Search results for " selection"

2015

We present a method to discover discriminative brain metabolism patterns in [18F] fluorodeoxyglucose positron emission tomography (PET) scans, facilitating the clinical diagnosis of Alzheimer's disease. In the work, the term "pattern" stands for a certain brain region that characterizes a target group of patients and can be used for a classification as well as interpretation purposes. Thus, it can be understood as a so-called "region of interest (ROI)". In the literature, an ROI is often found by a given brain atlas that defines a number of brain regions, which corresponds to an anatomical approach. The present work introduces a semi-data-driven approach that is based on learning the charac…

Analysis of compatibility between lighting devices and descriptive features using Parzen’s kernel: application to flaw inspection by artificial vision

2000

We present a supervised method, developed for industrial inspections by artificial vision, to obtain an adapted combination of descriptive features and a lighting device. This method must be implemented under real-time constraints and therefore a minimal number of features must be selected. The method is based on the assessment of the discrimination power of many descriptive features. The objective is to select the combination of descriptive features and lighting system best able to discriminate flawed classes from defect-free classes. In the first step, probability densities are computed for flawed and defect-free classes and for each tested combination. The discrimination power of the fea…

Assessment of the statistical significance of classifications in infrared spectroscopy based diagnostic models.

2014

Fourier transform infrared (IR) spectroscopy in combination with multivariate data analysis is a versatile tool that can be applied to disease diagnosis. However, a rigorous validation of the obtained models is necessary in order to obtain robust results. This work evaluates the advantages of the use of permutation testing for determining the statistical significance of the misclassification errors obtained from IR based diagnostic models through cross validation (CV). The model performance, estimated by CV, is compared to a distribution of CV-performance values obtained using randomly permuted class labels. The distribution of ‘random CV-values’ is considered as a null distribution and use…

Forecasting correlated time series with exponential smoothing models

2011

Abstract This paper presents the Bayesian analysis of a general multivariate exponential smoothing model that allows us to forecast time series jointly, subject to correlated random disturbances. The general multivariate model, which can be formulated as a seemingly unrelated regression model, includes the previously studied homogeneous multivariate Holt-Winters’ model as a special case when all of the univariate series share a common structure. MCMC simulation techniques are required in order to approach the non-analytically tractable posterior distribution of the model parameters. The predictive distribution is then estimated using Monte Carlo integration. A Bayesian model selection crite…

A narratological approach to content selection in audio description: towards a strategy for the description of narratological time

2012

As more and more countries start to provide audio description services for a growing range of products and events, research into this new discipline is growing and diversifying as well. Two questions that seem to be at the heart of much of this research focus on what should be described and how this should be done, in other words on content selection and formulation of the description. The present article looks at the first of these two questions and approaches it from a narratological point of view. After a general discussion of the use of narratology for audio description, the focus will shift to one particular constituent of narrative, namely time. The different temporal aspects will be …

Evolution education in natural history museums

2009

During 2009, scientists around the world will celebrate the 200th anniversary of the birth of Charles Darwin, the father of the theory of evolution, and the 150th anniversary of the publication of his main thesis, On the Origin of Species by Means of Natural Selection. Today, the theory of evolution is considered to be one of the greatest milestones in the history of science. Despite its undisputed merit in science, there seems to be constant turmoil around the theory in the public, which might be related to the incomplete understanding of the basic principles of evolution [1,2].

When to be sexual: sex allocation theory and population density-dependent induction of sex in cyclical parthenogens

2008

The timing of sex is a critical fitness component in the cyclically parthenogenetic life-cycle of rotifers. It has been hypothesized that sex in rotifers is optimally timed to high population density because male‐female encounters are more probable. Because sexual females produce either males or, if inseminated, diapausing eggs, the advantage of a higher male‐female encounter rate is that allocation to male production can be lower. This is paradoxical in the context of the sex allocation theory developed for rotifers, as the theory predicts equal numbers of male-producing and diapausing-egg producing females. We investigated this paradox using both empirical data and theoretical analysis. L…

Progreso, complejidad y evolución

2020

Ensayos en honor de Eloy Rada. [ES]: El progreso biológico es un tema ampliamente debatido en biología evolutiva que tiene partidarios y detractores. Sin embargo, no es una cuestión, a pesar de su importancia, de la que podamos afirmar que está resuelta desde el punto de vista científico. En este trabajo presento un análisis del concepto basado en la teoría de la evolución por selección natural, sus paralelismos con el también debatido concepto de “progreso” en la historia de la humanidad y, finalmente, se intenta orientarlo hacia formas accesibles a la investigación científica. Para ello, en lugar del concepto de progreso, recurro al de “complejidad biológica”. Si tenemos formas de medirla…

The logic of forms in the light of developmental biology and palaeontology.

2010

11 pages; If you ask palaeontologists, and indeed anyone interested in the theory of evolution, for the key words that encapsulate it, you will obtain the following results: adaptation, natural selection, speciation, but also ontogeny and phylogeny. The first three key words apply to the future of the individual and by extension to the future of the species: we are therefore dealing with adults of a reproductive age. The two other key words concern (i) the evolution of the morphology from the egg to the adult (individual ontogeny: short timescale) and especially what goes on in the black box called embryogenesis, and (ii) the modification of ontogenetic sequences over time, resulting in cha…

Testis asymmetry in birds: the influences of sexual and natural selection

2014

Gonad size and shape asymmetries are particularly common in birds. Although some obvious size and shape differences between the left and right testes in birds were first documented more than a century ago, little is known about what influences the variation across species in either the degree or the direction of these asymmetries. Here we show that a left bias in size is the most likely ancestral state in most orders and families, and that there is a weak but significant negative relation between the degree of size and shape asymmetries. In extant species, testis size and shape symmetries increase with the degree of sperm competition (relative testes mass), but those relations are significa…