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Iterative Fashion (iterative + fashion)
Selected AbstractsMeasuring finite-frequency body-wave amplitudes and traveltimesGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2006Karin Sigloch SUMMARY We have developed a method to measure finite-frequency amplitude and traveltime anomalies of teleseismic P waves. We use a matched filtering approach that models the first 25 s of a seismogram after the P arrival, which includes the depth phases pP and sP. Given a set of broad-band seismograms from a teleseismic event, we compute synthetic Green's functions using published moment tensor solutions. We jointly deconvolve global or regional sets of seismograms with their Green's functions to obtain the broad-band source time function. The matched filter of a seismogram is the convolution of the Green's function with the source time function. Traveltimes are computed by cross-correlating each seismogram with its matched filter. Amplitude anomalies are defined as the multiplicative factors that minimize the RMS misfit between matched filters and data. The procedure is implemented in an iterative fashion, which allows for joint inversion for the source time function, amplitudes, and a correction to the moment tensor. Cluster analysis is used to identify azimuthally distinct groups of seismograms when source effects with azimuthal dependence are prominent. We then invert for one source time function per group. We implement this inversion for a range of source depths to determine the most likely depth, as indicated by the overall RMS misfit, and by the non-negativity and compactness of the source time function. Finite-frequency measurements are obtained by filtering broad-band data and matched filters through a bank of passband filters. The method is validated on a set of 15 events of magnitude 5.8 to 6.9. Our focus is on the densely instrumented Western US. Quasi-duplet events (,quplets') are used to estimate measurement uncertainty on real data. Robust results are achieved for wave periods between 24 and 2 s. Traveltime dispersion is on the order of 0.5 s. Amplitude anomalies are on the order of 1 db in the lowest bands and 3 db in the highest bands, corresponding to amplification factors of 1.2 and 2.0, respectively. Measurement uncertainties for amplitudes and traveltimes depend mostly on station coverage, accuracy of the moment tensor estimate, and frequency band. We investigate the influence of those parameters in tests on synthetic data. Along the RISTRA array in the Western US, we observe amplitude and traveltime patterns that are coherent on scales of hundreds of kilometres. Below two sections of the array, we observe a combination of frequency-dependent amplitude and traveltime patterns that strongly suggest wavefront healing effects. [source] Maximum likelihood fitting using ordinary least squares algorithms,JOURNAL OF CHEMOMETRICS, Issue 8-10 2002Rasmus Bro Abstract In this paper a general algorithm is provided for maximum likelihood fitting of deterministic models subject to Gaussian-distributed residual variation (including any type of non-singular covariance). By deterministic models is meant models in which no distributional assumptions are valid (or applied) on the parameters. The algorithm may also more generally be used for weighted least squares (WLS) fitting in situations where either distributional assumptions are not available or other than statistical assumptions guide the choice of loss function. The algorithm to solve the associated problem is called MILES (Maximum likelihood via Iterative Least squares EStimation). It is shown that the sought parameters can be estimated using simple least squares (LS) algorithms in an iterative fashion. The algorithm is based on iterative majorization and extends earlier work for WLS fitting of models with heteroscedastic uncorrelated residual variation. The algorithm is shown to include several current algorithms as special cases. For example, maximum likelihood principal component analysis models with and without offsets can be easily fitted with MILES. The MILES algorithm is simple and can be implemented as an outer loop in any least squares algorithm, e.g. for analysis of variance, regression, response surface modeling, etc. Several examples are provided on the use of MILES. Copyright © 2002 John Wiley & Sons, Ltd. [source] A theoretical study of pentacyclo-undecane cage peptides of the type [Ac-X-Y-NHMe]JOURNAL OF PEPTIDE SCIENCE, Issue 2 2006Krishna Bisetty Abstract The conformational preferences of peptides of the type, Ac-X-Y-NHMe, where X and Y = Ala, cage and Pro, were studied by means of computational techniques within the framework of a molecular mechanics approach. For each of