Transient force atomic force microscopy, Dual $Q$ control in atomic force microscopy, Constructive control of quantum-mechanical systems, and Feedback control for real-time scheduling
Sahoo, Deepak (2006) Transient force atomic force microscopy, Dual $Q$ control in atomic force microscopy, Constructive control of quantum-mechanical systems, and Feedback control for real-time scheduling. PhD thesis, Iowa State University.
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In existing dynamic mode operation of Atomic Force Microscopes (AFMs) steady-state signals like amplitude and phase are used for detection and imaging of material. Due to the high quality factor of the cantilever probe the corresponding methods are inherently slow. In this dissertation, a novel methodology for fast interrogation of material that exploits the transient part of the cantilever motion is developed. This method effectively addresses the perceived fundamental limitation on bandwidth due to high quality factors. It is particularly suited for the detection of small time scale tip-sample interactions. Analysis and experiments show that the method results in significant increase in bandwidth and resolution as compared to the steady-state-based methods. In atomic force microscopy, bandwidth or resolution can be affected by active quality factor (Q) control. However, in existing methods the trade off between resolution and bandwidth remains inherent. Observer based Q control method provides greater flexibility in managing the tradeoff between resolution and bandwidth during imaging. It also facilitates theoretical analysis lacking in existing methods. In this dissertation we develop a method for exact constructive controllability of quantum-mechanical systems. The method has three steps, first a path from the initial state to the final state is determined and intermediate points chosen such that any two consecutive points are close, next small sinusoidal control signals are used to drive the system between the points, and finally quantum measurement technique is used to exactly achieve the desired state. The methodology is demonstrated for the control of spin-half particles in a Stern-Gerlach setting. Most of real-time scheduling algorithms are open-loop algorithms as the scheduling decisions are based on the worst-case estimates of task parameters. In this dissertation, a novel closed-loop approach for dynamically estimating the execution time of tasks based on both deadline miss ratio and task rejection ratio in the system is developed. This approach is highly preferable for firm/soft real-time systems since it provides a firm performance guarantee in terms of deadline misses while achieving a high guarantee ratio. Proportional-integral controller and H-infinity controller are designed for closed loop scheduling. The performance of the open-loop and the closed-loop approaches are evaluated using simulation studies. It is shown that the closed-loop dynamic scheduling offers a better performance over the open-loop scheduling under all the practical conditions.
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