Influence of ground anchors on topographic amplification at slope crests

One feature of earthquake loading in regions containing sloping ground is a marked increase in accelerations at the crests of slopes. Many field cases exist where such increased accelerations were measured. The observed increase in the amount and severity of observed building damage near the edge of cliff-type topographies has been attributed to the topographic amplification. To counter this, it has been shown that anchoring the soil mass responsible for this to the rest of the stable soil mass can reduce the amount of topographic amplification. In this study, dynamic centrifuge modelling will be used to identify the region affected by topographic amplification in a model slope. The soil accelerations recorded will be compared to those measured in a comparable model treated by anchors. In addition, the tension measured in the anchors will be examined in order to better understand how the anchors are transferring the loads and mitigating these amplifications. © 2010 Taylor & Francis Group, London.

Changes in the Mg profile and in dislocations induced by high temperature annealing of blue LEDs

The efficiency of the injection and recombination processes in InGaN/GaN LEDs is governed by the properties of the active region of the devices, which strongly depend on the conditions used for the growth of the epitaxial material. To improve device quality, it is very important to understand how the high temperatures used during the growth process can modify the quality of the epitaxial material. With this paper we present a study of the modifications in the properties of InGaN/GaN LED structures induced by high temperature annealing: thermal stress tests were carried out at 900 °C, in nitrogen atmosphere, on selected samples. The efficiency and the recombination dynamics were evaluated by photoluminescence measurements (both integrated and time-resolved), while the properties of the epitaxial material were studied by Secondary Ion Mass Spectroscopy (SIMS) and Rutherford Backscattering (RBS) channeling measurements. Results indicate that exposure to high temperatures may lead to: (i) a significant increase in the photoluminescence efficiency of the devices; (ii) a decrease in the parasitic emission bands located between 380 nm and 400 nm; (iii) an increase in carrier lifetime, as detected by time-resolved photoluminescence measurements. The increase in device efficiency is tentatively ascribed to an improvement in the crystallographic quality of the samples. © 2013 SPIE.