Estimating a Signal In the Presence of an Unknown Background

We describe a method for fitting distributions to data which only requires knowledge of the parametric form of either the signal or the background but not both. The unknown distribution is fit using a non-parametric kernel density estimator. The method returns parameter estimates as well as errors on those estimates. Simulation studies show that these estimates are unbiased and that the errors are correct

Correcting the Minimization Bias in Searches for Small Signals

We discuss a method for correcting the bias in the limits for small signals if those limits were found based on cuts that were chosen by minimizing a criterion such as sensitivity. Such a bias is commonly present when a "minimization" and an "evaluation" are done at the same time. We propose to use a variant of the bootstrap to adjust the limits. A Monte Carlo study shows that these new limits have correct coverage.Comment: 14 pages, 5 figue

Confidence Intervals and Upper Bounds for Small Signals in the Presence of Background Noise

We discuss a new method for setting limits on small signals in the presence of background noise. The method is based on a combination of a two dimensional confidence region and the large sample approximation to the likelihood ratio test statistic. It automatically quotes upper limits for small signals and two-sided confidence intervals for larger samples. We show that this method gives the correct coverage and also has good power.Comment: Document was created by Sciword V3.0, it consists of one main document (lrt.tex), eight figures (figure1.eps - figure8.eps) and one table (table.tex). Paper was revised after being accepted for publication in NIM A Paper was revised after being accepted for publication in NIM

Limits and Confidence Intervals in the Presence of Nuisance Parameters

We study the frequentist properties of confidence intervals computed by the method known to statisticians as the Profile Likelihood. It is seen that the coverage of these intervals is surprisingly good over a wide range of possible parameter values for important classes of problems, in particular whenever there are additional nuisance parameters with statistical or systematic errors. Programs are available for calculating these intervals.Comment: 6 figure

First-best, second-best and principal-agent problems

In some pure moral hazard situations the principal can implement a first-best allocation using an incentive contract constructed on the basis of a first-best payment scheme. Such a contract relies on the possibility of discriminate actions according to the outcome by imposing a penalty whenever the observed outcome is lower than the admissible ones. The elimination of inefficient behavior depends basically on the outcome function, and we find that the fine is finite in the more interesting cases. The implementation of the first-best solution does not depend on the principal's risk neutrality. Nevertheless, when the principal is risk neutral, the ef f icient contract is dichotomous. Moreover, we prove that the efficient allocation can be reached through such a dichotomous payment scheme if and only if the principal is risk neutral for a certain range of returns.

Criteria for efficient prevention of dissemination and successful eradication of Erwinia amylovora (the cause of fire blight) in Aragón, Spain

Erwinia amylovora was detected on pome fruits in the Aragón region (North-Eastern Spain), in a ca. 5 km radius area located in the mid Jalón river (mid Ebro Valley) in the province of Zaragoza, during 2000‒2003. Eight years have now passed since this pathogen was last detected, without new infections being reported in the same area. The bases for surveys and rapid eradication performed have been analyzed in detail to understand the reasons for the success in removing fireblight. The results demonstrate that intensive surveillance, risk assessment, plant analyses using accurate identification methods, and, especially, rapid total or selective eradication of infected trees in the plots have been very effective in preventing the generalized spread of fireblight and in delaying economic losses associated with this disease. Eradication and compensation to growers, estimated to cost approx. € 467,000, were clearly counterbalanced by the economic value of apple and pear production in the 2000‒2003 period (approx. € 368 million). Fire blight risk-assessment, using the MARYBLYT system, showed that climatic conditions in the studied area were favourable to infections during the analyzed period (1997‒2006). Molecular characterization of E. amylovora strains had revealed their homogeneity, suggesting that these fire blight episodes could have been caused by just one inoculum source, supporting the hypothesis that there was a unique introduction of E. amylovora in the studied area. Spatial spread of E. amylovora to trees was analyzed within six orchards, indicating an aggregated distribution model. This Spanish experience demonstrates the success of scientifically-based prevention methods that lead to the deployment of a fast and strict containment strategy, useful for other Mediterranean areassurveysrisk-assessmentspatial analysisstrain characterizationPublishe

