Spectral properties and transition to instability in neutral delay
differential equations are investigated in the limit of large delay. An
approximation of the upper boundary of stability is found and compared to an
analytically derived exact stability boundary. The approximate and exact
stability borders agree quite well for the large time delay, and the inclusion
of a time-delayed velocity feedback improves this agreement for small delays.
Theoretical results are complemented by a numerically computed spectrum of the
corresponding characteristic equations.Comment: 14 pages, 6 figure
