317,641 research outputs found
Origin of sawtooth domain walls in ferroelectrics
Domains and domain walls are among the key factors that determine the
performance of ferroelectric materials. In recent years, a unique type of
domain walls, i.e., the sawtooth-shaped domain walls, has been observed in
BiFeO and PbTiO. Here, we build a minimal model to reveal the
origin of these sawtooth-shaped domain walls. Incorporating this model into
Monte-Carlo simulations shows that (i) the competition between the long-range
Coulomb interaction (due to bound charges) and short-range interaction (due to
opposite dipoles) is responsible for the formation of these peculiar domain
walls and (ii) their relative strength is critical in determining the
periodicity of these sawtooth-shaped domain walls. Necessary conditions to form
such domain walls are also discussed
Polarized Curvature Radiation in Pulsar Magnetosphere
The propagation of polarized emission in pulsar magnetosphere is investigated
in this paper. The polarized waves are generated through curvature radiation
from the relativistic particles streaming along curved magnetic field lines and
co-rotating with the pulsar magnetosphere. Within the 1/{\deg} emission cone,
the waves can be divided into two natural wave mode components, the ordinary
(O) mode and the extraord nary (X) mode, with comparable intensities. Both
components propagate separately in magnetosphere, and are aligned within the
cone by adiabatic walking. The refraction of O-mode makes the two components
separated and incoherent. The detectable emission at a given height and a given
rotation phase consists of incoherent X-mode and O-mode components coming from
discrete emission regions. For four particle-density models in the form of
uniformity, cone, core and patches, we calculate the intensities for each mode
numerically within the entire pulsar beam. If the co-rotation of relativistic
particles with magnetosphere is not considered, the intensity distributions for
the X-mode and O-mode components are quite similar within the pulsar beam,
which causes serious depolarization. However, if the co-rotation of
relativistic particles is considered, the intensity distributions of the two
modes are very different, and the net polarization of out-coming emission
should be significant. Our numerical results are compared with observations,
and can naturally explain the orthogonal polarization modes of some pulsars.
Strong linear polarizations of some parts of pulsar profile can be reproduced
by curvature radiation and subsequent propagation effect.Comment: 12 pages, 9 figures, Accepted for publication in MNRA
Compact and Broadband Microstrip-Line-Fed Modified Rhombus Slot Antenna
The printed microstrip-line-fed broadband rhombus slot antenna is investigated in this paper. With the use of the offset microstrip feed line and the corner-truncated protruded ground plane, the bandwidth enhancement and the slot size reduction for the proposed slot antenna can be obtained. The experimental results demonstrate that the impedance bandwidth for 10 dB return loss reaches 5210 MHz (108.2%, 2210-7420 MHz), which is about 2.67 times of a conventional microstrip-line-fed rhombus slot antenna. This bandwidth can provide with the wireless communication services operating in wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) bands. Under the use of the protruded ground plane, the slot size can be reduced by about 52%. Details of simulated and measured results are presented and discussed
Effects of the sintering atmosphere on the superconductivity of SmFeAsO1-xFx compounds
A series of SmFeAsO1-xFx samples were sintered in quartz tubes filled with
air of different pressures. The effects of the sintering atmosphere on the
superconductivity were systematically investigated. The SmFeAsO1-xFx system
maintains a transition temperature (Tc) near 50 K until the concentration of
oxygen in quartz tubes increases to a certain threshold, after which Tc
decreases dramatically. Fluorine losses, whether due to vaporization, reactions
with starting materials, and reactions with oxygen, proved to be detrimental to
the superconductivity of this material. The deleterious effects of the oxygen
in the sintering atmosphere were also discussed in detail.Comment: 9 pages, 5 figure
Fiber Based Multiple-Access Optical Frequency Dissemination
We demonstrate a fiber based multiple-access optical frequency dissemination
scheme. Without using any additional laser sources, we reproduce the stable
disseminated frequency at an arbitrary point of fiber link. Relative frequency
stability of 3E10^{-16}/s and 4E10^{-18}/10^4s is obtained. A branching fiber
network for highly-precision synchronization of optical frequency is made
possible by this method and its applications are discussed.Comment: 5 pages, 3 figure
Geometric phase in dephasing systems
Beyond the quantum Markov approximation, we calculate the geometric phase of
a two-level system driven by a quantized magnetic field subject to phase
dephasing. The phase reduces to the standard geometric phase in the weak
coupling limit and it involves the phase information of the environment in
general. In contrast with the geometric phase in dissipative systems, the
geometric phase acquired by the system can be observed on a long time scale. We
also show that with the system decohering to its pointer states, the geometric
phase factor tends to a sum over the phase factors pertaining to the pointer
states.Comment: 4 page
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