1,721,034 research outputs found
CNT fibres - yarns between the extremes
No full textThe carbon nanotube community swims in the sea of superlatives. Researchers expect
mechanical performance to achieve two extremes, an ultrastrong fibre taking us into space, and a
superlubricant saving energy otherwise lost as heat. We examine CNT fibres in the light of
traditional yarn science and present an interpretation of properties which combines aspects of
these two extremes of performance
Mechanical Performance of CNT Fibres
No full textThe initial strength hype over carbon nanotubes arose from predictions of the strength of individual graphene layers, encouraged by measurements of individual MWCNTs and SWCNT bundles in AFM. The challenge for fibres composed of carbon nanotubes (CNTs) is to translate the impressive properties of the individual carbon nanotubes into the fibres. Yarn-like fibres composed of carbon nanotubes made by the direct spinning process have been used as the subject of this study. There have been occasional observations of strengths greater than 5 N/tex, which have served to maintain the enthusiasm for on-going developments. Here, we will re-examine those reports in the context of the response of nanotubes aggregates to applied tensile stress
Tensile Strength of CNT Fibres: Characteristic Length, Stress Transfer and other Impact Factors
No full textThe initial strength hype over carbon nanotubes arose from predictions of the strength of individual graphene layers, encouraged by measurements of individual MWCNTs and SWCNT bundles in AFM [1, 2]. However, while the scientists were professionally explicit as to what they had measured, the publicity assumed that these figures could also be readily realized in materials made from these components. It’s against a background of this overselling that we examine the gradual improvement in strength of macroscopically useful materials. Yarn-like fibres composed of carbon nanotubes made by the direct spinning process [3] have been used as the subject of this study. There have been occasional observations of strengths greater than 5 N/tex [4], which have served to maintain the enthusiasm for on-going developments. Here, we will re-examine those high strength reports in the context of the response of nanotubes aggregates to applied tensile stress
Mechanical properties of carbon nanotube fibres: St Venant’s principle at the limit and the role of imperfections
Get PDFCarbon nanotube (CNT) fibres, especially if perfect in terms of their purity and alignment,
are extremely anisotropic. With their high axial strength but ready slippage between the
CNTs, there is utmost difficulty in transferring uniformly any applied force. Finite element
analysis is used to predict the stress distribution in CNT fibres loaded by grips attached to
their surface, along with the resulting tensile stress–strain curves. This study demonstrates
that, in accordance with St Venant’s principle, very considerable length-to-diameter ratios
(103) are required before the stress becomes uniform across the fibre, even at low strains.
It is proposed that lack of perfect orientation and presence of carbonaceous material
between bundles greatly enhances the stress transfer, thus increasing the load the fibre
can carry before failing by shear. It is suggested that a very high strength batch of fibres previously
observed experimentally had an unusually high concentration of internal particles,
meaning that the pressure exerted by the grips would assist stress transfer between the
layers. We conclude that the strength of CNT fibres depends on the specific testing geometries
and that imperfections, whether by virtue of less-than-perfect orientation or of
embedded impurities, can act as major positive contributors to the observed strength
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
- …
