Domination Cover Pebbling: Structural Results

This paper continues the results of "Domination Cover Pebbling: Graph Families." An almost sharp bound for the domination cover pebbling (DCP) number for graphs G with specified diameter has been computed. For graphs of diameter two, a bound for the ratio between the cover pebbling number of G and the DCP number of G has been computed. A variant of domination cover pebbling, called subversion DCP is introducted, and preliminary results are discussed.Comment: 15 page

Cover pebbling numbers and bounds for certain families of graphs

Given a configuration of pebbles on the vertices of a graph, a pebbling move is defined by removing two pebbles from some vertex and placing one pebble on an adjacent vertex. The cover pebbling number of a graph, gamma(G), is the smallest number of pebbles such that through a sequence of pebbling moves, a pebble can eventually be placed on every vertex simultaneously, no matter how the pebbles are initially distributed. The cover pebbling number for complete multipartite graphs and wheel graphs is determined. We also prove a sharp bound for gamma(G) given the diameter and number of vertices of G.Comment: 10 pages, 1 figure, submitted to Discrete Mathematic

Stellar Velocity Dispersion in Dissipative Galaxy Mergers with Star Formation

In order to better understand stellar dynamics in merging systems, such as NGC 6240, we examine the evolution of central stellar velocity dispersion (\sig) in dissipative galaxy mergers using a suite of binary disk merger simulations that include feedback from stellar formation and active galactic nuclei (AGNs). We find that $\sigma_*$ undergoes the same general stages of evolution that were observed in our previous dissipationless simulations: coherent oscillation, then phase mixing, followed by dynamical equilibrium. We also find that measurements of $\sigma_*$ that are based only upon the youngest stars in simulations consistently yield lower values than measurements based upon the total stellar population. This finding appears to be consistent with the so-called "$\sigma_*$ discrepancy," observed in real galaxies. We note that quasar-level AGN activity is much more likely to occur when $\sigma_*$ is near its equilibrium value rather than during periods of extreme $\sigma_*$. Finally, we provide estimates of the scatter inherent in measuring $\sigma_*$ in ongoing mergers.Comment: 17 pages, 10 figures, accepted for publication in Ap

Radiative transfer dynamo effect

Magnetic fields in rotating and radiating astrophysical plasma can be produced due to a radiative interaction between plasma layers moving relative to each other. The efficiency of current drive, and with it the associated dynamo effect, is considered in a number of limits. It is shown here, however, that predictions for these generated magnetic fields can be significantly higher when kinetic effects, previously neglected, are taken into account.Comment: 6 pages, 4 figures, published in Physical Review