A star edge coloring of a graph is a proper edge coloring with no 2-colored path or cycle of length four. The star chromatic index χst′(G) of G is the minimum number t for which G has a star edge coloring with t colors. We prove upper bounds for the star chromatic index of bipartite graphs G where all vertices in one part have maximum degree 2 and all vertices in the other part has maximum degree b. Let k be an integer (k≥1); we prove that if b=2k+1, then χst′(G)≤3k+2; and if b=2k, then χst′(G)≤3k; both upper bounds are sharp. We also consider complete bipartite graphs; in particular we determine the star chromatic index of such graphs when one part has size at most 3, and prove upper bounds for the general case. Finally, we consider the well-known conjecture that subcubic graphs have star chromatic index at most 6; in particular we settle this conjecture for cubic Halin graphs.

In this paper, we continue the study of power domination in graphs (see [T. W. Haynes et al., SIAM J. Discrete Math., 15 (2002), pp. 519--529; P. Dorbec et al., SIAM J. Discrete Math., 22 (2008), pp. 554--567; A. Aazami et al., SIAM J. Discrete Math., 23 (2009), pp. 1382--1399]). Power domination in graphs was birthed from the problem of monitoring an electric power system by placing as few measurement devices in the system as possible. A set of vertices is defined to be a power dominating set of a graph if every vertex and every edge in the system is monitored by the set following a set of rules (according to Kirschoff laws) for power system monitoring. The minimum cardinality of a power dominating set of a graph is its power domination number. We show that the power domination of a connected cubic graph on $n$ vertices different from $K_{3,3}$ is at most $n/4$ and this bound is tight. More generally, we show that for $k \ge 1$, the $k$-power domination number of a connected $(k+2)$-regular graph on $n$ vertices different from $K_{k+2,k+2}$ is at most $n/(k+3)$, where the $1$-power domination number is the ordinary power domination number. We show that these bounds are tight.

We prove that for any positive integer k, the edges of any graph whose fractional arboricity is at most $k + 1/(3k+2)$ can be decomposed into k forests and a matching. This is a partial result in the direction of the “Nine Dragon Tree” conjecture of Montassier et al.

This paper addresses the one-to-all broadcasting problem and the one-to-many broadcasting problem, usually simply called broadcasting and multicasting, respectively. Broadcasting is the information dissemination problem in which a node of a network sends the same piece of information to all the other nodes. Multicasting is a partial broadcasting in the sense that only a subset of nodes forms the destination set. Both operations have many applications in parallel and distributed computing. In this paper, we study these problems in both line model, and cut-through model. The former assumes long distance calls between nonneighboring processors. The latter strengthens the line model by taking into account the use of a routing function. Long distance calls are possible in circuit-switched and wormhole-routed networks, and also in many networks supporting optical facilities. In the line model, it is well known that one can compute in polynomial time a [log/sub 2/n]-round broadcast or multicast protocol for any arbitrary network. Unfortunately such a protocol is often inefficient from a practical point of view because it does not use the resources of the network in a balanced way. In this paper, we present a new algorithm to compute broadcast or multicast protocols. This algorithm applies under both line and cut-through models. Moreover, it returns protocols that efficiently use the bandwidth of the network. From a complexity point of view, we also show that most of the optimization problems relative to the maximization of the efficiency of broadcast or multicast protocols in terms of switching time or vertex load are NP-complete. We have, however, derived polynomial efficient solutions for tree-networks.