In most animal species, vision is mediated by compound eyes, which offer lower resolution than vertebrate single-lens eyes, but significantly larger fields of view with negligible distortion and spherical aberration, as well as high temporal resolution in a tiny package. Compound eyes are ideally suited for fast panoramic motion perception. Engineering a miniature artificial compound eye is challenging because it requires accurate alignment of photoreceptive and optical components on a curved surface. Here, we describe a unique design method for biomimetic compound eyes featuring a panoramic, undistorted field of view in a very thin package. The design consists of three planar layers of separately produced arrays, namely, a microlens array, a neuromorphic photodetector array, and a flexible printed circuit board that are stacked, cut, and curved to produce a mechanically flexible imager. Following this method, we have prototyped and characterized an artificial compound eye bearing a hemispherical field of view with embedded and programmable low-power signal processing, high temporal resolution, and local adaptation to illumination. The prototyped artificial compound eye possesses several characteristics similar to the eye of the fruit fly Drosophila and other arthropod species. This design method opens up additional vistas for a broad range of applications in which wide field motion detection is at a premium, such as collision-free navigation of terrestrial and aerospace vehicles, and for the experimental testing of insect vision theories.
Interaction forces between ionizable surfaces across an electrolyte solution on the Poisson−Boltzmann level are discussed within the constant regulation approximation. The chemical response of each surface is expressed in terms of two parameters, namely, the diffuse layer potential and the regulation parameter p. Both parameters are easily available because they arise naturally within classical equilibrium models for a single noninteracting surface. This approximation, thus, eliminates the need to treat the more intricate problem of two chemical adsorption equilibria coupled to the overlapping double layers between the surfaces. The ensuing simplicity makes this approach extremely versatile for the analysis of experimental data. The classical boundary condition of constant potential corresponds to p = 0, and that of constant charge corresponds to p = 1. While this approximation is rigorously correct at large separations, we find that it remains excellent down to contact in many realistic situations, such as in symmetric or asymmetric systems involving metal oxides or silica described by the 1-pK basic Stern model.
The adsorption behavior of poly(amidoamine) dendrimers to mica surfaces was investigated as a function of ionic strength and pH. The conformation and lateral distribution of the adsorbed dendrimers of generations G8 and G10 were obtained ex situ by tapping mode atomic force microscopy (AFM). The deposition kinetics of the dendrimers was found to follow a diffusion-limited process. Fractional surface coverage and pair correlation functions of the adsorbed dendrimers were obtained from the AFM images. The data are interpreted in terms of the random sequential adsorption (RSA) model, where electrostatic repulsion due to overlapping double layers is considered. Although the general trends typical for an RSA-determined process are well-reproduced, quantitative agreement is lacking at low ionic strengths.
Sessile liquid drops are predicted to deform an elastic surface onto which they are placed because of the combined action of the liquid surface tension at the periphery of the drop and the capillary pressure inside the drop. Here, we show for the first time the in situ experimental confirmation of the effect of capillary pressure on this deformation. We demonstrate micrometer-scale deformations made possible by using a low Young's modulus material as an elastic surface. The experimental profiles of the deformed surfaces fit well the theoretical predictions for surfaces with a Young's modulus between 25 and 340 kPa.
A sessile droplet can deform the surface of a soft solid not only with its weight. The surface tension pulls up a ridge at the perimeter of the drop, and the capillary pressure embosses a quasi-spherical dimple underneath the drop. This holds for the case of a bulk solid. However, if the solid forms a film with thickness comparable to the deformation scale the shape and the depth of the dimple are strongly distorted. We investigated dimples on elastomer films with a Young's modulus of 25 kPa and thickness in the range 4-104 mm embossed by sessile ionic liquid droplets. The films are supported by an undeformable glass slide. Below a certain critical film thickness, the dimple is shallower and the ridge at the drop rim is less elevated than for the bulk elastomer. The deviations are more pronounced for thinner films. Further, troughs form at the two sides of the ridge. Their distance from the rim is equivalent to the layer thickness. The measurements are qualitatively reproduced by an analytical model and quantitatively by numerical simulations. A consistent physical picture of the deformation on the bulk elastomer and of the distortions on the thin films is given.
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