18,407 research outputs found
Social Data Offloading in D2D-Enhanced Cellular Networks by Network Formation Games
Recently, cellular networks are severely overloaded by social-based services,
such as YouTube, Facebook and Twitter, in which thousands of clients subscribe
a common content provider (e.g., a popular singer) and download his/her content
updates all the time. Offloading such traffic through complementary networks,
such as a delay tolerant network formed by device-to-device (D2D)
communications between mobile subscribers, is a promising solution to reduce
the cellular burdens. In the existing solutions, mobile users are assumed to be
volunteers who selfishlessly deliver the content to every other user in
proximity while moving. However, practical users are selfish and they will
evaluate their individual payoffs in the D2D sharing process, which may highly
influence the network performance compared to the case of selfishless users. In
this paper, we take user selfishness into consideration and propose a network
formation game to capture the dynamic characteristics of selfish behaviors. In
the proposed game, we provide the utility function of each user and specify the
conditions under which the subscribers are guaranteed to converge to a stable
network. Then, we propose a practical network formation algorithm in which the
users can decide their D2D sharing strategies based on their historical
records. Simulation results show that user selfishness can highly degrade the
efficiency of data offloading, compared with ideal volunteer users. Also, the
decrease caused by user selfishness can be highly affected by the cost ratio
between the cellular transmission and D2D transmission, the access delays, and
mobility patterns
Atomistic origin of metal versus charge-density-wave phase separation in indium atomic wires on Si(111)
We investigate in atomic scale the electronic phase separation occurring in
the well known quasi 1D charge-density wave (CDW) phase of the In atomic wire
array on a Si(111) surface. The characteristic atomic scale defects, originated
from excess In atoms, are found to be actively involved in the formation of the
phase boundary between the metallic and the CDW phases by extensive analysis of
scanning tunneling microscopy images at various temperatures. These particular
defects flip the phase of the quasi 1D CDW to impose strong local constraints
in the CDW correlation. We show that such local constraints and the substantial
interwire CDW interaction induce local condensates of CDW and the phase
separation between the metallic and the CDW phases. This work unveils the
atomistic origin of the electronic phase separation, highlighting the
importance of atomic scale structures of defects and their collective
interaction in electronically inhomogeneous materials
Pseudogap and weak multifractality in disordered Mott charge-density-wave insulator
The competition, coexistence and cooperation of various orders in
low-dimensional materials like spin, charge, topological orders and
charge-density-wave has been one of the most intriguing issues in condensed
matter physics. In particular, layered transition metal dichalcogenides provide
an ideal platform for studying such an interplay with a notable case of
1-TaS featuring Mott-insulating ground state, charge-density-wave,
spin frustration and emerging superconductivity together. We investigated local
electronic states of Se-substituted 1-TaS by scanning tunneling
microscopy/spectroscopy (STM/STS), where superconductivity emerges from the
unique Mott-CDW state. Spatially resolved STS measurements reveal that an
apparent V-shape pseudogap forms at the Fermi Level (E), with the origin
of the electronic states splitting and transformation from the Mott states, and
the CDW gaps are largely preserved. The formation of the pseudogap has little
correlation to the variation of local Se concentration, but appears to be a
global characteristics. Furthermore, the correlation length of local density of
states (LDOS) diverges at the Fermi energy and decays rapidly at high energies.
