PHD, Kent State University, 2009, College of Arts and Sciences / Department of Physics

Due to the many advantages of organic semiconductors over their inorganic counterparts, there is a strong and growing interest in their development. However, the large intermolecular spacing and other factors in organics result in a band structure that is narrow and often thermally disrupted, introducing disorder in the system and adversely affecting the conduction of charge. In this dissertation, we concentrate on three factors that influence the motion of charge: disorder, ionic impurities, and molecular design (and, in particular, the presence of pyridine). We discuss charge carrier mobility measurement in different organic semiconductors ranging from relatively ordered liquid crystalline systems to a highly disordered glassy material. Several theoretical approaches are used to analyze the results. For example, in a terpyridine-based high-order smectic liquid crystal we found surprisingly small, Poole-Frenkel mobilities (log(mobility) ~ E1/2) which may naively be described by either the Scher-Montroll (non-Gaussian transport) or Bassler's Gaussian transport model. However, the transient current traces did not comply with the universality and logarithmic slope predictions of the non-Gaussian model, but do follow the predictions of Bassler's model of Gaussian conduction. This various roles of diagonal (site energy) and off-diagonal (transfer integral) disorder are discussed. In the organic glassy material, the energy disorder of the transport sites plays the central role in determining the mobility. Using the spatially correlated disorder model of Kenkre, Dunlap, and coworkers, we are able to extract reasonable materials' parameters such as the Gaussian width of the hopping site energy distribution and the molecular dipole moment. Impurities also play several essential roles in organic semiconductors. Here we concentrate on itinerant ions in liquid crystalline semiconductors. Due to the low viscosity of the liquid crystalline system, mobile ions may influence the e (open full item for complete abstract)

Committee: Brett Ellman Dr. (Advisor); Elizabeth Mann Dr. (Committee Member); John Portman Dr. (Committee Member); Robert Twieg Dr. (Committee Member); Deng-Ke Yang Dr. (Committee Member); Bryan Anderson Dr. (Other); John R. D. Stalvey Dr. (Other) Subjects: Materials Science; Physics

Master of Science in Mechanical Engineering, Cleveland State University, 2009, Fenn College of Engineering

The objective of this thesis is to explore an innovative approach to the on-line health monitoring of rotating machinery in the presence of structural damage using active magnetic bearings (AMBs). First, the detailed model of the rotor with the breathing transverse crack is developed using finite element method. Next, the experimental data from the rotating magnetically levitated healthy and cracked shafts, under specially designed external excitation force, was collected, analyzed and compared with the computer simulation. The obtained results demonstrate that the presented on-line health monitoring technique is very effective for detection of the structural damage in rotating machinery, and it has a potential to be effectively applied in industry.

Committee: Dr. Jerzy Sawicki PhD (Committee Chair); Dr. John Frater PhD (Committee Member); Dr. Ana Stankovic PhD (Committee Member); Dr. John Lekki PhD (Committee Member) Subjects: Electromagnetism; Engineering; Mechanical Engineering