Length-scale dependent deformation behavior of nanolayered Cu-based micropillars

By using microcompression methodology, deformation of nanolayered crystal/crystal (C/C) Cu/Zr and Cu/ Cr, and crystal/amorphous (C/A) Cu/CuZr micropillars was systematically investigated within wide ranges of intrinsic layer thickness (5 – 150 nm) and extrinsic sample diameter (300 – 1500 nm). The intrinsic size effect, extrinsic size effect and their interplay were respectively revealed. Competition between the intrinsic and extrinsic size effects leads to a common experimental observation of a critical layer thickness of about 20 nm, above which the deformation is predominantly intrinsic-size-related and insensitive to sample size, while below which the two size effects are comparable. The underlying deformation mechanisms are proposed to transform from bulk-like to small-volume materials behavior. Deformation mode is correspondingly transited from homogeneous extrusion/barreling to inhomogeneous shear banding, and the two competing modes coexist in the layer thickness range from about 50 to 20 nm. Besides these generalities, specific deformation features of the C/C and C/A micropillars are respectively discussed. In particular, deformation-induced devitrification in the amorphous layers promotes an extraordinary plasticity in the C/A micropillars, which provides a viable route to enhance the controllability of plastic deformation in metallic glassy composites. A deformation mode map is further developed to clearly elucidate the coupling intrinsic and extrinsic size effects on the deformation mode of nanolayered micropillars

Complexity of the soundness problem of bounded workflow nets

Classical workflow nets (WF-nets) are an important class of Petri nets that are widely used to model and analyze workflow systems. Soundness is a crucial property that guarantees these systems are deadlock-free and bounded. Aalst et al. proved that the soundness problem is decidable, and proposed (but not proved) that the soundness problem is EXPSPACE-hard. In this paper, we show that the satisfiability problem of Boolean expression is polynomial time reducible to the liveness problem of bounded WF-nets, and soundness and liveness are equivalent for bounded WF-nets. As a result, the soundness problem of bounded WF-nets is co-NP-hard. Workflow nets with reset arcs (reWF-nets) are an extension to WF-nets, which enhance the expressiveness of WF-nets. Aalst et al. proved that the soundness problem of reWF-nets is undecidable. In this paper, we show that for bounded reWF-nets, the soundness problem is decidable and equivalent to the liveness problem. Furthermore, a bounded reWF-net can be constructed in polynomial time for every linear bounded automaton (LBA) with an input string, and we prove that the LBA accepts the input string if and only if the constructed reWF-net is live. As a result, the soundness problem of bounded reWF-nets is PSPACE-hard.No Full Tex

A formal framework for modeling and validating Simulink diagrams

10.1007/s00165-009-0108-9Formal Aspects of Computing215451-483FACM

Complexity of the soundness problem of workflow nets

Classical workflow nets (WF-nets for short) are an important subclass of Petri nets that are widely used to model and analyze workflow systems. Soundness is a crucial property of workflow systems and guarantees that these systems are deadlock-free and bounded. Aalst et al. proved that the soundness problem is decidable for WF-nets and can be polynomially solvable for free-choice WF-nets. This paper proves that the soundness problem is PSPACE-hard for WF-nets. Furthermore, it is proven that the soundness problem is PSPACE-complete for bounded WF-nets. Based on the above conclusion, it is derived that the soundness problem is also PSPACE-complete for bounded WF-nets with reset or inhibitor arcs (ReWF-nets and InWF-nets for short, resp.). ReWF- and InWF-nets are two extensions to WF-nets and their soundness problems were proven by Aalst et al. to be undecidable. Additionally, we prove that the soundness problem is co-NP-hard for asymmetric-choice WF-nets that are a larger class and can model more cases of interaction and resource allocation than free-choice ones.No Full Tex

Specifying and verifying sensor networks: An experiment of formal methods

10.1007/978-3-540-88194-0-20Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)5256 LNCS318-33