  Quantum conductance of 3D ballistic wires with idealy flat boundaries obeys
fluctuations with the properties quite distinguishable from those of universal
conductance fluctuations: Both their amplitude and the sensitivity to the
magnetic field flux $\Phi =HS$ penetrated into the sample cross-sectional area
$S$ are different and depend on details of the cross-sectioanl shape of the
wire. When the latter is integrable, conductance fluctuations have the enlarged
amplitude $\delta G\sim\left[(e^2/h)^3G\right]^{1/4}$. When the cross-sectional
shape of a wire is non-integrable, the irregular part of a conductance has the
$e^ 2/h$ scale, whereas the correlation field is reduced to the value of
$H_S\sim (\lambda_F/\sqrt S)^{1/2}(\Phi_0/S)$ and the correlation voltage of
the nonlinear conductance fluctuations has the scale of $eV_c\sim\hbar^2/mS\sim
E_F/(S/\lambda_F)$, where $\lambda_F=1/p_F$ is the Fermi wavelength.
