Micro-structure and Macro-performance:Surface Layer Evolution of Concrete under Long-term Exposure in Harsh Plateau Climate

We conducted a series tests on surface layers of plateau concrete at the ages of 180 and 540 days,including the most superficial cement paste,the 5 mm thick surface mortar,and the 50 mm thick surface concrete.Thermogravimetry and nitrogen absorption porosimetry on cement past,mercury intrusion porosimetry on mortar,and microhardness test on interface transition zone between mortar and coarse aggregate were conducted to evaluate the hydration degree and characterize the micro-structure.Whilst,tests for the rebound strength,abrasion resistance,and chloride ion impenetrability of concrete were conducted to assess the macro-performance.The experimental results show that,affected by the harsh plateau climate,outward surfaces have lower hydration degrees and worse pore structure than inward surfaces.As the hydration of concrete surface is ongoing after the age of 180 days,both the micro-structure and the macro-performance are continuously improved.In the long-term,either the orientation or the depth towards surface does not significantly affect concrete performance.Surface carbonation brings positive effects on mechanical properties but negative effects on the durability.Additionally,standard test result of chloride ion impenetrability is found significantly affected by the atmospheric pressure.For a same batch of concrete,charge passed in plateau regions is obviously lower than that in common regions.

Unraveling structure and performance of protein a ligands at liquid–solid interfaces: A multi-techniques analysis

Oriented ligand immobilization is one of the most effective strategies used in the design and construction of a high-capacity protein A chromatography. In this work, cysteine was introduced as anchoring sites by substituting a specific residue on Helix Ⅰ, Ⅱ, and at C-terminus of antibody binding domain Z from protein A, respectively, to investigate structural evolution and binding behavior of protein A ligands at liquid-solid interfaces. Among the three affinity dextran-coated Fe_(3)O_(4) magnetic nanoparticles(Fe_(3)O_(4)@Dx MNPs), affinity MNPs with the immobilized ligand via N11C on Helix Ⅰ(Fe_(3)O_(4)@Dx-Z_(1) MNPs) had the highest helical content, and MNPs with the immobilized ligand via G29C on Helix Ⅱ(Fe_(3)O_(4)@Dx-Z_(2) MNPs) had the lowest helical content at the same pHs. It was attributed to less electrostatic attraction of ligand to negatively charged surface on Fe_(3)O_(4)@Dx-Z_(1) MNPs because of less positive charged residues on Helix Ⅰ(K6) than Helix Ⅱ(R27/K35). Among the three affinity MNPs, moreover, the highest affinity to immunoglobulin G(IgG) binding was observed on Fe_(3)O_(4)@Dx-Z_(1) MNPs in isothermal titration calorimetry measurement, further validating greater structural integrity of the ligand on Fe_(3)O_(4)@Dx-Z_(1) MNPs. Finally,the study of IgG binding on MNPs and 96-well plates showed that anchoring sites for ligand immobilization had distinct influences on IgG binding and IgG-mediated antigen binding. This work illustrated that anchoring sites of the ligands had a striking significance for the molecular structure of the ligand at liquid-solid interfaces and raised an important implication for the design and optimization of protein A chromatography and protein A-based immunoassay analysis.

A METHOD FOR THE ANALYSIS OF DYNAMIC RESPONSE OF STRUCTURE CONTAINING NON-SMOOTH CONTACTABLE INTERFACES

A novel single-step method is proposed for the analysis of dynamic response of visco-elastic structures containing non-smooth contactable interfaces. In the method, a two-level algorithm is employed for dealing with a nonlinear boundary condition caused by the dynamic contact of interfaces. At the first level, an explicit method is adopted to calculate nodal displacements of global viscoelastic system without considering the effect of dynamic contact of interfaces and at the second level, by introducing contact conditions of interfaces, a group of equations of lower order is derived to calculate dynamic contact normal and shear forces on the interfaces. The method is convenient and efficient for the analysis of problems of dynamic contact. The accuracy of the method is of the second order and the numerical stability condition is wider than that of other explicit methods.

