Pratiques éducatives en education rurale: Enseigner les sciences naturelles

Se expone y analiza el proceso de diseño e implementación de secuencias de actividades propuestas desde los enfoques de indagación y modelización para generar aprendizajes en Ciencias Naturales, en la escolaridad primaria en plurigrado rural. Se trata de los resultados parciales de un trabajo de investigación interinstitucional desarrollado en Argentina (Provincia de Santa Fe), por dos Institutos de Educación Superior, que tomó como objeto de estudio las prácticas de enseñanza de las Ciencias Naturales en dos escuelas rurales de Educación Primaria con grados agrupados. Se muestran criterios de diseño y análisis de secuencias para este contexto y se concluye que el enfoque de indagación-modelización promueve el desarrollo de habilidades de indagación y la construcción de modelos explicativos por parte de los estudiantes, en un escenario que enriquece este tipo de propuestas, el plurigrado.The process of designing sequences of activities to generate learning in the context of rural plurigrado is exposed and analyzed. This is the partial results of an interinstitutional research project developed in Argentina (Province of Santa Fe), by two Institutes of Higher Education, which took as object of study the teaching practices of the Natural Sciences in two rural schools of Primary Education with grouped degrees. Design criterions and sequences analysis are shown for this context and it is concluded that the investigation/inquiry-modelling/representation approach promotes the development of inquiry/investigation abilities and the construction of explanatory models by students, in a scene that enriches/improves this kind of proposals, the multigrade.On expose et on analyse le processus de conception et d’application de séquences des activités proposées à partir des objectifs de la recherche et de la modélisation afin de produire des apprentissages en Sciences naturelles, à l’école primaire (en zone) rurale, regroupant plusieurs niveaux. Ce sont les résultats partiels d’un travail d’enquête inter-institutionnel, développé en Argentine (Province de Santa Fe), par deux Instituts d’Enseignement supérieur, qui a eu pour sujet d’étude les pratiques d’enseignement des Sciences naturelles dans deux écoles primaires rurales comprenant des niveaux regroupés. Les critères de conception et d’analyse des séquences pour ce cas sont mis en évidence. Ils conduisent à la conclusion que la mise en oeuvre d’un modèle opérationnel favorise le développement des compétences pour la recherche méthodique et initie l’élaboration de modèles explicatifs pour une partie des étudiants, dans une démarche enrichissant ce type d’initiative, le regroupement des scolaires de niveaux différents

LIQUID-PHASE SELECTIVE HYDROGENATION OF 1-HEPTYNE OVER Ni/Al2O3. EFFECT OF THE REACTION TEMPERATURE

En este trabajo fue evaluado el efecto de la temperatura de reacción en la hidrogenación selectiva de 1-heptino a 1-hepteno usando un catalizador de níquel soportado sobre γ -alúmina. Fueron estudiadas diferentes temperaturas operacionales (273, 303 y 323 K), obteniéndose mayor conversión total del reactivo a la mayor temperatura, con una selectividad próxima al 90%. El catalizador de níquel preparado puede considerarse como una alternativa más económica a nivel industrial frente a los ya conocidos catalizadores de paladio, no sólo debido al bajo costo del metal sino también debido a su bajo contenido metálico (3,6% en masa). El catalizador fue caracterizado por Difracción de Rayos X, Reducción a Temperatura Programada y Espectroscopía Fotoelectrónica de Rayos X. Estas indicaron la presencia de óxido de níquel a nivel másico con fuertes interacciones con el soporte y la existencia de especies electro-deficientes de níquel a nivel superficial quienes serían las especies activas durante la hidrogenación del alquino terminal.Fil: Maccarrone, María Juliana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; ArgentinaFil: Lederhos, Cecilia Rosa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; ArgentinaFil: Badano, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; ArgentinaFil: Quiroga, Monica Esther. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; ArgentinaFil: Yori, Juan Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; Argentin

Metal and precursor effect during 1-heptyne selective hydrogenation using an activated carbon as support

