Chain conditions for Leavitt path algebras

In this paper, results known about the artinian and noetherian conditions for the Leavitt path algebras of graphs with finitely many vertices are extended to all row-finite graphs. In our first main result, necessary and sufficient conditions on a row-finite graph E are given so that the corresponding (not necessarily unital) Leavitt path K-algebra L(E) is semisimple. These are precisely the algebras L(E)for which every corner is left (equivalently, right)artinian. They are also precisely the algebras L(E) for which every finitely generated left (equivalently, right) L(E)-module is artinian. In our second main result, we give necessary and sufficient conditions for every corner of L(E) to be left (equivalently, right) noetherian. They also turn out to be precisely those algebras L(E) for which every finitely generated left(equivalently, right) L(E)-module is noetherian. In both situations, isomorphisms between these algebras and appropriate direct sums of matrix rings over K or K[x, x−1] are provided. Likewise, in both situations, equivalent graph theoretic conditions on E are presented.

Emissions distribution in post-Kyoto international negotiations: a policy

An abundant scientific literature about climate change economics points out that the future participation of developing countries in international environmental policies will depend on their amount of pay offs inside and outside specific agreements. These studies are aimed at analyzing coalitions stability typically through a game theoretical approach. Though these contributions represent a corner stone in the research field investigating future plausible international coalitions and the reasons behind the difficulties incurred over time to implement emissions stabilizing actions, they cannot disentangle satisfactorily the role that equality play in inducing poor regions to tackle global warming. If we focus on the Stern Review findings stressing that climate change will generate heavy damages and policy actions will be costly in a finite time horizon, we understand why there is a great incentive to free ride in order to exploit benefits from emissions reduction efforts of others. The reluctance of poor countries in joining international agreements is mainly supported by historical responsibility of rich regions in generating atmospheric carbon concentration, whereas rich countries claim that emissions stabilizing policies will be effective only when developing countries will join them.Scholars recently outline that a perceived fairness in the distribution of emissions would facilitate a wide spread participation in international agreements. In this paper we overview the literature about distributional aspects of emissions by focusing on those contributions investigating past trends of emissions distribution through empirical data and future trajectories through simulations obtained by integrated assessment models. We will explain methodologies used to elaborate data and the link between real data and those coming from simulations. Results from this strand of research will be interpreted in order to discuss future negotiations for post Kyoto agreements that will be the focus of the next. Conference of the Parties in Copenhagen at the end of 2009. A particular attention will be devoted to the role that technological change will play in affecting the distribution of emissions over time and to how spillovers and experience diffusion could influence equality issues and future outcomes of policy negotiations.

Desenvolupament de codis numèrics per a la resolució de fluxos turbulents en ordinadors paral·lels emprant discretitzacions tipus symmetry-preserving

Projecte de recerca elaborat a partir d’una estada a la University of Groningen, Holanda, entre 2007 i 2009. La simulació directa de la turbulència (DNS) és una eina clau dins de la mecànica de fluids computacional. Per una banda permet conèixer millor la física de la turbulència i per l'altra els resultats obtinguts són claus per el desenvolupament dels models de turbulència. No obstant, el DNS no és una tècnica vàlida per a la gran majoria d'aplicacions industrials degut al elevats costos computacionals. Per tant, és necessari cert grau de modelització de la turbulència. En aquest context, s'han introduïts importants millores basades en la modelització del terme convectiu (no lineal) emprant symmetry-preserving regularizations. En tracta de modificar adequadament el terme convectiu a fi de reduir la producció d'escales més i més petites (vortex-stretching) tot mantenint tots els invariants de les equacions originals. Fins ara, aquest models s'han emprat amb èxit per nombres de Rayleigh (Ra) relativament elevats. En aquest punt, disposar de resultats DNS per a configuracions més complexes i nombres de Ra més elevats és clau. En aquest contexte, s'han dut a terme simulacions DNS en el supercomputador MareNostrum d'una Differentially Heated Cavity amb Ra=1e11 i Pr=0.71 durant el primer any dels dos que consta el projecte. A més a més, s'ha adaptat el codi a fi de poder simular el fluxe al voltant d'un cub sobre una pared amb Re=10000. Aquestes simulacions DNS són les més grans fetes fins ara per aquestes configuracions i la seva correcta modelització és un gran repte degut la complexitat dels fluxes. Aquestes noves simulacions DNS estan aportant nous coneixements a la física de la turbulència i aportant resultats indispensables per al progrés de les modelitzacións tipus symmetry-preserving regularization.

