Friction and Surface Damage of Several Corrosion-resistant Materials

Friction and surface damage of several materials that are resistant to corrosion due to liquid metals was studied in air. The values of kinetic friction coefficient at low sliding velocities and photomicrographs of surface damage were obtained. Appreciable surface damage was evident for all materials tested. The friction coefficients for the combinations of steel, stainless steel, and monel sliding against steel, stainless steel, nickel, Iconel, and Nichrome ranged from 0.55 for the monel-Inconel combination to 0.97 for the stainless-steel-nickel combination; for steel, stainless steel, monel, and tungsten carbide against zirconium, the friction coefficient was approximately 0.47. Lower coefficients of friction (0.20 to 0.60) and negligible surface failure at light loads were obtained with tungsten carbide when used in combination with various plate materials

Spatial patterns of woody plant encroachment in a temperate grassland

Context Woody encroachment is the process whereby grasslands transition to a woody-dominated state. This process is a global driver of grassland decline and is ultimately the outcome of increased woody plant recruitment in grasslands. Yet, little is known about how recruitment distances structure spatial patterns of encroachment. Objectives Here, we develop a recruitment curve to describe the scatter of woody plant recruitment around seed sources and examine how this structures spatial patterns of encroachment. Methods We developed a recruitment curve for Juniperus virginiana using an encroachment dataset that captures spread from tree plantings into treeless grassland sites in the Nebraska Sandhills (USA). In addition, we used height classes of encroaching J. virginiana as subsequent time steps of an encroachment process to examine how the leading edge of encroachment expanded over time. Results The recruitment curve was characterized by a fat-tailed distribution. Most recruitment occurred locally, within 157 m of seed sources (95th percentile distance), while, sparse long-distance recruitment characterized the curve’s tail. Expansion of the leading edge of encroachment was characterized by two features: (1) a slow moving, high density area near tree plantings and (2) rapid expansion of the distribution’s tail, driven by long-distance recruitment in treeless areas. Conclusion Our results show a high capacity for woody plant invasion of grasslands. Local recruitment drives transitions to woody dominance, while long-distance recruitment generates a rapidly advancing leading edge. Plans to conserve and restore grasslands will require spatially informed strategies that account for local and long-distance recruitment of woody plants