Artificial Compressibility Method and Lattice Boltzmann Method: Similarities and Differences

AbstractThe artificial compressibility method and the lattice Boltzmann method yield the solutions of the incompressible Navier–Stokes equations in the limit of the vanishing Mach number. The inclusion of the bulk viscosity is considered to be one of the reasons for the success of the lattice Boltzmann method at least in the 2D case. In the present paper, the robustness of the artificial compressibility method is enhanced by introducing a new dissipation term, which makes high cell-Reynolds number computation possible. The increase of the stability is also confirmed in the linear stability analysis; the magnitude of the eigenvalues are drastically reduced for low resolution. Comparisons are made with the lattice Boltzmann method. It is confirmed that the fortified ACM is more robust as well as more accurate than the lattice Boltzmann method

Mott gap excitations in twin-free YBa2Cu3O7-d (Tc = 93 K) studied by RIXS

Mott gap excitations in the high-Tc superconductor of the optimal doped YBa2Cu3O7-d (Tc = 93 K) have been studied by the resonant inelastic x-ray scattering method. Anisotropic spectra in the ab-plane are observed in a twin-free crystal. The excitation from the one-dimensional CuO chain is enhanced at 2 eV near the zone boundary of the b* direction, while the excitation from the CuO2 plane is broad at 1.5-4 eV and almost independent of the momentum transfer. Theoretical calculation based on the one-dimensional and two-dimensional Hubbard model reproduces the observed spectra by taking the different parameters of the on-site Coulomb energy. The fact of the Mott gap of the CuO chain site is much smaller than that of CuO2 plane site is observed for the first time

Connection between kinetic methods for fluid-dynamic equations and macroscopic finite-difference schemes

AbstractThe lattice Boltzmann method (LBM) for the incompressible Navier–Stokes (NS) equations and the gas kinetic scheme for the compressible NS equations are based on the kinetic theory of gases. In the latter case, however, it is shown that the kinetic formulation is necessary only in the discontinuous reconstruction of fluid-dynamic variables for shock capturing. Analogously we will discuss the reduction of a kinetic method for the incompressible case, where the LBM scheme will be shown to shrink to an artificial compressibility type finite-difference scheme. We will prove first that a simple and compact LBM scheme cannot catch rarefied effects beyond Navier–Stokes and hence that it is worth the effort to develop kinetic-based FD alternatives. Finally we will propose two improvements to existing kinetic-based FD schemes: first of all, (a) the proposed scheme is formulated purely in terms of macroscopic quantities on a compact stencil; secondly (b) the semi-implicit formulation is proposed in order to increase the stability. We think that this work may be useful to others in realizing the actual possibilities of simple LBM schemes beyond Navier–Stokes and in adopting the suggested improvements in their actual FD codes

Resonant inelastic x-ray scattering study of hole-doped manganites La1-xSrxMnO3 (x=0.2 and 0.4)

Electronic excitations near the Fermi energy in the hole doped manganese oxides (La1-xSrxMnO3, x=0.2 and 0.4) have been elucidated by using the resonant inelastic x-ray scattering (RIXS) method. A doping effect in the strongly correlated electron systems has been observed for the first time. The scattering spectra show that a salient peak appears in low energies indicating the persistence of the Mott gap. At the same time, the energy gap is partly filled by doping holes and the energy of the spectral weight shifts toward lower energies. The excitation spectra show little change in the momentum space as is in undoped LaMnO3, but the scattering intensities in the low energy excitations of x=0.2 are anisotropic as well as temperature dependent, which indicates a reminiscence of the orbital nature

N‐Substituted Nipecotic Acids as (S )‐SNAP‐5114 Analogues with Modified Lipophilic Domains

Potential mGAT4 inhibitors derived from the lead substance (S )‐SNAP‐5114 have been synthesized and characterized for their inhibitory potency. Variations from the parent compound included the substitution of one of its aromatic 4‐methoxy and 4‐methoxyphenyl groups, respectively, with a more polar moiety, including a carboxylic acid, alcohol, nitrile, carboxamide, sulfonamide, aldehyde or ketone function, or amino acid partial structures. Furthermore, it was investigated how the substitution of more than one of the aromatic 4‐methoxy groups affects the potency and selectivity of the resulting compounds. Among the synthesized test substances (S )‐1‐{2‐[(4‐formylphenyl)bis(4‐methoxyphenyl)‐methoxy]ethyl}piperidine‐3‐carboxylic acid, that features a carbaldehyde function in place of one of the aromatic 4‐methoxy moieties of (S )‐SNAP‐5114, was found to have a pIC50 value of 5.89±0.07, hence constituting a slightly more potent mGAT4 inhibitor than the parent substance while showing comparable subtype selectivity