Andries J. Krüger

The influence of acculturation on endocrine reactivity during acute stress in urban black males

Urbanization is a world-wide phenomenon and results in a radical and sometimes total change in living conditions. This process is accompanied by a significant increase in the incidence of western-type diseases virtually unknown in traditional rural communities. Especially in a multicultural society like South Africa, rural people moving to the city will experience cultural shock leading in many cases to a large degree of acculturation. In this study the effect of acculturation on endocrine reactivity was studied in a population of Tswanas. It was found that significant differences in endocrine reactivity exist not only between rural Tswanas and urban whites but in some instances also between rural Tswanas and urban Tswanas. During the cold pressor test, the testosterone reactivity and to a lesser extent the prolactin reactivity of the urban Tswanas tended to approach that of the white group as a function of their level of acculturation. All the Tswana groups had a significantly higher plasma renin activity during acute stress than the whites, which could have a bearing on the tendency of urban blacks to develop hypertension.

Effect of relative humidity and temperature on the mechanical properties of PFSA Nafion™-cation-exchanged membranes for electrochemical applications

Perfluorosulfonic acid (PFSA) polymer membranes, also known as PEM (proton-exchange membranes), such as NafionTM are widely used as electrolyte thin films in electrochemical hydrogen energy systems such as fuel cells, electrolysers and electrochemical hydrogen compressors. In the present work the effect of temperature and relative humidity on the elastic moduli of various PEMs were investigated through uniaxial and biaxial tensile testing. Results of the two techniques were analysed and compared to one another to determine the validity of bulge testing in the investigation of the mechanical properties of PEMs. The bulge test technique was applied to assess the effect of elevated temperatures, humidity levels and cation contamination on the rupture pressure of the membranes. The effects of cation exchange and water absorption on the mechanical strength of PEMs are discussed in terms of cation water interactions within the molecular structure of PFSA polymers.