12,714 research outputs found
Krylov implicit integration factor discontinuous Galerkin methods on sparse grids for high dimensional reaction-diffusion equations
Computational costs of numerically solving multidimensional partial
differential equations (PDEs) increase significantly when the spatial
dimensions of the PDEs are high, due to large number of spatial grid points.
For multidimensional reaction-diffusion equations, stiffness of the system
provides additional challenges for achieving efficient numerical simulations.
In this paper, we propose a class of Krylov implicit integration factor (IIF)
discontinuous Galerkin (DG) methods on sparse grids to solve reaction-diffusion
equations on high spatial dimensions. The key ingredient of spatial DG
discretization is the multiwavelet bases on nested sparse grids, which can
significantly reduce the numbers of degrees of freedom. To deal with the
stiffness of the DG spatial operator in discretizing reaction-diffusion
equations, we apply the efficient IIF time discretization methods, which are a
class of exponential integrators. Krylov subspace approximations are used to
evaluate the large size matrix exponentials resulting from IIF schemes for
solving PDEs on high spatial dimensions. Stability and error analysis for the
semi-discrete scheme are performed. Numerical examples of both scalar equations
and systems in two and three spatial dimensions are provided to demonstrate the
accuracy and efficiency of the methods. The stiffness of the reaction-diffusion
equations is resolved well and large time step size computations are obtained
Dark matter coupling to electroweak gauge and Higgs bosons: an effective field theory approach
If dark matter is a new species of particle produced in the early universe as
a cold thermal relic (a weakly-interacting massive particle-WIMP), its present
abundance, its scattering with matter in direct-detection experiments, its
present-day annihilation signature in indirect-detection experiments, and its
production and detection at colliders, depend crucially on the WIMP coupling to
standard-model (SM) particles. It is usually assumed that the WIMP couples to
the SM sector through its interactions with quarks and leptons. In this paper
we explore the possibility that the WIMP coupling to the SM sector is via
electroweak gauge and Higgs bosons. In the absence of an ultraviolet-complete
particle-physics model, we employ effective field theory to describe the
WIMP--SM coupling. We consider both scalars and Dirac fermions as possible
dark-matter candidates. Starting with an exhaustive list of operators up to
dimension 8, we present detailed calculation of dark-matter annihilations to
all possible final states, including gamma gamma, gamma Z, gamma h, ZZ, Zh, W+
W-, hh, and f fbar, and demonstrate the correlations among them. We compute the
mass scale of the effective field theory necessary to obtain the correct
dark-matter mass density, and well as the resulting photon line signals
Tetraaquabis[2-(thiosemicarbazonomethyl)benzenesulfonato]calcium(II)
In the title compound, [Ca(C8H8N3O3S2)2(H2O)4], the Ca atom (site symmetry ) adopts a slightly distorted octahedral CaO6 geometry and the molecular conformation is stabilized by intramolecular N—H⋯N interactions. In the crystal, the molecules are linked by O—H⋯O, O—H⋯S, N—H⋯O and N—H⋯S hydrogen bonds
Hexaaquamagnesium bis(4-amino-3-methylbenzenesulfonate)
In the title molecular salt, [Mg(H2O)6](C7H8NO3S)2, the Mg2+ cation lies on an inversion centre. In the crystal, the components are linked by N—H⋯O and O—H⋯O hydrogen bonds, thereby generating sheets parallel to (001)
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