Influences of H on the Adsorption of a Single Ag Atom on Si(111)-7 × 7 Surface

The adsorption of a single Ag atom on both clear Si(111)-7 × 7 and 19 hydrogen terminated Si(111)-7 × 7 (hereafter referred as 19H-Si(111)-7 × 7) surfaces has been investigated using first-principles calculations. The results indicated that the pre-adsorbed H on Si surface altered the surface electronic properties of Si and influenced the adsorption properties of Ag atom on the H terminated Si surface (e.g., adsorption site and bonding properties). Difference charge density data indicated that covalent bond is formed between adsorbed Ag and H atoms on 19H-Si(111)-7 × 7 surface, which increases the adsorption energy of Ag atom on Si surface

Some like it hot: are desert plants indifferent to climate change?

Deserts rank at the forefront of vulnerability to global change because their biota is expected to encounter large climatic changes while apparently existing at biological limits. We review the available evidence for climate change effects on arid lands, and specifically on vegetation because as primary producers, plants are main providers of ecosystem services. We summarize field experiments and correlative evidence from spatial and temporal climatic gradients. Surprisingly, only few climate manipulation experiments have been conducted in semideserts, none in arid regions, and almost none in cold drylands. We argue that correlative approaches do not yield the necessary knowledge to understand and thus mitigate potential changes due to their oversight of long-term evolutionary processes. Nonetheless, the limited mechanistic evidence suggests a surprisingly high resilience of desert vegetation to changes in precipitation and CO2. We suggest this resilience is due to specific adaptations that have evolved in response to stressful and highly variable climatic conditions