Rigorous derivation of a nonlinear diffusion equation as fast-reaction limit of a continuous coagulation-fragmentation model with diffusion

Weak solutions of the spatially inhomogeneous (diffusive) Aizenmann-Bak model of coagulation-breakup within a bounded domain with homogeneous Neumann boundary conditions are shown to converge, in the fast reaction limit, towards local equilibria determined by their mass. Moreover, this mass is the solution of a nonlinear diffusion equation whose nonlinearity depends on the (size-dependent) diffusion coefficient. Initial data are assumed to have integrable zero order moment and square integrable first order moment in size, and finite entropy. In contrast to our previous result [CDF2], we are able to show the convergence without assuming uniform bounds from above and below on the number density of clusters.

Monopolistic competition and different wage setting systems

In this paper we match the static disequilibrium unemployment model without frictions in the labor market and monopolistic competition with an infinite horizon model of growth. We compare the wages set at the firm, sector and national (centralized) levels, their unemployment rates and growth of the economic variables, for the Cobb-Douglas production function, in order to see under wich conditions the inverse U hypothesis between unemployment and centralization of wage bargain is confirmed. We also analyze, in the three wage setting systems, the effect of an increase in the monopoly power on employment and growth.

L'impacte dels sistemes multinivell en els sistemes de partits

Imaginemos que un observador quiere analizar el sistema político de los países de Europa Occidental. Si compara el sistema de partidos que hay a nivel nacional con los presentes en cada uno de los distritos de esta elección, apreciará notables diferencias entre países. Por ejemplo, si repara en Alemania, verá como los mismos cinco partidos presentes en el Bundestag compiten también en todos los distritos. Si por otra parte se fija en España, comprobará como en las Elecciones Generales españolas algunos partidos se presentan en todas las circunscripciones pero otros sólo lo hacen en una o en un puñado de ellas. Por lo tanto, mientras que en el primer caso tenemos que el sistema político nacional se reproduce de manera idéntica en cada distrito, en el segundo hay diferencias entre los partidos a nivel nacional y los presentes en determinados distritos. ¿Por qué existen estas divergencias? ¿Qué es lo que explica que esta situación sea estática o que cambie a lo largo del tiempo? En este anexo presento una memoria para justificar los principales avances en la investigación doctoral durante el periodo en que he disfrutado de la beca FI.

A geometric mechanism of diffusion: Rigorous verification in a priori unstable Hamiltonian systems

In this paper we consider a representative a priori unstable Hamiltonian system with 2+1/2 degrees of freedom, to which we apply the geometric mechanism for diffusion introduced in the paper Delshams et al., Mem.Amer.Math. Soc. 2006, and generalized in Delshams and Huguet, Nonlinearity 2009, and provide explicit, concrete and easily verifiable conditions for the existence of diffusing orbits. The simplification of the hypotheses allows us to perform explicitly the computations along the proof, which contribute to present in an easily understandable way the geometric mechanism of diffusion. In particular, we fully describe the construction of the scattering map and the combination of two types of dynamics on a normally hyperbolic invariant manifold.

Public and private learning from prices, strategic substitutability and complementarity, and equilibrium multiplicity

We study a general static noisy rational expectations model where investors have private information about asset payoffs, with common and private components, and about their own exposure to an aggregate risk factor, and derive conditions for existence and uniqueness (or multiplicity) of equilibria. We find that a main driver of the characterization of equilibria is whether the actions of investors are strategic substitutes or complements. This latter property in turn is driven by the strength of a private learning channel from prices, arising from the multidimensional sources of asymmetric information, in relation to the usual public learning channel. When the private learning channel is strong (weak) in relation to the public we have strong (weak) strategic complementarity in actions and potentially multiple (unique) equilibria. The results enable a precise characterization of whether information acquisition decisions are strategic substitutes or complements. We find that the strategic substitutability in information acquisition result obtained in Grossman and Stiglitz (1980) is robust. JEL Classification: D82, D83, G14 Keywords: Rational expectations equilibrium, asymmetric information, risk exposure, hedging, supply information, information acquisition.

