33,026 research outputs found
Local Null Controllability of a Chemotaxis System of Parabolic-Elliptic Type
In this paper, we are concerned with the controllability of a chemotaxis
system of parabolic-elliptic type. By linearizing the nonlinear system into two
separated linear equations to bypass the obstacle caused by the nonlinear drift
term, we establish the local null controllability of the original nonlinear
system. The approach is different from the usual way of treating the coupled
parabolic systems
A high-order lattice Boltzmann model for the Cahn-Hilliard equation
In this paper, a lattice Boltzmann model with the single-relaxation-time
model for the Cahn-Hilliard equation (CHE) is proposed. The discrete source
term is redesigned through a third-order Chapman-Enskog analysis. By coupling
the Navier-Stokes equations, the time-derivative term in the source term is
expressed as the relevant spatial derivatives. Furthermore, the source term on
the diffusive time scale is also proposed though recovering the macroscopic CHE
to third order. The model is tested by simulating diagonal motion of a circular
interface, Zalesak's disk rotation, circular interface in a shear flow and a
deformation field. It is shown that the proposed method can track the interface
with high accuracy and stability. For the complex flow, the source term on the
diffusive time scale should be considered for capturing the interface
correctly.Comment: 20 pages,11 figure
Fermi/LAT observations of Lobe-dominant Radio Galaxy 3C 207 and Possible Radiation Region of the Gamma-Rays
3C 207 is a lobe-dominant radio galaxy with one sided jet and the bright
knots in kpc-Mpc scale were resolved in the radio, optical and X-ray bands. It
was confirmed as a gamma-ray emitter with Fermi/LAT, but it is uncertain
whether the gamma-ray emission region is the core or knots due to the low
spatial resolution of Fermi/LAT. We present an analysis of its Fermi/LAT data
in the past 9 years. Different from the radio and optical emission from the
core, it is found that the gamma-ray emission is steady without detection of
flux variation over 2 sigma confidence level. This likely implies that the
gamma-ray emission is from its knots. We collect the radio, optical, and X-ray
data of knot-A, the closest knot from the core at 1 arcsec, and compile its
spectral energy distribution (SED). Although the single-zone
synchrotron+SSC+IC/CMB model by assuming knot-A at rest can reproduce the SED
in the radio-optical-X-ray band, the predicted gamma-ray flux is lower than the
LAT observations and the derived magnetic field strength deviates the
equipartition condition with 3 orders of magnitude. Assuming that knot-A is
relativistically moving, its SED from radio to gamma-ray bands would be well
represented with the single-zone synchrotron+SSC+IC/CMB model under the
equipartition condition. These results likely suggest that the gamma-ray
emission may be from knot-A via the IC/CMB process and the knot should have
relativistical motion. The jet power derived from our model parameters is also
roughly consistent with the kinetic power estimated with the radio data.Comment: 7 pages, 2 figures, accepted for publication in RA
Noncoherent Multiantenna Receivers for Cognitive Backscatter System with Multiple RF Sources
Cognitive backscattering, an integration of cognitive radio and backsatter
modulation, is emerging as a potential candidate for green Internet of Things
(IoT). In cognitive backscatter systems, the backscatter device (BD) shares not
only the same spectrum, but also the same radio-frequency (RF) source with the
legacy system. In this paper, we investigate the signal transmission problem,
in which a basic transmission model is considered which consists of K RF
sources, one BD and one reader equipped with M antennas. A non-cooperative
scenario is considered, where there is no cooperation between the legacy
systems and the backscatter system, and no pilots are transmitted from the RF
sources or BD to the reader. The on-off keying differential modulation is
adopted to achieve noncoherent transmission. Firstly, through the capacity
analyses, we point out that high-throughput backscatter transmission can be
achieved when the number of the receive antennas satisfies M>K. The Chernoff
Information (CI) is also derived to predict the detection performance. Next, we
address the signal detection problem at the reader. The optimal soft decision
(SD) and suboptimal hard decision (HD) detectors are designed based on the
maximum likelihood criterion. To tackle the non-cooperation challenge, a fully
blind channel estimation method is proposed to learn the detection-required
parameters based on clustering. Extensive numerical results verify the
effectiveness of the proposed detectors and the channel estimation method. In
addition, it is illustrated that the increase of K may not necessarily lead to
performance degradation when multiple receive antennas are exploited.Comment: 12 pages, 10 figure
Signal Shaping for Generalized Spatial Modulation and Generalized Quadrature Spatial Modulation
This paper investigates generic signal shaping methods for
multiple-data-stream generalized spatial modulation (GenSM) and generalized
quadrature spatial modulation (GenQSM) based on the maximizing the minimum
Euclidean distance (MMED) criterion. Three cases with different channel state
information at the transmitter (CSIT) are considered, including no CSIT,
statistical CSIT and perfect CSIT. A unified optimization problem is formulated
to find the optimal transmit vector set under size, power and sparsity
