1,720,956 research outputs found
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
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
Phase separation and phase preferences in pigmented, impact-modified PC/PBT blends
Get PDFPolycarbonate/poly(butylene terephthalate)/impact modifier (PC/PBT/IM) blends are a
commercially important type of polymer blend. In recent years, pigmented PC/PBT/IM blends
have been produced for specific applications, with particular attention being given to the method of
mass coloration. The useful properties of these pigmented blends are determined, to a large extent,
by the phase separation and phase preference phenomena that occur in these multi-component
polymeric systems. In this study, the thermodynamic origins of the phase separation and phase
preferences that exist in pigmented PC/PBT/IM blends have been assessed by means of inverse gas
chromatography (IGC). Subsequently, in order to characterise these blends both physically and
chemically, and to assess the influence of the pigment (C. I. Pigment Blue 28) on the physical
properties, on the mechanical properties, and on the morphology of the blends, several analytical
techniques and mechanical tests were used. These analytical techniques and mechanical tests, along
with the controlled surface modifications of the pigment (which were achieved by means of a
photo-sensitised grafting procedure), allowed for a rationalisation of the interactions that exist
between the components of the pigmented blends as encountered in the phase separation, the phase
preferences, the physical properties and the mechanical properties of these polymeric systems.
The Lewis acid/base interaction between the major components of these blends has been
proven to influence decisively the physical properties and the mechanical properties of the
pigmented PC/PBT/IM blends. Phase separation exists in PC/PBT/IM blends as the PBT molecules
are preferentially involved in specific intermolecular, and intramolecular, interactions with
themselves and other PBT molecules. Partial miscibility between the PC and the PBT has been
interpreted on the basis of the Lewis acid/base attraction between these polymers, with
contributions from the repulsion effect that exists between the Lewis basic centres in PBT. The
impact modifier is shown to interact preferentially with the PC phase rather than with the PBT
phase. This is due to the preference of the PBT molecules to interact with PBT molecules and to
the strong Lewis base/base repulsion between the impact modifier PMMA shell and the PBT
molecules. The fast crystallisation of PBT, favoured by the strong Lewis amphoteric character of
this polymer, also contributes to the expulsion of the IM particles, and of the PC, from the PBT
domains. The pigment interacts favourably with both the PBT and the PC, but preferentially with
the PBT phase. This is because of the Lewis amphoteric properties of C. I. Pigment Blue 28.
The pigment under study, C. I. Pigment Blue 28, influences significantly the physical
properties and the mechanical properties of the PC/PBT/IM blends. These effects differ for blends
that have been processed in equipment and/or under conditions that lead to a lesser or greater
degradation of the molecular weight of PC and of PBT. Also, the importance of the PBT-rich phase
and of the PC-rich phase, in relation to the viscoelastic properties of the PC/PBT/IM blends, depends on the magnitude of the molecular weights of PC and of PBT. The influence of the
pigment on the physical and mechanical properties of the pigmented blends has both direct and
indirect consequences. The direct consequences arise from the physical properties of the pigment
(particle size and particle size distribution, surface area) and from the chemical properties of the
pigment (inorganic nature, surface chemical composition). In particular, the surface chemical
composition and the surface area determine the interaction potential of the pigment with the other
components of the PC/PBT/IM blends. The indirect consequences stem from the influence the
pigment has on the occurrence of transesterification, on the crystalline properties of PBT, and on
the molecular weights of PC and of PBT. The influence of these factors on the physical properties
and on the mechanical properties of the pigmented blends has been rationalised.
C. I. Pigment Blue 28 enhances the impact resistance of the blends by means of altering the
mechanisms of absorption of the impact energy. The pigment decreases the crystallisation
activation energy and increases the rate of crystallisation of PBT. The crystallinity degree is not
directly affected by the presence of the pigment. At low loadings, the pigment enhances the
transesterification reactions that occur between PC and PBT and the thermal degradation of the
molecular weight of PBT. At greater pigment loadings, the pigment particles act as an inhibitor of
the transesterification reactions and of the polymer chains thermal scission. The effect that C. I.
Pigment Blue 28 has on the transesterification reactions is thought to be due mainly to the thermal
conductivity differences between the inorganic pigment particles and the polymers.
Microscopic evaluations have established that the pigment is preferentially located at the
PC/PBT interphase. This finding is in line with the predictions made from the IGC study and is
substantiated by thermal analytical techniques and by mechanical testing of the pigmented blends.
