Counterexample Generation in Probabilistic Model Checking

Providing evidence for the refutation of a property is an essential, if not the most important, feature of model checking. This paper considers algorithms for counterexample generation for probabilistic CTL formulae in discrete-time Markov chains. Finding the strongest evidence (i.e., the most probable path) violating a (bounded) until-formula is shown to be reducible to a single-source (hop-constrained) shortest path problem. Counterexamples of smallest size that deviate most from the required probability bound can be obtained by applying (small amendments to) k-shortest (hop-constrained) paths algorithms. These results can be extended to Markov chains with rewards, to LTL model checking, and are useful for Markov decision processes. Experimental results show that typically the size of a counterexample is excessive. To obtain much more compact representations, we present a simple algorithm to generate (minimal) regular expressions that can act as counterexamples. The feasibility of our approach is illustrated by means of two communication protocols: leader election in an anonymous ring network and the Crowds protocol

Worsening renal function and outcome in heart failure patients with reduced and preserved ejection fraction and the impact of angiotensin receptor blocker treatment: data from the CHARM-study programme

Aims We investigated the association between worsening renal function (WRF) that occurs during renin–angiotensin–aldosterone system inhibition initation and outcome in heart failure (HF) patients with preserved ejection fraction (HFPEF) and compared this with HF patients with reduced ejection fraction (HFREF). Methods and results We examined changes in estimated glomerular filtration rate (GFR) and the relationship between WRF (defined as ≥26.5 µmol/L and ≥25% increase in serum creatinine from baseline to 6 weeks) and outcome, according to randomized treatment, in patients with HFREF (EF <45%; n = 1569) and HFPEF (EF ≥45%; n = 836) in the CHARM programme. The primary outcome was cardiovascular death or HF hospitalization. Estimated GFR decreased 9.0 ± 21 vs. 4.0 ± 21 mL/min/1.73 m2 with candesartan and placebo, respectively, and this was similar in HFREF and HFPEF. WRF developed more frequently with candesartan, 16% vs. 7%, P < 0.001, with similar findings in patients with HFREF and HFPEF. WRF was associated with a higher risk of the primary outcome: multivariable hazard ratio (HR) 1.26, 95% confidence interval 1.03–1.54, P = 0.022, in both treatment groups, and in both HFREF and HFPEF (P for interaction 0.98). In HFREF, WRF was mostly related to HF hospitalization, while in HFPEF, WRF seemed more associated with mortality. Conclusions GFR decreased more and WRF was more common with candesartan compared with placebo, and this was similar in HFREF and HFPEF. WRF was associated with worse outcomes in HFREF and HFPEF. Although no formal interaction was present, the association between candesartan treatment, WRF, and type of clinical outcome was slightly different between HFREF and HFPEF

Cylinder morphology of a stretched and twisted ribbon

A rich zoology of shapes emerges from a simple stretched and twisted elastic ribbon. Despite a lot of interest, all these shape are not understood, in particular the shape that prevails at large tension and twist and that emerges from a transverse instability of the helicoid. Here, we propose a simple description for this cylindrical shape. By comparing its energy to the energy of other configurations, we are able to determine its location on the phase diagram. The theoretical predictions are in good agreement with our experimental results

Indigenous peoples and the right to adequate food : A dissertation discussing the content of an Indigenous Rights-Based Approach to indigenous food security and nutritional health and some methodological challenges surging from such an approach

Det er store forskjeller i kronisk underernæring og spedbarnsdødelighet mellom barn av urfolk og andre barn på det amerikanske kontinentet. Både underernæring og kroniske ernæringsrelaterte sykdommer rammer urfolk spesielt hardt. Feltstudier fra Argentina og Canada viser at statlige utviklingstiltak og tiltak mot matusikkerhet faktisk kan bidra til å forverre urfolks ernæringssituasjon. Sentrale nasjonale fattigdomsindikatorer er dessuten dårlig tilpasset tradisjonelle urfolks levesett og kan egne seg dårlig til å kartlegge fattigdom i disse gruppene. Dette åpner opp for en menneskerettighetsbasert analyse. Gjennom ratifisering av konvensjoner har stater påtatt seg å respektere, beskytte og fremme retten til mat og helse for alle innbyggere. Stater skal også beskytte og legge til rette for urfolks tradisjonelle tilpassning til sitt miljø og ressursbruk. Dagens ernæringsproblemer hos urfolk er knyttet til tap av land og tradisjonelle matressurser og også inntektsfattigdom. Underliggende faktorer er diskriminering, utilfredstillende skole- og helsetjenester samt manglende forståelse for urfolks kultur og rettigheter. En rettighetsbasert tilnærming vil gjøre statens rolle tydeligere og skape rom for ansvarliggjøring av statlige aktører. Materialet til avhandlingen er hentet fra ulike skriftlige kilder og informasjon fremskaffet gjennom feltarbeid, herunder egne intervjuer med urfolksrepresentanter og myndighetspersoner i nordlige Argentina og i Nunavut i Canada. ’Retten til mat’ er nedfelt i den internasjonale konvensjonen om økonomiske, sosiale og kulturelle rettigheter som er ratifisert av de fleste stater inkludert Argentina og Canada. Retten til mat innebærer at alle har en rett til tilstrekkelige mengder av ernæringsmessig fullgod, kulturelt akseptabel og trygg mat. Et rammeverk for analyse av staters forpliktelse i forhold til retten til mat som tidligere er utviklet innenfor doktorandens forskningsmiljø, ble brukt til å strukturere analysen

How Geometry Controls the Tearing of Adhesive Thin Films on Curved Surfaces

Flaps can be detached from a thin film glued on a solid substrate by tearing and peeling. For flat substrates, it has been shown that these flaps spontaneously narrow and collapse in pointy triangular shapes. Here we show that various shapes, triangular, elliptic, acuminate or spatulate, can be observed for the tears by adjusting the curvature of the substrate. From combined experiments and theoretical models, we show that the flap morphology is governed by simple geometric rules.Comment: 6 pages, 5 figure