A comparative investigation of an AB- and AA-stacked bilayer graphene sheet under an applied electric field:A density functional theory study

An AB-and AA-stacked bilayer graphene sheet （BLG） under an electric field is investigated by ab initio calculation. The interlayer distance between the two layers, band structures, and atomic charges of the system are investigated in the presence of different electric fields normal to the BLG. The AB-stacked BLG is able to tune the bandgap into 0.234 eV with the increase of the external electronic field to 1 V/nm, however, the AA-stacked BLG is not sensitive to the external electric field. In both the cases, the spacing between the BLG slightly change in terms of the electric field. The charges in the AB-stacked BLG are increased with the increase of the electric field, which is considered to be the reason that causes the bandgap opening in the AB-stacked BLG.

Using of Key Stratum Theory to Study the Structural Development of Roof Aquifer

During the underground mining of coal resources,overlying rocks on the roof of excavated tunnels will be destroyed due to ground pressure,and as a result,part of them will break and fall into the tunnels.How to determine the distribution of fractured areas and fissures presents a major problem for preserving the overlying aquifer.

The Theory Study of the Influence of the Topography on the Cold Frontal Motion

In order to study the characteristics of cold frontal motion over the arbitrary topography, the velocity of cold frontal movement is derived by using the one layer shallow-water model. The results show that there exist the retardation in upwind side and rapid descent in the lee slope when the cold front crosses the topography.

Study of Polymer Blends with Sub-cluster Theory PartⅠ Essential Concepts and Equations of Sub-cluster Theory

Various viscosity-composition curves of polymer blends are summarized in eight groups. To represent these curves. 'sub-cluster equations' are derived on the basis of so called 'sub-cluster theoryThe essential concepts of sub-cluster theory and the derivation of those 'Sub-cluster equations' are briefly introduced.

A PRELIMINARY STUDY ON THE THEORY OF THE SECOND AND THIRD ORDER DERIVATIVE ADSORPTION CHRONOPOTENTIOMETRY FOR A REVERSIBLE REACTION

The equations of the second and third order derivative curves of time with respect to potential for a reversible process in adsorption chronopotentiometry are derived and experimentally verified.

Study of Polymer Blends with Sub-cluster Theory Part 2 Comparison of PVC/ABS, PVC/SBS Blends

Series of PVC/ABS and PVC/SBS blends of composition 20/ 80. 40/ 60, 60 / 40 and 80 / 20were prepared in a screw extruder. The phase morphology, miscibility and rheological behaviour of two systems were investigated. The viscosity-composition plots were represented by sub-cluster equation, the various differences between two systems are interpreted with the equation parameters

Theory Study on Teachers＇ Happiness Degree in Private Colleges

Based on analyzing actual cases and referring to other discourses, this discourse analyzes the happiness of teachers in non-governmental funded universities from three perspectives： the subjectivity of ＂happiness＂, psychological condition and the influence of career. As a result, this discourse can find tools for evaluating happiness and use them to evaluate the degree of happiness in non-governmental funded universities.

Anderson's Cognitive Theory and Learning Strategy Studies in Second Language Acquisition

Second language acquisition can not be understood without addressing the interaction between language and cognition. Cognitive theory can extend to describe learning strategies as complex cognitive skills. Theoretical developments in Anderson’s production systems cover a broader range of behavior than other theories, including comprehension and production of oral and written texts as well as comprehension, problem solving, and verbal learning.Thus Anderson’s cognitive theory can be served as a rationale for learning strategy studies in second language acquisition.

A STUDY ON THE LOW SPEED SHIP THEORY

Based on Baba's assumption,the linearized free-surface boundary conditions at low speed are discussed in order to demonstrate the differences between Baba's and Dawson's free-surface boundary conditions.By using Fourier integral transfor- mation,a method of computing wave velocity potential ,which satisfies the boundary conditions of free-surface and hull surface,is presented.The solution of is found with the powerful technique of asymptotic expansions.With order comparison method,it is found that the hull surface boundary conditions can be neglected when only the ship wave resistance is concerned.The exact analytical solution of two-dimensional slow ship wave velocity potential is derived by neg- lecting hull effect.The results show that the inhomogeneous effect of free-surface is not negligible in the boundary value problems of slow ship velocity potential.

Variational transition state theory study of the reactions Li+HF and Li+HCl on the BO potential energy surfaces

Variational transition state theory is used to study the kinetics of the reactions Li+HF and Li+HCl on the BO potential energy surfaces, fitted to ab initio values by Lagana et al. The saddle point, the location of generalized transition state and other kinetic features on the bottleneck of the po- tential energy surface are obtained. We point out that the location of generalized transition state tends to the direction in which the two atoms with larger reduced mass separate off. It can be determined whether a potential energy surface is accurate or not by a fine analysis of its bottleneck region and a comparison of kinetic calculation with experimental result. This is helpful for building a more accurate potential energy surface.

