1,720,976 research outputs found
The role of solution calorimetry in investigating controlled-release processes from polymeric drug delivery systems
No full textIn this paper we investigate the potential role of solution calorimetry measurements in aiding the formulation of swellable matrices
containing a mixture of HPMC and NaCMC, an ionic cellulose derivate. These polymers show a synergistic effect in their ability to modulate
drug delivery rates; a matrix containing a 1:1 mixture of NaCMC and HPMC exhibits a significantly slower drug release rate than
either polymer shows alone. The exact cause of this synergism is not clear and it is not an easy effect to examine using conventional means
(such as dissolution testing). Here, we used solution calorimetry to study the system holistically. By comparing the measured response of
a physical blend with a theoretical one (obtained by summation of the power–time data for each material), it was possible to assess if
there was/was not any interaction which may explain the synergism. Furthermore, since a thermodynamic quantity was returned it was
possible to establish if the interaction was favourable or unfavourable and so to obtain useful information to understand and predict the
dissolution behaviour of polymeric systems containing the same materials.
An unfavourable interaction was noted between NaCMC and the model drug (Diltiazem HCl); no interaction was seen between
HPMC and the drug; and a favourable interaction was recorded when both polymers were formulated with the drug. The trend was
mirrored by the t90 (the time required for 90% drug release) values determined from dissolution testing; NaCMC 10.8 h, HPMC
16.4 h, NaCMC and HPMC 19.1 h. The data suggest that solution calorimetry measurements can be used to aid the selection of polymeric
excipients to design controlled-release drug delivery systems
The use of solution (ampoule-breaking) calorimetry quantitatively to assess the swelling of polymers and polymers blends
No full textSolution calorimetry to monitor swelling and dissolution of polymers and polymer blends
No full textIn this paper we investigate the potential role of solution calorimetry measurements in aiding the formulation of swellable matrices containing a mixture of HPMC and NaCMC, an ionic cellulose derivate. These polymers show a synergistic effect in their ability to modulate drug delivery rates; a matrix containing a 1:1 mixture of NaCMC and HPMC exhibits a significantly slower drug release rate than either polymer shows alone. The exact cause of this synergism is not clear and it is not an easy effect to examine using conventional means (such as dissolution testing). Here, we used solution calorimetry to study the system holistically. By comparing the measured response of a physical blend with a theoretical one (obtained by summation of the power–time data for each material), it was possible to assess if there was/was not any interaction which may explain the synergism. Furthermore, since a thermodynamic quantity was returned it was possible to establish if the interaction was favourable or unfavourable and so to obtain useful information to understand and predict the dissolution behaviour of polymeric systems containing the same materials.
An unfavourable interaction was noted between NaCMC and the model drug (Diltiazem HCl); no interaction was seen between HPMC and the drug; and a favourable interaction was recorded when both polymers were formulated with the drug. The trend was mirrored by the t90 (the time required for 90% drug release) values determined from dissolution testing; NaCMC 10.8 h, HPMC 16.4 h, NaCMC and HPMC 19.1 h. The data suggest that solution calorimetry measurements can be used to aid the selection of polymeric excipients to design controlled-release drug delivery systems
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
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