1,720,967 research outputs found
Effect of Hydration on Physicochemical Properties of End-Capped PLGA
Full text linkThe objective of this study was to assess the physicochemical effects of hydrating a hydrophobic end-capped poly(lactide-coglycolide)(PLGA)polymerintheliquidandvaporstate.PLGARG503polymerwasincubatedat37∘Cin0.5%polyvinylalcohol (PVA)solutionandat90%RH.Sampleswerewithdrawnatpredeterminedintervalsandchangestopolymerpropertieslikeglass transition temperature (Tg), moisture uptake, molecular weight change, and % acid number were determined using differential scanningcalorimetry,KarlFishertitrimetry,gelpermeationchromatography,andacidbasetitrimetry,respectively.Studyresults showed that Tg was depressed instantaneously upon hydration, indicating that bulk water acted as a plasticizer of hydrophobic end-cappedPLGA.Tg valuesdecreasedtolevelsbelowtheincubationtemperaturewhenhydratedin0.5%PVAsolutionbutnotin 90%RH.ThedropinTg exhibitedalinearrelationship(2 > 0.99)totheamountofwateruptakebythepolymer;highermoisture uptakewasnotedwithliquidwater.RemovalofmoisturefromthepolymermatrixresultedinrecoveryofTg,onlyuptoaperiod of14days.Presenceofwaterinliquidorvaporformcausedareductioninmolecularweightofthepolymerandacorresponding increasein%acidnumberoverthedurationofthestudy
Effect of agitation regimen on the in vitro release of leuprolide from poly(lactic-co-glycolic) acid microparticles
No full textBecause of the importance of in vitro release tests in establishing batch-to-batch reproducibility and in vitro-in vivo correlation, this study investigated the influence of agitation regimen on the in vitro release behavior of leuprolide from poly(lactic-co-glycolic) acid microparticles. Leuprolide-loaded microspheres were prepared using Resomer(®) RG502H and RG503H as polymers. Leuprolide in vitro release was performed in phosphate buffer solution under continuous or once-a-week agitation. At predetermined intervals, leuprolide release, polymer mass loss, and degree of hydration were investigated. Leuprolide release and polymer mass loss were higher under continuous agitation with respect to that under intermittent agitation. Using a modified version of Koizumi equation, it was possible to fit leuprolide release profiles. Similarity factor comparison showed a high level of similarity between experimental and modeled data in the case of once-a-week agitation regimen. This work highlights the importance of the in vitro release conditions on peptide release behavior from polyester microparticles
Accelerated polymer biodegradation of risperidone poly(D, L-lactide-co-glycolide) microspheres
No full textThe influence of a tertiary amine, namely risperidone (pKa = 7.9) on the degradation of poly(D, L lactide-co-glycolide) (PLGA) microspheres was elucidated. Risperidone and blank microspheres were fabricated at two lactide/glycolide ratios, 65:35 and 85:15. The microspheres were characterized for drug loading by high-performance liquid chromatography, particle size by laser diffractometry, and surface morphology by scanning electron microscopy. Polymer degradation studies were carried out with drug-loaded microspheres and blank microspheres in presence of free risperidone in 0.02 M PBS containing 0.02% Tween®80 at 37°C. Molecular weight was monitored by gel permeation chromatography. Risperidone and blank microspheres had similar size distribution and were spherical with a relatively nonporous smooth surface. The presence of risperidone within the microspheres enhanced the hydrolytic degradation in both polymeric matrices with faster degradation occurring in 65:35 PLGA. The molecular weight decreased according to pseudo-first-order kinetics for all the formulations. During the degradation study, the surface morphology of drug-loaded microspheres was affected by the presence of risperidone and resulted in shriveled microspheres in which there appeared to be an intrabatch variation with the larger microspheres being less shriveled than the smaller ones. When blank microspheres were incubated in free risperidone solutions, a concentration-dependent effect on the development of surface porosity could be observed. Risperidone accelerates the hydrolytic degradation of PLGA, presumably within the microenvironment of the drug-loaded particles, and this phenomenon must be taken into consideration in designing PLGA dosage forms of tertiary amine drugs
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
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
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