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See detailOn the choice of a phase interchange strategy for a multiscale DEM-VOF Method
Pozzetti, Gabriele UL; Peters, Bernhard UL

in AIP Conference Proceedings (2017), 1863

In this work a novel Multiscale DEM-VOF method is adopted to study three phase flows. It consists in solving the fluid momentum, mass conservation and the phase advection at a different scale with respect ... [more ▼]

In this work a novel Multiscale DEM-VOF method is adopted to study three phase flows. It consists in solving the fluid momentum, mass conservation and the phase advection at a different scale with respect to the fluid-particle coupling problem. This allows the VOF scheme to resolve smaller fluid structures than a classic DEM-VOF method, and opens the possibility of adopting different volume interchange techniques. Two different volume interchange techniques are here described and compared with reference to high and low particle concentration scenarios. Considerations about the respective computational costs are also proposed. [less ▲]

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See detailMultiscale-multiphysics approaches for engineering applications
Pozzetti, Gabriele UL; Peters, Bernhard UL

in AIP Conference Proceedings (2017), 1863(1), 180001

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See detailA force-based large increment method for 2D continuum solids and the mesh convergence study
Long, D.; Guo, Z.; Liu, X. et al

in AIP Conference Proceedings (2012), 1504

In this paper, a triangular plane stress element is implemented based on the large increment method (LIM) to solve 2D continuum mechanics problems. In the LIM, after the governing equations are ... [more ▼]

In this paper, a triangular plane stress element is implemented based on the large increment method (LIM) to solve 2D continuum mechanics problems. In the LIM, after the governing equations are established using the generalized elemental force variables as primary unknowns, an iteration procedure is employed to obtain an optimised approximate solution of the problem. Two numerical examples are investigated to study the mesh convergence of the proposed triangular LIM element. Structured meshes as well as unstructured meshes with different element densities are generated to illustrate the convergence of the total strain energy in both examples. The numerical results obtained from the LIM (including the total strain energy, the displacement and the stress) are compared with the analytical solutions as well as the results from the commercial FEM software ABAQUS. All the results show that the performance of the LIM is as good as the FEM in linear elastic problems. A simple elastoplastic example suggests that the LIM may obtain better result than the FEM. © 2012 American Institute of Physics. [less ▲]

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See detailRaman spectroscopy on single- and few-layer graphene
Graf, Davy; Molitor, Francoise; Ensslin, Klaus et al

in AIP Conference Proceedings (2007), 893

We report on Raman measurements of single- and few-layer graphene flakes. Raman mapping in combination with scanning force microscopy allows us to locally relate the thickness of the graphite flake with ... [more ▼]

We report on Raman measurements of single- and few-layer graphene flakes. Raman mapping in combination with scanning force microscopy allows us to locally relate the thickness of the graphite flake with the spectral properties. It turns out that the width of the D' line is highly sensitive to the transition from single- to double-layer graphene. The defect-induced D line is found to be most prominent at steps between sections of different height and along the edge of the graphite flake. [less ▲]

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See detailOptical absorption of hexagonal boron nitride and BN nanotubes
Wirtz, Ludger UL; Marini, A.; Rubio, A.

in AIP Conference Proceedings (2005), 786

present calculations for the optical absorption spectra of hexagonal boron nitride (hBN) and BN nanotubes, using many-body perturbation theory. Solution of the Bethe-Salpeter equation for hBN leads to ... [more ▼]

present calculations for the optical absorption spectra of hexagonal boron nitride (hBN) and BN nanotubes, using many-body perturbation theory. Solution of the Bethe-Salpeter equation for hBN leads to optical absorption and loss spectra where the positions and shapes of the peaks are strongly dominated by excitonic effects. The binding energy of the first exciton is about 0.71 eV. Comparison of the calculations with recently measured optical absorption and EELS demonstrates that DFT underestimates the "true" band gap of BN by 2.25 eV. This band gap difference can be partially (hot not completely) reproduced by a calculation of the quasi-particle band-structure on the level of the GW-approximation. We show, how the lower dimensionality of BN nanotubes leads to a much stronger excitonic binding energy and at the same time to a larger quasi-particle gap. This leaves the position of the first absorption peak almost unchanged. However, the difference in the series of excitonic peaks allows the spectroscopic distinction between BN nanotubes and bulk BN. [less ▲]

