Dissertations / Theses on the topic 'Electromagnetism and gravity'

This thesis investigates the problems within quantum mechanics for the Bohm model caused by Lorentz invariance and the existence of photons. A model describing the electromagnetic interactions of fermions is produced which does not use photons and avoids these problems. It is then shown how these techniques can be extended to linearised gravitational interactions. Finally semi-classical gravity and the possibility of gravitationally induced collapse are considered. In the first part of the thesis two modifications to the Bohm model are proposed. One takes account of Lorentz invariance, and the other is capable of describing photons. The main part of the thesis is devoted to describing interactions in a way which does not need extra gauge particles, and so is in the same spirit as the Bohm model. Electromagnetic interactions are formed using a 4-potential operator which is calculated directly, without imposing commutation relations on the 4-potential. This leads to an expression for the 4-potential in terms of the Dirac field, and results in there being no photon states. There are various ways of constructing the theory and the scattering matrix of standard QED is compared to the scattering matrix of the version which appears to be most similar. Considering only the matrix elements between fermion states, they are found to be in agreement at the order e(^2), but disagree at the order e(^4). It follows that this model, which otherwise appears to be a self consistent theory of QED, cannot agree with experiment. The same techniques can be used to quantise General Relativity when it is linearised about the Minkowski metric. The metric operator is calculated in terms of the Dirac field. The interaction is similar to that of electrodynamics, being of order 4 in the Dirac field. Finally issues relating to gravitational collapse are discussed.

Falkenberg area is located in southwest Sweden formed in the Sveconorwegian orogen and contains an extremely complex geological structure. Multiple geophysical datasets have been acquired and together with available petrophysical information, models corresponding to the subsurface geological structures were generated. The collected data comprise ground magnetic, AMT (Audio Magnetotelluric) and RMT (Radio Magnetotelluric) data. The available airborne magnetic and ground gravity data acquired by the Geological Survey of Sweden (SGU) as well as the reflection seismic section from a study made by Uppsala University further aids in obtaining substantially improved interpretation of the geometry of the structures along the AMT profile. The principal objective of this profile was to delineate and map the possible deformation zone crossed by the profile. The AMT study was expected to complement existing geophysical data and improve existing interpretations. The Ullared deformation zone contains decompressed eclogite facies rocks. The presented results were obtained by comparison of different geophysical methods along the profile. The susceptibility model and resistivity model show that eclogites have higher resistivity and susceptibility than the surrounding structures. However use of the Occam type of inversion on the AMT data, makes the resistivity model smoother than the susceptibility model and as a results it is difficult to estimate the dip of the structures. The AMT profile and the seismic section show the same dip direction (NE) for the eclogite bearing structures although due to the smoothing in the AMT model the dips seen in the seismic section cannot be recovered in the resistivity model.

Tese de mestrado em Física, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2012<br>Principais motivações que orientam a linha de investigação na qual a tese se insere: - Aprofundar o estudo da relação íntima entre geometria e física; - Estudar as analogias e o acoplamento entre gravidade e electromagnetismo usando métodos geométricos, compreendendo a possibilidade de importantes aplicações teóricas e tecnológicas, podendo mesmo ser relevante para a astrofísica, a cosmologia e, eventualmente, no caminho para uma teoria consistente da gravidade quântica; - Estudar o gravitoelectromagnetismo e suas aplicações astrofísicas e eventualmente tecnológicas; - Explorar a noção de torsão em geometria diferencial e sua importância em física, nomeadamente no âmbito das teorias de gravitação. Enquadramento geral e tópicos principais da dissertação. Relação entre geometria e Natureza - relação entre geometria e física. • Importância dos métodos geométricos no estudo do campo eletromagnético e da gravidade e na exploração das analogias e acoplamento entre estas duas interações: • Axiomática do electromagnetismo; • Gravitoelectromagnetismo; • Acoplamento entre gravidade e electromagnetismo; • Gravidade com torsão: - Relevância teórica. Diferentes modelos; - Alguns modelos cosmológicos; - Exploração das analogias entre gravidade e electromagnetismo; - Testes experimentais. A questão da interpretação do papel das estruturas geométricas do espaço-tempo em física é abordada, realçando algumas reflexões relacionadas com a geometrização da física, motivadas pelo estudo das analogias e acoplamento entre gravidade e electromagnetismo. Neste âmbito a noção da ontologia física do espaço-tempo é brevemente abordada na sua conexão com as teorias unificadas.<br>Although this work contains many personal investigations, interpretations and ideas, it was mainly constructed as a review compilation on several selected topics concerning the electromagnetic and gravitational studies using geometrical methods. The selected topics and their sources reflect the author’s interests and were compiled together and organized into a single framework in order to construct a meaningful and solid line of research on the related topics of gravitation and electromagnetism. One could say that this project fits within the wider scientific arena for research on the relation between geometry and physics and the nature of space and time. Some of the topics addressed, such as the coupling of gravity and electromagnetism, gravitoelectromagnetism and gravity with torsion, are areas of active research from the theoretical side but it’s the author’s conviction that these studies will eventually reveal many astonishing practical (technological) applications. Main motivations and research lines: - To deepen the study on the profound relation between geometry and physics and the nature of space and time; - To study the analogies and physical coupling between gravity and electromagnetism using geometrical methods, considering the possibility of important theoretical (and technological) applications, being relevant for astrophysics, cosmology and, eventually, for the search of a consistent theory of quantum gravity; - To study gravitoelectromagnetism from a theoretical point of view as well as its astrophysical and technological applications; - To explore the notion of torsion in differential geometry and its importance in physics, namely in classical and quantum gravitation, unified theories of interactions and cosmology; - To explore, using the already mentioned analogies, to which extent is it possible to have a geometrical explanation of “inertial forces” (compatible with the equivalence principle), seen as geometrical deformations of space-time, such as curvature and torsion. (Not all of these topics are covered in the present work but these are the main research lines that motivate this and future projects) General conceptual framework and main topics present in this thesis Relation between geometry and physics: Importance of geometrical methods in the study of the electromagnetic and gravitational fields and in the exploration of the analogies and coupling between these physical interactions: - Axiomatic of the electromagnetism; - Coupling between gravity and electromagnetism; - Gravitoelectromagnetism and GP-B experiment; - Gravity with torsion: • Theoretical relevance of extended theories of gravity. Different models with torsion and interpretations; • Some cosmological applications; • Exploration of the analogies and coupling between gravity and electromagnetism. • Testing space-time torsion - The work suggests the idea that the electromagnetic properties of “empty space” might be interpreted as geometrical properties of the space-time continuum and that electromagnetic and gravitational waves should be fundamentally connected and be mutually generated. In this sense, it also reinforces the need to rethink the concept of “vacuum” in physics. It is also briefly explored the possibility of a geometrical description of the electromagnetic field.. - Being essentially devoted to geometrical methods in the study of the electromagnetic and gravitational fields and to the role of space-time (geometrical) structures in these field theories, this work enhances the philosophical debate on the nature of space and time inspired by ideas coming from physics. On the last part it discusses some relevant open questions such as the possibility of a coherent physicalism of space-time and the geometrization of fundamental structures such as Higgs fields.

