The signed distance-$k$-domination number of a graph is a certain variant of the signed domination number. If $v$ is a vertex of a graph $G$, the open $k$-neighborhood of $v$, denoted by $N_k(v)$, is the set $N_k(v)=\lbrace u\mid u\ne v$ and $d(u,v)\le k\rbrace $. $N_k[v]=N_k(v)\cup \lbrace v\rbrace $ is the closed $k$-neighborhood of $v$. A function $f\: V\rightarrow \lbrace -1,1\rbrace $ is a signed distance-$k$-dominating function of $G$, if for every vertex $v\in V$, $f(N_k[v])=\sum _{u\in N_k[v]}f(u)\ge 1$. The signed distance-$k$-domination number, denoted by $\gamma _{k,s}(G)$, is the minimum weight of a signed distance-$k$-dominating function on $G$. The values of $\gamma _{2,s}(G)$ are found for graphs with small diameter, paths, circuits. At the end it is proved that $\gamma _{2,s}(T)$ is not bounded from below in general for any tree $T$.
The signed edge domination number of a graph is an edge variant of the signed domination number. The closed neighbourhood NG[e] of an edge e in a graph G is the set consisting of e and of all edges having a common end vertex with e. Let f be a mapping of the edge set E(G) of G into the set {−1, 1}. If ∑ x∈N[e] f(x) ≥ 1 for each e ∈ E(G), then f is called a signed edge dominating function on G. The minimum of the values ∑ x∈E(G) f(x), taken over all signed edge dominating function f on G, is called the signed edge domination number of G and is denoted by γ s(G). If instead of the closed neighbourhood NG[e] we use the open neighbourhood NG(e) = NG[e] − {e}, we obtain the definition of the signed edge total domination number γ st(G) of G. In this paper these concepts are studied for trees. The number γ s(T) is determined for T being a star of a path or a caterpillar. Moreover, also γ s(Cn) for a circuit of length n is determined. For a tree satisfying a certain condition the inequality γ s(T) ≥ γ (T) is stated. An existence theorem for a tree T with a given number of edges and given signed edge domination number is proved. At the end similar results are obtained for γ st(T).
We initiate the study of signed majority total domination in graphs. Let $G=(V,E)$ be a simple graph. For any real valued function $f\: V \rightarrow \mathbb{R}$ and ${S\subseteq V}$, let $f(S)=\sum _{v\in S}f(v)$. A signed majority total dominating function is a function $f\: V\rightarrow \lbrace -1,1\rbrace $ such that $f(N(v))\ge 1$ for at least a half of the vertices $v\in V$. The signed majority total domination number of a graph $G$ is $\gamma _{{\mathrm maj}}^{{\,\mathrm t}}(G)=\min \lbrace f(V)\mid f$ is a signed majority total dominating function on $G\rbrace $. We research some properties of the signed majority total domination number of a graph $G$ and obtain a few lower bounds of $\gamma _{{\mathrm maj}}^{{\,\mathrm t}}(G)$.
By a signpost system we mean an ordered pair $(W, P)$, where $W$ is a finite nonempty set, $P \subseteq W \times W \times W$ and the following statements hold: \[ \text{if } (u, v, w) \in P, \text{ then } (v, u, u) \in P\text{ and } (v, u, w) \notin P,\text{ for all }u, v, w \in W; \text{ if } u \ne v,i \text{ then there exists } r \in W \text{ such that } (u, r, v) \in P,\text{ for all } u, v \in W. \] We say that a signpost system $(W, P)$ is smooth if the folowing statement holds for all $u, v, x, y, z \in W$: if $(u, v, x), (u, v, z), (x, y, z) \in P$, then $(u, v, y) \in P$. We say thay a signpost system $(W, P)$ is simple if the following statement holds for all $u, v, x, y \in W$: if $(u, v, x), (x, y, v) \in P$, then $(u, v, y), (x, y, u) \in P$. By the underlying graph of a signpost system $(W, P)$ we mean the graph $G$ with $V(G) = W$ and such that the following statement holds for all distinct $u, v \in W$: $u$ and $v$ are adjacent in $G$ if and only if $(u,v, v) \in P$. The main result of this paper is as follows: If $G$ is a graph, then the following three statements are equivalent: $G$ is connected; $G$ is the underlying graph of a simple smooth signpost system; $G$ is the underlying graph of a smooth signpost system.
The boundary layer equations for the non-Newtonian power law fluid are examined under the classical conditions of uniform flow past a semi infinite flat plate. We investigate the behavior of the similarity solution and employing the Crocco-like transformation we establish the power series representation of the solution near the plate.
The limit behaviour of solutions of a singularly perturbed system is examined in the case where the fast flow need not converge to a stationary point. The topological convergence as well as information about the distribution of the values of the solutions can be determined in the case that the support of the limit invariant measure of the fast flow is an asymptotically stable attractor.
Let $R$ be a commutative ring, $M$ an $R$-module and $G$ a group of $R$-automorphisms of $M$, usually with some sort of rank restriction on $G$. We study the transfer of hypotheses between $M/C_M(G)$ and $[M,G]$ such as Noetherian or having finite composition length. In this we extend recent work of Dixon, Kurdachenko and Otal and of Kurdachenko, Subbotin and Chupordia. For example, suppose $[M,G]$ is $R$-Noetherian. If $G$ has finite rank, then $M/C_M(G)$ also is $R$-Noetherian. Further, if $[M,G]$ is $R$-Noetherian and if only certain abelian sections of $G$ have finite rank, then $G$ has finite rank and is soluble-by-finite. If $M/C_M(G)$ is $R$-Noetherian and $G$ has finite rank, then $[M,G]$ need not be $R$-Noetherian., Bertram A. F. Wehrfritz., and Obsahuje bibliografické odkazy
We investigate solution sets of a special kind of linear inequality systems. In particular, we derive characterizations of these sets in terms of minimal solution sets. The studied inequalities emerge as information inequalities in the context of Bayesian networks. This allows to deduce structural properties of Bayesian networks, which is important within causal inference.