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;

Geriatrische Interventie: een klinisch-empirisch onderzoek

In 1986 was ik als klinisch geriater werkzaam op een geriatrische afdeling van een psychiatrisch ziekenhuis (GAPZ) en was ik tevens consulent voor het algemeen ziekenhuis Leyenburg. In de daaropvolgende 4 jaren is mij duidelijk geworden wat de voor- en de nadelen zijn van de behandeling op een geriatrische afdeling versus geriatrische consulten en medebehandeling op andere afdelingen. Toen mijn werkveld naar het algemeen ziekenhuis Leyenburg werd verschoven stond ik voor de opdracht om in dit ziekenhuis de klinische geriatrie verder te ontwikkelen. Op dat ogenblik was er in het ziekenhuis een stijgende vraag naar geriatrische consulten. Geriatrische patienten bleken verspreid over alle afdelingen van het ziekenhuis voor te komen. Het werkelijke aantal geriatrische patienten in het ziekenhuis was op basis van de consulten moeilijk in te schatten. Wanneer een afdeling gedurende een jaar veel aandacht kreeg. steeg het aantal consulten zeer sterk. om daarna weer te dalen wanneer de consultatief werkende afdeling geriatrie er minder actief mee bezig was. Er zijn verschillende organisatorische modellen waarmee geriatrie in ziekenhuizen kan worden bedreven

Recording from two neurons: second order stimulus reconstruction from spike trains and population coding

We study the reconstruction of visual stimuli from spike trains, recording simultaneously from the two H1 neurons located in the lobula plate of the fly Chrysomya megacephala. The fly views two types of stimuli, corresponding to rotational and translational displacements. If the reconstructed stimulus is to be represented by a Volterra series and correlations between spikes are to be taken into account, first order expansions are insufficient and we have to go to second order, at least. In this case higher order correlation functions have to be manipulated, whose size may become prohibitively large. We therefore develop a Gaussian-like representation for fourth order correlation functions, which works exceedingly well in the case of the fly. The reconstructions using this Gaussian-like representation are very similar to the reconstructions using the experimental correlation functions. The overall contribution to rotational stimulus reconstruction of the second order kernels - measured by a chi-squared averaged over the whole experiment - is only about 8% of the first order contribution. Yet if we introduce an instant-dependent chi-square to measure the contribution of second order kernels at special events, we observe an up to 100% improvement. As may be expected, for translational stimuli the reconstructions are rather poor. The Gaussian-like representation could be a valuable aid in population coding with large number of neurons

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