Influence of yield strength and toughness on friction and wear of polycarbonate

Polycarbonate was chosen as a model material to study the influence of yield strength and toughness on the tribological behaviour of the polymer. Yield stress and toughness of polycarbonate were varied by controlled physical ageing or by mechanical or thermal rejuvenation. The yield stress ranged from about 40 MPa for mechanically rejuvenated to 70 MPa for annealed polycarbonate. The area under the stress-strain curve is considered to be a measure for the toughness. The strain-to-break decreases with physical ageing, which results in a decrease of the toughness of the polymer. It was shown that yield strength and toughness did not affect friction and abrasive wear of polycarbonate under several different test conditions. These findings are compared with the usual views in literature upon friction and wear of polymers. There are strong indications that the polymer network of polycarbonate plays an important role in the wear resistance. However, no wear improvement was found with an increase in molecular weight in the range of polycarbonates studied

Statistical means to enhance the comparability of data within a pooled analysis of individual data in neurobehavioral toxicology

19reservedmixedMeyer-Baron M; Schäper M; Knapp G; Lucchini R; Albini E; Bast-Pettersen R; He S; Yuan H; Niu Q; Wang XL; Yang YJ; Iregren A; Sjögren B; Blond M; Laursen P; Netterstrom B; Mergler D; Bowler R; van Thriel CMeyer Baron, M; Schäper, M; Knapp, G; Lucchini, Roberto; Albini, Elisa; Bast Pettersen, R; He, S; Yuan, H; Niu, Q; Wang, Xl; Yang, Yj; Iregren, A; Sjögren, B; Blond, M; Laursen, P; Netterstrom, B; Mergler, D; Bowler, R; van Thriel, C

The neurobehavioral impact of manganese-Results and challenges obtained by a meta-analysis of individual participant data.

Results from a meta-analysis of aggregated data provoked a new analysis using individual data on the neuropsychological performance of occupationally exposed workers. Data from eight studies examining 579 exposed and 433 reference participants were included, 28 performance variables analyzed. The performance scores were adjusted for well-known individual-level covariates; possible, but unknown study-level covariates were attenuated by means of a z-normalization. Associations between performance and exposure were estimated by ANOVAs and ANCOVAs, the latter representing multi-level models. Four cognitive and motor performance variables each indicated significantly lower performances of exposed individuals when confounding was considered; slowed motor performances and deficits in attention and short-term memory were found. Performance on a single test was significantly related to the biomarker manganese in blood. The outcomes on susceptibility were weak. The slowing of responses was the most distinct feature of performances of exposed workers. It remains unclear, whether this result is related to the employed tests or provides important information about early stages of the neurotoxic impairment. More specific cognitive tests need to be employed to answer this question. The lack of dose-response relationships was related to features of the biomarker: it does not reflect the Mn in brain responsible for changes in performances