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This work presents a brief description of the concept of phase transformation. It considers and implements models for nonisothermal reactions. The experimental study is based on electrical resistivity measurements, limiting three well defined regions where reactions occur in aluminum AA6061. The transformed fraction and the transformation rate is determined, and by using of the Ozawa’s thermokinetic model for non-isothermal transformations the heating function of the process that provides information on the rate of nucleation and the growth velocity of the precipitates in the alloy was determined. It is found that this function, and implicitly the nucleation rate, generates a Gaussian curve with a peak around 130 °C. By modeling and transmission electron microscopy it was found that the nucleation process occurs preferentially at grain boundaries. © 2014, Interamerican Society for Electron Microscopy (CIASEM). All rights reserved. Source

Rodriguez-Rodriguez J.H.,Instituto de Investigaciones Electricas
Measurement and Control (United Kingdom) | Year: 2014

This paper presents a simple and inexpensive powerless electrical insulated voltage measuring sensor using optical couplers for AC and DC voltage measurement, by harvesting the optical photovoltaic energy from a P-N collector-base junction in an opto-insulator to generate an output voltage proportional to the voltage input. A voltage transducer was built with a low-cost opto-insulator circuit and tested to evaluate the voltage measurement capabilities. The system proved to operate properly for AC power line and DC voltages and switching voltages with a bandwidth of 10 kHz. Applications for the powerless insulated DC-AC voltage sensor are in power electronics, voltage measurement, and control. © The Institute of Measurement and Control 2014. Source

This work analyzes and implements the proposed model by Mittemeijer to interpret the phase transformations in solid state thermally activated. The kinetic study is followed from measurements of electrical resistivity, at rates constant heating, for early stages of transformation in the aluminum AA6061, from room temperature to about 300°C. Microstructural analysis is done by electron microscopy, transmission and scanning, and elemental microanalysis by EDX spectroscopy. The implementation of the model allowed the determination and evaluation of overall effective activation energy, Ea. This parameter shows a exponential-parabolic behavior with the transformed fraction, with values, approximately, from 20 to 100 kJ/mol. A variant proposed, based on mathematical criteria and the Chiotti method, allowed the evaluation of the variable β, establishing that β evolves expo-parabolically with the transformed fraction, the temperature, time and the order of reaction. In regime of infinite dilution was found to: β(α→0) = 0, y β(α→1) @ 1. Characterization of β made possible the determination and evaluation of the reaction frequency factor, ko, showing a exponential-parabolic behavior with the transformed fraction, for values, approximately, from 103to 1015min-1. The evaluation of the reaction order parameter, n, showed that it is in the range 1.3 ≤ n ≤ 2.8. These values are associated to the diffusive nature of the process, to the presence of mixed mechanisms, nucleation and growth, with increase and subsequent decrease of the respective rates. © 2015, Interamerican Society for Electron Microscopy (CIASEM). Source

Ochoa M. J.L.,Instituto de Investigaciones Electricas | Arias A.R.P.,Technological University of the Central Region | Morales J.M.L.,Technological University of the Central Region
Acta Microscopica | Year: 2013

In this work it studied the influence of the early stages of decomposition microstructural over the electrical resistivity in AA6061 aluminum in state of supersaturated solid solution or heat treatment T6, between room temperature and about 200°C, these stages pre-precipitation with nucleation and growth correspond to the formation and transformation from the Guinier-Preston zones (z-GP), and the metastable phases β″ and β′. It found that the variations in the electrical resistivity are due to the evolution of the microstructure by the effect of thermal energy, for the presence and structural rearrangement, primarily, of the alloying elements, and the impurities. GP zones and β″ and β′ phases are primarily responsibles for this behavior, this being non-linear and non-monotonous. Optics microscopy and transmission electron microscopy reveal allowed the granular structure of this alloy, and the presence of secondary phases. The grain size variation and the growth of secondary phases are proportional to the electrical resistivity behavior. Source

The invention comprises real-time down-hole intelligent communication based on the characterisation of signal attenuation caused by a coaxial cable used as a communication medium and by frequency response changes of the electronic components of the transmitters and receivers, generated by the down-hole operating environment. The invention relates to a method for the real-time characterisation of the attenuation response of a two-way communication system using a coaxial cable, consisting in: generating test tones for the real-time characterisation of the attenuation response of a two-way communication system in the transmission and reception bands, measuring the signals received, estimating noise and the ratio to the communication signal, comparing with reference responses, adjusting the transmission and reception frequencies in order to maintain the communication with the maximum signal-to-noise ratio. The invention also relates to an adaptive two-way transmitter/receiver system for communication using coaxial cable as a link means, formed by: a transmitter with automatic adjustment of the operating band by means of the real-time characterisation of the attenuation response of a two-way communication system. The invention further relates to adjustable filtering and coupling devices for optimising the transmission and reception hands, and a control module capable of measuring the transmission and reception attenuation responses

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