Abstract Final organ size and shape result from volume expansion by growth changes contractility. Complex morphologies can also arise differences in rate between tissues. We address here how differential guides the morphogenesis of growing Drosophila wing imaginal disc. report that 3D morphology results elastic deformation due to anisotropy epithelial cell layer its enveloping extracellular matrix (ECM). While tissue grows plane, bottom ECM occurs is reduced magnitude, thereby causing...

We address the flutter instability of a flexible plate immersed in an axial flow. This is similar to flag and results from competition between destabilising pressure forces stabilising bending stiffness. In previous experimental studies, plates have always appeared much more stable than predictions two-dimensional models. discrepancy discussed clarified this paper by examining experimentally theoretically effect aspect ratio on threshold. show that limit cannot be achieved because...

Fish schooling is often modeled with self-propelled particles subject to phenomenological behavioral rules. Although fish are known sense and exploit flow features, these models usually neglect hydrodynamics. Here, we propose a novel model that couples rules far-field hydrodynamic interactions. We show (1) new "collective turning" phase emerges, (2) on average, individuals swim faster thanks the fluid, (3) enhances noise. The results of this suggest effects should be considered fully...

Abstract The implementation of collective motion, traditionally, disregard the limited sensing capabilities an individual, to instead assuming omniscient perception environment. This study implements a visual flocking model in ‘robot-in-the-loop’ approach reproduce these behaviors with flock composed 10 independent spherical robots. achieves robotic motion by only using panoramic information each robot, such as retinal position, optical size and optic flow neighboring We introduce virtual...

Examining botanical trees, Leonardo da Vinci noted that the total cross-section of branches is conserved across branching nodes. In this Letter, it proposed rule a consequence tree skeleton having self-similar structure and branch diameters being adjusted to resist wind-induced loads.

In a variety of biological processes, eukaryotic cells use cilia to transport flow. Although have remarkably conserved internal molecular structure, experimental observations report very diverse kinematics. To address this diversity, we determine numerically the kinematics and energetics most efficient cilium. Specifically, compute time-periodic deformation wall-bound elastic filament leading surrounding fluid at minimum energetic cost, where cost is taken be positive work done by all...

Flexibility of marine animal fins has been thought to enhance swimming performance. However, despite numerous experimental and numerical studies on flapping flexible foils, there is still no clear understanding the effect flexibility amplitude thrust generation efficiency. Here, address this question, we combine experiments a model system weakly nonlinear analysis. Experiments consist in immersing rectangular plate uniform flow forcing into heaving motion at its leading edge. A complementary...

Abstract Most aquatic vertebrates swim by passing a bending wave down their bodies, swimming mode known as undulatory propulsion. Except for very elongated swimmers like eels and lampreys, these animals have generally evolved to similar shape: an anterior streamlined region of large volume separated from caudal fin peduncle reduced cross-section. However, the link between this particular shape hydrodynamical constraints remains be explored. Here, question is addressed seeking optimal design...

Infotaxis is a popular search algorithm designed to track source of odour in turbulent environment using information provided by detections. To exemplify its capabilities, the source-tracking task was framed as partially observable Markov decision process consisting finding, fast possible, stationary target hidden two-dimensional grid stochastic partial observations location. Here, we provide an extended review infotaxis, together with toolkit for devising better strategies. We first...

Animal collective behavior is often modeled with self-propelled particles, assuming each individual has “omniscient” knowledge of its neighbors. Yet, neighbors may be hidden from view and we do not know the effect this information loss. To address question, propose a visual model where particle moves according to bioplausible cues, in particular optic flow. This successfully reproduces three classical behaviors: swarming, schooling, milling. offers potential solution for controlling...

Abstract The flapping flag instability occurs when a flexible cantilevered plate is immersed in uniform airflow. To this day, the nonlinear aspects of aeroelastic are largely unknown. In particular, experiments literature all report large hysteresis loop, while bifurcation numerical simulations either supercritical or subcritical with small loop. paper, discrepancy addressed. First, weakly stability analyses conducted slender-body and two-dimensional limits, and, second, new performed flat...

