Let $D=(V,A)$ be a finite simple directed graph. A function$f:Vlongrightarrow {-1,0,1}$ is called a twin minus dominatingfunction (TMDF) if $f(N^-[v])ge 1$ and $f(N^+[v])ge 1$ for eachvertex $vin V$. The twin minus domination number of $D$ is$gamma_{-}^*(D)=min{w(f)mid f mbox{ is a TMDF of } D}$. Inthis paper, we initiate the study of twin minus domination numbersin digraphs and present some lo...

In this paper, the definition of meet-continuity on $L$-directedcomplete posets (for short, $L$-dcpos) is introduced. As ageneralization of meet-continuity on crisp dcpos, meet-continuity on$L$-dcpos, based on the generalized Scott topology, ischaracterized. In particular, it is shown that every continuous$L$-dcpo is meet-continuous and $L$-continuous retracts ofmeet-continuous $L$-dcpos are al...

Prime graph of a ring R is a graph whose vertex set is the whole set R any any two elements $x$ and $y$ of $R$ are adjacent in the graph if and only if $xRy = 0$ or $yRx = 0$.  Prime graph of a ring is denoted by $PG(R)$. Directed prime graphs for non-commutative rings and connectivity in the graph are studied in the present paper. The diameter and girth of this graph are also studied in the pa...

Reading comprehension is one of the essential skills for learning in every language and in Iranian educational system, there seems a need to make some revisions in teaching reading comprehension. In an attempt to address this problem, this research set out to utilize Directed Reading –Thinking Activity (coined by Stauffer, 1969) as a teaching comprehension model which was expected to enhance st...

Introduction: There is a growing trend in online education coursesin higher education institutes. Previous studies have shown thathigh levels of self-direction are essential for successful onlinelearning. The present study aims to investigate challenges of andbarriers to self-directed virtual-learning among postgraduatestudents of medical sciences.Methods: 23 postgraduate virtual students of me...