Advances in two-dimensional heterostructures by mono-element intercalation underneath epitaxial graphene

Two-dimensional (2D) materials have displayed many remarkable physical properties, including 2D superconductivity, magnetism, and layer-dependent bandgaps. However, it is difficult for a single 2D material to meet complex practical requirements. Heterostructures obtained by vertically stacking different kinds of 2D materials have extensively attracted researchers’ attention because of their rich electronic features. With heterostructures, the constraints of lattice matching can be overcome. Meanwhile, high application potential has been explored for electronic and optoelectronic devices, including tunneling transistors, flexible electronics, and photodetectors. Specifically, graphene-based van der Waals heterostructures (vdWHs) by intercalation are emerging to realize various functional heterostructures-based electronic devices. Intercalating atoms under epitaxial graphene can efficiently decouple graphene from the substrate, and is expected to realize rich novel electronic properties in graphene. In this study, we systematically review the progress of the mono-element intercalation in graphene-based vdWHs, including the intercalation mechanism, intercalation-modified electronic properties, and the practical applications of 2D intercalated heterostructures. This work would inspire edge-cutting ideas in the scientific frontiers of 2D materials.     

Preparation of copper ferrite by sol–gel method and the synergistic catalytic for the thermal decomposition of ammonium perchlorate

Journal of Sol-Gel Science and Technology - In the present work, copper ferrite was prepared by a simple and mild sol–gel method followed by low-temperature calcination, and characterized by...     

毛细管电泳法高效筛选8-氧代鸟嘌呤DNA糖基化酶的核酸适配体

8-氧代鸟嘌呤DNA糖基化酶(OGG1)是人体中重要的功能蛋白,在修复DNA氧化性损伤过程中起关键作用。氧化应激等引起的氧化损伤易导致炎症反应的发生,对OGG1的抑制可以一定程度上起到缓解作用;对癌细胞OGG1的抑制有望作为癌症治疗的新方法。目前的研究多集中于小分子对OGG1功能的影响和调控,而OGG1的适配体筛选尚未见报道。作为功能配体,适配体具有合成简单、高亲和力及高特异性等优点。该文筛选了OGG1的核酸适配体,结合毛细管电泳高效快速的优点建立了两种基于毛细管电泳-指数富集进化(CE-SELEX)技术的筛选方法:同步竞争法和多轮筛选法。同步竞争法利用单链结合蛋白(SSB)与核酸库中单链核酸的强结合能力,与目标蛋白OGG1组成竞争体系,并通过增加SSB浓度来增加竞争筛选压力,以去除与OGG1弱结合的核酸序列,一步筛选即可获得与OGG1强结合的核酸序列。多轮筛选法在相同孵育条件和电泳条件下,经3轮筛选获得OGG1的核酸适配体。比较两种筛选方法的筛选结果,筛选结果中频次最高的3条候选核酸适配体序列一致,其解离常数(K_D)值在1.71~2.64 μmol/L之间。分子对接分析结果表明候选适配体1(Apt 1)可能与OGG1中具有修复氧化性损伤功能的活性口袋结合。通过对两种筛选方法的对比,证明同步竞争法更加快速高效,对其他蛋白核酸适配体筛选方法的选择具有一定的指导意义。得到的适配体有望用于OGG1功能调控,以抑制其修复功能。     

Thermo-mechanical large deformation response and constitutive modeling of viscoelastic polymers over a wide range of strain rates and temperatures

A phenomenological one-dimensional constitutive model, characterizing the complex and highly nonlinear finite thermo-mechanical behavior of viscoelastic polymers, is developed in this investigation. This simple differential form model is based on a combination of linear and nonlinear springs with dashpots, incorporating typical polymeric behavior such as shear thinning, thermal softening at higher temperatures and nonlinear dependence on deformation and loading rate. Another model, of integral form, namely the modified superposition principle (MSP), is also modified further and used to show the advantage of the newly developed model over MSP. The material parameters for both models are determined for Adiprene-L100, a polyurethane based rubber. The constants once determined are then utilized to predict the behavior under strain rate jump compression, multiple step stress relaxation loading experiment and free end torsion experiments. The new constitutive model shows very good agreement with the experimental data for Adiprene-L100 for the various finite loading paths considered here and provides a flexible framework for a three-dimensional generalization.     

