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Abstract A safety-critical measure of legged locomotion performance is a robot's ability to track its desired time-varying position trajectory in an environment, which is herein termed as “global-position tracking.” This paper introduces a nonlinear control approach that achieves asymptotic global-position tracking for three-dimensional (3D) bipedal robots. Designing a global-position tracking controller presents a challenging problem due to the complex hybrid robot model and the time-varying desired global-position trajectory. Toward tackling this problem, the first main contribution is the construction of impact invariance to ensure all desired trajectories respect the foot-landing impact dynamics, which is a necessary condition for realizing asymptotic tracking of hybrid walking systems. Thanks to their independence of the desired global position, these conditions can be exploited to decouple the higher-level planning of the global position and the lower-level planning of the remaining trajectories, thereby greatly alleviating the computational burden of motion planning. The second main contribution is the Lyapunov-based stability analysis of the hybrid closed-loop system, which produces sufficient conditions to guide the controller design for achieving asymptotic global-position tracking during fully actuated walking. Simulations and experiments on a 3D bipedal robot with twenty revolute joints confirm the validity of the proposed control approach in guaranteeing accurate tracking. 

Current stretchable conductors, often composed of elastomeric composites infused with rigid conductive fillers, suffer from limited stretchability and durability, and declined conductivity with stretching. These limitations hinder their potential applications as essential components such as interconnects, sensors, and actuators in stretchable electronics and soft machines. In this context, an innovative elastomeric composite that incorporates a 3D network of liquid metal (LM), offering exceptional stretchability, durability, and conductivity, is introduced. The mechanics model elucidates how the interconnected 3DLM architecture imparts softness and stretchability to the composites, allowing them to withstand tensile strains of up to 500% without rupture. The relatively low surface‐to‐volume ratio of the 3DLM network limits the reforming of the oxide layer during cyclic stretch, thereby contributing to low permanent strain and enhanced durability. Additionally, the 3D architecture facilitates crack blunting and stress delocalization, elevating fracture resistance, while simultaneously establishing continuous conductive pathways that result in high conductivity. Notably, the conductivity of the 3DLM composite increases with strain during substantial stretching, highlighting its strain‐enhanced conductivity. In comparison to other LM‐based composites featuring 0D LM droplets, the 3DLM composite stands out with superior properties.

 

Abstract. Ice crystal submicron structures have a large impact on the opticalproperties of cirrus clouds and consequently on their radiative effect.Although there is growing evidence that atmospheric ice crystals are rarelypristine, direct in situ observations of the degree of ice crystal complexityare largely missing. Here we show a comprehensive in situ data set of icecrystal complexity coupled with measurements of the cloud angular scatteringfunctions collected during a number of observational airborne campaigns atdiverse geographical locations. Our results demonstrate that an overwhelmingfraction (between 61 % and 81 %) of atmospheric ice crystals sampledin the different regions contain mesoscopic deformations and, as aconsequence, a similar flat and featureless angular scattering function isobserved. A comparison between the measurements and a database of opticalparticle properties showed that severely roughened hexagonal aggregatesoptimally represent the measurements in the observed angular range. Based onthis optical model, a new parameterization of the cloud bulk asymmetry factorwas introduced and its effects were tested in a global climate model. Themodelling results suggest that, due to ice crystal complexity, ice-containingclouds can induce an additional short-wave cooling effect of−1.12 W m2 on the top-of-the-atmosphere radiative budget that hasnot yet been considered.