1,720,962 research outputs found
Computational modeling of the effective Young’s modulus values of fullerene molecules: a combined molecular dynamics simulation and continuum shell model
No full textEstimating the Young’s modulus of a structure in the nanometer size range is a difficult task. The reliable determination of this parameter is, however, important in both basic and applied research. In this study, by combining molecular dynamics (MD) simulations and continuum shell theory, we designed a new approach to determining the Young’s modulus values of different spherical fullerenes. The results indicate that the Young’s modulus values of fullerene molecules decrease nonlinearly with increasing molecule size and understandably tend to the Young’s modulus of an ideal flat graphene sheet at large molecular radii. To the best of our knowledge, this is first time that a combined atomistic–continuum method which can predict the Young’s modulus values of fullerene molecules with high precision has been reported
Elastic properties of polymer composites reinforced with C60 fullerene and carbon onion: Molecular dynamics simulation
Get PDFIn this paper, the elastic properties of polymer nanocomposites reinforced with C60 fullerene and C60@C240 carbon onion are estimated by using a molecular dynamic (MD) simulation. The nanocomposites are constructed by embedding the buckminsterfullerene and the carbon onion into an amorphous polymer matrix with different weight fractions. The poly methyl methacrylate (PMMA) is chosen as the polymer matrix. The results demonstrate that Young's modulus of the composite increases with increasing the weight fractions of the nanoscopic additives, which is consistent with experimental observations. The nanocomposite containing 4 wt% of C60 exhibits Young's modulus of 3.774 GPa that is 24% higher than pure PMMA. In addition, the validity of the present simulation is verified by the comparison with the experimental results
Molecular dynamics simulations of structural instability of fullerene family under tension force
Get PDFFullerene molecules are cage-like nanoscopic structures with pentagonal and hexagonal faces. In practical applications such as fullerene-reinforced nanocomposites (FRNCs), these structures may be subjected to tension force. In this research, we employ molecular dynamics (MD) simulation to compute the behaviour and deformation of different fullerene molecules, ranging from C60 to C2000, under tension force. To model the interactions between carbon atoms in the MD simulations, the adaptive intermolecular reactive bond order (AIREBO) force field is used. The displacement–force and the displacement–strain energy curves are obtained. It is observed that a new type of structural instability occurs in the fullerene molecules when the applied tension force increases. This abnormal structural instability in the fullerenes is investigated for the first time in the literature. The critical tensile forces and the corresponding mode shapes are determined for different fullerenes. The results indicate that the critical forces and deformations strongly depend upon the number of carbon atoms
Combined molecular dynamics–micromechanics methods to predict Young's modulus of fullerene-reinforced polymer composites
Get PDFIn this paper, a multiscale method is developed to predict Young's modulus of fullerene-reinforced polymer nanocomposites (FRPNs). Polymethyl methacrylate is chosen as the polymer matrix, while C60 fullerene is considered as the reinforcement. First, molecular dynamics (MD) simulations are conducted to calculate the Young modulus of nanocomposite unit cell with different weight fractions of fullerene. Then, a micromechanics model for a composite with multi-inclusion reinforcements is developed based on the extension of the Mori–Tanaka model and generalized Eshelby's results. Numerical results obtained from the proposed micromechanics model are compared with those calculated from the MD simulations, and good agreement is achieved. In addition, we propose an extension for the Halpin–Tsai model to predict Young's modulus of the FRPNs
Torsional characteristics of carbon nanotubes: Micropolar elasticity models and molecular dynamics simulation
Get PDFEfficient application of carbon nanotubes (CNTs) in nano-devices and nano-materials requires comprehensive understanding of their mechanical properties. As observations suggest size dependent behaviour, non-classical theories preserving the memory of body’s internal structure via additional material parameters offer great potential when a continuum modelling is to be preferred. In the present study, micropolar theory of elasticity is adopted due to its peculiar character allowing for incorporation of scale effects through additional kinematic descriptors and work-conjugated stress measures. An optimisation approach is presented to provide unified material parameters for two specific class of single-walled carbon nanotubes (e.g., armchair and zigzag) by minimizing the difference between the apparent shear modulus obtained from molecular dynamics (MD) simulation and micropolar beam model considering both solid and tubular cross-sections. The results clearly reveal that micropolar theory is more suitable compared to internally constraint couple stress theory, due to the essentiality of having skew-symmetric stress and strain measures, as well as to the classical local theory (Cauchy of Grade 1), which cannot accounts for scale effects. To the best of authors’ knowledge, this is the first time that unified material parameters of CNTs are derived through a combined MD-micropolar continuum theory
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
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