Curve fitting with LsqFit

Thank you! It is much clearer now.
Yet, there is a new problem. Now i am trying to use a complex function with ternary operator:

model1(t, p) = @.(p[1] * exp(-p[2] * t) + p[3] * exp(-p[4] * t) * cos(p[5] * t + p[6])+ p[7] * (t > p[8] ? 0 : (1 - t / p[8])^2))

The error i get is the following:

ERROR: TypeError: non-boolean (BitArray{1}) used in boolean context
Stacktrace:
 [1] model1(::Array{Int64,1}, ::Array{Float64,1}) at .\REPL[184]:1
 [2] top-level scope at none:0

Many thanks in advance for tips.