Reaction-diffusion processes and non-perturbative renormalisation group

This paper is devoted to investigating non-equilibrium phase transitions to an absorbing state, which are generically encountered in reaction-diffusion processes. It is a review, based on [Phys. Rev. Lett. 92, 195703; Phys. Rev. Lett. 92, 255703; Phys. Rev. Lett. 95, 100601], of recent progress in this field that has been allowed by a non-perturbative renormalisation group approach. We mainly focus on branching and annihilating random walks and show that their critical properties strongly rely on non-perturbative features and that hence the use of a non-perturbative method turns out to be crucial to get a correct picture of the physics of these models.Comment: 14 pages, submitted to J. Phys. A for the proceedings of the conference 'Renormalization Group 2005', Helsink

General framework of the non-perturbative renormalization group for non-equilibrium steady states

This paper is devoted to presenting in detail the non-perturbative renormalization group (NPRG) formalism to investigate out-of-equilibrium systems and critical dynamics in statistical physics. The general NPRG framework for studying non-equilibrium steady states in stochastic models is expounded and fundamental technicalities are stressed, mainly regarding the role of causality and of Ito's discretization. We analyze the consequences of Ito's prescription in the NPRG framework and eventually provide an adequate regularization to encode them automatically. Besides, we show how to build a supersymmetric NPRG formalism with emphasis on time-reversal symmetric problems, whose supersymmetric structure allows for a particularly simple implementation of NPRG in which causality issues are transparent. We illustrate the two approaches on the example of Model A within the derivative expansion approximation at order two, and check that they yield identical results.Comment: 28 pages, 1 figure, minor corrections prior to publicatio

Repensant, reescrivint, refent o aprenent a ensenyar ciències mitjançant l'anglès

Es presenten les reflexions sobre didàctica de les ciències generades a partir de les revisions del material didàctic AICLE (ciències naturals en anglès) per a 1r d'ESO, realizades a la UAB durant les tutories amb la Dra. Cristina Escobar, de Didàctica de la Llengua, i la Dra. Neus Sanmartí, de Didàctica de les Ciències. Els materials han estat experimentats a l'Institut Montserrat amb un grup de 30 alumnes gràcies al Pla Experimental de Llengües Estrangeres concedit pel Departament d'Educaci

El valencià en l'església: 1707-2007

Felip V va respectar els concordats vigents i no va abolir els furs eclesiàstics, per això el decret de Nova Planta no va tindre una incidència directa sobre l’ús del valencià a l’església valentina. No obstant, de forma indirecta sí hi va influir, potenciant el procés castellanitzador que ja venia donant-se amb anterioritat. Pauta, aquesta, que arriba fins el concili Vaticà II i que, increïblement, no millora en els anys posteriors al mateix.Felipe V respetó los concordatos vigentes y no abolió los fueros eclesiásticos, por eso el decreto de Nueva Planta no tuvo una incidencia directa sobre el uso del valenciano en la iglesia valentina. No obstante, de forma indirecta sí influyó, potenciando el proceso castellanizador que ya venia dándose con anterioridad. Pauta, ésta, que llega hasta el concilio Vaticano II y que, increíblemente, no mejora en los años posteriores al mismo.Philip V respected the concordats in force and did not abolish the ecclesiastical privileges. Thus the Nueva Planta decree had no direct impact on the use of the Valencian language in the Valencian Church. Nevertheless it did have an indirect influence, favouring the process of castilianization which had started beforehand. This situation continues until the Second Vatican Council and, surprisingly, it is not altered in the years to follow

Single-site approximation for reaction-diffusion processes

We consider the branching and annihilating random walk $A\to 2A$ and $2A\to 0$ with reaction rates $\sigma$ and $\lambda$, respectively, and hopping rate $D$, and study the phase diagram in the $(\lambda/D,\sigma/D)$ plane. According to standard mean-field theory, this system is in an active state for all $\sigma/D>0$, and perturbative renormalization suggests that this mean-field result is valid for $d >2$; however, nonperturbative renormalization predicts that for all $d$ there is a phase transition line to an absorbing state in the $(\lambda/D,\sigma/D)$ plane. We show here that a simple single-site approximation reproduces with minimal effort the nonperturbative phase diagram both qualitatively and quantitatively for all dimensions $d>2$. We expect the approach to be useful for other reaction-diffusion processes involving absorbing state transitions.Comment: 15 pages, 2 figures, published versio

Large-scale structures in the stellar wind of fast-rotating stars spawned by the presence of Earth-like planets

Forming planets around young, fast-rotating solar-like stars are exposed to an intense X-ray/extreme ultraviolet radiation field and strongly magnetized stellar winds, as a consequence of the high magnetic activity of these stars. Under these conditions, Earth-like exoplanets may experience a rapid loss of their primordial hydrogen atmospheres, resulting in atmosphere-less rocky obstacles for the stellar winds. The interaction of stellar winds with those planets leads to the formation of potentially observable structures due to the formation of large-scale magnetic field and density disturbances in the vicinity of these planets, such as bow shocks, induced magnetospheres and comet-like tails. In this work, we study the interaction between the stellar winds of active, fast-rotating solar-like stars in the superfast-magnetosonic regime with Earth-like, unmagnetized, tenuous atmosphere, planetary obstacles through numerical 3D simulations using the PLUTO magnetohydrodynamical code. The properties of AB Doradus, a nearby young star with a small rotation period (0.51 days) and a strong flaring activity, have been used to parameterize this early wind state. Bow shock and induced magnetosphere formation are characterized through the alfv\'enic Mach number MA of the wind, for different stellar wind configurations. Large bow shocks, up to an extension of ~7.0 planetary radii are found for low-MA winds. The general increase of density, temperature and magnetic field in these large-scale structures formed around planets may result in potentially detectable spectral signatures

Mid-term report for the CORE Organic II funded project. “Innovative cropping Practices to increase soil health of organic fruit tree orchards” BIO-INCROP

Activities performed in the first part of BIO-INCROP project concern five of the eight main objectives fixed in the project proposal. They are: Evaluation of soil borne pest and pathogens involved in replant disease Role of rhizospheric bacterial and fungal communities in plant health Selection of naturally available resources to increase microbial diversity and biomass Compost and organic amendments Evaluation of biologically active formulates The document reports main research results and shows main items of dissemination activity performed in the first part of the project