Quasi-particle creation by analogue black holes

We discuss the issue of quasi-particle production by ``analogue black holes'' with particular attention to the possibility of reproducing Hawking radiation in a laboratory. By constructing simple geometric acoustic models, we obtain a somewhat unexpected result: We show that in order to obtain a stationary and Planckian emission of quasi-particles, it is not necessary to create an ergoregion in the acoustic spacetime (corresponding to a supersonic regime in the flow). It is sufficient to set up a dynamically changing flow either eventually generating an arbitrarily small sonic region v=c, but without any ergoregion, or even just asymptotically, in laboratory time, approaching a sonic regime with sufficient rapidity.Comment: 30 pages, 16 figure

Simulation of Acoustic Black Hole in a Laval Nozzle

A numerical simulation of fluid flows in a Laval nozzle is performed to observe formations of acoustic black holes and the classical counterpart to Hawking radiation under a realistic setting of the laboratory experiment. We determined the Hawking temperature of the acoustic black hole from obtained numerical data. Some noteworthy points in analyzing the experimental data are clarified through our numerical simulation.Comment: 26 pages, published versio

Metodologia del estudio de alternativas en el delta del llobregat

El Delta del Llobregat acoge en la actualidad la implantación de una nueva autovía y la remodelación de infraestructuras existentes determinada por la construcción de la denominada Pata Sur (acceso al Aeropuerto de Barcelona, el Nus del Llobregat y el Nus de Bellvitge). El estudio de planificación llevado a cabo combina las etapas de desarrollo clásicas, con la innovación metodológica derivada de las herramientas empleadas. La construcción semiautomática de modelos de grafos de transporte se ha realizado con el editor gráfico de redes GETRAM que permite a partir de una cartografía digitalizada la definición ágil de las características de las distintas secciones de la red modelizada en un ámbito de estudio (carriles, anchura, velocidad, longitud, capacidad). A partir del formato interno GETRAM se han podido generar: los modelos de grafos de la situación actual y de las alternativas de estudio en formato EMME/2, y los submodelos de puntos críticos a estudiar mediante la simulación microscópica con AIMSUN2. El modelo de planificación en EMME/2 ha permitido cuantificar la demanda actual, evaluar las alternativas propuestas y sus puntos críticos, así como facilitar las matrices de movilidad y proporciones de giro de los subámbitos a analizar mediante simulación microscópica.Peer ReviewedPostprint (published version

A methodology for private transportation planning assessment: GETRAM environment, an application to Barcelona's metropolitan area

Traffic assignment models based on the user equilibrium approach are one of the most widely used tools in transportation planning analysis. Based on Wardrop’s, principle as a behavioral principle modeling the route choice process, they lead to a nice mathematical model for which there are efficient algorithms that provide solutions in terms of the expected flows on network links. Resulting flows offer a static average view of the expected use of the road infrastructure under the modeling hypothesis. This information has usually been enough for the planning decisions. However, the evolution of advanced technologies and their application to modern traffic management systems require in most cases a dynamic view complementing the static estimates provided by the assignment tools. The planned infrastructure is probably sufficient for average demand, but time-varying traffic flows, i.e. at peak periods, combined with the influence of road geometry, can produce undesired congestion that can not be forecasted or analysed with the static tools. There is a clear case for a change in the analysis methodology such as combination of a well known traffic assignment tool, the EMME/2 model, with a microscopic traffic simulator, the AIMSUN2 (Advanced Interactive Microscopic Simulator for Urban and Non-urban Networks) which this paper proposes.Peer ReviewedPostprint (author's final draft

Time-resolved density correlations as probe of squeezing in toroidal Bose-Einstein condensates

