4,313 research outputs found
Temporal Ordered Clustering in Dynamic Networks: Unsupervised and Semi-supervised Learning Algorithms
In temporal ordered clustering, given a single snapshot of a dynamic network
in which nodes arrive at distinct time instants, we aim at partitioning its
nodes into ordered clusters such that for , nodes in cluster arrived
before nodes in cluster , with being a data-driven parameter
and not known upfront. Such a problem is of considerable significance in many
applications ranging from tracking the expansion of fake news to mapping the
spread of information. We first formulate our problem for a general dynamic
graph, and propose an integer programming framework that finds the optimal
clustering, represented as a strict partial order set, achieving the best
precision (i.e., fraction of successfully ordered node pairs) for a fixed
density (i.e., fraction of comparable node pairs). We then develop a sequential
importance procedure and design unsupervised and semi-supervised algorithms to
find temporal ordered clusters that efficiently approximate the optimal
solution. To illustrate the techniques, we apply our methods to the vertex
copying (duplication-divergence) model which exhibits some edge-case challenges
in inferring the clusters as compared to other network models. Finally, we
validate the performance of the proposed algorithms on synthetic and real-world
networks.Comment: 14 pages, 9 figures, and 3 tables. This version is submitted to a
journal. A shorter version of this work is published in the proceedings of
IEEE International Symposium on Information Theory (ISIT), 2020. The first
two authors contributed equall
Fine structure of helium-like ions and determination of the fine structure constant
We report a calculation of the fine structure splitting in light helium-like
atoms, which accounts for all quantum electrodynamical effects up to order
\alpha^5 Ry. For the helium atom, we resolve the previously reported
disagreement between theory and experiment and determine the fine structure
constant with an accuracy of 31 ppb. The calculational results are extensively
checked by comparison with the experimental data for different nuclear charges
and by evaluation of the hydrogenic limit of individual corrections.Comment: 4 pages, 3 tables, with a typo in Eq. (9) correcte
Strong-coupling solution of the bosonic dynamical mean-field theory
We derive an approximate analytical solution of the self-consistency
equations of the bosonic dynamical mean-field theory (B-DMFT) in the
strong-coupling limit. The approach is based on a linked-cluster expansion in
the hybridization function of normal bosons around the atomic limit. The
solution is used to compute the phase diagram of the bosonic Hubbard model for
different lattices. We compare our results with numerical solutions of the
B-DMFT equations and numerically exact methods, respectively. The very good
agreement with those numerical results demonstrates that our approach captures
the essential physics of correlated bosons both in the Mott insulator and in
the superfluid phase. Close to the transition into the superfluid phase the
momentum distribution function at zero momentum is found to be strongly
enhanced already in the normal phase. The linked-cluster expansion also allows
us to compute dynamical properties such as the spectral function of bosons. The
evolution of the spectral function across the transition from the normal to the
superfluid phase is seen to be characteristically different for the interaction
driven and density driven transition, respectively.Comment: 8 pages, 6 figure
Diffractive production of electroweak vector bosons at the LHC
We analyse diffractive electroweak vector boson production in hadronic
collisions and show that the single diffractive W boson production asymmetry in
rapidity is a particularly good observable at the LHC to test the concept of
the flavour symmetric pomeron parton distributions. It may also provide an
additional constraint for the parton distribution functions in the proton.Comment: 7 pages, 5 figure
CP-nets and Nash equilibria
We relate here two formalisms that are used for different purposes in
reasoning about multi-agent systems. One of them are strategic games that are
used to capture the idea that agents interact with each other while pursuing
their own interest. The other are CP-nets that were introduced to express
qualitative and conditional preferences of the users and which aim at
facilitating the process of preference elicitation. To relate these two
formalisms we introduce a natural, qualitative, extension of the notion of a
strategic game. We show then that the optimal outcomes of a CP-net are exactly
the Nash equilibria of an appropriately defined strategic game in the above
sense. This allows us to use the techniques of game theory to search for
optimal outcomes of CP-nets and vice-versa, to use techniques developed for
CP-nets to search for Nash equilibria of the considered games.Comment: 6 pages. in: roc. of the Third International Conference on
Computational Intelligence, Robotics and Autonomous Systems (CIRAS '05). To
appea
Coulomb Gas Representation of the SU(2) WZW Correlators at Higher Genera
We express the correlation functions of the SU(2) WZW conformal field theory
on Riemann surfaces of genus >1 by finite dimensional integrals.Comment: 9 pages, late
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