518 research outputs found
Aging phenomena in the two-dimensional complex Ginzburg-Landau equation
The complex Ginzburg-Landau equation with additive noise is a stochastic
partial differential equation that describes a remarkably wide range of
physical systems which include coupled non-linear oscillators subject to
external noise near a Hopf bifurcation instability and spontaneous structure
formation in non-equilibrium systems, e.g., in cyclically competing populations
or oscillatory chemical reactions. We employ a finite-difference method to
numerically solve the noisy complex Ginzburg-Landau equation on a
two-dimensional domain with the goal to investigate its non-equilibrium
dynamics when the system is quenched into the "defocusing spiral quadrant". We
observe slow coarsening dynamics as oppositely charged topological defects
annihilate each other, and characterize the ensuing aging scaling behavior. We
conclude that the physical aging features in this system are governed by
non-universal aging scaling exponents. We also investigate systems with control
parameters residing in the "focusing quadrant", and identify slow aging
kinetics in that regime as well. We provide heuristic criteria for the
existence of slow coarsening dynamics and physical aging behavior in the
complex Ginzburg-Landau equation.Comment: 7 pages, 3 figures, to appear in EPL (Europhys. Lett.
Enhancing physical layer security in wireless networks with cooperative approaches
Motivated by recent developments in wireless communication, this thesis aims to
characterize the secrecy performance in several types of typical wireless networks.
Advanced techniques are designed and evaluated to enhance physical layer security in
these networks with realistic assumptions, such as signal propagation loss, random node
distribution and non-instantaneous channel state information (CSI).
The first part of the thesis investigates secret communication through relay-assisted
cognitive interference channel. The primary and secondary base stations (PBS and SBS)
communicate with the primary and secondary receivers (PR and SR) respectively in the
presence of multiple eavesdroppers. The SBS is allowed to transmit simultaneously with
the PBS over the same spectrum instead of waiting for an idle channel. To improve
security, cognitive relays transmit cooperative jamming (CJ) signals to create additional
interferences in the direction of the eavesdroppers. Two CJ schemes are proposed to
improve the secrecy rate of cognitive interference channels depending on the structure of
cooperative relays. In the scheme where the multiple-antenna relay transmits weighted
jamming signals, the combined approach of CJ and beamforming is investigated. In
the scheme with multiple relays transmitting weighted jamming signals, the combined
approach of CJ and relay selection is analyzed. Numerical results show that both these
two schemes are effective in improving physical layer security of cognitive interference
channel.
In the second part, the focus is shifted to physical layer security in a random wireless
network where both legitimate and eavesdropping nodes are randomly distributed. Three
scenarios are analyzed to investigate the impact of various factors on security. In
scenario one, the basic scheme is studied without a protected zone and interference. The
probability distribution function (PDF) of channel gain with both fading and path loss
has been derived and further applied to derive secrecy connectivity and ergodic secrecy
capacity. In the second scenario, we studied using a protected zone surrounding the source
node to enhance security where interference is absent. Both the cases that eavesdroppers
are aware and unaware of the protected zone boundary are investigated. Based on the
above scenarios, further deployment of the protected zones at legitimate receivers is
designed to convert detrimental interference into a beneficial factor. Numerical results
are investigated to check the reliability of the PDF for reciprocal of channel gain and to
analyze the impact of protected zones on secrecy performance.
In the third part, physical layer security in the downlink transmission of cellular network
is studied. To model the repulsive property of the cellular network planning, we assume
that the base stations (BSs) follow the Mat´ern hard-core point process (HCPP), while
the eavesdroppers are deployed as an independent Poisson point process (PPP). The
distribution function of the distances from a typical point to the nodes of the HCPP is
derived. The noise-limited and interference-limited cellular networks are investigated
by applying the fractional frequency reuse (FFR) in the system. For the noise-limited
network, we derive the secrecy outage probability with two different strategies, i.e. the
best BS serve and the nearest BS serve, by analyzing the statistics of channel gains. For
the interference-limited network with the nearest BS serve, two transmission schemes are
analyzed, i.e., transmission with and without the FFR. Numerical results reveal that both
the schemes of transmitting with the best BS and the application of the FFR are beneficial
for physical layer security in the downlink cellular networks, while the improvement du
Consumption of Hydrogen Water Reduces Paraquat-Induced Acute Lung Injury in Rats
Exposure to paraquat leads to acute lung injury and oxidative stress is widely accepted as a contributor to paraquat-induced acute lung injury. Recent studies have reported that consumption of water with dissolved molecular hydrogen to a saturated level (hydrogen water) prevents oxidative stress-induced diseases. Here, we investigated whether consumption of saturated hydrogen saline protects rats against paraquat-induced acute lung injury. Adult male Sprague-Dawley (SD) rats were randomly divided into four groups: Control group; hydrogen water-only group (HW group); paraquat-only group (PQ group); paraquat and hydrogen water group (PQ + HW group). The rats in control group and HW group drank pure water or hydrogen water; the rats in PQ group and PQ + HW group were intraperitonealy injected with paraquat (35 mg/kg) and then provided pure water or hydrogen water. Both biochemical and histological lung alterations were measured. The results showed that hydrogen water ameliorated these alterations, demonstrating that hydrogen water alleviated paraquat-induced acute lung injury possibly by inhibition of oxidative damage
Modeling Fine-grained Information via Knowledge-aware Hierarchical Graph for Zero-shot Entity Retrieval
Zero-shot entity retrieval, aiming to link mentions to candidate entities
under the zero-shot setting, is vital for many tasks in Natural Language
Processing. Most existing methods represent mentions/entities via the sentence
embeddings of corresponding context from the Pre-trained Language Model.
