On the Decreasing Failure Rate property for general counting process. Results based on conditional interarrival times

In the present paper we consider general counting processes stopped at a random time $T$, independent of the process. Provided that $T$ has the decreasing failure rate (DFR) property, we give sufficient conditions on the arrival times so that the number of events occurring before $T$ preserves the DFR property of $T$. These conditions involve the study of the conditional interarrival times. As a main application, we prove the DFR property in a context of maintenance models in reliability, by the consideration of Kijima type I virtual age models under quite general assumptions

Critical state analysis of orthogonal flux interactions in pinned superconductors

We show that, based on the critical state model for flux-line pinning in hard superconductors, one can assess the magnetic moment relaxation induced by the oscillations of a perpendicular magnetic field. Our theory follows a recent proposal of using phenomenological 2D modeling for the description of crossed field dynamics in high-T$_c$ superconductors [{\tt arXiv:cond-mat/0703330}]. Stationary regimes with either saturation to metastable configurations, or complete decay to the thermodynamic equilibrium are obtained. The transition between both types of response is related to the disappearance of a flux free core within the sample. As a common feature, a step-like dependence in the time relaxation is predicted for both cases. The theory may be applied to long bars of arbitrary and non homogeneous cross section, under in-plane magnetic field processes.Comment: 11 figures, submitte

Inversion mechanism for the transport current in type-II superconductors

The longitudinal transport problem (the current is applied parallel to some bias magnetic field) in type-II superconductors is analyzed theoretically. Based on analytical results for simplified configurations, and relying on numerical studies for general scenarios, it is shown that a remarkable inversion of the current flow in a surface layer may be predicted under a wide set of experimental conditions. Strongly inhomogeneous current density profiles, characterized by enhanced transport toward the center and reduced, or even negative, values at the periphery of the conductor, are expected when the physical mechanisms of flux depinning and consumption (via line cutting) are recalled. A number of striking collateral effects, such as local and global paramagnetic behavior, are predicted. Our geometrical description of the macroscopic material laws allows a pictorial interpretation of the physical phenomena underlying the transport backflow.Comment: 8 pages, 6 figures (Best quality pictures are available by author's contact

Una nueva subespecie de bivalvo en el Mioceno marino catalán

La especie Thracia dollfusi original del Aquitaniense y Burdigaliense de Francia y Portugal se cita por primera vez en el Langhiense de Cataluña. Con los ejemplares catalanes se crea la n. ssp. viai, que se distingue de la especie por su borde umbonal anterior poco convexo y su diversa cronostratigrafia. Se sugiere que la especie Thracia eggenburgensis, endémica de la cuenca danubiana, sea simplemente otra subespecie

La poética teleológica de George Santayana. Inspiración, conocimiento y felicidad en La razón en el arte

La vida de la razón supone la consagración de George Santayana tanto por su extensión como por convertirse en el desarrollo más completo de su filosofía moral. El cuarto volumen de la obra, titulado La razón en el arte, investiga el origen tanto histórico como sincrónico de la obra de arte. Incluida por el autor dentro del ámbito de lo moral, la poética de Santayana se articula sobre una relación estrecha entre ética y estética, ingenium y ars, literatura y filosofía, construyendo una propuesta teleológica y eudemónica sobre tres núcleos concretos: inspiración, conocimiento y felicidad.With The Life of Reason George Santayana earned his reputation as philosopher; this is due to its length but also because it is his most detailed moral work. The fourth volume of the work, entitled Reason in Art, analyzes both the historical and synchronic origin of the work of art. Santayana's Poetics are built on the strained relationship he draws between, ethics and aesthetics, ingenium and ars, literature and philosophy. He develops a teleological and eudaimonistic approach which centres on three concrete loci: inspiration, knowledge and happiness

On the preservation of log convexity and log concavity under some classical Bernstein-type operators

AbstractThis paper analyzes the preservation of both the log convexity and the log concavity under certain Bernstein-type operators. Some results are provided for the Bernstein, Szász, Baskakov, the gamma-type and the Weierstrass operators. Probabilistic methods support the proofs of these results