1,721,152 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
Improving polyhydroxyalkanoate production from inexpensive carbon sources by genetic approaches: a review
No full textPolyhydroxyalkanoates (PHAs) are a family of biodegradable intracellular polyesters that a number of Eubacteria and Archaea can accumulate for energy and carbon storage. Most of the genetic modifications to the producing bacterial species have been accomplished to clarify basic biochemical, genetic, and metabolic aspects of PHA metabolism. However, due to its plastic-like properties and complete biodegradability, this bio-based polymer has attracted the attention of a variety of manufacturers. A number of genetic approaches have therefore been reported, aimed at improving the performance of the microorganisms with a potential for use in a production process. Indeed, genetic tools may find useful applications in all the phases of the PHA production chain, from the isolation and characterization of new microbial strains through all the production steps until they reach the downstream processes. The substrates generally used for PHA production are expensive, so the search for low-cost feedstock is necessary. These materials, possibly deriving from agri-food processes, are unfortunately not easily degraded or converted directly into PHAs. Thus, the development of engineered microbes is in progress to process waste streams and covert them to valuable polymers. This review will summarize the most relevant results obtained through genetic engineering tools for the production of PHAs from cheap carbon sources in view of possible industrial applications
Oenological yeasts as a source of extracellular enzymes for future applications in bioethanol production.
No full textBioethanol is an attractive, sustainable and alternative energy source to conventional fuel. Current ethanol production processes using crops (sugar cane and corn) as a starting substrate are well-established. However, a cheaper feedstock such as lignocellulosic biomass could make bioethanol more competitive with fossil fuel, although its complex structure makes this material more resistant to biological degradation.
Recent efforts have focused on the one-step microbial conversion of plant biomass into biofuel since simultaneous microbial hydrolysis and fermentation of lignocellulosic material could represent a strategy to allow cost-effective production of ethanol. Wild-type microorganisms having both the properties to utilise biomass polysaccharides and to produce ethanol have not been described. In this respect, yeasts isolated from oenological environments for their fermentative abilities and possessing efficient hydrolytic enzymes could be very promising.
The aim of this study was to investigate on the extracellular enzymatic activity profile of yeast strains previously selected on the basis of their optimal fermentative performance, in order to start the development of a strain suitable for the one-step bioconversion of biomass into ethanol. One hundred and eighty non-Saccharomyces strains and two hundred and twenty Saccharomyces cerevisiae strains isolated from grape marcs were screened for their activity on cellulose, hemicellulose, pectin, protein and starch.
Few strains showed activity on cellulose, pectin, protein and starch, while no xylanolytic strains were observed. Two non-Saccharomyces strains were found effective for the production of cellulase and starch-degrading enzymes. Thirteen strains of S. cerevisiae, potentially able to use starch as the sole carbon source, were selected (Favaro et al. , 2008). Their weak growth on starch minimal agar plates was unexpected since the common dogma (Pretorius, 1997) is that wild-type S. cerevisiae cannot grow on media where starch is the only carbon source.
In addition, extensive biochemical, physiological and genetic knowledge on their potentially amylolytic enzyme(s) was performed to look into this possible new starch-hydrolytic mechanism. The pattern of starch degradation halo of the selected S. cerevisiae strains was very similar to that exhibited by S. diastaticus, which is clearly related to S. cerevisiae, except for ethanol performance and extracellular glucoamylase production. Starch utilisation in S. diastaticus depends on the expression of three unlinked genes, sta1, sta2 and sta3. The search of the above genes or genes with the same function is in progress in the selected strains of S. cerevisiae mentioned above.
These observations provided the basis for a further research on the gene-regulation and enzymatic efficiency of these DNA-sequences in order to enhance and improve their starch degrading activity through molecular approaches.
Since at least few strains showed good hydrolytic activities on complex polysaccharides (cellulose and starch), main components of low-cost plant biomass, this study encourages the selection of oenological microorganisms possessing interesting enzymatic profiles for future applications in bioethanol production.
This approach could allow the development of one-step bioconversion process, relying on wild-type oenological yeasts with desired properties for both lignocellulose hydrolysis and fermentation. These natural yeasts could also be the base of genetic modification for the construction of more efficient recombinant strains
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
Is pyrolysis bio-oil prone to microbial conversion into added-value products?
Full text linkIn view of the potential application of pyrolysis-based biotechnologies, it is crucial to look for novel microorganisms able to convert pyrolysis-derived products, in particular bio-oil water-soluble constituent, into valuable compounds. For the first time, this paper proposed a survey on a collection of bacterial, yeast, and fungal strains with well-known industrial properties as well as new bacterial isolates in order to select microbes able to both tolerate bio-oil inhibitors and convert bio-oil into valuable products. This survey found that bio-oil aqueous phase (BOAP) obtained from intermediate pyrolysis could be metabolized as it is by fungal strains whereas several dilutions are needed to do not hamper cell viability of many tested yeast and bacterial isolates. To process BOAP into valuable products, the yeast Saccharomyces cerevisiae L13, selected as the most industrially relevant tested strain, was adopted to convert bio-oil aqueous fraction hydrolysate into ethanol without any detoxification step. The fermenting performances were much greater than those of the benchmark yeast strain and S. cerevisiae L13 proved to be a strong candidate for bioethanol production from BOAP hydrolysates. This study demonstrated that the search for microorganisms is a promising approach to the future development of pyrolysis oil-based biorefinery platforms
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
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