Safe Design Suggestions for Vegetated Roofs

Rooftop vegetation is becoming increasingly popular because of its environmental benefits and its ability to earn green-building certification credits. With the exception of one international guideline, there is little mention of worker safety and health in vegetated-roof codes and literature. Observations and field investigations of 19 vegetated roofs in the United States revealed unsafe access for workers and equipment, a lack of fall-protection measures, and other site-specific hazards. Design for safety strategies and the integration of life-cycle safety thinking with green-building credits systems are the preferred methods to reduce risk to workers on vegetated roofs. Design suggestions have been developed to add to the body of knowledge. The findings complement several National Institute for Occupational Safety and Health (NIOSH) construction and prevention through design (PtD) goals and are congruent with NIOSH’s Safe Green Jobs initiative. Organizations that install and maintain vegetated roofs can utilize the findings to understand hazards, take precautions, and incorporate safety into their bids The published version of this article is available here: 10.1061/(ASCE)CO.1943-7862.0000500Support from the the Virginia Tech Occupational Safety and Health Research Center through the Kevin P. Granata Pilot Program funded by the Institute for Critical Technology and Applied Sciences

Excitonic recombination dynamics in shallow quantum wells

We report a comprehensive study of carrier-recombination dynamics in shallow AlxGa1-xAs/GaAs quantum wells. At low crystal temperature (2 K), the excitonic radiative recombination time is shown to be strongly enhanced in shallow quantum wells with x>0.01, consistently with a model that takes into account the thermal equilibrium between the three-dimensional exciton gas of the barrier and the two-dimensional exciton gas, which are closer in energy as x decreases. Furthermore, we demonstrate the existence of a thermally activated escape mechanism due to the low effective barrier height in these structures. The nonradiative recombination is shown to dominate the carrier dynamics for temperatures as low as 10 K for x≈0.01. Our experimental observations are analyzed using three different variational exciton calculations. In particular, we study the crossover from the two-dimensional to the three-dimensional behavior of the exciton, which occurs for x as low as 0.01 and affects mainly the oscillator strength, whereas the transition energies in shallow quantum wells can be calculated, to a large extent, using the same approximations as for conventional quantum wells. The peculiar behavior of the oscillator strength at the crossover to the weak confinement regime is obtained by expansion in a large basis

Practical field use of eye-tracking devices for consumer research in the retail environment

Eye-tracking equipment is now affordable and portable, making it a practical instrument for consumer research. Engineered to best analyze gaze on a plane (e.g., a retail shelf), both portable eye-tracking glasses and computer monitor–mounted hardware can play key roles in analyzing merchandise displays to better understand what consumers view. Researchers and practitioners can use that information to improve the sales efficacy of displays. Eye-tracking hardware was nearly exclusively used to investigate the reading process but can now be used for a broader range of study, namely in retail settings. This article presents an approach to using glasses eye tracker (GET) and light eye tracker (LET) eye-tracking hardware for applied consumer research in the field. We outline equipment use, study construction, data extraction as well as benefits and limitations of the technology collected from several pilot studies