For the critical sandpile model of P. Bak et al., we present high statistics results obtained by a fast non-parallel algorithm. In particular, we give results for 2, 3, 4 and 5 dimensional hypercubic lattices, and for Bethe lattices. On the latter, the model is in the same universality class as (dynamic) percolation, but the upper critical dimension seems to be 4 instead of 6 as for percolation. Between d = 4 and d = 6, the model seems to correspond to branched true SAW's as suggested by Obukhov. But this breaks down definitely below d = 3
With the widespread use of wearable electronics, portable and flexible energy harvesting devices with a high sensitivity have attracted considerable interest. Herein, an ultrasensitive piezoelectric nanogenerator (PNG) made of a few layers of 2 D‐MoS2‐incorporated electrospun poly(vinlydine fluoride) (PVDF) nanofiber webs (NFW) is described for the first time. As a result of the semiconducting properties and piezoelectric functionalities of 2 D‐MoS2, the resultant piezoelectric performance of PNG can be modulated, which leads to a material suitable for wearable electronics to power devices and to fabricate self‐powered biomedical nanosensors for diagnosis, such as heartbeat monitoring, pressure mapping from footsteps, and speech signal abnormality. We have demonstrated that our PNG has a 70 times improvement in acoustic sensitivity than nanosensors made of neat PVDF NFW and are able to charge a capacitor quickly (e.g., 9 V is charged within 44 s). As a result of the ultrafast charging performance and external low‐impact detection capability of 2 D‐MoS2‐modulated PNG, this paves the way to design cost‐effective self‐powered wearable electronics and robotics.
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