An analytical symplectic approach to the vibration analysis of orthotropic graphene sheets

A nonlocal continuum orthotropic plate model is proposed to study the vibration behavior of single-layer graphene sheets (SLGSs) using an analytical symplectic approach. A Hamiltonian system is established by introducing a total unknown vector consisting of the displacement amplitude, rotation angle, shear force, and bending moment. The high-order governing differential equation of the vibration of SLGSs is transformed into a set of ordinary differential equations in symplectic space. Exact solutions for free vibration are obtianed by the method of separation of variables without any trial shape functions and can be expanded in series of symplectic eigenfunctions. Analytical frequency equations are derived for all six possible boundary conditions. Vibration modes are expressed in terms of the symplectic eigenfunctions. In the numerical examples, comparison is presented to verify the accuracy of the proposed method. Comprehensive numerical examples for graphene sheets with Levy-type boundary conditions are given. A parametric study of the natural frequency is also included.

Enhanced catalytic conversion of polysulfides using high-percentage 1T-phase metallic WS_(2) nanosheets for Li–S batteries

High-energy-density lithium-sulfur batteries has attracted substantial attention as competitive candidates for large-scale energy storage technologies.Still,the adverse“shuttle effect”and sluggish sulfur conversion reaction kinetics immensely obstruct their commercial viability.Herein,a two-dimensional metallic 1T phase WS_(2)(1T-WS_(2))nanosheets modified functional separator is developed to improve the electrochemical performance.Meanwhile,the semiconducting bulk-WS_(2) crystals,and 2H phase WS_(2)(2H-WS_(2))nanosheets with more basal-plane Svacancy defects are also prepared to probe the contributions of the crystal structure(phase),S-vacancy defects,and edges to the Li–S batteries performance experimentally and theoretically.In merits of the synergistic effect of high ion and electron conductivity,enhanced binding ability to lithium polysulfides(LiPSs),and sufficient electrocatalytic active sites,the 1T-WS_(2) shows highly efficient electrocatalysis of LiPSs conversion and further improves Li–S battery performance.As expected,thus-fabricated cells with 1T-WS_(2) nanosheets present superior cycle stability that maintain capacity decline of 0.039%per cycle after 1000 cycles at 1.0 C.The strategy presented here offers a viable approach to reveal the critical factors for LiPSs catalytic conversion,which is beneficial to developing advanced Li–S batteries with enhanced properties.

The Longest Railway Tunnel in China

After nearly 10 years of geological surveys, route design, and comparisons of tunnel construction technology and engineering design, the construction of the longest railway tunnel in Chinathe Gaoligong Mountain Tunnel, which has a full length of 34.5 km-began in December 2014. As the key works of the Dali-Ruili Railway in the west line of the Trans-Asia Railway, this tunnel is located in western Yunnan Province in southwestern China, and passes through the west of the Hengduan Mountains in the southern Qinghai-Tibet Plateau. It can be extended westward to connect with railways in Myanmar and India, thus connecting the Chinese railway system to railways in Southeast Asia, South Asia, and Europe to form an onshore transport corridor from the Pacific Ocean to the Indian Ocean. This linkage will promote commerce and trade along the line, reduce the cost of international trade, and play a positive role in enhancing exchanges between China and other Southeast Asian countries. In this way, it will allow China to adapt to the trend of economic globalization and achieve the sustainable development of its national economy.

Photovoltaics of low-bandgap inorganic perovskites

Low-bandgap inorganic perovskites are a group of materials that can simultaneously harness the stability merit of an all-inorganic composition and high photovoltaic efficiency potential of low-bandgap light absorbers as compared with other perovskite materials.Therefore,low-bandgap inorganic perovskites are promising materials options for the development of both single-junction and tandem solar cells.In this review,we summarize the recent studies addressing the major issues related to these perovskites,including the low phase stability and uncontrolled Sn-related defects.We also present a perspective discussion on future research directions related to these perovskites.We propose to gain insights into those unique thermodynamic and kinetic behaviors of these perovskites to understand and overcome their low phase stability.In particular,we envision that fundamental investigations leveraging 119Sn NMR may open a new pathway for understanding and alleviating Sn-related defects.Continued efforts in the discussed areas are expected to unleash the full technological potential of low-bandgap inorganic perovskites for high-performance solar cells and modules.