268,609 research outputs found
Peak structural response to nonstationary random excitations
Study establishes distribution function of peak response values, based on frequency interpretation. Excitations considered include impact loading on landing gears and aircraft gust loading. Because of relative severity of excitations, prediction of fatigue and maximum response characteristics is important part of task of structural analysis and design
Doping and temperature-dependent optical properties of oxygen-reduced BaTiO3-d
We report on optical properties of reduced BaTiO3-d at different doping
levels including insulating and metallic samples. In all the samples, including
metallic one, we observe structural phase transitions from the changes in the
infrared-active phonon modes. Metallic ground state is confirmed by the
Drude-type lowfrequency optical reflectance. Similar to SrTiO3-d we find that
the midinfrared-absorption band in BaTiO3-d appears and grows with an increase
in the oxygen-vacancy concentration. Upon decrease in temperature from 300 K,
the midinfrared band shifts slightly to higher frequency and evolves into two
bands: the existing band and a new and smaller band at lower frequency. The
appearance of the new and smaller band seems to be correlated with the
structural phase transitionsComment: 8 pages, 7 figure
Epitaxial Ferromagnetic Nanoislands of Cubic GdN in Hexagonal GaN
Periodic structures of GdN particles encapsulated in a single crystalline GaN
matrix were prepared by plasma assisted molecular beam epitaxy. High resolution
X-ray diffractometery shows that GdN islands, with rock salt structure are
epitaxially oriented to the wurtzite GaN matrix. Scanning transmission electron
microscopy combined with in-situ reflection high energy electron diffraction
allows for the study of island formation dynamics, which occurs after 1.2
monolayers of GdN coverage. Magnetometry reveals two ferromagnetic phases, one
due to GdN particles with Curie temperature of 70K and a second, anomalous room
temperature phase.Comment: 4 pages, 3 figure
Quantum steering of electron wave function in an InAs Y-branch switch
We report experiments on gated Y-branch switches made from InAs ballistic
electron wave guides. We demonstrate that gating modifies the electron wave
functions as well as their interference pattern, causing the anti-correlated,
oscillatory transconductances. Such previously unexpected phenomenon provides
evidence of steering the electron wave function in a multi-channel transistor
structure.Comment: 15 pages, including 3 figure
Sudden jumps and plateaus in the quench dynamics of a Bloch state
We take a one-dimensional tight binding chain with periodic boundary
condition and put a particle in an arbitrary Bloch state, then quench it by
suddenly changing the potential of an arbitrary site. In the ensuing time
evolution, the probability density of the wave function at an arbitrary site
\emph{jumps indefinitely between plateaus}. This phenomenon adds to a former
one in which the survival probability of the particle in the initial Bloch
state shows \emph{cusps} periodically, which was found in the same scenario
[Zhang J. M. and Yang H.-T., EPL, \textbf{114} (2016) 60001]. The plateaus
support the scattering wave picture of the quench dynamics of the Bloch state.
Underlying the cusps and jumps is the exactly solvable, nonanalytic dynamics of
a Luttinger-like model, based on which, the locations of the jumps and the
heights of the plateaus are accurately predicted.Comment: final versio
Asymmetric vortex solitons in nonlinear periodic lattices
We reveal the existence of asymmetric vortex solitons in ideally symmetric
periodic lattices, and show how such nonlinear localized structures describing
elementary circular flows can be analyzed systematically using the
energy-balance relations. We present the examples of rhomboid, rectangular, and
triangular vortex solitons on a square lattice, and also describe novel
coherent states where the populations of clockwise and anti-clockwise vortex
modes change periodically due to a nonlinearity-induced momentum exchange
through the lattice. Asymmetric vortex solitons are expected to exist in
different nonlinear lattice systems including optically-induced photonic
lattices, nonlinear photonic crystals, and Bose-Einstein condensates in optical
lattices.Comment: 4 pages, 5 figure
Differential Phase-contrast Interior Tomography
Differential phase contrast interior tomography allows for reconstruction of
a refractive index distribution over a region of interest (ROI) for
visualization and analysis of internal structures inside a large biological
specimen. In this imaging mode, x-ray beams target the ROI with a narrow beam
aperture, offering more imaging flexibility at less ionizing radiation.
Inspired by recently developed compressive sensing theory, in numerical
analysis framework, we prove that exact interior reconstruction can be achieved
on an ROI via the total variation minimization from truncated differential
projection data through the ROI, assuming a piecewise constant distribution of
the refractive index in the ROI. Then, we develop an iterative algorithm for
the interior reconstruction and perform numerical simulation experiments to
demonstrate the feasibility of our proposed approach
Antenna Miniaturization Based on Supperscattering Effect
Antennas are essential components of all existing radio equipments. The miniaturization of antenna is a key issue of antenna technology. Based on supperscattering effect, we found that when a small horn antenna is located inside of a dielectric core and covered with a complementary layer, its far field radiation pattern will be equivalent to a large horn antenna. The complementary layer with only axial parameters varying with radius is obtained using coordinate transformation theory. Besides, the influence of loss and perturbations of parameters on supperscattering effect is also investigated. Results show that the device is robust against the perturbation in the axial material parameters when the refractive index is kept invariant. Full-wave simulations based on finite element method are performed to validate the design
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