1,380 research outputs found
Rewritable nanoscale oxide photodetector
Nanophotonic devices seek to generate, guide, and/or detect light using
structures whose nanoscale dimensions are closely tied to their functionality.
Semiconducting nanowires, grown with tailored optoelectronic properties, have
been successfully placed into devices for a variety of applications. However,
the integration of photonic nanostructures with electronic circuitry has always
been one of the most challenging aspects of device development. Here we report
the development of rewritable nanoscale photodetectors created at the interface
between LaAlO3 and SrTiO3. Nanowire junctions with characteristic dimensions
2-3 nm are created using a reversible AFM writing technique. These nanoscale
devices exhibit a remarkably high gain for their size, in part because of the
large electric fields produced in the gap region. The photoconductive response
is gate-tunable and spans the visible-to-near-infrared regime. The ability to
integrate rewritable nanoscale photodetectors with nanowires and transistors in
a single materials platform foreshadows new families of integrated
optoelectronic devices and applications.Comment: 5 pages, 5 figures. Supplementary Information 7 pages, 9 figure
Binegativity and geometry of entangled states in two qubits
We prove that the binegativity is always positive for any two-qubit state. As
a result, as suggested by the previous works, the asymptotic relative entropy
of entanglement in two qubits does not exceed the Rains bound, and the
PPT-entanglement cost for any two-qubit state is determined to be the
logarithmic negativity of the state. Further, the proof reveals some
geometrical characteristics of the entangled states, and shows that the partial
transposition can give another separable approximation of the entangled state
in two qubits.Comment: 5 pages, 3 figures. I made the proof more transparen
Studying the Warm-Hot Intergalactic Medium in Emission
We assess the possibility to detect the warm-hot intergalactic medium (WHIM)
in emission and to characterize its physical conditions and spatial
distribution through spatially resolved X-ray spectroscopy, in the framework of
the recently proposed DIOS, EDGE, Xenia, and ORIGIN missions, all of which are
equipped with microcalorimeter-based detectors. For this purpose we analyze a
large set of mock emission spectra, extracted from a cosmological
hydrodynamical simulation. These mock X-ray spectra are searched for emission
features showing both the OVII K alpha triplet and OVIII Ly alpha line, which
constitute a typical signature of the warm hot gas. Our analysis shows that 1
Ms long exposures and energy resolution of 2.5 eV will allow us to detect about
400 such features per deg^2 with a significance >5 sigma and reveals that these
emission systems are typically associated with density ~100 above the mean. The
temperature can be estimated from the line ratio with a precision of ~20%. The
combined effect of contamination from other lines, variation in the level of
the continuum, and degradation of the energy resolution reduces these
estimates. Yet, with an energy resolution of 7 eV and all these effects taken
into account, one still expects about 160 detections per deg^2. These line
systems are sufficient to trace the spatial distribution of the line-emitting
gas, which constitute an additional information, independent from line
statistics, to constrain the poorly known cosmic chemical enrichment history
and the stellar feedback processes.Comment: 19 pages, 10 figures, ApJ in press; revised version according to
revie
In situ construction of heterostructured bimetallic sulfide/phosphide with rich interfaces for high-performance aqueous Zn-ion batteries
It is still challenging to develop suitable cathode structures for high-rate and stable aqueous Zn-ion batteries. Herein, a phosphating-assisted interfacial engineering strategy is designed for the controllable conversion of NiCo_{2}S_{4} nanosheets into heterostructured NiCoP/NiCo_{2}S_{4} as the cathodes in aqueous Zn-ion batteries. The multicomponent heterostructures with rich interfaces can not only improve the electrical conductivity but also enhance the diffusion pathways for Zn-ion storage. As expected, the NiCoP/NiCo_{2}S_{4} electrode has high performance with a large specific capacity of 251.1 mA h g^{â1} at a high current density of 10 A g^{â1} and excellent rate capability (retaining about 76% even at 50 A g^{â1}). Accordingly, the Zn-ion battery using NiCoP/NiCo_{2}S_{4} as the cathode delivers a high specific capacity (265.1 mA h g^{â1} at 5A g^{â1}), a long-term cycling stability (96.9% retention after 5000 cycles), and a competitive energy density (444.7 W h kg^{â1} at the power density of 8.4 kW kg^{â1}). This work therefore provides a simple phosphating-assisted interfacial engineering strategy to construct heterostructured electrode materials with rich interfaces for the development of high-performance energy storage devices in the future
Validation of a simplified micromodel for analysis of infilled RC frames exposed to cyclic lateral loads
An RC frame structure with masonry infill walls (ââframed-masonryââ) exposed
to lateral loads acts as a composite structure. Numerical simulation of framed-masonry is
difficult and generally unreliable due to many difficulties and uncertainties in its modelling.
