A novel feature set for low-dimensional signal representation, designed for classification or clustering of non-stationary signals with complex variation in time and frequency, is presented. The feature representation of a signal is given by the first left and right singular vectors of its ambiguity spectrum matrix. If the ambiguity matrix is of low rank, most signal information in time direction is captured by the first right singular vector while the signal's key frequency information is encoded by the first left singular vector. The resemblance of two signals is investigated by means of a suitable similarity assessment of the signals' respective singular vector pair. Application of multitapers for the calculation of the ambiguity spectrum gives an increased robustness to jitter and background noise and a consequent improvement in performance, as compared to estimation based on the ordinary single Hanning window spectrogram. The suggested feature-based signal compression is applied to a syllable-based analysis of a song from the bird species Great Reed Warbler and evaluated by comparison to manual auditive and/or visual signal classification. The results show that the proposed approach outperforms well-known approaches based on mel-frequency cepstral coefficients and spectrogram cross-correlation.

Selenomethionine (SeMet) is an important organic nutritional source of Se, but the uptake and metabolism of SeMet are poorly characterised in humans. Dynamic gamma camera images of the abdominal region were acquired from eight healthy young men after the ingestion of radioactive 75 Se-L-SeMet ( 75 Se-SeMet). Scanning started simultaneously to the ingestion of 75 Se-SeMet and lasted 120 min. We generated timeactivity curves from two-dimensional regions of interest in the stomach, small intestine and liver. During scanning, blood samples were collected at 10-min intervals to generate plasma time-activity curves. A four-compartment model, augmented with a delay between the liver and plasma, was fitted to individual participants' data. The mean rate constant for 75 Se-SeMet transport was 2·63 h -1 from the stomach to the small intestine, 13·2 h -1 from the small intestine to the liver, 0·261 h -1 from the liver to the plasma and 0·267 h -1 from the stomach to the plasma. The delay in the liver was 0·714 h. Gamma camera imaging provides data for use in compartmental modelling of 75 Se-SeMet absorption and metabolism in humans. In clinical settings, the obtained rate constants and the delay in the liver may be useful variables for quantifying reduced intestinal absorption capacity or liver function.Key words: Selenomethionine: 75 Se-L-selenomethionine: Absorption capacity: Metabolism: Gamma camera imaging: Compartmental modelling Selenomethionine (SeMet) is an important organic nutritional source of Se (1,2) . Absorption of various Se compounds occurs via different routes and mechanisms. Membrane transport of selenoamino acids, including SeMet, involves a specific suite of amino acid transporters (3) . The subsequent incorporation of dietary Se into selenoproteins occurs through a series of interconversions, of which many details remain unknown. Se metabolites are excreted in the urine and faeces and in exhaled air, mainly as selenosugars and methylated compounds (4) .The initial metabolism of Se in humans is poorly characterised. Estimates of Se absorption, whole-body retention and excretion have been made predominantly on whole-body counting (5) or the recovery of ingested tracers in the blood, urine and faeces (6) . Compartmental analyses of kinetic data from tracer studies have also been used to create a more integrated picture of whole-body Se utilisation in humans (7,8) . These studies characterised the long-term kinetics by the investigation of urine and faecal data collected over 12 d and blood samples drawn over 4 months. Through detailed mathematical modelling including several plasma pools, they were able to provide new insights into the long-run Se metabolism. However, because the study data only comprised hourly observations after dose administration, the initial Se kinetics could not be investigated and therefore still remained unclear. Our study tries to fill this gap and to provide deeper insight into the initial Se kinetics by focusing on frequent data collection within the first 2 h after a...

Summary Neurobiological data such as electroencephalography measurements pose a statistical challenge due to low spatial resolution and poor signal‐to‐noise ratio, as well as large variability from subject to subject. We propose a new modelling framework for this type of data based on stochastic processes. Stochastic differential equations with mixed effects are a popular framework for modelling biomedical data, e.g. in pharmacological studies. Whereas the inherent stochasticity of diffusion models accounts for prevalent model uncertainty or misspecification, random‐effects model intersubject variability. The two‐layer stochasticity, however, renders parameter inference challenging. Estimates are based on the discretized continuous time likelihood and we investigate finite sample and discretization bias. In applications, the comparison of, for example, treatment effects is often of interest. We discuss hypothesis testing and evaluate by simulations. Finally, we apply the framework to a statistical investigation of electroencephalography recordings from epileptic patients. We close the paper by examining asymptotics (the number of subjects going to ∞) of maximum likelihood estimators in multi‐dimensional, non‐linear and non‐homogeneous stochastic differential equations with random effects and included covariates.