A USM-Θ two-phase turbulence model for simulating dense gas-particle flows

A second-order moment two-phase turbulence model for simulating dense gas-particle flows (USM- model), combining the unified second-order moment two-phase turbulence model for dilute gas-particle flows with the kinetic theory of particle collision, is proposed. The interaction between gas and particle turbulence is simulated using the transport equation of two-phase velocity correlation with a two-time-scale dissipation closure. The proposed model is applied to simulate dense gas-particle flows in a horizontal channel and a downer. Simulation results and their comparison with experimental results show that the model accounting for both anisotropic particle turbulence and particle-particle collision is obviously better than models accounting for only particle turbulence or only particle-particle collision. The USM- model is also better than the k--kp- model and the k--kp-p- model in that the first model can simulate the redistribution of anisotropic particle Reynolds stress components due to inter-particle collision, whereas the second and third models cannot.The project supported by the Special Funds for Major State Basic Research of China (G-1999-0222-08), the National Natural Science Foundation of China (50376004), and Ph.D. Program Foundation, Ministry of Education of China (20030007028)     

RESEARCH ON ELECTROMAGNETIC RADIATION DURING THE EXPLOSION PROGRESS OF COMPOSITION B EXPLOSIVES$^{\bf 1)}$

炸药爆炸过程中产生明显的电磁辐射干扰在很多领域引起了重视, 爆炸产生电磁辐射的机理和理论模型都不成熟, 实验仍然是研究这一现象的重要手段. 本文设计了不同质量的B炸药爆炸电磁辐射实验, 测量了爆炸整个过程中不同时刻的电磁辐射信号. 通过小波分析方法对实测信号进行处理, 得到真实信号和信号的时频特点, 小波分析得到真实信号的频谱主要分布在0$\sim$50 kHz. 利用自主开发的EXPLOSION-3D软件对实验工况进行数值模拟, 得到爆炸过程不同时刻流场的特点. 对比实验结果和数值模拟结果得出: 第一个脉冲信号是由B炸药爆轰产生的高温高压等离子体直接产生的电磁脉冲; 第二个脉冲信号是由地面反射的冲击波追上前沿冲击波, 空气冲击波阵面处形成的等离子体产生的电磁脉冲; 第三个脉冲信号是冲击波撞击测量线圈引起的无效信号. 其中, 第一个电磁脉冲幅值与当量的1/3次方基本呈线性关系, 其到达时间对炸药药量不敏感; 第二个电磁脉冲出现的时间与炸药的当量成指数关系, 药量越大, 出现时间越晚. 通过对第二个脉冲信号的分析, 得出了冲击波反射形成电磁脉冲信号时的爆炸波流场特征, 为后续相关理论机理研究提供了验证数据.     

ELECTROELASTIC FIELD FOR AN IMPERMEABLE ANTI-PLANE SHEAR CRACK IN A PIEZOELECTRIC CERAMICS PLATE

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Transient response of a finite crack in an orthotropic strip under the in-plane shear impact

The transient response of a central crack in an orthotropic strip under the in-plane shear impact loading is studied by using the dual integral equation method proposed by Copson and Sih. The general formula for the shear stress intensity factor near the crack tip is derived. Numerical results of with in various cases are obtained by solving the second kind Fredholm integral equation and by performing the inverse Laplace transform.     

陕北晋西砂黄土的胶结物与胶结作用研究

在野外调查的基础上,采用SEM、XRD、土壤物理和土壤化学等方法,对陕北晋西12个县市的48个马兰黄土样品进 行了全分散法粒度组成测定、聚集体分析以及黄土胶结物组成的测试分析。结果表明,砂黄土中的粘土矿物和超细碳酸盐、 游离氧化物和有机质等胶结物质主要是以聚集体包膜的形式存在于碎屑颗粒表面,并构成砂黄土骨架间的结构联结,具有弱 胶结特性。砂黄土中粘土矿物和有机质为非水稳性胶结物质,仅在干燥状态具有较弱的胶结作用;黄土中的CaCO3呈粗颗粒 骨架和细分散超细碳酸钙两种形式存在,并分别起着骨架作用和胶结作用,超细碳酸钙为不可逆的胶结材料,在聚集体形成、 保存以及聚集体与碎屑颗粒之间的联结方面发挥着重要作用;非晶质游离氧化物(SiO2、Fe2O3、Al2O3)含量虽低,但由于他们 是以薄膜形式分布在颗粒表面,在黄土胶结作用中也是不可忽视的,并与上述各种胶结物共同起作用。通过统计分析认为, 凝聚系数可以较好地反映黄土的胶结程度,成为联系黄土胶结特性与黄土物理力学性质之间的桥梁。黄土胶结物组成及其 胶结机理的研究不仅有助于深化砂黄土工程特性的认识,而且对揭示黄土高原表生地球化学环境具有重要意义。     

A numerical model for reinforced concrete structures

This paper describes a two-dimensional approach to model fracture of reinforced concrete structures under (increasing) static loading conditions. The first part is dedicated to the concrete material. The concrete is described in compression by a non-local isotropic damage constitutive law. In tension, a fictitious crack/crack band model is proposed. The influence of biaxial stress states is incorporated in the constitutive relations. In the second part a bond model is described. It accounts for different failure mechanisms, a pullout failure and a splitting failure. This approach is applied to prestressed concrete beams with different failure mechanisms. The numerical results are compared to experimental data and show good agreement.