1,720,968 research outputs found
Produção, purificação e imobilização de lipases de Staphylococcus warneri EX17 produzidas em glicerol
Get PDFLipases (EC 3.1.1.3) são um grupo de enzimas que catalisam a hidrólise e síntese de triacilgliceróis. Estas enzimas apresentam estabilidade em diversos solventes orgânicos, podendo ser aplicadas como biocatalisadores em vários processos anteriormente realizados apenas por catalisadores químicos. Este trabalho teve como objetivo produzir, purificar e imobilizar lipases de Staphylococcus warneri EX17, cepa capaz de utilizar glicerol como fonte de carbono. Inicialmente, as condições de cultivo para produção de lipases foram otimizadas através de duas ferramentas de planejamento experimental: delineamento Placket Burman (P-B) e delineamento composto central rotacional (DCCR). Determinou-se que as melhores condições para produção desta enzima são: temperatura de 36 °C; pH 8,1; 30 g/L de glicerol; 3,0 g/L de óleo de oliva e 2,5 g/L de óleo de soja. Também se verificou ser possível a utilização de glicerol residual, oriundo da síntese enzimática de biodiesel como fonte de carbono. O extrato enzimático mostrou-se estável em três solventes orgânicos testados (metanol, etanol e η-hexano). Ainda visando a otimização das condições de cultivo, foram realizados cultivos submersos em biorreatores a fim de estudar a influência da taxa volumétrica de transferência de oxigênio (kLa) e do controle do pH, na produção da enzima. A maior produção de lipases ocorreu quando aplicado um kLa de 38 h-1 e com o pH controlado em 7,0 ao longo do cultivo, o que permitiu aumentar a produção da enzima em 5 vezes, em relação ao obtido nas condições anteriormente empregadas. A purificação da lipase foi realizada baseando-se no mecanismo de ativação interfacial destas enzimas sobre superfícies hidrofóbicas. Duas resinas foram testadas, octil-Sepharose e butil- Toyopearl. A lipase produzida foi purificada em apenas um passo utilizando esta última resina. Foi estudada a hiperativação da lipase purificada na presença de detergentes, a atividade lipolítica foi aumentada em 2,5 vezes na presença de 0,1% de Triton X-100. A lipase purificada foi imobilizada através de três estratégias: adsorção em suporte hidrofóbico; união covalente unipontual e união covalente multipontual. A influência da imobilização na modulação das propriedades da enzima foi estudada. A lipase apresentou maior estabilidade quando imobilizada multipontualmente. A hidrólise de distintos ésteres quirais pelos diferentes biocatalisadores obtidos também foi estudada. Os ésteres utilizados foram: (±) mandelato de metila, (±)-2-O-butiril-2-fenilacético e (±)-2-hidroxi-4-fenilbutirato de etilo. A especificidade da enzima foi muito dependente do método de imobilização, sendo que a lipase imobilizada unipontualmente foi mais específica para o substrato (±)-2-hidroxi-4-fenilbutirato de etilo, enquanto que para os outros dois substratos foi a lipase adsorvida hidrofobicamente. Este estudo demonstrou que a lipase de S. warneri EX17 pode ser produzida utilizando glicerol residual como fonte de carbono, levando a diminuição do custo na produção da enzima, que apresenta propriedades bastante interessantes para sua aplicação em biocatálise.Lipases (EC 3.1.1.3) constitute a group of enzymes that catalyze the hydrolysis and synthesis of triacylglycerols. These enzymes show stability in many organic solvents, being able to be used as biocatalysts in some processes that were once carried out only by chemical catalysys. The aim of this research was the production, purification, and immobilization of lipase by Staphylococcus warneri strain EX17 using glycerol as carbon source. Initially, the cultivation conditions for the production of lipases have been optimized through two statistical procedures, Plackett-Burman statistical design (PB) and central composite design (CCD). It was determined that the best conditions for this enzyme production are: temperature, 36 °C; pH, 8.1; glycerol, 30 g/L; olive oil, 3.0 g/L; and soybean oil, 2.5 g/L. It was also studied the use of raw glycerol from enzymatic synthesis of biodiesel as carbon source, and stability studies showed that this lipase from S. warneri EX17 was stable in methanol, ethanol and nhexane. Moreover, experiments were conducted in submerged bioreactors in order to study the influence of oxygen volumetric mass transfer rate (kLa) and the control of pH in the production of the enzyme. The higher lipase production occurred when the microorganism was submitted to a kLa of 38 h-1 and the pH controlled at 7.0 during the cultivation, which improved 5-fold the enzyme production, compared to the results obtained in shaker flasks. The lipase purification was carried out based on mechanisms of interfacial activation of these enzymes on hydrophobic surface. Two supports were tested, octyl-Sepharose and butyl-Toyopearl. The lipase produced was purified 20-fold in only one step of purification. The purified lipase was immobilized on cyanogens bromide activated agorese and its hyperactivation in the presence of detergents was studied. The lipolytic activity increased 2.5-fold in presence of 0.1% of Triton X-100. After this, lipase was immobilized by three strategies: adsorption on hydrophobic support, mild covalent attachment, and multipoint covalent attachment. The stability over thermal, organic solvent and detergent inactivation was verified, as well as the influence of the immobilization protocol in the modulation of the properties of the enzyme. The lipase showed higher stability when multipointly immobilized on glyoxyl agarose. The hydrolysis of different chiral esters by the three biocatalysts obtained was also studied. The esters used were: (±) methyl mandelate, ((±) methyl mandelate, (±)-2-O-butyryl-2-phenylacetic acid, (±)-2-hydroxy-4-phenyl-butyric acid ethyl ester. The specificity of the enzyme was highly dependent of the protocol of immobilization, and the lipase mildly immobilized on cyanogen bromide agarose was more specific to the hydrolysis of (±)-2-hydroxy-4-phenyl-butyric acid ethyl ester, while for the other two substrates was the lipase adsorbed on octyl agarose. This study demonstrated that the lipase from S. warneri EX17 can be produced using raw glycerol as carbon source, contributing to the reduction in production costs of the enzyme, and the enzyme, when immobilized on different supports, presented quite interesting properties that may be usefull as biocatalysts
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
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