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This thesis explores three new techniques for increasing the efficiency of constraint propagation: support for incremental propagation, improved representation of constraints, and abstractions to simplify propagation.  Support for incremental propagation is added to a propagator centered propagation system by adding a new intermediate layer of abstraction, advisors, that capture the essential aspects of a variable centered system. Advisors are used to give propagators a detailed view of the dynamic changes between propagator runs. Advisors enable the implementation of optimal algorithms for important constraints such as extensional constraints and Boolean linear in-equations, which is not possible in a propagator centered system lacking advisors.  Using Multivalued Decision Diagrams (MDD) as the representation for extensional constraints is shown to be useful for several reasons. Classical operations on MDDs can be used to optimize the representation, and thus speeding up the propagation. In particular, the reduction operation is stronger than the use of DFA minimization for the regular constraint. The use of MDDs is contrasted and compared to a recent proposal where tables are compressed.  Abstractions for constraint programs try to capture small and essential features of a model. These features may be much cheaper to propagate than the unabstracted program. The potential for abstraction is explored using several examples. These three techniques work on different levels. Support for incremental propagation is essential for the efficient implementation of some constraints, so that the algorithms have the right complexity. On a higher level, the question of representation looks at what a propagator should use for propagation. Finally, the question of abstraction can potentially look at several propagators, to find cases where abstractions might be fruitful. An essential feature of this thesis is a novel model for general placement constraints that uses regular expressions. The model is very versatile and can be used for several different kinds of placement problems. The model applied to the classic pentominoes puzzle will be used through-out the thesis as an example and for experiments. / Den här avhandlingen utforskar tre nya tekniker för att öka effektiviteten av villkorspropagering: stöd för inkrementell propagering, val av representation för villkor, samt abstraktion för att förenkla propagering. Ett propageringssystem organiserat efter propagerare utökas med stöd för inkrementell propagering genom att lägga till ett nytt abstraktionslager: rådgivare. Detta lager fångar de essentiella aspekterna hos system organiserade efter variabler. Rådgivare används för att ge propagerare detaljerad information om de dynamiska ändringarna i variabler mellan körningar av propageraren. Utökningen innebär att det går att implementera optimala algoritmer för vissa viktiga villkor såsom tabellvillkor och Boolska linjära olikheter, något som inte är möjligt i ett rent propagator-organiserat system. Användandet av så kallade Multivalued Decision Diagram (MDD) som representation för tabellvillkor visas vara användbart i flera avseenden. Klassiska MDD-operationer kan användas för att optimera representationen, vilket leder till snabbare propagering. Specifikt så är reduktionsoperationen kraftfullare än användandet av DFA-minimering för reguljära villkor. MDD-representationen jämförs också med ett nyligen framlagt förslag för komprimerade tabeller. Abstraktioner för villkorsprogram försöker fånga små men viktiga egenskaper i modeller. Sådana egenskaper kan vara mycket enklare att propagera än den konkreta modellen. Potentialen för abstraktioner undersöks för några exempel. Dessa tre tekniker fungerar på olika nivåer. Stöd för inkrementell propagering är nödvändigt för att kunna implementera vissa villkor effektivt med rätt komplexitet. Valet av representation för villkor är på en högre nivå, då det gäller att se vilka algoritmer som skall användas för ett villkor. Slutligen så måste flera villkor i en modell studeras för att finna rätt typ av abstraktioner. Ett utmärkande drag för den här avhandlingen är en ny modell för generella placeringsvillkor som använder reguljära uttryck. Modellen är mångsidig och kan användas för flera olika typer av placeringsproblem. Modellen specialiserad för pentominopussel används genomgående som exempel för experiment. / QC 20101117 / Coordinating Constraint Propagation

Scope and Contents: The first chapter of this thesis consists of a general introduction and a brief description of previous work done in this same laboratory. Also included is a preliminary description of the present experiment. This is followed, in Chapter 2, by a detailed description of the experimental apparatus. The third and last chapter contains a description of the procedure used in obtaining results, as well as the results themselves. Measurements were made of the diffraction patterns of a plastic prism, and five rods in a total of nine different cases. In all cases, the intensity measurements were made along the axis of propagation of the incident beam behind the diffracting object. A polarization normal to the axis of the rods was used. Theoretical calculations were made in three cases, and compared with the experimental results. / Thesis / Master of Science (MS)

A new active-passive approach for the control of noise radiated from a small axial fan was investigated. The approach involved the installation of an axial fan into a short duct with both passive and active noise control functions. First, a systematic methodology for the analytical modeling of finite-length ducts with multiple discontinuities was formulated. The procedure involved the modeling of a duct as a collection of simple duct sections, which were interconnected at multiple junctions. Analytical studies have shown that a short lined duct provides passive noise reduction effects through the mass-loading effect of the duct air volume at low frequencies and the sound absorption by a passive liner at high frequencies. It was also shown that active control can provide further noise attenuations at low-to-mid frequencies, thereby enhancing the overall noise control performance. Two alternate designs of active-passive noise control fan duct were considered. One was a simple non- segmented duct with a 2x2 active control and the other was an internally segmented duct with an 8x8 active control. It was indicated that the latter design possesses a significantly higher global noise control potential than the former with respect to both bandwidth and attenuation level. This was attributed to the reduction of the unwanted pressure contributions from the duct cross modes through the high frequency shifting of the associated cut-on frequencies. The experimental validation of the noise control approach was also carried out. An active-passive noise control fan duct incorporating the segmented duct design with 8x8 active control was constructed in conjunction with a hybrid feedforward-feedback control system. Experimental results have shown significant reductions in the total fan noise power associated with the first four BPF tones by the feedforward control and the broadband fan noise power by the feedback control. The overall active-passive noise control characteristics were observed to be in accordance with the analytical results. / Ph. D.