A recursive presentation for Mihailova's subgroup

"Vegeu el resum a l'inici del document del fitxer adjunt."

A numerical solver for a nonlinear Fokker-Planck equation representation of neuronal network dynamics

To describe the collective behavior of large ensembles of neurons in neuronal network, a kinetic theory description was developed in [13, 12], where a macroscopic representation of the network dynamics was directly derived from the microscopic dynamics of individual neurons, which are modeled by conductance-based, linear, integrate-and-fire point neurons. A diffusion approximation then led to a nonlinear Fokker-Planck equation for the probability density function of neuronal membrane potentials and synaptic conductances. In this work, we propose a deterministic numerical scheme for a Fokker-Planck model of an excitatory-only network. Our numerical solver allows us to obtain the time evolution of probability distribution functions, and thus, the evolution of all possible macroscopic quantities that are given by suitable moments of the probability density function. We show that this deterministic scheme is capable of capturing the bistability of stationary states observed in Monte Carlo simulations. Moreover, the transient behavior of the firing rates computed from the Fokker-Planck equation is analyzed in this bistable situation, where a bifurcation scenario, of asynchronous convergence towards stationary states, periodic synchronous solutions or damped oscillatory convergence towards stationary states, can be uncovered by increasing the strength of the excitatory coupling. Finally, the computation of moments of the probability distribution allows us to validate the applicability of a moment closure assumption used in [13] to further simplify the kinetic theory.

Introducció als Sistemes de Informació Geogràfica

Aquest document ens acosta als sistemes d'informació geogràfica donant-nos una definició de què fan, descrivint què són els objectes geogràfics (entitats amb informació geomètrica i temàtica) i tractant de la problemàtica de la seva representació. També ens mostra els passos que cal fer en un sistema d'informació geogràfica, des de la introducció de les dades fins a la presentació dels resultats, passant per la consulta i l'anàlisi.

Mètodes empírics en lingüística cognitiva

Peer-reviewed

Monocular-based 3-D seafloor reconstruction and ortho-mosaicing by piecewise planar representation

Photo-mosaicing techniques have become popular for seafloor mapping in various marine science applications. However, the common methods cannot accurately map regions with high relief and topographical variations. Ortho-mosaicing borrowed from photogrammetry is an alternative technique that enables taking into account the 3-D shape of the terrain. A serious bottleneck is the volume of elevation information that needs to be estimated from the video data, fused, and processed for the generation of a composite ortho-photo that covers a relatively large seafloor area. We present a framework that combines the advantages of dense depth-map and 3-D feature estimation techniques based on visual motion cues. The main goal is to identify and reconstruct certain key terrain feature points that adequately represent the surface with minimal complexity in the form of piecewise planar patches. The proposed implementation utilizes local depth maps for feature selection, while tracking over several views enables 3-D reconstruction by bundle adjustment. Experimental results with synthetic and real data validate the effectiveness of the proposed approach

Computational Representation of Collaborative Learning Flow Patterns Using IMS Learning Design

The identification and integration of reusable and customizable CSCL (Computer Supported Collaborative Learning) may benefit from the capture of best practices in collaborative learning structuring. The authors have proposed CLFPs (Collaborative Learning Flow Patterns) as a way of collecting these best practices. To facilitate the process of CLFPs by software systems, the paper proposes to specify these patterns using IMS Learning Design (IMS-LD). Thus, teachers without technical knowledge can particularize and integrate CSCL tools. Nevertheless, the support of IMS-LD for describing collaborative learning activities has some deficiencies: the collaborative tools that can be defined in these activities are limited. Thus, this paper proposes and discusses an extension to IMS-LD that enables to specify several characteristics of the use of tools that mediate collaboration. In order to obtain a Unit of Learning based on a CLFP, a three stage process is also proposed. A CLFP-based Unit of Learning example is used to illustrate the process and the need of the proposed extension.

