Influence Functions of the Spearman and Kendall Correlation Measures

Mathematics Subject Classification (2000) 62G35 · 62F99

Estimators of the multiple correlation coefficient: local robustness and confidence intervals.

Many robust regression estimators are defined by minimizing a measure of spread of the residuals. An accompanying R-2-measure, or multiple correlation coefficient, is then easily obtained. In this paper, local robustness properties of these robust R-2-coefficients axe investigated. It is also shown how confidence intervals for the population multiple correlation coefficient can be constructed in the case of multivariate normality.Cautionary note; High breakdown-point; Influence function; Intervals; Model; Multiple correlation coefficient; R-2-measure; Regression analysis; Residuals; Robustness; Squares regression;

The K-Step Spatial Sign Covariance Matrix

The Sign Covariance Matrix is an orthogonal equivariant estimator of mul- tivariate scale. It is often used as an easy-to-compute and highly robust estimator. In this paper we propose a k-step version of the Sign Covariance Matrix, which improves its e±ciency while keeping the maximal breakdown point. If k tends to infinity, Tyler's M-estimator is obtained. It turns out that even for very low values of k, one gets almost the same e±ciency as Tyler's M-estimator.

On the Optimality of Multivariate S-Estimators

In this paper we maximize the efficiency of a multivariate S-estimator under a constraint on the breakdown point. In the linear regression model, it is known that the highest possible efficiency of a maximum breakdown S-estimator is bounded above by 33% for Gaussian errors. We prove the surprising result that in dimensions larger than one, the efficiency of a maxi- mum breakdown S-estimator of location and scatter can get arbitrarily close to 100%, by an appropriate selection of the loss function.Breakdown point;Multivariate Location and Scatter;Robustness;S-estimator

Analyse canonique basée sur des estimateurs robustes de la matrice de covariance.

Model;

Bounded influence regression using high breakdown scatter matrices.

In this paper we estimate the parameters of a regression model using S-estimators of multivariate location and scatter. The approach is proven to be Fisher-consistent, and the influence functions are derived. The corresponding asymptotic variances are obtained and it is shown how they can be estimated in practice. A comparison with other recently proposed robust regression estimators is made.fisher-consistency; influence function; robust regression; s-estimators; scatter matrices; multivariate location; robust estimation; s-estimators; linear-regression; rank regression; covariance; squares; diagnostics; stability; efficiency;

A Verified Information-Flow Architecture

SAFE is a clean-slate design for a highly secure computer system, with pervasive mechanisms for tracking and limiting information flows. At the lowest level, the SAFE hardware supports fine-grained programmable tags, with efficient and flexible propagation and combination of tags as instructions are executed. The operating system virtualizes these generic facilities to present an information-flow abstract machine that allows user programs to label sensitive data with rich confidentiality policies. We present a formal, machine-checked model of the key hardware and software mechanisms used to dynamically control information flow in SAFE and an end-to-end proof of noninterference for this model. We use a refinement proof methodology to propagate the noninterference property of the abstract machine down to the concrete machine level. We use an intermediate layer in the refinement chain that factors out the details of the information-flow control policy and devise a code generator for compiling such information-flow policies into low-level monitor code. Finally, we verify the correctness of this generator using a dedicated Hoare logic that abstracts from low-level machine instructions into a reusable set of verified structured code generators

Présence de métaux lourds et de résidus médicamenteux dans les effluents des établissements de santé de Dakar (Sénégal)

L’objectif de cette étude est de quantifier les concentrations en métaux lourds et de rechercher la présence de résidus de molécules médicamenteuses des effluents de trois hôpitaux de Dakar (Sénégal). C’est ainsi que la collecte des effluents a été réalisée chaque jour sur une période de trois semaines à l’entrée du déversoir des services de radiologie, de médecine interne et d’odontologie. Ensuite, des échantillons composites par semaine ont été constitués pour rechercher leur composition en métaux lourds et en résidus médicamenteux. Le transport a été effectué à +4 °C et à l'obscurité pour assurer une conservation satisfaisante. Les métaux lourds ont été dosés par ICP-MS et les résidus de médicaments ont été recherchés par UPLCMS/ MS. Les médicaments identifiés dans les effluents sont essentiellement des analgésiques et des psychotropes. La concentration en métaux lourds des effluents des trois hôpitaux est inférieure aux normes sénégalaises et de celles de L’OMS fixant les conditions de rejet de métaux dans les eaux usées. Cependant, bien que les taux retrouvés soient tolérables, leur introduction continuelle en milieu aquatique pourrait être à l’origine d’effets néfastes sur les organismes marins par des phénomènes de bioaccumulation et de biomagnification. D’où l’importance et la nécessité des stations d’épuration pour une bonne gestion et une réduction des risques écotoxicologiques liés aux effluents liquides hospitaliers.Mots clés : Effluents hospitaliers, métaux lourds, résidus médicamenteux, toxicité

Ion-Induced Dipole Interactions and Fragmentation Times : Cα\alpha -Cβ\beta Chromophore Bond Dissociation Channel

The fragmentation times corresponding to the loss of the chromophore (C$\alpha$-- C$\beta$ bond dissociation channel) after photoexcitation at 263 nm have been investigated for several small peptides containing tryptophan or tyrosine. For tryptophan-containing peptides, the aromatic chromophore is lost as an ionic fragment (m/z 130), and the fragmentation time increases with the mass of the neutral fragment. In contrast, for tyrosine-containing peptides the aromatic chromophore is always lost as a neutral fragment (mass = 107 amu) and the fragmentation time is found to be fast (\textless{}20 ns). These different behaviors are explained by the role of the postfragmentation interaction in the complex formed after the C$\alpha$--C$\beta$ bond cleavage