Effect of focused ion beam sample preparation on the phase composition of zirconia

The investigation of phase transformations in metastable ceramic systems such as zirconia often requires local phase analysis within the areas of interest. Electron backscatter diffraction is a suitable method in combination with focused ion beam sample preparation. The interaction between ion beam and sample has to be carefully considered. In case of metastable Y-PSZ and Mg-PSZ, phase transformations were observed after FIB preparation with 30?kV, 30?nA and 5° incidence angle. Damage was the dominating effect for angles of 72°. The expected local temperature increase due to the ion bombardment with 30?kV and 30?nA is 700?K for ZrO₂. Thus, the observed phase transformations can be explained on the basis of the temperature increase in the corresponding Y-PSZ phase diagram. In case of Mg-PSZ, the transition temperature is 1083?°C. The local temperature increase was obviously lower. The excitation energy for the observed phase transformation was smaller than expected from the phase diagrams of the thermodynamic equilibrium. Using 5?kV, 4.8?nA and 5° incidence angle, no phase transformations and no damage were observed. Thus, these conditions are well suited for the FIB preparation of metastable zirconia.     

Effects of structural characteristics on microwave dielectric properties of low-loss (Zn1-xNix)ZrNbTaO8 ceramics

Low-loss (Zn_1-xNi_x)ZrNbTaO₈ (0.02?≤?x?≤?0.10) ceramics possessing single wolframite structure are initiatively synthesized by solid-state route. Based on the results of Rietveld refinement, complex chemical bond theory is used to establish the correlation between structural characteristics and microwave performance in this ceramic system. A small amount of Ni²⁺ (x?=?0.06) in A-site with the fixed substitution of Ta⁵⁺ in B-site can effectually raise the Q?×?f value of ZnZrNb₂O₈ ceramic, embodying a dense microstructure and high lattice energy. The dielectric constant and τ_f are mainly affected by bond ionicity and the average octahedral distortion. The (Zn_0.94Ni_0.06)ZrNbTaO₈ ceramic sample sintered at 1150?°C for 3?h exhibits an outstanding combination of microwave dielectric properties: ε_r =?27.88, Q?×?f?=?128,951?GHz, τ_f =?–39.9?ppm/°C. Thus, it is considered to be a candidate material for the communication device applications at high frequency.     

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.     

钢轨交流闪光焊接过程过梁爆破特征分析

以高速摄影技术作为主要研究手段，研究钢轨交流闪光焊接过程过梁爆破特征，并结合热成像系统采集焊接过程温度场，以此为数据基础定量分析了钢轨交流闪光焊接过梁爆破特征. 结果表明,钢轨交流脉动闪光焊接工艺模式下，加速闪光阶段具有几个阶段中最高的闪光频次46.93次/s，脉动闪光阶段具有最低的闪光频次11.07次/s；连续闪光阶段闪光烈度为0.009 2 mm/次，是几个阶段中最强的，脉动阶段的闪光烈度最弱，为0.003 8 mm/次；从闪光加热因子来看，脉动阶段最高，符合了该阶段积累热量的主要目的；加速闪光阶段最低，是由于该阶段为了制造保护气氛产生的气化过梁带走了较多的热量；从闪光均匀度看，闪光最不均匀的阶段是闪平阶段，最均匀的阶段是脉动阶段，这恰恰说明了两待焊端面的微观平行情况在闪平阶段最差、脉动阶段最佳.     

柱塞副微观表面对间隙油膜压力的影响

根据分形理论中的W-M函数建立柱塞与缸体孔表面三维形貌数学模型,并利用MATLAB软件编写程序,分析分形维数对表面微观形貌的影响。将柱塞副间隙油膜沿轴向展成平面,建立油膜厚度及压力分布计算模型,采用有限体积法求解二维雷诺方程,分析粗糙度对柱塞副间隙油膜压力分布的影响。结果表明:随着分形维数的增加,柱塞表面粗糙度呈增加趋势,且表面粗糙度越大,压力峰值越大。     

