Localized deformation patterns are a common motif in morphogenesis and are increasingly finding applications in materials science and engineering, in such instances as mechanical memories. Here, we describe the emergence of spatially localized deformations in a minimal mechanical system by exploring the impact of growth and shear on the conformation of a semi-flexible filament connected to a pliable shearable substrate. We combine numerical simulations of a discrete rod model with theoretical analysis of the differential equations recovered in the continuum limit to quantify (in the form of scaling laws) how geometry, mechanics and growth act together to give rise to such localized structures in this system. We find that spatially localized deformations along the filament emerge for intermediate shear modulus and increasing growth. Finally, we use experiments on a 3D-printed multi-material model system to demonstrate that external control of the amount of shear and growth may be used to regulate the spatial extent of the localized strain texture.

Moving along a straight path is a surprisingly difficult task. This is because, with each ensuing step, noise is generated in the motor and sensory systems, causing the animal to deviate from its intended route. When relying solely on internal sensory information to correct for this noise, the directional error generated with each stride accumulates, ultimately leading to a curved path. In contrast, external compass cues effectively allow the animal to correct for errors in its bearing. Here, we studied straight-line orientation in two different sized dung beetles. This allowed us to characterize and model the size of the directional error generated with each step, in the absence of external visual compass cues (motor error) as well as in the presence of these cues (compass and motor errors). In addition, we model how dung beetles balance the influence of internal and external orientation cues as they orient along straight paths under the open sky. We conclude that the directional error that unavoidably accumulates as the beetle travels is inversely proportional to the step size of the insect, and that both beetle species weigh the two sources of directional information in a similar fashion.

We describe a number of different phenomena seen
in the free-surface flow inside a partially filled circular cylinder
which is rotated about its horizontal axis of symmetry. At low
angular velocities the flow settles into a steady two-dimensional flow with a front where the coating film coalesces with
the pool at the bottom of the cylinder. This mode becomes
unstable at higher angular velocities, initially to a sloshing
mode on the rising side of the coating film and then to an axial
instability on the front. The undulations that appear on the
front grow into large-amplitude stationary patterns with
cusp-like features for some parameter values. At still higher
angular velocities and volume fractions, a number of different
inertial instabilities and patterns appear. We present a phase
diagram of the various transitions and characterize some of the
more prominent instabilities and patterns in detail, along with
some possible mechanisms for the observed behaviour.