Exclusion process subject to conformational size changes

We introduce a model for stochastic transport on a one-dimensional substrate with particles assuming different conformations during their stepping cycles. These conformations correspond to different footprints on the substrate: in order to advance, particles are subject to successive contraction and expansion steps with different characteristic rates. We thus extend the paradigmatic exclusion process, provide predictions for all regimes of these rates that are in excellent agreement with simulations, and show that the current-density relation may be affected considerably. Symmetries are discussed, and exploited. We discuss our results in the context of molecular motors, confronting a hand-over-hand and an inchworm stepping mechanism, as well as for ribosomes.

Methods for the Determination of Internal Energy Contribution to Rubber Elasticity

In order to determine exactly the contribution of internal energy component to retractive force (fe/f), two methods (one is Single Specimen Method [Successive Contraction Method] and the other Multi Specimen Method), two different reference lengths (one is the initial length of undeformed specimen and the other the final length including permanent set), and two instruments of different type (one is automatic balance type relax-o-meter [ROM] and the other tensile tester) were examined by using natural rubber, cis-1,4-polyisoprene, and polyurethane rubber. The apparent mechanical and thermo-dynamic properties were significantly dependent upon these methods and reference lengths. In spite of the variation of C1 and C2 in Mooney-Rivlin plot, fe/f was almost unaffected and the sign of this value coincided with that expected from the chain conformation as far as ROM-Single or Multi Specimen Method and the final length were adopted. The influences of permanent set, the time used to attain equilibrium, etc. were also discussed.