On the core structure and mobility of the〈100 〉{010} and〈100 〉 {01■} dislocations in B2 structure YAg and YCu

Dislocations are thought to be the principal mechanism of high ductility of the novel B2 structure intermetallic compounds YAg and YCu.In this paper, the edge dislocation core structures of two primary slip systems 〈100〉{010} and 〈100〉{01^-1} for YAg and YCu are presented theoretically within the lattice theory of dislocation.The governing dislocation equation is a nonlinear integro-differential equation and the variational method is applied to solve the equation.Peierls stresses for 〈100〉{010} and 〈100〉{01^-1} slip systems are calculated taking into consideration the contribution of the elastic strain energy.The core width and Peierls stress of a typical transition-metal aluminide NiAl is also reported for the purpose of verification and comparison.The Peierls stress of NiAl obtained here is in agreement with numerical results,which verifies the correctness of the results obtained for YAg and YCu.Peierls stresses of the 〈100〉{01^-1} slip system are smaller than those of 〈100〉{010} for the same intermetallic compounds originating from the smaller unstable stacking fault energy.The obvious high unstable stacking fault energy of NiAl results in a larger Peierls stress than those of YAg and YCu although they have the same B2 structure.The results show that the core structure and Peierls stress depend monotonically on the unstable stacking fault energy.

EXTENDED CORE STRUCTURE OF DISSOCIATED EDGE DISLOCATIONS IN FCC CRYSTALS WITH CONSIDERATION OF DISCRETENESS

The extended core structure of the dissociated edge dislocation in Al, Au, Ag, Cu and Ni is determined within lattice theory of dislocation. The 2D dislocation equation governing the displacements is coupled by the restoring forces that are determined by the parameterization of the generalized stacking fault energies. The Ritz variational method is presented to solve the dislocation equation and the trial solution is constituted by two arctan-type functions with two undetermined parameters. The core widths of partial dislocations are wider than that obtained in generalized Peierls-Nabarro model due to the consideration of discreteness of crystal.

On the Dynamics of Vortex Filaments and Their Core Structure

We give a brief review of the asymptotic theory of slender vortex filaments with emphases on (i) the choices of scalings and small parameters characterizing the physical problem,(ii) the key steps in the formulation of the theory and (iii) the assumptions and/or restrictions on the theory of Callegari and Ting (1978).We present highlights of an extension of the 1978 asymptotic theory:the analyses for core structures with axial variation.Making use of the physical insights gained from the analyses,we present a new derivation of the evolution equations for the core structure.The new one is simpler and straightforward and shows the physics clearly.

Enhancing electromagnetic wave absorption with core‐shell structured SiO_(2)@MXene@MoS_(2)nanospheres

Material composition and structural design are important factors influencing the electromagnetic wave(EMW)absorption performance of materials.To alleviate the impedance mismatch attributed to the high dielectric constant of Ti_(3)C_(2)T_(x)MXene,we have successfully synthesized core‐shell structured SiO_(2)@MXene@MoS_(2)nanospheres.This architecture,comprising SiO_(2)as the core,MXene as the intermediate layer,and MoS_(2)as the outer shell,is achieved through an electrostatic self‐assembly method combined with a hydrothermal process.This complex core‐shell structure not only provides a variety of loss mechanisms that effectively dissipate electromagnetic energy but also prevents self‐aggregation of MXene and MoS_(2)nanosheets.Notably,the synergistic combination of SiO_(2)and MoS_(2)with highly conductive MXene enables the suitable dielectric constant of the composites,ensuring optimal impedance matching.Therefore,the core‐shell structured SiO_(2)@MXene@MoS_(2)nanospheres exhibit excellent EMW absorption performance,featuring a remarkable minimum reflection loss(RL_(min))of−52.11 dB(2.4 mm).It is noteworthy that these nanospheres achieve an ultra‐wide effective absorption bandwidth(EAB)of 6.72 GHz.This work provides a novel approach for designing and synthesizing high‐performance EMW absorbers characterized by“wide bandwidth and strong reflection loss.”

Detecting the core of a network by the centralities of the nodes

Many networks exhibit the core/periphery structure.Core/periphery structure is a type of meso-scale structure that consists of densely connected core nodes and sparsely connected peripheral nodes.Core nodes tend to be well-connected,both among themselves and to peripheral nodes,which tend not to be well-connected to other nodes.In this brief report,we propose a new method to detect the core of a network by the centrality of each node.It is discovered that such nodes with non-negative centralities often consist in the core of the networks.The simulation is carried out on different real networks.The results are checked by the objective function.The checked results may show the effectiveness of the simulation results by the centralities of the nodes on the real networks.Furthermore,we discuss the characters of networks with the single core/periphery structure and point out the scope of the application of our method at the end of this paper.

