387 research outputs found
Electrochemical corrosion and inhibition mechanisms of galvannealed steel
10 páginas, 11 figuras, 2 tablas.[ES] Se ha estudiado el mecanismo de corrosión de un acero galvanorrecocido, en 0,6 M de
cloruro sódico, mediante espectroscopia de impedancia electroquÃmica. Los resultados
revelan que el sistema, para tiempos mayores de 48 h de inmersión y hasta 1 mes en
NaCl, está controlado por un proceso de difusión en capa finita. A su vez, se ha estudiado
la efectividad de sales de cerio como inhibidor añadido en el medio agresivo, obteniéndose
porcentajes de inhibición del 85% para concentraciones de 500 y 1.000 ppm a las 24 h
de exposición. Además, los espectros de impedancia electroquÃmica revelan un cambio
en el mecanismo de corrosión del galvanorrecocido por la adición del cerio en el medio.[EN] The corrosion mechanism of galvannealed in 0,6 M NaCl has been evaluated by means of
electrochemical impedance spectroscopy (EIS). After 48 hours and for longer immersion
time, up to 1 month, in sodium chloride, the system is controlled by a diffusion process at
finite layer. Moreover, the effectiveness of cerium salts as inhibitor added in the electrolyte
has been studied. Inhibition percentages of about 85% for 500 and 1000 ppm at 24
hours have been found. On the hand, changes in the corrosion mechanism due to the
cerium presence were shown.Peer reviewe
Corrosion protection of aluminium alloys by sol-gel coatings
[ES] En el presente trabajo se estudia la protección frente a la corrosión que proporcionan tres nuevos recubrimientos nanoméricos
de baja temperatura de curado obtenidos a partir de silanos modificados. La sÃntesis de estos recubrimientos se realiza a
partir de una mezcla de dos soles, GPTS (glicidoxipropiltrimetoxisilano) prehidrolizado y un segundo sol TEOS/MTES.
Añadiendo a este sol inicial una disolución coloidal de partÃculas se obtienen recubrimientos nanoméricos de mayor espesor.
En el presente trabajo los recubrimientos particulados se obtuvieron incorporando un 25% en peso de partÃculas comerciales
de SiO2, Aerosil 300 y Aerosil R972 respectivamente. Una vez sintetizados, se depositaron mediante el método de centrifugado,
sobre dos aleaciones de aluminio, 5555 y 3005 empleadas como substratos. El espesor final de los recubrimientos
es de orden de 10 ìm, para el recubrimiento sin partÃculas y algo superiores, 12-14 ìm aproximadamente, para los recubrimientos
con partÃculas. Los resultados electroquÃmicos indicaron que, en todos los casos, las muestras recubiertas presentaban
una mejora en el comportamiento frente a la corrosión respecto de los substratos sin recubrir. La velocidad de corrosión
disminuye 3 órdenes de magnitud para los recubrimientos con partÃculas y ésta disminución es algo inferior para aquellos
que no contienen partÃculas.[EN] Present paper studies the corrosion protection of three new nanomeric coatings obtained from modified silanes and cured at
low temperatures. The synthesis of these coatings is carried out starting from a mixture of two sols separately prepared: a
prehydrolized GPTS (glicidoxipropiltrimetoxisilano) and a second sol TEOS/MTES. Adding to this initial sol a colloidal solution
of 25% in weight of commercial particles of SiO2, Aerosil 300 and Aerosil R972 respectively can be obtained thicker
nanomeric coatings. Once synthesized, they were deposited by means of the spin coating method onto two aluminum alloys,
5555 and 3005 used as substrates. The final thickness of the coatings is about 10 μm, for the coating without particles and
slightly higher, 12-14 μm approximately, for the coatings with particles. The electrochemical results indicated that, in all
cases, the coated samples presented an improvement in the corrosion behavior in comparison with bare alloys in aggressive
media of NaCl. The corrosion rate decreased three orders of magnitude for the coatings with particles and lower for those
that do not contain particles.Los autores quieren agradecer al proyecto BRITE BE-5111:
"High Performance protection with sol-gel coatings on metals
and enamels" por financiar parte de este estudio.Peer reviewe
Derecho y bienestar en animales de trabajo
