Predicted defect induced vortex core switching in thin magnetic nanodisks

We investigate the influence of artificial defects (small holes) inserted into magnetic nanodisks on the vortex core dynamics. One and two holes (antidots) are considered. In general, the core falls into the hole but, in particular, we would like to remark an interesting phenomenon not yet observed, which is the vortex core switching induced by the vortex-hole interactions. It occurs for the case with only one hole and for very special conditions involving the hole size and position as well as the disk size. Any small deformation in the disk geometry such as the presence of a second antidot changes completely the vortex dynamics and the vortex core eventually falls into one of the defects. After trapped, the vortex center still oscillates with a very high frequency and small amplitude around the defect center.Comment: 11pages, Revtex format, 17 figure

Anaerobes beyond anaerobic digestion

Anaerobic microorganisms are widespread in nature. Sediments, gastrointestinal tracks, volcanic vents, geothermal sources are examples of habitats where anaerobic metabolism prevail, in some cases at extreme temperature, pH and pressure conditions. In such microbial ecosystems waste of some is food for others in a true integrated structure. Anaerobic microorganisms are able to use a wide variety of organic and inorganic compounds. Recalcitrant compounds, such as hydrocarbons, aromatics, fatty-acids, can be converted by anaerobic microbial mixed communities to a range of intermediary products or, ultimately, to methane and carbon dioxide. Inorganic compounds, for example sulphur and sulphur oxides, nitrogen oxides, iron, can act as electron acceptors during anaerobic conversion of organic molecules. A complex food-chain takes place in anaerobic microbial ecosystems with a great potential for the recovery of products with biotechnological interest. We focus on the study of microbial ecology and physiology of anaerobic mixed communities aiming at potential biotechnological applications. In parallel, pure culture studies are important to assess novel physiological traits and metabolic routes of anaerobic microorganisms. Bio-hydrogen production, syngas fermentation and long chain fatty-acids degradation are examples of microbial processes currently studied at our laboratory. Microbial communities involved in the production of bio-hydrogen were characterized by DGGE and cloning and sequencing approach1. Fermentation of syngas to methane and study of metabolic alternative routes for the production of other products, such as butanol, is being assessed by using pure cultures and defined mixed cultures. Microorganisms involved in the degradation of long chain fatty-acids have been extensively studied and a novel syntrophic bacterium, Syntrophomonas zehnderi, was isolated2. Complete genome sequencing of this bacterium is currently ongoing

Aprendizagem e disseminação de conhecimento nos colaboratórios das redes de pesquisa da Embrapa.

O objetivo deste artigo é apresentar e discutir uma proposta de modelo conceitual para a criação de Colaboratórios para as redes de pesquisa da Embrapa. Os Colaboratórios são espaços virtuais de aprendizagem que, estruturados sob uma lógica sócio-interacionista e com ferramentas da web 2.0, tendem a potencializar a construção de novos conhecimentos e aprendizagens entre os cientistas das redes de pesquisa, fomentando também a aprendizagem organizacional.SBIE 2012

Magneto-optical evidence of double exchange in a percolating lattice

Substituting $Eu$ by $Ca$ in ferromagnetic $EuB_6$ leads to a percolation limited magnetic ordering. We present and discuss magneto-optical data of the $Eu_{1-x}Ca_{x}B_6$ series, based on measurements of the reflectivity $R(\omega)$ from the far infrared up to the ultraviolet, as a function of temperature and magnetic field. Via the Kramers-Kronig transformation of $R(\omega)$ we extract the complete absorption spectra of samples with different values of $x$. The change of the spectral weight in the Drude component by increasing the magnetic field agrees with a scenario based on the double exchange model, and suggests a crossover from a ferromagnetic metal to a ferromagnetic Anderson insulator upon increasing $Ca$-content at low temperatures.Comment: 10 pages, 3 figure

Comunicação corporativa na era da televisão digital interativa.

Este artigo aborda a pesquisa que está sendo conduzida na empresa sobre o desenvolvimento de tecnologias e metodologias de produção de conteúdo para a TV digital, que visa criar um canal para divulgação científica e transferência de tecnologia cujo foco é amparado em um novo paradigma baseado no potencial das novas mídias para a democratização e a inclusão social de produtores rurais. Os estudos incluem o desenvolvimento de um ambiente interativo e a produção de conteúdos-piloto audiovisuais, envolvendo a participação da comunidade, tanto durante o processo construtivo quanto na validação das metodologias criadas, num processo interativo mediado pelas tecnologias multimídia

Assessment of methanogen survival in anaerobic enrichment cultures degrading long-chain fatty acids

Long-chain fatty acids (LCFA) are generally considered highly toxic towards methanogens. However, high methane yields have been obtained from high-load anaerobic digestion of LCFA, suggesting that methanogens can tolerate these compounds. In this work, hydrogenotrophic and acetoclastic methanogens were added to LCFA-degrading enrichments in order to evaluate their survival in the presence of unsaturated-LCFA (C18:1, oleate) and saturated-LCFA (C16:0, palmitate). Two hydrogenotrophs (Methanobacterium formicicum and Methanospirillum hungatei), and two acetoclasts (Methanosarcina mazei and Methanosaeta concilii) were tested. Oleate- and palmitate-enrichment cultures (OM and PM, respectively) were amended with each of the methanogens and incubated with 1 mM of the corresponding LCFA. Survival of methanogens after several transfers was evaluated by PCR-DGGE. For the hydrogenotrophs, results showed that M. formicicum survived in both OM and PM cultures, while M. hungatei only grew in the PM culture. Moreover, viability tests using live/dead staining coupled to fluorescent microscopy observation and cell counting indicated that M. hungatei is indeed more sensitive to oleate than M. formicicum. The percentage of damaged cells, caused by the exposure to low concentration of oleate (i.e. 0.5 mM), was very high in the case of M. hungatei (79%) contrasting with M. formicicum that was only slightly affected by this LCFA (8%). Regarding acetoclastic methanogens, both tested species prevailed in OM and PM cultures, although more abundant in PM enrichment. These results suggest that oleate is a more toxic compound for methanogens than palmitate. Nevertheless, all the methanogens studied, except M. hungatei, were found in the OM cultures