The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
A Tkachenko - One of the best experts on this subject based on the ideXlab platform.
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Grid Search in stellar parameters a software for spectrum analysis of single stars and binary systems
Astronomy and Astrophysics, 2015Co-Authors: A TkachenkoAbstract:Context. The currently operating space missions, as well as those that will be launched in the near future, will deliver high-quality data for millions of stellar objects. Since the majority of stellar astrophysical applications still (at least partly) rely on spectroscopic data, an efficient tool for the analysis of medium- to high-resolution spectroscopy is needed. Aims. We aim at developing an efficient software package for the analysis of medium- to high-resolution spectroscopy of single stars and those in binary systems. The major requirements are that the code should have a high performance, represent the state-of-the-art analysis tool, and provide accurate determinations of atmospheric parameters and chemical compositions for different types of stars. Methods. We use the method of atmosphere models and spectrum synthesis, which is one of the most commonly used approaches for the analysis of stellar spectra. Our Grid Search in Stellar Parameters (gssp) code makes use of the Message Passing Interface (OpenMPI) implementation, which makes it possible to run in parallel mode. The method is first tested on the simulated data and is then applied to the spectra of real stellar objects. Results. The majority of test runs on the simulated data were successful in that we were able to recover the initially assumed sets of atmospheric parameters. We experimentally find the limits in signal-to-noise ratios of the input spectra, below which the final set of parameters is significantly affected by the noise. Application of the gssp package to the spectra of three Keplerstars, KIC11285625, KIC6352430, and KIC4931738, was also largely successful. We found an overall agreement of the final sets of the fundamental parameters with the original studies. For KIC6352430, we found that dependence of the light dilution factor on wavelength cannot be ignored, as it has a significant impact on the determination of the atmospheric parameters of this binary system. Conclusions. The gssp software package is a compilation of three individual program modules suitable for spectrum analysis of single stars and individual binary components. The code is highly effective and can be used for spectrum analysis of large samples of stars.
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Grid Search in stellar parameters a software for spectrum analysis of single stars and binary systems
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: A TkachenkoAbstract:The currently operating space missions, as well as those that will be launched in the near future, (will) deliver high-quality data for millions of stellar objects. Since the majority of stellar astrophysical applications still (at least partly) rely on spectroscopic data, an efficient tool for the analysis of medium- to high-resolution spectroscopy is needed. We aim at developing an efficient software package for the analysis of medium- to high-resolution spectroscopy of single stars and those in binary systems. The major requirements are that the code has a high performance, represents the state-of-the-art analysis tool, and provides accurate determinations of atmospheric parameters and chemical compositions for different types of stars. We use the method of atmosphere models and spectrum synthesis, which is one of the most commonly used approaches for the analysis of stellar spectra. Our Grid Search in Stellar Parameters (GSSP) code makes use of the OpenMPI implementation, which makes it possible to run in parallel mode. The method is first tested on the simulated data and is then applied to the spectra of real stellar objects. The majority of test runs on the simulated data were successful in the sense that we could recover the initially assumed sets of atmospheric parameters. We experimentally find the limits in signal-to-noise ratios of the input spectra, below which the final set of parameters gets significantly affected by the noise. Application of the GSSP package to the spectra of three Kepler stars, KIC11285625, KIC6352430, and KIC4931738, was also largely successful. We found an overall agreement of the final sets of the fundamental parameters with the original studies. For KIC6352430, we found that dependence of the light dilution factor on wavelength cannot be ignored, as it has significant impact on the determination of the atmospheric parameters of this binary system.
Jose Morales - One of the best experts on this subject based on the ideXlab platform.
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moment tensor solutions for small and moderate earthquakes in the ibero maghreb region
Journal of Geophysical Research, 2003Co-Authors: Daniel Stich, Charles J Ammon, Jose MoralesAbstract:[1] We applied time domain moment tensor inversion of local and regional waveforms to small and moderate (Mw = 3.5–5.7) shallow earthquakes from the Iberian Peninsula, northern Morocco, and northern Algeria. For the 6+ years period from November 1995 to March 2002 and the previous Network of Autonomously Recording Seismograms (NARS) experiment, moment tensor solutions were obtained for 58 events, considerably increasing the total number of available solutions in the study area. For each event we performed a moment tensor inversion and a double-couple Grid Search. For simple faulting events the Grid Search is valuable as a quality test for its ability to reveal potential ambiguities of the solutions and to assess confidence limits of fault plane parameters or principal axes orientation. The computed mechanisms show regional consistency: A large part of the Iberian Peninsula is characterized by normal faulting mechanisms with SW-NE oriented T axes. Thrusting and SE-NW compression is dominant in Algeria. In the Alboran Sea, the westernmost part of the Mediterranean, and the transition between both regimes, strike-slip mechanisms dominate with approximately N-S oriented P axes. This pattern suggests a regional anomaly characterized by clockwise rotation of the principal horizontal stress orientations.
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moment tensor solutions for small and moderate earthquakes in the ibero maghreb region
Journal of Geophysical Research, 2003Co-Authors: Daniel Stich, Charles J Ammon, Jose MoralesAbstract:[1] We applied time domain moment tensor inversion of local and regional waveforms to small and moderate (Mw = 3.5–5.7) shallow earthquakes from the Iberian Peninsula, northern Morocco, and northern Algeria. For the 6+ years period from November 1995 to March 2002 and the previous Network of Autonomously Recording Seismograms (NARS) experiment, moment tensor solutions were obtained for 58 events, considerably increasing the total number of available solutions in the study area. For each event we performed a moment tensor inversion and a double-couple Grid Search. For simple faulting events the Grid Search is valuable as a quality test for its ability to reveal potential ambiguities of the solutions and to assess confidence limits of fault plane parameters or principal axes orientation. The computed mechanisms show regional consistency: A large part of the Iberian Peninsula is characterized by normal faulting mechanisms with SW-NE oriented T axes. Thrusting and SE-NW compression is dominant in Algeria. In the Alboran Sea, the westernmost part of the Mediterranean, and the transition between both regimes, strike-slip mechanisms dominate with approximately N-S oriented P axes. This pattern suggests a regional anomaly characterized by clockwise rotation of the principal horizontal stress orientations.