ON CORE STRUCTURE PROPERTIES AND PEIERLS STRESS OF DISSOCIATED SUPERDISLOCATIONS IN ALUMINIDES:NiAl AND FeAl

The study of dislocation properties in B2 structure intermetallics NiAl and FeAl is crucial to understand their mechanical behaviors. In this paper, the core structure and Peierls stress of collinear dissociated （111）{110} edge superdislocations in NiAl and FeAl are investigated with the modified P-N dislocation equation. The generalized stacking fault energy curve along （111） direction in {110} slip plane contains two modification factors that can assure the antiphase energy and the unstable stacking fault energy to change independently. The results show that the core width of superpartials decreases with the increasing unstable stacking fault energy, and increases with the increasing antiphase boundary energy. The calculated Peierls stress of （111）{ 110） edge superdislocations in NiAl and FeAl are 475 MPa and 3042 MPa, respectively. The values of Peierls stress in NiAl is in accordance in magnitude with the experimental and the molecular statics simulations results.

Preparation of a p-n heterojunction BiFeO_3@TiO_2 photocatalyst with a core–shell structure for visible-light photocatalytic degradation

Magnetically separable bismuth ferrite(BiFeO3)nanoparticles were fabricated by a citrate self‐combustion method and coated with titanium dioxide(TiO2)by hydrolysis of titanium butoxide(Ti(OBu)4)to form BiFeO3@TiO2core-shell nanocomposites with different mass ratios of TiO2to BiFeO3.The photocatalytic performance of the catalysts was comprehensively investigated via photocatalytic oxidation of methyl violet(MV)under both ultraviolet and visible‐light irradiation.The BiFeO3@TiO2samples exhibited better photocatalytic performance than either BiFeO3or TiO2alone,and a BiFeO3@TiO2sample with a mass ratio of1:1and TiO2shell thickness of50-100nm showed the highest photo‐oxidation activity of the catalysts.The enhanced photocatalytic activity was ascribed to the formation of a p‐n junction of BiFeO3and TiO2with high charge separation efficiency as well as strong light absorption ability.Photoelectrochemical Mott-Schottky(MS)measurements revealed that both the charge carrier transportation and donor density of BiFeO3were markedly enhanced after introduction of TiO2.The mechanism of MV degradation is mainly attributed to hydroxyl radicals and photogenerated electrons based on energy band theory and the formation of an internal electrostatic field.In addition,the unique core-shell structure of BiFeO3@TiO2also promotes charge transfer at the BiFeO3/TiO2interface by increasing the contact area between BiFeO3and TiO2.Finally,the photocatalytic activity of BiFeO3@TiO2was further confirmed by degradation of other industrial dyes under visible‐light irradiation.

Reduced-temperature ordering of FePt nanoparticle assembled films by Fe30Pt70/Fe3O4 core/shell structure

In this paper, Fe30Pt70/Fe3O4 core/shell nanoparticles were synthesized by chemical routine and the layered polyethylenimine （PEI）-Fe30Pt70/Fe3O4 structure was constructed by molecule-mediated self-assembly technique. The dimension of core/shell structured nanoparticles was that of 4nm core and 2 nm shell. After annealing under a flow of forming gas （50%Ar2＋30%H2） for 1 h at or above 400℃, the iron oxide shell was reduced to Fe and diffused to Pt-rieh core, which leaded to the formation of L1. phase FePt at low temperature. The x-ray diffraction results and magnetic properties measurement showed that the chemical ordering temperature of Fe30Pt70/Fe3O4 core/shell nanoparticles assembly can be reduced to as low as 400℃. The sample annealed at 400℃ showed the eoereivity of 4KOe with the applied field of 1.5T. The core/shell structure was suggested to be an effective way to reduce the ordering temperature obviously.

