Theses and Dissertations - Department of Electrical & Computer Engineering (ECE)

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5G wireless directional networking based on pattern division multiple access: algorithms, protocols and test-bed
(University of Alabama Libraries, 2018) Qi, Ji; Hu, Fei; University of Alabama Tuscaloosa
With the development of mobile services, the increase of wireless trac data will lead to higher requirements for the wireless communication networks. As one of the latest promising antenna techniques, multi-beam smart antennas (MBSAs) can achieve concurrent transmissions/receptions in multiple directions/beams. Thus it can significantly improve the network throughput. In this paper, we first describe the framework of our next generation MBSA wireless network. In our network, Pattern division multiple access (PDMA)is used for multi-user communication system, while Dynamic Channel Bonding (DyB) protocol is adopted to optimize the distribution of spectrum resource. Secondly, we present a Riverbed simulator implementation with both routing and medium access control (MAC) protocols for mobile ad-hoc network wireless networks with MBSAs. We describe the simulation models with the implementation of MBSA antenna model in physical layer, MAC layer, and routing layer protocols, all in Riverbed Modeler. Then we compare two routing scenarios, i.e., multi-hop diamond routing scenario and multi-path pipe routing. At last, we will elaborate our design methodology of a testbed for the study of multimedia over cognitive radio networks (CRNs) with directional antennas. We use compressive sensing to sample the wide bandwidth and cyclostationary domain features to detect the band signals. We also propose a Markov decision based spectrum hando control scheme that can switch channels in the proper times.
#Activism Amplified, Action Required: a Qualitative Case Study of One Institution's Response to a Student-Led Social Media Campaign
(University of Alabama Libraries, 2021) West, Keaton Elyse; Holley, Karri; University of Alabama Tuscaloosa
Student activism has been part of the American college experience since the beginning of American higher education (Thelin, 2004). American college students participated in physical demonstrations and protests throughout the history of higher education in the United States. College students continue to protest for their concerns and issues on campus today. However, social media and technology changed how American college students engage in student activism and activist behaviors. Technology and social media platforms give college students open access to information processing and sharing. More specifically, social media creates opportunities for students to engage in activism in a digital space. Due to the rapid nature of information sharing through social media, institutions of higher education choose how to respond to student-led social media campaigns. This qualitative study was conducted to learn about how one institution responded to a student-led social media campaign calling the institution to take action to improve the process in which sexual misconduct is handled on campus. Document analysis, participant interviews, and member checking focus groups were the data sources selected for this study. The data collected is used to examine how one institution responded to a social media campaign against campus sexual violence and to better understand why the institution responded the way that the institution did. Various factors come into play when responding in these types of situations and administrators must know their institutions and rely on guidance and feedback from internal campus experts and external organizations in order to respond.
Adaptive control methods for DC-DC switching power converters
(University of Alabama Libraries, 2011) Arikatla, VaraPrasad; Abu Qahouq, Jaber A.; University of Alabama Tuscaloosa
Tight regulation of the output voltage is often required in many power supply applications, despite the highly dynamic nature of the loads. This is conventionally obtained by the design of high bandwidth feedback loop or recently by using adaptive control methods. The control loop is designed with specified safe bandwidth and gain and phase margins such that it maintains stable operation under variable conditions and parameters. However, this results in a compromise between achievable dynamic performance and robustness of control loop. The large variations in operating points and load makes the system design challenging. The tight regulation requirements, in addition to size and weight requirements, are getting stricter by time, which makes it necessary to investigate new control concepts in order to meet these requirements. Not meeting the tight regulation requirements may result in either the malfunctioning of the device (load) being powered or the destruction of that device. This work focuses on the development and implementation of adaptive control methods that result in the improvement of the dynamic performance of power converter, by utilizing the flexibility of digital controllers to realize advanced control schemes. Four different methods are proposed that improve the dynamic performance of converter without compromising the steady-state performance. A Sensorless Adaptive Voltage Positioning (SLAVP) control scheme is proposed in Chapter 2, in order to realize Adaptive Voltage Positioning (AVP) control without the need for load or inductor current sensing and high-resolution high-speed Analog-to-Digital Converter (ADC) sampling. The SLAVP control law utilizes the readily available error signal of the conventional voltage-mode closed-loop compensated controller, or in other words the duty cycle of a DC-DC buck converter, in order to realize AVP control. The elimination of the need for high-speed and accurate sensing and sampling of currents using the proposed SLAVP control reduces the size and cost of the digital controller, reduces the power losses associated with current sensing and sampling, and simplifies hardware design, apart from improving dynamic performance. In Chapter 3, an Adaptive Digital PID (AD-PID) controller scheme is proposed. The controller