We report the high thermoelectric performance of p-type polycrystalline SnSe obtained by the synergistic tailoring of band structures and atomic-scale defect phonon scattering through (Na,K)-codoping. The energy offsets of multiple valence bands in SnSe are decreased after Na doping and further reduced by (Na,K)-codoping, resulting in an enhancement in the Seebeck coefficient and an increase in the power factor to 492 μW m K. The lattice thermal conductivity of polycrystalline SnSe is decreased by the introduction of effective phonon scattering centers, such as point defects and antiphase boundaries. The lattice thermal conductivity of the material is reduced to values as low as 0.29 W m K at 773 K, whereas ZT is increased from 0.3 for 1% Na-doped SnSe to 1.2 for 1% (Na,K)-codoped SnSe.
An electromagnetic shunt damper (EMSD) is composed of an electromagnetic damper connected to one or more RLC shunt circuits. Through a theoretical comparison, this paper reveals the similarity and difference between an EMSD and a tuned mass damper (TMD), both of which are resonant-type vibration absorbers. The equivalent mass, stiffness and damping coefficient of the EMSD are derived based on the transfer functions of structures with a TMD or an EMSD, and the functions of circuit capacitance and inductance are discussed accordingly. The optimal parameters of the RLC circuit in the EMSD are obtained through H∞ optimization. Despite their different optimal parameters, the EMSD and TMD exhibit comparable control performance with the same equivalent mass ratio. The dynamic analogy between these two types of dampers offers a new perspective for understanding novel EMSDs, given that TMDs have previously been extensively studied. The potentials and constraints of the EMSD are further discussed through numerical case studies in which EMSD control performance is examined in different situations.
Recent success in the synthesis of the two-dimensional borophene on silver substrates has attracted strong interest in exploring its extraordinary properties for potential technological applications. The single-layer borophene has a buckled structure with atomic ridges. By using the first-principles density functional theory calculations, we show that the two-dimensional borophene is highly stretchable with strong anisotropy The strain-to-failure in the direction along the atomic ridges is nearly twice as large as that across the atomic ridges. The straining-induced flattening and the subsequent stretch of the flat borophene are accounted for the large strain-to-failure for tension along the atomic ridges. We also investigated the mechanics of monolayer borophene under biaxial tension and we found that the biaxial tension increases the strength across the atomic ridges but decreases the failure strain along the atomic ridges. Furthermore, when the bilayer borophene is stretched along the cross-plane direction, the strength and failure strain of the bilalyer borophene are much higher than those of the bilayer graphene due to the very strong inter-layer chemical bonding.
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