Ab initio study of low-dimensional metallic systems

In the present Doctoral Thesis we gather all the research performed by the graduate student Jorge Botana Alcalde. Broadly speaking, the work consisted in the study of the structural, electrical and magnetic properties of a spread of low-dimensional systems, made up with transition metals. We can divide said systems in two categories: ultrathin film of iron and chromium, where the two iron layers are sandwiched around a central chromium layer, and atomic clusters, either made of gold or of an alloy of bismuth and manganese. This work was done using ab initio techniques, i.e. from first principles. In our systems that means to solve the non-relativistic Schrödinger equation for a many-electron system. Our approach to such a complex problem was by means of the density functional theory (DFT), which transforms the many-body problem, considering each electron interacting with every one of the other electrons, to a single-body problem, where each electron interacts only with an effective potential created by the electron density. The implementation of this approach for the calculation of our systems was performed using the deMon (density of Montreal) DFT software

Predicting Word Maturity from Frequency and Semantic Diversity: A Computational Study

Semantic word representation changes over different ages of childhood until it reaches its adult form. One method to formally model this change is the word maturity paradigm. This method uses a text sample for each age, including adult age, and transforms the samples into a semantic space by means of Latent Semantic Analysis. The representation of a word at every age is then compared with its adult representation via computational maturity indices. The present study used this paradigm to explore to the impact of word frequency and semantic diversity on maturation indices. To do this, word maturity indices were extracted from a Spanish incremental corpus and validated, using correlation scores with Age of Acquisition and Word Difficulty indices from previous studies. The results show that both frequency and semantic diversity predict word maturity but that the predictive capacity of frequency decreases as exposure to language increases. The latter result is discussed in terms of inductive processes suggested in previous studies

La técnica del Ánalisis de la Semántica Latente (LSA/LSI) como modelo informático de la comprensión del texto y el discurso: una aproximación distribuida al análisis semántico

Programa de doctorado de calidad: comprensión del texto y del discursoTesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Psicología. Departamento de Psicología Social y de Metodología. Fecha de lectura: 10 de diciembre de 2010El formato de esta tesis consiste en una colección de cuatro manuscritos individuales, que han sido recientemente aceptados o enviados para publicación a revistas internacionales de psicología experimental, lingüística o tecnología

Desarrollo de un cliente MQTT para comunicaciones seguras en sistemas embebidos

241 p. -- Bibliogr.: p. 240-241En el presente documento se expone el desarrollo de un cliente MQTT que permite realizar comunicaciones seguras mediante TLS, para ser usado en una aplicación que se ejecute sobre un sistema embebido. La aplicación creada también hace uso de otros protocolos TCP/IP, motivo por el cual se han desarrollado clientes adicionales que también son expuestos en este documento. El documento consta de dos partes. La primera parte es la memoria, y en ella se exponen aquellos aspectos teóricos y prácticos de los que es recomendable tener conocimiento para hacer uso del proyecto de programación creado, escrito en lenguaje C y que se encuentra en la segunda parte, de anexos

Can personality traits be measured analyzing written language? a meta-analytic study on computational methods

In the last two decades, empirical evidence has shown that personality traits could be related to the characteristics of written language. This study describes a meta-analysis that synthesizes 23 independent estimates of the correlations between the Big Five major personality traits, and some computationally obtained indicators from written language. The results show significant combined estimates of the correlations, albeit small to moderate according to Cohen's conventions to interpret effect sizes, for the five traits (between r = 0.26 for agreeableness and neuroticism, and 0.30 for openness). These estimates are moderated by the type of information in the texts, the use of prediction mechanisms, and the source of publication of the primary studies. Generally, the same effective moderators operate for the five traits. It is concluded that written language analyzed through computational methods could be used to extract relevant information of personality. But further research is still needed to consider it as predictive or explanatory tool for individual difference

Density functional study of the magnetic properties of Bi4Mn clusters: Discrepancy between theory and experiment

