Electrical conduction mechanisms and effect of atmosphere annealing on the electrical properties of BiFeO3-BaTiO3 ceramics

BiFeO₃-BaTiO₃ (BFBT) is a promising high temperature piezoelectric ceramic system, as it possesses both high electromechanical properties and high Curie temperature. However, pure BFBT commonly exhibits large electrical conductivity at high temperatures, and there is considerable disagreement on its electrical conduction mechanism. Here we investigated the electrical conduction mechanisms of 0.70BiFeO₃-0.30BaTiO₃ and 0.67BiFeO₃-0.33BaTiO₃ ceramics by systematic impedance spectroscopy measurements as a function of oxygen partial pressure and temperature. Both ceramics exhibit higher electrical conductivity with an increase of oxygen partial pressure, consistent with p-type semiconductor behaviors. Particularly, reduced conductivity and improved ferroelectric remanent polarization can be obtained in BFBT when annealed in inert atmosphere. This study provides fundamental basis for preparing insulating and high performance BFBT ceramics.     

镀镍钢带深冲时镀层失效原因的定性分析与仿真

针对镀镍低碳钢带在深冲变形过程中出现的镀层失效行为,结合对深冲变形中的应力和应变状态的分析,通过对镍和低碳钢“应力-应变”曲线的分析和比较,发现了引起镀层失效的根本原因：深冲变形时在镀层和钢带结合面两侧所受应力的大小不同,从而在结合面上产生了过大的切应力,并产生了过大的切应变进而造成了镀层的脱落,并利用有限元方法对该层间切应力的存在进行了仿真实验验证;另外因镍和低碳钢的弹性模量不同且二者厚度差别太大,在深冲外力撤除后因镀层的弹性回缩受制于钢带的弹性回缩,从而在镀层上产生了过大的残余拉应力,因该残余拉应力的缓慢释放而造成镀层的冲后脱落。这为制备满足深冲要求的镀镍深冲钢带指明了研究方向,为进一步的研究奠定了基础,同时也为镶嵌金属的深冲变形或拉伸变形提供了分析方法和参考。     

Determination of cobalt,copper and nickel in food samples after pre-concentration on a new pyrocatechol-functionalized polyurethane foam sorbent

Polyurethane foam functionalized with pyrocatechol by covalent coupling through –NC– group, is applied to an on-line pre-concentration system for cobalt, copper and nickel determination in food samples. The preparation of the packing material involved the reaction of 2,3-dihydroxybenzaldehyde with the amino groups of polyurethane foam. Metal ions were sorbed in the minicolumn, from which it could be eluted with acid solutions directly to the nebulizer-burner system of the flame atomic absorption spectrometer (FAAS). Under the optimum conditions, the enrichment factors obtained were 55, 42 and 54, for cobalt, copper and nickel, respectively, if used 180 s pre-concentration time. The detection limits of the proposed procedure were 0.5 (Co), 0.4 (Cu) and 0.6 (Ni) μg L⁻¹. The method was applied to determination of the metals in spinach, rice flour, corn flour and black tea samples. The accuracy of the developed procedure was evaluated by analysis of the certified reference material NIST 1570a Spinach Leaves.     

黄山野菊花中绿原酸含量的测定

采用紫外分光光度法对产于皖南黄山山脉的黄山野菊花中的绿原酸含量进行了测定,本法准确、精密度高、重现性好,绿原酸浓度线性范围5~20 mg/L(r=0.999 6);平均回收率为102.0%,RSD为0.83。该法可作为黄山野菊花及其制剂质量控制的—种方法。     

均匀设计法研究环境友好型水处理剂高铁酸钾制备

将均匀设计实验安排方法应用于高铁酸钾的制备过程中,确定了其最佳制备条件:氧化反应温度25℃,反应时间60 min,9水合硝酸铁质量分数5%,对实验数据的多元回归分析得到了可对不同实验条件所得产品产率进行预测的回归方程。制备过程中次氯酸钾为新制饱和溶液。此法制备的高铁酸钾最高产率可达97.4%。     

枇杷叶总黄酮提取工艺的优化

效应面法优化枇杷叶总黄酮的提取工艺。以乙醇浓度、料液比和提取时间为自变量,总黄酮提取率为因变量,通过自变量与因变量的完全二次响应面的回归拟合,用效应面法选取最佳工艺,并进行预测分析。结果表明:适宜的提取工艺是,提取液乙醇的体积分数为73%,料液比1∶11.5(g∶mL),提取2次,每次140 min。     

洋葱的成分及保健功能的研究进展

为了促进洋葱的开发利用,介绍了洋葱所含的化学成分和功效成分主要有含硫化合物、前列腺素A、洋葱类黄酮、硒、洋葱油树脂、苯丙素酚类和甾体皂苷类等,同时综述了其具有抑菌、降血脂、降血糖、抗血栓、抗肿瘤和抗氧化等保健功效,认为洋葱是一种具有较高的食用和药用的植物资源.     

铁营养强化剂对奶粉品质的影响

检测了四种铁营养强化剂对奶粉感官和理化指标的影响。通过"三点检验"实验发现,乙二胺四乙酸铁钠(NaFeEDTA)会对无糖奶粉在感官上产生影响(α<0.01),而对含糖奶粉没有显著影响(α>0.05)。采用"量值估计"实验考察了NaFeEDTA、乳酸亚铁、硫酸亚铁和焦磷酸铁对含糖和无糖奶粉的感官影响。结果表明:不同铁强化剂对无糖奶粉和含糖奶粉的外观颜色和组织状态影响无显著差异,添加NaFeEDTA及焦磷酸铁奶粉的气味、滋味和冲调性的评价得分明显高于乳酸亚铁和硫酸亚铁。四种铁强化剂对奶粉的酸度和含水量几乎无影响。     

用于GaN HEMT栅驱动芯片的快速响应LDO电路

设计了一种用于GaN高电子迁移率晶体管(High-Electron-Mobility Transistor,HEMT)器件栅驱动芯片的快速响应低压差线性稳压器(Low Dropout Regulator,LDO)电路,可为高速变化的数字电路提供快速响应的供电电压。该电路采用动态偏置结构,通过在大负载发生时给误差放大器增加一个额外的动态偏置结构,来加快输出端的瞬态响应速度。基于0.18μm BCD工艺,完成了电路设计验证。仿真结果显示LDO瞬态响应时间小于0.5μs,可满足频率达1 MHz的GaN HEMT器件栅驱动芯片应用要求。     

论徽州乡土文献的保护与利用

徽州乡土文献具有宝贵的历史、文化、经济等价值,对其保护与利用尤为必要,然而现状却令人担忧.对此通过阐述徽州乡土文献内涵,在理解该文献定义、内容、特征的基础上分别论述其保护与利用方面存在的问题,提出更新观念、加大投入、以行动出实效的策略建议,以期更好地保护与利用徽州乡土文献.