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Rigid Surface (rigid + surface)
Selected AbstractsSensitivity of alveolar macrophages to substrate mechanical and adhesive propertiesCYTOSKELETON, Issue 6 2006Sophie Féréol Abstract In order to understand the sensitivity of alveolar macrophages (AMs) to substrate properties, we have developed a new model of macrophages cultured on substrates of increasing Young's modulus: (i) a monolayer of alveolar epithelial cells representing the supple (,0.1 kPa) physiological substrate, (ii) polyacrylamide gels with two concentrations of bis-acrylamide representing low and high intermediate stiffness (respectively 40 kPa and 160 kPa) and, (iii) a highly rigid surface of plastic or glass (respectively 3 MPa and 70 MPa), the two latter being or not functionalized with type I-collagen. The macrophage response was studied through their shape (characterized by 3D-reconstructions of F-actin structure) and their cytoskeletal stiffness (estimated by transient twisting of magnetic RGD-coated beads and corrected for actual bead immersion). Macrophage shape dramatically changed from rounded to flattened as substrate stiffness increased from soft ((i) and (ii)) to rigid (iii) substrates, indicating a net sensitivity of alveolar macrophages to substrate stiffness but without generating F-actin stress fibers. Macrophage stiffness was also increased by large substrate stiffness increase but this increase was not due to an increase in internal tension assessed by the negligible effect of a F-actin depolymerizing drug (cytochalasine D) on bead twisting. The mechanical sensitivity of AMs could be partly explained by an idealized numerical model describing how low cell height enhances the substrate-stiffness-dependence of the apparent (measured) AM stiffness. Altogether, these results suggest that macrophages are able to probe their physical environment but the mechanosensitive mechanism behind appears quite different from tissue cells, since it occurs at no significant cell-scale prestress, shape changes through minimal actin remodeling and finally an AMs stiffness not affected by the loss in F-actin integrity. Cell Motil. Cytoskeleton 2006. © 2006 Wiley-Liss, Inc. [source] Numerical simulation of viscous flow interaction with an elastic membraneINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2008Lisa A. Matthews Abstract A numerical fluid,structure interaction model is developed for the analysis of viscous flow over elastic membrane structures. The Navier,Stokes equations are discretized on a moving body-fitted unstructured triangular grid using the finite volume method, taking into account grid non-orthogonality, and implementing the SIMPLE algorithm for pressure solution, power law implicit differencing and Rhie,Chow explicit mass flux interpolations. The membrane is discretized as a set of links that coincide with a subset of the fluid mesh edges. A new model is introduced to distribute local and global elastic effects to aid stability of the structure model and damping effects are also included. A pseudo-structural approach using a balance of mesh edge spring tensions and cell internal pressures controls the motion of fluid mesh nodes based on the displacements of the membrane. Following initial validation, the model is applied to the case of a two-dimensional membrane pinned at both ends at an angle of attack of 4° to the oncoming flow, at a Reynolds number based on the chord length of 4 × 103. A series of tests on membranes of different elastic stiffness investigates their unsteady movements over time. The membranes of higher elastic stiffness adopt a stable equilibrium shape, while the membrane of lowest elastic stiffness demonstrates unstable interactions between its inflated shape and the resulting unsteady wake. These unstable effects are shown to be significantly magnified by the flexible nature of the membrane compared with a rigid surface of the same average shape. Copyright © 2007 John Wiley & Sons, Ltd. [source] A position/force control for a robot finger with soft tip and uncertain kinematicsJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 3 2002Zoe Doulgeri We consider the position and force regulation problem for a soft tip robot finger in contact with a rigid surface under kinematic and dynamic parametric uncertainties. The reproducing force is assumed to be related to the displacement through a nonlinear function whose characteristics are unknown, but both the actual displacement and force can be directly measured. Kinematic uncertainties concern the rigid surface orientation and the contact point location. Kinematic parameters involved in the contact point location concern the length from the last joint to the contact point and the rest of the link lengths in the general case. An adaptive controller with a composite update parameter law is proposed, and the asymptotic stability of the force and estimated position errors under dynamic and kinematic uncertainties is shown for the planar case. Simulation results for a three-degrees-of-freedom planar robotic finger are presented. © 2002 Wiley Periodicals, Inc. [source] Mixed convection flow of non-Newtonian fluid from a slotted vertical surface with uniform surface heat fluxTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2009Rama Subba Reddy Gorla Abstract In the present paper, the combined convection flow of an Ostwald,de Waele type power-law non-Newtonian fluid past a vertical slotted surface has been investigated numerically. The boundary condition of uniform surface heat flux is considered. The equations governing the flow and the heat transfer are reduced to local non-similarity form. The transformed boundary layer equations are solved numerically using implicit finite difference method. Solutions for the heat transfer rate obtained for the rigid surface compare well with those documented in the published literature. From the present analysis, it is observed that, an increase in , leads to increase in skin friction as well as reduction in heat transfer at the surface. As the power-law index n increases, the friction factor as well as heat transfer increase. Dans cet article, on a étudié numériquement l'écoulement de convection combinée d'un fluide non-newtonien de loi de puissance de type Ostwald-de Waele en aval d'une surface perforée verticale. La condition limite d'un flux de chaleur de surface uniforme est considérée. Les équations gouvernant l'écoulement et le transfert de chaleur sont réduites à la forme de non-similarité locale. Les équations de couche limite transformées sont résolues numériquement par la méthode des différences finies implicites. Les solutions pour la vitesse de transfert de chaleur obtenues pour la surface rigide se comparent bien à celles qui sont décrites dans la littérature scientifique publiée. À partir de la présente analyse, on observe qu'une augmentation de , mène à une augmentation du frottement superficiel ainsi qu'à une réduction du transfert de chaleur à la surface. Lorsque l'indice de loi de puissance n augmente, le facteur de friction et le transfert de chaleur augmentent également. [source] | ||||||||||