A subset F ⊂ V (G) is called an Rk-vertex-cut of a graph G if G -F is disconnected and each vertex of G -F has at least k neighbors in G -F. The Rk-vertex-connectivity of G, denoted by κk(G), is the cardinality of a minimum Rk-vertex-cut of G. Let Bn be the bubble sort graph of dimension n. It is known that κk(Bn)=2k(n -k -1) for n ≥ 2k and k=1, 2. In this paper, we prove it for k=3 and conjecture that it is true for all k ∈ N. We also prove that the connectivity cannot be more than conjectured.
In this paper, generalized Latin matrix and orthogonal generalized Latin matrices are proposed. By using the property of orthogonal array, some methods for checking orthogonal generalized Latin matrices are presented. We study the relation between orthogonal array and orthogonal generalized Latin matrices and obtain some useful theorems for their construction. An example is given to illustrate applications of main theorems and a new class of mixed orthogonal arrays are obtained.