We define and study the following two-player game on a graph G. Let k ∈ N∗. A set of k guards is occupying some vertices of G while one spy is standing at some node. At each turn, first the spy may move along at most s edges, where s ∈ N∗ is his speed. Then, each guard may move along one edge. The spy and the guards may occupy the same vertices. The spy has to escape the surveillance of the gua...

CONFLICT OF INTEREST NONE DECLARED. INTRODUCTION Through psychological support for prison guard's awareness about professional stress and burn-out, cognitive assessment of stress consequences, insight in coping strategies, as well as prevention of stress consequences is achieved. AIM Evaluation of psychoeducation effects on professional stress consequences within prison guards. METHOD In ...

We consider the problem of searching a polygonal room with two guards starting at a specified door point. While maintaining mutual visibility and without crossing the door, the guards must move along the boundary of the room and eventually meet again. We give polynomial time algorithms for finding a search schedule that minimizes the total distance travelled by the guards and for minimizing the...

We use mobile guards on the vertices of a graph to defend it against an infinite sequence of attacks on its edges. A guard on an incident vertex moves across the attacked edge to defend it; other guards may also move to neighboring vertices. We prove upper and lower bounds on the minimum number of guards needed for this eternal vertex cover problem and characterize the graphs for which the uppe...

We consider the problem of triangle guarding (4-guarding) a simple, 2D polygon Q. A polygon Q is 4-guarded if every point q of Q is contained in the convex hull of some three guards that can all see q. This rather odd condition approximates a desire, for example, to see all sides of q or to locate (via triangulation) q from at least two angularly well-separated views. If we restrict the guards ...

Introduction: Snowboarding, both as an outdoor sport and cultural trend, has grown tremendously over the past three decades. As a result, the number of trauma related injuries and emergency room visits have risen significantly. According to the literature, more than 50% of upper extremity injuries involve the wrist. The primary mechanism of injury is a backwards fall onto outstretched hands, re...