3,189 research outputs found
A critical assessment of viscous models of trench topography and corner flow
Stresses for Newtonian viscous flow in a simple geometry (e.g., corner flow, bending flow) are obtained in order to study the effect of imposed velocity boundary conditions. Stress for a delta function velocity boundary condition decays as 1/R(2); for a step function velocity, stress goes as 1/R; for a discontinuity in curvature, the stress singularity is logarithmic. For corner flow, which has a discontinuity of velocity at a certain point, the corresponding stress has a 1/R singularity. However, for a more realistic circular-slab model, the stress singularity becomes logarithmic. Thus the stress distribution is very sensitive to the boundary conditions, and in evaluating the applicability of viscous models of trench topography it is essential to use realistic geometries. Topography and seismicity data from northern Hoshu, Japan, were used to construct a finite element model, with flow assumed tangent to the top of the grid, for both Newtonian and non-Newtonian flow (power law 3 rheology). Normal stresses at the top of the grid are compared to the observed trench topography and gravity anomalies. There is poor agreement. Purely viscous models of subducting slables with specified velocity boundary conditions do not predict normal stress patterns compatible with observed topography and gravity. Elasticity and plasticity appear to be important for the subduction process
Quantum Gates to other Universes
We present a microscopic model of a bridge connecting two large
Anti-de-Sitter Universes. The Universes admit a holographic description as
three-dimensional supersymmetric gauge theories based on large
linear quivers, and the bridge is a small rank- gauge group that acts as a
messenger. On the gravity side, the bridge is a piece of a highly-curved
AdSS throat carrying units of five-form flux. We derive a
universal expression for the mixing of the two massless gravitons: , where is the mass
splitting of the gravitons, are the
effective gravitational couplings of the AdS Universes, and is the
quantized charge of the gate. This agrees with earlier results based on
double-trace deformations, with the important difference that the effective
coupling is here quantized. We argue that the apparent non-localities of
holographic double-trace models are resolved by integrating-in the (scarce)
degrees of freedom of the gate.Comment: 17 pages, 8 figures. Note added about an implicit assumption in the
case of non-identical Universe
Lagrangian and geometric analysis of finite-time Euler singularities
We present a numerical method of analyzing possibly singular incompressible
3D Euler flows using massively parallel high-resolution adaptively refined
numerical simulations up to 8192^3 mesh points. Geometrical properties of
Lagrangian vortex line segments are used in combination with analytical
non-blowup criteria by Deng et al [Commun. PDE 31 (2006)] to reliably
distinguish between singular and near-singular flow evolution. We then apply
the presented technique to a class of high-symmetry initial conditions and
present numerical evidence against the formation of a finite-time singularity
in this case.Comment: arXiv admin note: text overlap with arXiv:1210.253
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