Correct and Efficient Antichain Algorithms for Refinement Checking

The notion of refinement plays an important role in software engineering. It is the basis of a stepwise development methodology in which the correctness of a system can be established by proving, or computing, that a system refines its specification. Wang et al. describe algorithms based on antichains for efficiently deciding trace refinement, stable failures refinement and failures-divergences refinement. We identify several issues pertaining to the soundness and performance in these algorithms and propose new, correct, antichain-based algorithms. Using a number of experiments we show that our algorithms outperform the original ones in terms of running time and memory usage. Furthermore, we show that additional run time improvements can be obtained by applying divergence-preserving branching bisimulation minimisation

A symmetric protocol to establish service level agreements

We present a symmetrical protocol to repeatedly negotiate a desired service level between two parties, where the service levels are taken from some totally ordered finite domain. The agreed service level is selected from levels dynamically proposed by both parties and parties can only decrease the desired service level during a negotiation. The correctness of the protocol is stated using modal formulas and its behaviour is explained using behavioural reductions of the external behaviour modulo weak trace equivalence and divergence-preserving branching bisimulation. Our protocol originates from an industrial use case and it turned out to be remarkably tricky to design correctly

Real Equation Systems with Alternating Fixed-points (full version with proofs)

We introduce the notion of a Real Equation System (RES), which lifts Boolean Equation Systems (BESs) to the domain of extended real numbers. Our RESs allow arbitrary nesting of least and greatest fixed-point operators. We show that each RES can be rewritten into an equivalent RES in normal form. These normal forms provide the basis for a complete procedure to solve RESs. This employs the elimination of the fixed-point variable at the left side of an equation from its right-hand side, combined with a technique often referred to as Gau{\ss}-elimination. We illustrate how this framework can be used to verify quantitative modal formulas with alternating fixed-point operators interpreted over probabilistic labelled transition systems.Comment: 25 pages. 2 Figures. 1 Table. This paper is published at Concur 2023, September 2023, Antwerp, Belgiu

Adherence in Rheumatoid Arthritis patients assessed with a validated Italian version of the 5-item compliance questionnaire for rheumatology

OBJECTIVES: The 5-item Compliance Questionnaire for Rheumatology (CQR5) proved reliability and validity in respect of identification of patients likely to be high adherers (HAs) to anti-rheumatic treatment, or low adherers (LAs), i.e. taking<80% of their medications correctly. The objective of the study was to validate an Italian version of CQR5 (I-CQR5) in rheumatoid arthritis (RA) patients and to investigate factors associated with high adherence. METHODS: RA patients, undergoing treatment with ≥1 self-administered conventional synthetic disease-modifying anti-rheumatic drug (csDMARD) or biological DMARD (bDMARD), were enrolled. The cross-cultural adaptation and validation of I-CQR5 followed standardised guidelines. I-CQR5 was completed by patients on one occasion. Data were subjected to factor analysis and Partial Credit model Parametrisation (PCM) to assess construct validity of I-CQR5. Analysis of factors associated with high adherence included demographic, social, clinical and treatment information. Factors achieving a p<0.10 in univariate analysis were included in multivariable analysis. RESULTS: Among 604 RA patients, 274 patients were included in the validation and 328 in the analysis of factors associated with adherence. Factor analysis and PCM confirmed the construct validity and consistency of I-CQR5. HAs were found to be 109 (35.2%) of the patients. bDMARD treatment and employment were found to be independently associated with high adherence: OR 2.88 (1.36-6.1), p=0.006 and OR 2.36 (1.21-4.62), p=0.012, respectively. CONCLUSIONS: Only one-third of RA patients were HAs according to I-CQR5. bDMARDs and employment status increased by almost 3-fold the likelihood of being highly adherent to the anti-rheumatic treatment.Peer reviewe

Linearization in parallel pCRL

We describe a linearization algorithm for parallel pCRL processes similar to the one implemented in the linearizer of the mcrl Toolset. This algorithm finds its roots in formal language theory: the `grammar' defining a process is transformed into a variant of Greibach Normal Form. Next, any such form is further reduced to emph{linear form, i.e., to an equation that resembles a right-linear, data-parametric grammar. We aim at proving the correctness of this linearization algorithm. To this end we define an equivalence relation on recursive specifications in mcrl that is model independent and does not involve an explicit notion of solution

Micro-ion Traps for Detection of (Pre)-Biotic Organic Compounds on Comets

Comets are currently believed to be a mixture of interstellar and nebular material. Many of the volatiles in comets are attributed to interstellar chemistry, because the same species of carbonaceous compounds are also observed in ices in interstellar molecular (ISM) clouds. Comets are thus likely to be a relatively pristine reservoir of primitive material and carbonaceous compounds in our solar system. They could be a major contributor to the delivery of prebiotic organic compounds, from which life emerged through impacts on early Earth. Mass spectrometers are very powerful tools to identify unknown chemicals, and much progress bas been made in miniaturizing mas spectrometers for space applications. Most miniatu rized mass spectrometers developed to date, however, are still relatively large, power hungry, complicated to assemble, and would have significant impact on space flight vehicle total payload and resource allocations

A strategy for the robust forecasting of gas turbine health subjected to fouling

Fouling represents a major problem for Gas Turbines (GTs) in both heavy-duty and aeropropulsion applications. Solid particles entering the engine can stick to the internal surfaces and form deposits. Components' lifetime and performance can dramatically vary as a consequence of this phenomenon. These effects impact the whole engine in terms of residual life, operating stability, and maintenance costs. In the High-Pressure Turbine (HPT), in particular, the high temperatures soft the particles and promote their adhesion, especially in the short term. Unfortunately, predicting the GT response to this detrimental issue is still an open problem for scientists. Furthermore, the stochastic variations of the components operating conditions increase the uncertainty of the forecasting results. In this work, a strategy to predict the effects of turbine fouling on the whole engine is proposed. A stationary Gas Path Analysis (GPA) has been performed for this scope to predict the GT health parameters. Their alteration as a consequence of fouling has been evaluated by scaling the turbine map. The scaling factor has been found by performing Computational Fluid Dynamic (CFD) simulations of a HPT nozzle with particle injection. Being its operating conditions strongly uncertain, a stochastic analysis has been conducted. The uncertainty sources considered are the circumferential hot core location and the turbulence level at the inlet. The study enables to build of confidence intervals on the GT health parameters predictions and represents a step forward towards a robust forecasting tool