2,674 research outputs found
Signals for Neutralino Box Effects at LEP2
We have computed the contribution to the observables of the final two fermion
channel at LEP2, at the limiting energy , coming from boxes
with two neutralinos of purely gaugino type, of mass . We find a
potentially visible effect only for the muon channel, in the cross section and,
to a lesser extent, in the forward-backward asymmetry. Analogous effects coming
from the chargino box are also briefly discussed.Comment: 10 pages and 2 figures. e-mail: [email protected]
Designing III-V Multijunction Solar Cells on Silicon
Single junction Si solar cells dominate photovoltaics but are close to their
efficiency limits. This paper presents ideal limiting efficiencies for tandem
and triple junction multijunction solar cells subject only to the constraint of
the Si bandgap and therefore recommending optimum cell structures departing
from the single junction ideal. The use of III-V materials is considered, using
a novel growth method capable of yielding low defect density III-V layers on
Si. In order to evaluate the real potential of these proposed multijunction
designs, a quantitative model is presented, the strength of which is the joint
modelling of external quantum efficiency and current-voltage characteristics
using the same parameters. The method yields a single parameter fit in terms of
the Shockley-Read-Hall lifetime. This model is validated by fitting
experimental data of external quantum efficiency, dark current, and conversion
efficiency of world record tandem and triple junction cells under terrestrial
solar spectra without concentration. We apply this quantitative model to the
design of tandem and triple junction solar cells, yielding cell designs capable
of reaching efficiencies without concentration of 32% for the best tandem cell
and 36% for the best triple junction cell. This demonstrates that efficiencies
within a few percent of world records are realistically achievable without the
use of concentrating optics, with growth methods being developed for
multijunction cells combining III-V and Si materials.Comment: Preprint of the paper submitted to the journal Progress in
Photovoltaics, selected by the Executive Committee of the 28th EU PVSEC 2013
for submission to Progress in Photovoltaics. 10 pages, 7 figure
Spin dynamics of hole doped Y2BaNiO5
Starting from a multiband Hamiltonian containing the relevant Ni and O
orbitals, we derive an effective Hamiltonian for the low energy
physics of doped YBaNiO For hole doping, describes O
fermions interacting with S=1 Ni spins in a chain, and cannot be further
reduced to a simple one-band model. Using numerical techniques, we obtain a
dynamical spin structure factor with weight inside the Haldane gap. The nature
of these low-energy excitations is identified and the emerging physical picture
is consistent with most of the experimental information in Y%
CaBaNiOComment: 4 pages, 2 figure
The roughness of stylolites: Implications of 3D high resolution topography measurements
Stylolites are natural pressure-dissolution surfaces in sedimentary rocks. We
present 3D high resolution measurements at laboratory scales of their complex
roughness. The topography is shown to be described by a self-affine scaling
invariance. At large scales, the Hurst exponent is and
very different from that at small scales where . A
cross-over length scale at around \L_c =1~mm is well characterized.
Measurements are consistent with a Langevin equation that describes the growth
of a stylolitic interface as a competition between stabilizing long range
elastic interactions at large scales or local surface tension effects at small
scales and a destabilizing quenched material disorder.Comment: 4 pages, 4 figure
Electron transport through antidot superlattices in heterostructures: new magnetoresistance resonances in lattices with large diameter antidots
In the present work we have investigated the transport properties in a number
of Si/SiGe samples with square antidot lattices of different periods. In
samples with lattice periods equal to 700 nm and 850 nm we have observed the
conventional low-field commensurability magnetoresistance peaks consistent with
the previous observations in GaAs/AlGaAs and Si/SiGe samples with antidot
lattices. In samples with a 600 nm lattice period a new series of
well-developed magnetoresistance oscillations has been found beyond the last
commensurability peak which are supposed to originate from periodic skipping
orbits encircling an antidot with a particular number of bounds.Comment: To appear in EuroPhys. Let
Identification of a paternal developmental effect on the cytoplasm of one-cell-stage mouse embryos.
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