6,120 research outputs found
Construction and Verification of Performance and Reliability Models
Over the last two decades formal methods have been extended towards performance and reliability evaluation. This paper tries to provide a rather intuitive explanation of the basic concepts and features in this area.
Instead of striving for mathematical rigour, the intention is to give an illustrative introduction to the basics of stochastic models, to stochastic modelling using process algebra, and to model checking as a technique to analyse stochastic models
Dependability checking with StoCharts: Is train radio reliable enough for trains?
Performance, dependability and quality of service (QoS) are prime aspects of the UML modelling domain. To capture these aspects effectively in the design phase, we have recently proposed STOCHARTS, a conservative extension of UML statechart diagrams. In this paper, we apply the STOCHART formalism to a safety critical design problem. We model a part of the European Train Control System specification, focusing on the risks of wireless communication failures in future high-speed cross-European trains. Stochastic model checking with the model checker PROVER enables us to derive constraints under which the central quality requirements are satisfied by the STOCHART model. The paper illustrates the flexibility and maturity of STOCHARTS to model real problems in safety critical system design
Conformal field theory construction for nonabelian hierarchy wave functions
The fractional quantum Hall effect is the paradigmatic example of
topologically ordered phases. One of its most fascinating aspects is the large
variety of different topological orders that may be realized, in particular
nonabelian ones. Here we analyze a class of nonabelian fractional quantum Hall
model states which are generalizations of the abelian Haldane-Halperin
hierarchy. We derive their topological properties and show that the
quasiparticles obey nonabelian fusion rules of type su(q)_k. For a subset of
these states we are able to derive the conformal field theory description that
makes the topological properties - in particular braiding - of the state
manifest. The model states we study provide explicit wave functions for a large
variety of interesting topological orders, which may be relevant for certain
fractional quantum Hall states observed in the first excited Landau level.Comment: extended introduction, added reference
Renyi entropies for classical stringnet models
In quantum mechanics, stringnet condensed states - a family of prototypical
states exhibiting non-trivial topological order - can be classified via their
long-range entanglement properties, in particular topological corrections to
the prevalent area law of the entanglement entropy. Here we consider classical
analogs of such stringnet models whose partition function is given by an
equal-weight superposition of classical stringnet configurations. Our analysis
of the Shannon and Renyi entropies for a bipartition of a given system reveals
that the prevalent volume law for these classical entropies is augmented by
subleading topological corrections that are intimately linked to the anyonic
theories underlying the construction of the classical models. We determine the
universal values of these topological corrections for a number of underlying
anyonic theories including su(2)_k, su(N)_1, and su(N)_2 theories
Quantum spin liquid with a Majorana Fermi surface on the three-dimensional hyperoctagon lattice
Motivated by the recent synthesis of -LiIrO -- a spin-orbit
entangled Mott insulator with a three-dimensional lattice structure of
the Ir ions -- we consider generalizations of the Kitaev model believed
to capture some of the microscopic interactions between the Iridium moments on
various trivalent lattice structures in three spatial dimensions. Of particular
interest is the so-called hyperoctagon lattice -- the premedial lattice of the
hyperkagome lattice, for which the ground state is a gapless quantum spin
liquid where the gapless Majorana modes form an extended two-dimensional
Majorana Fermi surface. We demonstrate that this Majorana Fermi surface is
inherently protected by lattice symmetries and discuss possible instabilities.
We thus provide the first example of an analytically tractable microscopic
model of interacting SU(2) spin-1/2 degrees of freedom in three spatial
dimensions that harbors a spin liquid with a two-dimensional spinon Fermi
surface
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