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SIMULACIÓN DE LA DISPERSIÓN DE CONTAMINANTES ATMOSFÉRICOS DE LA CD. DE CHIHUAHUA, UTILIZANDO EL CÓDIGO MCCM
No full textModelación de formación de nanopartículas de Zirconato de Sodio en un proceso de aspersión pirolítica
No full textLos materiales particulados en escala nanométrica (del orden 10-9 m), son de
considerable interés para una amplia variedad de aplicaciones. Algunos ejemplos
de éstos son materiales cerámicos, materiales con propiedades electrónicas,
magnéticas, ópticas y estructurales específicas, materiales para componentes
electrónicos, catalizadores, aceptores de gases, etc. Para aplicaciones químicas,
las propiedades catalizadoras y absorbentes son mejoradas debido al aumento del
área superficial por el pequeño tamaño de las partículas y a la disminución de
problemas de difusión. La eficiencia se incrementa y los tiempos de reacción se
reducen considerablemente al emplear reactivos particulados en escala
nanométrica.
De entre la gran variedad de materiales resaltan los aceptores de CO2 necesarios
en los procesos de reformación de vapores de gas metano (Steam Methane
Reforming) para la obtención de hidrógeno H2).
En el presente trabajo se estudia la formación de zirconato de sodio y se propone
un método viable teóricamente para producirlo en forma de partículas
nanométricas.
Existen varias técnicas para la síntesis de nanopartículas dependiendo del tipo del
estado del precursor: gaseoso [Pratsinis y Vemury, 1996], sólido [Swihart, 2003] o
líquido [Okuyama y Lenggoro, 2003]. En el caso de la técnica con precursores
gaseosos, éstos reaccionan a altas temperaturas para formar las moléculas del
producto, posteriormente las nanopartículas se forman por condensación o
coagulación. Una dificultad de esta técnica es la elevación de los costos de
operación y control del proceso. Con la técnica de precursores sólidos, primero se
vaporiza el material y después por medio de calentamiento y condensación se
sintetizan las nanopartículas [Munir and Anselmi, 1989]; añadiéndose un paso más
a la síntesis. Finalmente utilizando precursores líquidos, éstos se dispersan en
forma de un aerosol fino, el cual se calienta para reaccionar y formar la
composición deseada [Messing, et al., 1994]. La nanopartícula se forma por
nucleación, coagulación y cristalización. El procedimiento más sencillo y viable
utilizando precursores líquidos es el de la aspersión pirolítica. La aspersión
pirolítica es la base técnica elegida en esta tesis para la síntesis de nanopartículas
de zirconato de sodio.La aspersión pirolítica es un proceso que permite sintetizar una amplia variedad de
materiales en polvos finos [Messing, et al., 1993] y [Gurav, et al., 1993]. En la
Figura 1-1 se observan las partes principales del proceso. La aspersión pirolítica
consta de 3 elementos principales: dispositivo aspersor, horno tubular y
precipitador [Lenggoro, et al., 2000]. El dispositivo aspersor convierte la solución
precursora, dosificada mediante una bomba, en un conjunto de micro-gotas las
cuales son transportadas por un gas de arrastre hacia el horno tubular. Dentro de
él se llevan a cabo todos los cambios físicos y químicos que dan forma a las
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nanopartículas, por esta razón se puede nombrar reactor. Finalmente las
nanopartículas se recolectan en el precipitador.
Debido a que el proceso de aspersión pirolítica es novedoso, no se han llegado a
controlar todos los parámetros de operación ni se ha logrado predecir el
comportamiento cualitativo y cuantitativo de formación de las nanopartículas. Por
lo tanto, se desea que el presente trabajo contribuya tanto en la parte teórica como
en la técnica mediante la modelación y simulación numérica del proceso de
formación de nanopartículas considerando los parámetros de proceso de la
aspersión pirolítica.
