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Recently our group has reported experiments using an obstacle array to precondition the conformations of DNA molecules to facilitate their stretch in a microcontraction. Based upon previous successes simulating electrophoretic stretching in microcontractions without obstacles, we use our simulation model to study the deformation of DNA chains in a microcontraction preceded by an array of cylindrical obstacles. We compare our data to the experimental results and find good qualitative, and even quantitative, agreement concerning the behavior of the chains in the array; however, the simulations overpredict the mean stretch of the chains as they leave the contraction. We examine the amount of stretch gained between leaving the array and reaching the end of the contraction and speculate that the differences seen are caused by nonlinear electrokinetic effects that become important in the contraction due to a combination of field gradients and high field strengths. 相似文献
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This Special Topic section of Biomicrofluidics contains original contributions that were presented at the 82nd Colloid and Surface Science Symposium, which took place on 15–18 June 2008 at North Carolina State University. The Symposium covered a wide range of topics that are relevant to the fundamentals of fluidics and their application to biological systems.The recent interest in microfluidics and nanofluidics is constantly increasing due to the numerous applications that these techniques have to offer. They have been used for chemical and biomolecular sensing, separation of charged analytes, and single DNA molecule manipulation. These applications were facilitated by the significant increase in the range of advanced microfabrication and nanofabrication techniques. Improving and extending the range of applicability of micro- and nanofluidic techniques also requires better fundamental understanding of the physics of the transport at small length scales. The transport of fluids and solutes in microchannels and nanochannels usually occurs at very small Reynolds regime. The typical length scale and the surface forces (electrostatic, van der Waals, hydrophobic, hydration, etc.) may be comparable to the size of the channels. All these features often require the development of new experimental techniques and approaches for theoretical analysis.The importance and the substantial recent interest in micro- and nanofluidics prompted the organization of a special session on Electrokinetic Phenomena and Microfluidics as part of the program at the 82nd Colloid and Surface Science Symposium at North Carolina State University in June 2008. The collected papers in this issue of Biomicrofluidics cover some of the very important fundamental and engineering aspects of electrokinetic phenomena in micro- and nanofluidic channels. These include molecular dynamics simulation of biomolecules in confined spaces, analysis of the electric double layer effects on the fluid flow in nanochannels, hydrodynamic resistance to droplet motion in microchannels, electrophoresis in nanocomposite gels, and microfluidics for nanoparticle fabrication. The paper by Srivastava et al.1 explores the possibility of using microfluidics for fabrication of Janus nanofibers. Chang2 presented a theoretical analysis of the electro-osmosis on a salt-free microchannel by simultaneously solving the nonlinear Poisson–Boltzmann equation for the electrostatic potential distribution and the Navier–Stokes equations for the fluid flow. Trahan and Doyle3 reported theoretical analysis of DNA molecule interaction with obstacles in a microchannel. Finally, Labrot et al.4 presented studies on the droplet hydrodynamic resistance in a microfluidic channel.We hope that the reader will find the papers useful and informative. 相似文献
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Patrick T. Terenzini 《Higher Education》1999,38(1):33-48
This paper identifies some of the most significant -- and counterproductive -- gaps between what research reveals about how college students learn and how to maximize student learning, on the one hand, and, on the other, current academic, pedagogical, and administrative practices and policies. Drawing on research evidence from the cognitive and neural sciences, anthropology, sociology, psychology, education, and other sources, the paper first summarizes what is known about how students learn and what instructional practices and structures appear to be most effective in promoting student learning. The paper then contrasts this research-based evidence with current pedagogical, curricular, structural, and administrative practices and policies, and discusses the implications for instructional and organizational practices and policies. The paper concludes with a discussion of five explanations of why the gap exists and what might be done to close it. 相似文献
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