The star chromatic index χs(G) of a graph G is the minimum number of colors needed to properly color the edges of the graph so that no path or cycle of length four is bi-colored. We obtain a near-linear upper bound in terms of the maximum degree ∆ = ∆(G). Our best lower bound on χs in terms of ∆ is 2∆(1 + o(1)) valid for complete graphs. We also consider the special case of cubic graphs, for wh...

Waveguides with low confinement loss, low chromatic dispersion, and low nonlinear effects are used in optical communication systems. Optical fibers can also be employed in such systems. Besides optical fibers, photonic crystal fibers are also highly suitable transmission media for optical communication systems. In this paper, we introduce two new designs of index-guiding photonic crystal fiber ...

A vertex coloring of a graph G is called acyclic if no two adjacent vertices have the same color and there is no two-colored cycle in G. The acyclic chromatic number of G , denoted by A ( G ) , is the least number of colors in an acyclic coloring of G. We show that if G has maximum degree d, then A ( G ) = O(d413) as d+m. This settles a problem of Erdos who conjectured, in 1976, that A ( G ) = ...

We show that the 2-edge-colored chromatic number of a class of simple graphs is bounded if and only if the acyclic chromatic number is bounded for this class. Recently, the CSP dichotomy conjecture has been reduced to the case of 2-edge-colored homomorphism and to the case of 2-vertex-colored homomorphism. Both reductions are rather long and follow the reduction to the case of oriented homomorp...

The dichromatic number ~ χ(D) of a digraph D is the least number k such that the vertex set of D can be partitioned into k parts each of which induces an acyclic subdigraph. Introduced by Neumann-Lara in 1982, this digraph invariant shares many properties with the usual chromatic number of graphs and can be seen as the natural analog of the graph chromatic number. In this paper, we study the li...

In his Master’s thesis, Ján Mazák proved that the circular chromatic index of the type 1 generalized Blanuša snark B n equals 3+ 2 n . This result provided the first infinite set of values of the circular chromatic index of snarks. In this paper we show the type 2 generalized Blanuša snark B n has circular chromatic index 3 + 1 b1+3n/2c . In particular, this proves that all numbers 3 + 1/n with...