ALBERT

Description: Author(s): Christina L. Porter, Galen P. Miley, David J. Griffiths, and Erik Sánchez A phenomenon resembling natural ball lightning can be produced via electrical arcing through silicon. We use lump silicon instead of silicon wafers to achieve higher production rates and larger, longer-lived luminous balls than previously reported. The luminous balls consist of a silicon core surrou... [Phys. Rev. E 90, 063102] Published Tue Dec 02, 2014

Description: Author(s): Jukka-Pekka Onnela, Daniel J. Fenn, Stephen Reid, Mason A. Porter, Peter J. Mucha, Mark D. Fricker, and Nick S. Jones The study of networks has become a substantial interdisciplinary endeavor that encompasses myriad disciplines in the natural, social, and information sciences. Here we introduce a framework for constructing taxonomies of networks based on their structural similarities. These networks can arise from ... [Phys. Rev. E 86, 036104] Published Mon Sep 10, 2012

Description: Author(s): Sergey Melnik, Adam Hackett, Mason A. Porter, Peter J. Mucha, and James P. Gleeson We demonstrate that a tree-based theory for various dynamical processes operating on static, undirected networks yields extremely accurate results for several networks with high levels of clustering. We find that such a theory works well as long as the mean intervertex distance ℓ is sufficiently s... [Phys. Rev. E 83, 036112] Published Wed Mar 23, 2011

Description: Author(s): Daniel J. Fenn, Mason A. Porter, Stacy Williams, Mark McDonald, Neil F. Johnson, and Nick S. Jones We investigate financial market correlations using random matrix theory and principal component analysis. We use random matrix theory to demonstrate that correlation matrices of asset price changes contain structure that is incompatible with uncorrelated random price changes. We then identify the pr... [Phys. Rev. E 84, 026109] Published Mon Aug 08, 2011

Description: Author(s): James P. Gleeson, Sergey Melnik, Jonathan A. Ward, Mason A. Porter, and Peter J. Mucha Mean-field analysis is an important tool for understanding dynamics on complex networks. However, surprisingly little attention has been paid to the question of whether mean-field predictions are accurate, and this is particularly true for real-world networks with clustering and modular structure. I... [Phys. Rev. E 85, 026106] Published Tue Feb 07, 2012

Description: Author(s): Till Hoffmann, Mason A. Porter, and Renaud Lambiotte The traditional way of studying temporal networks is to aggregate the dynamics of the edges to create a static weighted network. This implicitly assumes that the edges are governed by Poisson processes, which is not typically the case in empirical temporal networks. Accordingly, we examine the effec... [Phys. Rev. E 86, 046102] Published Mon Oct 08, 2012

Description: The long and complex history of southern Africa makes it a geological nexus for understanding how crust forms, evolves and survives plate tectonic processes over billions of years. The goal of this study is to characterize the crustal thickness, composition, and Moho impedance contrasts across the Kaapvaal and Zimbabwe Cratons and surrounding mobile belts, which range in age from Archean to Palaeozoic. We use data gathered from the 1997–1999 Southern Africa Seismic Experiment, the Africa Array (2006–2007) and the Global Seismographic Network (1993–2009) to generate P -wave receiver function Gaussian-weighted common conversion point stacks across the region in order to provide a continuous 3-D image of crustal variations throughout southern Africa. We observe thickened crust associated with mobile belts and the intrusion of the Bushveld Complex relative to the less-deformed cratons. The southern Kaapvaal and eastern Zimbabwe Cratons have a well-defined Moho with an average depth of ~34 km and Vp / Vs of ~1.73, indicative of felsic average crustal composition. We explain the felsic composition observed in the Kaapvaal Craton in the context of significant crustal modification related to the deposition of the Ventersdorp lavas. We find that the Bushveld Province, the site of the world's largest layered mafic intrusion, has a thick (〉40 km) crust with a Vp / Vs 〉 1.8, indicative of a mafic average crustal composition. The magnitude of Moho conversions beneath the Bushveld Province is variable, with the lowest amplitude conversion appearing between the eastern and western limbs of the Bushveld Complex, indicative of mafic underplating beneath the region. In the Limpopo Belt and western Zimbabwe Craton, we observe low amplitude Moho conversions beneath the Okavango Dyke Swarm, and attribute this to the reworking of the crust by mafic underplating and intrusion during the Jurassic rifting of Gondwanaland. The Namaqua-Natal event thickened the crust and created a gradational transition from crust to mantle as seen by low amplitude Ps arrivals from receiver functions. Evidence for the presence of a mafic lower crust beneath the Namaqua-Natal Belt is observed in high Vp / Vs values (~1.8) and a high concentration of granulite xenoliths in kimberlite intrusions. In contrast to past interpretations for craton formation that suggest sharp Moho boundaries and low Vp / Vs ratios are characteristic of undisturbed cratons, we propose that these crustal properties are more controlled by tectonic events that later modify the existing cratonic crust. We cannot rule out secular crustal formation variations in the early Earth, but we propose that the southern African cratonic crust has been too heavily modified by later tectonic events to be used in arguments for secular variation, as may be the case for other cratons as well. Thus, it is important to consider the regional geological history of cratons to ensure that secular variation is not confused with the effects of later tectonic deformation and crustal modification.

Description: Author(s): Danielle S. Bassett, Eli T. Owens, Karen E. Daniels, and Mason A. Porter Granular media, whose features range from the particle scale to the force-chain scale and the bulk scale, are usually modeled as either particulate or continuum materials. In contrast with each of these approaches, network representations are natural for the simultaneous examination of microscopic, ... [Phys. Rev. E 86, 041306] Published Tue Oct 16, 2012