Superposition of dual electric fields in covalent organic frameworks for efficient photocatalytic hydrogen evolution

Covalent organic frameworks(COFs)are promising materials for converting solar energy into green hydrogen.However,limited charge separation and transport in COFs impede their application in the photocatalytic hydrogen evolution reaction(HER).In this study,the intrinsically tunable internal bond electric field(IBEF)at the imine bonds of COFs was manipulated to cooperate with the internal molecular electric field(IMEF)induced by the donor-acceptor(D-A)structure for an efficient HER.The aligned orientation of IBEF and IMEF resulted in a remarkable H_(2) evolution rate of 57.3 mmol·g^(-1)·h^(-1)on TNCA,which was approximately 520 times higher than that of TCNA(0.11 mmol·g^(-1)·h^(-1))with the opposing electric field orientation.The superposition of the dual electric fields enables the IBEF to function as an accelerating field for electron transfer,kinetically facilitat-ing the migration of photogenerated electrons from D to A.Furthermore,theoretical calculations indicate that the inhomogeneous charge distribution at the C and N atoms in TNCA not only pro-vides a strong driving force for carrier transfer but also effectively hinders the return of free elec-trons to the valence band,improving the utilization of photoelectrons.This strategy of fabricating dual electric fields in COFs offers a novel approach to designing photocatalysts for clean energy synthesis.

A MULTISCALE MECHANICAL MODEL FOR MATERIALS BASED ON VIRTUAL INTERNAL BOND THEORY

Only two macroscopic parameters are needed to describe the mechanical properties of linear elastic solids, i.e. the Poisson＇s ratio and Young＇s modulus. Correspondingly, there should be two microscopic parameters to determine the mechanical properties of material if the macroscopic mechanical properties of linear elastic solids are derived from the microscopic level. Enlightened by this idea, a multiscale mechanical model for material, the virtual multi-dimensional internal bonds （VMIB） model, is proposed by incorporating a shear bond into the virtual internal bond （VIB） model. By this modification, the VMIB model associates the macro mechanical properties of material with the microscopic mechanical properties of discrete structure and the corresponding relationship between micro and macro parameters is derived. The tensor quality of the energy density function, which contains coordinate vector, is mathematically proved. From the point of view of VMIB, the macroscopic nonlinear behaviors of material could be attributed to the evolution of virtual bond distribution density induced by the imposed deformation. With this theoretical hypothesis, as an application example, a uniaxial compressive failure of brittle material is simulated. Good agreement between the experimental results and the simulated ones is found.

Modeling rock fragmentation by coupling Voronoi diagram and discretized virtual internal bond

The rock fragmentation involves the inter-block and the intra-block fracture.A simulation method for rock fragmentation is developed by coupling Voronoi diagram(VD)and discretized virtual internal bond(DVIB).The DVIB is a lattice model that consists of bonds.The VD is used to generate the potential block structure in the DVIB mesh.Each potential block may contain any number of bond cells.To characterize the inter-block fracture,a hyperelastic bond potential is employed for the bond cells that are cut by the VD edges.While to characterize the intra-block fracture,an elastobrittle bond potential is adopted for the bonds in a block.By this method,both the inter-block and intra-block fracture can be well simulated.The simulation results suggest that this method is a simple and efficient approach to rock fragmentation simulation with block smash.

Bedding plane-embedded augmented virtual internal bonds for fracture propagation simulation in shale

To effectively simulate the fracture propagation in shale,the bedding plane(BP)effect is incorporated into the augmented virtual internal bond(AVIB)constitutive relation through BP tensor.Comparing the BP-embedded AVIB with the theory of transverse isotropy,it is found the approach can represent the anisotropic properties induced by parallel BPs.Through the simulation example,it is found that this method can simulate the stiffness anisotropy of shale and can represent the effect of BPs on hydraulic fracture propagation direction.Compared with the BP-embedded virtual internal bond(VIB),this method can account for the various Poisson’s ratio.It provides a feasible approach to simulate the fracture propagation in shale.

THE EFFECTS OF WETTING AND REDRYING CYCLE ON PHYSICAL PROPERTIES OF PARTICLEBOARD

The physical properties of six type particleboards bonded with different formaldehydebased resins were tested. arer wetting and redrying, Uiree PF bonded boards retained much higher pro portion of their initial dry strength than the boards bonded with resins containing urea. The strength lossis the results of mechanical forces, caused by particle movement, breaking adhesive bonds.

Numerical Simulation of Rock Fracturing under Uniaxial Compression Using Virtual Internal Bond Model

A multi-scale virtual internal bond (VIB) model for the isotropic materials has been recently proposed to describe the material deformation and fracturing. During the simulation process of material fracturing using VIB, the fracture criterion is directly built into the constitutive formulation of the material using the cohesive force law. Enlightened by the similarity of the damage constitutive model of rock under uniaxial compression and the cohesive force law of VIB, a VIB density function of rock under uniaxial compression is suggested. The elastic modulus tensor is formulated on the basis of the density function. Thus the complete deformation process of rock under the uniaxial compression is simulated.

Effects of Horizontal Density Distribution on Internal Bond Strength of Flakeboard

Horizontal density variation is a structural phenomenon of non-veneer wood composites. The variation and distribution characteristics of horizontal density have impacts on the products properties. In this study, veneer strip simulated flake boards with 4 kinds of density distribution were made using a mat model. The density variation of the modeled mats was discussed, as well as the relationship between sample size and density variation. The effects of density and density distribution of non-veneer composites on the internal bond strength were analyzed. Result shows that the horizontal density of random formed particleboard follows normal distribution. Density has remarkable influence on internal bond strength (IB). Increasing density helps to improve IB at lower density stage, but has negative impacts on IB at higher density stage. Density variation between testing specimens depends on their sizes. Properly increasing specimen size can decrease the variation of the IBs.

Effect of Ratio of Face to Core Particles on Mechanical and Physical Properties of Particleboard Manufactured from Ethiopian Highland Bamboo

The study was conducted to evaluate effect of ratio of face to core particles on mechanical and physical properties of oriented strand board produced from Ethiopian highland bamboo.Three-layered oriented particleboards were manufactured with 4 proportions of face to core particles at 750 kg/m^3 target density.Ten percent urea formaldehyde resin was used as a binder.Strength and dimensional stability performances of all boards were assessed based on ISO standards.The results showed that modulus of rupture...