On the reliability of unsaturated hydraulic conductivity calculated from the moisture retention curve

In comparison with direct measurements of unsaturated hydraulic conductivity, the methods of calculations from the moisture retention curve are attractive for their fast and simple use and low cost. These are the main reasons for their increasing use, mainly in spatial variability studies. On the other hand, it is known that their applicability is limited. The possibility of the use of the retention curve to indirectly determine hydraulic conductivities is analyzed as follows. The theoretical derivation of the relationK(h) – (h) is briefly discussed with regards to potential sources of inaccuracy. The sensitivity of the algorithm forK(h) calculation is studied as a response to possible inaccuracies in the retention curve determination. Conclusions about the usability of calculated hydraulic conductivities are drawn.     

钢中Si、Mn的电子探针定量分析与标样

采用特制的Fe-Si、Fe-Mn合金系列标样，用电子探针测定了钢或铁基合金中低含量的Si和Mn元素、与用纯元素作标样、经ZAF修正的结果相比较，提高了分析准确度．     

Electrostatics of phosphatidic acid monolayers: Insights from computer simulations

In this paper, we argue that many of the fascinating electrostatic effects that take place in amphiphilic systems are strongly related to the particular organization of the oxygen atoms within each individual molecule. In particular, we focus on two effects: charge inversion and dielectric overscreening. For that purpose, we present molecular dynamics simulations of phosphatidic acid (DMPA²⁻) in the presence of divalent counterions. Our results show that the many oxygens present in DMPA²⁻ cooperatively create strong binding sites for counterions, which in some cases lead to charge inversion. We also present an analysis of the role of interfacial water and relate our analysis to the phenomenon of dielectric overscreening. Several experimental implications are discussed in the conclusions.     

Simultaneous assay of four stereoisomers of diltiazem hydrochloride. Application to in vitro chiral inversion studies

Summary The simultaneous stereospecific assay of four stereoisomers of diltiazem hydrochloride in bulk drug and aqueous solution was developed using HPLC on a Chiralcel OF column. The four isomers were quantitated with good precision by the internal standard method. The chiral inversion of (+)-cis-diltiazem hydrochloride in vitro, stability of its (2S, 3S) configuration in the solid and aqueous states was examined by HPLC. Chiral inversion of (+)-cis-diltiazem hydrochloride was not observed in the solid state, and its (2S, 3S) configuration was stable to heat, humidity and light. Chiral inversion of (+)-cis-diltiazem hydrochloride (2S, 3S) was observed in aqueous solution under UV, but not in aqueous solution stored at 80°C for 5h nor under visible light for 10 h. The (+)-cis-diltiazem hydrochloride (2S, 3S) epimerized to (+)-trans-diltiazem hydrochloride (2R, 3S) with a half-life of 5h in aqueous solution under UV but the reverse chiral inversion of (+)-trans-diltiazem hydrochloride (2R, 3S) to (+)-cis-diltiazem hydrochloride (2S, 3S) was not observed.     

Ternary surface complexes by theE(%)-pH curve method

A new method for the study of ternary surface complexes at liquid-solid interface, theE(%) -pH curve method, was proposed. Four types ofE(%)-pH curves, namely, phenomenon of left-right shifts of S-shaped curve, V-shaped curve, monodirection shift curve and X-shaped curve, were discovered. Correspondingly, apart from type (I) ternary surface complex and type (II) ternary surface complex , a new type of ternary surface complex was discovered. Project supported by the National Natural Science Foundation of China and the Fund of Doctoral Degree’s Spot.     

桥联双β-环糊精对N-[4-(1-芘基)]丁酰-D/L-苯丙氨酸的手性识别及机理研究

利用紫外-可见吸收和荧光发射光谱, 结合非线性最小二乘法拟合曲线以及分子力学(MM2)模拟系统地研究了手性分子N-[4-(1-芘基)]丁酰-D/L-苯丙氨酸(PDP和PLP, 总称PPs)与β-环糊精(β-CD)、 2-位硒桥联双β-CD(2-SeCD)和2-位碲桥联双β-CD(2-TeCD)的包结能力大小及这3个环糊精对PPs手性识别能力的差异和识别机理. 研究结果表明, PPs不能与单疏水空腔的β-CD形成很好的包结复合物, 与具有较长桥联链的2-TeCD结合能力最强. 2-TeCD与PDP和PLP的结合常数分别为2.33×104和6.07×103 L/mol, 对PPs的手性识别比达到KD/KL=3.84, 高于2-SeCD(KD/KL=2.61). 用MM2模拟得出了PPs与这两个双环糊精形成复合物的三维结构: PPs的绝大部分位于双环糊精两个空腔之间, 但是在这两个复合物中, 苯环与芘环所成的二面角不同. 此外, PPs与这两个双环糊精作用时均存在明显的氢键相互作用, 且2-TeCD强于2-SeCD.     

负载型TiO2-聚酰亚胺亲水复合膜的制备与分离性能

采用溶解－流涎法，湿相转换法和干湿相转换法制轩了负载型ＴｉＯ２－聚酰亚胺亲水复合膜，采用扫描电镜，红外光谱，压汞和透气性实验等手段对该膜的孔径分布，表面结构及扩散性能进行了表征，并讨论了制备亲水对膜孔结构的影响，实验结果表明，三种膜均具有很好的亲水性能，而干湿相转换膜具有良好的孔径分布和分离性能。     

S1←S0 Vibronic spectra and the structure of acetyl fluoride-h3 and acetyl fluoride-d3 molecules

UV absorption spectra of acetyl fluoride-h₃ and -d₃ (CH₃COF and CD₃COF) molecules in the region of S₁S₀ electronic transitions are investigated. The origins (0⁰ ₀ or 14^0± ₀) of these transitions are observed at 39912 and 39904 cm^–1, respectively, and some of the fundamental frequencies of these molecules in the s₀ and S₁ states are determined. In particular, the systems of torsion and inversion (out-of-plane C=O vibrations) energy levels are studied. The geometric parameters of an acetyl fluoride-h₃ molecule in the S₁ state are estimated by the theoretical simulation of the rotational contours of the 0⁰ ₀ (14^0± ₀) band. These data are used to evaluate the potential barriers to internal rotation in the S₀ and S₁ states, which were found to be 360 and 560 cm^–1 for acetyl fluoride-h₃ and 380 and 770 cm^–1 for acetyl fluoride-d₃, respectively, as well as the potential barriers to inversion in the S₁ states, which were found to be 2090 and 2370 cm^–1 for acetyl fluoride-h₃ and acetyl fluoride-d₃, respectively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1957–1964, November, 1994.In conclusion, the authors would like to acknowledge T. S. Kuznetsova for the synthesis and purification of the AF samples.The research presented here was supported in part by the International Science Foundation under grant No. MJ 1000.     

溶剂浓度对PVDF相转换膜大孔结构的影响

提出决定大孔能否发展的初始分相点处溶剂浓度临界点的概念 ,认为初始分相点处较高的溶剂浓度有利于大孔的发展 ,溶剂浓度低于一定的界限后 ,大孔停止发展 ,转为海绵状结构 .实验考察了不同凝胶液组成下制得的PVDF中空膜的结构 ,建立了相应的传质模型 ,模拟不同制膜条件下初生态膜内的组成分布情况 ,根据初始分相点处溶剂浓度临界点的概念 ,预测膜的形态结构 .模拟结果与相应制膜条件下的电镜照片有很好的对应关系 ,证明了上述大孔形成机理的正确性 .