Preparation and upconversion luminescence properties of LaF_3:Yb^(3 +),Er^(3 +) /SiO_2 nanocomposites with core /shell structure

LaF^3＋ Yb^3＋ , Er^3＋ nanoparticles were successfully synthesized using solvothermal treatment, and LaF^3＋ Yb^3＋ , Er^3＋/SiO2 core/shell nanoparticles were also prepared with reverse microemulsion technique. The crystal structure, morphology and photoluminescence properties of as-prepared core/shell nanoparticles were in- vestigated by X-ray diffraction, transmission electron microscopy and fluorescence spectrophotometer. The re- sults showed thatLaF^3＋ Yb^3＋ , Er^3＋ nanoparticles are of hexagonal structure and SiO2 shell is amorphous. The size ofLaF^3＋ Yb^3＋ , Er^3＋. nanoparticles is 13 nm and the LaF^3＋ Yb^3＋ , Er^3＋/SiO2 nanoparticles present clearly a core/shell structure with 12 nm shell thickness. The solubility of LaF^3＋ Yb^3＋ , Er^3＋ nanocrystals in water and the biocompatibility are both improved by the SiO2 shell. The upconversion luminescence spectra suggested that the SiO~ shell has small effect on the upconversion luminescence properties of the LaF^3＋ Yb^3＋ , Er^3＋ nanocrys- tals. The core/shell structure LaF^3＋ Yb^3＋ , Er^3＋ /SiO2. nanopartlcles are expected to be used in biological appli- cations.

High-Resolution Simulation and Analysis of the Mature Structure of a Polar Low over the Sea of Japan on 21 January 1997

This paper presents a high-resolution simulation of a remarkable polar low observed over the Sea of Japan on 21 January 1997 by using a 5-km mesh non-hydrostatic model MRI-NHM (Meteorological Research Institute Non-Hydrostatic Model). A 24-hour simulation starting from 0000 UTC 21 January 1997 successfully reproduced the observed features of the polar low such as the wrapping of western part of an initial E-W orientation vortex, the spiral-shaped bands, the cloud-free 'eye', and the warm core structure at its mature stage. The 'eye' of the simulated polar low was relatively dry, and was associated with a strong downdraft. A thermodynamic budget analysis indicates that the 'warm core' in the 'eye' region was mainly caused by the adiabatic warming associated with the downdraft. The relationship among the condensational diabatic heating, the vertical velocity, the convergence of the moisture flux, and the circulation averaged within a 50 km×50 km square area around the polar low center shows that they form a positive feedback loop, and this loop is not inconsistent with the CISK (Conditional Instability of the Second Kind) mechanism during the developing stage of the polar low.

COUPLED VIBRATION OF STRUCTURAL THIN-WALLED CORES

This paper presents an analysis of the coupled vibration of asymmetric core structures in tall buildings. The governing equation of free vibration and its corresponding eigenvalue problem, which is a set of equations for laterally flexural vibrations in two different directions coupled by a warping-St. Venant torsional vibration, are derived. Based on the Calerkin method, a generalized approximate method is developed for the analysis of coupled vibration and thus proposed for determining the natural frequencies and mode shapes of the structure in triply-coupled vibration. The results of the proposed method for the example structure show good agreement with those of the FEM analysis. The proposed method has been shown to provide a simple and rapid, yet accurate, means for coupled vibration analysis of core structures.

Absorption performance of DMSA modified Fe_3O_4@SiO_2 core/shell magnetic nanocomposite for Pb^(2+) removal

The purpose of this study is to explore the adsorption performance of meso-2,3-dimercaptosuccinic acid(DMSA)modified Fe3O4@SiO2 magnetic nanocomposite(Fe3O4@SiO2@DMSA)for Pb2+ions removal from aqueous solutions.The effects of solution pH,initial concentration of Pb2+ions,contact time,and temperature on the amount of Pb2+adsorbed were investigated.Adsorption isotherms,adsorption kinetics,and thermodynamic analysis were also studied.The results showed that the maximum adsorption capacity of the Fe3O4@SiO2@DMSA composite is 50.5 mg/g at 298 K,which is higher than that of Fe3O4 and Fe3O4@SiO2 magnetic nanoparticles.The adsorption process agreed well with Langmuir adsorption isotherm models and pseudo second-order kinetics.The thermodynamic analysis revealed that the adsorption was spontaneous,endothermic and energetically driven in nature.

CO_(2) hydrogenation selectivity shift over In‐Co binary oxides catalysts:Catalytic mechanism and structure‐property relationship