Theoretical study on the formation mechanism of polychlorinated dibenzothiophenes/thianthrenes from 2-chlorothiophenol molecules

Homogeneous formation of polychlorinated dibenzothiophenes/thianthrenes（PCDT/TAs）,sulfurated compounds analogous to polychlorinated dibenzo-p-dioxin/dibenzofurans（PCDD/Fs）, has been well-documented to occur via radical–radical coupling reactions from chlorinated thiophenol precursors. However, the current understanding of the formation mechanism of PCDT/TAs is exclusively limited to the inherent point of view that chlorothiophenoxy radicals act as the only required intermediates for PCDT/TAs. This study investigates reaction pathways for the formation of PCDT/TAs involving two new types of radical species, i.e., substituted phenyl radicals and substituted thiophenoxyl diradicals. Taking 2-chlorothiophenol（2-CTP） as a model compound for chlorothiophenols,we found that apart from the mostly discussed chlorothiophenoxy radicals, substituted phenyl radicals and substituted thiophenoxyl diradicals could also be readily formed via the reaction of 2-CTP with H radicals. Furthermore, direct self-and cross-coupling of these radicals can result in the formation of PCDT/TAs, including 1-monochlorothianthrene（1-MCTA）, 1,6-dichlorothianthrene（1,6-DCTA）, 4,6-dichlorodibenzothiophene（4,6-DCDT）and 1,6-dichlorodibenzothiophene（1,6-DCDT）. The pathways proposed in this work are proven to be both thermodynamically and kinetically favorable. Particularly, comparisons were made between the formation mechanisms of sulfurated and oxygenated dioxin systems from an energetic point view, showing that replacing oxygen with sulfur atoms greatly reduces the activation barriers of the rate-controlling steps involved in the PCDT/TA formation processes compared with those involved for PCDD/Fs. The calculated results in this work may improve our understanding of the formation mechanism of PCDT/TAs from chlorothiophenol precursors and should be informative to environmental scientists.

A Brief Commentary: Promote Theory Studies and Improve Foreign Language Work

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A pH-universal ORR catalyst with atomic Fe-heteroatom(N,S)sites for high-performance Zn-air batteries

Developing innovative,easy-to-manufacture,and non-Pt-group-metal(non-PGM)electrocatalysts is essential for the highly efficient oxygen reduction reaction(ORR).Herein,we report a self-sacrificing post-synthetic strategy to synthesize highly loaded Fe-isolated single atoms anchored on the hierarchical porous N,S co-doped carbon matrix(Fe-SAs/S,N-C/rGO).The optimized Fe-SAs/S,N-C/rGO exhibits excellent ORR activity in the pH-universal range with half-wave potentials of 0.89,0.80,and 0.60 V in alkaline,acidic,and neutral media,comparable to the commercial Pt/C(0.85,0.81,and 0.64 V,respectively).The homemade liquid Zn-air battery(ZAB)with Fe-SAs/S,N-C/rGO as the cathode catalyst displays an open-circuit voltage(OCV)of~1.61 V,discharging specific capacity of 817.23 mAh·g^(-1),and long-term durability of~1865 cycles,outperforming those of the device with commercial Pt/C+RuO_(2)(1.49 V,657.32 mAh·g^(-1),and~120 cycles,respectively).Intriguingly,the corresponding flexible solidstate ZAB delivers satisfactory OCV,peak power density,foldability,and cycling stability at room temperature,as well as adaptability at a low temperature of -10℃.Besides,density functional theory(DFT)calculation reveals that the atomic FeN_(3)S moieties in Fe-SAs/S,N-C/rGO can cause charge redistribution and lower the binding strength of oxygen-containing intermediates,resulting in accelerated ORR kinetics and optimized catalytic activity.This work provides insights into experimental and theoretical guidance towards non-PGM electrocatalysts for efficient energy conversion.

Single-atom Fe-N_(5)catalyst for high-performance zinc-air batteries

Developing innovative and efficient non-precious-metal-group(non-PMG)electrocatalysts is crucial for the wide use of zinc-air batteries(ZABs).Herein,a single-atom catalyst(termed as Fe-N-C/rGO SAC)with unique five N-coordinated Fe(Fe-N_(5))centers is prepared by pyrolyzing the composite of zeolitic-imidazolate-frameworks-8(ZIF-8)and graphene oxide(GO).Specifically,the individual Fe site is stabilized by four equatorial and one axial N atoms donated by the N-doped carbon matrix and imidazole ring,respectively,thus forming an asymmetric electron depletion zone over the metal center,which can effectively promote the generation of reactive intermediates and accelerate the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)processes for ZABs.The rechargeable liquid ZAB with Fe-N-C/rGO catalyst exhibits an extremely high energy density(928.25 Wh·kg^(−1)),a remarkable peak power density(107.12 mW·cm^(−2)),and a long cycle life(400 h).Additionally,the corresponding flexible solid-state ZAB displays superior foldability and remarkable cycling stability.This work provides both experimental and theoretical guidance for rational design of non-PMG electrocatalyst-driven ZABs.

Selective 3,4-Polymerization Mechanism of Isoprene Catalyzed by Rare Earth Alkyl Complexes

The mechanism of selective 3,4-polymerization reaction of isoprene catalyzed by the rare earth lutecium（Ⅲ） alkyl complexes [2,6-Me2Ph-N-CH2-C（CH2SiMe3）=N-PhMe2-2,6]Lu（CH2SiMe3）2（THF）was investigated by means of the M06/sdd method with solvation effects taken into account.The results show that the structure of the catalyst core remained almost unchanged as the isoprene molecules were alternatively inserted into the complex at two opposite sides.The Gibbs free energies of the coordination complexes,transition state and intermediates indicate that all the isoprene molecules prefer to insert into the complex with the 3,4-polymerization selectivity as catalyzed by the catalyst,which is consistent with the experimental observations.It is found that the insertion reaction of each isoprene is exothermic,which comes mainly from the coordination of the isoprene molecule to the lutecium（Ⅲ） atom.The solvation effects were confirmed important in predicting the Gibbs free energies of the present reaction system.