Motionless mixers for the design of multitubular polymerization reactors

Experimental investigations of thermal bulk polymerization of styrene in pilot plants of different sizes have been performed. Each pilot plant is composed of a tubular recycle reactor, connected in series with a tubular reactor, both completely filled with Sulzer motionless mixers. Kinetic, reactor and viscosity models have been verified in a wide range of styrene conversions (up to 96%) temperatures (up to 210 °C) and polystyrene molar masses (up to 360 000). Scale-up studies were carried out which confirmed that multitubular reactors of special design can be applied for industrial polymerization process.     

Don't underestimate the problems of user centredness in software development projectsthere are many!

. On the basis of a longitudinal field study of 29 commercial software development projects, the pros and cons of user centredness in software development were analysed. We looked at two concepts: user participation-an organizational device-involving a user representative in the team, and user orientation-a cognitive-emotional concept-which pertains to positive attitudes towards users. Both were found to be associated with project difficulties relating to process and product quality as well as overall project success. We suggest that the issue is no longer whether or not to involve users, but instead to develop a realistic understanding of the difficulties associated with user centredness.     

A FORTRAN decoder and evaluator for use at operation time

Except for normative components, the calculation of which is sufficiently involved to require a separate subroutine, the compositional “derived variables” of chemical petrology may be cast readily in the form of simple arithmetic expressions. With regard to the design of petrographic data bases and their associated information systems, the practical question is whether these should be processed by the base builder, so that the values of each derived variable are incorporated in the base, by an ad hoc subroutine linked to the information system prior to each retrieval or reduction, or by permanent elements of the information system. The third option requires intrinsic capability for decoding and evaluating expressions received as character strings at operation time. Subroutines DKDXPR and EVLXPR provide that capability. Calling program IMDEVL provides a convenient conversational device for testing DKDXPR and EVLXPR.     

Highly conserved charge-pair networks in the mitochondrial carrier family

Selection for regain-of-function mutations in the yeast ADP/ATP carrier AAC2 has revealed an unexpected series of charge-pairs. Four of the six amino acids involved are found in the mitochondrial energy transfer motifs used to define this family of proteins. As such, the results found with the ADP/ATP carrier may apply to the family as a whole. Mitochondrial carriers are built from three homologous domains, each with the conserved motif PX(D,E)XX(K,R). Neutralization of the conserved positive charges at K48, R152 or R252 in these motifs results in respiration defective yeast. Neutralization of the negative charges at D149 and D249 also make respiration defective yeast, though E45G or E45Q mutants are able to grow on glycerol. Regain of function occurs when a complementary charge is lost from another site in the molecule. This phenomenon has been observed independently eight times and thus is strong evidence for charge-pairs existing between the affected residues. Five different charge-pairs have been detected in the yeast AAC2 by this method and three more can be predicted based on homology between the domains. The highly conserved charge-pairs occurring within or between the three mitochondrial energy transfer signatures seem to be a critical feature of mitochondrial carrier structure, independent of the substrates transported. Conformational switching between alternative charge-pairs may constitute part of the basis for transport.