The thesis describes the design of a fringe projection system to study the dynamics of condensation with potential application in a reduced gravity environment. The concept is that an optical system for imaging the condensation layer enables extraction of valuable data from the image because of the ability of the optical system to image the perturbations in the condensation films. By acquiring a sequence of images of the deformed fringe pattern, the change in the surface topology can be observed over time, giving greater understanding of condensation dynamics in reduced gravity.

The determination of the figure of the Earth and its gravity field has long relied on methodologies that approximate the Earth by a sphere, but this level of accuracy is no longer adequate for many applications, due to the advent of new and advanced measurement techniques. New, practical and highly accurate methodologies for gravity field modelling that describe the Earth as an oblate ellipsoid of revolution are therefore required. The foundation for these methodologies is formed by solutions to ellipsoidal geodetic boundary-value problems. In this thesis, new solutions to the ellipsoidal Dirichlet, Neumann and second-order boundary-value problems, as well as the fixed- and free-geodetic boundary-value problems, are derived. These solutions do not rely on any spherical approximation, but are nevertheless completely based on a simple spherical harmonic expansion of the function that is to be determined. They rely on new relations among spherical harmonic base functions. In the new solutions, solid spherical harmonic coefficients of the desired function are expressed as a weighted summation over surface spherical harmonic coefficients of the data on the ellipsoidal boundary, or alternatively as a weighted summation over coefficients that are computed under the approximation that the boundary is a sphere. / Specific applications of the new solutions are the computation of geopotential coefficients from terrestrial gravimetric data and local or regional gravimetric geoid determination. Numerical closed-loop simulations have shown that the accuracy of geopotential coefficients obtained with the new methods is significantly higher than the accuracy of existing methods that use the spherical harmonic framework. The ellipsoidal corrections to a Stokesian geoid determination computed from the new solutions show strong agreement with existing solutions. In addition, the importance of the choice of the reference sphere radius in Stokes's formula and its effect on the magnitude and spectral sensitivity of the ellipsoidal corrections are pointed out.

Abstract not available

Motiviert durch neuere Vorschläge zur experimentellen Untersuchung von Quantengravitationseffekten werden in der vorliegenden Arbeit Annahmen und Methoden untersucht, die für die Vorhersagen solcher Effekte im Rahmen der Loop-Quantengravitation verwendet werden können. Dazu wird als Modellsystem ein skalares Feld, gekoppelt an das Gravitationsfeld, betrachtet. <br /> Zunächst wird unter bestimmten Annahmen über die Dynamik des gekoppelten Systems eine Quantentheorie für das Skalarfeld vorgeschlagen. Unter der Annahme, dass sich das Gravitationsfeld in einem semiklassischen Zustand befindet, wird dann ein &quot;QFT auf gekrümmter Raumzeit-Limes&quot; dieser Theorie definiert. Im Gegensatz zur gewöhnlichen Quantenfeldtheorie auf gekrümmter Raumzeit beschreibt die Theorie in diesem Grenzfall jedoch ein quantisiertes Skalarfeld, das auf einem (klassisch beschriebenen) Zufallsgitter propagiert. <br /> Sodann werden Methoden vorgeschlagen, den Niederenergieliemes einer solchen Gittertheorie, vor allem hinsichtlich der resultierenden modifizierten Dispersonsrelation, zu berechnen. Diese Methoden werden anhand von einfachen Modellsystemen untersucht. <br /> Schließlich werden die entwickelten Methoden unter vereinfachenden Annahmen und der Benutzung einer speziellen Klasse von semiklassischen Zuständen angewandt, um Korrekturen zur Dispersionsrelation des skalaren und des elektromagnetischen Feldes im Rahmen der Loop-Quantengravitation zu berechnen. Diese Rechnungen haben vorläufigen Charakter, da viele Annahmen eingehen, deren Gültigkeit genauer untersucht werden muss. Zumindest zeigen sie aber Probleme und Möglichkeiten auf, im Rahmen der Loop-Quantengravitation Vorhersagen zu machen, die sich im Prinzip experimentell verifizieren lassen. / Motivated by recent proposals on the experimental detectability of quantum gravity effects, the present thesis investigates assumptions and methods which might be used for the prediction of such effects within the framework of loop quantum gravity. To this end, a scalar field coupled to gravity is considered as a model system. <br /> Starting from certain assumptions about the dynamics of the coupled gravity-matter system, a quantum theory for the scalar field is proposed. Then, assuming that the gravitational field is in a semiclassical state, a &quot;QFT on curved space-time limit&quot; of this theory is defined. In contrast to ordinary quantum field theory on curved space-time however, in this limit the theory describes a quantum scalar field propagating on a (classical) random lattice. <br /> Then, methods to obtain the low energy limit of such a lattice theory, especially regarding the resulting modified dispersion relations, are discussed and applied to simple model systems. <br /> Finally, under certain simplifying assumptions, using the methods developed before as well as a specific class of semiclassical states, corrections to the dispersion relations for the scalar and the electromagnetic field are computed within the framework of loop quantum gravity. These calculations are of preliminary character, as many assumptions enter whose validity remains to be studied more thoroughly. However they exemplify the problems and possibilities of making predictions based on loop quantum gravity that are in principle testable by experiment.

