Assessment of anaerobic power of swimmers: the correlation of laboratory tests on an arm ergometer with field tests in a swimming fool

The aim of this study was to verify the correlation between the Wingate arm crank test outputs (peak power, mean power, and fatigue index), obtained on a specific ergometer, and the performance in crawl stroke swim sprints of 14, 25, 50, and 400 m. The experiment was conducted with 9 healthy male volunteers (18.1 +/- 2.2 years of age; 172 +/- 0.04 cm; 67.7 +/- 5.92 kg and 15.7 +/- 4.57% body fat). on determined days, all individuals were submitted to the Wingate arm crank test and crawl freestyle sprints of 14, 25, 50, and 400 m as they were timed with a stopwatch. The peak power, the mean power, and the fatigue index, which were obtained during the Wingate arm crank test, were not significantly correlated with the maximum swim velocities during the crawl free-style tests of 14 (r = 0.40; r = 0.64; r = 0.11), 25 (r = 0.28; r = 0.39; r = -0.27), 50 (r = 0.03; r = 0.09; r = -0.31), and 400 (r = -0.52; r = -0.37; r = -0.65) m respectively. Thus, it is possible to conclude that the Wingate arm crank test is not suitable to assess the anaerobic power of swimmers under the described experimental conditions.

Degradabilidade in situ do Capim Panicum maximum cv. Tanzânia Incubado Cortado ou na Forma de Extrusa

The aim of this study was to compare the chemical composition, in vitro dry matter disappearance (IVDMD) and ruminal degradation of Panicum maximum, J. cv. Tanzania samples obtained by clipping (square method) or extrusa collection (animal selection). In the in situ trial, three ruminal fistulated dry crossbred cows, with 499 kg LW, were used in a completely randomized block design with split-plot arrangement design. Five grams of clipped (+/- 2 cm) grass or extrusa samples were placed in nylon bags (7 x 14 cm) and rumen incubated during 3, 6, 12, 24, 48, 96 and 120 hours. The IVDMD and the CP, NDF and ADF content were, respectively, 55.8, 7.6, 81.9 e 43.6%, for the clipped grass and .66.5, 12.1, 78.8 e 39.5%, for the extrusa samples. The potential degradability of DM, C P, NDF and ADF were 62.59, 80.88, 50.73 and 46.65%, for clipped grass; and 79.53, 90.97, 71.21 and 65.68%, for extrusa samples. The quality of the selected animal diet (extrusa) was better than the available forage in terms of IVDMD and chemical composition (high protein and low fiber content). In situ degradability trials carried out with clipped samples, and non selected by animal, could not supply reliable results closed to the animal diet.

The complementary exponential power lifetime model

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A unity power factor multiple isolated outputs switching mode power supply using a single switch

The authors present an offline switching power supply with multiple isolated outputs and unity power factor with the use of only one power processing stage, based on the DC-DC SEPIC (single ended primary inductance converter) modulated by variable hysteresis current control. The principle of operation, the theoretical analysis, the design procedure, an example, and simulation results are presented. A laboratory prototype, rated at 160 W, operating at a maximum switching frequency of 100 kHz, with isolated outputs rated at +5 V/15 A -5 V/1 A, +12 V/6 A and -12 V/1 A, has been built given an input power factor near unity.

Assessment of Anaerobic Power of Swimmers: The Correlation of Laboratory Tests on an Arm Ergometer with Field Tests in a Swimming Pool

The aim of this study was to verify the correlation between the Wingate arm crank test outputs (peak power, mean power, and fatigue index), obtained on a specific ergometer, and the performance in crawl stroke swim sprints of 14, 25, 50, and 400 m. The experiment was conducted with 9 healthy male volunteers (18.1 ± 2.2 years of age; 172 ± 0.04 cm; 67.7 ± 5.92 kg and 15.7 ± 4.57% body fat). On determined days, all individuals were submitted to the Wingate arm crank test and crawl freestyle sprints of 14, 25, 50, and 400 m as they were timed with a stopwatch. The peak power, the mean power, and the fatigue index, which were obtained during the Wingate arm crank test, were not significantly correlated with the maximum swim velocities during the crawl freestyle tests of 14 (r = 0.40; r = 0.64; r = 0.11), 25 (r = 0.28; r = 0.39; r = -0.17), 50 (r = 0.03; r = 0.09; r = -0.31), and 400 (r = -0.52; r = -0.37; r = -0.65) m, respectively. Thus, it is possible to conclude that the Wingate arm crank test is not suitable to assess the anaerobic power of swimmers under the described experimental conditions.

A neural approach to evaluate the effect of lightning in power transformers

This paper proposes the application of computational intelligence techniques to assist complex problems concerning lightning in transformers. In order to estimate the currents related to lightning in a transformer, a neural tool is presented. ATP has generated the training vectors. The input variables used in Artificial Neural Networks (ANN) were the wave front time, the wave tail time, the voltage variation rate and the output variable is the maximum current in the secondary of the transformer. These parameters can define the behavior and severity of lightning. Based on these concepts and from the results obtained, it can be verified that the overvoltages at the secondary of transformer are also affected by the discharge waveform in a similar way to the primary side. By using the tool developed, the high voltage process in the distribution transformers can be mapped and estimated with more precision aiding the transformer project process, minimizing empirics and evaluation errors, and contributing to minimize the failure rate of transformers. © 2009 The Berkeley Electronic Press. All rights reserved.

