Fancy Figures

Notice the option to the Plot command

Plot[ {f[10,1,x], f[10,1,x]^2,
       f[10,2,x], f[10,2,x]^2}, {x,0,10}, 
       Frame -> True,PlotStyle->{{Dashing[{0.02}],Hue[1.0],Thickness[0.01]},{Thickness[0.01]}}]

Another function

sig3[z_,zo_,b_] := 1./(1.+ Exp[b(z-zo)])

where zo is the threshold concentration and b is the attenuation constant.

fig1 = Plot[{sig3[x,10.,0.5],sig3[x,10.,1.],sig3[x,10.,2],sig3[x,10,5]},
      {x,0,20},PlotRange->{0,1.20},Frame->True,
      FrameLabel->{"z","f"},PlotStyle->{Thickness[0.01]},DisplayFunction->Identity];

DisplayFunction->Identity instructs Plot to save the plot in memory under the name "fig1".  The plot can be recall and shown using the Show function and the command DisplayFunction->$DisplayFunction, which is the default setting

FIG1 = Show[{fig1,Graphics[{Text["b=0.5",{5,.75}],
                           Text["b=5.0",{12,.9}]}]},
            DisplayFunction->$DisplayFunction,
            RotateLabel->False];