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Spectral Decomposition (spectral + decomposition)
Selected AbstractsSpectral decomposition of periodic ground water fluctuation in a coastal aquiferHYDROLOGICAL PROCESSES, Issue 12 2008David Ching-Fang Shih Abstract This research accomplished by the descriptive statistics and spectral analysis of six kinds of time series data gives a complete assessment of periodic fluctuation in significant constituents for the Huakang Shan earthquake monitoring site. Spectral analysis and bandpass filtering techniques are demonstrated to accurately analyse the significant component. Variation in relative ground water heads with a period of 12·6 h is found to be highly related to seawater level fluctuation. Time lag is estimated about 3·78 h. Based on these phenomena, the coastal aquifer formed in an unconsolidated formation can be affected by the nearby seawater body for the semi-diurnal component. Fluctuation in piezometric heads is found to correspond at a rate of 1000 m h,1. Atmospheric pressure presents the significant components at periods of 10·8 h and 7·2 h in a quite different type, compared to relative ground water head and seawater level. Copyright © 2008 John Wiley & Sons, Ltd. [source] Multifrequency VLBI observations of faint gigahertz peaked spectrum sourcesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2000I. A. G. Snellen We present the data and analysis of VLBI observations at 1.6, 5 and 15 GHz of a sample of faint gigahertz peaked spectrum (GPS) sources selected from the Westerbork Northern Sky Survey. The 5-GHz observations involved a global array of 16 stations and yielded data on the total sample of 47 sources. A subsample of 26 GPS sources with peak frequencies and/or peak flux densities was observed with the VLBA at 15 GHz. A second subsample of 29 sources, with was observed at 1.6 GHz using a 14-station global VLBI array. In this way, 44 of the 47 sources (94 per cent) in the sample were observed above and at or below their spectral peak. Spectral decomposition allowed us to identify three, 11, seven and two objects as compact symmetric objects, compact doubles, core,jet and complex sources, respectively. However, many of the sources classified as compact double or core,jet sources show only two components making their classification rather tentative. This may explain why the strong morphological dichotomy of GPS quasars and galaxies found for radio-bright GPS sources is not as clear in this faint sample. [source] On the investigation of shell buckling due to random geometrical imperfections implemented using Karhunen,Loève expansionsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2008K. J. Craig Abstract For the accurate prediction of the collapse behaviour of thin cylindrical shells, it is accepted that geometrical and other imperfections in material properties and loading have to be accounted for in the simulation. There are different methods of incorporating imperfections, depending on the availability of accurate imperfection data. The current paper uses a spectral decomposition of geometrical uncertainty (Karhunen,Loève expansions). To specify the covariance of the required random field, two methods are used. First, available experimentally measured imperfection fields are used as input for a principal component analysis based on pattern recognition literature, thereby reducing the cost of the eigenanalysis. Second, the covariance function is specified analytically and the resulting Friedholm integral equation of the second kind is solved using a wavelet-Galerkin approach. Experimentally determined correlation lengths are used as input for the analytical covariance functions. The above procedure enables the generation of imperfection fields for applications where the geometry is slightly modified from the original measured geometry. For example, 100 shells are perturbed with the resulting random fields obtained from both methods, and the results in the form of temporal normal forces during buckling, as simulated using LS-DYNA®, as well as the statistics of a Monte Carlo analysis of the 100 shells in each case are presented. Although numerically determined mean values of the limit load of the current and another numerical study differ from the experimental results due to the omission of imperfections other than geometrical, the coefficients of variation are shown to be in close agreement. Copyright © 2007 John Wiley & Sons, Ltd. [source] Computation of the matrix exponential and its derivatives by scaling and squaringINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2004T. C. FungArticle first published online: 4 FEB 200 Abstract In this paper, a simple method based on the scaling and squaring technique for the evaluation of the matrix exponential and its derivatives is presented. A more general formulation with non-constant first derivatives is considered here. Both higher order