Band Structure Effects in Quantum cascade Lasers

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Intervalley Scattering and the Role of Indirect Band Gap AlAs Barriers: Application to GaAs/AlGaAs Quantum Cascade Lasers

We report on the results of our simulations of Γ-X scattering in GaAs/AlGaAs heterostructures, discussing the importance of the mole fraction, doping density, and lattice and electron temperature in determining the scattering rates. We consider three systems, a single quantum well (for the investigation of Γ-X scattering), a double quantum well (to compare the Γ-X-G and Γ-Γ scattering rates), and an example of a GaAs/AlGaAs mid-infrared quantum cascade laser. Our simulations suggest that Γ-X scattering can be significant at room temperature but falls off rapidly at lower temperatures. One important factor determining the scattering rate is found to be the energy difference between the Γ- and X-states

To evaluate reforestation in farms: A tool for smallholders and the sustainability of their initiatives (EvaRefo).

International audienceDespite consensus on the necessity to reforest agricultural landscapes for climate change mitigation and adaptation, the experiences of many small landholders in reforestation are tarnished by difficulties leading to disillusionment and abandonment of initiatives. After clarifying with stakeholders of reforestation efforts in Balalaica, a biological subcorredor in Costa Rica, it became clear that the sustainability of an initiative depends on clear objectives, and a series of corresponding factors and well-timed decisions. In respond to these needs, we elaborated a simple evaluation tool, EvaRefo. On the basis of indicator development, EvaRefo accounts for the different dimensions of reforestation sustainability as perceived by small landholder reforestation initiatives (ecological, economic, social and cultural). It distinguishes the potential of a reforestation initiative (whether favorable conditions are gathered) and its performance (how well are the trees growing and fulfilling expectations). The tool makes the most of scientific and technical knowledge on reforestation conditions and processes, while remaining operationally simple so that small landholders can use it without specific investment nor high-level technical knowledge. The self-evaluation of initiatives facilitates learning and capacity-building directly from field experience. EvaRefo was applied to six types of reforestation initiatives, focusing on different primary objectives, to visualize the kinds of tradeoffs that are involved by focusing on one goal rather than another: timber production, water conservation, ecological conservation, rural and scientific tourism, agroforestry, and payments for environmental services. Consistently low scoring indicators corresponded to aspects of associative and technical capacities, self-sufficiency, and species suitability, revealing that the farmer involved in reforestation often finds himself isolated to successfully manage his reforestation initiative