Localization lengths of ultrathin disordered gold and silver nanowires

The localization lengths of ultrathin disordered Au and Ag nanowires are estimated by calculating the wire conductances as functions of wire lengths. We study Ag and Au monoatomic linear chains, and thicker Ag wires with very small cross sections. For the monoatomic chains we consider two types of disorder: bounded random fluctuations of the interatomic distances, and the presence of random substitutional impurities. The effect of impurity atoms on the nanowire conductance is much stronger. Our results show that electrical transport in ultrathin disordered wires may occur in the strong localization regime, and with relatively small amounts of disorder the localization lengths may be rather small. The localization length dependence on wire thickness is investigated for Ag nanowires with different impurity concentrations.Comment: 6 pages, postscript figures included, submitted to PR

Innovative in silico approaches to address avian flu using grid technology

The recent years have seen the emergence of diseases which have spread very quickly all around the world either through human travels like SARS or animal migration like avian flu. Among the biggest challenges raised by infectious emerging diseases, one is related to the constant mutation of the viruses which turns them into continuously moving targets for drug and vaccine discovery. Another challenge is related to the early detection and surveillance of the diseases as new cases can appear just anywhere due to the globalization of exchanges and the circulation of people and animals around the earth, as recently demonstrated by the avian flu epidemics. For 3 years now, a collaboration of teams in Europe and Asia has been exploring some innovative in silico approaches to better tackle avian flu taking advantage of the very large computing resources available on international grid infrastructures. Grids were used to study the impact of mutations on the effectiveness of existing drugs against H5N1 and to find potentially new leads active on mutated strains. Grids allow also the integration of distributed data in a completely secured way. The paper presents how we are currently exploring how to integrate the existing data sources towards a global surveillance network for molecular epidemiology.Comment: 7 pages, submitted to Infectious Disorders - Drug Target

Structural constraints in complex networks

We present a link rewiring mechanism to produce surrogates of a network where both the degree distribution and the rich--club connectivity are preserved. We consider three real networks, the AS--Internet, the protein interaction and the scientific collaboration. We show that for a given degree distribution, the rich--club connectivity is sensitive to the degree--degree correlation, and on the other hand the degree--degree correlation is constrained by the rich--club connectivity. In particular, in the case of the Internet, the assortative coefficient is always negative and a minor change in its value can reverse the network's rich--club structure completely; while fixing the degree distribution and the rich--club connectivity restricts the assortative coefficient to such a narrow range, that a reasonable model of the Internet can be produced by considering mainly the degree distribution and the rich--club connectivity. We also comment on the suitability of using the maximal random network as a null model to assess the rich--club connectivity in real networks.Comment: To appear in New Journal of Physics (www.njp.org

Simultaneous Dual Frequency Observations of Giant Pulses from the Crab Pulsar

Simultaneous measurements of giant pulses from the Crab pulsar were taken at two widely spaced frequencies using the real-time detection of a giant pulse at 1.4 GHz at the Very Large Array to trigger the observation of that same pulse at 0.6 GHz at a 25-m telescope in Green Bank, WV. Interstellar dispersion of the signals provided the necessary time to communicate the trigger across the country via the Internet. About 70% of the pulses are seen at both 1.4 GHz and 0.6 GHz, implying an emission mechanism bandwidth of at least 0.8 GHz at 1 GHz for pulse structure on time scales of one to ten microseconds. The arrival times at both frequencies display a jitter of 100 microseconds within the window defined by the average main pulse profile and are tightly correlated. This tight correlation places limits on both the emission mechanism and on frequency dependent propagation within the magnetosphere. At 1.4 GHz the giant pulses are resolved into several, closely spaced components. Simultaneous observations at 1.4 GHz and 4.9 GHz show that the component splitting is frequency independent. We conclude that the multiplicity of components is intrinsic to the emission from the pulsar, and reject the hypothesis that this is the result of multiple imaging as the signal propagates through the perturbed thermal plasma in the surrounding nebula. At both 1.4 GHz and 0.6 GHz the pulses are characterized by a fast rise time and an exponential decay time which are correlated. The pulse broadening with its exponential decay form is most likely the result of multipath propagation in intervening ionized gas.Comment: LaTeX, 18 pages, 7 figures, accepted for publication in The Astrophysical Journa

Prevalence of Xanthomonas perforans associated with bacterial spot in processing tomato crops in Brazil.

Resumo 1012

Extratos vegetais no controle in vitro do carrapato dos bovinos.

O objetivo deste trabalho foi avaliar a eficácia in vitro de extratos etanólicos e aquosos no controle de fêmeas ingurgitadas de Rhipicephalus (Boophilus) microplus. Foram testados os extratos etanólicos e aquosos dos frutos verdes de Enterolobium contortisiliquum e das folhas de Calotropis procera, e os extratos aquosos das partes aéreas de Hyptis suaveolens e das folhas de Tithonia diversifolia. Os bioensaios foram realizados pelo método de imersão das fêmeas ingurgitadas. O extrato etanólico de E. contortisiliquum possui eficácia parcial (47,4%) sobre o carrapato dos bovinos, e portanto, novos estudos deverão ser realizados com o intuito de potencializar este efeito.Edição dos Resumos do 7º Congresso Brasileiro de Agroecologia, Fortaleza-CE, dez. 2011

Manual do módulo de estágios do Sistema Integrado de Gestão e Pesquisa da Embrapa Gado de Corte: Pandora.

Considerando-se um contexto de busca de recursos humanos qualificados e dispostos a inovar e aprender foi criado o Módulo de Estágios do sistema Integrado de Gestão e Pesquisa da Embrapa Gado de Corte ? Pandora ? no qual este Manual está baseado. Buscando facilitar a compreensão dos usuários em relação à operacionalização desse sistema, o Manual divide-se em duas partes, uma referente aos procedimentos dos estagiários e outra, dos supervisores. Dessa forma, são utilizadas telas do sistema com os respectivos procedimentos para facilitar a compreensão dos usuários na utilização das ferramentas disponíveis.bitstream/item/77526/1/DOC191.pd