1,721,032 research outputs found
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
Lactate formation in Caldicellulosiruptor saccharolyticus is regulated by the energy carriers pyrophosphate and ATP
No full textCaldicellulosiruptor saccharolyticus displays superior H(2) yields on a wide range of carbon sources provided that lactate formation is avoided. Nevertheless, a low lactate flux is initiated as the growth rate declined in the transition to the stationary phase, which coincides with a drastic decrease in the glucose consumption and acetate production fluxes. In addition, the decrease in growth rate was accompanied by a sudden increase and then decrease in NADH levels. The V'(MAX) of the lactate dehydrogenase (LDH) doubled when the cells entered the stationary phase. Kinetic analysis revealed that at the metabolic level LDH activity is regulated through (i) competitive inhibition by pyrophosphate (PPi, k(i)=1.7mM) and NAD (k(i)=0.43mM) and (ii) allosteric activation by FBP (300%), ATP (160%) and ADP (140%). From these data a MWC-based model was derived. Simulations with this model could explain the observed lactate shift by displaying how the sensitivity of LDH activity to NADH/NAD ratio varied with different PP(i) concentrations. Moreover, the activation of LDH by ATP indicates that C. saccharolyticus uses LDH as a means to adjusts its flux of ATP and NADH production. To our knowledge, this is the first time PPi is observed as an effector of LDH
Developing a thermophilic hydrogen-producing co-culture for efficient utilization of mixed sugars
No full textPrevious studies on the extreme thermophile Caldicellulosiruptor saccharolyticus revealed that the organism produces high yields of hydrogen on glucose and xylose, the major components of lignocellulosic hydrolysates. Preliminary experiments on mixed sugar substrates, however, indicated that xylose was preferred over glucose. The sugar preference of some other extreme thermophiles, including Caldicellulosiruptor owensensis, Caldicellulosiruptor kristjanssonii and newly enriched, thermophilic compost sludge microflora, was investigated in an attempt to find complementary organisms to C. saccharolyticus for rapid and efficient utilization of lignocellulosic sugars. The behavior of C. owensensis and C. kristjanssonii appeared to be similar to that of C. saccharolyticus, either in pure cultures or in co-cultures with the latter. Co-culturing C. saccharolyticus with the enriched compost microflora resulted in fast, simultaneous consumption of both glucose and xylose in the medium with a relatively high specific hydrogen production rate, 40 mmol 1/(gCDW).h, and high volumetric productivity, 22.5 mmol/l.h
Growth and hydrogen production characteristics of Caldicellulosiruptor saccharolyticus on chemically defined minimal media
No full textCaldicellulosiruptor saccharolyticus is an extreme thermophilic bacterium recognized for its saccharolytic ability and superior ability to produce high yields of hydrogen. However,most studies have been made using yeast extract (YE) as a rich but expensive nutrient source. For the first time, we show that C. saccharolyticus is able to grow on defined minimal media, including essential vitamins, provided that CO2 was allowed to accumulate sufficiently in the culture broth to activate growth. Growth and hydrogen production performance on minimal media was analyzed in both batch and continuous mode. Absence of YE resulted in similar or higher hydrogen yields and specific hydrogen productivities but lower volumetric hydrogen productivities than with YE. The results also indicate that YE is used as a carbon- and energy source thus affecting metabolic flux calculations. This study clarified that YE is not essential making C. saccharolyticus more attractive for fundamental studies on its metabolism and future industrial exploitation
Nutrient requirements of lactococci in defined growth media
Full text linkMany attempts have been made for the last six decades to design defined media for species of the lactococcus group. The general outcome of the studies suggests that this group is heterogeneous with respect to specific requirements for nutrients. Lactococcal species are limited in various metabolic pathways. Early attempts to trace the required nutrients were not always successful because of the poor quality of analysis and the presence of impurities in the medium components
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