14,182 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
Robust Preparation of GHZ and W States of Three Distant Atoms
Schemes to generate Greenberger-Horne-Zeilinger(GHZ) and W states of three
distant atoms are proposed in this paper. The schemes use the effects of
quantum statistics of indistinguishable photons emitted by the atoms inside
optical cavities. The advantages of the schemes are their robustness against
detection inefficiency and asynchronous emission of the photons. Moreover, in
Lamb-Dicke limit, the schemes do not require simultaneous click of the
detectors, this makes the schemes more realizable in experiments.Comment: 5 pages, 1 fiure. Phys. Rev. A 75, 044301 (2007
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
Robust Face Recognition in Rotated Eigen Space
Face recognition is a very complex classification problem due to nuisance variations in different conditions. Most face recognition approaches either assume constant lighting condition or standard facial expressions, thus cannot deal with both kinds of variations simultaneously. Principal Component Analysis (PCA) cannot handle complex pattern variations such as illumination and expression. Adaptive PCA rotates eigenspace to extract more representative features thus improving the performance. In this paper, we present a way to extract various sets of features by different eigenspace rotations and propose a method to fuse these features to generate nonorthogonal mappings for face recognition. The proposed method is tested on the Asian Face Database with 856 images from 107 subjects with 5 lighting conditions and 4 expressions. We register only one normally lit neutral face image and test on the remaining face images with variations. Experiments show a 95% classification accuracy and a 20% reduction in error rate. This illustrates that the fused features can provide significantly improved pattern classification
Large spin relaxation rates in trapped submerged-shell atoms
Spin relaxation due to atom-atom collisions is measured for magnetically
trapped erbium and thulium atoms at a temperature near 500 mK. The rate
constants for Er-Er and Tm-Tm collisions are 3.0 times 10^-10 cm^3 s^-1 and 1.1
times 10^-10 cm^3 s^-1, respectively, 2-3 orders of magnitude larger than those
observed for highly magnetic S-state atoms. This is strong evidence for an
additional, dominant, spin relaxation mechanism, electrostatic anisotropy, in
collisions between these "submerged-shell" L > 0 atoms. These large spin
relaxation rates imply that evaporative cooling of these atoms in a magnetic
trap will be highly inefficient.Comment: 10 pages, 3 figure
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
Crystal isomorphisms in Fock spaces and Schensted correspondence in affine type A
We are interested in the structure of the crystal graph of level Fock
spaces representations of . Since
the work of Shan [26], we know that this graph encodes the modular branching
rule for a corresponding cyclotomic rational Cherednik algebra. Besides, it
appears to be closely related to the Harish-Chandra branching graph for the
appropriate finite unitary group, according to [8]. In this paper, we make
explicit a particular isomorphism between connected components of the crystal
graphs of Fock spaces. This so-called "canonical" crystal isomorphism turns out
to be expressible only in terms of: - Schensted's classic bumping procedure, -
the cyclage isomorphism defined in [13], - a new crystal isomorphism, easy to
describe, acting on cylindric multipartitions. We explain how this can be seen
as an analogue of the bumping algorithm for affine type . Moreover, it
yields a combinatorial characterisation of the vertices of any connected
component of the crystal of the Fock space
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