Entropic trapping of macromolecules by mesoscopic periodic voids in a polymer hydrogel

The separation of macromolecules such as polymers and DNA by means of electrophoresis, gel permeation chromatography or filtration exploits size-dependent differences in the time it takes for the molecules to migrate through a random porous network. Transport through the gel matrices, which usually consist of full swollen crosslinked polymers, depends on the relative size of the macromolecule compared with the pore radius. Sufficiently small molecules are thought to adopt an approximately spherical conformation when diffusing through the gel matrix, whereas larger ones are forced to migrate in a snake-like fashion. Molecules of intermediate size, however, can get temporarily trapped in the largest pores of the matrix, where the molecule can extend and thus maximize its conformational entropy. This 'entropic trapping' is thought to increase the dependence of diffusion rate on molecular size. Here we report the direct experimental verification of this phenomenon. Bragg diffraction from a hydrogel containing a periodic array of monodisperse water voids confirms that polymers of different weights partition between the hydrogel matrix and the water voids according to the predictions of the entropic trapping theory. Our approach might also lead to the design of improved separation media based on entropic trapping.     

带材厚度及其腹板宽度对简单断面型钢成型的影响

以弹塑性大变形有限元理论为基础,对槽钢成型过程做出合理简化,建立分析模型．利用MARC软件对槽钢辊弯成型进行了三维有限元数值模拟,分析得出带材厚度及其腹板宽度对槽钢成型的影响．     

基于R2出口测宽的宽度模型研究和优化

由于在2 050 mm热连轧机中只有粗轧机的立辊具有宽度压下的功能,粗轧出口宽度偏差在精轧及卷取机组基本无法进行弥补,因此粗轧宽度控制精度直接决定了精轧及卷取出口宽度精度,优化粗轧宽度控制模型以减少粗轧宽度偏差,是提高宽度控制水平的重要手段。粗轧R2出口新增测宽仪为模型的优化提供了基本条件,可以实测轧件在R2出口的宽度偏差,并基于实测数据进行模型的学习与后续轧机的设定修正,有利于宽度控制精度的提高。     

Capillary electrophoretic separation of nucleotide isomers via complexation with cyclodextrin and borate

The electrophoretic behaviour of monophosphorylated nucleotide isomers can be manipulated using complex-forming reactions with beta-cyclodextrin (beta-CD) and borate. Resolution of the 2'- and 3'-isomers of nucleotides is possible when the electrophoresis buffer contains 10 mM CD. The effect of beta-CD concentration on electrophoretic mobility is used to calculate the formation constant, K, of beta-CD-nucleotide complexes. The 3'-isomer of adenosine monophosphate (AMP) forms the strongest complex with beta-CD probably as a result of hydrogen bonding between the phosphate group of AMP and hydroxyls of beta-CD. In addition, complexation of 5'-nucleotides with borate increases the migration time window and leads to better separation. Complex-forming reactions of guanosine monophosphate and uridine monophosphate are shown to be strongly dependent on buffer pH. A mixture of 12 monophosphorylated nucleotides can be separated in less than 15 min using a buffer of 20 mM borate-10 mM beta-CD.