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  • Author or Editor: M. Villanueva x
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Abstract  

This work is a ‘historical’ revision of the evolution of an experimental procedure developed by Prof. Lisardo Nez and his research group TERBIPROMAT to study the sustainability and the soil health state. From the very beginning, in 1993, the microbial activity was the main bioindicator selected to analyse the ‘soil health state’. For this reason, a microcalorimetric technique was used lately to analyse the influence of different human activities such as reforestations, agricultural exploitation or pollution on the microbial activity in different soils. Microcalorimetry is the main scientific technique used in this research to follow the stimulation of the microbial activity by addition of glucose. The data obtained were complemented by a study of physical, chemical and biological parameters of soil and allowed to follow the microbial activity in soils of Galicia (Spain) along the year. The final results, still in revision, will be helpful in establishing a data basis for real maps of the ‘health state’ of different soils. Such maps could be used to design processes that help us to decide how we should exploit soils ensuring their sustainability.

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Journal of Thermal Analysis and Calorimetry
Authors: J. Salgado, M. Villanueva, O. Núñez-Fernández, J. Proupín-Castiñeiras, N. Barros, and J. Rodríguez-Añón

Abstract  

Isothermal and Differential Scanning Calorimetry is applied to analyze the evolution of soil using its microorganisms and organic matter as bioindicators of soil quality. This study was carried out with two similar soils under different agricultural activities: culture and pasture. Sampling and measurements were performed through 1 year in order to check the sensitivity of common calorimetric indicators of microbial activity and organic matter to the different climatic seasons in the sampling place: spring, summer, fall and winter. Results show that these indicators are sensitive to changes related to climatic conditions but the variability depended also on the nature of the soil: pasture or agricultural land. The results achieved through the present study show that the procedure here proposed could be used on any soil everywhere, providing the determination of the own parameters of soil and zones.

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Journal of Thermal Analysis and Calorimetry
Authors: Lisardo Núñez-Regueira, M. Villanueva, I. Fraga, C. A. Gracia-Fernández, and S. Gómez-Barreiro

Abstract  

The thermal degradation of an epoxy system consisting of a diglycidyl ether of bisphenol A (DGEBA, n=0) and m-xylylenediamine (m-XDA) was studied by both thermogravimetric analysis (TG) and dielectric analysis (DEA). It has been checked a deviation of the typical behaviour in the Arrhenius plot expected for this kind of systems, owing to the thermal degradation. Both, structural relaxation time and conductivity values, were represented as a function of the mass loss, that allow a relationship to be obtained between characteristic relaxation time and the degree of degradation at the beginning of the degradation process.

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Calorimetric approach to metabolic carbon conversion efficiency in soils

Comparison of experimental and theoretical models

Journal of Thermal Analysis and Calorimetry
Authors: N. Barros, J. Salgado, J. Rodríguez-Añón, J. Proupín, M. Villanueva, and L. Hansen

Abstract  

Soil carbon is the largest reservoir of organic carbon on the planet and CO2 production by soil thus has potentially large effects on atmospheric CO2. Carbon sequestration in soil is determined by the metabolic efficiency (substrate carbon conversion efficiency) of soil micro-organisms. That could be measured by calorespirometric methodology (parallel measurement of metabolic heat rate and CO2 production rate) and by theoretical thermodynamic models. Carbon conversion efficiency of the glucose degradation reaction in soil is calculated from both the calorespirometric ratio of heat rate to CO2 rate and from energy and mass balance models combined with calorimetric heat rates. Results obtained, 0.77 and 0.75, are in good agreement.

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Journal of Thermal Analysis and Calorimetry
Authors: M. Villanueva, J. Martín-Iglesias, J. Rodríguez-Añón, and J. Proupín-Castiñeiras

Abstract  

The thermal degradation of the epoxy system diglycidyl ether of bisphenol A (DGEBA n=0) and m-xylylenediamine (mXDA) containing different concentrations of polyhedral oligomeric silsesquioxanes (POSS) nanoparticles was studied by thermogravimetric analysis in order to determine the influence of both, the POSS concentration and the curing cycle on the degradation process and to compare it with the results for the non modified system. Glass transition temperatures for the same systems were also determined by differential scanning calorimetry. Different behaviors have been observed, depending on the POSS concentration and on the curing selection.

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