The abelian sandpile models feature a finite abelian group G generated by the operators corresponding to particle addition at various sites. We study the canonical decomposition of G as a product of cyclic groups G = Z d1 × Z d2 × Z d3 · · · × Z dg where g is the least number of generators of G, and d i is a multiple of d i+1. The structure of G is… (More)
We define and study a class of graphs, called 2-stab interval graphs (2SIG), with boxicity 2 which properly contains the class of interval graphs. A 2SIG is an axes-parallel rectangle intersection graph where the rectangles have unit height (that is, length of the side parallel to Y-axis) and intersects either of the two fixed lines, parallel to the X-axis,… (More)
Signed graphs are studied since the middle of the last century. Recently, the notion of homomorphism of signed graphs has been introduced since this notion captures a number of well known conjectures which can be reformulated using the definitions of signed homomorphism. In this paper, we introduce and study the properties of some target graphs for signed… (More)
The clique number of an undirected graph G is the maximum order of a complete subgraph of G and is a well-known lower bound for the chromatic number of G. Every proper k-coloring of G may be viewed as a homomorphism (an edge-preserving vertex mapping) of G to the complete graph of order k. By considering homomorphisms of oriented graphs (digraphs without… (More)
In this paper we determine, or give lower and upper bounds on, the 2-dipath and oriented L(2, 1)-span of the family of planar graphs, planar graphs with girth 5, 11, 16, partial k-trees, outerplanar graphs and cacti.
The first and second homology groups, H 1 and H 2 , are computed for configuration spaces of framed three-dimensional point-particles with annihilation included , when up to two particles and an antiparticle are present, the types of frames considered being S 2 and SO(3). Whereas a recent calculation for two-dimensional particles used the Mayer-Vietoris… (More)
An (m, n)-colored mixed graph G is a graph with its arcs having one of the m different colors and edges having one of the n different colors.