1,477 research outputs found
Transient Reward Approximation for Continuous-Time Markov Chains
We are interested in the analysis of very large continuous-time Markov chains
(CTMCs) with many distinct rates. Such models arise naturally in the context of
reliability analysis, e.g., of computer network performability analysis, of
power grids, of computer virus vulnerability, and in the study of crowd
dynamics. We use abstraction techniques together with novel algorithms for the
computation of bounds on the expected final and accumulated rewards in
continuous-time Markov decision processes (CTMDPs). These ingredients are
combined in a partly symbolic and partly explicit (symblicit) analysis
approach. In particular, we circumvent the use of multi-terminal decision
diagrams, because the latter do not work well if facing a large number of
different rates. We demonstrate the practical applicability and efficiency of
the approach on two case studies.Comment: Accepted for publication in IEEE Transactions on Reliabilit
MeGARA: Menu-based Game Abstraction and Abstraction Refinement of Markov Automata
Markov automata combine continuous time, probabilistic transitions, and
nondeterminism in a single model. They represent an important and powerful way
to model a wide range of complex real-life systems. However, such models tend
to be large and difficult to handle, making abstraction and abstraction
refinement necessary. In this paper we present an abstraction and abstraction
refinement technique for Markov automata, based on the game-based and
menu-based abstraction of probabilistic automata. First experiments show that a
significant reduction in size is possible using abstraction.Comment: In Proceedings QAPL 2014, arXiv:1406.156
Unconventional superconductivity and interaction induced Fermi surface reconstruction in the two-dimensional Edwards model
We study the competition between unconventional superconducting pairing and
charge density wave (CDW) formation for the two-dimensional Edwards Hamiltonian
at half filling, a very general two-dimensional transport model in which
fermionic charge carriers couple to a correlated background medium. Using the
projective renormalization method we find that a strong renormalization of the
original fermionic band causes a new hole-like Fermi surface to emerge near the
center of the Brillouin zone, before it eventually gives rise to the formation
of a charge density wave. On the new, disconnected parts of the Fermi surface
superconductivity is induced with a sign-changing order parameter. We discuss
these findings in the light of recent experiments on iron-based oxypnictide
superconductors.Comment: 13 pages, 2 figure
10271 Abstracts Collection -- Verification over discrete-continuous boundaries
From 4 July 2010 to 9 July 2010, the Dagstuhl Seminar 10271
``Verification over discrete-continuous boundaries\u27\u27
was held in Schloss Dagstuhl~--~Leibniz Center for Informatics.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general.
Links to extended abstracts or full papers are provided, if available
Excitonic resonances in the 2D extended Falicov-Kimball model
Using the projector-based renormalization method we investigate the formation
of the excitonic insulator phase in the two-dimensional (2D) spinless
Falicov-Kimball model with dispersive electrons and address the existence
of excitonic bound states at high temperatures on the semiconductor side of the
semimetal-semiconductor transition. To this end we calculate the imaginary part
of the dynamical electron-hole pair susceptibility and analyze the wave-vector
and energy dependence of excitonic resonances emerging in the band gap. We
thereby confirm the existence of the exciton insulator and its exciton
environment within a generic two-band lattice model with local Coulomb
attraction.Comment: 6 pages, 5 figures, final versio
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