1. Car, wheel position, driver, inflation pressure, and shoulder drop have a statistically significant effect upon wear loss and need to bo taken into consideration before material factors affecting wear can be studied. 2. Variations in macrostructure of the polymers are not found to have a significant effect on wear as compared to microstructure variations. 3. At least two material factors control wear loss of tire treads. 4. When polymers are tested near their glass transition temperature (within 80° C), wear loss is dominated by viscoelastic properties. Viscoelastic properties can be related to wear loss through Tg or the combined effect of the cis, trans, vinyl, and styrene content. 5. At higher test temperatures (over 100° C above Tg) wear loss is dominated by a material factor that has a positive correlation with temperature. This is particularly noticeable when treads are worn under mild conditions. However, there is evidence that this wear factor is present at the testing nearer to Tg but is masked by the dominant viscoelastic effect. 6. The combined effect upon wear of the different material factors leads to an optimum wear resistance for any polymer in the butadiene—styrene system in the range of 75°–105° C above the Tg for that polymer. 7. For polymers tested at the same ambient temperature, (T), the effect of viscoelastic properties decreases non-linearly as T−Tg increases. 8. In the range of test severity studied, severity has little effect upon the inter-relationship of material factors. 9. In the range of test temperature where Tg dominates wear loss, skid distance on wet asphalt pavement is inversely related to wear rating.

Due to their influence on traffic safety, skid resistance and drainage are important surface properties of a road and their optimization and durability is still focus of ongoing research. Under wet conditions, these two characteristics are connected as a wetted road cannot provide a sufficient skid resistance without a working drainage system. The wet friction is mainly affected by the road surface geometry and the water depth. Herein, we describe a novel numerical approach to study the influence of the surface texture – mainly the microtexture – on the wet friction coefficient. This method is based on the hysteresis effect, which is the main friction force on rough surfaces under wet conditions. We therefore use an already established friction model for dry surfaces and extend its range of application by an additional consideration of water films. A drainage model has been developed to calculate the water film thickness for a given road surface and geometry (pavement surface runoff model) as systematic measurements of water film thicknesses in situ are difficult. The water depth determines the number of contact points between the pavement and the tyre. Based on three-dimensional measurements of a surface texture, the friction coefficient is calculated. By this newly developed model approach, it is possible to identify the main factors influencing wet skid resistance in regard to the pavement surface microtexture and the water film thickness.

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We present infrared absorption measurements on the neutral charge state of the doubleacceptor zinc in silicon. An effective-mass-like Py2 spectrum for the excitation of the secondarily bound hole is found. The ground state is calculated to be 319.1+ 0.3 meV above the valence band. The observed splitting of the ground state into three sublevels is assigned to the hole-hole interaction and crystal-field splitting. The results are compared with recent findings on double acceptors in germanium.

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