  On the basis of linear programming, new sets of entanglement witnesses (EWs)
for 3x3 and 4x4 systems are constructed. In both cases, the constructed EWs
correspond to the hyperplanes contacting, without intersecting, the related
feasible regions at line segments and restricted planes respectively. Due to
the special property of the contacting area between the hyper-planes and the
feasible regions, the corresponding hyper-planes can be turned around the
contacting area throughout a bounded interval and hence create an infinite
number of EWs. As these EWs are able to detect entanglement of some PPT states,
they are non-decomposable (nd-EWs).
