13 research outputs found
Small-Angle Excess Scattering: Glassy Freezing or Local Orientational Ordering?
We present Monte Carlo simulations of a dense polymer melt which shows
glass-transition-like slowing-down upon cooling, as well as a build up of
nematic order. At small wave vectors q this model system shows excess
scattering similar to that recently reported for light-scattering experiments
on some polymeric and molecular glass-forming liquids. For our model system we
can provide clear evidence that this excess scattering is due to the onset of
short-range nematic order and not directly related to the glass transition.Comment: 3 Pages of Latex + 4 Figure
Configurational Entropy and Diffusivity of Supercooled Water
We calculate the configurational entropy S_conf for the SPC/E model of water
for state points covering a large region of the (T,rho) plane. We find that (i)
the (T,rho) dependence of S_conf correlates with the diffusion constant and
(ii) that the line of maxima in S_conf tracks the line of density maxima. Our
simulation data indicate that the dynamics are strongly influenced by S_conf
even above the mode-coupling temperature T_MCT(rho).Comment: Significant update of reference
Path integral for half-binding potentials as quantum mechanical analog for black hole partition functions
The semi-classical approximation to black hole partition functions is not
well-defined, because the classical action is unbounded and the first variation
of the uncorrected action does not vanish for all variations preserving the
boundary conditions. Both problems can be solved by adding a Hamilton-Jacobi
counterterm. I show that the same problem and solution arises in quantum
mechanics for half-binding potentials.Comment: 6 pages, proceedings contribution to "Path integrals - New Trends and
Perspectives", Dresden, September 200
Monte-Carlo Simulation of 3-Dimensional Glassy Polymer Melts: Reptation Versus Single Monomer Dynamics
A polymer melt is simulated at finite temperature by the Monte-Carlo method. We use a coarse-grained model for the polymer system, the bond-fluctuation model. Static properties of the melt can be obtained by generating configurations not with single-monomer-dynamics which moves individual monomers locally, but reptation-dynamics which allows collective motion of the chains. This algorithm can produce equilibrated configurations much faster. It is demonstrated that static properties do not differ from those obtained by single-monomer-dynamics. Values of the radius of gyration, the mean square bond length and similar quantities for different temperatures and densities are presented