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Thermoelectric properties of two-dimensional Dirac materials Hasdeo, Eddwi Hesky ; ; in AIP Conference Proceedings (2020), 2256(1), 030010 We performed Boltzmann transport calculation to obtain the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, and thermoelectric figure of merit (ZT) for Dirac systems. We ... [more ▼] We performed Boltzmann transport calculation to obtain the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, and thermoelectric figure of merit (ZT) for Dirac systems. We found an enhancement of ZT due to the gap opening. When the phonon thermal conductivity is small enough, the optimum ZT in gapped Dirac system can be larger than 1, which is preferable for thermoelectric applications. [less ▲] Detailed reference viewed: 11 (0 UL)Thermoelectric properties of two-dimensional hydrogenated borophene: A first-principles study ; Hasdeo, Eddwi Hesky ; et al in AIP Conference Proceedings (2020), 2256(1), 030017 We theoretically study electronic and thermoelectric properties of two-dimensional hydrogenated borophene (”boro-phane”). We show that, according to the first-principles calculation, hydrogenated ... [more ▼] We theoretically study electronic and thermoelectric properties of two-dimensional hydrogenated borophene (”boro-phane”). We show that, according to the first-principles calculation, hydrogenated borophene is semimetallic, with two bands meeting at a single point at the Fermi level. The thermoelectric properties evaluated by using the Boltzmann equation with a constant relaxation time approximation (CRTA). At room temperature, we obtain large power factor for electron doping regime. Therefore, appropriate doping to this material can enhance its thermoelectric efficiency. [less ▲] Detailed reference viewed: 23 (0 UL)Ab-initio calculation of muon spin polarization function to study lithium-ion diffusion in LiTi2O4 battery material ; ; et al in AIP Conference Proceedings (2020), 2256(1), 030015 We report the study of lithium-ion diffusion in LiTi2O4 battery material by the analysis of muon spin polarization function at the muon site by DFT calculation. The important parameters which explain the ... [more ▼] We report the study of lithium-ion diffusion in LiTi2O4 battery material by the analysis of muon spin polarization function at the muon site by DFT calculation. The important parameters which explain the lithium-ion diffusion will be derived from the function, including the field fluctuation rate and the local field distribution. The calculated results are shown in good agreement with the previously measured field distribution and the field fluctuation rate in LiTi2O4 at the ground state temperature. This method, therefore, may apply to the study of other battery materials. [less ▲] Detailed reference viewed: 52 (1 UL)Modulation of coherent phonon amplitudes in low-dimensional materials by ultrafast laser pulse trains ; ; et al in AIP Conference Proceedings (2020), 2256(1), 020005 We theoretically investigate how coherent phonon amplitudes in low dimensional materials can be modulated by ultrafast laser pulse trains. Important laser parameters for the modulation of coherent phonon ... [more ▼] We theoretically investigate how coherent phonon amplitudes in low dimensional materials can be modulated by ultrafast laser pulse trains. Important laser parameters for the modulation of coherent phonon amplitudes are the pulse width, repetition period, and number of pulses in the pulse train. We find that it is possible to switch on or switch off the radial breathing mode (RBM) and the G-band phonons in a single wall carbon nanotube (SWNT), as a typical model of low-dimensional materials. In particular, if the repetition period matches with integer multiple of the RBM phonon period, the RBM phonon could be switched on, while the other modes are switched off. On the other hand, for the G-band, which has a higher frequency (shorter period) than the RBM, the number of pulses in the pulse train also affects the switching process. The ratios of the G-band and RBM amplitudes are found to be significantly enhanced at certain integer multiples of pulse number as a function of SWNT diameter. Such a “magic number” phenomenon in ultrafast spectroscopy can be extended to other low-dimensional materials, in which we may realize a phonon switch in the future. [less ▲] Detailed reference viewed: 47 (2 UL)Concrete-Filled Steel Tubular (CFTS) Columns Subjected to Eccentric Compressive Load KEDZIORA, SLAWOMIR ; in AIP Conference Proceedings (2018, November 15) Concrete-steel composite structures are very efficient in carrying high loads as they combine benefits of both materials concrete and steel. The combination of them can significantly improve the strength ... [more ▼] Concrete-steel composite structures are very efficient in carrying high loads as they combine benefits of both materials concrete and steel. The combination of them can significantly improve the strength of the composite structure by taking advantage of high compression resistance of concrete and high strength of steel in tension. Recently, there has been renewed interest in the composite structures used in different forms, as beams, slabs, sandwich structures and columns and many methods of structural analyses were utilised. However, none of them was able to eliminate concrete material when it fractured. The presented work concerns circular composite columns CFST under eccentric compression. The principal objective of the project was to investigate a straightforward method based on a finite element analysis employed to estimate the load carrying capacity of columns. This study has also been set out to determine whether the Drucker-Prager material model of concrete without a crack capability could be used for analyses of the CFST columns with the additional elimination of the concrete material when concrete is damaged. The elaborated finite element model was verified with existing test data from the literature. The findings show that the correlation between the test results and the numerical analysis was excellent confirming the feasibility of usage of the proposed method for the