Ulm, Univ., Diss., 2007.

Thesis (Ph. D.)--Lehigh University, 1996. / Includes vita. Bibliography: leaves 276-284.

Marburg, Univ., Diss., 2009

Thesis (doctoral)--Rheinische Friedrich-Wilhelms-Universität Bonn, 1996. / Includes bibliographical references (p. 94-99).

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 202-212).

This thesis presents the design and the stability analysis of a hierarchical controller for unmanned aerial vehicles. We utilize non-linear control methodology to command dynamics of unmanned helicopter which has been divided into slower translational dynamics (outer-loop) and faster orientation dynamics (inner-loop), thus exhibiting hierarchical structure. The attitude angles and position which separately belongs to the inner-loop and the outer-loop can be independently controlled by backstepping control strategy. Stability analysis of the helicopter system including applying dynamics has been illustrated after designing. And relative comparison between linear and nonlinear controllers has been carried out. After studying linear control, nonlinear control and stability analysis of one small-scale helicopter, we think about control strategy of a group helicopter which can be called as consensus control.

Researchers have recently become interested in two-dimensional materials such as graphene, hexagonal boron nitride (h-BN), Transition Metal Dichalcogenides (TMDs), etc. Their 2D hexagonal structures result in unique properties, which make these materials attractive for scientists and engineers. In this work, we investigated the electronic properties of graphene, h-BN, and MoS2 based on density functional theory (DFT). We first studied the electronic properties of monolayers of different materials. We found a zero bandgap and observed massless Dirac Hamiltonian in graphene. For h-BN, a large bandgap at K-point was observed. Also, we observed the bandgap opening in MoS2 and a strong splitting of its bands. Then, we extended these studies to graphene and h-BN bilayers. For graphene bilayer, we observed a gapless material and massive Dirac fermions. For h-BN bilayer, an indirect bandgap was observed, smaller in comparison with its monolayer. The main focus of this study was the investigation of graphene/h-BN heterostructures for different stacking configurations. The suitability of h-BN as a substrate for graphene is due to its small lattice constant mismatch with graphene and its high insulating gap (~ 5 eV). Another important aspect to be observed in graphene/h-BN heterostructures is the gap opening brought by the h-BN layer proximity to the initially gapless graphene layer. We found the effect of bandgap opening in graphene/h- BN and determined the most stable configuration which is the AB[CB]. This work supports the findings of many researchers who demonstrate that graphene/h-BN heterostructures are very useful as building blocks for nanodevices with desirable electronic properties.

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