ParisTech

About: ParisTech is a education organization based out in Paris, France. It is known for research contribution in the topics: Residual stress & Finite element method. The organization has 1888 authors who have published 1965 publications receiving 55532 citations. The organization is also known as: Paris Institute of Technology & ParisTech Développement.

Wrinkling hierarchy in constrained thin sheets from suspended graphene to curtains.

Abstract: The drive towards miniaturization in technology is demanding for increasingly thinner components, raising new mechanical challenges. Thin films are however unstable to boundary or substrate-induced compressive loads. Moderate compression results in regular wrinkling while further confinement can lead to crumpling. Regions of stress focusing can be a hindrance, acting as nucleation points for mechanical failure. Conversely, they can be exploited constructively for tunable thin structures. For example, singular points of deformation dramatically affect the electronic properties of graphene. Here, we show that thin sheets under boundary confinement spontaneously generate a universal self-similar hierarchy of wrinkles; from strained suspended graphene to ordinary hanging curtains. We develop a formalism based on "wrinklons", a localized transition zone in the merging of two wrinkles, as building-blocks to describe these wrinkled patterns. Our approach may find applications in domains such as graphene-based electronics, fuel cell technology, thin-film solar cells or draping in virtual reality.

Modeling the Mediterranean Sea interannual variability during 1961–2000: Focus on the Eastern Mediterranean Transient

Abstract: [1] This work is dedicated to the study of the climate variability of the Mediterranean Sea, in particular the study of the Eastern Mediterranean Transient (EMT) which occurred in the early 1990s. Simulations of the 1961–2000 period have been carried out with an eddy-permitting Ocean General Circulation Model of the Mediterranean Sea, driven by realistic interannual high-resolution air-sea fluxes. Using different databases for the river runoff, Black Sea inflow, and Atlantic thermohaline characteristics at climatological or interannual scales, we assess the effects of the non-atmospheric hydrological forcings on the simulation of the interannual variations of the Mediterranean circulation. The evolution of the basin-scale heat content is in very good agreement with the observations (especially in the surface and intermediate layers), while the agreement is lower for the evolution of the salt content. Convection events in the Aegean Sea are noticed in the simulations between 1972 and 1976, in the late 1980s, and around the EMT period. The formation rates of Cretan Deep Water (CDW) are different during these periods, allowing or preventing the spreading of CDW into the eastern Mediterranean. The sequence of the EMT events is well reproduced: the high winter oceanic surface cooling and net evaporation over the Aegean Sea in the early 1990s, the high amount of dense CDW formed during these winters, and then the overflow and the spreading of this CDW in the eastern Mediterranean. Among the preconditioning processes suggested in the literature, we find that changes in the Levantine surface circulation, possibly induced by the presence in the Cretan Passage of anticyclonic eddies and a lasting period with reduced net precipitation over the eastern Mediterranean, lead to an increase of the salt content of the Aegean Sea. Changes in the Black Sea freshwater inflow or in the characteristic of the Atlantic Water entering at the Gibraltar Strait also modify the thermohaline state of the Aegean Sea before the EMT. But, as none of these preconditioning factors has a lasting impact on lowering the vertical stratification of the Aegean Sea, we conclude that concerning the EMT, the major triggering elements are the atmospheric fluxes and winds occurring in winters 1991–1992 and 1992–1993.

Plasma membrane tension orchestrates membrane trafficking, cytoskeletal remodeling, and biochemical signaling during phagocytosis

Abstract: Phagocytes clear the body of undesirable particles such as infectious agents and debris. To extend pseudopods over the surface of targeted particles during engulfment, cells must change shape through extensive membrane and cytoskeleton remodeling. We observed that pseudopod extension occurred in two phases. In the first phase, pseudopods extended rapidly, with actin polymerization pushing the plasma membrane forward. The second phase occurred once the membrane area from preexisting reservoirs was depleted, leading to increased membrane tension. Increased tension directly altered the small Rho GTPase Rac1, 3′-phosphoinositide, and cytoskeletal organization. Furthermore, it activated exocytosis of vesicles containing GPI-anchored proteins, increasing membrane area and phagocytosis efficiency for large particles. We thus propose that, during phagocytosis, membrane remodeling, cytoskeletal organization, and biochemical signaling are orchestrated by the mechanical signal of membrane tension. These results put a simple mechanical signal at the heart of understanding immunological responses.