1,721,020 research outputs found
Thermodynamic properties and conductivities of some dodecylsurfactants in water
No full textDensities, heat capacities, enthalpies of diln., osmotic coeffs. and conductivities are reported for dodecylamine hydrochloride, dodecyldimethylammonium and dodecyltrimethylammonium chloride in water over a wide range of concn. The last two properties were also measured for dodecyltrimethylammonium bromide. From the thermodn. data, partial molar volumes, heat capacities and relative enthalpies and nonideal free energies and entropies were derived as functions of the surfactant concn. The cmc's and degree of counterion dissocn. were also calcd. from the transport properties. The trends of vols., enthalpies, free energies and entropies are quite regular whereas heat capacities present max. and min. at concns. which depend on the nature of surfactants. Corresponding changes were obsd. in the osmotic coeffs. and specific conductivities. The thermodn. functions of micellization were evaluated on the basis of the pseudo-phase transition model. Finally, the effects of the introduction of Me groups in the hydrophilic moiety of the surfactant and of the nature of the counterion on the thermodn. properties of monomers and micelles are examd
Heat capacities, volumes and solubilities of pentanol in aqueous surfactant solution
No full textApparent molar heat capacities and vols. of pentanol 0.05 m in dodecyltrimethylammonium chloride (DTAC), dodecyldimethylammonium chloride (DDAC) and dodecylamine hydrochloride (DAC) micellar solns. were measured at 25°. The distribution const. between the aq. and the micellar phase and heat capacity and vol. of pentanol in both phases were derived. The presence of Me groups on the surfactant head group does not appreciably influence the apparent molar volume and heat capacity of pentanol in micellar phase and the free energy of transfer of pentanol from the aq. to the micellar phase. The apparent molar heat capacities of pentanol in micellar solns. as a function of surfactant concn. show evidence of two max. for DAC and of one max. for DTAC whereas no max. were detected for DDAC. These max. can be ascribed to the presence of structural post-micellar transitions. By comparing data for DTAC with those for the corresponding bromide, the role of the counterion nature in the thermodn. of solubilization of pentanol in micellar solns. is derived
In partibus infidelium ovvero L'insegnamento della Chimica Fisica nei corsi di Studio non chimici
No full textThermodynamic Properties of Sodium n-Perfluoroalkanoates in Water and in Water+Cyclodestrins Mixtures
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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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