1,720,971 research outputs found
Hidrogenação seletiva de oleo de soja : desempenho de catalisadores de niquel e influencia das condições de processo
No full textOrientador : Walter EstevesDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de AlimentosResumo: Óleo de soja, com catalisador disperso, foi hidrogenado em reator descontínuo, onde a pressão do sistema se igualou à pressão atmosférica. Seis catalisadores de níquel, codificados de A à F, foram comparados entre si nas seguintes condições de reação: concentração de catalisador de 1%, temperatura de 180ºC, grau de agitação de 650 rpm, fluxo de hidrogênio de 1 litro/minuto e tempo de reação de 240 minutos. A atividade dos catalisadores variou de 5,46 a 7,98 unidades de índice de iodo/hora, enquanto que esse índice nos produtos hidrogenados ficou entre 98,13 a 108,80. A seletividade linoleica esteve na faixa de 20,62 a 30,74 para os catalisadores A, B, C, D e F, sendo que o valor de 686 para E, foi à isomerização e não à hidrogenação. A seletividade linolênica e redução de linolênico atingida variou de 1,8 a 2,5 e 4,37 a 5,68%, respectivamente. O teor de ácidos graxos conjugados totais presente nos produtos hidrogenados variou de 1,58 a 16,23%, este último valor correspondente ao catalisador E. O conteúdo de isômeros trans e isomerização específica estavam entre 13,97 a 16,70% e 0,47 a 0,66, respectivamente. O conteúdo de gordura o sólida à 10 ºC variou de 6,42 a 14,30%, sendo este último valor correspondente ao teste com catalisador F, devido ao menor índice de iodo atingido pelo mesmo. O tempo de filtração para cada catalisador, nas condições do teste de filtrabilidade, foi de 2,5 a 16 minutos, sendo o menor e maior valor correspondentes à F e C, respectivamente. O catalisador F, nas condições testadas, atingiu maior atividade, menor tempo de filtração e isomerização específica e ainda, seletividade comparável aos demais, tendo sido assim, utilizado nos testes subsequentes, codificados de T1 a T9, nas seguintes condições: temperatura de 140 a 200 ºC, concentração de catalisador de 0,25 a 1%, grau de agitação de 280 e 650 rpm, fluxo de gás de 1 e 2 litros/minuto e tempo de reação de 180 a 240 minutos. A atividade, seletividade linolênica e linoleica variaram de 5,79 a 10,64; 1,7 a 2,2 e 19,13 a 46,61, respectivamente. O conteúdo de trans dos produtos hidrogenados e a isomerização específica ficaram entre 10,73 a 17,92% e 0,43 a 0,60, respectivamente. O teor de conjugados totais presente nos produtos hidrogenados esteve entre 0,97 a 2,64%. O teor de gordura sólida a 10ºC variou de 7,66 a 16,66%. A atividade variou com o catalisador utilizado, com o índice de iodo atingido e com as condições de reação empregadas, aumentando com temperatura e concentração do catalisador. A seletividade linoleica e isomerização dependeram tanto do catalisador quanto das condições de processo e do índice de iodo atingido na hidrogenização.Abstract: Soybean oil with dispersed catalyst was in hydrogenated in a discontinued reactor at pressure equal to atmospheric pressure. Six reactor nickel catalysts, codified from A to F, were compared under the were following reactions conditions: catalyst concentration = 1%, temperature = 180 ºC, agitation speed = 650 rpm, hydrogen flow rate = 1 liter/minute and reaction time = 240 minutes. The catalysts activities varied from 5,46 to 7,98 iodine value/hour units, while this parameter was between 98.13 and 108.80 for hydrogenated products. Linoleic selectivity was observed to be in a range from 20.62 to 30.74 for was catalysts A, B, C, D and F, whereas the value 686 found for E was due to isomerization and not hydrogenation. Linolenic selectivity and linolenic reduction varied from 1.8 to 2.5 and 4.37 to 5.68%, and respectively. Total conjugated fatty acids in hydrogenated products varied from 1.58 to 16.23%, this last value corresponding to catalyst E. The trans isomer content and specific isomerization varied from 13,97 to 16,70%. and 0,47 to 0,66, respectively. Solid fat content at 10°C was between 6.42 and 14,30%, this last value corresponding to the test with catalyst F, due to its lower iodine value. Filtration time for each catalyst, under filterbility test conditions, was found to be 2,5 to 16 minutes, being the lowest and highest values those corresponding to F and C, respectively. Catalyst F, under the experimental conditions used, achieved greater activity, lower filtration time and specific isomerization, and had selectivity similar to the other catalysts used. For these reasons, it was chosen for the subsequent tests, codified from T1 to T9, under the following conditions: temperatures from 140 to 200ºC, catalyst concentration from 0,25 to 1%, stirring rate of 280 and 650 rpm, gas flow rate of the 1 and 2 liters/minutes and reaction time from 180 to 240 minutes. Activity, linoleic selectivities varied from 5,79 to linolenic and 10,64; 1,7 to 2,2 and 19,13 to 46,61, respectively. The trans isomer content of the hydrogenated products and the specific isomerization were from 10.73 to 17.92% and 0.43 to 0.60, respectively. The total conjugated fatty acid content in hydrogenated products was found to be between 0.97 and 2.64%. Solid fat content at 10ºC varied from 7.66 to 16.66%. Activity varied catalyst used, iodine value and reaction conditions, increasing with an increase in temperature and catalyst concentration. The selectivity and isomerization depended on the catalyst and on the process conditions and iodine value reached in hydrogenation.MestradoMestre em Tecnologia de Alimento
MÉTODOS DE AVALIAÇÃO DA ESTABILIDADE OXIDATIVA DE ÓLEOS E GORDURAS
Full text linkApresenta revisão de literatura sobre métodos de
determinação da estabilidade oxidativa que surgiram numa
tentativa de se avaliar a resistência à oxidação dos óleos e
gorduras. Existe, atualmente, muita controvérsia sobre a
eficiência ou a capacidade destes métodos de predizerem
as alterações que ocorrerão nos óleos e gorduras, durante
o armazenamento. Foram discutidas as vantagens e
desvantagens de cada método e a sua importância na área
de tecnologia de óleos e gorduras. A padronização das
metodologias para determinação da estabilidade oxidativa,
seja pelo método de estufa ou pelos métodos automatizados,
é uma necessidade em função da grande quantidade de
dados relatados na literatura que foram obtidos em condições
muito diversas, dificultando sua utilização até para simples
comparação.
OXIDATIVE EVALUATION METHODS OF OILS AND FATS
Abstract
A literature review on the methods of determination of the oxidative stability originated
from an attempt to evaluate the oils and fats oxidation resistance is presented. Nowadays,
there is much controversy about the efficiency or the capacity of these methods to
predict the alterations that will occur in oils and fats during the storage. It is discussed
the advantages and the disadvantages of each methodology and its importance within
the area of the oils and fats technology. The standardization of the methodologies for
determination of the oxidative stability, by incubators or by automated methods, is a
necessity due to the great quantity of data related in literature which were obtained in
diverse conditions, making difficult its utilization even for simple comparation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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