25,443 research outputs found
Bump-on-tail instability of twisted excitations in rotating cold atomic clouds
We develop a kinetic theory for twisted density waves (phonons), carrying a
finite amount of orbital angular momentum, in large magneto optical traps,
where the collective processes due to the exchange of scattered photons are
considered. Explicit expressions for the dispersion relation and for the
kinetic (Landau) damping are derived and contributions from the orbital angular
momentum are discussed. We show that for rotating clouds, exhibiting
ring-shaped structures, phonons carrying orbital angular momentum can cross the
instability threshold and grow out of noise, while the usual plane wave
solutions are kinetically damped.Comment: 5 pages, 5 figure
A class of cubic Rauzy Fractals
In this paper, we study arithmetical and topological properties for a class
of Rauzy fractals given by the polynomial
where is an integer. In particular, we prove the number of neighbors
of in the periodic tiling is equal to . We also give
explicitly an automaton that generates the boundary of . As a
consequence, we prove that is homeomorphic to a topological
disk
Evidence of spontaneous spin polarized transport in magnetic nanowires
The exploitation of the spin in charge-based systems is opening revolutionary
opportunities for device architecture. Surprisingly, room temperature
electrical transport through magnetic nanowires is still an unresolved issue.
Here, we show that ferromagnetic (Co) suspended atom chains spontaneously
display an electron transport of half a conductance quantum, as expected for a
fully polarized conduction channel. Similar behavior has been observed for Pd
(a quasi-magnetic 4d metal) and Pt (a non-magnetic 5d metal). These results
suggest that the nanowire low dimensionality reinforces or induces magnetic
behavior, lifting off spin degeneracy even at room temperature and zero
external magnetic field.Comment: 4 pages, 3 eps fig
Comment on Solution of the Relativistic Dirac-Morse Problem
We do not think that the relativistic Morse potential problem has been
correctly formulated and solved by Alhaidari (Phys. Rev. Lett. 87, 210405
(2001)).Comment: Revtex, 4 pages, preprint "Notas de F\'\i sica"
CBPF-NF-011/02/Fev./200
- …