A multiresolution approach to time warping achieved by a Bayesian prior-posterior transfer fitting strategy.

The procedure known as warping aims at reducing phase variability in a sample of functional curve observations, by applying a smooth bijection to the argument of each of the functions. We propose a natural representation of warping functions in terms of a new type of elementary function named `warping component functions' which are combined into the warping function by composition. A sequential Bayesian estimation strategy is introduced, which fits a series of models and transfers the posterior of the previous fit into the prior of the next fit. Model selection is based on a warping analogue to wavelet thresholding, combined with Bayesian inference.Bayesian inference; Functional data analysis; Markov chain Monte Carlo sampling; Time warping; Warping components; Warping function;

Warping Functional Data in R and C via a Bayesian Multiresolution Approach

Phase variation in functional data obscures the true amplitude variation when a typical cross-sectional analysis of these responses would be performed. Time warping or curve registration aims at eliminating the phase variation, typically by applying transformations, the warping functions τn, to the function arguments. We propose a warping method that jointly estimates a decomposition of the warping function in warping components, and amplitude components. For the estimation routine, adaptive MCMC calculations are performed and implemented in C rather than R to increase computational speed. The R-C interface makes the program user-friendly, in that no knowledge of C is required and all input and output will be handled through R. The R package MRwarping contains all needed files

Speciation without chromatography: Part 2. Determination of tributyltin by chloride generation flow injection atomic absorption spectrometry

A procedure is described for the quantitation of tributyltin in aqueous samples and extracts based on its relatively high volatility in halide media, permitting vapour phase sampling from the headspace above such samples.Tributyltin chloride (TBT-C1) was purged from various chloride containing aqueous matrices and collected on the surface of an iridium treated graphite tube for subsequent quantitation by graphite furnace atomic absorption. Iodide, bromide and chloride matrices were compared for their generation efficiency. The effect of acidity of the sample was also studied. An absolute detection limit of 1.3 ng TBT (as tin) was estimated, corresponding to a detection limit of 0.33 ng ml 1 for a 4 ml sub-sample. Method validation was achieved using NRCC PACS-2 (sediment) Certified Reference Material, for which reasonable agreement between certified and measured values of tributyltin content was obtained. A procedural concentration limit of detection of 66 ng g 1 TBT in the sediment could be achieved