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See detailRaman spectroscopy of single-wall BN nanotubes
de la Concha, R. A.; Wirtz, Ludger UL; Mevellec, J. Y. et al

in AIP Conference Proceedings (2003), (685), 384-388

We present results on the vibrational properties of BN-SWNTs together with a study of the synthesis material by transmission electron microscopy. Phonon modes have been investigated by Raman spectroscopy ... [more ▼]

We present results on the vibrational properties of BN-SWNTs together with a study of the synthesis material by transmission electron microscopy. Phonon modes have been investigated by Raman spectroscopy with laser excitation wavelengths in the range from 363.8 to 676.44 nm. The assignment of the modes is guided by ab-initio calculations. [less ▲]

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See detailElectronic structure and optical properties of boron doped single-wall carbon nanotubes
Pichler, T.; Borowiak-Palen, E.; Fuentes, G. G. et al

in AIP Conference Proceedings (2003), 685

We present a study of the electronic structure and the optical properties of boron doped single walled carbon nanotubes which have been produced by a substitution reaction from nanotube templates. The ... [more ▼]

We present a study of the electronic structure and the optical properties of boron doped single walled carbon nanotubes which have been produced by a substitution reaction from nanotube templates. The morphology and crystal structure of the samples have been characterized by transmission electron microscopy and electron energy-loss spectroscopy. Clean boron doped SWCNT with an average boron content of 15 at% have been produced. The B1s and C1s core level spectra reveal that boron is in an sp(2) configuration and that the effective charge transfer is about 0.5 holes per boron to the C-derived states. The boron substitution also leads to new features in the optical absorption spectra which can be attributed to the appearance of an acceptor band about 0.1 eV above the top of the valence band of the SWCNT. These changes in the electronic structure and in the optical properties upon boron substitution are in good agreement with state of the art ab initio calculations. [less ▲]

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See detailBand structure of boron doped carbon nanotubes
Wirtz, Ludger UL; Rubio, A.

in AIP Conference Proceedings (2003), 685

We present ab initio and self-consistent tight-binding calculations on the band structure of single wall semiconducting carbon nanotubes with high degrees (up to 25 %) of boron substitution. Besides a ... [more ▼]

We present ab initio and self-consistent tight-binding calculations on the band structure of single wall semiconducting carbon nanotubes with high degrees (up to 25 %) of boron substitution. Besides a lowering of the Fermi energy into the valence band, a regular, periodic distribution of the p-dopants leads to the formation of a dispersive "acceptor"-like band in the band gap of the undoped tube. This comes from the superposition of acceptor levels at the boron atoms with the delocalized carbon pi-orbitals. Irregular (random) boron-doping leads to a high concentration of hybrids of acceptor and unoccupied carbon states above the Fermi edge. [less ▲]

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See detailOptical absorption in small BN and C nanotubes
Wirtz, Ludger UL; Olevano, V.; Marinopoulos, A. G. et al

in AIP Conference Proceedings (2003), 685

We present a theoretical study of the optical absorption spectrum of small boron-nitride and carbon nanotubes using time-dependent density-functional theory and the random phase approximation. Both for C ... [more ▼]

We present a theoretical study of the optical absorption spectrum of small boron-nitride and carbon nanotubes using time-dependent density-functional theory and the random phase approximation. Both for C and BN tubes, the absorption of light polarized perpendicular to the tube-axis is strongly suppressed due to local field effects. Since BN-tubes are wide band-gap insulators, they only absorb in the ultra-violet energy regime, independently of chirality and diameter. In comparison with the spectra of the single C and BN-sheets, the tubes display additional fine-structure which stems from the (quasi-) one-dimensionality of the tubes and sensitively depends on the chirality and tube diameter. This fine structure can provide additional information for the assignment of tube indices in high resolution optical absorption spectroscopy. [less ▲]

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See detailSuperheavy nuclei in selfconsistent nuclear calculations
Rutz, K.; Bender, M.; Bürvenich, T. et al

in AIP Conference Proceedings (1997), 56(1), 238-243

The shell structure of superheavy nuclei is investigated within various parametrizations of relativistic and nonrelativistic nuclear mean-field models. The heaviest known even-even nucleus 156 264Hs108 is ... [more ▼]

The shell structure of superheavy nuclei is investigated within various parametrizations of relativistic and nonrelativistic nuclear mean-field models. The heaviest known even-even nucleus 156 264Hs108 is used as a benchmark to estimate the predictive value of the models. From that starting point, doubly magic spherical nuclei are searched in the region Z51102140 and N5134–298. They are found at (Z5114 , N5184), (Z5120 , N5172), or at (Z5126 , N5184), depending on the parametrization. [less ▲]

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