On concentrators and related approximation constants

Pippenger [Pi77] showed the existence of (6m,4m,3m,6)-concentrator for each positive integer m using a probabilistic method. We generalize his approach and prove existence of (6m,4m,3m,5.05)-concentrator (which is no longer regular, but has fewer edges). We apply this result to improve the constant of approximation of almost additive set functions by additive set functions from 44.5 (established by Kalton and Roberts in [KaRo83] to 39. We show a more direct connection of the latter problem to the Whitney type estimate for approximation of continuous functions on a cube in &b&R&/b&&sup&d&/sup& by linear functions, and improve the estimate of this Whitney constant from 802 (proved by Brudnyi and Kalton in [BrKa00] to 73.

Testing the response of macroinvertebrate functional structure and biodiversity to flooding and confinement

The aim of the present study was to investigate the relative importance of flooding- and confinement-related environmentalfeatures in explaining macroinvertebrate trait structure and diversity in a pool of wetlands located in a Mediterranean riverfloodplain. To test hypothesized trait-environment relationships, we employed a recently implemented statistical procedure, thefourth-corner method. We found that flooding-related variables, mainly pH and turbidity, were related to traits that confer an abilityof the organism to resist flooding (e.g., small body-shape, protection of eggs) or recuperate faster after flooding (e.g., short life-span, asexual reproduction). In contrast, confinement-related variables, mainly temperature and organic matter, enhanced traits that allow organisms to interact and compete with other organisms (e.g., large size, sexual reproduction) and to efficiently use habitat and resources (e.g., diverse locomotion and feeding strategies). These results are in agreement with predictions made under the River Habitat Templet for lotic ecosystems, and demonstrate the ability of the fourth-corner method to test hypothesis that posit traitenvironment relationships. Trait diversity was slightly higher in flooded than in confined sites, whereas trait richness was not significantly different. This suggests that although trait structure may change in response to the main environmental factors, as evidenced by the fourth-corner method, the number of life-history strategies needed to persist in the face of such constraints remains more or less constant; only their relative dominance differs

A note on the coincidence between Stackelberg and Nash equilibria in a differential game between government and firms

[cat] A Navas i Marín Solano es va demostrar la coincidència entre els equilibris de Nash i de Stackelberg per a una versi´o modificada del joc diferencial proposat por Lancaster (1973). Amb l’objectiu d’obtenir una solució interior, es van imposar restriccions importants sobre el valors dels paràmetres del model. En aquest treball estenem aquest resultat, en el límit en que la taxa de descompte és igual a zero, eliminant les restriccions i considerant totes les solucions possibles.

Slow Dynamics of Ising Models with Energy Barriers

Using Monte Carlo simulations we study the dynamics of three-dimensional Ising models with nearest-, next-nearest-, and four-spin (plaquette) interactions. During coarsening, such models develop growing energy barriers, which leads to very slow dynamics at low temperature. As already reported, the model with only the plaquette interaction exhibits some of the features characteristic of ordinary glasses: strong metastability of the supercooled liquid, a weak increase of the characteristic length under cooling, stretched-exponential relaxation, and aging. The addition of two-spin interactions, in general, destroys such behavior: the liquid phase loses metastability and the slow-dynamics regime terminates well below the melting transition, which is presumably related with a certain corner-rounding transition. However, for a particular choice of interaction constants, when the ground state is strongly degenerate, our simulations suggest that the slow-dynamics regime extends up to the melting transition. The analysis of these models leads us to the conjecture that in the four-spin Ising model domain walls lose their tension at the glassy transition and that they are basically tensionless in the glassy phase.