Palladium, platinum, and ruthenium supported on activated carbon were used as catalysts for the selective hydrogenation of 1-heptyne, a terminal alkyne. All catalysts were characterized by temperature programmed reduction, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. TPR and XPS suggest that the metal in all catalysts is reduced after the pretreatment with H2 at 673 K. The TPR trace of the PdNRX catalyst shows that the support surface groups are greatly modified as a consequence of the use of HNO3 during the catalyst preparation. During the hydrogenation of 1-heptyne, both palladium catalysts were more active and selective than the platinum and ruthenium catalysts. The activity order of the catalysts is as follows: PdClRX > PdNRX > PtClRX ≫ RuClRX. This superior performance of PdClRX was attributed in part to the total occupancy of the d electronic levels of the Pd metal that is supposed to promote the rupture of the H2 bond during the hydrogenation reaction. The activity differences between PdClRX and PdNRX catalysts could be attributed to a better accessibility of the substrate to the active sites, as a consequence of steric and electronic effects of the superficial support groups. The order for the selectivity to 1-heptene is as follows: PdClRX = PdNRX > RuClRX > PtClRX, and it can be mainly attributed to thermodynamic effects.UNL and CONICET

Fatores influenciadores no uso de criptomoedas por pessoas físicas

As criptomoedas são ativos financeiros inovadores que surgiram a pouco mais de uma década e ainda não são amplamente conhecidas. A tecnologia por trás de seu desenvolvimento (Blockchain) possui um grande potencial de aplicação em diversas áreas, devido a sua natureza disruptiva. Por ser ainda uma tecnologia pouco explorada, se levantam questões sobre quais os elementos que levam à sua adoção pelos indivíduos, sendo este o motivador da realização do presente trabalho. Portanto, o objetivo deste estudo é identificar os fatores de uso de criptomoedas por pessoas físicas. Para o atingimento deste objetivo é elaborado um referencial teórico que aborda os principais assuntos sobre o tema. Para tanto, se é abordado brevemente o desenvolvimento das escolas de marketing e o campo de comportamento do consumidor, bem como as teorias derivadas sobre comportamento do consumidor (Teoria da Ação Racional, Teoria do Comportamento Planejado), modelos sobre a adoção de tecnologia (Modelo de Aceitação de Tecnologia, Modelo da Teoria Unificada de Aceitação e Uso de Tecnologia 2) e como se estruturam e funcionam as criptomoedas, de modo que se tenha maior familiaridade com o objeto estudado. A pesquisa é conduzida através de um instrumento qualitativo e quantitativo (questionários), onde foram realizadas perguntas de escopo amplo, perguntas de perfil dos usuários e seus graus de discordância e concordância acerca de temas referente a criptomoedas. Foram respondidos 126 questionários, dos quais 87 foram considerados válidos. A análise qualitativa serviu como suporte para melhor entendimento dos dados colhidos através dos dados quantitativos. A análise dos dados quantitativos se deu através de uma análise fatorial exploratória, onde posteriormente se foi medido o Alfa de Cronbach das variáveis selecionadas, onde se identificaram 8 fatores sobre o uso de criptomoedas, sendo eles apresentados do maior ao menor alfa: Atitude e Intenção de Uso (0.96), Motivação Hedônica (0.94), Utilidade Percebida (0.85), Facilidade de Uso (0.84), Mídias Sociais (0.83), Identificação e Internalização (0.78), Risco Percebido (0.74), Preço (0.53). Os fatores extraídos na análise fatorial exploratória se encontram alinhados com a literatura do tema, bem como com o modelo teórico de fatores proposto. A conclusão acerca do uso de criptomoedas é que o uso o seu uso é atrelado a especulação e descentralização da moeda, algo que é visto como um fator positivo pois elas estão menos suscetíveis a intervenção estatal, porém a atitude e intenção do indivíduo perante o comportamento é um fator forte, existindo uma percepção muito positiva pelos usuários no seu uso. Existe por parte dos usuários entusiasmo e um sentimento de recompensa no uso de criptomoedas como apontado no fator de motivação hedônica, os indivíduos têm uma crença na utilidade do uso de criptomoedas. Há divergências em relação aos riscos e percepção do preço, sendo estes os alfas mais baixos, o que pode ser também um fator a ser adaptado no instrumento, todavia estes elementos parecem não impactar tanto na intenção de uso dos usuários.Cryptocurrencies are innovative financial assets that emerged no more than a decade ago and are yet not fully known. The technology behind its development (Blockchain) has a big potential of application on several areas, due to its disruptive nature. Since it is still a not fully explored technology yet, some questions emerge about the factors that drive its adoption by its users and this is the main motivation for the development of this research. Therefore, the general objective of this work is to identify the factors of usage of cryptocurrencies by final users. For the achievement of this goal is elaborated a theorical framework that tackles the main subjects about the theme. For such, its briefly explained the development of marketing schools and the field of consumer behavior, as well the behavioral theories (Rational Action Theory, Planned Behavior Theory) and technology adoption models (Technology Acceptance Model, Unified Technology Acceptance and Use Theory Model 1) and how cryptocurrencies work and are structured. This is necessary to get more closeness and insights about the theme. The study is conducted through the usage of a qualitative and quantitative instrument (questionary), where were made broad scope questions, profile questions and it’s the degrees of agreement or disagreement with queries about cryptocurrencies. The survey was answered by 126 people, from which 87 were considered valid. The qualitative analysis served as a support to a better understanding of the data gathered by the quantitative portion of the research. The quantitative analysis was conducted through the usage of a exploratory factor analysis, followed by the measurement of the Cronbach Alpha of the variables, where it could be extracted 8 influence factors, that are sorted form largest to smaller in the following: Attitude and Intent of Usage (0.96), Hedonic Motivation (0.94), Perceived Utility (0.85), Perceived Ease of Use (0.84), Social Medias (0.83), Identification and Internalization (0.78), Perceived Risk (0.74), Price (0.53). The factors extracted from the exploratory factor analysis are aligned with the theorical framework as well the theoretical proposed model of influence. The conclusion about the usage of cryptocurrencies is that its usage is attached to speculation and decentralization, which is something perceived as good due to the perception of less influence by the governments, although there was observed that the attitude and intention towards the behavior as a strong factor, there is positive perception from the users in relation of its usage. There is between the users an enthusiasm and a rewarding felling in the usage of cryptocurrencies as pointed by the hedonic motivation factor, the individuals have a strong believe on the utility of cryptocurrencies. There is divergency about risks and price perception between the users, being these the lowers Alpha scores, these variables might have to be adapted on the research instrument, however these elements seems to not impact as much in the usage intention of the users

