An oriented walk double covering of a graph G is a set of oriented closed walks which, traversed successively, combined will have traced each edge of G once in each direction. A bidirectional double tracing of a graph G is an oriented walk double covering which consists of a single closed walk. A retracting in a closed walk is the immediate succession of an edge by its inverse. Every graph with...

A clique in a graph G is a complete subgraph of G. A clique covering (partition) of G is a collection C of cliques such that each edge of G occurs in at least (exactly) one clique in C. The clique covering (partition) number cc(G) (cp(G)) of G is the minimum size of a clique covering (partition) of G. This paper gives alternative proofs, using a unified approach, for the results on the clique c...

Let G be a simple graph of order n and size m. An edge covering of a graph is a set of edges such that every vertex of the graph is incident to at least one edge of the set. Here we introduce a new graph polynomial. The edge cover polynomial of G is the polynomial E(G, x) = ∑m i=1 e(G, i)x , where e(G, i) is the number of edge covering sets of G of size i. Let G and H be two graphs of order n s...

We investigate a new class of codes for the optimal covering of vertices in an undirected graphG such that any vertex in G can be uniquely identified by examining the vertices that cover it. We define a ball of radius t centered on a vertex v to be the set of vertices in G that are at distance at most t from v: The vertex v is then said to cover itself and every other vertex in the ball with ce...

In this paper, we investigate the weighted tree augmentation problem (TAP), where the goal is to augment a tree with a minimum cost set of edges such that the graph becomes two edge connected. First we show that in weighted TAP, we can restrict our attention to trees which are binary and where all the non-tree edges go between two leaves of the tree. We then give two different top-down coloring...

We show that for every cubic graph G with sufficiently large girth there exists a probability distribution on edge-cuts of G such that each edge is in a randomly chosen cut with probability at least 0.88672. This implies that G contains an edge-cut of size at least 1.33008n, where n is the number of vertices of G, and has fractional cut covering number at most 1.12776. The lower bound on the si...

We prove that an equivalent condition for a uniform space to be cov-erable is that the images of the natural projections in the fundamental inverse system are uniformly open in a certain sense. As corollaries we (1) obtain a concrete way to find covering entourage, (2) correct an error in [3], and (3) show that coverable is equivalent to chain connected and uniformly joinable in the sense of [5...

We define complex projective n-space CP as C \ {0} under the equivalence relation (z0 : z1 : ... : zn) ∼ (cz0 : cz1 : ... : czn) where c ∈ C\{0}. A complex projective curve is then the set of points (a0 : a1 : ... : an) ∈ CP such that p(a0, a1, ..., an) = 0 for a fixed complex homogeneous polynomial p(z0, z1, ..., zn). Such a curve is a 2-dimensional, real, orientable Riemannian manifold, or Ri...

The problem of finding the flow over a finite flat plate aligned with a uniform free stream is revisited. Multigrid is used to obtain accurate numerical solutions up to a Reynolds number of 4000. Fourier boundary conditions keep the computational domain small, with no loss of accuracy. Near the trailing edge, excellent agreement with first-order triple-deck theory is found. However, previous co...

Sensors are used to monitor traffic in networks. For example, in transportation networks, they may be used to measure traffic volumes on given arcs and paths of the network. This paper refers to an active sensor when it reads identifications of vehicles, including their routes in the network, that the vehicles actively provide when they use the network. On the other hand, the conventional induc...