1,720,956 research outputs found
New materials: multifunctional hydrophilic polymers
No full textDifferent types of multifunctional hydrophilic polymers were synthesized and characterized in view of their possible biomedical application. Several poly(amide)s and poly(ester-amide)s containing oligo(oxyethylene) segments and tartaric or succinic acid residues were prepared by activated polycondensation methods. New functional derivatives of beta-cyclodextrin were obtained by reaction with glycidyl ether of protected polyols. The mechanism of beta-cyclodextrin polymerization with epichlorohydrine was investigated by C-13-NMR spectroscopy
Kinetic investigation of the condensation reaction of activated ester-amides containing oligo(oxyethylene) segments
No full textThe kinetics of polycondensation of activated ester-amides, namely pentachlorophenyl alpha-amino-omega-oligo(ethyleneglycol)succinate hydrochlorides (PSPnNH)having a degree of oligomerization n = 1-3, were investigated in solution in dichloromethane in the presence of excess triethylamine. The large extinction coefficient of,the pentachlorophenate formed during the reaction allowed the use of the, stopped flow technique. Experimental, data resulted in agreement with the existence of concurrent first- and second-order processes, attributable to the intramolecular cyclization and intermolecular polycondensation reactions, respectively. The relative incidence of the cyclization reaction decreased on increasing the monomer concentration and on decreasing the number of oxyethylene units in the monomer. These hypotheses were confirmed by SEC, TLC, FT-IR, and NMR characterization. of the reaction products. The kinetics of PSP3NH are in very good agreement with the predictions of both the collision theory and the condensation theory of linear systems at equilibrium. However, the behavior of shorter chain monomers was opposite to that of the theoretical, one, demonstrating that other parameters, such as steric hindrance and solvent interactions; must be taken into proper account. The reported findings clearly evidenced that polymerization of the investigated ester-amides must be performed in bulk in order to suppress the cyclization reaction and to obtain high-molecular-weight polymers
Synthesis and Characterization of New Poly(ester-amide)s Containing Oligo(oxyethylene) Segments
No full textSegmented poly(ester-amide)s were prepared by polycondensation of a series of monoaminooligo(oxyethylene) pentachlorophenyl succinates, containing 1-3 oxyethylene units. The monomers were prepared by a four-step procedure from oligo(oxyethylene) monoamines consisting of: (1) protection of the primary amine group by di(t-butyl) carbonate, (2) succinoylation of the free hydroxyl group, (3) esterification of the resulting acid group with pentachlorophenol, and (4) deprotection of the amine group in anhydrous acid conditions. Polycondensation experiments were performed in solution and in bulk at room temperature by using triethylamine as a base to restore the active amine group of the monomer. Only bulk polymerization gave rise to high molecular weight polymers. Solubility and thermal properties of the materials were found to be related to the length of the oligo(oxyethylene) segment and the presence of strongly interacting amide groups
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
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