This paper proposes a method that minimizes the energy consumption in the locomotion of a biped robot. A real-coded genetic algorithm is employed in order to search for the optimal locomotion pattern, and at the same time the optimal locations of the mass centers of the links that compose the biped robot. Since many of the essential characteristics of the human walking motion can be captured with a seven-link planar biped walking in the saggital plane, a 6-DOF biped robot that consists of seven links is used as the model used in the work. For trajectories of the robot in a single stride, fourth-order polynomials are used as their basis functions to approximate the locomotion gait. The coefficients of the polynomials are defined as design variables. For the optimal locations of the mass centers of the links, three variables are added to the design variables under the assumption that the left and right legs are identical. Simulations were performed to compare locomotion trajectories obtained with the genetic algorithm and the one obtained with the gravity-compensated inverted pendulum mode (GCIPM). They show that the proposed trajectory with the optimized mass centers significantly reduces the energy consumption, indicating that the proposed optimized method is a valuable tool in the design of biped robots.

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Measuring thermal stability in magnetic random access memory devices is non-trivial. Recently, there has been much discussion on the appropriate model to use: single domain or domain wall nucleation. Of particular challenge is assessing the maximum size at which the single domain model can be assumed. Typically, this is estimated to be in the range of 20–30 nm based on a value of the exchange stiffness ([Formula: see text]) that is assumed, estimated using indirect measurements or derived from significantly thicker films. In this work, it is proposed that this maximum size can be measured directly via the “activation volume” ([Formula: see text]) or the “activation diameter” ([Formula: see text]), which originates from the concept of magnetic viscosity. This is conducted by measuring, using the time dependence of magnetization at different applied fields, [Formula: see text] in perpendicular magnetic tunnel junction pillars of varying effective anisotropy constant ([Formula: see text]) and diameter. It is shown that the trend in [Formula: see text] follows [Formula: see text] dependence, in good agreement with the analytic model for the critical diameter of coherent switching. Critically, it is also found that the smallest size for which a single domain, with coherent reversal, occurs is 20 nm. Thus, in devices with technologically relevant values of [Formula: see text], the macrospin model may only be used in 20 nm, or smaller, devices.