Dynamics of wrinkling in ultrathin elastic sheets

The wrinkling of thin elastic objects provides a means of generating regular patterning at small scales in applications ranging from photovoltaics to microfluidic devices. Static wrinkle patterns are known to be governed by an energetic balance between the object's bending stiffness and an effective substrate stiffness, which may originate from a true substrate stiffness or from tension and curvature along the wrinkles. Here we investigate dynamic wrinkling, induced by the impact of a solid sphere onto an ultra-thin polymer sheet floating on water. The vertical deflection of the sheet's centre induced by impact draws material radially inwards, resulting in an azimuthal compression that is relieved by the wrinkling of the entire sheet. We show that this wrinkling is truly dynamic, exhibiting features that are qualitatively different to those seen in quasi-static wrinkling experiments. Moreover, we show that the wrinkles coarsen dynamically because of the inhibiting effect of the fluid inertia. This dynamic coarsening can be understood heuristically as the result of a dynamic stiffness, which dominates the static stiffnesses reported thus far, and allows new controls of wrinkle wavelength.Comment: 8 pages, 4 figures. Please see published version for supplementary movies and SI Appendi

Ceramic matrix composites for liner system of radioactive waste disposal cells

Please click Additional Files below to see the full abstrac

Isolation and Characterization of Intestinal Stem Cells Based on Surface Marker Combinations and Colony-Formation Assay

Identification of intestinal stem cells (ISCs) has relied heavily on the use of transgenic reporters in mice, but this approach is limited by mosaic expression patterns and difficult to directly apply to human tissues. We sought to identify reliable surface markers of ISCs and establish a robust functional assay to characterize ISCs from mouse and human tissues

CERAMIC MATRIX COMPOSITES FOR LINER SYSTEM OF RADIOACTIVE WASTE DISPOSAL CELLS

International audienceThe Composite Ceramic Nuclear Liner project is part of the Cigéo project, a deep geological disposal facility for high-level and long-lived intermediate-level radioactive waste led by Andra, the French national agency for radioactive waste management. The concept of high level radioactive waste (HLW) disposal cells involves the installation of a liner consisting of a hollow cylinder inserted into a micro-tunnel dug into a clay formation. The main function of the liner is to allow the emplacement and the potential recovery of the HLW packages, during the entire period of reversible operation of the facility, estimated to be 100 years. The current preferred solution is a steel liner. However, corrosion of metals under anoxic conditions is likely to generate hydrogen. Among the potential areas of development of the disposal facility, Andra is studying alternative materials to metals for the liner. On top of the mechanical requirements already met by the metallic solutions identified, the new materials must be chemically inert with respect to the vitrified waste and the host rock [2].The objective of the feasibility assessment was to remove the technological barriers associated with the use of ceramic matrix composites (CMC) for the lining of HLW cells. It is an innovative application for materials initially developed for extreme temperatures applications. The project was divided into three parts: (i) literature study and characterization of commercial materials; (ii) in-situ conditions definition and structural analysis; (iii) production of a prototype and pre-industrial implementation. In the first step a state of the art was established and CMCs that could potentially meet the specific requirements of the HL cell liner have been preselected. These materials were of different nature, both in terms of reinforcements and matrix : Oxide/Oxide ; Carbon/Geopolymer (PyroKarb) and Oxide/Geopolymer (PyroXide) produced by the Pyromeral company ; Carbon/Carbon produced by the company Mersen - AW252 long fibres 2.5 D, A202 long fibres 2 D and A015 short fibres. In the second phase, a mechanical study was carried out on these potential materials [3] leading to a design of the liner architecture. Finally, proofs of concept were manufactured in order to validate {material/process} pairs

Composites à matrice céramique industriels et commerciaux pour le chemisage d’alvéole de stockage de déchets radioactifs

International audienc

Isolation and Characterization of Intestinal Stem Cells Based on Surface Marker Combinations and Colony-Formation Assay

BACKGROUND & AIMS: Identification of intestinal stem cells (ISCs) has relied heavily on the use of transgenic reporters in mice, but this approach is limited by mosaic expression patterns and difficult to directly apply to human tissues. We sought to identify reliable surface markers of ISCs and establish a robust functional assay to characterize ISCs from mouse and human tissues. METHODS: We used immunohistochemistry, real-time reverse-transcription polymerase chain reaction, and fluorescence-activated cell sorting (FACS) to analyze intestinal epithelial cells isolated from mouse and human intestinal tissues. We compared different combinations of surface markers among ISCs isolated based on expression of Lgr5–green fluorescent protein. We developed a culture protocol to facilitate the identification of functional ISCs from mice and then tested the assay with human intestinal crypts and putative ISCs. RESULTS: CD44(+)CD24(lo)CD166(+) cells, isolated by FACS from mouse small intestine and colon, expressed high levels of stem cell–associated genes. Transit-amplifying cells and progenitor cells were then excluded based on expression of GRP78 or c-Kit. CD44(+)CD24(lo)CD166(+) GRP78(lo/−) putative stem cells from mouse small intestine included Lgr5-GFP(hi) and Lgr5-GFP(med/lo) cells. Incubation of these cells with the GSK inhibitor CHIR99021 and the E-cadherin stabilizer Thiazovivin resulted in colony formation by 25% to 30% of single-sorted ISCs. CONCLUSIONS: We developed a culture protocol to identify putative ISCs from mouse and human tissues based on cell surface markers. CD44(+)CD24(lo)CD166(+), GRP78(lo/−), and c-Kit(−) facilitated identification of putative stem cells from the mouse small intestine and colon, respectively. CD44(+)CD24(−/lo)CD166(+) also identified putative human ISCs. These findings will facilitate functional studies of mouse and human ISCs