Yoshua Bengio - One of the best experts on this subject based on the ideXlab platform.
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random Search for hyper parameter optimization
Journal of Machine Learning Research, 2012Co-Authors: James Bergstra, Yoshua BengioAbstract:Grid Search and manual Search are the most widely used strategies for hyper-parameter optimization. This paper shows empirically and theoretically that randomly chosen trials are more efficient for hyper-parameter optimization than trials on a Grid. Empirical evidence comes from a comparison with a large previous study that used Grid Search and manual Search to configure neural networks and deep belief networks. Compared with neural networks configured by a pure Grid Search, we find that random Search over the same domain is able to find models that are as good or better within a small fraction of the computation time. Granting random Search the same computational budget, random Search finds better models by effectively Searching a larger, less promising configuration space. Compared with deep belief networks configured by a thoughtful combination of manual Search and Grid Search, purely random Search over the same 32-dimensional configuration space found statistically equal performance on four of seven data sets, and superior performance on one of seven. A Gaussian process analysis of the function from hyper-parameters to validation set performance reveals that for most data sets only a few of the hyper-parameters really matter, but that different hyper-parameters are important on different data sets. This phenomenon makes Grid Search a poor choice for configuring algorithms for new data sets. Our analysis casts some light on why recent "High Throughput" methods achieve surprising success--they appear to Search through a large number of hyper-parameters because most hyper-parameters do not matter much. We anticipate that growing interest in large hierarchical models will place an increasing burden on techniques for hyper-parameter optimization; this work shows that random Search is a natural baseline against which to judge progress in the development of adaptive (sequential) hyper-parameter optimization algorithms.
Lynda B M Ellis - One of the best experts on this subject based on the ideXlab platform.
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meta prediction of phosphorylation sites with weighted voting and restricted Grid Search parameter selection
Nucleic Acids Research, 2008Co-Authors: Ji Wan, Shuli Kang, Chuanning Tang, Jianhua Yan, Yongliang Ren, Jie Liu, Xiaolian Gao, Arindam Banerjee, Lynda B M EllisAbstract:Meta-predictors make predictions by organizing and processing the predictions produced by several other predictors in a defined problem domain. A proficient meta-predictor not only offers better predicting performance than the individual predictors from which it is constructed, but it also relieves experimentally reSearchers from making difficult judgments when faced with conflicting results made by multiple prediction programs. As increasing numbers of predicting programs are being developed in a large number of fields of life sciences, there is an urgent need for effective meta-prediction strategies to be investigated. We compiled four unbiased phosphorylation site datasets, each for one of the four major serine/threonine (S/T) protein kinase families—CDK, CK2, PKA and PKC. Using these datasets, we examined several meta-predicting strategies with 15 phosphorylation site predictors from six predicting programs: GPS, KinasePhos, NetPhosK, PPSP, PredPhospho and Scansite. Meta-predictors constructed with a generalized weighted voting meta-predicting strategy with parameters determined by restricted Grid Search possess the best performance, exceeding that of all individual predictors in predicting phosphorylation sites of all four kinase families. Our results demonstrate a useful decision-making tool for analysing the predictions of the various S/T phosphorylation site predictors. An implementation of these meta-predictors is available on the web at: http://MetaPred.umn.edu/MetaPredPS/.
H F Silverman - One of the best experts on this subject based on the ideXlab platform.
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a fast microphone array srp phat source location implementation using coarse to fine region contraction cfrc
Workshop on Applications of Signal Processing to Audio and Acoustics, 2007Co-Authors: H F SilvermanAbstract:Most real microphone-array applications require sound sources to be localized in a noisy, reverberant environment. In such conditions, the steered response power using the phase transform (SRP-PHAT) has been shown to be more robust than faster, two-stage, time-difference of arrival methods. The complication is that the SRP-PHAT space has many local extrema which has required computationally costly Grid-Search methods. In this paper, we introduce the use of coarse-to-fine region contraction (CFRC) to make computing the SRP practical. We compare CFRC cost and performance to that of using stochastic region contraction (SRC), a method we presented recently at ICASSP 2007, which showed the computation for SRC was reduced by about 3 orders of magnitude from a comparatively fine Grid-Search. Results here from real data from human talkers show that CFRC costs about the same as SRC overall, but requires only about 63% of SRC's cost under very noisy conditions.
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a real time srp phat source location implementation using stochastic region contraction src on a large aperture microphone array
International Conference on Acoustics Speech and Signal Processing, 2007Co-Authors: H F SilvermanAbstract:In most microphone array applications, it is essential to localize sources in a noisy, reverberant environment. It has been shown that computing the steered response power (SRP) is more robust than faster, two-stage, direct time-difference of arrival methods. The problem with computing SRP is that the SRP space has many local maxima and thus computationally-intensive Grid-Search methods are used to find a global maximum. Grid Search is too expensive for a real-time system. Several papers have addressed this issue. In this paper we propose using stochastic region contraction (SRC) to make computing the SRP practical. We discuss one important SRP method, computing it from the phase transform (SRP-PHAT), review SRC, and show the computational saving. Using real data from human talkers, we show that SRC saves computation by more than two orders of magnitude with almost no loss in accuracy.
