Estudo comparativo de suportes para reactores anaeróbios de leito fluidizado

O desempenho dos reactores anaeróbios de leito fluidizado é fortemente dependente do tipo de suporte que se utiliza para imobilização da biomassa. Neste trabalho é testada uma instalação laboratorial que permite comparar diversos materiais quanto à capacidade de retenção de biomassa, revelando-se um método expedito para obter informação preliminar sobre este aspecto particular dos suportes. Comparam-se cinco materiais diferentes (argila expandida, vidro poroso, vidro rugoso, vidro liso e policarbonato), concluindo-se que a argila e o vidro poroso retêm a maior quantidade de biomassa por unidade de volume e que o vidro rugoso, consegue fixar mais do dobro da quantidade de biomassa que o vidro liso. É estudada a influência dos vários materiais na actividade duma população mista de bactérias metanogénicas tendo-se concluído que nenhum dos materiais influencia fortemente essa actividade

Oxidative stress responses and cellular energy allocation changes in microalgae following exposure to widely used human antibiotics

The individual effect of four human antibiotics on the microalgae Raphidocelis subcapitata was investigated following a 120-h exposure. The effects were assessed by analyzing growth, and biochemical parameters related with: 1) antioxidant capacity and oxidative damage by measuring superoxide dismutase (SOD) activity and lipid peroxidation (LPO) levels; and 2) cellular energy allocation (CEA) by quantifying the content in energy reserves, which represents the energy available (Ea), and the electron transport system activity that represents a measure of oxygen and cellular energy consumption (Ec). Growth yield inhibitory concentrations of sulfamethoxazole (18-30%), clarithromycin (28.7%), ciprofloxacin (28%) and erythromycin (17-39%) were found to elicit a considerable increase in Ec, thereby causing a significant decrease in the CEA. The elevated Ec can be a result of the need to respond to oxidative stress occurring under those conditions given the significant increase in SOD activity at these levels. For sulfamethoxazole, erythromycin and ciprofloxacin, the antioxidant responses do not seem to be enough to cope with the reactive oxygen species and prevent oxidative damage, given the elevated LPO levels observed. A stimulatory effect on growth yield was observed (up to 16%) at ciprofloxacin lowest concentration, which highly correlated with the increase in CEA. Based on the no observed effect concentration (NOECs) and/or effective concentration (EC10) results, Ec, SOD and CEA were more sensitive than the classical endpoint of growth rate for all the tested antibiotics. By revealing the antibiotic stress effects in R. subcapitata at the cellular level, this study suggests CEA as a more reliable indicator of the organisms' physiological status.info:eu-repo/semantics/publishedVersio

Decoherence by Correlated Noise and Quantum Error Correction

We study the decoherence of a quantum computer in an environment which is inherently correlated in time and space. We first derive the nonunitary time evolution of the computer and environment in the presence of a stabilizer error correction code, providing a general way to quantify decoherence for a quantum computer. The general theory is then applied to the spin-boson model. Our results demonstrate that effects of long-range correlations can be systematically reduced by small changes in the error correction codes.Comment: 4 pages, 1 figure, Phys. Rev. Lett. in pres

Comparison of low and high pressure infiltration regimes on the density and highly porous microstructure of ceria ecoceramics made from sustainable cork templates

Cork templates were used to produce lightweight bulk biomimetic ecoceramic (environmentally conscious ceramic) monoliths. Bulk/monolithic ceramics are vital for many applications, i.e. energy materials and fuel cells. Using simple and flexible, aqueous green-chemistry procedures, for the first time the influence of infiltration regime, number of infiltration cycles and sintering temperature on ecoceramic density and microstructure was studied. This lightweight three-dimensionally ordered macroporous (3DOM) CeO2 preserved the hexagonal cellular structure of cork, but unlike the wood, the rear cell walls were open, greatly increasing open porosity. Higher sintering temperatures (1600 instead of 1000 °C) were required to produce cm size monolithic ecoceramics mechanically strong enough to be handled. The infiltration regime and number of infiltration cycles affected density and porosity. Lower infiltration pressure led to higher porosity ecoceramics (3.3–5.7%), which may favour catalytic performance, showing the possibility of tailoring porosity and specific surface area by modifying the number of infiltration cycles

