  On the supergravity side, we study the propagation of the RR scalar and the
dilaton in the D3-branes with NS $B$-field. To obtain the noncommutative
effect, we consider the case of $B\to \infty(\theta \to\pi/2)$. We approximate
this as the smeared D1-brane background with $F_5=H=0$. In this background, the
RR scalar induces an instability of the near-horizon geometry. However, it
turns out that the RR scalar is nonpropagating, while the dilaton is a
physically propagating mode. We calculate the s-wave absorption cross section
of the dilaton. One finds $\sigma_0^\phi |_{B\to\infty} \sim (\tilde \omega
\tilde R_{\pi \over 2})^{8.9} / \omega^5$ in the leading-order while
$\sigma_0^\phi|_{B=0} \sim (\tilde \omega R_0)^{8}/\omega^5$ in the D3-branes
without $B$-field. This means that although the dilaton belongs to a minimally
coupled scalar in the absence of $B$-field, it becomes a sort of fixed scalar
in the limit of $B \to \infty$.
