6,837 research outputs found
Equivalence Classes of Permutations Modulo Replacements Between 123 and Two-Integer Patterns
We explore a new type of replacement of patterns in permutations, suggested
by James Propp, that does not preserve the length of permutations. In
particular, we focus on replacements between 123 and a pattern of two integer
elements. We apply these replacements in the classical sense; that is, the
elements being replaced need not be adjacent in position or value. Given each
replacement, the set of all permutations is partitioned into equivalence
classes consisting of permutations reachable from one another through a series
of bi-directional replacements. We break the eighteen replacements of interest
into four categories by the structure of their classes and fully characterize
all of their classes.Comment: 14 page
Non-linear damping of visco-resistive Alfven waves in solar spicules
Interaction of Alfven waves with plasma inhomogeneities generates phase
mixing which can lead to dissipate Alfven waves and to heat the solar plasma.
Here we study the dissipation of Alfven waves by phase mixing due to viscosity
and resistivity variations with height. We also consider nonlinear
magnetohydrodynamic (MHD) equations in our theoretical model. Non-linear terms
of MHD equations include perturbed velocity, magnetic field, and density. To
investigate the damping of Alfven waves in a stratified atmosphere of solar
spicules, we solve the non-linear MHD equations in the x-z plane. Our
simulations show that the damping is enhanced due to viscosity and resistivity
gradients. Moreover, energy variations is influenced due to nonlinear terms in
MHD equations.Comment: Accepted for publication in Astrophysics and Space Science Journal.
arXiv admin note: substantial text overlap with arXiv:1304.776
Computational approach to quantum encoder design for purity optimization
In this paper, we address the problem of designing a quantum encoder that
maximizes the minimum output purity of a given decohering channel, where the
minimum is taken over all possible pure inputs. This problem is cast as a
max-min optimization problem with a rank constraint on an appropriately defined
matrix variable. The problem is computationally very hard because it is
non-convex with respect to both the objective function (output purity) and the
rank constraint. Despite this difficulty, we provide a tractable computational
algorithm that produces the exact optimal solution for codespace of dimension
two. Moreover, this algorithm is easily extended to cover the general class of
codespaces, in which case the solution is suboptimal in the sense that the
suboptimized output purity serves as a lower bound of the exact optimal purity.
The algorithm consists of a sequence of semidefinite programmings and can be
performed easily. Two typical quantum error channels are investigated to
illustrate the effectiveness of our method.Comment: 13 pages, 1 figur
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