1,720,983 research outputs found
A parallel molecular dynamics simulation code for dialkyl cationic surfactants
No full textWe have developed a new simulation code, COMFORT, for the study of assemblies of flexible surfactant molecules, structured for parallel execution and specialised to surfactants with dialkyl chain geometry. The approach is a hybrid domain-decomposition and systolic-loop algorithm which is suitable for systems composed of long chain molecules and with tens of thousands of atoms in total. The algorithm uses a modified Ewald technique for two dimensionally periodic systems which has been successfully parallelized. The code was designed to be highly portable between machines of different architectures. The code has been tested on a number of platforms including the Intel iPSC/860, the IBM SP1, the CRAY T3D, a SGI Power Challenge and a number of workstation clusters. We demonstrate that scalable parallel computing technology, combined with appropriate software, can provide a commercially viable simulation system for use in the exploration and development of surfactant assemblies
Efeito da adição de sais eletrolíticos monovalentes na estrutura, forma e ordem orientacional dos agregados micelares da mistura binária amônio pentadecafluorooctanoato e água
Get PDFTese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e matemáticas. Programa de Pós-graduação em FísicaO principal objetivo das pesquisas realizadas e apresentadas neste trabalho esta concentrada nos efeitos da adicao de sais eletroliticos monovalentes fortes, como o cloreto de amonio (NH4Cl) e o cloreto de potassio (KCl), na formação de novas estruturas com propriedades liquido-cristalinas ou mudanças drasticas nas estruturas micelares pré-existentes, nas fases micelares isotropica, nematica e lamelar presentes no sistema binario contendo o surfactante amonio entadeca°uorooctanoato e agua (APFO / H2O). Inves-tigamos tambem, a in°u^encia que os sais NH4Cl e KCl produziram na forma e no tamanho dos agregados micelares, bem como sua dependencia com a temperatura. Diversas tecnicas experimentais, como microscopia optica, refratometria de ABBE, tramitancia de luz, difraçao por raios X e etc, foram usadas e dos resultados destas medidas, suas temperaturas de transicoes de fases foram determinadas e uma nova estrutura, formada espontaneamente na solucao e denominada "vesiculas", foi identicada, isto e, estas vesiculas aparecem simplesmente pelo efeito do sal adicionado. Estudos teoricos usando campo medio (Maier-Saupe) em combinaçao, com resultados experimentais foram realizados e o comportamento do paramentro de ordem orientacional micelar com a temperatura, foram obtidas para varias amostras. The main aim of the research performed and presented in this work is concentrated in the e®ects of the addition of strongs monovalents electrolytic salts, as the ammonium chloride (NH4Cl) and the potassium chloride (KCl), in the formation of new structures with liquid-crystallines properties or drastic changes in pre-existing micellar structures in the isotropic, nematic and lamellar phases present in the binary system containing the surfactant pentadeca°uorooctanoate and water (APFO / H2O). We also investigated the in°uence that the salts (NH4Cl and KCl) had on the size and shape of the micellar aggregates as well as their dependency on temperature. Several experimental techniques such as polarizing optical microscopy, direct bulk solution observation, Abbe refractometry, laser light transmission and small angle X ray di®raction were used and from results of these measurements, phase transitions temperatures were determined and, a new structure, formed spontaneously in the solution and named "vesicles", was identi¯ed, i.e., these vesicles appear in the solution simply by the e®ect of the added salt. Theoretical studies using mean ¯eld approximation (Maier-Saupe) in combination with experimentals data were performed and the behavior of the micellar orientational order parameter on temperature, for several samples, obtained
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
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