Designing and verifying distributed cyber-physical systems using Multirate PALS: An airplane turning control system case study

Distributed cyber-physical systems (DCPS), such as aeronautics and ground transportation systems, are very hard to design and verify, because of asynchronous communication, network delays, and clock skews. Their model checking verification typically becomes unfeasible due to the huge state space explosion caused by the system's concurrency. The Multirate PALS ("physically asynchronous, logically synchronous") methodology has been proposed to reduce the design and verification of a DCPS to the much simpler task of designing and verifying its underlying synchronous version, where components may operate with different periods. This paper presents a methodology for formally modeling and verifying multirate DCPSs using Multirate PALS. In particular, this methodology explains how to deal with the system's physical environment in Multirate PALS. We illustrate our methodology with a multirate DCPS consisting of an airplane maneuvered by a pilot, who turns the airplane to a specified angle through a distributed control system. Our formal analysis using Real-Time Maude revealed that the original design did not achieve a smooth turning maneuver, and led to a redesign of the system. We then use model checking and Multirate PALS to prove that the redesigned system satisfies the desired correctness properties, whereas model checking the corresponding asynchronous model is unfeasible. This shows that Multirate PALS is not only effective for formal DCPS verification, but can also be used effectively in the DCPS design process. (C) 2014 Elsevier B.V. All rights reserved.111415sciescopu

Density Fitting and Cholesky Decomposition of the Two-Electron Integrals in Local Multireference Configuration Interaction Theory

To treat large molecules with accurate ab initio quantum chemistry, reduced scaling correlated wave function methods are now commonly employed. Optimization of these wave functions in practice requires some approximation of the two-electron integrals. Both Cholesky decomposition (CD) and density fitting (DF) are widely used approaches to approximate these integrals. Here, we compare CD and DF for use in local multireference singles and doubles configuration interaction (LMRSDCI). DF-LMRSDCI provides less accurate total energies than CD-LMRSDCI, but both methods are accurate for energy differences. However, DF-LMRSDCI is significantly less computationally expensive than CD-LMRSDCI on the molecules tested, suggesting that DF-LMRSDCI is an efficient, often sufficiently accurate alternative to our previously reported CD-LMRSDCI method

Ab Initio Reaction Kinetics of Hydrogen Abstraction from Methyl Formate by Hydrogen, Methyl, Oxygen, Hydroxyl, and Hydroperoxy Radicals

Combustion of renewable biofuels, including energydense biodiesel, is expected to contribute significantly toward meeting future energy demands in the transportation sector. Elucidating detailed reaction mechanisms will be crucial to understanding biodiesel combustion, and hydrogen abstraction reactions are expected to dominate biodiesel combustion during ignition. In this work, we investigate hydrogen abstraction by the radicals H·, CH 3·, O·, HO 2·, and OH· from methyl formate, the simplest surrogate for complex biodiesels. We evaluate the H abstraction barrier heights and reaction enthalpies, using multireference correlated wave function methods including size-extensivity corrections and extrapolation to the complete basis set limit. The barrier heights predicted for abstraction by H·, CH 3·, and O· are in excellent agreement with derived experimental values, with errors ≤1 kcal/mol. We also predict the reaction energetics for forming reactant complexes, transition states, and product complexes for reactions involving HO 2· and OH·. High-pressure-limit rate constants are computed using transition state theory within the separable-hindered-rotor approximation for torsions and the harmonic oscillator approximation for other vibrational modes. The predicted rate constants differ significantly from those appearing in the latest combustion kinetics models of these reactions. © 2012 American Chemical Society

Multireference Approaches for Excited States of Molecules

International audienceObtaining an understanding of the properties of electronically excited states is a challenging task that becomes increasingly important for numerous applications in Chemistry, Molecular Physics, Molecular Biology, and Materials Science. A substantial impact is exerted by the fascinating progress in time-resolved spectroscopy, which leads to a strongly growing demand for theoretical methods to describe the characteristic features of excited states accurately. Whereas for electronic ground state problems of stable molecules the quantum chemical methodology is now so well developed that informed non-experts can use it efficiently, the situation is entirely different concerning the investigation of excited states. This review is devoted to a specific class of approaches, usually denoted as multireference (MR) methods, the generality of which is needed for solving many spectroscopic or photodynamical problems. However, the understanding and proper application of these MR methods is often found to be difficult due to their complexity and their computational cost. The purpose of this review is to provide an overview of the most important facts about the different theoretical approaches available and to present by means of a collection of characteristic examples useful information, which can guide the reader in performing their own applications