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Correlation matrices are omnipresent in multivariate data analysis. When the number d of variables is large, the sample estimates of correlation matrices are typically noisy and conceal underlying dependence patterns. We consider the case when the variables can be grouped into K clusters with exchangeable dependence; this assumption is often made in applications, e.g., in finance and econometrics. Under this partial exchangeability condition, the corresponding correlation matrix has a block structure and the number of unknown parameters is reduced from d(d − 1)/2 to at most K(K + 1)/2. We propose a robust algorithm based on Kendall's rank correlation to identify the clusters without assuming the knowledge of K a priori or anything about the margins except continuity. The corresponding blockstructured estimator performs considerably better than the sample Kendall rank correlation matrix when K < d. The new estimator can also be much more efficient in finite samples even in the unstructured case K = d, although there is no gain asymptotically. When the distribution of the data is elliptical, the results extend to linear correlation matrices and their inverses. The procedure is illustrated on financial stock returns.

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In humans, DNA polymerase δ (Pol δ) holoenzymes, comprised of Pol δ and the processivity sliding clamp, proliferating cell nuclear antigen (PCNA), carry out DNA synthesis during lagging strand DNA replication, initiation of leading strand DNA replication, and the major DNA damage repair and tolerance pathways. Pol δ holoenzymes are assembled at primer/template (P/T) junctions and initiate DNA synthesis in a coordinated process involving the major single strand DNA-binding protein complex, replication protein A (RPA), the processivity sliding clamp loader, replication factor C (RFC), PCNA, and Pol δ. Each of these factors interact uniquely with a P/T junction and most directly engage one another. Currently, the interplay between these macromolecular interactions is largely unknown. In the present study, novel Förster Resonance Energy Transfer (FRET) assays reveal that dynamic interactions of RPA with a P/T junction during assembly of a Pol δ holoenzyme and initiation of DNA synthesis maintain RPA at a P/T junction and accommodate RFC, PCNA, and Pol δ, maximizing the efficiency of each process. Collectively, these studies significantly advance our understanding of human DNA replication and DNA repair.

Cet article analyse les réactions aux textes littéraires manifestées par un élève en difficulté pendant des discussions à l’intérieur d’un cercle de lecture. Neuf discussions d’un sous-groupe comprenant un élève en difficulté et quatre élèves réguliers ont été enregistrées et analysées à l’aide de grilles inspirées des travaux de Rosenblatt (1991) et de Langer (1990). Cette analyse a mis en évidence que l’élève en difficulté est aussi capable que ses pairs d’adopter des réactions personnelles basées sur une certaine forme de pensée critique, analytique et associative.This article analyzes the reactions of a troubled pupil to literary text during discussions by a reading group. Nine discussions held by a sub-group comprising a troubled pupil and four regular pupils were taped and analyzed using frameworks inspired by Rosenblatt (1991) and de Langer (1990). The analysis shows that the troubled pupil is just as capable as his peers of evincing personal reactions based on a certain form of critical, analytical, and associative thinking