Avaliação das principais t́cnicas para obtenção de MPPT de paińis fotovoltaicos

Electrical energy from photovoltaic panels (PV) has became an increasing viable alternative because of the great concern for environmental preservation and the possibility of the reduction of the conventional fuels, and this natural energy source is free, abundant and clean. In addition, Brazil is a privileged country because of the high levels of irradiation throughout its territory all over the year. Thus the exploitation of the energy from PV is one of the best alternatives to overcome the supply electrical energy issues. However, nowadays the energy conversion efficiency is low and the initial costs are high for these energy systems. Therefore, in order to increase the efficiency of these systems the extraction of the maximum power point (MPP) from PV is extremely necessary, and it is done using the maximum power point tracking (MPPT) techniques. The MPP of the PV varies non linearly with the environmental conditions and several MPPT techniques are available in literature, and this paper presents a careful comparison among the most usual techniques, doing meaningful comparisons with respect to the amount of energy extracted, PV voltage ripple, dynamic response and use of sensors, considering that the models are implemented via MatLab/Simulink®. © 2010 IEEE.

Single stage converters for low power stand-alone and grid-connected PV systems

This work presents the evaluation of different power electronic integrated converters suitable for photovoltaic applications, in order to reduce complexity and improve reliability. The rated voltages available in Photovoltaic (PV) modules have usually low values for applications such as regulated output voltages in stand-alone or grid-connected configurations. In these cases, a boost stage or a transformer will be necessary. Transformers have low efficiencies, heavy weights and have been used only when galvanic isolation is mandatory. Furthermore, high-frequency transformers increase the converter complexity. Therefore, the most usual topologies use a boost stage and one inverter stage cascaded. However, the complexity, size, weight, cost and lifetime might be improved considering the integration of both stages. In this context, some integrated converters are analyzed and compared in this paper in order to support future evaluations and trends for low power single-phase inverters for PV systems. Power decoupling, MPPT and Tri-State modulations are also considered. Finally, simulation and experimental results are presented and compared for the analyzed topologies. © 2011 IEEE.

Pricing of reactive power support provided by distributed generators in transmission systems

Distributed Generation, microgrid technologies, two-way communication systems, and demand response programs are issues that are being studied in recent years within the concept of smart grids. At some level of enough penetration, the Distributed Generators (DGs) can provide benefits for sub-transmission and transmission systems through the so-called ancillary services. This work is focused on the ancillary service of reactive power support provided by DGs, specifically Wind Turbine Generators (WTGs), with high level of impact on transmission systems. The main objective of this work is to propose an optimization methodology to price this service by determining the costs in which a DG incurs when it loses sales opportunity of active power, i.e, by determining the Loss of Opportunity Costs (LOC). LOC occur when more reactive power is required than available, and the active power generation has to be reduced in order to increase the reactive power capacity. In the optimization process, three objectives are considered: active power generation costs of DGs, voltage stability margin of the system, and losses in the lines of the network. Uncertainties of WTGs are reduced solving multi-objective optimal power flows in multiple probabilistic scenarios constructed by Monte Carlo simulations, and modeling the time series associated with the active power generation of each WTG via Fuzzy Logic and Markov Chains. The proposed methodology was tested using the IEEE 14 bus test system with two WTGs installed. © 2011 IEEE.

Evaluation of integrated inverter topologies for low power PV systems

This work presents the stage integration in power electronics converters as a suitable solution for solar photovoltaic inverters. The rated voltages available in Photovoltaic (PV) modules have usually low values for applications such as regulated output voltages in stand-alone or grid-connected configurations. In these cases, a boost stage or a transformer will be necessary. Transformers have low efficiencies, heavy weights and have been used only when galvanic isolation is mandatory. Furthermore, high-frequency transformers increase the converter complexity. Therefore, the most usual topologies use a boost stage and one inverter stage cascaded. However, the complexity, size, weight, cost and lifetime might be improved considering the integration of both stages. These are the expected features to turn attractive this kind of integrated structures. Therefore, some integrated converters are analyzed and compared in this paper in order to support future evaluations and trends for low power single-phase inverters for PV systems. © 2011 IEEE.

Parameterization technique for the continuation power flow using the trivial and tangent predictor

This paper presents efficient geometric parameterization techniques using the tangent and the trivial predictors for the continuation power flow, developed from observation of the trajectories of the load flow solution. The parameterization technique eliminates the Jacobian matrix singularity of load flow, and therefore all the consequent problems of ill-conditioning, by the addition of the line equations which pass through the points in the plane determined by the variables loading factor and the real power generated by the slack bus, two parameters with clear physical meaning. This paper also provides an automatic step size control around the maximum loading point. Thus, the resulting method enables not only the calculation of the maximum loading point, but also the complete tracing of P-V curves of electric power systems. The technique combines robustness with ease of understanding. The results to the IEEE 300-bus system and of large real systems show the effectiveness of the proposed method. © 2012 IEEE.

A single-phase single-stage buck-boost inverter intended for low power alternative energy conversion systems: Analysis, design and experimentation

This paper presents the operational analysis of the single-phase integrated buck-boost inverter. This topology is able to convert the DC input voltage into AC voltage with a high static gain, low harmonic content and acceptable efficiency, all in one single-stage. Main functionality aspects are explained, design procedure, system modeling and control, and also component requirements are detailed. Main simulation results are included, and two prototypes were implemented and experimentally tested, where its results are compared with those corresponding to similar topologies available in literature. © 2012 IEEE.

Sistema de extração de potência (power harvesting) usando transdutores piezelétricos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Requirements and methodology for the massive implementation of small hydro power stations in Latin America

Spanish version available

Controlador de demanda e fator de potência de baixo custo para unidades consumidoras de energia elétrica

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)