Condensation and Metastability in the 2D Potts Model

For the first order transition of the Ising model below $T_c$, Isakov has proven that the free energy possesses an essential singularity in the applied field. Such a singularity in the control parameter, anticipated by condensation theory, is believed to be a generic feature of first order transitions, but too weak to be observable. We study these issues for the temperature driven transition of the $q$ states 2D Potts model at $q>q_c=4$. Adapting the droplet model to this case, we relate its parameters to the critical properties at $q_c$ and confront the free energy to the many informations brought by previous works. The essential singularity predicted at the transition temperature leads to observable effects in numerical data. On a finite lattice, a metastability domain of temperatures is identified, which shrinks to zero in the thermodynamical limit. ~Comment: 32 pages, 6 figures, Late

Modeling of turbulent transport as a volume process

An alternative type of modeling was proposed for the turbulent transport terms in Reynolds-averaged equations. One particular implementation of the model was considered, based on the two-point velocity correlations. The model was found to reproduce the trends but not the magnitude of the nonisotropic behavior of the turbulent transport. Some interesting insights were developed concerning the shape of the contracted two-point correlation volume. This volume is strongly deformed by mean shear from the spherical shape found in unstrained flows. Of particular interest is the finding that the shape is sharply waisted, indicating preferential lines of communication, which should have a direct effect on turbulent transfer and on other processes

Hubbard Model with Luscher fermions

First applications of the new algorithm simulating dynamical fermions are reported. The method reproduces previous results obtained with different techniques.Comment: talk presented at the XII International Symposium LATTICE94, Bielefeld, Germany, September 1994, to appear in the Proceedings. 3 pages, LATEX, required Elsevier espcrc2.sty style file is attached at the end of this LATEX text. Postscript figures included in the latex document with the epsf facilit