We have performed collinear and noncollinear calculations on neutral Bi4Mn and collinear ones on ionized Bi4Mn with charges +1 and −1 to find out why theoretical calculations will not predict the magnetic state found in the experiment. We have used the density functional theory to find a fit between the theoretical prediction of the magnetic moment and the experimental value. Our calculations have consisted in a structural search of local energy minima, and the lowest energy magnetic state for each resulting isomer. The geometry optimization found three local minima whose fundamental state is the doublet spin state. These isomers could not be found in previous theoretical works, but they are higher in energy than the lowest-lying isomer by ≈1.75 eV. This magnetic state could help understand the experiment. Calculations of noncollinear magnetic states for the Bi4Mn do not lower the total magnetic moment. We conclude arguing how the three isomers with doublet state could actually be the ones measured in the experimentThis research has been done under the Projects No. MAT2009-08165 and No. INCITE08PXIB236052PR. One of the authors has been enjoying financial support from the Isabel Barreto programS

Quantifying the ideational context: political frames, meaning trajectories and punctuated equilibria in Spanish mainstream press during the Catalan nationalist challenge

This article presents a quantitative method for mapping semantic spaces and tracing political frames’ trajectories, that facilitate the analysis of the connections between changes in ideas and socio-political phenomena. We test our approach in Spain, where the Catalan conflict fostered a competition in terms of decontestation of meanings of key political concepts. Using unsupervised machine learning, we track the salience, level of semantic fragmentation and fluctuations in meanings of 216 frames in the two largest Spanish newspapers, El País and El Mundo, throughout 8 years. This is achieved via the extraction, vectorization, and comparison of over 70,000 words. We apply Latent Semantic Analysis, an innovative methodology for the alignment of semantic spaces, and new institutional theory. Our exploratory study suggests that the evolution of many nationalism-related frames resembles a punctuated equilibrium model, and that political events in Catalonia, acted as critical junctures, altering the meanings reflected in the Spanish press

Electronic structure analysis of the quasi-one-dimensional oxide Sr6Co5O15 within the LDA+U method

The quasi-one-dimensional cobalt oxide Sr6Co5O15 is studied using first-principles electronic-structure calculations and Boltzmann transport theory. We have been able to describe the electronic structure, characterized by the structural one-dimensionality and a particular type of charge ordering, with unexpected electronic structure of the different Co atoms. The origin of the large unquenched misaligned orbital angular momenta comes out naturally from a correct description of the different crystal-field environments. The evolution with the on-site Coulomb repulsion (U) of the electronic structure and the transport properties is discussed, with a best agreement with experiment found for the smallest value of U that allows to converge the correct in-chain ferrimagnetic ground stateThe authors thank the CESGA for the computing facilities, the Ministerio de Educación y Ciencia (MEC) for the financial support through the project MAT2009-08165, the Ministerio de Ciencia e Innovación (MICINN) for the project MAT2007-60536 and the Xunta de Galicia for the project INCITE08PXIB236052PR. A.S.B. thanks MEC for a FPU grant. M.P. and J.B. thank Isabel Barreto program and Deputación da Coruña, respectively, for financial supportS

Electrostatic force driven helium insertion into ammonia and water crystals under pressure

Abstract: Helium, ammonia and ice are among the major components of giant gas planets, and predictions of their chemical structures are therefore crucial in predicting planetary dynamics. Here we demonstrate a strong driving force originating from the alternation of the electrostatic interactions for helium to react with crystals of polar molecules such as ammonia and ice. We show that ammonia and helium can form thermodynamically stable compounds above 45 GPa, while ice and helium can form thermodynamically stable compounds above 300 GPa. The changes in the electrostatic interactions provide the driving force for helium insertion under high pressure, but the mechanism is very different to those that occur in ammonia and ice. This work extends the reactivity of helium into new types of compounds and demonstrates the richness of the chemistry of this most stable element in the periodic table