1,720,958 research outputs found
Evaluación de la factibilidad de la síntesis de nanotubos de carbono a partir de los productos de la gasificación de un carbón
Get PDFEn este trabajo se realizaron estudios de gasificación a diferentes temperaturas y concentración de agente gasificante (O2) a un carbón de bajo rango de Amagá, para obtener una mezcla de gases con una composición de monóxido de carbono que permitiera usar dicha mezcla gaseosa como precursor de carbono para la síntesis catalítica de nanotubos de carbono (CNT) por el método de deposición química de vapores o CVD por sus siglas en inglés, usando como catalizador un material mesoporoso (MCM-41) con 3% de Co. La mejor composición del gas fue: CO (11,75 %), CO2 (1,4%), CH4 (0,12 %) y H2 (0,72 %) a 1100 °C con 9,8% de O2. Se hicieron estudios isotérmicos y no-isotermicos con los modelos de Ozawa– Flynn–Wall (OFW) y Vyazovkin para hallar los parámetros cinéticos de la gasificación. Se caracterizó el carbón mediante análisis último y próximo. El catalizador fue sometido a análisis de difracción de rayos X, y superficie BET. Los nanotubos de carbono sintetizados fueron caracterizados mediante TGA, TEM y espectroscopia Raman.Abstract: In this work, gasification tests at different temperatures and concentration of gasification agent (O2) were carried out using a low-rank coal from Amagá in order to obtain a gas mixture with a relative high carbon monoxide composition which was used as a carbon precursor for catalytic synthesis of carbon nanotubes, using a mesoporous material (MCM-41 with 3% Co) as catalysts. The best composition of the gas was CO (11,75 %), CO2 (1,4%), CH4 (0,12 %) and H2 (0,72 %) at 1100 ° C with 9.8% O2. Isothermal and non-isothermal test were performed with the Ozawa-Flynn-Wall (OFW) and Vyazovkin models to find the kinetic parameters of gasification. The coal was characterized by proximate and ultimate analyses. The catalyst was subjected to X-ray diffraction analysis, and BET surface. The obtained carbon nanotubes were characterized by TGA and Raman spectroscopy.Maestrí
Evaluación teórica de óxido de fosforeno azul para la adsorción de gases de bajo peso molecular
Get PDFUna posible alternativa para detectar e identificar gases nocivos para la salud humana y el ambiente son las nanoestructuras en 2D. Estas han mostrado propiedades físico-químicas adecuadas para la elaboración de sensores de gases, debido a que generan diferentes respuestas electrónicas por la interacción con moléculas gaseosas, tienen gran estabilidad estructural, pueden tener diferente composición química y poseen alta relación superficie-volumen. El fosforeno azul (BP) es un ejemplo de estos materiales bidimensionaleses. Estudios sobre la capacidad de adsorción de gases del BP, han mostrado la posibilidad de disociación del O 2 , que da origen a enlaces covalentes entre los átomos de fósforo y los oxígenos. Lo anterior podría explicar la oxidación que presenta el fosforeno en condiciones ambientales. Teóricamente se ha mostrado que el óxido de fosforeno azul (BPO), es tan estable como el BP. Dado que los óxidos metálicos son altamente empleados como catalizadores y sensores de gases, el BPO podría ser pensando como un posible sensor de gases. Por lo anterior, en este trabajo se estudiaron las propiedades electrónicas del BPO con el fin de evaluar sus posibilidades como sensor de gases, en particular en la adsorción de gases de bajo peso molecular (CH4, CO2, CO, N2O, SO2 y O2). La investigación se realizó en el marco de la teoría del funcional de la densidad (DFT). La interacción de los gases con el BPO se evaluó en cuatro sitios diferentes sobre la nanoestructura, teniendo en cuenta la orientación de las moléculas. Los resultados obtenidos muestran que se produce una fisisorción para todas las moléculas gaseosas, sin embargo en el caso del átomo de hidrógeno su quimisorción sobre la superficie deforma la estructura del BPO. De los resultados obtenidos se puede destacar que la interacción del BPO con O2 y SO2 presentaron las mayores energías de adsorción. Adicionalmente, el BPO pasa de semiconductor a conductor, dependiendo de la orientación de las moléculas. En contraste, las moléculas que presentaron menor energía de adsorción fueron el CO y CO2 . Estos resultados sugieren que el BPO podría ser un candidato promisorio para el desarrollo de sensores de gases debido a que algunas de las moléculas modificaron las propiedades electrónicas del BPO.Abstract: A possible alternative to detect and recognize harmful gases for human health and the environment are 2D nanostructures. These have demonstrated adequate physical-chemical properties for the elaboration of gas sensors, because they have different electronic responses due to the interaction with gaseous molecules, they have great structural stability, they can have different chemical composition and connections with a high super-volume ratio. The Blue Phosphorene (BP) is an example of these nanomaterials. Studies on the gas adsorption capacity of BP have shown dissociation possibility of O2, which gives rise to covalent bonds between phosphorus atoms and oxygen. This could explain the oxidation that phosphorene presents in environmental conditions. Theoretically it has been shown that the Blue Phosphorene Oxide (BPO) is as stable as the BP. Since metal oxides are highly used as catalysts and gas sensors, the BPO could be thought of as a possible gas sensor. Therefore, in this work the electronic properties of the BPO were studied to test its possibilities as a gas sensor, in particular in the detection of low molecular weight gases (CH4, CO2, CO, N2O, SO2 and O2). The research was conducted within the framework of the density functional theory (DFT). The interaction of the gases with the BPO was evaluated in four different sites on the nanostructure, taking into account the orientation of the molecules. The obtained results show that a physisorption for all the gases molecules does take place; nevertheless, in the case of the hydrogen atom its chemisorption on the surface destroys the structure of the BPO. From the results obtained it can be noticed that the interaction of the BPO with O2 and SO2 had the highest adsorption energies, additionally, the BPO goes from semi-conductor to conductor, depending on the orientation of the molecules. In contrast, the molecules that showed the lowest adsorption energy were CO and CO2. These results suggest that the BPO could be a promising candidate for the development of gas sensors because some of the molecules modified the electronic properties of the BPO.Doctorad
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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