Evidence for electronic and ionic limitations at the origin of the second voltage plateau in nickel electrodes, as deduced from impedance spectroscopy measurements

The second plateau occurring during the reduction of the nickel oxyhydroxide electrode (NOE) was studied by impedance spectroscopy on a cell with a pasted electrode prepared from commercial undoped -Ni(OH)2. Measurements were performed at diverse states of reduction and a large variation of impedance upon the transition from the first to the second plateau was observed. This variation mainly takes place at low frequencies and is hence related to ionic diffusion. We observed that the impedance becomes more capacitive on the second plateau meaning that the proton diffusion is limited. These results would be consistent with the gradual formation of an insulating layer of nickel hydroxide at the interface between the NOE and the electrolyte upon reduction. Once this layer becomes compact the ionic diffusion would be hindered and forced to occur through this layer, which could explain the voltage drop observed

Nonclassical radiation from diamond nanocrystals

The quantum properties of the fluorescence light emitted by diamond nanocrystals containing a single nitrogen-vacancy (NV) colored center is investigated. We have observed photon antibunching with very low background light. This system is therefore a very good candidate for the production of single photon on demand. In addition, we have measured larger NV center lifetime in nanocrystals than in the bulk, in good agreement with a simple quantum electrodynamical model.Comment: 8 pages, 5 figures, revised version, to appear in PR

A sala: Exposições 2014: Projeto de Extensão Ações Educativas na Galeria de Arte A Sala do Centro de Artes da UFPel

A SALA é de suma importância, enquanto instância educacional e expositiva pública, localizada no Centro de Artes, que promove a partilha da produção artística contemporânea com o corpo docente, o corpo discente e com a comunidade em geral. É o espaço que apresenta a obra de arte e promove a sua fruição, como também envolve práticas profissionais que possibilitam aos estudantes de arte conhecer as etapas que envolvem a realização de uma exposição, ou seja, os projetos de curadoria, de expografia, a montagem, a produção gráfica de divulgação, encontros com o artista, ações educativas, a documentação, entre outras atividades necessárias para que as mostras aconteçam. De maneira intensa e constante os alunos são colaboradores e apreciadores das exposições, adquirindo saberes indispensáveis à formação universitária

Standardization of activated sludge for biodegradation tests

Activated sludges are an inoculum source commonly used in biodegradation studies, as wastewater treatment facilities constitute an entry point to the environment for many chemicals. In this paper, the main issues relating to the use of activated sludge in biodegradability tests are presented. Special attention is also devoted to discussing the factors affecting both the activity of the microbial communities and the test results. After a short survey of the state of the art of microbiology of activated sludge, the paper focuses on the methods used to reduce the variations in the diversity, quality and quantity of these communities. Finally, use of surrogates as reference materials in biodegradability tests is discussed

Ecologia da febre amarela no Brasil

Ministério da Saúde. Fundação Serviços de Saúde Pública. Instituto Evandro Chagas. Belém, PA, Brasil / ORSTOM.Ministério da Saúde. Fundação Serviços de Saúde Pública. Instituto Evandro Chagas. Belém, PA, Brasil.Os autores passam em revista os vetares potenciais e os hospedeiros vertebrados recenseados do vírus da Febre Amarela presentes no Brasil. Eles discutem brevemente seus papéis respectivos no ciclo silvestre desta arbovirose.The authors review the known ~tential vectors and the analysed vertebrate hosts of the Yellow Fever virus in Brazil. They briefly discuss their respective roles in the sylvatic cycle of this arbovirose