Solid-solid diffusion couples assembled with disks of copper, tin and intermetallics (Cu 3 Sn and Cu 6 Sn 5 ) were employed to investigate the Kirkendall effect in the copper-tin system at the temperature of 200°C. In the Cu(99.9%)/Sn diffusion couple, inert alumina particles used as markers were identified in the Cu 6 Sn 5 phase, while microvoids were observed at the Cu/Cu 3 Sn interface. The Cu(99.9%)/Sn and Cu(99.9%)/Cu 6 Sn 5 diffusion couples annealed at 200°C for 10 days were analyzed for intrinsic diffusion coefficients of Cu and Sn in the Cu 6 Sn 5 and Cu 3 Sn phases, respectively with due consideration of changes in molar volume. Interdiffusion, integrated and effective interdiffusion coefficients were also calculated for the intermetallic phases. Diffusion couples annealed at 125-400°C for various times were analyzed for the kinetic parameters such as growth rate constants and activation energies for the formation of Cu 3 Sn and Cu 6 Sn 5 phases. Uncertainties in the calculated intrinsic diffusivities of Cu and Sn arise mainly from the non-planar morphologies of the interfaces and the non-planar distribution of the markers. Intrinsic diffusion coefficients based on average locations of the marker plane indicate that Cu is the faster diffusing component than Sn in both the Cu 3 Sn and Cu 6 Sn 5 phases.

No abstract

The Himalayas are a global hotspot for bird diversity with a large number of threatened species, but little is known about seasonal changes in bird communities along elevational gradients in this region. We studied the seasonality of bird diversity in six valleys of the Central Himalayas, Nepal. Using 318 plots with a 50 m radius, located from 2200 to 3800 m a.s.l., and repeated sampling during different seasons (mainly pre-monsoon, monsoon, and post-monsoon), we analyzed 3642 occurrences of 178 species. Birds classified in the literature as resident were more species-rich than migratory birds (140 vs. 38 species). In all six valleys and within the studied elevation range, species richness of all birds showed a peak at mid-elevation levels of 2600 or 3000 m a.s.l. Similar patterns were found for the most species-rich feeding guilds of insectivores (96 species) and omnivores (24 species), whereas the species richness of herbivores (37 species including frugivores) increased towards higher elevations. Among these feeding guilds, only species richness of insectivores showed pronounced seasonal changes with higher species numbers during post-monsoon season. Similarly, individual bird species showed distinct spatio-temporal distribution patterns, with transitions from species dominated by elevational differences to those characterized by strong seasonal changes. In an era of climate change, the results demonstrate that individual bird species as well as feeding guilds might greatly differ in their responses to climate warming and changes in the seasonality of the precipitation regime, two aspects of climate change which should not be analyzed independently.

No abstract