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Dickcissel (Spiza americana) males occupying territories in cropland sites produced songs that were less similar on average to other Dickcissel songs in their neighborhood than did Dickcissels living in grasslands, where conformity to the local vocal culture was higher. Further, Dickcissel vocal culture changed more quickly over time in cropland sites relative to grassland sites. These differences may have resulted from the lower site fidelity we observed in Dickcissel males in cropland sites relative to grassland sites. We expected this link with site fidelity because we hypothesized that conformity to local culture in Oscine songbirds and the persistence of culture over time and space are promoted by habitats that facilitate stable populations. In contrast, sites in which habitat features cause rapid population turnover provide more territory vacancies and so more opportunities for colonization. Colonization should drive cultural change, either through adult colonists importing foreign cultural variants or young colonists making errors as they learn the local song. This potential link between population turnover and cultural stability may apply to animal cultures more broadly and so may be a fruitful area for further research. Besides the link between site fidelity and cultural change over time, we also investigated the possibility that habitats with different levels of site fidelity might show differences in the spatial scale of song similarity. However, we found no evidence of such a difference. Finally, although our conclusions regarding conformity and change in vocal culture were based on many recorded songs, automated assessments of song similarity imprecisely estimated the overall degree of song similarity. Thus, we may have underestimated the strength of the effects of time and distance on song similarity.

Binary composite endpoints offer some advantages as a way to succinctly combine evidence from a number of related binary endpoints recorded in the same clinical trial into a single outcome. However, as some concerns about the clinical relevance as well as the interpretation of such composite endpoints have been raised, it is recommended to evaluate the composite endpoint jointly with the involved components. We propose an approach for carrying out simultaneous inference based on separate model fits for each endpoint, yet controlling the familywise type I error rate asymptotically. The key idea is to stack parameter estimates from the different fits and derive their joint asymptotic distribution. Simulations show that the proposed approach comes closer to nominal levels and has comparable or higher power as compared to existing approaches, even for moderate sample sizes (around 100-200 observations). The method is compared to the gatekeeping approach and results are provided in the Supplementary Material. In two data examples we show how the procedure may be adapted to handle local significance levels specified through a priori given weights.

Animal culture often shows geographic structure, with individuals in close proximity sharing more cultural features than individuals further apart. However, spatial extent of cultural features, along with the degree of conformity to local cultures, vary within and among species. Further, rates of cultural change presumably also vary, though documentation of temporal variability lags behind documentation of spatial variability. Understanding both spatial and temporal variation is essential to understanding cultural evolution, but mechanisms likely to be driving this variation have not been sufficiently explored. We hypothesized that conformity to local culture in Oscine songbirds and the persistence of culture over time and space are promoted by habitats that facilitate stable populations in which individuals show relatively high site fidelity. In contrast, sites in which habitat features cause rapid population turnover provide more vacant territories and so more opportunities for colonization. Colonization should drive more rapid cultural change, either through adult colonists importing foreign cultural variants or young colonists making errors as they learn the local song. To test this set of hypotheses, we examined temporal and spatial variation in vocal culture in a songbird (dickcissel, Spiza americana) in two distinct habitat types. As predicted, we found high site fidelity in relatively stable native grasslands and much lower site fidelity in nearby cropland sites which were disturbed by farming practices during the breeding season. We also found evidence of higher levels of song sharing and slower changes in vocal culture in our grasslands relative to croplands, though we found no evidence of different spatial scales of song sharing between these habitats. This is the first study we know of correlating the temporal rate of cultural change to differences in a demographic factor between habitats. Although our conclusions are based on many recorded songs, automated assessments of song similarity were imprecise and so our results here underestimate the overall degree of song sharing and thus possibly the strength of the effects of time and distance on this sharing. Further, because we examined song sharing at only seven sites, firm conclusions about site fidelity and song sharing will require larger samples in the future.