Thermodynamical properties of Zr-based bulk metallic glasses

The temperature dependence of Gibb's free energy difference (ΔG), entropy difference (ΔS) and enthalpy difference (ΔH) between the undercooled melt and the corresponding equilibrium solid phases of bulk metallic glass (BMG) forming melts has been proved to be very useful in the study of their thermodynamical behavior. The present study is made by calculating ΔG, ΔS and ΔH in the entire temperature range T_m (melting temperature) to T_g (glass transition temperature) for three Zr-based samples of BMGs: Zr₅₇Cu_15.4Ni_12.6Al₁₀Nb₅, Zr_41.2Ti_13.8Ni₁₀Cu_12.5Be_22.5 and Zr_58.5Cu_15.6Ni_12.8Al_10.3Nb_2.8. The study is made on the basis of Taylor's series expansion and a comparative study is also performed between the present result and the result obtained in the framework of expansions proposed by earlier workers, and also with the experimental results. An attempt has also been made to study the glass forming ability for BMGs.     

Ni2O3掺杂对新固相源顶部籽晶熔渗生长法制备单畴GdBCO超导块材超导性能的影响

本文通过在新固相源中添加Ni₂O₃的方法, 采用顶部籽晶熔渗生长工艺(TSIG)制备出组分为(1-x) (Gd₂O₃+1.2BaCuO₂)+x Ni₂O₃、直径为20 mm的单畴GdBCO 超导块材(其中x = 0, 0.02, 0.06, 0.10, 0.14, 0.18, 0.30, 0.50 wt%), 并研究了Ni₂O₃的掺杂量x对样品的表面生长形貌、微观结构、临界温度T_c、磁悬浮力以及俘获磁通密度的影响. 研究结果表明, 当Ni₂O₃的掺杂量x在0–0.50 wt%的范围内时, 均可制备出单畴性良好的样品, 且Ni₂O₃的掺杂对样品中Gd211粒子的分布和粒径没有明显的影响. 在Ni₂O₃的掺杂量x从0增加到0.50 wt%的过程中, 样品的临界温度T_c呈现下降的趋势, 从x=0时的92.5 K下降到x=0.50 wt%时的86.5 K, 这是由于Ni^{3 +}替代GdBCO晶体中Cu^{2 +}所致; 样品磁悬浮力和俘获磁通密度均呈现先增大后减小的变化规律, x=0.14 wt%时, 磁悬浮力达到最大值34.2 N, x=0.10 wt%时, 俘获磁通密度达到最大值0.354 T. 样品磁悬浮力和俘获磁通密度的变化规律与Ni₂O₃的掺杂量x有密切关系, 只有当掺杂量x合适时, Ni³⁺对Cu^{2 +}的替代既不会造成T_c的明显下降, 但又能产生适量的Ni^{3 +}/Cu²⁺ 晶格畸变, 从而达到提高样品磁通钉扎能力和超导性能的效果.     

Efficient optimization of van der Waals parameters from bulk properties

Due to the computational cost involved, when developing a force field for new compounds, one often avoids fitting van der Waals (vdW) terms, instead relying on a general force field based on the atom type. Here, we provide a novel approach to efficiently optimize vdW terms, based on both ab initio dimer energies and condensed phase properties. The approach avoids the computational challenges of searching the parameter space by using an extrapolation method to obtain a reliable difference quotient for the parameter derivatives based on the central difference. The derivatives are then used in an active‐space optimization method which convergences quadratically. This method is applicable to polarizable and nonpolarizable force fields, although we focus on the parameterization of the AMBER force field. The scaling of the electrostatic potential (ESP) of the compounds is also studied. The algorithm is tested on 12 compounds, reducing the root mean squared error (RMSE) of the density from 0.061 g/cm³ with GAFF parameters to 0.004 g/cm³, and the heat of vaporization from 1.13 to 0.05 kcal/mol. This is done with only four iterations of molecular dynamic runs. Using the optimized vdW parameters, the RMSE of the self‐diffusion was reduced from 1.22 × 10^?9 to 0.78 × 10^?9 m² s^?1 and the RMSE of the hydration free energies was reduced from 0.30 to 0.26 kcal/mol. Scaling the ESP to improve dimer energies resulted in the RMSE improving to 0.77× 10^?9 m² s^?1, but the worsened to 0.33 kcal/mol. © 2013 Wiley Periodicals, Inc.     

A New Method for Characterizing Single Parametric Model Potential

A novel approach of characterizing single parametric model potential is proposed by equating total pair wise force to zero. Our well-established single parametric model potential is characterized using the proposed idea and compared the obtained parameter with parameters computed by previously used approaches. Thus characterized pseudopotential is then tested to compute total energy of alkali metals. The results establish the reliability of proposed idea of making total pair wise force to zero in determining the parameter of the pseudopotential.     

