109,853 research outputs found
Non-perturbative statistical theory of intermittency in ITG drift wave turbulence with zonal flows
The probability distribution functions (PDFs) of momentum flux and zonal flow formation in ion-temperature-gradient (ITG) turbulence are investigated in two different models. The first is a general five-field model (ni, , Ti, Te, vi) where a reductive perturbation method is used to derive dynamical equations for drift waves and a zonal flow. The second is a reduced two-field model (, Ti) that has an exact non-linear solution (bipolar vortex soliton). In both models the exponential tails of the zonal flow PDFs are found with the same scaling ( ), but with different coefficients cZF. The PDFs of momentum flux is, however, found to be qualitatively different with the scaling (PDF ~ exp{−cMRs}), where s = 2 and s = 3/2 in the five and two-field models, respectively
Universality class of the restricted solid-on-solid model with hopping
We study the restricted solid-on-solid (RSOS) model with finite hopping
distance , using both analytical and numerical methods. Analytically, we
use the hard-core bosonic field theory developed by the authors [Phys. Rev. E
{\bf 62}, 7642 (2000)] and derive the Villain-Lai-Das Sarma (VLD) equation for
the case which corresponds to the conserved RSOS (CRSOS) model
and the Kardar-Parisi-Zhang (KPZ) equation for all finite values of .
Consequently, we find that the CRSOS model belongs to the VLD universality
class and the RSOS models with any finite hopping distance belong to the KPZ
universality class. There is no phase transition at a certain finite hopping
distance contrary to the previous result. We confirm the analytic results using
the Monte Carlo simulations for several values of the finite hopping distance.Comment: 13 pages, 3 figure
Algorithms for Replica Placement in High-Availability Storage
A new model of causal failure is presented and used to solve a novel replica
placement problem in data centers. The model describes dependencies among
system components as a directed graph. A replica placement is defined as a
subset of vertices in such a graph. A criterion for optimizing replica
placements is formalized and explained. In this work, the optimization goal is
to avoid choosing placements in which a single failure event is likely to wipe
out multiple replicas. Using this criterion, a fast algorithm is given for the
scenario in which the dependency model is a tree. The main contribution of the
paper is an dynamic programming algorithm for placing
replicas on a tree with vertices. This algorithm exhibits the
interesting property that only two subproblems need to be recursively
considered at each stage. An greedy algorithm is also briefly
reported.Comment: 22 pages, 7 figures, 4 algorithm listing
Far-infrared measurements of oxygen-doped polycrystalline La2CuO4.0315 superconductor under slow-cooled and fast-cooled conditions
We have studied the far-infrared (far-IR) charge dynamics of an equilibrated
pure oxygen doped La2CuO4+0.0315 under slow-cooled and fast-cooled conditions.
The superconducting transition temperature (Tc) for the slow-cooled and that
for the fast-cooled processes were respectively found to be close to the two
intrinsic Tc's: One at 30 K and the other at 15 K. Direct comparison with our
previous results and other far-IR and Raman studies on single crystalline
La2-xSrxCuO4, we conclude that the topology of the pristine electronic phases
that are responsible for the two intrinsic Tc's is holes arranged into
two-dimensional (2D) square lattices.Comment: Submitted to PR
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