adaptively adjusts the integral constant (K_i) and the proportional constant (K_p) of the compensator following a new control law. The control law is a function of the magnitude change in the error signal and its peak value during dynamic transients. The proposed AD-PID controller adaptively detects the peak value of the error signal which is a function of the transient nature and magnitude and utilize it in the control law such that no ocillations are generated as a result of the adaptive operation. As a result, the dynamic output voltage deviation and the settling time of the output voltage are reduced. A novel Compensator Error Observe and Modulate method (CEO&M) for online closed-loop-compensator auto-tuning of digital power controller is proposed in Chapter 4. The proposed method is relatively simple and does not require the knowledge and/or measurement of the power stage or closed-loop frequency response. Moreover, the proposed method does not depend on conventional design methods and the associated rule of thumb design criteria in order to tune closed-loop feedback controllers of power converter for high, and possibly optimum, dynamic performance. Furthermore, two approaches for dynamic variable switching frequency digital control scheme under dynamic transients are proposed in Chapter 5 in order to improve the dynamic performance of the DC-DC switching power converter. The proposed controller varies the switching frequency of the converter, higher or lower than the steady-state frequency, during the transient as a function of peak and magnitude of error signal depending on the amount and type of the transient. Finally, Chapter 6 summarizes this work and provides conclusions before discussing future related research direction.
Additive increase-multiplicative decrease control of charging rate to enable mass EV-grid integration
(University of Alabama Libraries, 2019) Ucer, Emin Yilmaz; Kisacikoglu, Mithat C.; University of Alabama Tuscaloosa
Electric vehicles (EVs) are finally making their way onto the highways worldwide but the challenges with respect to their long charging time and its impact on the utility distribution grid are still waiting to be resolved. Uncontrolled charging is likely to cause power network congestion that will result in voltage violations, power losses and imbalances, overloading of grid infrastructure and even their failures. For this reason, many control algorithms considering centralized and decentralized solutions have been proposed. However, none has been standardized as a practical solution that can easily be implemented at end-nodes. The today's Internet also had a similar problem on its early days. Its core control protocol has led to its ever-growing nature that still stably operates today allowing for the integration of millions of new devices almost every day. Behind this success story of the Internet lies its congestion avoidance algorithm: Additive Increase and Multiplicative Decrease (AIMD). This algorithm has proven itself to provide a stable and fair operation, and therefore can be considered as an important candidate for the EV charging problem as well. This thesis work adapts the AIMD concept from the Internet and proposes a counterpart EV charging algorithm. It investigates the core similarities and differences between the Internet and power distribution network and presents a detailed analysis on distribution network modeling to show how AIMD can be adapted and implemented. Finally, it proposes some statistical methods for a fully decentralized and practical implementation of AIMD on real distribution networks.
Advanced control and synchronization approaches of voltage source converters for integration of distributed energy resources
(University of Alabama Libraries, 2018) Ramezani, Malek; Li, Shuhui; University of Alabama Tuscaloosa
Voltage source converter (VSC) is an inseparable interfacing fixture for utilizing distributed energy resource (DER) as an AC power supply. This dissertation investigates different control and synchronization techniques for stand-alone and grid-connected DC-AC VSCs. The most common control reference frame for VSCs is the dq reference frame (dq-RF), also known as the synchronous reference frame. The main challenge associated with the VSC control in this reference frame is the strong coupling between d and q axes. In this dissertation, a multi-loop dq-RF control system with a coupling compensation scheme is presented. Then, the droop-based power control technique, which eliminates the need for communication between parallel-connected VSCs and consequently offers a higher reliability, is investigated. A dq-RF-based approach of impedance design, for compensating the inequality of parallel VSCs connecting lines, along with the dq-RF droop control are also proposed. This approach results in an accurate power-sharing among parallel VSCs. The major challenges related to the synchronization unit of a grid-connected VSC control system in the presence of a distorted AC voltage are also briefly investigated in this dissertation. To deal with these challenges, an enhanced complex coefficient filter based PLL is designed and presented. This PLL completely removes the grid voltage imbalance and considerably attenuates the grid voltage dc offset and harmonics while maintaining a fast dynamic response and a simple structure. The VSC-interfaced DER is often required to switch between the islanded and grid-connected operation modes. The VSC integrated into the grid is current-controlled, while in the islanded operation mode is controlled as a voltage source. In the transition between these two modes, first the intended VSC operation mode should be detected, then its control system is reconfigured. To avoid the complexity of the control system and alleviate the drawbacks associated with the control mode transition, a VSC control approach, which mimics the traditional synchronous generator’s universal mode of operation, is studied. A method of power-based active synchronization of the VSC-interfaced DER, with the ability of seamless transition between the islanded mode and connected to the grid, is proposed and integrated with this technique of the VSC control.
