59,321 research outputs found
Geodynamo and mantle convection simulations on the Earth Simulator using the Yin-Yang grid
We have developed finite difference codes based on the Yin-Yang grid for the
geodynamo simulation and the mantle convection simulation. The Yin-Yang grid is
a kind of spherical overset grid that is composed of two identical component
grids. The intrinsic simplicity of the mesh configuration of the Yin-Yang grid
enables us to develop highly optimized simulation codes on massively parallel
supercomputers. The Yin-Yang geodynamo code has achieved 15.2 Tflops with 4096
processors on the Earth Simulator. This represents 46% of the theoretical peak
performance. The Yin-Yang mantle code has enabled us to carry out mantle
convection simulations in realistic regimes with a Rayleigh number of
including strongly temperature-dependent viscosity with spatial contrast up to
.Comment: Plenary talk at SciDAC 200
Depletion potentials in highly size-asymmetric binary hard-sphere mixtures: Comparison of accurate simulation results with theory
We report a detailed study, using state-of-the-art simulation and theoretical
methods, of the depletion potential between a pair of big hard spheres immersed
in a reservoir of much smaller hard spheres, the size disparity being measured
by the ratio of diameters q=\sigma_s/\sigma_b. Small particles are treated
grand canonically, their influence being parameterized in terms of their
packing fraction in the reservoir, \eta_s^r. Two specialized Monte Carlo
simulation schemes --the geometrical cluster algorithm, and staged particle
insertion-- are deployed to obtain accurate depletion potentials for a number
of combinations of q\leq 0.1 and \eta_s^r. After applying corrections for
simulation finite-size effects, the depletion potentials are compared with the
prediction of new density functional theory (DFT) calculations based on the
insertion trick using the Rosenfeld functional and several subsequent
modifications. While agreement between the DFT and simulation is generally
good, significant discrepancies are evident at the largest reservoir packing
fraction accessible to our simulation methods, namely \eta_s^r=0.35. These
discrepancies are, however, small compared to those between simulation and the
much poorer predictions of the Derjaguin approximation at this \eta_s^r. The
recently proposed morphometric approximation performs better than Derjaguin but
is somewhat poorer than DFT for the size ratios and small sphere packing
fractions that we consider. The effective potentials from simulation, DFT and
the morphometric approximation were used to compute the second virial
coefficient B_2 as a function of \eta_s^r. Comparison of the results enables an
assessment of the extent to which DFT can be expected to correctly predict the
propensity towards fluid fluid phase separation in additive binary hard sphere
mixtures with q\leq 0.1.Comment: 16 pages, 9 figures, revised treatment of morphometric approximation
and reordered some materia
- …