deletions | additions       diff --git a/Introduction.tex b/Introduction.tex  index baa0ae6..9370e84 100644  --- a/Introduction.tex  +++ b/Introduction.tex 
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In the thermoelastic regime, a local dilatation of the medium occurs. In an unbounded solid, this would lead to a curl-free displacement, so no shear wave would occur. However, in the case presented, the solid is semi-infinite (the laser beam is absorbed on one side of the medium), and the local expansion acts as dipolar forces parallel to the surface. A unidimension analysis lead to a local displacement $u_z$ along $z$ \cite{scruby1990laser}:  \begin{equation}  u_z = \frac{3 \frac{(3  \lambda + 2 \mu}{\lambda \mu)}{(\lambda  + 2\mu} 2\mu)}  \frac{\alpha \E}{\rho E}{\rho  C S} \label{eq:deplUnidim}  \end{equation}  where $\lambda$, $\mu$ are respectively the first and second Lamé's coefficient and $\alpha$ is the thermal dilatation coefficient. In a biological soft tissues, $\mu \gg \lambda$, so that \ref{eq:deplUnidim} becomes: 
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