José Ariza Carmona

Simulation of the thermogravimetry analysis of three non-wood pulps

In a study of three non-wood pulps (rice straw, EFB, and Hesperaloe), the standard pyrolysis model for biomass based on hemicellulose, cellulose, and lignin pseudo-components, was modified to include char volatilization. As a result, abnormally high values for lignin content have been avoided. On the other hand, the consideration of autocatalysis (Prout-Tompkins equation) for TGA data simulation under inert and oxidative atmospheres, allows obtaining a stable set of kinetic parameters that describe volatilization and char oxidation for different heating rates, including char ignition. These simulations allow us to investigate certain effects like oxygen influence on cellulose-char formation (including reduction in activation energy) and to calculate the composition of samples.

Use of autocatalytic kinetics to obtain composition of lignocellulosic materials.

Non-isothermal thermogravimetric analysis (TGA) data of biomasses and pulps originating from non-wood and alternatives materials (i.e., Tagasaste or rice straw) have been fitted with refined models, which include autocatalytic kinetics. Data sets were obtained for different experimental conditions, such as variations of heating rate and atmosphere, i.e., inert (pyrolysis) versus oxidative atmosphere (combustion). Besides the access to classical kinetic parameters (pre-exponential factor, activation energy, and reaction order), the improved data analysis enabled the determination of the chemical composition of the samples (cellulose, hemicellulose, extractives, lignin). The latter compared very well with those obtained by conventional methods (chemical analysis, HPLC). Given the reduced environmental impact and rapidness of the method, potential applications for research related to new biomasses and industrial processes can be foreseen. The herein implemented method is based on the assumption that samples contain pseudo-components, which independently degrade, and that combustion is the combination of an initial volatilization process (similar to pyrolysis) and a subsequent char oxidation process. Further, it was found that for a reliable modeling of the volatilization stage, extractives should be considered as well, together with the classical pseudo-components: hemicellulose, cellulose and lignin. The char oxidation stage has been simulated as a sum of the oxidation of three char types, one for each main pseudo-component. Importantly, fitting of TGA curves under consideration of autocatalytic kinetics allows the determination of a consistent set of kinetic parameters at different heating rates and leads to significant suppression of the compensation effect. While autocatalysis (characterized by the nucleation order) is not very significant for pyrolysis of biomasses, it can reach high levels for combustion, especially when high heating rates are used. In cellulosic char oxidation a nucleation order larger than one was fitted. The autocatalysis level of the char oxidation can rapidly increase with small modifications of the heating rate (i.e. to pass from 5 to 10 degrees C/min). In this case, the classically applied nth-order kinetic is particularly insufficient to fit experimental data with the same set of the kinetic parameters.

Validación del Cuestionario de Percepción de Soporte de la Autonomía en el Proceso de Entrenamiento (ASCQ) en jóvenes deportistas españoles

Resumen El objetivo de esta investigación fue validar al contexto español el Cuestionario de Percepción de Soporte de la Autonomía en el Proceso de Entrenamiento (ASCQ). Para ello, se llevaron a cabo tres estudios con muestras de deportistas federados, de edades entre 12 y 17 años. En el primero, el análisis factorial exploratorio del ASCQ reveló la existencia de dos factores: valoración del comportamiento autónomo e interés en la opinión del deportista. Además, el instrumento mostró una adecuada consistencia interna y estabilidad temporal. En el segundo estudio se confirmó la estructura factorial obtenida en el primero, consiguiendo unos índices de ajuste adecuados. Finalmente, en el tercer estudio se comprobó la invarianza por género y la validez de criterio mediante un análisis de correlación. Se encontró una correlación positiva entre la valoración del comportamiento autónomo y la intención de ser físicamente activo del deportista.

Effect of the previous composting on volatiles production during biomass pyrolysis.

Composting is a biological process of decomposition of organic materials in an aerobic environment, which modifies the chemical composition and the thermal behavior of biomass. During composting, fungi and bacteria promote the decomposition of hemicellulosic and cellulosic fractions, increasing the lignin proportion. Its product, compost, is usually used as an amendment to soil; however, its physicochemical characteristics turn it into an interesting feedstock in pyrolysis or gasification facilities. The changes that composting produces on biomass pyrolysis can be explained using an autocatalytic kinetic model (Prout-Tompkins). Thus, by means of a similar set of kinetic parameters for both the biomass and compost, it is possible to simulate the thermogravimetric analysis data (TG and DTG curves) of the materials as a sum of thermal degradations of its main pseudocomponents, hemicellulose, cellulose, lignin, and extractives. TG analysis coupled to mass spectrometry (MS) allows monitoring of the gas production during pyrolysis. Water and carbon oxide MS profiles can be simulated by an optimized linear combination of previously calculated DTG curves of pseudocomponents; however, in order to simulate the hydrogen MS signal, it is necessary to consider the char obtained in the course of the volatilization process. During pyrolysis, hydrogen production has two origins, volatilization of biomass pseudocomponents and charring. The last mechanism explains approximately 75% of the hydrogen obtained from compost. The pseudocomponent that produces more hydrogen by weight unit is lignin, showing a specific hydrogen production much higher than carbohydrates (3:1:8 for hemicellulose/cellulose/lignin). This fact, together with the greater lignin content in compost, explains the positive effect of composting on hydrogen production.

Health-risk behaviors in adolescents as indicators of unconventional lifestyles

This study analyses the dimensions of health-risk behaviors in adolescence. Based on the Theory of Problem Behavior, the study hypothesises that the structure of relations between risk behaviors may be explained in terms of their level of social transgression or unconventionality. With a sample of 771 adolescents, this study explores the association between the behaviors which, according to the WHO, have a greater impact on morbidity and mortality. The results of these analyses point to the existence of a latent variable grouping the risk behaviors that lead to greater confrontation with the norms of conventional society. The analysis of the relation of this latent variable with indicators of academic failure and satisfaction with peers and adults also produces findings that are consistent with the proposed interpretation. Finally, some recommendations are made for the planning of preventive interventions as a result of the findings.

Adult ADHD Self-Report Scale: Comprehensive Psychometric Study in a Spanish SUD Sample.

Objective: The purpose of this study is to provide reliability and validity evidence of the Adult Self-Report Scale (ASRS) scores on different versions and scoring procedures in a Spanish substance use disorder (SUD) sample. Method: The sample was made up of 170 outpatients diagnosed with SUD. The ASRS, the Mini-International Neuropsychiatric Interview (MINI), and the Substance Dependence Severity Scale were administered. Results: The results of the confirmatory factor analysis (CFA) showed adequate fit to the structure proposed by the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV) in the 18-item version. On the screening scale, best fit was found for a model with two correlated factors (inattention and hyperactivity). The exploratory factor analysis (EFA) showed that the ADHD items converge and are differentiated from symptoms of withdrawal. The regression analyses showed that severity of dependence is explained by the ASRS scores. Conclusion: Both versions of the ASRS showed adequate psychometric properties. The polytomous or dichotomous score is relevant in patient classification.