Approximation with Error Bounds in Spark

We introduce a sampling framework to support approximate computing with estimated error bounds in Spark. Our framework allows sampling to be performed at the beginning of a sequence of multiple transformations ending in an aggregation operation. The framework constructs a data provenance tree as the computation proceeds, then combines the tree with multi-stage sampling and population estimation theories to compute error bounds for the aggregation. When information about output keys are available early, the framework can also use adaptive stratified reservoir sampling to avoid (or reduce) key losses in the final output and to achieve more consistent error bounds across popular and rare keys. Finally, the framework includes an algorithm to dynamically choose sampling rates to meet user specified constraints on the CDF of error bounds in the outputs. We have implemented a prototype of our framework called ApproxSpark, and used it to implement five approximate applications from different domains. Evaluation results show that ApproxSpark can (a) significantly reduce execution time if users can tolerate small amounts of uncertainties and, in many cases, loss of rare keys, and (b) automatically find sampling rates to meet user specified constraints on error bounds. We also explore and discuss extensively trade-offs between sampling rates, execution time, accuracy and key loss

Paroles de témoins : vers une pluralisation du récit historique

Le retour de l'individu et du singulier dans l'écriture de l'histoire constitue l'un des changements majeurs qu'a connus l'histoire socioculturelle depuis les années 1980. Réhabilitée, après une longue période de règne de narratifs macrohistoriques et d'histoire sérielle, l'approche biographique en est sortie élargie, transformée en une donnée incontournable de la compréhension des contextes sociaux. En revenant sur ce changement de paradigme, cet article se focalise sur deux courants ayant ouvert de nouvelles perspectives qui pourraient trouver d'ultérieurs développements en histoire de l'éducation : la recherche sur les « egodocuments » et la microhistoire (« Microstoria »). Il analyse ensuite à titre d'exemple un « fait éducatif » local et non spectaculaire - l'institutionnalisation d'un séminaire de formation de maîtres et de maîtresses, au milieu du XVIIIe siècle - à travers les traces qu'il a laissées dans les archives

Conformational profiling of a G-rich sequence within the c-KIT promoter

G-quadruplexes (G4) within oncogene promoters are considered to be promising anticancer targets. However, often they undergo complex structural rearrangements that preclude a precise description of the optimal target. Moreover, even when solved structures are available, they refer to the thermodynamically stable forms but little or no information is supplied about their complex multistep folding pathway. To shed light on this issue, we systematically followed the kinetic behavior of a G-rich sequence located within the c-KIT proximal promoter (kit2) in the presence of monovalent cations K + and Na + . A very short-lived intermediate was observed to start the G4 folding process in both salt conditions. Subsequently, the two pathways diverge to produce distinct thermodynamically stable species (parallel and antiparallel G-quadruplex in K + and Na + , respectively). Remarkably, in K + -containing solution a branched pathway is required to drive the wild type sequence to distribute between a monomeric and dimeric G-quadruplex. Our approach has allowed us to identify transient forms whose relative abundance is regulated by the environment; some of them were characterized by a half-life within the timescale of physiological DNA processing events and thus may represent possible unexpected targets for ligands recognition

Interacción entre pares: terreno de aprendizaje matemático y de ‘empatía matemática’

El trabajo versa sobre el intercambio de resoluciones a una tarea de comparación de razones que llevan a cabo parejas de estudiantes de tercer grado de secundaria. Siguiendo los principios de la teoría fundamentada y del análisis de los argumentos de Toulmin, en el documento se argumenta que para que una interacción sea provechosa son necesarios los conocimientos matemáticos así como una actitud de ‘empatía matemática’. Se sugieren también algunas ‘características notables’ para que una interacción sea cognitivamente útil y enriquecedora para la pareja, características que pueden ser interesantes referencias para futuras investigaciones y de utilidad para los docentes

Least weight and least cost optimisation of a passenger vessel

In the scantling design of a passenger ship, minimum production costminimum weight and maximum moment of inertia (stiffness) are conflicting objectives. For that purpose, recent improvements have been made to the LBR-5 software (French acronym of Stiffened Panels Software”, version 5.0) to optimize the scantling of ship sections by considering production cost, weight and moment of inertia in the optimisation objective function. A real multi-criterion optimisation of a passenger ship is presented in this paper. Results highlight that LBR-5 is competitive software to optimise scantling of ships at very early design stage with management of critical problems studied normally at a later step of the design