Symbolic meaning of local identity – A case study on Barcelona place brand representation

The core objective of this research process was to design an operational tool for place brand analysis. By modelling the emotional significance and the deeper-lying symbols associated to a specific place identity I expected to create a semiotic tool that could be applied, mutatis mutandis, on other similar place brands. As a field case study to develop the instrument, my choice of the research arena was Barcelona city, the capital of Catalonia Autonomous Community, Spain. Barcelona brand identity was approached in the line of the Chicago Urban Anthropology School. The research methods were designed according to the prescriptions of the urban anthropology, namely qualitative methods: in-depth interviews and discourse analysis. The final research outcome was a model summarizing a range of specific emotional values that support a place brand to position in the collective mindset and to assume a positively valued status and identity in the world order.

Biased representation of homothetic preferences on homogeneous sets

In the homogeneous case of one-dimensional objects, we show that any preference relation that is positive and homothetic can be represented by a quantitative utility function and unique bias. This bias may favor or disfavor the preference for an object. In the first case, preferences are complete but not transitive and an object may be preferred even when its utility is lower. In the second case, preferences are asymmetric and transitive but not negatively transitive and it may not be sufficient for an object to have a greater utility for be preferred. In this manner, the bias reflects the extent to which preferences depart from the maximization of a utility function.

Econometrics and decision making: Effects of presentation mode

Much of empirical economics involves regression analysis. However, does thepresentation of results affect economists ability to make inferences for decision makingpurposes? In a survey, 257 academic economists were asked to make probabilisticinferences on the basis of the outputs of a regression analysis presented in a standardformat. Questions concerned the distribution of the dependent variable conditional onknown values of the independent variable. However, many respondents underestimateduncertainty by failing to take into account the standard deviation of the estimatedresiduals. The addition of graphs did not substantially improve inferences. On the otherhand, when only graphs were provided (i.e., with no statistics), respondents weresubstantially more accurate. We discuss implications for improving practice in reportingresults of regression analyses.

The so-called 'external partners' in the groups of corporations: A model of presentation in the consolidated statements

This paper studies, on the one hand, theories set out around theconsideration of the external partners in the consolidated informationand on the other hand, financial models that discuss the convenience ofthe separation or not of the different elements that form part of theliabilities of the balance sheet of the companies. A Model is proposed,the External Partners Model, which financially argues a certain presentationand processing of such and that, in our opinion, facilitates the analysisof the consolidated financial statements. This model is based on twohypotheses: (1) the economic and financial variables are not independentand (2) the value of the company depends, among other factors, of thetype of sources that constitute their capital. These two hypotheses willimply that a separation should be included in the consolidated balance sheet between equity and liabilities as they are different sources ofcapital and then its separation will give relevant information to itsusers.

The choice of the form of representation in multinational banking: Evidence from Spain

This paper investigates foreign direct investment in the bankingsector. The attention has been addressed to test the importanceof OLI advantages as the determinants of the bank's decisionto invest in foreign locations. Nevertheless, since banks canexpand their activities abroad through different organizationalforms that imply different levels of foreign involvement, theissue of the form of representation has been tackled. Theresults show the importance of OLI advantages in the form ofrepresentation in multinational banking.

Exact representation of antenna system diversity performance from input parameter description

A simplc formulation Io compute thc envelope correlation of anantenna divemiry system is dcrired. 11 is shown how to compute theenvelope correlation hom the S-parameter descnplian of the antennasystem. This approach has the advantage that i t does not require thecomputation nor the measurement of the radiation panem of theantenna system. It also offers the advantage of providing a clcaunderstanding ofthe effects ofmutual coupling and input match on thediversity performance of the antcnnii system.

On the spinning axis representation

A new spinning axis representation is introduced. It allows us to calculate the evolution operator of a system with slowly varying time dependent Hamiltonian with the desired degree of approximation in the parameter used for describing its dynamical evolution. The procedure is compared with a previously existing one and applied to a simple example.

Space and momentum representation analysis of Hartman's effect in wave packet transmission

The Hartman effect is analyzed in both the position and momentum representations of the problem. The importance of Wigner tunneling and deep tunneling is singled out. It is shown quantitatively how the barrier acts as a filter for low momenta (quantum speed up) as the width increases, and a detailed mechanism is proposed. Superluminal transmission is also discussed.