Petri nets have been extensively used in the modelling and analysis of concurrent and distributed systems. The verification and validation of Petri nets are of particular importance in the development of concurrent and distributed systems. As a complement to formal analysis techniques, testing has been proven to be effective in detecting system errors and is easy to apply. An open problem is how to test Petri nets systematically, effectively and efficiently. An approach to solve this problem is to develop test criteria so that test adequacy can be measured objectively and test cases can be generated efficiently, even automatically. In this paper, we present a methodology of testing high-level Petri nets based on our general theory of testing concurrent software systems. Four types of testing strategies are investigated, which include state-oriented testing, transition-oriented testing, flow-oriented testing and specification-oriented testing. For each strategy, a set of schemes to observe and record testing results and a set of coverage criteria to measure test adequacy are defined. The subsumption relationships and extraction relationships among the proposed testing methods are systematically investigated and formally proved.

Flexible devices have been attracting great attention recently due to their numerous advantages. But the energy densities of current energy sources are still not high enough to support flexible devices for a satisfactory length of time. Although proton exchange membrane fuel cells (PEMFCs) do have a high-energy density, traditional PEMFCs are usually too heavy, rigid, and bulky to be used in flexible devices. In this research, we successfully invented a light and flexible air-breathing PEMFC by using a new design of PEMFC and a flexible composite electrode. The flexible air-breathing PEMFC with 1 × 1 cm working area can be as light as 0.065 g and as thin as 0.22 mm. This new PEMFC exhibits an amazing specific volume power density as high as 5190 W L, which is much higher than traditional (air-breathing) PEMFCs. Also outstanding is that the flexible PEMFC retains 89.1% of its original performance after being bent 600 times, and it retains its original performance after being dropped five times from a height of 30 m. Moreover, the research has demonstrated that when stacked, the flexible PEMFCs are also useful in mobile applications such as mobile phones. Therefore, our research shows that PEMFCs can be made light, flexible, and suitable for applications in flexible devices. These innovative flexible PEMFCs may also notably advance the progress in the PEMFC field, because flexible PEMFCs can achieve high specific power density with small size, small volume, low weight, and much lower cost; they are also much easier to mass produce.

Thermoreversible supramolecular polymer gels were prepared via metal−ligand coordination by mixing a poly(4-vinylpyridine)-b-poly(ethyl acrylate)-b-poly(4-vinylpyridine) (P4VP−PEA− P4VP) triblock copolymer and zinc chloride (ZnCl 2 ) in a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imidide. FT-IR spectroscopy revealed metal−ligand coordination between zinc in ZnCl 2 and pyridine groups as ligands on P4VP blocks, even in an ionic liquid. Thermoreversible viscoelastic properties between a semisolid (gel-like) state and a liquid-like state were confirmed by temperature-ramp oscillatory shear measurements. It was also revealed that thermoreversibility of supramolecular polymer gels depended strongly on stoichiometry between ligands and metals, where the maximum of storage modulus-loss modulus crossover temperature (T gel ) as an indicator of gelation was achieved when a molar amount of available coordination sites was a certain excessive amount (coordination site/ ligand ratio ∼1.6). The molar ratio at the maximum T gel is nearly independent of the number of ligands per triblock copolymer. On the other hand, the number of ligands per triblock copolymer affected the T gel , where a larger number of ligands per triblock copolymer gave a higher T gel , regardless of almost the same molecular weight of triblock copolymers.

No abstract

No abstract

Extended light absorption and dynamic charge separation are vital factors that determine the effectiveness of photocatalysts. In this study, a nonmetallic plasmonic S-scheme photocatalyst was fabricated by loading 1D plasmonic W18O49 nanowires onto 2D g-C3N4 nanosheets. W18O49 nanowires play the dual role of a light absorption antenna-that extends light adsorption-and a hot electron donor-that assists the water reduction reaction in a wider light spectrum range. Moreover, S-scheme charge transfer resulting from the matching bandgaps of W18O49 and g-C3N4 can lead to strong redox capability and high migration speed of the photoinduced charges. Consequently, in this study, W18O49/g-C3N4 hybrids exhibited higher photocatalytic H2 generation than that of pristine g-C3N4 under light irradiation of 420-550 nm. Furthermore, the H2 production rate of the best-performing W18O49/g-C3N4 hybrid was 41.5 μmol•g −1 •h −1 upon exposure to monochromatic light at 550 nm, whereas pure g-C3N4 showed negligible activity. This study promotes novel and environmentally friendly hot-electron-assisted S-scheme photocatalysts for the broad-spectrum utilization of solar light.

No abstract

No abstract