Complex-Temperature Singularities of Ising Models

We report new results on complex-temperature properties of Ising models. These include studies of the $s=1/2$ model on triangular, honeycomb, kagom\'e, $3 \cdot 12^2$, and $4 \cdot 8^2$ lattices. We elucidate the complex--$T$ phase diagrams of the higher-spin 2D Ising models, using calculations of partition function zeros. Finally, we investigate the 2D Ising model in an external magnetic field, mapping the complex--$T$ phase diagram and exploring various singularities therein. For the case $\beta H=i\pi/2$, we give exact results on the phase diagram and obtain susceptibility exponents $\gamma'$ at various singularities from low-temperature series analyses.Comment: 4 pages, latex, to appear in the Proceedings of Lattice-9

Fat Fisher Zeroes

We show that it is possible to determine the locus of Fisher zeroes in the thermodynamic limit for the Ising model on planar (``fat'') phi4 random graphs and their dual quadrangulations by matching up the real part of the high and low temperature branches of the expression for the free energy. The form of this expression for the free energy also means that series expansion results for the zeroes may be obtained with rather less effort than might appear necessary at first sight by simply reverting the series expansion of a function g(z) which appears in the solution and taking a logarithm. Unlike regular 2D lattices where numerous unphysical critical points exist with non-standard exponents, the Ising model on planar phi4 graphs displays only the physical transition at c = exp (- 2 beta) = 1/4 and a mirror transition at c=-1/4 both with KPZ/DDK exponents (alpha = -1, beta = 1/2, gamma = 2). The relation between the phi4 locus and that of the dual quadrangulations is akin to that between the (regular) triangular and honeycomb lattices since there is no self-duality.Comment: 12 pages + 6 eps figure

Complexity computation for compact 3-manifolds via crystallizations and Heegaard diagrams

The idea of computing Matveev complexity by using Heegaard decompositions has been recently developed by two different approaches: the first one for closed 3-manifolds via crystallization theory, yielding the notion of Gem-Matveev complexity; the other one for compact orientable 3-manifolds via generalized Heegaard diagrams, yielding the notion of modified Heegaard complexity. In this paper we extend to the non-orientable case the definition of modified Heegaard complexity and prove that for closed 3-manifolds Gem-Matveev complexity and modified Heegaard complexity coincide. Hence, they turn out to be useful different tools to compute the same upper bound for Matveev complexity.Comment: 12 pages; accepted for publication in Topology and Its Applications, volume containing Proceedings of Prague Toposym 201

Complex-Temperature Phase Diagram of the 1D Z6Z_6 Clock Model and its Connection with Higher-Dimensional Models

We determine the exact complex-temperature (CT) phase diagram of the 1D $Z_6$ clock model. This is of interest because it is the first exactly solved system with a CT phase boundary exhibiting a finite-$K$ intersection point where an odd number of curves (namely, three) meet, and yields a deeper insight into this phenomenon. Such intersection points occur in the 3D spin 1/2 Ising model and appear to occur in the 2D spin 1 Ising model. Further, extending our earlier work on the higher-spin Ising model, we point out an intriguing connection between the CT phase diagrams for the 1D and 2D $Z_6$ clock models.Comment: 10 pages, latex, with two epsf figure

On the limiting parameters of artificial cavitation applied to reduce drag

Artificial cavitation, or ventilation, is produced by releasing gas into liquid flow. One objective of creating such a multiphase flow is to reduce frictional and sometimes wave resistance of a marine vehicle completely or partially immersed in the water. In this paper, flows around surface ships moving along the water-air boundary are considered. It is favorable to achieve a negative cavitation number in the developed cavitating flow under the vessel's bottom in order to generate additional lift. Cavities formed in the flow have limiting parameters that are affected by propulsive and lifting devices. Methods for calculating these influences and results of a parametric study are reported

Cardinal p and a theorem of Pelczynski

We show that it is consistent that for some uncountable cardinal k, all compactifications of the countable discrete space with remainders homeomorphic to $D^k$ are homeomorphic to each other. On the other hand, there are $2^c$ pairwise non-homeomorphic compactifications of the countable discrete space with remainders homeomorphic to $D^c$ (where c is the cardinality of the continuum)

On spaces in countable web

We show that a Tychonoff discretely star-Lindelof space can have arbitrarily big extent and note that there are consistent examples of normal discretely star-Lindelof spaces with uncountable extent