Time-triggered runtime verification

The goal of runtime verification is to monitor the behavior of a system to check its conformance to a set of desirable logical properties. The literature of runtime verification mostly focuses on event-triggered solutions, where a monitor is invoked when an event of interest occurs (e.g., change in the value of some variable). At invocation, the monitor evaluates the set of properties of the system that are affected by the occurrence of the event. This constant invocation introduces two major defects to the system under scrutiny at run time: (1) significant overhead, and (2) unpredictability of behavior. These defects are serious obstacles when applying runtime verification on safety-critical systems that are time-sensitive by nature. To circumvent the aforementioned defects in runtime verification, in this article, we introduce a novel time-triggered approach, where the monitor takes samples from the system with a constant frequency, in order to analyze the system’s health. We describe the formal semantics of time-triggered monitoring and discuss how to optimize the sampling period using minimum auxiliary memory. We show that such optimization is NP-complete and consequently introduce a mapping to Integer Linear Programming. Experiments on a real-time benchmark suite show that our approach introduces bounded overhead and effectively reduces the involvement of the monitor at run time by using negligible auxiliary memory. We also show that in some cases it is even possible to reduce the overall overhead of runtime verification by using our time-triggered approach when the structure of the system allows choosing a long enough sampling period.     

Interface-induced negative differential resistance and memristive behavior in Gr/MoSe2 heterostructure

Journal of Materials Science: Materials in Electronics - Heterostructures of materials can possess the prominent characteristics of their individual layers or gain newly emerged interface effects...     

Optimisation of the properties of siloxane coatings as anti-biofouling coatings: Comparison of PACVD and hybrid PACVD-PVD coatings

Plasma-assisted chemical vapour deposition (PACVD) siloxane coatings from a mixture of hexamethyldisiloxane (HMDSO) and O₂, and hybrid coatings deposited by simultaneous sputtering of silicon and plasma polymerisation of HMDSO + O₂ were prepared on glass and steel substrates. The effect of the addition of sputtered silicon was investigated for coatings with different HMDSO/O₂ ratios. The microstructure and composition of coatings were affected by the coating parameters used. Silicon content was roughly the same for all coatings; carbon content decreased while oxygen content and surface energy increased with decreasing HMDSO/O₂ ratio in hybrid coatings. Hardness and modulus were higher for hybrid coatings and increased with decreasing HMDSO/O₂ ratio. Hybrid coatings showed much better scratch and wear resistance than PACVD coatings. All coatings showed good fouling-release performance with the freshwater bacterium Pseudomonas fluorescens.     

Comparison of the curing kinetics of a DGEBA/acid anhydride epoxy resin system using differential scanning calorimetry and a microwave‐heated calorimeter

The cure of an epoxy resin system, based upon a diglycidyl ether of bisphenol‐A (DGEBA) with HY917 (an acid anhydride hardener) and DY073 (an amine–phenol complex that acted as an accelerator), was investigated using a conventional differential scanning calorimeter and a microwave‐heated power‐compensated calorimeter. Dynamic cure of the epoxy resin using four different heating rates and isothermal cure using four different temperatures were carried out and the degree of cure and reaction rates were compared. The cure kinetics were analyzed using several kinetics models. The results showed different activation energies for conventional and microwave curing and suggested different reaction mechanisms were responsible for curing using the two heating methods. Resins cured using conventional heating showed higher glass transition temperatures than did those cured using microwave heating. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2054–2063, 2007     

Comparison of the curing kinetics of the RTM6 epoxy resin system using differential scanning calorimetry and a microwave‐heated calorimeter

The cure of a commercial epoxy resin system, RTM6, was investigated using a conventional differential scanning calorimeter and a microwave‐heated calorimeter. Two curing methods, dynamic and isothermal, were carried out and the degree of cure and the reaction rates were compared. Several kinetics models ranging from a simple nth order model to more complicated models comprising nth order and autocatalytic kinetics models were used to describe the curing processes. The results showed that the resin cured isothermally showed similar cure times and final degree of cure using both conventional and microwave heating methods, suggesting similar curing mechanisms using both heating methods. The dynamic curing data were, however, different using two heating methods, possibly suggesting different curing mechanisms. Near‐infrared spectroscopy showed that in the dynamic curing of RTM6 using microwave heating, the epoxy‐amine reaction proceeded more rapidly than did the epoxy‐hydroxyl reaction. This was not the case during conventional curing of this resin. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3658–3668, 2006     

Polymer encapsulation of surface-modified carbon blacks using surfactant-free emulsion polymerisation

Polymer encapsulations of two different grades of water-dispersible, surface-sulfonated carbon black, Sterling-4620 with an aggregate size of 260 nm and Black Pearls-800 (BP-800) with an aggregate size of 45.7 nm, were carried out using surfactant-free emulsion polymerisation of butyl acrylate, methyl methacrylate and allyl methacrylate. High levels of initiator were required because carbon black acts as an efficient radical trap. Although polymerisation in the presence of Sterling-4620 proceeded satisfactorily using ammonium persulfate (APS), the much larger specific surface area of BP-800 inhibited polymerisation with APS and the sodium salt of 4,4′-azobis(4-cyanopentanoic acid), a non-oxidising initiator, was necessary for effective polymerisation in the presence of BP-800. Several polymer-encapsulated Sterling-4620 and BP-800 products were prepared successfully using different amounts and compositions of polymer, and have been characterised using solvent extraction, pyrolysis, thermogravimetry, infrared spectroscopy, transmission electron microscopy, differential scanning calorimetry and dynamic mechanical thermal analysis.