19,435 research outputs found
Exact Computation of Influence Spread by Binary Decision Diagrams
Evaluating influence spread in social networks is a fundamental procedure to
estimate the word-of-mouth effect in viral marketing. There are enormous
studies about this topic; however, under the standard stochastic cascade
models, the exact computation of influence spread is known to be #P-hard. Thus,
the existing studies have used Monte-Carlo simulation-based approximations to
avoid exact computation.
We propose the first algorithm to compute influence spread exactly under the
independent cascade model. The algorithm first constructs binary decision
diagrams (BDDs) for all possible realizations of influence spread, then
computes influence spread by dynamic programming on the constructed BDDs. To
construct the BDDs efficiently, we designed a new frontier-based search-type
procedure. The constructed BDDs can also be used to solve other
influence-spread related problems, such as random sampling without rejection,
conditional influence spread evaluation, dynamic probability update, and
gradient computation for probability optimization problems.
We conducted computational experiments to evaluate the proposed algorithm.
The algorithm successfully computed influence spread on real-world networks
with a hundred edges in a reasonable time, which is quite impossible by the
naive algorithm. We also conducted an experiment to evaluate the accuracy of
the Monte-Carlo simulation-based approximation by comparing exact influence
spread obtained by the proposed algorithm.Comment: WWW'1
Generarized Cubic Model for BaTiO-like Ferroelectric Substance
We propose an order-disorder type microscopic model for BaTiO-like
Ferroelectric Substance. Our model has three phase transitions and four phases.
The symmetry and directions of the polarizations of the ordered phases agree
with the experimental results of BaTiO. The intermediate phases in our
model are known as an incompletely ordered phase, which appears in a
generalized clock model.Comment: 6 pages, 4figure
Charmless decays and new physics effects in the mSUGRA model
By employing the QCD factorization approach, we calculate the new physics
contributions to the branching radios of the two-body charmless and
decays in the framework of the minimal supergravity (mSUGRA) model.
we choose three typical sets of the mSUGRA input parameters in which the Wilson
coefficient can be either SM-like (the case A and C) or has
a flipped-sign (the case B). We found numerically that (a) the SUSY
contributions are always very small for both case A and C; (b) for those
tree-dominated decays, the SUSY contributions in case B are also very small;
(c) for those QCD penguin-dominated decay modes, the SUSY contributions in case
B can be significant, and can provide an enhancement about to
the branching ratios of and decays, but a
reduction about to decays; and (d) the
large SUSY contributions in the case B may be masked by the large theoretical
errors dominated by the uncertainty from our ignorance of calculating the
annihilation contributions in the QCD factorization approach.Comment: 34 pages, 8 PS figures, this is the correct version
Observation of EAS using a large water tank
Using a large water tank (30 m in diameter, 4.5 m in depth) transition of extensive air showers (EAS) was investigated at Taro (200 m above sea level). There are set 150,0.4 sq m proportional counters on the bottom of the water tank. A conventional EAS array of 25 plastic scintillation detectors was arranged within several tens meter from the water tank. A proportional counter (10x10x200 cc x2) is made of a square shaped pipe of iron. Tungsten wire (100 mu m phi) is stretched tight in the center of the counter. A gas mixture of 90% argon and 10% methane is used at 760 mmHg. About 3000 EAS were obtained through 1 m of water since 1984
Fermi Surface of 3d^1 Perovskite CaVO3 Near the Mott Transition
We present a detailed de Haas van Alphen effect study of the perovskite
CaVO3, offering an unprecedented test of electronic structure calculations in a
3d transition metal oxide. Our experimental and calculated Fermi surfaces are
in good agreement -- but only if we ignore large orthorhombic distortions of
the cubic perovskite structure. Subtle discrepancies may shed light on an
apparent conflict between the low energy properties of CaVO3, which are those
of a simple metal, and high energy probes which reveal strong correlations that
place CaVO3 on the verge of a metal-insulator transition.Comment: 4 pages, 4 figures (REVTeX
Comparison of theory with experiment for positron production from high-energy electrons moving along crystal axes
Various positron distributions are obtained using an approach developed
earlier for the description of electron-photon showers in axially aligned
single crystals. Based on these distributions, characteristics of the positron
yield measured in recent experiments are calculated. Theoretical estimations
display a rather good agreement with experimental results obtained using 3 to
10 GeV electrons aligned to the - axis of the tungsten crystals.Comment: 10 pages, 6 Postscript figure
Microwave and millimeter wave spectroscopy in the slightly hole-doped ladders of SrCuO
We have measured the temperature- and frequency dependence of the microwave
and millimeter wave conductivity along both the ladder
(c-axis) and the leg (a-axis) directions in SrCuO. Below a
temperature (170 K), we observed a stronger frequency dependence in
than that in , forming a small
resonance peak developed between 30 GHz and 100 GHz. We also observed nonlinear
dc conduction along the c-axis at rather low electric fields below . These
results suggest some collective excitation contributes to the c-axis charge
dynamics of the slightly hole-doped ladders of SrCuO below
.Comment: 7 pages, 4 figure, to be published in Europhysics Letter
Renormalization Group Invariants in the MSSM and Its Extensions
We derive one-loop renormalization group (RG) invariant observables and
analyze their phenomenological implications in the MSSM and its \mu problem
solving extensions, U(1)' model and NMSSM. We show that there exist several RG
invariants in the gauge, Yukawa and soft-breaking sectors of each model. In
general, RG invariants are highly useful for projecting experimental data to
messenger scale, for revealing correlations among the model parameters, and for
probing the mechanism that breaks supersymmetry. The Yukawa couplings and
trilinear soft terms in U(1)' model and NMSSM do not form RG invariants though
there exist approximate invariants in low tan(beta). In the NMSSM, there are no
invariants that contain the Higgs mass-squareds. We provide a comparative
analysis of RG invariants in all three models and analyze their model-building
and phenomenological implications by a number of case studies.Comment: 32 pages, 5 tables; extended previous analysis to include U(1)'
models and NMSSM where a comparative discussion is give
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