Sequential decisions in allocation problems

[eng] In the context of cooperative TU-games, and given an order of players, we consider the problem of distributing the worth of the grand coalition as a sequentia decision problem. In each step of process, upper and lower bounds for the payoff of the players are required related to successive reduced games. Sequentially compatible payoffs are defined as those allocation vectors that meet these recursive bounds. The core of the game is reinterpreted as a set of sequentally compatible payoffs when the Davis-Maschler reduced game is considered (Th.1). Independently of the reduction, the core turns out to be the intersections of the family of the sets of sequentially compatible payoffs corresponding to the different possible orderings (Th.2), so it is in some sense order-independent. Finally, we analyze advantagenous properties for the first player

Some fundamental aspects of palentological methodology: its problems and incidence

Two trends which presently exist in relation to the concept of Paleontology are analyzed, pointing out some of the aspects which negative influence. Various reflections are made based on examples of some of the principal points of paleontological method, such as the influence of a punctual sampling, the meaning of size-frequency distribution and subjectivity in the identification of fossils. Topics which have a marked repercussion in diverse aspects of Paleontology are discussed.

Bubbles in Kaluza-Klein theories with spacelike or timelike internal dimensions

region to the other. We also present a C-type solution that describes neutral bubbles in uniform acceleration, and we use it to construct an instanton that mediates the breaking of a cosmic string by forming bubbles at its ends. The rate for this process is also calculated. Finally, we argue that a similar solution can be constructed for magnetic bubbles, and that it can be used to describe a semiclassical instability of the two-timing vacuum against production of massless monopole pairs.

Sequential decisions in allocation problems

[eng] In the context of cooperative TU-games, and given an order of players, we consider the problem of distributing the worth of the grand coalition as a sequentia decision problem. In each step of process, upper and lower bounds for the payoff of the players are required related to successive reduced games. Sequentially compatible payoffs are defined as those allocation vectors that meet these recursive bounds. The core of the game is reinterpreted as a set of sequentally compatible payoffs when the Davis-Maschler reduced game is considered (Th.1). Independently of the reduction, the core turns out to be the intersections of the family of the sets of sequentially compatible payoffs corresponding to the different possible orderings (Th.2), so it is in some sense order-independent. Finally, we analyze advantagenous properties for the first player

Heterogeneous discounting in consumption-investment problems. Time consistent solutions

[cat] En aquest treball s'analitza un model estocàstic en temps continu en el que l'agent decisor descompta les utilitats instantànies i la funció final amb taxes de preferència temporal constants però diferents. En aquest context es poden modelitzar problemes en els quals, quan el temps s'acosta al moment final, la valoració de la funció final incrementa en comparació amb les utilitats instantànies. Aquest tipus d'asimetria no es pot descriure ni amb un descompte estàndard ni amb un variable. Per tal d'obtenir solucions consistents temporalment es deriva l'equació de programació dinàmica estocàstica, les solucions de la qual són equilibris Markovians. Per a aquest tipus de preferències temporals, s'estudia el model clàssic de consum i inversió (Merton, 1971) per a les funcions d'utilitat del tipus CRRA i CARA, comparant els equilibris Markovians amb les solucions inconsistents temporalment. Finalment es discuteix la introducció del temps final aleatori.

European integration, FDI and the internal geography of trade : evidence from Western European border regions

In this paper we use a gravity model to study the trade performance of French and Spanishborder regions relatively to non-border regions, over the past two decades. We find that,controlling for their size, proximity and location characteristics, border regions trade onaverage between 62% and 193% more with their neighbouring country than other regions,and twice as much if they are endowed with good cross border transport infrastructures.Despite European integration, however, this trade outperformance has fallen for the mostperipheral regions within the EU. We show that this trend was linked in part to a shift in the propensity of foreign investors to move their affiliates from the regions near their home market to the regions bordering the EU core.

