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