1,720,953 research outputs found
Simulaciones moleculares de hidrato de metano. inhibición de formación de clatratos por vinilcaprolactama
Get PDFResumen
Los clatratos hidratos de gas natural o también llamados hidratos de gas natural son sólidos
cristalinos compuestos por agua y un gas. Existe dificultad para conocer la composición
(estequiometría) del hidrato de gas.
Existe un problema de formación de hielos de clatratos de metano en las tuberías de conducción
y extracción de hidrocarburos que tiene una gran relevancia industrial y económica,
por lo que se han desarrollado dos vías para inhibir su formación: a través de inhibidores
termodinámicos (ej: metanol) o utilizando inhibidores cinéticos como la vinilcaprolactama
(VCap).
En este trabajo se estudiará la posibilidad de inhibir el crecimiento del clatrato de metano
utilizando la VCap como inhibidor en un modelo molecular compuesto por una molécula
de metano y 20 moléculas de agua a través de simulaciones de dinámica molecular Born-
Oppenheimer (BOMD) y simulaciones de dinámica molecular clásica. Se utilizarán como
modelos de cajas clatratos las dos configuraciones estables de la red de agua alrededor del
metano encontradas por Bravo y Saint-Martín [49]: la configuración de dodecaedro (512,
Dod) y la configuración (4115262, Nax). Se realizaron simulaciones BOMD a nivel DFT
con un funcional híbrido de intercambio y correlación que ha demostrado ser confiable para
describir los efectos de dispersión en sistemas hidrofóbicos. El objetivo primario de esta
tesis es la validación de los potenciales clásicos comunmente utilizados para el estudio de la
interacción metano-agua en simulaciones de dinámica molecular clásica [42, 77, 78]. Para la
calibración de los potenciales clásicos utilizaremos como referencia las energías relativas de
cada estructura en las simulaciones BOMD respecto a la energía de la estructura inicial de
Dod y Nax optimizadas por m´étodos de química cuántica. El principal interés es determinar
si la dinámica molecular con potenciales clásicos estandar para el agua, el metano y la
vinilcaprolactama son capaces de reproducir cualitativamente la evolución tanto energética
como estructural de los sistemas metano-agua y metano-agua/VCap.
Para la realización de cálculos de energías clásicas se variaron los parámetros de referencia
para la molécula de metano, usando el modelo de átomo unido [30]. Para la molécula de
agua se utilizó el modelo de agua TIP4P/ICE [77] y para el inhibidor cinético vinilcaprolactama
(VCap) se tomaron los parámetros del Automated Topology Builder (ATB) and
Repository [78]. Para la comparación de modelos se utilizó el error cuadrático medio (rms).
Como resultado se observa que es necesario sobrestimar el error en las energías de la configuración
Dod, es decir, escoger el par de parámetros que minimizan el error rms de Nax cuando
el error rms de la configuración Dod es semejante al error de la configuración Nax. De esta
manera es razonable esperar que estos parámetros puedan ser utilizados en simulaciones
de dinámica clásica para cualquier tipo de hielo de clatratos de metano. Los parámetros
optimizados son " = 2.0KJ/mol y = 0.42nm
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
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
- …