Estudio de la accesibilidad de los documentos cientificos en soporte digital

Resumen: El artículo analiza los problemas de accesibilidad que actualmente presentan los artículos científicos en soporte digital. El estudio se centra en los aspectos de facilidad de uso del contenido de los documentos digitales según la forma en que se publiquen, sin entrar en el estudio de los distintos sistemas de recuperación. Se analizan los dos formatos más utilizados para la publicación de artículos científicos en soporte digital: HTML y PDF, estudiando el desempeño lector en relación a la presencia de sumarios o de tablas internas o vinculadas. El estudio se ha realizado con dos colectivos: 30 sujetos ciegos, usuarios de Jaws, contactados gracias a la mediación de la Fundación ONCE, y 30 sujetos no ciegos, profesores del Departamento de Biblioteconomía y Documentación de la Universidad de Barcelona. El estudio muestra que la localización de los datos contenidos en tablas se ve facilitada en documentos HTML por la inclusión de un sumario que vincule con la tabla, así como la inclusión de tablas completas en el cuerpo del documento HTML facilita la actividad lectora por parte de los usuarios ciegos. A nivel metodológico la presente investigación aporta dos novedades relevantes respecto a la literatura existente en los estudios de usabilidad con ciegos: estudia la usabilidad del formato PDF y es un test de usabilidad cuantitativo; este último hecho dificulta su comparación con la mayoría de artículos publicados. Abstract: This paper analyses the problems of accessibility posed by scientific articles published in digital format, focusing on the ease of use of their content with respect to the form in which they are published (irrespective of the recovery system). The two most widely used formats for the publication of scientific articles in digital format, HTML and PDF, are analysed, examining reader performance in relation to the presence of contents lists or internal or linked tables. The study involved two groups: 30 blind subjects, all JAWS users, contacted through the ONCE Foundation, and 30 sighted subjects, lecturers in the Department of Librarianship and Documentation of the University of Barcelona. The results shows the location of data in tables is easier in HTML documents through the inclusion of a contents list linked to these tables. Further, the inclusion of complete tables in the body of HTML document facilitates the reading activity of blind users. At the methodological level, this work reports two novelties with respect to the existing literature on usability by blind people: it examines the usability of the PDF format, and discusses a quantitative usability test. The latter hinders comparison with the majority of published articles.

La Participación de los estudiantes en la universidad: dificultades percibidas y propuestas de mejora = Student participation in the university: perceived problems and proposals for improvement

Este artículo se centra en el análisis de la participación de los estudiantes en el gobierno de la universidad y muestra específicamente las principales dificultades que hay para ella y las propuestas que pueden facilitar la implicación de los estudiantes en el funcionamiento de las universidades. A partir de una investigación desarrollada durante los cursos 2007-08 y 2008-09, en la que se utilizaron cuestionarios y grupos de discusión con estudiantes y entrevistas dirigidas al profesorado, se obtiene información sobre los principales obstáculos para la participación estudiantil. El estudio realizado muestra que, de acuerdo con la tónica general reflejada en otras investigaciones sobre esta misma temática en nuestro contexto, la participación de los estudiantes en los distintos estamentos universitarios es escasa. Ahora bien, la metodología seguida en esta investigación permite contrastar las opiniones de los estudiantes con las percepciones del profesorado y obtener así matices significativos que muestran las principales direcciones que hay que tomar para facilitar un cambio de orientación en el asunto. Los cambios que debemos emprender están relacionados no solo con la mejora de los mecanismos de información acerca de los canales de participación, sino también con el replanteamiento de los procesos participativos por parte de la universidad, así como del papel del profesorado y, específicamente, de los coordinadores de los órganos de gestión más próximos a los estudiantes. En las conclusiones del documento se presentan las propuestas de mejora dirigidas a potenciar la implicación de los estudiantes en el funcionamiento universitario. Entre ellas se apuntan las siguientes: mejorar la información y los canales de comunicación con los estudiantes, mejorar los procesos electorales, ofrecer formación a los estudiantes para la participación y formación al profesorado acerca de las metodologías, recursos e instrumentos que pueden repercutir en la motivación de los estudiantes

Width and serialization of classical planning problems

We introduce a width parameter that bounds the complexity of classical planning problems and domains, along with a simple but effective blind-search procedure that runs in time that is exponential in the problem width. We show that many benchmark domains have a bounded and small width provided thatgoals are restricted to single atoms, and hence that such problems are provably solvable in low polynomial time. We then focus on the practical value of these ideas over the existing benchmarks which feature conjunctive goals. We show that the blind-search procedure can be used for both serializing the goal into subgoals and for solving the resulting problems, resulting in a ‘blind’ planner that competes well with a best-first search planner guided by state-of-the-art heuristics. In addition, ideas like helpful actions and landmarks can be integrated as well, producing a planner with state-of-the-art performance.