Por todo lo anterior, se planteó como objetivo general de este trabajo el proponer,
entender y predecir el proceso de formación de nanopartículas de Zirconato de
sodio a través de la técnica de aspersión pirolítica. Este estudio se planteó el
resolver si el proceso de aspersion pirolítica es o no un proceso vable para formar
nanopartículas de zirconato de sodio. En efecto, no está demostrado que un
reactor con dimensiones y características razonables permita formar las
nanopartículas deseadas.
La presente tesis está estructurada en 3 capítulos. En el primer capítulo se explica
la base teórica y el estado del arte de los procesos químicos estudiados y del
proceso de aspersión pirolítica. En el segundo capítulo se muestra la metodología
empleada, finalmente el último capítulo muestra los resultados tanto teóricos como
experimentales de la obtención de zirconato de sodio y teóricos del proceso de
aspersión pirolítica.The particulate materials on the nanoscale (approximately 9.10 m), are of
considerable interest for a wide variety of applications. Some examples of these
are ceramic materials, materials with electronic, magnetic, optical and structural
specific materials for electronic components, catalysts, acceptor gas, etc. For
chemical, catalytic and absorbing properties are improved due to the increased
surface area by the small particle size and decreased diffusion problems. The
efficiency is increased and the reaction times are considerably reduced when using
particulate reagents in nanoscale.
Among the variety of materials highlight CO2 acceptors processes necessary
vapor reformation of methane gas (Methane Steam Reforming) for obtaining
hydrogen H2).
In this paper we study the formation of sodium zirconate and proposes a
theoretically viable method for producing shaped nanoparticles.
There are several techniques for the synthesis of nanoparticles depending on the
type of precursor state: gas [Pratsinis and Vemury, 1996], solid [Swihart, 2003] or
liquid [Okuyama and Lenggoro, 2003]. In the case of technique with gaseous
precursors, they react at high temperatures to form the product molecules, the
nanoparticles are then formed by condensation or coagulation. One difficulty with
this technique is the higher costs of operation and process control. With the
technique of solid precursors, the first material and is vaporized by heating after
condensation and nanoparticles are synthesized [Munir and Anselmi, 1989];
adding one step synthesis. Finally using liquid precursors, they are dispersed in a
fine mist form, which is heated to react and form the desired composition [Messing,
et al., 1994]. The nanoparticle is formed by nucleation and crystallization
coagulation. The simplest and viable using liquid precursors is the spray pyrolysis.
The spray pyrolysis technique is the basis chosen in this thesis for the synthesis of
sodium zirconate nanoparticles.
The spray pyrolysis is a process to synthesize a wide variety of materials in fine
powders [Messing, et al., 1993] and [Gurav, et al., 1993]. Figure 1-1 are seen the
main parts of the process. The spray pyrolysis consists of three main elements:
device sprinkler tube furnace and precipitator [Lenggoro, et al., 2000]. The
sprinkler device converts the precursor solution, dosed by a pump into a set of
micro-drops which are transported by a carrier gas into the tubular oven. Within it
are cconducted all physical and chemical changes that shape nanoparticles can
therefore appoint reactor. Finally nanoparticles are collected in the precipitator.
Because the spray pyrolysis process is novel, have not come to control all the
operating parameters has been achieved or predict the qualitative and quantitative
behavior of formation of nanoparticles. Therefore, it is desired that this work will
contribute both the theoretical and technique by modeling and numerical simulation
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of the formation of nanoparticles of considering the parameters of the spray
pyrolysis process.
Given the above, it was proposed as a general objective of this work is to propose,
understand and predict the formation of sodium zirconate nanoparticles via spray
pyrolysis technique. This study set the address if the spray pyrolysis process or not
a process is able energy to form sodium zirconate nanoparticles. Indeed, it is
shown that a reactor with dimensions and characteristics allow reasonable form
desired nanoparticles.
This thesis is divided into three chapters. In the first chapter explains the
theoretical basis and the state of the art processes and studied chemical spray
pyrolysis process. The second chapter describes the methodology used finally the
last chapter shows the theoretical and experimental results for obtaining sodium
zirconate and theoretical spray pyrolysis process
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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