1,720,964 research outputs found
Impact of chemical stressors on hydrogen metabolism
Full text linkThe effects of chemical stressing agents on H 2 metabolism were evaluated using thermodynamic, biochemical, genomic and statistical methods. The objectives of this study were to examine the role of homoacetogens and hydrogenotrophic methanogens exposed to different stress treatments under various fermentation conditions. Negligible H 2 consumption was observed at mesophilic and thermophilic temperature (at pH 4.5) when combined with the addition of 2 g L -1 linoleic acid (LA). Genomic analysis revealed that LA-treated cultures were dominated by Clostridium sp. whereas control cultures were dominated by homoacetogens and methanogens. Lauric acid (LUA), LA, fish oil and furfural affected H 2 consumption similarly to BES. The H 2 consumption (%) of the control and chemically treated cultures revealed the following trend: Control > Fish oil = LA = Furfural > BES > LUA. Treatment with different stressing agents also resulted in the formation of diverse fermentation metabolites. The long-term effects of different culture pretreatments under mesophilic condition resulted in higher mean H 2 yields compared to the yields from cultures incubated at thermophilic condition (after 5 glucose additions). Hydrogen consumption studies using long term stress treated cultures showed lower consumption at thermophilic temperature than at mesophilic temperature. Uptake hydrogenase activities correlated positively with the H 2 consumption data. Genomic analysis indicated that both methanogens and homoacetogens were present in control cultures, but they were absent from the pretreated cultures. Studies conducted in anaerobic sequencing batch reactors revealed that lowering the HRT from 37.5 h to 7.5 h reduced the methane yield and increased the H 2 yield. Higher H 2 yields were obtained in cultures operated at thermophilic temperature compared to mesophilic and psychrophilic temperature using corn stalk (CS) as substrate. Cultures fed CS liquor showed lower levels of specific methanogenic activities than cultures fed pure sugars. The results from these studies indicate that all the chemical stressing agents investigated were active against H 2 consumers (methanogens in particular). In addition to different stress treatments, proper control of operational parameters such as pH, HRT and temperature is required to minimize H 2 consumption and maximize H 2 production in dark fermentation process
Biological hydrogen production from lignocellulosic biomass in an up-flow anaerobic sludge blanket reactor using mixed microbial cultures
Full text linkThe current research investigated hydrogen (H 2 ) production potential from lignocellulosic biomass via dark-fermentation in upflow sludge blanket reactors (UASBRs) using mixed anaerobic culture. The effects of hydraulic retention time (HRT) and organic loading rate (OLR), on H 2 production were examined under mesophilic conditions using linoleic acid (LA), as a methanogenic inhibitor. The dynamics of the microbial community were explored using terminal restriction fragment length polymorphism analysis. Studies with pure glucose revealed that high H 2 yield greater than 2.1 mol mol -1 glucose was obtained in control cultures operating at HRTs ranging from 12 h to 20 h with OLRs corresponding to 16 g L -1 d -1 and 10 g L -1 d -1 , respectively. Species belonging to Clostridia was observed under these conditions. A further decrease with the HRT in control cultures reduced H 2 yields up to 1.3 mol mol -1 glucose, while addition of LA showed improved H 2 yields greater than 2.0 mol mol -1 glucose at HRTs ranging from 6 to 12 h. A maximum H 2 yield of 303±20 mL g -1 COD was obtained from switchgrass-derived sugars under the optimal conditions (pH 5.0, HRT 10 h and 1.75 g L -1 of LA) determined using response surface methodology. The microbial characterization under optimal conditions showed dominance of Ruminococcaceae and Clostridiaceae with efficient suppression of methanogens. Nitrogen sparging of the UASBRs under the optimal conditions, increased H 2 yield by 15% in comparison to unsparged cultures. Sparging the bioreactors increased the abundance of Clostridium sp. and Bacillus sp. under LA treated conditions. A stable H 2 yield of 274±40 mL g -1 COD was obtained by the control cultures fed corn stover hydrolysate and operating at 18 and 24 g COD L -1 d -1 , suggesting furans and phenols could serve as methanogenic inhibitors at low levels. The dominance of Clostridium sp., Flavobacterium sp. and Eubacterium sp., were observed under these H 2 -producing conditions. The results from current research suggest that H 2 production from lignocellulosic biomass is feasible and could be applied on a large scale by maintaining proper operational conditions
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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