Improving edge finite element assembly for geophysical electromagnetic modelling on shared-memory architectures

This work presents a set of node-level optimizations to perform the assembly of edge finite element matrices that arise in 3D geophysical electromagnetic modelling on shared-memory architectures. Firstly, we describe the traditional and sequential assembly approach. Secondly, we depict our vectorized and shared-memory strategy which does not require any low level instructions because it is based on an interpreted programming language, namely, Python. As a result, we obtained a simple parallel-vectorized algorithm whose runtime performance is considerably better than sequential version. The set of optimizations have been included to the work-flow of the Parallel Edge-based Tool for Geophysical Electromagnetic Modelling (PETGEM) which is developed as open-source at the Barcelona Supercomputing Center. Finally, we present numerical results for a set of tests in order to illustrate the performance of our strategy.This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 644202. The research leading to these results has received funding from the European Union's Horizon 2020 Programme (2014-2020) and from Brazilian Ministry of Science, Technology and Innovation through Rede Nacional de Pesquisa (RNP) under the HPC4E Project (www.hpc4e.eu), grant agreement No. 689772. Authors gratefully acknowledge the support from the Mexican National Council for Science and Technology (CONACYT). All numerical tests were performed on the MareNostrum supercomputer of the Barcelona Supercomputing Center - Centro Nacional de Supercomputación (www.bsc.es).Peer ReviewedPostprint (author's final draft

Intrinsic mechanism of phase locking in two-dimensional Josephson junction networks in presence of an external magnetic field

We present numerical simulations of the dynamics of two-dimensional Josephson junction arrays to study the mechanism of mutual phase locking. We show that in the presence of an external magnetic field two mechanisms are playing a role in phase locking: feedback through the external load and internal coupling between rows due to microwave currents induced by the field. We have found the parameter values (junction capacitance, cell loop inductance, impedance of the external load) for which the interplay of both these mechanisms leads to the in-phase solution. The case of unshunted arrays is discussed as well.Comment: 13 pages, incl. 6 ps figures, Subm. to Europhysics Letter

Numerical Aspects of the SAFT Equation of State

Equations of states are used to model fluid behavior. At a given temperature and pressure, for example, a mixture of water and alcohol might form a liquid and vapor phase, with the vapor phase being richer in alcohol and the liquid phase richer in water. In many industrial processes, such as distillation or extraction where mixtures of different compounds need to be separated, knowing how the fluid mixture will behave at various conditions helps make the operations more efficient and economical. While many equations of state exist, they differ in their accuracy in modeling systems and in their mathematical complexity. In particular, the Statistical Association Fluid Theory (SAFT) equation is a model that holds great promise as a predictive model because of its basis in statistical mechanics. Unlike many other equations of state, it is able to account for non-spherical shaped molecules, attraction and repulsion between molecules and site-site interactions. But while it has been able to successfully model a wide range of fluid systems where other models have failed, the SAFT equation is also mathematically complicated. This work focuses on the numerical difficulties and issues that arise in using the SAFT equation, and how they can be resolved. Numerical difficulties encountered in calculation of compressibility roots, mole fraction of unbonded sites, partial derivatives of the association term, and phase equilibria are addressed. Implications of simplifying assumptions about association strengths on different sites are also discussed. From the work done, it has been found that strategies making use of physically sound quantities in the SAFT model were successful in overcoming computational difficulties, which supports the predictive capabilities of the model. Current work is thus aimed at using the SAFT equation to model more complicated fluids, such as self-assembling surfactant systems, where it is expected that correct use of the sound physical basis of the model will lead to accurate results

Can Crop Insurance Premiums Be Reliably Estimated?

This paper develops and applies a methodology to assess the accuracy of historical loss-cost rating procedures, similar to those used by the U.S. Department of Agriculture’s Risk Management Agency (RMA), versus alternative parametric premium estimation methods. It finds that the accuracy of loss-cost procedures leaves much to be desired, but can be markedly improved through the use of alternative methods and increased farm-level yield sample sizes. Evidence suggests that the high degree of inaccuracy in crop insurance premium estimations through historical loss-cost procedures identified in the paper might be a major factor behind the need for substantial government subsidies to keep the program solvent.agricultural subsidies, crop insurance premium estimation, loss-cost procedures, Risk Management Agency, Agricultural and Food Policy, Agricultural Finance, Farm Management, Risk and Uncertainty,

Congresso Internacional sobre Património Geológico e Mineiro.Livro de resumos

Congreso Internacional sobre Patrimonio Geológico e Miner

Parallel 3-D marine controlled-source electromagnetic modelling using high-order tetrahedral Nédélec elements

We present a parallel and high-order Nédélec finite element solution for the marine controlled-source electromagnetic (CSEM) forward problem in 3-D media with isotropic conductivity. Our parallel Python code is implemented on unstructured tetrahedral meshes, which support multiple-scale structures and bathymetry for general marine 3-D CSEM modelling applications. Based on a primary/secondary field approach, we solve the diffusive form of Maxwell’s equations in the low-frequency domain. We investigate the accuracy and performance advantages of our new high-order algorithm against a low-order implementation proposed in our previous work. The numerical precision of our high-order method has been successfully verified by comparisons against previously published results that are relevant in terms of scale and geological properties. A convergence study confirms that high-order polynomials offer a better trade-off between accuracy and computation time. However, the optimum choice of the polynomial order depends on both the input model and the required accuracy as revealed by our tests. Also, we extend our adaptive-meshing strategy to high-order tetrahedral elements. Using adapted meshes to both physical parameters and high-order schemes, we are able to achieve a significant reduction in computational cost without sacrificing accuracy in the modelling. Furthermore, we demonstrate the excellent performance and quasi-linear scaling of our implementation in a state-of-the-art high-performance computing architecture.This project has received funding from the European Union's Horizon 2020 programme under the Marie Sklodowska-Curie grant agreement No. 777778. Furthermore, the research leading to these results has received funding from the European Union's Horizon 2020 programme under the ChEESE Project (https://cheese-coe.eu/ ), grant agreement No. 823844. In addition, the authors would also like to thank the support of the Ministerio de Educación y Ciencia (Spain) under Projects TEC2016-80386-P and TIN2016-80957-P. The authors would like to thank the Editors-in-Chief and to both reviewers, Dr. Martin Cuma and Dr. Raphael Rochlitz, for their valuable comments and suggestions which helped to improve the quality of the manuscript. This work benefited from the valuable suggestions, comments, and proofreading of Dr. Otilio Rojas (BSC). Last but not least, Octavio Castillo-Reyes thanks Natalia Gutierrez (BSC) for her support in CSEM modeling with BSIT.Peer ReviewedPostprint (author's final draft

Description of hysteretic current-voltage characteristics of SNS junctions

Simplified model for current-voltage characteristics of weak links is suggested. It is based on an approach considering the multiple Andreev reflection in metallic Josephson junction. The model allows to calculate current-voltage characteristics of the superconductor - normal metal - superconductor junctions with different thicknesses of normal layer at different temperatures. A hysteretic peculiarity of $V(I)$ dependence is described as result of the negative differential resistance. The current-voltage characteristic of high-$T_c$ composite YBCO +BaPbO${_3}$ were computed.Comment: 9 pages, 5 figures, submited to Supercond. Sci. Technol, replased Fig.5 for more correct comparison with experimen