Browsing by Subject "Space and time"

Now showing 1 - 7 of 7

Applications of noise theory to plasma fluctuations
(2007) Li, Bo, 1979-; Hazeltine, R. D. (Richard D.)
Fluctuation phenomena are important to many physical systems, such as the fusion plasma. Noise theory is used to study the time and space correlations of stationary Markovian fluctuations that are statistically homogeneous and isotropic. The relaxation of the fluctuations is modeled by the diffusion equation. The spatial correlations are modeled by the exponential decay. Based on these models, the correlation function and the power spectral density of random fluctuations. We also find that the fluctuation-induced transport coefficients may be estimated by the correlation length and the correlation time. The theoretical results are compared with the observed plasma density fluctuations from tokamak and helimak experiments.
Causality in quantum physics, the ensemble of beginnings of time, and the dispersion relations of wave function
(2008-08) Sato, Yoshihiro, Ph. D.; Böhm, Arno, 1936-
Computational and astrophysical studies of black hole spacetimes
(2004) Bonning, Erin Wells; Matzner, Richard A. (Richard Alfred), 1942-
This dissertation addresses three problems of interest concerning astrophysical black holes, namely the numerical solution of Einstein’s equations for a spacetime containing two orbiting and coalescing black holes, the simulation of a light curve from an accretion disk near the innermost orbit around a spinning black hole, and determining relations between central black hole mass and host galaxy properties in active galactic nuclei. I first address the problem of setting the initial conditions for the Cauchy formulation of general relativity. I present the solution of the constraint equations via a conformal decomposition and discuss the construction of the background fields as superposed Kerr-Schild black holes. The constraint equations are solved for two black holes with arbitrary linear and angular momenta. The binding energy and spin-spin coupling of the two holes are computed in the initial data slice and analyzed. I discuss the extent to which the superposed Kerr-Schild initial data limits extraneous radiation and estimate the accuracy of determinations of the innermost stable circular orbit through sequences of initial data. The second topic concerns the time variability of isotropically radiating material orbiting in an idealized accretion disk around a spinning black hole. I solve the geodesic equations for photon propagation from the surface of the disk to an observer for different orbital parameters. The general relativistic effects upon the signal received are calculated, including the energy shift, relativistic time delay, and gravitational lensing. I produce light curves showing the change in flux over time due to the relativistic effects. Applications of this model to stellar-mass systems as well as super-massive black holes are discussed. Lastly, I discuss the relationship between a galaxy’s central black hole and its evolutionary history. In particular I examine the correlations among host galaxy luminosity, stellar velocity dispersion, and central black hole mass in active galactic nuclei. I derive black hole masses and stellar velocity dispersions from quasar broad and narrow emission lines, respectively. The utility of using the narrow line emitting gas as a surrogate for stellar velocity dispersion is investigated through examining host magnitudes and narrow [O III] line widths for low redshift quasars.
How the hashtag revolutionizes the way we collectively contend for our interests
(2013-08) Borja, Eric Enrique; Young, Michael P.
Political contention has entered a new age. Over the past three years unprecedented large-scale movements have challenged states across the globe, and social media has been an important component in their development and articulation. With the advent of social media sites, such as Facebook and Twitter, ordinary people have the technological ability to instantaneously transcend space, time and resources (Aouraugh and Alexander 2011; Castells 2012; Earl and Kimport 2009, 2011; Eltantawy, Nahed and Wiest 2011; Gerbaudo 2012; Hands 2011; Holmes 2012; Mason 2012). Are we currently living in a historical moment where a new repertoire of contention is emerging? If so, how is social media changing the way we collectively contest for our interests? The theoretical framework I propose in this paper advances and elaborates a social geographic approach in the framing of political contention that emphasizes the importance of the spatiality and temporality created by the hashtag (#) in the development and articulation of today's social movements. In addition to secondary sources about the protests in Brazil (#VemPraRua), I draw on participant observations to analyze a new modular form of protest I call the "hashtag movement." I claim that the hashtag (#) creates a new space/time (Massey 1992, 2007; Soja 1996) that fundamentally shifts the process of nation-ness (Anderson 2006) and marks a new phase in the mediazation of modern culture (Thompson 1991); two fundamental shifts that I argue are comparable to the structural and cultural shifts that formed the modern repertoire of contention (Anderson 2006; Della Porta and Diani 1999; McAdam 1999; McAdam, Tarrow and Tilly 2001; Sewell 1990, 1996; Swidler 1986; Tarrow 1993, 1994; Tilly 1986, 1995a, 1995b; Young 2002).
In search of quantum de Sitter space: generalizing the Kodama state
(2007) Randono, Andrew Culp; Matzner, Richard A. (Richard Alfred), 1942-
The Kodama state is unique in being an exact solution to all the constraints of quantum gravity that also has a well defined semi-classical interpretation as the quantum version of a classical spacetime, namely de Sitter or anti-de sitter space. Despite this, the state fails to pass some of the key tests of a physically realistic quantum state. In an attempt to resolve this problem, we track down the root of the problem to a choice for a particular parameter: the Immirzi parameter. The Kodama state takes this parameter to be complex, whereas modern formulations of canonical quantum gravity require that the parameter is real. We generalize the Kodama state to real values of the Immirzi parameter, and find that the generalization opens up a large Hilbert space of states, one of which can be directly interpreted as particular slicing of de Sitter space. We then show that these states resolve, or are expected to resolve many of the problems associated with the original version of Kodama state. In order to resolve the interpretation of the multitude of states, we develop a new model of covariant classical and quantum gravity where the full Lorentz group is retained as a local symmetry group, and the canonical evolution generated by the constraints has a close relation to a larger group: that de Sitter group. This formalism gives strong evidence that the multitude of generalized Kodama states can be unified into a single quantum state that is quantum de Sitter space.
Radiative problems in black hole spacetimes
(1995-12) Marsa, Robert Lee; Not available
The structure of general relativity with a numerical illustration : the collision of two black holes
(1975) Smarr, Larry L.; DeWitt, Bryce S. (Bryce Seligman), 1923-2004
The splitting of spacetime into space and time is analyzed by abstract methods, coordinate methods, and numerical computer methods. General relativity is assumed to be the correct theory of gravity and the Einstein field equations are studied in their canonical form. A comparison is made of the initial value and evolution equations for gravity in different formalisms (ADM, geometry of spacelike hypersurfaces, timelike congruences). These equations are then illustrated by a number of cosmological and black hole space-times. A study of coordinate conditions is undertaken. The axisymmetric (non-stationary and non-spherical) Einstein equations are discussed, and it is shown how to set up a numerical computer program to integrate these equations starting with a given initial data set. Various applications of this computer approach are discussed: collapse of rotating non-spherical stars, "runaway" collapse, and headon collisions of black holes. All of these situations would involve generation of gravitational radiation from the formation of black holes. The particular case of two nonrotating black holes colliding headon is chosen as a test case for the computer. The initial value problem is reviewed and then a computer program is written to generate the spacetime. This generation involves solving four coupled quasilinear hyperbolic (evolution) equations and one linear elliptic equation (maximal slicing) on each spacelike sheet. The numerical difficulties are discussed and graphical methods are used to present the result of the computations.