Deborah Walter

Atomic number resolution for three spectral CT imaging systems

The material specificity of computed tomography is quantified using an experimental benchtop imaging system and a physics-based system model. The apparatus is operated with different detector and system configurations each giving X-ray energy spectral information but with different overlap among the energy-bin weightings and noise statistics. Multislice, computed tomography sinograms are acquired using dual kVp, sequential source filters or a detector with two scintillator/photodiodes layers. Basis-material and atomic number images are created by first applying a material decomposition algorithm followed by filtered backprojection. CT imaging of phantom materials with known elemental composition and density were used for model validation. X-ray scatter levels are measured with a beam-blocking technique and the impact to material accuracy is quantified. The image noise is related to the intensity and spectral characteristics of the X-ray source. For optimal energy separation adequate image noise is required. The system must be optimized to deliver the appropriate high mA at both energies. The dual kVp method supports the opportunity to separately engineer the photon flux at low and high kvp. As a result, an optimized system can achieve superior material specificity in a system with limited acquisition time or dose. In contrast, the dual-layer and sequential acquisition modes rely on a material absorption mechanism that yields weaker energy separation and lower overall performance.

Spectrum utilization efficiency of cognitive radio systems with limited sampling capability: The impact of spectrum non-contiguity

In cognitive radio systems, the available frequency bands are usually non-contiguous, which may cause impact on the spectrum utilization efficiency (SUE).When the receiver has a limited sampling capability, the aliasing phenomenon may cause interference among the signals at different frequency points, thus causing the loss of channel capacity. Information theoretic analysis is carried out to quantify the impact of spectrum non-contiguity on the channel capacity by analyzing the SUE. Beginning from the single sampler case, the analysis is also extended to the general case of sampler arrays. Numerical results are provided to answer several important questions on the impact of spectrum non-contiguity.

Multiple UAV tomography based geolocation of RF emitters

Various methods for discovering the location of radio frequency (RF) emitters using unmanned aerial vehicles (UAVs) have been the focus of research over the past several years. Our work is aimed at determining the effectiveness of lowaccuracy direction finding (DF) technology to locate RF emissions using multiple UAVs. Small, commercial-off-theshelf (COTS) antenna systems can provide a rough estimate of an emitters location within a 90 degree or 45 degree sector. Using these DF systems, a team of inexpensive UAVs can be deployed to collect low-accuracy data from multiple positions. A ground station would combine the information. In contrast to typical angle-of-arrival (AOA) methods, this unique technique does not require precise antenna arrays, complex hardware, or significant processing time to locate RF emissions. We present simulation results that show that accurate geolocation of emitters is possible with DF systems using only low accuracy (90-20 degrees) Angle of Arrival (AOA) information.

Models of adoption and best practices for mobile hands-on learning in electrical engineering

Pedagogical practices in electrical engineering education have been shifting away from teacher-centered learning during the past decade. An innovation that has enabled the adoption of inquiry-based and problem-based learning into the curriculum using experimentation coupled with simulation and analysis has been the development of portable oscilloscopes and other instruments that rely on tablet or laptop computers to perform some of the data processing and to act as the display. Faculty members at six institutions of higher learning have incorporated hands-on experimental activities into existing courses and/or developed new courses that take advantage of these new tools. Assessment data collected by these faculty members have demonstrated that the change towards student-centered learning facilitated by portable electronics increased student interest in electrical engineering, built student confidence in their ability to design circuits and systems, and supported the development of a deeper understanding of the theories that the students investigate or apply in the hands-on activities. A summary of the challenges that are faced in the different implementation models and a discussion of best practices are presented.

Localization of RF emitters using compressed sensing with multiple cooperative sensors

Small unmanned aerial vehicles (UAVs) have limits on the weight and size of direction finding (DF) systems that can be used. However, by employing multiple sensors that work cooperatively, simple DF systems need only to provide a rough estimate of the signals angle of arrival (AOA) and received signal strength (RSS). As the UAVs move, a plurality of data points can be obtained from diverse locations. Combining this information from multiple sensor locations can provide a low-cost and effective solution to electronic emitter location problems, using low-accuracy DF technology. In this paper we present an algorithm, based on the compressed sensing technique, that uses AOA and RSS from mobile sensors (UAVs) to geolocate the source of radio signals on the ground.

Hybrid Pursuit-Evasion Game between UAVs and RF Emitters with Controllable Observations: A Hawk-Dove Game

Unmanned aerial vehicles (UAVs) can be used to chase radio frequency (RF) emitters by sensing the signal sent out by the RF emitters. Meanwhile, the RF emitter can evade from the UAVs, thus forming a pursuit-evasion game. In contrast to traditional pursuit-evasion games, in which the players can always observe each other, the RF emitter can stop transmitting such that the UAVs lose the target. However, stopping the transmission also incurs cost to the RF emitter since it can no longer convey information to destinations. Hence, the RF emitter can take both continuous actions, i.e., the moving direction, and discrete actions, i.e., whether to stop transmission. Meanwhile, there are both discrete states, i.e., whether the RF transmitter is transmitting, and continuous states, i.e., the locations of UAVs and RF emitter, thus forming a hybrid system. We will study the game theoretic properties of this novel game and derive the optimal strategies for both parties under certain assumptions.

Work in progress — Merging science inquiry and engineering design: A summer workshop series for middle and high school science teachers

We report on a two-week professional development workshop for middle and high school science teachers offered as part of a three-year Indiana Department of Education Math-Science Partnership grant awarded to Rose-Hulman Institute of Technology (RHIT) and Vigo County School Corporation (VCSC).

Panel session - pen-based computing in the engineering and science classroom: Implementation scenarios from three institutions

As digital ink technology continues to make an impact on the technical classroom, faculty members are exploring the different strategies for using this technology to improve student learning. The purpose of this panel is to demonstrate how faculty members are implementing this technology in engineering and science classrooms at three different institutions: Rose-Hulman Institute of Technology, University of Texas at Austin, and University of Vermont. The panel is designed to show both experienced pen computing users and those who are new to the field the different ways this versatile technology may be employed. In addition to the demonstrations, the presenters will discuss the pedagogical implications that result from the implementations. Faculty who are interested in both the pedagogy and assessment of pen-based computing in the classroom should find the session informative and useful.

AC Circuit Analysis

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A study of the effect of instructional media in an undergraduate electrical circuits course

Studies have demonstrated that instructional media play an important role in instructorspsila teaching and studentspsila learning. The purpose of this study is to assess the studentspsila preferences for different instructional media and the impact of different instructional media on the studentspsila learning and course-related behavior in an undergraduate electrical circuitpsilas course. The instructional media under study are: computer-based PowerPoint presentation, whiteboard only, combination of PowerPoint and whiteboard and combination of printed handouts and whiteboard. In this study, nine sections of Introduction to Electrical Circuits sections were taught by 6 instructors using different instructional media. All the instructors used a common syllabus, labs, homework, and tests. Two midterm exams and one final exam were used to assess the learning effectiveness of different instructional media. At the end of the quarter, a questionnaire was collected from participating students to measure their preference for the instructional media. To understand the course related behavior, each of the instructors were asked to assess their studentspsila behavior in terms of attendance, amount of classroom interaction, percent of homework completion and Web logins.