A Surfactant Bridge Model for the Nonlinear Electrorheological Effects of Surfactant-Activated ER Suspensions

In surfactant-activated electrorheological (ER) suspensions it is observed that the ER response shows linear ER behavior (F~E(2)) at small surfactant concentrations and nonlinear ER behavior (F~E(n), n approximately 1) at large surfactant concentrations. Here, a surfactant bridge model is developed to explain the nonlinear ER behavior of surfactant-activated ER suspensions. The model shows that the formation and size of a surfactant bridge depend on various variables, especially the electric field strength, the surfactant surface tension, and the initially adsorbed amount of surfactants on particles. The predicted dependence of the formation and size of a surfactant bridge on the electric field strength and the initially adsorbed amount of surfactants is consistent with the observations. Also, the model indicates that there is a critical minimum electric field E(crit) for the formation of a surfactant bridge, and the estimated E(crit) shows good agreement with the observations. The force acting between particles is composed of the electrostatic force and force associated with surface tension. However, it is found that the contribution of the force associated with surface tension can be ignored and the electrostatic force is dominant regardless of the formation of surfactant bridges between particles. When surfactant bridges are formed between particles, the predicted force shows nonlinear ER behavior (F~E(n), n approximately 1), consistent with the observed nonlinear ER behavior at large surfactant concentrations. When no surfactant bridge is formed, the predicted force is proportional to the electric field squared (F~E(2)), consistent with the interfacial polarization. The model can successfully predict the nonlinear ER behavior at large surfactant concentrations, confirming that the nonlinear ER behavior of surfactant-activated ER suspensions arises from the observed formation of surfactant bridges between particles. Copyright 2001 Academic Press.     

Action on flag varieties: 2-Dimensional case

LetA be a finite dimensional commutative semisimple algebra over a fieldk and letV be a finitely generatedA-module. We examine the action of the general linear group GL _A (V) on the set of flags ofk-subspaces ofV. Also, let (V, B) be a finitely generated symplectic module overA. We also investigate the action of the symplectic group Sp _A (V, B) on the set of flags ofB-isotropick-subspaces ofV, whereB=°B is thek-symplectic form induced by a nonzerok-linear map :A k. In both cases, the orbits are completely classified in terms of certain integer invariants provided that dim _{k A}=2.This work is partially supported by a KOSEF research grant.     

白卡奴鸽动脉粥样硬化模型微量元素谱的计算机多元分析

用ＩＣＰ－ＡＥＳ测定了白卡奴鸽动脉粥样硬化模型和对照组的器官和组织中１９种元素含量，通过因子分析，取得一系列因子得分图，结果表明，动脉粥样硬化和对照组样品点分布在不同区域，且可分辨。     

FI－ICP－AES在线稀释间接测定表面活性剂─十二烷基苯磺酸钠

基于十二烷基苯磺酸钠（ＤＢＳ）与无机钠盐在无水乙醇中溶解度的差异，用乙醇选择提取ＤＢＳ，经水适当稀释，通过用ＦＩ－ＩＣＰ－ＡＥＳ测定其中的钠，从而间接测定ＤＢＳ的含量。     

Simulations of stochastic sensing of proteins

We have performed Langevin dynamics and Poisson-Nernst-Planck calculations to simulate detection of proteins by genetically engineered alpha-hemolysin channels. In the recent stochastic sensing experiments, one end of a flexible polymer chain is permanently anchored inside the protein channel at a specified location, and the other end undergoes complexation with an analyte. Our simulations, using coarse-grained modeling, reproduce all essential qualitative results of the electrophysiology measurements of stochastic sensing. In addition, the underlying macromolecular mechanisms behind stochastic sensing are revealed in vivid details. The entropic fluctuations of the conformations of the tethered polymer chain dictate crucially the unique signatures of the ionic current trace of the channel and provide design rules for successful stochastic sensing. The origin of strong fluctuations in the ionic current of the channel is found to arise from the obstruction of the entrance at the beta-barrel of the channel by the fluctuating segments of the tether. Silencing of the pore is due to the suppression of conformational fluctuations of the chain, and the permanent blockade of ionic current is due to the threading of the tether through the channel. The onset of silencing and permanent blockade of the channel current cannot necessarily be attributed to the capture of analytes. In order for detection events to be timed accurately, the length and anchoring location of the tether must be tuned appropriately.     

Study on inclusion complexes of meso-tetrakis(2-thienyl)porphyrin and Cu-meso-tetrakis(2-thienyl)porphyrin with cyclodextrins by spectroscopy method

In phosphate buffer solution of pH5.4, the interaction of meso-tetrakis(2-thienyl)porphyrin(H₂TTP) and Cu-meso-tetrakis(2-thienyl)porphyrin(Cu-TTP) with α-cyclodextrin(α-CD), β-CD, γ-CD, heptakis(2,3,6-tri-O-methyl)-β-CD(TM-β-CD) has been studied by means of UV-vis, fluorescence and ¹HNMR spectroscopy, respectively. The H₂TTP and Cu-TTP can form 1:2 inclusion complexes with TM-β-CD and 1:1 inclusion complexes with the other three cyclodextrins. In this paper, the inclusion constants (K) of H₂TTP and Cu-TTP for the formation of the inclusion complexes have been estimated from the changes of absorbance and fluorescence intensity in phosphate buffer solution. The inclusive capabilities of different kinds of cyclodextrins are compared. The result shows that the inclusion ability of α-CD with H₂TTP and Cu-TTP is the strongest among the three native CDs. The inclusion ability of modified β-CD with H₂TTP and Cu-TTP is stronger, compared to the native β-CD, which indicates that the capacity matching plays a crucial role in the inclusion procedure except for the hydrophobic effect. In addition ¹HNMR spectra supports the inclusion conformation of the TM-β-CD-Cu-TTP inclusion complex, indicating the interaction mechanism of inclusion processes.     

O(~1D)+Si(CH_3)_3Cl反应生成振动激发的OH(υ≤5)

实验光谱学和理论计算都发现,“重原子”能隔离分子中的某些振动能景,如SiH_4中Si—H振动泛频的“局域模”.Roger 等在研究F 原子与M(CH_2CH=CH_2)_4(M=Sn,Ge)的反应中,发现了Sn,Ge 对过剩能量转移到其它部分有强烈的阻碍作用(在中间态的寿命时间内).最近,在研究O(~1D)+M(CH_3)_4生成OH(v)反应中,观测到类似的现象.M=C 时,Lutz 用激光诱导荧光方法检测OH 的振动分布,振动是冷的,v=1与v=0的布居比为0.05,