and mixed derivatives are investigated. The method is based directly on the property of the exponential function and does not require the use of perturbation formulae for eigenvalues and eigenvectors. The approach provides a simple and direct algorithm for the computation of the matrix exponential and its derivatives regardless of degeneracy in the spectral decomposition of the matrix argument. If the derivatives are taken with respect to the entries of the matrix argument, the first and second linearizations can be obtained directly. Copyright © 2004 John Wiley & Sons, Ltd. [source] Giant low surface brightness haloes in distant radio galaxies: USS0828+193MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002M. Villar-Martín Abstract We present results on the spectroscopic study of the ionized gas in the high-redshift radio galaxy USS0828+193 at z= 2.57. Thanks to the high signal-to-noise (S/N) ratio of the emission lines in the Keck spectrum, we have been able to perform a detailed kinematic study by means of the spectral decomposition of the emission line profiles. This study reveals the existence of two types of material in this object: (i) a low surface brightness component with apparent quiescent kinematics consistent with gravitational motions and (ii) a perturbed component with rather extreme kinematics. The quiescent halo extends across the entire object for ,80 kpc. It is enriched with heavy elements and apparently ionized by the continuum from the active nucleus. The properties of the quiescent halo and its origin are discussed in this paper. We propose that it could be part of a structure that surrounds the entire object, although its nature is not clear (a rotating disc? low surface brightness satellites? a cooling flow nebula? material ejected in galactic winds? other?). [source] Comparison between the Fourier and Wavelet methods of spectral analysis applied to stationary and nonstationary heart period dataPSYCHOPHYSIOLOGY, Issue 5 2001Jan H. Houtveen The aim of this study was to assess the error made by violating the assumption of stationarity when using Fourier analysis for spectral decomposition of heart period power. A comparison was made between using Fourier and Wavelet analysis (the latter being a relatively new method without the assumption of stationarity). Both methods were compared separately for stationary and nonstationary segments. An ambulatory device was used to measure the heart period data of 40 young and healthy participants during a psychological stress task and during periods of rest. Surprisingly small differences (<1%) were found between the results of both methods, with differences being slightly larger for the nonstationary segments. It is concluded that both methods perform almost identically for computation of heart period power values. Thus, the Wavelet method is only superior for analyzing heart period data when additional analyses in the time-frequency domain are required. [source] Hierarchical Spatial Modeling of Additive and Dominance Genetic Variance for Large Spatial Trial DatasetsBIOMETRICS, Issue 2 2009Andrew O. Finley Summary This article expands upon recent interest in Bayesian hierarchical models in quantitative genetics by developing spatial process models for inference on additive and dominance genetic variance within the context of large spatially referenced trial datasets. Direct application of such models to large spatial datasets are, however, computationally infeasible because of cubic-order matrix algorithms involved in estimation. The situation is even worse in Markov chain Monte Carlo (MCMC) contexts where such computations are performed for several iterations. Here, we discuss approaches that help obviate these hurdles without sacrificing the richness in modeling. For genetic effects, we demonstrate how an initial spectral decomposition of the relationship matrices negate the expensive matrix inversions required in previously proposed MCMC methods. For spatial effects, we outline two approaches for circumventing the prohibitively expensive matrix decompositions: the first leverages analytical results from Ornstein,Uhlenbeck processes that yield computationally efficient tridiagonal structures, whereas the second derives a modified predictive process model from the original model by projecting its realizations to a lower-dimensional subspace, thereby reducing the computational burden. We illustrate the proposed methods using a synthetic dataset with additive, dominance, genetic effects and anisotropic spatial residuals, and a large dataset from a Scots pine (Pinus sylvestris L.) progeny study conducted in northern Sweden. Our approaches enable us to provide a comprehensive analysis of this large trial, which amply demonstrates that, in addition to violating basic assumptions of the linear model, ignoring spatial effects can result in downwardly biased measures of heritability. [source] | ||||||||||