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Cryo-electron microscopy (cryo-EM) has been widely used to reveal the structures of proteins at atomic resolution. One key challenge is that almost all proteins are predominantly adsorbed to the air-water interface during standard cryo-EM specimen preparation. The interaction of proteins with air-water interface will significantly impede the success of reconstruction and achievable resolution. Here, we highlight the critical role of impenetrable surfactant monolayers in passivating the air-water interface problems, and develop a robust effective method for high-resolution cryo-EM analysis, by using the superstructure GSAMs which comprises surfactant self-assembled monolayers (SAMs) and graphene membrane. The GSAMs works well in enriching the orientations and improving particle utilization ratio of multiple proteins, facilitating the 3.3-Å resolution reconstruction of a 100-kDa protein complex (ACE2-RBD), which shows strong preferential orientation using traditional specimen preparation protocol. Additionally, we demonstrate that GSAMs enables the successful determinations of small proteins (<100 kDa) at near-atomic resolution. This study expands the understanding of SAMs and provides a key to better control the interaction of protein with air-water interface. Air-water interface hinders cryo-EM reconstruction and achievable resolution. Here, a superstructure called GSAMs is developed to alleviate the air-water interface effect and improve the efficiency of cryo-EM analysis. [ABSTRACT FROM AUTHOR]

With more and more the transportation tunnels that have been and will be constructed in loess areas in Northwest China with high earthquake potential, the overall stability of tunnel portal sections under earthquake action and the related aseismic countermeasures has attracted the attention of both scholars and engineers, especially for tunnels in upper slope connecting high bridges crossing rivers or valleys. To study the dynamic response characteristics and damage evolution of steep loess slopes with tunnels under earthquake action, large-scale shaking table tests and numerical simulations were performed on steep loess slopes with tunnels. In particular, three-dimensional noncontact optical measurement techniques were used to obtain the slope surface displacements. The results showed that the main deformation patterns of the studied slopes were horizontal movement and settlement when the seismic waves were input in the X and X–Z directions, respectively. However, the seismic wave from the X direction had a greater impact on the deformation of a slope than that from the X–Z direction, and the tunnel portal slopes were ultimately destroyed under the action of a large horizontal seismic acceleration. Slope failure ahead of a tunnel was divided into four stages, i.e., the elastic deformation stage, plastic deformation accumulation stage, local failure stage, and overall failure stage. The existence of the tunnel had a great influence on the peak ground acceleration (PGA) and the PGA amplification factor (PGAAF) of the surrounding soil mass. The changes in the PGD and PGA on the slope surface determined via numerical simulation were basically consistent with the experimental results. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the dynamic response characteristics of subway station under earthquakes. To this end, seismic waves are transformed into equivalent nodal loads on viscoelastic artificial boundaries using theories and methods of wave motion. The calculation formulas for equivalent nodal loads of SV waves incident at any angle are established, and ANSYS' APDL program compiles to automatically generate the viscoelastic artificial boundary and input the seismic loads. A finite element model of soil-subway station interaction was established, and the seismic response characteristics of a two-story three-span subway station under different incidence angles of SV waves were investigated using the above seismic input method. The results indicate that the incidence angle of seismic waves has a significant impact on the seismic response of subway station. Inclined incidence of seismic waves causes non-uniform loading and deformation of the subway station. Specifically, a small angle leads to predominantly transverse shear deformation, while a large angle causes mainly vertical shear deformation. The inclined incidence of seismic waves significantly increases the vertical acceleration of the subway station, with the effect becoming more pronounced as the angle increases. Additionally, special attention should be given to the joints between the structural slab and the side wall, slab and center column, as well as the two ends of the center column as they are vulnerable areas during earthquakes and require careful consideration in seismic design. [ABSTRACT FROM AUTHOR]

The instability of the shallow tunnel with asymmetric loess cover affected by the earthquake has been one of the most prominent geotechnical disasters in the loess region. Under the shallow-focus earthquake, the tunnel is subjected to obliquely incident seismic waves, and its seismic response is significantly affected by the non-uniform ground motion caused by the obliquely incident waves. This study introduces a method of inputting an oblique incidence of SV wave by programming with finite element analysis program ANSYS to a bias loess slope. With the proposed numerical method, the seismic response and damage characteristics of a shallow tunnel with asymmetric loess cover under oblique incidence of seismic SV wave are analyzed. The results show that: (1) The input method of oblique incidence of SV wave and its combination with the finite element model are feasible to analyze the seismic response and damage characteristics of the shallow tunnel with asymmetric loess cover. (2) The principal tensile and compressive stresses of tunnel lining are distributed in the shapes of a butterfly and an X, respectively. The symmetry axes of the stresses show the characteristic of bias. (3) With the increase of slope angle, the plastic zone increases and develops toward the slope surface. (4) With the increase of thickness of soil cover, the plastic zone decreases. (5) With the increase of incidence angle, the distribution of principal tensile stress develops to a circle, and a through plastic zone connecting the slope toe and springline at the shallow-buried side occurs. [ABSTRACT FROM AUTHOR]