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991.
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Osmotic pressure measurements were satisfactorily used to compute the effective charge of poly(acrylic) acid (PAA) at different pHs and with different monovalent and divalent counterions. This experimental method is sensitive to the osmotically active species (polymer and counterions). After correction for the polymer contribution to the total osmotic pressure (solvency and excluded volume), the remaining pressure can be attributed to the polyelectrolyte counterions and processed with Donnan and equation of state in order to compute the effective charge number per polymeric chain (Zeff). The behavior of Zeff against the chain concentration and pH was investigated after neutralization of PAA with LiOH, NaOH, and TMAOH. The results clearly indicate that the nature of the monovalent counterion has no effect on Zeff leading to the conclusion that the interaction between monovalent counterions and the acrylate functionality is purely electrostatic in agreement with conductimetric and potentiometric results reported in the literature. The behavior of Zeff against the degree of ionization of the polymer and its concentration is also in good agreement with the theoretical expectations of the theory of ionic condensation. Osmotic measurements were also used in order to understand the influence of divalent cations (Mg2+, Ca2+, Ba2+) on Zeff of the sodium salt of PAA at pH 9 and at different divalent/acrylate molar ratio. All the divalent cations depress Zeff each of one at different degrees, confirming a specific divalent/polymer interaction. The energy of hydration of cations can explain most of the observed results with divalents. 相似文献
994.
995.
简短评述了大容量和超大容量光通信系统的WDM和OTDM技术,提出了一个在OTDM通信系统中用锁模光纤激光器做时钟提取器的新方法,给出了一个利用设置波分预标时钟脉冲方案构成的新的全光型OTDM通信实验系统结构。 相似文献
996.
Bernard Brogliato Rogelio Lozano 《International Journal of Adaptive Control and Signal Processing》1992,6(1):35-44
The standard least squares (LS) estimation algorithm is modified in such a way that it becomes passive. Therefore the scope of application of the LS algorithm is extended to those adaptive schemes whose convergence proof is based on passivity. The passive version of LS is presented in both continuous and discrete time. 相似文献
997.
Low-energy electron diffraction (LEED), Auger electron spectroscopy and X-ray photoelectron spectroscopy (XPS) investigations of both the growth of an iron film on silicon (100) at room temperature and the subsequent formation of iron silicide are the subjects of this paper. An in-situ cleaned silicon (100) wafer without carbon or oxygen contamination exhibiting the known 2 × 1 reconstruction in the LEED pattern served as the substrate. Iron was deposited on this reconstructed surface at 300 K. The comparison of theoretical calculations based on three growth mechanisms with XPS data obtained with take-off angles of 0° and 50° clearly demonstrates a layer-by-layer growth of the iron film on silicon (100). At 300 K no formation of iron silicide was observed, although an interaction between iron and silicon could be detected at the interface. The formation of iron silicide was observed at annealing temperatures of 630–730 K. Quantitative XPS analysis yields the presence of FeSi2, when the thickness is large enough. Neither the iron film on silicon nor the silicide shows any LEED pattern. 相似文献
998.
999.
王志军 《土木建筑与环境工程》1998,20(4):14-20
在深入研究各类迭代控制法的基础上,针对混凝土结构的非线性全过程分析,在常规的位移和弧长控制法中引入了简单适用的考虑路径搜寻和单因加速的方法,明显改善了收敛情况。 相似文献
1000.