What is meant by 'Memristance'?
So I did some simulations and found out this, Memristance is basically the quantification of the maximum change in resistance that can be achieved for a given Memrsitor. The 'achieved' part is important since from the equations:

You can see that the charge and current can turn out to be imaginary if we choose a wrong amplitude and omega in case of a sinusoidal wave. To further verify the basis of authors claims that Memristance decreases with omega for a sinusoidal wave I have plotted 2 plots for Resistance vs Time where Time is in the x-axis:

omega = 1000
omega = 5000
omega = 10000 for given fixed set of Memristor physical parameters and amplitude




As predicted by the authors you can clearly see Memristance decreases with increasing omega.