In this thesis we investigate two approaches to quantum gravity. The first is the emergence of gravity from a discrete fundamental theory, and the second is the direct quantisation of gravity. For the first we develop tools to determine with relatively high accuracy the speed of propagation of information in collective modes which ultimately should give us some information about the emergent causal structure. We found a way of finding the dependence on the relative interaction strengths of the Hamiltonian and we also managed to calculate this speed in the case where the operators in the Hamitonian were not necessarily bounded. For the second approach, we investigated the phenomenology of Loop Quantum Gravity. We found that ultra light black holes (lighter than the Planck mass) have interesting new properties on top of being non-singular. First their horizon is hidden behind a Plancksized wormhole, second their specific heat capacity is positive and they are quasi-stable, they take an infinite amount of time evaporate. We investigated the dynamics of their collapse and evaporation explicitly seeing that not only was there no singularity, but there is also no information loss problem. Looking at how primordial black holes were in existence, we found that they might account for a significant portion of dark matter. And if they did, their radiation spectrum is such that the black holes in the dark matter halo of our galaxy could be the source for the ultra high energy cosmic rays we observe on earth.

No description available.

This dissertation covers two di erent but related topics: the construction of new black hole solutions and the study of the microscopic origin of black hole entropy. In the solution part, two di erent sets of new solutions are found. The rst concerns a Plebanski-Demianski type solution in the ve-dimensional pure Einstein gravity, and the second concerns a three-charge (two of which equal) two-rotation solution to the ve-dimensional maximal supergravity. Obtaining new and interesting black hole solutions is an important and challenging task in studying general relativity and its extensions. During the past decade, the solutions become even more important because they might nd applications in the study of the gauge/gravity duality, which is currently in the central stage of the quantum gravity research. The Kerr/CFT correspondence is a recently propose example of the gauge/gravity duality. In the entropy part, we explicitly show that the Kerr/CFT correspondence can be applied to all known extremal stationary and axisymmetric black holes. We improve over previous works in showing that this can be done in a general fashion, rather than testing di erent solutions case by case. This e ort makes it obvious that the common structure of the near horizon metric for all known extremal stationary and axisymmetric black holes is playing a key role in the success of the Kerr/CFT correspondence. The discussion is made possible by the identi cation of two general ans atze that cover all such known solutions.

In this thesis massive higher derivative gravity theories are analyzed in some detail. One-particle scattering amplitude between two covariantly conserved sources mediated by a graviton exchange is found at tree-level in D dimensional (Anti)-de Sitter and flat spacetimes for the most general quadratic curvature theory augmented with the Pauli-Fierz mass term. From the amplitude expression, the Newtonian potential energies are calculated for various cases. Also, from this amplitude and the propagator structure, a three dimensional unitary theory is identified. In the second part of the thesis, the found three dimensional unitary theory is studied in more detail from a canonical point of view. The general higher order action is written in terms of gauge-invariant functions both in flat and de Sitter backgrounds. The analysis is extended by adding static sources, spinning masses and the gravitational Chern-Simons term separately to the theory in the case of flat spacetime. For all cases the microscopic spectrum and the masses are found. In the discussion of curved spacetime, the masses are found in the relativistic and non-relativistic limits. In the Appendix, some useful calculations that are frequently used in the bulk of the thesis are given.

While general relativity is a very successful theory of gravity, having thus far passed all observational tests with flying colors, it is thought to be incomplete. Indeed, we lack an ultimate high energy theory in which general relativity and quantum mechanics are both valid. We consider extensions to the action of general relativity, and seek to place constraints on these alternative theories using astrophysical tests. General relativity has been extensively tested in the solar system, but not with precision in strong gravity systems. We discuss constraints that could be placed on alternative theories using neutron stars. We find that we may not be able to distinguish between general relativity and some alternative theories in the spacetimes around black holes. We also discuss constraints from cosmological tests, and show that instabilities can appear.Adding higher-order terms to the action of general relativity can introduce new dynamical degrees of freedom and instabilities. From the standpoint of effective field theory however, these alternative theories are inconsistent because they are not unitary. In an effective field theory, no new degree of freedom is introduced. This also means that extra polarizations of gravitational waves, which are predicted by some alternative theories, would not be present in an effective field theory.We then consider an effective field theoretic formulation for gravitational radiation called Non-Relativistic General Relativity (NRGR). We study the gravitational wave emission in non-relativistic coalescing compact binaries, which are thought to be powerful emitters of gravitational waves. While NRGR is based on the post-newtonian (PN) approximation to general relativity, and should therefore be in complete agreement with other post-newtonian methods, the effective field theory approach provides two major advantages: it provides a consistent framework for the dynamics using a lagrangian formulation; also, one can in principle compute observables to all orders in the orbital velocity in a systematic way. We provide a brief overview of NRGR methods, and present the NRGR calculation of the subleading spin-orbit correction to the newtonian potential.

In this thesis we investigate two approaches to quantum gravity. The first is the emergence of gravity from a discrete fundamental theory, and the second is the direct quantisation of gravity. For the first we develop tools to determine with relatively high accuracy the speed of propagation of information in collective modes which ultimately should give us some information about the emergent causal structure. We found a way of finding the dependence on the relative interaction strengths of the Hamiltonian and we also managed to calculate this speed in the case where the operators in the Hamitonian were not necessarily bounded. For the second approach, we investigated the phenomenology of Loop Quantum Gravity. We found that ultra light black holes (lighter than the Planck mass) have interesting new properties on top of being non-singular. First their horizon is hidden behind a Plancksized wormhole, second their specific heat capacity is positive and they are quasi-stable, they take an infinite amount of time evaporate. We investigated the dynamics of their collapse and evaporation explicitly seeing that not only was there no singularity, but there is also no information loss problem. Looking at how primordial black holes were in existence, we found that they might account for a significant portion of dark matter. And if they did, their radiation spectrum is such that the black holes in the dark matter halo of our galaxy could be the source for the ultra high energy cosmic rays we observe on earth.