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Abstract  

The dynamic heating rate method developed by TA Instruments (Hi-ResTM) is a kind of sample controlled thermal analysis in which a linear relationship between the logarithm of the heating rate and the rate of mass change is imposed. It is shown in this paper that the reacted fraction at the maximum reaction rate strongly depends on the parameters selected for the Hi-Res heating algorithm, what invalidates the use of the Kissinger method for analysing Hi-Res data unless that the reaction fits a first order kinetic law. Only in this latter case, it has been demonstrated that it is not required that a constant value of the reacted fraction at the maximum reaction rate is fulfilled for determining the activation energy from the Kissinger method. In such a case the Kissinger plot gives the real activation energy, independently of both the heating schedule used and the value of the reacted fraction, αm, at the maximum.

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Abstract  

The SCTA method implies to control the temperature in such a way that the reaction rate changes with the time according to a function previously defined by the user. Constant Rate Thermal Analysis (CRTA) is one of the most commonly used SCTA methods and implies achieving a temperature profile at which the reaction rate remains constant all over the process at a value previously selected by the user. This method permits to minimize the influence of heat and mass transfer phenomena on the forward reaction. The scope of this work is to develop a universal CRTA temperature controller that could be adapted to any thermoanalytical device. The thermoanalytical signal is programmed to follow a preset linear trend by means of a conventional controller that at the time controls a second conventional temperature programmer that forces the temperature to change for achieving the trend programmed for the thermoanalytical signal. Examples of the performance of this control system with a Thermobalance and a Thermomechanical Analyser (TMA) are given.

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Abstract  

A critical study of the use of isoconversional methods for the kinetic analysis of non-isothermal data corresponding to processes with either a real or an apparent variation of the activation energy, E, with the reacted fraction, α, has been carried out using for the first time simulated curves. It has been shown that the activation energies obtained from model-free methods are independent of the heating rate. However, the activation energy shows a very strong dependence of the range of heating rates used for simulating the curves if the apparent change of E with α is caused by overlapping processes with different individual activation energies. This criterion perhaps could be used for determining if a real dependence between E and α is really occurring.

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Dependence of the preexponential factor on temperature

Errors in the activation energies calculated by assuming that Ais constant

Journal of Thermal Analysis and Calorimetry
Authors: J. M. Criado, L. A. Pérez-Maqueda, and P. E. Sánchez-Jiménez

Summary  

The dependence of the preexponential factor on the temperature has been examined and the errors involved in the activation energy calculated from isothermal and non-isothermal methods without considering such dependence have been estimated. It has been shown that the error in the determination of the activation energy calculated ignoring the dependence of Aon Tcan be rather large and it is dependent on x=E/RT, but independent of the experimental method used. It has been also shown that the error introduced by omitting the dependence of the preexponential factor on the temperature is considerably larger than the error due to the Arrhenius integral approach used for carrying out the kinetic analysis of TG data.

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Journal of Thermal Analysis and Calorimetry
Authors: V. Balek, M. Beneŝ, J. Ŝubrt, J. Pérez-Rodriguez, P. Sánchez-Jiménez, L. Pérez-Maqueda, and J. Pascual-Cosp

Abstract  

Emanation thermal analysis (ETA), thermogravimetry and high temperature XRD were used to characterize the thermal behavior during dehydration of natural Na montmorillonite (Upton Wyoming, USA) and homoionic montmorillonite (MMT) samples saturated with different cations, i.e. Li+, Cs+, NH4 +, Mg2+ and Al3+. ETA results characterized radon mobility and microstructure changes that accompanied the mass loss of the samples due to dehydration on heating in air. A collapse of interlayer space between the silicate sheets after water release from the MMT samples was characterized by a decrease of the radon release rate, ΔE. Decreases in c-axis basal spacing (d 001) values determined from XRD patterns for the different montmorillonite samples follow the sequence:

\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$Mg - MMT > Al - MMT > Li - MMT > Na - MMT > NH_4 - MMT > Cs - MMT$$ \end{document}
The decrease of the radon release rate (ΔE) determined by ETA that characterized microstructure changes due to collapse of interlayer space corresponded well to differences in the c-axis basal spacing (Δd 001) values determined from the XRD patterns before and after samples dehydration.

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Acta Physiologica Hungarica
Authors: DJ Ramos-Campo, F Martínez-Sánchez, P Esteban-García, JA Rubio-Arias, VJ Clemente-Suarez, and JF Jiménez-Díaz

The aim of the present research was to analyze modifications on hematological and aerobic performance parameters after a 7-week intermittent hypoxia training (IHT) program. Eighteen male trained triathletes were divided in two groups: an intermittent hypoxia training group (IHTG: n: 9; 26.0 ± 6.7 years; 173.3 ± 5.9 cm; 66.4 ± 5.9 kg; VO2max: 59.5 ± 5.0 ml/kg/min) that conducted a normoxic training plus an IHT and a control group (CG: n: 9; 29.3 ± 6.8 years; 174.9 ± 4.6 cm; 59.7 ± 6.8 kg; VO2max: 58.9 ± 4.5 ml/kg/min) that performed only a normoxic training. Training process was standardized across the two groups. The IHT program consisted of two 60-min sessions per week at intensities over the anaerobic threshold and atmospheric conditions between 14.5 and 15% FiO2. Before and after the 7-week training, aerobic performance in an incremental running test and hematological parameters were analyzed. After this training program, the IHTG showed higher hemoglobin and erythrocytes (p < 0.05) values than in the CG. In terms of physiological and performance variables, between the two groups no changes were found. The addition of an IHT program to normoxic training caused an improvement in hematological parameters but aerobic performance and physiological variables compared to similar training under normoxic conditions did not increase.

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