Comparative Statics in Cournot Free Entry Equilibrium

In this paper we study the effects of a change in an exogenous variable (the fixed cost or a parameter in the demand function) on the output and the number of active firms in a Symmetric Cournot Equilibrium with Free Entry (SCEFE). The results obtained here are different from those obtained in the Cournot model with a given number of firms. In particular, an increase in demand might yield a decrease in the output of the industry.We also show that any observation on prices, profits and number of firms is compatible with the assumption that the market is in a SCEFE. If fixed costs can be observed, there is a loose relationship between the profit rate and the number of active firms. This result is used as a warning against the use of the profit rate as a measure of an anticompetitive position and against the Structure–Conduct– Performance paradigm.Publicad

Neuronal Cultures: Exploring Biophysics, Complex Systems, and Medicine in a Dish

Neuronal cultures are one of the most important experimental models in modern interdisciplinary neuroscience, allowing to investigate in a control environment the emergence of complex behavior from an ensemble of interconnected neurons. Here, I review the research that we have conducted at the neurophysics laboratory at the University of Barcelona over the last 15 years, describing first the neuronal cultures that we prepare and the associated tools to acquire and analyze data, to next delve into the different research projects in which we actively participated to progress in the understanding of open questions, extend neuroscience research on new paradigms, and advance the treatment of neurological disorders. I finish the review by discussing the drawbacks and limitations of neuronal cultures, particularly in the context of brain-like models and biomedicine

Roughness experiments of viscous fluid interfaces in disordered Hele-Shaw cells

[spa] Se presenta un trabajo experimental sobre el crecimiento de interficies rugosas en medios desordenados. El experimento consiste en una celda de Hele-Shaw en cuya placa inferior se han distribuido una serie de obstáculos de cobre que hacen la función de desorden congelado. Un aceite de silicona es inyectado por uno de los extremos de la celda desplazando el aire inicialmente presente. El frente es estable por contraste de viscosidad pero se hace rugoso debido a la presencia del desorden. Los experimentos realizados se pueden clasificar en dos grupos principales según el tipo de mecanismo utilizado para la inyección del aceite: A- Velocidad constante y B- Presión constante. Para el Caso A- se han realizado multitud de experimentos variando la velocidad del fluido, el espaciado entre placas en la celda de Hele-Shaw y la configuración del desorden. Se ha observado que cuando la velocidad promedio del aceite es alta y/o la longitud de correlación del desorden en la dirección de crecimiento es baja (desorden débil), entonces el escalamiento de las fluctuaciones de la interfície sigue el escalamiento dinámico de Family-Vicsek, con un exponente de crecimiento de beta=0,50 independiente de la velocidad promedio de la interface, espaciado entre placas y configuración del desorden. También se ha estudiado del exponente de rugosidad, encontrando dos regímenes, alfa-1 a escalas pequeñas y alfa-2 a escalas grandes, con unos valores que dependen de la velocidad promedio, el espaciado entre placas y la configuración del desorden. Para velocidades grandes se obtienen un valor límite de alfa 1=1,3 y alfa 2=0 independientemente de los parámetros experimentales. También se ha caracterizado el punto de crossover entre alfa-1 y alfa-2, el cual escala con la velocidad con un exponente 0.5, de acuerdo con predicciones teóricas

Roughness experiments of viscous fluid interfaces in disordered Hele-Shaw cells

Se presenta un trabajo experimental sobre el crecimiento de interficies rugosas en medios desordenados. El experimento consiste en una celda de Hele-Shaw en cuya placa inferior se han distribuido una serie de obstáculos de cobre que hacen la función de desorden congelado. Un aceite de silicona es inyectado por uno de los extremos de la celda desplazando el aire inicialmente presente. El frente es estable por contraste de viscosidad pero se hace rugoso debido a la presencia del desorden. Los experimentos realizados se pueden clasificar en dos grupos principales según el tipo de mecanismo utilizado para la inyección del aceite: A- Velocidad constante y B- Presión constante. Para el Caso A- se han realizado multitud de experimentos variando la velocidad del fluido, el espaciado entre placas en la celda de Hele-Shaw y la configuración del desorden. Se ha observado que cuando la velocidad promedio del aceite es alta y/o la longitud de correlación del desorden en la dirección de crecimiento es baja (desorden débil), entonces el escalamiento de las fluctuaciones de la interfície sigue el escalamiento dinámico de Family-Vicsek, con un exponente de crecimiento de beta=0,50 independiente de la velocidad promedio de la interface, espaciado entre placas y configuración del desorden. También se ha estudiado del exponente de rugosidad, encontrando dos regímenes, alfa-1 a escalas pequeñas y alfa-2 a escalas grandes, con unos valores que dependen de la velocidad promedio, el espaciado entre placas y la configuración del desorden. Para velocidades grandes se obtienen un valor límite de alfa 1=1,3 y alfa 2=0 independientemente de los parámetros experimentales. También se ha caracterizado el punto de crossover entre alfa-1 y alfa-2, el cual escala con la velocidad con un exponente 0.5, de acuerdo con predicciones teóricas

Impact of Physical Obstacles on the Structural and Effective Connectivity of in silico Neuronal Circuits

