41 research outputs found
Analytic Solution of a Relativistic Two-dimensional Hydrogen-like Atom in a Constant Magnetic Field
We obtain exact solutions of the Klein-Gordon and Pauli Schroedinger
equations for a two-dimensional hydrogen-like atom in the presence of a
constant magnetic field. Analytic solutions for the energy spectrum are
obtained for particular values of the magnetic field strength. The results are
compared to those obtained in the non-relativistic and spinless case. We obtain
that the relativistic spectrum does not present s states.Comment: RevTeX, 8 pages, to be published in Phys. Lett.
Calculation of the energy spectrum of a two-electron spherical quantum dot
We study the energy spectrum of the two-electron spherical parabolic quantum
dot using the exact Schroedinger, the Hartree-Fock, and the Kohn-Sham
equations. The results obtained by applying the shifted-1/N method are compared
with those obtained by using an accurate numerical technique, showing that the
relative error is reasonably small, although the first method consistently
underestimates the correct values. The approximate ground-state Hartree-Fock
and local-density Kohn-Sham energies, estimated using the shifted-1/N method,
are compared with accurate numerical self-consistent solutions. We make some
perturbative analyses of the exact energy in terms of the confinement strength,
and we propose some interpolation formulae. Similar analysis is made for both
mean-field approximations and interpolation formulae are also proposed for
these exchange-only ground-state cases.Comment: 18 pages, LaTeX, 2 figures-ep
Physics of multi-GEM structures
We show that physics of multi-GEM structures is rather complex, regarding the
number of phenomena affecting detector performance. The high-pressure operation
in noble gases and the ion feedback are considered in more detail. It is
proposed that the dominant avalanche mechanism in He and Ne, at high pressures,
is the associative ionization. Ion feedback effects related to the dependence
on gas, pressure and gain and to possible avalanche extension outside the GEM
holes are discussed.Comment: Presented at the 8th International Conference on Instrumentation for
Colliding Beam Physics, Novosibirsk, Febuary 28 - March 6, 2002. To be
published in Nucl. Instr. and Meth.
Propagation and Structure of Planar Streamer Fronts
Streamers often constitute the first stage of dielectric breakdown in strong
electric fields: a nonlinear ionization wave transforms a non-ionized medium
into a weakly ionized nonequilibrium plasma. New understanding of this old
phenomenon can be gained through modern concepts of (interfacial) pattern
formation. As a first step towards an effective interface description, we
determine the front width, solve the selection problem for planar fronts and
calculate their properties. Our results are in good agreement with many
features of recent three-dimensional numerical simulations.
In the present long paper, you find the physics of the model and the
interfacial approach further explained. As a first ingredient of this approach,
we here analyze planar fronts, their profile and velocity. We encounter a
selection problem, recall some knowledge about such problems and apply it to
planar streamer fronts. We make analytical predictions on the selected front
profile and velocity and confirm them numerically.
(abbreviated abstract)Comment: 23 pages, revtex, 14 ps file