No abstract

We use a previously developed bead-spring Brownian dynamics model for simulating the topological interactions between polymers and thin obstacles to study electrophoretically translating DNA strands colliding directly with an immovable post over a wide range of chain lengths (25 e N K e 1500) and field strengths or velocities (10 -4 e Pe Kuhn e 10 °). Here N K is the number of Kuhn steps in the chain and Pe Kuhn is the Peclet number based on the Kuhn length. This Peclet number is the ratio of the field-induced polymer motion to the Brownian motion. We find that the mean distance 〈∆ x j〉 by which the chain migration is delayed by the entanglement interaction increases with higher fields, encompassing four distinct regimes. The two fastest regimes exhibit variations of the classic rope-and-pulley dynamics, in which the chain is draped around the entanglement and the longer of the two dangling arms pulls the shorter arm around the obstacle. In one of these regimes, occurring at the highest field strength, the dimensionless delay distance reaches its theoretical upper limit at 〈∆ x j〉/N K ) 0.5, and in the other, at moderately high field strength, the incomplete extension of each arm is modeled as a terminal relaxed "ball" attached to a fully extended "chain." In the two slower regimes, the polymer retains a coil-like shape as it diffuses laterally and eventually clears the post without deforming. We develop theoretical expressions that describe both the average delay and the distribution of delays for all regimes, except the slowest one, which is distinguished by a peculiar fractional power law relationship 〈∆ x j〉/N K ∝ Pe Kuhn 0.27 .

The University of Michigan (UM) ASEE Student Chapter continues to thrive as an active graduate student organization dedicated to providing a forum for furthering excellence in engineering education. The organization sponsors numerous events to help graduate students prepare for careers in academia, to help undergraduate students prepare for graduate school, and to support the involvement of underrepresented minorities in higher education. In this paper we highlight the activities of the ASEE student chapter at UM and demonstrate the important role that the student chapter has in promoting the nation's future engineering educators. The strategies employed by the student chapter to sustain viability will also be presented to encourage the formation and growth of ASEE student chapters at other institutions, and thereby build upon the mission of the national ASEE organization to develop the nation's future engineering educators.