1,720,964 research outputs found
The hydroxyl radical scavenging activity of chitosan, hyaluronan, starch and their O-carboxymethylated derivatives
No full textIn order to study the effect of active hydroxyl and amino groups on scavenging activity against hydroxyl radicals of polysaccharides, three kinds of carboxymethylated polysaccharides (carboxymethyl chitosan (O-CM-chitosan), carboxymethyl hyaluronan (CMHA), and carboxymethyl starch (CMS)) were prepared and their antioxidant activities against hydroxyl radicals were assessed, respectively. Results showed that O-CM-chitosan had lower scavenging ability on hydroxyl radicals than chitosan. CMHA and CMS had the same tendency. For the three kinds of polysaccharides, scavenging ability on hydroxyl radicals was found to be in the order of chitosan > HA > starch. The scavenging ability of carboxymethylated polysaccharides had the same order as related to its corresponding polysaccharides at higher concentrations (>= 0.8mg/ml). There were not only hydroxyl groups but also amino or acetamino (CH3CONH-) groups in the molecules of chitosan and HA, but only hydroxyl group for starch. It was suggested that the sequence influence the scavenging activity against hydroxyl radicals might be amino group > acetamide group > hydroxyl group. (C) 2010 Elsevier Ltd. All rights reserved.In order to study the effect of active hydroxyl and amino groups on scavenging activity against hydroxyl radicals of polysaccharides, three kinds of carboxymethylated polysaccharides (carboxymethyl chitosan (O-CM-chitosan), carboxymethyl hyaluronan (CMHA), and carboxymethyl starch (CMS)) were prepared and their antioxidant activities against hydroxyl radicals were assessed, respectively. Results showed that O-CM-chitosan had lower scavenging ability on hydroxyl radicals than chitosan. CMHA and CMS had the same tendency. For the three kinds of polysaccharides, scavenging ability on hydroxyl radicals was found to be in the order of chitosan > HA > starch. The scavenging ability of carboxymethylated polysaccharides had the same order as related to its corresponding polysaccharides at higher concentrations (>= 0.8mg/ml). There were not only hydroxyl groups but also amino or acetamino (CH(3)CONH-) groups in the molecules of chitosan and HA, but only hydroxyl group for starch. It was suggested that the sequence influence the scavenging activity against hydroxyl radicals might be amino group > acetamide group > hydroxyl group. (C) 2010 Elsevier Ltd. All rights reserved
Stability and changes in astaxanthin ester composition from Haematococcus pluvialis during storage
No full textIn this paper, we investigated the effects of temperature, oxygen, antioxidants, and corn germ oil on the stability of astaxanthin from Haematococcus pluvialis under different storage conditions, and changes in the composition of astaxanthin esters during storage using high performance liquid chromatography and spectrophotometry. Oxygen and high temperatures (22-25 degrees C) significantly reduced the stability of astaxanthin esters. Corn germ oil and antioxidants (ascorbic acid and vitamin E) failed to protect astaxanthin from oxidation, and actually significantly increased the instability of astaxanthin. A change in the relative composition of astaxanthin esters was observed after 96 weeks of long-term storage. During storage, the relative amounts of free astaxanthin and astaxanthin monoesters declined, while the relative amount of astaxanthin diesters increased. Thus, the ratio of astaxanthin diester to monoester increased, and this ratio could be used to indicate if astaxanthin esters have been properly preserved. If the ratio is greater than 0.2, it suggests that the decrease in astaxanthin content could be higher than 20%. Our results show that storing algal powder from H. pluvialis or other natural astaxanthin products under vacuum and in the dark below 4 degrees C is the most economical and applicable storage method for the large-scale production of astaxanthin from H. pluvialis. This storage method can produce an astaxanthin preservation rate of at least 80% after 96 weeks of storage
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
Synthesis and moisture absorption and retention activities of a carboxymethyl and a quaternary ammonium derivative of alpha,alpha-trehalose
No full textCarboxymethyl alpha,alpha-trehalose (CMT) and a quaternary ammonium derivative of alpha,alpha-trehalose (QT) were successfully prepared, and their moisture absorption and retention activities were assessed. Results showed that both CMT and QT had better moisture absorption abilities at 43% and 81% relative humidity (RH) than alpha,alpha-trehalose. In addition, the two alpha,alpha-trehalose derivatives had better moisture retention abilities than alpha,alpha-trehalose under three humidity conditions: 81% RH, 43% RH, and under dry conditions. Therefore, carboxymethylation and quaternarization could improve the moisture absorption and retention abilities of alpha,alpha-trehalose. CMT and QT showed better moisture absorption ability and moisture retention ability than that of hyaluronan (HA), and could potentially find a use as moisture retention ingredient, for example, in cosmetics. (C) 2009 Elsevier Ltd. All rights reserved.Carboxymethyl alpha,alpha-trehalose (CMT) and a quaternary ammonium derivative of alpha,alpha-trehalose (QT) were successfully prepared, and their moisture absorption and retention activities were assessed. Results showed that both CMT and QT had better moisture absorption abilities at 43% and 81% relative humidity (RH) than alpha,alpha-trehalose. In addition, the two alpha,alpha-trehalose derivatives had better moisture retention abilities than alpha,alpha-trehalose under three humidity conditions: 81% RH, 43% RH, and under dry conditions. Therefore, carboxymethylation and quaternarization could improve the moisture absorption and retention abilities of alpha,alpha-trehalose. CMT and QT showed better moisture absorption ability and moisture retention ability than that of hyaluronan (HA), and could potentially find a use as moisture retention ingredient, for example, in cosmetics. (C) 2009 Elsevier Ltd. All rights reserved
Comparison and Analysis of Hydrogen Production Capacity of 8 strains of marine green algae
No full textIn this study, four strains of Chlorella genus and four strains of Tetraselmis genus were investigated to research their in vitro hydrogenase activities and hydrogen productions. C.sp.-3 showed the second highest in vitro hydrogenase activity with 297.48 nmol H-2/(mu g Chla h) and the highest volume of H-2 production with 10.246 mu l/L among all the strains. Although T. sp.-3 exhibited a much low H-2 production of 0.298 mu l/L, its in vitro hydrogenase activity was the highest with 315.92 nmol H-2/(mu g Chla h). During the continuous culture of five weeks, the hydrogen production of C. sp.-3 reached the peak at 3rd weeks with 12.46 mu l H-2 per liter culture, and decreased subsequently. In contrast, that of T. sp.-3 increased slowly and gradually with the culturing time, and was much lower than that of C. sp.-3 at each culture phases. These results showed that hydrogen production was a complex process that was determined not only by strain types but also by other factors, and that both C.sp.-3 and T. sp.-3 in the 8 strains were the most promising ones in hydrogen production and were worthy of further research
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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