Localized Solid-State Amorphization at Grain Boundaries in a Nanocrystalline Al Solid Solution Subjected to Surface Mechanical Attrition

Using high-resolution electron microscopy, localized solid-state amorphization (SSA) was observed in a nanocrystalline (NC) Al solid solution (weight per cent 4.2 Cu, 0.3 Mn, the rest being Al) subjected to a surface mechanical attrition treatment. It was found that the deformation-induced SSA may occur at the grain boundary (GB) where either the high density dislocations or dislocation complexes are present. It is suggested that lattice instability due to elastic distortion within the dislocation core region plays a significant role in the initiation of the localized SSA at defective sites. Meanwhile, the GB of severely deformed NC grains exhibits a continuously varying atomic structure in such a way that while most of the GB is ordered but reveals corrugated configurations, localized amorphization may occur along the same GB.

Tutela del patrimonio cultural : marco jurídico estatal

Más de mil "bienes" se habían incorporado hasta el mes de octubre del año 2013 al Registro que lleva la "Comisión Nacional de Museos y de Monumentos y Lugares Históricos", organismo estatal creado en 1940 y que tiene como misión –en sustancia– preservar, defender y acrecentar el patrimonio histórico y artístico de la Nación Argentina. La riqueza y variedad del elenco, que se amplía año a año, son datos que informan acerca del magnífico patrimonio cultural que ostenta el país. Algo más de una quinta parte del Registro, cuyo catálogo se agrupa en diferentes "tipologías", atañe a bienes de naturaleza "religiosa", en altísimo porcentaje concernientes a la Iglesia Católica. Sólo en orden a exhibir la diversidad del repertorio, que atraviesa todo el territorio de la Nación, cabe señalar que fueron declarados como "Monumento Histórico" la Catedral de la ciudad de Salta (Provincia de Salta), el Santuario de Nuestro Señor de los Milagros de Mailín (Provincia de Santiago del Estero), el Monumento al Cristo Redentor de los Andes (Provincia de Mendoza), el Cementerio de la Misión Salesiana (Provincia de Tierra del Fuego) y las Capillas de los Cementerios Británico y Alemán (Ciudad de Buenos Aires)...

Polibio, el mundo helenístico y la problemática cultural : algunas líneas de reflexión en los últimos veinte años

Resumen: Nuestro conocimiento de algunos aspectos de las Historias de Polibio se ha incrementado significativamente durante las dos últimas décadas. En ese sentido, ha habido ciertos desarrollos importantes con respecto a aspectos culturales de la obra, cuyo alcance ha ido permitiendo repensar durante estos años algunos presupuestos clásicos sobre la relación entre Polibio, Roma y el mundo helenístico. Proponemos aquí ofrecer un rápido análisis de las tres principales líneas de estudio propuestas por los estudiosos, cuyo alcance es considerado, en efecto, como un total reubicación del historiador aqueo al interior del universo cultural del mundo helenístico.

Una inflación de tipo “cultural”

"El problema de la inflación en la Argentina data de largas décadas, y el país es conocido en el mundo como un caso de estudio específico, tanto a partir de la persistente inflación registrada desde la década de 1840 hasta la actualidad, como por el proceso hiperinflacionario de 1989. Hoy, una vez más, como desde hace 60 años, la Argentina se enfrenta a una inflación persistente. También a una carrera dólar paralelo vs dólar oficial. Los errores del pasado no han servido como aprendizaje, y se repiten una y otra vez..."

El aborto en la ley europea : derechos humanos, derechos sociales y la nueva tendencia cultural

Resumen: Este artículo se propone analizar: 1) si existe un verdadero “derecho al aborto” en la Convención Europea de Derechos Humanos, 2) si el aborto es una violación a los Derechos Sociales, 3) si la reciente tendencia en Europa frente a la restricción del aborto muestra que éste es un problema social y no un derecho o una libertad individual. Legisladores y organizaciones esperando proteger mejor a los niños y a las mujeres, del aborto, encontrarán críticas a la idea de la existencia de un derecho humano al aborto, así como el marco legal en el cual elaborar leyes protectorias.