Innovación y desarrollo económico local: Diagnóstico de la situación en unidades agropecuarias de Río Cuarto (Argentina) y su incidencia en el desarrollo económico local de la ciudad

120 p.Tesis dirigida por Francisco Alburquerque Llorens y tutor Raúl Caminati. El objeto de estudio de este trabajo es la Innovación y el Desarrollo Económico Local, orientados a la situación de Innovación que se presenta en las pequeñas y medianas unidades agropecuarias de Río Cuarto y su incidencia en el Desarrollo Económico Local de la Ciudad, presentándose tanto su análisis teórico como así también un estudio de campo. Lo que se pretende es identificar, elementos del contexto externo a la empresa como el estímulo social y cultural hacia la creatividad y la asunción de riesgo empresarial, la vinculación del sistema educativo a los requerimientos y problemas del sistema productivo local, el grado de exigencia planteado por proveedores y consumidores locales, y el acceso a líneas de financiamiento para microempresas y pequeñas y medianas empresas, entre otros. Y, por otro lado, también se busca ver la situación de ciertos elementos internos a la empresa, como el tipo de gestión y organización empresarial, el estilo de dirección, grado de involucramiento y motivación de los trabajadores, calidad de las relaciones laborales, capacitación empresarial y tecnológica, cualificación de los recursos humanos, y otros, tanto en las unidades agropecuarias, como en las actividades vinculadas a la misma. Lo que se busca, en este trabajo, no es hacer un diagnóstico con una óptica “desde arriba”, dónde predomina el modelo de carácter concentrador y basado en la gran empresa, en los procesos de industrialización, terciarización y urbanización. Sino que se trata de aplicar el diagnóstico utilizado en aquellas estrategias que asumen un punto de vista “desde abajo”, sustentadas en factores económicos, sociales, culturales y territoriales, que se basan en la utilización de recursos