Equilibrium points and central configurations for the Lennard-Jones 2-and 3-body problems

Abstract. In this paper we study the relative equilibria and their stability for a system of three point particles moving under the action of a Lennard{Jones potential. A central con guration is a special position of the particles where the position and acceleration vectors of each particle are proportional, and the constant of proportionality is the same for all particles. Since the Lennard{Jones potential depends only on the mutual distances among the particles, it is invariant under rotations. In a rotating frame the orbits coming from central con gurations become equilibrium points, the relative equilibria. Due to the form of the potential, the relative equilibria depend on the size of the system, that is, depend strongly of the momentum of inertia I. In this work we characterize the relative equilibria, we nd the bifurcation values of I for which the number of relative equilibria is changing, we also analyze the stability of the relative equilibria.

First-passage and escape problems in the Feller process

The Feller process is an one-dimensional diffusion process with linear drift and state-dependent diffusion coefficient vanishing at the origin. The process is positive definite and it is this property along with its linear character that have made Feller process a convenient candidate for the modeling of a number of phenomena ranging from single-neuron firing to volatility of financial assets. While general properties of the process have long been well known, less known are properties related to level crossing such as the first-passage and the escape problems. In this work we thoroughly address these questions.

Efficacy of a dilemma-focused intervention for unipolar depression: study protocol for a multicenter randomized controlled trial

Background Depression is one of the more severe and serious health problems because of its morbidity, disabling effects and for its societal and economic burden. Despite the variety of existing pharmacological and psychological treatments, most of the cases evolve with only partial remission, relapse and recurrence. Cognitive models have contributed significantly to the understanding of unipolar depression and its psychological treatment. However, success is only partial and many authors affirm the need to improve those models and also the treatment programs derived from them. One of the issues that requires further elaboration is the difficulty these patients experience in responding to treatment and in maintaining therapeutic gains across time without relapse or recurrence. Our research group has been working on the notion of cognitive conflict viewed as personal dilemmas according to personal construct theory. We use a novel method for identifying those conflicts using the repertory grid technique (RGT). Preliminary results with depressive patients show that about 90% of them have one or more of those conflicts. This fact might explain the blockage and the difficult progress of these patients, especially the more severe and/or chronic. These results justify the need for specific interventions focused on the resolution of these internal conflicts. This study aims to empirically test the hypothesis that an intervention focused on the dilemma(s) specifically detected for each patient will enhance the efficacy of cognitive behavioral therapy (CBT) for depression. Design A therapy manual for a dilemma-focused intervention will be tested using a randomized clinical trial by comparing the outcome of two treatment conditions: combined group CBT (eight, 2-hour weekly sessions) plus individual dilemma-focused therapy (eight, 1-hour weekly sessions) and CBT alone (eight, 2-hour group weekly sessions plus eight, 1-hour individual weekly sessions). Method Participants are patients aged over 18 years meeting diagnostic criteria for major depressive disorder or dysthymic disorder, with a score of 19 or above on the Beck depression inventory, second edition (BDI-II) and presenting at least one cognitive conflict (implicative dilemma or dilemmatic construct) as assessed using the RGT. The BDI-II is the primary outcome measure, collected at baseline, at the end of therapy, and at 3- and 12-month follow-up; other secondary measures are also used. Discussion We expect that adding a dilemma-focused intervention to CBT will increase the efficacy of one of the more prestigious therapies for depression, thus resulting in a significant contribution to the psychological treatment of depression. Trial registration ISRCTN92443999; ClinicalTrials.gov Identifier: NCT01542957.

The Gaussian assumption in second-order estimation problems in digital communications

This paper deals with the goodness of the Gaussian assumption when designing second-order blind estimationmethods in the context of digital communications. The low- andhigh-signal-to-noise ratio (SNR) asymptotic performance of the maximum likelihood estimator—derived assuming Gaussiantransmitted symbols—is compared with the performance of the optimal second-order estimator, which exploits the actualdistribution of the discrete constellation. The asymptotic study concludes that the Gaussian assumption leads to the optimalsecond-order solution if the SNR is very low or if the symbols belong to a multilevel constellation such as quadrature-amplitudemodulation (QAM) or amplitude-phase-shift keying (APSK). On the other hand, the Gaussian assumption can yield importantlosses at high SNR if the transmitted symbols are drawn from a constant modulus constellation such as phase-shift keying (PSK)or continuous-phase modulations (CPM). These conclusions are illustrated for the problem of direction-of-arrival (DOA) estimation of multiple digitally-modulated signals.