Los animales han contribuido de manera fundamental con su trabajo al desarrollo de la sociedad. Desde los paÃses más avanzados hasta los menos desarrollados, encontramos distintos tipos de actividades laborales en las que participan los animales. Pero a causa de la herencia cultural recibida, en la cual siempre han sido considerados y catalogados como meros objetos, propiedad de los seres humanos, se les ha impedido gozar nunca de ningún tipo de derechos en este ámbito. Este hecho se traduce en la ausencia de normas que determinen unas condiciones dignas en las que éstos desarrollen sus múltiples trabajos. En la actualidad existe una extensa legislación en materia de bienestar animal que podrÃa ser extrapolada para crear un marco de protección de los animales en este ámbito. Por este motivo, se hace necesaria la creación de un protocolo que, a modo de guÃa, recoja y adapte la legislación ya existente para otros sectores y que junto a los principios y criterios que han sido descritos como piezas clave para garantizar el bienestar animal, sirva para establecer unos requisitos mÃnimos de obligado cumplimiento que deben marcar el desarrollo de cualquiera de las actividades de trabajo desarrolladas por animales.Animals have made a vital contribution towards developing of society. Both in less developed countries and in highly industrialized nations it can be found different types of work activities performed by animals. However, due to cultural conceptions considering the animals as mere objects of human property left them unable to enjoy their rights. What this means in practice is no the absence of norms that determine decent conditions in which these develop their multiple works. At present, there is a large amount of animal welfare legislation that could be extrapolated to create a framework for the protection of animals. It is, therefore, necessary to elaborate a protocol that, as a guide, collects and adapts all existing legislation in relation to the protection of animals while working. These principles and criteria have to be key elements to ensure animal welfare, defining the essential mandatory compliance that should mark the development of any work activity developed by animals
Early Triassic-Early Jurassic Bivalve Diversity Dynamics
Bivalves are a highly diversified molluscan class, with a long history dating from early Cambrian times (Cope, 2000). Although the group already showed a steady diversification trend during the Paleozoic, it only became highly successful and expanded rapidly from the Mesozoic onward. The Triassic was, for bivalves, first a recovery period and later a biotic diversification event. It was also the time bivalves first fully exploited their evolutionary novelties.Facultad de Ciencias Naturales y Muse
Early Triassic-Early Jurassic Bivalve Diversity Dynamics
Bivalves are a highly diversified molluscan class, with a long history dating from early Cambrian times (Cope, 2000). Although the group already showed a steady diversification trend during the Paleozoic, it only became highly successful and expanded rapidly from the Mesozoic onward. The Triassic was, for bivalves, first a recovery period and later a biotic diversification event. It was also the time bivalves first fully exploited their evolutionary novelties.Facultad de Ciencias Naturales y Muse
Biofacies analysis of Hettangian-Sinemurian bivalve/brachiopod associations from the Neuquén Basin (Argentina)
Based upon extensive sampling with strict stratigraphical control on Hettangian and Sinemurian deposits cropping out at the river Atuel region (southwest Mendoza Province), the presence of all bivalve and brachiopod genera was recorded. Data gathered from the analysed interval were processed by multivariate analysis and the resulting Q-mode dendrogram was used to discriminate five associations (i.e. Entolium-limoids, Pholadomya-Pinna-Pleuromya, Weyla-Gryphaea, Lywea and Cardinioides). These are not in simple stratigraphical succession but are recurrent, reflecting palaeosynecological and biofacies influences. The palaeoenvironmental implications of these associations are analysed, as well as their geographical and stratigraphical distributions in the studied sections (Arroyo Malo, El Pedrero and Las Chilcas). The Cardinioides association is controlled by palaeosalinity and corresponds to a paralic/estuarine environment, of restricted geographical and stratigraphical distribution, whereas the remaining associations correspond to normal marine shelf to littoral environments. The Lywea association is interpreted as allochthonous and probably an impoverished subset derived from the diverse Weyla-Gryphaea association. On the basis of the palaeoautecological characteristics of the taxa involved in terms of guilds represented in these benthonic associations, it is concluded that most of the associations were dominated by the epifauna, whereas in the Pholadomya-Pinna-Pleuromya association the infauna and semi-infauna were particularly conspicuous and diverse, and the Cardinioides association was characterized by shallow infauna. Typical basinal biofacies from deeper, off-shore environments, and fresh-water biofacies, are both missing
