Procesos de severa deformación plástica para obtener materiales de grano nanométricos y ultrafinos

El objetivo del articulo es dar una visión global de uno de los más activos campos de investigación en el procesa- miento mecánico de materiales metálicos como es la obtención de materiales con grano nanométrico y ultrafino a través de la severa deformación plástica SDP. Se realiza una descripción de las más importantes técnicas pertenecientes a SDP, como lo son: la molienda mecánica, presión en canal angular constante, torsión a alta presión, unión por laminación acumulada, extrusión-compresión refiriéndose a los principios fundamentales, ventajas y limitaciones de cada una de ellas. Se incluyen resultados experimentales obtenidos por los presentes autores en la preparación de hierro y cobre. Adicionalmente, se presenta el gran potencial que tienen estos materiales en diferentes campos de aplicación, especialmente en la industria aeroespacial. Finalmente, se hace referencia a tendencias actuales de investigación comprendiendo dos áreas fundamentales, el estudio del comportamiento microestructural y mecánico, y el desarrollo de métodos de procesamiento escalables a nivel industrial.The aim of this paper is to provide a general overview of nanocrystalline and ultra-fine grain material production using severe plastic deformation (SPD), this being one of the most active research fields in the mechanical processing of materials. The paper gives an explanation of the more important SPD techniques (mechanical milling, equal channel angular pressing, high pressure torsion, extrusion-compression and accumulated roll-bond) as regards fundamental principles, advantages and limitations. Some experimental results for iron and copper obtained by this paper’s authors are attached. These materials’ great potential is shown in several fields of use, especially in the aerospace industry. Current research prospects are also referred to in terms of structural and mechanical behaviour and the development of large-scale industrial processing

Cobre nanocristalino y ultrafino obtenido por molienda mecánica

Este artículo presenta un método de obtención y caracterización de muestras masivas de cobre con tamaño de grano ultrafino (inferior a 1 μm) y nanocristalino (inferior a 100 nm). La fabricación del cobre se realiza inicialmente por el método de molien- da/aleado mecánico, obteniendo un polvo de estructura nanocristalina que posteriormente es consolidado por medio de un proceso de compactación en tibio a alta presión. El cobre masivo es sometido a caracterización microestructural analizando la evolución del tamaño de grano durante todas las etapas del proceso de fabricación, determinando las condiciones necesarias para desarrollar muestras en una amplia gama de tamaños de grano. La caracterización mecánica indica un incremento en la microdureza hasta valores de 3,40 GPa para el polvo NC sin consolidar. La resistencia a compresión se ve incrementada al re- ducir el tamaño de grano, obteniendo un límite elástico de 650 MPa para consolidados con tamaños de grano de ~62 nm.This article presents a method for the sample preparation and characterisation of bulk copper having grain size lower than 1 μm (ultra-fine grain) and lower than 100 nm grain size (nanocrystalline). Copper is initially manufactured by a milling/alloying me- chanical method thereby obtaining a powder having a nanocrystalline structure which is then consolidated through a process of warm compaction at high pressure. Microstructural characterisation of bulk copper samples showed the evolution of grain size during all stages involved in obtaining it. The results led to determining the necessary conditions for achieving a wide range of grain sizes. Mechanical characterisation indicated an increase in microhardness to values of around 3.40 GPa for unconsolida- ted nanocrystalline powder. Compressivee strength was increased by reducing the grain size, thereby obtaining an elastic limit of 650 MPa for consolidated copper having a ~ 62 nm grain size

Síncope secundario a arritmia ventricular en paciente con amiloidosis. ¿Un DAI siempre es la respuesta?

A 76 year-old man was admitted to our hospital because of a first episode of heart failure, with severe left ventricular dysfunction and ventricular hypertrophy. We performed an angiography, which was normal, so he was discharged to be studied in an oupatient center. He is then readmitted because of syncope. In the electrocardiographic monitoring, non-sustained ventricular monomorfic tachyarrythmia was observed. Cardiac magnetic resonance and scintigraphy with Tc99 were compatible with cardiac amyloidosis. Confirmatory biopsy was not possible. We thought about implanting an automatic defibrillator, finally discarding it because of lack of evidence. Finally, the patient died from pulseless electrical activity.Varón de 76 años que ingresa por insuficiencia cardíaca de debut con disfunción sistólica severa e hipertrofia ventricular. El estudio coronario no presenta lesiones, por lo que se da de alta como disfunción idiopática. Reingresa por síncope. Se mantiene monitorizado y se evidencia taquicardia ventricular monomorfa no sostenida que reproduce la clínica. Se amplía el estudio con resonancia magnética cardíaca y gammagrafía- Tc99, que resultan compatibles con amiloidosis cardíaca. No fue posible realizar biopsia confirmatoria. Se plantea el implante de desfibrilador automático implantable, descartándose por falta de evidencia. Final- mente, fallece por actividad eléctrica sin pulso