Control of the Lewis surface acid/base properties of C. I. Pigment Blue 28, by means of a photosensitised
surface modification procedure, allows one to modify the preferential location of the
pigment particles in the PC/PBT/IM blend. Accordingly, the physical properties and the
mechanical properties of these pigmented blends are influenced. When the Lewis acidity of the
pigment is significantly enhanced, the interaction of the inorganic particles with the PBT is
improved. This results in a more significant nucleating effect of the pigment, an increased rate of
crystallisation and an increased crystallinity degree of PBT. On subsequent reduction of the surface
Lewis acidity of the modified pigment by neutralisation of the surface carboxylic acid groups, the
interaction of the pigment particles with the PC phase is enhanced. The surface modifications lead
to improved adhesion between C. I. Pigment Blue 28 and the polymeric matrix. This improvement
in the adhesion, along with the changes to the phase preferences of the pigment, result in: 1) lower
viscosity of the pigmented blends, due to improved dispersion of the modified pigments in the
polymeric matrix; 2) very significant reduction of the transesterification reactions and of the
thermal scission of the polymers, namely at the lower pigment loadings; 3) more consistent
viscoelastic behaviour of the blends with varying pigment loading, and 4) less pronounced
dependence of the impact resistance on temperature
Phase separation and phase preferences in pigmented, impact-modified PC/PBT blends
Get PDFPolycarbonate/poly(butylene terephthalate)/impact modifier (PC/PBT/IM) blends are a
commercially important type of polymer blend. In recent years, pigmented PC/PBT/IM blends
have been produced for specific applications, with particular attention being given to the method of
mass coloration. The useful properties of these pigmented blends are determined, to a large extent,
by the phase separation and phase preference phenomena that occur in these multi-component
polymeric systems. In this study, the thermodynamic origins of the phase separation and phase
preferences that exist in pigmented PC/PBT/IM blends have been assessed by means of inverse gas
chromatography (IGC). Subsequently, in order to characterise these blends both physically and
chemically, and to assess the influence of the pigment (C. I. Pigment Blue 28) on the physical
properties, on the mechanical properties, and on the morphology of the blends, several analytical
techniques and mechanical tests were used. These analytical techniques and mechanical tests, along
with the controlled surface modifications of the pigment (which were achieved by means of a
photo-sensitised grafting procedure), allowed for a rationalisation of the interactions that exist
between the components of the pigmented blends as encountered in the phase separation, the phase
preferences, the physical properties and the mechanical properties of these polymeric systems.
The Lewis acid/base interaction between the major components of these blends has been
proven to influence decisively the physical properties and the mechanical properties of the
pigmented PC/PBT/IM blends. Phase separation exists in PC/PBT/IM blends as the PBT molecules
are preferentially involved in specific intermolecular, and intramolecular, interactions with
themselves and other PBT molecules. Partial miscibility between the PC and the PBT has been
interpreted on the basis of the Lewis acid/base attraction between these polymers, with
contributions from the repulsion effect that exists between the Lewis basic centres in PBT. The
impact modifier is shown to interact preferentially with the PC phase rather than with the PBT
phase. This is due to the preference of the PBT molecules to interact with PBT molecules and to
the strong Lewis base/base repulsion between the impact modifier PMMA shell and the PBT
molecules. The fast crystallisation of PBT, favoured by the strong Lewis amphoteric character of
this polymer, also contributes to the expulsion of the IM particles, and of the PC, from the PBT
domains. The pigment interacts favourably with both the PBT and the PC, but preferentially with
the PBT phase. This is because of the Lewis amphoteric properties of C. I. Pigment Blue 28.
The pigment under study, C. I. Pigment Blue 28, influences significantly the physical
properties and the mechanical properties of the PC/PBT/IM blends. These effects differ for blends
that have been processed in equipment and/or under conditions that lead to a lesser or greater
degradation of the molecular weight of PC and of PBT. Also, the importance of the PBT-rich phase
and of the PC-rich phase, in relation to the viscoelastic properties of the PC/PBT/IM blends, depends on the magnitude of the molecular weights of PC and of PBT. The influence of the
pigment on the physical and mechanical properties of the pigmented blends has both direct and
indirect consequences. The direct consequences arise from the physical properties of the pigment
(particle size and particle size distribution, surface area) and from the chemical properties of the
pigment (inorganic nature, surface chemical composition). In particular, the surface chemical
composition and the surface area determine the interaction potential of the pigment with the other
components of the PC/PBT/IM blends. The indirect consequences stem from the influence the
pigment has on the occurrence of transesterification, on the crystalline properties of PBT, and on
the molecular weights of PC and of PBT. The influence of these factors on the physical properties
and on the mechanical properties of the pigmented blends has been rationalised.
C. I. Pigment Blue 28 enhances the impact resistance of the blends by means of altering the
mechanisms of absorption of the impact energy. The pigment decreases the crystallisation
activation energy and increases the rate of crystallisation of PBT. The crystallinity degree is not
directly affected by the presence of the pigment. At low loadings, the pigment enhances the
transesterification reactions that occur between PC and PBT and the thermal degradation of the
molecular weight of PBT. At greater pigment loadings, the pigment particles act as an inhibitor of
the transesterification reactions and of the polymer chains thermal scission. The effect that C. I.
Pigment Blue 28 has on the transesterification reactions is thought to be due mainly to the thermal
conductivity differences between the inorganic pigment particles and the polymers.
Microscopic evaluations have established that the pigment is preferentially located at the
PC/PBT interphase. This finding is in line with the predictions made from the IGC study and is
substantiated by thermal analytical techniques and by mechanical testing of the pigmented blends.
Control of the Lewis surface acid/base properties of C. I. Pigment Blue 28, by means of a photosensitised
surface modification procedure, allows one to modify the preferential location of the
pigment particles in the PC/PBT/IM blend. Accordingly, the physical properties and the
mechanical properties of these pigmented blends are influenced. When the Lewis acidity of the
pigment is significantly enhanced, the interaction of the inorganic particles with the PBT is
improved. This results in a more significant nucleating effect of the pigment, an increased rate of
crystallisation and an increased crystallinity degree of PBT. On subsequent reduction of the surface
Lewis acidity of the modified pigment by neutralisation of the surface carboxylic acid groups, the
interaction of the pigment particles with the PC phase is enhanced. The surface modifications lead
to improved adhesion between C. I. Pigment Blue 28 and the polymeric matrix. This improvement
in the adhesion, along with the changes to the phase preferences of the pigment, result in: 1) lower
viscosity of the pigmented blends, due to improved dispersion of the modified pigments in the
polymeric matrix; 2) very significant reduction of the transesterification reactions and of the
thermal scission of the polymers, namely at the lower pigment loadings; 3) more consistent
viscoelastic behaviour of the blends with varying pigment loading, and 4) less pronounced
dependence of the impact resistance on temperature
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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