1,720,961 research outputs found
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
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
Development and application of a high throughput assay system for the detection of rieske dioxygenase activity
No full textAccess to thesis restricted until 05/2024.The chemical industry currently accounts for 14% of all greenhouse gas emissions and is
projected to become the largest global consumer of oil by 2030. In the Ball State Laboratory for
Biocatalysis Research, we strive to address this problem through the development and application
of novel enzymatic catalysts. Enzymatic catalysts are environmentally benign because they can be
used in aqueous solutions and are fully biodegradable. As such, they can play a role in eliminating
the need for petroleum-based solvents and toxic heavy-metal catalysts in the production of fine
chemicals.
Rieske dioxygenases (RDO) are a class of enzymes known for their ability to perform the
cis-dihydroxylation of aromatic compounds. They have been widely applied in synthetic chemistry
due to their ability to provide enantiopure metabolites that can be used in the synthesis of highvalue
compounds. Yet, the utility of these enzymes has been limited by their substrate scope and
strict selectivity.
Here, we seek to develop novel RDO catalysts with improved or expanded reactivity
through directed evolution. In order to detect the relative cis-dihydroxylation activity of engineered
Rieske dioxygenase variants, a novel high throughput assay system for the detection of their cisdiol
metabolites was developed. Here, the cis-diol metabolites produced by active dioxygenases
in aqueous fermentation broths are oxidized using sodium (meta)periodate to produce dienedialdehydes.
These dialdehydes are then conjugated with a reactive fluorescent probe to give a
strong, concentration-dependent fluorescent signal. In this way, this metaperiodate fluorescein cisdiol
assay (MPFCD) detects the relative activity of RDOs with different aromatic substrates. This
novel high throughput assay system has allowed for the activity of rationally engineered Rieske
dioxygenase variants, produced through saturation mutagenesis, to be determined, and for the
identification of variants that demonstrate significantly altered reactivity profiles in comparison to
the parent enzyme.Thesis (M.A.
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
Expansion of the substrate scope of Toluene Dioxygenase through enzyme engineering
No full textThe Rieske dioxygenase (RDO) family of enzymes is known for its ability to stereoselectively dihydroxylate aromatic substrates, to generate chiral diene-diol metabolites, which serve as precursors in the synthesis of valuable organic compounds. However, these enzymes have so far been unable to react with a number of substrates due to the steric and/or electronic nature of the relevant compounds. In an effort to expand the utility of these enzymes, the enzyme toluene dioxygenase (TDO) was engineered to develop TDO variants that possess novel activity for amide-functionalized substrates. This was performed by identifying active site residues for mutation, creating a series of mutant libraries via directed mutagenesis, and then assessing the activity of the mutants for amide-functionalized substrates via the MPFCD assay. Putative hits that demonstrated activity for these substrates were subjected to secondary screening to confirm the activity observed upon initial screening. Confirmed hits were then genetically sequenced in order to identify the beneficial mutations, and the activity of all confirmed hits were compared in parallel.Thesis (B.?)Honors Colleg
Improving the activity of rieske dioxygenases for benzoates through enzyme engineering
No full textRieske dioxygenases (RDOs) are well-known oxidoreductase enzymes commonly found
in soil bacteria. They participate in the metabolism of aromatic pollutants in their environment,
and their utility in organic synthesis has been noted due to RDOs ability to catalyze the
asymmetric dihydroxylation of aromatic compounds to form chiral cis-diene-diol metabolites.
RDOs are limited as green-chemical catalysts, however, because of steric and electronic
constraints within their active sites that lead to restricted substrate scopes and minimal activity
for specific substrate classes. This research consisted of using active site-targeted mutagenesis
alongside a recently developed high throughput assay system to develop novel toluene
dioxygenase (TDO) variants with appreciably increased activity in the dihydroxylation of esterfunctionalized
substrates, specifically methyl and ethyl benzoate, in comparison to the native
enzyme. Eight distinct point mutations were found to give improved activity for the chosen
substrates, including two novel mutations (I276C and I276T) that no other study has previously
identified as being beneficial. The activity level of these variants increased upon the native
enzyme’s activity for methyl benzoate by up to 594%, 590%, and 494% for I276V, M220A, and
L272W respectively. Likewise, the activity of variants M220A, I276C, and I276V were 9363%,
5461%, and 5342% respectively for ethyl benzoate compared to the unaltered TDO system.
Characterization of these variants has developed a library of beneficial mutations which will
guide the generation of enzyme variants with multiple substitutions to investigate potential
synergistic effects on activity and substrate scope. This study will serve to inform future
engineering studies targeting RDOs, thus broadening the utility of these environmentally friendly
catalysts as green-chemical tools for the creation of vital building blocks in organic synthesis.Thesis (B.?)Honors Colleg
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
Investigation of the effect of targeted active site mutations on the activity of Rieske dioxygenases
No full textRieske dioxygenases, a class of enzyme systems found in soil bacteria, play an important
role in the bacterial metabolism of aromatic “pollutants” in their environment. Rieske
dioxygenases have long been utilized in organic synthesis due to their ability to catalyze the
asymmetric dihydroxylation of aromatics to produce chiral diene-diol metabolites. Despite their
utility, the range of potential applications for these green catalysts has been limited by steric and
electronic constraints on their substrate scopes and on their activity.
Our work in the Ball State Laboratory for Biocatalysis Research is focused on the
development of new green-chemical tools, in the form of engineered enzymes that operate in
aqueous solutions, to help contribute to attenuating the reliance of chemical industry on nonrenewable
energy sources. To this end, we have applied active site targeted mutagenesis along
with a recently reported high throughput screening platform to develop engineered toluene
dioxygenase variants with significantly increased activity in the dihydroxylation of a broader range
of aromatic substrates, revealing key active site residues that modulate the enzyme’s activity and
selectivity. We aim to apply the knowledge gained in this study in engineering more improved
Rieske dioxygenase variants to broaden the utility of these environmentally sustainable catalystsM. S
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