分类: 物理学 >> 基本粒子与场物理学 提交时间: 2017-08-05
摘要: We investigate ac Josephson effect in the resonant tunneling through mesoscopic superconducting junctions. In the presence of microwave irradiation, we show that the trajectory of multiple Andreev reflections can be closed by emitting or absorbing photons. Consequently, photon-assisted Andreev states are formed and play the role of carrying supercurrent. On the Shapiro steps, dc component appears when the resonant level is near a series of positions with spacing of half of the microwave frequency. Analytical result is derived in the limit of infinite superconducting gap, based on which new features of ac Josephson effect are revealed.
分类: 生物学 >> 生态学 提交时间: 2017-07-18
摘要: Apparent activation energy (Ea) is one of the most important and sensitive parameters that control soil organic C (SOC) decomposition in prevailing earth system models (ESMs). The variation of apparent Ea is affected by multiple soil environmental factors, among which soil moisture exerts a strong effect. Aiming to better inform temperature sensitivity parameterization in ESMs, here we examined the relationship between apparent Ea and soil moisture with both incubation experiment and field measurement in subtropical forests. We found that apparent Ea declined as soil moisture increased, consistently in both incubation and field experiments. We speculated that this phenomenon was due to altered microbial community composition from changing soil moisture. Our results suggest that future warming and changing precipitation would significantly affect the decomposition of recalcitrant carbon pools in subtropical forests. Lacking representation of the impact of soil moisture on SOC decomposition temperature sensitivity in current ESMs might have biased climate projection.