Diffusion in spatially and temporarily inhomogeneous media

In this paper we consider diffusion of a passive substance C in a temporarily and spatially inhomogeneous two-dimensional medium. As a realization for the latter we choose a phase-separating medium consisting of two substances A and B, whose dynamics is determined by the Cahn-Hilliard equation. Assuming different diffusion coefficients of C in A and B, we find that the variance of the distribution function of the said substance grows less than linearly in time. We derive a simple identity for the variance using a probabilistic ansatz and are then able to identify the interface between A and B as the main cause for this nonlinear dependence. We argue that, finally, for very large times the here temporarily dependent diffusion "constant" goes like t-1/3 to a constant asymptotic value D¿. The latter is calculated approximately by employing the effective-medium approximation and by fitting the simulation data to the said time dependence.

Growth of unstable interfaces in disordered media

The effects of a disordered medium in the growth of unstable interfaces are studied by means of two local models with multiplicative and additive quenched disorder, respectively. For short times and large pushing the multiplicative quenched disorder is equivalent to a time-dependent noise. In this regime, the linear dispersion relation contains a destabilizing contribution introduced by the noise. For long times, the interface always gets pinned. We model the systematics of the pinned shapes by means of an effective nonlinear model. These results show good agreement with numerical simulations. For the additive noise we find numerically that a depinning transition occurs.

Front propagation in spatially modulated media

A two-dimensional reaction-diffusion front which propagates in a modulated medium is studied. The modulation consists of a spatial variation of the local front velocity in the transverse direction to that of the front propagation. We study analytically and numerically the final steady-state velocity and shape of the front, resulting from a nontrivial interplay between the local curvature effects and the global competition process between different maxima of the control parameter. The transient dynamics of the process is also studied numerically and analytically by means of singular perturbation techniques.

Wave competition in excitable modulated media.

The propagation of an initially planar front is studied within the framework of the photosensitive Belousov-Zhabotinsky reaction modulated by a smooth spatial variation of the local front velocity in the direction perpendicular to front propagation. Under this modulation, the wave front develops several fingers corresponding to the local maxima of the modulation function. After a transient, the wave front achieves a stationary shape that does not necessarily coincide with the one externally imposed by the modulation. Theoretical predictions for the selection criteria of fingers and steady-state velocity are experimentally validated.

Noise-enhanced excitability in bistable activator-inhibitor media

We show that external fluctuations induce excitable behavior in a bistable spatially extended system with activator-inhibitor dynamics of the FitzHugh-Nagumo type. This can be understood as a mechanism for sustained signal propagation in bistable media. The phase diagram of the stochastic system is analytically obtained and numerically verified. For small-noise intensities, front propagation becomes unstable, and excitable pulses arise as the only possible spatiotemporal behavior of the system. For large-noise intensities, on the other hand, the system enters an effective regime of oscillatory behavior, where it exhibits spontaneous nucleation of pulses and synchronized firing.

Percolation thresholds in chemical disordered excitable media

The behavior of chemical waves advancing through a disordered excitable medium is investigated in terms of percolation theory and autowave properties in the framework of the light-sensitive Belousov-Zhabotinsky reaction. By controlling the number of sites with a given illumination, different percolation thresholds for propagation are observed, which depend on the relative wave transmittances of the two-state medium considered.

Front dynamics in turbulent media

A study of a stable front propagating in a turbulent medium is presented. The front is generated through a reaction-diffusion equation, and the turbulent medium is statistically modeled using a Langevin equation. Numerical simulations indicate the presence of two different dynamical regimes. These regimes appear when the turbulent flow either wrinkles a still rather sharp propagating interfase or broadens it. Specific dependences of the propagating velocities on stirring intensities appropriate to each case are found and fitted when possible according to theoretically predicted laws. Different turbulent spectra are considered.

Filó d'Alexandria i el seu De opificio mundi (LIII-LXI): tot copsant les claus de la misogínia grega i occidental en un text jueu platonitzant.

L'objectiu d'aquest article és mostrar la secular tradició misògina occidental des dels seus orígens a Grècia tot analitzant un text de l'intèrpret al·legoric de la Bíblia Filó d'Alexandria, el De opificio mundi, al qual aplica una lectura fortament platonitzant. L'anàlisi acurada dels capítols dedicats a la creació divina de la dona i les seves conseqüències mostra fins a quin punt no és possible entendre aquest text sense tenir en compte una tradició filosòfica grega ja aleshores secular.

