W Pair Production at the LHC - I. Virtual O(alpha_s^2) Corrections in the High Energy Limit

We present the result for the two-loop and the one-loop squared virtual QCD corrections to the W boson pair production in the quark-anti-quark-annihilation channel in the limit where all kinematical invariants are large compared to the mass of the W boson. The infrared pole structure is in agreement with the prediction of Catani's general formalism for the singularities of two loop amplitudes.Comment: 22 pages, 1 figure, references added, typos corrected, final version as publishe

Cortante-fricción de los hormigones reciclados

The aim of this research was to determine the behavior of recycled concrete in response to the phenomenon of shear transfer. To perform it, a conventional control concrete and a concrete with 50% recycled coarse aggregate were designed. An additional goal was to shed light on how this behavior is modified with a pozzolanic addition, silica fume. Therefore, two types of concrete were designed, a conventional and a recycled concrete, both made with 8% of silica fume. In conclusion, a reduction of shear friction capacity was observed in recycled concretes, considerably higher in the case of the specimen without reinforcement. The addition of silica fume improved the behavior of recycled concretes. The results obtained were compared with the formulations of the different authors. In all cases, these were found to be conservative. However, the safety margins offered by recycled concretes are lower than those obtained with conventional concretes.En esta investigación se estudió el comportamiento de los hormigones reciclados frente al fenómeno de transmisión de cortante. Para ello se diseñó un hormigón convencional de control y un hormigón con el 50% del árido grueso reciclado. Adicionalmente, para determinar cómo este comportamiento se ve modificado con la incorporación de una adición puzolánica (humo de sílice), se procedió al diseño de un hormigón convencional y su correspondiente reciclado con un 8% de humo de sílice. Los resultados indicaron una disminución de la capacidad frente a este fenómeno en los hormigones reciclados, más acusada en ausencia de armadura pasante. La adición de humo de sílice mejora el comportamiento de este material. Los resultados experimentales obtenidos se compararon con formulaciones teóricas de diversos autores, concluyéndose que éstas son, en todos los casos, conservadoras, aunque reducen el margen de seguridad en los hormigones reciclados

Detection and partial molecular characterization of isolates of Grapevine leafroll-associated virus 4 and Grapevine rupestris vein feathering virus.

Resumo apresentado de número 371-2

Variáveis agronômicas e variabilidade viral entre videiras sintomáticas e assintomáticas para viroses.

Os objetivos deste trabalho foram avaliar variáveis agronômicas em videiras com e sem sintomas de virose e caracterizar isolados virais destas plantas

Investigation of dielectric anomalies at cryogenic temperatures in the (1-x)[Pb(Mg1/3 Nb2/3)O3]-xPbTiO3 system

Complex electrical permittivity measurements in (1-x)[Pb(Mg1/3 Nb2/3)O3]-xPbTiO3 ceramics for 0.10 x 0.40 were performed in the frequency and temperature range from 1 kHz to 100 kHz and from 15 to 600 K, respectively. Unexpected dielectric anomalies, which were frequency dependent, were found at cryogenic temperatures. It was verified that this dielectric behavior is always observed, independently of whether the composition presents a "normal" ferroelectric or a relaxor characteristic. The results were analyzed within the framework of two current models found in the literature. It was concluded that none of the proposed mechanisms uniquely satisfies the experimental results in the composition range investigated here.Comment: 9 pages, 7 figures - Accepted for publication in the Applied Physics Lette

Magnetic And Dielectric Proprieties Of Multiferroic (1-x)pb(fe 2/3w 1/3)o 3-xpbtio 3 Ceramics Prepared Via A Modified Two-stage Solid-state Reaction

Multiferroic Pb(Fe 2/3W 1/3)O 3-PbTiO 3 (PFW-PT) ceramics were synthesized via a modified two-stage solid-state reaction. This method utilized Fe 2WO 6, prepared at a first-stage, which was subsequently reacted with a stoichiometric amount of PbO and TiO 2 at the second stage. This procedure efficiently suppressed the formation of lead tungstates and leads to getting dense ceramics. Electric and dielectric properties of (1-x)Pb(Fe 2/3W 1/3)O 3-xPbTiO 3 solid solutions were investigated as a function of the frequency and temperature. All samples present density higher than 96% of the theoretical one, low percentage of pyrochlore phase (<2%) and relatively high electrical resistivity (>10 10 Ω.m). RF dielectric measurements over the temperature showed the presence of a peak, which is related to the ferro-paraelectric phase transition and conductive contributions (in the range 200-700 K), associated to a electronic hoping mechanism. The dielectric properties of the PFW shows a typical relaxor behaviour for x = 0 and 0.10 with frequency-dependent peak temperature (Tm), while the samples with higher PT-content undergo a 'normal' para-ferroelectric transition at the Curie temperature T C.The FE phase transition of PFW is shifted to higher temperatures by PbTiO 3 (PT) additions and high resistivity are obtained for PT containing samples. 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