139 research outputs found
Limit Synchronization in Markov Decision Processes
Markov decision processes (MDP) are finite-state systems with both strategic
and probabilistic choices. After fixing a strategy, an MDP produces a sequence
of probability distributions over states. The sequence is eventually
synchronizing if the probability mass accumulates in a single state, possibly
in the limit. Precisely, for 0 <= p <= 1 the sequence is p-synchronizing if a
probability distribution in the sequence assigns probability at least p to some
state, and we distinguish three synchronization modes: (i) sure winning if
there exists a strategy that produces a 1-synchronizing sequence; (ii)
almost-sure winning if there exists a strategy that produces a sequence that
is, for all epsilon > 0, a (1-epsilon)-synchronizing sequence; (iii) limit-sure
winning if for all epsilon > 0, there exists a strategy that produces a
(1-epsilon)-synchronizing sequence.
We consider the problem of deciding whether an MDP is sure, almost-sure,
limit-sure winning, and we establish the decidability and optimal complexity
for all modes, as well as the memory requirements for winning strategies. Our
main contributions are as follows: (a) for each winning modes we present
characterizations that give a PSPACE complexity for the decision problems, and
we establish matching PSPACE lower bounds; (b) we show that for sure winning
strategies, exponential memory is sufficient and may be necessary, and that in
general infinite memory is necessary for almost-sure winning, and unbounded
memory is necessary for limit-sure winning; (c) along with our results, we
establish new complexity results for alternating finite automata over a
one-letter alphabet
CCS with Hennessy's merge has no finite-equational axiomatization
Abstract
This paper confirms a conjecture of Bergstra and Klop¿s from 1984 by establishing that the process algebra obtained by adding an auxiliary operator proposed by Hennessy in 1981 to the recursion free fragment of Milner¿s Calculus of Communicationg Systems is not finitely based modulo bisimulation equivalence. Thus Hennessy¿s merge cannot replace the left merge and communication merge operators proposed by Bergstra and Klop, at least if a finite axiomatization of parallel composition is desired.
2000 MATHEMATICS SUBJECT CLASSIFICATION: 08A70, 03B45, 03C05, 68Q10, 68Q45, 68Q55, 68Q70.
CR SUBJECT CLASSIFICATION (1991): D.3.1, F.1.1, F.1.2, F.3.2, F.3.4, F.4.1.
KEYWORDS AND PHRASES: Concurrency, process algebra, CCS, bisimulation, Hennessy¿s merge, left merge, communication merge, parallel composition, equational logic, complete axiomatizations, non-finitely based algebras
Geometry-dependent electrostatics near contact lines
Long-ranged electrostatic interactions in electrolytes modify their contact
angles on charged substrates in a scale and geometry dependent manner. For
angles measured at scales smaller than the typical Debye screening length, the
wetting geometry near the contact line must be explicitly considered. Using
variational and asymptotic methods, we derive new transcendental equations for
the contact angle that depend on the electrostatic potential only at the three
phase contact line. Analytic expressions are found in certain limits and
compared with predictions for contact angles measured with lower resolution. An
estimate for electrostatic contributions to {\it line} tension is also given.Comment: 3 .eps figures, 5p
Hennessy-Milner Logic with Greatest Fixed Points as a Complete Behavioural Specification Theory
There are two fundamentally different approaches to specifying and verifying
properties of systems. The logical approach makes use of specifications given
as formulae of temporal or modal logics and relies on efficient model checking
algorithms; the behavioural approach exploits various equivalence or refinement
checking methods, provided the specifications are given in the same formalism
as implementations.
In this paper we provide translations between the logical formalism of
Hennessy-Milner logic with greatest fixed points and the behavioural formalism
of disjunctive modal transition systems. We also introduce a new operation of
quotient for the above equivalent formalisms, which is adjoint to structural
composition and allows synthesis of missing specifications from partial
implementations. This is a substantial generalisation of the quotient for
deterministic modal transition systems defined in earlier papers
Assurance of Distributed Algorithms and Systems: Runtime Checking of Safety and Liveness
This paper presents a general framework and methods for complete programming
and checking of distributed algorithms at a high-level, as in pseudocode
languages, but precisely specified and directly executable, as in formal
specification languages and practical programming languages, respectively. The
checking framework, as well as the writing of distributed algorithms and
specification of their safety and liveness properties, use DistAlgo, a
high-level language for distributed algorithms. We give a complete executable
specification of the checking framework, with a complete example algorithm and
example safety and liveness properties.Comment: Small fixes to improve property specifications, including
improvements not in the RV 2020 final versio
Multicore liquid perfluorocarbon-loaded multimodal nanoparticles for stable ultrasound and <sup>19</sup> F MRI applied to in vivo cell tracking
Ultrasound is the most commonly used clinical imaging modality. However, in applications requiring cell-labeling, the large size and short active lifetime of ultrasound contrast agents limit their longitudinal use. Here, 100 nm radius, clinically applicable, polymeric nanoparticles containing a liquid perfluorocarbon, which enhance ultrasound contrast during repeated ultrasound imaging over the course of at least 48 h, are described. The perfluorocarbon enables monitoring the nanoparticles with quantitative 19 F magnetic resonance imaging, making these particles effective multimodal imaging agents. Unlike typical core–shell perfluorocarbon-based ultrasound contrast agents, these nanoparticles have an atypical fractal internal structure. The nonvaporizing highly hydrophobic perfluorocarbon forms multiple cores within the polymeric matrix and is, surprisingly, hydrated with water, as determined from small-angle neutron scattering and nuclear magnetic resonance spectroscopy. Finally, the nanoparticles are used to image therapeutic dendritic cells with ultrasound in vivo, as well as with 19 F MRI and fluorescence imaging, demonstrating their potential for long-term in vivo multimodal imaging. </p
Reversibility in Chemical Reactions
open access bookIn this chapter we give an overview of techniques for the
modelling and reasoning about reversibility of systems, including outof-
causal-order reversibility, as it appears in chemical reactions. We consider
the autoprotolysis of water reaction, and model it with the Calculus
of Covalent Bonding, the Bonding Calculus, and Reversing Petri Nets.
This exercise demonstrates that the formalisms, developed for expressing
advanced forms of reversibility, are able to model autoprotolysis of
water very accurately. Characteristics and expressiveness of the three
formalisms are discussed and illustrated
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