Research on the Structural Rigidity Characteristics of a Reconfigurable TBM Thrust Mechanism

To improve the adaptability of TBMs in diverse geological environments,this paper proposes a reconfigurable Type-V thrust mechanism(V-TM)with rearrangeable working states,in which structural stiffness can be automatically altered during operation.Therefore,millions of configurations can be obtained,and thousands of instances of working status per configuration can be set respectively.Nonetheless,the complexity of configurations and diversity of working states contributes to further complications for the structural stiffness algorithm.This results in challenges such as difficulty calculating the payload compliance index and the environment adaptability index.To solve this problem,we use the configuration matrix to describe the relationship between propelling jacks under reconfiguration and adopt pattern vectors to describe the working state of each hydraulic cylinder.Then,both the dynamic compatible equation between propeller forces of the hydraulic cylinders and driving forces,and the kinematic harmonizing equation between the hydraulic cylinder displacements and their deformations are established.Next,we derive the stiffness analytical equation using Hooke’s law and the Jacobian Matrix.The proposed approach provides an effective algorithm to support structural rigidity analysis,and lays a solid theoretical foundation for calculating the performance indexes of the V-TM.We then analyze the rigidity characteristics of typical configurations under different working states,and obtain the main factors affecting structural stiffness of the V-TM.The results show the deviation degree of structural parameters in hydraulic cylinders within the same group,and the working status of propelling jacks.Finally,our constructive conclusions contribute valuable information for matching and optimization by drawing on the factors that affect the structural rigidity of the V-TM.

Water on surfaces from first-principles molecular dynamics

Water is ubiquitous and so is its presence in the proximity of surfaces.To determine and control the properties of interfacial water molecules at nanoscale is essential for its successful applications in environmental and energy-related fields.It is very challenging to explore the atomic structure and electronic properties of water under various conditions,especially at the surfaces.Here we review recent progress and open challenges in describing physicochemical properties of water on surfaces for solar water splitting,water corrosion,and desalination using first-principles approaches,and highlight the key role of these methods in understanding the complex electronic and dynamic interplay between water and surfaces.We aim at showing the importance of unraveling fundamental mechanisms and providing physical insights into the behavior of water on surfaces,in order to pave the way to water-related material design.

Driving forces for ultrafast laser-induced sp^(2) to sp^(3) structural transformation in graphite

Understanding the microscopic mechanism of photoinduced sp^(2)-to-sp^(3) structural transformation in graphite is a scientific challenge with great importance.Here,the ultrafast dynamics and characteristics of laser-induced structural transformation in graphite are revealed by non-adiabatic quantum dynamic simulations.Under laser irradiation,graphite undergoes an interlayer compression and sliding stage,followed by a key period of intralayer buckling and interlayer bonding to form an intermediate sp^(2)-sp^(3) hybrid structure,before completing the full transformation to hexagonal diamond.The process is driven by the cooperation of charge carrier multiplication and selective phonon excitations through electron-phonon interactions,in which photoexcited hot electrons scattered into unoccupied high-energy conduction bands play a key role in the introduction of in-plane instability in graphite.This work identifies a photoinduced non-adiabatic transition pathway from graphite to diamond and shows far-reaching implications for designing optically controlled structural phase transition in materials.

Water transport through subnanopores in the ultimate size limit: Mechanism from molecular dynamics

Ab initio and classical molecular dynamics simulations show that water can flow through graphdiyne—an experimentally fabricated graphene-like membrane with highly dense (2.4 × 10^18 pores/m^2), uniformly ordered, subnanometer pores (incircle diameter 0.57 nm and van der Waals area 0.06 nm^2). Water transports through subnanopores via a chemical-reaction-like activated process. The activated water flow can be precisely controlled through fine adjustment of working temperature and pressure. In contrast to a linear dependence on pressure for conventional membranes, here pressure directly modulates the activation energy, leading to a nonlinear water flow as a function of pressure. Consequently, high flux (1.6 L/Day/cm^2/MPa) with 100% salt rejection efficiency is achieved at reasonable temperatures and pressures, suggesting graphdiyne can serve as an excellent membrane for water desalination. We further show that to get through subnanopores water molecule must break redundant hydrogen bonds to form a two-hydrogen-bond transient structure. Our study unveils the principles and atomistic mechanism for water transport through pores in ultimate size limit, and offers new insights on water permeation through nanochannels, design of molecule sieving and nanofluidic manipulation.

金属玻璃薄膜中原子尺度分形结构的直接观测

由于非晶态物质的原子结构不具有周期性排列的特征,X-ray衍射等传统的结构分析技术很难给出其实际的原子结构信息.利用原子级分辨的扫描透射电子显微技术,本文直接观察到由气相沉积获得的具有原子级厚度的金属玻璃薄膜中的原子排列.通过数格子法计算,作者发现金属玻璃薄膜中的原子排列呈现出分形特征,其分形维数取决于原子面密度.对金属玻璃薄膜中的原子二维坐标进行分析,作者发现金属原子可以排列成多种多边形,原子之间的键角约在45°~55°之间.此外,作者证明了这里的分形结构与渗流理论是一致的,有助于理解金属玻璃薄膜和金属玻璃表面的快弛豫动力学和玻璃化转变过程.

Simultaneous switching of supramolecular chirality and organizational chirality driven by Coulomb expansion

Chiral switching is a fascinating topic and plays an important role in construction of homochirality.Nevertheless,due to the complexity and flexibility of noncovalent interactions,switching the chirality of entire supramolecular assemblies has hitherto remained a challenge.Here we report the electric field-controlled chirality switching of pentacene pinwheel arrays and two-dimensional(2D)network domains.Pentacene molecules on Cd(0001)surface form the porous network structure with building blocks of hexamer pinwheels.Driven by the electric field from a scanning tunneling microscopy(STM)tip,the supramolecular chirality of pentacene pinwheels and the organizational chirality of entire network domains can be simultaneously switched from one enantiomorph to another.Furthermore,such chiral switching is reversible and repeatable under successive voltage pulses.First-principles calculations demonstrate that electric field significantly modulates the interfacial charge transfer and induces the Coulomb expansion of pentacene layers,and the subsequent reaggregation leads to the chiral flipping of the supramolecular pinwheels and 2D domains.Our results provide a new strategy for dynamic control of the 2D chiral structures and help to steer the supramolecular assembly toward homochirality.