I study the evolution of mean field and linear quantum fluctuations in a toroidal Bose-Einstein condensate, whose interaction strength is quenched from a finite (repulsive) value to zero. The azimuthal equal-time density-density correlation function is calculated and shows temporal oscillations with twice the (final) excitation frequencies after the transition. These oscillations are a direct consequence of positive and negative frequency mixing during non-adiabatic evolution. I will argue that a time-resolved measurement of the equal-time density correlator might be used to calculate the moduli of the Bogoliubov coefficients and thus the amount of squeezing imposed on a mode, i.e., the number of atoms excited out of the condensate.Comment: 18 pages, IOP styl

Pla de restauració ambiental de l’àrea incendiada d’Andratx, Estellencs i Calvià. Metododologia i resum de les actuacions posteriors a l’incendi

Dia 26 de juliol de 2013 es va declarar a sa Coma Calenta (Andratx), un incendi forestal que va acabar afectant 2.406,75 ha al sud-oest de la Serra de Tramuntana. La gran superfície afectada, així com l‟elevat risc potencial d‟erosió del sòl degut a la complexa orografia, feren imprescindible i urgent l‟elaboració d‟un pla de restauració ambiental que definís i organitzés, en l‟espai i en el temps, les actuacions necessàries per a restaurar la zona afectada. Aquestes actuacions es varen orientar, primer, a garantir la seguretat per a les persones i els béns i, després, a prevenir i controlar la generació de processos erosius, prevenir l‟aparició de plagues o malalties, restablir els hàbitats naturals i recuperar la qualitat del paisatge alterat. A fi d‟establir un ordre de prioritats en la programació i ubicació dels treballs a executar, la zona afectada es va dividir en conques de drenatge que es classificaren segons la seva vulnerabilitat ecològica post incendi, determinada en funció d‟una avaluació ponderada de diferents variables referents al risc d‟erosió del sòl, el potencial de regeneració de la vegetació i l‟impacte visual. Per altra banda, l‟important impacte mediàtic i social generat es va aprofitar per sensibilitzar la societat sobre la cultura del risc i la necessitat d‟autoprotecció, i va alhora provocar iniciatives post incendi pioneres en l‟àmbit administratiu de les Illes, com la creació de la Comissió Tot(s) per sa Serra

Hawking radiation from "phase horizons" in laser filaments?

Belgiorno et al have reported on experiments aiming at the detection of (the analogue of) Hawking radiation using laser filaments [F. Belgiorno et al, Phys. Rev. Lett. 105, 203901 (2010)]. They sent intense focused Bessel pulses into a non-linear dielectric medium in order to change its refractive index via the Kerr effect and saw creation of photons orthogonal to the direction of travel of the pluses. Since the refractive index change in the pulse generated a "phase horizon" (where the phase velocity of these photons equals the pulse speed), they concluded that they observed the analogue of Hawking radiation. We study this scenario in a model with a phase horizon and a phase velocity very similar to that of their experiment and find that the effective metric does not quite correspond to a black hole. The photons created in this model are not due to the analogue of black hole evaporation but have more similarities to cosmological particle creation. Nevertheless, even this effect cannot explain the observations -- unless the pulse has significant small scale structure in both the longitudinal and transverse dimensions.Comment: 13 pages RevTeX, 2 figure

Experimental demonstration of the supersonic-subsonic bifurcation in the circular jump: A hydrodynamic white hole

We provide an experimental demonstration that the circular hydraulic jump represents a hydrodynamic white hole or gravitational fountain (the time-reverse of a black hole) by measuring the angle of the Mach cone created by an object in the "supersonic" inner flow region. We emphasise the general character of this gravitational analogy by showing theoretically that the white hole horizon constitutes a stationary and spatial saddle-node bifurcation within dynamical-systems theory. We also demonstrate that the inner region has a "superluminal" dispersion relation, i.e., that the group velocity of the surface waves increases with frequency, and discuss some possible consequences with respect to the robustness of Hawking radiation. Finally, we point out that our experiment shows a concrete example of a possible "transplanckian distortion" of black/white holes.Comment: 5 pages, 5 figures. New "transplanckian effect" described. Several clarifications, additional figures and references. Published versio