Search results for "Lattice"
showing 10 items of 3278 documents
Coupling of lattice-Boltzmann solvers with suspended particles using the MPI intercommunication framework
2017
Abstract The MPI intercommunication framework was used for coupling of two lattice-Boltzmann solvers with suspended particles, which model advection and diffusion respectively of these particles in a carrier fluid. Simulation domain was divided into two parts, one with advection and diffusion, and the other with diffusion only (no macroscopic flow). Particles were exchanged between these domains at their common boundary by a direct process to process communication. By analysing weak and strong scaling, it was shown that the linear scaling characteristics of the lattice-Boltzmann solvers were not compromised by their coupling.
Conditions for waveguide decoupling in square-lattice photonic crystals
2004
We study coupling and decoupling of parallel waveguides in two-dimensional square-lattice photonic crystals. We show that the waveguide coupling is prohibited at some wavelengths when there is an odd number of rows between the waveguides. In contrast, decoupling does not take place when there is even number of rows between the waveguides. Decoupling can be used to avoid cross talk between adjacent waveguides.
Analytic results for virtual QCD corrections to Higgs production and decay
2006
We consider the production of a Higgs boson via gluon-fusion and its decay into two photons. We compute the NLO virtual QCD corrections to these processes in a general framework in which the coupling of the Higgs boson to the external particles is mediated by a colored fermion and a colored scalar. We present compact analytic results for these two-loop corrections that are expressed in terms of Harmonic Polylogarithms. The expansion of these corrections in the low and high Higgs mass regimes, as well as the expression of the new Master Integrals which appear in the reduction of the two-loop amplitudes, are also provided. For the fermionic contribution, we provide an independent check of the…
Frequency-dependent response and dynamic disorder
1991
Abstract This paper discusses selected aspects of the application of dynamic percolation models to ionic transport in mixed-ion superionic conductors. The discussion is based on an AB lattice gas model with hard-core repulsions and a ratio of τ, 0 ⩽ τ ⩽ ∞, between the transition rates of particles A and B. The frequency-dependent conductivity for a tracer particle is calculated within an effective-medium theory. The motion of the background B-particles is regarded as providing a fluctuating disordered environment for the tracer particles A. A crossover frequency separating high-frequency and low-frequency response is found which scales with τ as ω c ∼ τ 1 2 . The results for the dc limit ar…
Hybrid DFT calculations of theFcenters in cubic ABO3perovskites
2008
We employed the hybrid DFT-LCAO approach as implemented in the CRYSTAL code for 135 atom supercell calculations of O vacancies with trapped electrons (known as the F centers) in three cubic perovskite crystals: SrTiO3, PbTiO3 and PbZrO3. The local lattice relaxation, charge redistribution and defect energy levels in the optical gap are compared. We demonstrate how difference in a chemical composition of host materials leads to quite different defect properties.
DSC, Dilatometric, Dielectric, and1H NMR Studies of Phase Transitions and Molecular Motions in [N(C2H5)4]3M2Cl9 (M = Sb, Bi) Crystals
1995
Results in the dependence of stoichiometry of obtained tetraethylammonium (TEA) chloroantiomonate and chlorobismuthate salts on the molar ratio of reactants used in the synthesis are presented. Seven tetraethylammonium salts are obtained: (TEA) 6 M 8 Cl 30 , TEAMCI 4 , (TEA) 3 M 2 Cl 9 (M = Sb, Bi) and (TEA) 2 SbCl 5 . Preliminary X-ray diffraction studies on (TEA) 3 M 2 Cl 9 (M = Sb, Bi) show that they are isomorphous, crystallizing at room temperature in monoclinic symmetry. The dilatometric, dielectric, and DSC studies show that (TEA) 3 Bi 2 Cl 9 undergoes two phase transitions at T c2 = 144 K and at T c1 = 322 K while (TEA) 3 Sb 2 Cl 9 undergoes three transitions at T c3 = 185, T c2 = 2…
The molecular glass state in KBr1-x (CN)x
1985
Structural and dynamic properties of the molecular glass KBr1-x (CN)X are reported. The low temperature state can be characterized as an averaged crystal, where clusters of correlated frozen-in CN- ions yield a distribution of frozen-in lattice strains which destroy the rigorous center-of-mass periodicty of the high temperature phase. The freezing process measured via cusps in the dipolar and quadrupolar susceptibilities is a relaxional phenomenon and depends sensitively on the timescale of the experiment.
First-principles calculations of the atomic and electronic structure of SrZrO3 and PbZrO3 (001) and (011) surfaces.
2010
We present the results of calculations of surface relaxations, rumplings, energetics, optical band gaps, and charge distribution for the SrZrO(3) and PbZrO(3) (001) and (011) surfaces using the ab initio code CRYSTAL and a hybrid description of exchange and correlation. We consider both SrO(PbO) and ZrO(2) terminations of the (001) surface and Sr(Pb), ZrO, and O terminations of the polar SrZrO(3) and PbZrO(3) (011) surfaces. On the (001) surfaces, we find that all upper and third layer atoms relax inward, while outward relaxations of all atoms in the second layer are found with the sole exception of the SrO-terminated SrZrO(3) (001) surface second layer O atom. Between all (001) and (011) s…
The Effect of Oxygen Vacancies on the Atomic and Electronic Structure of Cubic ABO3Perovskite Bulk and the (001) Surface:Abinitio Calculations
2009
We employed the hybrid DFT-LCAO and GGA-PW approaches as implemented in the CRYSTAL and VASP codes, respectively, for large supercell calculations of neutral O vacancies with trapped electrons (known as F centers) in the bulk and on the (001) surface of three cubic perovskite crystals (SrTiO 3 , PbTiO 3 , and PbZrO 3 ). The local lattice relaxation, charge redistribution, and positions of defect energy levels within the band gap are compared for three perovskites under study. We demonstrate how the difference in chemical composition of host materials leads to quite different defect properties.
Statics and Dynamics of a Glassy Crystal: A NMR- and Neutron Scattering Investigation of (NaCl) 0.35 (NaCN) 0.65
1987
The statics and the dynamics of the glass transition in (NaCl)0.35(NaCN)0.65 have been investigated by inelastic neutron scattering and are directly compared to NMR results. Insight into the relaxation dynamics is gained via the temperature dependence of the transverse acoustic phonon modes and via the spin relaxation time T1. The statics of the system is reflected by the growth of a central peak and by the distribution of electric-field gradients. Both quantities are directly related to the glass order parameter. The temperature dependence of the order parameter provides experimental evidence that in NaCl:NaCN mixed crystals the glass transition is dominated by random fields rather than by…