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41.
用原子力显微镜研究了胆固醇(Chol)对鞘磷脂(SM)/1,2-二油酸甘油-3-磷脂酰胆碱(DOPC)二元脂系统结构的影响和神经酰胺对SM/DOPC/Chol三元脂系统结构的影响. 实验发现, 在SM/DOPC二元脂系统中, 胆固醇和带饱和脂肪酸链的磷脂发生相互作用形成微区结构, 随着胆固醇含量的增加, 微区的面积逐渐增大, 形成了稳定的片层结构. 当把神经酰胺加入到等摩尔配比的SM/DOPC/Chol三元脂系统中时, 随着神经酰胺比例的增加, 先形成紧密的聚集态结构, 然后逐渐演变成具有特定微区的网状结构. 研究结果表明, 微区的形成主要是由分子不同的官能团之间的相互作用所决定, 这可能在细胞信号传导等生理活动中起到重要的作用. 相似文献
42.
浮区热毛细对流 总被引:1,自引:0,他引:1
概述了浮区中平行于自由面的表面张力梯度驱动热毛细对流领域的研究.
研究兴趣集中于振荡热毛细对流的起振,
或者说从定常流动到振荡流动的转捩. 起振依赖于一系列的临界参数,
临界关系可以表示为这些临界参数的复杂函数. 实验结果表明,
振荡流中速度的变化和平均流动的速度有相同的量级, 而其它量的变化,
比如温度和自由面半径的波动, 相比于它们的平均量而言则要小得多.
因此, 起振应是流体中动力学过程的结果, 该问题是强非线性的.
在过去几十年中, 一些理论模型被引入来研究这个问题,
使用的方法包括理论分析方法、 线性不稳定性分析方法、
能量稳定性分析方法以及非定常的三维直接数值模拟.
其中直接数值模拟被认为是对强非线性过程进行深入分析的最适合方法,
通常能得到和实验较符合的结果.
从振荡热毛细对流向湍流的转捩提供了一个研究混沌行为的新系统,
开创了一个非线性科学的新前沿, 是一个集中了大量近期工作的研究热点.
该文对浮区热毛细对流作了一个回顾, 包括理论模型和分析,
以及实验研究. 相似文献
43.
Dr. Ming Liang Koh Dr. Paul A. FitzGerald Prof. Gregory G. Warr Prof. Katrina A. Jolliffe Prof. Sébastien Perrier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(51):18419-18428
We present a fundamental study into the self‐assembly of (cyclic peptide)–polymer conjugates as a versatile supramolecular motif to engineer nanotubes with defined structure and dimensions, as characterised in solution using small‐angle neutron scattering (SANS). This work demonstrates the ability of the grafted polymer to stabilise and/or promote the formation of unaggregated nanotubes by the direct comparison to the unconjugated cyclic peptide precursor. This ideal case permitted a further study into the growth mechanism of self‐assembling cyclic peptides, allowing an estimation of the cooperativity. Furthermore, we show the dependency of the nanostructure on the polymer and peptide chemical functionality in solvent mixtures that vary in the ability to compete with the intermolecular associations between cyclic peptides and ability to solvate the polymer shell. 相似文献
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47.
Xiaohu Wei Graeme Moad Benjamin W. Muir Ezio Rizzardo Julien Rosselgong Wantai Yang San H. Thang 《Macromolecular rapid communications》2014,35(8):840-845
Redox‐cleavable mikto‐arm star polymers are prepared by an “arm‐first” approach involving copolymerization of a dimethacrylate mediated by a mixture of macroRAFT agents. Thus, RAFT copolymerization of the monomers BMA, DMAEMA, and OEGMA, with the disulfide dimethacrylate cross‐linker (DSDMA), bis(2‐methacryloyl)oxyethyl disulfide, mediated by a 1:1:1 mixture of three macroRAFT agents with markedly different properties [hydrophilic, poly[oligo(ethylene glycol) methacrylate]—P(OEGMA)8–9; cationizable, poly[2‐(dimethylamino)ethyl methacrylate]—P(DMAEMA); hydrophobic, poly(n‐butyl methacrylate)—P(BMA)] provides low dispersity mikto‐arm star polymers. Good control (Đ < 1.3) is observed for the target P(DMAEMA)/P(OEGMA)/P(BMA) (3:3:1) mikto‐arm star, a double hydrophilic P(DMAEMA)/P(OEGMA) (3:3) mikto‐arm star and a hydrophobic P(BMA) homo‐arm star. However, Đ for the target mikto‐arm stars increases with an increase in either the ratio [DSDMA]:[total macroRAFT] or the fraction of hydrophobic P(BMA) macroRAFT agent. The quaternized mikto‐arm star in dilute aqueous solution shows a monomodal particle size distribution and an average size of ≈145 nm.
