brain's sparsity, the most efficient codes would be the firing rate and interspike interval codes, with the latter being closely related to the firing rate code