50,767 research outputs found
A study of the electronic properties of liquid alkali metals. A self--consistent approach
We study the electronic properties (density of states, conductivity and
thermopower) of some nearly--free--electron systems: the liquid alkali metals
and two liquid alloys, Li-Na and Na-K. The study has been performed within the
self-consistent second order Renormalized Propagator Perturbation Expansion
(RPE) for the self-energy. The input ionic pseudopotentials and static
correlation functions are derived from the neutral pseudoatom method and the
modified hypernetted chain theory of liquids, respectively. Reasonable
agreement with experiment is found for Na, K, Rb and Na-K, whereas for Li and
Cs and Li-Na the agreement is less satisfactoryComment: 14 pages, Latex, 1 figure, 1 tabl
Interplay between the ionic and electronic density profiles in liquid metal surfaces
First principles molecular dynamics simulations have been performed for the
liquid-vapor interfaces of liquid Li, Mg, Al and Si. We analize the oscillatory
ionic and valence electronic density profiles obtained, their wavelengths and
the mechanisms behind their relative phase-shift.Comment: Accepted for publication in Journal of Chemical Physic
Injection statistics simulator for dynamic analysis of noise in mesoscopic devices
We present a model for electron injection from thermal reservoirs which is
applied to particle simulations of one-dimensional mesoscopic conductors. The
statistics of injected carriers is correctly described from nondegenerate to
completely degenerate conditions. The model is validated by comparing Monte
Carlo simulations with existing analytical results for the case of ballistic
conductors. An excellent agreement is found for average and noise
characteristics, in particular, the fundamental unities of electrical and
thermal conductances are exactly reproduced.Comment: 4 pages, revtex, 4 PS figures, accepted Semicond. Sci. Techno
Probing the geometry and motion of AGN coronae through accretion disc emissivity profiles
To gain a better understanding of the inner disc region that comprises active
galactic nuclei it is necessary to understand the pattern in which the disc is
illuminated (the emissivity profile) by X-rays emitted from the continuum
source above the black hole (corona). The differences in the emissivity
profiles produced by various corona geometries are explored via general
relativistic ray tracing simulations. Through the analysis of various
parameters of the geometries simulated it is found that emissivity profiles
produced by point source and extended geometries such as cylindrical slabs and
spheroidal coronae placed on the accretion disc are distinguishable. Profiles
produced by point source and conical geometries are not significantly
different, requiring an analysis of reflection fraction to differentiate the
two geometries. Beamed point and beamed conical sources are also simulated in
an effort to model jet-like coronae, though the differences here are most
evident in the reflection fraction. For a point source we determine an
approximation for the measured reflection fraction with the source height and
velocity. Simulating spectra from the emissivity profiles produced by the
various geometries produce distinguishable differences. Overall spectral
differences between the geometries do not exceed 15 per cent in the most
extreme cases. It is found that emissivity profiles can be useful in
distinguishing point source and extended geometries given high quality spectral
data of extreme, bright sources over long exposure times. In combination with
reflection fraction, timing, and spectral analysis we may use emissivity
profiles to discern the geometry of the X-ray source.Comment: 15 pages, 12 figures. Accepted for publication in MNRA
Excitons in coupled InAs/InP self-assembled quantum wires
Optical transitions in coupled InAs/InP self-assembled quantum wires are
studied within the single-band effective mass approximation including effects
due to strain. Both vertically and horizontally coupled quantum wires are
investigated and the ground state, excited states and the photoluminescence
peak energies are calculated. Where possible we compare with available
photo-luminescence data from which it was possible to determine the height of
the quantum wires. An anti-crossing of the energy of excited states is found
for vertically coupled wires signaling a change of symmetry of the exciton
wavefunction. This crossing is the signature of two different coupling regimes.Comment: 8 pages, 8 figures. To appear in Physical Review
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