A twofold 8-cycle system is an edge-disjoint decomposition of a twofold complete graph (which has two edges between every pair of vertices) into 8-cycles. The order of the complete graph is also called the order of the 8-cycle system. A twofold 2-perfect 8-cycle system is a twofold 8-cycle system such that the collection of distance 2 edges in each 8-cycle also cover the complete graph, forming a (twofold) 4-cycle system. Existence of 2-perfect 8-cycle systems for all admissible orders was shown in [1], although \(\lambda\)-fold existence for \(\lambda > 1\) has not been done.

In this paper, we impose an extra condition on the twofold \(2\)-perfect \(8\)-cycle system. We require that the two paths of length two between each pair of vertices, say \(x, a_{xy}, y\) and \(x, b_{xy}, y\), should be distinct, that is, with \(a_{xy} \neq b_{xy}\); thus they form a \(4\)-cycle \((x, a, y, b)\).

We completely solve the existence of such twofold 2-perfect 8-cycle systems with this “extra” property. All admissible orders congruent to $0$ or 1 modulo 8 can be achieved, apart from order 8.

We consider a storage/scheduling problem which, in addition to the standard restriction involving pairs of elements that cannot be placed together, considers pairs of elements that must be placed together. A set \( S \) is a colored-independent set if, for each color class \( V_i \), \( S \cap V_i = V_i \) or \( S \cap V_i = \emptyset \). In particular, \( \beta_{\mathrm{PRT}}(G) \), the independence-partition number, is determined for all paths of order \( n \). Finally, we show that the resulting decision problem for graphs is NP-complete even when the input graph is a path.

Given a partition \(\{P_1, \ldots, P_m\}\) of a \(v\)-set, a restricted simple \(1\)-design is a collection of distinct subsets (blocks) such that every element occurs in the same number of blocks, but any two elements from the same part do not occur together in the same block. We give a construction of restricted simple \(1\)-designs to show that the necessary conditions are sufficient for the existence of restricted simple \(1\)-designs.

An \((r, \lambda)\) overlap coloring of a graph \( G \) allocates \( r \) colors to each vertex subject to the condition that any pair of adjacent vertices shares exactly \( \lambda \) colors. The \((r, \lambda)\) overlap chromatic number of \( G \) is the least number of colors required for such a coloring. The overlap chromatic numbers of bipartite graphs are easy to find; those of odd cycle graphs have already been established. In this paper, we find the overlap chromatic numbers of the wheel graphs.

A family \(\mathcal{G}\) of connected graphs is a family with constant metric dimension if \(\dim(\mathcal{G})\) is finite and does not depend upon the choice of \(G\) in \(\mathcal{G}\).

The metric dimension of some classes of convex polytopes has been determined in \([8-12]\) and an open problem was raised in \([10]\): \emph{Let \(G\) be the graph of a convex polytope which is obtained by joining the graph of two different convex polytopes \(G_1\) and \(G_2\) (such that the outer cycle of \(G_1\) is the inner cycle of \(G_2\)) both having constant metric dimension. Is it the case that \(G\) will always have the constant metric dimension?}

In this paper, we study the metric dimension of an infinite class of convex polytopes which are obtained by the combinations of two different graphs of convex polytopes. It is shown that this infinite class of convex polytopes has constant metric dimension and only three vertices chosen appropriately suffice to resolve all the vertices of these classes of convex polytopes.

One natural extension of classical Ramsey numbers to multipartite graphs is to consider 2-colorings of the complete multipartite graph consisting of \( n \) parts, each of size \( k \), denoted \( K_{n \times k} \). We may then ask for the minimum integer \( n \) such that \( K_{n \times k} \rightarrow (G, H) \) for two given graphs \( G \) and \( H \). We study this number for the cases when \( G \) and \( H \) are paths or cycles and show some general bounds and relations to classical Ramsey theory.

By means of the \( q \)-finite differences and the derivative operator, we derive, from an alternating \( q \)-binomial sum identity with a free variable \( x \), several interesting identities concerning the generalized \( q \)-harmonic numbers.

In [A.G. Chetwynd and A.J.W. Hilton, Critical star multigraphs, Graphs and Combinatorics 2 (1986), 209-221] Chetwynd and Hilton started the investigations of the edge-chromatic properties of a particular class of multigraphs, which they called star multigraphs. A star multigraph is a multigraph such that there exists a vertex \(v^*\) that is incident with each multiple edge. Star multigraphs turn out to be useful tools in the study of the chromatic index of simple graphs.
The main goal of this paper is to provide shorter and simpler proofs of all the main theorems contained in the above mentioned paper. Most simplifications are achieved by means of a formula for the chromatic index recently obtained by the author and by a careful use of arguments involving fans.

Broadcasting is the process of message transmission in a communication network. The communication network is modeled by a graph \( G = (V, E) \), where the set of vertices \( V \) represents the network members and the set of edges \( E \) represents the communication links between two given vertices. We assume that \( G \) is connected and undirected. One vertex, called the \emph{originator} of the graph, holds a message that has to be transmitted to all vertices of the network by placing a series of calls over the network.

A \textbf{k-port} line broadcasting in \( G \) is a model in which an informed vertex can call, at each time unit, at most \( k \) vertices and transmit a message through a path, as long as two transmissions do not use the same edge at the same time. In case \( k \) is not bounded, the model is called the all-port line model.

In this paper, we extend Cohen’s work \([6]\), which handles the all-port line model.

In this paper we consider 1-movable dominating sets, motivated by the use of sensors employed to detect certain events in networks, where the sensors have a limited ability to react under changing conditions in the network. A 1-movable dominating set is a dominating set \( S \subseteq V(G) \) such that for every \( v \in S \), either \( S – \{v\} \) is a dominating set, or there exists a vertex \( u \in (V(G) – S) \cap N(v) \) such that \( (S – \{v\}) \cup \{u\} \) is a dominating set. We present computational complexity results and bounds on the size of 1-movable dominating sets in arbitrary graphs. We also give a polynomial time algorithm to find minimum 1-movable dominating sets for trees. We conclude by extending this idea to \( k \)-movable dominating sets.