Analysis of Non-Linear Probabilistic Hybrid Systems

This paper shows how to compute, for probabilistic hybrid systems, the clock approximation and linear phase-portrait approximation that have been proposed for non probabilistic processes by Henzinger et al. The techniques permit to define a rectangular probabilistic process from a non rectangular one, hence allowing the model-checking of any class of systems. Clock approximation, which applies under some restrictions, aims at replacing a non rectangular variable by a clock variable. Linear phase-approximation applies without restriction and yields an approximation that simulates the original process. The conditions that we need for probabilistic processes are the same as those for the classic case.Comment: In Proceedings QAPL 2011, arXiv:1107.074

Real-Reward Testing for Probabilistic Processes (Extended Abstract)

We introduce a notion of real-valued reward testing for probabilistic processes by extending the traditional nonnegative-reward testing with negative rewards. In this richer testing framework, the may and must preorders turn out to be inverses. We show that for convergent processes with finitely many states and transitions, but not in the presence of divergence, the real-reward must-testing preorder coincides with the nonnegative-reward must-testing preorder. To prove this coincidence we characterise the usual resolution-based testing in terms of the weak transitions of processes, without having to involve policies, adversaries, schedulers, resolutions, or similar structures that are external to the process under investigation. This requires establishing the continuity of our function for calculating testing outcomes.Comment: In Proceedings QAPL 2011, arXiv:1107.074

A Stochastic Broadcast Pi-Calculus

In this paper we propose a stochastic broadcast PI-calculus which can be used to model server-client based systems where synchronization is always governed by only one participant. Therefore, there is no need to determine the joint synchronization rates. We also take immediate transitions into account which is useful to model behaviors with no impact on the temporal properties of a system. Since immediate transitions may introduce non-determinism, we will show how these non-determinism can be resolved, and as result a valid CTMC will be obtained finally. Also some practical examples are given to show the application of this calculus.Comment: In Proceedings QAPL 2011, arXiv:1107.074

Synthesis of Heteroleptic Redox-active and Spin-crossover Complexes

The following research regarding heteroleptic redox-active complexes with the potential for spin-crossover is synthetic in nature. The intent behind incorporating the Schiff base ligand N-(8-quinolyl)salicylaldimine with some redox-active species into a mixed ligand complex featuring a d4-d7 metal ion center was to prime the material for spin-crossover based on strong intermolecular interactions that would enhance cooperativity of the system. Single component systems that display spin-crossover behaviour paired with other physical properties like electrical conductivity hold significance in the field of multifunctional materials, of which there are few examples that feature mixed ligand systems. Information describing this type of chemistry and the magnetic interactions that govern these characteristics is introduced in the first chapter of this work. The synthetic strategies toward mixed ligand complexes in the form of [(Qsal)Fe(RAL)]+X- and [(Qsal)Co(RAL)]+X- have been realized from the use of mononuclear [(Qsal)FeCl2(CH3OH)] and [(Qsal)Co(OAc)]+OAc- species, respectively. The redox-active ligand (RAL) component is an arylazo ligand like 10-(8-quinolylazo)-9-phenanthrol (Qapl) or 1-(2-Pyridylazo)-2-phenanthrol (Papl), which possess a low-lying π* MO that makes them susceptible to multi-step reductions that give rise to radical intermediates. Heteroleptic complexes that were synthesized and isolated like [(Qsal)Fe(Qapl)]+BPh4-, [(Cl-Qsal)Fe(Qapl)]+BPh4-- and homoleptic [Fe(Qapl)2]+BPh4- were diffracted and measured several intermolecular π-π contacts of distances typically between 3.5-3.7 Å, often between the phenanthrene rings of adjacent Qapl ligands. Complexes In the form of [(Qsal)Fe(Qapl)]+X (X= BPh4- or SCN-) showed early onset of spin transition in solution usually beyond 298 K. These complexes were overly reduced in the glovebox which resulted in their deterioration, presumably from the cleavage of the RAL azo bond. The framework developed for the heteroleptic Fe3+ coordination chemistry was applied to cobalt, with some amendments, and afforded several heterleoptic Co3+ complexes using Qsal with the arylazo ligands Qapl and Papl. The heteroleptic cobalt complexes presented here were found to be LS Co3+ which is diamagnetic. However, there is potential under inert atmosphere to produce Co2+ and possibly a phenoxyl radical species with redox-active valence tautomers

Two-Player Reachability-Price Games on Single-Clock Timed Automata

We study two player reachability-price games on single-clock timed automata. The problem is as follows: given a state of the automaton, determine whether the first player can guarantee reaching one of the designated goal locations. If a goal location can be reached then we also want to compute the optimum price of doing so. Our contribution is twofold. First, we develop a theory of cost functions, which provide a comprehensive methodology for the analysis of this problem. This theory allows us to establish our second contribution, an EXPTIME algorithm for computing the optimum reachability price, which improves the existing 3EXPTIME upper bound.Comment: In Proceedings QAPL 2011, arXiv:1107.074

Quantitative Aspects of Programming Languages and Systems (2011–12)

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Distances for Weighted Transition Systems: Games and Properties

We develop a general framework for reasoning about distances between transition systems with quantitative information. Taking as starting point an arbitrary distance on system traces, we show how this leads to natural definitions of a linear and a branching distance on states of such a transition system. We show that our framework generalizes and unifies a large variety of previously considered system distances, and we develop some general properties of our distances. We also show that if the trace distance admits a recursive characterization, then the corresponding branching distance can be obtained as a least fixed point to a similar recursive characterization. The central tool in our work is a theory of infinite path-building games with quantitative objectives.Comment: In Proceedings QAPL 2011, arXiv:1107.074

HYPE with stochastic events

The process algebra HYPE was recently proposed as a fine-grained modelling approach for capturing the behaviour of hybrid systems. In the original proposal, each flow or influence affecting a variable is modelled separately and the overall behaviour of the system then emerges as the composition of these flows. The discrete behaviour of the system is captured by instantaneous actions which might be urgent, taking effect as soon as some activation condition is satisfied, or non-urgent meaning that they can tolerate some (unknown) delay before happening. In this paper we refine the notion of non-urgent actions, to make such actions governed by a probability distribution. As a consequence of this we now give HYPE a semantics in terms of Transition-Driven Stochastic Hybrid Automata, which are a subset of a general class of stochastic processes termed Piecewise Deterministic Markov Processes.Comment: In Proceedings QAPL 2011, arXiv:1107.074