We consider close-packed dimers, or perfect matchings, on twodimensional regular lattices. We review known results and derive new expressions for the free energy, entropy, and the molecular freedom of dimers for a number of lattices including the simple-quartic (44), honeycomb (63), triangular (36), kagomé (3 · 6 · 3 · 6), 3-12 (3 · 122) and its dual [3 · 122], and 4-8 (4 · 82) and its dual Uni...

We compute coefficients of two-derivative terms in the hydrodynamic energy momentum tensor of a viscous fluid which has an AdSD dual with 3 ≤ D ≤ 7. For the case of D = 3 we obtain an exact AdS3 black hole solution, valid to all orders in a derivative expansion, dual to a perfect fluid in 1 + 1 dimensions. June 2008 e-mail: [email protected] e-mail: [email protected]...

The construction of joins and secant varieties is studied in the combinatorial context of monomial ideals. For ideals generated by quadratic monomials, the generators of the secant ideals are obstructions to graph colorings, and this leads to a commutative algebra version of the Strong Perfect Graph Theorem. Given any projective variety and any term order, we explore whether the initial ideal o...

I demonstrate that a consistent interpretation of Reichenbach’s (1947) primitives and their configurations enables the construction of an intuitive and elegant semantic space for all logically possible tense meanings, independent of their mode of expression. I argue that the property which defines the perfect in absolute tense systems is the dissociation of the temporal location of the situatio...

Lovász and Plummer conjectured, in the mid 1970’s, that every cubic graph G with no cutedge has an exponential in |V (G)| number of perfect matchings. In this work we show that every cubic planar graph G whose geometric dual graph is a stack triangulation has at least 3φ (G)|/72 distinct perfect matchings, where φ is the golden ratio. Our work builds on a novel approach relating Lovász and Plum...

Given a set S of 2n points in R d , a perfect matching of S is a set of n edges such that each point of S is a vertex of exactly one edge. The weight of a perfect matching is the sum of the Euclidean lengths of all edges. Rao and Smith have recently shown that there is a constant r > 1, that only depends on the dimension d, such that a perfect matching whose weight is less than or equal to r ti...

Matching preclusion is a measure of robustness in the event of edge failure in interconnection networks. The matching preclusion number of a graph G is the minimum number of edges whose deletion leaves the resulting graph without a perfect matching or an almost perfect matching, and the conditional matching preclusion number of G is the minimum number of edges whose deletion leaves the resultin...

By using recent results from graph theory, including the Strong Perfect Graph Theorem, we obtain a unifying framework for a number of tractable classes of constraint problems. These include problems with chordal microstructure; problems with chordal microstructure complement; problems with tree structure; and the “all-different” constraint. In each of these cases we show that the associated mic...

A graph G is perfect if for every induced subgraph H, the chromatic number of H equals the size of the largest complete subgraph of H, and G is Berge if no induced subgraph of G is an odd cycle of length at least 5 or the complement of one. The “strong perfect graph conjecture” (Berge, 1961) asserts that a graph is perfect if and only if it is Berge. A stronger conjecture was made recently by C...