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We are grateful for the Kern Family Foundation and the Searle Liberty Trust’s support for this project. We are indebted to Kathryn Ciffolillo and Susan Pasternack for careful editorial work, to Bruce Sanders and Robin Cheung for excellent design work, to Ashley Inman for table and figure

. We are indebted to Kathryn Ciffolillo and Susan Pasternack for careful editorial work, to Bruce Sanders, Robin Cheung and Max Harless for excellent design work, to Alexandra Mandzak, Amanda Olberg and Nick Tavares for table and figure construction, and to Antonio M. Wendland for administrative

Words Characters: 30000 Figures-4: figure 1: 1 column X 6cm=180x6=1080 figure 2: 1 column X 12cm=180x12=2160 figure 3: 1 column X 5cm=180x5=900 figure 4: 1 column X 5cm=180x5=900 Figures total = 5040 Equations: 42x60=2520 No tables Total character count: 37,540 characters 2 Abstract

of Southern California Los Angeles, CA 90089-2520 e-mail : alfredo@usc.edu The lab will charge a fee of $50 for tape, user's manual and delivery. (For FTP, send a request to the above e-mail address.) Copyright 1991 Brain Simulation Laboratory All Rights Reserved Alfredo Weitzenfeld: NSL 2.1 3 Table

Abstract. Eective recombination coecients are given for C ii transitions between doublet states. The cal-culations are carried out in the temperature range 500 − 20 000 K and for an electron density of 104 cm−3. The eects of electron collisions on the excited states are included. The necessary bound-bound and bound-free radiative data are obtained from a new R-matrix cal-culation in which photoionization resonances are fully delineated, thereby accurately incorporating the eects of both radiative and dielectronic recombination. The R-matrix calculation includes all bound states with principal quantum number n 15 and total orbital angular momentum L 4. The eect of moving the resonance features to their experimentally determined positions is also investigated and found to be important at low temperatures. Key words: atomic data | line: formation | H ii regions | planetary nebulae: general 1.

den angegebenen Quellen und Hilfsmitteln angefertigt zu haben. Alle Stellen, die aus Quellen entnommen wurden, sind als solche kenntlich gemacht. Diese Arbeit hat in gleicher oder ähnlicher Form noch keiner Prüfungsbehörde vorgelegen. Darmstadt, den 15.01.2013

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The recent discovery of dark energy has prompted an investigation of ways in which the accelerated expansion of the universe can be realized. In this dissertation, we present two separate projects related to dark energy. The first project analyzes a class of braneworld models in which multiple branes float in a five-dimensional anti-de Sitter bulk, while the second investigates a class of dark energy models from an effective field theory perspective. Investigations of models including extra dimensions have led to modifications of gravity involving a number of interesting features. In particular, the Randall-Sundrum model is well-known for achieving an amelioration of the hierarchy problem. However, the basic model relies on Minkowski branes and is subject to solar system constraints in the absence of a radion stabilization mechanism. We present a method by which a four-dimensional low-energy description can be obtained for braneworld scenarios, allowing for a number of generalizations to the original models. This method is applied to orbifolded and uncompactified N-brane models, deriving an effective four-dimensional action. The parameter space of this theory is constrained using observational evidence, and it is found that the generalizations do not weaken solar system constraints on the original model. Furthermore, we find that general

Building a more sustainable sensor network via protocol innovation