The Ability of Significant Tidal Stress to Initiate Plate Tectonics

Plate tectonics is a geophysical process currently unique to Earth, has an important role in regulating the Earth's climate, and may be better understood by identifying rocky planets outside our solar system with tectonic activity. The key criterion for whether or not plate tectonics may occur on a terrestrial planet is if the stress on a planet's lithosphere from mantle convection may overcome the lithosphere's yield stress. Although many rocky exoplanets closely orbiting their host stars have been detected, all studies to date of plate tectonics on exoplanets have neglected tidal stresses in the planet's lithosphere. Modeling a rocky exoplanet as a constant density, homogeneous, incompressible sphere, we show the tidal stress from the host star acting on close-in planets may become comparable to the stress on the lithosphere from mantle convection. We also show that tidal stresses from planet-planet interactions are unlikely to be significant for plate tectonics, but may be strong enough to trigger Earthquakes. Our work may imply planets orbiting close to their host stars are more likely to experience plate tectonics, with implications for exoplanetary geophysics and habitability. We produce a list of detected rocky exoplanets under the most intense stresses. Atmospheric and topographic observations may confirm our predictions in the near future. Investigations of planets with significant tidal stress can not only lead to observable parameters linked to the presence of active plate tectonics, but may also be used as a tool to test theories on the main driving force behind tectonic activity.Comment: 34 pages, 3 figures, 3 Tables, accepted to Icaru

Structure determination of the clean Co(110) surface by LEED

The atomic structure of the (11 0) surface of cobalt has been determined by LEED using six intensity spectra at normal incidence. The surface exhibits the truncated bulk structure with a contraction of the first interlayer spacing by about 8.5% with respect to the bulk value. Quantitative evaluation of the LEED spectra was done using Zanazzi and Jona's and Pendry's r-factors. The minimum averaged r-factors are and . No change of the interatomic distances within the plane could be detected and no rearrangement of the surface structure takes place up to temperatures shortly below the transition temperature

Nr-CAM and neurofascin interactions regulate ankyrin G and sodium channel clustering at the node of Ranvier

AbstractVoltage-dependent sodium (Na+) channels are highly concentrated at nodes of Ranvier in myelinated axons and play a key role in promoting rapid and efficient conduction of action potentials by saltatory conduction. The molecular mechanisms that direct their localization to the node are not well understood but are believed to involve contact-dependent signals from myelinating Schwann cells [1] and interactions of Na+ channels with the cytoskeletal protein, ankyrin G [2]. Two cell adhesion molecules (CAMs) expressed at the axon surface, Nr-CAM and neurofascin, are also linked to ankyrin G and accumulate at early stages of node formation, suggesting that they mediate contact-dependent Schwann cell signals to initiate node development [3]. To examine the potential role of Nr-CAM in this process, we treated myelinating cocultures of DRG (dorsal root ganglion) neurons and Schwann cells with an Nr-CAM-Fc (Nr-Fc) fusion protein. Nr-Fc had no effect on initial axon-Schwann cell interactions, including Schwann cell proliferation, or on the extent of myelination, but it strikingly and specifically inhibited Na+ channel and ankyrin G accumulation at the node. Nr-Fc bound directly to neurons and clustered and coprecipitated neurofascin expressed on axons. These results provide the first evidence that neurofascin plays a major role in the formation of nodes, possibly via interactions with Nr-CAM

Producción innovadora y sustentable en un sistema acuapónico en la provincia de Buenos Aires

Esta experiencia se realizó en el Laboratorio de Acuicultura (U.A.MdP-UTN), el objetivo fue producir peces y vegetales reduciendo la tasa de recambio de agua y su descarte hacia el ambiente, resultando en un uso más sustentable. Esto se traduce en menores costos operativos del sistema, aumentando la rentabilidad productiva y beneficiando al medio ambiente. En nuestro país aún no se han implementado sistemas de producción de acuaponia con la especie Oreochromis niloticus (Tilapia del Nilo), lo cual lo hace más novedoso. Esta experiencia se realiza en un sistema de recirculación con un mínimo recambio de agua semanal. Los sistemas utilizados para el cultivo hidropónico son los denominados Sistema de Balsas y NFT (Nutrient Film Technique) y para los peces SRA (Sistema de Recirculación Acuícola). Como resultado se obtuvo un buen crecimiento de las hortalizas, cosechando cada 50 días hierbas aromáticas y ciboulette y cada 45 días verduras de hoja y tomates cherry; respecto a los peces se cosecharon a los tres meses ejemplares de 300gs. Como resultado se obtuvieron vegetales y pescado de muy buena calidad, fortalecido por parte de un panel de evaluación sensorial con una muy buena aceptación. En base a todo lo expuesto podemos concluir que este novedoso sistema de producción alternativo no solo es factible de realizar a pequeña escala, sino también extrapolarlo a mediana o mayor escala y en espacios de poca dimensión

A leed analysis of the (2×1)H-Ni(110) structure

A monolayer of H atoms adsorbed on Ni(110) below 180 K forms a (2×1) structure. The unit cell exhibits a glide symmetry plane and contains two adsorbed atoms. Based on a quantitative comparison between experimental and calculated LEED I/V spectra using standard R-factors the following structure was derived: On the clean Ni(110) surface the separation between the first two atomic layers, d12, is contracted by 8.5%±1.5% with respect to the bulk value; those between the second and third and the third and fourth layer, d23 and d34, are expanded by 3.5%±1.5% and 1%±1.5%, respectively—in agreement with recent other results. In the presence of the H adlayer the contraction of d12 is reduced to 4.5%±1.5%, while the expansion of d23 is not affected within the limits of accuracy. The third interlayer spacing d34 returns to its bulk value. The H atoms occupy threefold-coordinated sites formed by two Ni atoms from the first layer and one Ni atom from the second layer which confirms previous more qualitative conclusions based on He diffraction and vibrational spectroscopy. The bond lengths between H and its neighbouring Ni atoms were determined to be equal, namely 1.72±0.1 Å