Scaffolds and patterned substrates are among the most successful strategies to dictate the connectivity between neurons in culture. Here, we used numerical simulations to investigate the capacity of physical obstacles placed on a flat substrate to shape structural connectivity, and in turn collective dynamics and effective connectivity, in biologically-realistic neuronal networks. We considered μ-sized obstacles placed in mm-sized networks. Three main obstacle shapes were explored, namely crosses, circles and triangles of isosceles profile. They occupied either a small area fraction of the substrate or populated it entirely in a periodic manner. From the point of view of structure, all obstacles promoted short length-scale connections, shifted the in- and out-degree distributions toward lower values, and increased the modularity of the networks. The capacity of obstacles to shape distinct structural traits depended on their density and the ratio between axonal length and substrate diameter. For high densities, different features were triggered depending on obstacle shape, with crosses trapping axons in their vicinity and triangles funneling axons along the reverse direction of their tip. From the point of view of dynamics, obstacles reduced the capacity of networks to spontaneously activate, with triangles in turn strongly dictating the direction of activity propagation. Effective connectivity networks, inferred using transfer entropy, exhibited distinct modular traits, indicating that the presence of obstacles facilitated the formation of local effective microcircuits. Our study illustrates the potential of physical constraints to shape structural blueprints and remodel collective activity, and may guide investigations aimed at mimicking organizational traits of biological neuronal circuits

Hydra Molecular Network Reaches Criticality at the Symmetry-Breaking Axis-Defining Moment

We study biological, multicellular symmetry breaking on a hollow cell sphere as it occurs during hydra regeneration from a random cell aggregate. We show that even a weak temperature gradient directs the axis of the regenerating animal but only if it is applied during the symmetry-breaking moment. We observe that the spatial distribution of the early expressed, head-specific gene k s 1 has become scale-free and fractal at that point. We suggest the self-organized critical state to reflect long range signaling, which is required for axis definition and arises from cell next-neighbor communication

Radial displacement of a fluid annulus in a rotating Hele-Shaw cell

The radial displacement of a fluid annulus in a rotating circular HeleShaw cell has been investigated experimentally. It has been found that the flow depends sensitively on the wetting conditions at the outer interface. Displacements in a prewet cell are well described by Darcy"s law in a wide range of experimental parameters, with little influence of capillary effects. In a dry cell, however, a more careful analysis of the interfacemotion is required; the interplay between a gradual loss of fluid at the inner interface, and the dependence of capillary forces at the outer interface on interfacial velocity and dynamic contact angle, result in a constant velocity for the interfaces. The experimental results in this case correlate in the form of an empirical scaling relation between the capillary number Ca and a dimensionless group, related to the ratio of centrifugal to capillary forces, which spans about three orders of magnitude in both quantities. Finally, the relative thickness of the coating film left by the inner interface is obtained as a function of Ca

Identification of neuronal network properties from the spectral analysis of calcium imaging signals in neuronal cultures

Neuronal networks in vitro are prominent systems to study the development of connections in living neuronal networks and the interplay between connectivity, activity and function. These cultured networks show a rich spontaneous activity that evolves concurrently with the connectivity of the underlying network. In this work we monitor the development of neuronal cultures, and record their activity using calcium fluorescence imaging. We use spectral analysis to characterize global dynamical and structural traits of the neuronal cultures. We first observe that the power spectrum can be used as a signature of the state of the network, for instance when inhibition is active or silent, as well as a measure of the network's connectivity strength. Second, the power spectrum identifies prominent developmental changes in the network such as GABAA switch. And third, the analysis of the spatial distribution of the spectral density, in experiments with a controlled disintegration of the network through CNQX, an AMPA-glutamate receptor antagonist in excitatory neurons, reveals the existence of communities of strongly connected, highly active neurons that display synchronous oscillations. Our work illustrates the interest of spectral analysis for the study of in vitro networks, and its potential use as a network-state indicator, for instance to compare healthy and diseased neuronal networks

La centralització tributària i el frau fiscal

Treballs Finals del Grau d'Economia, Facultat d'Economia i Empresa, Universitat de Barcelona, Curs: 2017-2018 , Tutor: Antoni Castells Oliveres(cat) El frau fiscal és una de les pitjors xacres de l’estat del benestar, provoca l’erosió de la capacitat de generar ingressos públics, distorsionant al mateix temps el sistema fiscal. Per aquest motiu en aquest treball intento acotar les causes del mateix. L’any 2014 l’AEAT (Agencia Estatal de Administración Tributaria) va recaptar el 70% dels impostos a l’estat espanyol, considero que aquest grau de centralització tributària podria estar causant part del frau fiscal. Per tal de trobar una relació empírica que avali aquesta hipòtesis he elaborat una regressió economètrica que pugui correlacionar aquestes dues variables. Les dades recollides per l’elaboració de la regressió provenen de diverses fonts. Tenint en compte les mancances de les dades utilitzades, he pogut arribar a una conclusió bastant clara. La centralització tributària de l’estat espanyol és una de les causes del frau fiscal, tot i que no ser la més important és una de les distorsions del sistema fiscal que s’ha d’eliminar