The hydrogenation of CO_(2) into methanol has attracted much attention and In_(2)O_(3) is a promising catalyst.Introducing metal elements into In_(2)O_(3)(M/In_(2)O_(3))is one of the main strategies to improve its performance.However,its mechanism and active sites remain unclear and need to be further elucidated.Here,the noble‐metal‐free In_(x)‐Co_(y) oxides catalysts were prepared.Much‐improved performance and obvious product selectivity shift were observed.The optimized catalyst(In_(1)‐Co_(4))(9.7 mmol g_(cat)^(–1) h^(–1))showed five times methanol yields than pure In_(2)O_(3)(2.2 mmol g_(cat)^(–1) h^(–1))(P=4.0 MPa,T=300°C,GHSV=24000 cm^(3)_(STP) g_(cat)^(–1) h^(–1),H_(2):CO_(2)=3).And the cobalt‐catalyzed CO_(2) methanation activity was suppressed,although cobalt was most of the metal element.To unravel this selectivity shift,detailed catalysts performance evaluation,together with several in‐situ and ex‐situ characterizations,were employed on cobalt and In‐Co for comparative study.The results indicated CO_(2) hydrogenation on cobalt and In‐Co catalyst both followed the formate pathway,and In‐Co reconstructed and generated a surface In_(2)O_(3)‐enriched core‐shell‐like structure under a reductive atmosphere.The enriched In_(2)O_(3) at the surface significantly enhanced CO_(2) adsorption capacity and well stabilized the intermediates of CO_(2) hydrogenation.CO_(2) and carbon‐containing intermediates adsorbed much stronger on In‐Co than cobalt led to a feasible surface C/H ratio,thus allowing the*CH_(3)O to desorb to produce CH_(3)OH instead of being over‐hydrogenated to CH_(4).

Co/Ni dual-metal embedded in heteroatom doped porous carbon core-shell bifunctional electrocatalyst for rechargeable Zn-air batteries

Rational construction of highly efficient and cheap bifunctional electrocatalysts to boost both oxygen evolution reaction(OER)and oxygen reduction reaction(ORR)is extremely essential for the wide application of rechargeable metal-air battery.In this work,we design a core-shell structural catalyst of CoNi dual-metal embedded in nitrogen doped porous carbon(NPC,CoNi@NPC),which is developed via the pyrolysis of CoNiMOFs,assisting by mesoporous SiO_(2) to effectively inhibit the aggregation of metal sites.Consequently,the asprepared CoNi@NPC manifests good ORR activity with half-wave potential up to 0.77 V.Specifically,the CoNi@NPC gives a very low OER over-potential of merely 101 mV in 6 M KOH along with high stability,outperforming the commercial Pt/C-RuO_(2).Moreover,the home-made zinc air battery with CoNi@NPC air cathode demonstrates excellent stability over long-term charging–discharging test,and delivers the maximum power density of 224 mW cm^(-2).The enhanced high performance of CoNi@NPC bifunctional catalyst for both ORR and OER can be ascribed to its unique core-shell structure and strong synergistic effect between the dual-bimetal active sites and the heteroatom doped carbon.This work opens a new avenue for the rational design of nonprecious metal bifunctional catalysts for rechargeable metal-air battery.

Reaction of Mo(CO)_6 with Alkoxide: Synthesis and Structure of the Mo(0)-OR Complex [Et_4N]_3[Mo_2(CO)_6(μ-OC_6H_4OCH_2C_6H_5)_3]

The reaction of molybdenum hexacarbonyl with C6H5CH2OC6H4ONa and Et4NBr in CH3CN at 60 ℃ afforded the di-nuclear Mo（0） compound [Et4N]3[Mo2（CO）6（μ-OC6H4OCH2C6H5）3] 1. 1 crystallizes in monoclinic, space group P21/c with a = 15.359（2）, b = 18.378（3）, c = 24.952（2） A, β = 102.268（4）°, V = 6882.3（1 6） A^3, Mr = 1348.34, Z = 4, Dc = 1.301 g/cm^3, F（000） = 2832 and μ= 0.424 mm^-1 The final R = 0.0606 and wR = 0.1552 for 9396 observed reflections （I 〉 2σ（I））. I contains a [Mo2O3]^3 core in triangular bi-pyralnidal configuration and each Mo atom adopts a distorted octahedral geometry with three carbon atoms from carbonyls and three ,μ-O atoms from C6H5CH2OC6H4O^- bridging ligands. The Mo…Mo distance is 3.30（8） A, indicating no metalmetal bonding. A formation pathway via forming a di-molybdenum（0） di-bridging OR compound [Mo2（μ-OR）2（CO）8]2 has been figured out and the reaction of Mo（CO）6 with alkoxide has also been discussed.

