LARGE MOTION VISUALIZATION AND ESTIMATION FOR FLAPPING WING SYSTEMS

Studies of fluid-structure interactions associated with flexible structures such as flapping wings require the capture and quantification of large motions of bodies that may be opaque. Motion capture of a free flying insect is considered by using three synchronized high-speed cameras. A solid finite element representation is used as a reference body and successive snapshots in time of the displacement fields are reconstructed via an optimization procedure. An objective function is formulated, and various shape difference definitions are considered. The proposed methodology is first studied for a synthetic case of a flexible cantilever structure undergoing large deformations, and then applied to a Manduca Sexta (hawkmoth) in free flight. The three-dimensional motions of this flapping system are reconstructed from image date collected by using three cameras. The complete deformation geometry of this system is analyzed. Finally, a computational investigation is carried out to understand the flow physics and aerodynamic performance by prescribing the body and wing motions in a fluid-body code. This thesis work contains one of the first set of such motion visualization and deformation analyses carried out for a hawkmoth in free flight. The tools and procedures used in this work are widely applicable to the studies of other flying animals with flexible wings as well as synthetic systems with flexible body elements.

Precoder Detection for Cooperative Decode-and-Forward Relaying in OFDMA Systems

We consider an LTE network where a secondary user acts as a relay, transmitting data to the primary user using a decode-and-forward mechanism, transparent to the base-station (eNodeB). Clearly, the relay can decode symbols more reliably if the employed precoder matrix indicators (PMIs) are known. However, for closed loop spatial multiplexing (CLSM) transmit mode, this information is not always embedded in the downlink signal, leading to a need for effective methods to determine the PMI. In this thesis, we consider 2x2 MIMO and 4x4 MIMO downlink channels corresponding to CLSM and formulate two techniques to estimate the PMI at the relay using a hypothesis testing framework. We evaluate their performance via simulations for various ITU channel models over a range of SNR and for different channel quality indicators (CQIs). We compare them to the case when the true PMI is known at the relay and show that the performance of the proposed schemes are within 2 dB at 10% block error rate (BLER) in almost all scenarios. Furthermore, the techniques add minimal computational overhead over existent receiver structure. Finally, we also identify scenarios when using the proposed precoder detection algorithms in conjunction with the cooperative decode-and-forward relaying mechanism benefits the PUE and improves the BLER performance for the PUE. Therefore, we conclude from this that the proposed algorithms as well as the cooperative relaying mechanism at the CMR can be gainfully employed in a variety of real-life scenarios in LTE networks.

Understanding the Reaction Mechanism of Nanocomposite Thermites

Nanocomposite energetics are a relatively new class of materials that combine nanoscale fuels and oxidizers to allow for the rapid release of large amounts of energy. In thermite systems (metal fuel with metal oxide oxidizer), the use of nanomaterials has been illustrated to increase reactivity by multiple orders of magnitude as a result of the higher specific surface area and smaller diffusion length scales. However, the highly dynamic and nanoscale processes intrinsic to these materials, as well as heating rate dependencies, have limited our understanding of the underlying processes that control reaction and propagation. For my dissertation, I have employed a variety of experimental approaches that have allowed me to probe these processes at heating rates representative of free combustion with the goal of understanding the fundamental mechanisms. Dynamic transmission electron microscopy (DTEM) was used to study the in situ morphological change that occurs in nanocomposite thermite materials subjected to rapid (10^11 K/s) heating. Aluminum nanoparticle (Al-NP) aggregates were found to lose their nanostructure through coalescence in as little as 10 ns, which is much faster than any other timescale of combustion. Further study of nanoscale reaction with CuO determined that a condensed phase interfacial reaction could occur within 0.5-5 µs in a manner consistent with bulk reaction, which supports that this mechanism plays a dominant role in the overall reaction process. Ta nanocomposites were also studied to determine if a high melting point (3280 K) affects the loss of nanostructure and rate of reaction. The condensed phase reaction pathway was further explored using reactive multilayers sputter deposited onto thin Pt wires to allow for temperature jump (T-Jump) heating at rates of ~5x10^5 K/s. High speed video and a time of flight mass spectrometry (TOFMS) were used to observe ignition temperature and speciation as a function of bilayer thickness. The ignition process was modeled and a low activation energy for effective diffusivity was determined. T-Jump TOFMS along with constant volume combustion cell studies were also used to determine the effect of gas release in nanoparticle systems by comparing the reaction properties of CuO and Cu2O.

SCHOOL DISTRICT GOVERNANCE AND KNOWLEDGE-FIT IN DECISION RIGHTS: HOW DISTRICTS RECRUIT AND HIRE SCHOOL LIBRARIANS

This study examines the organizational structures and decision-making processes used by school districts to recruit and hire school librarians. For students to acquire the information and technology literacy education they need, school libraries must be staffed with qualified individuals who can fulfill the librarian’s role as leader, teacher, instructional partner, information specialist, and program administrator. Principals are typically given decision rights for hiring staff, including school librarians. Research shows that principals have limited knowledge of the skills and abilities of the school librarian or the specific needs and functions of the library program. Research also indicates that those with specific knowledge of school library programs, namely school district library supervisors, are only consulted on recruiting and hiring about half the time. School districts entrust library supervisors with responsibilities such as professional development of school librarians only after they are hired. This study uses a theoretical lens from research on IT governance, which focuses on the use of knowledge-fit in applying decision rights in an organization. This framework is appropriate because of its incorporation of a specialist with a specific knowledge set in determining the placement of input and decision rights in the decision-making processes. The method used in this research was a multiple-case study design using five school districts as cases, varying by the involvement of the supervisors and other individuals in the hiring process. The data collected from each school district were interviews about the district’s recruiting and hiring practices with principals, an individual in HR, library supervisors, and recently hired school librarians. Data analysis was conducted through iterative coding from themes in the research questions, with continuous adjustments as new themes developed. Results from the study indicate that governance framework is applicable to evaluating the decision-making processes used in recruiting and hiring school librarians. However, a district’s use of governance did not consistently use knowledge-fit in the determination of input and decision rights. In the hiring process, governance was more likely to be based on placing decision rights at a certain level of the district hierarchy rather than the location of specific knowledge, most often resulting in site-based governance for decision rights at the school-building level. The governance of the recruiting process was most affected by the shortage or surplus of candidates available to the district to fill positions. Districts struggling with a shortage of candidates typically placed governance for the decision-making process on recruiting at the district level, giving the library supervisor more opportunity for input and collaboration with human resources. In districts that use site-based governance and that place all input and decision rights at the building level, some principals use their autonomy to eliminate the school library position in the allotment phase or hire librarians that, while certified through testing, do not have the same level of expertise as those who achieve certification through LIS programs. The principals in districts who use site-based governance for decision rights but call on the library supervisor for advisement stated how valuable they found the supervisor’s expertise in evaluating candidates for hire. In no district was a principal or school required to involve the library supervisor in the hiring of school librarians. With a better understanding of the tasks involved, the effect of district governance on decision-making, and the use of knowledge to assign input and decision rights, it is possible to look at how all of these factors affect the outcome in the quality of the hire. A next step is to look at the hiring process that school librarians went through and connect those with the measurable outcomes of hiring: school librarian success, retention, and attrition; the quality of school library program services, outreach, and involvement in a school; and the perceptions of the success of the school librarian and the library program as seen from students, teachers, administrators, parents, and other community stakeholders.