Search results for "selection"
showing 10 items of 1940 documents
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…
Towards unsupervised analysis of second-order chromatographic data: automated selection of number of components in multivariate curve-resolution meth…
2007
A method to apply multivariate curve-resolution unattendedly is presented. The algorithm is suitable to perform deconvolution of two-way data (e.g. retrieving the individual elution profiles and spectra of co-eluting compounds from signals obtained from a chromatograph equipped with multiple-channel detection: LC-DAD or GC-MS). The method is especially adequate to achieve the advantages of deconvolution approaches when huge amounts of data are present and manual application of multivariate techniques is too time-consuming. The philosophy of the algorithm is to mimic the reactions of an expert user when applying the orthogonal projection approach--multivariate curve-resolution techniques. Ba…
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…
Archetypal analysis: contributions for estimating boundary cases in multivariate accommodation problem
2013
[EN] The use of archetypal analysis is proposed in order to determine a set of representative cases that entail a certain percentage of the population, in the accommodation problem. A well-known anthropometric database has been used in order to compare our methodology with the common used PCA-approach, showing the advantages of our methodology: the level of accommodation is reached unlike the PCA approach, no more adjustments are necessary, the user can decide the number of archetypes to consider or leave the selection by a criterion. Unlike PCA, the objective of the archetypal analysis is obtaining extreme individuals, so it is the appropriate statistical technique for solving this type of…
The effect of genetic robustness on evolvability in digital organisms
2008
Abstract Background Recent work has revealed that many biological systems keep functioning in the face of mutations and therefore can be considered genetically robust. However, several issues related to robustness remain poorly understood, such as its implications for evolvability (the ability to produce adaptive evolutionary innovations). Results Here, we use the Avida digital evolution platform to explore the effects of genetic robustness on evolvability. First, we obtained digital organisms with varying levels of robustness by evolving them under combinations of mutation rates and population sizes previously shown to select for different levels of robustness. Then, we assessed the abilit…
Delayed lysis confers resistance to the nucleoside analogue 5-fluorouracil and alleviates mutation accumulation in the single-stranded DNA bacterioph…
2014
ABSTRACT Rates of spontaneous mutation determine viral fitness and adaptability. In RNA viruses, treatment with mutagenic nucleoside analogues selects for polymerase variants with increased fidelity, showing that viral mutation rates can be adjusted in response to imposed selective pressures. However, this type of resistance is not possible in viruses that do not encode their own polymerases, such as single-stranded DNA viruses. We previously showed that serial passaging of bacteriophage ϕX174 in the presence of the nucleoside analogue 5-fluorouracil (5-FU) favored substitutions in the lysis protein E (P. Domingo-Calap, M. Pereira-Gomez, and R. Sanjuán, J. Virol. 86: 9640–9646, 2012, doi:10…
Extremely high mutation rate of a hammerhead viroid
2009
Supporting information (Materials and methods, figs. S1-S3, suppl. references) available at: http://www.sciencemag.org/cgi/data/323/5919/1308/DC1/1
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…