Conquering Language: Using NLP on a Massive Scale to Build High Dimensional Language Models from the Web

International audienceDictionaries only contain some of the information we need to know about a language. The growth of the Web, the maturation of linguistic process-ing tools, and the decline in price of memory storage allow us to envision de-scriptions of languages that are much larger than before. We can conceive of building a complete language model for a language using all the text that is found on the Web for this language. This article describes our current project to do just that

Integrating sequence and array data to create an improved 1000 Genomes Project haplotype reference panel

A major use of the 1000 Genomes Project (1000GP) data is genotype imputation in genome-wide association studies (GWAS). Here we develop a method to estimate haplotypes from low-coverage sequencing data that can take advantage of single-nucleotide polymorphism (SNP) microarray genotypes on the same samples. First the SNP array data are phased to build a backbone (or 'scaffold') of haplotypes across each chromosome. We then phase the sequence data 'onto' this haplotype scaffold. This approach can take advantage of relatedness between sequenced and non-sequenced samples to improve accuracy. We use this method to create a new 1000GP haplotype reference set for use by the human genetic community. Using a set of validation genotypes at SNP and bi-allelic indels we show that these haplotypes have lower genotype discordance and improved imputation performance into downstream GWAS samples, especially at low-frequency variants. © 2014 Macmillan Publishers Limited. All rights reserved

DEVELOPMENT AND APPLICATION OF HIGH STRAIN RATE CONSTITUTIVE MODELS IN HYDROCODES

Un prérequis à la modélisation liée au dimensionnement d'ogives nucléaires et aux concepts correspondants est une compréhension fondamentale des réponses des matériaux sous des chargements très variés, allant du comportement élastique aux comportements plastique et hydrodynamique. Cet article décrit le développement et la mise en oeuvre au R.A.R.D.E. de lois de comportement améliorées prenant en compte les grandes vitesses de déformations pour une utilisation dans les hydrocodes. Les modèles déduits de la physique sont à même de décrire le comportement en déformation observé, et sont basés sur les travaux d'Armstrong et Zerilli. Ce modèle a été modifié et les paramètres identifiés pour les matériaux étudiés au RARDE à la fois dans leur état vierge et leur état choqué. L'importance de disposer d'un modèle semi-empirique (par ex. Johnson-Cook) est mise en évidence. L'utilisation originale d'hydrocodes en simulation d'essais de caractérisation donne un point de vue supplémentaire à la méthode d'analyse employée pour l'identification du modèle de comportement. Nous présentons des résultats qui fournissent une preuve irréfutable de la validité du modèle d'Armstrong-Zerilli pour un acier pur dans l'espace vitesse de déformation-défomation-températures pour les matériaux impactés ou par l'application réussie de ce modèle à la formation d'un projectile par charge explosive est aussi démontrée.A pre-requisite to the numerical modelling of warhead designs and concepts is a basic understanding of how materials behave under various loads, ranging from elastic to plastic through to hydrodynamic. This paper describes the development and application at RARDE of improved high strain rate material models for use in hydrocodes. These physically derived models are capable of describing the observed deformation behaviour and are based on the work of Armstrong and Zerilli. This model has been modified and constants derived for RARDE based material, both unshocked and shocked. The importance of having a physically based constitutive model, as opposed to a purely semi-empirical type model (e.g Johnson-Cook) is illustrated. The novel use of the hydrocodes in the simulation of the experimental material tests is shown to provide an extra insight into the method of analysis used in the derivation of a constitutive model. Results are presented which provide powerful evidence of the validity of the Armstrong-Zerilli model for pure iron in the high strain-rate, strain, and temperature regimes for both unshocked and shocked material. The successful application of this model to explosively formed projectile formation studies is also illustrated

Validation of a path-dependent constitutive model for FCC and BCC metals using "symmetric" Taylor impact

In this study, the rod-on-rod impact geometry was used at impact speeds of ca. 200 m s-1. This is widely believed to be equivalent to the impact of a single rod on an infinitely rigid target and hence an ideal form of the Taylor test as no real target is infinitely rigid. However, our modelling studies showed that the two rods do not behave symmetrically. Two metals were studied : AQ85 iron and XM copper. These were machined into cylinders 15mm long and 5.35mm in diameter. High-speed photographic sequences of the impacts were taken with an interframe time of 5 µs. These pictures were then digitised to obtain profiles as a function of time. The bcc material (iron) exhibited the classic "mushroom" shaped profile which was relatively easy to model as a function of time using existing constitutive models. However, the fcc material (copper) exhibited an additional bulge a few millimetres from the impact face. This behaviour proved impossible to simulate using path-independent models. It proved, however, possible to simulate the behaviour of fcc copper in the "symmetric" Taylor impact configuration using a newly-developed path-dependent constitutive model. The paper contains the results of this comparison between experiment, theory and modelling

A High-Speed Photographic Study of the Rapid Deformation of Metal Annuli : Comparison of Theory with Experiment

Pour vérifier le module de comportement d'un métal, il est important de déterminer comment il faut corriger les courbes contrainte-déformation obtenues en compression afin de tenir compte des effets de frottement. Des erreurs graves viennent d'être découvertes dans les modèles analytiques standards utilisés pour déterminer les dites corrections dans les barres de Hopkinson. Dans le présent article nous proposons une nouvelle méthode pour déterminer le coefficient de frottement dans la compression axiale dynamique d'un anneau. La méthode utilise la modération numérique et la photographie ultrarapide. Elle est validée en utilisant un acier à blindage.It is very important to know what friction correction to make to stress-strain curves obtained in compression so that constitutive models of metals can be accurately checked. However, it recently became apparent that standard analytical models commonly used to correct for friction in the split Hopkinson pressure bar have some serious errors. In this paper, we report a novel method of determining the friction coefficient for the case of axial compressive dynamic deformation of annuli. The method combines numerical modelling with high-speed photography and has been validated using Rolled Homogeneous Armour (RHA) steel

Simulation of explosive fracture cylinder test using DYNA

There is a great need in the area of dynamic fracture to develop precise validation tests which are simple, reproducible and provide a challenge to the simulation tools. One such test is the explosive fracture cylinder which comprises a cylinder of material (e.g. iron) with a small hole along the axis. The hole is filled with explosive and initiated at one end which results in a focussing of release waves at the other end of the cylinder to produce a fracture cone. By varying the length of the cylinder it is possible to either expel the cone or capture the conical crack at various points in its progression. Sectioning the cylinder thereby results in a detailed void growth pattern that can be studied and compared with simulation results. This paper describes a detailed comparison of the simulation with the experiments and discusses the influence of mesh size. shaw and explosive on the results. It is concluded that the Goldthorpe path Dependent Ductile Fracture Model represents a promising way forward for describing ductile fracture in continuum hydrocodes