31,721 research outputs found
Multi-population genetic algorithms with immigrants scheme for dynamic shortest path routing problems in mobile ad hoc networks
Copyright @ Springer-Verlag Berlin Heidelberg 2010.The static shortest path (SP) problem has been well addressed using intelligent optimization techniques, e.g., artificial neural networks, genetic algorithms (GAs), particle swarm optimization, etc. However, with the advancement in wireless communications, more and more mobile wireless networks appear, e.g., mobile ad hoc network (MANET), wireless mesh network, etc. One of the most important characteristics in mobile wireless networks is the topology dynamics, that is, the network topology changes over time due to energy conservation or node mobility. Therefore, the SP problem turns out to be a dynamic optimization problem in mobile wireless networks. In this paper, we propose to use multi-population GAs with immigrants scheme to solve the dynamic SP problem in MANETs which is the representative of new generation wireless networks. The experimental results show that the proposed GAs can quickly adapt to the environmental changes (i.e., the network topology change) and produce good solutions after each change.This work was supported by the Engineering and Physical Sciences Research Council(EPSRC) of UK under Grant EP/E060722/1
Combinatorial Voting
We study elections that simultaneously decide multiple issues, where voters have independent private values over bundles of issues. The innovation is in considering nonseparable preferences, where issues may be complements or substitutes. Voters face a political exposure problem: the optimal vote for a particular issue will depend on the resolution of the other issues. Moreover, the probabilities that the other issues will pass should be conditioned on being pivotal. We prove that equilibrium exists when distributions over values have full support or when issues are complements. We then study large elections with two issues. There exists a nonempty open set of distributions where the probability of either issue passing fails to converge to either 1 or 0 for all limit equilibria. Thus, the outcomes of large elections are not generically predictable with independent private values, despite the fact that there is no aggregate uncertainty regarding fundamentals. While the Condorcet winner is not necessarily the outcome of a multi-issue election, we provide sufficient conditions that guarantee the implementation of the Condorcet winner. © 2012 The Econometric Society
Meta-Stable Brane Configurations by Higher Order Polynomial Superpotential
We construct the type IIA nonsupersymmetric meta-stable brane configuration
consisting of (2k+1) NS5-branes and D4-branes where the electric gauge theory
superpotential has an order (2k+2) polynomial for the bifundamentals. We find a
rich pattern of nonsupersymmetric meta-stable states as well as the
supersymmetric stable ones. By adding the orientifold 4-plane to this brane
configuration, we also describe the intersecting brane configuration of type
IIA string theory corresponding to the meta-stable nonsupersymmetric vacua of
corresponding gauge theory.Comment: 27pp, 8 figures; some footnotes added; to appear in IJMP
The Full Structure of Quantum Super- Algebra
We present the complete structure of the nonlinear super extension of
Polyakov-Bershadsky, , algebra with the generic central charge, ,
at the {\it quantum} level. It contains extra two pairs of fermionic currents
with integer spins 1 and 2, besides the currents of superconformal and
algebras. For limit, the algebra reduces to
the classical one, which has been studied previously. The 'hybrid' field
realization of this algebra is also discussed.Comment: 8 pages, latex, no figure
Explicit Construction of Spin 4 Casimir Operator in the Coset Model
We generalize the Goddard-Kent-Olive (GKO) coset construction to the
dimension 5/2 operator for and compute the fourth order
Casimir invariant in the coset model with the generic unitary minimal
series that can be viewed as perturbations of the
limit, which has been investigated previously in the realization of
free fermion model.Comment: 11 page
Ferromagnetically coupled magnetic impurities in a quantum point contact
We investigate the ground and excited states of interacting electrons in a
quantum point contact using exact diagonalization method. We find that strongly
localized states in the point contact appear when a new conductance channel
opens due to momentum mismatch. These localized states form magnetic impurity
states which are stable in a finite regime of chemical potential and excitation
energy. Interestingly, these magnetic impurities have ferromagnetic coupling,
which shed light on the experimentally observed puzzling coexistence of Kondo
correlation and spin filtering in a quantum point contact
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