In this paper, a novel intelligent reflecting surface (IRS)-assisted wireless powered communication network (WPCN) architecture is proposed for power-constrained Internet-of-Things (IoT) smart ...devices, where IRS is exploited to improve the performance of WPCN under imperfect channel state information (CSI). We formulate a hybrid access point (HAP) transmit energy minimization problem by jointly optimizing time allocation, HAP energy beamforming, receiving beamforming, user transmit power allocation, IRS energy reflection coefficient and information reflection coefficient under the imperfect CSI and non-linear energy harvesting model. On account of the high coupling of optimization variables, the formulated problem is a non-convex optimization problem that is difficult to solve directly. To address the above-mentioned challenging problem, alternating optimization (AO) technique is applied to decouple the optimization variables to solve the problem. Specifically, through AO, time allocation, HAP energy beamforming, receiving beamforming, user transmit power allocation, IRS energy reflection coefficient and information reflection coefficient are divided into three sub-problems to be solved alternately. The difference-of-convex (DC) programming is used to solve the non-convex rank-one constraint in solving IRS energy reflection coefficient and information reflection coefficient. Numerical simulations verify the superiority of the proposed optimization algorithm in decreasing HAP transmit energy compared with other benchmark schemes.
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•A novel three-dimensional auxetic lattice is proposed by introducing a self-similar configuration into the vertex of the conventional re-entrant lattice.•The theoretical model for ...the elastic properties of the novel lattice is built and verified numerically and experimentally.•The novel lattice can possess the higher Young’s modulus and exhibit the more comprehensive auxetic effect flexibility than the conventional re-entrant lattice with equivalent relative density.•The axial internal force in the struts inhibits the auxetic behavior of the novel lattice along the three principal axes.
This work proposes a new auxetic lattice based on replacing the vertexes of traditional three-dimensional re-entrant structural with self-similar configurations. Derived by Castigliano's second theorem, a theoretical model is built to predict its elastic mechanical properties, including the homogenized Young’s modulus and Poisson’s ratio in all three principal directions. The overlapped nodes of struts are considered in the theoretical model due to their excessive strut thickness. The analytical results exhibit good agreement with the numerical and experimental results. The effects of the geometric parameters, internal force species, and hierarchical magnitude on the elastic property are carefully studied. The findings suggest that the axial internal force in the new structure inhibits its auxetic effects in the three principal directions. Compared with the traditional three-dimensional re-entrant lattice with equal relative density, the vertex-based hierarchical one exhibits more comprehensive designability of auxetic effect and enables higher Young’s modulus with specific geometrical parameters. The findings in this study contribute to the metamaterial advancement and provide an option for engineering applications requiring programmable and controllable elastic properties.
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•The hybrid method of TPMS structures realizes the smooth transition of geometric surfaces as well as the complementary effects of elastic properties.•RVE-based homogenization method ...is used to efficiently calculate the elastic properties of hybrid TPMS.•A quadratic multi-parameter model is proposed to characterize hybrid modulus.•The TPMS hybridizations can be tailored through the diverse configurations and proportions of components.
Hybrid design is an effective approach to construct functional mechanical metamaterials. In this study, a periodic hybrid method for the TPMS (triply periodic minimal surface) structures is proposed, maintaining the original surface connectivity and structural strength. It is implemented by the combination of implicit function Ψ(x,y,z) and transition function ηx,y,z of the TPMS governing equation. Furthermore, three classical TPMS, i.e., P (Schwarz Primitive), IWP (Schoen I-WP) and FRD (Schoen F-RD), are represented to study the elastic properties of hybridizations using FE (Finite Element) computational method and experiments. Through the RVE-based (Representative Volume Element) homogenization method, it is demonstrated how hybridization of TPMS expands the designable range of elastic modulus. In addition, the elastic properties of the hybridizations, such as axial modulus, diagonal modulus and anisotropy, etc., can be quantificationally tailored by turning the formal parameters of TPMS. This study can be considered as a foundational contribution for the advancement of hybrid TPMS metamaterials.
To enable next‐generation high‐power, high‐energy‐density lithium (Li) metal batteries (LMBs), an electrolyte possessing both high Li Coulombic efficiency (CE) at a high rate and good anodic ...stability on cathodes is critical. Acetonitrile (AN) is a well‐known organic solvent for high anodic stability and high ionic conductivity, yet its application in LMBs is limited due to its poor compatibility with Li metal anodes even at high salt concentration conditions. Here, a highly concentrated AN‐based electrolyte is developed with a vinylene carbonate (VC) additive to suppress Li+ depletion at high current densities. Addition of VC to the AN‐based electrolyte leads to the formation of a polycarbonate‐based solid electrolyte interphase, which minimizes Li corrosion and leads to a very high Li CE of up to 99.2% at a current density of 0.2 mA cm‐2. Using such an electrolyte, fast charging of Li||NMC333 cells is realized at a high current density of 3.6 mA cm‐2, and stable cycling of Li||NMC622 cells with a high cathode loading of 4 mAh cm‐2 is also demonstrated.
A highly concentrated acetonitrile‐based electrolyte with a vinylene carbonate additive is developed to significantly suppress Li+ depletion and side reactions on Li metal anode (LMA) at high current densities. High‐power Li metal batteries can be obtained using this electrolyte with a much stabilized LMA and accelerated ion transfer.
