1,720,955 research outputs found
Surface modifications and functionalization of highly aligned multi-walled carbon nanotubes
No full textHighly aligned multi-wall carbon nanotubes (MWCNTs) prepared as vertical arrays onto
a silicon substrate, were functionalized and ion-bombarded in clean controlled conditions,
to modify their electronic properties. We studied their morphology and electronic states,
before and after induced modifications, by X-ray photoelectron spectroscopy (XPS), Raman
spectroscopy and Scanning Electron Microscopy (SEM).
Ion-beam induced modifications were obtained by medium energy (3 keV) noble gas ions
of different mass (He, Ne, Ar), so to generate controlled defects without causing chemical
interaction with the carbon matrix. Ion irradiation leads to change in morphology, deformation
of the carbon (C) honeycomb lattice and different structural defects in MWCNTs. One
of the major effects is the production of bond distortions, as determined by micro-Raman
and micro-X-ray photoelectron spectroscopy. We observe an increase of sp3 distorted bonds
at higher binding energy with respect to the expected sp2 associated signal of the C 1s core
level, and increase of dangling bonds. Furthermore, the surface damage as determined by
the XPS C 1s core level is equivalent upon bombarding with ions of different mass, while the
impact and density of defects in the lattice of the MWCNTs, as determined by micro-Raman
and SEM, are dependent on the bombarding ion mass, huge damage for lighter helium ions,
smaller damage for heavier argon ions.
CNT functionalization has been achieved by exposing the nanotubes to atomic deuterium
in clean and controlled ultra-high-vacuum conditions. Bonding of deuterium (D) atoms on
the C mesh of the nanotubes has been established, so to modify the electronic response, without
changing the average morphology of the CNT arrays. X-ray photoelectron spectroscopy
of the C 1s core level provides clear evidence of deuterium and carbon chemical interaction,
by evidencing the establishment of sp3 bonds with suppression of the π plasmon excitation.
We demonstrate ∼70 at. % D:C percentage of deuterated carbon atoms in the MWCNTs.
The electronic structure modification induced by D chemisorption also affects the energy
loss spectrum extrinsically excited by the outgoing photoelectrons, showing quenching of the
π-plasmon. Ultraviolet photoelectron spectroscopy showed the opening of an energy gap in
the valence band of the D-MWCNTs, with the valence band maximum at about 3.2 eV below
the Fermi level. The bond distortion is also evidenced by the modification of the Raman
response at the deuterated nanotubes.
These results on controlled increase of sp3 distorted bonds via ion bombardment and
increasing D:C bonds via atomic deuterium irradiation on the MWCNTs, open new functionalization
perspective. This work represents that the molecular cracking of D2 in an
ultra-high vacuum is an efficient way to obtain stable, homogeneous and high uptake of
deuterium atoms with minimal induction of defects. Ion bombardment opens up the ways
to improve and increase atomic deuterium uptake on ion-bombarded MWCNTs, towards
potential applications in hydrogen storage into solid state
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
Evaluation of vertical alignment in carbon nanotubes: A quantitative approach
Get PDFAn automated quantitative study of the alignment of vertically aligned carbon nanotubes (VA-CNTs) from scanning electron microscopy (SEM) images has been demonstrated. It is based on the fact that the image gradient (directional change in intensity or color) at every pixel in the image contains the information about the anisotropy at that particular pixel i.e., the local alignment is maintained in the orthogonal direction to the gradient. Structure tensor metrics are formulated demonstrating to be able to summarize the distribution of gradient directions within the neighborhood of any pixel within a two-dimensional domain (surface). An image analysis is presented that evaluates the alignment in desired regions of interest (ROIs) in SEM images of VA-CNTs. This method has been exploited to study the alignment of two different kinds of VA-CNTs: one grown via the thermal chemical vapor deposition (T-CVD) method and the second synthesized via the plasma enhanced chemical vapor deposition (PE-CVD) method
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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