Advanced mobile applications for law enforcement
(University of Alabama Libraries, 2012) York, Matthew; Ricks, Kenneth G.; University of Alabama Tuscaloosa
In this paper, a novel mobile application for law enforcement personnel, AlaCOP Mobile, is presented. The application is designed for the iPhone and iPad platforms, utilizing their intentionally mobile-minded hardware design as a low cost alternative to laptops and their peripherals. Features include the ability to: capture and securely upload photos, audio and video; visualize agent locations in near real-time with interactive maps; and allow access to the National Criminal Information Center (NCIC). In addition, novel rendering and message threading techniques are discussed which utilize the multicore architecture implemented in the more recent versions of the iPhone (iPhone 4s) and iPad (iPad 2).
Analysis of a percussive bucket wheel implementation for a robotic planetary excavator
(University of Alabama Libraries, 2015) Headley, Justin Kyle; Ricks, Kenneth G.; University of Alabama Tuscaloosa
Percussive digging methods have shown to reduce excavation forces when applied in a regolith (extraterrestrial) environment. Similarly bucket wheel excavators lend themselves to be favorable for future robotic planetary or Lunar missions due to their simple construction and continuous operation. This thesis analyzes the possibility of combining these technologies and the effects they would have when implemented into a planetary rover. Specific focus is placed on electrical robustness, power systems, and autonomous operation. Contributions include an experimental prototype and a simulated power analysis. Results conclude that a percussive bucket wheel would suffer from increased power consumption while gaining the benefit of increased electrical robustness, improved autonomous operation, and reduced launch mass. Finally, future improvements are discussed and a concluding statement is provided.
Analysis of low voltage regulator efficiency based on ferrite inductor
(University of Alabama Libraries, 2010) Kothakonda, Mridula; Hong, Yang-Ki; University of Alabama Tuscaloosa
Low voltage regulator based on ferrite inductor, using single- and two-phase topologies, were designed and simulated in MATLAB. Simulated values of output voltage and current were used to evaluate the buck converter (i.e., low voltage regulator) for power efficiency and percentage ripple reduction at frequencies between 1 and 10 MHz with variable loads from 0.024 to 4 ohms. The parameters, such as inductance of 20 nH, quality factor of 15 of fabricated ferrite inductor and DC resistance (DCR) of 8.3 milli ohms, were used for efficiency analysis of the converter. High current around 40 A was achieved by the converter at low load values. Low output voltage in the range of 0.8-1.2 V was achieved. The simulated results for the single- and two-phase converter were compared for maximum efficiency and lowest ripple in output voltage and current. The maximum efficiency of 97 % with load of 0.33 ohms and the lowest ripple current of about 2.3 mA were estimated for the two-phase converter at 10 MHz. In summary, the two-phase converter showed higher efficiency and lower ripple voltage and current than those of the single-phase converter. In addition, the efficiency of single- and two-phase converters based on ferrite inductor was compared to single- and two-phase converters based on air-core inductor. It was found that the power efficiency of the two-phase converter using ferrite inductor was 10 % higher than the converter using air-core inductor at 10 MHz with a load of 0.024 ohms.
