1,721,000 research outputs found
SYNTHESIS AND CHARACTERIZATION OF SELF HEALING HYDROGELS BY MICELLAR POLYMERIZATION
No full textHydrogels are three-dimensional network of polymers, which have the capability to absorb a large amount of water or biological fluids. These materials consist of hydrophilic crosslinked polymer chain, which are able to swell, having a soft rubbery consistency similar to living tissues. For this reason, hydrogels are used for biomedical, biotechnology and pharmaceutical applications1,2. The nature of the used crosslinker divides hydrogels in two large families namely physical or chemical crosslinked. In chemical hydrogel, crosslinking is obtained by covalent bond, either during the polymerization or in a post polymerizzazion process3. Physical hydrogels are obtained using physical interaction such as hydrophobic association, ionic bond or hydrogen bond.
In this work we prepared physically crosslinked hydrogels by radical micellar polymerization. This type of polymerization involved the use of a hydrophilic monomer (Acrylamide), a hydrophobic monomer (Octadecylacrylate), a surfactant (Sodium dodecyl sulfate), and a salt (NaCl). The polymerization was initiated using a redox initiator system composed of ammonium persulfate and sodium metabisulfite. In addition, a multifunctional monomer, divinylbenzene, was used with the aim of creating branched chains to evaluate their effect on the characteristics of the materials. Three series of five samples were prepared by varying, within the series, the quantity of Octadecylacrylate (C18A), and, between the series, the quantity of Divinylbenzene (DVB).
The samples were characterized with thermal (DSC) and rheological analysis, both before and after the washing phase. As the concentration of C18A increases, the amount of water present at equilibrium within the hydrogels decreases. In addition, the melting and crystallization enthalpies increases and an increase is also seen in mechanical modulus G '.
On the other hand, as the DVB concentration increases, the water content decreases and the mechanical modulus increases. This phenomenon is probably caused by the formation of chemical cross-linking points within the polymer network. The self annealing behaviour of these materials was also demonstrated by several rheology measurements
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
SINTESI DI IDROGELI SELF-HEALING E SHAPE MEMORY OTTENUTI MEDIANTE POLIMERIZZAZIONE MICELLARE
No full textGli idrogeli sono reti polimeriche tridimensionali idrofiliche e reticolate in grado di assorbire grandi quantità di acqua. I punti di reticolazione possono essere chimici o fisici. Nel primo caso, la reticolazione si ottiene legando covalentemente le catene durante la polimerizzazione. Per ottenere idrogeli fisici, invece, si sfruttano fenomeni di interazione secondari.
In questo lavoro abbiamo realizzato idrogeli fisici mediante polimerizzazione micellare radicalica. In generale, questo tipo di polimerizzazione prevede l’utilizzo di un monomero idrofilico (acrilammide), uno idrofobico (ottadecilacrilato, C18A) che deve formare microblocchi idrofobici, un tensioattivo (SDS) e un sale (NaCl). L’ iniziatore, di tipo redox, è costituito da persolfato di ammonio e metabisolfito di sodio. Oltre ai monomeri indicati, è stato anche aggiunto un monomero multifunzionale, il divinilbenzene (DVB), con l'obiettivo di creare all’ interno dei microblocchi idrofobici, catene ramificate e valutarne l'effetto sulle caratteristiche del materiale.
Sono state preparate tre serie di campioni variando il rapporto tra acrilammide e ottadecilacrilato e la quantità di divinilbenzene. I campioni ottenuti sono stati caratterizzati mediante analisi di diffrazione dei raggi X e misure termo-reologiche. All’aumentare della concentrazione di C18A, diminuisce la quantità di acqua negli idrogeli, aumentano le entalpie di fusione e di cristallizzazione e aumenta il modulo meccanico G’. D’altra parte, all’aumentare della concentrazione di DVB diminuisce il contenuto d’acqua ed aumenta il modulo meccanico G’.
Il comportamento self-healing di questi materiali è stato studiato attraverso misure reologiche. La capacità self-healing diminuisce al diminuire del C18A ed all’aumentare del DVB
Pro-rich antimicrobial peptides from animals: structure, biological functions and mechanism of action
No full text
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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