1,720,979 research outputs found
Investigation of epoxy resin/multiwalled carbon nanotube nanocomposite behavior at low frequency
No full textIn this work, the electrical characterization of nanocomposites made of epoxy resins with multiwalled carbon nanotubes is presented. As the filler, two different types of multiwalled carbon nanotubes with different aspect ratios (280, 1250) and defectiveness were selected. The production procedure, the morphological characterization, the I-V DC characteristics, and the low frequency complex permittivity (in the range 100 kHz-12 MHz) of these nanocomposites are discussed. To investigate the dispersion of the solution, a study which linked the mixing time to the zeta potential was performed. The experimental results show that with the same matrix and by using the same measurement techniques, the two nanocomposites give different results and can be correlated with the characteristics of nanotubes. The dc conductivity of the nanocomposites was measured by means of a two-point probe technique. The conductivity in the frequency range 100 KHz-12 MHz was evaluated using a circular disk capacitor and measuring the impedance. The measured conductivity follows a percolation scaling law of the form r } (p pc)t. A best fit to the measured conductivity data was obtained and the values of the exponent t compared to those in the literature
ANALYSIS OF EPOXY/CARBON NANOTUBES COMPOSITES WITH DIFFERENT ASPECT RATIO AT MICROWAVE FREQUENCY
No full textCharacterization of nanocomposites based on MWCNTs for radar absorbing application
No full textA wide band microwave characterization of nanocomposites based on commercial multiwall carbon nanotubes (MWCNTs) and epoxy resin is presented. Field Emission Scanning Electron Microscopy is used for morphological samples analysis of nanocomposites and MWCNTs. Complex permittivity is measured using a commercial dielectric probe and a Network Analyzer. The reflection coefficient of a single-layer structure backed by a metallic plate was simulated taking into account the value of the measured permittivity and compared with RCS measurement
Analysis of MWCNT/epoxy composites at microwave frequency: reproducibility investigation
Get PDFA wide-band microwave characterization of nanocomposites based on commercial multiwalled carbon nanotubes (MWCNTs) and epoxy resin is presented. The sample preparation method is discussed in detail. Field emission scanning electron microscopy is used for morphological sample analysis of nanocomposites and MWCNTs. The complex permittivity is measured in a wide frequency band (3 to 18 GHz) using a commercial dielectric probe (Agilent 85070D) and a network analyzer (E8361A). A statistical analysis based on one-way analysis of variance (ANOVA) technique is performed. The aim of this statistical analysis is to investigate the influence of concentration of nanoparticles inside the polymer matrix on the complex permittivity. This can be significantly different in nanocomposites even if the samples have similar electrical properties
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
- …