An analysis of parasitic capacitances in ioimpedance spectroscopy and their impact on impedance measurements
(University of Alabama Libraries, 2019) Mathews, Robert Joseph; Freeborn, Todd J.; University of Alabama Tuscaloosa
Electrical Impedance Spectroscopy techniques have long been used to investigate the frequency dependent electrical properties of biological tissues. Typically termed BioImpedance Spectroscopy, or BIS, these measurements are used in many medical and fitness-related applications. However, many of these measurements suffer from a "hook-artifact", or erroneous increase in reactance at high ($f >$ 500 kHz) frequencies. Existing work models this hook with a stray capacitance in parallel with an existing tissue circuit model. While this model certainly produces a hook artifact, it does not account for the presence of electrodes in the circuit model. This thesis expands on this model to include the impedance of the electrode/tissue interface expected in bioimpedance measurements and include an additional stray capacitance that may exist as a result. This thesis develops the circuit theory to describe the impacts of the electrode/tissue impedance and parasitics in this expanded model. This circuit theory is validated through both simulation and experimental results of the proposed circuit model. From the proposed model, a correction technique to reduce the hook artifact based on measuring both the applied and return currents in a bioimpedance test setup is proposed and explored in simulations.
Analytical evaluation of effective solar sail attitude control using metasurfaces for deep space exploration
(University of Alabama Libraries, 2018) Ullery, Dylan; Kim, Seongsin; Kung, Patrick; University of Alabama Tuscaloosa
We examine the theoretical implications of incorporating metasurfaces on solar sails, and the effect they can have on the forces and torques applied to the sail. This would enable a significant enhancement over state-of-the- art attitude control by demonstrating a novel, propellant-free and low mass approach to induce a roll torque on the sail, which is a current limitation in present state-of-the-art technology. We do so by utilizing anomalous optical reflections from the metasurfaces to generate a net in-plane lateral force. This can lead to a net torque along the roll axis of the sail, in addition to the other spatial movements exhibited by the sail from solar radiation pressure. We characterize this net lateral force as a function of incidence angle. In addition, the influence of the phase gradients and anomalous conversion efficiency characteristics of the metasurfaces are independently considered. The optimum incidence angle that corresponded with the maximum net lateral-to-normal force ratio was found to be -30° for a metasurface exhibiting 75% anomalous conversion efficiency with a phase gradient of 0.71k0. Upon comparison with the force and torque plots from current reflection control devices such as those that were utilized on IKAROS, the anomalously reflecting metasurfaces offer a considerable increase in torque along the roll axis. This is important because up until this point, roll control has been a particularly difficult aspect of solar sail attitude control to manipulate without the use of reaction wheels or propellant. The torque along the roll axis can reach values of torque as high as 358 μN m under ideal conditions.
Analyzing the Mental Health and Resilience of Undergraduate Nursing Students During the COVID-19 Outbreak
(University of Alabama Libraries, 2021) Horton, Abby Grammer; Lawson, Michael A.; University of Alabama Tuscaloosa
The study of risk, resilience, and mental health is timely and important to nursing education because today’s nursing students are experiencing a global pandemic, with the rapid outbreak of COVID-19. This novel crisis and circumstances require research that documents how pre-service healthcare professionals are reacting and coping to the current global pandemic. This need is evident because COVID-19 has uniquely positioned nurses as first responders who often must risk their lives in order to provide patient care. This transformational role and experience will likely have a profound effect on the profession and those entering the profession. The purpose of this descriptive-exploratory study is to understand the relationship of risk (e.g., anxiety, stress, and COVID-19 Induced Risk Factors) resilience, and mental health factors among undergraduate nursing students in response to COVID-19. The sample population for this study is undergraduate nursing students enrolled in the upper division of a four-year BSN program at a large, public institution in the Southeastern United States. This study is designed as a descriptive-exploratory study to describe and explore the immediate reactions of nursing students to the COVID-19 Pandemic - a crisis that profoundly affects nurses and other healthcare professionals. Data was collected in the Spring Semester of 2020 using an online Qualtrics Survey emailed to participants via a student email list-serv with prior approval and after IRB approval was obtained. Students answered one survey with six instruments that were self-report measures for resilience, grit, stress, coping, depression, and anxiety. Students also answered demographic questions that addressed life events and environment changes due to COVID-19. Since many of today’s nursing pre-service professionals will enter the workforce while the current global crisis is on-going, research is needed that highlights the social, psychological, and instrumental supports that may protect the profession from undesirable attrition.
