deletions | additions       diff --git a/introduction.tex b/introduction.tex  index 101937d..409ec48 100644  --- a/introduction.tex  +++ b/introduction.tex 
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\begin{equation}  E_0 = \frac{\pi \mathcal{E}_g^2}{4 \hbar e^* v_F}  \end{equation}  where $\mathcal{E}_g$ is the pinning gap of CDW and $v_F$ is the Fermi velocity of electrons. The $e^*$ is the effective charge due to the shielding effect of CDW with $e^*/e \approx 10^{-4}$. Equation (3) directly contributes to the exponential term in equation (1) by reducing the fraction of conducting CDW by a factor of $P$.   Although the tunneling model explained the empirical expression, it didn't take applied AC voltage into account and its DC prediction deviated from the experimental data\cite{Gr_ner_1981}. The problem now is threefold.