Effects of Yttrium on the Microstructures and Interfaces in a Low Expansion Superalloy

The forms and structures of the phases in Fe-Ni-Co-Nb-Ti-Si low expansion superal-loys have been studied using analytical electron microscopy, high resolution electron microscopy, chemical phase analysis, X-ray diffraction, etc. The effects of yttrium on the microstructures and properties in the superalloys have also been investigated. The results reveal that trace yttrium mainly located in the platelet precipitates makes the crystal structure changed. The platelet precipitates become smaller, denser and rather homogeneous with appropriate yttrium addition. Compared with the conventional low expansion superalloy, the misfit of the platelet phase with the matrix in the yttrium-containing low expansion superalloy decreases from 0.7% to 0.07%, which indicates very low stress at the interface.

Directly Determining the Interface Structure and Band Offset of a Large-Lattice-Mismatched CdS/CdTe Heterostructure

The CdS/CdTe heterojunction plays an important role in determining the energy conversion efficiency of CdTe solar cells.However,the interface structure remains unknown,due to the large lattice mismatch between CdS and CdTe,posing great challenges to achieving an understanding of its interfacial effects.By combining a neuralnetwork-based machine-learning method and the stochastic surface walking-based global optimization method,we first train a neural network potential for CdSTe systems with demonstrated robustness and reliability.Based on the above potential,we then use simulated annealing to obtain the optimal structure of the CdS/CdTe interface.We find that the most stable structure has the features of both bulks and disorders.Using the obtained structure,we directly calculate the band offset between CdS and CdTe by aligning the core levels in the heterostructure with those in the bulks,using one-shot first-principles calculations.Our calculated band offset is 0.55 eV,in comparison with 0.70 eV,obtained using other indirect methods.The obtained interface structure should prove useful for further study of the properties of CdTe/CdS heterostructures.Our work also presents an example which is applicable to other complex interfaces.

EFFECTS OF BRAZING ATMOSPHERES ON INTERFACIAL MICROSTRUCTURE BETWEEN DIAMOND GRITS AND BRAZING ALLOY

The samples of brazed diamond grits with NiCr brazing alloy are prepared in vacuum and argon gas. The microstructures are analyzed with scanning electron microscope （SEM）, energy dispersive X-ray spectroscopy （EDS） and X-ray diffraction（XRD）. The effects of brazing atmospheres on the as-brazed NiCr brazing alloy composite structures and interracial microstructure are studied between diamond grits and brazing alloy. Results show that： （1） There are different composite structures of as-brazed NiCr brazing alloy under different oxygen partial pressures in vacuum and argon gas. B203 exists on the surface of the brazed samples under argon gas furnace brazing. It indicates that oxygen plays an important role in the resultants of as-brazed NiCr brazing alloy during the brazing process. （2） There are different interfacial microstructures in different brazing atmospheres, but the main reaction product is chromium carbides. The chromium carbides in argon gas furnace brazing grow in a disordered form, but those in vacuum furnace brazing grow radiated. And the scale of grains in argon gas is smaller than those in vacuum.

