用MVM准则求解轴对称弹塑性问题

本文采用MVM 屈服准则,用相关联流动法则建立材料的本构关系.对于实际工程中常见的轴对称问题(平面应力、平面应变),进行弹塑性分析,给出求解问题的一组微分方程.采用Prager 假设,给出应力场和位移场.在分析中可以看出:对于平面应变问题,当v≠0.5时,求解应力场的问题是非静定的;当v=0.5或在平面应力问题中,求解应力的问题是静定的,方程组易于求解.通过数值计算考察SD 效应对结构的影响.结果表明,在压缩过程中,SD 效应增强了结构抵抗塑性变形的能力.     

微波消解电感耦合等离子体质谱法测定桃中稀土元素及其分布

以市场销售的桃为实验材料,利用微波消解电感耦合等离子体质谱法(ICP-MS)同时测定桃中稀土元素的含量。样品经过硝酸-氢氟酸-双氧水微波消解,实现了桃中16种稀土元素的测定。各元素的检出限在0.004~0.020μg·g-1之间,方法精密度在0.78%~2.96%,回收率在95.0%~106.0%之间。比较了稀土元素在果皮和果肉中的分布。结果表明,稀土元素在果皮中的含量明显高于果肉。本法快速、准确,可用于桃等水果中稀土元素的测定。     

可实现防碰撞通信的新型声表面波温度传感器

针对多声表面波传感器系统中各传感器信息读取时会产生通信碰撞的问题,提出了一种可实现防碰撞通信的新型声表面波温度传感器;通过分析声表面波温度传感器的回波脉冲信号,将沃尔什码作为编码内容实现了多声表面波温度传感器系统中各传感器的正交编码;将传感器对应的匹配信号与系统回波信号进行互相关运算,提取了系统中各传感器的感测温度信息,达到了防碰撞通信的目标;该传感器兼顾编码效率和加工工艺两方面要求,简化感测信息提取的复杂程度;仿真实验验证了上述理论的正确性。     

Sorption of radioeuropium onto attapulgite: effect of experimental conditions

Batch sorption experiments were performed to remove Eu(III) ions from aqueous solutions by using attapulgite under ambient conditions. Different experimental conditions, such as contact time, solid content, foreign ions, pH, ionic strength, fulvic acid and temperature, have been investigated to study their effect on the sorption property. The results indicated that the sorption of Eu(III) onto attapulgite was strongly dependent on pH, ionic strength and temperature. The sorption increased from about 8.9 to 90% at pH ranging from 2 to 6 in 0.01 mol/L NaNO₃ solution. The Eu(III) kinetic sorption on attapulgite was fitted by the pseudo-second-order model better than by the pseudo-first-order model. The sorption of Eu(III) onto attapulgite increased with increasing temperature and decreasing ionic strength. The Langmuir and Freundlich models were used to simulate the sorption isotherms, and the results indicated that the Freundlich model simulated the data better than the Langmuir model. The thermodynamic parameters (∆G ^o, ∆S ^o, ∆H ^o) were determined from the temperature dependent isotherms at 298.15, 318.15 and 338.15 K, and the results indicated that the sorption reaction was an endothermic and spontaneous process. The results suggest that the attapulgite is a suitable material as an adsorbent for preconcentration and immobilization of Eu(III) from aqueous solutions.     

A novel nitrite sensor based on graphene/polypyrrole/chitosan nanocomposite modified glassy carbon electrode

A novel nitrite sensor was fabricated based on a graphene/polypyrrole/chitosan nanocomposite film modified glassy carbon electrode. The nanocomposite film was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. The electron transfer behaviour of the modified electrodes was investigated in [Fe(CN)(6)](3-)/(4-) redox probe using cyclic voltammetry and electrochemical impedance spectroscopy. Differential pulse voltammetry and amperometry were used to study the electrochemical properties of the proposed sensor. Under optimum conditions, the sensor exhibited good reproducibility and stability for nitrite determination. Linear response was obtained in the range of 0.5-722 μM with a detection limit of 0.1 μM (S/N = 3) for nitrite determination.     

Synthesis of 12‐aryl‐12H‐benzo[i][1,3]‐dioxolo[4,5‐b]xanthene‐6,11‐diones using silica sulfuric acid as an efficient and versatile catalyst under solvent‐free conditions

Some novel 12‐aryl‐12H‐benzo[i][1,3]‐dioxolo[4,5‐b]xanthene‐6,11‐diones can be rapidly and efficiently synthesized in excellent yields by condensing a variety of aldehydes with 3,4‐methylenedioxyphenol and 2‐hydroxy‐1,4‐naphthoquinone in the presence of a catalytic amount of silica sulfuric acid under solvent‐free conditions. The simple experimental procedure, solvent‐free reaction conditions, utilization of an inexpensive and readily available catalyst, short period of conversion, and excellent yields are the advantages of the present method. Furthermore, the catalyst can be recycled and reused three times without significant loss of activity. The structures of the novel compounds are confirmed by IR, ¹H‐NMR, ¹³C‐NMR, MS, and elemental analysis. J. Heterocyclic Chem., 2011.     

Hydrogen peroxide biosensor based on the immobilization of horseradish peroxidase on ��-Al2O3 nanoparticles/chitosan film-modified electrode

An amperometric biosensor based on horseradish peroxidase (HRP) and ??-Al₂O₃/chitosan composite film at a glassy carbon electrode has been developed. Hydrogen peroxide (H₂O₂) was detected with the aid of ferrocene monocarboxylic acid mediator to transfer electrons between the electrode and HRP. The morphology and composition of the modified electrode were characterized by scanning electron microscopy and electrochemical impedance spectroscopy. The electrochemical characteristics of the biosensor were studied by cyclic voltammetry and amperometry. The effects of HRP concentration, the applied potential, and the pH values of the buffer solution on the response of the sensor were investigated for optimum analytical performance. The proposed biosensor showed high sensitivity (0.249?A M^?1?cm^?2) and a fast response (<5?s) to H₂O₂ with the detection limit of 0.07???M. The linear response range of the enzyme electrode to H₂O₂ concentration was from 0.5 to 700???M with a correlation coefficient of 0.9998. The apparent Michaelis-Menten constant of the biosensor was calculated to be 0.818?mM, exhibiting a high enzymatic activity and affinity for H₂O₂.     

500—4250eV电子对CO2的散射全截面绝对测量

对中能电子与二氧化碳分子碰撞的散射全截面测量，给出５００－４２５０ｅＶ电子对ＣＯ２的绝对散射全截面。对测量结果作了曲线拟合，并与已有的实验和理论结果进行了比较     

Stability of Linear Integrodifferential Systems with Time-varied Confficients with Large Scale

51.IntroductionConsideralinearintegrodifferentialsystemswithtime-variedconfficientswherex6R",A(t)isanXnrealmatrixfunctioncontinuousforoO.ManyscholarshavecontributedtheirpaPers[1-4]todiscussstabilityofzerosolutionofsystem(1.l).Inthispaper,weassumethatsystem(1.1)canbedecomPOsedintotheform=n,A,j(t)isaniXnjrealmatrixfunctioncontinuousforo相似文献