1,246 research outputs found
Enhance synchronizability by structural perturbations
In this paper, we investigate the collective synchronization of system of
coupled oscillators on Barab\'{a}si-Albert scale-free network. We propose an
approach of structural perturbations aiming at those nodes with maximal
betweenness. This method can markedly enhance the network synchronizability,
and is easy to be realized. The simulation results show that the eigenratio
will sharply decrease to its half when only 0.6% of those hub nodes are under
3-division processes when network size N=2000. In addition, the present study
also provides a theoretical evidence that the maximal betweenness plays a main
role in network synchronization.Comment: 4 pages, 3 eps figure
Self-organized Boolean game on networks
A model of Boolean game with only one free parameter that denotes the
strength of herd behavior is proposed where each agent acts according to the
information obtained from his neighbors in network and those in the minority
are rewarded. The simulation results indicate that the dynamic of system is
sensitive to network topology, where the network of larger degree variance,
i.e. the system of greater information heterogeneity, leads to less system
profit. The system can self-organize to a stable state and perform better than
random choice game, although only the local information is available to the
agents. In addition, in heterogeneity networks, the agents with more
information gain more than those with less information for a wide extent of
herd strength .Comment: 5 pages, 5 eps figure
Dirac Fermion in Strongly-Bound Graphene Systems
It is highly desirable to integrate graphene into existing semiconductor
technology, where the combined system is thermodynamically stable yet maintain
a Dirac cone at the Fermi level. Firstprinciples calculations reveal that a
certain transition metal (TM) intercalated graphene/SiC(0001), such as the
strongly-bound graphene/intercalated-Mn/SiC, could be such a system. Different
from free-standing graphene, the hybridization between graphene and Mn/SiC
leads to the formation of a dispersive Dirac cone of primarily TM d characters.
The corresponding Dirac spectrum is still isotropic, and the transport behavior
is nearly identical to that of free-standing graphene for a bias as large as
0.6 V, except that the Fermi velocity is half that of graphene. A simple model
Hamiltonian is developed to qualitatively account for the physics of the
transfer of the Dirac cone from a dispersive system (e.g., graphene) to an
originally non-dispersive system (e.g., TM).Comment: Apr 25th, 2012 submitte
Analysis of Stress State of Bolts Under Different Anchorage Qualities
A series of pull-out tests were conducted in order to study the stress states of bolts under different anchorage qualities and to simulate the influence of quality defects in empty-slurry and low-strength mortar anchorage in actual engineering. The tests mainly investigated strain characteristics at different positions of the bolts and the effects of strains at the same positions under different anchorage conditions. The research led to the following conclusions: (1) under ultimate bearing capacity, the strain values decayed the fastest along the length of the bolt in the full-length anchorage, the strain values decayed the slowest in the empty-slurry and low-strength mortar anchorage, and the decaying speed of strains in the empty-slurry mortar anchorage was between that of the above two kinds of anchorages; (2) at almost 50% of the ultimate bearing capacity, the strain values were slightly different between the empty-slurry and low-strength mortar anchorage and the empty-slurry anchorage. Obvious differences in strain values occurred when the bolts were continued to be loaded. The strain values of the full-length anchorage bolts were different from those of the other two kinds of anchorages; (3) from the analysis of stress variation characteristics, the safety reserve was the highest for the full-length anchorage under the condition of ultimate bearing capacity, followed by the empty-slurry mortar anchorage, while the safety reserve was the lowest for the empty-slurry and low-strength mortar anchorage. However, in terms of uniformity of force and utilization of the material, the result was reverse
Pressure-dependent transition from atoms to nanoparticles in magnetron sputtering: Effect on WSi2 film roughness and stress
We report on the transition between two regimes from several-atom clusters to
much larger nanoparticles in Ar magnetron sputter deposition of WSi2, and the
effect of nanoparticles on the properties of amorphous thin films and
multilayers. Sputter deposition of thin films is monitored by in situ x-ray
scattering, including x-ray reflectivity and grazing incidence small angle
x-ray scattering. The results show an abrupt transition at an Ar background
pressure Pc; the transition is associated with the threshold for energetic
particle thermalization, which is known to scale as the product of the Ar
pressure and the working distance between the magnetron source and the
substrate surface. Below Pc smooth films are produced, while above Pc roughness
increases abruptly, consistent with a model in which particles aggregate in the
deposition flux before reaching the growth surface. The results from WSi2 films
are correlated with in situ measurement of stress in WSi2/Si multilayers, which
exhibits a corresponding transition from compressive to tensile stress at Pc.
The tensile stress is attributed to coalescence of nanoparticles and the
elimination of nano-voids.Comment: 16 pages, 10 figures; v3: published versio
A particle swarm based hybrid system for imbalanced medical data sampling
BackgroundMedical and biological data are commonly with small sample size, missing values, and most importantly, imbalanced class distribution. In this study we propose a particle swarm based hybrid system for remedying the class imbalance problem in medical and biological data mining. This hybrid system combines the particle swarm optimization (PSO) algorithm with multiple classifiers and evaluation metrics for evaluation fusion. Samples from the majority class are ranked using multiple objectives according to their merit in compensating the class imbalance, and then combined with the minority class to form a balanced dataset.ResultsOne important finding of this study is that different classifiers and metrics often provide different evaluation results. Nevertheless, the proposed hybrid system demonstrates consistent improvements over several alternative methods with three different metrics. The sampling results also demonstrate good generalization on different types of classification algorithms, indicating the advantage of information fusion applied in the hybrid system.ConclusionThe experimental results demonstrate that unlike many currently available methods which often perform unevenly with different datasets the proposed hybrid system has a better generalization property which alleviates the method-data dependency problem. From the biological perspective, the system provides indication for further investigation of the highly ranked samples, which may result in the discovery of new conditions or disease subtypes.<br /
Perturbation: the Catastrophe Causer in Scale-Free Networks
A new model about cascading occurrences caused by perturbation is established
to search after the mechanism because of which catastrophes in networks occur.
We investigate the avalanche dynamics of our model on 2-dimension Euclidean
lattices and scale-free networks and find out the avalanche dynamic behaviors
is very sensitive to the topological structure of networks. The experiments
show that the catastrophes occur much more frequently in scale-free networks
than in Euclidean lattices and the greatest catastrophe in scale-free networks
is much more serious than that in Euclidean lattices. Further more, we have
studied how to reduce the catastrophes' degree, and have schemed out an
effective strategy, called targeted safeguard-strategy for scale-free networks.Comment: 4 pages, 6 eps figure
Geometric entanglement from matrix product state representations
An efficient scheme to compute the geometric entanglement per lattice site
for quantum many-body systems on a periodic finite-size chain is proposed in
the context of a tensor network algorithm based on the matrix product state
representations. It is systematically tested for three prototypical critical
quantum spin chains, which belong to the same Ising universality class. The
simulation results lend strong support to the previous claim [Q.-Q. Shi, R.
Or\'{u}s, J. O. Fj{\ae}restad, and H.-Q. Zhou, New J. Phys \textbf{12}, 025008
(2010); J.-M. St\'{e}phan, G. Misguich, and F. Alet, Phys. Rev. B \textbf{82},
180406R (2010)] that the leading finite-size correction to the geometric
entanglement per lattice site is universal, with its remarkable connection to
the celebrated Affleck-Ludwig boundary entropy corresponding to a conformally
invariant boundary condition.Comment: 4+ pages, 3 figure
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