1,721,246 research outputs found
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
Field emission enhancement by graphitic nano scale channels through ta C layers
No full textA key issue in field emission FE from CVD diamond and other carbon films is to understand the role that non diamond inclusions and conduction pathways in the material have on the FE process. FE is significantly enhanced, apart from geometric enhancements due to rough surface morphologies, by the presence of non diamond phases embedded in the diamond matrix. These phases appear in the form of grain boundaries, graphitic inclusions, graphite nano particles and others. It is, however, not clear in most reports, what the relative contribution of surface morphology and the presence of conductive channels to improved emission is. To investigate the possibility of FE originating from graphitic regions in a perfectly smooth material, we performed ion irradiation to selectively transform diamond like carbon sp3 bonding into graphite like sp2 bonding material. Single ion tracks were formed by implanting high energy single ions at extremely low doses through a thin smooth amorphous tetrahedral amorphous carbon ta C layer. The layers were thin enough for the ions to penetrate through them and stop in the substrate. N doped conductive and un doped ta C films were used and the FE results were compared. Four ion implantation schemes were used a 1 GeV U ions at a low dose; b sub MeV Xe ions at a low dose; both were meant to form well separated single ion tracks through the material; c sub MeV C ions at a high dose, for complete material transformation; and d un implanted sample as a control. Field emission turn on conditions were carefully studied for these, employing a very slow voltage ramp up, to avoid undesired vacuum electric discharges, known to result in a conditioning affect on FE. Field emission seems to initiate at the lowest applied field for samples that include nano scale graphitized channels threading all the way through the layer, as realized by single ion implantations. A 40 reduction in the field required for emission onset is found for all samples with single ion tracks compared to the un implanted sample. However, the sample implanted for full coverage transformation shows no emission up to at least 100 V amp; 956;m. The observed improvement in FE is shown to be consistent with field enhancement calculations due to conductive pathways in the materia
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
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
Swift heavy ion beam-induced effects in amorphous and nanocrystalline soft magnetic materials
No full textCharacterization of radiation damage induced by swift heavy ions in graphite
No full textGraphite is a classical material in neutron radiation environments, being widely used in nuclear reactors and power plants as a moderator. For high energy particle accelerators, graphite provides ideal material properties because of the low Z of carbon and its corresponding low stopping power, thus when ion projectiles interact with graphite is the energy deposition rather low. This work aims to improve the understanding of how the irradiation with swift heavy ions (SHI) of kinetic energies in the range of MeV to GeV affects the structure of graphite and other carbon-based materials. Special focus of this project is given to beam induced changes of thermo-mechanical properties. For this purpose the Highly oriented pyrolytic graphite (HOPG) and glassy carbon (GC) (both serving as model materials), isotropic high density polycrystalline graphite (PG) and other carbon based materials like carbon fiber carbon composites (CFC), chemically expanded graphite (FG) and molybdenum carbide enhanced graphite composites (MoC) were exposed to different ions ranging from 131 Xe to 238 U provided by the UNILAC accelerator at GSI in Darmstadt, Germany. To investigate structural changes, various in-situ and off-line measurements were performed including Raman spectroscopy, x-ray diffraction and x-ray photo-electron spectroscopy. Thermo-mechanical properties were investigated using the laser-flash-analysis method, differential scanning calorimetry, micro/nano-indentation and 4-point electrical resistivity measurements. Beam induced stresses were investigated using profilometry. Obtained results provided clear evidence that ion beam-induced radiation damage leads to structural changes and degradation of thermal, mechanical and electrical properties ofgraphite. PG transforms towards a disordered sp 2 structure, comparable to GC at high fluences. Irradiation-induced embrittlement is strongly reducing the lifetime of most high-dose exposed accelerator components. For irradiation temperatures above 200 o C damage formation is mitigated due to defect annealing. Thus a controlled temperature of accelerator components is desirable in order to increase the lifetime. This thesis contributes to a better understanding of radiation damage in swift heavy ion-exposed graphite with the aim to optimize the design of beam catchers and production targets for secondary ion beams for the Super Fragment Separator (Super-FRS) at FAIR. Moreover, the results of this work provide important input data for simulations to describe the beam response and lifetime of high-dose exposed critical accelerator components
Conductive tracks of 30-MeV C60 clusters in doped and undoped tetrahedral amorphous carbon
No full textIn insulating tetrahedral amorphous carbon (ta-C), the irradiation with 30-MeV C60 cluster ions leads to the formation of well conducting tracks. While electrical currents through individual tracks produced with monoatomic projectiles (e.g. Au or U) often exhibit rather large track to track fluctuations, C60 clusters are shown to generate highly conducting tracks with very narrow current distributions. Additionally, all recorded current–voltage curves show linear characteristics. These findings are attributed to the large specific energy loss dE/dx of the 30-MeV C60 clusters. We also investigated C60 tracks in ta-C films which were slightly doped with B, N or Fe during film growth. Doping apparently increases the ion track conductivity. However, at the same time the insulating characteristics of the pristine ta-C film can be reduced. The present C60 results are compared with data from earlier experiments with monoatomic heavy ion beams. The investigations were performed by means of atomic force microscopy including temperature dependent conductivity measurements of single ion tracks
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