Invasion process of Limnoperna fortunei (Bivalvia: Mytilidae): the case of Uruguay river and emissaries of the Esteros del Iberá Wetland, Argentina
Limnoperna fortunei (Dunker, 1857), during its invasion process in South America, has caused severe impacts both on natural environments altering native biodiversity, ecosystem structure and function-, and on man-made structures causing economic looses. Twenty-one samples were taken from the right bank of the Uruguay River, from tributaries of the Uruguay and Paraná Rivers, the drainage of the Esteros del Ibera Wetland. Based on this fieldwork, the presence of larvae and adults of L. fortunei was determined. Also, through the comparison of environmental characteristic with the known tolerance limits for the species, the possibility of its establishment in environments not yet invaded was determined. Most of the sampling stations have features that allow the development of stable populations L. fortunei, including the rivers that drain the Esteros del Ibera, allowing access of this invasive species to this important wetland.Facultad de Ciencias Naturales y Muse
Invasion process of Limnoperna fortunei (Bivalvia: Mytilidae): the case of Uruguay river and emissaries of the Esteros del Iberá Wetland, Argentina
Limnoperna fortunei (Dunker, 1857), during its invasion process in South America, has caused severe impacts both on natural environments altering native biodiversity, ecosystem structure and function-, and on man-made structures causing economic looses. Twenty-one samples were taken from the right bank of the Uruguay River, from tributaries of the Uruguay and Paraná Rivers, the drainage of the Esteros del Ibera Wetland. Based on this fieldwork, the presence of larvae and adults of L. fortunei was determined. Also, through the comparison of environmental characteristic with the known tolerance limits for the species, the possibility of its establishment in environments not yet invaded was determined. Most of the sampling stations have features that allow the development of stable populations L. fortunei, including the rivers that drain the Esteros del Ibera, allowing access of this invasive species to this important wetland.Facultad de Ciencias Naturales y Muse
Colección helmintológica del Museo de La Plata: I. catálogo de preparaciones microscópicas, material tipo y no tipo
Slides refered to 106 helminth species, 11 Temnocephala, 1 Aspidogastrea, 11 Monogenes, 77 Digenea, 5 Cestoda and 1 Acanthocephala, held in the La Plata Museum helminthological collection are ctalogued. Species are organized according to their main taxonomic group and listed alphabetically according to the their original name. The registration number, indication of type rank, host, localization, locality is included. The original biliographic references where the specimens have been described are given, and when necesary supplementary references added. last, the cataloque is complemented with alphabetical list of 70 genera, of 100 helminth species and the 104 hosts included. In complience with Reccomentation 72D od the International Code of Zoological Nomeclature this catalogue includes type specimens in this collection aa no previous one has ever been published.Facultad de Ciencias Naturales y Muse
Colección helmintológica del Museo de La Plata: I. catálogo de preparaciones microscópicas, material tipo y no tipo
Slides refered to 106 helminth species, 11 Temnocephala, 1 Aspidogastrea, 11 Monogenes, 77 Digenea, 5 Cestoda and 1 Acanthocephala, held in the La Plata Museum helminthological collection are ctalogued. Species are organized according to their main taxonomic group and listed alphabetically according to the their original name. The registration number, indication of type rank, host, localization, locality is included. The original biliographic references where the specimens have been described are given, and when necesary supplementary references added. last, the cataloque is complemented with alphabetical list of 70 genera, of 100 helminth species and the 104 hosts included. In complience with Reccomentation 72D od the International Code of Zoological Nomeclature this catalogue includes type specimens in this collection aa no previous one has ever been published.Facultad de Ciencias Naturales y Muse
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