418,554 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
Iterative channel equalization, channel decoding and source decoding
The performance of soft source decoding is evaluated over dispersive AWGN channels. By employing source codes having error-correcting capabilities, such as Reversible Variable-Length Codes (RVLCs) and Variable-Length Error-Correcting (VLEC) codes, the softin/soft-out (SISO) source decoder benefits from exchanging information with the MAP equalizer, and effectively eliminates the inter-symbol interference (ISI) after a few iterations. It was also found that the soft source decoder is capable of significantly improving the attainable performance of the turbo receiver provided that channel equalization, channel decoding and source decoding are carried out jointly and iteratively. At SER = 10-4, the performance of this three-component turbo receiver is about 2 dB better in comparison to the benchmark scheme carrying out channel equalization and channel decoding jointly, but source decoding separately. At this SER value, the performance of the proposed scheme is about 1 dB worse than that of the ½-rate convolutional coded non-dispersive AWGN channel.<br/
First-principles investigation of transient current of molecular devices by using complex absorbing potential
Based on the non-equilibrium Green's function (NEGF) coupled with density
function theory (DFT), namely, NEGF-DFT quantum transport theory, we propose an
efficient formalism to calculate the transient current of molecular devices
under a step-like pulse from first principles. By combining NEGF-DFT with the
complex absorbing potential (CAP), the computational complexity of our
formalism (NEGF-DFT-CAP) is proportional to \emph{O}(N) where is the
number of time steps in the time-dependent transient calculation. Compared with
state-of-the-art algorithm of first principles time-dependent calculation that
scales with at least , this order N technique drastically reduces the
computational burden making it possible to tackle realistic molecular devices.
To ensure the accuracy of our method, we carry out the benchmark calculation
compared with exact NEGF-TDDFT formalism and they agree well with each other.
As an illustration, we investigate the transient current of molecular device
Al-C-Al from first principles
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The application of Han Dynasty cultural elements to modern product design
Chinese Han Culture, as Chinese nation's "core culture", is the cultural symbol of Chinese nation, and played an important role in the history of Chinese cultural development, even in the history of world cultural development. Designing in the Han Dynasty, while inheriting Chinese traditional culture, but also having its unique style, are appreciated and respected by the people nowadays. In a modern society where the design is becoming more diversified, the innovative design based on traditional culture and art has its unique charm and vitality. This paper presented our recent research on the application of Han Dynasty cultural elements to modern product design, reflected the local design connotation of Han Dynasty cultural elements
Turbo-Detected Unequal Error Protection Irregular Convolutional Codes Designed for the Wideband Advanced Multirate Speech Codec
Abstract—since the different bits of multimedia information, such as speech and video, have different error sensitivity, efficient unequalprotection channel coding schemes have to be used to ensure that the perceptually more important bits benefit from more powerful protection. Furthermore, in the context of turbo detection the channel codes should also match the characteristics of the channel for the sake of attaining a good convergence performance. In this paper, we address this design dilemma by using irregular convolutional codes (IRCCs) which constitute a family of different-rate subcodes. we benefit from the high design flexibility of IRCCs and hence excellent convergence properties are maintained while having unequal error protection capabilities matched to the requirements of the source. An EXIT chart based design procedure is proposed and used in the context of protecting the different-sensitivity speech bits of the wideband AMR speech codec. As a benefit, the unequalprotection system using IRCCs exhibits an SNR advantage of about 0.4dB over the equal-protection system employing regular convolutional codes, when communicating over a Gaussian channel
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
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