The strength of evidence of the food inspection after the Chernobyl accident proven by whole body measurements of Basel students

The radioactive contamination of the food consumed by the inhabitants of Basel after the Chernobyl fallout has been continuously controlled by our laboratory. The activity of ingested Cs-137 has been estimated and is compared here with the activity obtained through whole body counts. The satisfactory correlation between calculated and observed body activities enables an exact estimation of the people's doses applying the same model and demonstrate the reliability of the food control analysis.     

Reliability improvement of electronic circuits based on physical failure mechanisms in components

Traditionally the position of reliability analysis in the design and production process of electronic circuits is a position of reliability verification. A completed design is checked on reliability aspects and either rejected or accepted for production. This paper describes a method to model physical failure mechanisms within components in such a way that they can be used for reliability optimization, not after, but during the early phase of the design process. Furthermore a prototype of a CAD software tool is described, which can highlight components likely to fail and automatically adjust circuit parameters to improve product reliability.     

Site-specific mutations in a loop region of the C-terminal domain of the large subunit of ribulose bisphosphate carboxylase/oxygenase that influence substrate partitioning

Amino acids composing a flexible loop (loop 6) of the eight-stranded barrel domain of the L-subunit of Synechococcus ribulose bisphosphate carboxylase/oxygenase (EC 4.1.1.39) involved in reaction intermediate stabilization have been modified by site-specific mutagenesis. Changes at positions both distant and within the active site affect overall catalysis and substrate partitioning. Most significantly, replacement of the active site Lys (Lys-334) with Arg at the apex of the loop almost completely suppressed the carboxylase activity of the enzyme relative to oxygenation, with only a modest reduction in overall catalysis. Val-331 and Thr-342, more distant from the active site but with interacting side chains, were changed to larger and smaller residues with differential effects on both turnover and substrate partitioning. Substitution of the loop with the sequence found in more efficient carboxylases only increased partitioning marginally when accompanied by alterations in the C-terminal tail of the L-subunit that interacts with the loop. Generally, modifications to the loop composition also affected enediol formation, the first step of catalysis, suggesting that the geometry and hence flexibility of this segment affect more than just stabilization of the intermediates immediately following reaction with CO2 or O2.     

A modelling method for the development of groupware applications as socio-technical systems

Special methodological approaches are needed, particularly in the area of modelling, to develop socio-technical systems in the field of CSCW. Engineering tasks and the development of organizational structures have to be integrated including elements of participatory design. From a theoretical background, needs for new modelling concepts can be derived: representation of contingency, explicit incompleteness, multiplicity of perspectives and self-referential meta-relations. Based on these concepts we developed the semi-structured, socio-technical modelling method SeeMe and used it in five empirical cases to assess its practical relevance. We found that SeeMe can help people to become aware of the specific features and requirements of 'their' socio-technical system and therefore enables them to take part in processes of learning and improvement.     

Control of the rat T cell response to retroviral and bacterial superantigens by class II MHC products and Tcrb-V8.2 alleles

The in vitro response of unprimed rat T cells to retroviral and bacterial superantigens (SAg) was analyzed with TCR V beta 8.2-, 8.5-, 10-, and 16-specific mAbs. Specific stimulation of V beta 8.2 and 8.5 CD4 cells was observed in the response to Mls1a, the retroviral SAg encoded by integrated provirus Mtv-7 (Mtv-7 SAg), which was presented by mouse B cells or mouse fibroblasts transfected with DR1 genes and the Mtv-7 SAg. Additionally, a strong response of V beta 16 CD4 cells to an as yet unidentified mouse SAg was found. Only some of the bacterial SAg known to stimulate mouse and human T cells also activated rat lymph node cells. SEA, SEE, and TSST-1 stimulated rat T cells well; SEB, SEC1, and SED did not. This defect was apparently a result of weak binding to rat MHC class II molecules because presentation by human MHC class II molecules restored T cell activation. Under these conditions, SEB stimulated V beta 8.2+ and 8.5+ CD4 and CD8 cells from Lewis rats. A comparison of several rat strains revealed an unresponsiveness to SEB or Mtv-7 SAg for V beta 8.2 cells from F344 and DA rats. Determination of the nucleotide sequences of the Tcrb-V8.2 of these strains revealed differences between SAg-responsive and SAg-unresponsive Tcrb-V8.2 in seven amino acids, four of them located in the putative SAg contact site. The significance of these findings for the evolution of TCR-SAg interactions is discussed.