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access: v.11, no.01, Fall/Winter 1998
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A Numerical Study of the Black Hole Plus Brill Wave Spacetime
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Reason: Dissertation/ThesisDissertation/ThesisU of I Onl
Rotating black hole spacetimes
No full text"A new family of initial data sets, along with a study of their evolutions including
apparent horizons, event horizons and gravitational radiation, is presented. These
initial data sets represent distorted rotating black holes, and two types of non-rotating black holes with odd-parity radiation distortions. The first has the equatorial plane symmetry of the Kerr spacetime, the second has the equatorial plane symmetry of
the ""cosmic screw"" spacetime.
The Synergism of Analytic and Numerical Techniques in General Relativity: Calculation of Radiative Spacetimes
No full textThesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.The theoretical difficulty of identifying the radiative component of a general relativistic spacetime is manifested in numerical relativity as the problem of extracting asymptotic gravitational radiation waveforms at finite radii during simulations on spacelike slices. These waveforms can be contaminated by linear effects due to the choice of gauge and the wave's near zone field as well as by non-linear interactions. What is usually done is to extract the waveforms at large radii in the wave zone where these effects are assumed to be negligible using special radiative variables which have radiative terms rather than the mass monopole moment as the leading term in their asymptotic expansion. This approach can be wasteful of computer resources and is not very rigorous. We take a synergistic approach where a numerical solution of the Einstein equations coupled with hydrodynamics for the source and strong-field region is matched in the near zone or local wave zone onto a linear analytic solution used for the exterior region. No asymptotic flatness assumption is required; it is sufficient that the source be isolated enough that a local wave zone exists.First we develop general solutions to the linearized vacuum Einstein equations expanded in multipole moments. These solutions are employed in three matching schemes for extracting waveforms. In the first an infinitesimal gauge transformation is used to express the analytic solution in several gauges useful for numerical relativity and gauge-independent combinations of multipole amplitudes are formed. In the second, variables are constructed which are invariant under gauge-transformations. The third method uses surface integrals of Riemann tensor components to avoid gauge effects. In all three methods the near-zone field terms are separated off with an ordinary differential equation integration over a timelike cylinder. We give a prescription for calculating initial values for these ODEs from data on a spacelike hypersurface.These procedures are tested using simulated sinusoidal and non-sinusoidal pulsating neutron-star spacetimes. We demonstrate that each technique correctly matches the exterior and interior solutions to eliminate gauge effects and that the ODE integration separates off the near-zone field to yield asymptotic waveforms. We also present an application of these methods to Brill wave spacetimes. Discussion of non-linear effects in these spacetimes is also included.Made available in DSpace on 2014-12-16T00:55:18Z (GMT). No. of bitstreams: 1
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A Design Methodology for Efficient Implementation of Deconvolutional Neural Networks on an FPGA
Get PDFIn recent years deep learning algorithms have shown extremely high performance on machine learning tasks such as image classification and speech recognition. In support of such applications, various FPGA accelerator architectures have been proposed for convolutional neural networks (CNNs) that enable high performance for classification tasks at lower power than CPU and GPU processors. However, to date, there has been little research on the use of FPGA implementations of deconvolutional neural networks (DCNNs). DCNNs, also known as generative CNNs, encode high-dimensional probability distributions and have been widely used for computer vision applications such as scene completion, scene segmentation, image creation, image denoising, and super-resolution imaging. We propose an FPGA architecture for deconvolutional networks built around an accelerator which effectively handles the complex memory access patterns needed to perform strided deconvolutions, and that supports convolution as well. We also develop a three-step design optimization method that systematically exploits statistical analysis, design space exploration and VLSI optimization. To verify our FPGA deconvolutional accelerator design methodology we train DCNNs offline on two representative datasets using the generative adversarial network method (GAN) run on Tensorflow, and then map these DCNNs to an FPGA DCNN-plus-accelerator implementation to perform generative inference on a Xilinx Zynq-7000 FPGA. Our DCNN implementation achieves a peak performance density of 0.012 GOPs/DSP
A numerical study of 3D black hole spacetimes
Get PDFWe present results from numerical evolutions of vacuum black hole spacetimes in 3D Cartesian coordinates. We first studied the Schwarzschild spacetime, comparing
extensively with lD studies. We show that although accurate 3D evolutions are
possible, there are a number of difficulties in evolving 3D black holes, for which we
suggest approaches to overcome. With current limits on computer memory sizes, we show that with certain slicing conditions, the black hole can be evolved to about
t = 50M, where M is the black hole mass. We also present the first 3D evolutions
of colliding black holes, with evolutions of the axisymmetric Misner two-black hole
initial data sets. Here we demonstrate that the techniques we developed for the
Schwarzschild case carry over to other spacetimes. We also demonstrate the feasibility of extracting gravitational wave signals during 3D evolutions. We present new, fully 3D distorted black hole initial data sets, extending Bernstein's axisymmetric data sets in a straightforward way. Metric functions and waveforms from evolutions of these data sets in the axisymmetric limit are shown to agree with 2D calculations. For evolutions of the non-axisymmetric sets, which are the first truly 3D black hole data sets to be evolved, all non-trivial wave modes through l = 4 are presented. Finally, we point the way towards studying the evolution of these data sets with perturbation theory.thesisU of I Onl
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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