Interplay of frequency-synchronization with noise: current resonances, giant diffusion and diffusion-crests

We elucidate how the presence of noise may significantly interact with the synchronization mechanism of systems exhibiting frequency-locking. The response of these systems exhibits a rich variety of behaviors, such as resonances and anti-resonances which can be controlled by the intensity of noise. The transition between different locked regimes provokes the development of a multiple enhancement of the effective diffusion. This diffusion behavior is accompanied by a crest-like peak-splitting cascade when the distribution of the lockings is self-similar, as it occurs in periodic systems that are able to exhibit a Devil's staircase sequence of frequency-lockings.Comment: 7 pages, 6 figures, epl.cls. Accepted for publication in Europhysics Letter

A curve selection lemma in spaces of arcs and the image of the Nash map

International audienceWe prove a finiteness result in the space of arcs X∞ of a singular variety X, which is an extension of the stability result of Denef and Loeser (Germs of arcs on singular algebraic varieties and motivic integration, Invent. Math. 135 (1999), 201-232). From this follows a Curve selection lemma for generically stable subsets of X∞. As a consequence, we extend to all dimensions the problem of wedges, proposed by M. Lejeune-Jalabert (Arcs analytiques et résolution minimale des singularités des surfaces quasi-homogénes, Lecture Notes Springer Verlag 777, 1980, 303-336), and we obtain that an affirmative answer to this problem is equivalent to the surjectivity of the Nash map. This implies, for instance, that the Nash map is bijective for sandwiched surface singularities

La persona adecuada en el momento adecuado: los miembros del comité de auditoría y la calidad de la información financiera

We analyze some personal characteristics of the members of the audit committee of the Spanish listed firms and the relation between these characteristics and earnings management. We find a non-linear relation with tenure, so that long tenures can initially compromise the directors’ independence but, after a given threshold, longer tenures improve the expertise of the members. Serving in too many boards has a negative influence on the ability of directors to detect earnings management, and higher academic background and more diverse professional background improve the directors’ abilities.En el presente trabajo analizamos la relación entre algunas características personales de los miembros del comité de auditoría de las empresas cotizadas españolas y la gestión del resultado. Nuestros resultados muestran una relación no lineal con la antigüedad en el consejo: mientras que en los primeros estadios una mayor duración puede comprometer la independencia de los consejeros, llega un punto en el que la mayor antigüedad en el comité incrementa su experiencia. Formar parte de un número excesivo de consejos redunda en una menor capacidad de los consejeros para detectar la gestión del resultado. Una formación académica más elevada y una experiencia profesional más diversa contribuyen a mejorar la calidad de la información financiera

Emplacement of Cuban Ophiolites

According to their lithological and structural characteristics, three ophiolite bearing structural units are recognized in Cuba: 1) The Northern Ophiolitic Belt, a complex mélange that stretches more than 1000 km along the island; 2) The metamorphic basement of the Cretaceous Volcanic Arc Terrane; and 3) The tectonic slices in the high pressure metamorphic Escambray (Guamuhaya) Massif of south central Cuba. The available age constrains indicate that relics of oceanic lithosphere in Cuba are Late Mesozoic in age and probably originated in two different tectonic environments; 1) in a Late Jurassic- Neocomian small oceanic basin resulting from drifting between North America and a southern continent; and 2) in a suprasubduction marginal basin developed between the North American passive margin and an Aptian-Albian volcanic arc. Serpentinite slices and the high pressure amphibolites in the Mesozoic metasedimentary rocks of the Escambray (Guamuhaya) Massif originated during closure of a small oceanic basin, possibly during the Albian. The basement metamorphic rocks of the Volcanic Arc Terrane were derived from Upper Jurassic- Neocomian oceanic crust, metamorphosed during the development on this crust of a Middle Cretaceous volcanic arc. Ophiolites of the northern belt were probably derived from both the formerly mentioned small oceanic basin and suprasubduction marginal basin, and were emplaced in several episodes from the Campanian to the Middle Eocene. The different ophiolite types in Cuba represent relics of the oceanic lithosphere (the Proto-Caribbean oceanic basin) that developed between North and South America after the Pangea breakup. An alternative plate tectonic model is proposed and discussed

Entropic stochastic resonance: the constructive role of the unevenness

We demonstrate the existence of stochastic resonance (SR) in confined systems arising from entropy variations associated to the presence of irregular boundaries. When the motion of a Brownian particle is constrained to a region with uneven boundaries, the presence of a periodic input may give rise to a peak in the spectral amplification factor and therefore to the appearance of the SR phenomenon. We have proved that the amplification factor depends on the shape of the region through which the particle moves and that by adjusting its characteristic geometric parameters one may optimize the response of the system. The situation in which the appearance of such entropic stochastic resonance (ESR) occurs is common for small-scale systems in which confinement and noise play an prominent role. The novel mechanism found could thus constitute an important tool for the characterization of these systems and can put to use for controlling their basic properties.Comment: 8 pages, 8 figure

Biased diffusion in confined media: Test of the Fick-Jacobs approximation and validity criteria

We study biased, diffusive transport of Brownian particles through narrow, spatially periodic structures in which the motion is constrained in lateral directions. The problem is analyzed under the perspective of the Fick-Jacobs equation which accounts for the effect of the lateral confinement by introducing an entropic barrier in a one dimensional diffusion. The validity of this approximation, being based on the assumption of an instantaneous equilibration of the particle distribution in the cross-section of the structure, is analyzed by comparing the different time scales that characterize the problem. A validity criterion is established in terms of the shape of the structure and of the applied force. It is analytically corroborated and verified by numerical simulations that the critical value of the force up to which this description holds true scales as the square of the periodicity of the structure. The criterion can be visualized by means of a diagram representing the regions where the Fick-Jacobs description becomes inaccurate in terms of the scaled force versus the periodicity of the structure.Comment: 20 pages, 7 figure