1,720,963 research outputs found
Separation of CO2 and CH4 from biogas by formation of clathrate hydrates: importance of the driving force and kinetic promoters
No full textThis paper relates to the upgrading of model biogas mixtures, typically 60/40 CH4/CO2, by clathrate (gas) hydrates, which have recently been considered as a safe alternative to high-pressure or liquefied gas storage, and as an economic, chemical-free process for the separation of gas mixtures. Several factors affecting the driving force to hydrate formation are considered, such as the degree of over pressurization and the presence of chemical promoters. Promoters used were several anionic and zwitterionic surfactants
which are demonstrated to affect the hydrate-forming ability of water. Some lignin derivatives were also tested. Promoted hydrates were also compared to hydrate-based separation starting from nonpromoted water. Separation experiments were conducted under pressures of 4 and 2.5 MPa at 274 K, under either pressure-dropping or constant pressure conditions. Results show that the separation ability of clathrate hydrates as determined by the separation factor S is highest when no promoters are added to the water phase; the well-known promoter sodium dodecyl sulfate (SDS) shows a value of S which is approximately half the value of that in pure water while higher separations were obtained with some lignin derivatives and a non-surface-active naphthalenesulfonate derivative. We also show that the contribution of CO2 solubility in water to S is a main player in the overall process. Finally, the separation ability of hydrates seems to be inversely proportional to the amount of gas mixture enclathrated, i.e., the occupancy
Substrate Effect on alpha-Chymotrypsin Activity in Aqueous Solutions of "Big Head" Ammonium Salts
No full textThe effect of two ammonium salts with a bulky head group, the tetrabutylammonium bromide (TBABr) and the surfactant cetyltributylammonium
bromide (CTBABr) on alpha-chymotrypsin hydrolysis rate toward three peptidyl substrates was investigated. N-Succinyl-L-phenylalanine-p-nitroanilide
(SPpNA), N-succinyl-L-alanyl-L-alanyl-L-phenylalanine-p-nitroanilide (SAAPpNA) and N-succinyl-L-alanyl-L-alanyl-L-prolyl-L-phenylalaninep-
nitroanilide (SAAPPpNA), which contain the same chromogenic and N-protecting groups, but a different number of amino acidic residues, were selected.
The relative activity showed a bell-shaped dependence on additive concentration, with a maximum which ranged from 1×10−3 M to 5×10−3M
for CTBABr and at 0.3M for TBABr. Both the additives induced alpha-chymotrypsin superactivity, but their effect decreased as the peptide chain length of the substrate increased. Analysis of the kinetic parameters indicated that the activation was mainly due to an increase in kcat values, probably caused by enzyme conformational changes induced by the additives, while KM remained almost unchanged. The very notable effect of both CTBABr and TBABr on SPpNA hydrolysis rate and the limited activation with SAAPpNA and SAAPPpNA could be probably due to non-specific interactions between the
additives and the subsites next to the catalytic point within alpha-chymotrypsin active site, not allowed with the longer amino acidic chain substrates
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
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
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
- …
