荠菜中总黄酮的提取及含量测定

研究了从荠菜中提取总黄酮的工艺条件及其含量的测定条件,探讨了乙醇浓度、提取时间和投料液同比(荠菜质量与乙醇用量比)对提取率的影响.结果表明最佳提取工艺为:乙醇浓度70%,提取时间11 h,固液比为1:14;用分光光度法进行含量测定的适宜条件为:测定波长为510 nm,NaNO25%、Al(NO3),10%、NaOH 4...     

A Viscometric Study of the Miscibility Behaviour of Poly(N-Vinyl Pyrrolidone) Blends

The miscibility behaviour of blends of poly(N-vinyl pyrrolidone) (PVP) with poly(vinyl chloride) (PVC), poly(vinyl acetate) (PVAc) and vinyl chloride–vinyl acetate (VCVAc) copolymer has been investigated on the basis of a viscometric approach. PVP is found to be miscible with PVC over the entire composition range, as is evident from the high values observed for the intrinsic viscosity of transfer. This is further supported by the single glass transition temperature observed in differential scanning calorimetry studies of the blend films. Blends of PVP with VCVAc copolymer exhibit microphase separation which is shown clearly in the scanning electron micrographs of the films. PVAc/PVP blends show interaction only at low PVAc contents, but in general are immiscible. © of SCI.     

氨氮纳氏法测定中的影响因素分析

纳氏试剂测定氨氮时。纳氏试剂的配制方法,酒石酸钾钠的纯度,实验用水,样品的显色时间和温度,显色体系pH值和废水样品pH值均影响分析结果的准确度,本文对以上各因素进行试验比较,结果表明：选用第一种纳氏试剂配制方法;显色时间以10-~25min;显色温度20~C~30oc;废水样品的pH值大于2,显色体系的pH值在13．0-,13．6之间;用进口的酒石酸钾钠对样品测定能取得很好的效果。     

比沙可啶的合成工艺研究

以2-吡啶甲醛为起始原料,在浓硫酸催化下,与苯酚缩合得到4,4'-二羟基二苯基-(2-吡啶)-甲烷和2,4'-二羟基二苯基-(2-吡啶)-甲烷,利用二者在乙酸乙酯中溶解度的差别,分离得到4,4'-二羟基二苯基-(2-吡啶)-甲烷,用氢氧化钠转变得到酚钠盐后,经乙酰化得到比沙可啶。其结构经核磁共振氢谱确证,纯度经液相色谱分析为99%。改进后的合成工艺操作简便,收率可达58%。     

Effect of neck formation on the sintering of air-plasma-sprayed thermal barrier coating system

Sintering neck is a featured microstructure that may have significant effect on the sintering behaviour of air-plasma-sprayed thermal barrier coating system (APS TBCs). Based on experimental observations, a multi-necking wedge-shaped model for the sintering of APS TBCs was proposed by considering the sintering stress as surface tension and by employing the thermal-elasto-viscoplastic constitutive relation. Deformation pattern, stress distribution, sintering induced shrinkage, stiffening behaviour and temperature field were analysed by using finite element method. It is shown that the formation of sintering neck significantly affects thermal and mechanical properties related to sintering. Mechanisms of thermal and mechanical degradation induced by sintering were further elucidated.     

The porosity dependence of sound velocities in ceramic materials

The porosity dependence of transverse and longitudinal sound wave velocities is studied in statistically isotropic porous ceramics. Based on the model relations for elastic moduli six model relations are constructed for the prediction of the porosity dependence of these velocities. All of them predict a decrease of sound wave velocities with increasing porosity, but the Maxwell / Mori-Tanaka / MMT model leads to unrealistic predictions for high porosity. A velocity ratio function is defined which contains the porosity dependence of the effective Poisson ratio and enables the prediction of longitudinal wave velocities. A comparison with literature data shows that most data lie below the exponential prediction and above the numerical prediction for concave pores. The correlation of the normalized longitudinal wave velocities and relative transverse wave velocities shows that essentially all values are above the highest lower bound and are reasonably predicted by the differential, exponential and self-consistent models.     

A Fixed-Point Iteration Approach for Solving a BVP Arising in Chemical Reactor Theory

A numerical scheme aimed at solving a broad class of second-order nonlinear boundary value problems (BVPs) is presented, described, and then applied to a problem that appears in chemical reactor theory. In particular, the steady-state solution of the equation governing the model of the adiabatic tubular chemical reactor is investigated. The proposed method is based on expressing the particular solution of the governing equation in terms of an integral involving Green’s function. Then, the Krasnoselskii–Mann’s fixed-point scheme is implemented to an amended version of the resulting integral operator. The convergence of the iterative scheme is proved and its efficiency and applicability are demonstrated by solving the equation for selected values of the parameters that appear in the model. Residual error computation is adopted to confirm the accuracy of the results. In addition, the numerical outcomes of the proposed method are compared with those obtained by other existing numerical approaches.     

A model for determination of residual stresses in plasma coatings

The main reasons for the formation of residual (internal tensile) stresses in thermal spraying methods are the large differences in the temperatures of particles of deposited material on the surface of the substrate, the specific volumes of these particles at the moment of contact with the substrate and in the cooled condition, and also the non-uniformity of the distribution of temperature over the cross-section of the coating. The theory of hereditary elasticity is used to develop a mathematical model of theoretical justification of the process of formation and redistribution of the residual stresses which takes into account the relationship between the stresses and strains in the contact – substrate zone in heating and also the changes of their strength properties. Analytical dependences of controlling the technological parameters, such as the time and heating temperature, are proposed.     

斗笠式刀库自动换刀控制组态系统的开发

论述如何利用组态软件对斗笠式刀库自动换刀过程进行组态设计,实现对加工中心自动换刀动作的动态控制及监控功能。该组态系统对数控技术维修人员及时排除自动换刀系统故障、特别是职业院校进行数控机床维修实践教学及技能培训具有重要的指导作用。     

镍基单晶合金热处理的组织演化与有限元分析

通过对一种含Re单晶镍基高温合金热处理期间及不同时效温度组织形貌的观察,结合有限元分析,研究合金中γ′相在热处理期间及蠕变期间的组织演化规律。结果表明,在固溶热处理期间,γ′相以蝶形组合从基体中析出;一次时效期间,γ′相长大为立方体形貌;二次时效期间,γ′相略有长大,排列更加规则。经不同温度的一次时效后γ′相尺寸逐渐长大,立方度增加。最后确定出该合金合理的热处理工艺。