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This paper describes an energy management system and an algorithm for an energy-aware operation. The system obtains energy from an energy harvester and manages the energy adaptively according to the monitored energy status. Based on a low-power microcontroller, the system controls the energy harvester so that it always harvests energy at maximum power and tracks it when the operating condition changes. It also controls the power consumption of all parts of the system so that they are adjusted dynamically for the management of harvested or stored energy. To manage the energy transfer to a battery, a DC–DC converter, called the energy management IC, is optimized for the operating voltage control of the harvester. In an experiment using an energy harvester and a battery modified for the system, the energy management IC fabricated in a 0.18 μm process maximizes the energy transfer power with a simple, low-power algorithm. The proposed system is verified to be more efficient for low-energy harvesting by the adaptive energy and power management.

The suggestion that there is a maximum luminosity (maximum power) in nature has a long and somewhat convoluted history. Though this idea is commonly attributed to Freeman Dyson, he was actually much more circumspect in his views. What is certainly true is that dimensional analysis shows that the speed of light and Newton’s constant of gravitation can be combined to define a quantity $P_{\ast }=\frac{c^5}{G_N}$ with the dimensions of luminosity (equivalently, power). Then in any physical situation, we must have $P_{\mathrm{\text{physical}}}=\wp P_{\ast }$, where the quantity $\wp$ is some dimensionless function of dimensionless parameters. This led some authors to suggest a maximum luminosity/maximum power conjecture. Working within the framework of standard general relativity, we will re-assess this conjecture, paying particular attention to the extent to which various examples and counter-examples are physically reasonable. We focus specifically on Vaidya spacetimes, and on an evaporating version of Schwarzschild’s constant density star. For both of these spacetimes, luminosity can be arbitrarily large. We argue that any luminosity bound must depend on delicate internal features of the radiating object.

There are at least two ways to deduce Einstein’s field equations from the principle of maximum force $c^4/4G$ or from the equivalent principle of maximum power $c^5/4G$. Tests in gravitational wave astronomy, cosmology, and numerical gravitation confirm the two principles. Apparent paradoxes about the limits can all be resolved. Several related bounds arise. The limits illuminate the beauty, consistency and simplicity of general relativity from an unusual perspective.

Finger's action has been controlled by both intrinsic and extrinsic hand muscles. Characterizing the finger action with the activations of hand muscles could be useful for evaluating the neuromuscular control strategy of finger's motor functions. This study is designed to explore the correlation of isometric fingertip force production and frequency-domain features of surface electromyography (sEMG) recorded on extrinsic hand muscles. To this end, 13 subjects (five male and eight female university students) have been recruited to conduct a target force-tracking task. Each subject is required to produce a certain level of force with either the index or middle fingertip to match the pseudo-random ordered target force level (4N, 6N, or 8N) as accurate as possible. During the finger force production process, the sEMG signals are recorded on two extrinsic hand muscles: flex digitorum superficials (FDS) and extensor digitorum (ED). For each sEMG trail, the power spectrum is estimated with the autoregressive (AR) model and from which the maximum power is obtained. Our experimental results reveal three findings: (1) the maximum power increases with the force level regardless of the force producing finger (i.e. index or middle) and the extrinsic hand muscle (i.e. FDS or ED). (2) The sEMG maximum power of index finger is significantly lower than that of the middle finger under the same force level and extrinsic hand muscle. (3) No significant difference can be found between the maximum powers of FDS and ED. The results indicate that the activations of the extrinsic muscles are affected by both the force level and the force producing finger. Based on our findings, the sEMG maximum power of the extrinsic hand muscles could be used as a key parameter to describe the finger's actions.