Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item The Effects of Using Mental Imagery as a Comprehension Strategy for Middle School Students Reading Science Expository Texts(2009) Jenkins, Margaret H.; Dreher, Mariam J; Curriculum and Instruction; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study investigated the effects of mental imagery instruction using science expository texts on middle school students. Using a quasi-experimental pretest-posttest design, four intact classes (56 students) were randomly assigned to either an experimental or comparison group. Students in the experimental group received instruction on mental imagery strategies while comparison group students received no mental imagery instruction. After the 2-week intervention, students took Posttest 1. The comparison group students then received mental imagery instruction. Throughout the rest of the school year, all students were prompted at least two to three times a week to use mental imagery strategies. At the end of the school year, all participants took Posttest 2. Results indicated that there was a statistically significant interaction of time and group for the selected response (SR) portion of expository science text comprehension measure. Both groups appeared to make gains between Posttest 1 and Posttest 2, once both had received mental imagery instruction. The comparison group, which by chance included stronger readers, outperformed the experimental group. There were no statistically significant differences on the brief constructed response (BCR) measure. Analysis of the performance of low-, middle-, and high-comprehenders revealed statistically significant main effects for time and for type of comprehender on the SR portion of the comprehension task. While all students appeared to make gains between Posttest 1 and 2, the high- and middle-comprehenders consistently outperformed the low-comprehenders. For the BCR, there were no statistically significant effects of time or interaction; however, there was a statistically significant effect for type of comprehender. Pearson's product moment correlations revealed a statistically significant positive relation between vividness of mental imagery and motivation to read for middle-comprehenders and a statistically significant negative correlation between comprehension and vividness of mental imagery for high-comprehenders. Both experimental and comparison groups showed no statistically significant difference in motivation to read before and after mental imagery intervention. These results suggest that middle school students may benefit from mental imagery strategies when reading science expository texts. It is recommended that these strategies be used as a continuous effort in the classroom rather than a short term "quick-fix."Item Physics-Based Detection of Subpixel Targets in Hyperspectral Imagery(2007-04-25) Broadwater, Joshua Bret; Chellappa, Ramalingam; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hyperspectral imagery provides the ability to detect targets that are smaller than the size of a pixel. They provide this ability by measuring the reflection and absorption of light at different wavelengths creating a spectral signature for each pixel in the image. This spectral signature contains information about the different materials within the pixel; therefore, the challenge in subpixel target detection lies in separating the target's spectral signature from competing background signatures. Most research has approached this problem in a purely statistical manner. Our approach fuses statistical signal processing techniques with the physics of reflectance spectroscopy and radiative transfer theory. Using this approach, we provide novel algorithms for all aspects of subpixel detection from parameter estimation to threshold determination. Characterization of the target and background spectral signatures is a key part of subpixel detection. We develop an algorithm to generate target signatures based on radiative transfer theory using only the image and a reference signature without the need for calibration, weather information, or source-target-receiver geometries. For background signatures, our work identifies that even slight estimation errors in the number of background signatures can severely degrade detection performance. To this end, we present a new method to estimate the number of background signatures specifically for subpixel target detection. At the core of the dissertation is the development of two hybrid detectors which fuse spectroscopy with statistical hypothesis testing. Our results show that the hybrid detectors provide improved performance in three different ways: insensitivity to the number of background signatures, improved detection performance, and consistent performance across multiple images leading to improved receiver operating characteristic curves. Lastly, we present a novel adaptive threshold estimate via extreme value theory. The method can be used on any detector type - not just those that are constant false alarm rate (CFAR) detectors. Even on CFAR detectors our proposed method can estimate thresholds that are better than theoretical predictions due to the inherent mismatch between the CFAR model assumptions and real data. Additionally, our method works in the presence of target detections while still estimating an accurate threshold for a desired false alarm rate.