177,562 research outputs found
Quantized fracture mechanics and related applications for predicting the strength of defective nanotubes
No full textNanoscale Weibull statistics
No full textIn this paper a modification of the classical Weibull statistics is developed for nanoscale applications. It is called nanoscale Weibull statistics. A comparison between nanoscale and classical Weibull statistics applied to experimental results on fracture strength of carbon nanotubes clearly shows the effectiveness of the proposed modification. A Weibull's modulus of similar to 3 is deduced for nanotubes. The approach can treat (also) a small number of structural defects, as required for nearly defect-free structures (e.g., nanotubes) as well as a quantized crack propagation (e.g., as a consequence of the discrete nature of matter), allowing to remove the paradoxes caused by the presence of stress intensifications
Strength of Nanostructures. Do materials become insensitive to flaws at nanoscale?: an answer based on Quantized Fracture Mechanics and Nanoscale Weibull Statistics
No full textNanoscale Weibull Statistics for nanofibers and nanotubes
No full textIn this paper a modification of the classical Weibull statistics is applied to nanostructures. A comparison is presented of "nanoscale" versus classical Weibull statistics in treating recent experimental results on the fracture strength of C nanofibers and nanotubes, and WS2 nanotubes. "Nanoscale" Weibull moduli of 3.8 for electrospun and then heat-treated carbon nanofibers, 2.7 for arc-discharge synthesized multiwalled carbon nanotubes, 1.8 for chemical vapor deposited multiwalled carbon nanotubes, and 3.0 for multiwalled WS2 nanotubes, are deduced
CHARGE REARRANGEMENT IN (HCN)2 AND (HCN)3***
No full text Work supported by NSF and PRF. R. S. Ruoff, T. Emilsson, C. Chuang, T. D. Kiots, and H. S. Gutowsky. Chem. Phys. Letters 138, 553 (1987). R.S. Ruoff, T. Emlisson. T. D. Kiots, C. Chuang, and H. S. Gutowsky, J. Chem. Phys., submitted. E. J. Campbell and S. G. Kukolich, Chem. Phys. 76, 225 (1983).Author Institution: Noyes Chemical Laboratory, University of IllinoisCharge rearrangement during cluster formation may be determined from its effects upon the dipole moments u and the electric field gradients of the monomeric units,provided that corrections can be made for their vibrational averaging. An isotopic substitution method has enabled us to obtain vibrational amplitudes in the linear and A dipole moment of 6.552(35) D has been reported for the dimer3 and we have found 10.6(2) D for the These lead to induced dipole moments Au of 0.703(3) D for the dimer and 1.75(10) D for the trimer. A similar analysis was made of . A mutual polarization model was used to predict the induced dipole moments from the four known electrical multipole moments of HCN and its bond polarizabilities. The results are 0.703 D for the dimer and 1.68 D for the trimer. The calculations give ratios of the dipoles induced in the C-N bonds which are essentially identical with the ratios of the experimental . Equations are derived for calculation of Au of an infinite H-bonded chain and are applied to HCN. The convergence of multipale expansions for the electric field due to a molecular charge distribution will be discussed. The mutual polarization model works so well on HCN dimer and trimer that any charge transfer between the HCN monomers seems likely to be very small or negligible
Quantized fracture mechanics
No full textA new energy-based theory, quantized fracture mechanics (QFM), is pre-sented that modifies continuum-based fracture mechanics; stress- and strain-based QFM analogs are also proposed. The differentials in Griffith’s criterion are substituted with finite differences; the implications are remarkable. Fracture of tiny systems with a given geometry and type of loading occurs at ‘quantized’ stresses that are well predicted by QFM: strengths predicted by QFM are com-pared with experimental results on carbon nanotubes, -SiC nanorods, -Si3N4 whiskers, and polysilicon thin films; and also with molecular mechanics/dynamics simulation of fracture of carbon nanotubes and graphene with cracks and holes, and statistical mechanics-based simulations on fracture of two-dimensional spring networks. QFM is self-consistent, agreeing to first-order with linear elastic frac-ture mechanics (LEFM), and to second-order with non-linear fracture mechanics (NLFM). For vanishing crack length QFM predicts a finite ideal strength in agreement with Orowan’s prediction. In contrast to LEFM, QFM has no restric-tions on treating defect size and shape. The different fracture Modes (opening I, sliding II and tearing III), and the stability of the fracture propagations, are treated in a simple way
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
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