疏水性Silicalite-1外壳增强Cu/SAPO-34的选择性催化还原低温水热稳定性

采用二次生长法合成具有不同氟含量的Cu/SAPO-34@Silicalite-1核壳结构复合分子筛,通过调节晶种导向液中的氟含量,来调节核壳结构的疏水性,并利用X射线衍射、热重分析仪、扫描电子显微镜和微反等手段表征样品的结构和低温水热稳定性。结果表明:与Cu/SAPO-34核相比较,核壳结构分子筛具有更大的比表面积,更高的活性Cu^(2+)离子相对比例和强酸性比例,更好的疏水性和脱硝活性;添加氟化铵后增加了Cu/SAPO-34的结晶度,拓宽了Cu/SAPO-34的脱硝温度窗口,150℃湿烟气的脱硝率从82%提高到94%。

Influence of particle size on the breaking of aluminum particle shells

Rupturing the alumina shell(shell-breaking)is a prerequisite for releasing energy from aluminum powder.Thermal stress overload in a high-temperature environment is an important factor in the rupture of the alumina shell.COMSOL Multiphysics was used to simulate and analyze the shell-breaking response of micron-scale aluminum particles with different particle sizes at 650℃in vacuum.The simulation results show that the thermal stability time and shell-breaking response time of 10μm–100μm aluminum particles are 0.15μs–11.44μs and 0.08μs–3.94μs,respectively.They also reveal the direct causes of shell breaking for aluminum particles with different particle sizes.When the particle size is less than 80μm,the shell-breaking response is a direct result of compressive stress overload.When the particle size is between80μm and 100μm,the shell-breaking response is a direct result of tensile stress overload.This article provides useful guidance for research into the energy release of aluminum powder.

Atomistic Simulation of Undissociated 60°Basal Dislocation in Wurtzite GaN.

We have carried out computer atomistic simulations, based on an efficient density functional based tight binding method, to investigate the core configurations of the 60°basal dislocation in GaN wurtzite. Our energetic calculations, on the undissociated dislocation, demonstrate that the glide configuration with N polarity is the most energetically favorable over both the glide and the shuffle sets.

Microwave Absorption of Crystalline Fe/MnO@C Nanocapsules Embedded in Amorphous Carbon

Crystalline Fe/MnO@C core–shell nanocapsules inlaid in porous amorphous carbon matrix(FMCA)was synthesized successfully with a novel confinement strategy.The heterogeneous Fe/MnO nanocrystals are with approximate single-domain size which gives rise to natural resonance in 2–18 GHz.The addition of MnO2 confines degree of graphitization catalyzed by iron and contributes to the formation of amorphous carbon.The heterogeneous materials composed of crystalline–amorphous structures disperse evenly and its density is significantly reduced on account of porous properties.Meanwhile,adjustable dielectric loss is achieved by interrupting Fe core aggregation and stacking graphene conductive network.The dielectric loss synergistically with magnetic loss endows the FMCA enhanced absorption.The optimal reflection loss(RL)is up to−45 dB,and the effective bandwidth(RL<−10 dB)is 5.0 GHz with 2.0 mm thickness.The proposed confinement strategy not only lays the foundation for designing high-performance microwave absorber,but also offers a general duty synthesis method for heterogeneous crystalline–amorphous composites with tunable composition in other fields.

Decellularized Extracellular Matrix Containing Electrospun Fibers for Nerve Regeneration:A Comparison Between Core–Shell Structured and Preblended Composites

Advanced biomaterial-based strategies for treatment of peripheral nerve injury require precise control over both topological and biological cues for facilitating rapid and directed nerve regeneration.As a highly bioactive and tissue-specifc natural material,decellularized extracellular matrix(dECM)derived from peripheral nerves(decellularized nerve matrix,DNM)has drawn increasing attention in the feld of regenerative medicine,due to its outstanding capabilities in facilitating neurite outgrowth and remyelination.To induce and maintain sufcient topological guidance,electrospinning was conducted for fabrication of axially aligned nanofbers consisting of DNM and poly(ε-caprolactone)(PCL).Core–shell structured fbers were prepared by coaxial electrospinning using DNM as the shell and PCL as the core.Compared to the aligned electrospun fbers using preblended DNM/PCL,the core–shell structured fbers exhibited lower tensile strength,faster degradation,but considerable toughness for nerve guidance conduit preparation and relatively intact fbrous structure after long-term degradation.More importantly,the full DNM surface coverage of the aligned core–shell fbers efectively promoted axonal extension and Schwann cells migration.The DNM contents further triggered neurite bundling and myelin formation toward nerve fber maturation and functionalization.Herein,we not only pursue a multi-functional scafold design for nerve regeneration,a detailed comparison between core–shell structured and preblended electrospinning of DNM/PCL composites was also provided as an applicable paradigm for advanced tissue-engineered strategies using dECM-based biomaterials.