具有低噪声及高线性度的高性能MOCVD-SiN_(x)/AlN/GaN毫米波MIS-HEMTs

文章在超薄势垒AlN/GaN异质结构上采用金属有机化学气相沉积(MOCVD)原位生长SiN_(x)栅介质,成功制备了高性能的SiN_(x)/AlN/GaN金属-绝缘体-半导体高电子迁移率晶体管(MIS-HEMTs)。深能级瞬态谱(DLTS)技术测试SiN_(x)/AlN的界面信息,显示其缺陷能级深度为0.236 eV,俘获截面为3.06×10^(-19)cm^(-2),提取的界面态密度为10^(10)~10^(12)cm^(-2)eV^(-1),表明MOCVD原位生长的SiN_(x)可以有效降低界面态。同时器件表现出优越的直流、小信号和噪声性能。栅长为0.15μm的器件在2 V的栅极电压(Vgs)下具有2.2 A/mm的最大饱和输出电流,峰值跨导为506 mS/mm,最大电流截止频率(fT)和最大功率截止频率(fMAX)分别达到了65 GHz和123 GHz,40 GHz下的最小噪声系数(NFmin)为1.07 dB,增益为9.93 dB。Vds=6 V时对器件进行双音测试,器件的三阶交调输出功率(OIP3)为32.6 dBm,OIP3/Pdc达到11.2 dB。得益于高质量的SiN_(x)/AlN界面,SiN_(x)/AlN/GaN MISHEMT显示出了卓越的低噪声及高线性度,在毫米波领域具有一定的应用潜力。

Monolithic approach to thermal fluid-structure interaction withnonconforming interfaces

This paper presents a monolithic approach to the thermal fluidstructure interaction （FSI） with nonconforming interfaces. The thermal viscous flow is governed by the Boussinesq approximation and the incompressible NavierStokes equations. The motion of the fluid domain is accounted for by an arbitrary LagrangianEulerian （ALE） strategy. A pseudosolid formulation is used to manage the deformation of the fluid do main. The structure is described by the geometrically nonlinear thermoelastic dynamics. An efficient data transfer strategy based on the Gauss points is proposed to guarantee the equilibrium of the stresses and heat along the interface. The resulting strongly coupled set of nonlinear equations for the fluid, solution procedure. A numerical example efficiency of the methodology. structure, and heat is solved by a monolithic is presented to demonstrate the robustness and

对MIS结构热弛豫时间的分析计算

对MIS(金属-绝缘层-半导体)结构从深耗尽过渡至强反型状态所需的热弛豫时间进行了研究。通过建立较教科书更精确的模型,对热弛豫时间τth与深耗尽时耗尽区宽度x d0、强反型时耗尽区最大宽度x dm、耗尽区内少子净产生率G和掺杂浓度N D等关键物理量之间的关联进行了推导,并基于MEDICI平台对推导结果完成了仿真验证,从而加强了学生对半导体表面效应的理解,也利于他们未来从事半导体方面的创新研究。

Graphene Aerogel Composites with Self‑Organized Nanowires‑Packed Honeycomb Structure for Highly Efficient Electromagnetic Wave Absorption

With vigorous developments in nanotechnology,the elaborate regulation of microstructure shows attractive potential in the design of electromagnetic wave absorbers.Herein,a hierarchical porous structure and composite heterogeneous interface are constructed successfully to optimize the electromagnetic loss capacity.The macro–micro-synergistic graphene aerogel formed by the ice template‑assisted 3D printing strategy is cut by silicon carbide nanowires(SiC_(nws))grown in situ,while boron nitride(BN)interfacial structure is introduced on graphene nanoplates.The unique composite structure forces multiple scattering of incident EMWs,ensuring the combined effects of interfacial polarization,conduction networks,and magnetic-dielectric synergy.Therefore,the as-prepared composites present a minimum reflection loss value of−37.8 dB and a wide effective absorption bandwidth(EAB)of 9.2 GHz(from 8.8 to 18.0 GHz)at 2.5 mm.Besides,relying on the intrinsic high-temperature resistance of SiC_(nws) and BN,the EAB also remains above 5.0 GHz after annealing in air environment at 600℃ for 10 h.

Resistive switching behavior and mechanism of HfO_(x) films with large on/off ratio by structure design

Different bilayer structures of HfO_(x)/Ti(TiO_(x)) are designed for hafnium-based memory to investigate the switching characteristics. The chemical states in the films and near the interface are characterized by x-ray photoelectron spectroscopy,and the oxygen vacancies are analyzed. Highly improved on/off ratio(~104) and much uniform switching parameters are observed for bilayer structures compared to single layer HfO_(x) sample, which can be attributed to the modulation of oxygen vacancies at the interface and better control of the growth of filaments. Furthermore, the reliability of the prepared samples is investigated. The carrier conduction behaviors of HfO_(x)-based samples can be attributed to the trapping and de-trapping process of oxygen vacancies and a filamentary model is proposed. In addition, the rupture of filaments during the reset process for the bilayer structures occur at the weak points near the interface by the recovery of oxygen vacancies accompanied by the variation of barrier height. The re-formation of fixed filaments due to the residual filaments as lightning rods results in the better switching performance of the bilayer structure.

