In recent years, features have been identified by the engineering community as meaningful abstractions with which humans can reason about products and processes. From the designer's point of view, features are functional primitives, which serve as the basis for sufficient product representation, improving the quality of design and the link to life cycle activities, such as process planning and manufacturing. Up to now, virtually no commercial wire frame CAD system gives the user the possibility to design with features. All objects in a drawing are loose CAD entities (points, lines, arcs,…) that can not be recognised as features. Feature based CAD systems mostly offer the user a fixed feature catalogue to design with. In many cases this feature catalogue is too rigid (a fixed set of feature types with fixed parameters) and does not correspond to the features that are used in a company for other feature based applications (e.g. process planning, NC programming,…). This paper describes a method for defining and extracting user definable manufacturing feature information from several wire frame and feature based CAD systems. This method is applied in a software module that interfaces CAD systems and a feature based process planning system [18,19]. The development of this module, called the CAD Process Planning Interface (CAD PPI), was carried out in the framework of the Esprit project 6805 COMPLAN [22].
A number of 5-substituted pyrimidine deoxyribonucleoside (dThd or dCyd) derivatives have been evaluated for their effects on the incorporation of dThd and dCyd into the nucleotide pool and nucleic acids of murine leukemia L1210 cells. Several observations indicate that the dThd kinase and dCyd kinase activity of the cells and the differential affinities of these enzymes for the pyrimidine deoxyribonucleosides determine the incorporation of dThd and dCyd into the cells: (i) dThd and dCyd were not incorporated into mutant L1210 cells deficient in either dThd kinase or dCyd kinase activity; (ii) for a series of 5-substituted dThd and dCyd analogues a strong correlation was found between their inhibitory effects on the incorporation of dThd or dCyd into cell material and their Ki/Km for dThd kinase and dCyd kinase (r = 0.92 and 0.97, respectively); (iii) inhibitors of DNA synthesis (i.e. araC) and RNA synthesis (i.e. actinomycin D) suppressed the incorporation of dThd, most likely due to an inhibitory activity at the dThd kinase level (through the allosteric action of dTTP or slow regeneration of dThd kinase).
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