Phase behavior of hyperbranched polymer solutions in mixed solvents

Hyperbranched polymers get more and more interesting for several applications due to their tailor-made properties influenced by the architecture and the functional groups of the polymer. The liquid–liquid phase behavior of hyperbranched polymer solutions is an important issue for various applications. Until now, the calculations of these phase equilibria are limited to solutions of hyperbranched polymers in a single solvent using Lattice Cluster theory (LCT). The LCT permits the incorporation of the architecture of the polymer directly in thermodynamic properties, as the Helmholtz energy, without any additional adjustable parameter.This papers aims at the extension of the LCT to ternary systems made from hyperbranched polymer (Boltorn H20), water and propanol. The derived expression for the Helmholtz energy allows for the first time the prediction of miscibility gaps in the ternary system based on experimental data of the binary subsystems.Additionally to the architecture of hyperbranched polymers also the functional groups of hyperbranched polymers play an important role in phase equilibrium. In order to include the association phenomena in the theoretical framework, a modified version of the Wertheim association theory is used. However, during the application of this approach the model lost its predictive power, because ternary data must be used for the parameter estimation procedure. Nevertheless, the combined theory is able to model the experimental phase behavior within the experimental accuracy.     

Theoretical investigation of anisotropic mechanical and thermal properties of ABO3 (A=Sr,Ba; B=Ti,Zr, Hf) perovskites

As promising TBC (thermal barrier coating) candidates, perovskite oxides own designable properties for their various options of cations and structural diversity, but limited comprehensions of structure‐property relationship delay their engineering applications. In this work, mechanical/thermal properties of ABO₃ (A=Sr, Ba; B=Ti, Zr, Hf) perovskites and their anisotropic nature are predicted employing density functional theory. Their theoretical minimum thermal conductivities range from 1.09 to 1.74 W·m^?1·K^?1, being lower than Y₂O₃ partially stabilized ZrO₂. Reduced thermal conductivities up to 16% along particular directions are reached after considering thermal conductivity anisotropy. All compounds own high hardness while SrZrO₃, SrHfO₃, and BaHfO₃ possess well damage tolerance. We found that small electronegativity discrepancy leads to big anisotropy of chemical bond, Young's/shear moduli and thermal conductivities, together with good damage tolerance. These results suggest that the next generation TBCs with extra low thermal conductivity should be achieved through combining material design and orientation‐growth tailoring.     

Shear‐induced brittle failure of titanium carbide from quantum mechanics simulations

Titanium carbide (TiC) has a wide range of engineering applications such as structural components, protective coating materials for cutting tools and strengthening phase because of such superior properties as high wear resistance, high hardness, and good chemical resistance. However, the intrinsic failure mechanism of TiC remains unknown, which limits its extended engineering applications. Here, we used density‐functional theory (DFT) at the Perdew‐Burke‐Ernzerhof (PBE) level to examine the shear‐induced failure mechanism of TiC along various plausible slip systems. We found that the (110)[1 0] slip system has the lowest critical shear strength under both pure shear and indentation stress conditions, suggesting that it is the most plausible failure system under both conditions. The failure mechanism arises from the Ti–C bond stretching and finally breaking with the increase in shear strain. The deformation modes along other possible slip systems are also investigated, which illustrate the failure mechanism along other slip systems. Our results provide atomistic explanation of the brittle failure of TiC, which will be useful for designing TiC based hard materials with improved mechanical properties.     

Possible origin of ferromagnetism in antiferromagnetic orthorhombic-YFeO3: A first-principles study

Rare-earth orthoferrites (RFeO₃) are well-known for the antiferromagnetic ground state. However, some of the recent experimental results suggest that the few members of RFeO₃ family possess ferromagnetism. In the present investigation we report the possible origin of ferromagnetism in antiferromagnetic YFeO₃ using density functional theory. For this purpose, we have considered pure as well as self-doping in YFeO₃ i.e. by considering the point defect at Y, Fe and O sites. Our finding suggests that the point defects in YFeO₃ results in the mixed-valence state of Fe, which may result in ferromagnetism through Zener double exchange mechanism.     

A new one parameter viscosity model for binary mixtures

The Grunberg & Nissian equation with one parameter is widely recommended in the viscosity calculation. However, it is demonstrated that this equation fails to generate satisfactory results for size‐asymmetric mixtures containing large and small molecules. In this work, a new one parameter viscosity model for binary mixtures has been developed on the basis of Eyring's absolute reaction rate theory and the Flory‐Huggins equation. The concept of molecular surface fraction is introduced for modeling liquid mixture viscosities. The viscosity calculations of the new equation are compared with the Grunberg & Nissian equation for a broad range of chemical mixtures including 527 binary systems (containing 63 binary ionic liquid cosolvent systems) and total 17,268 viscosity points. The new equation was found to have an improved performance over the frequently employed Grunberg & Nissian equation, especially for size‐asymmetric mixtures containing large and small molecules. © 2010 American Institute of Chemical Engineers AIChE J, 57: 517–524, 2011     

钢筋混凝土双向板塑性计算表格方法的讨论

本文讨论了“用塑性理论计算钢筋砼双向板的实用表格方法”一文中的一些问题，修正了该文提出的双向板计算方法，补充了一些弯矩系数计算公式及其数值表，供工程设计采用     

Fundamental solutions for plane problem of piezoelectric materials

Based on the basic equations of two-dimensional, transversely isotropic, piezoelectric elasticity, a group of general solutions for body force problem is obtained. And by utilizing this group of general solutions and employing the body potential theory and the integral method, the closed-form solutions of displacements and electric potential for an infinite piezoelectric plane loaded by point forces and point charge are acquired. Therefore, the fundamental solutions, which are very important and useful in the boundary element method (BEM), are presented.     

新媒体条件下大学生思想政治理论宣传的创新研究

新媒体的迅速发展以及应用,对大学生思想政治理论宣传的创新研究起到了十分重要的作用。在新媒体的条件下,我们要努力探索新的大学生思想政治理论宣传的方式,同时,进一步加强和改进新形势下的大学生思想政治教育。我们需要把握住新媒体技术给大学生思想政治教育带来的机遇和挑战,努力为加强大学生的思想政治理论宣传做出巨大的贡献,从而努力改变大学生获取信息的方式以及与人交流的方式等。     

基于原型范畴理论的大学英语词汇教学研究

范畴化是一种抽象的认知活动,是概念和语义形成的出发点。它基于身体体验,随着认识的发展和特殊的需要不断形成新范畴,扩展老范畴。因此,对于范畴的界定应该是动态的。在英语词汇学习中,可以通过形成词汇链、建立多义词语义网络和积累下义层次词这些静态手段,培养学生的范畴化能力。学生还可以根据自己的学习任务,通过各种手段自主地进行范畴化,使符合任务要求的词汇进入到一个临时建构的范畴中。通过词汇的范畴化和重新范畴化过程,充分发挥学生的能动性,提高学生的学习效率和英语综合能力。     

基于评价理论的小说《凉亭》中介入资源分析

雷蒙德·卡佛是美国著名的小说家和诗人,其作品语言平铺直叙、精干冷硬。目前大多数研究都从其文本的"极简主义"特点出发,而鲜有研究从系统功能语法的评价理论角度入手。对小说中的评价性资源,如介入资源的自言、借言以及不同性质介入资源的使用和分布进行分析,对于探究其作品风格、语言特点等都有着重大的作用,同时,也为研究雷蒙德·卡佛的作品提供了新的视角和途径。