23,010 research outputs found
Negative Differential Resistance Induced by Mn Substitution at SrRuO3/Nb:SrTiO3 Schottky Interfaces
We observed a strong modulation in the current-voltage characteristics of
SrRuO/Nb:SrTiO Schottky junctions by Mn substitution in SrRuO,
which induces a metal-insulator transition in bulk. The temperature dependence
of the junction ideality factor indicates an increased spatial inhomogeneity of
the interface potential with substitution. Furthermore, negative differential
resistance was observed at low temperatures, indicating the formation of a
resonant state by Mn substitution. By spatially varying the position of the Mn
dopants across the interface with single unit cell control, we can isolate the
origin of this resonant state to the interface SrRuO layer. These results
demonstrate a conceptually different approach to controlling interface states
by utilizing the highly sensitive response of conducting perovskites to
impurities
Nanometer scale electronic reconstruction at the interface between LaVO3 and LaVO4
Electrons at interfaces, driven to minimize their free energy, are
distributed differently than in bulk. This can be dramatic at interfaces
involving heterovalent compounds. Here we profile an abrupt interface between V
3d2 LaVO3 and V 3d0 LaVO4 using electron energy loss spectroscopy. Although no
bulk phase of LaVOx with a V 3d1 configuration exists, we find a nanometer-wide
region of V 3d1 at the LaVO3/LaVO4 interface, rather than a mixture of V 3d0
and V 3d2. The two-dimensional sheet of 3d1 electrons is a prototypical
electronic reconstruction at an interface between competing ground states.Comment: 14 pages, 5 figure
Gravitational Waves from Axisymmetric, Rotational Stellar Core Collapse
We have carried out an extensive set of two-dimensional, axisymmetric,
purely-hydrodynamic calculations of rotational stellar core collapse with a
realistic, finite-temperature nuclear equation of state and realistic massive
star progenitor models. For each of the total number of 72 different
simulations we performed, the gravitational wave signature was extracted via
the quadrupole formula in the slow-motion, weak-field approximation. We
investigate the consequences of variation in the initial ratio of rotational
kinetic energy to gravitational potential energy and in the initial degree of
differential rotation. Furthermore, we include in our model suite progenitors
from recent evolutionary calculations that take into account the effects of
rotation and magnetic torques. For each model, we calculate gravitational
radiation wave forms, characteristic wave strain spectra, energy spectra, final
rotational profiles, and total radiated energy. In addition, we compare our
model signals with the anticipated sensitivities of the 1st- and 2nd-generation
LIGO detectors coming on line. We find that most of our models are detectable
by LIGO from anywhere in the Milky Way.Comment: 13 pages, 22 figures, accepted for publication in ApJ (v600, Jan.
2004). Revised version: Corrected typos and minor mistakes in text and
references. Minor additions to the text according to the referee's
suggestions, conclusions unchange
Evaluation of ASTER GDEM ver2 using GPS measurements and SRTM ver4.1 in China
The freely available ASTER GDEM ver2 was released by NASA and METI on October 17, 2011. As one of the most complete high resolution digital topographic data sets of the world to date, the ASTER GDEM covers land surfaces between 83°N and 83°S at a spatial resolution of 1 arc-second and will be a useful product for many applications, such as relief analysis, hydrological studies and radar interferometry. The stated improvements in the second version of ASTER GDEM benefit from finer horizontal resolution, offset adjustment and water body detection in addition to new observed ASTER scenes. This study investigates the absolute vertical accuracy of the ASTER GDEM ver2 at five study sites in China using ground control points (GCPs) from high accuracy GPS benchmarks, and also using a DEM-to-DEM comparison with the Consultative Group for International Agriculture Research Consortium for Spatial Information (CGIAR-CSI) SRTM DEM (Version 4.1). And then, the results are separated into GlobCover land cover classes to derive the spatial pattern of error. It is demonstrated that the RMSE (19m) and mean (-13m) values of ASTER GDEM ver2 against GPS-GCPs in the five study areas is lower than its first version ASTER GDEM ver1 (26m and -21m) as a result of the adjustment of the elevation offsets in the new version. It should be noted that the five study areas in this study are representative in terms of terrain types and land covers in China, and even for most of mid-latitude zones. It is believed that the ASTER GDEM offers a major alternative in accessibility to high quality elevation data
Multi-Dimensional Simulations of the Accretion-Induced Collapse of White Dwarfs to Neutron Stars
We present 2.5D radiation-hydrodynamics simulations of the accretion-induced
collapse (AIC) of white dwarfs, starting from 2D rotational equilibrium
configurations of a 1.46-Msun and a 1.92-Msun model. Electron capture leads to
the collapse to nuclear densities of these cores within a few tens of
milliseconds. The shock generated at bounce moves slowly, but steadily,
outwards. Within 50-100ms, the stalled shock breaks out of the white dwarf
along the poles. The blast is followed by a neutrino-driven wind that develops
within the white dwarf, in a cone of ~40deg opening angle about the poles, with
a mass loss rate of 5-8 x 10^{-3} Msun/yr. The ejecta have an entropy on the
order of 20-50 k_B/baryon, and an electron fraction distribution that is
bimodal. By the end of the simulations, at >600ms after bounce, the explosion
energy has reached 3-4 x 10^{49}erg and the total ejecta mass has reached a few
times 0.001Msun. We estimate the asymptotic explosion energies to be lower than
10^{50}erg, significantly lower than those inferred for standard core collapse.
