Tube of (Circle F, D0, D2) Bound State in Melvin Background
  By using the Born-Infeld action we show that the $m$ circular fundamental strings, $n$ D2-branes and $k$ D0-branes could become a tubular bound state which is prevented from collapsing by the magnetic force in the Melvin background. However, if the ratio $m/n$ is larger then a critical value the tube will become unstable and collapse to zero radius. We make analyses to find the critical value and tube radius therein. The tube configurations we found are different from the well known tubular bound states of straight fundamental strings, D0 and D2-branes, which are supported by the angular momentum. 
Wung-Hong Huang