Synchronous Closing and Flow Analysis for Model Checking Timed Systems

Abstract. Formal methods, in particular model checking, are increas-ingly accepted as integral part of system development. With large soft-ware systems beyond the range of fully automatic verification, however, a combination of decomposition and abstraction techniques is needed. To model check components of a system, a standard approach is to close the component with an abstraction of its environment, as standard model checkers often do not handle open reactive systems directly. To make it useful in practice, the closing of the component should be automatic, both for data and for control abstraction. Specifically for model checking asynchronous open systems, external input queues should be removed, as they are a potential source of a combinatorial state explosion. In this paper we investigate a class of environmental processes for which the asynchronous communication scheme can safely be replaced by a synchronous one. Such a replacement is possible only if the environment is constructed under rather a severe restriction on the behavior, which can be partially softened via the use of a discrete-time semantics. We employ data-flow analysis to detect instances of variables and timers influenced by the data passing between the system and the environment

The Science Performance of JWST as Characterized in Commissioning

This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies