The Influence of Inner Component and Topographical Properties on Tribological Parameters of Injection-Moulded Microparts

Tribological parameters are dependent upon inter alia, inner component properties which may vary with the temperature-time behaviour of the polymer melt used. This temperature-time behaviour can be influenced by dynamic mould temperature control. The present paper presents a new dynamic tempering concept, which enables a targeted temperature-time control via shifting a mould cavity within two different tempered mould areas at a defined point in time. By influencing the temperature-time development by means of a mould temperature and isothermal holding time variation, micro tensile bars with different inner component properties are produced. To show the influence of inner component properties on tribological parameters, pin-on-disc wear tests are performed. Furthermore, tribological tests with different surface topographies are performed to show the influence of topographical properties on tribological parameters. Results indicate that the tribological properties of microparts are mainly influenced by the nature of the skin near layers, which can be influenced by the application of different mould temperatures. Variations in the isothermal holding time show no significant impact on the material examined. A more distinct roughness of the disc surface topography not only shows higher values for the measured tribological parameters but also different wear behaviour in general

Spatial patterns of large African cats : a large-scale study on density, home range size, and home range overlap of lions Panthera leo and leopards Panthera pardus

Spatial patterns of and competition for resources by territorial carnivores are typically explained by two hypotheses: 1) the territorial defence hypothesis and 2) the searching efficiency hypothesis. According to the territorial defence hypothesis, when food resources are abundant, carnivore densities will be high and home ranges small. In addition, carnivores can maximise their necessary energy intake with minimal territorial defence. At medium resource levels, larger ranges will be needed, and it will become more economically beneficial to defend resources against a lower density of competitors. At low resource levels, carnivore densities will be low and home ranges large, but resources will be too scarce to make it beneficial to defend such large territories. Thus, home range overlap will be minimal at intermediate carnivore densities. According to the searching efficiency hypothesis, there is a cost to knowing a home range. Larger areas are harder to learn and easier to forget, so carnivores constantly need to keep their cognitive map updated by regularly revisiting parts of their home ranges. Consequently, when resources are scarce, carnivores require larger home ranges to acquire sufficient food. These larger home ranges lead to more overlap among individuals' ranges, so that overlap in home ranges is largest when food availability is the lowest. Since conspecific density is low when food availability is low, this hypothesis predicts that overlap is largest when densities are the lowest. We measured home range overlap and used a novel method to compare intraspecific home range overlaps for lions Panthera leo (n = 149) and leopards Panthera pardus (n = 111) in Africa. We estimated home range sizes from telemetry location data and gathered carnivore density data from the literature. Our results did not support the territorial defence hypothesis for either species. Lion prides increased their home range overlap at conspecific lower densities whereas leopards did not. Lion pride changes in overlap were primarily due to increases in group size at lower densities. By contrast, the unique dispersal strategies of leopards led to reduced overlap at lower densities. However, when human-caused mortality was higher, leopards increased their home range overlap. Although lions and leopards are territorial, their territorial behaviour was less important than the acquisition of food in determining their space use. Such information is crucial for the future conservation of these two iconic African carnivores