However, we argue that such coarse-grained sentence embeddings can not fully
model the mentions/entities, especially when the attention scores towards
mentions/entities are relatively low. In this work, we propose GER, a
\textbf{G}raph enhanced \textbf{E}ntity \textbf{R}etrieval framework, to
capture more fine-grained information as complementary to sentence embeddings.
We extract the knowledge units from the corresponding context and then
construct a mention/entity centralized graph. Hence, we can learn the
fine-grained information about mention/entity by aggregating information from
these knowledge units. To avoid the graph information bottleneck for the
central mention/entity node, we construct a hierarchical graph and design a
novel Hierarchical Graph Attention Network~(HGAN). Experimental results on
popular benchmarks demonstrate that our proposed GER framework performs better
than previous state-of-the-art models. The code has been available at
https://github.com/wutaiqiang/GER-WSDM2023.Comment: 9 pages, 5 figure
Changes and driving forces analysis of alpine wetlands in the first meander of the Yellow River based on long-term time series remote sensing data
IntroductionAs a vital component of the ecosystem of the Qinghai-Tibet Plateau, alpine wetlands coexist with their vulnerability, sensitivity, and abundant biodiversity, propelling the material cycle and energy flux of the entire plateau ecosystem. In recent decades, climate change and human activities have significantly altered the regional landscape. Monitoring and assessing changes in the alpine wetlands on the Qinghai-Tibet Plateau requires the efficient and accurate collection of long-term information.MethodsHere, we interpreted the remote sensing data of the first meander of the Yellow River of alpine wetlands from 1990 to 2020 based on Google Earth Engine (GEE) platform, using geographic information system (GIS) and landscape pattern index to analyze the spatial and temporal evolution of wetland landscape patterns, and the primary drivers of changes in wetland area were explored by GeoDetector.ResultsOur result showed that most wetland areas were found in regions with gradients less than 12° and elevations between 3315 and 3600 m. From 1990 to 2010, the area of alpine wetland in the study area decreased by 25.43%. During the period between 2010 and 2020 to the 1990s, the wetland area decreased by 322.9 km2. Conversion to and from grassland was the primary form of wetland transfer out and in, respectively. The overall migration of the wetland centroid in the study area was to the southwest between 1990 and 2010 and to the north between 2010 and 2020. The geometry of the wetland landscape was relatively simple, the landscape was relatively intact, and patches retained a high level of agglomeration and connectivity. However, their level of agglomeration and connectivity was disrupted. A quantitative analysis of the factor detector in GeoDetector revealed that the DEM, slope, and evaporation were the most important driving factors influencing the change of wetland area, with socioeconomic development also influencing changes in the wetland area to a lesser extent.DiscussionUsing interaction detectors, it was discovered that the interaction of various driving factors could better explain the long-term variations in wetland areas, with a greater degree of explanation than that of each driving factor alone
A porous metal-organic framework with ultrahigh acetylene uptake capacity under ambient conditions
Acetylene, an important petrochemical raw material, is very difficult to store safely under compression because of its highly explosive nature. Here we present a porous metal-organic framework named FJI-H8, with both suitable pore space and rich open metal sites, for efficient storage of acetylene under ambient conditions. Compared with existing reports, FJI-H8 shows a record-high gravimetric acetylene uptake of 224 cm(3) (STP) g(−1) and the second-highest volumetric uptake of 196 cm(3) (STP) cm(−3) at 295 K and 1 atm. Increasing the storage temperature to 308 K has only a small effect on its acetylene storage capacity (∼200 cm(3) (STP) g(−1)). Furthermore, FJI-H8 exhibits an excellent repeatability with only 3.8% loss of its acetylene storage capacity after five cycles of adsorption–desorption tests. Grand canonical Monte Carlo simulation reveals that not only open metal sites but also the suitable pore space and geometry play key roles in its remarkable acetylene uptake
Unburned carbon measurement in fly ash using laser-induced breakdown spectroscopy with short nanosecond pulse width laser
The unburned carbon in fly ash is one of the important factors for the boiler combustion condition. Controlling the unburned carbon in fly ash is beneficial for fly ash recycle and to improve the combustion efficiency of the coal. Laser-induced breakdown spectroscopy (LIBS) technology has been applied to measure the fly ash contents due to its merits of non-contact, fast response, high sensitivity, and real-time measurement. In this study, experimental measurements have been adopted for fly ash flows with the surrounding gases of N2 and CO2, while the CO2 concentration varified to evaluate the CO2 effect on the unburned carbon signal from fly ash powder. Two kinds of pulse width lasers, 6ns and 1ns, were separately adopted to compare the influence of laser pulse width. Results showed that compared with 6ns pulse width laser, plasma temperature was lower and had less dependence on delay time when using 1ns pulse width laser, and spectra had more stable background. By using 1ns pulse width laser, the emission signal from surrounding CO2 also decreased because of the less surrounding gas breakdown. The solid powder breakdown signals also became more stable when using 1ns pulse width laser. So it is demonstrated that 1ns pulse width laser has the merits for fly ash flow measurement using LIBS
Bio-oil based biorefinery strategy for the production of succinic acid
Background: Succinic acid is one of the key platform chemicals which can be produced via biotechnology process instead of petrochemical process. Biomass derived bio-oil have been investigated intensively as an alternative of diesel and gasoline fuels. Bio-oil could be fractionized into organic phase and aqueous phase parts. The organic phase bio-oil can be easily upgraded to transport fuel. The aqueous phase bio-oil (AP-bio-oil) is of low value. There is no report for its usage or upgrading via biological methods. In this paper, the use of AP-bio-oil for the production of succinic acid was investigated
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