The AIC of white dwarfs thus represents one instance where a neutrino mechanism
leads undoubtedly to a successful, albeit weak, explosion.
We document in detail the numerous effects of the fast rotation of the
progenitors: The neutron stars are aspherical; the ``nu_mu'' and anti-nu_e
neutrino luminosities are reduced compared to the nu_e neutrino luminosity; the
deleptonized region has a butterfly shape; the neutrino flux and electron
fraction depend strongly upon latitude (a la von Zeipel); and a quasi-Keplerian
0.1-0.5-Msun accretion disk is formed.Comment: 25 pages, 19 figures, accpeted to ApJ, high resolution of the paper
and movies available at http://hermes.as.arizona.edu/~luc/aic/aic.htm
Stochastic backgrounds of gravitational waves from extragalactic sources
Astrophysical sources emit gravitational waves in a large variety of
processes occurred since the beginning of star and galaxy formation. These
waves permeate our high redshift Universe, and form a background which is the
result of the superposition of different components, each associated to a
specific astrophysical process. Each component has different spectral
properties and features that it is important to investigate in view of a
possible, future detection. In this contribution, we will review recent
theoretical predictions for backgrounds produced by extragalactic sources and
discuss their detectability with current and future gravitational wave
observatories.Comment: 10 pages, 9 figures, proceedings of the GWDAW 10 Conference,
submitted to Class. & Quantum Gra
Valley spin polarization by using the extraordinary Rashba effect on silicon
The addition of the valley degree of freedom to a two-dimensional spin-polarized electronic system provides the opportunity to multiply the functionality of next-generation devices. So far, however, such devices have not been realized due to the difficulty to polarize the valleys, which is an indispensable step to activate this degree of freedom. Here we show the formation of 100% spin-polarized valleys by a simple and easy way using the Rashba effect on a system with C-3 symmetry. This polarization, which is much higher than those in ordinary Rashba systems, results in the valleys acting as filters that can suppress the backscattering of spin-charge. The present system is formed on a silicon substrate, and therefore opens a new avenue towards the realization of silicon spintronic devices with high efficiency.X114334Nsciescopu
Mightyl: A compositional translation from mitl to timed automata
Metric Interval Temporal Logic (MITL) was first proposed in the early 1990s as a specification formalism for real-time systems. Apart from its appealing intuitive syntax, there are also theoretical evidences that make MITL a prime real-time counterpart of Linear Temporal Logic (LTL). Unfortunately, the tool support for MITL verification is still lacking to this day. In this paper, we propose a new construction from MITL to timed automata via very-weak one-clock alternating timed automata. Our construction subsumes the well-known construction from LTL to Büchi automata by Gastin and Oddoux and yet has the additional benefits of being compositional and integrating easily with existing tools. We implement the construction in our new tool MightyL and report on experiments using Uppaal and LTSmin as back-ends
Correlations, inhomogeneous screening, and suppression of spin-splitting in quantum wires at strong magnetic fields
A self-consistent treatment of exchange and correlation interactions in a
quantum wire (QW) subject to a strong perpendicular magnetic field is presented
using a modified local-density approximation (MLDA). The influence of many-body
interactions on the spin-splitting between the two lowest Landau levels (LLs)
is calculated within the screened Hartree-Fock approximation (SHFA), for
filling factor \nu=1, and the strong spatial dependence of the screening
properties of electrons is taken into account. In comparison with the
Hartree-Fock result, the spatial behavior of the occupied LL in a QW is
strongly modified when correlations are included. Correlations caused by
screening at the edges strongly suppress the exchange splitting and smoothen
the energy dispersion at the edges. The theory accounts well for the
experimentally observed strong suppression of the spin-splitting pertinent to
the \nu=1 quantum Hall effect (QHE) state as well as the destruction of this
state in long, quasi-ballistic GaAlAs/GaAs QWs.Comment: Text 23 pages in Latex/Revtex/preprint format, 6 Postscript figures,
submitted to Physical Review
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