Impacts of the Tropical Pacific/Indian Oceans on the Seasonal Cycle of the West African Monsoon

The current consensus is that drought has developed in the Sahel during the second half of the twentieth century as a result of remote effects of oceanic anomalies amplified by local land–atmosphere interactions. This paper focuses on the impacts of oceanic anomalies upon West African climate and specifically aims to identify those from SST anomalies in the Pacific/Indian Oceans during spring and summer seasons, when they were significant. Idealized sensitivity experiments are performed with four atmospheric general circulation models (AGCMs). The prescribed SST patterns used in the AGCMs are based on the leading mode of covariability between SST anomalies over the Pacific/Indian Oceans and summer rainfall over West Africa. The results show that such oceanic anomalies in the Pacific/Indian Ocean lead to a northward shift of an anomalous dry belt from the Gulf of Guinea to the Sahel as the season advances. In the Sahel, the magnitude of rainfall anomalies is comparable to that obtained by other authors using SST anomalies confined to the proximity of the Atlantic Ocean. The mechanism connecting the Pacific/Indian SST anomalies with West African rainfall has a strong seasonal cycle. In spring (May and June), anomalous subsidence develops over both the Maritime Continent and the equatorial Atlantic in response to the enhanced equatorial heating. Precipitation increases over continental West Africa in association with stronger zonal convergence of moisture. In addition, precipitation decreases over the Gulf of Guinea. During the monsoon peak (July and August), the SST anomalies move westward over the equatorial Pacific and the two regions where subsidence occurred earlier in the seasons merge over West Africa. The monsoon weakens and rainfall decreases over the Sahel, especially in August.Peer reviewe

Search for heavy resonances decaying to two Higgs bosons in final states containing four b quarks

A search is presented for narrow heavy resonances X decaying into pairs of Higgs bosons (H) in proton-proton collisions collected by the CMS experiment at the LHC at root s = 8 TeV. The data correspond to an integrated luminosity of 19.7 fb(-1). The search considers HH resonances with masses between 1 and 3 TeV, having final states of two b quark pairs. Each Higgs boson is produced with large momentum, and the hadronization products of the pair of b quarks can usually be reconstructed as single large jets. The background from multijet and t (t) over bar events is significantly reduced by applying requirements related to the flavor of the jet, its mass, and its substructure. The signal would be identified as a peak on top of the dijet invariant mass spectrum of the remaining background events. No evidence is observed for such a signal. Upper limits obtained at 95 confidence level for the product of the production cross section and branching fraction sigma(gg -> X) B(X -> HH -> b (b) over barb (b) over bar) range from 10 to 1.5 fb for the mass of X from 1.15 to 2.0 TeV, significantly extending previous searches. For a warped extra dimension theory with amass scale Lambda(R) = 1 TeV, the data exclude radion scalar masses between 1.15 and 1.55 TeV

Measurement of the top quark mass using charged particles in pp collisions at root s=8 TeV

Peer reviewe

Nanocrystalline and ultrafine grain copper obtained by mechanical attrition

This article presents a method for the sample preparation and characterisation of bulk copper having grain size lower than 1 μm (ultra-fine grain) and lower than 100 nm grain size (nanocrystalline). Copper is initially manufactured by a milling/alloying me- chanical method thereby obtaining a powder having a nanocrystalline structure which is then consolidated through a process of warm compaction at high pressure. Microstructural characterisation of bulk copper samples showed the evolution of grain size during all stages involved in obtaining it. The results led to determining the necessary conditions for achieving a wide range of grain sizes. Mechanical characterisation indicated an increase in microhardness to values of around 3.40 GPa for unconsolida- ted nanocrystalline powder. Compressivee strength was increased by reducing the grain size, thereby obtaining an elastic limit of 650 MPa for consolidated copper having a ~ 62 nm grain size