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A Control Theoretic Approach for Resilient Network Services

Description: Resilient networks have the ability to provide the desired level of service, despite challenges such as malicious attacks and misconfigurations. The primary goal of this dissertation is to be able to provide uninterrupted network services in the face of an attack or any failures. This dissertation attempts to apply control system theory techniques with a focus on system identification and closed-loop feedback control. It explores the benefits of system identification technique in designing and validating the model for the complex and dynamic networks. Further, this dissertation focuses on designing robust feedback control mechanisms that are both scalable and effective in real-time. It focuses on employing dynamic and predictive control approaches to reduce the impact of an attack on network services. The closed-loop feedback control mechanisms tackle this issue by degrading the network services gracefully to an acceptable level and then stabilizing the network in real-time (less than 50 seconds). Employing these feedback mechanisms also provide the ability to automatically configure the settings such that the QoS metrics of the network is consistent with those specified in the service level agreements.
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Date: December 2018
Creator: Vempati, Jagannadh Ambareesh
Partner: UNT Libraries

Fast methods for static Hamilton-Jacobi Partial Differential Equations

Description: The authors develop a family of fast methods approximating the solution to a wide class of static Hamilton-Jacobi partial differential equations. These partial differential equations are considered in the context of control-theoretic and front-propagation problems. In general, to produce a numerical solution to such a problem, one has to solve a large system of coupled non-linear discretized equations. The techniques use partial information about the characteristic directions to de-couple the system. Previously known fast methods, available for isotropic problems, are discussed in detail. They introduce a family of new Ordered Upwinding Methods (OUM) for general (anisotropic) problems and prove convergence to the viscosity solution of the corresponding Hamilton-Jacobi partial differential equation. The hybrid methods introduced here are based on the analysis of the role played by anisotropy in the context of front propagation and optimal trajectory problems. The performance of the methods is analyzed and compared to that of several other numerical approaches to these problems. Computational experiments are performed using test problems from control theory, computational geometry and seismology.
Date: May 1, 2001
Creator: Vladimirsky, Alexander Boris
Partner: UNT Libraries Government Documents Department

Control of nonlinear systems using periodic parametric perturbations with application to a reversed field pinch

Description: In this thesis, the possibility of controlling low- and high-dimensional chaotic systems by periodically driving an accessible system parameter is examined. This method has been carried out on several numerical systems and the MST Reversed Field Pinch. The numerical systems investigated include the logistic equation, the Lorenz equations, the Roessler equations, a coupled lattice of logistic equations, a coupled lattice of Lorenz equations, the Yoshida equations, which model tearing mode fluctuations in a plasma, and a neural net model for magnetic fluctuations on MST. This method was tested on the MST by sinusoidally driving a magnetic flux through the toroidal gap of the device. Numerically, periodic drives were found to be most effective at producing limit cycle behavior or significantly reducing the dimension of the system when the perturbation frequency was near natural frequencies of unstable periodic orbits embedded in the attractor of the unperturbed system. Several different unstable periodic orbits have been stabilized in this way for the low-dimensional numerical systems, sometimes with perturbation amplitudes that were less than 5% of the nominal value of the parameter being perturbed. In high-dimensional systems, limit cycle behavior and significant decreases in the system dimension were also achieved using perturbations with frequencies near the natural unstable periodic orbit frequencies. Results for the MST were not this encouraging, most likely because of an insufficient drive amplitude, the extremely high dimension of the plasma behavior, large amounts of noise, and a lack of stationarity in the transient plasma pulses.
Date: June 1, 1998
Creator: Mirus, K.A.
Partner: UNT Libraries Government Documents Department

Networking and Decentralized Control in Layered Networks: a Theoretical Study and Test-bed Development

Description: Layered structures are commonly used in communication systems, but their roles in decentralized control are not understood well. In the first part of this thesis, a theoretical study of consensus (a typical decentralized control task) in layered structures is conducted. The unique graph topology approach permits explicit characterization of consensus performance based on simple graphical characteristics of MLMG structures. In the second part of this thesis, a generic LEGO test-bed to mimic multi-domain communication with layered structures is described. A search-and-rescue scenario is implemented to demonstrate the use of the test-bed.
Date: December 2014
Creator: Sheth, Vardhman Jayeshkumar
Partner: UNT Libraries

Digital signal processing control of induction machine`s torque and stator flux utilizing the direct stator flux field orientation method

Description: This paper presents a review of the Direct Stator Flux Field Orientation control method. This method can be used to control an induction motor`s torque and flux directly and is the application of interest for this thesis. This control method is implemented without the traditional feedback loops and associated hardware. Predictions are made, by mathematical calculations, of the stator voltage vector. The voltage vector is determined twice a switching period. The switching period is fixed throughout the analysis. The three phase inverter duty cycle necessary to control the torque and flux of the induction machine is determined by the voltage space vector Pulse Width Modulation (PWM) technique. Transient performance of either the flux or torque requires an alternate modulation scheme which is also addressed in this thesis. A block diagram of this closed loop system is provided. 22 figs., 7 tabs.
Date: April 1, 1997
Creator: Seiz, J.B.
Partner: UNT Libraries Government Documents Department

Effects of Control Theory Training Upon Self-Concept and Locus of Control Among Selected University Freshmen

Description: This study examined the effects of Control Theory training upon self-concept and locus of control among students enrolled in the Provisional Admission Program (PAP) at the University of Texas at Arlington. Twenty-nine students randomly assigned to treatment or placebo control groups took the Coppersmith Self-Esteem Inventory (CSSEI-A) and the Adult Nowicki-Strickland Internal-External Locus of Control Scale (ANSIE) as pre- and posttests. Participants in the placebo control group attended their regular educational program for the same amount of time given to the treatment group. No significant differences were found on the Analysis of Covariance for CSSEI—A or ANSIE scores following the training period. CSSEI-A and ANSIE scores were elevated, indicating that PAP students think of themselves internally as do other college students, regardless of their SAT scores. The results of this study indicate that Control Theory training is insignificantly effective in producing changes in the self-concept and locus of control among PAP students. Control Theory research may need to be carried out with a smaller group size, use larger samples, provide more time to address the issues specific to PAP student needs, include a stronger counseling emphasis to meet their needs, use more sensitive instruments to detect such changes, and allow more time for the learning to occur before the administration of the posttest.
Date: August 1987
Creator: Smadi, Ahmad Abdel-Majid
Partner: UNT Libraries

The Industrial Representative's Perception of the Impact of Managerial Control Systems on Performance

Description: The objective of this study was to examine whether the factors which constitute the manufacturer/industrial-representative relationship, influence performance as predicted by control theory. In addition, the study evaluated the contribution of selected demographic factors such as size of the firm, and the representative's experience, on performance.
Date: August 1995
Creator: Dunipace, Richard A. (Richard Alan)
Partner: UNT Libraries

Understanding How Jurors Award Civil Damages: A Test of Affect Control Theory

Description: This dissertation examines predictors of juror-determined damage awards among 377 juror eligible mock jurors. Citizens reporting for jury duty in a large metropolitan county on five days when the study was conducted were invited to participate. Scenarios were created that varied both case facts and witness emotion during trial testimony. Results indicate that Affect Control Theory can be applied to the situation of juror-determined damage awards and is helpful in scientifically explaining some of the variation of both compensatory and punitive damage awards.
Date: August 2004
Creator: McDonald, Emily
Partner: UNT Libraries