Lithium (Li) metal is a key anode material for constructing next generation high energy density batteries. However, dendritic Li deposition and unstable solid electrolyte interphase (SEI) layers ...still prevent practical application of Li metal anodes. In this work, it is demonstrated that an uniform Li coating can be achieved in a lithium fluoride (LiF) decorated layered structure of stacked graphene (SG), leading to the formation of an SEI‐functionalized membrane that retards electron transfer by three orders of magnitude to avoid undesirable Li deposition on the top surface, and ameliorates Li+ ion migration to enable uniform and dendrite‐free Li deposition beneath such an interlayer. Surface chemistry analysis and density functional theory calculations demonstrate that these beneficial features arise from the formation of C–Fx surface components on the SG sheets during the Li coating process. Based on such an SEI‐functionalized membrane, stable cycling at high current densities up to 3 mA cm−2 and Li plating capacities up to 4 mAh cm−2 can be realized in LiPF6/carbonate electrolytes. This work elucidates the promising strategy of modifying Li plating behavior through the SEI‐functionalized carbon structure, with significantly improved cycling stability of rechargeable Li metal anodes.
A surface conversion of LiF into C–Fx components on a defective carbon sheet can be achieved during Li plating to provide a solid electrolyte interphase (SEI)‐functionalization of a layered carbon structure. Uniform Li deposition with dendrite‐free features can be realized beneath the SEI‐functionalized layer for significantly improved cycling stability of Li metal anodes.
Spin-flip time-dependent density functional theory (SF-TD-DFT) with the full noncollinear hybrid exchange-correlation kernel and its approximate variants are critically assessed, both formally and ...numerically. As demonstrated by the ethylene torsion and the C(2v) ring-opening of oxirane, SF-TD-DFT is very useful for describing nearly degenerate situations. However, it may occasionally yield unphysical results. This stems from the noncollinear form of the generalized gradient approximation, which becomes numerically instable in the presence of spin-flip excitations from the closed- to vacant-shell orbitals of an open-shell reference. To cure this defect, a simple modification, dubbed as ALDA0, is proposed in the spirit of adiabatic local density approximation (ALDA). It is applicable to all kinds of density functionals and yields stable results without too much loss of accuracy. In particular, the combination of ALDA0 with the Tamm-Dancoff approximation is a promising tool for studying global potential energy surfaces. In addition to the kernel problem, SF-TD-DFT is also rather sensitive to the choice of reference states, as demonstrated by the spin multiplet states of closed-shell molecules of H(2)O, CH(2)O, and C(2)H(4). Surprisingly, SF-TD-DFT with pure density functionals may also fail for valance excitations with large orbital overlaps, at variance with the spin-conserving counterpart (SC-TD-DFT). In this case, the inclusion of a large amount of Hartree-Fock exchange is mandatory for quantitative results. Nonetheless, for spatially degenerate cases such as CF, CH, and NH(+), SF-TD-DFT is more advantageous than SC-TD-DFT, unless the latter is also space adapted. These findings are very instructive for future development and applications of TD-DFT.
Acoustic metamaterials with broadband sound-absorbing capacity open up applications in aerospace, automotive, marine, defense, etc. For such applications, sound-absorbing materials that can withstand ...complex loading conditions are essential. Hence, to address acoustic and mechanical requirements simultaneously, we propose plate-reinforced dual-functional micro-lattice metamaterials (PDMMs) that exhibit elastic isotropy, dual crushing stages with a specific energy absorption up to 25.82 kJ/kg, and ultra-broadband sound absorption from 0.97 kHz to 6.30 kHz. The remarkable elastic isotropy lies in the topology-induced structural stiffness homogenising effect. The transition from single to dual plateau anti-compression stages is controlled by tailoring the structural local strength. On-demand broadband sound absorption is achieved by modulating the parallel coupling and cascade resonance effects, and the physical mechanism is revealed by examining impedance matching and system damping states. Overall, the presented novel metamaterials exhibit exceptional application potentials by overcoming the trade-offs usually found in traditional mechanical and acoustic metamaterials.
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•A lattice design strategy of self-similar embedded hierarchical structure is proposed.•The influence mechanism of hierarchical configuration on plateau response is clarified.•The ...plateau response can be flexibly customized via multiple approach.
Customizable stress plateau of lattice structure is sought-after for various engineering applications. In this study, we present a new design strategy to achieve customizable plateau, by introducing the concept of embedding self-similar structure in a face-centered cubic (FCC) lattice, which thereby constitutes a novel FCC hierarchical lattice (FCCH). These FCCH specimens were experimentally validated through quasi-static compression tests, on samples 3D-printed through selective laser melting using SS316L. These deformation characteristics were clarified by finite element analysis. The experimental and numerical results consistently show the serrated, dual, and upward plateaus were experienced for the 0th-order FCC, 1st-order FCCH, and 2nd-order FCCH structures, respectively. The mechanical reinforcements are based on the stronger interactions between unit cells induced by the embedded sub-structures. The deformation mechanisms dominated by hierarchical order are determined by horizontal layer-by-layer interaction as well as longitudinal buckling and collapse. The effect of geometric configuration show that stress plateau can be customized via optimizing different slave-cell sizes, connecting face-centers of lattice components, and arranging row layered gradient strategies.
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