Approximate dynamic programming and artificial neural network control of electric vehicles: from motor drives to grid integration
(University of Alabama Libraries, 2019) Sun, Yang; Li, Shuhui; University of Alabama Tuscaloosa
The drive system of an electric vehicle (EV) includes two major parts- the powertrain and charging system. This dissertation investigates the implementation of the approximate dynamics programming (ADP) based artificial neural network (ANN) control on these two parts to increase the efficiency, stability and reliability of EVs. The major challenge of the powertrain control is to control the EV motor, which is usually an interior mounted permanent magnetic motor(IPM). By using the conventional vector controller, the IPM encounters high current distortion and speed oscillation especially when working in overmodulation area, due to the decoupling inaccuracy issue. The ADP-ANN controller resolves the decoupling issue and guarantees better speed and current tracking performance. For industrial implementation, the motor control algorithm is normally achieved by a digital signal processor (DSP), which has limited computational resources. As ADP-ANN has more complex structure than the conventional controller, whether it can be put into a DSP need to be tested. This dissertation optimized the ADP-ANN algortithm and make it successfully running in a TMS320F28335 DSP platform. To control a gird-connected solar based EV charging system, the dc-bus voltage stability of the solar inverter need to be maintained to acquire high charging efficiency and reduce the grid current distortion. This will become a challenge to conventional vector controller when the solar irradiation level changing rapidly. The implementation of the proposed controller allows the solar inverter improve the dc-bus voltage stability, energy capture efficiency, adaptivity, power conversion efficiency and power quality. Multiple EVs can be used to supply reactive power to the grid when connected with the charging system. But, a great challenge is that grid integration inverters would fight each other when operated autonomously in participating grid voltage control using the conventional control methods. The ADP-ANN control is able to properly handle the inverter constraints in achieving Voltage/Var control objectives at the grid edge and overcomes the challenges of conventional DER inverter control techniques.
Architectures and control for energy storage systems with wired and wireless power transfer
(University of Alabama Libraries, 2019) Cao, Yuan; Abu Qahouq, Jaber; University of Alabama Tuscaloosa
In the past two decades, the performance of battery energy storage systems (BESS) has been significantly improved with the utilization of advanced architectures and control methods and new electronic devices. However, the increasing demands imposed by BESS applications still necessitate the need for additional performance improvement and/or create new issues that need to be addressed. These can be summarized as follows: (1) The imbalance in the state-of-charge (SOC) between cells might occur, which might degrade the performance of the battery system. (2) In a BESS, with the increasingly advanced functions and control methods, the number of required components is increased. (3) In electrical vehicles (EVs) applications, the limited driving range and the needed charging time of the lithium-ion (Li-Ion) battery pack is one of the major reasons slowing down the adoption of EVs. (4) The transmission efficiency of wireless power transfer (WPT) systems is decreased as the distance and misalignment between transmitter (Tx) and receiver (Rx) increase. (5) In order to realize the wireless power transfer in BESS, additional components such as DC-AC inverter Tx coil, Rx coil and AC-DC rectifier are required, which increase the cost and size of the system. This dissertation work focuses on investigating the challenges mentioned above to further improve the overall performance of battery system, reduce the number of components and converters, increase the system efficiency and realize a robust and cost-effective battery energy storage system. Chapter 2 and Chapter 3 focus on the challengers related to SOC balancing and large number of components in battery systems. In Chapter 4, one unique aspect of the WEDES system is used in order to add flexibility and improve safety. Chapter 5 and Chapter 6 address the challenge related to decreased transmission efficiency in wireless power transfer when charging a battery. In Chapter 7, in order to deal with the challenge that additional components are required to realize wireless power transfer, a single dual-type-output power converter is discussed and analyzed. Chapter 8 provides a summary and conclusion for the work presented in this dissertation and discusses some potential future work.
