Rheological behaviour of polysaccharide aqueous solutions

Several data relative to the viscosity of water-soluble polysaccharide solutions were collected from the literature and processed by different rheological models. Some relationships between the viscosity of these polymer solutions, their molecular weight and their solution concentrations, were established and their validity checked. Thus, an accurate equation correlating the viscosity and both the shear rate and the solution concentration of different water soluble polysaccharides (xanthan, hyaluronan, carboxymethylcellulose) was deduced on the basis of Cross' model which suggests two domains in which the viscosity is constant, i.e. very low and very high shear rate ranges. Then, an expression relating the zero-shear viscosity (A) and the concentration of their solutions was proposed. Finally, an alternative equation to that of Mark–Houwink correlating the molecular weight and the intrinsic viscosity of the water-soluble polysaccharides studied in this paper was found.     

不同频率激励信号下土壤水分传感器性能试验

激励信号频率是影响高频电容式土壤水分传感器性能的重要因素。利用去离子水和2—异丙氧基乙醇(2—isoproxyethanol)或二氧六环(dioxane)2种溶液混合,配制了一系列等效土壤体积含水率为0.9%~51.8%的待测介电溶液来替代土样。从与土壤含水率的函数关系、温度变异性2个方面,分别对激励信号频率为40,50,60,70,80,90,100 MHz的7种土壤水分传感器进行了性能测试与分析。结果表明:7种频率的传感器的输出电压均与土壤体积含水率呈线性负相关,其相关系数R2均大于0.94;激励信号频率不影响传感器输出电压的温度变异性,温差是影响温度变异性的主要因素,其最大变异率均小于4%。试验结果可为设计高频电容式土壤水分传感器时选择激励信号频率提供依据。     

鲁棒性项目调度中缓冲设置方法

研究应对不确定因素的鲁棒性项目调度, 针对其所用时间缓冲区技术中的两种重要方法——集中缓冲和STC (starting time criticality) 分散缓冲, 采用仿真模拟实验, 以项目管理库中的帕特森例1 为对象, 进行详细的比较研究. 研究结果表明, 分散缓冲法具有更好的解鲁棒性; 当活动时间的不确定性程度较大时, 集中缓冲法的质量鲁棒性较好; 当项目工期较紧时, 分散缓冲法具有更好的鲁棒性. 这些研究结论为管理者在特定的项目环境下选择合适的缓冲方法提供了决策依据.     

中国汞污染的现状及防治对策

综述了环境汞污染的主要来源及特点,分析了中国现阶段汞污染的现状,提出加强燃煤汞污染的控制、削减工业汞使用量、提高社会公众的参与意识是治理我国汞污染当采取的有效措施。     

Methods to determine solubility parameters of polymers using inverse gas chromatography

Experimental values of the Flory–Huggins parameter, χ, between polymers and solvents, are frequently used to determine the solubility parameters of the polymers. A method using nonlinear curve fitting of RTχ/V was compared to the linear regression method commonly used. It was found that the formulas for the solubility parameter were the same, but the linear method produced a slightly different entropy term. The nonlinear method gave a lower correlation coefficient and wider confidence intervals and was more effective at distinguishing systems than the linear model. The effect of the deviation of probes in the solubility parameter model is discussed. Using probes with low solubility parameters to measure the polymer solubility parameter gave wider confidence intervals. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2894–2902, 2004     

微孔发泡过程中聚合物/超临界CO2均相体系形成的研究

阐述以超临界CO2为发泡剂的微孔发泡中均相体系的形成过程，研究聚合物熔体和气体的混合机理，并分析影响均相体系形成过程的因素。结果表明，聚合物和气体本身的结构和性质、工艺条件、加工设备、外力场等均影响均相体系的形成，振动力场的引入可以提高多相体系的混合程度，在聚合物／气体均相体系的形成过程中引入振动力场是一个全新的研究方向。     

Redox Properties and Catalytic Behavior of Praseodymium-Modified (Ce-Zr)O2 Solid Solutions in Three-Way Catalysts

The three-way catalyst promoters (Ce-Zr)O₂, (Pr-Ce-Zr)O₂ and (Pr-Zr)O₂ were prepared by the sol-gel method. The reduction/oxidation behavior of these mixed oxides was compared. It is shown that the formation of (Pr-Zr)O₂ cubic solid solution at high temperature up to 800 °C makes it more reducible, and that the ternary solid solution that formed in (Pr-Ce-Zr)O₂ mixed oxides plays an important role in the reduction process. The catalytic performance tests reveal that the introduction of a small amount of praseodymium into (Ce-Zr)O₂ favors the light-off temperature of C₃H₆ and NO and the effectiveness for NO conversion at the lean region.     

