DRUM Collection: Electrical & Computer Engineering Theses and Dissertations
http://hdl.handle.net/1903/2765
Wed, 23 Apr 2014 11:49:08 GMT2014-04-23T11:49:08ZAn Analysis of Network Flow Records for Inferring Web Browser Redirection
http://hdl.handle.net/1903/14935
Title: An Analysis of Network Flow Records for Inferring Web Browser Redirection
Authors: Hemingway, Frank Shawn
Abstract: Legitimate web browser redirection is often used to take users to web pages that have moved or to help users find the correct website when they have entered the web address incorrectly. Unfortunately, computer network attackers can use web browser redirection to manage malware-serving hosts and conceal their activity. An analysis of network flow records yields heuristics for flow size, flow duration, and inter-flow duration that indicate flows where web browser redirection is likely to have occurred. Results show that flows matching these redirection heuristics are indeed several times more likely to communicate with Internet hosts that have exhibited a history of malicious behavior. A network security administrator can thus filter large sets of network flow records to reveal flows most likely to contain web browser redirection. This capability reduces the sample space when looking for evidence of malicious activity targeting web browsers and contributes more generally to the expanding field of flow-based application recognition.Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/1903/149352013-01-01T00:00:00ZTRANSVERSE CHARACTERIZATION AND CONTROL OF BEAMS WITH SPACE CHARGE
http://hdl.handle.net/1903/14902
Title: TRANSVERSE CHARACTERIZATION AND CONTROL OF BEAMS WITH SPACE CHARGE
Authors: Poor Rezaie, Kamal
Abstract: The characterization of the transverse phase space of beams is a fundamental requirement for particle accelerators. As accelerators shift toward higher intensity beam regimes, the transverse dynamics of beams becomes more influenced by interparticle forces known as the space charge forces. Therefore, it is increasingly important to take space charge into account in studying the beam dynamics. In this thesis, two novel approaches are presented for measurement of transverse emittance for beams with space charge, an important quality indicator of transverse phase space. It is also discussed the experimental work on orbit characterization and control done for space charge dominated beams of the University of Maryland Electron Ring (UMER).
The first method developed for measuring the emittance, utilizes a lens-drift-screen setup similar to that of a conventional quadrupole scan emittance measurement. Measurements of radius and divergence that can be obtained from beam produced radiation, e.g. optical transition, are used to calculate the beam cross correlation term and therefore the rms emittance. A linear space charge model is used in the envelope equations; hence the errors in the measurement relate to the non-uniformity of the beam distribution. The emittance obtained with our method shows small deviation from those obtained by WARP simulations for beams with high space charge, in contrast to other techniques.
In addition, a second method is presented for determining emittance that works for beams with intense space charge and, theoretically, does not require an a priori assumption about the beam distribution. In this method, the same lens-drift-screen setup as the previous method is used, except that the beam size and divergence are scanned to find the minimum of product of the measured quantities. Such minimum is shown to be equal to the rms emittance under specific conditions that usually can be satisfied by adjusting the experiment parameters such as the drift length. The result of numerical analysis of the method done for a realistic accelerator confirms the applicability of method for intense beams with nonuniform distribution.
Finally, the experimental work for characterization and control of beam centroid motions in UMER are discussed. Such work is important because at high space charge intensities, the nonlinearities of the lenses impose stricter constraints on the swing of beam centroid in the pipe. On the characterization side, we show new methods for more accurate measurements of the average orbit of particles, including inside the quadrupoles where there is no monitor. Based on this more precise orbit information, the beam orbit is corrected and its result is presented.Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/1903/149022013-01-01T00:00:00ZImplications of the Dichotomy of Modal Participation Factors for Monitoring and Control of Electric Power Networks
http://hdl.handle.net/1903/14855
Title: Implications of the Dichotomy of Modal Participation Factors for Monitoring and Control of Electric Power Networks
Authors: Tschirhart, Paul Kenton
Abstract: Steadily increasing demand for electricity has led to today's electric power
networks often being stressed to their stability limits. Improved methods of stability
monitoring and control placement are needed to manage the increased stress on
power networks. Modal participation factors have been used for several decades
in the analysis of modal behavior in power networks. Recently a dichotomy was
discovered in modal participation, indicating that the participation of system states
in system modes should be calculated differently from the participation of system
modes in system states. This masters thesis numerically explores possible roles for
these new participation factor definitions in power network monitoring and control.
The results suggest that the mode in state participation factors are best employed in
modal monitoring (especially in deciding which variables to monitor to best detect
specific modes), while the state in mode participation factors are best suited to
control applications (such as controller placement).Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/1903/148552013-01-01T00:00:00ZResource-Based Spike Mitigation Stochastic Control Problems
http://hdl.handle.net/1903/14848
Title: Resource-Based Spike Mitigation Stochastic Control Problems
Authors: McCready, Keith
Abstract: Resource-based spike mitigation stochastic control problems are a class of stochastic control problems, akin to inventory control problems or linear quadratic regulator (LQR) problems. These problems involve consuming a resource to mitigate large, fast losses to a primary state ("spikes"). These properties, included with stochastic elements, draw out a unique behavior where optimal control policies conserve resources during "lucky streaks" and spend the resources during "unlucky streaks." However, these problems often have too many time steps and states to compute an optimal control policy with dynamic programming. This thesis gives examples of such problems and demonstrates how to effectively approximate solutions using suboptimal control methods.Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/1903/148482013-01-01T00:00:00Z