In this paper, the instability of a fluid inside precessing cylinder is addressed theoretically and experimentally. The precessional motion forces Kelvin modes in cylinder, which can become resonant for given frequencies aspect ratios. When Reynolds number large enough, these forced eventually unstable. A linear stability analysis based on triadic resonance between mode two additional free carried out. This allows us to predict spatial structure its threshold. These predictions are compared...

Abstract Trees are self-similar structures: their branch lengths and diameters vary allometrically within the tree architecture, with longer thicker branches near ground. These allometries often attributed to optimisation of hydraulic sap transport safety against elastic buckling. Here, we show that these also emerge from a model includes competition for light, wind biomechanics no hydraulics. We have developed MECHATREE, numerical trees growing evolving on virtual island. With this model,...

We investigate the collective dynamics of self-propelled particles able to probe and anticipate orientation their neighbors. show that a simple anticipation strategy hinders emergence homogeneous flocking patterns. Yet, promotes two other forms self-organization: spinning swarming. In phase, all follow synchronous circular orbits, while in swarming population condensates into single compact swarm cruises coherently without requiring any cohesive interactions. quantitatively characterize...

In this paper, we report experimental and theoretical results on the flow inside a precessing rotating cylinder. Particle image velocimetry measurements have revealed instantaneous structure of confirmed that it is sum forced inertial (Kelvin) modes, as predicted by classical linear inviscid theory. But theory predicts also amplitude mode diverges when its natural frequency equals precession frequency. A viscous weakly nonlinear has therefore been developed at resonance. This compared to...

Experimental visualizations of the coupled flutter an assembly two, three, and four flexible parallel cantilevered plates immersed in axial uniform flow are presented. Depending on velocity, interplate distance, plate length, different modes observed. Selected associated thresholds frequencies compared with results a linear stability analysis.

Abstract Many eukaryotic cells use the active waving motion of flexible flagella to self-propel in viscous fluids. However, criterion governing selection particular flagellar waveforms among all possible shapes has proved elusive so far. To address this question, we derive computationally optimal shape an internally forced periodic planar flagellum deforming as a travelling wave. The optimum is here defined leading given swimming speed with minimum energetic cost. calculate cost, consider...

In marine plankton, many swimming species can perceive their environment with flow sensors. Can they use this information to travel faster in turbulence? To address question, we consider plankters at constant speed, whose goal is move upward. We propose a robust analytical behavior that allows choose direction according the local gradients. show numerically such "surf" on turbulence and reach net vertical speeds up twice speed. This new physics-based model suggests planktonic organisms...

The hydrodynamic forces acting on an undulating swimming fish consist of two components: a drag-based resistive force, and reactive force originating from the necessary acceleration added mass water. Lighthill’s elongated-body theory, based potential flow, provides framework for calculating this force. By leveraging high aspect ratio most fish, theory simplifies problem into series independent two-dimensional slices fluids along fish’s body, which exchange momentum with body neighbouring...

The linear stability of Burgers and Lamb–Oseen vortices is addressed when the vortex circulation Γ radius δ subjected to an additional strain field rate s perpendicular vorticity axis. resulting non-axisymmetric analysed in limit large Reynolds number R = / v small [Lt ] /δ 2 by considering approximations obtained Moffatt et al . (1994) Jiménez (1996) for each case respectively. For both vortices, TWMS instability (Tsai & Widnall 1976; Moore Saffman 1975) shown be active, i.e. stationary...

In this letter, we report experimental results on the stability of a fluid inside precessing and resonant cylinder. Above critical Reynolds number, Kelvin mode forced by precession triggers an instability which saturates at intermediate Re leads to turbulent flow high numbers. Particle image velocimetry measurements in two different sections cylinder have revealed three-dimensional structure instability. It is composed free modes whose wavenumbers frequencies respect conditions for triadic...