Deformation mechanisms of face-centered-cubic metal nanowires with twin boundaries

This letter addresses the issue of deformation mechanisms and mechanical tensile behavior of the twinned metal nanowires using atomistic simulations. Free surfaces are always the preferential dislocation nucleation sites in the initial inelastic deformation stage, while with further plastic deformation, twin boundary interfaces will act as sources of dislocations with the assistance of the newly formed defects. The smaller the twin boundary spacing, the higher the yielding stresses of the twinned nanowires. Twin boundaries, which serve both as obstacles to dislocation motion and dislocation sources, can lead to hardening effects and contribute to the tensile ductility. This work illustrates that the mechanical properties of metal nanowires could be controlled by tailoring internal growth twin structures. (c) 2007 American Institute of Physics.

Legislação sobre patrimônio cultural

Reúne o conjunto de normas existentes sobre patrimônio cultural no plano da legislação infraconstitucional. Traz as normas legais que se referem à preservação do patrimônio cultural, desde o primeiro ato normativo que criou a figura jurídica do tombamento, passando pela instituição do registro como instrumento tutelar do patrimônio imaterial, até as convenções mundiais estabelecidas pela Unesco, das quais o Brasil é signatário, que foram incorporadas ao ordenamento jurídico brasileiro, através de decretos legislativos.

Molecular dynamics simulation of interaction of a dislocation array from a crack tip with grain boundaries

The interaction of a dislocation array emitted from a crack tip under mode II loading with asymmetric tilt grain boundaries (GBs) is analysed by the molecular dynamics method. The GBs can generally be described by planar and linear matching zones and unmatching zones. All GBs are observed to emit dislocations. The GBs migrated easily due to their planar and linear matching structure and asymmetrical type. The diffusion induced by stress concentration is found to promote the GB migration. The transmissions of dislocations are either along the matched plane or along another plane depending on tilt angle theta. Alternate processes of stress concentration and stress relaxation take place ahead of the pileup. The stress concentration can be released either by transmission of dislocations, by atom diffusion along GBs, or by migration of GBs by formation of twinning bands. The simulated results also unequivocally demonstrate two processes, i.e. asymmetrical GBs evolving into symmetrical ones and unmatching zones evolving into matching ones during the loading process.

An analysis of the effects of symmetrical tilt grain boundaries on the plastic deformation

A numerical investigation on the simple polycrystals containing three symmetrical tilt grain boundaries (GBs) is carried out within the framework of crystal plasticity which precisely considers the finite deformation and finite lattice rotation as well as elastic anisotropy. The calculated results show that the slip geometry and the redistribution of stresses arising from the anisotropy and boundary constraint play an important role in the plastic deformation in the simple polycrystals. The stress level along GB is sensitive to the load level and misorientation, and the stresses along QB are distributed nonuniformly. The GB may exhibit a softening or strengthening feature, which depends on the misorientation angle. The localized deformation bands usually develop accompanying the GB plastic deformation, the impingement of the localized band on the GB may result in another localized deformation band. The yield stresses with different misorientation angles are favorably compared with the experimental results.

Molecular dynamics studies on the local disordering of σ3 and σ11 grain boundaries in aluminium bicrystal

Molecular dynamics (MD) simulations using Morse interaction potential are performed in studies of [110] symmetrical tilt grain boundary (GB) structures with mis-orientation angles 50.5 degrees(Sigma 11), 129.5 degrees(Sigma 11), 70.5 degrees(Sigma 3) and 109.5 degrees(Sigma 3) at various tempratures. The GB structures are found to start local disordering at about 0.5T(m)(T-m is the melting point of aluminium) for 50.5 degrees(Sigma 11), 0.32T(m) for 129.5 degrees(Sigma 11) and 0.38T(m) for 70.5 degrees(Sigma 3), respectively. These results agree with conclusions deduced from the anelastic measurements. But, for twin-boundary structure 109.5 degrees(Sigma 3), this disordering has not been found even when temperature increases up to 0.9T(m).