Are They As Engaged As They Say? A Study of Anticipated and Actual Engagement of First-Year Freshmen
(University of Alabama Libraries, 2020) Gorman, Brian Jacob; Laanan, Frankie Santos; University of Alabama Tuscaloosa
Not only is achieving a four-year degree beneficial for individual students, keeping students enrolled until graduation is beneficial for the institution as well. Decreases in state funding of higher education as well as the increasing number of states having adopted some kind of performance based funding (PFB) model, have resulted in many institutions relying on enrollment and retention for fiscal purposes. Because attrition rates are highest during students’ first year of college, it is important for institutions to find ways of engaging first-time, full-time freshmen in educationally purposeful activities early in their college career to aid in retention efforts. Early-enrollment instruments and the use of data analytics can be useful in identifying student risk factors that may lead to their not returning to college for their second year. Institutions can utilize early-enrollment instruments not only to identify risk factors, but also to create a holistic plan for college success during their first year. This study investigated first-time, full-time freshmen participating in a special admission program at a large, research institution in the South, exploring the influence of background characteristics on student anticipated engagement prior to enrollment, and actual engagement in the first semester, and how background characteristics, anticipated engagement, and actual advising and Student Life engagement predict first-term GPA, first-term credits earned, and continued enrollment in the next consecutive term. Findings indicate significant differences in anticipated and actual engagement by background characteristics, and the background characteristics, and anticipated and actual engagement can predict student success measures such as GPA and credits earned.
Automatic test program generation and novel test techniques for testing radio frequency and high-voltage device interface boards
(University of Alabama Libraries, 2013) Kannan, Sukeshwar; Kim, Bruce C.; University of Alabama Tuscaloosa
This dissertation describes the development and application of two software tools: RF Analyzer and Diagnostic Program Generation (RADPro), and High-Voltage Program Generation (HVPro). We developed these tools to automate the process of testing device interface boards for production testing of IC chips. Testing device interface board is an essential part of a production testing to ensure all components on the board are assembled properly and operational before the actual IC chips can be tested. Our software tools utilize the netlist, bill of materials and component model library. Automatic test program generation by RADPro and HVPro reduces design expense and time to market a new IC product significantly by reducing manual handcoding work. We have validated some of our pseudocode with the existing automatic test equipment at Texas Instruments, Inc.
Battery charge and discharge control for energy management in EDV and utility integration
(University of Alabama Libraries, 2012) Bao, Ke; Li, Shuhui; University of Alabama Tuscaloosa
Electric drive vehicles (EDVs) have many benefits as compared to normal petrol or gas cars. Moreover, the electrification of transportation systems would enable increased electricity generation from carbon-free and renewable energy sources, such as wind, solar, and hydro. However, due to highly distributed and mobile nature as well as high charge and discharge power demand of EDVs, it is important to investigate how to manage EDV charge and discharge to enhance the usage of renewable enough resources in the future smart grid framework. For this purpose, this thesis first investigates typical battery electrochemical properties which are important concerns for the design of EDV charge and discharge. In this section, mathematical and circuit-oriented battery models are investigated to reflect typical battery electrochemical properties. Meanwhile, the relation between mathematical and circuit-oriented battery models is analyzed. Then, this thesis presents an energy control study in a charging station, a typical integrated EDV and utility system. The charging station consists of an AC/DC converter for grid interface and multiple dc/dc converters for EDV battery management. For the grid-side converter, a direct-current control mechanism is employed for reactive power, ac system bus voltage, and DC-link voltage control. For the EDV-side converters, constant-current and constant-voltage control mechanisms are investigated for charging and discharging control. The thesis considers energy management need for charge and discharge of multiple EDVs simultaneously as well as energy transferring from vehicle to grid and grid to vehicle requirements. A real-time simulation model is investigated and the performance of the integrated EDV and utility system is investigated.
Black Men's Choice Process in Attending a Historically Black College and University Medical School
(University of Alabama Libraries, 2021) Powers, Brenton; Bray, Nathaniel J.; University of Alabama Tuscaloosa
This qualitative study examines Black men's graduate school choice process enrolled in a Doctor of Medicine (MD) degree program at a historically Black college or university (HBCU) medical school. While there is foundational literature regarding graduate school decision-making (Olson & King, 1985), the literature on graduate school choice is limited. Recent work of English and Umbach's (2016) four-layer graduate school choice conceptual model, adapted from Perna's (2006) college choice model, serves as a theoretical framework and a basis throughout the literature landscape of graduate school choice. Furthermore, when exploring the medical school choice, there is little current literature that examines the choice process for Black men in attending HBCU medical schools. The decreasing presence of Black men in medical school commands attention to graduate school choice for these students. Through this study, a critical gap in medical education scholarly work will be filled. The purpose of this research is to ascertain the school choice process for Black men enrolled in an MD program at an HBCU medical school, using in-depth individual interviews with these students. Extracting from English and Umbach's (2016) four-layer graduate school choice conceptual model and McDonough et al. (1997) Black college choice model, this study expects for Black men's medical school choice to be determined by habitus, the context of school and community, the context of higher education, and context of social, economic, and policy. This research provides an essential perspective into Black male students' medical school choice process by investigating these influences. This study advances the knowledge of a budding body of research associated with graduate school choice and assists HBCU medical schools in identifying the factors attributed to Black male enrollment in HBCU medical schools. Having this knowledge empowers HBCU medical schools to better prepare for Black male medical students' recruitment and retention.