A Modified Model for Soil–Structure Interface Considering Random Damage of Mesoscopic Contact Elements

The interaction between soil and marine structures like submarine pipeline/pipe pile/suction caisson is a complicated geotechnical mechanism process.In this study,the interface is discretized into multiple mesoscopic contact elements that are damaged randomly throughout the shearing process due to the natural heterogeneity.The evolution equation of damage variable is developed based on the Weibull function,which is able to cover a rather wide range of distribution shapes by only two parameters,making it applicable for varying scenarios.Accordingly,a statistical damage model is established by incorporating Mohr–Coulomb strength criterion,in which the interfacial residual strength is considered whereby the strain softening behavior can be described.A concept of“semi-softening”characteristic point on shear stress–displacement curve is proposed for effectively modeling the evolution of strain softening.Finally,a series of ring shear tests of the interfaces between fine sea sand and smooth/rough steel surfaces are conducted.The predicted results using the proposed model are compared with experimental data of this study as well as some results from existing literature,indicating that the model has a good performance in modeling the progressive failure and strain softening behavior for various types of soil–structure interfaces.

Progress in molecular-simulation-based research on the effects of interface-induced fluid microstructures on flow resistance

In modern chemical engineering processes, solid interface involvement is the most important component of process intensification techniques, such as nanoporous membrane separation and heterogeneous catalysis. The fundamental mechanism underlying interfacial transport remains incompletely understood given the complexity of heterogeneous interfacial molecular interactions and the high nonideality of the fluid involved. Thus, understanding the effects of interface-induced fluid microstructures on flow resistance is the first step in further understanding interfacial transport. Molecular simulation has become an indispensable method for the investigation of fluid microstructure and flow resistance. Here, we reviewed the recent research progress of our group and the latest relevant works to elucidate the contribution of interface-induced fluid microstructures to flow resistance.We specifically focused on water, ionic aqueous solutions, and alcohol–water mixtures given the ubiquity of these fluid systems in modern chemical engineering processes. We discussed the effects of the interfaceinduced hydrogen bond networks of water molecules, the ionic hydration of ionic aqueous solutions, and the spatial distributions of alcohol and alcohol–water mixtures on flow resistance on the basis of the distinctive characteristics of different fluid systems.

A STUDY OF THE STRUCTURAL LAYERS OF COUPLING AGENTS AND THE MICROSCOPIC RHEOLOGY IN THE INTERFACES OF GF/UP SYSTEMS

The coupling agents content and thickness on glass fiber (GF) surfaces which have been treated with silanes and titanates under different conditions are tested by means of XRF (X-Ray Fluorescent spectrometry). And the rheological characteristics of the dispersed systems prepared from the above glass fibers combined with unsaturated polyester resin (UP) are discussed. The results show that the rigidity of the internal layers of silane coupling agent absorbed by glass surfaces is greater than the one of the external layers; while the effect of the titanate coupling agents on the rheolo- gical characteristics of the system is approximately the same in each structural layer, that is due to the fact that both the internal and external layers of titanates on glass surfaces have the similar flexible structures.

Dye-sensitized solar cells: Atomic scale investigation of interface structure and dynamics

Recent progress in dye-sensitized solar cells （DSC） research is reviewed, focusing on atomic-scale investigations of the interface electronic structures and dynamical processes, including the structure of dye adsorption onto Ti02, ultrafast electron injection, hot-electron injection, multiple-exciton generation, and electron-hole recombination. Advanced exper- imental techniques and theoretical approaches are briefly summarized, and then progressive achievements in photovoltaic device optimization based on insights from atomic scale investigations are introduced. Finally, some challenges and oppor- tunities for further improvement of dye solar cells are presented.