The spatial correlation shows a power-law decay close to the Fermi energy. Our
statistics analysis of the LDOS indicates that our system exhibits weak
multifractal behavior of the wave functions. These findings strongly support a
correlated metallic state induced by disorder in our system, which provides an
new insight into the novel mechanism of emerging superconductivity in the
two-dimensional correlated electronic systems
GCN-RL Circuit Designer: Transferable Transistor Sizing with Graph Neural Networks and Reinforcement Learning
Automatic transistor sizing is a challenging problem in circuit design due to
the large design space, complex performance trade-offs, and fast technological
advancements. Although there has been plenty of work on transistor sizing
targeting on one circuit, limited research has been done on transferring the
knowledge from one circuit to another to reduce the re-design overhead. In this
paper, we present GCN-RL Circuit Designer, leveraging reinforcement learning
(RL) to transfer the knowledge between different technology nodes and
topologies. Moreover, inspired by the simple fact that circuit is a graph, we
learn on the circuit topology representation with graph convolutional neural
networks (GCN). The GCN-RL agent extracts features of the topology graph whose
vertices are transistors, edges are wires. Our learning-based optimization
consistently achieves the highest Figures of Merit (FoM) on four different
circuits compared with conventional black-box optimization methods (Bayesian
Optimization, Evolutionary Algorithms), random search, and human expert
designs. Experiments on transfer learning between five technology nodes and two
circuit topologies demonstrate that RL with transfer learning can achieve much
higher FoMs than methods without knowledge transfer. Our transferable
optimization method makes transistor sizing and design porting more effective
and efficient.Comment: Accepted to the 57th Design Automation Conference (DAC 2020); 6
pages, 8 figure
Modeling and Model Predictive Power and Rate Control of Wireless Communication Networks
A novel power and rate control system model for wireless communication networks is presented, which includes uncertainties, input constraints, and time-varying delays in both state and control input. A robust delay-dependent model predictive power and rate control method is proposed, and the state feedback control law is obtained by solving an optimization problem that is derived by using linear matrix inequality (LMI) techniques. Simulation results are given to illustrate the effectiveness of the proposed method
Genetic and phylogenetic analysis of ten Gobiidae species in China based on amplified fragment length polymorphism (AFLP) analysis
To study the genetic and phylogenetic relationship of gobioid fishes in China, the representatives of 10 gobioid fishes from 2 subfamilies in China were examined by amplified fragment length polymorphism (AFLP) analysis. We established 220 AFLP bands for 45 individuals from the 10 species, and the percentage of polymorphic bands was 100%. The percentage of polymorphic loci within species ranged from 3.61 to 58.56%. Chaeturichthys stigmatias showed the greatest percentage of polymorphic loci (58.56%), the highest Neiās genetic diversity (0.2421 Ā± 0.2190) and Shannonās information index (0.3506 Ā± 0.3092), while Pterogobius zacalles showed the lowest percentage polymorphic loci (3.61%), the lowest Neiās genetic diversity (0.0150 Ā± 0.0778) and lowest Shannonās information index (0.0219 Ā± 0.1136). The topology of UPGMA tree showed that the individuals from the same species clustered together and the 10 species formed two major clades. One clade consisted Cryptocentrus filifer, P. zacalles, Tridentiger trigonocephalus, Chaeturichthys hexanema, C. stigmatias, Acanthogobius flavimanus and Synechogobius ommaturus, and the other clade consisted Odontamblyopus rubicundus, Trypauchen vagina and Ctenotrypauchen microcephalus. The results agreed with the traditional taxonomy of the morphological characters. AFLP fingerprints were successfully used to study the phylogenetic relationship of the gobioid fishes and it identified species origins of morphologically similar taxa.Key words: Phylogenetic, amplified fragment length polymorphism (AFLP), gobiidae, Amblyopinae, gobiinae
Kinematics of a Trinal-Branch Space Robotic Manipulator with Redundancy
AbstractThis paper presents a trinal branch space robotic manipulator with redundancy, due to hash application environments, such as in the station. One end- effector of the manipulator can be attached to the base, and other two be controlled to accomplish tasks. The manipulator permits operation of science payload, during periods when astronauts may not be present. In order to provide theoretic basis for kinematics optimization, dynamics optimization and fault-tolerant control, its inverse kinematics is analyzed by using screw theory, and its unified formulation is established. Base on closed form resolution of spherical wrist, a simplified inverse kinematics is proposed. Computer simulation results demonstrate the validity of the proposed inverse kinematics
A Fully-Integrated Reconfigurable Dual-Band Transceiver for Short Range Wireless Communications in 180 nm CMOS
Ā© 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.A fully-integrated reconfigurable dual-band (760-960 MHz and 2.4-2.5 GHz) transceiver (TRX) for short range wireless communications is presented. The TRX consists of two individually-optimized RF front-ends for each band and one shared power-scalable analog baseband. The sub-GHz receiver has achieved the maximum 75 dBc 3rd-order harmonic rejection ratio (HRR3) by inserting a Q-enhanced notch filtering RF amplifier (RFA). In 2.4 GHz band, a single-ended-to-differential RFA with gain/phase imbalance compensation is proposed in the receiver. A Ī£Ī fractional-N PLL frequency synthesizer with two switchable Class-C VCOs is employed to provide the LOs. Moreover, the integrated multi-mode PAs achieve the output P1dB (OP1dB) of 16.3 dBm and 14.1 dBm with both 25% PAE for sub-GHz and 2.4 GHz bands, respectively. A power-control loop is proposed to detect the input signal PAPR in real-time and flexibly reconfigure the PA's operation modes to enhance the back-off efficiency. With this proposed technique, the PAE of the sub-GHz PA is improved by x3.24 and x1.41 at 9 dB and 3 dB back-off powers, respectively, and the PAE of the 2.4 GHz PA is improved by x2.17 at 6 dB back-off power. The presented transceiver has achieved comparable or even better performance in terms of noise figure, HRR, OP1dB and power efficiency compared with the state-of-the-art.Peer reviewe
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