Table 1 Comparison of the upper bounds of the decay rate for different delays

${\mathit{\mu }}_{\mathbf{2}}\mathbf{=}\mathbf{0.2}$

${\mathit{\mu }}_{\mathbf{2}}\mathbf{=}\mathbf{0.5}$

${\mathit{\mu }}_{\mathbf{2}}\mathbf{=}\mathbf{0.8}$

${\mathit{\mu }}_{\mathbf{2}}\mathbf{=}\mathbf{1}$

${\mathit{\mu }}_{\mathbf{2}}\mathbf{=}\mathbf{1.2}$