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http://hdl.handle.net/2440/12035
2014-09-22T02:11:55ZEvolution of the earliest horses driven by climate change in the Paleocene-Eocene Thermal Maximum
http://hdl.handle.net/2440/85215
Title: Evolution of the earliest horses driven by climate change in the Paleocene-Eocene Thermal Maximum
Author: Secord, R.; Bloch, J.I.; Chester, S.G.B.; Boyer, D.M.; Wood, A.R.; Wing, S.L.; Kraus, M.J.; McInerney, F.A.; Krigbaum, J.
Abstract: Body size plays a critical role in mammalian ecology and physiology. Previous research has shown that many mammals became smaller during the Paleocene-Eocene Thermal Maximum (PETM), but the timing and magnitude of that change relative to climate change have been unclear. A high-resolution record of continental climate and equid body size change shows a directional size decrease of ~30% over the first ~130,000 years of the PETM, followed by a ~76% increase in the recovery phase of the PETM. These size changes are negatively correlated with temperature inferred from oxygen isotopes in mammal teeth and were probably driven by shifts in temperature and possibly high atmospheric CO2 concentrations. These findings could be important for understanding mammalian evolutionary responses to future global warming.2011-12-31T13:30:00ZA goal-oriented adaptive finite-element approach for plane wave 3-D electromagnetic modelling
http://hdl.handle.net/2440/85092
Title: A goal-oriented adaptive finite-element approach for plane wave 3-D electromagnetic modelling
Author: Ren, Z.; Kalscheuer, T.; Greenhalgh, S.; Maurer, H.
Abstract: We have developed a novel goal-oriented adaptive mesh refinement approach for finite-element methods to model plane wave electromagnetic (EM) fields in 3-D earth models based on the electric field differential equation. To handle complicated models of arbitrary conductivity, magnetic permeability and dielectric permittivity involving curved boundaries and surface topography, we employ an unstructured grid approach. The electric field is approximated by linear curl-conforming shape functions which guarantee the divergence-free condition of the electric field within each tetrahedron and continuity of the tangential component of the electric field across the interior boundaries. Based on the non-zero residuals of the approximated electric field and the yet to be satisfied boundary conditions of continuity of both the normal component of the total current density and the tangential component of the magnetic field strength across the interior interfaces, three a-posterior error estimators are proposed as a means to drive the goal-oriented adaptive refinement procedure. The first a-posterior error estimator relies on a combination of the residual of the electric field, the discontinuity of the normal component of the total current density and the discontinuity of the tangential component of the magnetic field strength across the interior faces shared by tetrahedra. The second a-posterior error estimator is expressed in terms of the discontinuity of the normal component of the total current density (conduction plus displacement current). The discontinuity of the tangential component of the magnetic field forms the third a-posterior error estimator. Analytical solutions for magnetotelluric (MT) and radiomagnetotelluric (RMT) fields impinging on a homogeneous half-space model are used to test the performances of the newly developed goal-oriented algorithms using the above three a-posterior error estimators. A trapezoidal topographical model, using normally incident EM waves at both MT and RMT frequencies, is adopted to further test the convergence of the newly developed algorithms against a surface integral approach. Next, the 3D-1 benchmark model from the COMMEMI project is used to show the efficiency of the goal-oriented adaptive algorithm and to compare our solutions against volume integral solutions and other finite-element solutions. For all three test cases, we found that the error estimator using face jumps of normal components of current density embedded in the goal-oriented adaptive refinement procedure shows the most robust performance.2012-12-31T13:30:00ZCrustal root of the Eastern Dharwar Craton: zircon U-Pb age and Lu-Hf isotopic evolution of the East Salem Block, southeast India
http://hdl.handle.net/2440/85017
Title: Crustal root of the Eastern Dharwar Craton: zircon U-Pb age and Lu-Hf isotopic evolution of the East Salem Block, southeast India
Author: Glorie, S.; De Grave, J.; Singh, T.; Payne, J.; Collins, A.2013-12-31T13:30:00ZGeoelectric experimental design — Efficient acquisition and exploitation of complete pole-bipole data sets
http://hdl.handle.net/2440/84891
Title: Geoelectric experimental design — Efficient acquisition and exploitation of complete pole-bipole data sets
Author: Blome, M.; Maurer, H.; Greenhalgh, S.
Abstract: Exploiting the information content offered by geoelectric data in an efficient manner requires careful selection of the electrode configurations to be used. This can be achieved using sequential experimental design techniques proposed over the past few years. However, these techniques become impractical when large-scale 2D or 3D experiments have to be designed. Even if sequential experimental design were applicable, acquisition of the resulting data sets would require an unreasonably large effort using traditional multielectrode arrays. We present a new, fully parallelized pole-bipole measuring strategy by which large amounts of data can be acquired swiftly. Furthermore, we introduce a new experimental design concept that is based on “complete” data sets in terms of linear independence. Complete data sets include a relatively small number of basis electrode configurations, from which any other configuration can be reconstructedby superposition. The totality of possible configurations is referred to as the comprehensive data set. We demonstrate the benefits of such reconstructions using eigenvalue analyses for the case of noise-free data. In the presence of realistic noise, such reconstructions lead to unstable results when only four-point (bipole-bipole) configurations are considered. In contrast, complete three-point (pole-bipole) data sets allow more stable reconstructions. Moreover, complete pole-bipole data sets can be acquired very efficiently with a fully parallelized system. Resolution properties of complete pole-bipole data sets are illustrated using both noise-free and noisy synthetic data sets. We also show results from a field survey performed over a buried waste disposal site, which further demonstrates the usefulness of our approach. Although this paper is restricted to 2D examples, it is trivial to extend the concept to 3D surveys, where the advantages of parallelized pole-bipole data acquisition become very significant.2010-12-31T13:30:00Z