1,721,036 research outputs found
Influence of the threshold settings of photon counting detectors on the observed speckle contrast in coherent scattering experiments
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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
Plasmonic Supercrystals with a Layered Structure Studied by a Combined TEM-SAXS-XCCA Approach
No full textSupercrystals composed of plasmonic nanoparticles constitute a promising material platform for tailored light-matter interactions. The optimization of their optical properties requires precise syntheses and a detailed structural characterization that addresses not only the basic geometrical parameters but also the degree of order. Herein, plasmonic supercrystals with a well-defined layered structure are studied by a combined transmission electron microscopy, small-angle X-ray scattering and X-ray cross-correlation analysis (TEM-SAXS-XCCA) approach. It is demonstrated that scanning small-angle x-ray scattering (SAXS) data can unambiguously be assigned to the number of crystalline layers by comparison with complementary transmission electron microscopy (TEM) experiments on the same regions of interest. A small but significant increase of the lattice constant with increasing number of layers and a high degree of orientational order irrespective of the number of layers is found. This points to specifics of the supercrystal formation mechanism that could be utilized to improve the control of self-assembly for supercrystal geometries with subnanometer precision
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
Real-Time X-ray Scattering Discovers Rich Phase Behavior in PbS Nanocrystal Superlattices during in Situ Assembly
No full textDuring the self-organization of colloidal semiconductor nanoparticles by solvent evaporation, nanoparticle interactions are substantially determined by the organic ligands covering the inorganic core. However, the influence of the ligand grafting density on the assembly pathway is often not considered in experiments. Here, we carry out an in situ synchrotron small-angle X-ray scattering and X-ray cross-correlation analysis study of the real-time assembly of oleic acid-capped PbS nanocrystals at a low ligand coverage of 2.7 molecules/nm2. With high temporal and spatial resolution, we monitor the transitions from the colloidal suspension through the solvated superlattice states into the final dried superstructure. In a single in situ experiment, we observe a two-dimensional hexagonal, hexagonal close-packed, body-centered cubic, body-centered tetragonal (with different degrees of tetragonal distortion), and face-centered cubic superlattice phases. Our results are compared to the self-organization of PbS nanocrystals with a higher ligand coverage up to 4.5 molecules/nm2, revealing different assembly pathways. This highlights the importance of determining the ligand coverage in assembly experiments to approach a complete understanding of the assembly mechanism as well as to be able to predict and produce the targeted superstructures
Three-step colloidal gelation revealed by time-resolved x-ray photon correlation spectroscopy
Full text linkThe gelation of PEGylated gold nanoparticles dispersed in a glycerol-water mixture is probed in situ by x-ray photon correlation spectroscopy. Following the evolution of structure and dynamics over 104 s, a three-step gelation process is found. First, a simultaneous increase of the Ornstein-Zernike length ζ and slowdown of dynamics is characterized by an anomalous q-dependence of the relaxation times of τ ∝ q-6 and strongly stretched intermediate scattering functions. After the structure of the gel network has been established, evidenced by a constant ζ, the dynamics show aging during the second gelation step accompanied by a change toward ballistic dynamics with τ ∝ q-1 and compressed correlation functions. In the third step, aging continues after the arrest of particle motion. Our observations further suggest that gelation is characterized by stress release as evidenced by anisotropic dynamics once gelation sets in
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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