溢出效应和网络贴合度扰动下的二级供应链网络广告投放策略分析

为研究溢出效应和网络贴合度扰动下,二级供应链的网络广告投放策略问题,以强势制造商和两个网络零售商组成的二级供应链为研究对象,考虑产品的网络贴合度和网络广告计费特征,构建基于溢出效应的期望需求模型,通过博弈论方法给出了完全不合作、合作、半合作、战略联盟等4种模式下的均衡解,并对以上4种均衡结果进行比较分析。研究结果表明:无论在何种模式下,制造商批发价格与产品的网络贴合度成反比;固定位网络广告投资额和网络广告投资总额与产品的网络贴合度成正比,固定位网络广告投资额与溢出效应成反比;合作状态下的利润总额通常情况下较低;当产品的网络贴合度超过一定阈值范围时,采用战略联盟使得供应链成员利润最大化。     

神经网络全局势函数在多相催化中的应用

当今的多相催化研究需要新的技术和方法从原子尺度上表征活性中心结构和反应中间体。本文作者课题组近期开发了理论模拟新技术来探索催化剂活性位点结构，即基于神经网络势函数的大规模原子模拟（LASP）软件中实现的全局神经网络势函数计算方法。本文介绍了该方法可以显著降低催化体系的计算代价，而维持与密度泛函理论同一级别的计算精度，从而解决多相催化中的许多复杂问题。本文对神经网络势函数方法的实现细节和目前已实现的应用场景进行了详细介绍。神经网络势函数可以用来预测材料晶体结构，理解高压氢化条件下TiO₂表面的结构演化和确定三元氧化物ZnCrO晶相中合成气制甲醇活性位点。最后文章分析了神经网络势函数的局限性和今后可能的三个研究方向，即材料性质预测、多元素体系神经网络势函数构造和化学反应拟合。     

Machining accuracy improvement for a dual-spindle ultra-precision drum roll lathe based on geometric error analysis and calibration

This paper performs a comprehensive analysis and calibration on the geometric error of the ultra-precision drum roll lathe with dual-spindle symmetrical structure and cross slider layout. Firstly, the volumetric error model which contains all geometric errors of the dual-spindle ultra-precision drum roll lathe (DSUPDRL) is developed based on the combination of the homogenous transfer matrix (HTM) and multi-body system (MBS) theory. Secondly, sensitivity analysis for the volumetric error model is conducted to identify the sensitive geometric error components of the DSUPDRL using an improved Sobol method based on the quasi-Monte Carlo algorithm. The result of sensitivity analysis laid the foundation for the subsequent geometric error calibration. Then, some sensitive error components along the X and Z directions are calibrated using a laser interferometer and a pair of inductance displacement probes. Besides the volumetric error model, the concentricity error caused by dual-spindle symmetrical structure is proposed and calibrated by the on-machine measurement using a classic reversal method. Finally, a large-scale roller mold with a diameter of 250 mm and a length of 600 mm is machined using the DSUPDRL after calibration. The experimental result shows that 1.4 μm/600 mm generatrix accuracy is obtained, which validate the effectiveness of the geometric error analysis and calibration.     

A Novel Beam Search to Improve Neural Machine Translation for English-Chinese

Neural Machine Translation (NMT) is an end-to-end learning approach for automated translation, overcoming the weaknesses of conventional phrase-based translation systems. Although NMT based systems have gained their popularity in commercial translation applications, there is still plenty of room for improvement. Being the most popular search algorithm in NMT, beam search is vital to the translation result. However, traditional beam search can produce duplicate or missing translation due to its target sequence selection strategy. Aiming to alleviate this problem, this paper proposed neural machine translation improvements based on a novel beam search evaluation function. And we use reinforcement learning to train a translation evaluation system to select better candidate words for generating translations. In the experiments, we conducted extensive experiments to evaluate our methods. CASIA corpus and the 1,000,000 pairs of bilingual corpora of NiuTrans are used in our experiments. The experiment results prove that the proposed methods can effectively improve the English to Chinese translation quality.     

毫米波波束管理的设计与研究

毫米波是第五代移动通信系统的重要通信技术,因其频谱特性可以利用大带宽承载大量信息,有效提升系统的吞吐量。高频段毫米波传输具有高损耗性,且受环境影响较大,为了支持非视距和移动性,必须支持准确且实时的波束跟踪以确保信号传输质量。波束管理的目的是使得基站与终端之间发送与接收波束对准以提高链路的性能。文中根据3GPP协议规范设计了波束管理方案,包括以下几方面的内容:波束扫描、波束测量、波束上报、波束指示、波束失败恢复。