Analysis of the quasi-nonlocal approximation of linear and circular chains in the plane

We give an analysis of the stability and displacement error for linear and circular atomistic chains in the plane when the atomistic energy is approximated by the Cauchy-Born continuum energy and by the quasi-nonlocal atomistic-to-continuum coupling energy. We consider atomistic energies that include Lennard-Jones type nearest neighbor and next nearest neighbor pair-potential interactions. Previous analyses for linear chains have shown that the Cauchy-Born and quasi-nonlocal approximations reproduce (up to the order of the lattice spacing) the atomistic lattice stability for perturbations that are constrained to the line of the chain. However, we show that the Cauchy-Born and quasi-nonlocal approximations give a finite increase for the lattice stability of a linear or circular chain under compression when general perturbations in the plane are allowed. We also analyze the increase of the lattice stability under compression when pair-potential energies are augmented by bond-angle energies. Our estimates of the largest strain for lattice stability (the critical strain) are sharp (exact up to the order of the lattice scale). We then use these stability estimates and modeling error estimates for the linearized Cauchy-Born and quasi-nonlocal energies to give an optimal order (in the lattice scale) {\em a priori} error analysis for the approximation of the atomistic strain in $\ell^2_\epsilon$ due to an external force.Comment: 27 pages, 0 figure

The analysis of split graphs in social networks based on the K-Cardinality assignment problem

In terms of social networks, split graphs correspond to the variety of interpersonal and intergroup relations. In this paper we analyse the interaction between the cliques (socially strong and trusty groups) and the independent sets (fragmented and non-connected groups of people) as the basic components of any split graph. Based on the Semi-Lagrangean relaxation for the kcardinality assignment problem, we show the way of minimizing the socially risky interactions between the cliques and the independent sets within the social network

Food Insecurity In Countries With Low Development: New Trends.

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Modelling first and second language acquisition and processing with temporal self-organizing maps

