23,036 research outputs found
Low energy sputtering of cobalt by cesium ions
An experimental facility to investigate low energy (less than 500 eV) sputtering of metal surfaces with ions produced by an ion gun is described. Results are reported on the sputtering yield of cobalt by cesium ions in the 100 to 500 eV energy range at a pressure of 1 times 10(exp -6) Torr. The target was electroplated on a copper substrate. The sputtered atoms were collected on a cobalt foil surrounding the target. Co-57 was used as a tracer to determine the sputtering yield
Electrode erosion in low power arcjet thrusters
Low power arcjet thrusters (0.5 to 3 kW) are currently being considered for North-South station keeping of geosynchronous communication satellites. The erosion mechanisms of cathodes in these thrusters are not well understood. The experimental set-up to produce a steady state electric arc in a gas flow is described and some preliminary theoretical results on cathode erosion are presented
Ultracold bosons in a synthetic periodic magnetic field: Mott phases and re-entrant superfluid-insulator transitions
We study Mott phases and superfluid-insulator (SI) transitions of ultracold
bosonic atoms in a two-dimensional square optical lattice at commensurate
filling and in the presence of a synthetic periodic vector potential
characterized by a strength and a period , where is an integer
and is the lattice spacing. We show that the Schr\"odinger equation for the
non-interacting bosons in the presence of such a periodic vector potential can
be reduced to an one-dimensional Harper-like equation which yields energy
bands. The lowest of these bands have either single or double minima whose
position within the magnetic Brillouin zone can be tuned by varying for a
given . Using these energies and a strong-coupling expansion technique, we
compute the phase diagram of these bosons in the presence of a deep optical
lattice. We chart out the and dependence of the momentum distribution
of the bosons in the Mott phases near the SI transitions and demonstrate that
the bosons exhibit several re-entrant field-induced SI transitions for any
fixed period . We also predict that the superfluid density of the resultant
superfluid state near such a SI transition has a periodicity () in
real space for odd (even) and suggest experiments to test our theory.Comment: 8 pages, 11 figures, v
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