  dc and ac magnetic properties of two thin-walled superconducting Nb cylinders
with a rectangular cross-section are reported. Magnetization curves and the ac
response were studied on as-prepared and patterned samples in magnetic fields
parallel to the cylinder axis. A row of micron-sized antidots (holes) was made
in the film along the cylinder axis. Avalanche-like jumps of the magnetization
are observed for both samples at low temperatures for magnetic fields not only
above $H_{c1}$, but in fields lower than $H_{c1}$ in the vortex-free region.
The positions of the jumps are not reproducible and they change from one
experiment to another, resembling vortex lattice instabilities usually observed
for magnetic fields larger than $H_{c1}$. At temperatures above $0.66T_c$ and
$0.78T_c$ the magnetization curves become smooth for the patterned and the
as-prepared samples, respectively. The magnetization curve of a reference
planar Nb film in the parallel field geometry does not exhibit jumps in the
entire range of accessible temperatures. The ac response was measured in
constant and swept dc magnetic field modes. Experiment shows that ac losses at
low magnetic fields in a swept field mode are smaller for the patterned sample.
For both samples the shapes of the field dependences of losses and the
amplitude of the third harmonic are the same in constant and swept field near
$H_{c3}$. This similarity does not exist at low fields in a swept mode.