Starting from the evidence provided by researchers at ComPhys Lab of the Institute for Computational Linguistics, Italian National Research Council (Pisa, ILC-CNR), the main goal of my thesis was to extend the application of computational modelling of language acquisition in monolingual and bilingual contexts to Spanish, which has not yet been treated within the given research framework. For the first step, I briefly outlined some of the most prominent psycholinguistic approaches to the study of language acquisition. Secondly, three major models of morphological processing has been presented. For instance, three models of lexical representation and processing has been explained, following the classification proposed by Bybee (1995), i.e. dual-processing model, connectionist model, and network model. The difference between these three models lies in whether they make a distinction between regular and irregular verbs and their processing models, and whether or not the type/token frequency of verbal morphological patterns plays any role at all. The experimental part of this study was focussed on the first and second language acquisition of Spanish verbs, contrasted with parallel datasets in the Italian and German languages. In order to compile the dataset, I extracted the 50 most frequent verb paradigms from European Spanish Web Corpus (2011), available in Sketch Engine, for a total of 750 inflected forms (corresponding to the forms of the infinitive, present, and past participle, singular and plural simple present, singular and plural simple past). The frequency distribution was provided for each inflected form. For an analysis and evaluation of the emergent organization of paradigmatic relations, I annotated each form with morpho-syntactic information (i.e. stem and affix length, paradigmatic cell, formal (ir)regularity, paradigm). Specific difficulties arose during the segmentation of Spanish verbs, due to the peculiarities of some irregular patterns. The computational modelling and processing of Spanish verbs forms has been simulated with Temporal Self-Organizing Maps (TSOMs), based on Kohonen¿s Self-Organizing Maps (2001), augmented with a temporal layer. Basically, this computational model reproduces dynamics of lexical learning and processing by imitating the emergence of neural self-organization, through the incremental adaptation of topologically and temporally aligned synaptic connections. I concluded that an adaptive self-organization during learning is conducive to the emergence of relations between word forms, which are stored in the mental lexicon in a concurrent and competitive dynamic. In particular, in a bilingual perspective, monitoring the acquisitional trajectories of more than one lexica (in both L1+L2 and L1/L1 contexts) showed how recycled memory resources and weaker connections affect L2 acquisition and processing, with a smaller specialization for context-specific input chunks, depending on the exposure conditions.El principal objetivo de la tesis es ampliar la aplicación del modelado computacional de la adquisición del lenguaje en contextos monolingües y bilingües del español, que todavía no ha sido tratado dentro del marco de investigación dado, a partir de las pruebas aportadas por los investigadores del ComPhys Lab del Instituto de Lingüística Computacional, Consejo Nacional Italiano de Investigación (Pisa, ILC-CNR). En primer lugar, resumimos brevemente algunos de los enfoques psicolingüísticos más destacados para el estudio de la adquisición del lenguaje. En segundo lugar, presentamos los tres modelos principales de procesamiento morfológico. Por ejemplo, se han explicado tres modelos de representación y procesamiento léxico, siguiendo la clasificación propuesta por Bybee (1995), es decir, el modelo de procesamiento dual, el modelo conexionista y el modelo de red. La diferencia entre estos tres modelos radica en si hacen una distinción entre verbos regulares e irregulares y sus modelos de procesamiento, y si la frecuencia tipo/caso de los patrones morfológicos verbales representan alguna función. La parte experimental del estudio se centró en la adquisición de la primera y segunda lengua en los verbos en español, en contraste con el conjunto de datos paralelos en italiano y alemán. Para compilar los datos, extrajimos los 50 paradigmas verbales más frecuentes del European Spanish Web Corpus (2011), disponible en Sketch Engine, de un total de 750 formas flexionadas (correspondientes a las formas del infinitivo, presente y participio pasado, singular y plural del presente simple, singular y plural de pasado simple). Se proporcionó la distribución de la frecuencia para cada forma flexionada. Para un análisis y evaluación de la organización emergente de las relaciones paradigmáticas, anotamos cada forma con información morfo-sintáctica (es decir, longitud de raíz y afijo, elemento paradigmático, (ir) regularidad formal, paradigma). Surgieron dificultades específicas durante la segmentación de los verbos en español, debido a las particularidades de algunos patrones irregulares. El modelo computacional y el proceso de las formas verbales españolas ha sido simulado con Temporal Self-Organizing Maps (TSOMs), basado en Kohonen¿s Self-Organizing Maps (2001), mejorado con una capa temporal. Básicamente, este modelo computacional reproduce las dinámicas de aprendizaje y procesamiento léxico imitando la aparición del auto organización neural, a través de la adaptación incremental de conexiones sinápticas alineadas topológica y temporalmente. Podemos concluir que una auto-organización adaptativa durante el aprendizaje conduce a la aparición de las relaciones entre las formas de las palabras, que se almacenan en el léxico mental en una dinámica concurrente y competitiva. En particular, en una perspectiva bilingüe, el monitoreo de las trayectorias de adquisición de más de una unidad léxica (en ambos contextos L1+L2 y L1/L1) mostró cómo los recursos de memoria reciclados y las conexiones más débiles afectan la adquisición y procesamiento de L2, con una especialización menor para los fragmentos de entradas específicos del contexto, dependiendo de las condiciones de exposición.Belik, P. (2017). Modelación computacional del aprendizaje y procesamiento de primera y segunda lengua con los mapas temporales auto-organizados. http://hdl.handle.net/10251/86383TFG

Food insecurity in countries with low development : new trends

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Accelerating random walks by disorder

We investigate the dynamic impact of heterogeneous environments on superdiffusive random walks known as L\'evy flights. We devote particular attention to the relative weight of source and target locations on the rates for spatial displacements of the random walk. Unlike ordinary random walks which are slowed down for all values of the relative weight of source and target, non-local superdiffusive processes show distinct regimes of attenuation and acceleration for increased source and target weight, respectively. Consequently, spatial inhomogeneities can facilitate the spread of superdiffusive processes, in contrast to common belief that external disorder generally slows down stochastic processes. Our results are based on a novel type of fractional Fokker-Planck equation which we investigate numerically and by perturbation theory for weak disorder.Comment: 8 pages, 5 figure

Discovery of blue companions to two southern Cepheids: WW Car and FN Vel

A large number of high-dispersion spectra of classical Cepheids were obtained in the region of the CaII H+K spectral lines. The analysis of these spectra allowed us to detect the presence of a strong Balmer line, H$\epsilon$, for several Cepheids, interpreted as the signature of a blue companion: the presence of a sufficiently bright blue companion to the Cepheid results in a discernible strengthening of the CaII H + Hepsilon line relative to the CaII K line. We investigated 103 Cepheids, including those with known hot companions (B5-B6 main-sequence stars) in order to test the method. We could confirm the presence of a companion to WW Car and FN Vel (the existence of the former was only suspected before) and we found that these companions are blue hot stars. The method remains efficient when the orbital velocity changes in a binary system cannot be revealed and other methods of binarity detection are not efficient.Comment: 6 pages, 5 figures, 4 tables, published on MNRAS in March 201