The dorsal visual system

The dorsal visual system computes information about where objects are in space, and their motion, and this is used for actions performed in space. This requires coordinate transforms from retinal coordinates to head based coordinates, and then in parietal cortex areas to coordinates for reaching into space, and for allocentric, world-based, spatial coordinates. Recent approaches to how these transforms are performed, with analogies to transform invariance learning in the ventral visual system, are described.

The validation of new phase-dependent gait stability measures: a modeling approach

ABSTRACTIdentification of individuals at risk of falling is important when designing fall prevention methods. Current stability measures that estimate gait stability and robustness appear limited in predicting falls in older adults. Inspired by recent findings of phase-dependent local stability changes within a gait cycle, we used compass-walker models to test several phase-dependent stability metrics for their usefulness to predict gait robustness. These metrics are closely related to the often-employed maximum finite-time Lyapunov exponent and maximum Floquet multiplier. They entail linearizing the system in a rotating hypersurface orthogonal to the period-one solution, and estimating the local divergence rate of the swing phases and the foot strikes. We correlated the metrics with the gait robustness of two compass walker models with either point or circular feet to estimate their prediction accuracy. To also test for the metrics’ invariance under coordinate transform, we represented the point-feet walker in both Euler-Lagrange and Hamiltonian canonical form. Our simulations revealed that for most of the metrics, correlations differ between models and also change under coordinate transforms, severely limiting the prediction accuracy of gait robustness. The only exception that consistently correlated with gait robustness is the divergence of foot strikes. These results admit challenges of using phase-dependent stability metrics as objective measure to quantify gait robustness.

Role of nanophotonics in the birth of seismic megastructures

The discovery of photonic crystals 30 years ago in conjunction with research advances in plasmonics and metamaterials, has inspired the concept of decameter scale metasurfaces, coined seismic metamaterials for an enhanced control of surface (Love and Rayleigh) and bulk (shear and pressure) elastodynamic waves. These powerful mathematical tools of coordinate transforms, effective medium and Floquet-Bloch theories which have revolutionized nanophotonics, can be translated in the language of civil engineering and geophysics. Experiments on seismic metamaterials made of buried elements in the soil demonstrate that the fore mentioned tools make a possible novel description of complex phenomena of soil-structure interaction during a seismic disturbance. But the concepts are already moving to more futuristic concepts and the same notions developed for structured soils are now used to examine the effects of buildings viewed as above surface resonators in megastructures such as metacities. But this perspective of future should not make us forget the heritage of the ancient peoples. Indeed, we finally point out the striking similarity between an invisible cloak design and the architecture of some ancient megastructures as the antique Gallo-Roman theaters and amphitheatres.

Wavelet-based adaptive unsteady Reynolds-averaged turbulence modelling of external flows

The recent development of the adaptive-anisotropic wavelet-collocation method, which incorporates the use of coordinate transforms, opens new horizons for wavelet-based simulations of wall-bounded turbulent flows. The new wavelet-based adaptive unsteady Reynolds-averaged Navier–Stokes approach for computational modelling of turbulent flows is presented. The proposed methodology that is integrated with anisotropic wavelet-based mesh refinement is demonstrated for a two-equation eddy-viscosity turbulence model. The performance of the method is assessed by conducting numerical simulations of the turbulent flow past a circular cylinder at subcritical Reynolds number. The present study demonstrates both the feasibility and the effectiveness of the new wavelet-based adaptive unsteady Reynolds-averaged turbulence modelling procedure for external flows.