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We compute the distribution function of single-level curvatures, $P(k)$, for a tight binding model with site disorder, on a cubic lattice. In metals $P(k)$ is very close to the predictions of the random-matrix theory (RMT). In insulators $P(k)$ has a logarithmically-normal form. At the Anderson localization-delocalization transition $P(k)$ fits very well the proposed novel distribution $P(k)\propto (1+k^{\mu})^{3/\mu}$ with $\mu \approx 1.58$, which approaches the RMT result for large $k$ and is non-analytical at small $k$. We ascribe such a non-analiticity to the spatial multifractality of the critical wave functions., Comment: 4 ReVTeX pages and 4(.epsi)figures included in one uuencoded package

Recently it has been found that different physical systems driven by identical random noise behave exactly identical after a long time. It is also suggested that this is an outcome of finite precision in numerical experiments. Here we show that the origin of the non-chaotic behavior lies in the structural instability of the attractor of these systems which changes to a stable fixed point for strong enough drive. We see this to be true in all the systems studied in literature. Thus we affirm that in chaotic systems, synchronization can not occur only by addition of noise unless the noise destroys the strange attractor and the system is no longer chaotic., Comment: Figures could be obtained from gade@ictp.trieste.it. The document below is a latex file