La "máquina" o "generador" de terremotos en un laboratorio universitario

La máquina o generador de terremotos es un dispositivo experimental que trata de modelizar el comportamiento de una falla. En la actividad propuesta, se le muestra al alumnado la complejidad de ciertos sistemas, así como la dificultad de predecir su comportamiento. Aunque inicialmente se postuló como un experimento abierto dirigido a estudiantes de enseñanza secundaria y bachillerato, la calidad de los datos que pueden obtenerse permite que pueda plantearse como un experimento en unlaboratorio universitario de ciencias de la Tierra. Los datos obtenidos en una experiencia de este tipo pueden ser equiparables, en cierto sentido, a los datos obtenidos por redes sísmicas regionales, en especial, los datos referentes a la sismicidad generada por una falla o sistema de fallas, en términos de magnitud, tiempo y caída de esfuerzos. Eso sí, con la clara ventaja de que en pocos minutos puede reproducirse lo que serían cientos o miles de años de acción de las fuerzas tectónicas. En función del nivel del curso en el que se proponga dicha experiencia, planteándose en este caso como una experiencia cerrada centrada en la obtención de determinados resultados, se pueden utilizar diferentes análisis de datos, fundamentalmente de tipo estadístico. Estos análisis permitirán conocer el nivel de predictibilidad de un modelo de estas características. Este trabajo plantea diferentes métodos y analiza los resultados que pueden obtenerse con este modelo mecánic

Experimental status of the ππ\pi\pi isoscalar S wave at low energy: f0(600)f_0(600) pole and scattering length

The experimental results obtained in the last few years on kaon decays (K$\to2\pi$ and, above all, Ke4 decays) allow a reliable, model independent determination of low energy $\pi\pi$ scattering in the S0 wave. Using them and, eventually, other sets of data, it is possible to give a precise parametrization of the S0 wave as well as to find the scattering length and effective range parameter. One can also perform an extrapolation to the pole of the "$\sigma$ resonance" [$f_0(600)$]. We obtain the results $$a_0^{(0)}=0.233\pm0.013 M^{-1}_\pi,\quad b_0^{(0)}=0.285\pm0.012 M^{-3}_\pi$$ and, for the $\sigma$ pole, M_\sigma=484\pm17 \mev,\quad\gammav_\sigma/2= 255\pm10 {\rm MeV}.Comment: Plain TeX;4 figures; improved data used; version to appear in Phys. Rev.

Light propagation through optical media using metric contact geometry

In this work, we show that the orthogonality between rays and fronts of light propagation in a medium is expressed in terms of a suitable metric contact structure of the optical medium without boundaries. Moreover, we show that considering interfaces (modeled as boundaries) orthogonality is no longer fulfilled, leading to optical aberrations and in some cases total internal reflection. We present some illustrative examples of this latter point.Comment: 8 pages, 7 figure

Signaling alterations and cytokine profiles in late metastatic colorectal cancer promote an antiinflammatory profile and proliferation enhacement

Comunicaciones a congreso

The Complementarity between segment disclosure and earnings quality, and its effect on cost of capital

We investigate the role of earnings quality in determining the levels of segment disclosure, and whether and how better quality earnings and segment disclosure influences cost of capital. Using a large US sample for the period 2001-2006, we find a positive relation between earnings quality and levels of segment disclosures. We also find that firms providing better quality segment information, contingent upon good earnings quality, enjoy lower cost of capital. We base our empirical tests on a self created index of segment disclosure. Our results contribute to a better understanding of (1) the incentives for providing segment disclosures, and (2) how accounting quality (quality of segment information and earnings quality) is related to the cost of capital

Chiral condensate thermal evolution at finite baryon chemical potential within Chiral Perturbation Theory

We present a model independent study of the chiral condensate evolution in a hadronic gas, in terms of temperature and baryon chemical potential. The meson-meson interactions are described within Chiral Perturbation Theory and the pion-nucleon interaction by means of Heavy Baryon Chiral Perturbation Theory, both at one loop, and nucleon-nucleon interactions can be safely neglected within our hadronic gas domain of validity. Together with the virial expansion, this provides a systematic expansion at low temperatures and chemical potentials, which includes the physical quark masses. This can serve as a guideline for further studies on the lattice. We also obtain estimates of the critical line of temperature and chemical potential where the chiral condensate melts, which systematically lie somewhat higher than recent lattice calculations but are consistent with several hadronic models. We have also estimated uncertainties due to chiral parameters, heavier hadrons and higher orders through unitarized Chiral Perturbation Theory.Comment: 15 pages, 15 figures, 3 tables, ReVTeX. Version to appear in Phys. Rev. D. References added. More conservative estimate of applicability domain, with new figure. More detailed explanation of final results with two more figures. Results unchange

Development of a Dynamic Goniometer with an Incremental Encoder

Angle dynamic measurements of body joints have become an important parameter to know for sportsmen, physicians and analysts of rehabilitation processes. The development of devices that allows those measurements turns out to be a hard work for biomedical engineers because during the acquisition process the mechanical system usually affects the natural joints movements. Digital goniometers have been constructed using different electronic principles, especially using resistance variations in potentiometers. In this paper we propose the construction of a dynamic goniometer with an incremental encoder using a mechanical transmission between a hinge and a pulley connected to an optical disk. The rotation is detected with an infrared led and a phototransistor. Calculations are done through a microcontroller and finally shown in real time using a liquid crystal display (LCD).La medición dinámica de los ángulos articulares se ha convertido en un parámetro fundamental para deportistas, médicos y analistas de los procesos de rehabilitación. El desarrollo de dispositivos para estas aplicaciones ha presentado retos importantes debido a la imposibilidad de implementar los sistemas mecánicos requeridos para la medición, sin afectar el movimiento natural de las articulaciones. Los goniómetros digitales se han construido a partir de diferentes principios electrónicos, particularmente basados en las variaciones resistivas de potenciómetros. Este trabajo muestra el desarrollo e implementación de un goniómetro dinámico basado en un encoder incremental con un sistema de transmisión mecánico entre una articulación de tipo bisagra y una polea conectada a un disco óptico. La rotación se detecta con un LED infrarrojo y un fototransistor. El cálculo del movimiento angular en la articulación se realiza con un microcontrolador. Finalmente los datos se muestran en tiempo real en una pantalla de cristal líquido (LCD)

Statistical analysis of Ni nanowires breaking processes: a numerical simulation study

A statistical analysis of the breaking behavior of Ni nanowires is presented. Using molecular dynamic simulations, we have determined the time evolution of both the nanowire atomic structure and its minimum cross section (Sm(t)). Accumulating thousands of independent breaking events, Sm histograms are built and used to study the influence of the temperature, the crystalline stretching direction and the initial nanowire size. The proportion of monomers, dimers and more complex structures at the latest stages of the breaking process are calculated, finding important differences among results obtained for different nanowire orientations and sizes. Three main cases have been observed. (A) [111] stretching direction and large nanowire sizes: the wire evolves from more complex structures to monomers and dimers prior its rupture; well ordered structures is presented during the breaking process. (B) Large nanowires stretched along the [100] and [110] directions: the system mainly breaks from complex structures (low probability of finding monomers and dimers), having disordered regions during their breakage; at room temperature, a huge histogram peak around Sm=5 appears, showing the presence of long staggered pentagonal Ni wires with ...-5-1-5-... structure. (C) Initial wire size is small: strong size effects independently on the temperature and stretching direction. Finally, the local structure around monomers and dimmers do not depend on the stretching direction. These configurations differ from those usually chosen in static studies of conductance.Comment: 18 pages, 13 figure