Woody Allen i l'esperit de la tragèdia grega: de Crimes and Misdemeanors a Match Point

Nombrosos són ja els estudis que s'han centrat en l'anomenat "cinema seriós" de Woody Allen i, entre ells, paga la pena de mencionar el que Pau Gilabert Barberà, autor d'aquest article, va escriure (2006) sobre el que, en opinió seva, és el llegat sofístic subjacent en el guió de Crimes and Misdemeanors. En aquesta ocasió, el seu objectiu és analitzar la trajectòria fluctuant del director americà en relació a la tragèdia grega, des de la convicció que, només així, és possible revelar la seva empatia amb l'esperit tràgic dels grecs i comprendre la seva necessitat de presentar aquell gènere literari com un paradigma des del qual entendre les grandeses i misèries del món contemporani.

Cassandra's Dream de Woody Allen. La contemporaneïtat de la tragèdia grega

Cassandra's Dream, de Woody Allen (2007), no tingué les crítiques excel·lents de pel·lícules anteriors com ara Crimes and Misdemeanors i Match Point, on s'abordaven temes semblants. Tanmateix, segons l'opinió de l'autor d'aquest article, analitzada des de la perspectiva del llegat de la tragèdia grega en la cultura occidental, els mèrits d¿aquest film no són pas menyspreables. Les nombroses referències a la tragèdia grega, ja siguin títols o personatges, demostren la voluntat del director americà d'il·lustrar la contemporaneïtat del gènere esmentat, com també de presentar els homes i les dones d¿avui com a víctimes d'una gairebé omnipotent i sorneguera ironia tràgica. L'autor es proposa també de mostrar-hi les relacions evidents d'aquest guió amb el de Match Point i, sobretot, amb el que considera guió matriu de totes tres: Crimes and Misdemeanors.

"Classicisme versus Medievalisme a l'Anglaterra Victoriano-Eduardina; "A Room with a View" d'E. M. Forster com a exemple

L'objectiu d'aquest article és il·lustrar la ben coneguda oposició classicisme / medievalisme a l'Anglaterra Victoriano-Eduardina tot analitzant acuradament A Room with a View d'E. M. Forster des de la perspectiva de la Tradició Clàssica i, consegüentment, parant esment especial en el significant i la importància del conjunt de les seves referències clàssiques -grecollatines.

Tradició misògina grega en el De amore d'Andreu el Capellà

L'objectiu d'aquest article és mostrar com els trets fonamentals de la misogínia grega, que és a la base de la secular misoginia occidental -i que no és només un llegat judeucristià- perviu en un text medieval del segle XIII com ara el De amore d'Andreas Capellanus. L'autor assenyala igualment les vies de transmissió més versemblants des de la Grècia Antiga fins al món medieval.

"Classicism versus Mediaevalism in Victorian-Edwardian England: E. M. Forter's "A Room with a View" as an example

The aim of this article is to illustrate the well-known opposition classicism / medievalism in the Victorian-Edwardian England by analysing accurately E. M. Forster's A Room with a View from the point of view of the Classical Tradition and, therefore, focusing on both the meaning and significance of all its classical -Greek and Roman- references.

"Clasicismo versus Medievalismo en la Inglaterra Victoriano-Eduardina; "A Room with a View"" de E. M. Forster como ejemplo

El objetivo de este artículo es ilustrar la bien conocida oposición clasicismo / medievalismo en la Inglaterra Victoriano-Eduardina analizando minuciosamente A Room with a View de E. M. Forster desde la perspectiva de la Tradición Clásica y, por consiguiente, centrando la atención en el significado e importancia del conjunto de sus referencias clásicas ¿grecolatinas.

Media, investors and bubbles

We analysed the specific case of how information in the financial press influences economic bubbles. We found considerable flaws in the information market due to several factors: demand, the predominance of what are termed “irrational investors” (herding), and supply, which has the problem that the sources of information are biasedand feeds. A financial bubble is a deviation between real value of a financial asset and its persistent market price in time, which also has a speculative origin fed back by the illusion of the owners of these financial values, who will take benefits because of the future prices, which must be higher than the previous ones. The economical information in the media is submitting three problems. First of all, it is information generated by companies. In second place, the information circuit is fed back. A problem of informative independence becomes created, particularly serious in the case of the banks, which are very were as creditors. And in a third place, some informative biases are manifested for the companies of regulated sectors which are starring the economical information in the media.