Home About us Contact
|
Home About us Contact | ||
|
|
||
Global Optimization Technique (global + optimization_technique)
Selected AbstractsWaveform modelling of teleseismic S, Sp, SsPmP, and shear-coupled PL waves for crust- and upper-mantle velocity structure beneath AfricaGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2007Abhijit Gangopadhyay SUMMARY We describe a waveform modelling technique and demonstrate its application to determine the crust- and upper-mantle velocity structure beneath Africa. Our technique uses a parallelized reflectivity method to compute synthetic seismograms and fits the observed waveforms by a global optimization technique based on a Very Fast Simulated Annealing (VFSA). We match the S, Sp, SsPmP and shear-coupled PL phases in seismograms of deep (200,800 km), moderate-to-large magnitude (5.5,7.0) earthquakes recorded teleseismically at permanent broad-band seismic stations in Africa. Using our technique we produce P - and S -wave velocity models of crust and upper mantle beneath Africa. Additionally, our use of the shear-coupled PL phase, wherever observed, improves the constraints for lower crust- and upper-mantle velocity structure beneath the corresponding seismic stations. Our technique retains the advantages of receiver function methods, uses a different part of the seismogram, is sensitive to both P - and S -wave velocities directly, and obtains helpful constraints in model parameters in the vicinity of the Moho. The resulting range of crustal thicknesses beneath Africa (21,46 km) indicates that the crust is thicker in south Africa, thinner in east Africa and intermediate in north and west Africa. Crustal P - (4.7,8 km s,1) and S -wave velocities (2.5,4.7 km s,1) obtained in this study show that in some parts of the models, these are slower in east Africa and faster in north, west and south Africa. Anomalous crustal low-velocity zones are also observed in the models for seismic stations in the cratonic regions of north, west and south Africa. Overall, the results of our study are consistent with earlier models and regional tectonics of Africa. [source] Detection of preferential infiltration pathways in sinkholes using joint inversion of self-potential and EM-34 conductivity dataGEOPHYSICAL PROSPECTING, Issue 5 2007A. Jardani ABSTRACT The percolation of water in the ground is responsible for measurable electric potentials called self-potentials. These potentials are influenced by the distribution of the electrical conductivity of the ground. Because sinkholes are associated both with self-potential and electrical conductivity anomalies, a joint inversion of EM-34 conductivity and self-potential data is proposed as a way of delineating the location of these features. Self-potential and EM conductivity data were obtained at a test site in Normandy (France) where sinkholes and crypto-sinkholes are present over a karstic area in a chalk substratum overlain by clay-with-flint and loess covers. The presence of sinkholes and crypto-sinkholes is associated with negative self-potential anomalies with respect to a reference electrode located outside the area where the sinkholes are clustered. The sinkholes also have a conductivity signature identified by the EM-34 conductivity data. We used the simulated-annealing method, which is a global optimization technique, to invert jointly EM-34 conductivity and self-potential data. Self-potential and electrical conductivity provide clear complementary information to determine the interface between the loess and clay-with-flint formations. The sinkholes and crypto-sinkholes are marked by depressions in this interface, focusing the groundwater flow towards the aquifer contained in the chalk substratum. [source] A novel global optimization technique for high dimensional functionsINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 4 2009Crina Grosan Several types of line search methods are documented in the literature and are well known for unconstraint optimization problems. This paper proposes a modified line search method, which makes use of partial derivatives and restarts the search process after a given number of iterations by modifying the boundaries based on the best solution obtained at the previous iteration (or set of iterations). Using several high-dimensional benchmark functions, we illustrate that the proposed line search restart (LSRS) approach is very suitable for high-dimensional global optimization problems. Performance of the proposed algorithm is compared with two popular global optimization approaches, namely, genetic algorithm and particle swarm optimization method. Empirical results for up to 2000 dimensions clearly illustrate that the proposed approach performs very well for the tested high-dimensional functions. © 2009 Wiley Periodicals, Inc. [source] Chlorartinite, a volcanic exhalation product also found in industrial magnesia screedJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2006Kunihisa Sugimoto The volcanic exhalation product chlorartinite, [Mg2(CO3)(H2O)(OH)]Cl·H2O, has recently been found to be a minor, and in some samples a major, component of magnesia floors for industrial use. In order to be able to perform quantitative phase analysis using the Rietveld method, its crystal structure was determined from high-resolution synchrotron powder diffraction data by the global optimization technique of simulated annealing and Rietveld refinement. The final Rp and Rwp values are 5.23% and 6.56%, respectively. Chlorartinite crystallizes in the rhombohedral space group R3c (No. 161), with a = 23.14422,(16),Å, c = 7.22333,(5),Å, V = 3350.84,(5),Å3, Z = 18. The building units of chlorartinite consist of MgO6 octahedra forming 15-membered puckered rings which are interconnected by CO3 triangular moieties. The rings are stacked to form a honeycomb-like three-dimensional framework structure with large isolated channels. Within the channels, free chlorine atoms and disordered water molecules are located. [source] Wavelength selection with Tabu SearchJOURNAL OF CHEMOMETRICS, Issue 8-9 2003J. A. Hageman Abstract This paper introduces Tabu Search in analytical chemistry by applying it to wavelength selection. Tabu Search is a deterministic global optimization technique loosely based on concepts from artificial intelligence. Wavelength selection is a method which can be used for improving the quality of calibration models. Tabu Search uses basic, problem-specific operators to explore a search space, and memory to keep track of parts already visited. Several implementational aspects of wavelength selection with Tabu Search will be discussed. Two ways of memorizing the search space are investigated: storing the actual solutions and storing the steps necessary to create them. Parameters associated with Tabu Search are configured with a Plackett,Burman design. In addition, two extension schemes for Tabu Search, intensification and diversification, have been implemented and are applied with good results. Eventually, two implementations of wavelength selection with Tabu Search are tested, one which searches for a solution with a constant number of wavelengths and one with a variable number of wavelengths. Both implementations are compared with results obtained by wavelength selection methods based on simulated annealing (SA) and genetic algorithms (GAs). It is demonstrated with three real-world data sets that Tabu Search performs equally well as and can be a valuable alternative to SA and GAs. The improvements in predictive abilities increased by a factor of 20 for data set 1 and by a factor of 2 for data sets 2 and 3. In addition, when the number of wavelengths in a solution is variable, measurements on the coverage of the search space show that the coverage is usually higher for Tabu Search compared with SA and GAs. Copyright © 2003 John Wiley & Sons, Ltd. [source] | |||||||||||||