1,721,036 research outputs found
Separation of metallic and semiconducting single-walled carbon nanotubes via covalent functionatization
No full textFifteen years after their discovery,[1,2] carbon nanotubes
continue to fascinate the scientific community. Single-walled
carbon nanotubes (SWNTs) can be seen as sheets of graphite
rolled up to form hollow tubes. Depending on the orientation
of the tube axis with respect to the hexagonal lattice,
the structure of a nanotube can be completely specified
through its chiral vector, which is denoted by the chiral indices
(n,m). Nanotubes in which n=m are metallic and quasi
metallic (with a tiny bandgap) if nm is divisible by 3. All
other tubes are semiconducting with bandgaps of the order
of 0.5 eV. The electronic properties of SWNTs depend on
the geometry of the tube: to date, carbon nanotubes are the
only material known to have this unique propert
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
Electrochemical growth of PAH-dendrimers supramolecular films. An integrated experimental-theoretical approach
No full textThe electrochemical oxidation of a polyphenylene-based dendrimer containing 96 sp2 carbon atoms (PPD) allows
obtaining a more extended conjugated carbon framework, polymer PPD (pPPD), starting from the parent fused-
benzene-based PPD. The structure and electronic properties of the polymeric thin film obtained by electrochemical
oxidation have been characterized by Near Edge X-Ray Absorption Fine Structure (NEXAFS) spectroscopy.
Structural properties of the thin film formed upon electrochemical oxidation of PPD, are characterized
by Matrix-Assisted Laser Desorption/Ionization (MALDI-TOF) and Gel-Permeation Chromatography (GPC)
measurements. The degree of order of the layers as well as the virtual, and occupied, electronic states are
addressed and exploited to obtain information on conjugation and oligomer size within the polymeric pPPD film.
The experimental results are compared with DFT, B3LYP/6–31G(d), calculations. The overall results suggest that
the thin film formed on the electrode surface is mainly formed by PPD dimer and trimer upon electrochemical
oxidation
Microscopic and spectroscopic characterization of paintbrush-like single-walled carbon nanotubes
No full textUnderstanding and controlling the chemical reactivity of carbon nanotubes (CNTs) is a fundamental requisite to prepare novel nanoscopic
structures with practical uses in materials applications. Here, we present a comprehensive microscopic and spectroscopic characterization of
carbon nanotubes which have been chemically modified. Specifically, scanning tunneling microscopy (STM) investigations of short-oxidized
single-walled carbon nanotubes (SWNTs) functionalized with aliphatic chains via amide reaction reveal the presence of bright lumps both on
the sidewalls and at the tips. The functionalization pattern is consistent with the oxidation reaction which mainly occurs at the nanotube tips.
Thermogravimetric analysis (TGA), steady-state electronic absorption (UV-vis-NIR), and Raman spectroscopic studies confirm the STM
observations
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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