In this paper, we reviewed the usability of an advanced non-linear FEM computer
program to accurately predict the behaviour of framed-masonry elements when exposed to
cyclic lateral loading. Numerical results are validated against the test results of framedmasonry
specimens, with and without openings. Initial simplified micromodels were calibrated
by adjustment of the input parameters within the physically justifiable borders, in
order to obtain the best correlation between the experimental and numerical results. It has
been shown that the use of simplified micromodels for the investigation of composite
masonry-infilled RC frames requires in-depth knowledge and engineering judgement in
order to be used with confidence. Modelling problems were identified and explained in
detail, which in turn offer an insight to practising engineers on how to deal with them
Numerical simulations of the Warm-Hot Intergalactic Medium
In this paper we review the current predictions of numerical simulations for
the origin and observability of the warm hot intergalactic medium (WHIM), the
diffuse gas that contains up to 50 per cent of the baryons at z~0. During
structure formation, gravitational accretion shocks emerging from collapsing
regions gradually heat the intergalactic medium (IGM) to temperatures in the
range T~10^5-10^7 K. The WHIM is predicted to radiate most of its energy in the
ultraviolet (UV) and X-ray bands and to contribute a significant fraction of
the soft X-ray background emission. While O VI and C IV absorption systems
arising in the cooler fraction of the WHIM with T~10^5-10^5.5 K are seen in
FUSE and HST observations, models agree that current X-ray telescopes such as
Chandra and XMM-Newton do not have enough sensitivity to detect the hotter
WHIM. However, future missions such as Constellation-X and XEUS might be able
to detect both emission lines and absorption systems from highly ionised atoms
such as O VII, O VIII and Fe XVII.Comment: 18 pages, 5 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 14; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Recovering the Inflationary Potential
A procedure is developed for the recovery of the inflationary potential over
the interval that affects astrophysical scales (\approx 1\Mpc - 10^4\Mpc).
The amplitudes of the scalar and tensor metric perturbations and their
power-spectrum indices, which can in principle be inferred from large-angle CBR
anisotropy experiments and other cosmological data, determine the value of the
inflationary potential and its first two derivatives. From these, the
inflationary potential can be reconstructed in a Taylor series and the
consistency of the inflationary hypothesis tested. A number of examples are
presented, and the effect of observational uncertainties is discussed.Comment: 13 pages LaTeX, 6 Figs. available on request, FNAL-Pub-93/182-
UHECR Acceleration in Dark Matter Filaments of Cosmological Structure Formation
A mechanism for proton acceleration to ~10^21eV is suggested. It may operate
in accretion flows onto thin dark matter filaments of cosmic structure
formation. The flow compresses the ambient magnetic field to strongly increase
and align it with the filament. Particles begin the acceleration by the ExB
drift with the accretion flow. The energy gain in the drift regime is limited
by the conservation of the adiabatic invariant p_perp^2/B. Upon approaching the
filament, the drift turns into the gyro-motion around the filament so that the
particle moves parallel to the azimuthal electric field. In this 'betatron'
regime the acceleration speeds up to rapidly reach the electrodynamic limit
for an accelerator with magnetic field and the orbit radius
(Larmor radius). The periodic orbit becomes unstable and the particle
slings out of the filament to the region of a weak (uncompressed) magnetic
field, which terminates the acceleration.
The mechanism requires pre-acceleration that is likely to occur in structure
formation shocks upstream or nearby the filament accretion flow. Previous
studies identify such shocks as efficient proton accelerators to a firm upper
limit ~10^19.5 eV placed by the catastrophic photo-pion losses. The present
mechanism combines explosive energy gain in its final (betatron) phase with
prompt particle release from the region of strong magnetic field. It is this
combination that allows protons to overcome both the photo-pion and the
synchrotron-Compton losses and therefore attain energy 10^21 eV. A requirement
on accelerator to reach a given E_max placed by the accelerator energy
dissipation \propto E_{max}^{2}/Z_0 due to the finite vacuum impedance Z_0 is
circumvented by the cyclic operation of the accelerator.Comment: 34 pages, 10 figures, to be published in JCA
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