Flocs vs granules : differentiation by fractal dimension

High rate anaerobic wastewater treatment systems usually give rise to biomass structured in different types of aggregates, depending on prevalent environmental conditions. Although highly dependent on wastewater characteristics, granules are generally formed and found in UASB reactors, whereas flocs are mainly found in fixed bed reactors. Different structures usually have different shapes and surface roughness. The aim of this work is to provide a contribution to the differentiation of those kinds of aggregates. A numerical parameter, the fractal dimension, was used to quantify the surface roughness. The fractal dimension, of two families of particles, was measured by two methods: (i) a box counting method; (ii) a method based on an area-size relationship. In both cases, the differences were highly statistically significant. Using the box counting method, for each of the 54 particles of each family, the average fractal dimension was 1.90 ± 0.02 for flocs and 1.95 ± 0.01 for granules (±99% confidence interval). The log-log plot of area vs longest size was linear and the calculated fractal dimensions from this plot were 1.84 ± 0.13 and 2.14 ± 0.08 (±99% confidence interval) for flocs and granules, respectively. Fractal dimension was proven to be a suitable parameter to quantify and differentiate surface roughness of different microbial aggregates present in high rate anaerobic digesters.União Europeia. Comissão - Human Capital and Mobility programme

O desafio de introduzir o modelo de ensino por pesquisa nas escolas públicas de pernambuco

Essa pesquisa avaliou se um programa de formação continuada fundamentado numa visão sistêmica e na Didática das Ciências favoreceu a introdução de mudanças didático-pedagógica nas escolas. Estratégias foram planejadas para facilitar aos cursistas a superação de suas dificuldades. Duzentos professores de Ciências e Matemática foram capazes de elaborar e desenvolver projetos de intervenção pedagógica em suas salas de aula, assumindo o modelo de Ensino por Pesquisa. Os resultados foram alcançados na medida em que os professores foram apoiados para introduzirem as mudanças tendo seus saberes práticos respeitados

Dispersion of carbon nanotubes in poly(lactic acid)

Carbon nanotubes (CNT) present excellent mechanical, electrical and thermal properties, and are expected to impart these properties into their composites. However, the CNT are grown as entangled bundles that are difficult to disperse in polymer matrices, or even in solvents. Several approaches have been tried for the efficient dispersion of CNT in polymer matrices, ranging from the CNT chemical modification to the use of different mixing methods. Previous studies have shown that the resulting filler dispersion is strongly dependent on the characteristics of the melt mixing equipment [1]. It is also known that the dispersion level of nanofillers strongly affects the final nanocomposite properties [2]. The present work reports the optimization of the CNT dispersion in poly (lactic acid) (PLA) using a small-scale twin-screw extruder. The CNT were chemically modified for improved interaction with PLA. The effect of varying the mixing parameters on the dispersion level of the CNT and functionalized CNT was evaluated using optical and electron microscopy. The electrical resistivity and mechanical properties of the composites were measured. It was observed that the incorporation of 1% (weight) of CNT reduced the electrical resistivity of the composite to 400 Ohm.m, and that 3% CNT rendered the composite conductive, with an electrical resistivity of 0.6 Ohm.m.Fundação para a Ciência e a Tecnologia (FCT) - POCI/QUI/59835/2004, bolsa de doutoramento SFRH/BD/32189/2006

A comparative study of the dispersion of carbon nanofibres in polymer melts

The dispersion of carbon nanofibres (CNF) in a polymer matrix using two melt mixing methods is studied. Distributive and dispersive mixing were evaluated by optical and electron microscopy. The CNF were chemically modified to improve the interface with the matrix. The results showed that the two methods produced good distribution of the filler, but extensional stresses induced higher dispersion. The latter correlated well with a decrease in electrical resistivity. Also, the chemical modification largely improved the CNF/polymer interfaceFundação para a Ciência e a Tecnologia (FCT