Building practical apertureless scanning near-field microscopy
(University of Alabama Libraries, 2017) Gungordu, Muhammed Zeki; Kim, Seongsin; University of Alabama Tuscaloosa
The fundamental objective of this study is to establish a functional, practical apertureless type scanning near-field optical microscope, and to figure out the working mechanism behind it. Whereas a far-field microscope can measure the propagating field’s components, this gives us little information about the features of the sample. The resolution is limited to about half of the wavelength of the illuminating light. On the other hand, the a-SNOM system enables achieving non-propagating components of the field, which provides more details about the sample’s features. It is really difficult to measure because the amplitude of this field decays exponentially when the tip is moved away from the sample. The sharpness of the tip is the only limitation for resolution of the a-SNOM system. Consequently, the sharp tips are achieved by using electrochemical etching, and these tips are used to detect near-field signal. Separating the weak a-SNOM system signals from the undesired background signal, the higher demodulation background suppression is utilized by lock-in detection.
Characteristics of thz carrier dynamics in gan thin film and zno nanowires by temperature dependent terahertz time domain spectroscopy measurement
(University of Alabama Libraries, 2012) Balci, Soner; Kim, Seongsin; University of Alabama Tuscaloosa
We present a comprehensive study of the characteristics of carrier dynamics using temperature dependent Terahertz Time Domain Spectroscopy. By utilizing this technique in combination with numerical calculations, the complex refractive index, dielectric function, and conductivity of n-GaN, undoped ZnO NWs, and Al-doped ZnO NWs were obtained. The unique temperature dependent behaviors of major material parameters were studied at THz frequencies, including plasma frequency, relaxation time, carrier concentration and mobility. Frequency and temperature dependent carrier dynamics were subsequently analyzed in these materials through the use of the Drude and the Drude-Smith models.
Cognitive heterogeneous sensor platform for human biometric and activity pattern analysis
(University of Alabama Libraries, 2016) Ma, Rui; Hu, Fei; University of Alabama Tuscaloosa
Human biometric and activities can be acquired from their motions and postures. Conventional video cameras have many limitations. In this dissertation research our goal is to develop sensor hardware as well as machine learning algorithms/software to achieve motion recognition with low communication bandwidth and processing complexity. We have designed the wireless sensing systems targeting the following two applications: (1) Binary compressive sensing (CS) systems for smart home. The binary sensing systems are designed to obtain the geometric information of human motions for the recognition of indoor activities. CS theory is used in the design of sensor sampling structure. We employ Buffon's Needle model of integral geometry to describe human gait changes, and use Hidden Markov Model (HMM) to extract the statistic features for motion recognition. Pyroelectric Infrared (PIR) sensors are used for human gait recognition. Both passive PIR sensor network and active PIR sensors are developed to detect moving and static thermal targets respectively. Laser sensors are used for gait disorder recognition with metrics of symmetry, coordination, and balance. Fiber optic sensors have been deployed and encoded on the ground for multiple human subject location based on Low density parity check (LDPC) codes. (2) Motion capture system for rehabilitation training. Many patients who suffer from the paralysis can recover body functions by taking appropriate rehabilitation training. This study aims to develop a home-oriented cyber-physical system (CPS) to help the patients improve their motion ability via physical training. The system provides quantitative evaluation for the performed motions. The measures evaluated by the system include the motion style of the legs, the periodicity of the foot trajectory, and the foot balance level. The motions of legs and feet are recorded by the thermal camera, and the plantar pressure is measured by the insole pressure sensors. We have developed algorithms to extract the leg skeletons from the thermal images, and to implement motion auto-segmentation, recognition and analysis for the above mentioned measures. This dissertation explores the frontier of intelligent sensing systems for human motion recognition. We have conducted many experiments to demonstrate the efficiency and capability of our methods and systems.

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