The presented thesis spans over a number of related topics with a com- mon theme - the so-called universality. Classical fields exhibiting this property serve as exact solutions to virtually any higher-order theory irrespective of the particular form of the field equations, being thus of particular interest in ef- fective field theories. The aim of this work is to study various aspects of such solutions in the context of gravity, electrodynamics, as well as more general nonabelian gauge theories. The results are concentrated in four chapters, the first of which is devoted to what we call the almost universal spacetimes. Due to their nice curvature properties, these spacetimes provide an efficient method for simplifying and solving the field equations of higher-order gravity theories. We illustrate this feature of almost universal metrics by finding new vacuum solutions to quadratic gravity and six-dimensional conformal gravity. In the second chapter, we shift our attention towards electrodynamics. Following up on recent results on universal electromagnetic fields, we deal with Einstein- Maxwell fields which simultaneously solve also any higher-order modification of the Einstein-Maxwell theory. In particular, we identify solutions with this remarkable property as plane-fronted gravitational and...

Electromagnetic levitation experiments provide a powerful tool that allows for the study of nucleation, solidification and growth in a containerless processing environment. Containerless processing allows for the study of reactive melts at elevated temperatures without chemical interactions or contamination from a container. Further, by removing the interface between the liquid and its container, this processing technique allows for greater access to the undercooled region for solidification studies. However, in these experiments it is important to understand the magnetohydrodynamic flow within the sample and the effects that this fluid flow has on the experiment. A recent solidification study found that aluminum-nickel alloy sample have an unusual response of the growth rate of the solid to changes in undercooling. This alloy experienced a decrease in the growth velocity as the initial undercooling deepened, instead of the expected increase in solidification velocity with deepening undercoolings. Current work is exploring several different theories to explain this phenomenon. Distinguishing among these theories requires a comprehensive understanding of the behavior of the internal fluid flow. Our project, USTIP, has done flow modeling to support this and multiple other collaborators on ISS-EML. The fluid flow models presented for the aluminum-nickel sample provide critical insights into the nature of the flow within the aluminum-nickel alloy experiments conducted in the ISS-EML facility. These models have found that for this sample the RNG k-ε model should be used with this sample at temperatures greater than 1800 K and the laminar flow model should be used at temperatures lower than 1600 K. Other work in the ISS-EML, has studied the thermophysical properties of liquid germanium and has found the most recent measurements using oscillating drop techniques to have a discrepancy from the expected property measurements taken terrestrially. Investigating this discrepancy required the quantification of the velocity and characterization of the internal fluid flow in the drop. The models have found that the flow within the sample maintains turbulent behavior throughout cooling. This thesis presents the analysis of the internal flow of four additional samples processed in the International Space Station Electromagnetic Levitation facility. These samples consist of the following alloys: Ti39.5Zr39.5Ni21, Cu50Zr50, Vitreloy 106, and Zr64Ni36. Our collaborators work required the internal flow to be characterized and quantified for their work on solidification. In addition to quantifying the velocity of the flow, the Reynolds number was calculated to characterize the flow during processing. Additionally, the shear-strain rate was calculated for the flow during processing up to the recalescence of the melt.