2,882 research outputs found
Explosive events associated with a surge
The solar atmosphere contains a wide variety of small-scale transient
features. Here, we explore the inter-relation between some of them such as
surges, explosive events and blinkers via simultaneous spectral and imaging
data taken with the TRACE imager, the SUMER, and CDS spectrometers on board
SoHO, and SVST La Palma. The alignment of all data both in time and solar XY
shows that SUMER line profiles, which are attributed to explosive events, are
due to a surge phenomenon. The surge is triggered, most probably, by one or
more Elerman bombs which are best visible in Halpha +-350 A but were also
registered by TRACE Fe IX/X 171 A and correspond to a strong radiance increase
in the CDS Mg IX 368.07 A line. With the present study we demonstrate that the
division of small-scale transient events into a number of different subgroups,
for instance explosive events, blinkers, spicules, surges or just brightenings,
is ambiguous, implying that the definition of a feature based only on either
spectroscopic or imaging characteristics as well as insufficient spectral and
spatial resolution can be incomplete.Comment: 17 pages, 7 figures, 1 tabl
Observation of First-Order Metal-Insulator Transition without Structural Phase Transition in VO_2
An abrupt first-order metal-insulator transition (MIT) without structural
phase transition is first observed by current-voltage measurements and
micro-Raman scattering experiments, when a DC electric field is applied to a
Mott insulator VO_2 based two-terminal device. An abrupt current jump is
measured at a critical electric field. The Raman-shift frequency and the
bandwidth of the most predominant Raman-active A_g mode, excited by the
electric field, do not change through the abrupt MIT, while, they, excited by
temperature, pronouncedly soften and damp (structural MIT), respectively. This
structural MIT is found to occur secondarily.Comment: 4 pages, 4 figure
Correlated metallic state of vanadium dioxide
The metal-insulator transition and unconventional metallic transport in
vanadium dioxide (VO) are investigated with a combination of spectroscopic
ellipsometry and reflectance measurements. The data indicates that electronic
correlations, not electron-phonon interactions, govern charge dynamics in the
metallic state of VO. This study focuses on the frequency and temperature
dependence of the conductivity in the regime of extremely short mean free path
violating the Ioffe-Regel-Mott limit of metallic transport. The standard
quasiparticle picture of charge conduction is found to be untenable in metallic
VO.Comment: 5 pages, 3 figure
Asymmetry in fatigue and recovery in ferroelectric Pb(Zr,Ti)O3 thin-film capacitors
We investigate the fatigue and refreshment by dc-electrical field of the
electrical properties of Pt/Pb(Ti,Zr)O/Pt ferroelectric capacitors. We find
an asymmetry in the refreshment, that is, the fatigued state can be refreshed
by application of negative high dc-voltage to the top electrode, but no
refreshment is measured by positive dc-voltage application. We also find that
the fatigue can be prevented by driving the capacitor asymmetrically.Comment: 4 pages, 5 figure
Electrodynamics of the vanadium oxides VO2 and V2O3
The optical/infrared properties of films of vanadium dioxide (VO2) and
vanadium sesquioxide (V2O3) have been investigated via ellipsometry and
near-normal incidence reflectance measurements from far infrared to ultraviolet
frequencies. Significant changes occur in the optical conductivity of both VO2
and V2O3 across the metal-insulator transitions at least up to (and possibly
beyond) 6 eV. We argue that such changes in optical conductivity and electronic
spectral weight over a broad frequency range is evidence of the important role
of electronic correlations to the metal-insulator transitions in both of these
vanadium oxides. We observe a sharp optical transition with possible final
state (exciton) effects in the insulating phase of VO2. This sharp optical
transition occurs between narrow a1g bands that arise from the
quasi-one-dimensional chains of vanadium dimers. Electronic correlations in the
metallic phases of both VO2 and V2O3 lead to reduction of the kinetic energy of
the charge carriers compared to band theory values, with paramagnetic metallic
V2O3 showing evidence of stronger correlations compared to rutile metallic VO2.Comment: 11 pages, 7 figure
Electronic structure studies of Fe- ZnO nanorods by x-ray absorption fine structure
We report the electronic structure studies of well characterized
polycrystalline Zn_{1-x}Fe_xO (x = 0.0, 0.01, 0.03, and 0.05) nanorods
synthesized by a co-precipitation method through x-ray absorption fine
structure (XAFS). X-ray diffraction (XRD) reveals that Fe doped ZnO
crystallizes in a single phase wurtzite structure without any secondary phase.
From the XRD pattern, it is observed that peak positions shift towards lower
2\theta value with Fe doping. The change in the peak positions with increase in
Fe contents clearly indicates that Fe ions are replacing Zn ions in the ZnO
matrix. Linear combination fittings (LCF) at Fe K-edge demonstrate that Fe is
in mixed valent state (Fe3+/Fe2+) with a ratio of ~ 7:3 (Fe3+:Fe2+). XAFS data
is successfully fitted to wurtzite structure using IFEFFIT and Artemis. The
results indicate that Fe substitutes Zn site in the ZnO matrix in tetrahedral
symmetry.Comment: 7 pages, 5 figures, 2 tables, regular articl
A compact and reconfigurable silicon nitride time-bin entanglement circuit
Photonic chip based time-bin entanglement has attracted significant attention
because of its potential for quantum communication and computation. Useful
time-bin entanglement systems must be able to generate, manipulate and analyze
entangled photons on a photonic chip for stable, scalable and reconfigurable
operation. Here we report the first time-bin entanglement photonic chip that
integrates time-bin generation, wavelength demultiplexing and entanglement
analysis. A two-photon interference fringe with an 88.4% visibility is measured
(without subtracting any noise), indicating the high performance of the chip.
Our approach, based on a silicon nitride photonic circuit, which combines the
low-loss characteristic of silica and tight integration features of silicon,
paves the way for scalable real-world quantum information processors.Comment: 4 pages, 5 figure
Global classical solutions for partially dissipative hyperbolic system of balance laws
This work is concerned with (-component) hyperbolic system of balance laws
in arbitrary space dimensions. Under entropy dissipative assumption and the
Shizuta-Kawashima algebraic condition, a general theory on the well-posedness
of classical solutions in the framework of Chemin-Lerner's spaces with critical
regularity is established. To do this, we first explore the functional space
theory and develop an elementary fact that indicates the relation between
homogeneous and inhomogeneous Chemin-Lerner's spaces. Then this fact allows to
prove the local well-posedness for general data and global well-posedness for
small data by using the Fourier frequency-localization argument. Finally, we
apply the new existence theory to a specific fluid model-the compressible Euler
equations with damping, and obtain the corresponding results in critical
spaces.Comment: 39 page
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