Density-dependent electron scattering in photoexcited GaAs in strongly diffusive regime

Mics Z, D'Angio A, Jensen SA, Bonn M, Turchinovich D. Density-dependent electron scattering in photoexcited GaAs in strongly diffusive regime. Applied Physics Letters. 2013;102(23).In a series of systematic optical pump–terahertz probe experiments, we study the density-dependent electron scattering rate in photoexcited GaAs in the regime of strong carrier diffusion. The terahertz frequency-resolved transient sheet conductivity spectra are perfectly described by the Drude model, directly yielding the electron scattering rates. A diffusion model is applied to determine the spatial extent of the photoexcited electron-hole gas at each moment after photoexcitation, yielding the time-dependent electron density, and hence the density-dependent electron scattering time. We find that the electron scattering time decreases from 320 to 60 fs, as the electron density changes from 1015 to 1019 cm−3

Rainforests at the beginning of the 21st century

Rainforests are situated at low latitude where forests enjoy steady and strong radiation. Biodiversity in rainforests has been very high, for historical and climatic reasons. The number of species is very high and tends to increase with precipitation and decrease with seasonality. Disturbance, soil fertility and forest stature also influence the species richness and high turnover of species contribute to diversity. Field observation and studies revealed that large scale deforestation could alter the regional and global climate significantly. Deforestation alters the surface albedo which leads to climate change. Regional land use contributes to climate change through surface-energy budget, as well as the carbon cycle. Forest fragmentation, logging, overhunting, fire and the expanding agriculture threaten the biodiversity. Rainforest covered area has significantly shrunk in the last decades. It is hard to protect the forests because of the growing demand for agricultural area and forest-derived products. Most measures proved ineffective to slow down the destruction. Hence, more forest will be lost in the future. Conservationists should take into consideration the secondary forests because biodiversity can be high enough and it is worth protecting them

Single-pulse terahertz coherent control of spin resonance in the canted antiferromagnet YFeO₃, mediated by dielectric anisotropy

We report on the coherent control of terahertz (THz) spin waves in a canted antiferromagnet, YFeO3, associated with a quasi-ferromagnetic spin resonance at a frequency of 0.3 THz, using a single THz pulse. The intrinsic dielectric anisotropy of YFeO3 in the THz range allows for coherent control of both amplitude and phase of the excited spin wave

Nutrition Policy in the Post-devolution Context in Pakistan: An Analysis of Provincial Opportunities and Barriers

In this article we take a comparative look at strategic opportunities and barriers for action on nutrition in Pakistan's four provinces in the post?devolution context. Provinces have faced historically common constraints of lack of a comprehensive policy and minimal allocations by the state, driven by low visibility of nutrition, siloed working of sectors and weak coalitions. Provinces also face common contextual impediments of poverty, patriarchy, and inadequate health and WASH coverage, with two provinces also constrained by inequitable power structures. Recent focusing events have provided a window of opportunity to the provinces for action on nutrition leading to definite movement towards horizontal coordination for nutrition, upscaled funding and stronger vertical integration. However, there are variations in the extent of coalition building on nutrition, supportive leadership, governance and community outreach. The Pakistan experience shows that strategising for nutrition needs to move beyond a closely tailored national policy to accounting for sub?national potential and constraints