École Polytechnique

About: École Polytechnique is a education organization based out in Palaiseau, France. It is known for research contribution in the topics: Laser & Plasma. The organization has 18995 authors who have published 39265 publications receiving 1225163 citations. The organization is also known as: Ecole Polytechnique & Polytechnique.

Global stability of a jet in crossflow

Abstract: A linear stability analysis shows that the jet in crossflow is characterized by self-sustained global oscillations for a jet-to-crossflow velocity ratio of 3. A fully three-dimensional unstable steady-state solution and its associated global eigenmodes are computed by direct numerical simulations and iterative eigenvalue routines. The steady flow, obtained by means of selective frequency damping, consists mainly of a (steady) counter-rotating vortex pair (CVP) in the far field and horseshoe-shaped vortices close to the wall. High-frequency unstable global eigenmodes associated with shear-layer instabilities on the CVP and low-frequency modes associated with shedding vortices in the wake of the jet are identified. Furthermore, different spanwise symmetries of the global modes are discussed. This work constitutes the first simulation-based global stability analysis of a fully three-dimensional base flow.

Collaborative web-based experimentation in flexible engineering education

Abstract: The Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne, Switzerland, is deploying a flexible learning scheme for selected pilot courses in engineering education. In such a scheme, traditional lectures and written exercises are combined with additional Web-based learning resources. The main objective of this initiative is to sustain the evolution from traditional teaching to active learning and to better integrate the increasing number of educational resources available online. In engineering education, a key activity to sustain the learning process is hands-on experimentation carried out using either simulation tools or real equipment. This paper describes how a collaborative Web-based experimentation environment has been introduced at the EPFL for providing more flexibility to students performing laboratory experiments in automatic control, biomechanics, and fluid mechanics. It particularly describes the eJournal, a Web service integrated in the proposed learning environment that enables the collection and sharing of preparatory notes and experimental results with both peers and teaching assistants.

Polarimetric imaging of uterine cervix: a case study

Abstract: We present a preliminary investigation of macroscopic polarimetric imaging of uterine cervix. Orthogonal state contrast (OSC) images of healthy and anomalous cervices have been taken in vivo at 550 nm. Four ex vivo cervix samples have been studied in full Muller polarimetry, at 550 nm and 700 nm, and characterized in detail by standard pathology. One sample was totally healthy, another one carried CIN lesions at very early stage (CIN1) in its visible exocervical region, while for the other two samples more advanced (CIN3) lesions were present, together with visible glandular epithelium (ectropion). Significant birefringence has been observed in the healthy regions of all six samples, both in vivo and ex vivo. Standard treatments of the Mueller images of the ex vivo samples allowed to quantify both retardation and depolarization. Retardation reached 60° in healthy regions, and disappeared in the anomalous regions of the other three ex vivo samples. The depolarization power was largest in healthy regions, and lower in CINs and ectropion. Possible origins of the observed effects are briefly discussed.

Image Data Resource: a bioimage data integration and publication platform

Abstract: Access to primary research data is vital for the advancement of science. To extend the data types supported by community repositories, we built a prototype Image Data Resource (IDR) that collects and integrates imaging data acquired across many different imaging modalities. IDR links data from several imaging modalities, including high-content screening, super-resolution and time-lapse microscopy, digital pathology, public genetic or chemical databases, and cell and tissue phenotypes expressed using controlled ontologies. Using this integration, IDR facilitates the analysis of gene networks and reveals functional interactions that are inaccessible to individual studies. To enable re-analysis, we also established a computational resource based on Jupyter notebooks that allows remote access to the entire IDR. IDR is also an open source platform that others can use to publish their own image data. Thus IDR provides both a novel on-line resource and a software infrastructure that promotes and extends publication and re-analysis of scientific image data.

Anti-de Sitter D-branes

Abstract: We study D-branes of the SL(2,) WZW model and of its discrete orbifolds. Gluing the currents by group automorphisms leads to three types of D-branes: two-dimensional hyperbolic planes (H2), de Sitter branes (dS2), or anti-de Sitter branes (AdS2). We explain that the dS2 branes are unphysical, because the electric field on their world-volume is supercritical. By combining SL(2,) and SU(2), we exhibit a class of supersymmetric AdS2 × S2 three-brane world-volumes, and consider their possible embeddings in the near-horizon region of stringy black holes. We point out the intriguing difference between the induced and the effective geometries of these D-branes, and speculate on its possible significance.