Filtration effectiveness of HVAC systems at near‐roadway schools

Concern for the exposure of children attending schools located near busy roadways to toxic, traffic‐related air pollutants has raised questions regarding the environmental benefits of advanced heating, ventilation, and air‐conditioning (HVAC) filtration systems for near‐road pollution. Levels of black carbon and gaseous pollutants were measured at three indoor classroom sites and at seven outdoor monitoring sites at Las Vegas schools. Initial HVAC filtration systems effected a 31–66% reduction in black carbon particle concentrations inside three schools compared with ambient air concentrations. After improved filtration systems were installed, black carbon particle concentrations were reduced by 74–97% inside three classrooms relative to ambient air concentrations. Average black carbon particle concentrations inside the schools with improved filtration systems were lower than typical ambient Las Vegas concentrations by 49–96%. Gaseous pollutants were higher indoors than outdoors. The higher indoor concentrations most likely originated at least partially from indoor sources, which were not targeted as part of this intervention.     

Photoconductivity in p-i-n Quantum Well Optical Modulators

Abstract

We have studied the temperature dependence of the current due to photoexcited carriers in p-i-n single quantum-well optical modulators, in order to ascertain the dominant transport mechanisms involved. A model describing the photocurrent is presented which includes the temperature and field dependence of the thermal emission, the tunnelling, the mobility and the recombination rate. A comparison between the experimental results and the model is also presented, outlining the probable transport processes.     

Spectral and spatial artifacts from the use of desktop scanners for remote sensing

Inexpensive desktop scanners are frequently used for the scanning of small format aerial photographic images. However, these scanners do not always conform to the spectral and spatial quality required for subsequent image analysis. This Letter outlines simple tests that can be conducted to characterize the properties of desktop scanners and illustrates the performance of a specific instrument. Spectral and spatial artifacts introduced by this scanner are outlined. It is important for image analysts to be aware of these scanner properties, and decide in each case whether the use of these instruments is warranted for quantitative applications.     

Conceptualizing models using multidimensional constructs: a review and guidelines for their use

While information on multidimensional constructs and empirical methods has become more accessible, there remain substantial challenges to theorizing about their form and implications. There are at least two ostensible reasons for such difficulties. First is the issue of terminology; many different terms are currently used to represent the same structural concept, and there is no evidence of standardization taking place around a single set of terms. Second, many studies do not clearly explain the theoretical reasons for choosing the specific multidimensional form of their constructs. To address these deficiencies, we use concepts from the research methods literature, and illustrations from the information systems (IS) literature, to review definitions and issues related to conceptualizing and operationalizing structural models that include multidimensional constructs. Such advice is necessary if we are going to develop and test increasingly sophisticated theoretical models in IS research. We also offer guidelines about how to conceptualize specific forms of multidimensional constructs. By lending greater conceptual clarity to the literature, we believe that this paper provides a foundation for future research incorporating multidimensional constructs in empirical analysis.