FINE STRUCTURES OF BOTH INTERFACES AND INTERFACIAL REACTION PRODUCTS

The characteristic of interface depending on the atomic structure exerts an inportant,and sometime controlling,influence on performance of the interacial materials. The present paper reviews the main studies on fine structure of both the materials inter- faces and interfacial reaction products in semiconductor uperlattice,metal multilayer ceram- ics and composite materials by mean of selected area electron doffraction patterns and high resolution electron microscopy. The following features of interfaces are reviewed:the orientation relationships;the char- acteristic of steps,facets and ronghness of interfaces;atomic bonding across the interface;the degree of coherency,the structure of misfit dislocations and elastic relaxations at the inter- faces:the presence of defects at the onterfaces:the structure of the interfacial reaction prod- ucts as well as the reaction kinetics and reaetion mechanism.

Constitutive model of disturbed soil-structure interface within mining subsidence areas

The characteristics of a disturbed soil-structure interface were studied based on the variation regularities of the disturbed soil within its mining subsidence area using direct shear tests.The effects of the initial moisture content on the shear strength parameters of the soil-structure interfaces were analyzed.The results indicate that the cohesion of the interface initially increased and then decreased as the initial moisture content increased.In addition,the friction angle of the interface decreased as the initial moisture content increased.A constitutive model of the disturbed soil-structure interface,a rigid-plastic model based on the initial void ratio and saturability(VSRP) model,was established based on the results.In order to validate this model,a finite element analysis of DRS-1 direct shear tests was conducted.The finite element model calculations coincided with the results of the DRS-1 direct shear tests.The proposed model also reflected the nonlinear features of the soil-structure interface.

THE THERMAL STRESS ANALYSIS OF THE INTERFACIAL EDGE IN DISSIMILAR STRUCTURE AND THE EFFECTS OF GEOMETRIC SHAPE

This paper describes the analysis of the thermal stress concentration and the effects of geometrical shape in the interfacial edge by FEM. It is shown that the elevated stress in a dissimilar material caused by temperature is only restricted in a minor region of the interfacial edge, where the stress peak value and and the stress gradient are high. It is also found that narrowing the boundary angle can effectively reduce the peak value of stress components on the interfacial layer, especially the peeling stress σ y , which is a condition of the debonding failure in the interface.θ=60, an obvious variation, proves that selecting a reasonable edge geometrical shape helps to reduce the value of the maximum stress. At last the methods of relaxing stress concentration and effects of the geometric blunt are also discussed.

Properties and interfacial microstructure of cement-based materials with composite micro-grains

Silica fume, fly ash and nano-fiber mineral materials (NR powder) are employed to incorporate into cement-based materials. According to the grain grading mathematical model of cement-based materials, two packing systems, namely, spherical grading system and nano-fiber reinforced system were designed. Properties and interfacial microstructure of the two systems were studied according to secondary interface theory. It was shown that nano-fiber mineral materials can improve the grain grading of the admixture, increase the density of the system, improve the microstructure of the interface and the hardened paste, and enhance the uniformity of cement-based materials mixed with composite micro-grains and greatly increase their wearable rigidity and flexure strength. In this paper, two kinds of interface models, including spherical grain model and nano-fiber reinforced interface model of the cement-based materials mixed with composite micro-grains, were brought forward.

Impact of the Opto-Geometric Parameters on the Band Diagram and Transmission and Reflection Spectrum of the Bragg Structure

Knowledge of the band gap and transmission and reflection spectrum of a photonic crystal is essential elements for their design. A graphical interface that quickly determines the banding pattern and spectrum based on the Plane Wave Method (PWM) and coupled modes method (CMM) respectively is created. It is used to explore the behavior of a Bragg structure with the ability to easily vary the important parameters such as refractive indices, number and thickness of layers.