Investigation of generation -recombination noise and related processes in aluminum gallium arsenide TEGFETs and Hall structures with quantum wells

Experimental and theoretical studies regarding noise processes in various kinds of AlGaAs/GaAs heterostructures with a quantum well are reported. The measurement processes, involving a Fast Fourier Transform and analog wave analyzer in the frequency range from 10 Hz to 1 MHz, a computerized data storage and processing system, and cryostat in the temperature range from 78 K to 300 K are described in detail. The current noise spectra are obtained with the “three-point method”, using a Quan-Tech and avalanche noise source for calibration. ^ The properties of both GaAs and AlGaAs materials and field effect transistors, based on the two-dimensional electron gas in the interface quantum well, are discussed. Extensive measurements are performed in three types of heterostructures, viz., Hall structures with a large spacer layer, modulation-doped non-gated FETs, and more standard gated FETs; all structures are grown by MBE techniques. ^ The Hall structures show Lorentzian generation-recombination noise spectra with near temperature independent relaxation times. This noise is attributed to g-r processes in the 2D electron gas. For the TEGFET structures, we observe several Lorentzian g-r noise components which have strongly temperature dependent relaxation times. This noise is attributed to trapping processes in the doped AlGaAs layer. The trap level energies are determined from an Arrhenius plot of log (τT2) versus 1/T as well as from the plateau values. The theory to interpret these measurements and to extract the defect level data is reviewed and further developed. Good agreement with the data is found for all reported devices. ^

The use of curriculum modifications and instructional accommodations to provide access for middle school students with autism to the general curriculum

The number of students identified as having autism increased by 500% in the past 10 years (United States Government Accountability Office, 2005). All students with disabilities are required to be placed in least restrictive environments and to be given access to the general curriculum in the major subjects of math, reading, writing, and science as mandated by federal legislation such as the Individuals with Disabilities Education Act (IDEA, 2004) and No Child Left Behind (NCLB, 2001). As a result of this legislation, an increasing number of students with autism are being educated in inclusive classrooms. Most studies on general education access and curriculum modifications and/or instructional accommodations center on students with intellectual disabilities (e.g. Soukup, Wehmeyer, Bashinski, & Boviard, 2007; Wehmeyer, Lattin, Lapp-Rincker, & Agran, 2003). Wehmeyer et al. (2003) and Soukup et al. (2007) found included students with intellectual disabilities had more access to the general curriculum than mostly self-contained students. This meant included students were more likely to be working on the general curriculum as mandated by NCLB than those in only self-contained classrooms. This study builds and expands the research of Wehmeyer et al., as well as Soukup et al., by examining how students with autism are given access to the general curriculum through curriculum modifications and instructional accommodations used by general education teachers in three schools. This investigation focused on nine inclusive classrooms for students with autism using a parallel mixed methods design (Newman, Newman, & Newman, 2011). Classroom observations using both an IEP related checklist and field notes, teacher interviews, an archival document review of the Individual Education Plan (IEP) for the selected students with autism were performed. Findings of this study were organized by interview questions and subsequent coding categories. Quantitative data were organized in a nominal scale. Participants asserted that their middle school students with autism functioned well in their classrooms, occasionally exhibiting behavioral differences. Most instructional accommodations on IEPs were being implemented by participants, and participants often provided additional instructional accommodations not mandated by the IEP. The majority of participants credited county workshops for their knowledge of instructional accommodations.

Turning Passive Detection Systems into Field Experiments: An Application Using Wetland Fishes and Enclosures to Track Fine-Scale Movement and Habitat Choice

Understanding habitat selection and movement remains a key question in behavioral ecology. Yet, obtaining a sufficiently high spatiotemporal resolution of the movement paths of organisms remains a major challenge, despite recent technological advances. Observing fine-scale movement and habitat choice decisions in the field can prove to be difficult and expensive, particularly in expansive habitats such as wetlands. We describe the application of passive integrated transponder (PIT) systems to field enclosures for tracking detailed fish behaviors in an experimental setting. PIT systems have been applied to habitats with clear passageways, at fixed locations or in controlled laboratory and mesocosm settings, but their use in unconfined habitats and field-based experimental setups remains limited. In an Everglades enclosure, we continuously tracked the movement and habitat use of PIT-tagged centrarchids across three habitats of varying depth and complexity using multiple flatbed antennas for 14 days. Fish used all three habitats, with marked species-specific diel movement patterns across habitats, and short-lived movements that would be likely missed by other tracking techniques. Findings suggest that the application of PIT systems to field enclosures can be an insightful approach for gaining continuous, undisturbed and detailed movement data in unconfined habitats, and for experimentally manipulating both internal and external drivers of these behaviors.