343,446 research outputs found
PTAS for Minimax Approval Voting
We consider Approval Voting systems where each voter decides on a subset to
candidates he/she approves. We focus on the optimization problem of finding the
committee of fixed size k minimizing the maximal Hamming distance from a vote.
In this paper we give a PTAS for this problem and hence resolve the open
question raised by Carragianis et al. [AAAI'10]. The result is obtained by
adapting the techniques developed by Li et al. [JACM'02] originally used for
the less constrained Closest String problem. The technique relies on extracting
information and structural properties of constant size subsets of votes.Comment: 15 pages, 1 figur
The gravitational field of a global monopole
We present an exact solution to the non-linear equation which describes a
global monopole in the flat space. We re-examine the metric and the geodesics
outside the global monopole. We will see that a global monopole produces a
repulsive gravitational field outside the core in addition to a solid angular
deficit. The lensing property of the global monopole and the global
monopole-antimonopole annihilation mechanism are studied.Comment: 8 pages, no figure
Statistical Complexity of Simple 1D Spin Systems
We present exact results for two complementary measures of spatial structure
generated by 1D spin systems with finite-range interactions. The first, excess
entropy, measures the apparent spatial memory stored in configurations. The
second, statistical complexity, measures the amount of memory needed to
optimally predict the chain of spin values. These statistics capture distinct
properties and are different from existing thermodynamic quantities.Comment: 4 pages with 2 eps Figures. Uses RevTeX macros. Also available at
http://www.santafe.edu/projects/CompMech/papers/CompMechCommun.htm
Interdot Coulomb repulsion effect on the charge transport of parallel double single electron transistors
The charge transport behaviors of parallel double single electron transistors
(SETs) are investigated by the Anderson model with two impurity levels. The
nonequilibrium Keldysh Green's technique is used to calculate the
current-voltage characteristics of system. For SETs implemented by quantum dots
(QDs) embedded into a thin layer, the interdot Coulomb repulsion is
more important than the interdot electron hopping as a result of high potential
barrier height between QDs and . We found that the interdot Coulomb
repulsion not onlyleads to new resonant levels, but also creates negative
differential conductances.Comment: 12 pages, 7 figure
Ratcheting Heat Flux against a Thermal Bias
Merely rocking the temperature in one heat bath can direct a steady heat flux
from cold to hot against a non-zero thermal bias in stylized nonlinear lattice
junctions that are sandwiched between two heat baths. Likewise, for an average
zero-temperature difference between the two contacts a net, ratchet-like heat
flux emerges. Computer simulations show that this very heat flux can be
controlled and reversed by suitably tailoring the frequency ( 100
MHz) of the alternating temperature field.Comment: 5 pages, 6 figure
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