有机体异质结太阳能电池的数值分析

介绍了一种有机体异质结太阳能电池的数值模拟方法,模型使用Onsager提出的成对复合理论,并结合了完善的无机半导体理论而提出来的,其结果与实验结果符合较好,证明了模型的正确性.在此基础上分析了器件的内建电场与工作温度对器件性能的影响,以及影响器件光电流的主要因素. 关键词： 有机太阳能电池 体异质结 数值分析     

Multistage polar switching in bent-core mesogens

We report a novel type of electro-optical switching in a tilted smectic phase of bent-shaped mesogens. The switching consists of a continuous stage and two bistable transitions. Detailed optical and electro-optical measurements using high-speed imaging are given and possible interpretations of the experimental results are discussed.     

Higher borides and oxygen-enriched Mg–B–O inclusions as possible pinning centers in nanostructural magnesium diboride and the influence of additives on their formation

The study of high pressure (2 GPa) synthesized MgB₂-based materials allows us to conclude that higher borides (with near MgB₁₂ stoichiometry) and oxygen-enriched Mg–B–O inclusions can be pinning centers in nanostructural magnesium diboride matrix (with average grain sizes of 15–37 nm). It has been established that additions of Ti or SiC as well as manufacturing temperature can affect the size, amount and distribution of these inclusions in the material structure and thus, influence critical current density. The superconducting behavior of materials with near MgB₁₂ stoichiometry of matrix is discussed.     

High-pressure studies on electronic and mechanical properties of FeBO3 (B = Ti,Mn, Cr) ceramics – a first-principles study

Using the density functional theory (DFT) method, the electronic and mechanical properties of perovskites FeBO₃ (B = Ti, Mn, Cr) nanostructures were studied in the pressure range of 0–100 GPa. The band structure studies show the change in the band structure upon substitution of different B cation in FeBO₃ perovskite structure. The density of states spectrum gives the perception of change in the electronic properties of FeBO₃ with the substitution of B cation. The bulk, shear and Young's moduli were calculated and an increase in the moduli is noticed. Moreover, the hardness increases under high pressure. The high-pressure studies of FeBO₃ perovskite nanostructures are explored at atomistic level. The findings show that ductility and hardness of FeBO₃ get increased upon an increase in the applied pressure. The substitution of Ti, Mn and Cr on FeBO₃ shows a significant change in the electronic and mechanical properties.     

Tunable Gas-Gas Reactions through Nanobubble Pathway

Combustible gas-gas reactions usually do not occur spontaneously upon mixing without ignition or other triggers to lower the activation energy barrier. Nanobubbles, however, could provide such a possibility in solution under ambient conditions due to high inner pressure and catalytic radicals within their boundary layers. Herein, a tunable gas-gas reaction strategy via bulk nanobubble pathway is developed by tuning the interface charge of one type of bulk nanobubble and promoting its fusion and reaction with another, where the reaction-accompanied size and number concentration change of the bulk nanobubbles and the corresponding thermal effect clearly confirm the occurrence of the nanobubble-based H₂/O₂ combustion. In addition, abundant radicals can be detected during the reaction, which is considered to be critical to ignite the gas reaction during the fusion of nanobubbles in water at room temperature. Therefore, the nanobubble-based gas-gas reactions provide a safe and efficient pathway to produce energy and synthesize new matter inaccessible under mild or ambient conditions.     

一种混合高温超导磁体及其电磁特性研究

近年来, 高温超导磁体由于载流能力高、 磁场强等优点在磁悬浮列车、 医疗成像、 飞轮储能器等系统具有广阔的应用前景. 在这些应用中, 工作面上磁场越强, 系统的性能越优. 高温超导块材能够俘获强磁场, 但因为尺寸的限制, 其磁场发散区域小, 在大气隙条件下工作面区域磁场弱. 相比而言, 高温超导线圈的尺寸不受限制, 但其磁场会随着口径的增大而降低. 因此, 本文将高温超导线圈和块材结合, 提出了一种结构紧凑、 口径大、 磁场强的混合高温超导磁体. 同时, 利用有限元仿真软件建立混合高温超导磁体的二维轴对称自洽模型并进行了实验验证, 仿真计算了混合高温超导磁体的磁场分布以及不同温度下的临界电流和最大磁场强度. 结果表明, 混合高温超导磁体可显著增加工作面的磁场, 相比于独立的高温超导线圈和高温超导块材最大磁场分别最小提升了102% 和12% .另外, 混合高温超导磁体工作面上的有效磁通相比于高温超导块材也提高了.