12,831 research outputs found
Suppression of electron scattering resonances in graphene by quantum dots
Transmission of low-energetic electrons through two-dimensional materials
leads to unique scattering resonances. These resonances contribute to
photoemission from occupied bands where they appear as strongly dispersive
features of suppressed photoelectron intensity. Using angle-resolved
photoemission we have systematically studied scattering resonances in epitaxial
graphene grown on the chemically differing substrates Ir(111), Bi/Ir, Ni(111)
as well as in graphene/Ir(111) nanopatterned with a superlattice of uniform Ir
quantum dots. While the strength of the chemical interaction with the substrate
has almost no effect on the dispersion of the scattering resonances, their
energy can be controlled by the magnitude of charge transfer from/to graphene.
At the same time, a superlattice of small quantum dots deposited on graphene
eliminates the resonances completely. We ascribe this effect to a
nanodot-induced buckling of graphene and its local rehybridization from
sp to sp towards a three-dimensional structure. Our results suggest
nanopatterning as a prospective tool for tuning optoelectronic properties of
two-dimensional materials with graphene-like structure.Comment: The following article has been submitted to Applied Physics Letters.
If it is published, it will be found online at http://apl.aip.or
Rashba splitting of 100 meV in Au-intercalated graphene on SiC
Intercalation of Au can produce giant Rashba-type spin-orbit splittings in
graphene but this has not yet been achieved on a semiconductor substrate. For
graphene/SiC(0001), Au intercalation yields two phases with different doping.
Here, we report the preparation of an almost pure p-type graphene phase after
Au intercalation. We observe a 100 meV Rashba-type spin-orbit splitting at 0.9
eV binding energy. We show that this giant splitting is due to hybridization
and much more limited in energy and momentum space than for Au-intercalated
graphene on Ni
Limb imaging of the Venus O2 visible nightglow with the Venus Monitoring Camera
We investigated the Venus O2 visible nightglow with imagery from the Venus
Monitoring Camera on Venus Express. Drawing from data collected between April
2007 and January 2011, we study the global distribution of this emission,
discovered in the late 70s by the Venera 9 and 10 missions. The inferred
limb-viewing intensities are on the order of 150 kiloRayleighs at the lower
latitudes and seem to drop somewhat towards the poles. The emission is
generally stable, although there are episodes when the intensities rise up to
500 kR. We compare a set of Venus Monitoring Camera observations with
coincident measurements of the O2 nightglow at 1.27 {\mu}m made with the
Visible and Infrared Thermal Imaging Spectrometer, also on Venus Express. From
the evidence gathered in this and past works, we suggest a direct correlation
between the instantaneous emissions from the two O2 nightglow systems. Possible
implications regarding the uncertain origin of the atomic oxygen green line at
557.7 nm are noted.Comment: 7 pages, 3 figure
Comportamiento de elementos estructurales de compuestos híbridos base cemento frente a impacto de torre de caída
The performance, under drop-weight impact load, of hybrid cement composite (HCC) elements, consisting of a top layer of plain concrete (PC) and a bottom layer of fibre reinforced concrete (FRC), in comparison with full-depth FRC and PC was studied. Apart from improving the tensile capacity of PC and saving fibre steel reinforcements of FRC, the results showed that HCC can effectively control the deformations and enhance the impact performance of the structural members as its outcomes were similar to that of a full-depth FRC. The analytical studies using Hughes empirical formulae (HEF) and yield line theory (YLT) adopted to investigate the practical use of HCC showed that they are applicable for design such HCC elements against impacts.Se estudió el comportamiento, frente a impacto de torre de caída, de elementos híbridos base cemento (HCC), formados por una capa superior de hormigón en masa (PC) y una capa inferior de hormigón reforzado con fibras (FRC) en comparación con elementos análogos íntegramente fabricados con FRC y PC. Además de proporcionar una mejora en la resistencia frente a flexo-tracción de los PC y un ahorro en refuerzo usando fibras de acero en el caso de los FRC, los resultados mostraron que el HCC puede controlar eficazmente las deformaciones y mejorar el rendimiento frente a impacto de los elementos estructurales ya que sus resultados fueron análogos a la de los FRC. Los estudios analíticos, utilizando HEF e YLT, adoptados para investigar el uso práctico de los HCC mostraron que los mismos son aplicables para el diseño de estos elementos frente a impacto
Two new pulsating low-mass pre-white dwarfs or SX Phenix stars?*
Context. The discovery of pulsations in low-mass stars opens an opportunity
for probing their interiors and to determine their evolution, by employing the
tools of asteroseismology. Aims. We aim to analyze high-speed photometry of
SDSSJ145847.02070754.46 and SDSSJ173001.94070600.25 and discover
brightness variabilities. In order to locate these stars in the diagram we fit optical spectra (SDSS) with synthetic non-magnetic
spectra derived from model atmospheres. Methods. To carry out this study, we
used the photometric data obtained by us for these stars with the 2.15m
telescope at CASLEO, Argentina. We analyzed their light curves and we apply the
Discrete Fourier Transform to determine the pulsation frequencies. Finally, we
compare both stars in the diagram, with known two
pre-white dwarfs, seven pulsating pre-ELM white dwarf stars, Scuti and
SX Phe stars. Results. We report the discovery of pulsations in
SDSSJ145847.02070754.46 and SDSSJ173001.94070600.25. We determine their
effective temperature and surface gravity to be = 7 972 200
K, = 4.25 0.5 and = 7 925 200 K, =
4.25 0.5, respectively. With these parameters these new pulsating
low-mass stars can be identified with either ELM white dwarfs (with ~ 0.17 Mo)
or more massive SX Phe stars. We identified pulsation periods of 3 278.7 and 1
633.9 s for SDSSJ145847.02070754.46 and a pulsation period of 3 367.1 s for
SDSSJ173001.94070600.25. These two new objects together with those of Maxted
et al. (2013, 2014) indicate the possible existence of a new instability domain
towards the late stages of evolution of low-mass white dwarf stars, although
their identification with SX Phe stars cannot be discarded.Comment: 5 pages, 5 figures, 1 table, accepted for publication in A&A
Nonlinear stochastic discrete drift-diffusion theory of charge fluctuations and domain relocation times in semiconductor superlattices
A stochastic discrete drift-diffusion model is proposed to account for the
effects of shot noise in weakly coupled, highly doped semiconductor
superlattices. Their current-voltage characteristics consist of a number stable
multistable branches corresponding to electric field profiles displaying two
domains separated by a domain wall. If the initial state corresponds to a
voltage on the middle of a stable branch and a sudden voltage is switched so
that the final voltage corresponds to the next branch, the domains relocate
after a certain delay time. Shot noise causes the distribution of delay times
to change from a Gaussian to a first passage time distribution as the final
voltage approaches that of the end of the first current branch. These results
agree qualitatively with experiments by Rogozia {\it et al} (Phys. Rev. B {\bf
64}, 041308(R) (2001)).Comment: 9 pages, 12 figures, 2 column forma
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