DRUM Community: Physics
http://hdl.handle.net/1903/2269
Wed, 22 Oct 2014 22:22:20 GMT2014-10-22T22:22:20ZGlobal Inequality in Energy Consumption from 1980 to 2010
http://hdl.handle.net/1903/15855
Title: Global Inequality in Energy Consumption from 1980 to 2010
Authors: Lawrence, Scott; Liu, Qin; Yakovenko, Victor M.
Abstract: We study the global probability distribution of energy consumption per capita
around the world using data from the U.S. Energy Information Administration (EIA) for
1980–2010. We find that the Lorenz curves have moved up during this time period, and the
Gini coefficient, G, has decreased from 0.66 in 1980 to 0.55 in 2010, indicating a decrease
in inequality. The global probability distribution of energy consumption per capita in 2010 is
close to the exponential distribution with G = 0.5. We attribute this result to the globalization
of the world economy, which mixes the world and brings it closer to the state of maximal
entropy. We argue that global energy production is a limited resource that is partitioned
among the world population. The most probable partition is the one that maximizes entropy,
thus resulting in the exponential distribution function. A consequence of the latter is the law
of 1/3: the top 1/3 of the world population consumes 2/3 of produced energy. We also find
similar results for the global probability distribution of CO2 emissions per capita.
Description: Funding for Open Access provided by the UMD Libraries Open Access Publishing Fund.Mon, 16 Dec 2013 00:00:00 GMThttp://hdl.handle.net/1903/158552013-12-16T00:00:00ZRealization and Modeling of Metamaterials Made of rf Superconducting Quantum-Interference Devices
http://hdl.handle.net/1903/15853
Title: Realization and Modeling of Metamaterials Made of rf Superconducting Quantum-Interference Devices
Authors: Trepanier, M.; Zhang, Daimeng; Mukhanov, Oleg; Anlage, Steven M.
Abstract: We have prepared meta-atoms based on radio-frequency superconducting quantum-interference devices
(rf SQUIDs) and examined their tunability with dc magnetic field, rf current, and temperature. rf SQUIDs
are superconducting split-ring resonators in which the usual capacitance is supplemented with a Josephson
junction, which introduces strong nonlinearity in the rf properties. We find excellent agreement between
the data and a model that regards the Josephson junction as the resistively and capacitively shunted
junction. A magnetic field tunability of 80 THz=G at 12 GHz is observed, a total tunability of 56% is
achieved, and a unique electromagnetically induced transparency feature at intermediate excitation
powers is demonstrated for the first time. An rf SQUID metamaterial is shown to have qualitatively
the same behavior as a single rf SQUID with regard to dc flux and temperature tuning.
Description: Funding for Open Access provided by the UMD Libraries Open Access Publishing Fund.Wed, 18 Dec 2013 00:00:00 GMThttp://hdl.handle.net/1903/158532013-12-18T00:00:00ZFast Prediction and Evaluation of Gravitational Waveforms Using Surrogate Models
http://hdl.handle.net/1903/15849
Title: Fast Prediction and Evaluation of Gravitational Waveforms Using Surrogate Models
Authors: Field, Scott E.; Galley, Chad R.; Hesthaven, Jan S.; Kaye, Jason; Tiglio, Manuel
Abstract: We propose a solution to the problem of quickly and accurately predicting gravitational waveforms within any given physical model. The method is relevant for both real-time applications and more traditional scenarios where the generation of waveforms using standard methods can be prohibitively expensive. Our approach is based on three offline steps resulting in an accurate reduced order model in both parameter and physical dimensions that can be used as a surrogate for the true or fiducial waveform family. First, a set of m parameter values is determined using a greedy algorithm from which a reduced basis representation is constructed. Second, these m parameters induce the selection of m time values for interpolating a waveform time series using an empirical interpolant that is built for the fiducial waveform family. Third, a fit in the parameter dimension is performed for the waveform’s value at each of these m times. The cost of predicting L waveform time samples for a generic parameter choice is of order O(mL+mcfit) online operations, where cfit denotes the fitting function operation count and, typically, m≪L. The result is a compact, computationally efficient, and accurate surrogate model that retains the original physics of the fiducial waveform family while also being fast to evaluate. We generate accurate surrogate models for effective-one-body waveforms of nonspinning binary black hole coalescences with durations as long as 105M, mass ratios from 1 to 10, and for multiple spherical harmonic modes. We find that these surrogates are more than 3 orders of magnitude faster to evaluate as compared to the cost of generating effective-one-body waveforms in standard ways. Surrogate model building for other waveform families and models follows the same steps and has the same low computational online scaling cost. For expensive numerical simulations of binary black hole coalescences, we thus anticipate extremely large speedups in generating new waveforms with a surrogate. As waveform generation is one of the dominant costs in parameter estimation algorithms and parameter space exploration, surrogate models offer a new and practical way to dramatically accelerate such studies without impacting accuracy. Surrogates built in this paper, as well as others, are available from GWSurrogate, a publicly available python package.
Description: Funding for Open Access provided by the UMD Libraries Open Access Publishing Fund.Mon, 14 Jul 2014 00:00:00 GMThttp://hdl.handle.net/1903/158492014-07-14T00:00:00ZDuality methods in networks, computer science models, and disordered condensed matter systems
http://hdl.handle.net/1903/15829
Title: Duality methods in networks, computer science models, and disordered condensed matter systems
Authors: Mitchell, Joe Dan
Abstract: In this thesis, I explore lattice independent duality and systems to which it can be applied. I first demonstrate classical duality on models in an external field, including the Ising, Potts, and x-y models, showing in particular how this modifies duality to be lattice independent and applicable to networks. I then present a novel application of duality on the boolean satsifiability problem, one of the most important problems in computational complexity, through mapping to a low temperature Ising model. This establishes the equivalence between boolean satisfiability and a problem of enumerating the positive solutions to a Diophantine system of equations. I continue by combining duality with a prominent tool for models on networks, belief propagation, deriving a new message passing procedure, dual belief propagation. In the final part of my thesis, I shift to propose and examine a semiclassical model, the two-component Coulomb glass model, which can explain the giant magnetoresistance peak present in disordered films near a superconductor-insulator transition as the effect of competition between single particle and localized pair transport. I numerically analyze the density of states and transport properties of this model.Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/1903/158292014-01-01T00:00:00Z