1,721,100 research outputs found
Modular and conservative procedure for the quantification of amino functionalities bonded to solid porous matrices
No full textNowadays solid materials in which amino groups are linked to silica matrices through alkyl chains of different length (C18, C8, C4) are successfully employed in CO2 capture and storage technologies, as well as in a variety of chromatographic applications. In particular, their use as stationary phases finds remarkable success in performing HILIC separations and, in general, in the effective resolution of important compound classes (e.g. mixtures of mono- or oligo-saccharides). In this study an original and operationally simple procedure designed to quantify the density of basic groups (typically amino groups) chemically bonded to the surface of porous solids, which also allows a full recovery of the analysed material, is presented. The method is based on the preventive acid-base reaction of the basic groups linked to the solid by 3,5-dinitrobenzoic acid (DNBA). The quantification of the basic functionalities is then performed by an UV-spectrophotometric retro-titration of the thus salified solid matrix (or, alternatively, by HPLC approach), resorting to a preventive either acid or basic displacement of DNBA from the matrix. The uncertainty of the density measurements is assessed by 13%. (C) 2019 Elsevier B.V. All rights reserved
3,5-Dinitrobenzoyl-9-amino-9-deoxy-9-epiquinine as Pirkle-Anion Exchange Hybrid-Type Chiral Selector in High-Performance Liquid Chromatography
No full textA new chiral stationary phase was designed by
introducing 9-amino-9-deoxy-9-epiquinine, one of the
most versatile organocatalysts in asymmetric synthesis, as
chiral scaffold. The derivatization of its amino group with
the 3,5-dinitrobenzoyl (DNB) fragment provided hydrogen
bonding and π–π donor/acceptor systems in addition to
the quinoline and quinuclidine moieties having two nitrogen
atoms with different basicities. The selector offers
multiple interaction sites in both typical of the Pirkle-type
phases and classical of weak-anion-exchanger phases. The
immobilization step took place through thiol-ene addition
onto 3-mercaptopropyl-silica gel and gave a grafting
density of 180 μmol of chiral selector per gram of silica.
A silica with reduced particle size (Daisogel silica, pore
size 120 Å, particle size 2.5 μm, and specific surface area
343 m2 g−1) has been employed to improve the efficiency
and the speed of separations. The chiral stationary phase
was packed in a small format column (50 × 4.6 mm) that
allowed, by van Deemter analysis, 180,000 plates/m and
approximately 5.1 μm of plate height. The ability of chiral
discrimination was then studied with more than 30 test
compounds using both polar-organic and normal phase
conditions. In polar-organic mode, N-protected amino acids, α-aryloxy carboxylic acids, as well the non-steroidal
anti-inflammatory profens were analyzed. Interesting
results were obtained in normal phase elution, where
the chiral selector behaves like a Pirkle-type stationary
phase. Aryl amides, esterified DNB-amino acids, benzodiazepines,
and binaphthol were well resolved with a very
good peak symmetry and in short analysis time (mainly in
less than 5 min)
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
Pirkle-type chiral stationary phase on core-shell and fully porous particles: are superficially porous particles always the better choice toward ultrafast high-performance enantioseparations?
No full textPirkle-type Whelk-O1 chiral stationary phase (CSP) was prepared on 2.6μm superficially porous particles (SPPs). The chromatographic behavior of columns packed with this new CSP was compared with that of columns packed respectively with 1.8 and 2.5μm Whelk-O1 fully porous particles (FPPs). In the comparison, both thermodynamic and kinetic aspects were considered. Contrary to initial expectations, chiral columns packed with 2.6μm SPPs were quasi-comparable to those packed with 2.5μm FPPs, apparently due to larger contributions to band broadening from both eddy dispersion and, especially for the second eluted enantiomer, adsorption-desorption kinetics. These findings raise the question if SPPs, in spite of the undeniable advantages of their morphology to speed up mass transfer, are always the best choice for high-efficient ultrafast chiral separations. The last part of the work focuses on the use of short columns (10mm long) and very high flow rates to realize the separation of the enantiomers of trans-stilbene oxide (TSO) in normal phase mode in less than 1s
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
One Text, Two Receptions: Mahfouz's Children of the Alley
No full textA Master of Arts thesis in Translation and Interpreting (English/Arabic/English) by Muhammad Ismail Muhammad Ismail Omar Ghorab entitled, "One Text, Two Receptions: Mahfouz's Children of the Alley," December 2013. Thesis advisor is Dr. Said Faiq. Available are both hard and soft copies of the thesis.Received wisdom in translation studies tells us that both source and target texts should enjoy the same reception by the source and target cultures. However, Mahfouz's Children of the Alley has been negatively received in the East, banned in all Arab countries for alleged blasphemy over its allegorical portrayal of Allah and faiths, but positively received in the West, even the Nobel Committee referred to it when Mahfouz was awarded the Nobel Prize for literature in 1988. Taking Children of the Alley as its case study, the aim of this thesis is to explore the reasons behind different receptions of the same text. The East-West duality is examined to establish why and how reception of this text is different. The thesis examines examples from Mahfouz's original Arabic text as well as its English translation by Peter Theroux. It may be concluded that the English translation of the novel seems to manipulate reception.College of Arts and SciencesDepartment of Arabic and Translation StudiesMaster of Arts in English/Arabic/English Translation and Interpreting (MATI
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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