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http://hdl.handle.net/123456789/2942
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| Title: | DIFFUSION IN RANDOM MEDIA |
| Authors: | SOLOMON, NEGASH ASFAW |
| Advisors: | Dr. TATEK YERGOU |
| Keywords: | physics |
| Copyright: | Jun-2010 |
| Date Added: | 10-May-2012 |
| Publisher: | AAU |
| Abstract: | In this work we present Monte Carlo simulations of particle and polymer diffusion in two
dimensional (2D) media with obstacles distributed randomly. For diffusion of a particle,
the mean-square displacement of the diffusing species is proportional to time for normal
diffusion. But in disordered systems anomalous diffusion may occur, in which the mean-
square displacement is proportional to some other power of time. In the presence of
moderate concentration of obstacles, diffusion is anomalous for short times and normal
for long times. Monte Carlo calculations are used to characterize anomalous diffusion
for obstacle concentrations between zero and the percolation threshold. As the obstacle
concentration approaches the percolation threshold, diffusion becomes more anomalous
for long times; the anomalous diffusion exponent increases. In polymer diffusion, we
present a new effective algorithm to simulate dynamic properties of polymeric systems
confined to lattice. The algorithm displays Rouse behavior for all spatial dimensions. The
systems are simulated by bond fluctuation method to study both the static and dynamic
properties of the polymer chains. For static properties we calculated the average mean-
2
square end-to-end distance R2 (N ) and the mean-square radius of gyration Rg (N ) .
Both the end-to-end distance and the radius of gyration are proportional to some power
2
of the number of monomers (N), R2 (N ) ∝ N 3/2 and Rg (N ) ∝ N 3/2 . For dynamical
properties we look at the mean-square displacement of the total chain. For short times
the mean-square displacement of the monomers g1 (t) and the mean-square displacement
of the monomers relative to the chains center of mass g2 (t) show the same behavior and
for long times the mean-square displacement of the center of mass g3 (t) takes over. |
| URI: | http://hdl.handle.net/123456789/2942 |
| Appears in: | Thesis - Physics
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