Comparison of human enamel and polymer-infiltrated-ceramic-network material “ENAMIC” through micro- and nano-mechanical testing

The mechanical behaviours of a polymer-infiltrated-ceramic-network (PICN) material and human enamel were compared using micro- and nano-mechanical testing. The Vickers hardness and fracture resistance of the two materials were evaluated by the micro-indentation technique. A comparison of the microstructure and crack propagation of both materials was performed by scanning electron microscopy (SEM). From the micro-mechanical level, the Vickers hardness of PICN (3.31±0.11 GPa) was similar to that of human enamel (3.43±0.16 GPa), and the micro-creep behaviours of both materials were also alike. However, the average indentation fracture resistance (K_C) of the enamel (1.26±0.05 MPa·m^1/2) was significantly lower than that of the PICN (1.81±0.08 MPa·m^1/2). Cracks in human enamel are prone to propagate along the rod sheath, while within the PICN, these mainly extend through the ceramic matrix, and are deflected at the polymer–ceramic interfaces. From the nano-mechanical testing, the nanohardness, elastic modulus and nanoindentation creep response of PICN were significant different from that of human enamel. Furthermore, the creep capacity of the PICN was mainly influenced by the infiltrated polymer matrix. Overall, PICN has been found to be more effective than human enamel in crack growth resistance at the microscopic level. The mutually chimeric network structure improves PICN's nano-mechanical behaviour, and the infiltrated polymer matrix facilitates time-dependent deformation that helps dissipate strain energy and prevent fracture.     

Synthesis and properties of 1D Sm-doped CeO2 composite nanofibers fabricated using a coupled electrospinning and sol–gel methodology

Ce_1−xSm_xO₂(x=0, 0.2, 0.5 and 0.8) nanofibers (NFs) were synthesized by coupling sol–gel with electrospinning and using poly-vinyl pyrrolidone (PVP) as the polymer medium, in an ethanol/water mixture. Control over the fabrication conditions was achieved through analysis of the most key synthetic factors, which include: (i) the applied field strength; (ii) the solution feed rate and (iii) the PVP content in the electrospinning solution. The optimum microstructural fiber morphology (high quality beeds-free fibers) was achieved using the following electrospinning parameters: an applied voltage of 18.5 kV, a 7 ml/h of solution feed rate and a 12% (w/w) of PVP composition. Morphological features of the resulting fibers were examined by scanning electron microscopy (SEM). The average fiber diameter was typically found to be in the range of 200–1100 nm and 50–300 nm, before and after calcination at 500 °C, respectively. X-ray diffraction (XRD) results showed that the fluorite cubic structure was preserved for the entire Ce_1−xSm_xO₂ compositional range studied, while elemental analysis using EELS and X-ray photoelectron spectroscopy (XPS) confirmed the purity of the bulk and surface composition of the fibers. Selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM) proved that the NFs are highly crystalline. The thermal stability of the composite (polymer/inorganic nitrate salts) NFs was further investigated in an inert atmosphere (N₂) using thermogravimetric analysis (TGA), which allowed the transformation process of the NFs from composite to oxide to be monitored. The reducibility of the metal oxide NFs (mobility of oxygen species in the fluorite cubic lattice) as well as their thermal stability in successive oxidation–reduction cycles was evaluated using temperature-programmed reduction in a H₂ atmosphere (H₂-TPR). Acidic–basic features of the NFs and powder surfaces were studied through temperature programmed desorption (TPD) using NH₃ and CO₂ as probe molecules, where weak, medium and strong acid sites were successfully traced with profound differences depending on the morphology. The NFs' potential performance towards NH₃ oxidation was also evaluated. Two types of basic sites, hydroxyl groups and surface lattice oxygen are present on the NFs, as probed by CO₂ adsorption. Pyridine adsorption followed by infrared spectroscopy (Py-FT-IR) studies unveiled the more profound Lewis acid presence in Ce_0.5Sm_0.5O₂ NFs compared to bulk powder Ce_0.5Sm_0.5O₂.     

Raman spectra and ferromagnetism of nanocrystalline Fe-doped Li0.43Nb0.57O3+δ

Nanocrystalline undoped LiNbO₃ and LiNbO₃ doped with x% Fe (x=0.5, 1, 2, 3, 5) were synthesized via a combustion method. Fe-doped LiNbO₃ with a 1 mol% doping concentration exhibited a room-temperature ferromagnetism of 0.06 emu/g. There was an abrupt change in properties when the doping concentration of Fe reached 2 mol%, where the lattice contracted obviously and the saturation magnetization (M_s) increased an order of magnitude to 0.275 emu/g; M_s slightly increased to its maximum value of 1.18 emu/g when the doping concentration was further increased to 5 mol%. Raman spectra showed that the substitution of Li by Fe occurred at small doping concentrations and the substitution of Nb at the Nb site occurred at higher doping concentrations. The results suggest that Fe³⁺ replaced Nb_Li⁴⁺ first and the weaker ferromagnetism is due to the minor fraction of Nb_Li⁴⁺ in LiNbO₃. Then, Fe³⁺ substituted Li⁺, resulting in large lattice distortion and much stronger spin coupling of Fe–Nb. Finally, the excess Fe³⁺ started to replace Nb⁵⁺at the Nb sites, where the spin coupling of Fe–Nb is weaker than that at the Li site. An analysis of the experimental results suggests that the congruent Fe-doped LiNbO₃ is a promising room-temperature single-phase multiferroic material.     

