Stochastic heat engines are devices that generate work from random thermal motion using a small number of highly fluctuating degrees of freedom. Proposals for such devices have existed for more than a century and include the Maxwell demon and the Feynman ratchet. Only recently have they been demonstrated experimentally, using, e.g., thermal cycles implemented in optical traps. However, recent experimental demonstrations of classical stochastic heat engines are nonautonomous, since they require an external control system that prescribes a heating and cooling cycle and consume more energy than they produce. We present a heat engine consisting of three coupled mechanical resonators (two ribbons and a cantilever) subject to a stochastic drive. The engine uses geometric nonlinearities in the resonating ribbons to autonomously convert a random excitation into a low-entropy, nonpassive oscillation of the cantilever. The engine presents the anomalous heat transport property of negative thermal conductivity, consisting in the ability to passively transfer energy from a cold reservoir to a hot reservoir. DOI: 10.1103/PhysRevLett.117.010602 Thermodynamics in low-dimensional systems far from equilibrium is not well understood, to the point that essential quantities such as work [1] or entropy [2] do not have universally valid definitions in such systems. Formulating a physical theory for thermal processes in low-dimensional systems is the subject of stochastic thermodynamics [3], an emergent field that has resulted in the discovery of a variety of microscopic heat engines [4][5][6][7][8][9][10][11][12] and fluctuation theorems [13][14][15][16], and has provided new insights on the connection between information and energy [5,[17][18][19][20]. A central problem in stochastic thermodynamics is the construction and analysis of stochastic heat engines, the low-dimensional analogs of conventional thermal machines. A stochastic heat engine is a low-dimensional device that operates between two thermal baths at different temperatures, and is able to produce work while suppressing the randomness inherent in thermal motion [1,[4][5][6][7][21][22][23]. Thermal engine operation is characterized by the presence of nonpassive states of motion, which have lower entropy (for the same energy) than equilibrium states [24,25] and therefore allow the extraction of energy without an associated entropy flow [1]. The interest in stochastic heat machines is motivated by the desire to understand energy conversion processes at the fundamental level. This understanding, coupled with modern nanofabrication techniques, is expected to result in more efficient and powerful thermal machines.The concept of the stochastic heat engine dates back to the classical thought experiments of the Maxwell demon [18,26] and the Feynman ratchet [27,28]. Only very recently have working experimental realizations of the stochastic heat engine been reported on [4][5][6][7][8]. The bulk of these experimental realizations is based on the manipulation of a particle in an o...

In the present work we test experimentally and compute numerically the stability and dynamics of harmonically driven monoatomic granular chains composed of an increasing number of particles N (N = 1-50). In particular, we investigate the inherent effects of dissipation and finite size on the evolution of bifurcation instabilities in the statically compressed case. The findings of the study suggest that the nonlinear bifurcation phenomena, which arise due to finite size, can be useful for efficient energy transfer away from the drive frequency in transmitted waves.

Recent numerical studies on an infinite number of identical spherical beads in Hertzian contact showed the presence of frequency bands [Jayaprakash, Starosvetsky, Vakakis, Peeters, and Kerschen, Nonlinear Dyn. 63, 359 (2011)]. These bands, denoted here as propagation and attenuation bands (PBs and ABs), are typically present in linear or weakly nonlinear periodic media; however, their counterparts are not intuitive in essentially nonlinear periodic media where there is a complete lack of classical linear acoustics, i.e., in "sonic vacua." Here, we study the effects of PBs and ABs on the forced dynamics of ordered, uncompressed granular systems. Through numerical and experimental techniques, we find that the dynamics of these systems depends critically on the frequency and amplitude of the applied harmonic excitation. For fixed forcing amplitude, at lower frequencies, the oscillations are large in amplitude and governed by strongly nonlinear and nonsmooth dynamics, indicating PB behavior. At higher frequencies the dynamics is weakly nonlinear and smooth, in the form of compressed low-amplitude oscillations, indicating AB behavior. At the boundary between the PB and the AB large-amplitude oscillations due to resonance occur, giving rise to collisions between beads and chaotic dynamics; this renders the forced dynamics sensitive to initial and forcing conditions, and hence unpredictable. Finally, we study asymptotically the near field standing wave dynamics occurring for high frequencies, well inside the AB.