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A simulation study on the combined effects of nanotube shape and shear flow on the electrical percolation thresholds of carbon nanotube/polymer composites J. Appl. Phys. 109, 084342 (2011); 10.1063/1.3573668Determinant role of tunneling resistance in electrical conductivity of polymer composites reinforced by well dispersed carbon nanotubes This paper investigated the effect of carbon nanotube (CNT) agglomeration on the electrical conductivity of CNT-polymer composites by experimental characterization and theoretical modeling. The present experimental results show that the acid treatment of CNTs has significantly alleviated the CNT agglomeration in CNT-polymer composites and improved the electrical conductivity of the composites compared with CNT-polymer composites made from the same pristine CNTs. The improvement by the acid treatment is further studied by a multiscale CNT percolation network model that considers the CNT agglomeration based on experimental observation. Numerical results are in good agreement with the experimental data. The smaller the size of CNT agglomerates is in the experiments, the closer the measured electrical conductivity of CNT-polymer composites is to its theoretical limit. The current study verifies that (i) the CNT agglomeration is the main cause that leads to a lower electrical conductivity of CNT-polymer composites than their theoretical limit, and (ii) the current multiscale percolation network model can quantitatively predict the electrical conductivity of CNT-polymer composites with CNT agglomeration. The comprehensiveness of the developed modeling approach enables an evaluation of results in conjunction with experimental data in future works. V C 2014 AIP Publishing LLC. [http://dx.

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The isotope and hyperfine shifts for the Yb 'So(6s 2) _ 3 Pi(6s6p) transition were determined with an acoustooptic modulator used to frequency shift part of a laser beam. The frequency-shifted and-unshifted laser beams were superimposed and excited an atomic beam. The laser was scanned across the transition while fluorescence produced by the radiative decay of the excited state was detected by a photomultiplier. Each isotope generated two peaks in the spectrum separated by the acousto-optic shift, which permitted the frequency to be calibrated. This relatively simple method yields results that agree well with the most accurate existing data, which were obtained by measurement of frequency shifts with a Fabry-Perot talon whose length was stabilized with a helium-neon laser locked to an iodine line.

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