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971.
Neto R.M.F. Tofoli F.L. de Freitas L.C. 《Industrial Electronics, IEEE Transactions on》2005,52(5):1278-1285
This paper proposes a high-power-factor half-bridge doubler boost converter without commutation losses, which provides high output voltages, i.e., from 600 to 900 V. The voltages across the semiconductor devices are low and approximately equal to the output voltage, as doubled output voltages and reduced high-frequency ripple can be achieved. A detailed mathematical analysis concerning its operation is presented, and simulation and experimental results describe the converter performance. 相似文献
972.
Sandra Aparecida de Assis Antônio Baldo Geraldo Martins Olga Maria Mascarenhas de Faria Oliveira 《Journal of the science of food and agriculture》2007,87(10):1845-1849
The enzyme pectinmethylesterase (PME) from acerola was extracted and purified by gel anion‐exchange chromatography (Q Sepharose) and filtration on Sephadex G‐100. The results showed two different PME isoforms (PME1 and PME2), with molecular masses of 25.10 and 5.20 kDa, respectively. PME1 specific activity increased by 9.63% after 60 min incubation at 98 °C, while PME2 retained 66% of its specific activity under the same conditions. The Km values of PME1, PME2 and concentrated PME were 0.94, 0.08 and 0.08 mg mL?1, respectively. The Vmax value of PME1, PME2 and concentrated were 204.08, 2, 158.73 and 2.92 µmol min?1 mg?1 protein, respectively. Copyright © 2007 Society of Chemical Industry 相似文献
973.
Planar circularly symmetric EBG structures for reducing surface waves in printed antennas 总被引:1,自引:0,他引:1
Llombart N. Neto A. Gerini G. de Maagt P. 《Antennas and Propagation, IEEE Transactions on》2005,53(10):3210-3218
This paper discusses the design and analysis of planar circularly symmetric (PCS) electromagnetic band gap (EBG) structures for reducing the surface waves excited by printed antennas on dense dielectric substrates. The key advantage of the circularly symmetric geometries is that a surface wave generated by a source located at its center experiences the same band gap effect in all radial directions. To obtain simple design rules of the PCS-EBGs for the optimization of the bandwidth, an equivalence is established between 2-D-EBGs and PCS-EBGs. Integrated planar printed antennas with bandwidths up to 20% are designed, manufactured and tested. 相似文献
974.
Neto A.C. Rodrigues A.B. Prada R.B. da Guia da Silva M. 《Power Systems, IEEE Transactions on》2008,23(3):889-895
975.
Using space-time TCM with rotated constellations for transmissionover mobile communications channels
Space-time trellis coded modulation is combined with a rotated signal set for transmission in mobile communication channels. Two systems are proposed and their performances simulated over slow selective fading channels 相似文献
976.
Paulino Florêncio de Souza Dário Santos Jr. Paulo dos Santos Roldan Adriana Paiva de Oliveira José Anchieta Gomes Neto Francisco José Krug 《Sensing and Instrumentation for Food Quality and Safety》2007,1(4):176-182
An alternative procedure that improves the performance of graphite atomizers for the determination of Pb in sugar by electrothermal
atomic absorption spectrometry is described. The procedure is based on the injection of 10 μl of an acidified aqueous solution
containing 8% w/v sugar and 0.2% v/v HNO3 into integrated graphite platforms. Either transversely (THGA) as well as longitudinally heated graphite atomizers (LHGA)
were evaluated by using conventional co-injection of 0.03% Pd + 0.05% Mg(NO3)2 or thermally treated platforms with 250 μg W + 200 μg Rh and co-injection of 5 μg l−1 Rh solution. With W-Rh under the same analytical conditions, the lifetimes of THGA and LHGA reached up to 1110 and 900 firings,
respectively. With Pd + Mg the LHGA tube lifetime was limited to approximately 500 firings, but for THGA up to 1020 firings
were made with a single tube. Characteristic masses were 11 and 29 pg Pb for LHGA and THGA, respectively. Detection limits
(3 s) based on sugar blank solution and on integrated absorbance were 5.0 mg kg−1 with LHGA and 9.3 mg kg−1 Pb for THGA. In general, the coefficients of variation of 20 consecutive measurements of a solution containing 50 μg l−1 Pb were lower than 5%. The obtained detection limits are in consonance with the Codex Alimentarius recommendation for the
maximum Pb content in the sugar. 相似文献
977.
978.
The first experimental evidence of director fluctuations in a micellar lyotropic liquid crystal, studied by 1H spin-lattice relaxation rate, is reported. The system is constituted by the ternary mixture: potassium laurate/1-decanol/water. With the aim to test the slow dynamics, the experiment has been performed over a broad range of Larmor frequencies (2 ×
103− 6.6 × 106 Hz), using fast field-cycling NMR relaxometry. The results evidence that in the nematic and isotropic mesophases and the
poliphasyc region, director fluctuations are responsible for the spin-lattice relaxation dispersion in the low Larmor frequency
range (<105 Hz). By increasing the intermicellar water content, a crossover was found between a quasi-isotropic 3D director fluctuations
behavior to a 2D pseudo-lamellar undulation fluctuations. In order to explain the higher frequency range (>105 Hz), two relaxation mechanisms are assigned: i) molecular reorientation by translational diffusion on the micellar surface,
and ii) molecular exchange between the micelle and the bulk.
Received: 30 March 2000 相似文献
979.
Bispo D. Martins L. Neto de Resende J.T. de Andrade D.A. 《Industry Applications, IEEE Transactions on》2001,37(6):1710-1719
This paper presents a new strategy for modeling the saturated induction machine. Saturation is considered by means of "magnetic harmonic functions," defined in the model and obtained experimentally, considering the fundamental and third harmonic of the spatial flux density distribution. It is shown that the distortions on voltage and current waveforms are due to harmonic content in the main flux, caused by saturation. Experimental and theoretical results for a capacitor self-excited induction generator are presented to show the validity of the proposed model 相似文献
980.
D. Sperti P. S. André B. Neto A. M. Rocha A. Bononi F. da Rocha M. Facão 《Photonic Network Communications》2008,16(3):195-202
Raman amplification will, in a closer future, penetrate into the access network, bringing new challenges and difficulties to be overcome. In this article, we present the performance assessment of Raman amplification solutions suitable for Coarse Wavelength Division Multiplexing (CWDM) access networks applications. For this purpose, a pumping scheme with three lasers allows a bandwidth of 78 nm which is suitable for four CWDM channels. For this scheme, the gain and noise figure dependence with the pumping configuration was evaluated. The gain equalization was experimentally obtained based on a previously developed model using the Genetic Algorithm (GA) for pump allocation. A comparative study of Raman amplification in different types of Raman fibers (single mode fiber and dispersion shifted fiber) is also presented as well as the use of composite links. Those applications were tested in a local network and the obtained results comply with the modeling foreknowledge, showing the feasibility of Raman amplification over CWDM networks. 相似文献