Growth in a Cross-Section of Cities: Location, Increasing Returns or Random Growth?

This article analyzes empirically the main existing theories on income and population city growth: increasing returns to scale, locational fundamentals and random growth. To do this we implement a threshold nonlinearity test that extends standard linear growth regression models to a dataset on urban, climatological and macroeconomic variables on 1,175 U.S. cities. Our analysis reveals the existence of increasing returns when per-capita income levels are beyond $19; 264. Despite this, income growth is mostly explained by social and locational fundamentals. Population growth also exhibits two distinct equilibria determined by a threshold value of 116,300 inhabitants beyond which city population grows at a higher rate. Income and population growth do not go hand in hand, implying an optimal level of population beyond which income growth stagnates or deteriorates

Estudi d'eines CASE que suporten OCLper a la generació automàtica de codi Java

Es tracta d'una recerca d'eines CASEque actualment suporten OCL en la generació automàtica de codi Java per estudiar-les ianalitzar-les a través d'un model de proves consistent en un diagrama de classes del modelestàtic de l'UML i una mostra variada d'instruccions OCL, amb l'objectiu de detectar lesseves mancances, analitzant el codi obtingut i determinar si controla o no cada tipus derestricció, i si s'han implementat bé en el codi.

Comparación de analizadores estáticos para código java

El objetivo principal de este artículo es la selección y comparación de dos herramientas de análisis estático para java, esta tarea necesita de estudiar previamente el estado del arte de estos analizadores, ver qué características son deseables para este tipo de analizadores y finalmente compararlas en ejecución sobre los dos proyectos de software libre elegidos argoUML y openProj. Se compara FindBugs con PMD, dos analizadores que pueden utilizarse con la versión 1.6. de JDK. Los resultados de la comparación nos permiten deducir que los analizadores se complementan en cuanto a bugs detectados, hay pocos solapamientos. Como conclusiones podemos decir que la búsqueda de bugs necesita de más de una herramienta de análisis estático.

An Ontology for Open Rubric Exchange on the Web

While the Internet has given educators access to a steady supply of Open Educational Resources, the educational rubrics commonly shared on the Web are generally in the form of static, non-semantic presentational documents or in the proprietary data structures of commercial content and learning management systems.With the advent of Semantic Web Standards, producers of online resources have a new framework to support the open exchange of software-readable datasets. Despite these advances, the state of the art of digital representation of rubrics as sharable documents has not progressed.This paper proposes an ontological model for digital rubrics. This model is built upon the Semantic Web Standards of the World Wide Web Consortium (W3C), principally the Resource Description Framework (RDF) and Web Ontology Language (OWL).

DinaWEB : l'organització de recursos accessibles en línia a la Biblioteca Virtual de la Universitat Oberta de Catalunya

El DinaWEB (Dinàmic WEB), és una base de dades desenvolupada per la Universitat Oberta de Catalunya, que té com a objectiu organitzar la informació i els recursos disponibles a la Biblioteca Virtual de la UOC de forma àgil per els usuaris i que permet a l'administrador l'actualització i modificació d'aquests recursos de forma més amigable que fins l'actualitat. La seva funció és substituir les pàgines estàtiques de la intranet de la Biblioteca Virtual de la UOC, per pàgines dinàmiques, generades automàticament per aquesta base de dades.

Dam wall detection and tracking using a Mechanically Scanned Imaging Sonar

In dam inspection tasks, an underwater robot has to grab images while surveying the wall meanwhile maintaining a certain distance and relative orientation. This paper proposes the use of an MSIS (mechanically scanned imaging sonar) for relative positioning of a robot with respect to the wall. An imaging sonar gathers polar image scans from which depth images (range & bearing) are generated. Depth scans are first processed to extract a line corresponding to the wall (with the Hough transform), which is then tracked by means of an EKF (Extended Kalman Filter) using a static motion model and an implicit measurement equation associating the sensed points to the candidate line. The line estimate is referenced to the robot fixed frame and represented in polar coordinates (rho&thetas) which directly corresponds to the actual distance and relative orientation of the robot with respect to the wall. The proposed system has been tested in simulation as well as in water tank conditions

