93 resultados para AK15-1364


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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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A performance comparison between a recently proposed novel technique known as fast orthogonal frequency-division multiplexing (FOFDM) and conventional orthogonal frequency-division multiplexing (OFDM) is undertaken over unamplified, intensity-modulated, and direct-detected directly modulated laser-based optical signals. Key transceiver parameters, such as the maximum achievable transmission capacity and the digital-to-analog/analog-to-digital converter (DAC/ADC) effects are explored thoroughly. It is shown that, similarly to conventional OFDM, the least complex and bandwidth efficient FOFDM can support up to similar to 20 Gb/s over 500 m worst-case multimode fiber (MMF) links having 3 dB effective bandwidths of similar to 200 MHz X km. For compensation of the DAC/ADC roll-off, a power-loading (PL) algorithm is adopted, leading to an FOFDM system improvement of similar to 4 dB. FOFDM and conventional OFDM give similar optimum DAC/ADC parameters over 500 m worst-case MMF, while over 50 km single-mode fiber a maximum deviation of only similar to 1 dB in clipping ratio is observed due to the imperfect chromatic dispersion compensation caused by one-tap equalizers.

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Aims: To determine the prevalence and molecular characteristics of Shiga toxin-producing Escherichia coli (STEC) isolates from bovine mastitic milk in Brazil.Methods and Results: A total of 2144 milk samples from dairy cattle showing mastitis were screened for the presence of E. coli. A total of 182 E. coli isolates were selected and examined. All were subjected to dot blot analysis using the CVD419 probe for the detection of the enterohaemolysin (hly) gene, and to a multiplex PCR for the detection of stx1, stx2 and eaeA genes. STEC were isolated from 22 (12.08%) milk samples. All the STEC isolates were tested for sensibility to 10 antimicrobials; the resistances most commonly observed were to cephalothin (86.3%), tetracycline (63.6%) and doxycycline (63.6%).Conclusion: STEC isolates were found in bovine mastitic milk in Brazil.Significance and Impact of the Study: STEC isolates from mastitic milk were potentially pathogenic for human in that they belonged to serogroups associated with diarrhoea and haemolytic-uraemic syndrome, some of them were stx2, eaeA and hly positive.

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Measurement of the phase difference between the 0th and the 1st transmitted diffraction orders of a symmetrical surface-relief grating recorded on a photoresist film is carried out by replacement of the grating in the same setup with which it was recorded. The measurement does not depend on lateral shifts of the replaced grating relative to the interference pattern, on environmental phase perturbations or on the wave-front quality of the interfering beams. The experimental data agree rather well with theoretical results calculated for sinusoidal profiled gratings. (C) 2003 Optical Society of America.

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Aims: the aim of this study was to obtain improved strains of pectinolytic yeasts adapted to the conditions of an industrial fermentation process, which was continuously operated to convert citrus molasses into ethanol.Methods and Results: the starter yeast of the industrial fermentation process was a commercial baker's yeast, which was capable of growing without forming any secretion halo of pectinase activity on solid medium. Nevertheless, isolates showing secretion of pectinolytic activity on plates were obtained from the fermentation process. The secretion of pectin-degrading activity by isolates on plates was repressed by galactose and improved as the result of colony aging on polygalacturonic acid plates at 30 degrees C. Liquefaction of polygalacturonate gels as well as the splitting of the pectin-degrading activity into a wall-linked and a supernatant fraction were also observed when the starter yeast was propagated under agitation in liquid medium containing pectin.Conclusions: Isolates capable of secreting pectinolytic activity on plates were predominant at the end of the citrus molasses fermentation. Nevertheless, the sizes of the secretion haloes on plates were not necessarily an indication of the levels of pectinolytic activity secreted in the liquid medium.Significance and Impact of the Study: Improved pectinolytic strains of Saccharomyces can be used as a source of pectinases for a variety of applications. This organism also participates in plant deterioration processes.