48.
Temperature scanning X-ray diffraction at phase transitions of biologically related lipid assemblies
Ichiro Hatta 《Journal of Thermal Analysis and Calorimetry》2005,82(1):189-192
Summary Based upon the results of ac calorimetry and temperature scanning X-ray diffraction in the phospholipid/cholesterol system,
the phase diagram was constructed by taking into account the ripple structure. From the analysis of the cholesterol concentration
dependence of the modified ripple structure the cholesterol-rich state which lies in the higher cholesterol concentration
than 20 mol% in the phase diagram is proposed. It is proposed that this is a fundamental complex that appears generally in
lipid/cholesterol systems. 相似文献
49.
Fluidic communication between multiple vertically segregated microfluidic channels connected by nanocapillary array membranes 总被引:1,自引:0,他引:1
Hybrid microfluidic/nanofluidic devices offer unique capabilities for manipulating and analyzing minute volumes of expensive or hard-to-obtain samples. Here, multilayer poly-(methyl methacrylate) microchips, with multiple spatially isolated microfluidic channels interconnected by nanocapillary array membranes (NCAMs), are fabricated using an adhesive contact printing process. The NCAMs, positioned between the microfluidic channel layers, add functionality to the inter-microchannel fluid transfer unit operation. They do so because the transport of specific analytes through the NCAM can be controlled by adjusting the ionic strength, the polarity of the applied bias, the surface charge density, and the pore size. A simplified, floating injection technique for NCAM-coupled nanofluidic devices is described and compared with conventional biased injection. In the floating injection approach, a voltage is applied across the injection channel and the slight electric field extension at the cross-section is used to transfer analytes through the nanopores to the separation channel. Floating injection excels in plug reproducibility, separation resolution, and operation simplicity, although it decreases assay throughput relative to biased injection. Floating injection can avoid the uneven distribution of analytes in the microfluidic channel that sometimes results from biased injection because of the volume mismatch between NCAM nanopore transport capacity and the supply of fluid. Moreover, the pressure-driven flow caused by the mismatch of the EOFs in the microfluidic channels connected by an NCAM must be considered when using NCAMs with pore diameters below 50 nm. 相似文献
50.
We introduce herein an efficient microfluidic approach for continuous transport and localized collection of nanoparticles via hybrid electrokinetics, which delicately combines linear and nonlinear electrokinetics driven by a composite DC-biased AC voltage signal. The proposed technique utilizes a simple geometrical structure, in which one or a series of metal strips serving as floating electrode (FE) are attached to the substrate surface and arranged in parallel between a pair of coplanar driving electrodes (DE) in a straight microchannel. On application of a DC-biased AC electric field across the channel, nanoparticles can be transported continuously by DC bulk electroosmotic flow, and then trapped selectively onto the metal strips due to AC-field induced-charge electrokinetic (ICEK) phenomenon, which behaves as counter-rotating micro-vortices around the ideally polarizable surfaces of FE. Finite-element simulation is carried out by coupling the dual-frequency electric field, flow field and sample mass transfer in sequence, for guiding a practical design of the microfluidic nanoparticle concentrator. With the optimal device geometry, the actual performance of the technique is investigated with respect to DC bias, AC voltage amplitude, and field frequency by using both latex nanospheres (∼500 nm) and BSA molecules (∼10 nm). Our experimental observation indicates nanoparticles are always enriched into a narrow bright band on the surface of each FE, and a horizontal concentration gradient even emerges in the presence of multiple metal strips, which therefore permits localized analyte enrichment. The proposed trapping method is supposed to guide an elaborate design of flexible electrokinetic frameworks embedding FE for continuous-flow analyte manipulation in modern microfluidic systems. 相似文献