ALBERT

Description: Contraction of basal filopodia controls periodic feather branching via Notch and FGF signaling Contraction of basal filopodia controls periodic feather branching via Notch and FGF signaling, Published online: 09 April 2018; doi:10.1038/s41467-018-03801-z Keratinocytes are organised into a periodic pattern in feather branching, but how this is regulated is unclear. Here, the authors show that there is a coordinated change in cell shape and adherence, mediated by Notch, FGF signalling and Rho GTPases, which in turn regulates feather branching.

Description: Diverse feather shape evolution enabled by coupling anisotropic signalling modules with self-organizing branching programme Nature Communications, Published online: 20 January 2017; doi:10.1038/ncomms14139 Asymmetric feather vane shape was a critical innovation in feather evolution and adaptation for flight. Here, Li and colleagues characterize the multi-module regulatory network that controls feather vane shape and underlies feather diversification.

Description: A quantitative theoretical model is developed to describe the time-dependent draining of an initially uniform-thickness fluid squeeze film between an infinitely flexible membrane-bound fluid cell and a planar rigid surface or between two symmetrically loaded cells subject to impulsive loading. The solution of the coupled nonlinear membrane-fluid-film equations shows that two characteristic times and length scales are required to describe the membrane deformation and draining behaviour of the fluid film. The early-time behaviour is strikingly different from that predicted by elasto hydrodynamic squeeze-film theory (Christensen 1962), where the local elastic deformation of the boundary is not controlled by membrane tension but is proportional to the local film pressure. While fluid trapping occurs in both cases, a bidirectional flow is set up during the early-time period in the membrane squeeze film owing to the establishment of an off-axis pressure maximum near the edge of the near contact area. Fluid is driven radially inward, causing upwelling of the membrane in the central region, and driven radially outward near the edge of the contact area., causing this region to form a narrow fluid gap. After the narrow-edge region has formed, the off-axis pressure maximum gradually disappears and is replaced by a pressure plateau in the interior and a radial outflow at all locations that is similar to the elasto hydrodynamic squeeze film. The present problem is closely related to the fluid films studied by Hartland (1967,1968,1969), Jones & Wilson (1978) and others when a, small spherical particle or fluid droplet rises or settles under gravity towards a uniform-tension fluid-fluid interface. These studies have theoretically and experimentally examined the long-time drainage of the film after the narrow edge region has formed and the fluid-trapping phenomenon is established. The solutions to the initial-value problem described herein show how this asymptotic quasi-steady drainage state is reached. A simple experiment has been constructed to confirm qualitatively the theoretically predicted short-time behaviour. Experimental photographs graphically illustrate the gradual thickening of the lubricating layer near the origin and the formation and draining of the edge region as predicted by the membrane squeeze-film theory. © 1982, Cambridge University Press. All rights reserved.

Description: Determination of vertical effective stress along piles is an essential part of calculation of both pile axial and lateral capacities under scour conditions. However, the current design manuals including those from the US Federal Highway Administration (FHWA) and American Petroleum Institute (API) recommend different methods for calculating vertical effective stress. Moreover, they are effective only for restricted scour-hole dimensions. This study presents an improved closed-form solution that allows estimation of the vertical effective stress for a wide range of scour-hole dimensions including scour depth, width, and slope angle. Using the improved analytical solution for stress, API p–y curves for sand were modified to compute pile lateral capacity at different scour-hole conditions. Based on a series of parametric analyses for laterally loaded piles in sand, errors of calculation using the existing methods were quantified and a simplified method was proposed for practical applications. Effects of different scour-hole dimensions on both vertical effective stress and pile lateral capacity were also discussed.