Change-Point Method Applied to the Detection of Temporal Variations in Seafloor Bacterial Mat Coverage

The paper is aimed at a methodological development of change-point detection, applicable in dentifying abrupt changes in temporal or spatial data sequences. In earlier papers we developed a method for detecting a change in the parameters of a discrete distribution, with the simultaneous estimation of the (deterministic but unknown) distribution parameters before and after the change. In this paper we not only extend this method to the case of normal distributions, but also provide a new algorithm for the iterative refining of the estimation of the change-point, based on a "cleaning" of mixed-up parts of the samples. The appropriate size of reduced part of the sample is analytically calculated for the case of normal distributions. This "cleaning" is combined with our original change-point detection method. Our new algorithm is not only validated on artificial data, but also applied to a real environmental data set collected and analysed by other authors in a seafloor observatory. Our results detecting abrupt changes of bacterial mat coverage of a seafloor area are in harmony with the biological fluctuations and changes in the abiotic environment, analysed recently by other authors using a different method. We also provide a comparison with other existing change-point detection methods: a one-dimensional version of the gradient method widely used for edge detection, and a maximum type statistical method well-known in environmental studies. Although normality conditions of our method are rather restrictive, its application potential for environmental data sets is also demonstrated

Evolution of cation and spin orders in the double–double-double perovskite series CaxMn2−xFeReO6

International audienc

Interaction of molecular and atomic hydrogen with (5,5) and (6,6) single-wall carbon nanotubes

Density functional theory has been used to study the interaction of molecular and atomic hydrogen with (5,5) and (6,6) single-wall carbon nanotubes. Static calculations allowing for different degrees of structural relaxation are performed, in addition to dynamical simulations. Molecular physisorption inside and outside the nanotube walls is predicted to be the most stable state of those systems. The binding energies for physisorption of the H2 molecule outside the nanotube are in the range 0.04–0.07 eV. This means that uptake and release of molecular hydrogen from nanotubes is a relatively easy process, as many experiments have proved. A chemisorption state, with the molecule dissociated and the two hydrogen atoms bonded to neighbor carbon atoms, has also been found. However, reaching this dissociative chemisorption state for an incoming molecule, or starting from the physisorbed molecule, is difficult because of the existence of a substantial activation barrier. The dissociative chemisorption deforms the tube and weakens the C-C bond. This effect can catalyze the shattering and scission of the tube by incoming hydrogen molecules with sufficient kinetic energy.This work was supported by DGESIC (Grant No. PB98-0345) and European Community (RTN-COMELCAN). We acknowledge the computational facilities provided by CESCA and CEPBA.Peer reviewe

Transporte marítimo de corta distancia entre España e Italia: perfil de las empresas usuarias

El Transporte Marítimo de Corta Distancia (TMCD) ha sido catalogado por la Comisión Europea como el único modo de transporte que ofrece posibilidades reales de lograr un transvase de carga desde la carretera, mejorando además la competitividad y reduciendo los costes ambientales. En los últimos años se han llevado a cabo diversos estudios donde se han tratado de identificar líneas de TMCD con un potencial de futuro importante. Sin embargo, no se han abordado trabajos donde se evalúe el perfil de las empresas de transporte internacional por carretera que hacen uso de esta modalidad de transporte. Con el propósito de cubrir este déficit, en el presente trabajo se procede, sobre una muestra de 81 empresas de transporte internacional por carretera (41 españolas, 3 portuguesas y 37 italianas) que hacen uso de las líneas de TMCD entre España e Italia, a delimitar el perfil de dichas empresas, a la vez que a analizar ciertos elementos inherentes a la relación que mantienen con las navieras con las que trabaja