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.

Mechanisms of pathogen entry through the endosomal compartments.

Abstract: Several pathogens - bacteria, viruses and parasites - must enter mammalian cells for survival, replication and immune-system evasion. These pathogens generally make use of existing cellular pathways that are designed for nutrient uptake, receptor downregulation and signalling. Because most of these pathways end in lysosomes, an organelle that is capable of killing microorganisms, pathogens have developed remarkable means to avoid interactions with this lytic organelle.

Search for invisible decays of a dark photon produced in e+e- collisions at BaBar

Abstract: We search for single-photon events in 53 fb^{-1} of e^{+}e^{-} collision data collected with the BABAR detector at the PEP-II B-Factory. We look for events with a single high-energy photon and a large missing momentum and energy, consistent with production of a spin-1 particle A^{'} through the process e^{+}e^{-}→γA^{'}; A^{'}→invisible. Such particles, referred to as "dark photons," are motivated by theories applying a U(1) gauge symmetry to dark matter. We find no evidence for such processes and set 90% confidence level upper limits on the coupling strength of A^{'} to e^{+}e^{-} in the mass range m_{A^{'}}≤8 GeV. In particular, our limits exclude the values of the A^{'} coupling suggested by the dark-photon interpretation of the muon (g-2)_{μ} anomaly, as well as a broad range of parameters for the dark-sector models.

A single mode of DNA base-pair opening drives imino proton exchange

Abstract: The opening of base pairs of double-stranded DNA is an important process, being a prerequisite for replication and transcription and possibly a factor in the recognition, flexibility and structure of DNA. The kinetics of base-pair opening have, however, been controversial. Base-pair opening can be studied by following the exchange of protons from imino groups with water, a process that seems only to occur from open base pairs. We have recently demonstrated catalysis by proton acceptors of imino proton exchange in nucleic acids. This has enabled us to determine the base-pair lifetimes, which are in the region of 10 ms at room temperature1,2. In earlier reports it had been considered that proton exchange is limited by the rate of base-pair opening, which had led to estimates of base-pair lifetimes that were larger by one or two orders of magnitude3–17. There are also important discrepan-cies between recent and early estimates of the base-pair dissociation constant. Earlier estimates of base-pair lifetimes correspond in fact to the time required for proton exchange in the absence of added catalyst (AAC exchange). This could be a distinct mode of base-pair opening with a very long open lifetime, different from the mode revealed by the effect of catalyst. The evidence reported here suggests on the contrary that there is only a single mode of base-pair opening and that proton exchange in the absence of added catalyst is in fact catalysed by a proton acceptor intrinsic to the nucleic acid, most probably the other base of the open pair.

Random quasi-phase-matching in bulk polycrystalline isotropic nonlinear materials.

Abstract: Three-wave mixing in nonlinear materials—the interaction of two light waves to produce a third—is a convenient way of generating new optical frequencies from common laser sources. However, the resulting optical conversion yield is generally poor, because the relative phases of the three interacting waves change continuously as they propagate through the material1. This phenomenon, known as phase mismatch, is a consequence of optical dispersion (wave velocity is frequency dependent), and is responsible for the poor optical conversion potential of isotropic nonlinear materials2. Here we show that exploiting the random motion of the relative phases in highly transparent polycrystalline materials can be an effective strategy for achieving efficient phase matching in isotropic materials. Distinctive features of this ‘random quasi-phase-matching’ approach are a linear dependence of the conversion yield with sample thickness (predicted in ref. 3), the absence of the need for either preferential materials orientation or specific polarization selection rules, and the existence of a wavelength-dependent resonant size for the polycrystalline grains.

Bone regeneration and stem cells

Abstract: This invited review covers research areas of central importance for orthopaedic and maxillofacial bone tissue repair, including normal fracture healing and healing problems, biomaterial scaffolds for tissue engineering, mesenchymal and foetal stem cells, effects of sex steroids on mesenchymal stem cells, use of platelet-rich plasma for tissue repair, osteogenesis and its molecular markers. A variety of cells in addition to stem cells, as well as advances in materials science to meet specific requirements for bone and soft tissue regeneration by addition of bioactive molecules, are discussed.