École normale supérieure de Cachan

About: École normale supérieure de Cachan is a education organization based out in Cachan, Île-de-France, France. It is known for research contribution in the topics: Decidability & Finite element method. The organization has 2717 authors who have published 5585 publications receiving 175925 citations.

Space-efficient and exact de Bruijn graph representation based on a Bloom filter

Abstract: The de Bruijn graph data structure is widely used in next-generation sequencing (NGS). Many programs, e.g. de novo assemblers, rely on in-memory representation of this graph. However, current techniques for representing the de Bruijn graph of a human genome require a large amount of memory (≥30 GB). We propose a new encoding of the de Bruijn graph, which occupies an order of magnitude less space than current representations. The encoding is based on a Bloom filter, with an additional structure to remove critical false positives. An assembly software implementing this structure, Minia, performed a complete de novo assembly of human genome short reads using 5.7 GB of memory in 23 hours.

Asymptotics for the minimization of a Ginzburg-Landau functional

Abstract: LetΩ ⊂ ℝ2 be a smooth bounded simply connected domain. Consider the functional $$E_\varepsilon (u) = \frac{1}{2}\int\limits_\Omega {\left| { abla u} \right|^2 + \frac{1}{{4\varepsilon ^2 }}} \int\limits_\Omega {(|u|^2 - 1)^2 } $$ on the classH g 1 ={u eH 1(Ω; ℂ);u=g on ∂Ω} whereg:∂Ω∂ → ℂ is a prescribed smooth map with ¦g¦=1 on ∂Ω∂ and deg(g, ∂Ω)=0. Let uu e be a minimizer for Ee onH g 1 . We prove that ue → u0 in $$C^{1,\alpha } (\bar \Omega )$$ as e → 0, where u0 is identified. Moreover $$\left\| {u_\varepsilon - u_0 } \right\|_{L^\infty } \leqslant C\varepsilon ^2 $$ .

Diffusion Weighted Image Denoising Using Overcomplete Local PCA

Abstract: Diffusion Weighted Images (DWI) normally shows a low Signal to Noise Ratio (SNR) due to the presence of noise from the measurement process that complicates and biases the estimation of quantitative diffusion parameters. In this paper, a new denoising methodology is proposed that takes into consideration the multicomponent nature of multi-directional DWI datasets such as those employed in diffusion imaging. This new filter reduces random noise in multicomponent DWI by locally shrinking less significant Principal Components using an overcomplete approach. The proposed method is compared with state-of-the-art methods using synthetic and real clinical MR images, showing improved performance in terms of denoising quality and estimation of diffusion parameters.

Verifying privacy-type properties of electronic voting protocols

Abstract: Electronic voting promises the possibility of a convenient, efficient and secure facility for recording and tallying votes in an election. Recently highlighted inadequacies of implemented systems have demonstrated the importance of formally verifying the underlying voting protocols. We study three privacy-type properties of electronic voting protocols: in increasing order of strength, they are vote-privacy, receipt-freeness and coercion-resistance. We use the applied pi calculus, a formalism well adapted to modelling such protocols, which has the advantages of being based on well-understood concepts. The privacy-type properties are expressed using observational equivalence and we show in accordance with intuition that coercion-resistance implies receipt-freeness, which implies vote-privacy. We illustrate our definitions on three electronic voting protocols from the literature. Ideally, these three properties should hold even if the election officials are corrupt. However, protocols that were designed to satisfy receipt-freeness or coercion-resistance may not do so in the presence of corrupt officials. Our model and definitions allow us to specify and easily change which authorities are supposed to be trustworthy.

Flow and fracture characteristics of aluminium alloy AA5083–H116 as function of strain rate, temperature and triaxiality

Abstract: This paper presents a part of an on-going study of light-weight shelters made of aluminium alloy AA5083–H116. A necessary prerequisite for numerical simulations of impact behaviour of such shelters is a calibrated numerical model. Slightly modified versions of the two Johnson–Cook models describing flow stress and fracture strain are applied. In addition to ordinary quasistatic tests with smooth specimens, these models demand tests at elevated temperatures and strain rates, and different triaxiality ratios. All tests to be presented in this paper are uniaxial tension tests performed in servohydraulic test machines or a Split–Hopkinson bar. The test programme involves approximately 100 specimens, and includes coupons from three different directions of the plate material, thereby taking account for the anisotropy. The AA5083 alloy is susceptible to dynamic strain ageing, and this phenomenon is shown to result in serrated stress–strain curves and negative strain rate sensitivity for a rather wide range of strain rates. In particular, the specimen geometry seems to have a strong influence on the serrated curves. The calibration shows that the Johnson–Cook–type models represent most of the observed material behaviour reasonably well, although the negative strain rate sensitivity is not adequately described.