Ciudadanos en defensa del patrimonio mundial: el caso de la Mezquita de Córdoba

La Mezquita de Córdoba fue reconocida por Unesco en 1984 como Patrimonio Mundial por constituir la obra cumbre del arte islámico y andalusí en Europa y ser paradigma universal de concordia entre culturas. Construida en el año 785 por Abderramán I, en 1523 Carlos I autoriza edificar en su interior una Catedral renacentista que rompió la infinitud del bosque de columnas al tiempo que precipitó un mestizaje sin precedentes del islam y el cristianismo. Ambas realidades artísticas, históricas y culturales han convivido durante siglos en Córdoba hasta que en 1998, el Cabildo catedralicio, sus actuales gestores, se propusieron borrar la huella andalusí de todos los documentos oficiales de divulgación hasta el punto de eliminar el nombre de Mezquita y suprimir toda alusión a la arquitectura y herencia omeya de un monumento que es conocido en todo el mundo como el edificio andalusí emblemático por excelencia. En un acto de intolerancia y expolio cultural, el Obispado pretendió roclamar la supremacía católica sobre el Islam a costa del sentido común, de la historia, del arte, de la arquitectura y de la memoria de Córdoba y su significado en el mundo. En febrero de 2014, un grupo de ciudadanos cordobeses organizados como “Plataforma Mezquita-Catedral, Patrimonio de Tod@s” lanzó una campaña de denuncia que ha logrado reunir más de 385.000 firmas para reclamar la restitución del nombre y la memoria del universal monumento y exigir una gestión profesional. Entre los firmantes, se encuentran personalidades de la cultura de la talla de Juan Goytisolo, José Manuel Caballero Bonald, Emilio Lledó, Josefina Molina, Antonio Muñoz Molina, Antonio Gala, Rosa Montero, Norman Foster, Eduardo Galeano, Federico Mayor Zaragoza, Manolo Sanlúcar, José Chamizo y muchos otros de reconocido prestigio. La Plataforma ciudadana estima que la actual gestión de la Mezquita-Catedral de Córdoba es profundamente lesiva para la integridad del monumento, desleal con su historia, ofensiva con la memoria de Córdoba y contraria a los valores fundamentales sobre los que la Unesco la reconoció en 1984 como Patrimonio Mundial.

Reconfigurable computing for Monte Carlo simulations: results and prospects of the Janus project

We describe Janus, a massively parallel FPGA-based computer optimized for the simulation of spin glasses, theoretical models for the behavior of glassy materials. FPGAs (as compared to GPUs or many-core processors) provide a complementary approach to massively parallel computing. In particular, our model problem is formulated in terms of binary variables, and floating-point operations can be (almost) completely avoided. The FPGA architecture allows us to run many independent threads with almost no latencies in memory access, thus updating up to 1024 spins per cycle. We describe Janus in detail and we summarize the physics results obtained in four years of operation of this machine; we discuss two types of physics applications: long simulations on very large systems (which try to mimic and provide understanding about the experimental non equilibrium dynamics), and low-temperature equilibrium simulations using an artificial parallel tempering dynamics. The time scale of our non-equilibrium simulations spans eleven orders of magnitude (from picoseconds to a tenth of a second). On the other hand, our equilibrium simulations are unprecedented both because of the low temperatures reached and for the large systems that we have brought to equilibrium. A finite-time scaling ansatz emerges from the detailed comparison of the two sets of simulations. Janus has made it possible to perform spin glass simulations that would take several decades on more conventional architectures. The paper ends with an assessment of the potential of possible future versions of the Janus architecture, based on state-of-the-art technology.

Tethered Monte Carlo: computing the effective potential without critical slowing down

We present Tethered Monte Carlo, a simple, general purpose method of computing the effective potential of the order parameter (Helmholtz free energy). This formalism is based on a new statistical ensemble, closely related to the micromagnetic one, but with an extended configuration space (through Creutz-like demons). Canonical averages for arbitrary values of the external magnetic field are computed without additional simulations. The method is put to work in the two-dimensional Ising model, where the existence of exact results enables us to perform high precision checks. A rather peculiar feature of our implementation, which employs a local Metropolis algorithm, is the total absence, within errors, of critical slowing down for magnetic observables. Indeed, high accuracy results are presented for lattices as large as L = 1024.

Mean-value identities as an opportunity for Monte Carlo error reduction

In the Monte Carlo simulation of both lattice field theories and of models of statistical mechanics, identities verified by exact mean values, such as Schwinger-Dyson equations, Guerra relations, Callen identities, etc., provide well-known and sensitive tests of thermalization bias as well as checks of pseudo-random-number generators. We point out that they can be further exploited as control variates to reduce statistical errors. The strategy is general, very simple, and almost costless in CPU time. The method is demonstrated in the twodimensional Ising model at criticality, where the CPU gain factor lies between 2 and 4.

Tethered Monte Carlo: computing the effective potential without critical slowing down

We present Tethered Monte Carlo, a simple, general purpose method of computing the effective potential of the order parameter (Helmholtz free energy). This formalism is based on a new statistical ensemble, closely related to the micromagnetic one, but with an extended configuration space (through Creutz-like demons). Canonical averages for arbitrary values of the external magnetic field are computed without additional simulations. The method is put to work in the two-dimensional Ising model, where the existence of exact results enables us to perform high precision checks. A rather peculiar feature of our implementation, which employs a local Metropolis algorithm, is the total absence, within errors, of critical slowing down for magnetic observables. Indeed, high accuracy results are presented for lattices as large as L = 1024.

Optimized Monte Carlo method for glasses

A new Monte Carlo algorithm is introduced for the simulation of supercooled liquids and glass formers, and tested in two model glasses. The algorithm thermalizes well below the Mode Coupling temperature and outperforms other optimized Monte Carlo methods.