The effect of ionic strength on soil P reactions is negligible

The electrolyte concentration of the soil solution affects the availability of some nutrients in the soil, especially of P, but it is not know at what salt concentration the reactions start to be significantly affected and their magnitude. This study was carried out to evaluate the effect of rates of potassium chloride (KCl) on some soil parameters that determine supplying of P, K, Ca, Mg, and Al in an unlimed acid soil. Increasing rates of KCl (from zero up to 2000 mg K kg^–1) were applied to soil samples fertilized with 360 mg P kg^–1. Solution (C_li) and exchangeable (C_si) forms of P, Ca, Mg, K, and Al were determined in the treated soil samples after 30-days of incubation; cation activity in solution and their selectivity coefficients were then calculated. Addition of KCl at rates equal to or above 500 mg K kg^–1 caused a large relative increase on P in the soil solution (P_li) but a small and insignificant increase on the absolute value of P_li. All forms of soil K increased with increases on K applied, and buffer power for K varied according to the range of soil K. At all KCl rates, K displaced Ca, Mg, and Al from the solid phase to the soil solution, but had no effect on the extractable values. The relative preference of cations for the adsorption sites increased with increase on cation valency, and only those selectivity coefficients involving K were affected by K applied.     

用电势法测定混合电解质溶液中各个组分的活度系数

本文用无液接电势电池：Ｎａ－ＩＳＥ（或Ｋ－ＩＳＥ）｜（ＮａＣｌ（ｍＡ），ＫＣｌ（ｍＢ），Ｈ２Ｏ｜Ｃｌ－ＩＳＥ同时测定了２９８．１５Ｋ，溶液离子强度Ｉ：０．１、０．５、１．０、１．５、２．０和２．５ｍｏｌ／ｋｇ时，钠电极与氯电极组成的电池和钾电极与氯电极组成的电池的可逆电势值，根据Ｎｅｒｎｓｔ方程分别求出ＮａＣｌ－ＫＣｌ－Ｈ２Ｏ体系中，ＮａＣｌ和ＫＣｌ的平均活度系数。用Ｐｉｔｚｅｒ方程拟合两套实验数据，求出两套基本一致的Ｐｉｔｚｅｒ混合参数θＮａ－Ｋ和。将混合参数代回Ｐｉｔｚｅｒ方程，分别求出另一组分的平均活度系数，计算值与实验值比较，标准偏差分别为：０．００８１（ＮａＣｌ）和０．００７３（ＫＣｌ）。     

PAAD-16酸液稠化剂的合成与性能

以二甲氨基丙基甲基丙烯酰胺和溴代十六烷为原料,丙酮为溶剂,合成了一种疏水单体——二甲基十六烷基(2-甲基丙烯酰胺基丙基)溴化铵(DHAB),并以DHAB、2-甲基-2-丙烯酰胺基丙磺酸(AMPS)和丙烯酰胺(AM)为单体,以自由基水溶液聚合法合成了一种疏水缔合聚合物P(AM-AMPS-DHAB)(PAAD-16),用IR、荧光光谱(FL)和SEM对其进行了结构表征。结果表明:PAAD-16的酸溶时间约为90 min;以该疏水缔合聚合物为主要添加剂配制而成的稠化酸在30℃、170s~(–1)下的表观黏度为59m Pa×s,在60、90℃下的热稳定性(ω)分别为85.0%和66.1%,在该条件下连续剪切120 min后剪切稳定性(ω')为81.4%,具有良好的增黏性、耐温抗剪切性和缓速性能。