1,721,055 research outputs found
Optical Properties of Silver Nanoshells from Time-Dependent Density Functional Theory Calculations
No full textThe absorption spectra of Ag monatomic nanoshells of size between
12 and 272 atoms with different shapes (icosahedra, cuboctahedra, and truncated
octahedra) are theoretically studied via a time-dependent density functional theory
approach and compared with previous results on compact nanoparticles of similar
size and shape. Three main findings are drawn from this study: (a) Ag monatomic
nanoshells possess absorption spectra exhibiting clear plasmonic features starting
already with the 92-atom system; (b) the position of the absorption peaks moves
toward lower energy as the radius of the nanoshells increases, with a blue shift of
≈0.2 eV for icosahedral with respect to cuboctahedral shells (also, the peak
substantially gains in intensity with increasing size); (c) the absorption maxima are
strongly red-shifted by 0.8−1.0 eV with respect to homologous compact
arrangements. The red-shift phenomenon (c) is shown to be due not to a
combination mode of internal and external surface plasmon resonances, as in
thicker nanoshells, but rather to the relief of the charge compression by the
underlying metallic layers on the resonating electrons. An analysis of the character of the electronic transitions mostly
contributing to the absorption peaks finally provides information on the atomistic character of the corresponding modes
Au24(SAdm)16 Nanomolecules: X-ray Crystal Structure, Theoretical Analysis, Adaptability of Adamantane Ligands to Form Au23(SAdm)16 and Au25(SAdm)16, and Its Relation to Au25(SR)18
No full textHere we present the crystal structure, experimental
and theoretical characterization of a Au24(SAdm)16
nanomolecule. The composition was verified by X-ray
crystallography and mass spectrometry, and its optical and
electronic properties were investigated via experiments and firstprinciples
calculations. Most importantly, the focus of this work
is to demonstrate how the use of bulky thiolate ligands, such as
adamantanethiol, versus the commonly studied phenylethanethiolate
ligands leads to a great structural flexibility, where the
metal core changes its shape from five-fold to crystalline-like
motifs and can adapt to the formation of Au24±1(SAdm)16, namely, Au23(SAdm)16, Au24(SAdm)16, and Au25(SAdm)16. The basis
for the construction of a thermodynamic phase diagram of Au nanomolecules in terms of ligands and solvent features is also
outlined
Dramatic Increase in the Oxygen Reduction Reaction for Platinum Cathodes from Tuning the Solvent Dielectric Constant
No full text
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
Experimental and Theoretical Scanning Tunneling Spectroscopy Analysis of an Ultrathin Titania Film and Adsorbed Au Nanoparticles
No full textWe present a detailed experimental and theoretical investigation of the ultrathin titania z'-TiOx/Pt(111) phase and Au nanoparticles assembled on it. Scanning tunneling spectroscopy (STS) at two different tip stabilization biases (TSB) is measured at three different locations on the bare titania phase and on top of the Au nanoparticles (NPs). STS data are compared with the results of first-principles calculations based on a Tersoff-Hamann approach for simulating tunneling currents. We obtain a coherent framework in which STS features can be used as fingerprints with atomistic resolution of the local density of states. On the bare titania, Shockley states coming from the 0 atoms dominate the occupied DOS, while resonant states coming from the Ti atoms dominate the DOS above the Fermi level. The ultrathin film is partially metallized, with DOS empty channels at the hole sites, hence lying in an intermediate state between a semiconducting oxide and a conductor. Finally, STS data on top of Au nanoparticles provide information on the coordination environment of the Au atom in direct contact with the titania phase, discriminating between the Au metallic or nonmetallic regime
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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