assessment of complex cases of the CFST columns. A new part of the work is the employment of a death element feature to eliminate concrete material, which theoretically is not taking any load after reaching its tensile strength. A criterion to eliminate elements from the model is the maximum principal stress greater than tensile strength. The obtained results are excellent; the established goal was met entirely. [less ▲] Detailed reference viewed: 146 (24 UL)On the choice of a phase interchange strategy for a multiscale DEM-VOF Method Pozzetti, Gabriele ; Peters, Bernhard 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 ▲] Detailed reference viewed: 277 (49 UL)Hierarchical control of aerial manipulation vehicle Kannan, Somasundar ; Bezzaoucha, Souad ; Quintanar Guzman, Serket et al in AIP Conference Proceedings (2017), 1798(1), 020069 Hierarchical Control of the Aerial Manipulator is treated here. The modelling aspect of the highly coupled Aerial Vehicle which includes Quadrotor and manipulator is discussed. The control design to ... [more ▼] Hierarchical Control of the Aerial Manipulator is treated here. The modelling aspect of the highly coupled Aerial Vehicle which includes Quadrotor and manipulator is discussed. The control design to perform tasks in operational space is addressed along with stability discussion. The simulation studies are successfully performed to validate the design methodology. [less ▲] Detailed reference viewed: 154 (15 UL)Multiscale-multiphysics approaches for engineering applications Pozzetti, Gabriele ; Peters, Bernhard in AIP Conference Proceedings (2017), 1863(1), 180001 Detailed reference viewed: 114 (14 UL)A force-based large increment method for 2D continuum solids and the mesh convergence study ; ; 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 ▲] Detailed reference viewed: 297 (5 UL)An element nodal force-based large increment method for elastoplasticity ; ; et al in AIP Conference Proceedings (2010), 1233(PART 1), 1401-1405 This paper presents a new method for establishing the basic equations in the novel force-based large increment method (LIM) for continuum elastoplastic problems. In LIM, unlike traditional displacement ... [more ▼] This paper presents a new method for establishing the basic equations in the novel force-based large increment method (LIM) for continuum elastoplastic problems. In LIM, unlike traditional displacement methods, the (generalised) elemental force variables are adopted as system unknowns. The equilibrium equations can then be obtained directly at every nodal degree of freedom without physical equations (i.e., constitutive equations) involved. The generalised inverse of the non-square system of equations is employed to obtain the set of solutions of the non-square matrix equations directly. A conjugate gradient procedure is then used to find the correct solution from this set of solutions by optimising the compatibility of the solution based on the fact that the correct solution should also satisfy the constitutive equations and the compatibility equations. In this paper, the generalised elemental force variables are defined based on the element nodal forces. The LIM framework is therefore successfully applied to elements based on this definition. The efficiency and accuracy of the LIM are illustrated with a few benchmark problems and the results are compared with the analytical solution and the conventional displacement-based finite element method. [less ▲] Detailed reference viewed: 88 (0 UL)On the structure of a new superhard hexagonal carbon phase ; ; et al in AIP Conference Proceedings (2010), 1233(PART 1), 489-493 Molecular dynamics simulations show that graphite will transform into a superhard phase under cold compression. Recent experiments show that there is a sp 3-rich hexagonal carbon polymorph (a 0=2.496 Å, c ... [more ▼] Molecular dynamics simulations show that graphite will transform into a superhard phase under cold compression. Recent experiments show that there is a sp 3-rich hexagonal carbon polymorph (a 0=2.496 Å, c 0=4.123Å) with a bulk modulus of 447 GPa and average density about 3.6g/cm 3, restricted to the space group of P-62c (No. 190), but the detailed atomic structure was not obtained [Wang et al., P. Natl. Acad. Sci. 101(38), 13699]. Here we set carbon atoms occupying P-62c 4f Wyckoff positions of P-62c, and calculate the total energy of the different structures changing the internal parameter z by first-principles calculations using geometry optimisation algorithm in CASTEP code, which shows that the stable structures in energy (at local minimum points) are hexagonal carbon (z=1/4) and hexagonal diamond (z=1/16). The calculated mechanical properties and lattice parameters of the structure P-62c 4f (z=1/4) are in good agreement with those of the new hexagonal carbon proposed by Wang et al., which indicates that the atomic structure is a possible candidate. © 2010 American Institute of Physics. [less ▲] Detailed reference viewed: 84 (0 UL)Raman spectroscopy on single- and few-layer graphene ; ; 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 ▲] Detailed reference viewed: 113 (0 UL)Optical absorption of hexagonal boron nitride and BN nanotubes Wirtz, Ludger ; ; 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 ▲] Detailed reference viewed: 124 (2 UL)Electronic structure and optical properties of boron doped single-wall carbon nanotubes ; ; 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 ▲] Detailed reference viewed: 97 (0 UL)Optical absorption in small BN and C nanotubes Wirtz, Ludger ; ; 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 ▲] Detailed reference viewed: 81 (0 UL)Raman spectroscopy of single-wall BN nanotubes ; Wirtz, Ludger ; 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 ▲] Detailed reference viewed: 85 (0 UL)Band structure of boron doped carbon nanotubes Wirtz, Ludger ; 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 ▲] Detailed reference viewed: 92 (0 UL)Superheavy nuclei in selfconsistent nuclear calculations ; ; 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 ▲] Detailed reference viewed: 61 (0 UL) |
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