Conceptual structures for modeling in CIM

The International Standards Organization (ISO) will release in 1993 the first version of the STEP standard, which is dedicated to the exchange of product model data, and is seen as the basis of the next generation of enterprise information modeling tools. Almost in the same time frame ANSI will release the Information Resource Dictionary System(IRDS) Conceptual Schema standard, which recommends the conceptual graphs (CGs) or other representation languages based on logic to be used for enterprise information modeling and integration. In this paper we develop the foundations for the utilization of conceptual structures (CS) in combination with EXPRESS and STEP Application Protocols in the field of Computer Integrated Manufacturing (CIM). The most important result described here is a mapping of EXPRESS into CGs. Around it we develop the architecture of a system able to analyze and translate some of the semantics of information models. Our overall strategy consists of representing the semantics of the language, including the informal meanings represented in the EXPRESS manual in plain English, in a systematic way in CS, and then use this block of knowledge, that can be processed by a machine, for the increasingly automatic analysis, translation and integration of enterprise information models. The work here described is one of the components of a prototype of a model management system under development at IBM, Kingston NY, coordinated by the CIM Architecture group

Atmospheric breakdown chemistry of the new "green" solvent 2,2,5,5-tetramethyloxolane via gas-phase reactions with OH and Cl radicals

The atmospheric chemistry of 2,2,5,5-tetramethyloxolane (TMO), a promising "green"solvent replacement for toluene, was investigated in laboratory-based experiments and computational calculations. Results from both absolute and relative rate studies demonstrated that the reaction OH + TMO (Reaction R1) proceeds with a rate coefficient k1(296 K) = (3.1±0.4) ×10-12 cm3 molecule-1 s-1, a factor of 3 smaller than predicted by recent structure-activity relationships. Quantum chemical calculations (CBS-QB3 and G4) demonstrated that the reaction pathway via the lowest-energy transition state was characterised by a hydrogen-bonded pre-reaction complex, leading to thermodynamically less favoured products. Steric hindrance from the four methyl substituents in TMO prevents formation of such H-bonded complexes on the pathways to thermodynamically favoured products, a likely explanation for the anomalous slow rate of Reaction (R1). Further evidence for a complex mechanism was provided by k1(294-502 K), characterised by a local minimum at around T=340 K. An estimated atmospheric lifetime of τ1 ≈3 d was calculated for TMO, approximately 50 % longer than toluene, indicating that any air pollution impacts from TMO emission would be less localised. An estimated photochemical ozone creation potential (POCPE) of 18 was calculated for TMO in north-western Europe conditions, less than half the equivalent value for toluene. Relative rate experiments were used to determine a rate coefficient of k2(296 K) = (1.2±0.1) ×10-10 cm3 molecule-1 s-1 for Cl + TMO (Reaction R2); together with Reaction (R1), which is slow, this may indicate an additional contribution to TMO removal in regions impacted by high levels of atmospheric chlorine. All results from this work indicate that TMO is a less problematic volatile organic compound (VOC) than toluene