the eight peptide analogues, extensive conformational searches were carried out using molecular dynamics (MD) and simulated annealing (SA) protocols in an iterative fashion. Both results are in good agreement and complement each other. The conformational search indicates that the cage residue restricts the conformational freedom of the dipeptide considerably in comparison with the other model residues used. This study revealed that proline exhibits a greater tendency in promoting reverse-turn characteristics in comparison to the cage peptides, which show promising ,-turn characteristics. It was also found that 300,500 K is not sufficient to overcome rotational barriers for cage peptides. In all cases, the low-energy conformers have a tendency to form bent structures. Copyright © 2005 European Peptide Society and John Wiley & Sons, Ltd. [source] European Federation of Neurological Societies/Peripheral Nerve Society Guideline on management of chronic inflammatory demyelinating polyradiculoneuropathy: Report of a joint task force of the European Federation of Neurological Societies and the Peripheral Nerve Society , First RevisionJOURNAL OF THE PERIPHERAL NERVOUS SYSTEM, Issue 1 2010Joint Task Force of the EFNS, the PNS Background: Consensus guidelines on the definition, investigation, and treatment of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) have been published (J Peripher Nerv Syst 2005; 10: 220,228, Eur J Neurol 2006; 13: 326,332). Objectives: To revise these guidelines. Methods: Disease experts, including a representative of patients, considered references retrieved from MEDLINE and Cochrane Systematic Reviews published between August 2004 and July 2009 and prepared statements that were agreed in an iterative fashion. Recommendations: The Task Force agreed on Good Practice Points to define clinical and electrophysiological diagnostic criteria for CIDP with or without concomitant diseases and investigations to be considered. The principal treatment recommendations were: (i) intravenous immunoglobulin (IVIg) (Recommendation Level A) or corticosteroids (Recommendation Level C) should be considered in sensory and motor CIDP; (ii) IVIg should be considered as the initial treatment in pure motor CIDP (Good Practice Point); (iii) if IVIg and corticosteroids are ineffective, plasma exchange (PE) should be considered (Recommendation Level A); (iv) if the response is inadequate or the maintenance doses of the initial treatment are high, combination treatments or adding an immunosuppressant or immunomodulatory drug should be considered (Good Practice Point); (v) symptomatic treatment and multidisciplinary management should be considered (Good Practice Point). [source] European Federation of Neurological Societies/Peripheral Nerve Society Guideline, on management of multifocal motor neuropathy.JOURNAL OF THE PERIPHERAL NERVOUS SYSTEM, Issue 1 2006Report of a joint task force of the European Federation of Neurological Societies, the Peripheral Nerve Society Abstract Background: Several diagnostic criteria for multifocal motor neuropathy (MMN) have been proposed in recent years, and a beneficial effect of intravenous immunoglobulin (IVIg) and various other immunomodulatory drugs has been suggested in several trials and uncontrolled studies. Objectives: The aim of this guideline was to prepare consensus guidelines on the definition, investigation, and treatment of MMN. Methods: Disease experts and a representative of patients considered references retrieved from MEDLINE and the Cochrane Library in July 2004 and prepared statements that were agreed in an iterative fashion. Recommendations: The Task Force agreed on good practice points to define clinical and electrophysiological diagnostic criteria for MMN and investigations to be considered. The principal recommendations and good practice points were as follows: (1) IVIg (2 g/kg given over 2,5 days) should be considered as the first line of treatment (level A recommendation) when disability is sufficiently severe to warrant treatment; (2) corticosteroids are not recommended (good practice point); (3) if initial treatment with IVIg is effective, repeated IVIg treatment should be considered (level C recommendation). The frequency of IVIg maintenance therapy should be guided by the individual response (good practice point). Typical treatment regimens are 1 g/kg every 2,4 weeks or 2 g/kg every 4,8 weeks (good practice point); (4) if IVIg is not (or not sufficiently) effective, then immunosuppressive treatment may be considered. Cyclophosphamide, cyclosporine, azathioprine, interferon-,1a, or rituximab are possible agents (good practice point); and (5) toxicity makes cyclophosphamide a less desirable option (good practice point). [source] | ||||||||||