Experiments and characterization of low-frequency oscillations in a granular column

The behaviour of a vertically vibrated granular bed is reminiscent of a liquid in that it exhibits many phenomena such as convection and Faraday-like surface waves. However, when the lateral dimensions of the bed are confined such that a quasi-one-dimensional geometry is formed, the only phenomena that remain are bouncing bed and the granular Leidenfrost effect. This permits the observation of the granular Leidenfrost state for a wide range of energy injection parameters, and more specifically allows for a thorough characterisation of the low-frequency oscillation (LFO) that is present in this state. In both experiments and particle simulations we determine the LFO frequency from the power spectral density of the centre of mass signal of the grains, varying the amplitude and frequency of the driving, the particle diameter and the number of layers in the system. We thus find that (i) the LFO frequency is inversely proportional to the fast inertial time scale and (ii) decorrelates with a typical decay time proportional to the slow dissipative time scale in the system. The latter is consistent with the view that the LFO is driven by the inherent noise that is present in the granular Leidenfrost state with a low number of particles

Hydro-micromechanical modeling of wave propagation in saturated granular media

Biot's theory predicts the wave velocities of a saturated poroelastic granular medium from the elastic properties, density and geometry of its dry solid matrix and the pore fluid, neglecting the interaction between constituent particles and local flow. However, when the frequencies become high and the wavelengths comparable with particle size, the details of the microstructure start to play an important role. Here, a novel hydro-micromechanical numerical model is proposed by coupling the lattice Boltzmann method (LBM) with the discrete element method (DEM. The model allows to investigate the details of the particle-fluid interaction during propagation of elastic waves While the DEM is tracking the translational and rotational motion of each solid particle, the LBM can resolve the pore-scale hydrodynamics. Solid and fluid phases are two-way coupled through momentum exchange. The coupling scheme is benchmarked with the terminal velocity of a single sphere settling in a fluid. To mimic a pressure wave entering a saturated granular medium, an oscillating pressure boundary condition on the fluid is implemented and benchmarked with one-dimensional wave equations. Using a face centered cubic structure, the effects of input waveforms and frequencies on the dispersion relations are investigated. Finally, the wave velocities at various effective confining pressures predicted by the numerical model are compared with with Biot's analytical solution, and a very good agreement is found. In addition to the pressure and shear waves, slow compressional waves are observed in the simulations, as predicted by Biot's theory.Comment: Manuscript submitted to International Journal for Numerical and Analytical Methods in Geomechanic

On the steady streaming flow due to high-frequency vibration in nearly inviscid liquid bridges

The steady streaming flow due to vibration in capillary bridges is considered in the limiting case when both the capillary Reynolds number and the non-dimensional vibration frequency (based on the capillary time) are large. An asymptotic model is obtained that provides the streaming flow in the bulk, outside the thin oscillatory boundary layers near the disks and the interface. Numerical integration of this model shows that several symmetric and non-symmetric streaming flow patterns are obtained for varying values of the vibration parameters. As a by-product, the quantitative response of the liquid bridge to high-frequency axial vibrations of the disks is also obtained

Metabolismo de metilglioxal en macroalgas durante desecación

Indexación: Scielo; Web of Science.In primary producers, diverse stressors cause an over-production of methylglyoxal (MG), which is principally detoxified by glyoxalase I (GLO1) activity. A recent proteomic study found that GLO1 was up-regulated during natural desiccation in the red seaweed Pyropia orbicularis, which inhabits the upper intertidal rocky zone and compared to other species, is highly tolerant to air exposure. To better understand and determine differential responses to desiccation stress, this study evaluated MG concentration and GLO1 activity in two species with contrasted vertical distribution, P. orbicularis and Lessonia spicata (lower distribution). Results showed that P. orbicularis successfully scavenges MG via increased GLO1 activity during desiccation. In contrast, GLO1 activity in L. spicata did not increase during desiccation, resulting in MG overproduction. This study is the first to quantify MG and GLO1 levels in seaweeds during natural stress, and partly explain the mechanisms by which P. orbicularis is dominant in the upper rocky intertidal zone.http://ref.scielo.org/tp4sn

¿Rebelión en Cataluña? La Fiscalía de la Audiencia Nacional persigue “sombras rebeldes”

La declaración de independencia realizada por el Parlament de Cataluña el 9 de noviembre de 2015 y la actuación posterior de algunos ayuntamientos catalanes han sido calificadas por la Fiscalía de la Audiencia Nacional como posible delito de rebelión. En el texto se exponen argumentos jurídicos (penales y constitucionales) para contradecir rotundamente dicha afirmación, que hace sospechar la utilización política de la Fiscalía, en contra de su estatuto constitucional de imparcialidad. Palabras clave: Rebelión, estado de sitio, Constitución, poder militar, orden público, independencia, Cataluña, País Vasco. Abstract: The declaration of independence by the Parliament of Catalonia on 9 November 2015 and the subsequent actions of some municipalities have been ranked by the prosecutor of the “Audiencia Nacional” as a possible crime of rebellion. The article contradicts this claim from a criminal and constitutional perspective, and raises suspicion about the political use of the public prosecution and the fulfillment of its constitutional duties of impartiality. Keywords: Rebellion, state of siege, constitution, military power, public order, independence, Catalonia, Basque country

Aspectos políticos y jurisdiccionales del mecanismo de solución de controversias de la Organización Mundial de Comercio

El procedimiento de solución de diferencias constituye la piedraangular o base del sistema multilateral de comercio y una contribuciónexcepcional de la Organización Mundial de Comercio (OMC) a laestabilidad de la economía mundial tanto en su dimensión políticacomo jurisdiccional. En ese sentido, el procedimiento de la OMC poneel énfasis en el imperio de la ley y otorga mayor seguridad y previsibilidadal sistema de comercio/ fundamentándose en normas claramentedefinidas y estableciendo plazos para ultimar el procedimiento