battery maintenance and replacement will be practically infeasible. In addition, it is also challenging to recharge or replace batteries in harsh environments, such as the deep ocean and high air. In this regard, energy harvesting technology may be considered an ultimate solution to replace batteries, realize self-powered IoT components, and thus provide a long-term power supply for wireless sensor networks. [4,5] From the viewpoint of environmental pollution, the elimination of batteries, which are classified as "hazardous wastes," is also of great significance. [6] Among a large number of harvestable energy sources, like vibration, [7,8] radiation, [9,10] and magnetic/electric fields, [11,12] stray magnetic energy generated from power transmission cables, industrial machines, household appliances, etc., is technically favored because of the fixed frequency of 50 or 60 Hz and the ubiquitous distribution. [13][14][15][16] Coil devices based on electromagnetic induction principles are conventionally adopted to capture the ambient but wasted magnetic field energy. [13,17] However, the output power from compact coils is very limited in the case of low-frequency magnetic field energy harvesting. In contrast, magneto-mechano-electric (MME) generators are considered the most promising options to scavenge disused magnetic field energy. [12] The earliest design of a typical A magneto-mechano-electric (MME) generator that can harvest ambient magnetic noise plays a significant role in powering Internet of Things (IoT) sensor networks. However, it is still a challenge to capture sufficient energy and continuously drive IoT nodes from extremely low-intensity magnetic noise below 1 Oe. To circumvent the close dependence of the resonant frequency on the magnetic proof mass in conventional MME generators, a new clampedclamped (C-C) MME generator is proposed, that allows a much heavier magnetic mass to be attached at the beam center. Under weak magnetic fields of 0.48 and 0.96 Oe at 50 Hz, optimized output powers of 370 and 970 μW RMS , respectively are achieved, which shows an enhancement of ≈120% over that of cantilevered MME generators. The underlying mechanics are theoretically revealed by comparing the lumped parameters with a cantilevered MME generator and by calculating their deflection gain. Finally, it is demonstrated that the harvested energy from the proposed C-C MME generator from a 0.48 Oe magnetic field at 50 Hz is sufficient to continuously drive an IoT sensor without any additional intervals for recharging. It is believed that this work will open new possibilities for designing MME generators suitable for weak field energy harvesting.

Epidemic control is of great importance for human society. Adjusting interacting partners is an effective individualized control strategy. Intuitively, it is done either by shortening the interaction time between susceptible and infected individuals or by increasing the opportunities for contact between susceptible individuals. Here, we provide a comparative study on these two control strategies by establishing an epidemic model with nonuniform stochastic interactions. It seems that the two strategies should be similar, since shortening the interaction time between susceptible and infected individuals somehow increases the chances for contact between susceptible individuals. However, analytical results indicate that the effectiveness of the former strategy sensitively depends on the infectious intensity and the combinations of different interaction rates, whereas the latter one is quite robust and efficient. Simulations are shown to verify our analytical predictions. Our work may shed light on the strategic choice of disease control.

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