196 research outputs found
Bound on global error of the fast multipole method for Helmholtz equation in 2-D
This paper analyze the global error of the fast multipole method(FMM) for
two-dimensional Helmholtz equation. We first propose the global error of the
FMM for the discretized boundary integral operator. The error is caused by
truncating Graf's addition theorem, according to the limiting forms of Bessel
and Neumann functions, we provide sharper and more precise estimates for the
truncations of Graf's addition theorem. Finally, using the estimates we derive
the explicit bound and convergence rate for the global error of the FMM for
Helmholtz equation, numerical experiments show that the results are valid. The
method in this paper can also be applied to the FMM for other problems such as
potential problems, elastostatic problems, Stokes flow problems and so on
Treating Coulomb exchange contributions in relativistic mean field calculations: why and how
The energy density functional (EDF) method is very widely used in nuclear
physics, and among the various existing functionals those based on the
relativistic Hartree (RH) approximation are very popular because the exchange
contributions (Fock terms) are numerically rather onerous to calculate.
Although it is possible to somehow 'mock up' the effects of meson-induced
exchange terms by adjusting the meson-nucleon couplings, the lack of Coulomb
exchange contributions hampers the accuracy of predictions. In this note, we
show that the Coulomb exchange effects can be easily included with a good
accuracy in a perturbative approach. Therefore, it would be desirable for
future relativistic EDF models to incorporate Coulomb exchange effects, at
least to some order of perturbation.Comment: 3 pages, 1 figure, Proceedings of the 20th Nuclear Physics Workshop
"Marie & Pierre Curie", Kazimierz, Poland, 25-29 September, 201
Identifying Influential Users Of Micro-Blogging Services: A Dynamic Action-Based Network Approach
In this paper, we present a dynamic model to identify influential users of micro-blogging services. Micro-blogging services, such as Twitter, allow their users (twitterers) to publish tweets and choose to follow other users to receive tweets. Previous work on user influence on Twitter, concerns more on following link structure and the contents user published, seldom emphasizes the importance of interactions among users. We argue that, by emphasizing on user actions in micro-blogging platform, user influence could be measured more accurately. Since micro-blogging is a powerful social media and communication platform, identifying influential users according to user interactions has more practical meanings, e.g., advertisers may concern how many actions – buying, in this scenario – the influential users could initiate rather than how many advertisements they spread. By introducing the idea of PageRank algorithm, innovatively, we propose our model using action-based network which could capture the ability of influential users when they interacting with micro-blogging platform. Taking the evolving prosperity of micro-blogging into consideration, we extend our action-based user influence model into a dynamic one, which could distinguish influential users in different time periods. Simulation results demonstrate that our models could support and give reasonable explanations for the scenarios that we considered
New effective interactions in RMF theory with non-linear terms and density-dependent meson-nucleon coupling
New parameter sets for the Lagrangian density in the relativistic mean field
(RMF) theory, PK1 with nonlinear sigma- and omega-meson self-coupling, PK1R
with nonlinear sigma-, omega- and rho-meson self-coupling and PKDD with the
density-dependent meson-nucleon coupling, are proposed. They are able to
provide an excellent description not only for the properties of nuclear matter
but also for the nuclei in and far from the valley of beta-stability. For the
first time in the parametrization of the RMF Lagrangian density, the
center-of-mass correction is treated by a microscopic way, which is essential
to unify the description of nuclei from light to heavy regions with one
effective interaction.Comment: 22 pages, 16 EPS figures, RevTeX
Deep Neural Network Representation of Density Functional Theory Hamiltonian
The marriage of density functional theory (DFT) and deep learning methods has
the potential to revolutionize modern research of material science. Here we
study the crucial problem of representing DFT Hamiltonian for crystalline
materials of arbitrary configurations via deep neural network. A general
framework is proposed to deal with the infinite dimensionality and covariance
transformation of DFT Hamiltonian matrix in virtue of locality and use message
passing neural network together with graph representation for deep learning.
Our example study on graphene-based systems demonstrates that high accuracy
(meV) and good transferability can be obtained for DFT Hamiltonian,
ensuring accurate predictions of materials properties without DFT. The Deep
Hamiltonian method provides a solution to the accuracy-efficiency dilemma of
DFT and opens new opportunities to explore large-scale materials and physics.Comment: 5 pages, 4 figure
Evolution of Nuclear Shell Structure due to the Pion Exchange Potential
The evolution of nuclear shell structure is investigated for the first time
within density-dependent relativistic Hartree-Fock theory and the role of
-exchange potential is studied in detail. The energy differences between
the neutron orbits \Lrb{\nu1h_{9/2},\nu 1i_{13/2}} in the N=82 isotones and
between the proton ones \Lrb{\pi1g_{7/2},\pi1h_{11/2}} in the Z=50 isotopes
are extracted as a function of neutron excess . A kink around for
the N=82 isotones is found as an effect resulting from pion correlations. It is
shown that the inclusion of -coupling plays a central role to provide
realistic isospin dependence of the energy differences. In particular, the
tensor part of the -coupling has an important effect on the characteristic
isospin dependence observed in recent experiments.Comment: 4 pages and 4 figure
Characterization and determination of holin protein of Streptococcus suis bacteriophage SMP in heterologous host
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