Electrophoretic separations in poly(dimethylsiloxane) microchips using a mixture of ionic and zwitterionic surfactants

The use of mixtures of ionic and zwitterionic surfactants in poly(dimethylsiloxane) (PDMS) microchips is reported. The effect of surfactant concentration on electroosmotic flow (EOF) was studied for a single anionic surfactant (sodium dodecyl sulfate, SDS), a single zwitterionic surfactant (N-tetradecylammonium-N,N-dimethyl-3-ammonio-1-propanesulfonate, TDAPS), and a mixed SDS/TDAPS surfactant system. SDS increased the EOF as reported previously while TDAPS showed an initial increase in EOF followed by a reduction at higher concentrations. When TDAPS was added to a solution containing SDS, the EOF decreased in a concentration-dependent manner. The EOF for all three surfactant systems followed expected pH trends, with increasing EOF at higher pH. The mixed surfactant system allowed tuning of the EOF across a range of pH and concentration conditions. After establishing the EOF behavior, the adsorption/desorption kinetics were measured and showed a slower adsorption/desorption rate for TDAPS than SDS. Finally, the separation and electrochemical detection of model catecholamines in buffer and reduced glutathione in red blood cell lysate using the mixed surfactant system were explored. The mixed surfactant system provided shorter analysis times and/or improved resolution when compared to the single surfactant systems.     

Electrophoretic separations in poly(dimethylsiloxane) microchips using mixtures of ionic,nonionic and zwitterionic surfactants

The use of surfactant mixtures to affect both EOF and separation selectivity in electrophoresis with PDMS substrates is reported, and capacitively coupled contactless conductivity detection is introduced for EOF measurement on PDMS microchips. First, the EOF was measured for two nonionic surfactants (Tween 20 and Triton X‐100), mixed ionic/nonionic surfactant systems (SDS/Tween 20 and SDS/Triton X‐100), and finally for the first time, mixed zwitterionic/nonionic surfactant systems (TDAPS/Tween 20 and TDAPS/Triton X‐100). EOF for the nonionic surfactants decreased with increasing surfactant concentration. The addition of SDS or TDAPS to a nonionic surfactant increased EOF. After establishing the EOF behavior, the separation of model catecholamines was explored to show the impact on separations. Similar analyte resolution with greater peak heights was achieved with mixed surfactant systems containing Tween 20 and TDAPS relative to the single surfactant system. Finally, the detection of catecholamine release from PC12 cells by stimulation with 80 mM K⁺ was performed to demonstrate the usefulness of mixed surfactant systems to provide resolution of biological compounds in complex samples.     

氮杂Brazilin/二芳基茚杂合物的合成研究

天然产物在药物化学中具有非常重要的地位,天然产物杂合物的设计合成,可以为药物筛选提供数目更多、结构更多样化的生物活性分子,是发现更多的新药先导化合物的一条非常重要的途径.以邻苯二甲醚为原料,经傅克酰基化、酮酯缩合、Knoevenagel缩合、Nazarov环化、酮酸酯的胺解、1,3-二羰基化合物的α-羟基化、酮羰基和酰胺的还原及分子内的傅克环化共9步反应,合成了氮杂brazilin(Aza-brazilin)与1,3-二芳基茚类化合物的一个杂合物.     

A theoretical study of the dependence of the ASxSi6−x cluster structures and properties on composition

The effect of the composition ratio between arsenic and silicon atoms on the structures and properties of As_xSi_6?x (x = 0–6) have been systematically investigated using the density functional theory at the B3LYP/6‐311+G* level. The As_xSi_6?x clusters prefer substitutional rather than attaching structures; the Si‐rich clusters favor Si₆‐like structures, whereas the As‐rich clusters prefer As₆‐like structures. The As atoms locating at the framework may explain the difficulty of removal of arsenic impurities from polycrystalline silicon. In general, the average binding energies gradually decrease, implying the As_xSi_6?x clusters become increasingly unstable as x increases. Both the HOMO‐LUMO gaps and the As‐dissociation energies present a strong even–odd alternation, implying alternating chemical stability, with the even x members being more stable than the odd ones. The dissociation energies of an As atom from As_xSi_6?x are: 3.07, 2.84, 1.84, 2.52, 1.86, and 2.85 eV, for x = 1–6, respectively, and 3.80, 3.08, 2.64, 3.01, 2.93, 3.16 eV for Si (x = 0–5). These dissociation energy results should provide a useful reference for further experimental investigations. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Numerical analysis for the scattering by obstacles in a homogeneous chiral environment

The scattering of time-harmonic electromagnetic waves propagating in a homogeneous chiral environment by obstacles is studied. The problem is simplified to a two-dimensional scattering problem, and the existence and the uniqueness of solutions are discussed by a variational approach. The diffraction problem is solved by a finite element method with perfectly matched absorbing layers. Our computational experiments indicate that the method is efficient.     

Hopf bifurcation control in the XCP for the Internet congestion control system

In this paper, we investigated the Hopf bifurcation of the eXplicit Control Protocol (XCP) for the Internet congestion control system. These bifurcation behaviors may cause heavy oscillation of average queue length and induce network instability. A time-delayed feedback control method was proposed for controlling Hopf bifurcation in the XCP system. Numerical simulation results are presented to show that the time-delayed feedback controller is efficient in controlling Hopf bifurcation.     

Leader-following finite-time consensus for multi-agent systems with jointly-reachable leader

Finite-time consensus problems of the leader-following multi-agent systems with jointly-reachable leader and switching jointly-reachable leader are studied in this paper. Based on the graph theory, LaSalle’s invariance principle and Lyapunov stability theory, the finite-time consensus protocols are presented for the first-order and second-order leader-following systems. Some examples and simulation results are given to illustrate the effectiveness of the obtained theoretical results.     

Consensus of second-order and high-order discrete-time multi-agent systems with random networks

This paper studies the convergence and convergence speed for the second-order and the high-order discrete-time multi-agent systems with random networks and arbitrary weights. Random networks mean that the existence of any edge is probabilistic and independent of any other edge. By introducing the agreement set, velocity control gain and high-order state control gain, some consensus protocols are provided for the discrete-time random networks. Moreover, the per-step and asymptotic convergence factors are proposed to measure the convergence and convergence speed. Some examples and simulation results are given to illustrate the effectiveness of the obtained theoretical results.     

星形裂纹的应力分析

利用复变函数的方法, 通过构造适当的保角映射研究了星形裂纹的平面弹性问题,给出了裂纹尖端I型与II型问题应力强度因子的解析解.并由此模拟出了经典的Griffith裂纹,共点均匀分布三裂纹,十字裂纹,对称八裂纹问题.      

发光二极管诱导荧光检测器*

发光二极管诱导荧光检测器（LED-IF）是近十年来发展起来的一种微型化荧光检测器,在流动注射、毛细管液相色谱、毛细管电泳及芯片电泳等微流动分析系统中具有广泛的应用。本文讨论了LED-IF的4种光学结构,并对其主要器件,包括光源、滤光片、透镜、光纤、光电检测器以及检测池作了详细讨论,还介绍了LED-IF与其它技术的联用及其在生物、医药和环境样品检测中的应用,对未来的发展趋势作了展望。