Alkyne Selective Hydrogenation with Mono- and Bimetallic- Anchored Catalysts

Partial hydrogenation of alkynes has industrial and academic relevance on a large scale; industries such as petrochemical, pharmacological and agrochemical use these compounds as raw material. Finding an economic, active and selective catalyst for the production of alkenes through partial hydrogenation of alkynes is thus an important challenge. Mono- and bimetallic catalysts (palladium, ruthenium and nickel) were synthetized by the incipient wetness technique using gamma alumina and an activated carbon as supports. The catalysts were characterized by inductively coupled plasma, hydrogen chemisorption, temperature-programmed reduction and X-ray photoelectronic spectroscopy (XPS). The objective of this work is to study 1-heptyne-selective hydrogenation using supported catalysts influenced by different factors: (a) pretreatment reduction temperature, (b) reaction temperature, (c) type of support, (d) metal loading, (e) precursor salt and (f) addition of a second metal to monometallic palladium catalyst. The Lindlar commercial catalyst, commonly used in these types of reactions, was used for comparative purposes. XPS technique allowed verifying that the presence of electron-deficient species on the catalyst surface with high metal loading affects the conversion and selectivity to the desired product. Nevertheless, the influence of geometrical effects and/or mixed active sites in the catalysts, as well as metal-metal and metal-support interactions, cannot be neglected

Olefin Purification and Selective Hydrogenation of Alkynes with Low Loaded Pd Nanoparticle Catalysts

The catalytic performance of Pd-nanoparticle catalysts for the selective hydrogenation of alkynes at mild conditions (150 kPa and 303 K) was evaluated. A Lindlar commercial catalyst was also tested for comparison. The effects of acidity, amount of active sites and dispersion on the catalytic activity and selectivity were studied. At mild conditions, Pd-nanoparticle catalysts were considerably more active and slightly more selective than the Lindlar catalyst. The best synthesized catalyst for the purification of 1-pentene was Pd/Al2O3-Mg (r0 = 41.1 mol gPd–1 min–1, 94% selectivity). The activity and selectivity of Pd/CaCO3 were similar to those of the Lindlar catalyst. The smallest particle sizes (3–4.5 nm) favored the dissociative adsorption of hydrogen over Pd° active sites and a good catalytic behavior. The weaker acid centers (Lewis) of Pd/Al2O3-Mg and Pd/CaCO3 favored higher selectivities to the desired alkene. Pd/Al2O3 was the most active catalyst but also the least selective. This was due to strong acid sites, remnant Bronsted acid sites, which provide extra hydrogen that favors the alkyne hydrogenation rate and also the undesired overhydrogenation of the alkene and/or the isomerization.The financial support provided by UNL (Grants CAI+D 50420150100074LI and 50420150100028LI), CONICET (Grant PIP 11220130100457CO), and ANPCyT (Grant PICT 2016 1453) are acknowledged

Kinetic study of the selective hydrogenation of styrene over a Pd egg-shell composite catalyst

This is a study on the kinetics of the liquid-phase hydrogenation of styrene to ethylbenzene over a catalyst of palladium supported on an inorganic–organic composite. This support has a better mechanical resistance than other commercial supports, e.g. alumina, and yields catalysts with egg-shell structure and a very thin active Pd layer. Catalytic tests were carried out in a batch reactor by varying temperature, total pressure and styrene initial concentration between 353–393 K, 10–30 bar, and 0.26–0.60 mol L−1. Kinetic models were developed on the assumptions of dissociative hydrogen chemisorption and non-negligible adsorption of hydrogen and styrene. Final chemical reaction expressions useful for reactor design were obtained. The models that best fitted the experimental data were those ones that considered the surface reaction as the limiting step. In this sense, a two-step Horiuti–Polanyi working mechanism with half hydrogenation intermediates gave the best fit of the experimental data. The heats of adsorption of styrene and ethylbenzene were also estimated.The authors are gratefully indebted to CONICET, ANPCyT and Universidad Nacional del Litoral for financially sponsoring this research work

Activity and sulfur resistance of Rh(I) and Pd(II) complexes

Two complexes of Rh(I) and Pd(II) with chloride and tridecylamine ligands were obtained and characterized by Elementary Analysis and by XPS and FTIR spectroscopies. Complexes anchored on γ-Al2O3 were tested in the styrene semi-hydrogenation reaction carried out in the absence or presence of a sulfur poison. Although both low loaded catalysts were highly selective, the Pd(II) complex was three times more active than the Rh(I) complex. The rhodium complex was more sulfur resistant but less active than the palladium complex. Differences in conversion and sulfur resistance between both complexes could be related to electronic and/or geometric effects