A note on the coincidence between Stackelberg and Nash equilibria in a differential game between government and firms

[cat] A Navas i Marín Solano es va demostrar la coincidència entre els equilibris de Nash i de Stackelberg per a una versi´o modificada del joc diferencial proposat por Lancaster (1973). Amb l’objectiu d’obtenir una solució interior, es van imposar restriccions importants sobre el valors dels paràmetres del model. En aquest treball estenem aquest resultat, en el límit en que la taxa de descompte és igual a zero, eliminant les restriccions i considerant totes les solucions possibles.

Efectivitat dels diferents tipus de colpeig a pilota aturada en el futbol platja

El propòsit d’aquest estudi és analitzar quin és l’índex d’efectivitat en diferents situacions a pilota aturada (penals, faltes sense barrera i córners) en el futbol platja dins el context d’equips amateurs que participen en els tornejos de Blanes i Tossa de Mar. A l’hora de realitzar-lo he tingut en compte una sèrie de variables, com ara la precisió del colpeig, el tipus de colpeig, la superfície de contacte o la situació inicial de la pilota, és a dir, des d’on provenia la trajectòria inicial d’ aquesta, tot comprovant també com canvien els resultats en funció de la zona i del costat que es realitza el remat. Respecte els resultats, aquests demostren que l’índex d’efectivitat en aquest tipus d’accions és més baix en relació amb altres esports semblants com el futbol i el futbol sala.

La importància de les accions a pilota aturada en el futbol professional

L’objectiu del present estudi va consistir en estudiar el percentatge de gols a pilota aturada de la Lliga BBVA i la Premier League, establint el percentatge d’efectivitat de cadascuna d’elles. A més, es volia analitzar la freqüència de les diferents tipus d’accions a pilota aturada i substituir el terme estratègia per accions a pilota aturada. Amb aquest objectiu es van analitzar 80 partits disputats per equips de futbol professional en la temporada 2012-13 de la Lliga BBVA i la Premier League mitjançant l’anàlisi de vídeos. Les variable dependent era la consecució o no del gol, tenint com a variables independents 4 tipus d’accions a pilota aturada: tirs lliures directes, tirs lliures indirectes, córners i penals. Els resultats indiquen un major número de gols provinents d’accions a pilota aturada en la Lliga BBVA que en la Premier League, 29,8% per un 23,4% respectivament. Tot i això, s’ha comprovat com els percentatges d’efectivitat són pràcticament idèntics: 4,54% a la Lliga BBVA i 4,58% a la Premier League. Finalment, s’ha identificat el córner com l’acció que més es produeix en el joc, seguit de les faltes directes, els penals i les faltes indirectes.

Les lletres de confegir: l’atenció a la diversitat en el procés d’aprenentatge de la lectoescriptura

L’aprenentatge de la lectoescriptura és complex. Aprendre a llegir i escriure implica dominar moltes habilitats. A l’escola habitualment es treballa de forma mecànica i poc significativa. L’objectiu d’aquest projecte és conèixer si les lletres de confegir de Maria Montessori encara tenen vigència en l’actualitat. En aquest sentit, s’ha valorat el racó on hi ha aquest material, ja existent a l’escola, per posteriorment fer una proposta de millora i desenvolupar-la dins el marc d’una aula de P5. A través d’algunes situacions reals d’aula volem il·lustrar les possibilitats de la nostra proposta. L’experiència realitzada amb infants de l’últim curs d’Educació Infantil indica que treballar el procés de lectoescriptura amb aquest material és una bona eina per atendre a la diversitat existent a les aules actuals.

Análisis de la eficacia de los saques de esquina en la copa del mundo de fútbol 2010. Un intento de identificación de variables explicativas

In soccer, dead-ball moves are those in which the ball is returned to play from a stationary position following an interruption of play. The aim of this study was to analyse the effectiveness of one such dead-ball move, namely corner kicks, and to identify the key variables that determine the success of a shot or header following a corner, thereby enabling a model of successful corner kicks to be proposed. We recorded 554 corner kicks performed during the 2010 World Cup in South Africa and carried out a univariate, bivariate and multivariate analysis of the data. The results indicated that corners were of limited effectiveness in terms of the success of subsequent shots or headers. The analysis also revealed a series of variables that were significantly related to one another, and this enabled us to propose an explanatory model. Although this model had limited explanatory power, it nonetheless helps to understand the execution of corner kicks in practical terms.