constraints. We propose an optimization-based signal shaping (OBSS) approach by
solving the formulated problem directly and a codebook-based signal shaping
(CBSS) approach by finding sub-optimal solutions in discrete space. In the OBSS
approach, we reformulate the original problem to optimize the signal
constellations used for each transmit antenna combination (TAC). Both the size
and entry of all signal constellations are optimized. Specifically, we suggest
the use of a recursive design for size optimization. The entry optimization is
formulated as a non-convex large-scale quadratically constrained quadratic
programming (QCQP) problem and can be solved by existing optimization
techniques with rather high complexity. To reduce the complexity, we propose
the CBSS approach using a codebook generated by quadrature amplitude modulation
(QAM) symbols and a low-complexity selection algorithm to choose the optimal
transmit vector set. Simulation results show that the OBSS approach exhibits
the optimal performance in comparison with existing benchmarks. However, the
OBSS approach is impractical for large-size signal shaping and adaptive signal
shaping with instantaneous CSIT due to the demand of high computational
complexity. As a low-complexity approach, CBSS shows comparable performance and
can be easily implemented in large-size systems.Comment: Summited to IEEE TW
Symbiotic Radio: A New Communication Paradigm for Passive Internet-of-Things
In this paper, a novel technique, called symbiotic radio (SR), is proposed
for passive Internet-of-Things (IoT), in which a backscatter device (BD) is
integrated with a primary transmission. The primary transmitter is designed to
assist the primary and BD transmissions, and the primary receiver decodes the
information from the primary transmitter as well as the BD. We consider a
multiple-input single-output (MISO) SR and the symbol period for BD
transmission is designed to be either the same as or much longer than that of
the primary system, resulting in parasitic or commensal relationship between
the primary and BD transmissions. We first derive the achievable rates for the
primary system and the BD transmission. Then, we formulate two transmit
beamforming optimization problems, i.e., the weighted sum-rate maximization
problem and the transmit power minimization problem, and solve these non-convex
problems by applying semi-definite relaxation technique. In addition, a novel
transmit beamforming structure is proposed to reduce the computational
complexity of the solutions. Simulation results show that when the BD
transmission rate is properly designed, the proposed SR not only enables the
opportunistic transmission for the BD via energy-efficient passive
backscattering, but also enhances the achievable rate of the primary system by
properly exploiting the additional signal path from the BD
Local Exact Controllability of a Parabolic System of Chemotaxis
This paper studies the controllability problem of a parabolic system of
chemotaxis. The local exact controllability to trajectories of the system
imposed one control force only is obtained by applying Kakutani's fixed point
theorem combined with the null controllability of the associated linearized
parabolic system. The control function is shown to be in , which
is estimated by using the methods of maximal regularity and -
estimates of parabolic equations
Observation of Mollow triplet with metastability exchange collisions in 3He atoms
We study the dressed states of 3He atoms and experimentally observe the
Mollow triplet (MT) induced with an ultra-low-frequency (ULF) oscillating
magnetic field as low as 4 Hz. The ULF MT signatures from the ground states of
3He atoms are transferred to the metastable states by metastability-exchange
collisions (MECs) and measured optically, which demonstrates 2 s coherence time
in the dressed ground states. The result shows the possibility of ULF magnetic
field amplitude measurement and a new scheme for optical frequency modulation
AI-Powered Text Generation for Harmonious Human-Machine Interaction: Current State and Future Directions
In the last two decades, the landscape of text generation has undergone
tremendous changes and is being reshaped by the success of deep learning. New
technologies for text generation ranging from template-based methods to neural
network-based methods emerged. Meanwhile, the research objectives have also
changed from generating smooth and coherent sentences to infusing personalized
traits to enrich the diversification of newly generated content. With the rapid
development of text generation solutions, one comprehensive survey is urgent to
summarize the achievements and track the state of the arts. In this survey
paper, we present the general systematical framework, illustrate the widely
utilized models and summarize the classic applications of text generation.Comment: Accepted by IEEE UIC 201
Observation of Mollow quintuplet in F=3/2 hyperfine structure state of 3He atomic cell
We experimentally observed the Mollow quintuplet (MQ) in F=3/2 hyperfine
structure state of 3He atoms. The metastability-exchange collisions (MECs)
transfer the Mollow Triplet (MT) from the ground states of 3He atoms to the
metastable states, and the MQ is demonstrated by four Zeeman levels of F=3/2
hyperfine states with linearly polarized light. The similar effect also
achieves in the mixture cell of 3He and 4He.Comment: 4 pages, 6 figures. arXiv admin note: text overlap with
arXiv:1810.1177
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