Effect of a Bi–Cr–O synthetic multi-phase on the microstructure and electrical properties of ZnO–Bi2O3 varistor ceramics

ZnO–Bi₂O₃–MnO₂ (ZBM)-based varistors were fabricated via doping a novel synthetic multi-phase (SMP) additive produced by calcining the mixture of 18Bi₂O₃·Cr₂O₃ at a given temperature. The effects of the SMP on the microstructural and electrical properties of ZBM varistors were investigated. It was found that the SMP dopant was a compound crystalline phases including Bi–Cr–O phases (Bi_7.38Cr_0.62O_12+x and CrBi₁₈O₃₀) and small amounts of Bi₂O₃ rather than a synthesized polycrystal. The Bi–Cr–O phases were not emerged for samples with x=1, indicating that the amount of it is tiny and the small Bi₂O₃ may accelerate ZnO grain growth. With more SMP doping (x>1) in the ZBM ceramics, it acted as a barrier inhibiting grain growth. For samples with x=5, excellent electrical properties were obtained: the nonlinear coefficient α increased up to 50.19 corresponding to the highly barrier height of 2.62 eV; the leakage current I_L reduced to 0.3 μA. The dielectric constant ε_a is proportional to the ratio of the grain size d to the thickness of the depletion layer width t, which explained the ε_a increased at f=1 kHz for the samples with x=1 and 5. The improvement of the electrical properties can be explained by the oxygen absorption mechanism.     

控制大体积混凝土底板裂缝的施工技术

采用了五项具体措施控制大体积混凝土裂缝取得了良好的效果。     

A discrete artificial bee colony algorithm for the total flowtime minimization in permutation flow shops

Obtaining an optimal solution for a permutation flowshop scheduling problem with the total flowtime criterion in a reasonable computational timeframe using traditional approaches and optimization tools has been a challenge. This paper presents a discrete artificial bee colony algorithm hybridized with a variant of iterated greedy algorithms to find the permutation that gives the smallest total flowtime. Iterated greedy algorithms are comprised of local search procedures based on insertion and swap neighborhood structures. In the same context, we also consider a discrete differential evolution algorithm from our previous work. The performance of the proposed algorithms is tested on the well-known benchmark suite of Taillard. The highly effective performance of the discrete artificial bee colony and hybrid differential evolution algorithms is compared against the best performing algorithms from the existing literature in terms of both solution quality and CPU times. Ultimately, 44 out of the 90 best known solutions provided very recently by the best performing estimation of distribution and genetic local search algorithms are further improved by the proposed algorithms with short-term searches. The solutions known to be the best to date are reported for the benchmark suite of Taillard with long-term searches, as well.     

求解批量流水线调度问题的改进和声搜索算法

针对以最大完工时间为目标的批量流水线调度问题,提出一种改进的和声搜索优化算法。该算法采用ROV规则的编码方式,使具有连续本质的和声搜索算法能直接应用于调度问题。对和声库的初始化和候选解的产生方式进行改进。针对该算法容易陷入局部最优的缺陷,将其与阈值接受算法结合,得到2种混合算法。仿真结果证明了该算法的有效性。     

一种低代价的图形用户界面回归测试框架

图形用户界面(GUI)采用快速原型法生成,具有一些不同于传统软件的特性,使得传统软件测试技术不能直接应用于GUI。为此,分析GUI事件的交互,研究事件交互可能导致缺陷的原因,进而提出一个低代价的基于事件交互图的GUI自动化回归测试框架及相应的回归测试过程,用于提供最优的缺陷发现率和成本组合。     

坝体—库水—淤积层—地基系统地震动分析

为明确地震中坝体—库水—淤积层—地基系统相互作用下坝体的反应,将泥沙淤积层作为粘性、可压缩及大密度流体,考虑柔性地基作用建立了二维计算模型。本模型计算结果与以往报道结果相一致:柔性地基与淤积层都能够降低库坝系统的共振频率及反应幅值。此外,本文提出的方法简单、编程方便及运算速度快等特点可以较方便地应用到混凝土坝体非线性动力响应计算中。     

Gödel命题逻辑中公式概率真度的相似度及伪距离

通过引入赋值密度函数、边缘密度函数等概念,给出了连续值命题逻辑系统G?del中公式概率真度的定义,研究了概率真度的推理规则,在此基础上给出了三种相似度,讨论了其性质及关系,并由此定义了三种伪距离,讨论了逻辑度量空间的结构及其性质,为推理程度的数值化提供了依据。