11,757 research outputs found
Network calculus for parallel processing
In this note, we present preliminary results on the use of "network calculus"
for parallel processing systems, specifically MapReduce
The wedding of modified dynamics and non-exotic dark matter in galaxy clusters
We summarize the status of Modified Newtonian Dynamics (MOND) in galaxy
clusters. The observed acceleration is typically larger than the acceleration
threshold of MOND in the central regions, implying that some dark matter is
necessary to explain the mass discrepancy there. A plausible resolution of this
issue is that the unseen mass in MOND is in the form of ordinary neutrinos with
masses just below the experimentally detectable limit. In particular, we show
that the lensing mass reconstructions of the clusters 1E0657-56 (the bullet
cluster) and Cl0024+17 (the ring) do not pose a new challenge to this scenario.
However, the mass discrepancy for cool X-ray emitting groups, in which
neutrinos cannot cluster, pose a more serious problem, meaning that dark
baryons could present a more satisfactory solution to the problem of unseen
mass in MOND clusters.Comment: to appear in World Scientific, proceedings of DARK 200
Diffusion in a multi-component Lattice Boltzmann Equation model
Diffusion phenomena in a multiple component lattice Boltzmann Equation (LBE)
model are discussed in detail. The mass fluxes associated with different
mechanical driving forces are obtained using a Chapman-Enskog analysis. This
model is found to have correct diffusion behavior and the multiple diffusion
coefficients are obtained analytically. The analytical results are further
confirmed by numerical simulations in a few solvable limiting cases. The LBE
model is established as a useful computational tool for the simulation of mass
transfer in fluid systems with external forces.Comment: To appear in Aug 1 issue of PR
Galilean invariance of lattice Boltzmann models
It is well-known that the original lattice Boltzmann (LB) equation deviates
from the Navier-Stokes equations due to an unphysical velocity dependent
viscosity. This unphysical dependency violates the Galilean invariance and
limits the validation domain of the LB method to near incompressible flows. As
previously shown, recovery of correct transport phenomena in kinetic equations
depends on the higher hydrodynamic moments. In this Letter, we give specific
criteria for recovery of various transport coefficients. The Galilean
invariance of a general class of LB models is demonstrated via numerical
experiments
Multiscale lattice Boltzmann approach to modeling gas flows
For multiscale gas flows, kinetic-continuum hybrid method is usually used to
balance the computational accuracy and efficiency. However, the
kinetic-continuum coupling is not straightforward since the coupled methods are
based on different theoretical frameworks. In particular, it is not easy to
recover the non-equilibrium information required by the kinetic method which is
lost by the continuum model at the coupling interface. Therefore, we present a
multiscale lattice Boltzmann (LB) method which deploys high-order LB models in
highly rarefied flow regions and low-order ones in less rarefied regions. Since
this multiscale approach is based on the same theoretical framework, the
coupling precess becomes simple. The non-equilibrium information will not be
lost at the interface as low-order LB models can also retain this information.
The simulation results confirm that the present method can achieve model
accuracy with reduced computational cost
The Norm of the Learning-Disability Checklist for Elementary and Middle School Children (in Chinese)
The Learning-Disabilities Checklist for Elementary and Middle School Children was administered to 1067 subjects in Shanghai. The data analyses brought us the following: 1) The mean and standard deviation of each variable of raw data; 2) There were significant age differences and sex differences for each variable; 3) The reliability and validity of this test was up to the criteria of psychometrology; 4) A Shanghai norm was made
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