An improved method for discovering link criticality in transport networks

Quantitatively assessing the importance or criticality of each link in a network is of practical value to operators, as that can help them to increase the network's resilience, provide more efficient services, or improve some other aspect of the service. Betweenness is a graph-theoretical measure of centrality that can be applied to communication networks to evaluate link importance. However, as we illustrate in this paper, the basic definition of betweenness centrality produces inaccurate estimations as it does not take into account some aspects relevant to networking, such as the heterogeneity in link capacity or the difference between node-pairs in their contribution to the total traffic. A new algorithm for discovering link centrality in transport networks is proposed in this paper. It requires only static or semi-static network and topology attributes, and yet produces estimations of good accuracy, as verified through extensive simulations. Its potential value is demonstrated by an example application. In the example, the simple shortest-path routing algorithm is improved in such a way that it outperforms other more advanced algorithms in terms of blocking ratio

Failure mechanism under tensile loads in CFRP 0-90º cross-ply laminates containing voids

The failure mechanism of a voided CFRP 0-90° cross-ply laminate under tensile loads applied in one direction was studied in this Final Degree Project. For this purpose, voided coupons were manufactured for being tested and a FEA was done. In both investigations, voids were placed in 90º and 0º direction, in order to understand the void location influence. On the one hand, the behaviour of the voided laminates was investigated through a FEM in order to preview the stress distribution within the material. On the other hand, voided specimens where manufactured by applying blowing agent in between the inner layers. These specimens were tested by a quasi-static step wise tensile test where data showing its real behaviour was collected. Specimens were X-rayed after each step of the test in order to investigate the failure mechanism of the composite. Data from the test was studied so that relations such as strength of the laminates, crack density per stress, void length per first crack at the void and void area per first crack at the specimen could be characterized

Theoretical study of the second-order vibrational Stark effect

The behaviour of the harmonic infrared frequency of diatomic molecules subjected to moderate static uniform electric fields is analysed. The potential energy expression has been developed as a function of a static uniform electric field, which brings about a formulation describing the frequency versus field strength curve. With the help of the first and second derivatives of the expressions obtained, which correspond to the first- and second-order Stark effects, it was possible to find the maxima of the frequency versus field strength curves for a series of molecules using a Newton-Raphson search. A method is proposed which requires only the calculation of a few energy derivatives at a particular value of the field strength. At the same time, the expression for the dependence of the interatomic distance on the electric field strength is derived and the minimum of this curve is found for the same species. Derived expressions and numerical results are discussed and compared with other studi

Anharmonicity contributions to the vibrational second hyperpolarizability of conjugated oligomers

Restricted Hartree-Fock 6-31G calculations of electrical and mechanical anharmonicity contributions to the longitudinal vibrational second hyperpolarizability have been carried out for eight homologous series of conjugated oligomers - polyacetylene, polyyne, polydiacetylene, polybutatriene, polycumulene, polysilane, polymethineimine, and polypyrrole. To draw conclusions about the limiting infinite polymer behavior, chains containing up to 12 heavy atoms along the conjugated backbone were considered. In general, the vibrational hyperpolarizabilities are substantial in comparison with their static electronic counterparts for the dc-Kerr and degenerate four-wave mixing processes (as well as for static fields) but not for electric field-induced second harmonic generation or third harmonic generation. Anharmonicity terms due to nuclear relaxation are important for the dc-Kerr effect (and for the static hyperpolarizability) in the σ-conjugated polymer, polysilane, as well as the nonplanar π systems polymethineimine and polypyrrole. Restricting polypyrrole to be planar, as it is in the crystal phase, causes these anharmonic terms to become negligible. When the same restriction is applied to polymethineimine the effect is reduced but remains quantitatively significant due to the first-order contribution. We conclude that anharmonicity associated with nuclear relaxation can be ignored, for semiquantitative purposes, in planar π-conjugated polymers. The role of zero-point vibrational averaging remains to be evaluated