Let G be a connected graph that is the edge-disjoint union of two paths of length n, where n ≥ 2. Using a result of Thomason on decompositions of 4-regular graphs into pairs of Hamiltonian cycles, we prove that G has a third path of length n. The “two-path conjecture” states that if a graph G is the edge-disjoint union of two paths of length n with at least one common vertex, then the graph has...

For any two vertices u and v in a graph G (digraph D, respectively), a u-v geodesic is a shortest path between u and v (from u to v, respectively). Let I(u, v) (ID(u, v), respectively) denote the set of all vertices lying on a u-v geodesic. For a vertex subset S, let IG(S) (ID(S), respectively) denote the union of all IG(u, v) (ID(u, v), respectively) for u, v ∈ S. The geodetic number g(G) (g(D...

A recent variation of the classical geodetic problem, the strong geodetic problem, is defined as follows. If G is a graph, then sg(G) is the cardinality of a smallest vertex subset S, such that one can assign a fixed geodesic to each pair {x, y} ⊆ S so that these (|S| 2 ) geodesics cover all the vertices of G. In this paper, the strong geodetic problem is studied on Cartesian product graphs. A ...

A decade of observations in geodetic mode with the VLBA network gave valuable results. Approximately 1/5 of all geodetic observations are recorded in VLBA mode and processed at the Socorro correlator. Ten years of observations allowed us to reliably measure slow intra-plate motion of the VLBA stations located on the North-American plate. It also helped us to achieve scientific objectives of geo...

Let $G$ be a finite group and $pi(G)$ be the set of all the prime‎ ‎divisors of $|G|$‎. ‎The prime graph of $G$ is a simple graph‎ ‎$Gamma(G)$ whose vertex set is $pi(G)$ and two distinct vertices‎ ‎$p$ and $q$ are joined by an edge if and only if $G$ has an‎ ‎element of order $pq$‎, ‎and in this case we will write $psim q$‎. ‎The degree of $p$ is the number of vertices adjacent to $p$ and is‎ ...

The prime graph $Gamma(G)$ of a group $G$ is a graph with vertex set $pi(G)$, the set of primes dividing the order of $G$, and two distinct vertices $p$ and $q$ are adjacent by an edge written $psim q$ if there is an element in $G$ of order $pq$. Let $pi(G)={p_{1},p_{2},...,p_{k}}$. For $pinpi(G)$, set $deg(p):=|{q inpi(G)| psim q}|$, which is called the degree of $p$. We also set $D(G):...

Let G be a group. Recall that the intersection graph of subgroups of G is an undirected graph whose vertex set is the set of all nontrivial subgroups of G and distinct vertices H,K are joined by an edge in this graph if and only if the intersection of H and K is nontrivial. The aim of this article is to investigate the interplay between the group-theoretic properties of a finite group G and the...

We use theoretical X-ray absorption near-edge spectroscopy (XANES) to investigate the electronic structure of active sites on Co3O4 (001) surface during 2-propanol oxidation acetone in humid conditions. In gas phase, O K-edge spectra and acetone, as well that 2-propoxide considered a reaction intermediate, present no pre-edge peaks. Upon adsorption at Co site surface, spectrum presents distinct...

the zagros fold-and-thrust belt is tectonically active and often has active faults with insensible and slow motions. determining the rate of movement and displacement in these faults requires very precise measurements. one of the measurement methods of fault movements is using geodetic and micro-geodetic studies. this research is focused on one of the active faults in the north of shiraz city, ...